Graduate School ETD Form 9 (Revised 12/07)
PURDUE UNIVERSITY GRADUATE SCHOOL Thesis/Dissertation Acceptance This is to certify that the thesis/dissertation prepared By Travis R. Sippel Entitled Characterization of Aluminum and Ice Solid Propellants
For the degree of Master of Science in Mechanical Engineering
Is approved by the final examining committee: Steven F. Son Chair
Timothee L. Pourpoint
Li Qiao
To the best of my knowledge and as understood by the student in the Research Integrity and Copyright Disclaimer (Graduate School Form 20), this thesis/dissertation adheres to the provisions of Purdue University’s “Policy on Integrity in Research” and the use of copyrighted material.
Steven F. Son Approved by Major Professor(s): ____________________________________
____________________________________ Approved by: E. Dan Hirleman
April 28, 2009 Head of the Graduate Program
Date
Graduate School Form 20 (Revised 10/07)
PURDUE UNIVERSITY GRADUATE SCHOOL Research Integrity and Copyright Disclaimer
Title of Thesis/Dissertation: Characterization of Aluminum and Ice Solid Propellants
Master of Science in Mechanical Engineering For the degree of ________________________________________________________________
I certify that in the preparation of this thesis, I have observed the provisions of Purdue University Executive Memorandum No. C-22, September 6, 1991, Policy on Integrity in Research.* Further, I certify that this work is free of plagiarism and all materials appearing in this thesis/dissertation have been properly quoted and attributed. I certify that all copyrighted material incorporated into this thesis/dissertation is in compliance with the United States’ copyright law and that I have received written permission from the copyright owners for my use of their work, which is beyond the scope of the law. I agree to indemnify and save harmless Purdue University from any and all claims that may be asserted or that may arise from any copyright violation.
Travis R. Sippel ________________________________ Signature of Candidate
April 10, 2009 ________________________________ Date
*Located at http://www.purdue.edu/policies/pages/teach_res_outreach/c_22.html
CHARACTERIZATION OF NANOSCALE ALUMINUM AND ICE SOLID PROPELLANTS
A Thesis Submitted to the Faculty of Purdue University by Travis R. Sippel
In Partial Fulfillment of the Requirements for the Degree of Master of Science in Mechanical Engineering
May 2009 Purdue University West Lafayette, Indiana
ii
ACKNOWLEDGMENTS
The author would like to thank Dr. Steven Son for his guidance over the course of this work. Thanks are also due to Drs. Timothee Pourpoint, Grant Risha, and Richard Yetter for their help and guidance. The author would like to thank Dr. Mitat Birkan and the organizations AFOSR and NASA for their financial support. Special thanks are due to Tyler Wood, Cody Dezelan, Tyler Williams, and Kevin Zaseck who helped with the progression of this research. Credit for TEM and SEM microscopy work is due to Debby Sherman of the Purdue Life Sciences Microscopy Lab. Lastly, the author would like to thank all of the faculty, researchers, and staff at Purdue University’s Zucrow Laboratories. The work described herein would not be possible without the help of these skilled individuals and the opportunity provided by such a one-of-a-kind laboratory facility.
iii
TABLE OF CONTENTS
Page LIST OF TABLES .................................................................................................. v! LIST OF FIGURES ............................................................................................... vi! ABSTRACT ......................................................................................................... viii! CHAPTER 1. BACKGROUND INFORMATION .................................................... 1! 1.1. Background and Motivation......................................................................... 1! 1.2. Objectives.................................................................................................... 2! 1.3. Organization ................................................................................................ 3! CHAPTER 2. LITERATURE REVIEW................................................................... 5! 2.1. Introduction.................................................................................................. 5! 2.2. Early Aluminum-Water Research ................................................................ 5! 2.3. Aluminum Nanoparticles ............................................................................. 8! 2.3.1. Production Methods .............................................................................. 8! 2.3.2. Unique Properties & Characterization ................................................... 9! 2.3.3. Coatings .............................................................................................. 12! 2.4. Previous Nanoaluminum-Water Research ................................................ 14! 2.5. Summary ................................................................................................... 18! CHAPTER 3. DESIGN AND CONSTRUCTION OF EXPERIMENTAL EQUIPMENT ................................................................................. 20 3.1. Electrostatic Discharge Sensitivity Testing Machine ................................. 20! 3.1.1. Background & Machine Design ........................................................... 20! 3.1.2. ESD Machine Operating Procedure .................................................... 24! 3.2. Impact Sensitivity Testing.......................................................................... 26! 3.3. Shock Sensitivity Testing .......................................................................... 30! 3.4. Crash Deposition Viton Coating Technique .............................................. 31! 3.5. Crawford Combustion Bomb Strand Burn Experiments ............................ 32! 3.6. Active Aluminum Content Testing ............................................................. 37! 3.7. Full Scale Mixing Procedure...................................................................... 40! CHAPTER 4. MATERIAL CHARACTERIZATION............................................... 43! 4.1. Aluminum Powder Varieties ...................................................................... 43! 4.2. TEM and SEM Particle Imagery ................................................................ 46! 4.2.1. Overview ............................................................................................. 46! 4.2.2. SEM Particle Imaging Procedure ........................................................ 46! 4.2.3. TEM Particle Imaging Procedure ........................................................ 47! 4.2.4. SEM and TEM Particle Imaging Results ............................................. 47! 4.2.5. Particle Size Measurement ................................................................. 51!
iv Page 4.3. Particle Coating Thickness Measurement ................................................. 53! CHAPTER 5. PROPELLANT AGING TESTING ................................................. 57! 5.1. Background Information ............................................................................ 57! 5.2. Experiment Setup ...................................................................................... 57! 5.3. Results and Discussion ............................................................................. 58! CHAPTER 6. ALICE COMBUSTION AND SAFETY CHARACTERIZATION ..... 60! 6.1. Equilibrium Calculations ............................................................................ 60! 6.1.1. Purpose ............................................................................................... 60! 6.1.2. Cheetah Batch Post Processor Program ............................................ 60! 6.1.3. ALICE Variation of Stoichiometry and Addition of Hydrogen Peroxide to ALICE............................................................................... 61! 6.1.4. Addition of Viton .................................................................................. 65! 6.2. Strand Combustion Studies....................................................................... 67! 6.2.1. Experimentation .................................................................................. 67! 6.2.2. Results ................................................................................................ 68! 6.3. ALICE Steady State Thermal Profile Energy............................................. 78! CHAPTER 7. MIXING SCALEUP AND LARGE SCALE MIXING ....................... 83! 7.1. Use of Inert Ingredients in Mixing Tests .................................................... 83! 7.2. Mixing Observations and Lessons Learned .............................................. 86! CHAPTER 8. USING HYDROGEN PEROXIDE AS AN ALICE BURN RATE MODIFIER ..................................................................................... 87! 8.1. Background ............................................................................................... 87! 8.2. Effect on Stability....................................................................................... 87! 8.2.1. Effect on Propellant Shock Sensitivity................................................. 89! 8.2.2. Effect on Impact Sensitivity ................................................................. 91! 8.2.3. Effect on ESD Sensitivity..................................................................... 92! CHAPTER 9. VITON AND PALMITIC ACID COATED PARTICLES................... 94! 9.1. Motivation .................................................................................................. 94! 9.2. Effect on Mixing ......................................................................................... 94! 9.3. Effect on ESD Sensitivity........................................................................... 96! CHAPTER 10. FINAL REMARKS ....................................................................... 97! 10.1. Summary and Conclusions ..................................................................... 97! 10.2. Recommendations For Future Work ....................................................... 98! LIST OF REFERENCES ................................................................................... 100! APPENDICES Appendix A. ESD Sensitivity Test Results ..................................................... 108! Appendix B. Experimental Procedures........................................................... 110! Appendix C. Program Code ........................................................................... 126! Appendix D. Particle Size Measurement Analysis ......................................... 148! Appendix E. Particle Oxide Coating Analysis Results .................................... 151! Appendix F. Instruction Manual for Cheetah Post 4 Program ........................ 155!
v
LIST OF TABLES
Table Page 4.1 Nanoaluminum Powder Characteristics. ....................................................... 45! 4.2 Nano-aluminum SEM and TEM Samples...................................................... 46! 4.3 Lognormal Particle Diameters. ...................................................................... 52! 4.4 Particle Coating Analysis Results.................................................................. 55! 6.1 ALICE Frozen Packing Densities at -25ºC. ................................................... 69! 7.1 Inert Mixture Component Properties. ............................................................ 84! 8.1 Detonability Sensitivity of Stoichiometric ALICE Mixtures. ............................ 91! 8.2 Impact Sensitivity of ALICE and Hydrogen Peroxide Mixtures...................... 92! 8.3 Stoichiometric ALICE ESD Sensitivity. .......................................................... 93! 9.1 Amount Surfactant Required to Mix Stoichiometric LALEX 50 With Water. .. 95!
vi
LIST OF FIGURES
Figure Page 3.1 ESD Testing Machine Circuit Diagram. ......................................................... 23! 3.2 ESD Testing Machine and Sealed Environmental Chamber......................... 24! 3.3 Impact Testing Machine Chamber Diagram. ................................................. 27! 3.4 Impact Testing Machine Assembled. ............................................................ 28! 3.5 Typical pressure trace of a failed ignition and a successful ignition. ............. 29! 3.6 Impact chamber typical results. ..................................................................... 29! 3.7 Witness Plate Experimental Setup. ............................................................... 31! 3.8 Picture of Crawford Combustion Bomb and Canon XL2A Camera. .............. 33! 3.9 Schematic of Combustion Bomb, Strand, and Igniter. .................................. 33! 3.10 Typical Combustion Bomb Pressurization................................................... 35! 3.11 Tracker Video Analysis and Curve Fitting Procedure.................................. 36! 3.12 Volumetric Method Hydrogen Measurement Apparatus. ............................ 40! 3.13 Purdue Solid Propellant Mixing Facility. ...................................................... 42! 4.1 a) TEM of Novacentrix 80 nm M2666; b) TEM of Novacentrix 80 nm M2665B; c) TEM of Argonide 100 nm ALEX; d) TEM of Argonide 50 nm ALEX; e) TEM of Argonide 50 nm LALEX with palmitic acid coating; f) TEM of Novacentrix 80 nm with 10% Viton coating; g) SEM of Argonide 50 nm LALEX with palmitic acid coating; h) SEM of Novacentrix 80 nm with 10% Viton coating. ................................. 50! 4.2 Aluminum Powder Particle Size Distributions Measured from TEM.............. 53! 4.3 Typical Intensity Plot of Aluminum Particle Oxide Coating (ALEX 50 Particles Shown)............................................................................................ 54! 4.4 Lognormal Oxide/Coating Thicknesses......................................................... 55! 5.1 ALICE Aging Results Compared to Results of Cliff et al.29 ........................... 59! 6.1 Cheetah Post Processor Program................................................................. 61! 6.2 Vacuum ISP (seconds), from 6.9 MPa Chamber Pressure With Varying H2O2 Concentration and Solid-Liquids Ratio. ................................................ 63! 6.3 Chamber Temperature (Kelvin) for 6.9 MPa Chamber Pressure With Varying H2O2 Concentration and Solid-Liquids Ratio.................................... 64! 6.4 Effect of addition of 10 wt % Viton to an Al-H2O2-H2O mixture with 10 wt % H2O2 in H2O2-H2O mixture is presented. Vacuum ISP is calculated using a 6.9 MPa chamber pressure and expansion ratio of 100. ........................................................................................................... 66!
vii Figure Page 6.5 Gaseous exhaust product concentrations of an Al-Viton-H2O2-H2O propellant with 10% Viton and 10% H2O2 in H2O2-H2O is presented. Vacuum ISP is calculated using a 6.9 MPa chamber pressure. ..................... 66! 6.6 Video Image Sequence of ALICE Propellant Strand Burning in Crawford Bomb.............................................................................................. 67! 6.7 Nova 80 Variation of Packing Density With Equivalence Ratio. .................... 70! 6.8 Novacentrix-Based 80 nm ALICE Linear Combustion Rate Pressure Dependence For Various Stoichiometries. Al-Liquid Water Measurements By Risha et al.43 ......................................................... 73! 6.9 Novacentrix-Based 80 nm ALICE Combustion Pressure Dependence at Low Pressures. ..................................................................................................... 74! 6.10 Argonide ALICE Linear Combustion Rate Pressure Dependence. ............. 75! 6.11 Selected ALICE Mixture Linear Combustion Rate Pressure Dependence.. 76! 6.12 Nova 80 ALICE Hand Mixed and Mixer Mixed Burn Rate Comparison. Mixer Mix Data Used With Permission From T. D. Wood. Al-Liquid Water Fit From Risha et al.43 .................................................................................................. 77! 6.13 ALICE Mass Burn Rate Per Unit Area Compared to Aluminum-Water Data by Risha et al. 42 ................................................................................. 78! 6.14 Steady State Thermal Profile Energy of ALICE Propellant. ........................ 81! 6.15 Thermal Profile Thickness. .......................................................................... 82! 7.1 Inert Ingredients Mix Results. ........................................................................ 84! 8.1 Hydrogen Peroxide-Aluminum Incompatability Experiments. ....................... 88! 8.2 Witness Plates After Testing With ALICE Mixtures: (a) Control Experiment With 2.5 cm Air Gap, (b) ALEX 50 ALICE (!=1), 10% H2O2, (c) Control Experiment With Ice Only.......................................... 90! A.1 Aluminum Nanopowder ESD Testing Results, Grouped Bruceton Method. ....................................................................................................... 108! A.2 Aluminum Nanopowder ESD Testing Raw Data......................................... 109! D.1 Lognormal Particle Size Distributions, Means, and Standard Deviations. .. 148! D.2 Lognormal Particle Probability Distributions. (a) Nova 80 with 10% Viton Coating, (b) Nova 80, (c) LALEX 50, (d) ALEX 50, (e) ALEX 100............... 149! D.3 Lognormal Particle Thickness Measurement Fit......................................... 150! E.1 Particle Coating Thickness Lognormal Distributions................................... 151! E.2 Coating Thickness Lognormal Fits and Thickness Histogram. ................... 152! E.3 Particle Coating Thickness Continuous Distribution Functions, Raw Data, and 95% Confidence Intervals................................................... 153! E.4 Comparison of Lognormal and Normal Fits. ............................................... 154!
viii
ABSTRACT
Sippel, Travis R. M.S.M.E., Purdue University, May, 2009. Characterization of Nanoscale Aluminum and Ice Solid Propellants. Major Professor: Steven F. Son, School of Mechanical Engineering.
Solid rocket motors are favored for launch applications because of their simplicity and high thrust to weight ratio. Longer space missions and manned missions will require new, higher performance propellants. Preliminary calculations by others have identified the aluminum and water combustion system as having high potential for propulsion applications. Problems achieving and sustaining combustion experienced by early research have been solved through the development of aluminum nanoparticles. As a result, aluminum and water propellants have received renewed attention. Nearly all recent work on nanoscale aluminum and water propellants has been small in scale. The purpose of this work is to provide fundamental propellant characterization and safety testing, providing a foundation for scale up and development of these propellants. The first part of this work presents a historical overview of research pertinent to the development of aluminum and water propellants. It also discusses aluminum nanoparticles and their characterization. This work also examines the combustion characterization of aluminum and ice propellants experimentally, computationally, and analytically. The safety characterization of propellant formulations in terms of impact, shock, and electrostatic discharge sensitivity are also examined. Procedures for large-scale mixing of the propellant are presented.
ix Results of this work are as follows: Equilibrium combustion calculations predict Al/H2O/H2O2 propellants to have theoretical vacuum specific impulses of over 350 seconds. The linear burning rate pressure dependence of formulations has been experimentally shown to vary between 0.25-0.43 depending on formulation. Hydrogen peroxide was used to enhance the burn rate of aluminum ice mixtures containing larger nanoparticles to replicate burning characteristics of aluminum ice formulations containing smaller aluminum nanoparticles. The surfactant Neodol 91-6 was successfully used to mix hydrophobic palmitic acid coated aluminum. Sensitivity testing reveals that palmitic acid and Viton aluminum particle coatings have the potential to dramatically decrease the electrostatic discharge ignition sensitivity of dry aluminum Nanopowders. Shock sensitivity tests reveal that mixtures of aluminum and water containing 5% hydrogen peroxide in the water are detonable. Stoichiometric aluminum-ice propellants containing 38 nm Technanogy aluminum were determined to be weakly detonable. All mixtures of aluminum and ice containing between 0-10% hydrogen peroxide were insensitive to impact ignition.
1
CHAPTER 1. BACKGROUND INFORMATION
1.1. Background and Motivation Most first stage space propulsion systems to date have relied on liquid hydrogen-liquid oxygen (LH-LOX), composite AP-HTPB-Al (ammonium perchlorate-hydroxyl terminated polybutadiene-aluminum) solid propellants, or a mixture of the two. For high thrust applications such as takeoff, solid rocket motors are highly desirable. Their thrust/weight ratio is typically higher than liquid propulsion systems due to their simplicity and lack of fluid processing equipment. However, there has been little change to solid propellants used for space exploration in the past several decades. Long duration manned missions to the moon, mars, and beyond will require a great deal more equipment and supplies than current missions which are short in duration. As the launch weight of spacecraft increase, the size of solid rocket motors must also increase to provide increased thrust. Solid rocket motor size can only increase to a point where it remains structurally sound under the limitations imposed on it by gravity and takeoff. A designer is faced with two options, they can either increase the structural integrity of the motor’s casing using stronger, lighter materials or a new, higher performance (structural and or burning characteristics) propellant formulation must be sought. No one number can be more descriptive of a propellant’s performance than it’s specific impulse (ISP). Specific impulse can be thought of simply as a measure of a propellant’s impulse provided per unit propellant weight. From a measure of ISP, those propellants that have high solid density but quickly decompose into low molecular weight gaseous products are the most attractive.
