| he fractal dimensionality is a quantitative measure of the degree of surface roughness of a solid. The fractal dimensionality of an Argonne: Upper Freeport, Pittsburgh No. 8, Illinois No. 6, Wyodak-Anderson coals and a Beulah Zap lignite were successfully determined from their small angle X-ray scattering curves.;The fractal dimensionality of the Argonne coals could not be determined from the variation of measured coal surface areas on the size of the adsorbate molecule using a homologous series of cyclic aliphatic hydrocarbon gases (cyclopropane, cyclobutane, cyclopentane, and cyclohexane). A steep coal surface area dependence on the adsorbate size lead to the conclusion that the majority of the surface area of coals is present in pores which are closed to the external surface. These internal coal pores cannot be reached by diffusion through an interconnected pore network, but can only be reached by diffusion though solid coal. Carbon dioxide gives accurate total surface areas of coals because it dissolves in and rapidly diffuses through solid coals, reaching all the internal coal pores. Carbon dioxide coal surface areas are irrelevant to penetrants which are only slightly soluble or insoluble in coals, such as aliphatic hydrocarbons, since these penetrants can only reach a small portion of the total coal porosity. Slow diffusion of the cyclic hydrocarbon gases through coals was verified by monitoring the rate of hydrocarbon uptake as a function time. The diffusion rate of a penetrant through solid coal controls the measured coal surface area. Coals cannot be considered as high (hundreds of m;Micropore size distributions of the Argonne coals were determined using... |
