CRYSTAL GROWTH LIMITATION IN AQUEOUS FOAM CRYSTALLIZATION

Abstract

We present results concerning the limitation of maximum crystal size by pre-foaming an aqueous supersaturated solution, followed by its crystallization. Foams are generated by adding specific surface active agents to the solution and by air injection under continuous high shear agitation, leading to a gas-liquid stable dispersion having polyhedral internal structures with thin separating liquid films. This spatial dispersion structuration, by locally reducing the amount of solute available for each crystal growth, permits the limitation of the resulting crystal sizes. It is shown that, under these conditions, the initial film thickness and mean bubble radius, obtained for a given volume fraction of gas in the foam, can control the final crystal size distribution. The foam expansion ratio thus appears to be a new operating parameter for crystal growth limitation when using a foam crystallization technique.