Quantitative analysis of silicate glass in ceramic materials by the Rietveld method

The modelling of silica glass, following the work of Le Bail [1], has been introduced in a Rietveld general procedure developed for quantitative phase analysis. The method approximates the amorphous phase as a nanocrystalline solid where the long-range order is lost. As pointed out by the same author, the model is not sufficient to describe exactly the amorphous structure. Moreover, from a fitting point of view, it provides nearly the same results as those obtained by reverse Monte Carlo simulation (RMC). This study shows how this approach can be successfully used to determine the amorphous fraction in ceramic materials containing a glassy phase. The "crystal structure" of silica, as determined by Le Bail [1], has been used, whereas the nanocrystalline behaviour is obtained using the line-broadening theory reported in [2] with a crystallite size of about one cell. The method has been tested on synthetic mixtures and ceramic-wars materials using X-ray diffraction. It provides an accurate, fast and standardless method of analysis suitable for quality and research controls. Other amorphous phases can be analysed providing a "crystal structure" model previously refined on a sufficiently pure sample.