Polymorphism Studied by Lattice Phonon Raman Spectroscopy and Statistical Mixture Analysis Method. Application to Calcium Carbonate Polymorphs during Batch Crystallization

Abstract

This 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.