ISSUES IN THE SYNTHESIS AND FABRICATION OF REFRACTORY CARBIDES, BORIDES, SILICIDES AND THEIR MIXTURES

Among the non-oxide ceramics, certain carbides and borides possess attractive combination of properties and good potential for applications but are difficult to fabricate, because of their physico-chemical and mechanical characteristics. The synthesis of boron carbide, borides of titanium, zirconium, hafnium, chromium and rare earth elements, their fabrication to consolidated pieces and determination of their properties in various stages of processing as well as in the final form, have been investigated. While the selection of the compounds for investigation was guided by their immediate technological applications, working with them brought to the fore several issues relating to their preparation and processing and these are covered in this paper. Boron carbide as well as the borides were synthesized from constituent elements, by chemical reaction of compound intermediates and also by fused salt electrolysis. Fine powder was obtained from the as reduced material by mechanical milling using special equipments. The densification by cold compaction and sintering as well as by hot pressing was investigated. Property measurements on the final products were carried out to relate the present material with the standards. The possibility of synthesizing and mixing silicides of refractory metals with borides for enhancing the high temperature oxidation resistance of borides was also investigated.