Preparation And Application Of Micro/Nanostructured Alumina Powder

The micro/nanostructured alumina has been widely used as adsorbent, luminescence andcatalyst etc, due to its excellent advantages of nano and micro structure. In this dissertation,plate-like-Al2O3is prepared by precipitation method, and the micro/nanostructuredspherical, fiber-like and3dimensional (3D) flower-like alumina are obtained successfully byhydrothermal method. Besides, the applications in the fields of adsorption, luminescent andthe thermal conduction are investigated.The precipitation is most common method to prepared nano-alumina powder, but it isstill a challenge for obtain the micro/nanostructured alumina at a lower temperature. In thisresearch, the nano-sized-Al2O3with different morphologies is synthesized bydecomposition of AACH precursor. The results present that the morphology andtransformation temperature of-Al2O3is determined by the morphology and grain size of theprecursor which are affected by the reaction temperature and the reaction system. In thedeionized water system, nano-sized pherical, fiber-like and3D flower-like AACH precursoris synthesized by adjusting reaction temperature in the range of5~50°C. While in ethanol-water system, the micro-sized spherical and fiber bundle-like AACH are obtained bycontrolling reaction temperature.In order to prepare micro/nanostructured and plate-like-Al2O3at a lower temperature,hydrofluoric acid (HF) is used as acidifier. In this work, micro/nanostructured and plate-like-Al2O3is sythesized at850°C by decomposition of AACH precursor treated in the HFsolution. The results indicate that (NH4)AlF6with plate-like morphology is obtained when theprecursor is treated in20mL HF solution with5wt%for6h. In the following decompositionprocess, the plate-like θ-Al2O3with sharp edges is prepared at700°C, and the plate-like-Al2O3with smooth edges is synthesized at850°C.As the applications of alumina have a close relationship with its morphology and grainsize, the hydrothermal method is induced to prepare micro/nanostructured alumina withcontrollable morphology. The results illustrate that the hydrothermal temperature determinesthe morphology of precursor. AlOOH microspheres, microfibers and3D hierarchical structureare synthesized at hydrothermal temperature of90°C,120°C and150°C, respectively. AlOOHtransforms to γ-Al2O3with unobvious morphology change and volume shrinkage at800°C,and the mesopores are distributed evenly in γ-Al2O3structure, and γ-Al2O3is transformedcompletely to-Al2O3with morphology inherited at1150°C. Based on the experimentalresults, the temperature-dependent formation mechanism is proposed. In addition, we also find that the AlOOH precursor is tranfomed to AACH with no morphology change byprolonging the hydrothermal time. The research above makes contributions to preparingmicro/nanostructured alumina with controlling morphology.Besides, the applications of γ-Al2O3and-Al2O3are introduced. The plate-like-Al2O3obtained by precipitation method and fiber-like-Al2O3obtained by hydrothermal method areused as thermal conductive fillers. The results indicate that the conductivity coefficient ofEpoxy with plate-like alumina is0.81W/m K when the stuffing fraction is60wt%, while theconductivity coefficient of Epoxy with fiber-like alumina is0.72W/m K, which illustratesthat plate-like alumina is a potential candidate material of thermal conductivity filler.Meanwhile, the applications of γ-Al2O3used as absorbent and luminecent material areinvestigated. Experimental results present that hierarchically structured γ-Al2O3as absorbentcan remove about99%of Congo red for a while, which inllusrates that the obtainedhierarchically structured γ-Al2O3presents excellent adsorption property in the potentialapplication of waste water treatment. The PL spectrums of γ-Al2O3calcined at800°C presenta strong wide emission bands centred at410cm-1and460cm-1, due to the electron transition,which indicates that γ-Al2O3is a kind of excellent luminecent material.