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Ternary systems

According to the phase rule, a system with three independent components has F=5-P degrees of freedom. An invariant point in a ternary system thus contains 5 different phases in equilibrium with each other. An invariant point can for example consist of a vapor phase, a liquid phase, and three solid phases in equilibrium with each other. 

A ternary system with three phases (solid-liquid-vapor) in equilibrium with each other has two degrees of freedom. If the temperature is fixed, one degree of freedom remains. A phase diagram isotherm showing a ternary system with a vapor phase and a liquid phase requires therefore a line to mark the concentration range in which a solid phase is in equilibrium with the other two phases. A point is needed to mark concentrations where two solid phases are in equilibrium with liquid and vapor.

On these pages, phase diagrams for several ternary systems are shown. The phase diagrams were all calculated with the Extended UNIQUAC thermodynamic model. Choose the various systems from the menu in the left frame.