2 Current solid propellants have a vacuum ISP of between 230-280 s, which is relatively low in comparison to LH-LOX propulsion systems, which may have an ISP as high as 480 s. Despite their lower ISP values, solid propulsion systems are favored for launch and orbital escape applications because of their unsurpassed simplicity and low flight weight. While composite propellants with 200 s ISP performance may be sufficient for missions requiring a single orbital escape, manned missions to other planets requiring a second launch may require higher performance propulsion systems. Performance could be further improved if some or all of the propellant required for a return mission could be synthesized from resources available on the planet to be visited. Aluminum and ice propellants may be capable of providing the improved performance necessary for applications of these types. The theoretical potential of aluminum and water propellants was studied by Ingenito and Bruno and will be discussed in detail later.2 Briefly, they found that mixtures of aluminum and water can produce theoretical ISP values of over 300 s. Furthermore, aluminum is the second most abundant metallic element on the moon and is in similar abundance on Mars. Water has been found on Mars and there is evidence it exists on the moon as well. Takeoff weight for missions such as these could be decreased significantly by carrying water to be used in synthesizing aluminum-water propellant in-situ. Conversion from conventional solid propellants to aluminum-ice has environmental impact as well. Combustion of the ammonium perchlorate oxidizer commonly found in composite solid propellants yields hydrochloric acid which is corrosive and toxic. Products of aluminum and ice combustion are environmentally benign alumina and hydrogen gas.
1.2. Objectives The overall goal of this research is to assess the feasibility of aluminumice propellants for space propulsion systems. The specific aims are to: 1.
Perform fundamental aluminum nanoparticle characterization.
2.
Perform aluminum and ice propellant safety characterization.
3 3.
Investigate the combustion behavior of aluminum-ice propellants.
4.
Determine the effect of addition of hydrogen peroxide to aluminum-ice propellants.
5.
Determine the effect of nanoparticle coatings and additives on aluminum-ice propellants.
6.
Perform preliminary work on scaling up the production of aluminum-ice propellants.
1.3. Organization This thesis is organized into 10 chapters. Chapter 2 provides information on previous work related to development of nanoscale aluminum-ice solid propellants. It covers early developments in aluminum and water combustion, aluminum nanoparticle characterization, and nanoaluminum-water research. Chapter 3 discusses the design, construction, and operation of all experiments described in this work. Chapter 4 deals with characterization techniques applied to aluminum nanoparticles. Particular detail is given to particle size and coating thickness analysis using microscopy and image analysis techniques. Chapter 5 discusses the storage stability of aluminum-ice propellants. Chapter 6 presents results of combustion characterization of aluminum and ice propellants. Equilibrium calculations are performed to determine the performance effect of various additives. Experiments are performed to determine the combustion performance. Chapter 7 describes the process of scaling up aluminum-ice propellant mixing as well as the findings of doing so. Chapter 8 discusses the combustion effects of addition of hydrogen peroxide as a burn rate modifier to aluminum-ice propellants. Chapter 9 discusses the effect of addition of nanoparticle coatings to aluminum-ice propellants.
4 Chapter 10 provides a summary of findings as well as recommendations for future work.
5
CHAPTER 2. LITERATURE REVIEW
2.1. Introduction The purpose of this chapter is to provide fundamental motivation for the development of aluminum and ice propellants and to provide a historical perspective on previous research related to aluminum and ice (ALICE) propellant development. Pertinent topics that will be treated include early aluminum and water research, nanoaluminum particles and their characteristics, and recent aluminum and water research.
2.2. Early Aluminum-Water Research Research into the combustion reaction of aluminum and water dates back to the 1940s with nearly all research being conducted by the U.S. and the former U.S.S.R. During the period from the 1940s-1970s there was a significant disparity between Soviet and U.S. aluminum-water research, with U.S. research trailing Soviet research by nearly twenty years. Early U.S. Research involved the study of reactions of molten bulk aluminum with water. The first reported application of the aluminum and water reaction as an energy storage medium was in 1942 by Rasor3 in which the aluminum and water reaction was proposed as a method of underwater propulsion. Rasor’s invention reacted molten aluminum with ocean water to produce hydrogen gas and steam for propulsion. His concept appeared to be premature and predated key aluminum-water research but was later implemented and studied in more detail by others.4,5 One of the earliest reported U.S. aluminum-water research efforts was performed by Elgert and Brown in 1956.6 Their work involves the use of uranium-
6 235 radiation bombardment to superheat aluminum-water mixtures. The motivation for their work was to determine the possibility of an explosive reaction between aluminum and water. Tests were conducted in which aluminum and enough uranium-235 to promote melting of the aluminum were placed in an autoclave containing water and were irradiated for 6-18 seconds during which time temperature and pressure inside the autoclave were measured. Temperatures exceeded 2200 ºF and transient pressures of between 8000 and 23,000 psi were achieved. Gas analysis revealed the formation of H2 gas and Xray diffraction revealed that only 0.2 weight percent aluminum was converted to alumina. From 1968 to 1973 further experiments were conducted on the combustion behavior of molten aluminum and water. In 1968 Brauer et al. performed experiments to determine the mechanism of “vapor explosion” and metal fragmentation that occurred upon quenching of molten aluminum in water. Brauer hypothesized that the minimum temperature required to produce aluminum fragmentation upon quenching was the melting temperature of aluminum. Five years later both Bradley and Witte7,8 used high-speed streak photography to observe the process of hot liquid aluminum injection into a pool of cooled water. The degree of aluminum fragmentation upon impacting the pool was characterized and the reaction mechanism was determined to be thermally controlled. They hypothesized that the amount of interfacial surface area between the aluminum and the water played an important role in determining the intensity of the vapor explosion process. Shidlovskij made significant contributions to the Soviet body of aluminumwater research in the 1940s.9,10 In 1946, he performed detonability tests on aluminum-water-methanol mixtures.9 Large samples (50-100 g) of aluminum powder and water-methanol were mixed stoichiometrically in a thick-walled lead container and ignited using ~10 g tetryl boosters. Tests showed that using 4 wtpercent gellant in the water resulted in complete destruction of the lead can.
7 Results showed that mixtures of aluminum and water are detonable in large quantities when exposed to a strong initiating shock. In the same year Shidlovskij also conducted deflagration quench diameter studies on stoichiometric mixtures of aluminum powder and water.10 Samples were packed in cylindrical tubes of diameter 32 and 80 mm. Ignition was achieved using a magnesium and iron oxide thermite initiator. The 80 mm samples were found to burn uniformly while 32 mm samples could not be ignited. In 1965 Kaplan recognized the potential of the aluminum-water reaction as a means to produce fine aluminum oxide powder.11 Aluminum vapor and water vapor or oxygen were reacted by heating aluminum at a vacuum pressure of 10-3 torr. Rates of aluminum oxide deposition from this process were found to be 10100 times faster in water vapor than in oxygen, showing for these conditions the favorability of the aluminum-water reaction over aluminum-oxygen. In 1967 a significant achievement was made by Liebowitz and Mischler12, which marked the first fast reaction of aluminum-water mixtures in which a significant amount of aluminum was oxidized. Mixtures of aluminum powder and water were mixed together and heated with a ruby laser at pressures of 0.03, 1, and 10 atm. Mixtures at 1 and 10 atm were found to ignite while mixtures at 0.03 atm did not. Liebowitz and Mischler hypothesized that particle ignition and reaction occur when particle temperature reaches the melting point of Al2O3 and that at temperatures above this point, a heterogeneous reaction is controlled by diffusion of water through a hydrogen gas product film surrounding the particle. The reaction of aluminum and water was further studied by Shidlovskij in 1946.10 Shidlovskij created large (40-100 g), heavily confined mixtures of aluminum/magnesium powder, water, and methyl alcohol. The mixtures were ignited with a magnesium-iron oxide thermite mixture. Shidlovskij observed that aluminum-water-methanol mixtures burned steadily in confined diameters larger than 32 mm. Shidlovskij reported difficulty in igniting the mixtures and that successful ignitions often resulted in melting of the confinement vessel.
8 In 1970 Khaikin et al.13 performed experiments that provided understanding of the ignition and oxidation kinetics of aluminum. Aluminum particles of size 10-100 "m in various oxidizers were studied. The ignition temperature of aluminum particles was determined to be near the melting point of the oxide film, 2300 K. Khaikin et al. hypothesized that the oxide film is permeable and that combustion of aluminum particles is controlled by diffusion of aluminum and oxidizer through this layer. MacDonald and Butler14, in 1973, derived potential-pH diagrams describing the aluminum-water system at various temperatures and pHs. Calculations suggest that oxidation of aluminum occurs more favorably for higher temperatures and for more basic pH. In that same year Smith15 devised a method of reacting aluminum-mercury alloy sheets with water as a source of hydrogen fuel. His method proved to be superior on a mass basis to all other hydrogen production methods available at the time.
2.3. Aluminum Nanoparticles Little aluminum-water research occurred between the late 1970s and early 1990s. However, the increased production of nanoaluminum occurred in the mid 1990s, providing an opportunity to improve the combustion performance of aluminum and water mixtures. A significant portion of this work focuses on the characterization of commercial nanoaluminum formulations, so a brief treatment of the subject will be presented here.
2.3.1. Production Methods Aluminum nanopowders (nAl) may be produced using a variety of methods, all of which have specific advantages or disadvantages. One of the earliest and still most common methods of nAl production is electrical explosion of wire (ALEX).16-18 Aluminum nanopowder manufactured in this way is produced by discharging a high voltage (~10,000 volts) through a wire measuring fractions
9 of a millimeter in diameter. The current passing through the wire, in excess of 1,000 amps, vaporizes the aluminum wire in 10 to 20 micro seconds, converting it to plasma. The aluminum then condenses in an inert atmosphere of argon. After production, the aluminum powder is passivated with a thin (1-3 nm) thick coating of aluminum oxide and/or aluminum nitride through exposure with dry air, nitrogen, or oxygen-argon mixtures. This production technique is used by the commercial nAl manufacturer, Argonide (Sanford, Fl). Another conceptually similar production method used by Novacentrix Corp. (Austin, TX) involves the use of high voltage, pulsed plasma ablation of bulk aluminum. Other methods of aluminum production involve boiling of aluminum under inert environment or chemical vapor deposition.
2.3.2. Unique Properties & Characterization Particles are typically called “nano” if their diameter is on the order of 1 to 100 nm. Properties of nanoparticles such as melting temperature19,20, ignition temperature5,21, electrical resistivity, and magnetivity22 can be very different from those of their bulk constituents and can change very drastically with small diameter changes. Nanoaluminum, for instance, has extremely high reactivity due to its high specific surface area (SSA). Nanoaluminum can have specific surface areas on the order of 50 m2/g. Particle ignition temperatures of nAl particles have been experimentally measured below 1000 K23-25, while the ignition temperature of micron and larger aluminum is near the melting point of aluminum oxide (2300 K). A good summary of the experimental data collected on aluminum particle ignition temperature as a function of particle diameter is given by Trunov et al.26 Nanoaluminum ignition delay and burn time are both shorter than for micron aluminum. Both of these characteristics lead to higher performance in solid propulsion systems. Nanonaluminum particles are typically spherical in size and have an alumina shell of thickness 1.5-3 nm. The properties of nAl particles can vary greatly between different production methods, manufacturers, and individual
10 batches. Understanding the formation of nAl particles from high energy processes is still incomplete. Thus, a significant amount of effort has been expended trying to characterize the different types of nAl commercially available. Characteristics that have been identified as being important to the combustion applications are the specific surface area (SSA), particle size distribution, morphology, degree of agglomeration, and oxide shell thickness. Most efforts to characterize the physical structure of nAl particles rely on the use of direct visual methods such as TEM (transmission electron microscopy), SEM (scanning electron microscopy), and AFM (atomic force microscopy). These methods all produce visual images of small samples of the particles and can provide information about particle shape and size, oxide coating thickness, elemental composition, and surface roughness. Reliance on these methods alone to characterize nAl may result in inaccurate characterization due to the statistical insignificance of a single microscopy image. Mang et al. 27 conducted a series of nAl particle measurements in which small angle x-ray scattering (SAXS) and small angle neutron scattering (SANS) were used in conjunction with SEM image-driven modeling to improve statistical significance. Mang’s method provided data for a sample volume on the order of 1 to 200 mm3 and is described in more detail in Section 4.2. Another important characteristic of nAl is the passivation coating. The coating typically contains aluminum oxide but may also contain aluminum nitride as well as hydrocarbon and other impurities. Rudimentary methods of determining the mass percentage of the particle which is coated involves the use of chemical reactions to produce and measure the amount of hydrogen gas produced from reaction of elemental aluminum with water. 28,29 This volumetric method first described by Fedotova30 and Cliff29 is described in detail in Section 3.6. The volumetric method, however is unable to accurately measure the amount of elemental aluminum or coating mass in particles coated with nonaluminum oxide and non aluminum nitride coatings. Hence it was replaced with
11 the cerimetric and permanganatometric methods which are also described in detail in Section 3.6.28 Further research into coating composition was performed by Kwok in 31
2002. . Kwok found through use of Auger electron spectroscopy (AES) and xray photoelectron scattering (XPS), surfaces of 180 nm nAl (Argonide) are hydrated oxide layers containing sorbed hydrocarbon vapor, oxy-carbon, and oxy-nitrogen species as well as an appreciable amount of aluminum nitride. The temperature dependence of nAl oxidation and nitridation has been studied extensively by many.23,31,32 Il’in et al. performed thermogravimetric analysis (TGA) experiments on 130 nm ALEX powders to determine the thermal oxidation behavior of ALEX in air. They found that heating samples of powder at the rate of 10 ºC/min resulted in a rapid exotherm accompanied by rapid mass increase around 550-600 ºC (Tmelt,Aluminum=660 ºC). A second but less rapid mass increase occurred from 700-1000 ºC. Similar experiments by Kwok et al. showed a rapid exothermic heat release and mass increase from 400 to 500 ºC in air and a more gradual mass increase from 700 to 800 ºC in nitrogen gas.31 Johnson et al.32 found that oxidation of nAl particles of size 80 and 120 nm, oxidation begins at 520 and 600 ºC, respectively. The electrostatic discharge (ESD) ignitability of aluminum powder is size dependent as well. This observation poses many safety concerns regarding aluminum-water propellant preparation and handling. Little is known about the ESD ignition mechanism of nanoaluminum particles. ESD ignition of micron sized energetic material particles was studied by Skinner et al. in 1997.33 They suggested that the ESD ignition of micron powdered energetic materials is dependent on the rate kinetics of the material and that ignition can be predicted based on a critical temperature criteria. Skinner et al. calculated these critical temperatures for a large variety of energetic materials using the FrankKamenetskii formula for 20 "m diameter particles. The results of this correlation compared well with ESD sensitivites obtained experimentally using an approaching needle ESD testing apparatus.
12 It is unlikely Skinner’s method can be used to predict ESD sensitivity of nAl. Some ESD sensitivity data for nAl powders have been reported by Higa.34 Higa’s observations indicate that ESD ignition of nAl is also strongly dependent upon humidity, agglomeration, compaction, and confinement. He reported ESD sensitivities of 0.2, 0.8, 0.1, and 2,500 mJ for particle sizes of 33, 80, 208, and 5,000 nm, respectively. Higa also noted that solvent sonication of 80 nm particles followed by drying decreased ESD sensitivity from 0.4 to 1.2 mJ. No results for the ESD sensitivity of aluminum-water mixtures have been reported to date.
2.3.3. Coatings The increased reactivity of nAl particles is beneficial to combustion applications but poses storage problems. Others have shown that nAl particles, when stored in humid, room-temperature environments, will oxidize completely to aluminum oxide.29 This oxidation is a result of diffusion of water and oxygen through the aluminum oxide particle coating to the solid aluminum core. Application of a different surface material with lower diffusivity would prevent this oxidation from occurring. Other characteristics to consider when selecting a coating include heat of combustion, density, decomposition temperature, application process, and compatibility with other propellant ingredients. Yagodnikov et al.35 performed thermodynamic calculations on the combustion of aluminum and oxygen with the addition of various fluorine containing polymer coatings in order to determine the effect of polymer coatings on specific impulse and condensed combustion products. Calculations were performed for coating weight percents from 0 to 8%. Results show that for all but one of the fluorinated coatings studied, specific impulse increases linearly for coating mass additions up to 8%. The highest specific impulse increase was 0.25% and was caused by addition of 8 weight percent [tetrakis(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyloxi)silane] (Si[OCH2(CF2-CF2 )3 H]4), which is referred to as coating A2 by Yagodnikov et al. Addition of this same coating proved to be the most effective at reducing condensed phase combustion
13 products, causing a mass reduction of nearly 4%. Addition of [bis(2,2,3,3,4,4,5,5-octafluoropentyloxy)dichlorosilane] (Cl2Si[OCH2(CF2-CF2)2H]2 (coating A3) had a nearly similar effect on reduction of condensed phase combustion products. Glotov36 later performed an experimental investigation of the effect of the aluminum coatings researched by Yagodnikov et al. on combustion and the condensed combustion products Various coatings were applied to ASD-4 aluminum powder (average diameter 8 to 9 "m) and mixed uncoated and coated varieties of ASD-4 into similar formulations of AP/Al/HMX composite propellant. Propellant was cast into 8 mm diameter cylindrical strands. Samples were ignited in inert argon at 0.15 and 4.6 MPa inside a Crawford bomb modified to allow collection of condensed combustion products. The condensed combustion products were collected after each test and analyzed. Results show that for all propellants an increase in pressure caused an increase in agglomerate size and a decrease in mass of agglomerates. Addition of coating A3 decreased the amount of unreacted aluminum in condensed phase products at low pressures but significantly increased the amount of unreacted aluminum left at high pressure. Coating A2 caused a noticeable decrease in propellant linear burn rate at both low and high pressures. Coating A3 was very effective at reducing the mass of agglomerates at high pressures but was ineffective at low pressure. Organic acid coatings have been studied by Gromov et al.37,38 and have been recommended to prevent oxidation of nAl particles in aluminum-water applications. In one study, ALEX nanoaluminum powder was coated with organic coatings of 0.1 weight percent of stearic acid (C18H36O2) or oleic acid (C18H34O2). The percent active aluminum in samples was analyzed, samples were imaged using TEM, and elemental analysis was performed using XRD. Traces of Al4C3 were detected on samples with stearic acid and oleic acid coatings, indicating carbidization of the exterior of the aluminum particle by the acid. In the case of stearic acid, this carbidization protected the aluminum particle better than the aluminum oxide coating found on uncoated particles. The elemental aluminum
14 content of the uncoated and stearic acid coated particles were 74% and 86% by weight respectively. Application of the oleic acid coating severely carbidized the nAl powder, leaving only 45% of the particle unreacted elemental aluminum. TEM imagery of oleic and stearic acid coated particles showed two concentric coatings on particles. The exterior coating is believed to be palmitic acid, but it is unclear whether the interior coating is aluminum oxide or aluminum carbide. TGA analysis showed that oleic acid coated particles began to oxidize at 486 ºC compared to uncoated particles, which began oxidizing at 560 ºC.
