4. Solidus and liquidus surfaces of ternary systems

4.1 Total miscibility in liquid and solid phases

If the constituents are fully miscible in both solid and liquid phases, they form binary diagrams with either a single solidification spindle, or a double spindle with a congruence point at a temperature extremum. The resulting ternary diagrams are generally of the same type. If no binary has a congruent melting composition, the same is generally true in ternary diagrams. If all binaries show a congruence point, the ternary diagram also has a ternary congruent melting composition distinct from the three binary congruent compositions. Ternary congruence is also conceivable in systems with a single or even two binary congruences. We won't go into detail here.