EFFECT OF A SMALL AMOUNT OF LIQUID-FORMING ADDITIVES ON THE MICROSTRUCTURE OF AL2O3 CERAMICS

Sintering behaviour and microstructure of Al2O3 ceramics without additives and with 0.02-0.25 mol % CaO + SiO2 (CaO/SiO2 = 1) were investigated. When Al2O3 bodies were sintered at 1400-degrees-C, the sinterability and the grain size decreased as the content of CaO + SiO2 increased. When Al2O3 ceramics with 0.05-0.25 mol % CaO + SiO2 were sintered at higher sintering temperature, both CaO and SiO2 reacted with Al2O3 to produce the liquid phase along grain boundaries, and exaggerated platelet Al2O3 grains, with an aspect ratio of about 4.5, were formed. Because the size of platelet grains decreased as the content of CaO + SiO2 increased, the distribution of either SiO2 particles or this intergranular phase of CaO-Al2O3-SiO2 might control the microstructure.