Analysis Gases
Determining what gas to use for analysis.
Helium is the most used gas for pycnometry
due to its ideal behavior; however, there are times where other gases can be
substituted for helium.
Helium has the ability to permeate
into pores that are closed from the surface and interacts with some organic
materials and microporous carbons.
The solution is to use another gas such as nitrogen, argon,
or air. Larger molecules such as sulfur hexafluoride can be used to include the
volume of very small pores in volume results.
Care should be taken to select a gas
that does not interact with the sample material.