PRE-FREEZING AND PRE-MELTING

When attempts are made to interpret the solid-liquid transition in terms of molecular structure, highly significant information can emerge from phemomena of pre-melting and pre-freezing. Empirically, on approaching the transition between solid and liquid, characteristic parameters of the phase under examination may show an accelerated rate of change, in the sense of a premonition of the change due to take place at the transition point itself. It is convenient to consider separately thermodynamic parameters such as the heat content, the volume, and derived quantities, and rate process parameters which have included critical shear strength and diffusion for the solid, and viscosity and other transport parameters for the melt. In certain cases many other methods have become available in recent years, especially in studying pre-melting. Depending on the nature of the crystal, thermodynamic phenomena of pre-melting may be very prominent, or almost imperceptible. Prominent examples with various crystal structures include heat content and volum