A simple thermal decomposition-nitridation route to nanocrystalline boron nitride (BN) from a single N and B source precursor

Article abstract of DOI:10.1016/j.jallcom.2011.03.109

Nanocrystalline boron nitride (BN) was synthesized via a simple thermal decomposition-nitridation route by the reaction of hydrated ammonium tetraborate (NH₄HB₄O₇·3H₂O) and metallic magnesium powders in an autoc

Full text of DOI:10.1016/j.jallcom.2011.03.109

Journal of Alloys and Compounds 509 (2011) 6616–6620
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Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
A simple thermal decomposition–nitridation route to nanocrystalline boron
nitride (BN) from a single N and B source precursor
Hong Zhanga, Youjian Chena, Jianhua Maa,b,∗, Hanxuan Tongc, Jiang Yangc, Danwei Nic,
Huiming Huc, Fangqing Zhengc
a College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, Zhejiang 325027, PR China
b Nanomaterials and Chemistry Key Laboratory, Advanced Materials Research Center of Wenzhou, Wenzhou University, Wenzhou, Zhejiang 325027, PR China
c Oujiang College, Wenzhou University, Wenzhou, Zhejiang 325027, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Nanocrystalline boron nitride (BN) was synthesized via a simple thermal decomposition–nitridation
route by the reaction of hydrated ammonium tetraborate (NH4HB4O7·3H2O) and metallic magnesium
powders in an autoclave at 650 ◦C. The crystal phase, morphology, grain size, and chemical composition
of the as-prepared products were characterized in detail by X-ray powder diffraction (XRD), energy dis-
persion spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron
microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron
microscopy (HRTEM). The products were also studied by FT-IR and the thermogravimetric analysis (TGA).
Results revealed that the as-synthesized nanocrystalline were h-BN, and they had diameters within
100 nm. They had good thermal stability and oxidation resistance in high temperature.
Received 30 November 2010
Received in revised form 16 March 2011
Accepted 17 March 2011
Available online 29 March 2011
Keywords:
Boron nitride
Chemical synthesis
X-ray diffraction
HRTEM
© 2011 Elsevier B.V. All rights reserved.
Thermogravimetric analysis
1. Introduction
the reaction of NaBH4 and NaN3 in an autoclave at 600 ◦C. Li et al.
[17] reported that hexagonal BN (h-BN) particles were prepared by
Boron nitride (BN) has attracted intense interest due to its
many unique physical and chemical properties, such as low density,
high temperature stability, high thermal conductivity, high melt-
ing point, low dielectric constant and chemical inertness. Owing to
these properties, boron nitride can be used as lubricants, electrical
insulators, refractory and so forth [1–5].
Boron nitride (BN) has several different phases: such as cubic
(c-BN), hexagonal (h-BN), wurtzite (w-BN), and rhombohedral (r-
BN) etc. [6–8]. Among them, h-BN has a similar carbon graphite-
like structure. In hexagonal structure, the interlayer interactions
are weak (van der Waals type) and the intralayer interactions are
strong (covalent B–N bonds (sp2)) [9]. So boron nitride (BN) is often
referred to as “white graphite” [10].
using BBr3, NH4Br and metallic Na as reactants in stainless steel
autoclaves at 450 ◦C for 24 h. Zhang et al. [9] prepared high-purity
and bulk-quantity boron nitride spheres at 1400 ◦C via a simple
polymer-chemical route.
In this paper, we use NH4HB4O7·3H2O as boron source and
nitrogen source, metallic Mg powders as reductant. Nanocrystalline
hexagonal boron nitride has been synthesized via a simple ther-
mal decomposition–nitridation route by the reaction of hydrated
ammonium tetraborate (NH4HB4O7·3H2O) with metallic Mg pow-
ders in an autoclave at 650 ◦C for 8 h. Compared to the previous
methods, this simple route has the primary advantage, i.e., B and N
sources from a single cheap safe precursor NH4HB4O7·3H2O.
Traditionally, many approaches have been developed for prepa-
ration of BN, such as the direct reaction of boron and nitrogen [11],
and the carbothermic reduction of boric oxide [12]. In addition,
other methods have also been developed to prepare BN [13–16].
Recently, some new methods have been used to synthesize boron
nitride. Ma et al. [10] prepared nanocrystalline boron nitride by
2. Experimental
All of the manipulations were carried out in a dry glove box with flowing
nitrogen gas. In a typical experiment, 0.02 mol (about 4.57 g) analytical grade
NH4HB4O7·3H2O and 0.11 mol (about 2.64 g) analytical grade metallic Mg powders
were put into a mortar, followed by mixing these powders thoroughly. Then the mix-
ture was put into a stainless steel autoclave. After sealing under argon atmosphere,
the autoclave was heated at 650 ◦C for 8 h, followed by cooling to room tempera-
ture in the furnace. The obtained product from the autoclave was washed several
times with absolute ethanol, dilute HCl aqueous solution, distilled water to remove
the impurities. Finally the product was washed three times with absolute ethanol to
remove water. The final product was vacuum-dried at 60 ◦C for 12 h. White powders
were obtained.
∗
Corresponding author at: College of Chemistry and Materials Engineering, Wen-
zhou University, Wenzhou, Zhejiang 325027, PR China. Tel.: +86 577 86669317;
fax: +86 577 86689508.
E-mail address: mjh820@ustc.edu (J. Ma).
0925-8388/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2011.03.109

