Reaction characteristics of Al/Fe 2 O 3 nanocomposites Moon-Soo Shin a , Jae-Kyeong Kim a , Jun-Woo Kim a , Carlos Alberto Mendes Moraes b , Hyoun-Soo Kim c , Kee-Kahb Koo a, * a Department of Chemical and Biomolecular Engineering, Sogang University, Seoul 121-742, Republic of Korea b University of Vale do Rio Sinos- UNISINOS, Materials Characterization Research Group, Avenue UNISINOS, 950 Sa˜o Leopoldo, 93.022-000, RS, Brazil c Agency for Defense Development, Daejeon 305-600, Republic of Korea 1. Introduction Energetic materials are a class of substances with high amount stored chemical energy that can be released [1]. In general, traditional energetic materials are classified into three classes such as explosives, propellants, and pyrotechnics. The thermite is a well-known example of pyrotechnic composition with a metal powder and a metal oxide that induces an exothermic oxidation– reduction reaction known as thermite reaction. The thermite mixture of iron(III) oxide (Fe 2 O 3 ) and aluminum (Al), which produces high temperature by self-propagating reaction, has been used to a lot of engineering applications such as welding and cutting materials, portable heat source, pyrotechnics, and explo- sives [2]. Nanostructured energetic materials have superior burning rate compared with conventional energetic materials [3]. Nanostruc- tured materials may be produced by various methods such as physical mixing, sol–gel synthesis, electrostatical assembly, deposition of multi-layer foils of oxidizer and fuel, and oxidizer coated with fuel [4–8]. In recent years, Gash et al. reported that a sol–gel method can be used to make the nanostructured Al/Fe 2 O 3 thermite composite with very intimate mixing [5,9]. In the present work, three different nanostructured Al/Fe 2 O 3 composites were prepared:a nanocomposite with particulate Al dispersed in bulk xerogel Fe 2 O 3 by sol–gel process, a nano- composite of particulate Al and heat treated ground xerogel Fe 2 O 3 by ultrasonic mixing and a nanocomposite of particulate Al and particulate Fe 2 O 3 by ultrasonic mixing. In this context, the aims of this work are to investigate (i) effect of synthetic method of nanocomposites on the Al/Fe 2 O 3 thermite reaction, (ii) effect of chemical composition of nanocomposites on the thermal performance, and (iii) the mechanism of Al/Fe 2 O 3 thermite reaction accompanied by melting of unreacted alumi- num. 2. Experimental 2.1. Materials Particulate Al (mean size of 100 nm) and Fe 2 O 3 (mean size of 50 nm) were purchased from Nano-Technology (Korea) and Sigma Aldrich (USA), respectively. In the preparation of Al/Fe 2 O 3 thermite by ultrasonic mixing, n-hexane (C 6 H 14 ; 98+%, Sigma Aldrich, USA) was used as a dispersion medium. In the synthesis of xerogel Fe 2 O 3 , iron(III) nitrate nonahydrate (Fe(NO 3 ) 3 9H 2 O; 98+%, Sigma Aldrich, USA), propylene oxide (C 3 H 6 O; 98+%, Sigma Aldrich, USA), and n- propanol (C 3 H 8 O; 98+%, DaeJung Chemicals, Korea) were used as a starting material, a gelation agent and a solvent, respectively. Potassium bromide (KBr; BDH VWR International, Belgium) was used to prepare KBr pellets for Fourier transform infrared spectroscopy (FT-IR) analysis. Journal of Industrial and Engineering Chemistry 18 (2012) 1768–1773 A R T I C L E I N F O Article history: Received 17 January 2012 Accepted 2 April 2012 Available online 17 April 2012 Keywords: Thermite Sol–gel Nanocomposite A B S T R A C T Al/Fe 2 O 3 nonacomposites have explosive and high exothermic properties by thermite reaction. In this study, Al/Fe 2 O 3 xerogel nanocomposites were prepared by sol–gel method and thermite reaction performance was compared with those prepared by physical mixing with sonication. Scanning electron microscopy (SEM) images of Al/Fe 2 O 3 xerogel nanocomposites show that network structure of Fe 2 O 3 gel covers Al nanoparticles efficiently and this indicates that improvement of thermite reaction performance due to close contact between a fuel and an oxidizer. Optimum mole ratio of Al/Fe was determined to be 2 by thermite reaction performance by differential scanning calorimetry (DSC) analysis. At Al/Fe ratio of 2, thermite reaction enthalpy of the Al/Fe 2 O 3 xerogel nancomposite was 991.4 J/g, which was higher by a factor of four than that of the nanocomposite prepared by physical mixing. ß 2012 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +82 2 705 8680; fax: +82 2 711 0439. E-mail address: koo@sogang.ac.kr (K.-K. Koo). Contents lists available at SciVerse ScienceDirect Journal of Industrial and Engineering Chemistry jou r n al h o mep ag e: w ww .elsevier .co m /loc ate/jiec 1226-086X/$ – see front matter ß 2012 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2012.04.003