Glossary of Terms for Phase Equilibria Diagrams
- Le Chatelier's Theorem
If a system in equilibrium is disturbed, a reaction tends to
take place which opposes the effect of the disturbance, i.e., one by which the effect is partially annulled. The theorem
of Le Chatelier is an important augment to the phase rule for it enables one to predict
qualitatively the effect of external changes on the equilibrium of a system.
Reference: Levin, E.M., McMurdie, H.F., and Hall, F.P., Phase Diagrams for
Ceramists: Volume 1, The American Ceramic Society, Columbus, Ohio, p. 7, 1956.
- Lever Rule (or Center of Gravity Principle)
When a particular composition separates into only two phases, the given composition and that
of the two phases are colinear; furthermore, the amounts of the two separated phases are inversely
proportional to their distances from the given composition.
Reference: Levin, E.M., McMurdie, H.F., and Hall, F.P., Phase Diagrams
for Ceramists: Volume 1, The American Ceramic Society, Columbus, Ohio, p. 7, 1956.
- Liquidus
The locus of temperature-composition points representing the maximum solubility (saturation) of
a solid phase in the liquid phase. In a binary system, it is a line; and in a ternary
system, it is a surface, usually curved. At temperatures above the liquidus, the system is completely
liquid, and a point on the liquidus represents equilibrium between liquid and, in general,
one crystalline phase (the primary one).
Reference: Levin, E.M., McMurdie, H.F., and Hall, F.P., Phase Diagrams
for Ceramists: Volume 1, The American Ceramic Society, Columbus, Ohio, p. 7, 1956.
Example of Liquidus
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