Combustion Synthesis of Ceramic Powders with Controlled Grain Morphologies

Combustion synthesis, which is also known as self-propagating high-temperature synthesis (SHS), is a facile and economic technique to prepare a large variety of advanced materials, such as ceramics, intermetallics, composites, and functionally-graded materials [1-4]. By this technique, new materials are synthesized from self-sustained exothermic chemical reactions instead of long-time heat treatment by furnace. Once the reactants are ignited, a large amount of heat energy is produced to support the reaction to continue. With the propagation of combustion wave through the whole sample, the reactants are converted into products. Because exothermic combustion reactions occur quickly, a non-equilibrium state is usually involved in combustion synthesis and characterized by high temperatures and fast heating or cooling rates. This non-equilibrium reaction state offers an opportunity for controlling the microstructure of products. Among the extensive applications of combustion synthesis, the fabrication of advanced ceramic powders is an important and successful practice. By combustion synthesis, many kinds of ceramic powders have been prepared, including nitrides (Si3N4, AlN, TiN, BN, SiAlON, etc.), carbides (SiC, TiC, ZrC, Ti3SiC2, Ti3AlC2, Ti2AlC, etc.), borides (MgB2, TiB2, ZrB2, etc.), silicides (e.g. MoSi2), and oxides (e.g. ferrites, Y-Ba-Cu-O superconductors). The grain size and morphology of the ceramic powders can be manipulated by controlling the processing parameters, such as proportion of diluents, porosity of green compacts, and particle size distribution of raw materials. This chapter presents some recent results on combustion synthesis of ceramic powders, with an emphasis on the investigation of crystal growth kinetics and control of final grain morphologies. Four kinds of ceramic powders (TiN, SiC, SiAlON, and Ti-Al-C) with different grain morphologies are reported as examples. The grain growth mechanisms involved in combustion synthesis of these ceramic powders are discussed in detail.