Effect of pH value on phase transformation of Al_2O_3 synthesized through precipitation process

In order to obtain Al2O3 powder,the Al(OH)3 precursors were prepared by chemical precipitation method from an aqueous solution of Al(NO3)3 and NH3·H2O under different pH values.TEM,XRD,and TGA were used to characterize the Al(OH)3 precursors.The transformation of the precursor prepared under pH=5 mainly was via amorphous Al(OH)3→amorphous Al2O3→α-Al2O3.The transformation of the precursors prepared under pH=9 and pH=11 mainly was via Al(OH)3→γ-Al2O3→θ-Al2O3→α-Al2O3.The results of XRD indicated that the precursors prepared under the lower pH values transformed easily to α-Al2O3.The precursor prepared under pH=5 transformed into α-Al2O3 at 1 100 ℃,whereas the precursors prepared under pH=9 and 11 transformed into α-Al2O3 at 1 150 ℃ and 1 200 ℃,respectively.The results show that the pH value remarkably influences the phase composition,morphology and phase transition of the precursors.