Impurity‐Dependent Morphology and Grain Growth in Liquid‐Phase‐Sintered Alumina

The alumina grains in liquid‐phase‐sintered (LPS) materials prepared from different commercial sources have a predominantly platelet morphology. Generally, the MgO:(CaO + BaO + Na 2 O + K 2 O) ratio in the chemical composition controls the morphology in LPS alumina that is 91–94 wt% pure. Within a given range of SiO 2 content (i.e., 4.3–5.2 wt% in the chemical composition), a low MgO:(CaO + BaO + Na 2 O + K 2 O) ratio (i.e., <1.0) in the LPS compositions favors the formation of elongated grains, whereas ratios of >1.0 result in equiaxed grains. SiO 2 contents outside the 4.3–5.2 wt% range favor the formation 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 + Na 2 O + K 2 O) ratio and the SiO 2 content are relatively low. The sintered density generally increases as the SiO 2 content in the chemical composition decreases.