Basic aspects of phase changes under high pressure.

Some substances of technological importance reveal phase change phenomena in the pressure and temperature range typically applied in biotechnology and food processing. For example, media with high molar volumes like edible oils and fats undergo liquid-solid phase transition at pressure increases up to several hundred megapascals. This article is concerned with theoretical considerations of the line of coexistence of solid and liquid phases in the pressure and temperature domain that corresponds to the phase boundary as a function of temperature and pressure. A universal model equation based on the equilibrium thermodynamics allowing prediction of the phase transition line of homogeneous media with high molar volume is presented. Approximate solutions of the model equation are discussed, which allow the phase boundary of substances with high molar volume to be described by a linear relation at least sequentially. The methods of experimental determination of the phase boundary under high pressure are presented and an attempt is made to validate the theoretical model with respect to the experimental data.