Hydrolysis Kinetic Of Aluminum Isopropoxide And The Effects Of Hydrothermal Process On Properties Of Product

In this thesis, the hydrolyzed kinetic parameters were obtained by studying the hydrolysis of aluminum isopropoxide using aluminum isopropoxide and water as raw material, isopropyl alcohol as solvent. Hydrolysis kinetic model was employed to analysis the hydrolysis process of aluminum isopropoxide. IR, XRD and HRTEM were utilized to characterize hydrothermal product of aluminum isopropoxide and to analysis the mechanism of hydrothermal conditions. TG-DSC was utilized to characterize calcined product obtained under differernt calcination temperature, and to analysis the mechanism of material transformation. The calcined kinetic of hydrothermal product was studied by applying Popescu method. Results are as follows:By analyzing the hydrolysis process, the hydrolysis and polycondensation reaction rate constants at20℃and25℃were obtained. The hydrolysis and polycondensation reaction rate constant equations were got from the rate constants.Hydrolysis kinetic model and computer program were taken to simulate the hydrolysis process under different concentrations of raw materials, and the analysis shows that the initial reactants concentrations and reaction temperature have a significant influence on the hydrolysis reaction rate, and affects the final status of products and the terminated reaction time to a certain extent.Through simulating hydrolysis process under different temperatures, the relationship of temperature dependence for the terminated reaction time under the condition of a raw materials molar ratio of1:3([A1(OR)3]=3.568mol/L,[H2O]=10.704mol/L) were obtained.With the increase of hydrothermal temperature and concentration of raw material, the hydrothermal product transform from pseudo-boehmite to boehmite, the crystal growth becomes better, and the morphology gradually changes from irregular shape to diamond flake-like grain whose thickness increases. The reason may be due to the oriented attachment of the growth units and the hydrogen-bond interaction of the lamellar units. The crystal plane index of exposed surface of flake-like boehmite is (031), and the crystal plane indices of the two vertical planes of the exposed surface are (200) and (051).The morphology of boehmite obtained by hydrothermal method don’t change much after600℃calcinations. Only the compact structure changes into the porous structure, which is due to the removal of constitution water. The crystal structure transforms from γ-AlOOH to γ-Al2O3after calcination, and the higher the hydrothermal temperature, the better the crystal growth, which maybe due to new phase is formed from the phase boundary movement in the inner crystal because of the dehydration of boehmite.Boehmite obtained at different hydrothermal temperature becomes very different after calcined at1200℃. With the increase of hydrothermal temperature, calcined product gradually transforms from dumbbell-like morphology to flake granular morphology, and its crystal structure gradually changes from α-Al2O3into θ-Al2O3. The reason may be attributed to the better crystal growth of the hydrothermal product, the higher the activation energy of transforming into α-Al2O3, so that it is maintained flake-like θ-Al2O3after calcined at1200℃.The crystal plane index of exposed surface of flake γ-Al2O3is (112), and the crystal plane indices of the two vertical planes of the exposed surface are (111) and (220). The crystal plane index of exposed surface of flake α-Al2O3is (0001), and the crystal plane indices of the vertical planes of the exposed surface are (1100),(0110) and (1010).Informed by Popescu method, the process of removing the adsorbed water of y-AlOOH belongs to the three-dimensional phase boundary reaction R3model, whose average activation energy is42.969kJ/mol, pre-exponential factor ranges from2.190×105to1.308×106, and average correlation coefficient is0.9740. The process of removing the constitution water belongs to three-dimensional diffusion process D4model, whose average activation energy is156.071kJ/mol, pre-exponential factor ranges from7.124×108to5.442×1010, and average correlation coefficient is0.9846.