2.4. Previous Nanoaluminum-Water Research In the late 1990s and 2000s, aluminum-water research received new interest following the commercialization of nanoaluminum production. Early aluminum-water research progressed slowly because of the difficulty in igniting aluminum-water mixtures, but replacement of "Al with nAl improved propellant ignition, combustion efficiency, and burn rate. The first reported combustion study of nanoaluminum and water mixtures was performed in 2001 by Ivanov et al.39 They created stoichiometric 10 g mixtures of 140 "m aluminum and water. Three weight percent of a polyacrylamide gellant was added to the water prior to mixing with aluminum. The purpose of the gellant is to increase the viscosity of the water such that the aluminum powder remains suspended in the water as a quasi-homogenous mixture. Mixtures are held at constant temperatures between 50 and 75ºC for up to 40 minutes while the volume of hydrogen gas produced from the reaction is continuously measured. Gas production was slow, taking between 10 and 40 minutes to complete, depending on the temperature. Results indicate that the aluminum and water reaction is capable of proceeding even at moderate temperatures when nanoaluminum is used. Ivanov et al. observed that induction time for the reaction of nAl and water exponentially decreases with increasing temperatures at moderate temperatures.
15 Ivanov’s moderate temperature gas measurement experiments were repeated again in 2005 by Streletskii et al.40 Ultrafine aluminum powder (UFAP) of 120 and 220 nm diameters was vibrationally milled with carbon to create an Al/C composite powder. This powder was mixed with water and held isothermally at temperatures between 50-90 ºC in a similar fashion. Streletskii et al. found that at temperatures below 90ºC the reaction proceeds slowly over the course of 1040 minutes but transits to a fast thermal explosion upon heating beyond 90ºC. They further determined by XRD that in the low temperature reaction regime, production of solid pseudobohemite (AlOOH) is more important than production of aluminum oxide. For temperatures above 90º, the majority of solid products was !-Al2O3 and Al4C3. In 2004 Ingenito and Bruno2 performed detailed calculations on the application of aluminum and water propulsion systems for space propulsion. They studied the effect of equivalence ratio, expansion ratio, chamber pressure, addition of hydrogen peroxide, and oxide thickness. Their results show that vacuum specific impulses of the aluminum and water combustion system can achieve specific impulses in excess of 300 s and that performance can be increased to 310 s with addition of 65% hydrogen peroxide (chamber pressure of 10 atm and expansion ratio of 100). Ingenito and Bruno concluded that a nanoaluminum-water propellant would have application in space propulsion and would be particularly suited to microthrusters. In 2006 Shafirovich et al. used nanoaluminum to improve combustion stability and the hydrogen yield of sodium borohydride (NaBH4)-water reactions and eliminated the reaction’s need for a ruthenium catalyst.41 The combustion system was determined to have high theoretical hydrogen yields of 6 to 11% by weight depending on stoichiometry. Experiments were carried out using 80 nm aluminum (manufactured by Nanotechnologies). Experimental hydrogen yields were around 70 to 80% of theoretical maximum values. The highest experimental yield of 6.5 weight percent was achieved for an Al:NaBH4 mass ratio of 1:3. Shafirovich et al. added small amounts of sodium hydroxide (NaOH) to their
16 mixtures in order to stabilize the borohydride at room temperature. They may have been able to achieve higher conversion efficiency if they had been able to eliminate the NaOH, which may be decomposing the aluminum oxide shell on aluminum nanoparticles, causing aluminum to prematurely oxidize. Shafirovitch et al. also reported achieving 5.6% by weight hydrogen yield for stoichiometric aluminum and water. This result is 50% of the theoretical maximum amount of hydrogen. In 2007 Risha et al.42 performed detailed combustion experiments on nanoscale aluminum and water propellants. This work marked the first aluminumwater combustion experiments in which a gellant was shown to be unnecessary. The effect of pressure, equivalence ratio, percent aluminum oxide, and particle size on the linear and mass burning rate were determined. Calculations of the adiabatic flame temperature were also carried out. Mixtures of aluminum and water were loaded into 8 mm diameter quartz tubes and ignited in an argon filled Crawford bomb at various pressures and room temperature. Risha et al. found that for pressures ranging from 0.1 to 4.2 MPa, the linear burn rate of mixtures of 38 nm aluminum-water had a pressure exponent of 0.47 and that pressure dependence was insensitive to variation of equivalence ratio. Risha performed experiments with particle diameters of 50, 80, and 130 nm. Based on experiments with these three particle sizes, data suggests that bulk propellant linear and mass burning rates are inversely proportional to particle diameter. In 2008 Risha et al.43 continued work on aluminum-water propellants by measuring the H2 conversion efficiency of propellants. Risha et al. combusted small samples of aluminum-water propellant in a small volume Parr cell combustion bomb filled with argon pre-pressurant. Samples were ignited using a nickel-chromium hot wire and the gaseous combustion products were analyzed using a gas chromatograph. Conversion efficiencies for aluminum-water propellants were found to vary between 75%-95% for mixtures containing 38 nm particles. Conversion efficiency was found to be sensitive to confinement and packing. Addition of 3% polyacrylamide gellant appeared to have minimal effect
17 on conversion efficiency. Initial pressure affected conversion efficiency only slightly. Mixtures using 80 nm and 130 nm particles were extremely difficult to ignite. Nearly all conversion efficiencies were higher than those published by Shafirovich, which were around 50%.41 The relationship between mass burning rate and particle diameter was also examined for stoichiometric aluminum-water mixtures. As particle diameter is further decreased, mass burn rate appears to increase almost exponentially. In 2008 Risha et al.44 investigated the effect of hydrogen peroxide addition on the combustion of aluminum and water propellants. Hydrogen peroxide concentration was varied between 0-32% and small samples of propellant were ignites in a Crawford pressure vessel bomb described in Risha et al, 2007.42 Experimentation revealed that addition of 32% hydrogen peroxide results in an increase in linear burning rate from 9.6 to 58 cm/s and a mass burning rate increase from 6.9 to 37.0 g/cm2-s. Mass fractions of hydrogen peroxide above 32% resulted in an accelerated combustion behavior that destroyed the quartz sample holders. High speed imagery reveals the presence of flame fingers penetrating past the flame front and into the unburned propellant. Experiments with 10% and 25% hydrogen peroxide suggest mass burning rate pressure exponents of 0.44 and 0.38, respectively. These exponents are similar to those reported for pure nAl-H2O combustion and suggest an overall first-order reaction.42 Pressure dependence above 5 MPa appears to be less sensitive. One explanation for this behavior is the dilution of the propellant caused by interstitial penetration of high pressure, inert argon gas during testing. Shortly after the work of Risha et al. in 2007,44 Pérut et al. of SNPE Matériaux Energétiques45 presented limited initial experiments on a functional aluminum-ice-cryogenic solid propulsion system. Strand burn tests conducted in a pressurized Crawford bomb suggested that the pressure exponent of compositions using bimodal micron-nano aluminum particle distributions are sensitive to composition. A pressure exponent of 0.36 was found for compositions containing only 60% water and 40% nanoaluminum by weight. The
18 pressure exponent decreased to 0.3 when 50% of the nanoaluminum was replaced with micron sized aluminum, and a pressure dependence of 0.12 was found by replacing 75% of the nanoaluminum with micron-sized aluminum. SNPE molded a formulation of H2O/5 "m Aluminum/200 nm Aluminum (60%/20%/20%) into a center perforated propellant grain of 86 mm outer diameter, 60 mm inner diameter, and length 157 mm. With a nozzle sized to maintain a chamber pressure of 3 MPa, the aluminum and ice motor was ignited using an HTPB/AP/Al composite igniter. SNPE hypothesized that grain ignition is not homogenous across the entire burning surface. This resulted in chamber pressures only reaching 2 MPa instead of the predicted 3 MPa. Analysis of the condensed phase products inside the grain revealed that 17% of the aluminum remained unoxidized.
2.5. Summary Early research into the combustion behavior of aluminum and water recognized the energetic potential of the reaction. Early experimentation typically required addition of a substantial amount of energy to mixtures to cause ignition and typically resulted in highly incomplete combustion. Nanoaluminum solved many of the difficulties encountered by early aluminum-water research, improving ignitability, increasing combustion efficiency, and increasing burn rate. A significant amount of work has been done in the last five years on the characterization of nanoaluminum and water propellants. However, little investigation has been done on their safety characterization. Ivanov’s work shows that nanoaluminum and water mixtures produce hydrogen gas at moderate temperatures. A method of propellant storage preventing this reaction must be implemented to suppress the reaction until ignition is desired. Ivanov’s work shows that the rate of reaction is strongly dependent upon temperature.39 Ivanov’s and SNPE’s works together suggest that freezing the water in an aluminum-water propellant may prolong storage and make it feasible as a propellant. Particle coatings have also been shown to improve the storage
19 properties of aluminum nanoparticles in air and may prevent nanoaluminum and water propellants from reacting at storage temperature. The theoretical performance of aluminum-water propellants is higher than composite HTPB-APAl propellants and may be a feasible alternative in some applications.
20
CHAPTER 3. DESIGN AND CONSTRUCTION OF EXPERIMENTAL EQUIPMENT
3.1. Electrostatic Discharge Sensitivity Testing Machine
3.1.1. Background & Machine Design Many propellants are sensitive to and can be initiated by electrostatic discharge (ESD). In many situations, it is possible for a static spark emitted from a person’s hand to initiate a propellant. In order to determine the ESD ignition susceptibility of different aluminum-ice (ALICE) propellants, an ESD testing apparatus was created. The modified design was based on a device designed and constructed at Los Alamos National Lab. A circuit diagram of the Purdue ESD machine is shown in Figure 3.1. The Purdue ESD machine has the capability to test over a wide range of energies. The energy delivered to a sample is calculated using the equation E = 1/2 * C *V 2 , where E is the energy in Joules, C is the total capacitance in
Farads, and V is the charging voltage in Volts. With a voltage range of 0 to 8 kV !
and a capacitance range of 0.1 to 1.1 µF, the Purdue ESD machine has a testing energy range of 0 to 35.2 J. Several modifications were made to the Los Alamos design to improve safety and reliability. The machine uses a 15 W, 10 kV Ultravolt high-voltage DC power supply. The power supply is equipped with a current limiter and is designed specifically for capacitor charging applications. The charging voltage is controlled using a 10 k# potentiometer. Vacuum relay switches are used to disconnect the high voltage power supply from the capacitor bank before discharge through the material. This eliminates the possibility of a high voltage
21 overload caused by ground return circuit leakage. As a safety precaution, an additional vacuum relay is placed across the capacitor bank such that its circuit remains open while the machine is powered and the capacitor bank has been stored in an isolation box separate from the rest of the machine. In the event that the machine loses power (machine is shut off or unplugged), the vacuum relay short circuits and discharges the capacitor bank, allowing the capacitors to be safely handled. High voltage, 10 kV wiring and potting compound are used to make all high voltage connections. The time constant, ", of the circuit is the amount of time required to charge the circuit to 63% of its peak capacity. With a 1.1 µF capacitor bank the time constant of the circuit is 1.1 ms. Time to charge the capacitor bank to within 99.9% of its peak capacity is 6.6 ms. An optional resistor and capacitor are placed inline after the capacitor bank in order to mimic the resistivity and capacitance of the human body. Typical values of this resistor and capacitor range from 150-1500 # and 60-300 pF, respectively.46 Static buildup that causes ESD is highly sensitive to environmental humidity conditions. To control the humidity of the testing environment, the ESD testing stand is placed inside a sealed polycarbonate glove box (Figure 3.2). The relative humidity inside the glove box is controlled using a saturated potassium bicarbonate solution. Potassium bicarbonate is used as the salt, as it will maintain a relative humidity of 50% inside the chamber.47 When relative humidity is below 50%, some of the water in the bath is released into the air. This in turn causes some of the salt in solution to settle to the bottom of the water bath. When humidity in the chamber is higher than 50%, undissolved salt in the bath causes water vapor to condense in the bath, adding liquid to the bath. Undissolved salt on the bottom of the bath then becomes suspended in the solution to maintain the bath at a fully saturated state. Access to the machine and addition/removal of test articles is accomplished through the use of two hand ports on the front of the box as shown in Figure 3.2. The machine output voltage is sampled at various potentiometer
22 settings and a linear equation is created relating potentiometer setting and output voltage.
23
Figure 3.1 ESD Testing Machine Circuit Diagram.
24
Figure 3.2 ESD Testing Machine and Sealed Environmental Chamber.
3.1.2. ESD Machine Operating Procedure Prior to each test the machine’s stainless steel needle and the aluminum sample holder are replaced. The chamber’s relative humidity and temperature are recorded. An aluminum sample holder is loaded with 0.05 g of sample and is placed on the copper contact on the bottom of the test stand. An initial energy level is selected (typically 1 mJ) to begin testing at. The required capacitance and 2
charge voltage are calculated using the energy equation, E = 1/2CV . The capacitor bank is loaded with the proper capacitors and the machine is plugged in. The calibration curve is used to determine the set the
!
25 potentiometer to deliver the proper charge voltage. The charge button is then turned on for ten seconds. The charge switch is then turned off, isolating the high voltage power supply from the capacitor bank and the test stand. The needle is then slowly lowered toward the test article until a spark arcs from the needle to the sample. A positive ignition is characterized by visible deflagration, a small explosion, or visible combustion products. Prior to conducting a new test, the copper contact is cleaned with acetone (if necessary) and the contact needle and aluminum sample holder are replaced. The energy level, sample mass, and whether the test was a “GO” or a “NO GO” are recorded. If the test was a “GO,” the next energy level will be selected as one log unit lower than the previous test. If the test was a “NO GO,” the next energy level will be one log unit higher. When a point at which the result of the test begins to alternate between “GO” and “NO GO” occurs, 20 or more tests are conducted and recorded. The Bruceton statistical formula is used by calculating the 50% ignition energy level using the lesser of
50% LEVEL = E min + E int erval
" (L * n ) " (n ) " (L * n ) " (n ) GO
(3.1)
GO
50% LEVEL = E min + E int erval !
NOGO
(3.2)
NOGO
In the Bruceton formula, Emin is the minimum energy level tested at and Einterval is the energy interval size. L is the level of the step height. The lowest energy level
!
in the series is designated as level zero and the next energy is designated as level one. The number of successful ignitions and failed ignitions at a given energy level are designed by nGO and nNOGO, respectively.48 In addition to testing the materials of interest, other common “baseline” materials such as PETN (pentaerythritol tetranitrate) are tested. This allows the 50% ignition levels of ALICE propellants and nAl powders to be compared to the levels of other commonly documented explosives and propellants. There is a significant amount of discrepancy in determining whether ESD events are “GO”
26 events or “NO GO” events. For this reason, each user of the machine performs his or her own baseline tests of PETN or another commonly documented material.
3.2. Impact Sensitivity Testing When classifying the safety of a propellant it is necessary to think of all ways that the propellant could be accidentally initiated. Those initiation modes that are most common should be examined first to determine the propellant’s sensitivity to a particular event or situation. Many accidental propellant initiations involve a combination of two initiation modes. Often a propellant may be insensitive to both of these modes, but the combination of the two modes may still result in accidental initiation. It is difficult, likely impossible, to identify and test for every single accidental initiation method. However, testing of those that are most common can provide a rudimentary idea about how sensitive a propellant is. One particularly common accidental situation involves blunt impact to the propellant. This blunt impact could be imposed by accidentally dropping a piece of propellant, striking a piece of equipment against the propellant, or impacting the propellant with a high energy projectile such as a bullet. An impact chamber apparatus from a previous project was used to test the impact sensitivity of ALICE propellants. The apparatus uses a 5 kg weight dropped from various heights using an electromagnet to determine the drop height necessary to ignite a sample of propellant.
27
Figure 3.3 Impact Testing Machine Chamber Diagram.
The apparatus consists of an enclosed chamber in which a sample of 0.050 g of propellant is loaded onto a 1 inch square piece of 120 grit sand paper according to MIL-STD 175148. The entire chamber is assembled with test sample inside as shown in Figure 3.3. The chamber is then secured to the base of the drop tower using the retainer ring as shown in Figure 3.3. The 5 kg weight is then raised to the desired drop height and is secured using an electromagnet. The weight is then dropped remotely by turning off power to the electromagnet. Pressurization of the chamber is measured using a PCB Model 102M232 5,000 psi dynamic pressure transducer and Tektronix TDS1002B oscilloscope. Ignition is determined based on the pressure waveform acquired using the oscilloscope, visual inspection of remnants inside the impact chamber, and sound. The waveform of a typical positive ignition is shown in Figure 3.5. Results of a test performed on PETN powder are shown in Figure 3.6. The drop height of the weight is adjusted based on the outcome of the previous drop using the Bruceton method as described in Section 3.1.2.
28
Figure 3.4 Impact Testing Machine Assembled.
29
Figure 3.5 Typical pressure trace of a failed ignition (left) and a successful ignition (right).
Figure 3.6 Impact chamber typical results. TOP: failed ignition. BOTTOM: successful ignition.
30 3.3. Shock Sensitivity Testing Solid propellants contain a high amount of energy that can potentially be released. Accumulation of large quantities of confined propellant could pose a risk of detonation through deflagration to detonation transition (DDT). Furthermore, because of their energetic nature, it is possible that a propellant production facility or propellant storage bunker could be the target of a terrorist attack. Briefly, during a DDT event, an accelerating deflagration wave accelerates through a solid. As propellant is consumed, pressurization occurs locally in front of the traveling deflagration due to propellant compaction. Similar to the Doppler effect experienced by an observer as a vehicle approaches, the frequency of the pressure perturbation is higher in front of the traveling deflagration. Velocity of the deflagration continues to increase to near the speed of sound in the unburned propellant, at which time the waves begin to pile up on top of each other. A shock wave is formed either at the front of the compacting plug or further into the unreacted propellant. Detonation travels quickly through the remaining propellant while the plug remains unburnt.49 Similar to DDT, the shock wave resulting from explosion of a nearby warhead could cause nearby propellant to detonate as well. In order to develop propellant formulations that are resistant to DDT and shock initiation, it is desirable to study the fundamental behavior of propellant when exposed to a shock wave. Witness plate experiments similar to those described by Suceska50 have been performed on various formulations of ALICE in order to determine whether or not a propellant will detonate when exposed to a strong shock wave. A 1” by 1” by 1.75” 6061-aluminum block is center-drilled with a hole of diameter 3/8”. The center-drilled block is placed atop a 1.5” square 6061aluminum witness plate of thickness 1/2” as shown in Figure 6.1. The centerdrilled block is filled with 3 grams of ALICE propellant and is placed in a freezer at -25 °C until frozen. Three grams of plasticized PETN explosive is placed on top of and in direct contact with the ALICE. An EBW (exploding bridge wire)
31 detonator is placed in the center of the PETN charge. The assembled test article is then placed in a fragment box and the EBW is initiated remotely using a capacitor discharge unit (CDU). The EBW ignites the PETN, which detonates and serves as a donor charge. The shock wave generated by the detonation of the PETN contacts the ALICE and is either dissipated and “knocked down” by the ALICE or is strong enough to initiate significant reaction within the ALICE that is capable of supporting the shock. Detonation of the ALICE propellant is indicated by a dent in the witness plate where the detonation shock wave impacts the plate and destruction of the center-drilled block into small pieces. Failed detonation is characterized by lack of indentation on the witness plate and larger pieces of the recovered center-drilled block.
