GB996916A - Improvements in or relating to boron phosphorous compounds - Google Patents

Abstract

The invention comprises crystalline rhombohedral boron phosphide having a boron to phosphorus atomic ratio greater than 7 to 1, e.g. of general formula BnP where n = 10, 20, 40, 70 and 100. These compounds may be made by heating to elevated temperatures B6P or mixtures of BP and P, or elemental B and P, or a metal phosphide or phosphorus alloy and a metal boride or boron alloy or carbide, or a boron halide, hydride or alkyl and P vapour and H2 or a phosphorus halide or hydride. The temperature used is at least 800 DEG C. but preferably 1200 DEG to 1600 DEG C. whilst the partial pressure of phosphorus in the system is maintained below the decomposition pressure of B6P at the prevailing temperature. B6P is heated using a thermogravimetric technique to give the required B: P atomic ratio. If BP is used as a starting material then at least 6 atomic proportions of elemental B is used. If elemental B and P are used then they are present in an atomic ratio of B: P greater than 7: 1. If metal phosphide or phosphorus alloy is used together with a metal boride, boron alloy or carbide, then the boron phosphide is separated by dissolving out the residue with acid, e.g. H2SO4, to leave the phosphide. The phosphorus compound may be e.g. ferrophosphorus. The boron compound may be e.g. BCl3 or ferroboron.