Glossary of Terms for Phase Equilibria Diagrams

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

Incongruent Melting Point
Indifferent Point
Invariant Point
Inversion Point
Isobar
Isofract
Isopleth
Isoplethal Study
Isotherm
Isothermal Study

  • Incongruent Melting Point
    At a specified pressure the temperature at which one solid phase transforms into another solid phase plus a liquid phase both of different chemical compositions than the original substance.

    Reference: Levin, E.M., McMurdie, H.F., and Hall, F.P., Phase Diagrams for Ceramists: Volume 1, The American Ceramic Society, Columbus, Ohio, p. 6, 1956.

    Example of Incongruent Melting Point

    Example of Incongruent Melting Point



  • Indifferent Point
    In a two or more component system the special conditions where two phases become identical in composition and the system loses one degree of freedom. Typical cases include the maximum or minimum in a solid solution series and the melting point of a congruently melting compound.

    Reference: Levin, E.M., McMurdie, H.F., and Hall, F.P., Phase Diagrams for Ceramists: Volume 1, The American Ceramic Society, Columbus, Ohio, p. 6, 1956.

    Example of Indifferent Point

    Example of Indifferent Point



  • Invariant Point
    The particular conditions within a system, in terms of pressure, temperature, and composition, for which the system possesses no degrees of freedom constitute the invariant points. Stated differently, at an invariant point, no independent changes in the state of the system can be made.

    Reference: Levin, E.M., McMurdie, H.F., and Hall, F.P., Phase Diagrams for Ceramists: Volume 1, The American Ceramic Society, Columbus, Ohio, p. 6, 1956.

    Examples of Invariant Points

    Examples of Invariant Points



  • Inversion Point
    The temperature at which one polymorphic form of a substance changes into another under invariant conditions.

    Reference: Levin, E.M., McMurdie, H.F., and Hall, F.P., Phase Diagrams for Ceramists: Volume 1, The American Ceramic Society, Columbus, Ohio, p. 6, 1956.

    Examples of Inversion Points

    Examples of Inversion Points



  • Isobar
    The locus of all points of constant pressure.

    Reference: Levin, E.M., McMurdie, H.F., and Hall, F.P., Phase Diagrams for Ceramists: Volume 1, The American Ceramic Society, Columbus, Ohio, p. 6, 1956.

    Example of Isobar

    Example of Isobar



  • Isofract
    For compositions within a ternary system the locus of all glasses of constant index of refraction.

    Reference: Levin, E.M., McMurdie, H.F., and Hall, F.P., Phase Diagrams for Ceramists: Volume 1, The American Ceramic Society, Columbus, Ohio, p. 6, 1956.



  • Isopleth
    A line in a phase diagram of constant 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.

    Examples of Isopleths

    Examples of Isopleths



  • Isoplethal Study
    The method of considering the changes occurring in a system in which the composition variable is held constant and the temperature varied.

    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.

    Examples of Isoplethal Studies

    Examples of Isoplethal Studies



  • Isotherm
    In a ternary system the locus of all points on the liquidus of constant temperature.

    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.

    Examples of Isotherms

    Examples of Isotherms



  • Isothermal Study
    The method of considering the changes occurring in a system in which the temperature variable is held constant and the composition (or pressure) is varied.

    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.

    Examples of Isothermal Studies

    Examples of Isothermal Studies






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