Glossary of Terms for Phase Equilibria Diagrams
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
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