GasLiquidSolid

Gasliquidsolid is a descriptive term used to refer to a substance or system that can exist as gas, liquid, or solid depending on temperature and pressure. In practice, it describes the full range of phase behavior of a material, rather than a distinct new state of matter.

Phase diagrams map the stable phases of a substance in pressure–temperature space. The boundaries between phases correspond to melting (solid–liquid), sublimation/deposition (solid–gas), and vaporization/condensation (liquid–gas). The point where all three boundaries meet is called the triple point, a condition under which solid, liquid, and gas are simultaneously in equilibrium. At a fixed pressure, varying temperature can drive transitions: solid to liquid (melting), liquid to gas (vaporization), or solid to gas (sublimation). The reverse transitions occur with cooling or pressure changes.

Examples include water and carbon dioxide, each with a characteristic triple point (water at 0.01 °C and 611.7 pascals; CO2 at −56.6 °C and 5.11 atmospheres). In most regions of a phase diagram, two phases coexist; only at the triple point do three phases coexist. The concept is widely used in thermodynamics, materials science, and geophysics to understand processes such as crystallization, sublimation, drying, and the behavior of substances near the supercritical region, where liquid and gas become indistinguishable.