Crystallization behavior of high purity o-terphenyl

The crystallization behavior of high purity o-terphenyl has been investigated over a range of undercooling up to 70 °C. The material was prepared by multiple pass zone refining (153 passes). The growth rate reaches a maximum in the range of 10^-3 cm sec^-1 at an undercooling of about 20 °C, and decreases to about 10^-7 cm sec^-1 at the lowest temperature of study. The reduced growth rate versus undercooling relation has been constructed, and indicates an interface site factor which increases continuously with increasing undercooling. The logarithm of (growth rate × viscosity) does not decrease linearly with increasing 1/TΔT. The variation of the growth rate with temperature cannot be described in satisfactory detail by the standard theoretical models for surface nucleation growth, but exhibits a form predicted by recent computer simulations of crystal growth. The high purity of the present material, combined with the similar logarithm of (growth rate × viscosity) versus 1/TΔT curves observed with other materials, suggest that such relations are characteristic of the crystallization process. In all materials investigated, the increase of the interface site factors with increasing undercooling as well as the faceted interface morphologies are in agreement with the predictions of Jackson for materials characterized by large entropies of fusion.