THE PHASE RULE AND THE PHASE-DIAGRAM

The disappearance of a component at a point in the phase diagram or the loss of a degree of freedom makes it unique in its relation to the Phase Rule. Once it is realized that there are unique points in the phase diagram, it is no longer necessary to divide it in order to clarify the application of the Phase Rule. In a hypothetical binary system where a critical phase appears directly below the congruent melting point, the same alloy may be regarded as having alternatively two components and a single component as the temperature is increased from low values to beyond the melting point.