Adsorption Characterization of porous materials Part 3

# Adsorption Characterization of porous materials Part 3

## Adsorption Characterization of porous materials Part 3

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##### Presentation Transcript

1. European Master Adsorption Characterization of porous materials Part 3 Bogdan Kuchta Laboratoire MADIREL Université Aix-Marseille

2. m Basis of the specific surface measurements by adsorption = quantity required to cover 1 gram of adsorbent with one layer m = surface occupied by one molecule Specific surface For N2 at 77,35 K m = 0,162 nm2 Is the gas volume (STP) adsorbed required tobuildone layer on 1 gram of adsorbent where

3. Structure of adsorbed molecules Hypothesis * molecules are modeled by spheres with radius r each of them occupies a surface m on a solid totally covered with 1 layer * the layer is supposed to be: - compact (hexagonal dense arrangement) - liquid (corresponding to density l at temperature of adsorption) Calculations NA is the Avogadro constant M is the molecular mass adsorbate Numerical applications :N2 at 77,35 K m = 0,162 nm2 H2O at 300 K m = 0,105 nm2

4. Application of BET model:example : alumina NPL / N2 / 77 K

5. Application of BET model:example : alumina NPL / N2 / 77 K

6. Application of BET model:example : alumina NPL / N2 / 77 K Slope : Coordinate :

7. Application of BET model:example : alumina NPL / N2 / 77 K

8. + p/p° + Hypothesis  C >> 1  coordinate = 0 «Method of 1 point» for fast determination of the specific surface This method is recommended only for fast estimations.

9. Application of BET model:example : alumina NPL / N2 / 77 K

10. Comments on BET model applications • This method may be applied when the isotherm of adsorption of the type II is observed at 77 K when nitrogen is the adsorbed gaz. • 2. It is also possible to use it with isotherms of the type IV id the capillary condensation is not observed up to the relative pressure 0.35.