Oxygen and structure transformations of h-BN in focal zone of an optical furnace
In this contribution the recent results on a synthesis of the new structures of boron nitride are presented. Light-induced catalyst-free heating of fine-grained graphite-like h-BN powders was performed in the flow of dried and purified nitrogen in an optical furnace. The new structures of boron nitr...
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Інститут проблем матеріалознавства імені І.М. Францевича НАН України
2009
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| Cite this: | Oxygen and structure transformations of h-BN in focal zone of an optical furnace / L.L. Sartinska, V.A. Tinkov, A.A. Frolov // Современные проблемы физического материаловедения: Сб. научн . тр. — К.: ІПМ НАН України, 2009. — Вип. 18. — С. 54-59. — Бібліогр.: 11 назв. — англ. |
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| citation_txt | Oxygen and structure transformations of h-BN in focal zone of an optical furnace / L.L. Sartinska, V.A. Tinkov, A.A. Frolov // Современные проблемы физического материаловедения: Сб. научн . тр. — К.: ІПМ НАН України, 2009. — Вип. 18. — С. 54-59. — Бібліогр.: 11 назв. — англ. |
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| description | In this contribution the recent results on a synthesis of the new structures of boron nitride are presented. Light-induced catalyst-free heating of fine-grained graphite-like h-BN powders was performed in the flow of dried and purified nitrogen in an optical furnace. The new structures of boron nitride were obtained. Scanning electron microscopy JSM-6490 supplemented with combined Energy Dispersive X-ray Spectroscopy (EDS) and Electron Backscatter Diffraction (EBSD) provided information about structures, phase and element transformation of fine-grained graphite-like h-BN powders. The coarse structures, thread-like nanostructures (whiskers or dendritic structures) and new morphologies were formed due to the interaction of BN plume with nitrogen ambient on the surface of the heated compacted h-BN samples. Complicated structure and element composition of the whiskers which were formed on the surface of heated samples of compacted h-BN powders were studied by scanning electron microscopy (SEM). X-ray Diffraction (XRD) study demonstrates presence of amorphous phase, pure boron of different modifications and boron nitride of different phase compositions on the surface of these substrates. The process of the synthesis, formation and growth of the nanostructures in an optical furnace was analyzed and understood. A role of oxygen in formation and growth mechanism of BN whiskers was proposed.
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UDC 661.65:661.55;539.22-620.18
Oxygen and structure transformations of h-BN in focal
zone of an optical furnace
L. L. Sartinska, V. A. Tinkov*, A. A. Frolov
*Kurdyumov Institute for Metal Physics of NASU, Kiev, Ukraine
In this contribution the recent results on a synthesis of the new structures of boron
nitride are presented. Light-induced catalyst-free heating of fine-grained graphite-like
h-BN powders was performed in the flow of dried and purified nitrogen in an optical
furnace. The new structures of boron nitride were obtained. Scanning electron
microscopy JSM-6490 supplemented with combined Energy Dispersive X-ray
Spectroscopy (EDS) and Electron Backscatter Diffraction (EBSD) provided information
about structures, phase and element transformation of fine-grained graphite-like h-BN
powders. The coarse structures, thread-like nanostructures (whiskers or dendritic
structures) and new morphologies were formed due to the interaction of BN plume with
nitrogen ambient on the surface of the heated compacted h-BN samples. Complicated
structure and element composition of the whiskers which were formed on the surface of
heated samples of compacted h-BN powders were studied by scanning electron
microscopy (SEM). X-ray Diffraction (XRD) study demonstrates presence of amorphous
phase, pure boron of different modifications and boron nitride of different phase
compositions on the surface of these substrates. The process of the synthesis, formation
and growth of the nanostructures in an optical furnace was analyzed and understood. A
role of oxygen in formation and growth mechanism of BN whiskers was proposed.
Introduction
Boron nitride (BN) has attracted considerable interest over the past decade
as a technologically important material, possessing at the same time an
interesting combination of physical and chemical properties. BN occurs in
several structures ranging from the sp2-bonded hexagonal BN (h-BN) or sp3-
bonded cubic BN (c-BN) to nanotube or fullarene structures [1, 2].
