Jan 9, 1997 - parameters of all of the prepared mixtures, while plastic RDX-. Semtex gave the highest heat of combustion. Keywords: combustion, detonation ...
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Heat of Combustion and Detonation Characteristics of HNIW Bonded by Different Plastic Matrices A. ELBEIH 1*, S. ZEMAN 1, J. PACHMAN 1, Z. AKSTEIN2 and M. SUĆESKA3 1- Institute of Energetic Materials, Faculty of Chemical Technology, University of Pardubice, CZ-532 10 Pardubice, Czech Republic; 2- Research Institute of Industrial Chemistry, Explosia, CZ-531 17 Pardubice, Czech Republic; 3- Brodarski Institut - Marine Research & Special Technologies, HR-10020 Zagreb, Croatia polymorphs, it has TMD (2.04 g cm-3), positive heat of formation (~ 419 kJ mol-1) and high performance [3,4]. The study is aimed to develop plastic explosive formulations that are pressable and other extrudable based on HNIW. Four types of plastic matrices were studied which are the plastic matrix of composition C4, the plastic matrix of Semtex 10 (a plastic explosive for special use on the basis of inert plasticizer with PETN as an active component and it is used for special destruction, blasting works and underwater blasting works; it can be shaped well and has good adhesive properties [5]), Viton A 200 and Fluorel FT-2481. For comparison RDX (1,3,5-trinitro-1,3,5-triazinane), which is a widely used explosive and is the main explosive filler in composition C4, is studied with the same kinds of polymeric matrices. The calculations of the detonation parameters of all the prepared samples were done by EXPLO 5 code [6] and modification of Kamlet and Jacobs method [7].
Abstract: HNIW (ε-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12hexaazaisowurtzitane, ε-CL-20) was studied as a plastic explosive bonded with four different plastic matrices, two of them are the plastic matrices used in composition C4 and Semtex10, while the others are Viton A 200 and Fluorel FT2481. Also RDX (1,3,5-trinitro-1,3,5-triazinane) was studied for comparison with the same types of binders. The heat of combustion, ΔHC, of all the prepared mixtures was measured using calorimetric bomb. The detonation velocity, D, of all the mixtures was measured. Their thermal stability was determined using non-isothermal differential thermal analysis (DTA). The detonation parameters were also calculated by means of Kamlet & Jacobs method and EXPLO5 code version 4 for all the mixtures. While the C4 and Semtex10 matrices lower the thermal stability of the resulting explosives, Viton A and Fluorel enhance this stability. A relationship between the heat of combustion and the detonation velocity shows good correlation between plastic explosives based on the C4 matrix and those based on Semtex10 matrix. The pressed HNIW-Viton A mixture has the highest detonation parameters of all of the prepared mixtures, while plastic RDXSemtex gave the highest heat of combustion.
2. EXPERIMENTAL 2.1 Preparation of Plastic Explosives based on C4 matrix All the plastic explosives based on C4 and Semtex10 matrices were prepared at Explosia Pardubice (Research Institute of Industrial Chemistry) [8,9]. The used RDX is a product of Dyno Nobel (mixture of Classes 2 and 5 according to the standard [10]) and technical-grade -HNIW was a product of Explosia pilot plant and recrystallized at the Institute of Energetic Materials (IEM). The C4 matrix is a mixture of polyisobutylene (PIB) 25% wt, dioctyl sebacate (DOS) 59% wt and oily material (HM46) 16% wt. The preparation of the binder was produced by mixing small pieces of polyisobutylene with the sebacate and the oil under specific conditions. The explosive 91% wt. was mixed with the binder matrix 9% wt at 70 0C for 70 min under vacuum using computerized mixer Plastograph BRABENDER.
Keywords: combustion, detonation, HNIW, RDX, Viton A, Fluorel, C4 matrix, Semtex 10 matrix. 1. INTRODUCTION In the recent decades, much attention in the area of high-energy materials has been given to investigation of the properties of HNIW (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, ε-CL-20) [1], it is considered today the most powerful explosive, it belongs to the family of polycyclic-cage nitramines, it has four stable polymorphs (α, β, ε, γ) which are known to exist at ambient conditions [2]. The ε-polymorph has high symmetry and has the highest density than the other three
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CONTRIBUTED PAPER 2.2 Preparation of Plastic explosives based on Semtex 10 matrix
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contact with the air. The tested sample (0.05 g) was placed in a test tube made of Simax glass, 5 mm in diameter and 50 mm long. The reference standard was 0.05 g aluminum oxide. A linear heating rate of 5 oC min-1 was used. The results presented in Fig. 1 show the exothermic effect of the thermal decomposition and the endothermic peaks of the prepared samples in addition to results for the pure explosives as a reference. Peak temperatures of exothermic thermal decomposition at a linear heating rate of 5 °C min-1 for all samples are presented in Table 1.
