Studing thermodynamics of metastable states

Simple classical thermodynamic approach to the general description ofmetastable states is presented. It makes possible to calculate the explicitdependence of the Gibbs free energy on temperature, to calculate the heat capacity,the thermodynamic barrier, dividing metastable and more stable states, and thethermal expansion coefficient. Thermodynamic stability under mechanical loadingis considered. The influence of the heating (cooling) rate on the measured dynamicheat capacity is investigated. A phase shift of the temperature oscillations of an acheated sample is shown to be determined by the relaxation time of the relaxation ofthe metastable nonequilibrium state back to the metastable equilibrium one. Thisdependence allows one to calculate the relaxation time. A general description of themetastable phase equilibrium is proposed. Metastable states in AB3 alloys areconsidered. Reasons for the change from the diffusional mechanism of thesupercritical nucleus growth to the martensitic one as the heating rate increasesare discussed. The Ostwald stage rule is derived.