The liquidus is the temperature above which the substance is stable in a liquid state.

The solidus is the temperature below which the substance is stable in the solid state. For example, the water phase diagram has a triple point corresponding to the single temperature and pressure at which solid, liquid, and gaseous water can coexist in a stable equilibrium ( 273.16 K and a partial vapor pressure of 611.657 Pa). Triple points mark conditions at which three different phases can coexist. Triple points are points on phase diagrams where lines of equilibrium intersect. Metastable phases are not shown in phase diagrams as, despite their common occurrence, they are not equilibrium phases. Phase transitions occur along lines of equilibrium.

Simplified temperature/pressure phase change diagram for waterĪ phase diagram in physical chemistry, engineering, mineralogy, and materials science is a type of chart used to show conditions (pressure, temperature, volume, etc.) at which thermodynamically distinct phases (such as solid, liquid or gaseous states) occur and coexist at equilibrium.Ĭommon components of a phase diagram are lines of equilibrium or phase boundaries, which refer to lines that mark conditions under which multiple phases can coexist at equilibrium.

3d substance