Glossary of Terms for Phase Equilibria Diagrams

A B C D E G H I J L M P S T V

Le Chatelier's Theorem
Lever Rule (or Center of Gravity Principle)
Liquidus

  • 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

    Example of Liquidus






Privacy Statement/Security Notice
Disclaimer | FOIA

NIST is an agency of the
U.S. Commerce Department

Date created: 08 February 2001
Last updated: 01 July 2008


Technical inquiries:
Ceramics Division
NIST, 100 Bureau Drive, Stop 8520, Gaithersburg, MD 20899-8520.
Phone (301) 975-6119
Fax (301) 975-5334

Ceramics website comments:
Ceramics Webmaster

General NIST inquiries:
Public Inquiries Unit:
Phone (301) 975-NIST (6478)
TTY (301) 975-8295