On-line X-ray diffraction for quantitative phase analysis: an industrial application of the Rietveld method

Material properties and plant operations are governed by mineralogy not chemistry. However, they are most often controlled in production by simple measurement of bulk chemistry. If used at all, mineralogy is derived from chemistry through normative calculation. Methods of this nature are fraught with inaccuracy due to the necessary assumptions regarding the exact chemical formulae of each of the component phases. One example is the Bogue method which is the industry standard for Portland cement production. Using X-ray diffraction (XRD), Portland cement remains a notoriously difficult material to quantify due to (i) the number of phases present, and hence degree of peak overlap, (ii) the variable composition of individual phases, and (iii) the presence of polymorphism. Typical cement plant control relies upon intermittent (say, four-hourly) X-ray fluorescence (XRF) analyses of bulk chemistry from which mineralogy is derived.