Present-day understanding of crystal growth from aqueous solutions

Abstract

Recent results on the kinetics of crystal growth from aqueous solutions are reviewed, with the emphasis placed on the KDP group of crystals. Elementary parameters of spiral growth are discussed. Nonlinear dependences of step velocity on supersaturation, incompatible with the Burton-Cabrera-Frank theory, are analysed, and a new more general theory is presented. Morphological stability of stepped vicinal faces is considered, with due account of the influence of solution hydrodynamics and impurities. New experiments are described, in which reproducible growth of the ADP dipyramidal face by two-dimensional (2D) nucleation is found. Effective step energy is deduced. At low supersaturations the preferential 2D nucleation is demonstrated to occur on active sites, whereas at high supersaturations the 2D nucleation seems to be homogeneous. Secondary nucleation in aqueous solutions is analysed. New experiments demonstrating a direct correlation between secondary nucleation and basic crystal cracking are described and discussed. Therefore, the achievement of high supersaturations and thus high growth rates is closely related to high crystal perfection, and vice versa. Selected achievements in biological crystallization, primarily in nucleation and growth of protein, viruses and other crystals built up of large molecules or colloidal particles, are briefly discussed.