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BET Surface Area Analysis

BET theory aims to explain the physical adsorption of gas molecules on a solid surface and serves as the basis for an important analysis technique for the measurement of the specific surface area of materials.

Brunauer-Emmett-Teller (BET) surface area analysis is commonly used to evaluate the gas adsorption data and generate a specific surface area result expressed in units of area per mass of sample (m2/g). The technique is referenced by several standard organizations such as ISO, USP and ASTM.

Widely used for most materials, this method is most reliable for materials with a Type II or Type IV isotherm with sufficient level of interaction between the adsorbate gas and the surface. e results.

The specific surface area of a material is then determined by the physical adsorption of a gas (typically nitrogen, krypton, or argon) onto the surface of the sample at cryogenic temperatures (typically liquid nitrogen or liquid argon temperatures). The choice of gas to be used is dependent on the expected surface area and the properties of the sample. Once the amount of adsorbate gas has been measured (either by a volumetric or continuous flow technique), calculations which assume a monomolecular layer of the known gas are applied. BET surface area analysis must be done in the linear region of the BET plot, which could be systematically evaluated using the Rouquerol transform.

 

BET Surface Area Analysis

Brunauer–Emmett–Teller (BET) theory aims to explain the physical adsorption of gas molecules on a solid surface and serves as the basis for an important analysis technique for the measurement of the specific surface area of materials. The observations are very often referred to as physical adsorption or physisorption.

In 1938, Stephen Brunauer, Paul Hugh Emmett, and Edward Teller presented their theory in the Journal of the American Chemical Society. BET theory applies to systems of multilayer adsorption that usually utilizes a probing gas (called the adsorbate) that do not react chemically with the adsorptive (the material upon which the gas attaches to and the gas phase is called the adsorptive) to quantify specific surface area. Nitrogen is the most commonly employed gaseous adsorbate for probing surface(s).

For this reason, standard BET analysis is most often conducted at the boiling temperature of N2 (77 K). Other probing adsorbates are also utilized, albeit less often, allowing the measurement of surface area at different temperatures and measurement scales. These include argon, carbon dioxide, and water. Specific surface area is a scale-dependent property, with no single true value of specific surface area definable, and thus quantities of specific surface area determined through BET theory may depend on the adsorbate molecule utilized and its adsorption cross section.

References

[1] Wikipedia: BET Theory –  https://en.wikipedia.org/wiki/BET_theory

[2] PTL: BET Surface Area –  Link

Gas, Chemisorption and Physisorption Analysers

TOP-200

TOP-200 gas adsorption analyzer is compact and powerful, and can accurately test micropores, mesopores and surface area to study the adsorption behavior of different adsorbates at different temperatures.

QUICK-200

The Quick series gas adsorption analyzer features a compact body, very small dead volume, stable vacuum, excellent cold bath liquid surface constant technology and is the first choice for R&D and quality control.

DENSI-100

Gas replacement ( gas gravity) is the most reliable method for measuring apparent volume and density. The method is more accurate and reproducible than the traditional Acimede immersion method.

AMI-300

The AMI-300 is the “flagship” chemisorption analyser of the AMI family. It is a single station instrument with a standalone PC and LabVIEW-based control software. It is the instrument upon which the rest of the AMI-technology and software is based.

AMI-300IR

The AMI-300IR is a new instrument that uses a heated IR transmission cell coupled with an FTIR to gather information in real time on what is actually occurring on the surface of a catalyst.

AMI-300RHP

The AMI-300RHP is a custom high-pressure version of the AMI-300 with a liquid feed via a HPLC pump. It is equipped to provide 100 bar (or more) of operating pressure during an experiment. The AMI-300RHP was the first high-pressure chemisorption analyzer on the market.

AMI-300Lite

AMI-300 Lite allows for rapid chemisorption studies in a compact, affordable package. The AMI-300 Lite was designed specifically for budget conscious customers and is the only fully automated entry-level chemisorption analyzer on the market today.

AMI Surface DX

A multi-station instrument specifically for dynamic BET analysis. The AMI Surface DX is compact and can perform simultaneous analysis on four samples. This high-throughput and fully automated analyzer ensures the utmost efficiency in any laboratory.

AMI Meso Series

The AMI Meso Series of BET surface area instruments utilises the static volumetric method to measure isotherms. The AMI Meso Series is designed specifically to characterize mesoporous materials and can even be adapted with multiple analysis ports for high-throughput testing.

AMI Micro Series

The AMI Micro series of sorption instruments is designed to determine specific surface area, pore size distribution, and pore volume in everything from carbon black to pigments to zeolites and can be adapted with multiple analysis ports for high-throughput sample testing.

AMI Sync Series

The AMI Sync Series is a high throughput BET analyser with up to four measuring stations and a separate p0 measuring cell for simultaneous measurement of saturation vapor pressure.

 

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