Biomedical Engineering Reference
In-Depth Information
were used for the characterization of the hydrogen adsorption
properties of nanostructured carbon materials. Browning
[10]
used their unthermostatted system to measure hydrogen uptake by
carbon nanofibres (CNFs) at ambient temperature and 12 MPa, and
Blackman
et al.
[11] demonstrated their improved, thermostatted,
version by measuring the uptake of hydrogen by CNFs and a series
of activated carbons at 303 K and 10 MPa. However, both of these
systems allow the measurement of only single isotherm points
and cannot measure desorbed quantities. It is therefore difficult
to determine the physical plausibility or accuracy of the results.
Furthermore, the measurements are also restricted to a limited
measurement
et al.
temperature
range.
The
system
presented
by
Zielinski
[9], meanwhile, can measure complete adsorption
and desorption isotherms, and its use was demonstrated by the
measurement of hydrogen adsorption by an activated carbon, as well
as Na-A zeolite, up to a pressure of around 11 MPa in the temperature
range 273-323 K. Methane adsorption was also measured for the
zeolite sample at 303 K up to a pressure of 11 MPa. Furthermore,
the data for the carbon sample compared well with gravimetrically
determined isotherms measured under the same conditions. In these
differential instruments, the principle of operation is the expansion
of the gas into dual sample cells, one of which contains the sample
itself, while the other acts as a reference. The amount of adsorption
is then calculated by the pressure differential between each arm of
the apparatus.
et al.
1..
Temperature-Programmed Desorption
Temperature-programmed desorption (TPD), which is also known as
thermal desorption spectroscopy (TDS), determines the amount of
hydrogen desorbed from a sample as a function of temperature. The
desorbed hydrogen can be detected in a number of ways. TDS is often
the terminology reserved for the technique that uses a quadrupole
mass spectrometer to detect the desorbed hydrogen [12-14], but
other methods can also be used. These include the measurement of
the increase in pressure in a fixed volume, the pressure above the
vacuum pump system into which the hydrogen is being desorbed, the
use of a thermal conductivity detector (TCD) and the measurement
of weight loss by the sample (
TGA) [15].
However, generally speaking, the first two of these alternatives are
thermogravimetric analysis,
