Microstructural development of interface layers between co-sintered alumina and spinel compacts

Tests were performed to investigate the microstructure of the interface between alumina and spinel materials after high temperature thermal treatment (1500 °C). The first test involved co-sintering of co-pressed alumina and spinel compacts. Microstructures were investigated by SEM, EDS, WDS and EBSD. A microstructurally distinct layer with columnar grains of up to 40 μm length and 5 μm width was observed after 16 h at 1500 °C. Growth rate of the columnar spinel grains from parent spinel towards alumina follows parabolic kinetics, controlled by a mixed process of O²⁻ ion diffusion and interface reaction. Diffusion couples of spinel and alumina were investigated. Same columnar spinel grains were observed at the interface which grew into alumina during thermal treatment with the same kinetics as in co-sintering experiments. The shape of the phase boundaries between spinel and alumina can be a further indication of the direction of their growth.