Sintering behaviour of spinel-alumina composites

Study of alumina-magnesia binary phase diagram reveals that around 40–50 wt% alumina dissolves in spinel (MgAl₂O₄) at 1600°C. Solid solubility of alumina in spinel decreases rapidly with decreasing temperature, which causes exsolution of alumina from spinel phase. Previous work of one of the authors revealed that the exsolution of alumina makes some interlocking structures in between alumina and spinel phases. In the present investigation, refractory grade calcined alumina and spinel powder were used to make different batch compositions. Green pellets, formed at a pressure of 1550 kg cm⁻² were fired at different temperatures of 1500°, 1550° and 1600°C for 2 h soaking time. Bulk density, percent apparent porosity, firing shrinkage etc were measured at each temperature. Sintering results were analysed to understand the mechanism of spinel-alumina interactions. SEM study of present samples does not reveal the distinct precipitation of needle shaped α-alumina from spinel, but has some effect on densification process of spinel-alumina composites. Microstructural differences between present and previous work suggest an ample scope of further work in spinel-alumina composites.