Figure 3.7 Witness Plate Experimental Setup.
3.4. Crash Deposition Viton Coating Technique As suggested by Cliff et al., Viton is an attractive candidate for coating aluminum particles because of its high halogen content and inherent ability to reduce the amount of solid combustion product through formation of gaseous aluminum oxy-fluorides.29 Viton coatings have been shown to reduce
32 electrostatic discharge sensitivity of nanoscale thermites.51 In order to study the effect of addition of a Viton coating to aluminum nanoparticles, a coating was applied to a batch of 80 nm Novacentrix aluminum powder. The coating was applied by dissolving Viton in a solution of acetone in a beaker for 24 hours. Aluminum nano-powder was added to the solution and sonicated for 2 minutes with a Branson Model 450 sonicator with straight horn. The resulting solution was dark gray in color and the aluminum powder settled out of the solution very slowly. A volume of hexane 5 times larger than the volume of the solution was added to the solution of hexanes, Viton, and nano-aluminum while sonication was continued for another 2 minutes. After addition of the hexanes, a think coating of Viton was observed to settle out of solution on the side of the beaker and sonicator horn. When sonication was stopped, the resulting particles fell out of solution much quicker than before addition of hexanes, indicating increased agglomeration of particles. The particles were allowed to settle and excess hexanes/acetone solution was evaporated off. The resulting powder was dark grey in color and exhibited partial hydrophobicity. When vigorously mixed with water, a fraction of the powder mixed successfully while the rest remained on the surface of the water without mixing.
3.5. Crawford Combustion Bomb Strand Burn Experiments A Crawford style combustion bomb was used to carry out combustion experiments in the absence of air and at near constant pressures. The combustion bomb used in these experiments has a working pressure of 0 to 6,000 psia and chamber volume of 1.6 L.52 An image of the combustion bomb and a schematic diagram of the experimental setup can be seen in Figure 3.8 and Figure 3.9, respectively.
33
Figure 3.8 Picture of Crawford Combustion Bomb and Canon XL2A Camera.
Figure 3.9 Schematic of Combustion Bomb, Strand, and Igniter.
Propellant ingredients are weighed using a Mettler Toledo XS105 analytical balance and are mixed either by hand or in a Ross DPM-1Q dual
34 planetary mixer and loaded via syringe injection or packing into quartz tubes of 8 mm ID, 10 mm OD, and 60 mm length (ChemGlass PN: CGQ-0800T-16) and are frozen for 24 hours. Prior to packing, the end of the quartz tubes are epoxied to the head of a $” long %-20 bolt to provide a mounting fixture for the strand in the combustion bomb. Sample dimensions and mass are recorded prior to and after freezing to determine percent increase in volume and propellant packing density. Samples are then loaded into the Crawford bomb strand holder. An igniter consisting of a 24 gauge nickel-chromium wire coated with a dried slurry of Bullseye™ smokeless powder and acetone the size and shape of a pencil eraser is inserted into the top end of the strand sample as shown in Figure 3.9.52 Prior to ignition, the bomb is purged with argon for approximately 20 seconds and is then pressurized to the desired combustion pressure. Typical electrical current required to initiate the igniter is 3 A. Backlit video of the burning strand is acquired through the polycarbonate window of the combustion bomb using a Canon XL2A digital video camera typically set to a shutter speed of 1/4000 and an F-stop of 11. Internal bomb pressure during the combustion process is monitored and recorded using a Setra Model 207, 10,000 psig static pressure transducer and National Instruments NI USB-6281 data acquisition system. A typical pressure signal from a strand burn is shown in Figure 3.10.
35
Figure 3.10 Typical Combustion Bomb Pressurization.
Figure 3.11 Tracker Video Analysis and Curve Fitting Procedure. 36
37 The resulting video from a strand burn is then analyzed using the computer program Tracker53 to manually determine the regression rate of the burning surface during the combustion event. An image of the regressing burn front and the Tracker curve fitting procedure can be seen in Figure 3.11. This process is repeated for several samples over a range of pressures and a St. n
Robert’s Law fit, rb = AP , is assumed to get a power-law fit for linear burn rate, rb (cm/s) as a function of pressure, P (MPa), and two constants—a preexponential, A, and a pressure exponent, n. Mass burn rate per unit burning
! area is then calculated as the product of bulk measured propellant surface density, ! (g/cm3), and the linear burn rate.
3.6. Active Aluminum Content Testing The degree of aluminum oxidation on nanoparticles can vary greatly with particle passivation process, particle size, morphology, and production process. Typical aluminum nanopowders of commercial availability have aluminum oxide coatings of 2-3 nm in thickness. Nanoaluminum particle sizes can typically vary from 30-120 nm in average particle sizes. For this range of particle sizes, a 2.5 nm thick oxide shell around the outside of the particle can account for anywhere between 19% and 91% of the particle’s total weight. Determination of the mass percentage of aluminum oxide on the outside of aluminum nanoparticles is necessary to determine mixture stoichiometry and to assess the quality of aluminum nanopowders. Several methods exist to determine the aluminum oxide content of aluminum nanoparticles. Visual methods typically involve TEM (transmission electron microscopy) imaging of particles and visual measurement of the mean oxide thickness and mean particle diameter. An aluminum oxide density of 3.9 g/cm3 is assumed and the particles are approximated as spherical in order to determine the mass percentage aluminum oxide. This method of determining percentage active
38 aluminum is inaccurate for a number of reasons. Measurements contrived from a few microscope images may not be statistically representative of an entire sample of aluminum powder. Furthermore, aluminum nanoparticles typically form agglomerates and are not always perfectly spherical. Small angle x-ray scattering (SAXS) is an alternative to microscopy that can perform measurements over a large sample volume, yielding statistically significant results. The disadvantage of SAXS is that it requires an x-ray beam source and development of a materialspecific analysis procedure.27 A permanganatometric method can also be used in which Al is reacted with Fe3+ according to the reactions Al + 3Fe 3+ " Al 3+ + 3Fe 2+ and
MNO4 + 8H + + 5Fe 2+ # Mn 2+ + 4H 2O + 5Fe 3+ .28,54 The electrical potential of MNO4"
3+ and MN2+ is known to be 1.51 ! V and the electrical potential of Al and Al is
!
known to be -1.66 V. Potential difference may be calculated and then the quantity of aluminum may be determined based on back-calculation of molar quantities once the above referenced potentials are reached during mixing. Furthermore, equivalence in the second equation is also indicated visually, as excess MNO4will cause the solution to become pink in coloration. The permanganatometric method can be applied to a bulk sample of aluminum, giving a more representative result than imaging. The permanganatometric method has proven to be inaccurate when used on particles containing coatings due to competing reactions with the coating and the chemicals used in the method.28 The volumetric method involves reacting Al with H2O directly and measuring the quantity of H2 gas evolved from the reaction volumetrically to determine the quantity of Al present.28 The reaction of Al with H2O is sped up during the reaction process by adding NaOH to the water prior to mixing. Addition of NaOH to the solution will break down any Al2O3 surrounding the aluminumcore particles, speeding the reaction of Al with H2O according to
1Al2O3(s) + 2NaOH(s) " 2AlNaO(s) + H 2O(l ). The volumetric method is easy to use and requires few chemicals but is prone to error. The reaction of Al with H2O is
!
highly exothermic and can produce enough heat to locally vaporize some water.
39 Time must be allotted to allow the temperature of the water to equilibrate to room temperature. Furthermore, the volumetric method has been shown to overestimate the amount of active aluminum in powders containing protective coatings due to competing reactions between the coating and the NaOH, resulting in additional gas production.30 A diagram of the apparatus used in the volumetric method is shown in Figure 3.12. The apparatus consists of a sealed reaction vessel connected to an open burette tube and a leveling bulb open to the atmosphere. The leveling bulb and burette tube are partially filled with water and the Al, H2O, and NaOH are allowed to react in the reaction vessel. During the reaction process, gas is produced in the reaction vessel, causing an increase in pressure and resulting in a difference in water level readings in the burette and leveling bulb. During reaction the leveling bulb is lowered to keep the pressure within the reaction vessel near atmospheric and reduce the risk of leaking. Volumes are read on the burette prior to and after reaction and the amount of aluminum present in the sample of known mass is calculated using the ideal gas law. The volumetric method was chosen and used with samples of Al powder and ALICE to determine the amount of active aluminum present in the sample. In some cases, the method was also used on coated particles, as SAXS was not available.
40
Figure 3.12 Volumetric Method Hydrogen Measurement Apparatus.
3.7. Full Scale Mixing Procedure Mixing ALICE propellant in an automated mixer poses several difficulties. The propellant is difficult to mix because of the high specific surface area (SSA) of the aluminum nano particles. The aluminum powder used in the mixing process is also an ESD safety concern as well as believed to be a health hazard.55 Furthermore, it has been found that the propellant must be kept cold to prevent thermal cooking and possible self-sustained combustion from occurring. Propellant mixes using inert particles were performed to safely simulate ALICE mixing conditions. A detailed, rigorous safety procedure was developed in order to take into account the safety hazards of mixing ALICE. A mixing procedure for AP-Al-HTPB composite propellant was modified in order to suit ALICE mixing.52 The full mixing procedure can be seen in Appendix B. Some of the modifications to the AP-Al-HTPB procedure are as follows:
41
•
A Brinkman-Lauda RC20 chiller set to 0º C is used to chill the bowl while mixing.
•
The total mass of nano aluminum to be added to the propellant is separated into 4 or more mass additions and mass additions are mixed for 5-10 minutes each.
•
HEPA approved respirators (as specified by nanoaluminum manufacturer Novacentrix), safety glasses, ESD static resistant lab coats, ESD wrist straps, and ESD heel straps (optional) are used when exposed to unwetted aluminum powder.
•
Propellant is vibrated into phenolic tube using a spatula and vibrating shaker table (McMaster PN: 5817K18).
•
Unused propellant and propellant-contaminated waste is disposed of immediately after use in a 5-gallon bucket full of cool to room temperature water. Waste is left in bucket outside for 24 hours to ensure complete oxidation of nano-aluminum waste.
•
MET-LX fire fighting agent and Class D fire extinguishers are kept nearby during the mixing procedure. All large scale ALICE and inert mixes were performed in the Purdue
propellant mixing facility, using a Ross DPM-1Q, explosion proof, 1 quart, double planetary bowl mixer. The mixer is equipped with both heating and cooling capability and can be observed and operated remotely. Images of the Purdue mixing facility are shown in Figure 3.13.
42
Figure 3.13 Purdue Solid Propellant Mixing Facility.
43
CHAPTER 4. MATERIAL CHARACTERIZATION
4.1. Aluminum Powder Varieties Aluminum nano-powder used to make the ALICE propellant was sourced from the companies Novacentrix (Austin, TX), Argonide (Sanford, FL), and the former company Technanogy (Irvine, CA). Average particle sizes ranged from 38 to 100 nm (hundreds of atoms in diameter). Powders from Novacentrix Corp. are produced using a plasma synthesis process16,56 and are passivated in an argon and oxygen environment to create a 2-2.5 nm thick aluminum oxide shell on the outside of the particles. Novacentrix Corp. characterizes each batch of nAl powder produced, measuring the percent active aluminum, Brunauer, Emmett, and Teller (BET) specific surface area, the nominal particle diameter, and the calculated passivation layer thickness.57 The manufacturer-reported active aluminum content of 77%-80% mass was verified using a volumetric method similar to that described by Cliff et al. and Fedotova et al. 28,29 Powders from Argonide Corp. are produced from an aluminum electro-exploded wire technique (ALEX) and are passivated in an air environment.18,32,58 Active aluminum content of Argonide powders was measured to be 74%-90% using the volumetric method. SEM and TEM analysis show that particle sizes of these commercially available powders are normally distributed.27,59 The exploded wire technique used to make Argonide ALEX material typically results in a broader range of particle sizes and a larger standard deviation.32 Aluminum nanopowders are observed to slowly react with air in atmospheric conditions. Samples of aluminum and water left at room conditions have been observed to thermally “cook,” resulting in surface temperatures in excess of 200°C.60
44 Some of the Argonide powders are passivated with what is believed to be a monomolecular layer of palmitic acid that is 2% of the total particle weight (LALEX). Coating production results in reaction of the particles’ surface aluminum with palmitic acid to form an aluminum carboxylate salt protective layer.29 Another variety of LALEX contains a 3% coating of paraffin over the palmitic acid coating. This double-coated form of LALEX was available from Argonide in limited quantities and was observed to burn poorly in air at atmospheric conditions. Detailed information about aluminum powders used is shown in Table 4.1. The palmitic acid-coated and paraffin-coated particles are observed to be more agglomerated than uncoated varieties and exhibit hydrophobicity when mixed with water. Bulk powder color is observed to vary from light gray (Argonide), dark gray (Novacentrix), to black (Technanogy). Color is a function of particle size, degree of oxidation, and coating type. All nano aluminum powder used in these experiments was stored in a Vacuum Atmospheres glove box filled with commercial grade Argon. Both H2O and O2 levels in the box were constantly monitored and never allowed to exceed 1%.
Table 4.1 Nanoaluminum Powder Characteristics. Material Designator
Manufacturer
Mfg. Reported Avg. Particle Size (nm)
M2665 M2666 M2668 M2672 M2609 M2658-B M2665-B M2654 M2548 ALEX-100 ALEX-50
Novacentrix Novacentrix Novacentrix Novacentrix Novacentrix Novacentrix Novacentrix Novacentrix Novacentrix Argonide Argonide
80 80 80 80 80 80 80 80 80 100 50-70
Specific Surface Area (m2/g) 24.4 24.7 25.3 26.1 27.1 27.4 24.4 26.5 25.7 12.7 ___
77 76 79 76 80 79 77 77 79 86 74
Calculated Oxide Shell Thickness (nm) 2.4 2.6 2.2 2.6 2.1 2.2 2.4 2.4 2.2 1.8 2.1
LALEX-100
Argonide
100
12.329
___
___
LALEX-50
Argonide
50-70
___
89.8
___
LALEX-100 DC
Argonide
100
___
___
___
Tech-38
Technanogy
38
49.854.127,42
54.3
2.727
Mass percentage Aluminum
Particle Coating ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ 2% palmitic acid 2% palmitic acid 2% palmitic acid, 3% paraffin ___
45
46
4.2. TEM and SEM Particle Imagery
4.2.1. Overview SEM (scanning electron microscopy) and TEM (transmission electron microscopy) were used to image individual particles and agglomerated groups of particles in order to characterize particle size, oxide coating thickness, sphericality, and degree of agglomeration. Six samples were examined under microscope and are listed in Table 4.2. Sample 6 contains a 10 wt% Viton coating that was applied using a crash deposition technique described in Section 3.4.
Table 4.2 Nano-aluminum SEM and TEM Samples. Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6
Novacentrix 80 nm (M2666) Novacentrix 80 nm (M2665B) Argonide 100 nm ALEX Argonide 50 nm ALEX Argonide 50 nm LALEX, palmitic acid coated Novacentrix 80 nm (M2665B), 10 wt% Viton coated
4.2.2. SEM Particle Imaging Procedure Powder samples were sonicated for approximately 2 minutes using a Branson Model 450 sonicator with straight horn in a solution of hexanes prior to imaging. Samples were kept wet under hexanes solution until imaging. Dried powder was sprinkled onto a sample stub covered with double-coated scotch tape. Excess sample was blown off with a duster and sample was then sputter coated with Pt (platinum) for 30 seconds prior to imaging. Samples were imaged using a FEI NOA nanoSEM field emission scanning electron microscope (FEI Company, Hillsboro, OR) using the through-the-lense high-resolution detector and operating parameters of 5 kV, spot 2.5 and 3.5 mm
47 WD and 200,000X magnification. Images were captured on Kodak SO-163 electron image film. SEM images of samples are shown in Figure 4.1. TEM images were obtained using the bright field method in which the intensity (darkness) of the image is directly related to the molecular weight of the atoms being observed and the thickness of the material. Thus, for individual particles, we infer that higher intensity areas are due to increased Al content and lighter areas indicate presence of Al2O3, palmitic acid (CH3(CH2)14COOH), or Viton.
4.2.3. TEM Particle Imaging Procedure Powder samples were sonicated for approximately 2 minutes using a Branson Model 450 sonicator with straight horn in a solution of hexanes 24 hours prior to imaging. Samples were kept wet under hexanes solution until imaging. Dried powder was sprinkled on a 400 mesh copper grid with formvar and carbon coating that was glow discharged before use. Imaging was carried out using a Philips CM-100 TEM operated at 100 kV, spot 3, 200 µm condenser aperture, and 70 µm objective aperture. Magnification was 52,000X read-out and 52,500X as calibrated with replica grating. Images were captured to Kodak SO-163 electron image film.
