초록 ▼

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, silic

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.

대표청구항 ▼

1. A method of producing dense, polycrystalline silicon nitride articles having surface layers of controlled composition comprising the steps of: (a) providing a finely divided mixture of from about 80 mole percent to about 95 mole percent silicon nitride, from about 2 mole percent to about 10 mo

1. A method of producing dense, polycrystalline silicon nitride articles having surface layers of controlled composition comprising the steps of: (a) providing a finely divided mixture of from about 80 mole percent to about 95 mole percent silicon nitride, from about 2 mole percent to about 10 mole percent silicon dioxide and from about 2 mole percent to about 15 mole percent yttrium oxide; (b) pressing the mixture to form a sinterable compact; (c) embedding the sinterable compact in a non-sinterable setter bed powder mixture of a composition different from that of the powder compact, with a content of from about 48 mole percent to about 94 mole percent silicon nitride, the balance consisting essentially of yttrium oxide and silicon dioxide wherein the mole ratio of yttrium oxide to silicon oxide is between 0 and about 2; and (d) heating the sinterable compact and nonsinterable setter bed powder mixture at a temperature and for a period sufficient to sinter the compact to a densified composite article having a density of at least 98% of theoretical, wherein said step of heating is carried out in a nitrogen atmosphere at a pressure which is related to the temperature of heating by the expression: ##EQU##P=e [(-a/T )+b]