Faasidiagrammin

Faasidiagrammin, commonly translated as a phase diagram, is a graphical representation of the equilibrium phases that a material system can adopt under varying conditions of temperature, pressure, and composition. It is used to summarize how phases appear and transform as these conditions change, providing a concise map of stability domains for solids, liquids, and gases, or for different solid solutions in alloys.

In practice, phase diagrams display regions in which a single phase is stable and lines or curves on which two or more phases coexist at equilibrium. The points where phase boundaries meet are invariant points, such as eutectic or peritectic reactions in alloy systems. The phase rule, F = C − P + 2, relates the degrees of freedom (F) to the number of components (C) and phases (P) present, helping interpret how many conditions can be varied independently at a given point.

Common diagram types include P–T (pressure–temperature) diagrams for pure substances, and T–X or P–X diagrams for multi-component systems like binary alloys. Binary phase diagrams show how solubility limits and phase regions evolve with composition and temperature, while ternary diagrams extend these ideas to three components and often require three-dimensional or projection representations. Modern approaches frequently use thermodynamic databases and CALPHAD methods to predict phase behavior.

Notable examples include the water phase diagram, which illustrates solid, liquid, and gas regions as well as the triple point, and the iron–carbon diagram, a cornerstone in metallurgy for predicting steel microstructures. Faasidiagrammin supports material design, heat treatment planning, crystallization processes, and the understanding of phase transformations in a wide range of scientific and engineering contexts.