Composition of a Ternary Compound

Three-Component (Ternary) Phase Diagrams 3.1.4.1 Composition of a Ternary Compound 

The lengths of the normals are proportional to the percentages of the component designated at the opposite end. 

Occasionally, it is required to express the composition of a ternary phase X in terms of the components, located at the apices, and a binary phase, located on a side of the triangle. Then point X might be expressed in term of A, C, and D (binary phase B3C2) on the line (compatibiHty join, conode) AD. This construction yields A = DF-IOO/AD = 20%, D = AE-IOO/AD = 34.5%, and C = EF-100/ 

2 Phase Boundary Lines, Eutectic Points, and D ees of Freedom 

According to Gibbs condensed phase rule, at the ternary eutectic points four phases coexist (G = 3, P = 4, F = 0) three solid phases and one Hquid melt phase. For example, at the ternary eutecHc point Ei the two ternary phases X and Z, the binary phase A2C, and the melt (not shown in projection) coexist. By definition, this point is invariant (F = 0) to changes in temperature and/or composition, as each departure from its values will displace the system from point Ej. A composition anywhere along a phase boundary Hnes is subject to a univariant equUibrium (F = 1), since it is possible to alter either the temperature or the concentration of one of the two components without leaving the boundary line between two 

---