Editing Eutectic system (section)

===Peritectic===
[[File:Phasendiagramm Gold-Aluminium.svg|upright=1.25|thumb|Gold–aluminium [[phase diagram]]]]
Peritectic transformations are also similar to eutectic reactions. Here, a liquid and solid phase of fixed proportions react at a fixed temperature to yield a single solid phase. Since the solid product forms at the interface between the two reactants, it can form a diffusion barrier and generally causes such reactions to proceed much more slowly than eutectic or eutectoid transformations. Because of this, when a peritectic composition solidifies it does not show the [[lamellar structure]] that is found with eutectic solidification.

Such a transformation exists in the iron-carbon system, as seen near the upper-left corner of the figure.  It resembles an inverted eutectic, with the δ phase combining with the liquid to produce pure [[austenite]] at {{convert|1495|C|abbr=on}} and 0.17% carbon.

At the peritectic decomposition temperature the compound, rather than melting, decomposes into another solid compound and a liquid. The proportion of each is determined by the [[lever rule]]. In the [[Gold-aluminium intermetallic|Al-Au]] phase diagram, for example, it can be seen that only two of the phases melt congruently, [[Gold-aluminium intermetallic|AuAl<sub>2</sub>]] and [[Gold-aluminium intermetallic|Au<sub>2</sub>Al]], while the rest peritectically decompose.