Page 306 - Gas Adsorption Equilibria

292 Chapter 6

is related to the complex impedance function (Z (p)) and admittance functions
(Y (p)) of the capacitor system by

Here the function (Z (p) = 1 / Y (p)) is defined by the generalized Ohm’s law

with

being the Laplace transform of the electric current (I (t)).

Choosing for the complex frequency the values
the functions

resulting from the measured complex capacitance C = C(p), (6.6) can be used
to characterize the capacitor itself and any kind of adsorption system included
in it. The real part of the complex capacitance (C(p)) describes
reversible interactions between the atoms and molecules of the system and the
electric field applied leading to periodic polarization of the molecules. The
imaginary part of the complex capacitance (C(p)) describes
irreversible interactions between the electric field and the atoms and
molecules, namely Ohmian heating of the material due to its often small but
nontheless existing electric conductivity [6.1, 6.13].

As an example, data for the capacitor shown in Fig. 6.2 taken in vacuum
and for gases p = 12.3 MPa; CO, p = 13.5 MPa) at T =
298 K are shown for frequencies up to 13 MHz in Figure 6.3. Note that the
real part of the capacitance of the system is given in units
Farad.