The polymeric matrix of Semtex10 contains nitrile rubber as a binder with non energetic plasticizer (unpublished). The explosives 85% wt. were mixed with the polymeric matrix 15% wt. at 70 oC for 70 min. under vacuum using computerizing mixer Plastograph. It was observed that the temperature of the mixer and the time of mixing affect the characteristics of the prepared samples. All the prepared samples based on C4 and Semtex10 matrices were extruded with a 40 mm screw extruder to obtain long charges of plastic explosive with 16 mm diameter.
2.6 Heat of combustion Automatic Combustion Calorimeter MS10A was used for measuring the heat of combustion of the samples. The samples were prepared and placed in bomb containing 5 ml of water then filled with an excess of oxygen [15]; the data obtained from the measurements are reported in Table 1 as heat of combustion. These data were used for calculation of the heat of formation of the samples (it is obtained by the summation of the heat of combustion of the sample and the heat of formation of the products obtained from the combustion process which are CO2(g) and H2O(L)), and these heats were used for the theoretical calculations
2.3 Preparation of Plastic bonded Explosives based on Viton A and Fluorel The samples based on Viton A 200 and Fluorel FT-2481 as binders were prepared by modified water-solvent slurry method [11]. Viton A 200, producer DuPont Performance Elastomers, is a copolymer with a fluorine content of 66%, it consists of 60/40 weight ratio of vinylidene fluoride (VF2) to hexafluoropropene (HFP) monomers [12]. While Fluorel FT2481, producer 3M company, is terpolymer of 45 wt% VF2, 32 wt% HFP and 23 wt% tetrafluoroethene (TFE) cured by aromatic polyhydroxy crosslinking agent [13]. The nitramine is slurred in water (aqueous phase) and the fluorocarbon binder is dissolved in an organic solvent with low boiling point, immiscible with water, which is added during the process. This process is carried out under vigorous stirring (500 – 600 rpm). The solvent is removed by distillation under continuous stirring, and the polymer precipitates on the surface of the crystals of the explosive at the end of the solvent elimination. All the prepared samples have 91% wt. of explosive and 9% wt. of the fluorinated binder.
2.7 Pressing of the samples The plastic bonded explosives based on Viton A and Fluorel were pressed at the Explosia Co. Pardubice using hydraulic pressing machine (PYE 100). All the samples were pressed at a pressure of 486 MPa under vacuum for 10 seconds. Cylinders with diameter 16 mm were obtained. For each composition, 18 cylinders were prepared and glued together as three charges made of 6 cylinders.
2.4 Elemental Analysis Fisons - EA-1108 CHNS-O elemental analyzer was used for the determination of C, H and N in the prepared samples. The results of the elemental analysis in addition to the fluorine content calculated theoretically were recalculated to match the N content with the individual explosive and reported in Table 1 as a hypothetical formula. Then the calculated formula was used as if it were a single explosive and it was submitted to EXPLO5 [6] and Kamlet & Jacobs methods [7] for calculations of the detonation parameters. 2.5 Thermal stability Fig. 1 Typical DTA curves of the pure explosives and the prepared samples (at heating rate 5 °C min-1).
A DTA 550 Ex apparatus was used for thermal analysis of explosives [14]. The measurements were carried out at atmospheric pressure, with the tested sample in a direct
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CONTRIBUTED PAPER 2.8 Detonation velocity measurements
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Calculated Detonation Pressure/ GPa
40
The detonation velocity of all prepared mixtures was measured by the ionization copper probe method [16] where the data were recorded on an oscilloscope (Tektronix TDS 3012). The plastic samples were prepared in the form of cylinder 16 mm in diameter and 200 mm long. The copper probes were inserted in the charge. The first probe was inserted at distance of 50 mm from the booster and the second probe was inserted at 100 mm distance from the first probe. In the case of the pressed charges, the first probe was inserted between the first and the second prepared cylinder while the second probe was inserted between the fifth and the last cylinder where the distance between the two probes was 80 mm. Both probes were connected to the oscilloscope via coaxial cable. Charges were set off using a booster charge (Semtex 1A with mass of 6 g and diameter of 16 mm) initiated with an electric detonator. For each sample, three measurements were performed and the mean value (max. ± 74) for each is reported in Table 2.
