Unsteady-state inhibition of crystal growth caused by solution impurities

Abstract

The competitive adsorption model under unsteady state conditions (CAMUS) is presented and validated against experimental results of crystal growth inhibition in the presence of impurities. Particular emphasis is given to peculiar growth rate trends documented in the literature that are unexpected by the existing theories. These behaviours include intermittent crystal growth, increasing growth rates with time, and inverted U-shaped growth curves, which have been reported to occur in very diverse systems such as sucrose–sugarcane impurities (P. M. Martins, A. Ferreira, S. Polanco, F. Rocha, A. M. Damas and P. Rein, J. Cryst. Growth, 2009, 311, 3841–3848), barite crystals grown in the presence of carbonate ion (N. Sánchez-Pastor, C. M. Pina, L. Fernández-Díaz and J. M. Astilleros, Surf. Sci., 2006, 600, 1369–1381) or L-glutamic acid crystals grown in the presence of L-phenylalanine (M. Kitamura and T. Ishizu, J. Cryst. Growth, 1998, 192, 225–235). The CAMUS adequately describes the experimental observations as a result of dynamic equilibrium between impurity and solute molecules, with the impurity being adsorbed first at the crystal surface and then being gradually replaced by the crystallizing solute until the steady state is reached. The set of CAMUS parameters that best fit the experimental results were determined for each case analyzed in this study.