University of Utah Research Foundation

Ford Motor Company Limited

Ronald S Gordon

Anil Vasudeo Virkar

Ivan B Cutler

Gerald J Tennenhouse

Arun D Jatkar

Mark L Miller

Ralph W Sutton

Mohammed N Shaikh

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

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 shaped, green ceramic compacts suitable for firing to form high density .beta.'-alumina containing ceramic bodies comprising: (1) mixing between about 2.5 parts by weight and about 4.5 parts by weight of a ceramic composition comprising at least about 80 weight percent of aluminum oxide and from about 5 to about 15 weight percent of sodium oxide with 1 part by weight of a binder composition consisting essentially of between about 20 weight percent and about 35 weight percent of polyvinyl pyrrolidone having a number average molecular weight (M.sub.n) between about 20,000 and about 160,000 and between about 80 weight percent and about 65 weight percent of ethylene glycol; (2) extruding the mixture so formed through a die of desired configuration; and (3) heating the extrudate at temperatures and for periods of time necessary to evaporate the ethylene glycol solvent and burn off the polyvinyl pyrrolidone.

Method for preparing shaped, green ceramic compacts

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:

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Salt Lake City, UT, United States of America

Ronald S Gordon