Page 132 - Gas Adsorption Equilibria

118 Chapter 3

balances is given in Table 1 below [3.7-3.9]. Automated instruments
including microbalances are available for various purposes among them water
vapor adsorption/desorption measurements and thermogravimetry, cp. Tab. 2,
[3.6, 3.10]. Technical progress in the design and application of microbalances
is mirrored in a series of (small) tri-annual conferences on vacuum
microbalance techniques (VMT) whose proceedings are a very useful source
of technical information in this field [3.11]. The physics of gravimetric
sorption measurements is not as simple as it may occur on the first glance. As
the sorbent material always is surrounded by a sorptive gas (or liquid, cp.
Sect. 4.4), the microbalance can only register the difference between the
sample’s weight and its buoyancy force which includes the volume of the
porous sample. It is this quantity which normally is not known exactly and
therefore has to be approximated, similar to what is necessary in the
volumetric/manometric method, Chap. 2.

* ) This table in no way claims to be exclusive or complete.