Combustion synthesis compounds

Apart from simple compounds, composite materials may also be prepared by combustion synthesis. Thus a composite of TiB2 and MgO can be formed... 

Intermetallic compound formation may be observed as the result from the diffusion across an interface between the two solids. The transient formation of a liquid phase may aid the synthesis and densification processes. A further aid to the reaction speed and completeness may come from the non-negligible volatility of the component(s). An important factor influencing the feasibility of the reactions between mixed powders is represented by the heat of formation of the desired alloy the reaction will be easier if it is more exothermic. Heat must generally be supplied to start the reaction but then an exothermic reaction can become self-sustaining. Such reactions are also known as combustion synthesis, reactive synthesis, self-propagating high-temperature synthesis. 

In addition to conventional sintering, reactive powder processing, also called combustion synthesis or self-propagating high-temperature synthesis (SHS), can be used if the target compounds can be synthezised from the starting powder mixture (Stangle and Miyamoto, 1995). This process comprises a rapid and exothermic chemical reaction to simultaneously synthesize some or all of the constituent phases in the FGM and density the component. 

In some cases, several refractory compounds can result from two or more parallel reactions occurring simultaneously in the combustion wave. A typical example of this type is the Ti-C-B system, where both the Ti+C and Ti-I-2B reactions affect the combustion synthesis and structure formation processes (Shcherbakov and Pityulin, 1983). By adjusting the contents of carbon and boron powders in the reactant mixture, either carbide- or boride-based ceramics can be obtained. 

Among intermetallic compounds not mentioned previously, Mg2Ni is a promising material for storing hydrogen. It has been shown that the combustion synthesis of this material is feasible, in spite of a relatively low heat of reaction. 

Kaieda, Y., Nakamura, M., Otaguchi, M., and Oguro, N., Combustion synthesis of TiAl intermetallic compounds. Proceedings of the First US-Japanese Workshop on Combustion Synthesis, Tokyo, Japan, 207 (1990a). 

Yi,. H. C., and Moore, J. J., Combustion synthesis of TiNi intermetallic compounds. Part 1 Determination of heat of fusion of TiNi and heat capacity of liquid TiNi. / Mater. Sci., 24,3449(1989). 

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