GB870083A - Improvements in or relating to the manufacture of borides - Google Patents

Abstract

Boron carbide is prepared by heating a mixture of carbon and boric oxide (or one or more substances which provide boric oxide on heating) together with an organic binder to provide an expanded carbon skeleton or framework on which the other ingredients of the mixture are supported, and subsequently heating to 1300 DEG -1900 DEG C., e.g. in a carbon resistance furnace. The binder is a carbonaceous material which will on heating char and expand forming the coherent carbon skeleton, e.g. sucrose, molasses, starch pitch, asphalt, tar, cork dust, leather dust, resin, or rubber. The initial mixture may be moulded into cylinders or formed into pellets, and the binder may be mixed with water. The ratio of boric oxide to carbon in the initial mixture including C in the binder is 1.6:1 to 2.5:1. The mixture may be first heated to 700 DEG C., or slowly dried at stepwise increases from 110 to 600 DEG C., to expand and render the binder coherent. To remove oxides of carbon during boride formation the pressure may be reduced, or a current of inert gas, or a mixture 90/10 N2/H2 may be passed through. In a modification an oxide of Ti, Zr, Nb, Ta, Mo, W, Cr, Ni, or a rare earth metal of At. No. 57-71 is added to the initial mixture to form the corresponding metal borides. Boron nitride may be prepared by passing N2 into the boron carbide forming mixture when heated to 1300 DEG -1900 DEG C. Boron trichloride is formed by passing Cl, over the boron carbide at above 300 DEG C. Boron tribromide is formed by passing Br2 vapour over the boron carbide at above 600 DEG C. Boron sulphide is formed by passing S vapour over the boron carbide at above 1000 DEG C. Specification 870,084 is referred to.