Precursor routes to Group 4 metal borides, and metal boride/carbide and metal boride/nitride composites

Precursor routes to Group 4 metal borides, as well as metal-boride/carbide and metal-boride/nitride composites, that employ metal-oxide/polymer and metal/polymer dispersions are described. The metal boride precursors were initially obtained by dispersing metal oxides in a decaborane-dicyanopentane polymer, but better results have now been achieved using a newly developed polyhexenyldecaborane polymer. Subsequent pyrolyses of the metal-oxide/polymer dispersions afford metal borides, including TiB2, ZrB2, and HfB2 in high chemical and ceramic yields. On the other hand, pyrolyses of hafnium/polyhexenyldecaborane dispersions provide an efficient route to hafnium-boride/carbide composites. Metal-boride/nitride composites, including TiB2/TiN and HfB2/HfN materials, are also readily obtained by pyrolyses of metal dispersions in the boron-nitrogen polymer polyborazylene, (B3N3H4)(X). The high ceramic yields of the metal-boride/nitride systems (similar to98%), enable their use for the controlled formation of shaped monolithic TiB2/TiN or HfB2/HfN materials by pyrolysis of pressed precursor green bodies. (C) 2004 Kluwer Academic Publishers.