Specific surface area measurement by BET (Brunauer–Emmett–Teller)
Specific surface area measurement by BET 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, cosmetics, and pharmaceutical industries.
What is the BET method for measuring specific surface area?
The BET (Brunauer–Emmett–Teller) method is a physicochemical analysis technique used to determine the specific surface area of a solid material, that is, the total surface area available per unit mass (expressed in m²/g). It is based on the principle of adsorption of an inert gas (usually nitrogen) onto the surface of the material at low temperature.
The BET theoretical 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 area occupied by the gas molecules.
How the BET method works
BET analysis is based on a physical adsorption process of a gas onto 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 is generally carried out at 77 K (temperature of liquid nitrogen).
- Progressive nitrogen injection: the gas is adsorbed onto the surface of the material; the adsorbed quantities are measured at different relative pressures.
- Construction of the adsorption isotherm: the data obtained allows us to plot an adsorption/desorption curve.
- Calculation of specific surface area: the BET equation is applied to obtain the surface area in m²/g.
Technical characteristics of the BET analysis
- Principle : physical adsorption of inert gas (often nitrogen)
- Analysis temperature : typically 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?
Specific surface area measurement by BET is mainly applicable to solid materials in powder or porous form:
Main industrial applications
The BET method is essential in many industrial sectors where specific surface area determines product performance :
Léa Géréec
Technical and scientific expert
