Experimental Studies of the Crystallization of Supercooled Water

Abstract

The crystal fabric of ice formed by the freezing of supercooled water was examined in polarized light. Drops of radius 0.1 cm were frozen by homogeneous nucleation at ?33C, by various foreign particles in suspension, or by impaction on a plane single crystal ice substrate. Bulk water, volume about 1.0 cm3, was frozen by the insertion of a single crystal of ice. Between 0 and ?5C crystals invariably grew with a single orientation, identical with the nucleating crystal. With decrease of temperature increasing numbers of crystals with new orientations appeared, there being several hundred per drop when nucleation took place at ?33C. Drops impacting on a substrate with vertical ?c? axis froze with horizontal ?c? axis in the temperature interval ?5 to ?15C. When the substrate was heated to 0C, drops always took the substrate orientation, even when supercooled to ?22C. Measurements of the growth rate component parallel to the basal plane of dendrites growing in water at supercooling (?T) down to 20C followed the relation: U=0.08?T1.9 cm sec ?1. Dendrite arm width and spacing decreased with increase of supercooling, both following the relation 10?2/?T cm. Below ?8C the envelope of dendrite tips in the basal plane became hexagonal and by ?16C growth rate perpendicular to the basal plane became comparable with that parallel to the basal plane. Results are interpreted in terms of different kinetic processes on different crystal faces.