kristallisuuden

Kristallisuus, or crystallinity, is the extent to which a material shows a long-range, repeating arrangement of its atoms or molecules. Materials can be crystalline, semi-crystalline, or amorphous. In polymers, crystallinity is often described as a percentage of crystalline material. In Finnish, the concept is referred to as kristallisuus or kristallisuuden.

In crystalline regions, units are arranged in an orderly lattice; amorphous regions lack long-range order. A material may contain small crystallites, a single crystal, or crystalline domains within an amorphous matrix. Metals and ceramics commonly exhibit high crystallinity.

Measuring crystallinity uses several techniques. X-ray diffraction (XRD) is the primary method, identifying the presence and fraction of ordered regions. Differential scanning calorimetry (DSC) estimates crystallinity from the heat of fusion. Other approaches include Raman spectroscopy and solid-state NMR.

Crystallinity influences properties. Higher crystallinity generally raises stiffness, strength, density, and thermal resistance, while reducing impact toughness and sometimes increasing brittleness in polymers. It also affects optical transparency and barrier properties.

Control and processing: cooling rate, nucleating agents, annealing, and pressure alter crystallinity. In polymers, slower cooling and annealing tend to increase crystalline fraction; in metals, heat treatment shapes grain structure.

Applications and examples: semicrystalline polymers such as polyethylene and PET rely on crystallinity for mechanical performance and barrier properties; fully crystalline metals and ceramics gain strength and heat resistance; amorphous glasses lack crystallinity and are typically isotropic. Understanding kristallisuuden helps tailor material performance across plastics, metals, and ceramics.