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Propellants Explos. Pyrotech. 2009, 34, 506 – 512

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Experimental Study of the Effect of Metal Nanopowders on the Decomposition of HMX, AP and AN Alexander Gromov*, Yulia Strokova, Alexey Kabardin Tomsk Polytechnic University, 30, Lenin Prospekt, 634050, Tomsk, Russia Alexander Vorozhtsov Institute for Problems of Chemical and Energetic Technologies, 1, Socialisticheskaya Ulitsa, 659322, Biysk, Russia Ulrich Teipel Georg-Simon-Ohm University of Applied Sciences Nrnberg, Kesslerplatz 12, 90489 Nrnberg, Germany Received: April 29, 2008; revised version: July 15, 2009 DOI: 10.1002/prep.200800030

Abstract

2 Experimental Results and Discussion

The effect of metal nanopowders (Al, Fe, W, Ni, Cu, and Cu-Ni alloys) on the decomposition of energetic materials (HMX, AP, and AN) with DTA – TGA method was studied and it was found that the catalytic action appears in the case of Cu-Ni nanopowders with the three studied energetic materials. The temperature of decomposition of energetic materials with the addition of metal nanopowders could be lowered by 82 8C for AN, 161 8C for AP, and 96 8C for HMX. The reaction mechanism of metal nanopowders enhancing the decomposition of energetic materials is discussed.

2.1 Preparation of Metal Nanopowders and Experimental Approach

Keywords: AN, AP, Decomposition, DTA – TGA, HMX, Metal Nanopowders

1 Introduction The decomposition temperature for a wide class of energetic materials can be lowered by the catalytic effect of metal nanopowders (NPs) [1 – 2]. Experimental data as well as the reaction mechanism of such a catalytic process [3] for the reaction of metal NPs with the components of propellants still need to be obtained. The effect of metal NPs produced by the electro-explosive method [4] was tested in this work to investigate the catalytic activity of metal NPs mixed with AP, AN, and HMX. The Al, Fe, W, Ni, Cu, and (Cu – Ni) NPs mixed with the energetic materials (AP, AN, and HMX) as well as micrometer sized Al powder (ASD-4) were tested.

* Corresponding author; e-mail: [email protected]

2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

The production of the metal NP samples was carried out using an electrical explosion of wires (EEW) machine UDP-4G, which was constructed for the production of metal powders at the High Voltage Research Institute, Tomsk Polytechnic University, Russia [5]. The initial metal wires used for the production of NPs were 0.2 – 0.4 mm in diameter and of 99.8 % purity. The rate of wire feeding was about 50 mm s1 and the explosions were repeated with a frequency 1 Hz. The samples studied within this work and their specific surface area (Ssp) determined by BET method, as well as the metal content (CMe) after passivation measured by TG curves [6], and the surface mean particle diameter (as) calculated from Ssp are shown in Table 1. Ten samples of metal NPs were studied in this work. The particles of the Al NP as well as other metal NPs had spherical shapes, which is typical for EEW-produced NPs [3, 7]. The application of the AlB2 passivation coating was performed to increase the particles stability to the oxidation and to decrease the agglomeration of Al particles [7]. The specific surface area of powder with the AlB2 coating was 2.5 times higher than for the Al powder, which had the oxide passivating layer (Table 1). The application of a nitrocellulose (NC) coating was performed to study the activation of the oxidation of aluminum due to the high exothermic effect of the decomposition of NC at 180 8C. Coating of the powders by NC, which contains 12.4 wt.-% of nitrogen, was done by stirring the powder in 10 wt.-%

Experimental Study of the Effect of Metal Nanopowders on the Decomposition of HMX, AP and AN

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Table 1. Characteristics of metal nanopowders and industrial powder ASD-4. No

Sample Code

Initial Wire Composition

1 2 3 4 5 6 7 8 9 10

Al NP-Al2O3 Al NP-AlB2 Al NP-NC ASD-4 Fe NP Ni NP Cu NP W NP Cu-6% Ni NP Cu-45% Ni NP

Al Ar Al ( B ) Ar Al Ar Micrometer sized industrial powder Fe Ar Ni Ar Cu Ar W Ar Cu-6% Ni Ar Cu-45% Ni Ar

a)

Gas Media in Explosive Chamber

Passivation Condition

Ssp ( BET ), m2 g1

as,a) nm

CMe, wt.-%

Air Air Nitrocellulose Air in ethanol Air Air Air Air Air Air

7.0 17.0 5.0 0.4 18.2 20.3 16.8 5.2 5.9 6.4

317 131 444 5555 95 120 156 359 326 331

76.1 78.2 67.5 98.5 88.9 91.0 93.2 98.0 96.5 96.7

For spherical particles as ¼ 6/( Ssp *1Al ).

