GB777234A - Boron nitride shapes and method of making - Google Patents

Abstract

A boron nitride body stable to water and alcohol is produced by hot-moulding a mixture of boron nitride to a stabilizer which forms with boric oxide under the conditions of moulding a material which is substantially, insoluble in water and alcohol and which is an alkaline earth compound other than tricalcium phosphate or a mixture of such compounds and/or a rare earth compound or a mixture of such compounds. The proportion of stabilizer may be up to 10 per cent. Stabilizers specified are calcium, barium, strontium and magnesium, carbonate, sulphate and oxide. The boron nitride may have a particle size not exceeding 0.5 microns. The material may be hot pressed at a temperature of 1500-1900 DEG C. under a pressure of 400 psi or more. The resulting body may have a sand blast penetration not less than that of plate glass, an apparent density of not less than 1.9 gm./c.c. and an alcohol-soluble content, calculated as B2O3, of less than 10 per cent. The boron nitride to be hot pressed may be produced by heating boric oxide in an atmosphere of ammonia at a temperature of 800-1100 DEG C. in the presence of an acid soluble inert diluent which is tricalcium phosphate or a stabilizer as defined above. It may alternatively be produced by heating a mixture of boric oxide with previously formed boron nitride at a temperature of 800-1100 DEG C. in an atmosphere of ammonia.