Ternary Phase Diagrams - General Rules
- A congruently melting compound will lie within the primary phase field for that compound.
- An incongruently melting compound will not lie in the field of that compound.
- Ternary diagrams which do not exhibit solid solution effects will contain at least one ternary eutectic, i.e. the lowest temperature at which liquid can exist.
- In systems with no solid solution conjugation lines or Alkemade lines within such systems are thermal barriers.
- Ternary systems which contain an incongruently melting compound will contain at least one ternary peritectic.
- Ternary systems which exhibit complete solid solution effects will not contain a ternary eutectic within the triangular area representing the system.
- For any ternary diagram identify all Alkemade lines. For every boundary curve there exists an Alkemade line.
- Consider the relation between a boundary curve and its pertinent Alkemade line;
- i) The actual or projected intersections between boundary curve and its pertinent Alkemade line represents a temperature maximum of the boundary curve.
- ii) If tangents drawn from the boundary curve intersect the pertinent Alkemade line, then that part of the boundary curve is a subtraction curve.
- iii) If tangents drawn from the boundary curve intersect an extension of the pertinent Alkemade line, then that part of the boundary curve is a reaction curve.
- After the thermal slopes, i.e. the direction of falling temperature, of the boundary curves are determined, the various ternary invariant points can be identified as either eutectic, tributary or distributary reaction points.
Subtraction Curve - That part of the boundary curve along which crystalline material precipitates from the liquid.
Reaction Curve - That part of the boundary curve along which crystalline materials both precipitate and dissolve.