Preparation of Ultrafine α-Al_2O_3 Powders by Thermal Decomposition of AACH

Ammonium aluminum carbonate hydroxide(AACH) was synthesized as the precursor by the precipitation reaction of ammonium aluminum sulfate and ammonium hydro-carbonate.Then the precursor was calcined to get ultrafine α-Al2O3 powder.The effects of pH value,adding rate and a mixed solvent of ethanol-water on the reaction product of AACH were researched.Phase transformation of AACH upon heating and effect of α-Al2O3 seed on the transformation kinetics were also analyzed.The structural properties of powders were characterized by XRD,TEM and BET.The results show that the AACH nanoparticles with uniform particle size and well-distribution can be synthesized in ethanol-water solvent by adding ammonium aluminum sulfate solution to ammonium hydro-carbonate solution with a rate less than 18 mL/min and controlling the pH value between 9 and 10.For the sample without seed,the temperature of transforming completely into α-Al2O3 is 1150 ℃,and particle size of the α-Al2O3 powder is about 100 nm.By adding α-Al2O3 seed,the temperature can be reduced to 1050 ℃,and particle size of α-Al2O3 powder is about 70 nm.