Abstract: Tough ceramic products can be prepared without exotic pressure fabricating techniques by use of a matrix laminate comprising a continuous fiber ceramic reinforcement in tow or woven form for strength, stiffness, and toughness and a ceramic matrix generally comprising (a) a filler, such as mullite; (b) ceramic reinforcing whiskers, such as silicon nitride or silicon carbide, for fine-scale interlaminar shear resistance (c) a binder, such as colloidal silica; and (d) an activator, such as a trona-like material including sodium and carbonate. The matrix is brushed into the fiber reinforcement, which is then laid up, dried, and cured. Tandem ceramic composites can be fabricated.

Abstract: Oxide-based ceramic fibers are treated in a novel process to create a substantially uniform boron nitride barrier coating at their surface. The process involves heating the fibers in a nitriding atmosphere at between about 2200-2600.degree. F. to create a BN coating at the surface of the fiber from boron initially within the fiber.

Abstract: A broadband high temperature radome includes a high density outer skin layer and a low density core layer made from a ceramic material selected from the group consisting of silicon nitride and barium-aluminum silicate. Silicon nitride is sintered, reaction-sintered or chemically vapor-deposited. The outer skin has a moderate dielectric constant of about 5.0 and the core layer has a low dielectric constant of about 1.8. Both dielectric constants do not sigificantly vary at temperatures up to 1500.degree. C. Low thermal expansion of the core and skin layers are matched by the thermal expansion of a base connector constructed in a laminated form of graphite/polyimide. The thickness of the core layer to the thickness of the skin layer is given by the ratio of about 15:1 where the skin layer thickness is about 0.030 inch. Polyimide resin is used for the high temperature adhesive to adhere the connector to the core and skin layers. The core layer is impregnated with a dielectric filler, if desired.

Abstract: Oxide-based ceramic fibers are treated in a novel process to create a substantially uniform boron nitride barrier coating at their surface. The process includes the step of heating the fiber, preferably an aluminoborosilicate fiber like NEXTEL, for between about 5-90 minutes in a nitriding atmosphere of ammonia, hydrogen and nitrogen at a temperature of between about 2200.degree.-2600.degree. F. to diffuse boron from the fiber to the surface of the fiber where it reacts to form the boron nitride coating.

Abstract: Method for producing .alpha.-silicon nitride whiskers. Silicon is blended with composition particles able to sublime without leaving a residue, such as naphthalene particles. The blend is compacted to a desired shape, after which the composition particles are sublimed from the blend to form a porous silicon precursor compact having the desired shape. The silicon precursor is reacted with a substance that releases free nitrogen, such as nitrogen or dry ammonia. The reaction is carried out at a temperature sufficiently high to form an identically shaped porous compact of .alpha.-silicon nitride whiskers but sufficiently low to avoid subliming substantially all of the formed whiskers. Preferably, the reaction is carried out in a range between about 2100.degree. F. and 2750.degree. F. The shaped porous compact of .alpha.-silicon nitride whiskers may be impregnated with a resin binder, a liquid metal, a colloidal suspension, an ionic solution or a gaseous material to form an isotropic composite.