9. Quasi-binary sections of ternary diagrams

9.1 Quasi-binary plan

Some isopleth sections of ternary systems contain the equilibrium conodes between the phases in this plane. They therefore enjoy the properties of binary systems, even if some of the phases in equilibrium are ternary. These isopleths are called quasi-binary or pseudo-binary sections. Often, they join one vertex of the composition triangle to a highly stable (congruent melting) binary compound on the opposite side. They can also join two congruently fused binary or ternary compounds. In the (Al, Mg, Si) system [M 76,1]-13 to [M 76,1]-14. The compound Mg ₂ Si plays the role of a true pure body, and the isopleth cut joining Al to Mg ₂ Si separates the ternary diagram into two...