pH值对沉淀法制备Al_2O_3相转变的影响

为获得Al2O3粉体,以Al(NO3)3为原料,NH3.H2O为沉淀剂,采用液相化学沉淀法,在不同pH值下制备了Al(OH)3前驱体,并利用TEM,XRD,TGA等分析手段对前驱体进行了表征。pH=5时前驱体的相转变主要是由非晶Al(OH)3→非晶Al2O3→α-Al2O3;pH=9及pH=11前驱体的相转变主要是由Al(OH)3→γ-Al2O3→θ-Al2O3→α-Al2O3。XRD结果表明,低pH值时制备的Al(OH)3更容易转化为α-Al2O3稳定相。pH=5时前驱体在1 100℃就可转变为α-Al2O3稳定相,而pH=9和pH=11时制备的前驱体则分别需在1 150℃和1 200℃才能转变为α-AlO。研究表明,pH值对制备的前驱体的物相、形貌、相转变都有很大影响。

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

In order to obtain Al_2O_3 powder, the Al(OH)_3 precursors were prepared by chemical precipitation method from an aqueous solution of Al(NO_3)_3 and NH_3·H_2O 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 Al_2O_3→α-Al_2O_3. The transformation of the precursors prepared under pH=9 and pH=11 mainly was via Al(OH)_3→γ-Al_2O_3→θ-Al_2O_3→α-Al_2O_3. The results of XRD indicated that the precursors prepared under the lower pH values transformed easily to α-Al_2O_3. The precursor prepared under pH=5 transformed into α-Al_2O_3 at 1100 ℃, whereas the precursors prepared under pH=9 and 11 transformed into α-Al_2O_3 at 1150 ℃ and 1200 ℃, respectively. The results show that the pH value remarkably influences the phase composition, morphology and phase transition of the precursors.