Biomedical Engineering Reference
In-Depth Information
all investigated UDD the main products of desorption were H
O
2
(100-600°C), CO
(above
800°C), as shown in Fig. 6.3 for two different samples. In some cases
traces of hydrocarbons (200-400°C), HCN (above 800°C), HCl, and
SO
(200-600°C), CO (500-1100°C), and H
2
2
(400-600°C) were also observed (not shown in Fig. 6.3). Some
features of thermal desorption of H
2
O, CO, and CO
are presented in
2
2
Table 6.2.
Table 6.2
Total amounts (in relative units) and temperature peaks
(shown in parenthesis) of H
desorbed from
UDD of different types under heating up to 1100°C
O, CO, and CO
2
2
CH-7
S-1
K-2
B-1
A-1
A-2
G-1
H
O
1.21
(360, 580)
0.72
(140, 370)
1.06
(130, 480)
1.48
(215)
0.59
(360)
1.03
(350, 590)
1.07
(140, 480)
2
CO
3.22
(340, 710)
7.46
(475)
9.32
(580, 840,
1000)
6.95
(710)
3.43
(640)
2.20
(740)
8.7
(600, 800,
1030)
CO
1.06
(330, 480)
3.65
(440)
1.96
(550)
2.23
(430)
1.35
(450-550)
0.6
(400-600)
1.94
(540)
2
The difference between the investigated samples consists, first
of all, in the CO and CO
contents and in the temperature profiles of
desorption of such species. In the general case the spectra of thermal
desorption of CO and CO
2
(Fig. 6.4) result from the superposition of
several desorption peaks with the maxima in the range 300-1000°C.
Each peak corresponds to the decomposition of a specific functional
group. A more accurate analysis of the profiles of thermal desorption
can be performed by the mathematical decomposition into separate
Gaussian components [42]. As an example, the profile of thermal
desorption of CO from the sample K-2, reported in the insert of
Fig. 6.4, is satisfactorily described by the superposition of five bands
with maxima near 560, 630, 720, 850, and 1020°C, respectively, and
with a half-width of 110-150°C.
2
desorption profiles under linear heating
of UDD can be explained by the following simplified scheme [46, 42].
The carboxyl groups are decomposed at low temperatures (below
400°C) giving rise to the desorption of CO
The trend of CO and CO
2
. In the range 400-600°C
the acid anhydride groups are destroyed with the desorption of both
CO and CO
2
observed at 600-700°C
can be connected to the decomposition of lactone groups. The
. Noticeable desorption of CO
2
2
