By a generic application of the thermodynamics of irreversible processes and de Donder's notion of frozen-in structural parametersξthe course of the thermodynamics functions of a melt upon vitrification and in the glass→melt transition is constructed using a simple geometric approach. The temperature of vitrification, T_g, at a given cooling rate is defined by the inflection point of the (dξ/dT) curve, i.e. by the nullification of the (d~3ξ/dT~3) derivative. Thermodynamically this implies for the configurational specific heats [d~2ΔCp(T)/dT~2]_(Tg) = 0. The analysis demonstrates the existence of a temperature region between (T_g +Δ~*/2) and (T_g -Δ~*/2) where a substantial difference in the thermodynamic potentialΔG(T) upon cooling and heating runs is to be expected. Upon the approximation (Δ~*/2)→0 the conventional geometry of vitrification thermodynamics is obtained as a particular case. From the approach employed the basic kinetic dependencies of vitrification also follow.
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