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

摘要

A method is disclosed for preparing a dense, B"-alumina- containing ceramic body exhibiting an electrical resistivity for sodium ion conduction at 300 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 C. and about 1600 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 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.