Impurity-dependent morphology and grain growth in liquid-phase-sintered alumina

The alumina grains in liquid-phase-sintered (LPS) materials prepared from d ifferent commercial sources have a predominantly platelet morphology. Gener ally, the MgO:(CaO + BaO + Na2O + K2O) ratio in the chemical composition co ntrols the morphology in LPS alumina that is 91-94 wt% pure. Within a given range of SiO2 content (i.e., 4.3-5.2wt% in the chemical composition), a lo w MgO:(CaO + BaO + Na2O + K2O) ratio (i.e., <1.0) in the LPS compositions f avors the formation of elongated grains, whereas ratios of >1.0 result in e quiaxed grains. SiO2 contents outside the 4.3-5.2 wt% range favor, the form ation of elongated grains. A tendency to form platelike grains is observed for LPS alumina with a purity of 91-94 wt% when both the MgO:(CaO + BaO + N a2O + K2O) ratio and the SiO2 content are relatively low. The sintered dens ity generally increases as the SiO2 content in the chemical composition dec reases.