The characteristic ofthe close packed Al2O3 grains can be explained by the use of fine particle sized MgO which promotes the mobility of the liquid phase during the sintering process. As a result, more areas of Al2O3 can be affected by the liquid phase, producing uniform and small grain sizes. Samples with 500 nm (Fig. 4(c)) and 7000 nm (Fig. 4(d)) sized MgO showed comparable micrographs, but they also exhibited a few large sized Al2O3 grains and a low level of grain distribution, which is not observed in samples with MgO nano-particles. This might be caused by limited liquid phase mobility during the sintering process as described by Lumley and Schaffer, whereby the use of coarser additives result in a highly localized and poorly distributed liquid.