Synthesis of pure YB4powder via the reaction of Y 2O3with B4C

Article abstract of DOI:10.1111/j.1551-2916.2012.05272.x

Pure YB₄powder was synthesized via the reaction of Y ₂O₃with B₄C under a vacuum pressure within the range of 20-50 Pa using spark plasma sintering (SPS) route. The effect of temperature and the molar ratio of the starting materials was studied. The role of the YBO₃, an intermediate product, in the synthesis of YB ₄was investigated. For preparation of high purity YB₄, the molar proportion of B₄C to Y₂O₃should not be higher than the stoichiometric ratio (15/7). YBO₃can be removed through decomposing to Y₂O₃and B₂O ₃or reacting with B₄C to form YB₄and B ₂O₃at a temperature above 1650°C. The little residual impurities, such as Y₂O₃and YBO₃, can be removed by hydrochloric acid washing. Thus, a high purity YB₄powder has been synthesized. The oxygen content of the obtained YB₄is about 0.007% and the particle size is in the range of 3-10 μm.

Full text of DOI:10.1111/j.1551-2916.2012.05272.x

J. Am. Ceram. Soc., 1–3 (2012)
DOI: 10.1111/j.1551-2916.2012.05272.x
©
2012 The American Ceramic Society
ournal
J
Synthesis of Pure YB Powder via the Reaction of Y O with B C
4
2
3
4
†
Junguo Li, Aiyi Peng, Yong He, Huiping Yuan, Qilong Guo, Qiang Shen, and Liangmeng Zhang
School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, China
Pure YB
4
powder was synthesized via the reaction of Y
O
2 3
with
4
Co. Ltd, Ganzhou, Jiangxi, China) and B C powder (purity
B C under a vacuum pressure within the range of 20–50 Pa using
4
> 99.9%, 10 lm; Alfa Aesar Co. Ltd., Ward Hill, MA).
spark plasma sintering (SPS) route. The effect of temperature
and the molar ratio of the starting materials was studied. The
role of the YBO , an intermediate product, in the synthesis of
3
Firstly, Y O and B C powder were mixed in an agate
2
3
4
mortar in different molar ratios as shown in Table I. Then
the mixtures were pressed into pellets and placed in a graph-
ite die, and then sintered for 30 min at different temperatures
using spark plasma sintering (SPS) under an initial vacuum
YB was investigated. For preparation of high purity YB , the
4
4
molar proportion of B
4
C to Y
O
2 3
should not be higher than the
stoichiometric ratio (15/7). YBO
decomposing to Y and B or reacting with B
YB and B O at a temperature above 1650°C. The little resid-
3
can be removed through
pressure of 20 Pa. YBO
reaction between Y and H
added to YB4 or B C and held for 30 min at different
3
powder was synthesized by the
O
2 3
O
2 3
4
C to form
2
O
3
3
BO . The YBO powder was
3
3
4
2
3
4
ual impurities, such as Y
hydrochloric acid washing. Thus, a high purity YB
been synthesized. The oxygen content of the obtained YB
2
O
3
and YBO
3
, can be removed by
powder has
is
temperatures to research the role of YBO
processing of YB . The phase compositions of synthesized
3
in the synthesis
4
4
4
powder were analyzed using X-ray diffraction (XRD; Rigaku
Ultima III, Tokyo, Japan). The morphology was observed
using a scanning electron microscope (SEM; Hitachi 3400N,
Tokyo, Japan). The oxygen content was detected using an
oxygen analyzer (Model TC600; Leco, St. Joseph, MI).
about 0.007% and the particle size is in the range of 3–10 lm.
I. Introduction
TTRIUM tetraboride (YB ) possesses some unique prop-
4
Y
electrical and magnetic properties,
for application in some extreme (ultra high temperature,
nuclear, etc.) environments.
Yttrium tetraboride is not commercially available and the
synthesis method of YB has not been widely explored. Until
4
now, only a few methods, such as solid-state reaction method
