A New Technique for following Rapid Rates of Crystallization

Abstract

TECHNIQUES for measuring rates of crystallization have been the subject of recent reviews^1,2. Most of the methods described are not applicable to fast rates. A microscope-ciné camera technique³ can be used when the species crystallizes in visibly discernible forms; but interpretation of results is sometimes complicated by impingement of boundaries between the crystalline entities. A method independent of the texture of the crystallizing species but requiring birefringence in the crystallized specimen has been developed in these laboratories. This consists, essentially, of following the increase in depolarization of plane-polarized light by the crystallizing specimen. Birefringence and crystallinity do not occur concurrently under all conditions of crystallization⁴, but it is believed that when crystallization takes place from a melt under no external stress, measurement of rate of depolarization of light by the crystallizing sample parallels the development of crystallinity.