FULLY HYDRATED LAUMONTITE - A STRUCTURE STUDY BY FLAT-PLATE AND CAPILLARY POWDER DIFFRACTION TECHNIQUES

The structure refinement of laumontite [Ca4Si16Al8O48.18 H2O; Z= 1, CuKalpha radiation; T = 295 K; cell a = 14.845(9), b = 13.167(2), c = 7.5414(8) angstrom; beta = 110.34(2)-degrees, C2/m, D(x) = 2.306, M(r) = 1917.80] was completed from X-ray powder data obtained with two different techniques using a fully hydrous sample. Data collection was performed using (a) a mylar-sealed flat-plate holder with the sample submerged into water, Bragg-Brentano geometry, and a conventional two-circle Philips goniometer, and (b) the sample in a water-filled glass capillary, Debye-Scherrer geometry, and an INEL CPS120 position sensitive detector. The results obtained by Rietveld refinement of the two independent data sets are compared and found to be in full agreement. The water content of fully hydrated laumontite is shown to be 18.0 water molecules per cell. The excess water molecules present in laumontite with respect to leonhardite completely stabilize a 7-coordinated geometry for the Ca atoms in the channels. This study shows that reliable structural information not accessible with other techniques can be extracted by Rietveld refinement of powder data collected with unconventional experimental geometries and sample preparation techniques.