Biomedical Engineering Reference
In-Depth Information
kinetics,
correspond to the respective diffusion-adsorbate
activation energies.
When the TPD peaks A and B (curve 3 in Fig. 2.9a) are separated
and the areas of the peaks
E
and
E
A
B
t
→
S
(
T
(
t
))
,
S
(
T
(
∞
))
≈ S
S
and
,
,
A
A
∞A
∞B
S
), we can
estimate the relative adsorbate concentrations corresponding to
different temperatures and heating times using the expressions
(
T
(
t
)) are determined for the different temperatures
T
(
t
B
X
(
T t
( ))
S
S
(
T t
( ))
,
A
A
A
(2.28)
X
S
0A
A
X
(
T t
( ))
S
S
(
T t
( ))
,
B
B
B
(2.29)
X
S
0B
B
where
X
and
X
are the initial concentrations of the adsorbed
0A
0B
hydrogen at
= 0. Next, we can determine the desorption activation
energies of the processes A and B using the formulas
t
X
/
T
E
A
A
(2.30)
ln
-
const.,
[
S
-
S
(
T t
( ))]/
S
RT
A
A
A
X
/
T
E
B
B
ln
-
const.,
(2.31)
[
S
-
S
(
T t
( ))]/
S
RT
B
B
B
The estimation of desorption activation energies for the
processes corresponding to the TPD peaks A and B (curve 3 in
Fig. 2.9a) from Eqs. (2.27)-(2.31) yields values
E
≈ E
≈ Q
close to
A
B
I
the diffusion activation energy
for chemisorption process I (see
Table 2.1). This agrees with the results of the analysis (presented in
Table 2.2) of thermal desorption data in works [26, 70], where the
Kissinger method has been used.
Similar estimates for TPD peaks for isotropic graphite [51,
53] (see Figs. 2.5 and 2.7a), for irradiated isotropic graphite [53]
(Fig. 2.7b) and for nanostructured graphite [14, 53] (Fig. 2.7c), yield
values of
Q
I
E
des
close to those of
Q
Q
, and
Q
in Table 2.1. Similarly,
,
a
III
IV
II
E
des
we can obtain values of
for the TPD peaks
β
and
γ
for GNF samples
a
[12] (see Fig. 2.6) that are close to
respectively. The same
method can be used for the complex processing and comparison of
gravimetric (integral) and TPD (differential) data presented, e.g., in
Ref. [12].
Q
and
Q
,
II
III
