摘要
盐类和氧化物等活性组分在一定条件下,可在高比表面载体上自发分散。研究这些过程对多相催化剂、吸附剂的制备过程理解和控制无疑是重要的。这类分散过程已被系统地研究,并提出了单层分散模型,对CuCl_2/γ-Al_2O_3、HgCl_2/活性炭等多种体系,测定了单层分散阈值。表面化学习惯上理解为就是二维的化学。早在1931年Tayor就指出表面是不均匀的,但这种不均匀性是作为对理想二维表面的修正而引入的,如TLK模型。表面科学的这些基本概念其数学基础是欧基里德几何学,其物理背景是晶体结构。
The concept of fractal was applied to interpret the surface of porous solids and the processes proceeded on them. The fractal dimensions were determined from the saturation coverage with different adsorbates.The number of molecules reaching mon olayer coverage scale down with increasing σ as
N～σ^(-D/2)
where σ is the cross section of the probe molecule.
As the porous materials (such as porous silica gel, alumina) were mixed with a few of other active components (Zn(Ac)_2, CuCl_2) , it is found that the fractal dimensions of the mixtures measured by the method mentioned above were nearly invariable. The value of D of the mixtures are the same as that of the pure carriers. It shows that the surface of the carriers does not change as mixing with active components at room temperature, there is not any reaction occuring on the surface of the carriers besides the two phases were mixed.
Otherwise, after the mixtures were heated at given temperatures, the values of D are different from the original mixtures. It gives us some informations about the surface process. It means the surface of the carrier has changed quite a lot, solid/solid diffusion occured on the surface. Although the content of Zn(Ac)_2 (or CuCl_2)is only 3%, which can be hardly detected by the conventional X-ray diffraction method, but the change of D is not difficult to measure.
Furthermore the change of D implied that the surface becomes more smooth during solid/solid diffusion and the active components do not disperse homogeneously on the surface of the carriers.
出处
《物理化学学报》
SCIE
CAS
CSCD
北大核心
1991年第2期202-206,共5页
Acta Physico-Chimica Sinica
基金
国家自然科学基金
关键词
表面分散
分形
分维
多孔材料
Dispersion on surface, Fractal, Fractal dimension
