University of Utah Research Foundation

Ivan B Cutler

Anil Vasudeo Virkar

Ronald S Gordon

Mark L Miller

Patrick D Miller

Arun D Jatkar

Mohammed N Shaikh

A solid solution and a process for producing a solid solution, the solid solution including at least the compounds: silicon carbide and aluminum oxycarbide, and also aluminum nitride. The new material including all three compounds is referred to by the acronym, SiCAlON, which is a coined term consisting of the chemical abbreviations for the elements present in the solid solution. The solid solution is obtained by heating an intimate mixture of reactants above about 1550.degree. C. The silicon carbide in the solid solution has the alpha or hexagonal structure and the aluminum nitride has the wurtzite or hexagonal structure. The solid solution is characterized by the substantial absence of iron or other impurities that tend to encourage the formation of silicon carbide as a separate phase having a beta or cubic structure.

Solid solution and process for producing a solid solution

A method is disclosed for preparing a dense, B'-alumina-containing ceramic body exhibiting an electrical resistivity for sodium ion conduction at 300.degree. C. between about 3 and about 20 ohm-cm, by sintering a green ceramic body formed from a composition comprising at least about 90 weight percent of aluminum oxide, about 8.7 to 9.4 weight percent of sodium oxide, about 0.7-0.9 weight percent of lithium oxide, and from 0.0 to about 4.0 weight percent of magnesium oxide at a temperature between about 1400.degree. C. and about 1600.degree. C., for between about three (3) minutes and about 180 minutes to obtain a body containing both B and B'-alumina crystalline forms. The sintered body exhibits a density greater than 90% of theoretical for polycrystalline B'-alumina and a uniform grain size between about 20 and 100 micrometers. All of these compositions were prepared by using either a binary liquid forming mixture between sodium aluminate (NaAlO.sub.2) and lithium aluminate (LiAlO.sub.2), a ternary liquid forming mixture between sodium aluminate, lithium aluminate and B'-Al.sub.2 O.sub.3, or a ternary liquid forming ingredient between magnesium aluminate (MgAl.sub.2 O.sub.4), sodium aluminate and lithium aluminate, in combination with different alpha alumina powders with a range of crystallite sizes (0.3 - 5 micrometer). Depending on the state of aggregation of and the preparative technique for the liquid forming mixtures and the particle size and distribution of the alumina, resistivities (at 300.degree. C.) after sintering varied between extremes of 18-20 ohm-cm on the high side and 3-5 ohm-cm on the low side. Conditions which maximize the sintered density and minimize the resistivity for the lowest possible temperature are those preparations consisting of a fine binary or ternary liquid forming ingredient mixed with a calcined Na.sub.2 CO.sub.3 -Al.sub.2 O.sub.3 mixture. Attainment of these properties is enhanced with the use of an alpha-Al.sub.2 O.sub.3 with a wide particle size distribution (i.e., a size range of 0.3 to 6 micrometers) and an average particle size of about 5 micrometers. These low temperatures of sintering simultaneously help curtail the evaporation of soda and make an open air sintering process feasible.

Method for preparing dense, beta-alumina ceramic bodies by liquid phase

A process for removing silicon from a silicate-bearing material. The silicate-bearing material is analyzed for its silicon content and mixed with a controlled quantity of carbon as indicated by the analysis. The carbon is limited to an amount less than the stoichiometric amount necessary to react with the silicon to form silicon carbide. The silicate-bearing material/carbon mixture is formed into a first phase and interposed with a second phase containing additional carbon to form a reaction mixture. The reaction mixture is subjected to a carbothermal reduction reaction to reduce silica in the silicate-bearing material to silicon monoxide. At the temperatures involved in the reaction, the silicon monoxide is in the gaseous phase and readily diffuses from the first phase into the second phase where the diffused silicon monoxide reacts with the additional carbon in the second phase to form silicon carbide. The silicon carbide formation reaction occurs in the gaseous phase so that the silicon carbide is deposited in the second phase in the form of fine fibers. The silicon carbide fibers may be separated from the reaction mixture residue by conventional mechanical separation techniques. The first phase residue has a reduced silica content and may also be mechanically separated from the second phase.

Process for separating silica from silicate-bearing materials

Methods of preparing a dense and strong polycrystalline .beta.'-alumina-containing ceramic body exhibiting an electrical resistivity for sodium ion conduction at 300.degree. C of 9 ohm-cm or lower obtained directly after sintering and having a controlled fine microstructure exhibiting a uniform grain size under 50 micrometers. The invention more particularly relates to methods of uniformly distributing selected metal ions having a valence not greater than 2, e.g. lithium or magnesium, uniformly throughout the beta-type alumina composition prior to sintering to form .beta.'-alumina. This uniform distribution allows more complete conversion of .beta.-alumina to .beta.'-alumina during sintering. As a result, the polycrystalline .beta.'-alumina containing ceramic bodies obtained by methods of this invention exhibit high density, low porosity, high strength, fine grain size (i.e. no grains over 25-50 micrometers with an average size under 5-10 micrometers), low electrical resistivity and a high resistance to degradation by water vapor in an ambient atmosphere.

Method of preparing dense, high strength, and electrically conductive

A method for preparing a dense and strong polycrystalline .beta.'-alumina-containing ceramic body exhibiting an elecrical resistivity at 300.degree. C of 5 ohm-cm or lower, and a controlled and uniform grain size under 50 micrometers, comprising:

Method for preparing dense, .beta.-alumina ceramic bodies

A method of producing a sinterable refractory material having a low coefficient of thermal expansion and comprising essentially a dispersion of aluminum oxide throughout a silicon nitride matrix, herein called SIALON. The process includes obtaining aluminum and silicon from generally readily available raw material sources.

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Salt Lake City, UT, United States of America

Ivan B Cutler