Interaction of diamond with ultrafine Fe powders prepared by different procedures

Article abstract of DOI:10.1134/S0020168511070077

We have studied the interaction of synthetic diamond crystals with ultrafine Fe powders during catalytic diamond gasification in a hydrogen atmosphere at 900°C. The Fe powders were prepared by three procedures: reduction of Fe₂O₃ nan

Full text of DOI:10.1134/S0020168511070077

ISSN 0020ꢀ1685, Inorganic Materials, 2011, Vol. 47, No. 8, pp. 864–868. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © A.I. Chepurov, V.M. Sonin, A.A. Chepurov, E.I. Zhimulev, B.P. Tolochko, V.S. Eliseev, 2011, published in Neorganicheskie Materialy, 2011, Vol. 47,
No. 8, pp. 957–961.
Interaction of Diamond with Ultrafine Fe Powders
Prepared by Different Procedures
A. I. Chepurova, V. M. Sonina, A. A. Chepurova, E. I. Zhimuleva,
B. P. Tolochkob, and V. S. Eliseevc
a Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences,
pr. Akademika Koptyuga 3, Novosibirsk, 630090 Russia
b Institute of SolidꢀState Chemistry and Mechanochemistry, Siberian Branch, Russian Academy of Sciences,
ul. Kutateladze 18, Novosibirsk, 630128 Russia
c Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 11, Novosibirsk, 630090 Russia
eꢀmail: chepurov@uiggm.nsc.ru
Received November 9, 2010
Abstract—We have studied the interaction of synthetic diamond crystals with ultrafine Fe powders during
catalytic diamond gasification in a hydrogen atmosphere at 900°C. The Fe powders were prepared by three
procedures: reduction of Fe2O3 nanopowder; evaporation using an ELVꢀ6 electron accelerator, followed by
condensation; and reduction of ferric chloride. The surfaceꢀprocessed diamond crystals were examined by
electron microscopy. The results indicate that ultrafine powders produced by the first two procedures cause
predominantly lateral etching of diamond. The Fe particles prepared by the third procedure penetrate into
the bulk of diamond crystals and produce etch pits and “tunnels,” thereby markedly increasing the specific
surface area of the crystals.
DOI: 10.1134/S0020168511070077
INTRODUCTION
laterally (along their faces), whereas natural diamond is
etched along the normal to its faces, with the formation
of very rough surfaces. Such studies were carried out for
Thermochemical (nonabrasive) processing of synꢀ
thetic and natural diamond is a chemical process
because it relies on catalytic diamond gasification in a
hydrogen atmosphere [1]. This process involves four
steps:
(1) transfer of carbon atoms from diamond to the
surface layer of the metal catalyst,
metal particles ranging in size from 1 to 3 m.
µ
This work examines the interaction of diamond with
smaller Fe particles (100 nm or less in size) prepared by
different procedures with the aim of studying the etching
behavior of diamond in the course of hydrogenolysis.
(2) carbon diffusion in the bulk of the metal,
(3) vaporization of the carbon dissolved in the metal,
and
EXPERIMENTAL
(4) the removal of the gaseous carbonꢀcontaining
species from the reaction zone.
Experiments were carried out in flowing hydrogen in
a waterꢀcooled temperatureꢀcontrolled microchamber
equipped with an observation window. The process was
followed using an MBSꢀ9 optical microscope. Hydroꢀ
gen was produced by an SGSꢀ2 electrolytic generator
and was introduced into the microchamber at a flow
rate of 3 l/h. The temperature was measured by a W/Re
thermocouple. The investigation technique was similar
to that described elsewhere [6, 7].
Several techniques for diamond processing are based
on this process: marking (including engraving), cutting,
deep pattern etching, lapping, polishing, and brazing of
metallic contacts to diamond [2]. In the last case, a
microscopically rough diamond surface is needed [3].
There is solid experimental evidence that, when
powder catalysts are used, etching with transition metal
particles depends on the crystallographic orientation of
the face and the structure of the diamond crystals [4, 5].
We studied diamond crystals grown on (001)ꢀoriꢀ
This effect is particularly highlighted by comparison of ented seeds in the Fe–Ni–C system at 5.5 GPa and
synthetic and natural diamond crystals. This is caused 1500 using a splitꢀsphere multianvil highꢀpressure
°C
by the presence of defects, around which interaction apparatus and a procedure described earlier [8]. The
mainly occurs. Synthetic diamond crystals grown under crystals had octahedral habits with cube and trapezoheꢀ
stable conditions are more perfect than natural diaꢀ dron modifying facets and belonged to type Iba accordꢀ
mond. For this reason, they are etched for the most part ing to the physical classification.
864

