| In this dissertation different morphology of the spherical structure aluminum hydroxide powder have been synthesized by hydrothermal method, with aluminum sulfate as raw material, urea as precipitant, water and ethanol as the medium on certain proportion of the alcohol-water and hydrothermal condition after a certain drying treatment. The microstructure and the thermal decomposition process of the obtained powder were studied by SEM, XRD test and TG-DSC analysis. Different calcined temperatures were identified through analyzing the thermal analysis dynamics mechanism of different morphology of aluminum hydroxide powders,and different crystal forms of Al2O3powders were obtained by calcining the hydrothermal products for a certain time under those temperatures. The microstructure evolution and crystal transformation of sample powders during the calcining process were inspected by SEM and XRD. The influence of microstructure of different morphology of aluminum hydroxide powders was researched.Solid sphere, core-shell structure and hollow spherical aluminum hydroxide powders have been prepared via hydrothermal method. In this dissertation, the dynamics of these morphology of aluminum hydroxide in the calcining process were analyzed mainly by the Popescu, Doyle-Ozawa and Kissinger method.The results indicate that solid spherical aluminum hydroxide is amorphous boehmite before calcining. After calcining at600℃it becomes evenly dispersed ρ-Al2O3with the size around2μm. At last, it transfers to spherical α-Al2O3which is stacked by chips after calcining at1200℃and still maintains the size and dispersity. There are two main dynamics processes which are the desorption process of adsorbed water in300K-500K and the desorption process of structure water in600K-800K during calcinations process. The weight loss of removing the absorbed water is6.76wt%. The process keeps to the one-dimensional diffusion mechanism which is named D1model. The average activation energy of the process is42.976kJ/mol calculated by the three different methods. The weight loss of removing the structure water is10.01%. The whole weight losses of the two processes are16.77wt%, and the latter process is dominated by the spherical symmetry three-dimensional diffusion (Jander eq.) which is named D3model. The average activation energy of the latter process is139.182kJ/mol calculated by the three different methods.Pseudo-boehmite with core-shell structure transform to the γ-Al2O3which still keeps a core-shell structure. And last it becomes to the core-shell structure θ-Al2O3with the collapse of the shell surface and the loose slice layered stacking of the internal solid ball. There are two main dynamics processes which are the first dehydration process in300K-450K and the second dehydration process in580K-800K during the calcining process. The weight losses of the two processes are3.86wt%and12.21wt%, the whole losses are16.07wt%. The first dehydration process belong to the Three-dimensional diffusion(G-B eq.a) which is named D4model, and the second dehydration process is dominated by the spherical symmetry three-dimensional diffusion(Jander eq.). The average activation energy of the two process is54.674kJ/mol and155.474kJ/mol calculated by the three different methods.At the whole calcination process, hollow spherical pseudo-boehmite gradually translates into the hollow spherical γ-Al2O3. The hollow spherical γ-Al2O3still keeps the size and morphology of the hollow spherical pseudo-boehmite, but its hollow size increased. Then the hollow spherical γ-Al2O3transforms to hollow spherical α-Al2O3with partly collapse of the surface slice and the further larger hollow. There is only a dynamics process in650K-810K during the calcining process. It is the desorption of the absorbed water of the hollow sphere and the structure water of the sphere inner wall. The weight loss of the process is10.51wt%. The average activation energy of the process is172.709kJ/mol calculated by the three different methods. |
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