Effect of sodium polyacrylate molecular weight on the crystallogenesis of calcium carbonate

• Published in: Journal of crystal growth 2007-08, Vol.306 (2), p.373-382
• Main Authors: Jada, A., Ait Akbour, R., Jacquemet, C., Suau, J.M., Guerret, O.
• Format: Article
• Language: English
• Subjects: A1. Complexation; A1. Induction time; A1. Polymorphs; A2. Crystallogenesis; B1. Calcium carbonate; B1. Sodium polyacrylates; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; General studies of phase transitions; Growth from solutions; Materials science; Methods of crystal growth; physics of crystal growth; Nucleation; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2007.05.046

Aqueous solutions of sodium polyacrylates (NaPA) series having molecular weights ( M w) ranging from 2540 to 9890 g mol −1 are used as precipitation media to control the size and shape of calcium carbonate (CaCO 3) particles. The retarding effect of polyacrylates on CaCO 3 nucleation is evidenced by the increase of the induction time, τ, of the precipitated CaCO 3, from τ=55 s in the absence of additives, to τ values in the range 100–2500 s in the presence of NaPA samples. The data also show the coexistence of two polymorphs, calcite and vaterite, for CaCO 3 particles as prepared in the presence of NaPA samples. The vaterite fraction, f v, varies in all instances with the polymer concentration, Cpoly (g. L −1), and reaches its maximum value, f v,max at optimal ratio, R (mol. g −1), of Ca ion to polymer (NaPA), R=[Ca]/([NaPA]=Cpoly). No simple general trend is found to explain the influence of the molecular weight ( M w) of NaPA on the induction time, τ, and on the vaterite fraction, f v, since these two parameters are found to vary with Cpoly and M w. However, under certain experimental conditions, an optimum polymer molecular weight ( M w=5530 g mol −1) of the NaPA series, gives the highest values of f v,max and τ. Such optimum indicates the influence of M w of NaPA on CaCO 3 nucleation and growth, and it is related to the surface density and the rate of adsorption of the polymer onto the growing crystal. The CaCO 3 particle size is reduced from about 20 μm, as obtained in the control experiment, to sizes varying in the range 2–8 μm in the presence NaPA samples. Polymers having low M w values ( M w