Abstract: Thin, single-crystal SiC films are obtained by means of a pyrolysis process, the substrate to be coated being covered with a carbonaceous polysilane, the adhering layer being pyrolyzed in an inert atmosphere and the amorphous layer of SiC obtained in this way being crystallized by maintaining it at a temperature of over 700.degree. C. Using a special variation of the process, it is easy to form doped SiC films. To this end the dopant is added in the form of a silane compound.

Abstract: Ceramic radomes are fabricated using a method which reduces the dielectric losses of the ceramic material. A Si.sub.3 N.sub.4 ceramic powder is mixed with a suitable densification aid and then sintered to form a dense ceramic having a glassy phase. Silicon dioxide is then provided on the surface of the ceramic by packing it in silicon dioxide powder or by heating it in air to oxidize its surface. The ceramic and silicon dioxide are heated at a temperature sufficient to cause diffusion of impurities and additive cations from the glassy phase into the silicon dioxide. The surface of the ceramic is then ground to remove pits and to shape the ceramic into a radome.

Abstract: Damage-tolerant, continuous fiber ceramic matrix composites are fabricated to fill the space between the fibers with a powder. The powder particles are heat treated to form a porous framework without shrinkage, which is then strengthened with an inorganic synthesized from a precursor in solution. High particle packing densities is achieved within the fiber preform using a small particle-to-fiber diameter ratio. Filling the interstices with a powder increases the composite density and also limits the size of the crack-like voids within the matrix. The ceramic matrix composite (CMC) has mechanical characteristics similar to those found in wood. It is also affordable and inherently oxidation resistant. The composite is characterized by a heterogeneous distribution of fibers within a porous matrix having a homogeneous, fine porosity. A residual stress from thermal expansion mismatch of the matrix and fibers is created in the composite. The illustrated embodiment uses Al.sub.2 O.sub.

Abstract: In a Ce-ZrO.sub.2 -based laminar composite having enhanced fracture toughness, alternating barrier layers comprise a ceramic material that undergoes stress-induced phase transformation, if any, less readily than Ce-ZrO.sub.2. Separation of the barrier layers is normally in the range of about 10-200 .mu.m, with optimum individual barrier layer thicknesses at the lower end of the range. Powders of ceramic materials comprising the individual layers of the composite are dispersed in separate slurries. The pH of the slurries is adjusted to form coagulations in which the particles settle without mass segregation and can be consolidated to high density by centrifuging. After centrifuging, the supernatant liquid can be removed and a desired volume of another slurry can be added on top of the first layer of consolidated material. This process can be repeated indefinitely to form a consolidated structure having individual layers as thin as approximately 10 .mu.m.

Abstract: A method of preparing dense ceramic product is described, wherein a coagulated network of ceramic powder particles in water is formed and then treated to increase the volume fraction of particles, thereby forming a water-saturated powder compact. The compact is formed into a desired shape and fired to provide the dense ceramic product. A coagulated network may advantageously be formed by mixing a ceramic powder with water at a pH that produces a net surface charge, to form a dispersed slurry and adding a sufficient amount of salt to the dispersed slurry to cause particles within the slurry to form the coagulated network.

Abstract: The present invention relates to processes to produce ceramic reinforced and ceramic-metal matrix composite articles. More specifically, the invention concerns the use of pressure filtration to infiltrate a reinforcing organic or inorganic network with ceramic particles. Centrifugation is also used to separate the liquid form the slurry. After heating the reinforced ceramic article is produced. Pressure filtration is also used to infiltrate an organic polymer or organic fiber network with ceramic particles. The solvent is removed carefully followed by intermediate heating to remove the organic network without deforming the preform shape. After densification, the preform is heated and contacted with molten metal (optionally) with pressure to infiltrate the open channel network. Upon cooling the ceramic metal matrix composite is obtained. The reinforced matrix articles are useful in high temperature and high stress applications, e.g.

Abstract: The present invention relates to an article having improved physical properties as compared to the individual components, which article comprises:a laminated ceramic fiber composite of alternating layers of discrete thin solid sheets of ceramic A having a substantially large upper and lower surface bonded to discrete thin sheets B comprising fibers and having large upper and lower surfaces using a suitable bonding agent.

Abstract: A ceramic is fabricated by dispersing ceramic particles in a liquid, sedimenting the dispersion to remove large particles, and then changing its pH to flocculate the dispersed particles. The size distribution of the particles in each individual floc is similar to the size distribution of particles throughout the dispersion. The supernate is removed and the flocs are cast by centrifuging them into a mold. The cast flocs are dried and sintered to form the ceramic. To provide a multiphase ceramic, particles of two or more ceramics can be mixed together and flocced prior to centrifuging.

Abstract: Si.sub.3 N.sub.4 ceramics having a glassy phase densification aid are heated while their surface is in contact with SiO.sub.2. The SiO.sub.2 forms one side of a diffusion couple and draws the glassy phase out of the ceramic. The SiO.sub.2 can be provided by heating the ceramic in air to form an SiO.sub.2 scale by the oxidation of Si.sub.3 N.sub.4, or by imbedding the ceramic in SiO.sub.2 powder. Surface pits, if any, formed during oxidation, are removed by grinding.

