Biomedical Engineering Reference
In-Depth Information
30 MPa. Figure 2.17 puts in evidence that when the single-wall
nanotube samples are saturated with hydrogen, the Langmuir
saturation (H
/C) ≈ 0.055 reveals fully itself at pressures ≥ 30 MPa,
corresponding to (H
2
s
) ≈ 0.18 (Eq. (2.33)) and agrees with the
sorption monolayer model. No disintegration of the bundles has been
evidenced in this case, although the pressures have been 10 times
higher than those used in Ref. [77], which, in particular, corroborates
the data on the electric resistivity of the samples due to hydrogen
sorption at different pressures [74]. Therefore, high pressure does not
play a great role in the anomalous sorption of hydrogen (see Fig. 2.16)
and it is not the main reason for the occurrence of the anomalous
sorption or disintegration of the single-wall nanotubes bundles,
contrary to the assumption in Ref. [77].
We note that the experimental value of a maximum sorption
capacity (0.9 wt%, or (H
/C
exp
2
/C)
≈
0.055) of the single-wall nanotube
samples used in Ref. [74] (see Fig. 2.17) agrees with the reduced
sorption capacity value of about 1.1 wt% per 1000 m
2
, which is
quite close to the similar characteristic, 1.5 wt% per 1000 m
2
g
−1
2
−1
g
, for
carbon sorbents obtained in Ref. [29].
Figure 2.17
Hydrogen sorption isotherms at 294 K for the clean single-wall
nanotubes (1) and activated carbon (2) (from
Ref
. [77]).
The sorption data gathered in Ref. [74] for single-wall nanotube
samples can be described via the Henry-Langmuir adsorption isotherm
using Eqs. (2.14) and (2.15) with the values of ∆
ads
ads
H
and ∆
S
close
to those for chemisorption process I (∆
H
and ∆
S
), listed in
(13)I
(13)I
Table 2.1.
