Abstract: Multiphase ceramic composites containing single phase silicon aluminum oxynitride and boron nitride wherein the boron nitride is one phase in the composite and the single phase silicon aluminum oxynitride is the matrix phase in the composite. The boron nitride phase is uniformly distributed in the form of discrete particles throughout the single phase silicon aluminum oxynitride matrix. A window transparent to electromagnetic radiation in a predetermined frequency spectrum is made by forming a homogeneous, finely-divided mixture of boron nitride and single phase silicon aluminum oxynitride matrix-forming compound and compacting the homogeneous, finely-divided mixture at an elevated temperature and pressure for a sufficient time to form the composite. In a preferred embodiment, about 75% by weight homogeneous, finely-divided mixture of single phase silicon aluminum oxynitride matrix-forming compound and the balance boron nitride is densified at a temperature of 1,760.degree. C.

Abstract: Multiphase ceramic composites containing 47% to 52% by weight aluminum nitride, 23% to 27% by weight silica, 3% to 7% alumina and the balance boron nitride wherein the boron nitride is one phase in the composition and the reaction products of aluminum nitride, silica and alumina are the other phase in the composite. The boron nitride phase is uniformly distributed in the form of discrete particles throughout the reaction products of aluminum nitride, silica and alumina. A window transparent to electromagnetic radiation in a predetermined frequency spectrum is made by forming a homogeneous, finely-divided mixture of the foregoing composite and compacting the homogeneous, finely-divided mixture at an elevated temperature and pressure for a sufficient time to form reaction products of the aluminum nitride, silica and alumina. In preferred embodiments, the homogeneous, finely-divided mixture of aluminum nitride, silica, boron nitride and alumina is densified at a temperature of 1760.degree. C.

Abstract: A thermal insulating device for use as the exterior coating of a space vehicle which consists essentially of a rigid carbon-carbon foam having an elastomeric foam bonded to the rear surface thereof and having a chemically vapor deposited coating applied to the front and side surfaces thereof.

Abstract: An optical solar reflector comprising a layer of silicon nitride having a reflective metallic coating on one side thereof and an optional dielectric coating on the opposite side.

Abstract: A silicon solar cell having a coverplate made of .beta.-silicon carbide.

Abstract: A process for making a structural ceramic article, such as, an electromagnetic window, is disclosed, wherein the ceramic article is comprised of a densified mixture of not less than 50% by volume aluminum nitride and up to about 50% by volume boron nitride. The ceramic article of the present invention may be used as a shield or protective barrier such as an electromagnetic window for communication or detection devices on high speed transportation or delivery vehicles passing through extremely hostile environments, where it exhibits radar transparency, congruent vaporization kinetics, tailorable dielectric properties, improved thermal shock resistance, improved mechanical toughness and strength, improved spall resistance, improved recession rate, i.e. erosion rate and ablation rate, and high refractoriness.