Biomedical Engineering Reference
In-Depth Information
oxidation processes of nanodiamonds of different types. Noticeable
oxidation with mass loss begins at temperatures of 430-450°C; the
maximum is reached in the temperature range 520-560°C. The
specific surface area of nanodiamond powders (280-320 m
)
only slightly depends on the type of nanodiamonds [26]. The main
differences among UDD of different types are the nature of surface
impurities and the structure of functional surface groups. Elemental
analysis (for
2
g
-1
> 27) of nanodiamonds showed the presence of Fe, Cr,
Si, Ca, Cl, and S with different abundance of the order of 10
M
−
1
wt.%,
strongly depending on the UDD types [26].
These impurities are introduced mainly at the stage of the
chemical procedures for diamond extraction from detonation soot.
The whole surface concentration of these impurities in UDD particle
with the mean size of ~4 nm does not exceed 0.05 monolayer, at
least an order of magnitude lower than the concentration of surface
functional groups.
A clear difference was observed also in the amounts of the
volatile products released in vacuum from samples heated to
1100°C (the onset of intensive graphitization of nanodiamond
[3, 59]). It was established that the evolved gas volume (per sample
mass unit) can vary by a factor two for the different samples of UDD
with approximately the same specific surface area [26]. The mass
loss of UDD heated up to 1100°C in vacuum can reach 20-25% for
some samples. This result indicates that almost the whole surface of
UDD particle is covered by chemical functionalities forming volatile
products under heating. No distinct correlation was found between
the sedimentation stability of UDD colloids on one hand and both
concentrations of trace impurities and whole amounts of volatile
products on the other hand [26].
Some properties of investigated UDD samples are summarized in
Table 6.1.
6.3.3
FTIR Spectroscopy of UDD of Different Types
The high transparency of diamond in the infrared spectral range
and the high surface-to-volume aspect ratio of UDD allow to study
the surface chemistry of UDD using the IR-spectroscopy. The FTIR
spectra of as-received UDD powders of five different types, measured
in the diffuse reflection mode, are shown in Fig. 6.2. Different UDD
samples exhibit the following IR features similar to those observed
