Thermal desorption of gases Thermal desorption of gases Thermal desorption is the process by which molecules adsorbed to a substrate are released due to increasing kinetic energy. The substance which adsorbs and desorbs is referred to as the adsorbate. The substance to which the adsorbate adsorbs is called the substrate. The two types of adsorption to a surface are chemisorption and physisorption.
Chemisorption involves the actual formation of bonds between the adsorbate and the substrate.
The second type of adsorption, and the type thoroughly discussed in this mathematical discussion, is physisorption. This type of adsorption involves van der Waals interactions such as dispersion forces or a dipolar interaction. Since these interactions are very weak, a physisorbed molecule can be easily desorbed simply by raising the temperature, thus increasing the kinetic energy and breaking the interacting forces between the adsorbate and substrate. Accurate and extensive data acquisition is fundamental in order to observe the desorption phenomenon. While observing temperature and pressure with time, a sudden increase in pressure should be observed as the temperature rises to a point where there is enough thermal energy to increase the kinetic energy of the adsorbate to the point where it will break free of the substrate.