Nitride ceramics synthesis

A less explored area of transition metal catalysis involves bond formation between Group 14 elements and nitrogen. In direct analogy to previously discussed areas of research, silicon-nitrogen bonds can be formed by dehydrocoupling, hydrosilylation, and dehydrogenative silylation. The compounds produced are valuable for use in organic synthesis or as polymer precursors to silicon nitride ceramics. 

All silicon nitride ceramics are derived from synthetic materials, exclusively. The first report on the synthesis of Si3N4 was in 1859 by Sainte-Claire Deville and Wohler [3]. Among the problems of greatest concern to chemists in those days was the utilisation of atmospheric nitrogen for agricultural and industrial purposes. In particular, there was a need for a highly effective... 

Aluminum nitride is most commonly used for its high thermal conductivity. Recently, a poreless composite material, TiAl-TiB2-AlN, was obtained by reacting a Ti-F(0.7-0.95)A1+(0.05-0.50)8 mixture at 30- to 100-atm nitrogen pressure (Yamada, 1994). The use of high-pressure nitrogen gas was found to be effective for simultaneous synthesis and consolidation of nitride ceramics with dispersed intermetallic compounds (e.g., TiAl). Dense, crack-free products with uniform grains (approximately 10 mm in size) were obtained. 

The thermodynamics of the above-elucidated SiC/C and SijN Si composites are determined by the decomposition of silicon carbide and silicon nitride, respectively, into their elements. The chemistry of ternary Si-C-N composites is more complex. If producing Si-C-N ceramics for applications at elevated temperature, reactions between carbon and silicon nitride have to be considered. Figure 18.2, which exhibits a ternary phase diagram valid up to 1484°C (1 bar N2) displays the situation. The only stable crystalline phases under these conditions are silicon carbide and silicon nitride. Ceramics with compositions in the three-phase field SiC/Si3N4/N are unknown (this is a consequence of the thermal instability of C-N bonds). Although composites within the three-phase field SiC/Si3N4/Si are thermodynamically stable even above 1500°C, such materials are rare. The reasons are difficulties in the synthesis of the required precursors and silicon melting above 1414°C. The latter aspect is of relevance, since liquid silicon dramatically worsens the mechanical properties of the derived ceramics. 

Omotowa BA, Phillips BS, Zabinski JS et al (2004) Phosphazene-based ionic liquids synthesis, temperature-dependent viscosity, and effect as additives in water lubrication of silicon nitride ceramics. Inorg Chem 43 5466-5471... 

Nitride Ceramics Combustion Synthesis, Properties, and Applications, First Edition. 

Loryan, V. (1995) Self-propagating High-temperature Synthesis of Nitride Ceramics at High Pressure of Nitrogen. 

Combustion Synthesis of Boron Nitride Ceramics Fundamentals and Applications... 

Yeh, CL. and Chuang, H.C. (2004) Experimental studies on self-propagating combustion synthesis of niobium nitride. Ceram. Int, 30 (5), TSi-l S. 

S. Kamimura, K. Watanabe, N. Kasai, T. Seguchl and K. Okamura, Silicon nitride fiber synthesis from polycarbosilane fiber by radiation curing and pyrolysis under ammonia, Ceram. Transactions, 58, 281-286 (1995). 

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