REDOX BEHAVIOR OF NI YTTRIA-STABILIZED ZI RCONIA (YSZ) CERMETS AND OXYGEN GAS SHIELDING PROPERTIES

The influences of redox treatments on the mechanical and gas permeable properties of Ni-yttria stabilized zirconia (YSZ) cermets were invest igated. The bending strength decreased successively with the continuou s redox treatments. The porosity and the mean pore diameter increased by the first reduction, decreased to be close to the initial levels by the subsequent oxidation, and then again increased by the second redu ction. With the oxidation treatment, the surface region of the cermet disk restored the tight microstructure consisting of well-packed grain s, while the inside remained porous. This preferential oxidation in th e surface region resulted in the negligibly small permeation of nitrog en gas, indicating a possibility of utilizing the cermets a shielding membrane against oxygen permeation. The oxygen gas shielding was exper imentally confirmed to occur at around 500 degrees C.