Microstructure–stress relationships in liquid-phase sintered alumina modified by the addition of 5 wt.% of calcia–silica additives Original Research Article

Hot-pressed alumina samples, with 5 wt.% additions of CaO:SiO2 possessing molar ratios ranging between 1:5 and 10:1 were studied by electron microscopy. Marked differences in microstructure (e.g. grain size, secondary crystalline phases and grain boundary film thickness) were observed, which depended on the composition of sintering additives. The compositions of glassy phases in triple pockets and in grain boundaries varied markedly depending on sintering additives, but also within individual specimens. High residual compressive stresses were measured in alumina grains of samples which contained low thermal expansion crystalline phases such as anorthite and grossite, while gehlenite-containing samples were correspondingly less stressed.