ZrO2表面B2O3的分散及其作用状态

用XPS、FT IR和FT Raman等技术研究了ZrO2表面B2O3的分散及其作用状态,测定了B2O3在ZrO2表面的分散阈值.结果表明：B2O3在ZrO2表面可以三配位BO3和四配位BO4结构单元存在;载体ZrO2的预焙烧温度和硼含量对B2O3的分散及作用状态有较大影响,并改变BO3与BO4结构单元之间的比例.实验测得B2O3在ZrO2载体上的单层分散阈值为0.05 gB2O3/gZrO2（或B2O3的质量分数w=4.76％）,处在此单层中的硼原子以BO4为结构单元直接与ZrO2表面相作用.只有当B2O3的负载量超过此（单层）分散阈值时, BO3结构单元才会形成.

Dispersion and Interaction State of Boria on Zirconia Surface

Dispersion of B2O3 on zirconia surface with load levels up to 20％B2O3 was explored with samples that were prepared by impregnation of boric acid onto porous ZrO2 obtained by precalcination of ZrO(OH)2 at different temperatures (110－700 ℃). After calcination at 350 ℃, the B2O3/ZrO2 samples were characterized with FT IR, XPS and FT Raman techniques to determine the interaction state of B2O3 on the surface. Both tetrahedral BO4 and trigonal BO3 were detected as the basic units of the dispersed B2O3. The ratio of BO4 to BO3 units depended strongly on the temperature of the precalcination and the load level of boria. At lower precalcination temperature for the support and at low levels of boria load, B2O3 interacts directly with the support surface in BO4 units and forms monolayer dispersion. Inversely,multilayer dispersion with BO3 as the structural unit forms over the support precalcined at high temperature. The XPS and Raman data also provide good measurements for monolayer dispersion capacity of boria; with ZrO2 precalcined at 500 ℃, this capacity is 0.05 g/g(or mass fraction of B2O3 w=4.7 6 ％). A model for the dispersion structure of B2O3/ZrO2 has been proposed.