THERMODYNAMIC-EQUILIBRIUM BETWEEN ICE AND WATER IN POROUS-MEDIA

A derivation is given for the equation of thermodynamic equilibrium between ice and water in porous media. The equation accounts for a difference between the pressure of the ice phase and the total potential (in pressure units) of the water phase. Emphasis is laid on the distinction between the total potential and the hydrostatic pressure and osmotic pressure of the unfrozen soil solution. The difference between the hydrostatic pressure of the solution and the ice pressure is accounted for by the ice-water interfacial tension, as expressed by the generalized form of Laplace’s equation. The resulting generalized form of the Clausius-Clapeyron equation is an equilibrium expression, whereas the Laplace equation only expresses a definition, valid under any circumstances. It is emphasized that all influences of the pore wall, which may or may not work via the diffuse double layer, and which cause the liquid to have lower Gibbs free energy than the equilibrium liquid at the same temperature, are collected in the osmotic pressure term. © 1978 The Williams & Wilkins Co.