Irreversible Expansion Behavior of Mn[sub 3]O[sub 4+δ] Spinel and Shrinkage Behavior of La[sub 0.6]Sr[sub 0.4]MnO[sub 3] Composites with the Spinel during Thermal Cycling in O[sub 2] Atmosphere

The thermal expansion behaviors of the porous and dense spinel bodies, and the cathode with the spinel in high temperature solid oxide fuel cells have been investigated during a thermal cycle measurement in an atmosphere. The porous body with relative density of 81% showed a large expansion at temperatures between 1018 and 1064°C during the heating cycle and its expansion continued irreversibly every heating cycle. The first large expansion value of this sample showed 1.56% and the expansion had a tendency to decrease with thermal cycles. On the other hand, the dense body with relative density of 98% showed no anomalous expansion. From the results of thermogravimetry and high temperature X-ray diffractometry, the irreversible expansion of the porous body relates to the phase change from into by the oxygen release, and no phase change during the thermal cycle measurement was observed for the dense body. Although the porous body of showed no shrinkage behavior during the thermal cycle measurement, the one of composite with 20 vol % spinel shrank.