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Journal of Physical Chemistry B, Vol.101, No.35, 7027-7032, 1997
Heat of Fusion and Surface-Tension of Solids Confined in Porous Materials Derived from a Combined Use of NMR and Calorimetry
Assuming the heat of fusion (Delta h(f)) of a material confined in a porous material to be approximated by a function Delta h(f) = Delta h(0) (1 + a(0)(10(3)/T) + a(1)(10(3)/T)(2)), where T is the absolute temperature, a theoretical model is derived that enables the coefficients a(i) to be determined from a combined use of NMR and calorimetric measurements. The model has been applied on solid ice confined in cement pastes resulting in a(0) = -0.136 K and a(1) = -0.00413 K-2 in the temperature range 273 K > T > 210 K. Delta h(0) was determined from the known value of Delta h(f) of bulk water at 273 K, giving Delta h(0) = 749 J/g. Likewise, assuming the surface tension (gamma) of the ice-water interface to be approximated by a corresponding second-order polynomial in 1/T, i.e., gamma = gamma(0) (1 + b(0)(10(3)/T) + b(1)(10(3)/T)(2)), the coefficients b(i) were determined from the Gibbs-Thomson equation : Delta T = K-f(gamma/rho Delta h(f))(1/R), where K-f is a constant, rho the density, and Delta T the lowering of the melting point of ice confined in pores with radius R. The model fit revealed a best fit to a linear function in 1/T, with b(1) = 0 and b(0) = -(0.114 +/- 0.033) K. The gamma(0) was determined from the known value of gamma at 273 K, resulting in gamma(0) = 130 erg/cm.