4.2.4. SEM and TEM Particle Imaging Results In Figure 4.1, all samples were shown to contain small round particles that tended to aggregate into clumps. The particle surfaces appear smooth. Sphericality and particle sizes of M2666 (image a) and M2665B (image b) appear to be similar, indicating little variation between batches of Novacentrix aluminum. A thin band of low intensity, approximately 2 to 5 nm in thickness is visible around many of the particles. The lower intensity of this band indicates the
48 presence of the aluminum oxide particle coating. Analysis of the oxide coating thickness from intensity analysis is explained in Section 4.3. ALEX 100 (image c) appears to have more variation in particle size than Novacentrix aluminum samples, with some very large particles of size 200 nm and some very small particles around 30 nm in diameter. This is expected, as the exploded wire technique used to produce ALEX particles typically produces particles ranging in size by a factor of about 20.32 Many of the smaller particles appear to be of irregular shape or more agglomerated than the Novacentrix samples. This is due to collision of exploded aluminum ions during the deionization and condensation event that occurs during powder manufacture.56 Samples of ALEX 50 (image d) appear to have similar particle sizes to ALEX 100. ALEX 50 particles appear to be much more spherical than ALEX 100 particles and have smaller, less densely packed agglomerate chains. Large particles of 200 nm also appear to be present in ALEX 50. Palmitic acid coated LALEX 50 is shown in image e. The effect of coating application on the morphology and size of particles appears to be negligible. As in previous images, a thin band of low intensity of a few nanometers in thickness can be seen around the perimeter of most of the particles. This band may indicate the palmitic acid coating present in LALEX particles. An analysis of the band thickness follows in Section 4.3. Image g shows an SEM of the same material and reveals small particulate and particle surface features that were not visible in TEM images. Image f shows Novacentrix material coated with 10% Viton using a crash deposition technique described in Section 3.4. Examination using a TEM (Figure 4.1, image f) shows that particle size and agglomeration appear to be unchanged by the coating process. A large, non-circular feature can be seen in the top right corner of the image. This feature is believed to be a large piece of Viton that failed to coat as it fell out of solution. The Viton appears to have failed to coat the particles and is merely attached to agglomerated particle groups. SEM microscopy (image h) shows that uniform particle coating was not achieved.
49 Evidence of partial coating can be seen on the particle closest to the bottom left corner of the image, however, for most coating, it is difficult to discern between agglomeration due to powder production, agglomeration due to the SEM sputter coating process, and agglomeration due to the Viton coating.
50
Figure 4.1 a) TEM of Novacentrix 80 nm M2666; b) TEM of Novacentrix 80 nm M2665B; c) TEM of Argonide 100 nm ALEX; d) TEM of Argonide 50 nm ALEX; e) TEM of Argonide 50 nm LALEX with palmitic acid coating; f) TEM of Novacentrix 80 nm with 10% Viton coating; g) SEM of Argonide 50 nm LALEX with palmitic acid coating; h) SEM of Novacentrix 80 nm with 10% Viton coating.
51 4.2.5. Particle Size Measurement Determining a size distribution directly from SEM image is only representative of a very small portion of a sample and may not reflect the particle size and morphology of an entire batch of aluminum. However, Mang et al. have characterized aluminum nanoparticle diameters and mean oxide coating thickness with small angle x-ray scattering (SAXS) and small angle neutron scattering (SANS), finding that their results are similar to results obtained through measuring SEM and TEM images.27 Small angle scattering (SAS) looks at an aluminum powder sample size on the order of 1-200 mm3, yielding results that are statistically accurate. In this work SEM and TEM images of M2666, M2665-B, ALEX 100, ALEX 50, and LALEX 50 aluminum powders were analyzed using a Matlab image analysis code and the free program ImageJ.61 ImageJ was used to calculate the gradient of the intensity images. The resulting gradient images were used in the Matlab program “particle_measurement.m” shown in Appendix C to measure the size of particles shown in the images. Sample sizes for each image analyzed exceeded 100 particles and multiple images were used for each aluminum type. Data for diameter, D, was fit to the lognormal probability distribution, (4.1)
and resulted in the parameters µ and !, which are the mean and standard deviation of the diameter’s natural logarithm. The physical mean particle diameter, Dm, was calculated for each particle type according to (4.2) Data was typically within a 95% confidence interval for the fits. The resulting probability density functions and cumulative density functions as well as fit information are shown in Appendix D. A summary of the statistical fits is shown in Figure 4.2. Table 4.3 shows how the fits compare to data collected by Mang et al.
52 Table 4.3 Lognormal Particle Diameters. Dm (nm) 116 101 99 79
Sample ALEX-100 ALEX-50 LALEX-50 Nova 80 Nova 80, 10% Viton 77 †Reported by Mang et al.27
! --4.66 4.55 4.51 4.25
" --0.424 0.350 0.417 0.481
n, meas 192 100 202 492
Dav, BET (nm)† ------70
Dav, SAS (nm)† ------71±7
4.25
0.431
301
---
---
It was found that all particle size distributions are lognormal. This finding agrees with the findings of Mang et al. and the random growth duration model suggested by Kiss et al.27,62 Mang et al. observed a mean particle diameter of 71±7 nm for Nova 80 powder. Standard deviation data was not reported. Little difference in particle size was observed between coated and uncoated 80 nm Novacentrix, suggesting that the Viton incompletely coated the particles, possibly merely increasing agglomeration. There appears to be little difference in the mean particle size of ALEX 50 and ALEX 100. The mean particle size of 50 nm LALEX is slightly smaller than that of ALEX 50, which may be due to errors in the measurement code and the relatively small sample size, n, of hundreds of particles. The palmitic acid coating appears to have an immeasurable effect on particle diameter.
53
Figure 4.2 Aluminum Powder Particle Size Distributions Measured from TEM.
4.3. Particle Coating Thickness Measurement TEM images were analyzed to determine the thickness of Al2O3 and palmitic acid on the outside of aluminum particles. Images used were taken at a magnification of 52,000X. For each particle in an image, the intensity of the image was measured at a random surface location and plotted radially at the particle surface. This process is illustrated more clearly in Figure 4.3. The intensity of the TEM image background is typically around 240 and the intensity of the Al2O3-Al interface is typically between 140 and 180 and is characterized by an abrupt decreasing gradient. For particles that are coated with palmitic acid, the coating-Al interface typically has intensity of 120 to 140.
54 Oxide/coating layer thicknesses are then statistically analyzed using Matlab. Similar to the particle diameter analysis presented in the previous section, thicknesses were fitted to lognormal distributions and were characterized by the mean (µ) and standard deviation (!) of natural log of the thickness. The mean coating thickness, tav, is calculated and reported for each particle type using (4.2). Results of the analysis and the particle distributions are shown in Table 4.1 and Figure 4.4. Detailed results of the analysis are shown in Appendix E.
Figure 4.3 Typical Intensity Plot of Aluminum Particle Oxide Coating (ALEX 50 Particles Shown).
55 Table 4.4 Particle Coating Analysis Results. tav, !, ", meas meas meas Sample (nm) ----ALEX-100 ------ALEX-50 2.38 0.821 0.304 LALEX-50 3.3 1.10 0.433 Nova 80 2.54 0.863 0.376 Nova 80, 10% Viton ------27 †Reported by Mang et al. ‡Calculated from BET specific surface area *Coating is palmitic acid
n, meas ----150 152 123 ---
tav, SSA (nm)‡ 1.76 2.10 2.92* 2.34 ---
Figure 4.4 Lognormal Oxide/Coating Thicknesses.
tav, SAS (nm)† ------2.4 ---
56 The average coating thickness of Novacentrix 80 aluminum was close to the average thickness predicted by the SAS technique used by Mang et al. The coating thickness calculated from BET specific surface area and the assumption of uniform spherical particles. The coating on the LALEX 50 particles appears to have a larger standard deviation than the oxide coated particles. This is likely a result of the non-uniformity of the palmitic acid coating resulting from the coating application process. Both the palmitic acid coating and the aluminum oxide coating thickness appear to both be strongly lognormal, as is shown in Appendix E. This is interesting because of the dissimilarities of the palmitic acid coating process and the Al2O3 passivation process.
57
CHAPTER 5. PROPELLANT AGING TESTING
5.1. Background Information The purpose of this section is to provide motivation that decreasing the storage temperature to below freezing has a significant effect on the rate of oxidation of aluminum with either oxygen or water. Cliff et al.29have studied the effect of oxygen and water exposure time on the aluminum content of aluminum nanopowders. They used an “accelerated aging” technique in which the aluminum powder is stored in controlled high humidity, high temperature environment. At different times during the experiment, Cliff et al. used a volumetric method similar to that explained in Section 3.6 to determine the amount of active aluminum present in a sample of aluminum powder.
5.2. Experiment Setup A similar approach to that taken by Cliff et al. was used to measure the reactivity of samples of aluminum nanopowders in intimate contact with solidified water. Small samples of approximately 0.1 g of stoichiometric ALICE were sandwiched between two one-inch square strips of Teflon to minimize the amount of surface area exposed to air and external moisture. Strips were labeled, mass of mixture recorded, and then placed in a temperature-controlled freezer accurate to ±0.1 °C. Strips were periodically tested over the course of several months. The volumetric method described in Section 3.6 was used to determine the amount of aluminum present in the sample at each time. The aging results were then compared to results obtained by Cliff et al. and are shown in Figure 5.1.
58 5.3. Results and Discussion Cliff et al.29 found that decreases in temperature decreased the rate at which aluminum nanoparticles oxidize in humid air. They found that for both environments tested, oxidation of the aluminum ceased after 10 to 20 days when the particles contained about 5% aluminum by weight. In our work, samples mixed with water and frozen at -25º C showed negligible oxidation within measurement error after 200 days of storage. It is impractical to keep mixtures of stoichiometric ALICE at temperatures at or above room temperature based on results shown by Ivanov39 and Cliff29. If able to do so, ALICE mixtures would likely oxidize quicker than the samples of powder in air since water appears to be a better oxidizer of nano aluminum than air.29 It is unclear how much of an effect temperature decrease alone has on the slowing of the aluminum oxidation rate and to what extent solidification of the water in ALICE contributes to this slowing.
59
Figure 5.1 ALICE Aging Results Compared to Results of Cliff et al.29
60
CHAPTER 6. ALICE COMBUSTION AND SAFETY CHARACTERIZATION
6.1. Equilibrium Calculations
6.1.1. Purpose The purpose of this section is to provide motivation for the experiments described in successive sections and to provide insight into the chemical and kinetic intricacies of ALICE combustion as well as the effect of various additives. In this section the equilibrium analysis process is described and three combustion systems are looked at in detail: Aluminum-Ice (ALICE), ALICEPeroxide, ALICE-Viton.
6.1.2. Cheetah Batch Post Processor Program Equilibrium combustion calculations were performed using the Cheetah 4 and CEA combustion codes.63,64 An interactive GUI-driven pre processing and post processing program was written to setup batch Cheetah calculations and analyze the resulting Cheetah 4 output.65 The program was developed using Matlab 2007R14 and has the capability to quickly plot any number of input or output parameters as well as output an entire data matrix or select table of parameters for analysis in Excel or another program. Code for the program, “cheetah_gui.m,” is shown in Appendix C. The program being used to analyze a Cheetah 4 batch calculation is shown in Figure 6.1. The instruction manual for the post processor program is shown in Appendix F.
61
Figure 6.1 Cheetah Post Processor Program.
6.1.3. ALICE Variation of Stoichiometry and Addition of Hydrogen Peroxide to ALICE Equilibrium calculations were performed to examine the effect of stoichiometry and addition of hydrogen peroxide (H2O2) and Viton on vacuum ISP, exhaust temperature, and exhaust products. Ingenito and Bruno2 have performed vacuum specific impulse calculations of Al-H2O-H2O2 propellants over a range of pressures from 0.1 to 1 MPa. Their results show a peak vacuum ISP of ~310 s with a mixture of 65% H2O2-35% H2O with an oxidizer to fuel ratio of 1.2. Similar vacuum ISP calculations have been computed using Cheetah 4 here for a chamber pressure of 6.9 MPa, an expansion ratio of 100, and varying the mass balance of H2O2 in the H2O-H2O2 mixture and the overall mass Al-mass oxidizer
62 ratio. The mass fraction of hydrogen peroxide was represented as mass of hydrogen peroxide in the total mass of liquids, as this corresponds to the way the propellant is typically mixed—all liquids are mixed first and then added to the aluminum powder. All calculations assume an exit pressure of 0.0001 atm. Resulting vacuum ISP and chamber temperature from these calculations are shown in Figure 6.2 and Figure 6.3, respectively. A maximum vacuum ISP of ~370 s occurs with a mixture of 25% H2O2 and an Al-oxidizer ratio of 1.0. Mixtures of Al-H2O-H2O2 with ~30% H2O2 in the H2OH2O2 mixture were experimentally shown to transition to a violent, convective burning regime.44 Due to this violent combustion behavior and the ability for nanoaluminum-water mixtures to react spontaneously at room temperatures39, propellant mixtures containing more than 25% H2O2 are unattractive. Additionally, the freezing temperature of 25% H2O2-75% H2O mixtures is near -20° C.66 Lower concentrations of H2O2, however, are of particular interest. Values of vacuum ISP of over 300 s are produced over the large stoichiometry range of 0.5 to 1.6 and from 0 to 25% H2O2 addition. The decrease in gradients for vacuum ISP vales near 360 to 370 s suggests that vacuum ISP approaches an asymptote for a solids/liquids ratio of 1.0 and 100% hydrogen peroxide in liquids. As shown in Figure 6.3, temperature gradient with respect to the solids/liquids ratio is much higher for lean mixtures, indicating the improved cooling benefits of lean mixtures associated with water’s high heat capacity. Chamber temperature is an important consideration when using an aluminumwater-hydrogen peroxide propellant in an application, as high temperatures and temperature gradients within a rocket’s structural casing or other components could lead to a multitude of problems. Decreasing the amount of solids in the propellant is also desirable to prevent clogging of the rocket nozzle. Excess water gasifies more readily than excess aluminum, which boils at near the chamber temperatures observed in the aluminum-water-hydrogen peroxide combustion system. By adding 10% hydrogen peroxide to liquids and selecting a fuel lean mixture with a solids/liquids ratio of 0.70, it is possible to duplicate the
63 performance of stoichiometric aluminum-water while reducing the chamber temperature by nearly 300 K. This point of interest is called out on Figure 6.2 and Figure 6.3.
Figure 6.2 Vacuum ISP (seconds), from 6.9 MPa Chamber Pressure With Varying H2O2 Concentration and Solid-Liquids Ratio.
64
Figure 6.3 Chamber Temperature (Kelvin) for 6.9 MPa Chamber Pressure With Varying H2O2 Concentration and Solid-Liquids Ratio.
65 6.1.4. Addition of Viton Performance may be further improved through addition of Viton. Viton can be used to coat nAl particles, making them hydrophobic to improve long-term storage properties, resistance to dry powder ESD ignition51, and prevent accidental propellant ignition in the event that a propellant grain thaws. Equilibrium calculations were performed to investigate the effect of adding 10% Viton to Al-H2O2-H2O propellants. Results of this calculation are shown in Figure 6.4 and Figure 6.5. Addition of 10% Viton results in a maximum ISP of 370 s with an exhaust temperature of 950 K. Exhaust product concentrations for products of interest are shown in Figure 6.5. H2 gas production appears to be insensitive to wt % of aluminum. Concentration of corrosive hydrogen fluoride (HF) gas increases as wt % aluminum drops below 50%. Peak performance appears to occur around 44 wt % Al, at which point formation of aluminum-oxy-fluorides (AlFxOy) becomes prominent. These aluminum-oxy-fluorides decrease the high levels of Al2O3 produced by the combustion of Al-H2O. Reduction of Al2O3 formation is desirable, as it can lead to a reduction of condensed phase exhaust products and can prevent clogging of rocket nozzles and alumina deposition on the inner surface of motors.
66
Figure 6.4 Effect of addition of 10 wt % Viton to an Al-H2O2-H2O mixture with 10 wt % H2O2 in H2O2-H2O mixture is presented. Vacuum ISP is calculated using a 6.9 MPa chamber pressure and expansion ratio of 100.
Figure 6.5 Gaseous exhaust product concentrations of an Al-Viton-H2O2-H2O propellant with 10% Viton and 10% H2O2 in H2O2-H2O is presented. Vacuum ISP is calculated using a 6.9 MPa chamber pressure.
67 6.2. Strand Combustion Studies
6.2.1. Experimentation Strand combustion studies were done on ALICE mixtures in order to determine the effect of variation of stoichiometry for different aluminum nanopowders. Propellant mixing was done in small batches by hand and the testing procedure in Section 3.5 was followed for all tests. A video image sequence of a strand burning in the Crawford bomb is shown in Figure 6.6. Frozen packing densities for different fuels were measured and are shown in Table 6.1 and Figure 6.7. Linear burn rate data are shown in Figure 6.8, Figure 6.10, and Figure 6.11. Mass burn rate data is shown in Figure 6.13. Fuel-rich mixtures and mixtures with 3% polyacrylamide gellant (Poly-A) added to water had a thick, clay-like consistency. Varieties of this consistency were difficult to pack into the 8 mm ID quartz tubes. Mixtures having fuel-lean stoichiometry and especially those mixtures using ALEX and LALEX aluminum had low enough viscosities to allow for injection of the propellant into the quartz sample tubes using a syringe.
Figure 6.6 Video Image Sequence of ALICE Propellant Strand Burning in Crawford Bomb.
68 6.2.2. Results Table 6.1 indicates that packing densities vary between 0.9 g/cm3 for stoichiometric Tech 38 ALICE and 1.6 g/cm3 for stoichiometric Nova 80 ALICE. The %TMD (percent theoretical maximum density) of Tech 38 ALICE was around 42%, while %TMD of all other mixtures were between 60%-80%, indicating difficult in packing the 38 nm stoichiometric material. Argonide ALEX and LALEX mixtures all have larger particle size distributions than Nova 80, inferring a lower specific area and decreased alumina content. This along with the lower densities of hydrogen peroxide and Neodol 91-6 of 1.44 and 1.22 g/cm3, respectively leads to a decrease in packing density. One explanation for the lower %TMD of peroxide containing mixtures may be the formation of voids within the propellant caused by reaction of the peroxide with aluminum during the freezing process. Figure 6.7 shows the effect of variation of stoichiometry on Nova 80 ALICE. The consistency of Nova 80 materials ranged from runny like water to thick like clay for equivalence ratios ranging from 0.5 to 1.33. Despite the change in consistency and the difference in packing method discussed on the previous page, the %TMD remained constant around 80%.
69
Table 6.1 ALICE Frozen Packing Densities at -25 ºC. Variety
Additive
!
