Influence of different amounts of hematite seedings on the temperature of phase transformation of transition aluminas into corundum

Abstract Corundum (α-Al 2 O 3 ) is the only stable oxide in the aluminium-oxygen system and is characterized by its high mechanical and chemical stability. But there are some problems in producing very fine corundum powders. Usually α-Al 2 O 3 is obtained from transition aluminas at temperatures in the range of 1100–1200°C. At this temperatures the dispersity of the corundum formed is reduced due to the start of grain growth processes. That is the reason for our investigations in preparing α-Al 2 O 3 at lower temperatures. Therefore aluminium-secondary-butoxide was hydrolysed in water and seeded with different amounts of hematite. The dried powders were investigated for instance by using differential thermal analysis. A nearly linear relation between seeding amount and transformation temperature was found. The formation temperature of corundum was decreased by seeding with 10 wt% hematite from about 1100 to 970°C.