分形理论及其在炭素材料研究中的应用(2)——炭素材料中的分形研究

FRACTAL THEORY AND ITS APPLICATIONS IN THE RESEARCH OF CARBON MATERIALS(Ⅱ)—FRACTAL STUDIES ON CARBON MATERIALS

炭素材料中广泛存在具有分形结构的体系。本文综述了有关石墨、炭黑、焦、玻璃炭及木炭等多种嵌素材料中气孔界面分形结构的研究,说明在这些材料中气孔界面均是分形结构,且分形维数可取2～3之间的任何数值。这些研究同时表明,对炭素材料由不同的吸附质进行吸附或采用不同的理论测得的比表面均可以产生很大差别,但所得分形维数的数值却是一致的,预示分形维数在某些场合下能更好地描述材料的结构。毫无疑问,此时讨论比表面随吸附质截面的变化率——分形维数较比较比表面的具体数值大小更有意义。

In carbon materials, there are a number of objects which are fractal. This paper reviews some studies on the fractal property of pore-solid interface of carbon materials, including fractals in graphites, carbon black, coke, glassy carbons and charcoals. The results show that the pore-solid interfaces in these materials are all fractal and the fractal dimensions can be any value between 2 and 3. It is also shown that there may be marked differences in the values of specific surface area of carbon materials determined using different adsorbates and/or by different theoretical equations, but the values of fractal dimension determined are in good agreement within the experimental error bands. This implies that in some cases, fractal dimension may be regarded as a better parameter than surface area. Therefore, under such circumstances, it is more reasonable to pay one's attention to the increase rate of surface area as a function of the cross section of adsorbates, i.e. the fractal dimension rather than the absolute values of surface area itself.