Two Component Systems

TWO COMPONENT SYSTEMS

1. Reduced phase rule (or) Condensed system

The maximum number of degree of freedom in a two component system will be three, when the system exists as a single phase.

F = C - P + 2; F = 2 - 1 +  2; F = 3

In order to represent the conditions of equilibrium graphically, it requires three co-ordinates, namely P,T and C. This requires three dimensional diagram, which cannot be conveniently represented on paper. Therefore, any two of the three variables must be chosen for graphical representation.

A solid-liquid equilibrium of an alloy has practically no gaseous phase and the effect of pressure is negligible. Therefore, experiments are conducted under atmospheric pressure. Thus the system in which only the solid and liquid phases are considered and the gas phase is ignored is called a condensed system. Since the pressure is kept constant, the phase rule becomes

F' = C – P + 1

This equation is called reduced phase rule or condensed phase rule.