Controllable Synthesis Of Nanometer Cerium Oxide

In recent years, nanoparticles have aroused extensive attention of many scholars at homeand abroad due to their special physical and chemical properties such as optical, magnetic,mechanical and catalytic characters. Cerium oxide is seen as an important rare earth oxidematerial and it has a wide range of applications in automobile exhaust purification,ultraviolet absorption and polishing fields. The most attractive thing is that the use of CeO₂polishing powder and polishing solution has got an increasing trend. Although China has alarge output of polishing powder, the production of polishing solution is not enough. Themain restraining factor is that CeO₂particles have big grain sizes, uneven distributions,irregular morphology, and so on.In this study, the main objective is to find a process for preparing spherical nano-CeO₂particles with small particle sizes and even distribution. And the main work andexperimental results can be seen as follows:First of all, to choose four different precipitants to titrate cerium nitrate solution to getfour precursors. First, the precursor thermogravimetry-differential thermal gravimetricanalysis was carried out to obtain precursors with thermal decomposition temperature. Thenthe precursors were calcined at the thermal decomposition temperature to get the requiredCeO₂.The detection and analysis of CeO₂was performed using scanning electronmicroscopy and the results showed that four CeO₂particles of totally different morphologieswere found and they had different particle shapes--long hexagonal schistose, acicular,quadrangular, powder or ball-like. In this way, the preparation method for four CeO₂particles with different morphologies was obtained. The precipitants were selected foreffective preparation of CeO₂particles for further work.Next, the optimum conditions for the preparation of CeO₂nanoparticles weredetermined: the drying temperature and time of the precursors were80℃and2h respectively;the calcination temperature and time were400℃and2h separately. An excellent precipitantwas selected to prepare CeO₂nanoparticles and six different dispersants were added in orderto reduce particle agglomeration and refine particles. In the end, six groups of CeO₂nanoparticles were obtained, with the smallest sub-grain size of4nm and the largest36.2nm.The CeO₂nanoparticle size was mainly about100nm and there were agglomerationsbetween the non-standard spherical particles. Thirdly, with the other conditions unchanged, the reaction mixture was replaced byabsolute ethyl alcohol in the process of precipitation reaction in order to exclude theagglomeration of capillary stress formed by the evaporation of water in the process of dryingprecursors. The particle size of final CeO₂nanoparticles became significantly small. At thesame time, the shapes of particles had no remarkable change and the agglomeration of theparticles was decreased to some extent.Eventually, the preparation of polishing solution was initially conducted, but theprepared solution precipitated and then layered, and the thixotropy of polishing solution wasnot good enough, so further research work should be carried out in the future.