Fabrication 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 aluminum sulfate and ammonium carbonate.Then the precursor was calcined to get α-Al_2O_3 powder.The effect factors of reaction on preparing AACH,such as the order and methods of adding materials,pH value and surfactant,were discussed,and the thermal decomposition reaction of AACH was also analyzed.The structural properties of powders were characterized by XRD,SEM,DTA/TGA and BET measurements.The results show that the AACH particles with uniform particle size and well-distributed can be synthesized with aluminum sulfate(atomizing) into ammonium carbonate,adding suitable amounts of PEG1000 as dispersant,and controlling the pH value(over) 8.The phase transformation of AACH in calcination process is as: AACH→AlOOH→amorphous Al_2O_3→(γ-Al_2O_3)→θ-Al_2O_3→α-Al_2O_3.The ultrafine α-Al_2O_3 with uniform particle size and in spherical shape and well dispersed were obtained by AACH calcined at 1200℃ for 2h.