Abstract

The behaviour of commercial zirconia ceramics containing metal particles is of interest in the development of anodes for solid oxide fuel cells. The present work describes a study of zirconia reinforced with iron, chromium and stainless steel particles in which the electrical and thermal conductivity have been measured. Both of these properties increase with increasing metal content and in the case of electrical conductivity a discontinuous increase occurs when a critical concentration (20 vol.%) of metal particles are incorporated into the insulating zirconia matrix. The three systems studied show distinctly different behaviour and this is reported and explained. With chromium particles there is no chemical or physical reaction between reinforcant and matrix. However, with iron particles there is a chemical interfacial reaction between iron and the stabilising oxide (yttria) in the zirconia solid solution. Finally, with stainless steel particles the difference in coefficient of thermal expansion between the steel and zirconia leads to extensive microcracking of the composite after cooling from fabrication temperature. These phenomena are described and interpreted in terms of a functional model for thermal diffusivity and a microstructural model for the electrical percolation threshold in the zirconia composites.

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