Nonsublimation

Nonsublimation is a qualitative term used to describe the apparent resistance of a material to undergo sublimation, the direct transition from a solid to a gas, under a specified range of temperature and pressure. In this sense, a substance can be described as nonsublimating when it does not exhibit measurable sublimation within the conditions used, often because it instead melts, decomposes, or forms a surface layer that suppresses vaporization. The concept is not a formal thermodynamic phase but a practical description used in materials science, vacuum technology, and planetary science.

The phenomenon arises from several possible mechanisms. Melting before sublimation occurs when the solid reaches its melting point at a given pressure, producing a liquid that may later vaporize at higher temperatures. Decomposition happens when the solid chemically breaks down into other species that do not pass through a simple solid-to-gas transition. Surface passivation can reduce the effective vapor pressure, for example through the formation of oxide or other coatings. Kinetic barriers or extremely low intrinsic vapor pressure can also render sublimation negligible on experimental timescales.

Because sublimation depends on both temperature and pressure, the designation of nonsublimating is conditional. A material described as nonsublimating under one set of conditions may sublimate under different atmospheric or thermal circumstances. In practice, this term is used cautiously and supported by vapor-pressure data and phase behavior rather than as a universal property.

See also: Sublimation, Phase diagram, Thermal decomposition, Vacuum processing.