BET Specific Surface Area
The BET (Brunauer, Emmett and Teller) theory 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.
This method is widely used for most materials, but 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. For materials with other types of isotherms, the BET theory may not apply for various reasons and therefore should be treated with caution.
Prior to analysis, the sample must be preconditioned to remove physically bonded impurities from the surface of the powder in a process called degassing or outgassing. This is typically accomplished by applying elevated temperature to the sample in conjunction with vacuum or continuously flowing inert gas. This process must be carefully controlled and monitored in order to generate the most accurate and repeatable 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.
Specific surface area can also be expressed in units of area per volume of sample (m2/cm3). This value is termed volume-specific surface area (VSSA) and is obtained by multiplying the BET surface area with the density of the material. Per the 2011 European Commission Recommendation on the definition of nanomaterials, the VSSA can be used as a complementary qualifier to identify a potential nanomaterial in addition to the particle size distribution of the material. PTL also has the capability to perform density analyses as well as particle size analyses of your materials.
PTL can advise whether Static Pressure (Volumetric) or Dynamic Flow (Continuous Flow) will be most suitable for you, and/or whether nitrogen, krypton, or argon gas is best in any particular case. Our lab is well equipped with instruments capable of either adsorption technique, and we possess the technical expertise to provide meticulously executed surface area analysis using the most appropriate gas and procedure. The volumetric analyses can be extended in-house to provide information on the porosity of the material as well.
Single and multi-point BET analyses are available.
Advantages
- PTL can conduct both dynamic flow and volumetric techniques
- Nitrogen, Argon, Krypton available for adsorbate gases
- Several instrument options to ensure best fit for material
Considerations
- 1-point BET is appropriate for a quick analysis for quality control, with an established linear BET. Recommend at least 3-point BET analysis
- BET testing alone does not provide pore measurements; these would be determined with a gas physisorption isotherm analysis
- Appropriate for dry material only
Sample Requirements
Ideally, 2 to 5 grams of test material would be optimum for completing the Specific Surface Area BET testing. Please note the most commonly used analytical cell is shaped similarly to a test tube, with a 9 mm opening at the top, and a bulb at the bottom. The sample must pass through the tube, which is about 9 mm in diameter, and then it has to sit in the bottom of the bulb (sizes are 2 mL, 4 mL and 7 mL). Larger solid sample pieces can also be accommodated in special analytical cells.
Questions on sample needs – please contact us to share specific information about your sample and options for suitable sample quantities.
Detection Range
PTL’s Surface Area department can measure from 0.01 m2/g to > 1000 m2/g depending on the adsorbate gas utilized and instrument manufacturer.
Data Reported
The BET (Brunauer, Emmett and Teller) theory 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).
Specific surface area can also be expressed in units of area per volume of sample (m2/cm3). This value is termed volume-specific surface area (VSSA) and is obtained by multiplying the BET surface area with the density of the material.
Instrumentation
Particle Technology Labs has some of the top players in the industry, such as Micromeritics and Anton Paar/Quantatec.
Micromeritics 3Flex
Anton Paar/Quantatec AutoFlow BET+
Micromeritics Tristar II 3020
Anton Paar/Quantatec NOVA 800