Boron nitride has a great potential in nanotechnology. Nanotubes of BN can
be produced and have a structure similar to that of carbon nanotubes, however
the properties are very different: whereas carbon nanotubes can be metallic or
semiconducting depending on the rolling direction and radius, a BN nanotube is
an electrical insulator with a wide band gap of ~5,5 eV (same as in diamond),
which is almost independent of tube chirality and morphology. Similar to other
BN forms, BN nanotubes are more thermally and chemically stable than carbon
nanotubes which favors them for applications.
Understanding the structure transformation mechanism of boron nitride is
of great fundamental and technological interest as point structure
transformations play a critical role in the growth of this material and are crucial
for the final electronic structure and mechanical properties of BN [3]. In
general, the exposure of the BN surface to the energetic light beam, to the
bombardment by energetic ions or other particles can give rise to substantial
changes within the volume of the material. Among them, local densification or
melting, compressive stress or production of point defects are shown to play
the dominant role in properties of the final material [4—6]. Molecular nitrogen,
© L. L. Sartinska , V. A. Tinkov, A. A. Frolov, 2009
54
http://en.wikipedia.org/wiki/Carbon_nanotube
N2, may also form easily N–N bonds in BN during ion-bombardment as N
atoms [7, 8].
High-temperature methods for structure and phase transformations of boron
nitride and carbon all involve sublimating in a reduced atmosphere or rare
(inert) gases, brought to temperatures above 3200 oC and condensing the
resulting vapor under a high temperature gradient. What differences the various
processes is the method used for sublimating. This can be an electric arc formed
between two electrodes, an ablation induced by a pulsed laser or a vaporization
induced by a solar or a continuous laser beam.
The solar method, which can be compared with continuous laser
vaporization, uses a solar furnace to focus the sunlight on a target and vaporize
one. Under clear-sky conditions, temperatures of around 3000 oC can be
reached at the 2 kW set-up of the solar station.
As an optical furnace can be used instead of solar furnace of the same power
capacity in any season of year it is important also to research effect of heating in
an optical furnace in nitrogen flow on the structure, morphology and phase
transformation of BN powders, to analyze the process of formation and growth
of nanostructures and to understand the role of an oxygen in the process of
structure transformations of pure graphite-like boron nitride to whiskers.
Experimental
The platelet-like fine-grained powders of boron nitride (Chempur,
CH070802 ) have been used as a initial. The origin powders are h-BN textured
on 002 with impurity of B2O3. The diameter of platelets of boron nitride is
~0,6—1,0 μm and thickness ~0,1 μm. Detail description of origin powders and
experimental procedure presented in [9—11].
A quartz chamber was used for process of sublimation of powders (fig.1).
Heating of the surface of initial powders was done in a furnace of high intensity
optical energy in the flow of nitrogen. An optical light source such as the three
xenon light sources can produce over 2 kW of the energy concentrated in the
focal zone. A diameter of the spot is 10 mm.
The optical furnace involves also three ellipsoidal reflectors. Xenon tubes
are centered in the focus of every ellipsoidal reflector. The calculated value of
the density of the light flux energy in the focal zone is about E = 1,4·104 kW/m2
a b
Fig. 1. Chamber for h-B transformations: a — during the heating; b — after
experiment.
55
if the current in the tubes is I = 300 A. Because of an emission spectrum of the
xenon tubes is closely matched by that of the black-body radiation the
calculated temperature in the focal zone is ~4000 K.
Produced compacted samples of origin h-BN powders were tablets
(diameter 20 mm and thickness 10 mm). The last were placed on a copper
water-cooling screen of the quartz chamber. The chamber was positioned in the
centre of radiation of the three xenon emitters. Direct measurements of the
temperature were not provided. However heating of h-BN was carried out at the
average densities of light flux energy in focal zone of set-up Е ∼ 0,7 ⋅ 104
kW/m2. Temperature of the blackbody are matched to the xenon tube emission
corresponds to ∼1400 К. Time of the experiment was 60 min.
