Crystallizations

Crystallizations encompass various processes by which crystals form, typically from solutions, melts, or vapors. The resulting solid exhibits a regular lattice that determines properties such as solubility, melting point, and mechanical behavior.

Crystallization occurs when a phase becomes supersaturated. Nucleation, which can be primary (new clusters forming) or secondary (initiated by existing crystals or seeds), marks the start of solid formation. After nucleation, crystal growth proceeds as molecules or ions add to the lattice. Ostwald ripening may occur when larger crystals grow at the expense of smaller ones through dissolution and re-precipitation.

Common types include solution crystallization, which can be driven by cooling, solvent evaporation, or the addition of an antisolvent. Melt crystallization happens as a molten material solidifies upon cooling. Gas-phase crystallization, such as in vapor deposition or sublimation, forms crystals from vapor or gas-phase reactions.

Factors shaping crystallization outcomes include solvent choice, temperature trajectory, level of supersaturation, impurities, agitation, and the presence of seeds or additives. These variables influence nucleation rate, crystal size distribution, and crystal habit.

Crystal quality is described by size distribution, morphology, purity, and polymorphism—the ability of a compound to exist in more than one crystal structure, which can affect properties like solubility. Hydrates and solvates may form under specific conditions. Seeding and controlled nucleation are common strategies to achieve desired crystal forms and sizes.

Applications span purification and isolation of chemical products, production of pharmaceuticals with defined crystal forms, and creation of materials with targeted optical or mechanical properties. Crystallization remains a central technique in both industrial synthesis and materials science, as well as in research into phase behavior and crystal engineering.