38
y = 0.1936x + 4.6276 R 2 = 0.9857
36
HNIW-VitonA HNIW-Fluorel
34 32 30
HNIW-C4
28
RDX-VitonA
RDX-Fluorel
26
HNIW-Semtex RDX-C4
24 22
RDX-Semtex
20 80
90
100
110
120
130
140
150
160
170
Experimental ρD 2 / GPa
Fig. 2 Relationship between the calculated detonation pressure and the experimental ρ.D2 C4 and Semtex10 matrices. The above mentioned observation are reminiscent of the older finding [17] that a film of inert liquid (here it might be fluorinated polymers) inhibits the thermal decomposition of RDX, while an additive of solvent type (here DOS plasticiser) accelerates this decomposition.
2.9 Calculation of the detonation characteristics The theoretical detonation characteristics (detonation velocity, D, heat of explosion or detonation, Q, detonation pressure, P) of the prepared samples as well as the pure explosives were calculated by the use of EXPLO5 code [6] and Kamlet & Jacobs method [7]. In the case of EXPLO5 code, the new version (version 4) modified by Sućeska for also calculation of the fluorine containing explosives was used, the BKWN set of parameters for the BKW EOS was applied, these parameters are: α = 0.5, β = 0.176, κ = 14.71, θ = 6620. The calculated detonation characteristics of all the tested explosives are reported in Table 2.
Regarding to the calculations of the detonation characteristics, it is obvious that; in case of calculation by Kamlet & Jacobs method, the D values for all the samples are different from the experimental values within rang of -5.3% differences. While the results of the EXPLO 5 code showed D values closer to the experimental results with difference in the range between +2 to -3% (see also Table 2). From studying of the theory of explosion, it is well known that the detonation pressure is directly proportional to square of the detonation velocity. In our study it was observed a mutual comparison of experimental results (here a term ρ.D2) and calculated detonation pressures by Kamlet & Jacobs method as shown in Fig. 2, which confirms the conformity of the experimental and the calculated results in this paper.
3. RESULTS AND DISCUSSION The DTA measurements of plastic explosives based on C4 and Semtex10 matrices show that the peak temperatures for these mixtures are lower than those of pure explosives as shown in Fig. 1; this is most likely due to the presence of the polar plasticizers (DOS in C4 matrix) in binders which acts as a solvent for the nitramines used and leads to the decrease of the mixture’s decomposition temperature as reported in [8].
A relationship between the heat of combustion and the experimental detonation velocity is presented in Fig. 3, a good mutual correlation was observed in the case of the Plastic explosives based on C4 and Semtex10 matrices, where the heat of combustion is inversely proportional to the detonation velocity and this is due to increasing the binder percentage (as in the samples based on Semtex10 matrix) which decreases the detonation velocity and in the same time increases the heat of combustion, this prove that both the C4 and Semtex10 matrices contain ingredients that increase the heat of combustion of the applied pure explosives. While the fluorinated polymers have higher density so they increase the detonation velocity of the samples and in the same time they have lower heat of combustion compared with the plastic matrices.
In the case of the explosives bonded by Viton A and fluorel, it is clear that the peak temperatures for all prepared mixtures are slightly higher than those of pure explosives within range from 1-7 0C as shown in Fig. 1; this fact proves that the presence of fluorinated polymer in the mixture enhances the thermal stability of the nitramines applied in these mixtures. It is obvious that mixtures bonded by Viton A and fluorel have higher thermal stability than the mixtures based on
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CONTRIBUTED PAPER HNIW-VitonA
9000
HNIW-Viton A showed the highest detonation parameters and the highest measured detonation velocity (9023 m.s-1). The D value of HNIW-C4 is higher than that of RDX-Viton A at nearly the same loading density by more than 300 m.s-1. The density of HNIW-semtex10 (85 wt% HNIW) is lower than that of RDX-Viton A (91 wt% RDX) but it has slightly lower detonation velocity. These facts show that HNIW is interesting explosive and its application in the military field is promising.
y = -0.6091x + 15560 R 2 = 0.9973
HNIW-Fluorel
8800
HNIW-C4
8600 8400
RDX-VitonA
1
Experimental detonation velocity / m s
-
9200
8200 8000
y = -0.7101x + 15075 R 2 = 0.9213
HNIW-Semtex
RDX-Fluorel
RDX-C4
7800
RDX-Semtex
7600 7400 8000
8500
9000
4. CONCLUSION
9500 10000 10500 11000 11500 12000 12500 13000 13500
Heat of combustion / J g-1
From the previous results, it was concluded that:
Detonation velocity of pressed HNIW-Viton A is higher than that of pressed RDX-Viton A by 738 m s -1, while detonation velocity of plastic HNIW-C4 is higher than that of composition C4 by only 539 m s-1. The difference in the reading is higher in case of samples based on Viton A due to the high density of Viton A compared with C4 matrix.
