Fusion

Fusion, change of a substance from the solid to the liquid state, usually by the application of heat. The process of fusion is the same as melting, but the term fusion is usually applied to substances such as metals that become liquid at high temperatures, and to crystalline solids. When a substance is at its melting or fusing temperature, additional heat is absorbed by the substance in changing its state without raising its temperature. This additional heat is known as the heat of fusion (see Freezing Point). The term fusion applies also to the process of heating a mixture of solids to give a single liquid solution, as in the formation of alloys.

For a discussion of nuclear fusion, see Atom; Nuclear Energy.