Biomedical Engineering Reference
In-Depth Information
On the basis of Eqs. (2.5), (2.6), (2.14), and (2.15), the
thermodynamic characteristics of a sorption process, including ∆
ads
,
can be determined from experiments evaluating the dependence of
a TPD peak area on the temperature and pressure of the hydrogen-
saturated material, controlling the way for reaching the equilibrium
state [10, 51].
Overall, the total equilibrium concentration
H
of
the hydrogen absorbed by the carbon material (at hydrogen
saturation temperature
X
=
(H/C)
∑
Σ
), which corresponds to
chemisorption processes I-IV, can be described by the equation
T
and pressure
P
H
2
s
def
I
I
C
C
C
C
def
(2.32)
X
2
X
+ 2
X
+
X
+
X
I
II
III
IV
C
C
C
C
where the atomic fractions of the localized regions with different
chemisorption centers in the material are taken into account.
The methods used to indirectly determine through experiments
the atomic fractions of the surface sorption-active regions and the
maximum local concentrations of adsorbent and the method used
to identify the nature of process, are discussed and illustrated by
examples in the next section, along with the analysis of the results
presented in Refs. [26, 62-64, 70, 72].
2.2.4 Use of Novel Approaches in the Sorption
Data Analysis
2.2.4.1
Method for Determining the Fraction of Surface
Carbon Atoms and Active Sorption Centers in Single-
Wall Nanotubes: Sorption Monolayer Model
We examine the widely cited data [26] (see Figs. 2.4 and 2.9; Dillon
et al.
) on the TPD peaks A and B for single-wall nanotube samples
(0.1-0.2 wt%) with a predominant content of soot and amorphous
carbon (about 80 wt%) and a metallic catalytic agent (about
20 wt% Co). It should be noted that nobody has so far been able to
reproduce these data. The hydrogen saturation has been done for
10 min at 273 K and a hydrogen pressure up to 40 kPa with
subsequent ageing and additional hydrogen saturation for 3 min
at 133 K. The experimental value of thermal adsorption activation
energy (
des
−1
, Eq. (2.19)) obtained in Ref. [26] for the
TPD peak B (Fig. 2.9c) coincides with the value of
E
≈ 19.6 kJ mol
a
Q
in Table 2.1. It
I
