Ternary Phase Diagram with Phase Envelope

This Demonstration shows a ternary phase diagram, including the phase envelope. This diagram is used to represent the phase behavior of mixtures of three components that are only partially miscible over a range of compositions so that phase separation occurs. The black point represents the overall composition of the mixture, while each corner of the triangle corresponds to a pure component. The mass fraction of a component in the mixture is read off the axis that is the same color as that component in the standard view. A line is drawn through the point parallel to the base of the triangle that is opposite the corner corresponding to that pure component. In "view phases" mode, the single-phase region is light red, and the two-phase region (phase envelope) is light blue. In "view diagram" mode, gray tie lines are shown in the two-phase region when the "show tie lines" option is selected. The endpoints of each tie line correspond to the compositions of the two phases in equilibrium (

α

phase and

β

phase), and these compositions are shown when the "show

α

phase" and "show

β

phase" options are selected. The points along the left of the phase envelope boundary belong to the

α

phase, and the points along the right belong to the

β

phase. The point at which the

α

phase switches to

β

phase on the phase envelope is the plait point, which is found by following the tie lines up until a tie line is tangent to the phase envelope boundary. The point of intersection is the plait point. These diagrams could also be drawn with mole fractions instead of mass fractions.