Supersaturation dependence of crystal growth in solutions in the presence of impurity

It is proposed to describe the rate of crystal growth in solution in the presence of impurity as a function of supersaturation. The theoretical equations are based on the pinning mechanism of Cabrera and Vermilyea for the inhibition of step advancement, assuming that impurity species are adsorbed one-dimensionally on the step lines. The Langmuir adsorption isotherm is assumed to hold for impurity adsorption. Experimental growth rate data from the literature are used to assess the model. The supersaturation dependence of crystal growth rate in the presence of impurity is also well described with the model. The critical supersaturation below which a crystal does not grow is correlated with the impurity concentration. For the case where an impurity has no effect at high supersaturation, two possible mechanisms are discussed: one related to a change of rate-determining process and the other related to competition between impurity adsorption and growth unit deposition processes.