Abstract: A pressureless sintered silicon nitride-boron nitride composite having high density and low elastic modulus has a composition of 2 to 30 wt. % boron nitride and 70 to 98% of a blend of yttrium oxide, aluminum nitride and silicon nitride.

Abstract: Silicon aluminum oxynitride materials having high hardness and high density are formed by pressureless sintering of silicon nitride, yttrium oxide and aluminum nitride. The materials contain at least 75 weight percent of alpha prime phase sialon.

Abstract: A small amount of boron nitride is added to a mixture of silicon nitride, aluminum nitride and yttrium oxide, prior to sintering, to increase modulus of rupture and/or elastic modulus of the sintered material.

Abstract: A sintered silicon nitride ceramic having high stiffness consists of, in weight percent, 10.1 to 13.5 aluminum nitride, 6 to 7.5 yttrium oxide, 0.05 to 5 molybdenum disilicide, balance silicon nitride.

Abstract: A process is disclosed for reacting the oxides of lanthanum and aluminum.

Abstract: A pressureless sintering process is disclosed for producing silicon nitride bodies of near theoretical density from an admixture of silicon nitride and sintering aids of mixtures of lanthanum oxide and aluminum oxide, lanthanum aluminate, and mixtures of lanthanum aluminate and aluminum oxide and mixtures of lanthanum aluminate and lanthanum oxide.

Abstract: Silicon aluminum oxynitride materials having high hardness and high density are formed by pressureless sintering of silicon nitride, yttrium oxide and aluminum nitride. The materials contain at least 75 weight percent of alpha prime phase sialon.

Abstract: A process is disclosed for producing corrosion resistant silicon nitride bodies from compositions of pure silicon nitride, lanthanum oxide with and without aluminum oxide by hot pressing.

Abstract: A ceramic dielectric having a low dielectric constant and a low dielectric loss tangent from room temperature to at least about 1100.degree. C. comprises a silicon nitride based material containing an effective amount of magnesium oxide as a sintering aid and an effective amount of a low dielectric loss promoter comprising iron oxide and/or chromium oxide.

Abstract: A composition having a low dielectric constant and low dielectric loss tangent from room temperature to at least about 1100.degree. C. which comprises a silicon nitride based material containing an effective amount of a sintering aid selected from lanthanum oxide, yttrium oxide, lanthanum aluminate, yttrium aluminate, aluminum oxide and mixtures thereof and an effective amount of a low dielectric loss promotor selected from the group consisting of iron, chromium and mixtures thereof is a suitable radome material and electromagnetic window material.

Abstract: A composition having a low dielectric constant and low dielectric loss tangent from room temperature to at least about 1100.degree. C. comprises a silicon nitride based material containing an effective amount of a sintering aid and an effective amount of a low dielectric loss promoter.

Abstract: A process is disclosed for reacting oxides of yttrium and aluminum.

Abstract: A process is disclosed for producing a ceramic body coated with boron nitride. A green ceramic body is coated with boron nitride and sintered at a temperature and for a time sufficient for the body to achieve near theoretical density.Ceramic bodies of near theoretical density can be produced without deformation by coating the bodies with boron nitride, assembling the bodies with a supporting ceramic member which is also coated with boron nitride, sintering the assembly at a temperature and for a time for the bodies to achieve near theoretical density without deformation.

Abstract: Compositions consisting of silicon nitride, hard materials such as titanium carbide and titanium nitride, and densifying agents such as lanthanum oxide or lanthanum aluminum compounds are disclosed for silicon nitride bodies.