The chamber was flowed by purified and dried nitrogen. Cooper chips
heated up to 500 oC purified the nitrogen from oxygen and other pollutions.
Platelets of KOH made drying of nitrogen from the water.
Obtained new structures of the BN powders on the surfaces of h-BN
compacted samples were examined by optical microscopy and scanning electron
microscopy (JSM-6490, JEOL, Japan). The TEM study of whisker structures
obtained on the surface of h-BN compacted sample was also carried out. The
structure information has been supplemented by X-ray Diffraction (XRD) study
(diffractometer DRON-3.0, radiation of КαСu) of phase composition.
Results and discussion
Surface observation of the heat treated compacted samples of h-BN has
demonstrated the formation of the new different structures (fig. 2, 3). Process of
heating in optical furnace induced by a light beam involve vaporation and
sublimating in a atmosphere of nitrogen, bring to temperatures above 3000 oC
and condensing the resulting vapor under a high temperature gradient. As a
result, whiskers were formed at the edge of the crater on the surface of
compacted samples of the initial h-BN powders. Such structures were not found
in any of the other parts of chamber. It means that occur a proper temperature
gradient in the compacting powder enabling vapor transporting from the lower
part of the powder to the surface and the growth of filamentary structures only
on the surface of compacted samples. The vapors of boron and nitrogen will re-
condense and re-vaporize as they are rising and will favour the appearance of
bushy whiskers and tiny droplets around crater edge during the light heating
(fig. 3) if keep the proper temperature gradient in the samples.
The obtained whiskers were pure, their composition is boron and nitrogen in
different proportion of components (fig. 4) that can be explained by turbulence of
nitrogen flow in the centre of crater. Generally, whiskers didn’t include oxygen.
The drops of different sizes have the elevated boron content and negligible
quantity of oxygen (fig. 5). This can be explained by removing of nitrogen from
the surface in the process of sublimating and melting of surface layer of the
initial powders of h-BN.
Carefully observation of the top of the whiskers demonstrated that their
structures are tangled straight sticks fully covered by melted droplets (fig. 6). It
is of interest to note that element composition of the top and of the foot of
whiskers includes oxygen (fig. 7). Presence of oxygen in the foot of whiskers
can be explained by its availability in initial powers of h-BN and its direct
lifting movement.
56
Fig. 2. Surface of compacted h-BN sample after
heating in optical furnace.
a
Fig. 3. Whiskers and drops formed on the surface of heated h-BN sample around
a crater.
Fig. 4. Element distribution of the obtained whiskers.
57
Fig. 5. Element distribution of obtained drop.
Fig. 6. Structure of the whiskers top.
a
b
Fig. 7. Element composition of the top and of the foot of the whiskers.
58
Based on above mentioned result and the principal trend of the oxygen to go
up during heating from the a bottom layers of initial material it is possible to
suppose that oxygen together with temperature gradients are the main driving
force for the growth of whiskers.
Conclusions
Thus, heating in focal zone of an optical furnace initiates a structure
transformation of h-BN in pure BN whiskers.
The lifting motion of oxygen from the bottom layers of initial material
under light heating of the surface at the temperature gradient is the main driving
force, which contribute to whisker formation and growth.
Acknowledgements
We acknowledge support of STCU project No. 4133.
1. Chopra N. G., Luyken R. J., Cherrey K. et al. // Science. — 1995. — 26. — P. 966.
2. Goldberg D., Bando Y., Han W. et al. // Chem. Phys. Lett. — 1999. — 308. — P. 337.
3. Mosuang T. E., Lowther J. E. // Phys. Rev. B 66 (2002) 014112.
4. Hofsдss H., Feldermann H., Eyhusen S., Ronning C. // Ibid. B 65 (2002) 115410.
5. Jimйnez I. et al. // Ibid. B 55 (1997) 12025
6. Gago R., Abendroth B., Cerdб J. I. et al. // Ibid. B 76 (2007) 174111.
7. Hecht J.-D., Frost F., Hirsch D. et al. // J. Appl. Phys. 90 (2001) 6066.
8. Petravic M., Gao Q., Llewellyn D. // Chem. Phys. Lett. 425 (2006) 262.
9. Frolov A. A., Andrievskaya E. P., Sartinska L. L. // Inttrnat. conf. “Modern
Materials Science: Achievements & Problems", Proc., 26—30 Sept. 2005. Kyiv,
Ukraine, 174—175pp. (in Russian).