between the elements, borothermic reduction method, and
erties, such as high melting point(2800°C), high hard-
III. Results and Discussion
ness and strength, excellent chemical stability, and good
which makes it suitable
1
–5
Figure 1 shows the effect of temperature on the synthesis of
. After treatment at 1500°C for 30 min, the starting
C and Y can be found still in the sample,
YB
materials, B
4
4
2 3
O
indicating that the reaction (Eq. (1)) cannot complete under
this condition. In this sample, some yttrium borates, such as
YBO
powder Y
tion (1).
3
, appear due to the reaction between the starting
and the B produced from the reac-
A small amount of YBO3 still remains in the
2
0,11
O
3
2 3
O
1
1
,3–9
aluminothermal method have been reported.
In the solid-
sample fired at 1600°C and totally disappears after being
treated at 1700°C. The results show that the temperature
plays an important role in the transition of YBO to YB .
3 4
state reaction method between the elements, the use of raw
materials including the pure metal Y and B results in the
high cost. The same disadvantage exists in the borothermic
reduction method, whereas in the aluminothermal method,
more impurities, such as the impurity of alumina, are intro-
duced in the complex, high cost process. Recently, boron car-
bide/carbothermal reduction method was applied to
7Y2O3 þ 15B4C ¼ 14YB4 þ 15CO þ 2B2O3:
To reveal the change in YBO during the heating, 20 vol%
ð1Þ
3
5
YBO is mixed with B C or YB , and then the mixtures are
3
4
4
synthesize YB4 ceramics. Zaykoski prepared YB4 ceramics
treated at 1500°C–1700°C for 30 min. The XRD patterns of
the products are shown in Figs. 2 and 3, respectively. After
by firing the mixture of Y
for 2 h. However, some impurities, such as YBO
YB , are present in the ceramics, and the reaction process
is still not clear. In this study, YB4 was synthesized using
and B C as starting materials, the effect of temperature
and the proportion of starting materials on the reaction
2
O
3
and B
4
C or B
4
C/C at 1800°C
3
and
treated at 1500°C, the mixture of YBO
any phase change (Fig. 2). The content of YBO
the Y
600°C. The results show that YBO can decompose to Y O
3
and YB
4
does not have
decreases and
2 2
C
3
2
3
O content increases with the rise in temperature above
Y
2
O
3
4
1
3
2
3
3
and B O above 1600°C (Eq. (2)). The vapor pressure of B O
2 3 2
12
between Y O and B C was investigated.
4
2
3
as a function of temperature has been given by Eq. (3). The
nominal pressure maintained during the SPS process ranged
II. Experimental Procedure
2
0–50 Pa. From Eq. (3), the vapor pressure of B O reaches
2 3
2 3
the pressure at 1340–1400°C. Therefore, B O should boil at
The raw materials used in this study were as follows: Y O3
2
powder (purity > 99.9%, 2–5 lm; Jiarun advanced materials
1
400°C and above, and then B
pellet and be removed using the pumped vacuum, with Y O
2 3
O can evaporate from the
2
3
left in the sample. From Fig. 3, we can see that YBO
with B C to form YB at 1500°C (Eq. (4)). However, the reac-
tion is not completed after 30 min at 1500°C and 1600°C
there are still YBO in the products). Above 1650°C, another
3
can react
4
4
J. Zaykoski—contributing editor
(
3
reaction (Eq. (5)) can occur to form YB
pears. These results indicate that YBO
temperature above 1650°C. When the B
excessive YBO3 will transform to Y O . When B C is
6
whereas YBO
can be removed at a
C is insufficient, the
3
disap-
3
4
Manuscript No. 30700. Received November 20, 2011; approved April 16, 2012.
Author to whom correspondence should be addressed. e-mail: lijg000@126.com
†
2
3
4
1

