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(
in Fig. 2.6), indicating the release of the residual fraction
(about 25%) of the adsorbate [(H/C)
β
and
γ
≤
2].
The analysis of the experimental data [12] carried out in Refs.
[10, 17-25, 97] shows that these TPD peaks
β
+
γ
are fairly
well described by thermodynamic and diffusion equations and
characteristics corresponding to the respective chemisorption
processes II and III. In other words, about 25% of the data obtained
in Ref. [12] in 1999, referring to TPD peaks
β
and
γ
, fairly well agree
with the data obtained by other researchers (see Refs. [14, 51-56,
61, 62, 94, 95]) in the period from 1999 to 2005 (Table 2.1 and
Figs. 2.5 and 2.7).
As a consequence, for at least 25% of the data reported in Ref.
[12], no mention is made of large and systematic methodological
errors, delusions, or mystifications. This fact is not mentioned
anywhere except in our series of papers [10, 17-25, 97]. We
therefore believe that it is useful to consider the theoretical
possibility, nature, and characteristics of the sorption process
αX
β
and
γ
that prevails in GNF [12] and which could satisfy the main
technical requirements [3-5], that sorbent materials have to
meet if hydrogen is to be accumulated on-board for vehicular
applications. To establish the nature of the
process in the GNF
samples studied in Ref. [12], similarly to the study reported in
Ref. [94] for an
αX
process in the GNF samples, we have to estimate
the corresponding diffusivity by equations of type (2.22) and
(2.25), corresponding to the fundamental diffusion law [68, 71].
We can use the data reported in Ref. [12], regarding the
release of about 33 wt% of hydrogen [(H/C)
α
≤ 6] corresponding
αX
to the sorption capacity for
αX
process by the hydrogen-saturated
samples kept at 298 K for
≥ 10 min. The remaining adsorbent
(about 15 wt% of hydrogen, (H/C)
τ
≤ 2) is released only after
thermal desorption, induced by heating up to about 1223 K, which
manifests itself in two high-temperature TPD peaks (
β
+
γ
in
Fig. 2.6). Assuming that the characteristic diffusion path is
comparable with the linear size of the GNF samples [12] (
β
and
γ
≈ 0.5
cm) and the diffusion time at 298 K is about 5 min, we obtain the
diffusivity value
L
⋅
-4
2
-1
D
αX
≈ 8
10
cm
s
for hydrogen in process
αX
.
As in the case of
α
process in GNF samples [94], the obtained
value of
D
αX
is several orders of magnitude greater than the value
of
(at 298 K) corresponding to chemisorption process I and it is
several orders of magnitude less than the gas diffusivity [68]. It is
D
I
