Biomedical Engineering Reference
In-Depth Information
(sample S-1), and reflects the substantially different structure of
the oxygen-containing groups. This signal has practically identical
position (1800-1810 cm
-1
) after thermal oxidation regardless of the
type of UDD.
The TDMS method can be successfully used for determining the
optimum regime (temperature and duration) of thermal oxidation
of UDD and for checking the state of the oxidized surface. Figure 6.8
demonstrates the variations of the profiles of thermal desorption
of CO and CO
with the temperature of oxidation in air during
40 minutes for sample CH-7. The noticeable modification of surface
(increase in the desorption rate of CO
2
and CO near 600°C) is
observed at oxidation temperature as low as 300°C (Fig. 6.8, curve 3).
The main changes in the desorption profiles occur in the range
of 300-400°C. A further rising of oxidation temperature must be
avoided because of the possible losses of material (combustion) and
the increase in the concentration of nonvolatile impurities (metals,
etc.) on the surface due to the combustion of diamond.
The thermal oxidation in air seems to be an effective way to
unify the surface properties of various UDD and certainly is more
environment-friendly than acid treatment or the modification by
ozone [39, 40]. The additional advantage of thermal oxidation could
be the removal of non-diamond carbon from UDD as shown in
Ref. [77].
2
565
o
530
o
760
o
CO
CO
2
5
5
4
4
3
3
2
2
1
1
0
200
400
600
800
1000
0
200
400
600
800
1000 1200
TEMPERATURE,
o
C
Figure 6.8
Temperature profiles of CO and CO
release from UDD
CH-7 after heating in air at different temperatures: (1) without
heating; (2) heating temperature 200°C; (3) 300°C; (4) 400°C;
and (5) 450°C.
2
