Some factors affecting supercooling and the equilibrium freezing point in soil–water systems

For six monomineral, homoionic clayey soils, the temperature of spontaneous nucleation Tsn and the equilibrium freezing point Tf were determined by use of the Differential Scanning Calorimetry (DSC) technique. The temperature of spontaneous nucleation Tsn was determined on the cooling run, as the initial temperature of the observed exothermic peak. The temperature of equilibrium freezing (or melting) Tf was interpreted as the initial temperature of the last non-zero thermal impulse in the diagram of real thermal impulses distribution q(T) obtained on warming. The supercooling Ψ was calculated as the difference between Tf and Tsn. The obtained results testify the strong dependency of the equilibrium freezing point Tf on the water content w. It has been proved that Tf can be expressed as a power function of the water content w and the plasticity limit wP, with an asymptote at w equal to the unfreezable water content wnf. In contrary, a scatter of results was observed for Tsn and Ψ, which could be related to the effect of factors other than the water content. The best fitted model expresses the temperature of non-equilibrium freezing Tsn as a function of the water content w, the plastic limit wP and an extensive parameter of the sample, i.e. its mass m, the effect of which proved fully statistically significant. The results give evidence of the strong effect of both soil plasticity and the sample mass on the temperature of spontaneous nucleation and the supercooling. By use of auxiliary empirical function, relating the unfreezable water content wnf to the plastic limit wP, it was possible to calculate such a mass mΨ = 0 of a soil sample, for which the supercooling equals zero. At high water contents the predicted supercooling tends to zero for very large sample masses, from about 105 kg in a practically uncohesive soil (wP = 1%) to 108 kg in an extremely cohesive soil (wP = 100%).