Fasetilstand

Fasetilstand, or phase state, refers to the physical state of a material under given thermodynamic conditions such as temperature, pressure and composition. It encompasses the traditional states solid, liquid and gas, as well as more complex condensed states like plasma, amorphous solids, crystalline polymorphs and supercritical fluids. The fasetilstand of a substance is determined by thermodynamic stability: under specific conditions the phase with the lowest Gibbs free energy is the stable state, while other phases may persist as metastable forms.

Phase diagrams are the primary tool for understanding fasetilstander. They map which phase is stable at different temperatures and pressures for a given composition. Points where two phases coexist in equilibrium are called phase boundaries; a triple point marks the temperature and pressure where three phases meet. Substances can exhibit polymorphism, where the same chemical composition forms multiple solid structures with distinct properties. Common examples include water’s ice and liquid phases, and carbon’s various graphite and diamond forms under different conditions.

Phase transitions describe how fasetilstand changes. First-order transitions involve a discontinuous change in properties such as density and enthalpy and typically absorb or release latent heat. Second-order or continuous transitions change properties gradually without latent heat. Metastable fasetilstander can exist when a material remains in a non-equilibrium phase, such as supercooled liquids or supersaturated solutions, until nucleation of a more stable phase occurs.

Techniques to study fasetilstand include calorimetry, X-ray diffraction, differential scanning calorimetry, spectroscopy and microscopy. Knowledge of fasetilstand is essential in materials science, metallurgy, geoscience, polymer science and energy storage, informing design and processing across many industries.