Phase Transformations and Control of Habit in Lyothermal Synthesis of α-Al₂O₃

The phase transformation of gibbsite to corundum (α-Al₂0₃) in 1,5-pentanediol (glycothermal treatment) was investigated between 270 and 450°C and between 10 and 50 MPa. The kinetics of transformation to corundum in this range are hindered. Only the formation of microcrystalline tohdite (5 A1₂0₃ : 1H₂0 ) can be observed. The lowering of the nucleation energy of corundum by adding α-Al₂0₃ seeds enables the synthesis of microcrystalline corundum at 330°C. The size of the gibbsite particles and the size and quantity of the α-Al₂0₃ seeds are important for the homogeneity and particle size of the resulting corundum. The particle size and the
morphology of glycothermal α-Al₂0₃ powders were compared with the results of hydrothermal synthesis of α-Al₂0₃.