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 °C. In the absence of impurities, the interface was found to be stable for long periods (24 h) at 1600 °C and to retain its ability to prevent crack growth by debonding. However, in the presence of alkali metal or divalent elements (K, Mg, Ca and others) at a free surface, La-containing β-alumina-magnetoplumbite platelets form near the interface. It is proposed that these elements stabilize the β-alumina-magnetoplumbite structure by tending to form the more stable ‘stuffed’ structure closer to the magnetoplumbit type.