NC solution in acetone, followed by the evaporation of acetone at room temperature. Al NP-NC had a content of NC of 33 wt.-%. The other metals were passivated by air with the standard procedure [8] and had relatively high metal content, except for Fe NP (Table 1).

2.2 DTA – TGA Study of Metal Nanopowders The metal NPs as well as micrometer sized powder ASD-4 were tested by the DTA – TGA. DTA – TGA (Universal 2.4 F TA Instruments) was used for testing the nonisothermal behavior of the components with a heating rate of 10 K min1. DTA – TGA results for metal NPs are given in Figures 1 and 2 (in air) and Figure 3 (in nitrogen). The onset temperature of the oxidation (Ton, 8C) and mass increase (þ Dm, % wt) of the studied NPs were not depending on the particle size. Micrometer sized powder ASD-4 had Ton ¼ 580 8C, while for Al NP-Al2O3 this temperature was 510 8C (Figure 1, a). For Al NPs, the considerably stronger reaction with air is observed in comparison with the micrometer sized powder ASD-4 (Figure 1). Al NP with the coating of AlB2 had a higher Ton ¼ 560 8C (Table 2) in comparison with the Al NP-Al2O3 (510 8C). This is probably caused by the protective film of the refractory AlB2 on the surface of the particles. The degrees of the oxidation of the samples Al NP-Al2O3 and Al NP-AlB2 are higher than the others at 660 8C and approximately identical. In the DTA curve for sample Al NP-NC two exothermic effects appear, which are, respectively, the NC decomposition in the temperature range of 180 – 220 8C with a 25.0 wt.-% decrease and the Al metal oxidation (510 – 620 8C). The gasification of the carbonaceous species, which were formed during the NC decomposition, occurred in the temperature range of 280 – 510 8C. The total weight loss at the stage of the NC decomposition (on TG) was 31.2%. The intensive Al oxidation for the sample Al NP-NC occurred under T ¼ 525 – 620 8C. Thus, the processes of NC decomposition and Al oxidation under heating in air proceed independently of each other (according to the DTA curves). The parameters of thermal decomposition of NC and the parameters of Al


Figure 1. DTA (a) and TGA (b) curves of the studied Al NP in air (m ¼ 3 mg, vheat ¼ 10 K min1, etalon a-Al2O3).

NP oxidation remained at the same level as for the individual substances. According to Figures 1, 2 and Table 2, metal NPs are themselves very reactive to heating in air. As shown by Ivanov et al. [9] the metal NPs with the lower chemical reactivity, unexpectedly, have a lower Ton, a fact that is explained by the structure of oxide films. This is confirmed

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A. Gromov, Y. Strokova, A. Kabardin, A. Vorozhtsov, U. Teipel

Figure 2. (a). DTA curves of the studied metal NPs in air (m ¼ 3 mg, vheat ¼ 10 K min1, etalon a-Al2O3). (b). TGA curves of the studied metal NP in air (m ¼ 3 mg, vheat ¼ 10 K min1, etalon a-Al2O3).

by the DTA and TGA curves – the Ton < 200 8C for Cu NP as well as for the alloy Cu-45% Ni NP, while the Ton is 352 8C for the reactive Fe. Compared to ASD-4 and Al NPs, the samples 5 – 10 (Table 2) had low temperatures of the oxidation onset (174 – 352 8C), while DHoxid for all metals was relatively high, except the W NP. The high reactivity of metal NPs in air does not allow to define the catalytic effect of their interaction with EMs. Thus, the following experiments were performed in nitrogen. Except for Al NP [10, 11], the other metal NPs were poorly nitridized, while being heated in nitrogen (Figure 3, Table 3). Except for Fe and Cu NPs, nitrogen did not react with the other metals (Figure 3). The nitridation exotherm appeared only on the DTA curve of the Fe NP (Figure 3, a). The DTA – TGA study of the mixtures (metal NP þ energetic material) showed only interaction in binary systems, except the reaction of components with nitrogen as could be concluded on the basis of the experimental data.