Plastic HNIW-Semtex, which has density 1.64 g cm-3 (containing 85 wt% HNIW), has slightly lower detonation velocity (58 m s-1 lower) than the pressed RDX-Viton A, which has density 1.76 g cm-3 (containing 91 wt% RDX), while explosives bonded by Semtex10 matrix can be easily shaped, have good adhesive properties and have many applications.
Explosives bonded by Viton A have higher detonation characteristics than that bonded by Fluorel.
According to the DTA measurements, Viton A and Fluorel binders enhance the thermal stability of the pure explosives, while Semtex10 matrix decreases the thermal stability much more than C4 matrix.
Explosives bonded by C4 and Semtex10 matrices have higher heat of combustion than those bonded by Viton A and fluorel for the same individual explosive.
Appling EXPLO 5 code and Kamlet & Jacobs method for calculation of the detonation parameters showed good agreement, while regarding to the experimentally measured detonation velocities, EXPLO 5 showed closer results.
Fig. 3 Relationship between the experimental detonation velocities and heats of combustion of the studied samples Relationship between the experimental D values and loading density, of the prepared samples is shown in Fig. 4, it is obvious from this fig. that the samples based on the fluorinated binders have higher loading density and higher detonation velocities than the samples bonded by C4 and Semtex10 matrices. At the same time, the prepared samples based on Viton A have higher detonation velocities than that based on fluorel, and this fact is mostly due to the curing of the fluorel binder by aromatic polyhydroxy crosslinking agent which affect the detonation velocity in the prepared samples. While the detonation velocities of the plastic explosives based on C4 matrix are higher than that based on Semtex10 matrix for the same individual explosive and this is due to the lower weight percentage of explosive bonded by semtex10 matrix (85%) than that bonded by C4 matrix (91%). 9400
Experimental detonation velocity / m s-1
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9200 HNIW-VitonA
9000 y = 4065.9x + 1471.7 2 R = 0.9649
8800
HNIW-Fluorel HNIW-C4
8600
y = 4243.9x + 753.72 2 R = 0.9834
8400 RDX-VitonA
HNIW-Semtex
8200
RDX-Fluorel
RDX-C4
8000 7800 7600
RDX-Semtex
7400 1.4
1.5
1.6
1.7
1.8
1.9
2
2.1
Loading density / g cm-3
Fig. 4 Relationship between the experimental detonation velocity and loading density for the prepared samples
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CONTRIBUTED PAPER ACKNOWLEDGEMENT Authors are indebted to Mr. Jiří Těšitel, M.Sc. from Explosia Co., Pardubice for his help in charges pressing. The work was created as a part of the project of the Ministry of Education, Youth and Sports of Czech Republic No. MSM 00221627501. REFERENCES [1]
N. V. Latypov, U. Wellmar, P. Goede, and A. J. Bellamy, “Synthesis and scale-up of 2,4,6,8,10,12-hexanitro2,4,6,8,10,12-hexaazaisowurtzitane from 2,6,8,12tetraacetyl-4,10-dibenzyl-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW, CL-20)”, J. Org. Process Res. Dev., 4, No. 3, 156–158 (2000).
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[11]
Kim H.-S., Park B.-S., “Characteristics of the insensitive pressed plastic bonded explosive, DXD-59”, Propellants, Explos., Pyrotech., 1999, 24, 217-220.
[12]
Hoffman D. M., “Dynamic mechanical signature of Viton A and plastic bonded explosives based on this polymer”, Polymer Eng. Sci.,2003, 43(1), 139-156.
[13]
International patent, “Improved scorch safety of curable fluoroelastomer composition”, International publication no. WO 97/00906, publication date: 9 Jan. 1997.
[14]
Krupka M., “Devices and equipments for testing of energetic materials”, in: J. Vágenknecht (Ed.), Proc. 4th Seminar “New Trends in Research of Energetic Materials”, Univ. Pardubice, April 2001, p. 222.
[2]
Simpson, R.L., Urtiew, P.A.; &nellas, DL.; Moody, G.L.; Scribner, K.J & Hoffman, D.M., “CL-20 performs exceeds that of HMX and its sensitivity is moderate”, Prop. Explo., Pyrotech., 1997,22,249.
[15]
Solid fuels – Determination of heat of combustion by calorimetric method in the pressure vessel and calculation of calorific value, Czech Tech. Standard ČSN ISO 1928, Czech Inst. of Standards, June 1999.
