Impact of grain boundaries on properties of mullite as a solid electrolyte

Abstract

Basic properties of muUite such as chemical composition, phase stability, crystalline structure and microstructure are briefly reviewed. Effect of impurities, resulting in the formation of grain boundary glassy precipitates on high temperature properties such as mechanical properties and ionic conductivity is considered. Properties of mullite which is free of the glassy phase are analyzed as an ionic conductor for high temperature oxygen sensors. Electromotive force (EMF) of an oxygen concentration cell, based on mullite (which is free of impurities or involving an excess of silica) as an oxygen conductor, indicates that the electronic conductivity component at high temperatures assumes negligible values especially at very low oxygen activities (below 5ppm). © 1995 Elsevier B.V.