Page 144 - Gas Adsorption Equilibria

130 Chapter 3

2. MSBs should be cleaned from time to time as small particles, for example
activated carbon or zeolite powders may be transferred from the sorbent
basket to the permanent magnet. Here they can change the magnetic field
permanently and by this cause systematic uncertainties or errors of
measurement. Once these are detected, they may be corrected by
recalibrating the “zero load position” of the balance, cp. Fig. 4.12.

3. Electro smog as it may be caused by – undetected – wires and cables
should be avoided. These electromagnetic fields, especially if enhanced by
direct or nearby lightning, can seriously disturb measurements.

Figure 3.4. Schematic diagram of a gravimetric apparatus for gas adsorption measurements
using a magnetic suspension balance (Rubotherm GmbH, Bochum, Germany).

4. It should be emphasized that MSBs today are used not only for gravimetric
gas adsorption measurement but also for a still growing variety of other
thermo-physical measurements of vertical forces at extreme pressures,
temperatures, and chemical conditions, cp. Chap. 4 and [3.5, 3. 6, 3.26,
3.53, 3.54]. Besides, simple mechanical spring balances are still in use.
They can give quick, but often only approximate data of adsorption
equilibria, which however still may be useful for orientational purposes
[3.1, 3.9].