Method of producing dense silicon nitride ceramic articles having controlled surface layer composition

Abstract From the Canadian patent

Abstract of the Disclosure, Dense, composite polycrystalline ceramic articles, comprising silicon nitride silicon dioxide, and yttrium, oxide and having thin surface layers of controlled composition are formed by sintering pre-pressed compacts embedded in setter bed powder mixtures having compositions of silicon nitride, silicon dioxide, and yttrium oxide which differ from that of the pressed compact. Employing the method of this invention articles are, produced which have surface layers in which the minor phase of the article is enriched with either yttrium or silicon.