Desorption

Desorption ( from the Latin de - sorbere; sorbere: suck in ( ) ) refers to the process, leaving the surface of a solid in which atoms or molecules. The desorption thus represents the reverse process of sorption dar.

In order to desorb the particles must have enough energy to overcome the binding energy or get fed.

Classification

According to the origin of the energy required for this there is the

• Thermal desorption ( Temperaturwechseldesorption; temperature swing )
• Optical desorption ( by absorption of photons)
• Acoustic desorption by ultrasound
• Electrical desorption
• Ionenstimulierte desorption ( by bombardment with fast ions )
• Typographical desorption ( Druckwechseldesorption; pressure swing )
• Technical desorption ( desorption, for example, with different fixed bed, moving bed, fluidized bed)
• Displacement desorption ( using a more readily adsorbable substance; technically mostly water vapor)

Desorption rate

Thermal desorption

The desorption of the particles from the surface depends primarily on the number n of the adsorbed or absorbed particles / molecules, the temperature T and the desorption (also binding energy )

Wherein an oscillation frequency, Boltzmann's constant and m is the Desorptionsordnung.

The Desorptionsordnung depends on the specific mechanism of desorbing:

• M = 0: desorption of a multilayer
• M = 1: desorption of atoms
• M = 2: desorption of diatomic molecules
• Etc.

Ionenstimulierte desorption

Observed desorption rates of the ion- stimulated desorption range from 1 (normal incidence, low energies of the incident ions ) to about 25,000 ( grazing incidence, energies of a few MeV / u incident ions ). In general, the desorption rate is a function of ionenstimulierte:

Wherein the penetration depth of the ions into the material of the electronic energy loss per penetration depth, the angle of incidence and a first empirically determined constant. The rate of desorption and the energy required is an important factor as to whether a combination of adsorption and desorption is used as a technical process in question.

Application

In the epitaxial desorption is used to maintain a certain concentration in the gas phase.

In research ionenstimulierte desorption is used to clean surfaces of adsorbates, which could not be cleaned by thermal desorption.