Abstract: A method is disclosed for making a more densified silicon nitride comprising object under less stringent heating conditions without sacrificing physical properties. A mixture of silicon powder, 6-18% yttrium silicon oxynitride (a major proportion of which is the Y.sub.10 Si.sub.6 O.sub.24 N.sub.2 phase), 0.4-3% Al.sub.2 O.sub.3, and possibly up to 2% of an oxynitride forming oxide (Y.sub.2 O.sub.3) is compacted, nitrided, and sintered to produce a silicon nitride/YSiO.sub.2 N comprising object of relatively high density.

Abstract: A method of making a powder additive consisting of yttrium silicon oxynitrides, preferably of the Y.sub.10 Si.sub.6 O.sub.24 N.sub.2 or YSiO.sub.2 N phases, is disclosed. Stoichiometric amounts of Y.sub.2 O.sub.3, SiO.sub.2, and Si.sub.3 N.sub.4 are mixed and arranged in intimate reactive contact, the amounts being to form a desired oxynitride according to the formula Y.sub.a Si.sub.b O.sub.c N.sub.d, where a, b, c and d represent the required element parts of the compound in equilibrium with the mixture elements. The mixture is heated in an inert atmosphere to a temperature and for a time sufficient to convert the stoichiometric amounts of the mixture to the desired yttrium silicon oxynitride. The heat agglomerated mixture is then ground to a powder.

Abstract: A method of making a densified silicon nitride/oxynitride composite is disclosed. The method comprises: (a) shaping a substantially homogeneous powder mixture of silicon nitride, 6-18% yttrium silicon oxynitride of the Y.sub.10 Si.sub.6 O.sub.24 N.sub.2 phase in an amount to form a viscous solution with at least a portion of the silicon nitride, and (b) densifying the body by heat fusion, with or without the use of mechanical pressure, to a density and a dimension required for the final product.

Abstract: A method of joining silicon nitride based ceramic bodies is disclosed. At least one interfacing surface of shaped bodies (one or both of which may be hot-pressed or reaction-sintered) receives a layer of metallic aluminum based material. The bodies with the metallic aluminum based material therebetween are subjected to heating at 1400.degree.1900.degree. C. for a period typically 0.5-2 hours in a nitriding atmosphere to effect a chemical bond consisting of a conversion of the interfacing ceramic to a Si--Al--O--N system.