CHEMICAL COMPATIBILITY OF PEROVSKITE-TYPE OXIDE LA0.7CA0.3CR1-YCOYO3 WITH Y2O3 STABILIZED ZRO2

In order to evaluate the compatibility between the SOFC(Solid Oxide Fuel Cells) interconnector material of the perovskite-type La0.7Ca0.3Cr1-yCoyO3 (y=0.05, 0.1 and 0.2) and 8mol% Y2O3-ZrO2 (YSZ), two types of experiments were carried out in air. One was by the reaction of powder mixtures. The reaction products were identified by X-ray analysis after heating at 1000-1300 degrees C. The other was the experiments using diffusion couples. The distribution of elements at the interface was observed by EPMA for the couples heated at 1300 degrees C and 1400 degrees C. The reaction progressed mainly by the dissolusion of calcium ions from the perovskite phase into YSZ. In the perovskite phase, due to the loss of A-site Ca ion, the activity of B-site ions increased, resulting in the deposition of the spinel-type CoCr2O4. The excess amount of calcium ions incorporated in YSZ reacted ZrO2 to form CaZrO3. Increase of cobalt content enlarge the reactivity of the perovskite phase with YSZ. The parabolic rate constant of the reaction, k(p), was determined by the thickness of CaZrO3 at the interface of the diffusion couples. Calculated k(p) were 2.9 x 10(-12)cm(2)sec(-1) and 2.1 x 10(-11)cm(2)sec(-1) at 1300 degrees C and 1400 degrees C, respectively. For the practical application as the SOFC interconnector material, the content of cobalt as a sintering accelerator in (La, Ca)CrO3 must be controlled at low level to keep the chemical interaction to a minimum.