US 4,113,928 A · Method of preparing dense, high strength, and electrically conductive ceramics containing .beta."-alumina

Abstract

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.

Claims26

Dependent claims

A method for preparing a dense, strong polycrystalline .beta."-alumina-containing ceramic body exhibiting (i) an electrical resistivity for sodium ion conduction at 300.degree. C. of less than or equal to about 9 ohm-cm, and (ii) a fine, uniform microstructure and resultant fracture strength comparable to that achieved by hot pressing techniques, comprising:

(A) preparing a powder mixture comprising aluminum oxide, sodium oxide and lithium oxide in stoichiometric proportions required to produce .beta."-alumina upon being heated to crystal forming temperatures, said lithium oxide being present in amounts ranging from about 0.1 to about 5 weight percent of the total of said mixture and being provided by a lithium aluminate compound having the formula Li.sub.2 O:nAl.sub.2 O.sub.3 wherein n equals at least 5;
(B) green forming said preparing mixture to the desired shape;
and
(C) sintering the green formed body at a temperature above about 1500.degree. C. until desirable conversion to .beta."-alumina and near theoretical density for same are achieved.

1 more element

Dependencies are inferred from the claim text.

Method of preparing dense, high strength, and electrically conductive ceramics containing .beta."-alumina

Life of this patent

Method of preparing dense, high strength, and electrically conductive ceramics containing .beta."-alumina

Life of this patent

Abstract

Claims26