Abstract: Fracture toughness and strength of .beta.-Al.sub.2 O.sub.3, .beta."-Al.sub.2 O.sub.3, and Na.sub.1+x Zr.sub.2 Si.sub.x P.sub.3-x O.sub.12 solid electrolytes are increased by incorporating metastable grains of tetragonal ZrO.sub.2 in the structure. The ZrO.sub.2 occupies from 5 to 40% of the volume of the ceramic. To enable retention of the metastable tetragonal structure at room temperature, the ZrO.sub.2 has a grain size less than about 2 .mu.m and has dissolved in it a rare earth oxide such as Y.sub.2 O.sub.3, CeO.sub.2, La.sub.2 O.sub.3 and/or Er.sub.2 O.sub.3.

Abstract: Fracture toughness and strength of an Al.sub.2 O.sub.3 /ZrO.sub.2 ceramic is increased by incorporating metastable grains of tetragonal ZrO.sub.2 in the structure. During cracking, the metastable tetragonal ZrO.sub.2 transforms to a stable monoclinic structure thus increasing the energy required for the crack to propagate and retarding its growth. The ZrO.sub.2 occupies from 5 to 95% of the volume of the ceramic and has dissolved in it a rare earth oxide such as Y.sub.2 O.sub.3, CeO.sub.2, La.sub.2 O.sub.3 and/or Er.sub.2 O.sub.3 to promote retention of the metastable tetragonal ZrO.sub.2.

Abstract: A densified silicon nitride-silicon carbide composite material formed by hot-pressing a mixture of silicon nitride (Si.sub.3 N.sub.4) powder, which forms the matrix up to 40 volume percent and preferably from 5-30 volume percent silicon carbide (SiC) powder, and a densification aid such as magnesium oxide (MgO). The average size of the silicon carbide particles is to be less than about 5 microns. The densified composite material is characterized by higher thermal conductivity and strength at high temperatures relative to silicon nitride. The flexural strength at 1400.degree. C. of the composite material being at least double that of sintered silicon nitride.

Abstract: A densified silicon nitride-silicon carbide composite material formed by hot-pressing a mixture of silicon nitride (Si.sub.3 N.sub.4) powder, which forms the matrix, up to 40 volume percent and preferably from 5-30 volume percent silicon carbide (SiC) powder, and a densification aid such as magnesium oxide (MgO). The average size of the silicon carbide particles is to be less than about 5 microns. The densified composite material is characterized by higher thermal conductivity and strength at high temperatures relative to silicon nitride. The flexural strength at 1400.degree. C. of the composite material being at least double that of sintered silicon nitride.

Abstract: Articles made from Si.sub.3 N.sub.4 ceramic alloy powders are protected during heating by loosely packing them in Si.sub.3 N.sub.4 before heating. Compacts made from Si.sub.3 N.sub.4 ceramic alloys are protected from both oxidation and from volatilization by the encompassing powder even though the furnace atmosphere is air.

Abstract: A method of producing cast articles having internal cavities is disclosed. The method is particularly suitable for casting gas turbine components from nickel base and cobalt base superalloys. The method comprises: forming a core to the desired cavity configuration, the core consisting essentially of densified silicon nitride; securing the core within a mold; casting the alloy within the mold and around the core; removing the solidified cast article from the mold; and leaching the silicon nitride core from the casting in molten sodium hydroxide.

Abstract: Dense, ceramic compositions fabricated within the Si.sub.3 N.sub.4 -Si.sub.2 N.sub.2 O-Y.sub.2 Si.sub.2 O.sub.7 compatibility triangle in the Si.sub.3 N.sub.4 -SiO.sub.2 -Y.sub.2 O.sub.3 system are extremely stable in oxidizing environments and particularly suited for use as a high temperature structural material. In addition, the hot-pressed, densified articles fabricated from compositions within the compatibility triangle exhibit improved strength and creep resistance at elevated temperatures relative to commercial Si.sub.3 N.sub.4.

Abstract: This invention relates generally to ceramic materials formed from powder, and more particularly to hot-pressed structural materials comprising silicon nitride (Si.sub.3 N.sub.4) wherein the oxygen content is controlled by maintaining the molar ratio of MgO and SiO.sub.2.

Abstract: A method for densifying to near theoretical density a shaped body of compacted powdered particles, particularly of a refractory material, by preforming a shaped body of compacted particles of a powdered material characterized by voids, enclosing the shaped body within a loose mass of a pressure-transmitting powder disposed within a confining mold, applying a unidirectional pressure to the pressure-transmitting powder within the mold in order to compress the shaped body more compactly while heating the body to at least the densification temperature of the body, preferably in a controlled atmosphere, the temperature and/or pressure being increased incrementally up to the densification temperature of the refractory material, whereby substantially all voids within the compacted shaped body are collapsed.

Abstract: A method of producing a silicon nitride article by powder techniques, wherein silicon nitride powder is used as a starting material. The silicon nitride powder, mixed with a densification aid, is heated rapidly to the sintering/densification temperature (1500.degree. to 1750.degree. C) in the absence of pressure, held there a short, closely controlled time (5 to 30 minutes) and thereafter rapidly cooled. This provides a strong product with controlled dimensional tolerances.

Abstract: Fully dense ceramic articles are prepared by mixing powders of silicon nide, aluminum oxide and magnesium oxide to form a composite powder composition wherein the magnesium oxide acts as a sintering aid, forming the composite powder into a desired shape, and heating the shaped composite powder composition in the absence of applied pressure at a temperature sufficient to effect sintering of the composition.