Solidifying

Solidifying is the process by which a substance changes from a liquid to a solid, typically by cooling below its melting point. In materials science, solidification describes how a liquid becomes a solid through nucleation of the solid phase and subsequent growth of crystals. The resulting microstructure depends on cooling rate, composition, and thermal history.

Nucleation may be homogeneous, occurring spontaneously in the liquid, or heterogeneous, occurring at interfaces or impurities. Once nuclei form, atoms diffuse to the solid–liquid interface and arrange into a crystal lattice. Growth competes with continued nucleation; fast cooling can produce many nuclei leading to fine grains, while slow cooling yields coarse grains. If cooling is rapid enough to suppress crystallization, an amorphous solid (glass) can form instead of crystals.

Factors influencing solidification include temperature gradient, cooling rate, alloying elements, impurities, pressure, and the presence of interfaces. The latent heat of fusion must be removed during solidification, shaping the temperature history and process control. Solidification can produce distinct morphologies, such as columnar or equiaxed grains, and can be affected by alloying and inoculants in casting.

Contexts and applications: In metallurgy, solidification is central to casting, welding, and crystal growth. In polymers, crystallization from the melt similarly affects mechanical properties. In geology, solidification of silicate melts forms igneous rocks. Understanding solidification is essential for controlling microstructure and properties of materials.