A phase diagram is drawn for a mixture of two substances at a fixed pressure p with one liquid phase and two solid phases (Fig. 6.19). The substances are labelled 1 and 2 and the diagram is shown as a function of the concentration c₁ of substance 1. This diagram presents what is called a eutectic point. At the eutectic concentration c^E₁, the freezing temperature is the lowest. In particular, it is lower than the freezing temperatures of the pure substances (points C and D). At the eutectic, the liquid freezes into a mixture of two solid phases, the α and β phases.

In Figure 6.19

a) Consider a liquid at concentration c^A₁. As the temperature is lowered, the point A is reached. Describe qualitatively what happens then.b) Describe what happens if a liquid of composition c^E₁ is cooled.

Transcribed Image Text:

T C Solid phase 3 0 Liquid BL E A c₁ B Solid phase a 1 B 1 1 1 1 I T 1 1 I I 1 D C1