Training in the BET technique for laboratories

What is the principle of BET surface analysis?

The principle of surface analysis by BET consists in designating the real surface as opposed to the apparent surface. Thus, it represents the total surface per unit of mass and is expressed in m²/g.

Three categories are to be found to classify the various methods of measurements and analysis of specific surface by BET:

• Gas adsorption (i.e. measurement of the number of gas molecules adsorbed in one or more layers on the solid),
• The adsorption in liquid phase (like fatty acids, dyes, …)
• Physical methods (with X-rays, radioactivity, heat of adsorption, …).

Among these three methods of analysis mentioned above, one is described by Brunauer, Emmett and Teller. This is how these three researchers describe the determination by gas adsorption, which is why it is known as the “BET method or technique”. This method is also the most important and widely used.

This well-known BET method determines the amount of gas required to form a monomolecular layer around the solid sample. As the cross-section of the molecules is a specific characteristic for each gas, it is then possible to determine the total surface area of the solid.