lämpölaajenemiskertoimen

Thermal expansion is the tendency of matter to change its size or volume in response to a change in temperature. In Finnish, the phenomenon is called lämpölaajeneminen. It affects solids, liquids, and gases and has practical implications for engineering, construction, and everyday objects.

Expansion is described by coefficients of thermal expansion. For solids, the linear coefficient α measures relative change in length: ΔL = αL0ΔT. The volumetric coefficient β describes changes in volume: ΔV = βV0ΔT, with β approximately equal to 3α for isotropic materials.

Different states behave differently. Gases show large expansions with temperature and pressure changes following the ideal gas law. Liquids expand with temperature, though some exhibit anomalous behavior near phase transitions; water expands upon cooling below 4°C, causing ice to be less dense than liquid water. Solids expand more modestly, with material-specific α values and possible anisotropy in crystals.

Applications and implications: thermal expansion influences tolerances in mechanical assemblies, bridges, rails, and electronics. Devices such as bimetallic strips and thermostats exploit differential expansion. Improperly accounted expansion can cause warping, cracking, or joint failure, so engineers select materials with compatible CTEs and incorporate expansion joints, slack, or flexible couplings.

Measurement and values: common solids have α ranging from about 5×10^-6/°C to over 25×10^-6/°C; steel around 11–13×10^-6/°C, aluminum about 23×10^-6/°C, copper about 16.5×10^-6/°C, some glasses and polymers vary widely. Techniques include dilatometry and interferometry. Temperature gradients can create internal stresses if parts are restrained.