Surface area and porosimetry


3Flex (Micromeritics), TriStar (Micromeritics)

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Surface area and porosimetry

BET, macro/meso/micropores

Alfatestlab provides BET specific surface area, as well as pores dimensional distribution and volume analysis of solids and powders with gas physisorption techniques. Surface area and porosity are physical properties that influence the quality and behaviour of porous materials: materials with identical weight and volume but different specific surface area may differ in terms of surface activity and adsorption volume. During a manufacturing process, especially in reducing particle size, the specific surface of the product may change. Any subsequent modification during the production process can affect the porosity and the specific surface of a product, leading to an unexpected change in the desired performance. In Alfatestlab it is possible to perform surface area and porosimetry measurements on various types of solid materials or powders thanks to different gases available for the analysis: N2, Kr and Ar.

Surface and porosimetry measurements provide useful information for many industries and for many types of products, including catalysts, zeolites, MOFs, coals, batteries, sanitary napkins, artificial dentures, pharmaceuticals, ceramic products, metal powders for additive manufacturing.

More Details

Samples are commonly prepared by heating them under vacuum or under a gas stream to remove impurities. The samples are then analyzed by measuring the volume of adsorbed gas, for example nitrogen, at specific pressures and at low temperatures, for example at 77K in liquid nitrogen.

The surface area is a measure of the exposed surface of a solid sample on a molecular scale. The BET theory is the most used model to determine the area but the results can also be obtained according to the Langmuir model.

To measure pore size by gas adsorption, isotherms are recorded in the range from low pressures to saturation pressure. The pressure range is determined by the pore size range to be measured: microporous materials are measured by isotherms in the pressure range 0.00001-0.1 torr, while mesoporous materials typically in a pressure range 1 – 760 torr.

The methods available for measuring micropore distribution include: Density Functional Theory (DFT), MP-Method, Dubinin Plots (Dubinin-Radushkevich D-R, Dubinin-Astakov D-A) and Horvath-Kawazoe (H-K). Methods available for Mesopores include: Barrett method, Joyner and Halenda (BJH) and Density Functional Theory (DFT).