Crystallization Path Analysis in Ternary Phase Diagrams

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Crystallization Path AnalysisinTernary Phase
Diagrams
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• First, identify the compounds
• on the diagram.

• And their corresponding
• primary crystallization fields.

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• Then connect compounds,
• whose primary crystallization
• fields share a boundary, with
• Alkemade lines.

• The Alkemade lines form
• compatibility triangles.

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• Remember that where Alkemade lines
• cross boundary lines the boundary
• lines are at a local maximum and
• the Alkemade lines are at a local
• minimum in temperature.

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• Now we are ready to trace the
• cooling path of a simple random
• composition.

• First add a composition to the
• diagram.

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• Next determine its primary
• crystallization field.

b

• Compatibility triangle

AC B C

• And final liquid composition
• The final liquid composition is the
• ternary invariant point where all
• three compounds in the compatibility
• triangle meet.

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• Now draw a tie line from the
• primary phase B through the
• point to the boundary with ac.

• The crystallization path begins
• at the point and moves away
• from the the primary phase as B
• begins to crystallize out of the
• composition.

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• Now AC begins to crystallize
• out as the path follows the
• boundary line to its ternary
• invariant point.

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• At the ternary invariant
• point all of the remaining
• liquid crystallizes.

• The path is complete.

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Summary
First, get a feel for the diagram identifying its
compounds, crystallization fields, Alkemade
lines, compatibility triangles, as well as its
highs and lows.
Second, after selecting a composition identify
the PCF, compatibility triangle, and its final
liquid composition, or ternary invariant point.
Finally, keep in mind what is crystallizing out
at each part of the diagram.
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The End