10. Sartinska L. L., Frolov A. A., Koval’ A. Yu. et al. Transformation of fine-grained
graphite boron nitride induced by concentrated light energy // Mater. Chem. and
Phys. — 2008. — 109. — P. 20—25.
11. Frolov A. A., Sartinska L. L., Koval’ A. Yu., Danilenko N. A. Application of the
optical furnace for nanosized boron nitride production // Nanomaterials. —2008. —
No. 2—4. — P. 115—120. (in Russian).
59
L. L. Sartinska, V. A. Tinkov*, A. A. Frolov
*Kurdyumov Institute for Metal Physics of NASU, Kiev, Ukraine
|
| id | nasplib_isofts_kiev_ua-123456789-28655 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | XXXX-0073 |
| language | English |
| last_indexed | 2025-12-07T17:15:21Z |
| publishDate | 2009 |
| publisher | Інститут проблем матеріалознавства імені І.М. Францевича НАН України |
| record_format | dspace |
| spelling | Sartinska, L.L. Tinkov, V.A. Frolov, A.A. 2011-11-15T18:29:35Z 2011-11-15T18:29:35Z 2009 Oxygen and structure transformations of h-BN in focal zone of an optical furnace / L.L. Sartinska, V.A. Tinkov, A.A. Frolov // Современные проблемы физического материаловедения: Сб. научн . тр. — К.: ІПМ НАН України, 2009. — Вип. 18. — С. 54-59. — Бібліогр.: 11 назв. — англ. XXXX-0073 https://nasplib.isofts.kiev.ua/handle/123456789/28655 661.65:661.55;539.22-620.18 In this contribution the recent results on a synthesis of the new structures of boron nitride are presented. Light-induced catalyst-free heating of fine-grained graphite-like h-BN powders was performed in the flow of dried and purified nitrogen in an optical furnace. The new structures of boron nitride were obtained. Scanning electron microscopy JSM-6490 supplemented with combined Energy Dispersive X-ray Spectroscopy (EDS) and Electron Backscatter Diffraction (EBSD) provided information about structures, phase and element transformation of fine-grained graphite-like h-BN powders. The coarse structures, thread-like nanostructures (whiskers or dendritic structures) and new morphologies were formed due to the interaction of BN plume with nitrogen ambient on the surface of the heated compacted h-BN samples. Complicated structure and element composition of the whiskers which were formed on the surface of heated samples of compacted h-BN powders were studied by scanning electron microscopy (SEM). X-ray Diffraction (XRD) study demonstrates presence of amorphous phase, pure boron of different modifications and boron nitride of different phase compositions on the surface of these substrates. The process of the synthesis, formation and growth of the nanostructures in an optical furnace was analyzed and understood. A role of oxygen in formation and growth mechanism of BN whiskers was proposed. We acknowledge support of STCU project No. 4133. en Інститут проблем матеріалознавства імені І.М. Францевича НАН України Современные проблемы физического материаловедения Oxygen and structure transformations of h-BN in focal zone of an optical furnace Article published earlier |
| spellingShingle | Oxygen and structure transformations of h-BN in focal zone of an optical furnace Sartinska, L.L. Tinkov, V.A. Frolov, A.A. |
| title | Oxygen and structure transformations of h-BN in focal zone of an optical furnace |
| title_full | Oxygen and structure transformations of h-BN in focal zone of an optical furnace |
| title_fullStr | Oxygen and structure transformations of h-BN in focal zone of an optical furnace |
| title_full_unstemmed | Oxygen and structure transformations of h-BN in focal zone of an optical furnace |
| title_short | Oxygen and structure transformations of h-BN in focal zone of an optical furnace |
| title_sort | oxygen and structure transformations of h-bn in focal zone of an optical furnace |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/28655 |
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