SURFACE FRACTAL DIMENSIONS OF SOME INDUSTRIAL MINERALS FROM GAS-PHASE ADSORPTION-ISOTHERMS

A high precision gravimetric method was used to investigate the adsorption of nitrogen (N2) and carbon tetrachloride (CCl4), respectively, at 77 and 298 K, onto various industrial minerals. The solids investigated include silica isomorphs, blast furnace slags, an Y-zeolite, and several naturally occurring fibrous minerals. The adsorption isotherms were analyzed to derive surface areas, BET constants (C), and surface fractal parameters (D). The latter were obtained through an approach recently suggested by Avnir and Jaroniec,1 using multilayer adsorption data; D values obtained for the various gas-solid systems investigated cover the range 2.1-3.0. A systematic comparison between D values inferred from N2 and CCl4 adsorption data shows that the CCl4 molecule probes the surface roughness in a more discriminate fashion than N2. In most cases, the differences between D(N2) and D(CCl4) appear to reflect changes due to sample preparation more than intrinsic differences amongst the various solids.