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# Ternary Phase Diagrams

Phase diagrams have been constructed for the case of one component ( - diagrams for a pure material), and for two component systems ( - diagrams drawn at constant pressure). Each time a new component is added, another intensive variable must be held constant if the phase diagram is to be drawn in two-dimensions.

For ternary systems, there are three components. Let the three components be denoted by , , and . Because, , the system can be represented by two components, say , and , and the phase diagram could be represented in the following coordinate system:

Question: what is the maximum number of phases that can be in equilibrium at one point in Figure 31-1?

It may be possible to represent such a diagram in two dimensions by taking slices at constant composition, for instance:

Ternary phase diagrams are traditionally drawn at constant pressure and temperature--and the following scheme is used to represent all three components:

For example, a ternary phase diagram may look something like this:

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W. Craig Carter 2002-12-03