INTERACTION OF DIAMOND WITH ULTRAFINE Fe POWDERS
865
The catalyst used was ultrafine Fe powder, which
offers the highest catalytic activity for the process in
question [9, 10]. Fe particles suspended in a drop of ethꢀ
anol or BFꢀ6 adhesive diluted with ethanol were applied
to {111} faces of diamond crystals cleaned with a mixꢀ
1
2
3
ture of K2Cr2O7, H2SO4, HCl, and H2O and dried. After
ethanol evaporation, the crystals were placed in the
microchamber.
Ultrafine Fe powders were prepared by different
procedures.
4
In one procedure, ferric oxide (Fe2O3) powder
(OSCh 2ꢀ4 grade, Donetsk Plant of Chemical
Reagents) was reduced directly in the microchamber
during heating. The particle size ranged from 100 to
300 nm as determined by electron microscopy. The ferꢀ
ric oxide particles formed spherical agglomerates up to
10
µ
m in size.
In another procedure, Fe powder was prepared using
an experimental setup built around an ELVꢀ6 commerꢀ
cial electron accelerator (Budker Institute of Nuclear
Physics, Siberian Branch, Russian Academy of Sciꢀ
ences).
Fig. 1. Schematic of the experimental setup for the prepaꢀ
ration of metal nanoparticles using an ELVꢀ6 accelerator:
(
(
1
) ELVꢀ6 electron accelerator, (
2) evaporator reactor,
The setup for the preparation of metal nanoparticles
comprised the ELVꢀ6 accelerator, an evaporator reacꢀ
tor, a condenser, and a filtration system (Fig. 1). The
accelerator parameters are as follows: electron energies
from 0.8 to 1.5 MeV; beam power, up to 100 kW; and
beam current, up to 100 mA. In our experiments, the
accelerator parameters were as follows: electron energy,
1.4 MeV; beam current, 3 mA; and beam power, 4.2 kW.
To produce nanoparticles in this setup, a metal is heated
by an electron beam to boiling in the evaporator reactor
and evaporated. The vapor is then cooled in a flowing
inert gas (argon) in the condenser. This procedure
ensures an almost inertialess energy transfer to a subꢀ
stance, with keyhole melting and effective evaporation
of the metal. The Fe particles obtained using the ELVꢀ6
accelerator ranged in size from 100 to 300 nm.
3) condenser, ( ) filtration system.
4
cursor to ultrafine Fe particles. A drop of the solution
was placed on the surface of a diamond crystal. After
drying, the crystal was placed in the microchamber,
where the ferric chloride was reduced to metallic Fe in
hydrogen.
All experiments were performed under standard
conditions: 900°C, 1 h (one experiment took 15 min;
the crystals were then examined under an MBIꢀ15 optiꢀ
cal microscope and again heated). Next, the surface of
the diamond crystals was examined on an LEO
1430 electron microscope.
In addition, to minimize Fe particle agglomeration
we attempted to deposit particles onto the surface of
diamond crystals directly in the setup. Several diamond
crystals were glued with BFꢀ6 in different parts of the
setup: on the lateral, cylindrical surface and lid of the
condenser, on the lateral surface and bottom of the conꢀ
tainer in the filtration system, and in the outlet pipe
downstream of the filter. To study the deposited partiꢀ
cles, a special film was glued in the condenser.
In that experiment, no inert gas was used because we
wanted to obtain iron oxide particles. This was done
because iron oxide particles crystallizing from the vapor
phase were faceted and were expected to acquire an
active surface during hydrogen reduction.
The resultant particles ranged in size from 20 to
100 nm (Fig. 2). The experiment was performed at an
electron energy of 1.4 MeV (Fig. 3).
20 nm
In a third procedure, FeCl3
⋅ 6H2O (pure grade, RF
State Standard GOST 4147ꢀ74) in solution (1 or 5 g of
ferric chloride for 100 ml of water) was used as the preꢀ
Fig. 2. Iron oxide particles deposited on film in the conꢀ
denser of the setup at the ELVꢀ6 accelerator.
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866
CHEPUROV et al.
One drawback to this process is particle agglomeraꢀ
tion. Agglomerated particles make broad, striated
grooves where an individual stria corresponds to an
individual particle. Large agglomerates of Fe particles
typically move in one direction and rarely change the
direction of their motion. In addition, the Fe particles
have faceting elements in the form of small flat facets.
As expected, the number of particles deposited onto
the surface of diamond crystals using the electron accelꢀ
erator was very small and had a local distribution. Most
of the particles were not agglomerated and ranged
widely in size. The number of particles on the crystals
situated in the container of the filtration system
exceeded that on the crystals in the condenser. Neverꢀ
theless, the interaction of Fe particles with the surface
of diamond crystals was similar to that in the experiꢀ
ments described above (Fig. 5). The size of the etch
grooves was minimal across the samples. The correꢀ
sponding size of the Fe particles was ~50 nm.
Thus, the key features of the interaction of the
ultrafine Fe particles prepared using the ELVꢀ6 electron
accelerator and by reducing Fe2O3 with the octahedron
faces of synthetic diamond crystals in a hydrogen atmoꢀ
sphere are predominantly lateral etching and random
migration of the particles over the octahedron faces.
This is in full accord with earlier results for micronꢀ
sized Fe particles [5, 6].
The results obtained by reducing FeCl3 differed
drastically from those above. There was little or no latꢀ
eral etching, i.e., no migration of Fe particles over the
surface of diamond crystals and no etch grooves. The Fe
particles produced by hydrogen reduction rapidly penꢀ
etrated into the bulk of the crystals and produced etch
pits and “tunnels” (Fig. 6). The individual pits ranged
in size from ~200–300 to 50 nm or, possibly, less. These
values are the sizes of the Fe particles.
Thus, when ultrafine Fe particles are prepared via
reduction of ferric chloride, diamond crystals are
etched only along the normal to their faces. It is also of
great interest that this etching behavior is independent
of the crystallographic orientation of diamond crystal
4.2
0
1
3
Time, min
Fig. 3. Accelerator current vs. time in an experiment aimed
at depositing iron oxide particles onto diamond crystals.
RESULTS AND DISCUSSION
The interaction of diamond with Fe particles preꢀ
pared by reducing OSCh 2ꢀ4 Fe2O3 or using the ELVꢀ6
electron accelerator produced complex etch patterns in
the form of numerous grooves on the octahedron faces
of synthetic diamond crystals in hydrogen (Fig. 4). The
etch patterns are traces of Fe particles migrating over
the diamond surface. Their width corresponds to the
size of the Fe particles. Some of the grooves have a flat
bottom parallel to the (111) plane. There are few or no
straight grooves: they are typically tortuous, with many
irregular bends. From a local area of a face, Fe particles
may migrate in various directions, even in opposite
directions. The grooves intersect at various angles. The
behavior of Fe particles in an already existing groove is
also irregular: they may move in the same direction as
the preceding particle, intersect its trace, or move in the
opposite direction.
20 µm
100 µm
(а)
(b)
Fig. 4. Typical etch patterns produced on the octahedron faces of diamond crystals by hydrogenolysis catalyzed by Fe particles
prepared (a) by reducing Fe O and (b) using the ELVꢀ6 electron accelerator.
2
3
INORGANIC MATERIALS Vol. 47
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2011

