BET Surface Area Analysis

Measurement of the surface area and pore size distribution of solid materials using gas adsorption

Surface Area

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Surface area helps determine such things as how solids burn, dissolve, and react with other materials. To determine the surface area, solid samples are pre-treated by applying some combination of heat, vacuum, and /or flowing gas to remove adsorbed contaminants acquired (typically water and carbon-dioxide) from atmospheric exposure. The solid is then cooled, under vacuum, usually to cryogenic temperature (77 k, -195 °C). An adsorptive (typically nitrogen) is dosed to the solid in controlled increments. After each dose of adsorptive, the pressure is allowed to equilibrate and the quantity adsorbed is calculated. The quantity adsorbed at each pressure (and temperature) defines an adsorption isotherm, from which the quantity of gas required to form a monolayer over the external surface of the solid is determined. With the area covered by each adsorbed gas molecule known, the surface area can be calculated.

Porosity, Pore Sizes and Pore Distributions

Surface area determinations involve creating the conditions required to adsorb an average monolayer of molecules onto a sample. By extending this process so that the gas is allowed to condense in the pores, the sample’s fine pore structure can be evaluated. The pressure is increased until saturation is reached, at which time all pores are filled with liquid. The adsorptive gas pressure then is reduced incrementally, evaporating the condensed gas from the system. Evaluation of the adsorption and desorption branches of these isotherms and the hysteresis between them reveals information about the size, volume, and area.

escubed measures Specific Surface Area using a Micromeritics TriStar II 3020 which uses the Brunauer-Emmett-Teller (BET) equation to describe the Surface Area and Barrett-Joyner-Halenda (BJH) equation to describe the pore size and volume. escubed can provide;

  • Single- and multipoint BET surface area
  • Total pore volume
  • Langmuir surface area and isotherm reports
  • BJH adsorption and desorption average pore diameter (4V/A) determinations
  • Mesopore and Macropore – Volume and area distributions by pore size

  • Get in touch to see how we can help you understand the surface area properties of your materials.

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