Calculate Free Space Values for Micropore Analyses
Many microporous materials, such as zeolites and activated carbons, trap and hold helium in their complex pore structures for many hours after being exposed to helium. Helium trapped in micropores can interfere with the analysis at low pressures, causing an “S”-shaped curve at the lower end of the isotherm. For this reason, it is recommended that you enter the ambient and analysis free space volumes when performing micropore analyses, therefore avoiding exposure of the sample to helium. Two techniques can be used for determining ambient and analysis free-space values.
The first method is to perform a short analysis on the sample after partial degassing (one pressure point with no incremental dosing), but prior to final sample preparation. Measure the free space during this analysis. The measured free space values will be printed on the report and may then be entered into the sample file after more thorough sample preparation.
The second method requires prior tests using empty tubes that will be employed later for the sample analyses. The measured free space data can be used thereafter on every analysis performed using these sample tubes. This small initial investment of time will save considerable time later. Perform an empty tube analysis on each sample tube you intend to use for micropore analysis. Measure the free space of each sample tube, taking only one pressure point
- Create a sample tube file from each empty tube test.
- Use the Load from Sample File button to read in the measured free space from the empty tube tests.
- In the sample file for the sample analysis, pick the appropriate sample tube from the sample tube list.
- Enter the mass and density of the sample.
- Choose Calculate in the free space options in the analysis conditions.
Copyright © 2014 - 2018. Micromeritics Instrument Corporation. All rights reserved.