In Situ Monitoring of Calcium Carbonate Polymorphs during Batch Crystallization in the Presence of Polymeric Additives Using Raman Spectroscopy

Abstract

Polycarboxylic acids are well-known to affect calcium carbonate crystallization. Agarwal et al. (Ind. Eng. Chem. Res. 2003, in press) reported previously the synthesis of polymaleimide by a variety of techniques and initiators. In the present work, the effect of these polymers on calcium carbonate crystallization was studied by a variety of techniques. Crystallization experiments were carried out in a 1-L LABMAX automated batch reactor, and the concentration of calcium in solution was determined in real time. Raman spectroscopy was used to determine the relative amount of various calcium carbonate polymorphs as the crystallization occurred. However, Raman spectroscopy is a scattering technique, which may make it surface selective, and therefore results from solids may not be representative of bulk of sample. X-ray diffraction (XRD) was used to compare the results obtained by Raman spectroscopy. Peak intensity ratios were used for both Raman spectroscopy and XRD for calibration and measurement purposes. The results obtained by these two techniques for final percent vaterite for calcium carbonate crystallization in the presence of polymeric additives were in agreement within 2%. Therefore, use of Raman spectroscopy for in situ measurement of polymorph composition during calcium carbonate crystallization appears accurate. Scanning electron microscopy (SEM) data were useful in understanding the crystal morphology and to determine crystal size.

Characterization and Selective Crystallization of Famotidine Polymorphs

“…6 The traditional methods, such as varying solvent, 7 temperature, 8 supersaturation, 9 cooling rate, 10 and seeding strategy, 11,12 have been extensively applied to control the polymorphic behavior of a compound during its crystallization process. 13 Recent approaches for discovery and selection of polymorphic forms of a compound include crystallization with tailor-made soluble additives, [14][15][16][17] polymer heteronuclei, 18,19 crystallization on various substrates and templates, [20][21][22] laser induced nucleation, 23 solventdrop grinding, 24 spray drying, 25 supercritical fluid crystallization, 26 capillary crystallization, 27,28 crystallization confined in nanopores, 29 etc. In spite of above great efforts the fundamental mechanisms and molecular properties that drive crystal form diversity, specifically the nucleation of polymorphic forms, are not well understood.…”

Calcium carbonate crystallization in tailored constrained environments

“…Raman spectroscopy is an appropriate method for monitoring the formation and evolution of CaCO 3 polymorphs. 38 These analyses showed the presence of calcite and vaterite in the microwells when lecithin was used as an additive. The results of dynamic light scattering analysis show that lecithin assembly is not strongly affected by its concentration until a highly viscous sol forms (Table 1).…”

A novel approach to consolidation of historical limestone: the calcium alkoxides

“…The coating thickness ranged from 0.8 to 1.5 µm and particle morphology strictly resembled vaterite. [59] The pore network was coated for the whole frit thickness, indicating that the alkoxide ensures a penetration depth of 3.5 mm at least.…”