GB828211A - Method of making dense silicon carbide articles - Google Patents

Abstract

A dense body of silicon carbide having a density of about 3 is produced by impregnation of a porous body of silicon carbide with carbon and then heating in the presence of silicon. The silicon carbide body is preferably fired before the impregnation with carbon. A porous silicon carbide body having a porosity of 25-30% may be produced by mixing silicon carbide of 100-1000 mesh with a phenolic resin and pine oil as temporary binder, cold pressing the mix at 5000-10,000 p.s.i., oven drying the moulded article, and firing at a temperature of 2300 DEG C. in a high-frequency furnace, recrystallization thereby taking place. Firing may also take place at lower temperatures without recrystallization. Alternatively the porous body may be produced by first forming a porous moulded body of silicon carbide and silicon and firing said body in a carbonaceous atmosphere at a temperature of 1350 DEG C. Impregnation with carbon may be effected in one or more treatments by introducing furfural and/or furfuryl alcohol into the porous body and then exposing to gaseous hydrogen chloride, (or) by introducing a liquid phenol-formaldehyde resin into the porous body and then thermally decomposing the resin, or by heating the porous body in methane or acetylene. The conversion of the introduced carbon to silicon carbide is effected by heating the impregnated body at a temperature of 2000 DEG C. or more in the presence of silicon or silicon nitride. A temperature of 2100-2300 DEG C. is preferably employed for sufficient time to effect recrystallization and vaporization of residual silicon. Residual silicon may alternatively be removed by leaching with a solution of nitric and hydrofluoric acid. The complete treatment may be repeated.