Intermetallic compounds combustion synthesis

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. 

For metals promoting other metals, an interesting case was studied by Hurst and Rideal.2 In the combustion of mixtures of hydrogen and carbon monoxide, using copper as the basic catalyst the ratio of the gases burnt depends on the temperature, and also on the amount of small additions of palladium made to the copper. The proportion of carbon monoxide burnt is increased by addition of palladium, a maximum proportion of carbon monoxide being burnt when 0-2 per cent, of palladium is. present. With further amounts of palladium, the ratio CO H2 burnt falls off slowly until, with 5 per cent, palladium, it is nearly the same as with pure copper. This effect of palladium is ascribed to the introduction of a new type of surface, the line of contact between palladium and copper, though the proof that this is the cause of promotion is perhaps not complete. Mit-tasch and others,3 in elaborate studies of the promotion of various metal catalysts, particularly molybdenum, for the synthesis or decomposition of ammonia, concluded that the formation of intermetallic compounds... 

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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