Tech 38 Nova 80 Nova 80 ALEX 100 ALEX 100 ALEX 100 LALEX 50 Nova 80 Nova 80 Nova 80 Nova 80 Nova 80
----3% Poly-A 10% Perox, 3% PolyA
1 1 1
Avg Density 0.92 1.59 1.59
1
20% Perox 10% Perox 10% Perox, 3% Neodol -----------
0.092 0.070 0.28
% TMD 42% 80% 80%
1.38
0.048
70%
1
1.27
0.004
64%
1
1.22
0.10
62%
1
1.28
0.039
72%
0.5 0.67 0.75 1.25 1.33
1.32 1.48 1.50 1.66 1.69
0.035 0.023 0.039 0.042 ---
79% 82% 81% 80% 79%
Stdev
70
Figure 6.7 Nova 80 Variation of Packing Density With Equivalence Ratio.
Figure 6.8 shows the effect of variation of stoichiometry and pressure on the linear burn rate of Nova 80 ALICE propellants. Addition of the Poly-A gellant to propellants made them unfavorably dry and difficult to pack. This resulted in more scatter in burn rate data for these propellants. The drier propellant produced grains with cracks which resulted in higher burn rates and a higher overall pressure dependence due to incomplete combustion and flame spread in cracks. Obtaining a fit for all data points with a stoichiometry of 1 results in a pressure exponent of 0.23, which is similar to the exponent of 0.27, reported by Risha et al. 43 for stoichiometric Nova 80 aluminum and liquid water mixtures. Further examination of the stoichiometric data suggests that there is an exponent
71 break in the pressure dependence of ALICE mixtures. This observation, though not completely understood, is similar to observations made by Ivanov et al.67 and Risha et al.43 Risha et al. hypothesized that decreased pressure dependence at higher pressures could be a result of high pressure argon gas penetrating and diluting the propellant. This effect is most easily seen for mixtures with an equivalence ratio of 1 and at pressures above 10 MPa. Fitting of only the lower pressure trend results in pressure exponents of 0.425, 0.496, and 0.478 for stoichiometries of 1, 0.75, and 0.67, respectively. These fits are shown in Figure 6.9 and suggest that for pressures below 10 MPa, pressure dependence and overall burn rates are insensitive to changes in equivalence ratio. This suggests that reduction of the use of aluminum nanopowder could decrease costs without having a strong effect on linear burn rate. Figure 6.10 shows the pressure dependence of various ALEX and LALEX mixtures. In all of these mixtures 10% hydrogen peroxide is added to the water in order to increase the burn rate. ALEX and water alone is difficult to ignite and burns slowly due to the lower specific surface areas and increased melting and ignition temperatures characteristic of larger particles.68 Mixtures containing LALEX palmitic acid coated aluminum particles also contain either Tergitol TMN3 (Dow Chemical) or Neodol 91-6 (Shell Chemical)—both long chained hydrocarbon based surfactants. Addition of a surfactant is necessary to enable mixing of the water and hydrophobic aluminum particles. Pressure exponents for ALEX and LALEX mixtures vary from 0.25 to 0.44. LALEX mixtures were balanced to the aluminum-water reaction of 2Al+3H2O ! 1Al2O3 + 3H2, excluding palmitic acid and Neodol/Tergitol. The combination of both of these fuels cause the overall stoichiometry of the reaction to be fuel-rich, resulting in decreased linear burn rates. Figure 6.11 shows selected burn rate data from Figure 6.8 and Figure 6.10. Addition of 10% hydrogen peroxide to ALEX 100 mixtures causes it to burn similar to stoichiometric Nova 80 mixtures. Figure 6.12 shows burn rates for hand mixed and mixer mixed Nova 80 ALICE propellants with a stoichiometry of 0.75.
72 Mixtures show similar burn rate and pressure dependence. Mixer mixed strands were created by Wood and were mixed according to the Mixing Scaleup Procedure shown in Appendix B. Wood noted that some propellant strands burned incompletely and abnormally fast at pressures above 8 MPa. These results were not shown in the fit. Currently there is no explanation for the faster burning exhibited by some mixer mixed propellant strands. Figure 6.13 shows the mass burn rate of selected ALICE mixtures. Mass burn rate was calculated from average packing density and linear burn rate and is reported in units of mass per unit burning surface. Mass burn rates of ALEX 100 propellants with 10% hydrogen peroxide are similar to those of Nova 80 propellants as well as those Nova 80 aluminum-liquid water mixtures tested by Risha et al.42,43
Figure 6.8 Novacentrix-Based 80 nm ALICE Linear Combustion Rate Pressure Dependence For Various Stoichiometries. Al-Liquid Water Measurements By Risha et al.43
73
Figure 6.9 Novacentrix-Based 80 nm ALICE Combustion Pressure Dependence at Low Pressures.
74
Figure 6.10 Argonide ALICE Linear Combustion Rate Pressure Dependence.
75
Figure 6.11 Selected ALICE Mixture Linear Combustion Rate Pressure Dependence.
76
Figure 6.12 Nova 80 ALICE Hand Mixed and Mixer Mixed Burn Rate Comparison. Mixer Mix Data Used With Permission From T. D. Wood. Al-Liquid Water Fit From Risha et al.43
77
78
Figure 6.13 ALICE Mass Burn Rate Per Unit Area Compared to Aluminum-Water Data by Risha et al. 42
6.3. ALICE Steady State Thermal Profile Energy Much of the difficulty in ALICE ignition can be explained by its thermally thick nature. Thermal thickness, !", is calculated by !" =#$/rb where $#and rb are the thermal diffusivity of ALICE and linear burn rate, respectively. The thermal diffusivity of ALICE is roughly approximated as the mass weighted thermal diffusivity of its constituents--aluminum, aluminum oxide, and water. Calculations were carried out for stoichiometric ALICE using aluminum powder containing 78% aluminum and 22% aluminum oxide. For comparison, the
79 thermal thickness of AP-Al-HTPB composite propellant was calculated using data from Son69. Figure 6.15 shows the thermal thickness of ALICE and AP-Al-HTPB composite propellant as a function of pressure. The steady state thermal thickness of ALICE is almost two orders of magnitudes greater than that of composite propellant. The thermally thick properties of ALICE explain the difficulty in igniting the propellant. For ignition to occur, both a minimum surface temperature must be met and thermal energy must be conducted to a depth on the order of the steady state thermal thickness. The total amount of energy within the thermal profile of steady burning ALICE propellant was also investigated. The thermally thick nature of ALICE and its high heat capacity require a substantial amount of thermal energy to be present in the thermal profile of ALICE burning at steady conditions. In order to calculate the steady state thermal profile energy, the temperature profile within the solid is modeled as a Michelson exponential profile, defined as
$r x' T(x) = (Ts " T0 )exp& b ) + T0 %# (
(6.1)
where x is depth into the propellant, T is temperature at depth x, Ts is surface
!
temperature, T0 is ambient temperature, rb is pressure-dependant linear burn rate determined from a St. Roberts law fit, and ! is thermal diffusivity. Integration of this thermal profile over the entire depth of the propellant and multiplication by the condensed phase density and specific heat yields an expression describing the amount of thermal energy within the propellant condensed phase during steady state burning, x= 0
Qc = "C p
%r x( (Ts # T0 )exp' b *dx &$ ) x=#+
,
(6.2)
where x=0 represents the burning surface, x=-! represents an infinite depth into
!
the propellant, and ", Cp, and k are the propellant density, specific heat, and thermal conductivity, respectively.
80 The thermal conductivity and specific heat of ALICE were approximated by the mass weight averaged properties of its constituents. The thermal profile energy for AP-Al-HTPB composite propellants was estimated as well. Values of !, Cp, k, and rb(P) for composite propellant were taken from 69 and 70. The thermal profile energy was calculated over a range of pressures for a unit of burning surface area and is shown in Figure 6.14. Similar to thermal profile thickness, the amount of energy in the thermal profile of ALICE is more than an order of magnitude higher than that of composite propellant. The approximately inverse exponential relationship with pressure is inherent from the pressure dependence of burn rate. Although this measured thickness is for a steady state burning propellant, it is a close estimate of the conditions necessary for propellant ignition. This thickness is approximate for steady state conditions and experimental conditions will oscillate due to combustion instabilities. Briefly, as pressure rises, the flame front is driven closer to the burning surface, increasing thermal feedback to the propellant and the rate of solid pyrolysis. As a result of increased pyrolysis rate, conduction of heat into the propellant becomes less effective and the thermal profile becomes thinner, slowing pyrolysis and in turn pressure. Solid propellant is pyrolized quicker than heat can conduct into the propellant and the amount of energy within the thermal profile decreases.
81
Figure 6.14 Steady State Thermal Profile Energy of ALICE Propellant.
82
Figure 6.15 Thermal Profile Thickness.
83
CHAPTER 7. MIXING SCALEUP AND LARGE SCALE MIXING
7.1. Use of Inert Ingredients in Mixing Tests Mixes with inert ingredients were conducted in the Purdue Propellant Mixing Facility (Figure 3.13) prior to conducing large-scale mixes with ALICE propellant. Inert mixes provide an opportunity to observe and resolve any problems that may occur during ALICE mixing without wasting costly nano aluminum or exposing lab workers to unnecessary hazards. Solid inert mix ingredients were selected in order to simulate the wetting characteristics of nano aluminum. A mixture of Cab-O-Sil fumed silica (T. H. Hillson), and ceramic microspheres (3M Corporation) were used to create a solids mixture that had the same specific surface area characteristics as nano aluminum. Ideally aluminum oxide nano powder was to be used, as surface characteristics and wetting characteristics are most similar to those of aluminum nano powder. Characteristics of the fumed silica and ceramic microspheres are shown in Table 7.1. Cab-O-Sil and ceramic microspheres were mixed in a mass ratio of 1:8.2 in order to produce a specific surface area of 24 m2/g, similar to that of Nova 80 aluminum powder. Inert mixtures were mixed “stoichiometrically” with water under the assumption that ~80% of the inert powder was aluminum and the remaining 20% was aluminum oxide particle coating.
84
Table 7.1 Inert Mixture Component Properties. BET Specific Surface Area‡ m2/g Cab-O-Sil M5 Fumed Silica 3M ceramic microspheres ‡ Reported by Vendor
200 5.167
Davg
Density
!m 0.20.3 5.7
g/cm3 2.2 2.61
Inert mixes with volumes up to 0.5 quart were performed in the Ross dual planetary mixer. Solids were added incrementally to the water and the bowl was chilled to near 0ºC during the mixing process. Mass additions were separated by mixing cycles of approximately 5-10 minutes each. An image sequence of the mixing process is shown in Figure 7.1.
Figure 7.1 Inert Ingredients Mix Results.
85 Initial mass additions of inert powder resulted in successively higher viscosity mixtures. Balling of the propellant occurred at around 67% to 69% total solids addition. Further addition of solids appeared to result in formation of large “towers.” Mixture viscosity eventually decreased with more mixing at around 72% mass solids and remained low for the rest of the duration of the mix. The increase in viscosity and formation of towers is likely due to incomplete mixing and failure to break up agglomerates. The morphology of CabO-Sil fumed silica is 0.2-0.3 !m long chains of silica particles. The chains typically clump together in large visible agglomerates, as is evident from visual inspection of the powder. The decrease in viscosity occurring after mixing is likely due to breakup of agglomerates and silica chains. Single chain size and silica particle diameter are an order of magnitude smaller than the diameter of the ceramic nanospheres. When well mixed, the silica particles act as bearings, lubricating motion within the mixture and decreasing shear. The inert powder appeared to wet easier than aluminum powder, likely due to fumed silica’s strong affinity for water. The mixture of inert ingredient powder and water was used to fill and pack a 3” diameter phenolic tube. The propellant was then frozen then studied. The resulting mixture exhibited large, non-connected porosity due to entrainment of air in the mixing and packing process. The inert powder provided a means to practice the mixing procedure without using aluminum nanopowder but failed to replicated the behavior of nanoaluminum when mixed with water. The inert powder wetted much easier than the aluminum nanopowder and had a bimodal particle distribution, causing inert batches to all be less viscous than aluminum and water batches. The inert propellant did not appear to exhibit thixotropic flow properties, but did suggest that an alternative method of packing would be necessary to remove air filled voids from propellant. The aluminum and water mixture mixed thus far have exhibited thixotropic properties and begin to “set up” when agitation of the propellant ceases.
86 7.2. Mixing Observations and Lessons Learned Although there were several differences in ALICE and inert propellant behavior, several lessons were learned form performing inert mixes and initial ALICE mixes: 1. Another method of bubble removal is necessary to eliminate entrained air bubbles from the propellant. Inert mixture products were dried and fractured. Internal structure of the dried propellants reveled air pockets approximately 1 to 5 mm in diameter. Vibration of the propellant during loading using a vibratory table (McMaster PN:5817K18) decreased viscosity of the propellant enough that some of the bubbles were able to be removed from the propellant by buoyancy forces. 2. Aluminum and liquid water is thixotropic and begins to “set up” if agitation is not constantly applied to the propellant. Constant vibration of propellant during handling using the vibratory table helped loading and propellant handling greatly. 3. The mixture must not be allowed to freeze and successively thaw during mixing. When the water in the ALICE freezes and then thaws, the mixture becomes inhomogeneous, with spheres of higher equivalence ratio forming within the mixture. 4. Application of high, downward directed shear prevents propellant form balling in the dual planetary mixer. 5. All propellant contaminated tools, gloves, paper towels, etc should be stored in or disposed of in a 5 gallon bucket of water in order to oxidize the nanoaluminum without risk of fire.
87
CHAPTER 8. HYDROGEN PEROXIDE AS AN ALICE BURN RATE MODIFIER
8.1. Background Hydrogen peroxide (H2O2) is a common propellant oxidizer and has been used extensively in liquid bipropellant and hybrid propulsion systems.71-73 Sabourin et al. studied the combustion of aluminum, water, and hydrogen peroxide mixtures extensively.44 They found that addition of hydrogen peroxide to an aluminum and water combustion system increases flame temperature, combustion heat release, and linear and mass burning rates significantly. They also found that higher concentrations of hydrogen peroxide (around 32%) can lead to transition to a violent convective burning regime. This chapter explores whether ALICE with hydrogen peroxide exhibits the same characteristics that aluminum-water-hydrogen peroxide propellants exhibit.
8.2. Effect on Stability Nanoaluminum and water mixtures are capable of autoignition at atmospheric conditions. Hydrogen peroxide could increase the risk of autoignition or cause aluminum gasification. Furthermore, there is potential for the hydrogen peroxide to decompose to O2 and H2O on its own, upon initiation by an impurity or other chemical catalyst in the propellant. During several Crawford bomb experiments, samples of ALICE containing hydrogen peroxide were observed to thaw, react, and bubble prior to ignition. In order to test this further, two samples of stoichiometric ALICE were packed into 8 mm ID quartz tubes. One sample contained ALEX 50 aluminum, and 10% hydrogen peroxide. The other sample contained LALEX 50, 10% hydrogen peroxide, and 3% Neodol 91-6. A third sample (not shown) containing
88 stoichiometric ALEX 50 and water was also packed. Samples were frozen and exposed to ambient room conditions for 30 minutes in order to determine if any reaction occurred. A timed sequence of still images from the experiment are shown in Figure 8.1.
Figure 8.1 Hydrogen Peroxide-Aluminum Incompatability Experiments.
Experimentation showed that the volume of the ALEX 50-hydrogen peroxide-water mixture increased 47% over the duration of 30 minutes. Both the LALEX 50-hydrogen peroxide-water and the ALEX 50-water mixtures showed no gasification over this time period. The experiment indicates one of two possibilities:
89 1. Aluminum is reacting with hydrogen peroxide to form aluminum oxide and hydrogen gas. 2. Hydrogen peroxide decomposition to water and oxygen is occurring due to the presence of a catalyst or impurity. The second possibility is much less likely than the first, as preparation methods for all three samples tested were exactly the same. Absence of expansion in the LALEX 50 sample indicates that application of a palmitic acid coating around aluminum is effective in preventing the reaction. There also appears to be no incompatibilities between hydrogen peroxide, palmitic acid, and Neodol at ambient conditions and times up to 30 minutes. Experiments suggest different results for longer exposures, however. Longer tests conducted by T. D. Wood suggest that gas is produced from mixtures of LALEX, Neodol, hydrogen peroxide, and water. The source of the gas production is yet unknown, but may be H2 gas formation as a result of incomplete coating of the nanoaluminum.
8.2.1. Effect on Propellant Shock Sensitivity The effect on detonability of addition of hydrogen peroxide to ALICE propellants was examined using the witness plate procedure described in Section 3.3. Experimental results for ALICE were compared to control tests replacing the ALICE propellant with an air gap and another control placing the PETN booster charge in direct contact with the witness plate. Tests were also done on aluminized AP-HTPB propellant. Images of selected test results are shown in Figure 8.2.
90
Figure 8.2 Witness Plates After Testing With ALICE Mixtures: (a) Control Experiment With 2.5 cm Air Gap, (b) ALEX 50 ALICE (!=1), 10% H2O2, (c) Control Experiment With Ice Only.
Figure 8.2 (a) shows a typical control experiment result using an air gap between the PETN booster and the witness plate. All control experiments using air gaps resulted in fragmentation of the center-drilled block into shards averaging about 1-2 cm in length and severe, global deformation of the witness plate. Control witness plates also exhibited a large divot approximately 0.5 cm deep. The divot likely formed from forceful deformation and localized melting/ejection of aluminum from the portion of the plate nearest to the detonation. Figure 8.2 (b) shows a typical “Go” result from testing an ALEX 50 mixture containing 10% hydrogen peroxide. A square indentation indicating the exterior of the center-drilled block is visible as well as a small indentation below the center-drilled hole. Figure 8.2 (c) shows the result of a control test using only 3 g of ice and a PETN booster charge. The only visible damage inflicted to the witness plate is a faint circular outline indicating placement of the center-drilled hole. All detonability test results are shown in Table 8.1. All compositions containing more than 10% H2O2 in liquids were sensitive to detonation. One test
91 was conducted using 5% H2O2 in water with stoichiometric Nova 80 aluminum. This sample failed to detonate. Samples of AP-Al-HTPB composite propellant was tested as well. Witness plates from AP composite tests indicated presence of a weak detonation. Samples of Tech 38 and water indicated presence of a weak detonation as well. This suggests that aluminum particle size also plays a role in the detonability of ALICE propellants.