H. Zhang et al. / Journal of Alloys and Compounds 509 (2011) 6616–6620
3. Results and discussion
6617
3.1. X-ray diffraction
Fig. 1 shows the XRD patterns of the as-prepared samples and
the standard pattern of BN. The pattern (a) is about the product pre-
pared by the reaction of NH4HB4O7·3H2O and Mg powders under
650 ◦C and 8 h. In the pattern (a), there are four obvious diffrac-
tion peaks on this pattern. And all these diffraction peaks ((0 0 2),
(1 0 0), (1 0 1) and (1 1 0)) at different d-space can be indexed as
hexagonal boron nitride (BN). The refinement gives the cell con-
˚
˚
stants (a = 2.504 A, c = 6.668 A), which is consistent with the value
˚
˚
reported in the literature (a = 2.504 A, c = 6.656 A) (JCPDS card no.
34-0421). No evidences of impurities such as B, B2O3, other boron
nitrides, can be found in this XRD patterns. It should be noted that
the disappearance of some weak peaks (such as 50.149◦ 2-theta and
55.164◦ 2-theta) existing in standard h-BN spectra may indicate
the imperfect crystallization of the final product. The discrepancy
between the observed and the theoretical peak positions is most
probably caused by the defects and the curvature of the layered
structure [9].
Fig. 1. XRD patterns of the as-prepared samples and standard pattern.
3.2. Scanning electron microscopy
The obtained sample was analyzed by powder X-ray diffraction (XRD) on a
Bruker D8 Advance X-ray powder diffractometer using Cu K-␣ radiation (wave-
length ꢀ = 1.54178 A) and X-ray photoelectron spectra (XPS) analysis was performed
The morphology of the prepared BN samples was investigated
by field emission scanning electron microscopy. Fig. 2(a) and (b)
shows typical SEM images of the BN sample. They reveal that the
BN sample consists of particles within 100 nm in diameters. These
particles exhibit slightly agglomerated particle morphology due to
the ultrafine size of the sample.
˚
on a AXIS ULTRA DLD X-ray photoelectron spectrometer, using Monochrome Al
Ka as the excitation source. The morphology of the sample was examined on a
JEOL JSM-6700F scanning electron microscope at an accelerating voltage of 10 kV.
Energy dispersive spectrometry (EDS) analysis of the product was carried out on
an OXFORD INCA instrument attached to the scanning electron microscopy in the
scanning range of 0–20 kV. The microstructure and morphologies of the samples
were also obtained from transmission electron microscopy (TEM) images and high-
resolution TEM (HRTEM) images were recorded on a FEI Tecnai F-20 transmission
electron microscopy at an acceleration voltage of 200 kV. Fourier transformation
infrared spectroscopy (FT-IR) spectra were obtained using a Shimadzu IR-400 spec-
trometer by using pressed KBr disks. The thermogravimetric analysis was performed
on a thermal analyzer (Model: Q600) below 1000 ◦C in air at a rate of 10 ◦C min−1
to study its thermal stability and oxidation behavior. All the measurements were
carried out at room temperature.
3.3. EDS spectrum and XPS spectra
The EDS spectrum in Fig. 3 further demonstrates that the prod-
uct prepared at 650 ◦C for 8 h is composed of nearly stoichiometric
B and N (the atomic ratio of B to N was estimated to be 46.48:53.52),
without the contamination of oxygen.
Fig. 2. SEM images of the as-prepared BN samples.

