Chemical Vapor Deposition of NbB2 and TaB2 through Heating by Concentration of Solar Radiation

Abstract

NbB$sub 2$ or TaB$sub 2$ can be derived from a mixture of BBr$sub 3$ and NbBr$sub 5$ or TaBr$sub 5$ by thermal dissociation. Reactions are carried out at low pressure and without hydrogen. A description is given of a synthesis device which uses the concentration of solar radiation as the heating procedure. The effect of different experimental parameters is discussed. It is shown how to obtain a compact, adhesive diboride or oriented deposits. Development of microcrystals was observed which look like 15--20$mu$m hexagonal basis pyramids. (auth)