which possess high energetic and oxidation potentials, by vacuum evaporation followed by deposition. The phase composition, the morphology, and the size of.
Doklady Physical Chemistry, Vol. 383, Nos. 1–3, 2002, pp. 81–83. Translated from Doklady Akademii Nauk, Vol. 383, No. 2, 2002, pp. 227–229. Original Russian Text Copyright © 2002 by Frolov, Pivkina, Zav’yalov.
PHYSICAL CHEMISTRY
Preparation of Nanosized Particles of Energetic Substances Yu. V. Frolov*, A. N. Pivkina*, and S. A. Zav’yalov** Presented by Academician A.L. Buchachenko October 20, 2001 Received December 4, 2001
Nanoparticles whose size is in the 1–100 nm range exhibit new and/or improved properties compared to the properties of materials formed by micrometer-size particles [1]. Size effects largely change the macroscopic properties of materials. Among these changes, one can distinguish an increase in the electrical conductivity of ceramic nanocomposites, an increase in the electrical resistance of nanometals, improvement of the plasticity of ceramics, a decrease in the melting point, an increase in the chemical reactivity, etc. The properties previously regarded as invariable for a given substance become controllable on passing to the nanosize region. Studies showed that the vacuum deposition method can, in principle, be used to synthesize nanomaterials as polymeric matrices filled by metal nanoparticles [2, 3]. Sol–gel technologies have been used to prepare nanostructured materials [4]. It was found that the burning rate and temperature of these systems are higher than those for traditional materials containing micrometersize particles. This work deals with the preparation of nanoparticles of individual ammonium nitrate and hexogen, which possess high energetic and oxidation potentials, by vacuum evaporation followed by deposition. The phase composition, the morphology, and the size of crystallites were determined using X-ray powder diffraction analysis and atomic-force microscopy. It was found that the size of crystallites of these substances does not exceed 100 nm. A composite material containing nanoparticles of both components was also obtained by vacuum deposition.
followed by vapor deposition on a cooled substrate. A liquid-nitrogen cooled metallic disc with fused silica substrates is located in the deposition zone. After condensation, the substrates with the deposited material are taken out of the reactor for analysis. In each experiment, the deposition was carried out onto three identical quartz substrates. The evaporation temperature and the deposition time were varied in the experiments. The X-ray diffraction analysis of the resulting materials was performed on a Rigaku D/Max-IIIC diffractometer. The substances were identified using D/MAX-B Application Software. The surface morphology and the structure of the composite were studied using a Solver P47 atomic-force microscope. Ammonium nitrate. Figure 2a shows the X-ray diffraction pattern of the sample prepared by evaporation and deposition on a substrate of pure ammonium nitrate. The evaporation temperature was 133°ë, and the process time was 90 min. The results indicate that both the initial substance and the synthesized material are single-phase, chemically homogeneous NH4NO3 (IV, the orthorhombic bipyramidal crystalline form). The spectra recorded with variation of the evaporation temperature from 121 to 145°ë and variation of the evaporation time from 1 to 120 min are identical to those presented in Fig. 2a. Liquid nitrogen
EXPERIMENTAL Figure 1 presents the diagram of the experimental setup used for the synthesis of nanomaterials in the mode of vacuum evaporation of the initial compounds * Semenov Institute of Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 117977 Russia ** Karpov Research Institute of Physical Chemistry, ul. Vorontsovo pole 10, Moscow, 103064 Russia
Computer/ADC
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Fig. 1. Diagram of the experimental setup for vacuum deposition of composite materials.
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Fig. 2. X-ray diffraction patterns of the products of synthesis: (a) 100% ammonium nitrate (IV); (b) 100% hexogen.
Figure 3 shows a section of the surface of the ammonium nitrate sample synthesized at a temperature of 145°ë and a synthesis time of 6 min. The ammonium nitrate crystallites are rather uniform in shape and size; the diameter at the bottom of the particles does not exceed 50 nm. Hexogen. The X-ray diffraction pattern of the synthesized sample of hexogen ë3H6N3(NO2)3 is presented in Fig. 2b. The evaporation temperature was 137°ë, and the process time was 150 min. The product was hexogen of 100% chemical purity. Hexogen/Ammonium nitrate. The simultaneous use of two vaporizers in the experimental setup (Fig. 1) made it possible to prepare binary composite systems containing ammonium nitrate and hexogen. Figure 4 shows the X-ray diffraction spectrum of the composite; the sample consists of two components, namely, pure hexogen and pure ammonium nitrate, which occurs in two crystalline forms, orthorhombic bipyramidal ammonium nitrate (IV) and tetragonal ammonium nitrate (V). The product does not contain any substances other than those mentioned above. The crystallite sizes, calculated from peak broadening, were 55 nm for ammonium nitrate particles and 31 nm for hexogen particles. Thus, nanosized energetic materials, ammonium nitrate and hexogen, were obtained with retention of their chemical nature by vacuum deposition onto a cooled surface. The average size of ammonium nitrate
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Fig. 3. AFM image of the surface of the ammonium nitrate sample prepared. The scanning area was 1.2 µm × 1.2 µm. The crystallites with sizes of less than 50 nm and heights of less than 5 nm can be clearly seen. DOKLADY PHYSICAL CHEMISTRY
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PREPARATION OF NANOSIZED PARTICLES OF ENERGETIC SUBSTANCES Intensity, arb.units 100
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Fig. 4. X-ray diffraction pattern of the composite material prepared by joint vacuum deposition of (1) ammonium nitrate and (2) hexogen. Sample composition: hexogen, 56.1%; ammonium nitrate IV, 39.7%; ammonium nitrate V, 4.2%.
crystallites is 50 nm. The crystallite size in the ammonium nitrate–hexogen binary system does not exceed 100 nm, which proves the correctness of terming this product a “nanocomposite material.” ACKNOWLEDGMENTS This work was supported by the Russian Foundation for Basic Research (project no. 01–03–32530). We are grateful to P.A. Ul’yanova for active participation in the experiments.
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REFERENCES 1. Pomogailo, A.D., Rozenberg, A.S., and Ufland, U.E., Nanochastitsy metallov v polimerakh (Metal Nanoparticles in Polymers), Moscow: Khimiya, 2000. 2. Zavyalov, S., Yablokov, M., Pivkina, A., et al., Proc. Annual ESF-NANO Meeting, 10–11 December, 1999, Duisburg, 1999, pp. 28/1–28/4. 3. Zavyalov, S.A., Pivkina, A.N., and Schoonman, J., Proc. Polymer Electrolytes Symp. PES2001, 14–16 May, 2001, Noordwijkerhout, 2001, p. 55. 4. Gash, A.E., Simpson, R.L., Tillotson, T.M., et al., Proc. XXVII IPS, 16–21 July, 2000, Denver (Col), 2000, pp. 41–53.
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