Page 266 - Gas Adsorption Equilibria

252 Chapter 5

The dispersions have to be calculated via Eq. (5.39) from

experimental uncertainties of the logarithmic decrement and of
the frequency of the various oscillations. In the scheme below all
parameters (x) and related dispersions together with numerical data of
their ratio according to our laboratory experience are listed [5.7, 5.16].

These numerical values of dispersions provided one can expect relative
uncertainties of Gibbs excess masses measured with the rational pendulum to
be limited by This is about the accuracy of standardized
volumetric / manometric measurements, cp. Chap. 2. To realize accurate
oscillometric measurements it is most important to determine the and
parameters related to the various oscillations of the pendulum as accurate as
possible, cp. Eq. (5.39). For this it is necessary to choose an initial amplitude
of about 2-3 times the size of but less than 60 ° as for higher
values of measurable deviations of the oscillation from ideal harmonic
behavior occur. Also it is necessary to observe at least 10 periods within an
oscillation if not more, to get reliable To ensure this, the use of
diodes with characteristic detection times less than 0.1 ms is recommended
[5.7].

2.4 Examples

The rotational pendulum depicted in Fig. 5.1 has been used to perform gas
adsorption equilibria measurements on a variety of sorbent materials and
sorptive gases. Some geometric and physical parameters of the instrument are
given in Table 5.1, cp. also Fig. 5.4.

We here present only adsorption measurements of He and on
activated carbon (AC) Norit R1 Extra at 293 K. Physico-chemical parameters
of this sorbent material have been given in Chap. 3, Sect. 2.3. Also, some