International audienceThis paper investigated the crystallization of calcium carbonate in saline solution at different temperatures using Raman spectroscopy. Application of an advanced mixture analysis algorithm based on Bayesian theory (BPSS) allowed recovery of the Raman spectra of the three pure anhydrous polymorphs (vaterite, aragonite, and calcite). In particular, the low wavenumber range between 50 and 300 cm-1, characteristic of crystallographic structure phonons, clearly distinguished the three structures. Contour plots of the polymorph concentrations during the crystallization process vs temperature and time have been established and discussed. This study demonstrated the ability of low wavenumber Raman spectroscopy combined with BPSS analysis to identify the different polymorphs (known or unknown) during a crystallization process and to assay their relative amounts without calibration

Raman spectroscopy is an ideal method for identifying polymorphs, because it provides excellent fingerprint spectra specific to each crystal structure. Currently, Raman spectroscopy is successfully used forthe quantitative polymorphic analysis of calcium carbonate only in the case of binary mixtures. When a third polymorph is present in the mixture, errors in the quantitative determination increase due to the difficulty in discriminating the different phases in the Raman spectra. In the present work, a new method is developed for mixtures containing more than two polymorphs and tested in the case of vaterite, aragonite, and calcite mixtures of different compositions. It is proved that Raman spectroscopy is a powerful, accurate, and reliable technique for quantitative determinationofpolymorphmixturesofcalcium carbonate.Themethodcanbe usedforothercompoundsexhibitingmultiplepolymorphs.