Ripening of faceted ice crystals

Ripening of an ensemble of progressively faceting ice crystals in aqueous f ructose solution is studied by characterising the change in average crystal size, number density, and size distribution with time, as well as tracking individual crystals, so as to follow the evolution of crystal anisotropy w ith time. The results are compared to theoretical models developed for an e nsemble of spherical crystals, which consider the ripening process to be li mited by either: (i) diffusion processes, or (ii) reaction kinetics at the crystal-fluid interface. It is found that the results obtained conform neit her with true diffusion, nor reaction-controlled, ripening. It is suggested that the system appears to be approaching "near" diffusion control at long times, but that initially when the crystals are sufficiently small, there may be a period where growth; onto the prism plane is limited by reaction k inetics. The growths of the prism and basal planes of ice crystals in the e nsemble are found to display marked anisotropy, presumably as a result of t he relative roughening transitions of these planes. However, since the pris m plane appears to facet while the crystals are still comparatively small, it is suggested that the crystals are able to grow towards their Wulff shap e, which is thought to be a hexagonal column at -19 degreesC. (C) 2001 Publ ished by Elsevier Science B.V.