Correlation of Melting Results for Both Pure Substances and Impure Substances

Abstract

Melting experiments were performed encompassing both pure and impure substances. The pure substances included n-octadecane paraffin and n-eicosane paraffin, while the impure substances were mixtures synthesized from the pure paraffins. The experiments were carried out in a closed vertical tube whose wall was subjected to a step-change increase in temperature to initiate the melting. For each impure substance, supplementary measurements were made of two characteristic temperatures: the temperature T** at which melting of the solid phase first begins and the lowest temperature T* at which the melting can go to completion. For a pure substance, T** = T*. The time-dependent melting results for all the investigated substances, both pure and impure, were well correlated as a function of FoSte**(Gr**)1/8 alone, where the ** signifies the presence of T** in the temperature difference which appears in Ste and Gr. This correlation enables melting rates for impure substances to be determined from melting rates for pure substances. The T** values needed for the implementation of the correlation can be obtained from simple experiments, obviating the need for the complete equilibrium phase diagram.