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Saturday, 11 April 2015

Sublimation

sublimation


The sublimation of a simple substance or a chemical compound is its phase transition from the solid to the gaseous state, without passing through the liquid state. 

In the current language, since it implies the passage through an equilibrium condition (see diagram phase), is also used generically to indicate the opposite process as it would be more correct to icing up or reverse sublimation.

The chemical compounds and simple substances can have three different states of matter: solid, liquid and gaseous. Their status depends on the temperature and pressure and is described by phase diagrams. Usually, in normal environmental conditions, to switch from solid to gaseous need to cross the liquid state. Under certain conditions of pressure, the temperature changes, you can go directly from a solid to a gaseous, this direct transition from ice to gaseous, was observed on the surface of Mars by the probe Phoenix. 

It is noted that the reference pressure is the vapor pressure of the substance and not the pressure of the entire system. An example of sublimation inverse consists of the sulfur vapor, which undergo sublimation for cooling at atmospheric pressure, this is the reason to the base of the deposits of sulfur often present and visible on the ground in so-called solfataras.


An application of this physical property, it is the thermo-sublimation, a technique widely used for textile printing. In chemistry, the sublimation is exploited for the purification of substances by heating under vacuum of the solid in suitable equipment. In these conditions the solid goes into aeriform phase and subsequently will be made to solidify on a cooled surface, with the impurities which will constitute the residue remaining on the bottom of the chamber of sublimation.