纳米材料和纳米结构第四讲.ppt

A micrograph of cubic particles prepared under the following conditions: Product: Y2O3: Eu Reaction temperature: 22 °C; pH of solution: 4; Titration rate: 5 ml/min; Cation ion concentration: 0.05 M (Y3+) 2-5 Application of Co-Precipitation Method In Preparation of YBa2Cu3O7 Powders: the ideal pH for complete precipitation of all metal ions is ~11, the particle size of precipitate is determined by the surface charge, concentration of reactants, degree of mixing and recrystallization of precipitate particles. Particles grow by an agglomeration model. In Preparation of BaTiO3 Powders: the most predominant factor that affects the products is the titration method. When ethanol solution of oxalic acid is titrated into Ba2+/Ti4+ solution, the fired precipitate is a single phase of BaTiO3; however, if the Ba2+/Ti4+ solution is titrated into ethanol solution containing oxalic acid, a mixed phase is formed on calcination of the precipitate. Lower temperature and fast titration lead to almost perfect stoichiometry. Summary The chemical co-precipitation technique is widely used to synthesize oxide complexes. The most used precipitating anion agent is oxalic acid or ammonium oxalate. The processing parameters of starting raw materials, reaction temperature, solution pH, titration rates, even stirring rate have effect on properties of final particles, such as particle size and size distribution, shape, even chemical stoichiometry. Thank You for Your Attention! 纳米材料和纳米结构 水解和化学共沉淀法 Forced Hydrolysis and Chemical Co-Precipitation 第四讲 Both methods are techniques to separate metal ions from a salt solution Advantages of chemical co-precipitation Cheap raw materials Ease of handling Large-scale production Advantages of forced hydrolysis Producing fine, spherical nanoparticles Improving chemical purity, chemical homogeneity Controlling particle size A Brief Description： Forced Hydro