Table 8.1 Detonability Sensitivity of Stoichiometric ALICE Mixtures. Description Air gap, PETN charge at top of block No propellant, no air gap, PETN only Ice as propellant and PETN above ice AP composite propellant (aluminized) Nova 80 Nova 80, 5% Hydrogen Peroxide Nova 80, 10% Hydrogen Peroxide ALEX 50, 10% Hydrogen Peroxide ALEX 100, 10% Hydrogen Peroxide Tech 38 5! Al (phi=1)
#Go/#Total 1/1 1/1 0/1 3/3 0/3 0/1 1/1 3/4 2/2 3/3 0/1
Det Sensitivity Yes Yes No Yes (weak) No No Yes Yes Yes Yes (weak) No
8.2.2. Effect on Impact Sensitivity Impact sensitivity of mixtures of ALICE with hydrogen peroxide were tested with varying hydrogen peroxide concentrations. The procedure for impact testing shown in Section 3.2 was followed for all tests. Results of the tests are shown in Table 8.2. Ignition of all ALICE-based propellants shown below was unachievable with the Purdue impact-testing machine, as impact levels exceeded the machine’s maximum drop height of 2.2 meters. Ignition of AP powder in the Purdue machine at a height of 13 to 16 cm suggests that ALICE propellants are far less sensitive to impact ignition than AP-based composite propellants.
92
Table 8.2 Impact Sensitivity of ALICE and Hydrogen Peroxide Mixtures. Material PETN AP (200 µm) Nova 80 ALICE, !=1 Nova 80 ALICE, !=1, 10% Hydrogen Peroxide Tech 38 ALICE, !=1
LANL 50% Level74 13-16 cm 55 cm* Unavail.
Purdue 50% Level 10 cm 38.5 cm > 2.2 meters
Unavail. Unavail.
> 2.2 meters > 2.2 meters
8.2.3. Effect on ESD Sensitivity The effect of hydrogen peroxide addition on ESD sensitivity of the propellant was also investigated. The ESD testing apparatus and procedure described in Section 3.1 was used to test all samples. During testing the machine capacitance was held constant at 0.01 "F. An inline resistance of zero ohms was used to replicate a worst-case scenario. The amount of energy applied to the sample was adjusted by varying the capacitor charge voltage. All tests were conducted in a room temperature environment with 50% relative humidity. Hydrogen peroxide concentration in the stoichiometric samples was varied from 0% to 20%. Results suggest that hydrogen peroxide concentration has no effect on ESD sensitivity of ALICE propellants. All samples were insensitive to ESD ignition, having 50% ignition levels of over 1000 times the ignition energy released by a human static spark. Results of the ESD study are shown in Table 8.3.
93
Table 8.3 Stoichiometric ALICE ESD Sensitivity.
1
50% Ignition Energy >2 J
1
>580 mJ
1 1 1
>430 mJ >430 mJ >400 mJ
mAl/mH2O Nova 80 LALEX 50, 10% Hydrogen Peroxide, 3% Neodol 91-6 ALEX 50, 10% Hydrogen Peroxide Nova 80, 10% Hydrogen Peroxide Nova 80, 20% Hydrogen Peroxide
In all cases of testing ALICE mixtures, no visible flame or combustion event occurred as with testing of aluminum powders. An ignition event for ALICE mixtures was determined as a mass ejection of solid propellant from the bulk sample. This mass ejection may be caused by localized boiling of water and aluminum inside a piece of ALICE propellant, leading to internal pressurization and mass ejection. Another theory is that plasma contact causes localized combustion of ALICE to occur, but combustion cannot be sustained because the short timescale of the plasma event (on the order of !s) is insufficient to allow sufficient conduction into the propellant to develop a thermal layer capable of sustaining combustion. The thermally thick nature of ALICE propellants is examined in Section 6.3.
94
CHAPTER 9. VITON AND PALMITIC ACID COATED PARTICLES
9.1. Motivation The ability of particle coatings to prevent the reaction of aluminum with hydrogen peroxide and water was shown in Section 8.2. Particle coatings may also simplify storage and handling procedures for dry aluminum powder. Nanopowder typically has to be kept in an inert environment to prevent oxidation. Many commercially available polymers and other substances that have low oxygen permeability have been successfully applied to aluminum particles and have been shown to greatly increase aluminum powder storage time.75-77 Coatings also have an added benefit in that they may change the surface characteristics of aluminum particles and decrease agglomeration. 78 Adding fluorine containing polymer coatings to an aluminum-water combustion system has the potential to reduce the amount of aluminum oxide slag buildup inside the chamber and prevent clogging by reducing aluminum oxide formation. Use of a fluorinated coating material such as Viton has been shown in Section 6.1.4 to increase formation of aluminum oxy-fluorides (AlFOx).
9.2. Effect on Mixing Passivation of aluminum particles using Viton and palmitic acid causes particles to become hydrophobic, preventing water from diffusing to the particles’ aluminum core. However, hydrophobicity also inhibits mixing of the aluminum particles with water. In order to achieve mixing, addition of a small amount of surfactant is necessary. A surfactant is any substance that lowers the surface tension of the medium in which it is dissolved. Surfactant molecules typically have one end that is hydrophobic and one end that is hydrophilic, allowing them
95 to act as an intermediate between water and a hydrophobic material. The hydrocarbon end of the surfactant molecule attaches to the hydrophobic material, while the hydrophilic end attaches to water.79 Several different surfactants were considered when considering the best way to mix palmitic acid coated aluminum particles. Palmitic acid coated aluminum particles (LALEX) were used in determining the mixability because they were readily available from the manufacturer, Argonide, and because the Viton coating process produced a great deal of solvents waste. Different concentrations of surfactant were used in water in order to determine the minimum amount surfactant necessary to promote mixing. All mixing tests were conducted with LALEX 50 particles. A summary of the findings is shown in Table 9.1.
Table 9.1 Amount of Surfactant Required to Mix Stoichiometric LALEX 50 With Water. Surfactant Methanol Neodol 91-6 Tergitol TMN-3
Mass Percentage Reqd in H2O 10% 3% 1%
Compatible w/ 33% H2O2 Yes Yes for < 30 min No
Addition of surfactants significantly decreases the burn rate of the propellant because of the addition of extra fuel from the surfactant and the particle coating. Addition of hydrogen peroxide is desirable in order to speed the burn rate and to bring the propellant composition closer to stoichiometric. The large amount of methanol required to promote mixing slows combustion rates too much to make it a desirable surfactant. Mixtures of Tergitol and 33% hydrogen peroxide exhibited noticeable gas production within 30 minutes of mixing, indicating incompatability. This makes it an unlikely candidate for mixtures requiring hydrogen peroxide addition. Of the three surfactants tested, Neodol 916 is the most effective. It allows mixing with addition of 3 wt% to liquids and has
96 been tested to be compatible with hydrogen peroxide in concentrations up to 33% H2O2 for up to 30 minutes.
9.3. Effect on ESD Sensitivity Aluminum nanopowder ESD sensitivity was tested and is shown in Appendix A. Mixtures of LALEX 50 and LALEX 100 had similar or better resistance to ESD ignition than their respective uncoated varieties. Mixtures of LALEX 100 have an ESD ignition energy threshold 3 times higher than uncoated ALEX 100 powders. ESD testing performed by China Lake found similar results34. When a 10 wt% palmitic acid coating was added to 80 nm Novacentrix aluminum, ESD ignition energy was increased from 1.2 to 6.4 mJ.34 ALEX 50 particles appeared less sensitive to ESD than ALEX 100 particles. Discrepancies in test results may be due to slight variations in the relative humidity and temperature within the chamber. Tech 38 powder was highly ESD sensitive, having an ignition sensitivity threshold of 0.5 mJ.
97
CHAPTER 10. FINAL REMARKS
10.1. Summary and Conclusions The combustion behavior of aluminum and water has been studied for more than half a century and has shown energetic potential as a combustion system. The combustion of nanoaluminum and water has drawn attention in recent years and holds promise as a propellant. Safety characterization shows that ALICE mixtures kept at -25 ºC temperatures have storage periods of around 200 days. The propellant has also been shown in many formulations to be less sensitive than AP composite propellants to shock and impact. Following is a brief discussion of important findings discussed in the chapters of this thesis. Chapter 4 discussed characterization of aluminum nanoparticles. The amount of elemental aluminum in each of the samples was tested and SEM and TEM images of the particles were taken. Images show that the aluminum particles are highly spherical agglomerated clusters. Image analysis was performed on the aluminum nanoparticles in order statistically measure the particle size distributions. Comparison to more complex techniques found in literature showed excellent agreement. The thickness of the oxide coating and passivation coating was also measured and statistically quantified using image intensity analysis. Chapter 5 suggests that storage of nanoscale aluminum-ice propellants at temperatures around -25 ºC can prolong the storage period of the propellant to over 200 days without appreciable degradation of performance. This finding provides fundamental motivation for application of aluminum and ice as a propulsion system.
98 In chapter 6 equilibrium calculations are performed showing the effect of peroxide addition on the performance of aluminum and ice propellants. Addition of 10% hydrogen peroxide to the water in aluminum-ice propellants can improve the vacuum specific impulse by nearly 10 seconds, resulting in an vacuum ISP of nearly 347 s. The effect of Viton addition to the aluminum and water combustion system was also investigated. Addition of Viton has the potential to decrease the formation of aluminum oxide but also may cause formation of HF gas for fuel lean mixtures. The workings of a post processing analysis program that was designed to automate operation of the Cheetah equilibrium code was also discussed. Chapter 7 describes the process used to scale up mixing of the aluminum and ice propellant as well as lessons learned in doing so. Experiences in mixing scale up provided many fundamental learnings necessary. Chapter 8 describes use of hydrogen peroxide as a burn rate modifier and the safety implications of its use. Aluminum-ice mixtures with over 5% hydrogen peroxide appeared to be shock sensitive in 3 gram quantities. Hydrogen peroxide addition appeared to have no effect on the impact sensitivity or ESD sensitivity of the propellant. Chapter 9 discusses addition of Viton and palmitic acid nanoparticle coatings to aluminum-ice propellants. Mixing of the hydrophobic Viton and palmitic acid coated nanoparticles could be achieved through the use of surfactants. Addition of coatings to aluminum nanoparticles appeared to decrease their sensitivity to ESD ignition in most cases. The coatings had no effect on the shock sensitivity or impact sensitivity of the propellant.
10.2. Recommendations For Future Work While much of the work involved creation of experimental apparatus and testing of fundamental mixtures of aluminum and water, particle coatings should be further pursued. Nickel coatings have recently shown promise in preventing oxidation of aluminum particles in air. They may also have potential to decrease
99 ignition transient and overall particle burn times, increasing the propellant performance. It is also possible that metal coatings may not increase the agglomeration of particles in the same manner that solvent-polymer coating processes do. Coating processes in which coatings can be chemically bonded to particle surfaces should also be studied. Chapter 8 discusses the incompatibility of hydrogen peroxide with some surfactants as well as its detonable nature when added to aluminum-water. These results, however, should in no way discourage further research involving use of peroxide with aluminum and water. Many applications of this chemical system exist in which there is no risk of detonation. Hydrogen generation is one example. The high amount of agglomerated aluminum oxide in condensed phase combustion products poses several potential problems regarding implementation of the propellant in a rocket motor. The aluminum mass loading of ALICE propellants is between 2-3 times higher than composite propellants and a significant amount of solid product exits the nozzle of a motor during operation, leading to two-phase losses as well as energy loss due to burning particles outside of the chamber. Second, the high flame temperatures of aluminum-water combustion may cause molten alumina to pool inside the motor posing a melting hazard for motor components and the potential to clog the nozzle. Energetic propellant additives that have the potential to form more gaseous products.
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100
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APPENDICES
108 Appendix A. ESD Sensitivity Test Results
Figure A.1 Aluminum Nanopowder ESD Testing Results, Grouped Bruceton Method.
109
Figure A.2 Aluminum Nanopowder ESD Testing Raw Data.
110 Appendix B. Experimental Procedures Aluminum and Water Large Scale Mixing and Casting
111
112
113
114
115
116
117
ESD Testing Procedure
118
119
120
Impact Chamber Testing Procedure
121
122
123
124
125
126 Appendix C. Program Code particle_measurement.m % particle_measurement.m % Load grayscale or RGB TEM image if nanoparticles and use 3-point % algorithm to collect data on particle locations and diameters. Output % results to csv file for further analysis using post_process.m % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % Travis Sippel %
[email protected] % Feb 4, 2009 % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % clear; clc; close all; % variable declaration units = 'cat'; fname = '5751-10 viton novacentrix 80nmBottom.tif'; figure(1); img = imread(fname); goodimage = image(img); grid on; title(fname); xlabel('pixels'); ylabel('pixels'); % set scale disp('Select left and right corner of scale'); [x y] = ginput(2); scaleval = input('How long is scale?'); scale = abs(scaleval/(x(1)-x(2))); % take data points hold on; % numpoints = input('Number of particles to measure?'); numpoints = 10000; %override question for i = 1:numpoints; xlabel(['Count= ' num2str(i)]); for j = 1:3; [xp(i,j) yp(i,j)] = ginput(1); end; % setup equations x1 = xp(i,1); y1 = yp(i,1); x2 = xp(i,2); y2 = yp(i,2); x3 = xp(i,3); y3 = yp(i,3); eqtn1 = ['(' num2str(x1) ' + cx)^2 + (' num2str(y1) ' + cy)^2 - r^2 = 0']; eqtn2 = ['(' num2str(x2) ' + cx)^2 + (' num2str(y2) ' + cy)^2 - r^2 = 0']; eqtn3 = ['(' num2str(x3) ' + cx)^2 + (' num2str(y3) ' + cy)^2 - r^2 = 0']; %calculate centers and radii solution(i) = solve(eqtn1,eqtn2,eqtn3); radius(i) = abs(double(solution(1,i).r(2))); diameter_nm(i) = 2*scale*radius(i); cx(i) = abs(double(solution(1,i).cx(1))); cy(i) = abs(double(solution(1,i).cy(1))); %draw x on graph where particle center is. % plot(cx(i), cy(i), 'rx', 'MarkerSize', 10); % annotation('ellipse', 'Position', [cx/size(img,2), 1-cy/size(img,1), radius(1)/size(img,2), radius(1)/size(img,1)], 'FaceColor', 'red') plot(cx,cy,'r*', 'MarkerSize', 10, 'LineWidth', .75) end; hold off; figure(2); round_diameter_nm = round(sort(diameter_nm)); hist(round_diameter_nm);
127 xlabel('Size (nm)'); ylabel('Frequency'); % output resulting raw data in csv form csvwrite([fname '.csv'],[diameter_nm' cx' cy']); dfittool;
!Published with MATLAB® 7.7
128 post_process.m % post_process.m % Read in data from particle size measurement program and perform % distribution fits and statistical analysis % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % Travis Sippel %
[email protected] % Feb 9, 2009 % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % clear; clc; close all; LALEX50_1 = csvread('5753-AlexL 50nm.tif.csv'); LALEX50_2 = csvread('5755-AlexL 50nmBottom.tif.csv'); LALEX50_3 = csvread('5755-AlexL 50nmTop.tif.csv'); ALEX100_1 = csvread('ALEX 100 5412Bottom.tif.csv'); ALEX100_2 = csvread('ALEX 100 5412Top.tif.csv'); ALEX50_1 = csvread('Argonide ALEX 50 5417.tif.csv'); M2665B_1 = csvread('Novacentrix M2665B 5410Bottom.tif.csv'); M2665B_2 = csvread('Novacentrix M2665B 5410Top.tif.csv'); M2666_1 = csvread('Novacentrix M2666 5406Bottom.tif.csv'); M2666_2 = csvread('Novacentrix M2666 5406Top.tif.csv'); Nova80Viton_1 = csvread('5751-10 viton novacentrix 80nmBottom.tif.csv'); Nova80Viton_2 = csvread('5751-10 viton novacentrix 80nmTop.tif.csv'); LALEX50 = sort([LALEX50_1(:,1); LALEX50_2(:,1); LALEX50_3(:,1)]); ALEX100 = sort([ALEX100_1(:,1); ALEX100_2(:,1)]); ALEX50 = sort(ALEX50_1(:,1)); M2665B = sort([M2665B_1(:,1); M2665B_2(:,1)]); M2666 = sort([M2666_1(:,1); M2666_2(:,1)]); Nova80 = sort([M2665B; M2666]); Nova80_10Viton = sort([Nova80Viton_1(:,1); Nova80Viton_2(:,1)]); greater_than = 500; for i = length(LALEX50):1; if LALEX50(i) > 500; clear(LALEX50(i)); end; end; for i = length(Nova80):1; if Nova80(i) > 500; clear(Nova80(i)); end; end; dfittool; %run statistical curve fitting toolbox
!Published with MATLAB® 7.7
129 image_process.m % image_process.m % Image Analysis of color gradient data and statistical fitting of coating % thickness % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % Travis Sippel %
[email protected] % Feb 17, 2009 % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % clear; clc; close all; suffix = [2:50]; num_samples = length(suffix) for i = 1:length(suffix); fname = ['untitled text ', num2str(suffix(i)) ]; vars = load(fname); figure(1); % img = imread(fname); % image(img); title('RGB image') plot(vars(:,1),vars(:,2)); grid on; xlabel('Size (nm)'); ylabel('Grayscale Intensity'); title(fname); % disp('Select two x values that are 40 nm away from each other'); % [xleft yleft] = ginput(1); % [xright yright] = ginput(1); disp('Select left and right point of boundary'); [xl yl] = ginput(1); [xr yr] = ginput(1); % thickness(i) = abs((xr-xl)*(40)/(xright-xleft)); thickness(i) = abs((xr-xl)); end; close all; disp('::::::OUTPUT:::::'); for i = suffix(1):suffix(length(suffix)); disp(['untitled text ' num2str(suffix(i)) ' thickness=' num2str(thickness(i)) ' nm']); end; xlswrite('results.xls',thickness');
