A miscibility gap is a region in a
phase diagram for a
mixture
In chemistry, a mixture is a material made up of two or more different chemical substances which can be separated by physical method. It is an impure substance made up of 2 or more elements or compounds mechanically mixed together in any proporti ...
of components where the mixture exists as two or more
phases – any region of composition of mixtures where the constituents are not completely miscible.
The
IUPAC Gold Book defines ''miscibility gap'' as "Area within the coexistence curve of an isobaric phase diagram (temperature vs composition) or an isothermal phase diagram (pressure vs composition)."
A miscibility gap between isostructural phases may be described as the ''
solvus'', a term also used to describe the boundary on a phase diagram between a miscibility gap and other phases.
Thermodynamically, miscibility gaps indicate a maximum (''e.g.'' of
Gibbs energy) in the composition range.
The miscibility gap condition is a candidate for
thermal storage.
Named miscibility gaps
A number of miscibility gaps in phase systems are named, including
* The ''huttenlocher'' (found in
bytownite, anorthite composition An55-95.), ''boggild'' (in
labradorite, An39-48 and An53-63.) and peristerite (in
oligoclase, ~An5-15.) miscibility gaps in the
plagioclase feldspars.
* A ''Nishwawa horn'', term for a miscibility gap existing when phases with different magnetic properties co-exist in the phase diagram.
* Miscibility gaps in liquid states can cause
spinodal decomposition, commonly referred to as ''oiling out'', as commonly occurs in oil/water mixtures.
See also
*
Miscibility
*
Solid solution
*
Incongruent melting
References
{{Authority control
Materials science
Phase transitions
Geochemistry