In engineering materials, a crystal is usually referred to as a grain. The crystals increase in size by the progressive addition of atoms and grow until they impinge upon adjacent growing crystal.Ī) Nucleation of crystals, b) crystal growth, c) irregular grains form as crystals grow together, d) grain boundaries as seen in a microscope. The final sizes of the individual crystals depend on the number of nucleation points. At the solidification temperature, atoms of a liquid, such as melted metal, begin to bond together at the nucleation points and start to form crystals. The moment a crystal begins to grow is know as nucleation and the point where it occurs is the nucleation point. Normally when a material begins to solidify, multiple crystals begin to grow in the liquid and a polycrystalline (more than one crystal) solid forms. The expense of producing single crystal materials is only justified for special applications, such as turbine engine blades, solar cells, and piezoelectric materials. In engineering materials, single crystals are produced only under carefully controlled conditions.
The crystallization of a large amount of material from a single point of nucleation results in a single crystal.
