GB895769A - Improvements in or relating to shaped silicon nitride bodies and their manufacture - Google Patents

Abstract

A shaped body of self-bonded silicon nitride designed to withstand high temperature and to resist creep and thermal shock at such temperature, is made by compacting powdered silicon into a block, firing the block in an atmosphere of nitrogen at below the melting point of silicon and for at least one hour to produce a self-supporting readily machineable block, working the block to the required finished shape and firing the shaped body in an atmosphere of nitrogen so as to effect complete nitriding of the silicon. The compacting may be done by cold-pressing silicon powder in a die-set, preferably with the addition of a lubricant, e.g. water. The initial nitriding may be carried out at 1200 DEG C. for one hour. After machining the partially nitrided block to the required finished shape, the final nitriding may be carried out in two stages, initially at 1250 DEG C., and then at 1450 DEG C. The product may be provided with a glaze coating by applying a mixture of 5% by weight finely divided alumina, 93% by weight silicon powder and 2% by weight ferric oxide bound together with cetyl alcohol to the cleaned surface of the body, slowly raising to 1300 DEG -1500 DEG C. in oxygen for a period of 3 to 4 hours and then slowly cooling. The Provisional Specification refers to the use of silicon nitride as a Stator Blade material, an electrical insulator, refractory supports in industrial processes, a dielectric, and a supporting p vehicle for high temperature catalysts. Specification 726,812 also is referred to.