[3]
U. R. Nair, 1 R. Sivabalan,1 G. M. Gore, “Hexanitrohexaazaisowurtzitane (CL-20) and CL-20Based Formulations”, Combust., Explos. Shock Waves, 41 (No. 2) (2005), 121–132.
[16]
Sućeska M., “Test methods for Explosives”, Springer, Heideleberg, 1995.
[17]
Maksimov Yu. Ya., “Thermal Decomposition of Hexogen and Octogen”, Tr. Mosk. Khim.-Teknol. Inst. im. Mendeleeva, 1967, 53, 73-84.
[4]
S. S. Samudre, U. R. Nair, G. M. Gore, R. K. Sinha, “Studied on an improved plastic bonded explosive (PBX) for shaped charges”, Propellants, Explos. Pyrotech. 34 (2009) 145-150.
[5]
Web site of the Explosia http://www.explosia.cz, 28/4/2010.
[6]
Sućeska M., “Calculation of detonation parameters by EXPLO5 computer program”. Materials Science Forum, 2004, 465-466, Explosion, Shock Wave and Hypervelocity Phenomena in Materials, 325-330.
[7]
Short J. M., Helm F. H., Frank H., Finger M., Kamlet M. J., The chemistry of detonations. Part VII. “A simplified method for predicting explosive performance in the cylinder test, Combust. Flame”, 1981, 43(1), 99-109.
[8]
Elbeih A., Pachman J., Trzciński W. A., Zeman S., Akštein Z., Šelešovský J., “Study of plastic explosives based on attractive cyclic nitramines”. Part I. Detonation characteristics of explosives with C4 binder. Contribution to Propellants, Explos., Pyrotechnics – in press.
[9]
Elbeih A., Pachman J., Zeman S., Akstein Z., “Replacement of PETN by Bicyclo-HMX in semtex 10”, 8th International armament conference on scientific aspects & safety technology, Oct. 2010.
[10]
Detail specification RDX, Military Standard MIL-DTL398D, US Dept. of Defence, April 17, 1999.
Company,
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Table 1 The data obtained from the experimental measurements
Sample
Mol. weight
formula
(g mol-1)
Heat of combustion, ΔHC (J g-1)
Heat of formation (kJ mol-1)
DTA peak at 5oC min-1(°C)
HNIW-C4
C9.17H12.09N12O12.19
485.4
11452
201.1
212.3
HNIW-Semtex10
C.9.85H12.88N12O12.55
502.2
11992
259.5
196
HNIW-Fluorel
C7.18 H6.65 F1.57 N12 O11.97
479.5
8634
133.1
223.9
HNIW-Viton A
C7.22 H6.83 F1.51 N12 O11.93
481.3
8661
127.7
223.5
RDX-C4
C4.66H8.04N6 O5.99
243.7
12356
22.0
212.9
RDX-Semtex10
C5.31H8.92N6O6.23
256.5
13093
-15.3
208
RDX-Fluorel
C3.60 H6.32 F0.79 N6 O5.96
244.1
9662
-76.4
221.5
RDX-Viton A
C3.63 H6.46 F0.77 N6 O5.95
244.0
9726
-90.3
222.2
Table 2 Results of experimental detonation velocity measurements and the calculated detonation characteristics EXPLO5 calculation Density Explosive
(g cm-3)
Dexp -1
(m s )
D (m s-1)
Dcalc-Dexp Dexp/100 (%)
P (GPa)
Kamlet & Jacobs calculation Heat of detonation Qdet.
D (m s-1)
(J g-1)
Dcalc-Dexp Dexp/100 (%)
P (GPa)
Heat of explosion Qmax (J g-1)
HNIW-C4
1.77
8594
8425
-1.9
29.64
5744
8263
-3.8
29.98
5969
HNIWSemtex10
1.64
8228
7979
-3
25.11
5809
7790
-5.3
25.41
6013
1.92
8855
8780
-0.8
35.57
6051
8605
-2.8
34.11
5963
1.94
9023
8850
-1.9
36.33
6022
8667
-3.9
34.81
5939
1.61
8055
7856
-2.5
23.36
5512
7682
-4.6
24.42
5694
1.54
7621
7490
-1.7
20.53
5344
7320
-3.9
21.54
5510
1.74
8087
8243
+1.9
28.55
5673
7981
-1.3
27.68
5568
1.76
8285
8300
+0.2
29.03
5614
8024
-3.1
28.18
5505
HNIWFluorel HNIWVitonA RDX-C4 RDXSemtex10 RDXFluorel RDX-Viton A
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