GROWTH OF TUBULAR BORON-NITRIDE FILAMENTS

Considering the similarity between graphite and hexagonal boron nitride (h-BN) structures, this study aims to elaborate boron nitride filaments analogous to filamentous carbon. Filamentous carbon is obtained by decomposition of a hydrocarbon coming into contact with a metal belonging to the iron family. Dissolving carbon in this metal leads to the precipitation of filamentous carbon around metallic grains. In the case of h-BN, the metallic phase may be zirconium owing to the solubility of C and N in this metal, although in practice it is easier to use ZrB2. BN filaments were obtained when B2H6 and NH3 (or N-2) came into contact with this compound (or borides of related metals) at temperatures around 1100 degrees C. Nevertheless it has been shown that BN filaments also occurred in the absence of B2H6; therefore the boron of the filaments originates in the boride. TEM observations showed that BN filaments exhibit structure, morphology and dimensions (phi-0.1 mu m, L similar to 1-10 mu m) analogous to those of C filaments, although the formation mechanisms are different.