Sublimationspunkt

Sublimationspunkt, commonly known as the sublimation point, is the specific temperature at which a solid compound transitions directly into the gaseous phase without passing through a liquid state. This phase change occurs under conditions of pressure where the solid’s vapor pressure equals the external atmospheric pressure. The sublimation point is a characteristic property of a substance and is distinct from both its melting point and boiling point.

The phenomenon is most readily observed at low atmospheric pressures, where the liquid phase becomes thermodynamically unstable. Classic examples include dry ice (solid carbon dioxide) sublimating at –78.5 °C under standard atmospheric pressure, as well as iodine crystals subliming at around 184 °C. Organic compounds such as naphthalene and camphor also exhibit clear sublimation behavior, which is exploited in purification techniques like sublimation chromatography.

In scientific measurement, the sublimation point is determined through techniques that monitor the onset of gas production as the temperature is increased. Differential scanning calorimetry (DSC) can identify the energy change associated with sublimation, while mass spectrometry can detect the emerging vapor. The precise sublimation point depends on the external pressure; at the triple point of a substance, the solid, liquid, and gas phases coexist in equilibrium, defining a unique combination of temperature and pressure.

Understanding the sublimation point is important in fields ranging from materials science to environmental chemistry. It informs the design of storage conditions for volatile solids, aids in the development of phase-change materials for thermal management, and contributes to the modeling of atmospheric processes where sublimation of ice or other solids releases gases.