Fasenlijnen

Fasenlijnen, or phase lines, are curves on a phase diagram that indicate the boundaries between regions of single‑phase stability and regions where two or more phases are in equilibrium. They describe the conditions under which phase changes occur, typically as a function of temperature, composition, and pressure. At a fixed pressure, these lines are defined by the equality of chemical potentials for the coexisting phases, satisfying thermodynamic equilibrium.

In binary alloy systems, the phase diagram commonly features a liquidus line and a solidus line. The region between them is two‑phase, containing both solid and liquid. Features such as eutectic points (where a liquid transforms into two solid phases at a single temperature and composition) and peritectic points (where a solid and a liquid react to form a second solid phase) are defined by phase‑lines. Tie lines connect the compositions of the coexisting phases within a two‑phase field.

In geology and petrology, phase diagrams describe mineral stability as temperature and pressure change. The phase lines delineate stability fields for minerals and reactions during metamorphism and magmatic processes. The concepts of phase boundaries also apply to ceramics and other multi‑component materials.

Phase‑lines are determined experimentally and computationally. Experimental methods include calorimetry, differential thermal analysis, and X‑ray diffraction. Computational approaches, such as CALPHAD (CALculation of PHAse Diagrams) and phase‑field modeling, predict phase boundaries for complex systems. The Gibbs phase rule provides a framework for understanding the degrees of freedom in a multiphase region.

Related topics include phase diagram, phase boundary, liquidus, solidus, eutectic, peritectic, tie line, CALPHAD, and phase‑field.