Preparation of alumina gel derived from boehmite sol and its sintering behavior

Sintered alumina samples were prepared by sol-gel method with three types of boehmite powders as starting materials. All dried gels were completely transformed to corundum phase at temperature above 1200 degrees C. Sintering characteristics of the dried gels were investigated according to heat treatment temperature. Relative densities of these gels dried at 1000 degrees C, 1200 degrees C and 1400 degrees C were 40%, 65% and 75% respectively, indicating incomplete densification. Specific surface areas of the dried gels heated at temperature up to 1000 degrees C depended on crystal grain sizes of boehmite powder used. However, specific surface areas of samples heated at 1200 degrees C were almost the same (range, 7.4 similar to 8.3 m(2)/g). Overall pore volume decreased with increasing sintering temperature. However, macropore gradually expanded due to sintering shrinkage of crystal grains, reaching a maximum at 1400 degrees C. Sintered body had a vermicular porous structure at sintering temperature up to 1300 degrees C. However, sintered body at sintering temperature of 1400 degrees C contained a relatively large amount of closed pores.