Which equation represents a peritectic reaction? Write it in the direction of cooling.

Answer: C. L + α → β

A peritectic reaction is one in which, on cooling, the liquid L reacts with a previously formed solid α to produce a different solid β: L + α → β. The name comes from the new β phase forming around the α grains as if wrapping them. In the Fe-C system δ + L → γ occurs at about 1495 °C, and peritectics are common in the Cu-Zn and Cu-Sn systems. L → α + β is the eutectic reaction, in which two solids form simultaneously from the liquid, and γ → α + β is the eutectoid reaction, in which two solids form from a solid (such as γ → α + Fe₃C in the Fe-C system). In a peritectic reaction, the β product coats the α and hinders diffusion, so in real solidification the reaction does not go to completion and α tends to remain.