A FRACTAL STUDY ON THE DISPERSING PROCESSES ON THE SURFACE

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 monolayer coverage scale down with increasing sigma as N similar to sigma(-D/2) where sigma 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), CuCl2), 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 structure 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 information 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 (Av)(2) (or CuCl2)is only 3%, which can be hardly detected by the conventional X-ray diffraction metho, 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