INTERACTION OF DIAMOND WITH ULTRAFINE Fe POWDERS
867
2
µ
m
20 µm
(b)
(а)
Fig. 5. Etch patterns produced on the octahedron faces of diamond crystals by hydrogenolysis catalyzed by Fe particles prepared
by reducing ferric oxide deposited using the ELVꢀ6 electron accelerator. The arrows show the migration direction of a metal parꢀ
ticle.
10
µ
m
200 nm
(а)
(b)
Fig. 6. Etch patterns produced on the octahedron faces of diamond crystals by hydrogenolysis catalyzed by Fe particles prepared
by reducing ferric chloride.
faces; i.e., faces differing in Miller indices have similar preparation procedure. One possible reason for this is
etch patterns. Such processing produces extremely that the preparation procedure influences the surface
active diamond surfaces, which suggests that this effect activity (degree of faceting) of the particles. Ultrafine
might be used not only to fabricate composite materials powder prepared by reducing ferric chloride markedly
with brazed diamond layers and tools containing diaꢀ increases the specific surface area of diamond crystals,
mond parts brazed to metallic holders but also to preꢀ thereby extending the field of their potential applicaꢀ
pare active diamond powder adsorbents for chromatogꢀ tions.
raphy, diamond whiskers, etc. The described approach
is competitive with processes that rely on the oxidation
of diamond surfaces [11, 12].
ACKNOWLEDGMENTS
Note that the effect in question requires further
investigation because a transition from one rateꢀlimitꢀ
ing steep to another is possible during catalytic diamond
hydrogenolysis.
This work was supported by the Siberian Branch of
the Russian Academy of Sciences through the interdisꢀ
ciplinary integrated project no. 35: Thermochemical
Processing of Synthetic Diamond Crystals with Metal
and Alloy Nanoparticles.
CONCLUSIONS
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