RIETVELD ANALYSIS / WHOLE PATTERN FITTING METHOD FOR QUANTIFICATION OF CLAY COMPONENTS

This study explores an alternative technique for quantitative clay analysis. The current technique utilizes preferred orientation to determine the components in a clay system. This method requires X-Ray diffraction analysis of the clay under three different conditions; under ambient conditions, after the crystalline lattice is expanded by glycolization and after heating to promote collapse the lattice. This technique is cumbersome and we feel the analysis could be better accomplished with Rietveld techniques.

Rietveld Refinement uses known atomic structure to model the phase components present. This allows the refinement of atomic parameters through least squares analysis until the calculated pattern, generated by the model, agrees with the experimental pattern. Rietveld analysis can yield accurate and reproducible quantitative results. The traditional methods are highly subjective to variations in diffracted peak intensity due to preferred orientation. This is not a limitation in the Rietveld method.

While the starting atomic positions of the expanded lattice are difficult to determine, its experimental diffraction pattern can be readily measured. To use Rietveld analysis we propose to use the atomic positions of the unaltered clay structure as a starting model for the analysis. A least square refinement will generate a simulated crystal structure of the expanded system. This new expanded clay model then becomes the starting atomic model for Rietveld Refinements for the purpose of quantifying the expandable specimen component.