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H. Zhang et al. / Journal of Alloys and Compounds 509 (2011) 6616–6620
N1s
O1s
C1s
B1s
Fig. 3. EDS spectrum of the as-prepared h-BN sample.
The composition and purity of the as-synthesized BN nanopar-
ticles are further investigated by XPS. Fig. 4 shows the results of the
XPS spectra. They show that the sample surface consists of nitrogen,
boron, carbon and oxygen, with binding energies of N 1s, B 1s, C 1s
and O 1s at 395.5, 190.89, 281.95 and 529.85 eV, respectively. The C
1s and O 1s peaks indicate that there exists a small amount of impu-
rity elements such as C and O due to the adsorption of CO2, H2O and
O2 on the surface of the sample. The B 1s peak at 190.89 eV and the
N 1s peak at 395.5 eV indicate BN, in good agreement with those in
the literature [18]. The quantification of B 1s and N 1s peaks con-
firmed that the atomic ratio of B:N was 1.07:1, which closely agrees
with the stoichiometric composition of BN. This result is consistent
with the XRD and EDS pattern presented above.
0
200
400
600
Binding Energy / eV
B1s
3.4. TEM images and SAED pattern
The morphologies and microstructures of BN were further
investigated by TEM and SAED. Fig. 5(a) shows a typical TEM image
of the prepared BN superstructures.
The image shows that it consists of particles that have an average
diameter of 100 nm.
The particle is further confirmed by the HRTEM image presented
in Fig. 5(b). As shown in the image, the adjacent lattice fringes have
score break, which are in accord with the analysis of the XRD pat-
tern presented above. The SAED pattern of BN samples is Fig. 5(c).
In this pattern, two obvious diffraction rings can be found. These
rings can be indexed as (0 0 2) and (1 0 0). And the SAED pattern of
the sample can also confirm the crystallinity of BN, in which the
diffraction ring diameters again correspond well to the hexagonal
BN structure.
186
188
190
192
194
196
Binding Energy / eV
N1s
3.5. FT-IR spectra
Fig. 6 shows the FT-IR spectra of the particle BN sample at room
temperature. Two strong peaks around 1385 and 795 cm−1could
be observed clearly for the sample, which are assigned to the B–N
stretching vibrations and B–N–B bending vibrations, respectively
[19,20]. A weak peak around 3421 cm−1 could be attributed to the
moisture absorbed on the surface of the sample.
3.6. Thermogravimetric analysis
396
398
400
402
Binding Energy / eV
To investigate the thermal stability and the oxidation resistance
of the as-prepared nanocrystalline BN, A typical TGA/DTA was car-
ried out at temperatures below 1000 ◦C under flowing air. Fig. 7
shows the TGA/DTA curves of the sample. From the TGA curve, we
can find that the weight of the product has not changed significantly
below 900 ◦C except a slight water weight loss on the surface. But
the quantity of the adsorbed water is very small. As the temperature
keeps on rising from 900 ◦C to 950 ◦C, there is an obvious weight
Fig. 4. XPS survey spectrum of the as-prepared h-BN sample.
gain during the process, indicating that the BN sample is oxidized
into B2O3 and nitrogen oxides. This can also be confirmed by the
DTA curve of the sample, shown in the Fig. 7. In this DTA curve,
there is a big exothermic peak at 940 ◦C relative to the extensive
oxidation of the sample. Around 1000 ◦C B2O3 is evaporating exten-

