HIGH-TEMPERATURE STABILITY OF MONAZITE-ALUMINA COMPOSITES

The chemical and morphological stability and debonding characteristics of monazite/alumina interfaces were examined at temperatures of 1400 and 1600 degrees C. In the absence of impurities, the interface was fo und to be stable for long periods (24 h) at 1600 degrees C and to reta in its ability to prevent crack growth by debonding. However, in the p resence of alkali metal or divalent elements (K, Mg, Ca and others) at a free surface, La-containing beta-alumina-magnetoplumbite platelets form near the interface. It is proposed that these elements stabilize the beta-alumina-magnetoplumbite structure by tending to form the more stable 'stuffed' structure closer to the magnetoplumbite type.