School of Earth and Environment


The BET (Brunauer, Emmett and Teller) measures the specific surface area of a sample including the pore size distribution. The volume of gas adsorbed to the surface of the particles is measured at the boiling point of nitrogen (-196°C). The amount of adsorbed gas is correlated to the total surface area of the particles including pores in the surface. The calculation is based on the BET theory. Traditionally nitrogen is used as adsorbate gas. Helium is used to measure dead volume.

BET instrument in Cohen (SEE)
BET instrument in Cohen (SEE)

Instrument capabilities

We have a Micromeritics Gemini VII 2390a BET which can provide single- and multipoint surface area and pore size measurements.


The sample and balance tubes are immersed in a liquid nitrogen bath. This allows both the internal volume and the temperature surrounding the tubes to be maintained at identical conditions. The only difference is the presence of the sample in the sample tube.


As the sample adsorbs the analysis gas the pressure drops and the BET acts to restore the pressure balance between the tubes by admitting more gas into the sample tube. As many as 50 points can be collected and reported with BET, Langmuir or t-Method.


Surface areas as low as 0.01m2/g can be determined using nitrogen gas as the adsorbate. We have the facilities to use other kinds of gas if required.

Practical advice

Sample Considerations and Preparations

Samples should be dried and degassed before measurement. The BET has a degassing module attached which can help achieve this.

You will need 0.5-2g – more sample for larger particle size:

  • For surface area 5 m2/g you need 2-3 g
  • For surface area 10 m2/g you need 2-3 g
  • For surface area 30 m2/g you need 0.5-1 g
  • For surface are 60 m2/g you need 0.25-0.5 g

It is a non-destructive technique and so you can get your sample back!You can generally run 5-6 samples per day.

Data handling and results

The BET can produce surface area and pore size distributions using various mathematical techniques. Values are given with relevant correlation coefficients and error bars.



Written by Andy Connelly (12/5/2014)