Biomedical Engineering Reference
In-Depth Information
s
def
close (in the order of magnitude) to the values of
(Sections
3.3 and 5.1; Tables 2.1 and 2.2) characteristic for the van der Walls
interaction, which, obviously, points to the physical mechanism of
sorption process
D
and
D
.
The very high sorption capacity of
αX
≤ 6] is
considerably greater than the maximum hypothetical chemisorption of
H corresponding to the formation of CH
αX
process [(H/C)
αX
chemicomplexes. It points to
the physical mechanism of sorption, which can be theoretically related
to clusterization [31, 102], condensation [29, 30], and/or polylayer
intercalation [12, 103] of the adsorbate. A similar situation occurs in
the case of the anomalous process of unsaturable H sorption in single-
wall nanotube samples examined in Ref. [77] (see Fig. 2.16), up to the
adsorbate concentrations (H/C) ≈ 1 and (H/C
4
s
) ≈ 4 at 80 K and 12
MPa. This situation is believed to be the cause of the disintegration or
“swelling” of bundles of single-wall carbon nanotubes.
A similar situation also occurs for the process of super-
adsorption of hydrogen in GNF samples studied in a series of
experiments performed in Ref. [104]. The highest concentration
reached in these experiments is about 17 wt%, with (H/C) ≈ 2.5 at
about 300 K and 8 MPa, which concentration would match the DOE
requirements [1-3] on the “gravimetric” capacity.
The process reported in Ref. [104] results in a very distinct
nanostratification (of the intercalation nature) of the GNF bundles
structure (Fig. 2.20). These data may be considered as a direct
experimental proof of the mechanism of polylayer hydrogen
intercalation in GNF structures. The observed multilayer intercalation
has been induced by the monolayer chemisorption of types II and III
(Table 2.1).
A rather high value of the adsorbate volume (mass) density can be
estimated from data reported in Ref. [104]. It can provide a carryout
of the DOE requirements [1-3] on “volumetric” density. Overall,
the experimental multilayer intercalation phenomenon shown in
Ref. [104] seems to be coherent with the super-adsorption
sensational data reported for GNFs in Ref. [12], about 40 wt%
(hydrogen mass on the total carbon plus hydrogen masses), charging
at 300 K and with a H
exp
gas pressure of 11 MPa.
This result might be attributed, according to the above analysis,
to multilayer hydrogen intercalation (or condensation) between
the graphene sheets in GNFs induced by monolayer chemisorption
of types II and III (Fig. 2.6). Comparing Fig. 2.6 to Fig. 2.1 from
2
