Sublimation is the transition of a substance directly from the
solid to the
gas phase, without passing through the intermediate
liquid phase.
Sublimation is an
endothermic process that occurs at temperatures and pressures below a substance's
triple point in its
phase diagram, which corresponds to the lowest pressure at which the substance can exist as a liquid. The reverse process of sublimation is
deposition or desublimation, in which a substance passes directly from a gas to a solid phase. Sublimation has also been used as a generic term to describe a solid-to-gas transition (sublimation) followed by a gas-to-solid transition (
deposition). While a transition from liquid to gas is described as
evaporation if it occurs below the boiling point of the liquid, and as
boiling if it occurs at the boiling point, there is no such distinction within the solid-to-gas transition, which is always described as sublimation.