Specific surface area measurement by BET (Brunauer–Emmett–Teller)
BET specific surface area measurement is a technique for characterizing solid materials that quantifies the total surface area available for physical or chemical interactions, based on gas adsorption. Essential for the analysis of powders, pigments, catalysts, or porous materials, this method is a standard in the materials, chemical, environmental, cosmetic, and pharmaceutical sectors.
What is the BET method for specific surface area measurement?
The BET (Brunauer–Emmett–Teller) method is a physicochemical analysis technique used to determine the specific surface area of a solid material, i.e. the total available surface area per unit mass (expressed in m²/g). It is based on the principle of adsorption of an inert gas (usually nitrogen) on the surface of the material at low temperature.
The theoretical BET model is an extension of the Langmuir model, taking into account multilayer adsorption . It allows the calculation, from an adsorption isotherm , of the quantity of gas adsorbed at saturation, and therefore the surface occupied by the gas molecules.
How the BET method works
BET analysis is based on a process of physical adsorption of a gas on the surface of a solid:
- Sample preparation: The material is degassed under vacuum or inert gas to remove any traces of moisture or contaminants.
- Cryogenic cooling: the analysis generally takes place at 77 K (liquid nitrogen temperature).
- Progressive injection of nitrogen: the gas is adsorbed on the surface of the material; the adsorbed quantities are measured at different relative pressures.
- Construction of the adsorption isotherm: the data obtained allow an adsorption/desorption curve to be plotted.
- Calculation of specific surface area: the BET equation is applied to obtain the surface area in m²/g.
Technical characteristics of BET analysis
- Principle : physical adsorption of inert gas (often nitrogen)
- Analysis temperature : generally 77 K (liquid nitrogen)
- Model used : BET theory, sometimes coupled with the BJH method for pore size analysis
- Applicable standards : ISO 9277, DIN 66131, DIN 66132
- Measured parameters : specific surface area (m²/g), pore volume, pore size distribution (optional)
For which matrices?
The measurement of specific surface area by BET mainly applies to solid materials in powder or porous form:
Main industrial applications
The BET method is essential in many industrial sectors where the specific surface determines the performance of the product :
Léa Géréec
Technical and scientific advisor
