Effects of Thermal Treatment on the Properties of γ-Al2O3 and θ-Al2O3
1.State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, China;
2.Department of Chemical Engineering, Fuzhou University Zhicheng College, Fuzhou 350002, China;
3.National Engineering Research Center of Chemical Fertilizer, Fuzhou University, Fuzhou 350116, China
Abstract γ-Al2O3 and θ-Al2O3 were thermally treated under different calcination temperatures and time. The properties of these two kinds of alumina before and after treatments were characterized by X-ray diffraction(XRD), N2 physical adsorption-desorption and fourier infrared(FT-IR), which revealed effects of the calcination temperatures and time on the properties of these two alumina. The phase transition mechanism of Al2O3 was also analyzed based on the characterization results. The results showed that both γ-Al2O3 and θ-Al2O3 possessed a certain level of structural stability at relative low temperature. However, a transformation of γ-Al2O3 and θ-Al2O3 into α-Al2O3 occurred at a high calcination temperature. When these alumina were calcined under phase transition temperature, the specific surface area and the total pore volume of the two kinds of Al2O3 decreased with the increase of the calcination temperature. Nevertheless, the specific surface area and the total pore volume of the two kinds of Al2O3 decreased with the prolonged heat treatment. With high temperature treatment, γ-Al2O3 was transformed into θ-Al2O3 and α-Al2O3 at 900 ℃ and 1 200 ℃, respectively. θ-Al2O3 was gradually transformed to α phase from 1 100 to 1 200 ℃. With the increase of calcination time, the content of α phase gradually increased and rapidly transformed into a single α phase at 1 200 ℃. When the two kinds of Al2O3 were transformed into α phase under the condition of high temperature, the pore structure completely collapsed to cause the specific surface area and the total pore volume to decrease rapidly to form the dense structure α-Al2O3.
