https://doi.org/10.1351/goldbook.15324
Isobaric, reversible melting or dissolution with either complete or partial dissociation on heating of a solid compound, \(\ce{A_{\rm{a}}B_{\rm{b}}}\), formed by components \(\ce{A}\) and \(\ce{B}\) \[\ce{A_{\rm{a}}B_{\rm{b}}(s) <=> A_{\rm{a}}B_{\rm{b}}(l) <=> {\rm{a}}A(l) + {\rm{b}}B(l)}\] where the forward arrows indicate the direction of heating.
Notes:
- The dystectic temperature is a maximum (\({\rm{d}}T/{\rm{d}}x = 0\)) of the melting temperature-composition curve. The dystectic point is the isobarically invariant maximum at the dystectic composition and dystectic temperature, where the compositions of the liquid and solid phases are equal. The composition of a non-stoichiometric compound is also equal to that of the melt at the dystectic temperature and composition.
- From Greek δύστηκτος, difficult (or highest) melting.
- Occasionally, a similar reaction takes place in the subsolidus region. Quite appropriately, it is called a dystectoid reaction.
Examples: Systems \(\ce{SO3 + H2O}\), \(\ce{Mg + Sn}\)