2.3 DTA – TGA Study of the Mixtures (metal NP þ HMX) The mixtures (metal NP þ 50 wt.-% energetic material) were suspended in ethanol (C2H6O), dried in air and then analyzed by DTA – TGA. The size of the particles of energetic materials (HMX, AP, and AN) was 100 mm. The DTA – TGA results of the mixtures (Al NP-Al2O3 þ 50 wt.-% HMX) showed that in the studied mixture Ton was 260 8C for HMX (Figure 4), which was 28 8C lower than that for the HMX itself (Ton ¼ 288 8C). Hence, Al NP-Al2O3 initiated the decomposition of HMX at a lower temperature. The parameters of the Al oxidation of the Al NP-Al2O3 sample in the presence of HMX were not changed (Figure 4). The Al NP covered by AlB2 and NC had an analogous effect on the Ton of HMX, i.e., the Ton was


Table 2. DTA – TGA study of metal nanopowders and industrial powder ASD-4 in air. No

Sample Code

Ton, 8C

D Hoxid Me, J g1

þ Dm (to 600 8C ), % wt

1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Al NP-Al2O3 Al NP-AlB2 Al NP-NC ASD-4 Fe NP (1b)) Ni NP (3b)) Cu NP (2b)) W NP (6b)) Cu-6% Ni NP (5b)) Cu-45% Ni NP (4b))

510 560 525 580 352 337 181 284 239 174

4730 6232 5790 220 4180 4870 4040 611 2408a) 1766a)

28 22 19 1 35 19 23 14 11 16

a)

Two peaks of oxidation;

b)

nos. on Figure 2 and 3.

decreased down to 240 8C and 250 8C, respectively. The small decrease in the Ton for the HMX (down to 270 8C) was also observed on the DTA curve of the mixture (ASD-4 þ 50% HMX). The degree of ASD-4 oxidation in the mixture with the HMX was considerably lower in comparison with the oxidation of the sample Al NP-Al2O3 (Figure 4, a). The Fe, Cu-45% Ni, and Cu-6% Ni NPs (Table 4, Figure 5) strongly affected the HMX decomposition. For the Cu-45% Ni NP and Cu-6% Ni NP the strong effect (Table 4) could be caused by a catalytic process because the NP themselves did not react with the nitrogen atmosphere (Figure 3), but only with HMX. The decomposition temperature of HMX was 96 8C lower as a result of the Fe NP interaction with HMX. There was a simultaneous interaction of the Fe NP with the nitrogen atmosphere in the case of Fe interaction with solid HMX (Figure 2). Surprisingly, neither pure Ni nor Cu NPs decreased the Ton of HMX significantly. Only Cu-Ni alloys worked as catalysts. The W and Ni NPs had no interaction with the HMX. The main products of HMX decomposi-




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Table 3. DTA – TGA study of metal nanopowders and industrial powder ASD-4 in nitrogen. No Sample Code

Ton, 8C

D Hnitrid Me, þ Dm J g1 (to 600 8C ), % wt

1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

749 749 553 No reaction 145 No reaction No reaction No reaction 237 No reaction

2740 534 3940 No reaction 7810 No reaction No reaction No reaction 489 No reaction

a)

Al NP-Al2O3 Al NP-AlB2 Al NP-NC ASD-4 Fe NP (1b)) Ni NP (2b)) Cu NP (3b)) W NP (6b)) Cu-6% Ni NP (5b)) Cu-45% Ni NP (4b))

Up to 1000 8C;

b)

nos. on Figure 1 – 3;

c)

38a 33a 29 0 18 0 1 1c) 1c) 0

() – mass decreasing.

tion – gaseous carbon oxides and nitrogen oxides [12] appeared at temperatures higher than 250 8C and could not promote the “solid HMX – solid NP” reaction.

2.4 DTA – TGA Study of the Mixtures (metal NP þ AP) The parameters of the AP decomposition were practically not changed for the mixture (Al NP-Al2O3 þ 50% AP).

Figure 3. (a). DTA curves of the studied metal NPs in N2 (m ¼ 3 mg, vheat ¼ 10 K min1, etalon a-Al2O3). (b). TGA curves of the studied metal NPs in N2 (m ¼ 3 mg, vheat ¼ 10 K min1, etalon aAl2O3). Figure 4. DTA (a) and TGA (b) curves of the mixtures (Al NP þ 50 wt.-% HMX) in N2. (m ¼ 3 mg, vheat ¼ 10 K min1, etalon a-Al2O3)




510

A. Gromov, Y. Strokova, A. Kabardin, A. Vorozhtsov, U. Teipel Table 4. DTA – TGA study of mixtures ( Metal NP þ 50% HMX ). No Sample Code

