Gas-Solid Phase Equilibrium, Sublimation

Sublimation is the direct phase change of a substance from the solid into the gas state. Desublimation is the reverse process. 

In thermal separation processes sublimation is of practical interest in freeze or sublimation drying. Heat transfer into the system causes moisture to sublime directly from the frozen solid into the vapor phase (see Chapter 5.10). Desublimation is important for the separation of gas mixtures if components of the mixture change directly from the gas into the solid state when heat is removed, these components can be sepa- 

The gas-solid phase equilibrium at sublimation or desublimation is described by the generaUzed Clausius-Clapeyron equation, see Eq. (1.71) and Fig. 1-32 

If steam at a constant pressure is cooled below the triple point, a solid is often not crystallized immediately after passing the sublimation pressure line. Crystallization 

This phenomenon is similar to the supersolubility of a solid dissolving in a solvent (see Chapter 1.4.5). 

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