Crystals, crystal growth, and nucleation

Publisher Summary This chapter discusses the basics of crystals and their structure. Crystals are solids in which the atoms are arranged in a periodic repeating pattern that extends in three dimensions. While all crystals are solids, not all solids are crystals. Crystals are characterized by the lattice parameters. Another property of each crystal system that distinguishes one system from another is called symmetry. In the simplest actual crystal, the atoms coincide with the points of one of the Bravais lattices. In a more complex arrangement, more than one atom of the same type can be associated with each lattice point. However, a given chemical species can have more than one possible crystal structure. The phenomenon of a chemical species that have more than one possible crystal form is known as polymorphism. The crystals also show isomorphism characteristics. Crystallization from solution can be thought of as a two-step process. The first step is the phase separation or “birth” of new crystals. The second step is the growth of these crystals to larger sizes. These two processes are known as nucleation and crystal growth, respectively. Analysis of industrial crystallization processes requires knowledge of both nucleation and crystal growth.