Remark Ton, DT, D Hexo, -Dm 8C 8C J g1 (300 8C ), %

1 2 3 4 5 6 7 8 9 10 11

288 242 240 250 270 192 283 228 284 193 196

HMX Al NP-Al2O3 Al NP-AlB2 Al NP-NC ASD-4 Fe NP Ni NP Cu NP W NP Cu-6% Ni NP Cu-45% Ni NP

– 46 48 38 18 96 5 60 4 95 92

3240 n/a n/a n/a n/a 1500 747 2270 611 1800 4831

70 25 33 42 17 48 45 34 14 39 48

Medium effect Medium effect Medium effect No effect Strong effect No effect Medium effect No effect Strong effect Strong effect

Table 5. DTA – TGA study of mixtures ( Metal NP þ 50% AP ). No Sample Code

Ton, DT, D H, 8C 8C J g1

Dm Remark (to 500 8C ), %

1. 2. 3. 4. 5. 6. 7. 8.

307 – 8960 320 13 n/a 244 63 þ 3996a) 291 16 þ 2490 146 161 þ 5150a) 311 4b) þ 324 246 61 þ 4950 277 30 þ 3154a)

100 40 42 48 40 50 40 50

a)

AP Al NP-Al2O3 Fe NP Ni NP Cu NP W NP Cu-6% Ni NP Cu-45% Ni NP


b)

No effect Medium effect No effect Strong effect No effect Medium effect Medium effect

Ton is higher than for pure AP.

Oxidation of Al NP-Al2O3 in the mixture with AP began at 30 8C lower (Ton ¼ 480 8C) in comparison with the oxidation of pure Al NP-Al2O3 (Figure 6). For other metal NPs (Table 5, Figure 7), the AP affected their oxidation (not v.v.) because AP had a higher Ton than all the studied metals and AP evolved oxidative gases by decomposition itself.

2.5 DTA – TGA Study of the Mixtures (metal NP þ AN) The data on the effect of metal NPs to AN decomposition are summarized in Table 6. Except the Fe and W NPs, the other metals started to react intensively with the AN after the third polymorph transformation of AN (Figure 8). The process of metals reacting with the AN occurred simultaneously with the decomposition of AN.

3 Conclusion

Figure 5. (a). DTA curves for metal NPs mixtures with HMX under non-isothermal heating in N2 (m ¼ 3 mg, vheat ¼ 10 K min1, etalon a-Al2O3). (b). TGA curves for metal NPs mixtures with HMX under non-isothermal heating in N2 (m ¼ 3 mg, vheat ¼ 10 K min1, etalon a-Al2O3).


The metal nanopowders (Fe, Cu, Cu-Ni, W, Al [13]) were intensively oxidized in air by heating from 100 8C. This is why a DTA – TGA study of the interaction of energetic materials with metal nanopowders should be performed in an inert atmosphere (N2 or Ar). The results of experimental studies of the effect of metal nanopowders on the HMX, AP,




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Table 6. DTA – TGA study of mixtures ( Metal NP þ 50% AN ). No Sample Code

Ton, DT, D H, 8C 8C J g1

1. 2. 3. 4. 5. 6. 7.

166 161 149 132 155 84 87

a)

AN Fe NP Ni NP Cu NP W NP Cu-6% Ni NP Cu-45% Ni NP


– 17 34 11 82 79 b)

8130b) 2809 þ 4152a) þ 672 3265 þ 1024 þ 1368a)

Dm Remark (to 500 8C ), % 100 49 43 39 49 33 38

Medium effect No effect Medium effect No effect Strong effect Strong effect

(þ)-exo, ()-endo.

Figure 6. DTA (a) and TGA (b) curves for Al NP mixture with AP under non-isothermal heating in N2 (m ¼ 3 mg, vheat ¼ 10 K min1, etalon a-Al2O3).

and AN decomposition were presented. They showed the strong effect of Fe, Cu, and Cu-Ni NPs on the HMX decomposition temperature, which is lowered by more than 90 8C. For the decomposition of AN and AP, the decomposition started itself after the metals reacted with the nitrogen media or decomposition products. For all the three studied energetic materials, the metal NPs seemed to show a catalytic effect: Cu-Ni for AN (Fe, Wand Ni – no effect); CuNi, Cu and Fe – for AP (Al, W and Ni – no effect), Cu-Ni, Cu and Fe – for HMX (W and Ni – no effect).


Figure 7. (a). DTA curves for metal NPs mixtures with AP under non-isothermal heating in N2 (m ¼ 3 mg, vheat ¼ 10 K min1, etalon a-Al2O3). (b). TGA curves for metal NPs mixtures with AP under non-isothermal heating in N2 (m ¼ 3 mg, vheat ¼ 10 K min1, etalon a-Al2O3).



