Hydrothermal synthesis of boehmites with various particle sizes and transition to α-Al_2O_3 powders by calcination

Boehmite powders with various particle sizes have been prepared by hydrothermal method and the α-Al2O3 powders yielded after subsequent calcination have been studied. Dispersive crystalline boehmite powders of 30-100 nm, 0.4-0.6μm and 1μm in size were obtained respectively by changing the hydrothermal precursors and the pH value of hydrothermal slurry. Calcination of boehmite powders of 30-100 nm at 1250℃ for 1h resulted in the formation of single-phase α-Al2O3 , and the products consisted of vermicular particles. The boehmite powders of 0.4-0.6μm were also fully converted to α-Al2O3 at 1250℃, and the products consisted of plate-like particles with the same size of 0.4-0.6μm. The boehmite powders of 1μm calcined at 1350℃ for 2h were still composed of a little proportions of transition aluminas besides α-Al2O3, and the particles sintered severely. The reaction processes for the formation of crystalline boehmites under hydrothermal conditions and α-Al2O3 powders during calcination have been discussed.

Boehmite powders with various particle sizes have becn prepared by hydrothermal method and the α-Al2O3 powders yieldcd after subsequent calcination have been studied, Dispersive crystalline boehmite powders of 30-100 nm, 0, 4-0, 6μm and 1μm in size were obtained respectively by changing the hydrothermal precursors and the pH value of hydrothermal slurry. Calcination of boehmite powders of 30-100 nm at 1250℃ for lh resulted in the formation of single phase α-Al2O3, and the products consisted of vermicular particles. The boehmite powders of 0.4-0, 6μm were also fully converted to α-Al2O3 at 1250℃, and the products consisted of plate-like particles with the same size of 0, 4-0, 6μm, The boehmite powders of 1μm calcined at 1350℃ for 2h were still composed of a little proportions of transition aluminas besides α-Al2O3, and the particles sitiered severely. The reaction processes for the formation of crystalline boehmites under hydrothermal conditions and α-Al2O3 powders during calcination have been discussed.