Biomedical Engineering Reference
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ch
monatomic centers (C
) corresponding to model G in Fig. 2.8. For
diatomic carbon centers corresponding to model F, instead of a stage
similar to (2.12), the following reaction must be considered:
s
s
s
s
2H
+ C
(C
= 2H)
(12a)
2ch
2
ch
s
where H
are the hydrogen atoms on the surface areas of the material
s
(C
) outside the diatomic carbon chemisorption centers (C
), and
ch
2
s
ch are the adsorbed pairs of hydrogen atoms at the diatomic
carbon centers localized on the material surface.
Process I is described by expressions similar to (2.14)-(2.18)
and can be characterized by the experimental value [31, 51] (Section
2.2.2.4) of the standard enthalpy of adsorption of one hydrogen
molecules mole
(C
=2H)
s
2
,
D
D D
D D
 
-1
H
H
H
H
H
10 7kJ mol (H )
(13)I
dis
(12)I
dis
(12a)I
2
where ∆
(2H) is the experimental
value of the enthalpy of C=2H chemical bonds formation, linking two
hydrogen atoms to one carbon atom, or of C2-2H bonds, linking two
hydrogen atoms to two carbon atoms on the surface of the adsorbent
(see Fig. 2.8, models G and F, respectively).
Process I is characterized by the experimental value reported in
Refs. [26, 62-64] for the effective enthalpy of the hydrogen-molecule
diffusion activation
H
≈ ∆
H
= −460 ± 10 kJ mol
−1
(12)I
(12a)I
s
s
Q
Q
-
H
= 20 ± 2 kJ mol
(H2), where
Q
= 10
-1
I
(13)I
± 8 kJ mol
(H2) is the experimental value of the energy of hydrogen-
molecule diffusion activation on the surface of the material or at the
maximum (carbohydride) filling of the chemisorption centers of a
diffusant capture.
We believe that
-1
s
def
−1
(H2) and that such values
of the energy for activation of the hydrogen-molecule diffusion in
carbon materials occur in the process of nondissociative physical
sorption of hydrogen.
We also note that the experimental values of the diffusion
characteristics
Q
Q
≈ 10 kJ mol
s
def
l
are of the same order of magnitude
of the values of the energy of activation for hydrogen diffusion in
nanostructured graphite obtained in NMR studies [65]. Apparently,
this corresponds to the conditions required for evidencing the
hydrogen-graphite van der Waals interaction and also agrees with
theoretical values in Refs. [40, 66, 67] for the diffusion characteristics
Q
,
Q
, and
Q
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