In situobservation of subcritical crystalline particles and their behavior on growth of KDP crystals from aqueous solution by light-scattering technique

Abstract

By the 90° laser light-scattering technique, it was possible to visualize ultrafine crystalline particles and to investigate their behavior in relation to the growth of KDP crystals in an aqueous solution. It was found that the scattered microparticles move randomly and exist inhomogeneously in the solution. The density of microparticles increases with increasing supersaturation. Whereas in the bulk solution, the movements of the particles are slow, as soon as they approach the crystal, they are rapidly sucked into the surface to within a certain distance, corresponding to the thickness of the diffusion boundary layer. On the growing surface, they move or shake themselves for a while, and eventually become invisible. The crystal growth rate increases proportionally with increasing the density of the microparticles and the supersaturation. The results suggest that they are subcritical crystalline particles which are formed in the KDP solution, and contribute to the crystallization of KDP from the aqueous solution.