Comparison of Techniques for Determining the Fractal Dimensions of Clay Minerals

Kalumbu Malekani1, James A. Rice1 and Jar-Shyong Lin2
1 Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota 57007
2 Center for Small-Angle Scattering, Solid-State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831

Abstract: Small-angle X-ray scattering (SAXS), adsorption and nuclear magnetic resonance (NMR) techniques were used to determine the fractal dimensions (D) of 3 natural reference clays: 1) a kaolinite (KGa-2); 2) a hectorite (SHCa-1), and 3) a Ca-montmorillonite (STx-1). The surfaces of these clays were found to be fractal with D values close to 2.0. This is consistent with the common description of clay mineral surfaces as smooth and planar. Some surface irregularities were observed for hectorite and Ca- montmorillonite as a result of impurities in the materials. The SAXS method generated comparable D values for KGa-2 and STx-1. These results are supported by scanning electron microscopy (SEM). The SAXS and adsorption methods were found to probe the surface irregularities of the clays while the nuclear magnetic resonance (NMR) technique seems to reflect the mass distribution of certain sites in the material. Since the surface nature of clays is responsible for their reactivity in natural systems, SAXS and adsorption techniques would be the methods of choice for their fractal characterization. Due to its wider applicable characterization size-range, the SAXS method appears to be better suited for the determination of the fractal dimensions of clay minerals.

Key Words: Adsorption • Clay • Fractal • NMR • Small-angle x-ray scattering

Clays and Clay Minerals; October 1996 v. 44; no. 5; p. 677-685; DOI: 10.1346/CCMN.1996.0440511
© 1996, The Clay Minerals Society
Clay Minerals Society (www.clays.org)