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This Demonstration shows a
ternary phase diagram with a 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, which can be moved to any location within
the triangle by clicking on that location, represents the overall
composition of the mixture. 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. These axes are labeled by drawing a line through the point; this
line is parallel to the base of the triangle that is opposite the corner corresponding
to that pure component. View phases mode identifies the
one-phase region and the two-phase region (phase
envelope). 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 and ß phases), and these
compositions are shown when the show α phase and show ß phase
options are selected. Points along the left of the phase envelope
boundary belong to the α phase, and the points along the right belong
to the ß phase. The point at which the a phase switches to ß 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.

These simulations require the Mathematica CDF player,
available for free from the Wolfram website.
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