Growth kinetics and morphology of potassium dihydrogen phosphate crystal faces in solutions of varying acidity

Abstract

Changes in the solution acidity do not influence the growth rate of bipyramidal faces, however, within the limits of 20% it can be changed by uncontrollable impurities existing in the solution. For steps on prismatic faces in acid and alkali solutions a decrease of the critical supersaturation σ∗, at which a sharp increase of the velocity occurs, is observed. This is indicative of the decrease of the surface concentration of the adsorbed impurity, which retards the growth. The more the solution composition deviates from the stoichiometric one, the more does the value of σ∗ diminish. It is shown that pH does not affect the free surface energy of end faces of steps and their kinetic coefficients. The values of kinetic coefficients of steps of different orientation on prismatic and pyramidal faces are determined. The features of the macrosteps formation with the supersaturation increase are described in solutions of varying acidity. The effect of pH on the crystal habit is discussed.