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

For six monomineral, homoionic clayey soils, the temperature of spontaneous nucleation T-sn and the equilibrium freezing point T-f 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 T was calculated as the difference between T-f and T-sn. The obtained results testify the strong dependency of the equilibrium freezing point Tron 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 w(F), with an asymptote at w equal to the unfreezable water content w(nf). In contrary a scatter of results was observed for Tsn and W, 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 T,, as a function of the water content w, the plastic limit W-p 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 W-P, it was possible to calculate such a mass m(Psi=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 (w(p) = 1%) to 108 kg in an extremely cohesive soil (w(p) = 100%). (C) 2009 Elsevier B.V. All rights reserved.