Determination of the crystallized fractions of a largely amorphous multiphase material by the Rietveld method

The Rietveld method has proved to be a very effective means to characterize and quantify the crystalline phases and the amorphous phase in glass ceram ic materials using X-ray powder diffraction data. The technique was applied to a borosilicate glass of the type used for high-level nuclear-waste cont ainment, in order to measure the proportions of the crystallized phases aft er heat treatment and, thus, to qualify the thermal stability of the glass. Six crystalline phases were analysed in this way in an almost entirely (>9 5 wt%) amorphous material after adding a known proportion of an internal st andard (TiO2). The quantitative analyses were corrected to allow for microa bsorption effects resulting from grain-size and absorption-contrast effects . In addition to the quantitative data, unit-cell parameters and site-occup ancy refinements revealed solid-solution and substitution phenomena in the crystal.