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4 References [1] Leili Liu, Fengsheng Li, Linghua Tan, Li Ming, Yang Yi. Effects of Nanometer Ni, Cu, Al and NiCu Powders on the Thermal Decomposition of Ammonium Perchlorate, Propellants, Explos., Pyrotech. 2004, 29, 34. [2] N. Kubota. Propellants and Explosives: Thermochemical Aspects of Combustion. Wiley-VCH, Weinheim, 2001. [3] Yu. F. Ivanov, M. N. Osmonoliev, V. S. Sedoi, V. A. Arkhipov, S. S. Bondarchuk, B. A. Vorozhtsov, A. G. Korotkikh, V. T. Kuznetsov, Productions of Ultra-Fine Powders and Their Use in High Energetic Compositions, Propellants, Explos., Pyrotech. 2003, 28, 319. [4] Y. S. Kwon, Y. H. Jung, N. A. Yavorovsky, A. P. Ilyin, J. S. Kim. Ultrafine Metal Powders by Wires Electric Explosion Method, Scr. Mater. 2001, 44, 2247. [5] E. I. Azarkevich, A. P. Ilyin, D. V. Tikhonov, G. V. Yablunowskii, Electric Explosion Synthesis of Ultradispersed Powders of Metals, Alloys and Chemical Compounds, Physica i Khimiya Obrabotki Materialov. 1997. 4, 85, [in Russian]. [6] M. M. Mench, K. K. Kuo, C. L. Yeh, Y. C. Lu, Comparison of thermal Behavior of Regular and Ultrafine Aluminum Powders (Alex) Made from Plasma Explosion Process, Combust. Sci. Technol. 1998. 135, 269. [7] Y. S. Kwon, A. A. Gromov, A. P. Ilyin. Reactivity of Superfine Aluminum Powder Stabilized by Aluminum Diboride, Combustion and Flame. 2002, 131, 349. [8] Y. S. Kwon, A. A. Gromov, A. P. Ilyin, G. H. Rim. Passivation Process for Superfine Aluminum Powders Obtained by Electrical Explosion of Wires, Appl. Surf. Sci. 2003, 211, 57. [9] V. G. Ivanov, O. V. Gavrilyuk. Specific Features of the Oxidation and Self-Ignition of Electroexplosive Ultradisperse Metal Powders in Air, Combustion, Explosion Shock Waves 1999, 35, 648. [10] A. A. Gromov, A. P. Ilyin, U. Fçrter-Barth, U. Teipel. Study of Non-isothermal Nitridation of Aluminum Nanopowders Passivated by Non-oxide Layers, Cent. Eur. J. Energ. Mater. 2006, 3, 65. [11] A. Ilyin, A. Gromov, V. An, F. Faubert, C. de Izarra, A. Espagnacq, L. Brunet, Characterization of Aluminum Powders I. Parameters of Reactivity of Aluminum Powders, Propellants, Explos., Pyrotech. 2002, 27, 361. [12] L. Huwei, F. Rionong. Investigation of Thermal Decomposition of HMX and RDX by Pyrolysis-Gas Chromatography, Thermochim. Acta 1989, 138, 167. [13] A. Gromov, A. Ilyin, U. Fçrter-Barth, U. Teipel, Characterization of Aluminum Powders: II. Aluminum Nanopowders Passivated by Non-Inert Coatings, Propellants, Explos., Pyrotech. 2006, 31, 401.

Acknowledgement This work has been financially supported by the Russian Foundation for Basic Research (grant No. 08-08-12013), and Russian President Grant MD –2.37.2009.8

List of Abbreviations

Figure 8. (a). DTA curves for metal NPs mixtures with AN under non-isothermal heating in N2 (m ¼ 3 mg, vheat ¼ 10 K min1, etalon a-Al2O3). (b). TGA curves for metal NPs mixtures with AN under non-isothermal heating in N2 (m ¼ 3 mg, vheat ¼ 10 K min1, etalon a-Al2O3).


AN AP as BET method CMe DTA EEW HMX NP SEM Ssp TGA


Ammonium nitrate, NH4NO3 Ammonium perchlorate, NH4ClO4 Surface mean particle diameter, nm Brunauer, Emmett, Teller Method Metal content, wt.-% Differential thermal analysis Electrical explosion of wires Octogen, (CH2NNO2)4 Nanopowder Scanning electron microscopy Area of the specific surface, m2 g1 Thermogravimetric analysis
