Abstract: An abrasive article having certain minimum levels of permeability to fluids comprises about 40 to 80%, by volume interconnected porosity and effective amounts of abrasive grain and bond to carry out soft grinding and deep cut grinding operations. The high permeability to the passage of fluids and interconnected porosity provides an open structure of channels to permit the passage of fluid through the abrasive article and the removal of swarf from the workpiece during grinding operations.

Abstract: A composite ceramic structure which does not fail catastrophically and thus is useful as a ceramic rolling contact bearing assembly is disclosed. The structure is a ceramic monolith bonded through an interlayer to a fiber-reinforced ceramic body. The structure is useful at elevated temperatures.

Abstract: A friable silicon nitride body is prepared by infiltrating a non-friable silicon nitride body with a fluid which expands upon freezing, rapidly freezing the fluid, and thawing the frozen fluid. Silicon nitride flakes and chunks obtained with only light pressure on the friable body may then be final milled to a desired particle size more rapidly and with less energy input than with conventionally processed silicon nitride. The silicon nitride body may have a higher density than has previously been used to prepare silicon nitride powders, thereby preventing the generation of potentially hazardous whiskers in the final powder product.

Abstract: Tough composites of polymer derived silicon carbide fibers in silicon nitride matrices, especially reaction bonded silicon nitride matrices, can be made by precoating the fibers with pyrolytic carbon and controlling the nitridation or other process which forms the silicon nitride matrix so that a thickness of at least 5 nanometers of carbon remains in the composite after it is formed. Failure of such composites is non-catastrophic. Alternatively, with at least some specific types of polymer derived silicon carbide fibers, composites with non-catastrophic failure can be made by controlling the nitriding conditions to produce an essentially void space around the fibers in the final composites. As still another alternative, the space around the fibers may be partially filled with silicon nitride whiskers generated during the nitridation process.

Abstract: Very tough composites of silicon carbide fibers in silicon nitride matrices, especially reaction bonded silicon nitride matrices, can be made by precoating the fibers with pyrolytic carbon and controlling the nitridation or other process which forms the silicon nitride matrix so that a thickness of at least 5 nanometers of carbon remains in the composite after it is formed. Failure of such composites is non-catastrophic.

Abstract: A structural ceramic material comprising single phase polycrystalline cubic aluminum oxynitride preferably with at least 97% of theoretical density which displays transparency and isotropic optical, thermal and electrical properties, an infrared cutoff at about 5.2 microns wavelength, and which shows no chemical or physical property change after heating in air (atmosphere) at 1100.degree. C.