!Published with MATLAB® 7.7
130 cheetah_batch_input_generator.m % % % % % % %
cheetah_batch_input_generator.m Generates a text file for use as a batch input .chi file for Cheetah 4 % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % Travis Sippel
[email protected] Nov 30, 2008 % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % %
% % % % % % % %
INPUT PARAMETERS x - mass fraction of AN or AP or other oxidizer dissolved in water xmax - Maximum value of x, determined by solubilty limits b - mass of oxidizer used per unit mass of LALEX powder (70 nm) flocation - directory on computer for output of file fname - name of file for output pc = chamber pressure (atm) pe = exhaust pressure (atm)
% clear; clc; close all; % % Chemical reaction equation by mass % AN: NH4NO3 % AP: NH4ClO4 % Palmitic acid AN Neodol* % 1 (0.95 Al + 0.03 Al2O3 + 0.02 C16_H32_O2) + b (x N2H4O3 + 0.03 C8H18O* + (1-x0.03)H2O) % --> e CO2 + f N2 + g Al2O3 + h H2 % *Neodol approximated by octanol formula. % % % % % %
% % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % DEFINE INPUT PARAMETERS % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % xmax = 1/(100/190+1); % x = .0001:.01:xmax; % b = .2:.05:.8;
c = 0.0001:.0025:0.176; pc = 68.03; %atm pe = 0.01; %atm % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % parameters = strcat('rocket, chamber, ', num2str(pc), ', exhaust, ',num2str(pe), '\n'); delete cheetah.chi; fout = fopen('cheetah.chi','w'); % Import values from cheeta_input_generator solver. % % mfAl = Al_MF; % % mfAl2O3 = Al2O3_MF; % % mfPalmitic = C16H32O2_MF; % % mfAN = NH4ClO4_MF; % % mfNeodol = C8H18_MF; % % mfH2O = H2O_MF; mAl(1:length(c)) = 0.95; mAl2O3(1:length(c)) = 0.03; mPalmitic(1:length(c)) = 0.02; mAP(1:length(c)) = c; mNeodol(1:length(c)) = 0.02938; mH2O(1:length(c)) = 0.95; mTotal(1:length(c)) = mAl + mAl2O3 + mPalmitic + mAP + mNeodol + mH2O; mfAl = mAl./mTotal; mfAl2O3 = mAl2O3./mTotal; mfPalmitic = mPalmitic./mTotal; mfAP = mAP./mTotal;
131 mfNeodol = mNeodol./mTotal; mfH2O = mH2O./mTotal;
% for i = 1:length(xlist); for i = 1:length(c); composition = strcat('composition, al, ', num2str(mfAl(i)), ', alumina, ', num2str(mfAl2O3(i)), ', palmitic_acid, ', num2str(mfPalmitic(i)), ', ap, ', num2str(mfAP(i)), ', neodol_(1-octanol), ', num2str(mfNeodol(i)), ', water, ', num2str(mfH2O(i)), ', weight\n');
% % end;
fprintf(fout, composition); fprintf(fout, parameters); disp(composition); disp(parameters);
disp(strcat('Total number of Cheetah runs is ',num2str(length(mfAl(:,1))*length(mfAl(1,:))))); fprintf(fout, '\n\n'); fclose(fout); disp('Program exited successfully. Check the file cheetah.chi for result');
!Published with MATLAB® 7.7
132 cheetah_post_gui.m % % % % % % % % % % % % % % %
% % % % % % % % % % % % % % %
% % % % % % % % % % % % % % %
% % % % % % % % % % % % % % %
% % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % Cheetah Post Processor % % % % Purdue Energetic Materials Laboratory % % % % Travis Sippel % % % %
[email protected] % % % % Cole Yarrington % % % %
[email protected] % % % % % % % % Last updated: % % % % 1-Mar-2008 % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % %
function varargout = cheetah_gui(varargin) % CHEETAH_GUI M-file for cheetah_gui.fig % CHEETAH_GUI, by itself, creates a new CHEETAH_GUI or raises the existing % singleton*. % % H = CHEETAH_GUI returns the handle to a new CHEETAH_GUI or the handle to % the existing singleton*. % % CHEETAH_GUI('CALLBACK',hObject,eventData,handles,...) calls the local % function named CALLBACK in CHEETAH_GUI.M with the given input arguments. % % CHEETAH_GUI('Property','Value',...) creates a new CHEETAH_GUI or raises the % existing singleton*. Starting from the left, property value pairs are % applied to the GUI before cheetah_gui_OpeningFcn gets called. An % unrecognized property name or invalid value makes property application % stop. All inputs are passed to cheetah_gui_OpeningFcn via varargin. % % *See GUI Options on GUIDE's Tools menu. Choose "GUI allows only one % instance to run (singleton)". % % See also: GUIDE, GUIDATA, GUIHANDLES % Edit the above text to modify the response to help cheetah_gui % Last Modified by GUIDE v2.5 07-Mar-2008 17:47:22 % Begin initialization code - DO NOT EDIT gui_Singleton = 1; gui_State = struct('gui_Name', mfilename, ... 'gui_Singleton', gui_Singleton, ... 'gui_OpeningFcn', @cheetah_gui_OpeningFcn, ... 'gui_OutputFcn', @cheetah_gui_OutputFcn, ... 'gui_LayoutFcn', [] , ... 'gui_Callback', []); if nargin && ischar(vararginver) gui_State.gui_Callback = str2func(varargin{1}); end if nargout [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:}); else gui_mainfcn(gui_State, varargin{:}); end % End initialization code - DO NOT EDIT % --- Executes just before cheetah_gui is made visible. function cheetah_gui_OpeningFcn(hObject, eventdata, handles, varargin) % This function has no output args, see OutputFcn. % hObject handle to figure % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA)
133 % varargin
command line arguments to cheetah_gui (see VARARGIN)
% Choose default command line output for cheetah_gui handles.output = hObject; % Update handles structure guidata(hObject, handles); % UIWAIT makes cheetah_gui wait for user response (see UIRESUME) % uiwait(handles.figure1);
% --- Outputs from this function are returned to the command line. function varargout = cheetah_gui_OutputFcn(hObject, eventdata, handles) % varargout cell array for returning output args (see VARARGOUT); % hObject handle to figure % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) % Get default command line output from handles structure varargout{1} = handles.output; % --- Executes on button press in pushbutton1. function pushbutton1_Callback(hObject, eventdata, handles) % hObject handle to pushbutton1 (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) %%%Function parses input from Cheetah .cho file clc; global React; FILENAME = get(handles.edit1, 'String'); NumRuns = get(handles.edit2,'String'); NumRuns = str2num(NumRuns); %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %BEGIN CHEETAH POST PROCESS PROGRAM %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % % % Cheetah Post Processor % % % Purdue University % % % Energetic Materials Lab % % % Travis Sippel % % %
[email protected] % % % Cole Yarrington % % %
[email protected] % % % 2-19-2008 % % % Modified 3/1/2008 % % % by Travis Sippel % % %
[email protected] % % % INPUT DATA INTO MATLAB FROM TEXT FILE %get total number of runs %name of .chs summary output file %fid = fopen('Batch_Cheetah_Si20.cho') fid = fopen(FILENAME); run = 1; while run = 3; output = [output, num2str(cell2mat(PlotVars(j,i))), ' ']; else; output = [output, cell2mat(PlotVars(j,i)), ' ']; end; end; outp = [outp; output]; end; outp = char(outp) dialog_box(handles.edit1, 'Space-delimited output has been dumped to the command window for copy and paste.'); % clipboard('copy', output); % --- Executes on button press in pushbutton8. function pushbutton8_Callback(hObject, eventdata, handles) % hObject handle to pushbutton8 (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) % PLOT TO NEW FIGURE WINDOW clc; plot_Cheetah(hObject, eventdata, handles, 2)
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% --- Executes on button press in pushbutton9. function pushbutton9_Callback(hObject, eventdata, handles) % hObject handle to pushbutton9 (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) % PLOT ALL VARIABLES IN Y AXIS. % PLOTS CHEETAH SELECTED VARIABLES TO EITHER THE ON SCREEN PLOT % OR A NEW FIGURE PLOT function plot_Cheetah(hObject, eventdata, handles, graphtype) % graphtype==1: plot will be sent to handles.axes2 % graphtype==2: plot will be sent to figure(1) XIndex = get(handles.listbox2, 'Value'); Y1Index = get(handles.listbox4, 'Value'); Y2Index = get(handles.listbox5, 'Value'); list_entries = get(handles.listbox2,'String'); %Throw error if number of Y2 plot variables is more than 1 if length(Y1Index) > 48; dialog_box(handles.text1, 'Too many Y1 variables selected. Number of Y1 variables must be less than 48.'); return; end; % Read in reactant matirx and headings ReactIn = get(handles.text15, 'UserData'); for i = 1:length(ReactIn(1,:)); Heading(i) = strcat(ReactIn(1,i), ', ', ReactIn(2,i)); end; XValues = ReactIn(3:length(ReactIn(:,1)),XIndex); for i = 1:length(Y1Index); Y1Values(:,i) = ReactIn(3:length(ReactIn(:,1)),Y1Index(i)); end; Y2Values = ReactIn(3:length(ReactIn(:,1)),Y2Index); XValues = cell2mat(XValues); Y1Values = cell2mat(Y1Values); Y2Values = cell2mat(Y2Values); %create plot line styles matrix col = ['b'; 'g'; 'r'; 'c'; 'm'; 'y']; bul = ['+'; 'o'; '*'; '.'; 'x'; '^'; 'v'; '>'; ' 3) for index = 1:2:(nargin-3), if nargin-3==index, break, end switch lower(varargin{index}) case 'title' set(hObject, 'Name', varargin{index+1}); case 'string' set(handles.text1, 'String', varargin{index+1}); end end end % Determine the position of the dialog - centered on the callback figure % if available, else, centered on the screen FigPos=get(0,'DefaultFigurePosition'); OldUnits = get(hObject, 'Units'); set(hObject, 'Units', 'pixels'); OldPos = get(hObject,'Position'); FigWidth = OldPos(3); FigHeight = OldPos(4); if isempty(gcbf) ScreenUnits=get(0,'Units'); set(0,'Units','pixels'); ScreenSize=get(0,'ScreenSize'); set(0,'Units',ScreenUnits); FigPos(1)=1/2*(ScreenSize(3)-FigWidth); FigPos(2)=2/3*(ScreenSize(4)-FigHeight); else GCBFOldUnits = get(gcbf,'Units'); set(gcbf,'Units','pixels'); GCBFPos = get(gcbf,'Position'); set(gcbf,'Units',GCBFOldUnits); FigPos(1:2) = [(GCBFPos(1) + GCBFPos(3) / 2) - FigWidth / 2, ... (GCBFPos(2) + GCBFPos(4) / 2) - FigHeight / 2]; end FigPos(3:4)=[FigWidth FigHeight]; set(hObject, 'Position', FigPos); set(hObject, 'Units', OldUnits); % Show a question icon from dialogicons.mat - variables questIconData % and questIconMap load dialogicons.mat IconData=questIconData; questIconMap(256,:) = get(handles.figure1, 'Color'); IconCMap=questIconMap; Img=image(IconData, 'Parent', handles.axes1); set(handles.figure1, 'Colormap', IconCMap); set(handles.axes1, ... 'Visible', 'off', ... 'YDir' , 'reverse' , ... 'XLim' , get(Img,'XData'), ... 'YLim' , get(Img,'YData') ... ); % Make the GUI modal set(handles.figure1,'WindowStyle','modal') % UIWAIT makes dialog_box wait for user response (see UIRESUME) uiwait(handles.figure1); % --- Outputs from this function are returned to the command line. function varargout = dialog_box_OutputFcn(hObject, eventdata, handles) % varargout cell array for returning output args (see VARARGOUT); % hObject handle to figure % eventdata reserved - to be defined in a future version of MATLAB
144 % handles
structure with handles and user data (see GUIDATA)
% Get default command line output from handles structure varargout{1} = handles.output; % The figure can be deleted now delete(handles.figure1); % --- Executes on button press in pushbutton1. function pushbutton1_Callback(hObject, eventdata, handles) % hObject handle to pushbutton1 (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) % OK BUTTON close;
% --- Executes on button press in pushbutton2. function pushbutton2_Callback(hObject, eventdata, handles) % hObject handle to pushbutton2 (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) handles.output = get(hObject,'String'); % Update handles structure guidata(hObject, handles); % Use UIRESUME instead of delete because the OutputFcn needs % to get the updated handles structure. uiresume(handles.figure1); % --- Executes when user attempts to close figure1. function figure1_CloseRequestFcn(hObject, eventdata, handles) % hObject handle to figure1 (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) if isequal(get(handles.figure1, 'waitstatus'), 'waiting') % The GUI is still in UIWAIT, us UIRESUME uiresume(handles.figure1); else % The GUI is no longer waiting, just close it delete(handles.figure1); end % --- Executes on key press over figure1 with no controls selected. function figure1_KeyPressFcn(hObject, eventdata, handles) % hObject handle to figure1 (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) % Check for "enter" or "escape" if isequal(get(hObject,'CurrentKey'),'escape') % User said no by hitting escape handles.output = 'No'; % Update handles structure guidata(hObject, handles); uiresume(handles.figure1); end if isequal(get(hObject,'CurrentKey'),'return') uiresume(handles.figure1); end
!Published with MATLAB® 7.7
145 copy_output.m – dependent of cheetah_post_gui.m function varargout = copy_output(varargin) % COPY_OUTPUT M-file for copy_output.fig % COPY_OUTPUT, by itself, creates a new COPY_OUTPUT or raises the existing % singleton*. % % H = COPY_OUTPUT returns the handle to a new COPY_OUTPUT or the handle to % the existing singleton*. % % COPY_OUTPUT('CALLBACK',hObject,eventData,handles,...) calls the local % function named CALLBACK in COPY_OUTPUT.M with the given input arguments. % % COPY_OUTPUT('Property','Value',...) creates a new COPY_OUTPUT or raises the % existing singleton*. Starting from the left, property value pairs are % applied to the GUI before copy_output_OpeningFcn gets called. An % unrecognized property name or invalid value makes property application % stop. All inputs are passed to copy_output_OpeningFcn via varargin. % % *See GUI Options on GUIDE's Tools menu. Choose "GUI allows only one % instance to run (singleton)". % % See also: GUIDE, GUIDATA, GUIHANDLES % Edit the above text to modify the response to help copy_output % Last Modified by GUIDE v2.5 08-Mar-2008 19:42:05 % Begin initialization code - DO NOT EDIT gui_Singleton = 1; gui_State = struct('gui_Name', mfilename, ... 'gui_Singleton', gui_Singleton, ... 'gui_OpeningFcn', @copy_output_OpeningFcn, ... 'gui_OutputFcn', @copy_output_OutputFcn, ... 'gui_LayoutFcn', [] , ... 'gui_Callback', []); if nargin && ischar(varargin{1}) gui_State.gui_Callback = str2func(varargin{1}); end if nargout [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:}); else gui_mainfcn(gui_State, varargin{:}); end % End initialization code - DO NOT EDIT % --- Executes just before copy_output is made visible. function copy_output_OpeningFcn(hObject, eventdata, handles, varargin) % This function has no output args, see OutputFcn. % hObject handle to figure % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) % varargin command line arguments to copy_output (see VARARGIN) % Choose default command line output for copy_output handles.output = hObject; % Update handles structure guidata(hObject, handles); % UIWAIT makes copy_output wait for user response (see UIRESUME) % uiwait(handles.figure1); set(handles.edit1, 'String', varargin(2)); % --- Outputs from this function are returned to the command line. function varargout = copy_output_OutputFcn(hObject, eventdata, handles) % varargout cell array for returning output args (see VARARGOUT); % hObject handle to figure
146 % eventdata % handles
reserved - to be defined in a future version of MATLAB structure with handles and user data (see GUIDATA)
% Get default command line output from handles structure varargout{1} = handles.output;
function edit1_Callback(hObject, eventdata, handles) % hObject handle to edit1 (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) % Hints: get(hObject,'String') returns contents of edit1 as text % str2double(get(hObject,'String')) returns contents of edit1 as a double % --- Executes during object creation, after setting all properties. function edit1_CreateFcn(hObject, eventdata, handles) % hObject handle to edit1 (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles empty - handles not created until after all CreateFcns called % Hint: edit controls usually have a white background on Windows. % See ISPC and COMPUTER. if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor')) set(hObject,'BackgroundColor','white'); end % --- Executes on button press in pushbutton1. function pushbutton1_Callback(hObject, eventdata, handles) % hObject handle to pushbutton1 (see GCBO) % eventdata reserved - to be defined in a future version of MATLAB % handles structure with handles and user data (see GUIDATA) close;
!Published with MATLAB® 7.7
147 strand_burn_analysis.m % Strand Burn Analysis Program % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % Travis Sippel % 12/13/07 %
[email protected] % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % clear; close all; clc; [num, txt] = xlsread('matlab_input.xls'); %Get length of excel array [m,n] = size(num); [m1,n1] = size(txt); if m1 > m; m = m1; end; if n1 > n; n = n1; end; %Get Pertinent Data Headers = txt(1,:); TubeID = num(2:m,1); ParticleType = txt(2:m,2); Coating = txt(2:m,3); Gelling = txt(2:m,4); NomEquivRatio = num(2:m,11); EquivRatio = num(2:m,12); DateMixed = num(2:m,13); DateTested = num(2:m,14); Pressure = num(2:m,15); Rb = num(2:m,16); Mb = num(2:m,26); Comments = txt(2:m,27); %Sort out bad data j = 1 for i = 1:m-1; if Rb(i,1) ~= NaN; g(j) = i; end; j = j+1; end; %Determine unique data sets for i = 1:m-1; Label(i) = strcat(ParticleType(i), ', Equiv=', num2str(NomEquivRatio(i))); end; Types(1) = Label(1); for i = 1:m-1; if Label(i) ~= ''; j = 1; for j = 1:length(Types); if Label(i) ~= Types(j); Types(length(Types)+1) = Label(i); end; j = j+1; end; end; end;
!Published with MATLAB® 7.7
148 Appendix D. Particle Size Measurement Analysis
Figure D.1 Lognormal Particle Size Distributions, Means, and Standard Deviations.
Figure C.3 Lognormal Particle Probability Distributions. (a) Nova 80 with 10% Viton Coating, (b) Nova 80, (c) LALEX 50, (d) ALEX 50, (e) ALEX 100. 149
150
Figure D.3 Lognormal Particle Thickness Measurement Fit.
151 Appendix E. Particle Oxide Coating Analysis Results
Figure E.1 Particle Coating Thickness Lognormal Distributions.
152
Figure E.2 Coating Thickness Lognormal Fits and Thickness Histogram.
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Figure E.3 Particle Coating Thickness Continuous Distribution Functions, Raw Data, and 95% Confidence Intervals.
154
Figure E.4 Comparison of Lognormal and Normal Fits.
155 Appendix F. Instruction Manual for Cheetah Post 4 Program
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