Rietveld quantitative amorphous content analysis

A procedure for Rietveld quantitative amorphous content analysis (RQACA) is outlined, in which the effects of systematic errors in the powder patterns are studied. The method derives the amorphous content from the small overe stimation of an internal crystalline standard in a Rietveld refinement of a n appropriate mixture. Of several standards studied, Al2O3 gave the best re sults. The statistical analysis of standard mixtures with a known amount of amorphous content indicated that this is a precise and accurate tool. It e nables the measurement of the amorphous content with an accuracy close to 1 %. Sample preparation and Rietveld analysis need to be optimized in order t o minimize the systematic errors. The analysis of samples with phases displ aying strong preferred orientation effects gives very high errors in the am orphous content. Samples with different absorption coefficients have also b een studied in order to evaluate the importance of microabsorption. This pl ays an important role but it can be adequately corrected if the absorption coefficients of the standard and the sample are not very different. RQACA h as been applied to tricalcium silicate, C3S, which is the main component of Portland cement. The average amorphous content of C3S, after microabsorpti on correction using two standards of higher and lower absorption coefficien ts, was found to be 19%.