2
Rapid Communications of the American Ceramic Society
Table I. Molar Ratio of the Starting Powder
Sample
B
4
C(mol)
2 3
Y O (mol)
S1
S2
S3
2.1
2.2
2.3
1
1
1
Fig. 3. X-ray diffraction patterns for mixture of 20 vol% YBO
and 80 vol% B C heated to various temperatures.
3
4
Fig. 1. X-ray diffraction patterns for the productions fabricated at
different temperatures from the B
ratio in 2.1.
4 2 3
C and Y O mixture with a molar
Fig. 4. X-ray diffraction patterns of the productions obtained using
sintering at 1700°C for 30 min from different molar ratio of B C to
. S1:2.1, S2:2.2 and S3:2.3.
4
2 3
Y O
Figure 4 shows the XRD patterns of the products
obtained using sintering at 1700°C for 30 min from different
molar ratios of starting materials. The main phase is YB in
all the samples. However, in sample S1 and S2, Y O phase
4
Fig. 2. X-ray diffraction patterns for mixture of 20 vol% YBO
and 80 vol% YB heated to various temperatures.
3
2
3
is detected, indicating that Y
with B C and transform to YB
2
O
3
cannot completely react
. The oxygen content in the
4
4
4
three samples is 1.78%, 0.61%, and 0.41%, respectively,
decreasing with the increase in the molar ratio between B C
excessive, YBO will transform to YB or YB . In both cases,
the evaporation of B O is necessary. The evaporation of B O
3
3
4
6
4
2
3
2
and Y
observed (Fig. 5), indicating that B
to the reaction between B C and Y O (Eq. (1)), the stoichi-
2
O
3
. In sample S2 and S3, a few B
4
C particles can be
depends on the temperature, the vacuum pressure, and the
time. Under the experimental vacuum pressure, B should
4
C is excessive. According
2 3
O
4
2
3
boil. If the temperature has reached the temperature at which
the reaction (2) (4) and (5) can occur, the B O produced can
be easily removed using the pumped vacuum, meanwhile
ometric ratio should be 15/7. In sample S2 and S3, the ratio
of B C to Y is higher than this value and then the exces-
sive B C remains in the products. For preparation of high
purity YB , the ratio of B C to Y O in the starting materi-
2
3
4
2 3
O
4
YBO
3
is removed.
4
4
2
3
4
als should be lower than the stoichiometric ratio, as B C
2
YBO3 ¼ Y2O3 þ B2O3
ð2Þ
cannot be easily removed using common mechanical or
chemical methods whereas Y O can be removed by washing
with acid.
1
9236
1
2
2
3
log p
ðatmÞ ¼ 8:244 ꢀ
ð3Þ
B
2
O
3
T
After grinding, the production of S1 was placed in hydro-
chloric acid (2 mol/L) and heated to 60°C with continuous
stirring for 2 h. Then the powder was washed by distilled
water for 3–5 times until it appears neutral. After being dried
1
4YBO3 þ 15B4C ¼ 14YB4 þ 15CO þ 9B2O3
YBO3 þ 3B4C ¼ 2YB6 þ 3CO þ B2O3
ð4Þ
ð5Þ
2

Rapid Communications of the American Ceramic Society
3
(
a)
(b)
4
Fig. 5. Backscatter electron images for sample S2 (a) and S3 (b). The arrow points to B C particles (dark area).
(
b)
(
a)
4
Fig. 6. XRD pattern (a) and SEM image (b) for the obtained YB .
in an oven at 100°C for 2 h, YB
Fig. 6(a) shows the XRD patterns of the synthesized YB4.
There were only YB peaks in the XRD pattern, showing
that the Y was removed by hydrochloric acid washing.
Y O can react with HCl to transform into water-soluble
4
powder was obtained.
of the obtained YB
range of 3–10 lm.
4
is ~0.007% and the particle size is in the
4
2
O
3
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3
1
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4
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3
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8
3
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3
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9
4
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0
¨
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high purity YB powder has been synthesized by treating the
4
mixture of B C and Y O with a molar ratio in 2.1 at 1700°C
4
2
3
h
for 30 min under a vacuum pressure of 20–50 Pa and fol-
lowed by a hydrochloric acid washing. The oxygen content