SYNTHESIS AND CHARACTERIZATION OF NANODIAMONDS FROM
DIFFERENT CARBON PRECURSORS"
DIAMOND AND DIAMOND-LIKE CARBONS
J.B.Donnet 1, C. Le Moigne 1, T.K. Wang 1, and M. Samirant 2
ILab. Chimie Physique, ENSCMu, 3, rue A. Werner, 68093 Mulhouse cedex, France, 21nstitut de
Recherche Franco-Allemand de Saint-Louis, 5, Rue du Gdndral Cassagnou, 68300 Saint Louis, France
Results and Discussion
Introduction
(1) Explosion method
Synthetic diamonds can be prepared by static,
dynamic and chemical vapor deposition (CVD) methods.
The static method has been used industrially since a long
time and the CVD method has been considerably improved
in recent years. However, the dynamic method advanced
just smoothly and the mechanisms of diamond formation is
still controversed.
In this study, diamonds have been synthesized with
two dynamic methods: (1) The explosion method using
directly the carbon rich explosives as precursors; (2) The
shock wave method using the projectile impact and
different carbon precursors. The diamonds obtained have a
powder form with the particle size in the nanometer scale.
They have been characterized by several methods such as
the X-ray diffraction (XRD), electron diffraction (ED) and
transmission electron microscopy (TEM).
The HP and HT produced during the explosion in
our experiments are sufficient to transform the carbon
contained in explosives into diamonds. But the yields
depend strongly on the environmental media used. In the
air, the explosive was totally converted into gases and no
solid deposit was recovered. The light illumination and
temperature detection showed a post-combustion process.
In nitrogen gas, this combustion was inhibited and a
diamond containing soot mixture was obtained. If the
explosives (-250g) are immersed in water, the diamond
yields were seemingly improved. In the carbonaceous solid
mixture,, diamond content can reach 60% in weight after
the elimination of graphitic carbon.
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Experimental
Diamond synthesis
(1) Explosion method A mixture of explosives was
used as either high pressure (HP) and high temperature
(HT) producer or a carbon-rich precursor. The mixture is
composed of three explosives: trinitro-2,4,6 toluene
(C7HsN306, TNT),
cyclo- 1,3,5-trimethylene-2,4,6trinitramine (C3H6N606, RDX) and pentrite (CsHsO12N4,
PETN). The mixture was placed to the center of a closed
metal vessel equipped with two thermocouples measuring
the temperature till 1250°C, two optic fibers connected to
two oscilloscopes to detect the illumination signals during
1 microsecond and a system for the analysis of the gases
produced by the explosion. The experiments were realized
in air, nitrogen and water respectively.
(2) Shock wave method. Different carbon precursors,
such as graphite and carbon blacks mixed with copper
powder (5/95 w/w), were compressed into a cylindrical
slice of 12 mm in diameter and 1 mm in thickness and
confined into a still capsule. The projection system was
similar to that used by others [1 ]. The explosive used for
the projection was a TNT/RDX mixture (65/35) and can
give a detonation velocity of 8 km/s.
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50
40
Intensity
t
i
30 i
20
10
0
10
(220)d
20
30
40
50
60
70
80
90
100
20
Figure 1. X-ray diffraction (XCuKC1.5406A) pattem of
purified diamond obtained by the explosion method
X-ray diffraction (Fig. 1) and electron diffraction
results show that the diamonds obtained by explosion
method has a cubic crystalline structure. The size of the
diamond particles are quite homogeneous and are about
5-7 nm in diameter (Fig. 2). This agrees well with the
specific surface area measurement by nitrogen adsorption
(-~280m2/g). Interestingly, the surface of the particles
obtained directly by the explosion in water medium
contains many hydroxyl groups.
When the nanodiamond particles were heated at
1500°C in vacuum, onion-like carbon was obtained (Fig.
3). The of the onion-like particle has nearly the same size
as the diamond precursor, suggesting a in-situ transformation.
heterogeneity of the diamond particle size and morphology
favors the reconstructive diamond formation mechanism.
60.
55 i.
50 1!
45
40
35
Intensity
(002)g
(111)d
|
30
25
(220)d
15 ................................
10
20
30
40
50
60
70
80
(31 l)d
90
100
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Figure 4. X-ray diffraction pattern (XCuKC1.5406/~) of a
diamond-containing carbon obtained by projectile impact
on carbon black N 110.
Figure 2. TEM image of the nanodiamond particles
obtained with explosion method.
Figure 5. TEM image of a carbon particle with a diamond
core and graphitic shell, obtained by the shock wave
method with the carbon black N 110 as precursor.
Figure 3. Onion-like carbon obtained by heating the
nanodiamond at 1500°C in vacuum.
Conclusions
(2) Shock wave method
Nanodiamonds were synthesized by both explosion
and shock wave methods. The results suggest a reconstructive mechanism for diamond formation.
Diamonds were obtained both with graphite and
carbon black (Fig. 4) precursors. Copper was proved to be
necessary as quenching agent and catalyst. Typically, the
diamond-containing carbon particles have a diamond core
and graphitic shell structure (Fig. 5). The diamond core
can be monocristalline (Fig. 5) or polycristalline. The
graphitic shell structure contributes at least partly to the
(002)g peak of the X-ray diffraction pattern (Fig. 4) and
could be formed by the regraphitization process. The
References:
1. F. R. Norwood, R. A. Graham, A. Sawaoka, in Shock
Waves in Condensed Matter (ed. Y. M. Gupta), Plenum
Press, New York, 1986, p.837
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