TERMS USED IN EQUILIBRIUM DIAGRAMS

The following terms are frequently used in the study of solid phases and phase diagrams:

 i. Alloy

 ii. System

 iii. Components

 iv. Phase

 v. Phase diagram

 vi. Phase Equilibrium

 vii. Phase Transformation

 viii. Structural constituents

 ix. GIBB’S PHASE RULE OR THE PHASE RULE OR CONDENSED PHASE RULE 

Components

          These are the substances, either chemical elements or chemical compounds, whose presence is essential and sufficient to make a system. A system consist of one or more components, A pure metal is called a one-component system, an alloy of two metals is called a binary or two component system, etc.,

Phase

          It is a homogeneous portion of a system that has uniform physical and chemical characteristics. The number of phases in a system is the number of different substances that exist in it in a homogeneous system. A homogeneous liquid solution is a single-phase system; a mixture of crystals of two types, differing in composition and structure separated by an interface, or the coexistence of the liquid alloy and its crystals comprise two-phase system.

Phase diagram

          A graphical representation of the relationship between environmental constraints (e.g. temperature and sometimes pressure), composition, and region of phase stability, ordinarily under conditions of equilibrium.

          Most phase diagrams are prepared by using slow cooling conditions whereby phases are in equilibrium. One can get following important information's from the phase diagrams

• Phases at different composition and temperature
• Equilibrium solubility of one element or compound in another element
• Melting points of different phases in an alloy
• Temperature of solidification or range of solidification of an alloy.