BET theory aims to explain the physical adsorption of gas molecules on a solid surface and a practical use in the estimation of the specific surface area (SSA) of a material.

BET paper grabIn 1938, Stephen Brunauer, Paul Hugh Emmett, and Edward Teller published a famous article Adsorption of Gases in Multimolecular Layers – their extension of Langmuir theory (which describes monolayers of gas adsorption) onto surfaces in J. Am. Chem. Soc., 1938, 60, 309. A paper that became one of the most cited publications in analytical science.

An introductory explanation of SSA and BET is on Wikipedia site and a fuller explanation is in  “Analytical Methods in Fine Particle Technology”–  by Paul Webb and Dr. Clyde Orr available to order from us under Part No. 008-42001-00 or from Micromeritics.

Automatic selection of data used for calculating the BET surface area of a fluid cracking catalyst.

Automatic selection of data used for calculating the BET surface area of a fluid cracking catalyst.


But things aren’t all in the past. Gas adsorption technology has developed with newer theories like Density Functional Theory (DFT) and more recently with Non Local Density Functional Theory (NLDFT) for pore filling by Jacek Jagiello and James Olivier of Micromeritics.

More recently Professor Jean Rouquerol (CNRS Marseille, France) demonstrated fascinating rules that allow for the automatic selection of points to calculate the surface area in the proper linear range.

This was always one of the irksome realities of BET, that you needed to check the relative pressure range for your sample, something many analysts forgot to check. And for some materials this was not easy, with negative C values resulting. The sample shown left actually is linear from 0.003 too 0.025 P/P0. Rouquerol transform for SSA is now part of MicroActive and embedded in Tristar Plus II (3030) and 3Flex software.


 Manufacturer Instruments Micromeritics technology
Micromeritics Gemini MicroActive software
Micromeritics web site Tristar Automated BET point selection
3Flex DFT reporting YouTube
ASAP NLDFT for porous materials
Basics of gas physisorption 1/3 video
Basics of BET 2/3 video
Part 3 of physi video