Formation of Nanostructured Energetic Materials via Modified Sol-Gel Synthesis
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Formation of Nanostructured Energetic Materials via Modified Sol-Gel Synthesis Jeremy Walker and Rina Tannenbaum*, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332. (*[email protected]) ABSTRACT This study is concerned with the development of a modified sol-gel synthesis of Fe2O3 xerogels that would allow the design and control of the interfacial area between the oxidant iron oxide matrix and the metal reducing agent, thus optimizing the energetic yield of these highly energetic reactions. The modification consisted in the addition of a new class of di-functional template molecules, such as diamines or di-acids, as gelation agents. pH profile measurements indicated that the mechanism of reaction of propylene oxide and of succinic acid as the gelation agents was fundamentally different. Propylene oxide acts as a proton scavenger, reducing the hydrated iron species to Fe2O3, thus reducing the concentration of protons in the reaction mixture leading to an increase in pH. When succinic acid is used as the gelation agent, a decrease in pH versus time during the reaction indicates the formation of carboxylate ions, thus creating reactive molecules that are capable of stabilizing the Fe2O3 clusters during the growth process. Infrared spectra of the products in both reactions support presence of carboxylate groups in the Fe2O3 xerogels. X-ray diffraction analyses revealed low levels of crystallinity in both products, and the presence of different phases of Fe2O3. INTRODUCTION Nanoenergetic structural materials have superior exothermic characteristics [1,2]. These materials may be used for military applications in both “smart” target-penetrating and explodingon-contact missiles, due to an increased allowance in the amount of high explosive material that can be placed in each missile and, also, an increase in energetic properties. They are comprised of a nanometer-scaled particulate metal fuel (e.g. Al, Fe, Cr) closely mixed with metal oxide particles, which, after a stress-induced oxidation-reduction reaction, result in a substantial exothermic heat release [1,2]. In these materials, reactions between different metal oxide networks (oxidants) and dispersed metallic particles (fuels) will result in different energetic release rates, as shown in the following typical exothermic reaction: kJ ) (1) mol An important parameter of the material is the pore size around the metal oxide clusters. Pore size and metal oxide matrix geometry are significant variables in controlling the exothermic characteristics of the material because they directly affect the interfacial area and reactivity between the metal fuel and the metal oxide particles. Therefore, the ability to control pore size will directly translate into an ability to modulate the extent of interfacial area, and as a consequence, the efficiency of the oxidation-reduction reaction. One way to accomplish this is to modify the original sol-gel reaction developed by Gash et al. [3] by introducing different types o
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