Experimental Research Of Metal Oxide Ultrafine Particles Preparation By Supercritical Hydrothermal Synthesis

The preparation technology of metal oxide particles by supercritical hydrothermal synthesis has been rapidly developed. The technology introduces supercritical fluid into the traditional hydrothermal synthesis method. The advantage of the partiles obtained is characterized by high purity, good dispersion, highly crystalline which can be well controlled, short reaction time and environment-friendly.The experimental setup is build upon the reconstruction of Supercritical Water Oxidation. A series of pipes and valves are reasonable modified, a small autoclave reactor and the circulating water cooling system are added, which can not only meet the equipment requirements of the experiment, but also enhance the experimental flexibility, equipment safety, and save energy required. At the same time, the equipment and the experimental process parameters are more easily to operate, measure and control.Zinc acetate, cobaltous Acetate, zirconium oxychloride and manganese acetate are used as typical experimental materials. The effects of four process parameters, like temperature, pressure, material concentration and water flowrate, on the particles size and distribution of the metal oxides are well investigated. The as-prepared powders are fully characterized by complementary experiments: X-ray diffraction(XRD), scanning electron microscope (SEM) and Zetasizer Analysis Apparatus(Zetasizer). The nucleation mechanism is preliminary analyzed by thermodynamics. The main experimental research results and conclusions are as follows:The experimental pressure, temperature and material concentration are the most important factors to effect particle size. Both the increasing operating pressure and decreasing operating temperature lead to an increase in the particle size. Besides, the increasing concentration of reactants also results in the particle with larger diameter. The strong influence of increasing water flowrate on the particle size is not obviously observed. It is just a little decrease in the particle size with the increasing water flowrate.The high-purity ZnO spherical particles with minimal average particle size of 9.55nm. CoO hexahedral particles with minimal average particle size of 138nm, ZrO₂ spherical particles with minimal average particle size of 170nm, and Mn₃O₄ spherical particles with minimal average particle size of 305nm are successfully obtained. The narrow particle size distribution is found as well.The solute particles crystallization trends and the formation and growth process of nucleation in hydrothermal synthesis are analyzed using preliminary thermodynamic theory. The rate formula for nuclear formation and its growth are educed, which explaine some experiments phenomena successfully and provide a certain theoretical reference for the future more in-depth thermodynamic and dynamical analysis.Through this work, the experiment technique of ultrafine metal oxide particles synthesis is investigated deeply. The basic influence rules of the process parameters working on the particle size and morphology are understood detailed. It provides experimental basis for the thermodynamic analysis behind, necessary basic data for future industrialization.