Biomedical Engineering Reference
In-Depth Information
Figure 2.10
The TPD spectra (peaks A and B) for hydrogen in the single-
wall nanotube samples, hydrogen-saturated for 1 h at 298 K
and 2 MPa [70]. Different TPD curves correspond to different
heating rates (
min
-1
). The inset shows a dependence
(in Kissinger coordinates) of the TPD peak maximum A on
the heating rate of the sample.
β
, K
ads
des
D
H
ads
=
E
-
E
,
(2.26)
a
a
provided that the direct and “inverse” reactions follow the same path.
In the typical case where
E
des
E
des
ads
[63, 70].
It is also advisable to examine a possible method to estimate the
activation energy
= 0, we have ∆
H
=
-
a
a
E
des
of sorption processes using the sample TPD
spectra with a single heating rate
a
, ensuring a sufficient “spread” of
processes in temperature and time. This alternative method, simple
and efficient if compared to the Kissinger one, can be illustrated
considering the curve 3 (peaks A and B) in Fig. 2.9a, which can be
described (up to a constant “scaling” factor) by the equation
β
X
X
1
A
+
B
-
[
K
X
(
T t
( )) +
K
X
(
T t
( ))],
(2.27)
b
A
A
B
B
T
T
are the rate constants.
)) are the running values
of adsorbate concentration in the heated sample for different
temperatures
X
(
T
(
t
)) and
X
(
T
(
t
A
B
E
des
) of
the corresponding desorption processes. In the case of diffusion
T
(
t
),
E
and
E
are the activation energies (
A
B
a
