Page 310 - Gas Adsorption Equilibria

296 Chapter 6

For cylindrical capacitors we have, cp. Fig. 6.2:

h ... height of cylinder
... radius of outer cylinder
... radius of inner cylinder

The parameter in (6.11, 6.13) is the electric field constant or dielectric
permittivity of the vacuum. Its numerical value depends on the system of units
chosen [6.3, 6.21-6.24]. For the international system of units that we prefer
here, its value is given in (6.12), [6.20, 6.21].
The product

often is called absolute dielectric permittivity, whereas the quantity
is the relative permittivity of the material included in the capacitor.
It should be emphasized that is in a thermodynamic sense an intensive
quantity of state. For a rigid, inert sorbent / sorbate system it is a function of
the relative amount of mass adsorbed or the sorptive gas pressure (p)
and the temperature (T) of the system, hence

These equations represent different forms of the dielectric equation of state
(DEOS) for the sorbent / sorbate system. It can be used to characterize the
system and is of importance for electrostriction phenomena and / or the
electro-adsorptive effect – especially for continuous non-rigid materials,
[6.16, 6.17, 6.4]. The dielectric permittivity is a phenomenological
measure of the interaction between the electric field and the material within
the capacitor. Numerical values of for static electric fields range as follows
[6.5-6.7, 6.20, 6.21]:

Vacuum 1
Gases
Liquids 2-100
Solids 2-10,000