Biomedical Engineering Reference
In-Depth Information
[109] (0.3 and 0.7 wt%; see also Fig. 2.3, [16]), but are significantly
different (by two to three orders of magnitude) from the data in Refs.
[12, 104] (see Fig. 2.20). Based on these facts, Blackman
[107]
together with many other researchers, conclude that the anomalous
results [12, 104] and those presented in Figs. 2.3 and 2.4 may be
caused by methodological factors.
In such context, it is worth noticing that the data in Ref. [107]
are close to the sorption data in Ref. [64] (see Figs. 2.11 and 2.12),
obtained by the same volumetric method combined with diferential-
pressure measurements. The considerations made in the course of
this chapter show that the data of both researchers groups, as well
as the data of the other well-known studies [16, 84, 108, 109], may
correspond to the manifestation of another sorption process (physical-
like monolayer chemisorption of type I, Table 2.1), in contrast to the
anomalous data [12, 104] here examined (see Figs. 2.6 and 2.20). As
a consequence the “diagnosis” made by many researchers concerning
the methodological reasons for the experimental anomalies [12, 104],
and Figs. 2.3 and 2.4 do not seem to be sufficiently justified.
It is also useful to consider the data in Ref. [61] (see Fig. 2.4)
on the anomalously low sorption capacity and extremely slow
thermal desorption of deuterium (with the activation energy
et al.
des
E
≈
a
Q
Table 2.1) from the single-wall nanotube samples deformed by
ball-milling and saturated at room temperature and 0.08 MPa. The
analysis of these data (see Section 4) using Eqs. (2.22)-(2.24) and
the characteristics for process II (Table 2.1), shows that the sorption
process is limited by diffusion (
II
,
D
) of deuterium over the distance
II
L
≈ 20 µm (comparable with the thickness of the single-wall nanotube
sample), corresponding to chemisorption process II. Hence and
differently from the consideration done in Ref. [8], the data in
Ref. [61] are not in contrast with the ones in Refs. [12, 104] on the
anomalously high sorption capacity of the material (H/C)
≤ 6 (≤40
wt%) and very fast (physical) kinetics of hydrogen desorption from
the material (
αX
).
In the review [110], carbon nanomaterials (GNFs), as well as
Mg-based materials, and complex light-metal hydrides are regarded
as the most promising adsorbents of hydrogen, capable of ensuring a
very high sorption capacity and desorption kinetics; the researchers
noted the need for further basic research in this field.
D
αX
>>
D
II
