Page 253 - Gas Adsorption Equilibria

5. Oscillometry 239

For the instrument shown in Figs. 5.1, 5.2 we could observe for various gases
at different pressures rotational oscillations for up to 30 minutes having
oscillation times of about (30-45) seconds and logarithmic decrements of
about cp. Sect. 2.2. For choice of materials and design information, hints
already given in the foregoing chapters should be observed. Details can also
be found in [5.2, 5.7, 5.11-5.13]. Here we point out that

oscillation experiments only should be started if one reasonably can expect
that adsorption equilibrium is attained, i. e. the pendulum does not seem to
be suited for adsorption kinetic measurements and
the sorptive gas pressure should be at “intermediate level” as for very low
pressures the theory presently available for the motion of the pendulum
fails, cp. Sect. 2.2, and for high gas pressures the viscous damping of the
motion of the pendulum is so severe that only few oscillations or mere
creeping motions can be observed [5.2, 5.7]. In practice, measurements of
adsorption equilibria of methane on activated carbon at 293 K with
our instrument were limited to the pressure range 0.5 MPa – 10 MPa. We
expect however, that these limits can be overcome or at least shifted
considerably by proper, i. e. optimized, design of the pendulum.

Figure 5.3. Electric signals of the photodiodes initiated by the reflected laser
beam crossing diode channel 2.