Brunauer-Emmett-Teller (BET) analysis

What is BET analysis?

BET analysis is an analytical technique utilized for determining specific surface areas and pore size distributions of solid materials. The technique is based on the physical adsorption of inert gas, such as nitrogen, on the solid surface of the sample. The measured specific surface area is given in m²/g.

What is BET analysis used for?

BET analysis is mainly used for analyzing the fineness of cement and concrete, the adsorption capability of activated carbon, catalyst characterization, the adsorption performance of gas purifiers, and studying nanomaterials. Nanomaterial identification can be based on measuring volume-specific surface area (VSSA), which can be determined using BET and He pycnometry.

How is BET surface area determined?

The specific surface area of the BET sample is determined by the physisorption of an inert gas, typically nitrogen, argon, or krypton, on the sample surface. The surface area determination should be carried out at a constant temperature (isothermal). The appropriate temperature depends on the inert gas used (e.g. 77 K for liquid nitrogen). The properties of the sample define the suitable inert gas for the analysis.

The small gas molecules are attracted to the surface of the solid sample and open a porous structure forming a monolayer of adsorbed gas. After the gaseous monolayer of molecules is created, the sample is placed into a non-nitrogen atmosphere and heated. This allows the release of the adsorbed nitrogen gas molecules from the surface of the sample. The released gas molecules can then be quantified and the surface area and porosity calculated.

Sample requirements and preparation

BET is suitable for the characterization of powders and monolithic solids. Usually, around 500 mg to 1 g of sample material is needed to obtain reliable results, but sometimes smaller sample amounts can be used. Sample preconditioning is an essential step before starting a specific surface area measurement. All possible physically bonded surface impurities including moisture must be removed via a degassing step. The degassing step is performed under vacuum conditions and at high temperatures for no less than 16 hours. Before starting the actual BET measurement, the setup should be calibrated by performing a blank run with helium gas. The helium will not typically be adsorbed on the surface of the solid sample.

Need a BET analysis?

Measurlabs offers BET analysis services of high quality with fast results and affordable prices. If you have any questions about your sample or its suitability for the method, our experts are always happy to help. You can contact us through the form below or by emailing us at info@measurlabs.com.