MgO-ZrO2共沉淀体系的结构表征及单层分散现象

用共沉淀法制备了一系列MgO-ZrO₂复合氧化物, 用XRD、XPS、BET、DTA、EXAFS和TEM等进行了表征. 结果表明, 500 ℃与600 ℃下焙烧得到的MgO-ZrO₂复合氧化物, 在ZrO₂高含量一端, MgO倾向于固溶到ZrO₂中, 最大固溶量可达到1:1(摩尔比)；固溶达到饱和后, MgO开始在固溶体表面分散, 并析出单独的MgO晶粒；在MgO高含量端, 少量的ZrO₂以分散态存在于MgO的表面, 并使其表面性质发生较明显的变化. 这些结果表明, 在共沉淀法制备的MgO-ZrO₂样品中, 在一定相对含量范围内, 会出现一种组分在另一种组分或由两种组分形成的固溶体上的单层分散现象.

Structure Characterization and Monolayer Dispersion Phenomenon of MgO-ZrO2 Prepared by Co-precipitation

A series of MgO-ZrO₂ composites with various compositions were prepared by co-precipitation with NH4OH from mixed aqueous solution of nitrates and calcination at 500 ℃ and 600 ℃ respectively. The samples were characterized by XRD, XPS, BET, TEM, EXAFS and DTA measurements. The results exhibit that MgO tends to dissolve into the bulk phase of ZrO₂ to form solid solution as Mg/Zr molar ratio is lower than 1. After the dissolution reaches saturation, MgO starts to disperse onto the surface of the solid solution, and at the same time the separate crystalline phase of MgO appears. However, when the content of MgO is high, ZrO₂ does not dissolve into the bulk phase of MgO and not form the separate crystalline phase of ZrO₂, but disperses onto the surface of the crystallite of MgO. And the properties of the surfaces of the samples were obviously affected by the dispersion of ZrO₂. These results suggest that in the samples prepared by co-precipitation, one component can disperse as a monolayer onto the surface of the separate crystalline phase of the other component or the solid solutions composed of the two components in a certain content range. This phenomenon might exist in many binary oxide systems and deserves much more attention.