摘要
应用XRD和BET方法,研究了四种二元复氧化物在不同配比及不同焙烧温度下界面过渡层的结构。XRD证明各组分都在另一组分表面具有分散阈值,其值远大于单层饱和容量且与焙烧温度无显著关系;“阈值后”剩余晶相量与加入晶相量虽呈线性关系,但斜率并不都近于1,有的明显小于1。BET比表面测定表明,各纯氧化物及不同配比试样的比表面较γ-Al_2O_3的小得多。对过渡层提出了球形八面体二维密置的非单层双向分散模型,计算了各项模型参数,较好地解释了高分散阈值与低比表面积之间的关联,并与O^(2-)密置的单层模型作了对比。讨论了晶相消失的机理,以及非晶相与非单层分散厚度的关联。
The non-crystalline dispersion on interfaces of MoOs-V2O5, MoO3-TiO2(anatase), MoO3-WO3 and MoO3-ZrO2 systems was studied by XRD and BET. XRD quantitative extrapolation indicates that there are the dispersed threshold values (maximum dispersion) of each component oxide on another surface, what is called "both sides dispersed threshold value" of interface transition layer in this article. Exceeding threshold value, many of the extrapolated slops between residual crystalline and added crystalline are obviously less than 1; "crystalline residual ratio" is intro-duced to describe and explain these smaller slopes. BET measurements show that specific surface areas of all samples are much smaller(<10m2/g) than that of carriers such as γ-Al2O3,etc. The above dispersed threshold values (0.34- 1.43g/100m2) from XRD are more than their monolayer dispersion capacities (0.088- 0.264g/100m2) calculated from a non-monolayer model proposed in this article. According to the model each component oxide is dispersed on another surface by ball octahedra (MeO6) which is closed-packed by sharing O atoms in a layer, and limited several of such layers are stacked up to form the non-monolayer dispersion on interface transition layer. The threshold values from XRD are much more especially than monolayer dispersion capacities from O= closed-packed model (0.117 g/100m2). To sum up, monolayer dispersion model is proved to be not suitable for binary oxide interface though it is suitable for MoO3/γ-Al2O3, etc. Parameters of non-monolayer model are calculated and listed.
