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Quantitative X-ray diffraction analysis in cement production control: part one

World Cement,

Quantitative X-­ray diffraction analysis (QXrD) can be used to determine the phase composition of clinker and cement. However, its implementation into the quality control in cement production as an automated analytical process, including sampling, preparation, and evaluation does not allow for a validation of each single measurement. On the other hand, the plant operator requires reliable phase determination with good reproducibility, taking into account challenges such as production fluctuations or the quantification of cements with partially amorphous main constituents. While QXrD is well established in some cement plants as a crucial operational tool, many cement producers do not yet take advantage of this fast and automatable measurement method. Sufficiently accurate QXrD could supplement or even replace reference tests as part of factory production control and third­party inspection.

Phase analysis with QXRD can be applied on numerous materials within the cement production process. Most common are analyses on clinker samples which are suitable for this method as they usually consist of well structured, crystalline phases. The evaluated phase composition reflects the kiln feed mixture and the burning and cooling conditions. Raw materials like limestone are analysed as a main part of the raw meal or as main or minor cement constituents. Sulphate agents can be analysed despite their status of dehydration, and dusts to be fed back appropriately into the production process. Furthermore, the quantification of partially X-ray amorphous main constituents like slags or fly ashes can be achieved under special circumstances, so that even quite complex cement compositions can be evaluated with acceptable precision.

Preparation and measurement

For all kinds of comparative X-ray analysis on powder specimens, continuity in the sample preparation is of crucial importance. This is achieved by commercially available preparation robots which are implemented in auto-labs. But the preparation routine itself must be carefully defined. In contrast to XRF preparations where the highest milling grade is the optimum for the analytical precision later on, the preparation of XRD samples must take into account the structural decay of some weak or cleavable mineral phases like gyp sum, anhydrite or calcite. In practice, the XRD measurements are thus performed on cement samples of the usual technical fineness.

This is part 1 of a 2-part article that was originally published in Newsletter 3/2015 of the European Cement Research Academy and is reproduced by kind permission of ECRA.

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