Question

Using phase diagrams and free energy curves explain what a metasable phase diagram is, and the concept of t0.

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Answer 1

Metastable state is the intermediate state between stable and unstable states of a material. The system may remain in this state forever if no external energy is provided to it, but if it is done so, it may go to most least energy state, i.e. the stable state.

Phase stability is generally represented by phase diagrams using temperature and composition factors. Metastable phase diagrams consider those phases which are not permitted by thermodynamics laws. If experimental data is available for a system, phase diagram can be obtained. I show you below, one example of metastable phase diagram.

T₀ curve is the locus of temperatures and compositions where free energies of two phases are equal. A curve between liquid and solid phase determines least undercooling condition of the liquid for partitionless formation of solid with same composition.