Page 262 - Gas Adsorption Equilibria
P. 262

248                                                        Chapter 5


          with   being  the  ring  slit volume





          and           indicating  the  sorptive gas density.

             The effective mass     of the boundary layer of the pendulum occurring
          during its motion has to be determined by calibration experiments using non-
          adsorbing pellets – preferably quartz glass spheres – having a similar surface
          as the sorbent pellets [5.2].

             Combining equations (5.25),  (5.40) we  have for  the  Gibbs excess  mass
          adsorbed




          with       to be calculated from oscillations measurement by (5.39) and the

          density     to  be determined  from (T,  p)-Measurements using the EOS  of
          the sorptive gas.


             Applying the formalism presented above to measurements performed with
          non-adsorbing  material    for  example glass  spheres  or cylinders  of the
          size of the original adsorbent pellets, leads similar to (5.42) to the relation





          which allows to write    as





          Here     is the net volume of the glass material of mass   It most easily
          can be measured using buoyancy effects at a microbalance. The experimental
          quantity       again has  to be calculated from Eq. (5.39) referring now to
          measurements  with the pendulum filled with non-adsorbing material (glass)
          [5.2, 5.7]

             Auxiliary remarks:

             1.   The slow motion/laminar flow condition (5.28) does not hold in the
                  low pressure region        as then       and  hence        In
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