Method of producing a dense refractory silicon nitride (si.sub.3

Abstract

An improved process for forming a dense silicon nitride compact having improved high temperature properties comprises: forming a glass using compounds, containing Al, Si, O, N, and a rare-earth element, known to form one or more crystalline phases; mixing this preformed glass in particulate form with silicon nitride powder; and densifying the mixture at an elevated temperature; and then forming one or more crystalline intergranular phases from the glass to thereby improve the high temperature characteristics of the resultant dense silicon nitride compact. In a preferred embodiment, the process includes heating the dense compact to a first temperature to form nucleates; and then heating the dense compact at a second temperature to grow the desired one or more crystalline intergranular phases on the nucleates. In another embodiment, the crystallization may be carried out by controlled direct cooling of the compact from the sintering temperature. The use of particles of a preformed glass, made from compounds known to form one or more crystalline phases, as the desification material provides a homogeneous mixture to ensure subsequent formation of the desired crystalline intergranular phases.