H. Zhang et al. / Journal of Alloys and Compounds 509 (2011) 6616–6620
6619
Fig. 5. (a) TEM image, (b) HRTEM image and (c) SAED pattern of the as-prepared h-BN sample.
In our experiments, as the temperature rose, NH4HB4O7·3H2O
could decompose generating NH3 and H2O gases and B2O3. So the
pressure in the autoclave may be very high. At the reaction tem-
perature, B2O3, NH3 and metallic magnesium powders could react
with each other to produce BN. The high pressure in the auto-
clave would be helpful for reducing the reaction temperature and
enhancing the reaction speed. The produced H2O gas could react
with Mg powders producing H2 gas. Therefore, the possible thermal
decomposition–nitridation route might be expressed as follows:
795(hBN TO)
H-O
NH4HB4O7·3H2O → NH3 + 2B2O3 + 4H2O
B2O3 + 3Mg → 2B ∗ + 3MgO
2H2O + Mg → Mg(OH)2 + H2
Mg(OH)2 → MgO + H2O
2B ∗ + 2NH3 → 2BN + 3H2
And the total reaction process can be represented as the follow-
ing:
(1)
(2)
(3)
(4)
(5)
1385(hBN TO)
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber / cm-1
Fig. 6. FT-IR spectra of the BN sample.
2NH4HB4O7·3H2O + 11Mg = 2BN + 11MgO + 3B2O3 + 11H2 (6)
In the reaction, the prepared B2O3 would react with H2O into
HBO2 or H3BO3. HBO2 (or H3BO3) and MgO would be removed
through HCl aqueous solution and distilled water. The final product
was nanocrystalline BN.
In this route, the B source has not made the most of utility. In
order to make the full use of the B source, we optimize the synthesis
method, i.e. NH4Cl as other N source. BN can also be produced by
the reaction of 0.01 mol NH4HB4O7·3H2O, 0.12 mol Mg powders
and 0.03 mol NH4Cl in an autoclave at 600 ◦C for 8 h. Fig. 1(b) is the
XRD pattern of the as-prepared sample with new route, it shows
that the product is also hexagonal BN. Fig. 2(c) is the SEM image
of the new route BN sample, it can be observed that the sample
mainly consists of particles within 100 nm in diameters.
sively [21], which counteracts the weight gain due to the oxidation
of BN, so the weight levels off. Thus, B2O3 evaporation results in
the final weight gain less than the theoretical one (41.67%) [22].
These indicate that the prepared BN has good thermal stability and
anti-oxidation property under 900 ◦C.
16
14
12
10
8
4. Conclusion
In summary, nanocrystalline BN has been prepared via a sim-
ple thermal decomposition–nitridation route by the reaction of
hydrated ammonium tetraborate (NH4HB4O7·3H2O) with metal-
lic Mg powders in an autoclave at 650 ◦C for 8 h. The product has
the nanocrystalline h-BN structure, it consists of particles within
100 nm in diameters, and the product has good thermal stability
and oxidation resistance below 900 ◦C.
6
DTA
4
2
TGA
0
-2
0
100 200 300 400 500 600 700 800 900 1000 1100
Temperature / oC
Acknowledgments
This work was supported by Innovation and Promotion
of Science-Technology Project of Zhejiang Province and the
Fig. 7. TGA/DTA curves heated in flowing air for the BN sample.

6620
H. Zhang et al. / Journal of Alloys and Compounds 509 (2011) 6616–6620
Department of Education of Zhejiang Province of China under Grant
No. 20070546.
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[12] K.A. Schwetz, A. Lipp, in: W. Gerhartz, al. et (Eds.), Ulmann’s Encylopedia of
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