The Dissection of Phase Volumes in Ternary Phase Diagrams

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The Dissection of Phase Volumes in Ternary Phase
Diagrams
By Roger Smith
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Complete Diagram
Here is a theoretical, 3 component phase diagram
in three dimensions.
Temperature
A
C
By stripping away the color and adding hidden
lines, we can see the entire diagram.
The region above the curved surfaces is the
liquid region, containing only homogeneous three
component liquid.
B
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Solid Section Removed
We begin our dissection by first removing
everything below the eutectic or sub-solodus
surface of the diagram.
This portion contains only crystalline phases
composed of crystals of A, B, and C.
A
C
B
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1 Comp Sections Removed
Next we remove the primary crystallization
volumes.
A
C
Each of these three volumes contains its end
member plus a homogeneous three component liquid.
(i.e. A Liquid)
B
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2 Comp Sections Removed
Now we separate the secondary crystallization
volumes.
Each of these volumes contain the two end
members touching the volume and a homogeneous
three component liquid. (i.e. A B Liq)
A
C
A
C
B
B
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Isopleth Intro
Let us examine an isoplethal analysis where we
shall choose a specific composition and cool it
from a liquid to a solid.
A
C
B
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Isopleth Analysis
We begin with a simple theoretical ternary
diagram.
Now we determine our composition, which has been
indicated by the red line passing through the
diagram.
We begin at a very high temperature, where we
have a pure homogeneous liquid.
As we cool past the liquidus surface, we begin to
precipitate out solid. In this region, we find a
combination of solid A and liquid.
As we continue to cool, we begin to precipitate
out two solids. Now we have solids A and C plus
liquid.
Finally, once we cool past the sub-solidus
surface, we have a pure crystalline solid
consisting of our original composition.
A
A
C
A
C
B
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Summary

• Primary Crystallization volumes contain a single
  phase solid and a homogeneous three component
  liquid.
• Secondary Crystallization volumes contain two
  single phase solids and a homogeneous three
  component liquid.
• Below the eutectic temperature are only three
  component solids.

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The End