U.S. patent application number 15/955211 was filed with the patent office on 2018-08-16 for method of producing spherical boron nitride fine particles.
The applicant listed for this patent is DENKA COMPANY LIMITED, NATIONAL INSTITUTE FOR MATERIALS SCIENCE. Invention is credited to Yoshio BANDO, Dmitri GOLBERG, Takashi KAWASAKI, Seitaro KOBAYASHI, Fumihiro KUROKAWA, Go TAKEDA.
Application Number | 20180230012 15/955211 |
Document ID | / |
Family ID | 53800122 |
Filed Date | 2018-08-16 |
United States Patent
Application |
20180230012 |
Kind Code |
A1 |
KUROKAWA; Fumihiro ; et
al. |
August 16, 2018 |
METHOD OF PRODUCING SPHERICAL BORON NITRIDE FINE PARTICLES
Abstract
A method of producing a spherical boron nitride fine particle
includes reacting ammonia with an alkoxide borate at an
ammonia/alkoxide borate molar ratio of 1 to 10 in an inert gas
stream at 750.degree. C. or higher within 30 seconds, then applying
heat treatment to a reaction product in an atmosphere of ammonia
gas or a mixed gas of ammonia gas and an inert gas at 1,000 to
1,600.degree. C. for at least 1 hour, and further firing the
reaction product in an inert gas atmosphere at 1,800 to
2,200.degree. C. for at least 0.5 hour.
Inventors: |
KUROKAWA; Fumihiro;
(Omuta-shi, JP) ; KOBAYASHI; Seitaro; (Omuta-shi,
JP) ; KAWASAKI; Takashi; (Tokyo, JP) ; TAKEDA;
Go; (Tokyo, JP) ; BANDO; Yoshio; (Tsukuba-shi,
JP) ; GOLBERG; Dmitri; (Tsukuba-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DENKA COMPANY LIMITED
NATIONAL INSTITUTE FOR MATERIALS SCIENCE |
Tokyo
Tsukuba-shi |
|
JP
JP |
|
|
Family ID: |
53800122 |
Appl. No.: |
15/955211 |
Filed: |
April 17, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15117853 |
Aug 10, 2016 |
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PCT/JP2015/053489 |
Feb 9, 2015 |
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15955211 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C01P 2004/03 20130101;
C01P 2004/04 20130101; C01P 2006/80 20130101; C01B 21/0646
20130101; C01P 2004/32 20130101; C01P 2004/62 20130101; C01P
2004/64 20130101 |
International
Class: |
C01B 21/064 20060101
C01B021/064 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 12, 2014 |
JP |
2014-024009 |
Claims
1. A method of producing a spherical boron nitride fine particle,
characterized by reacting ammonia with an alkoxide borate at an
ammonia/alkoxide borate molar ratio of 1 to 10 in an inert gas
stream at 750.degree. C. or higher within 30 seconds, then applying
heat treatment to a reaction product in an atmosphere of ammonia
gas or a mixed gas of ammonia gas and an inert gas at 1,000 to
1,600.degree. C. for at least 1 hour, and further firing the
reaction product in an inert gas atmosphere at 1,800 to
2,200.degree. C. for at least 0.5 hour.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This is a divisional application Ser. No. 15/117,853 filed
Aug. 10, 2016, which is a National Phase of International
Application No. PCT/JP2015/053489 filed Feb. 9, 2015, and claims
priority from Japanese Patent Application No. 2014-024009 filed
Feb. 12, 2014, the disclosure of which is hereby incorporated by
reference herein in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a spherical boron nitride
fine particle well suited for use as a highly thermoconductive
filler or the like, and a production method thereof.
BACKGROUND ART
[0003] Hexagonal boron nitride (hereinafter called "boron
nitride"), because of having lubrication capability, high thermal
conductivity and insulation capability, is now widely used as
releasing agents for solid lubricants, molten glasses and aluminum
or the like as well as fillers for thermal radiation materials.
[0004] To be compatible with higher performances of recent
computers and electronic hardware in particular, measures against
thermal radiation have increased in importance and attention has
been directed to the high thermal conductivity of boron
nitride.
[0005] In recent years, it has been studied to add boron nitride to
the resin layers of printed wiring boards and flexible copper-clad
laminated sheets for the purpose of imparting high thermal
conductivity and insulation to them.
[0006] While generally available boron nitride has an average
particle diameter of a few .mu.m to 20 .mu.m, some resin substrates
for printed wiring boards and flexible copper-clad laminated sheets
have a thickness of the order of several tens .mu.m, and large
average particle diameters of boron nitride result in poor
dispersability in resins, failing to obtain smooth surfaces, or
with that boron nitride dispersed, there are hard spots appearing,
often making it impossible to keep the strength of the resin layer
high. For these reasons, there is mounting demand for boron nitride
fine particles of the submicron order (0.1 .mu.m).
[0007] To have high thermal conductivity, the boron nitride must be
of high purity and high crystallinity, and the same goes for boron
nitrite fine particles on the submicron order (0.1 .mu.m).
[0008] On the other hand, the boron nitride has a characteristic
scaly shape, and its thermal properties are overwhelmingly better
in the major or minor diameter direction than in the thickness or
perpendicular direction. For this reason, the thermal properties of
a composite material having boron nitride filled or packed in a
resin such as silicone are considerably affected by the
directionality of boron nitride fine particles in the composite
material.
[0009] For instance when the composite material is provided in a
sheet form, however, the boron nitride fine particles are often apt
to lie down laterally and the necessary sufficient thermal
properties are not obtained anymore in the longitudinal
direction.
[0010] It follows that in order to be well fitted as a highly
thermoconductive filler, the boron nitride must be configured into
a spherical or aggregate shape thereby keeping the influence of
directionality less.
[0011] The boron nitride is generally obtained by reactions at high
temperatures between a boron source (boric acid, borax, etc.) and a
nitrogen source (urea, melamine, ammonia, etc.), and a "pineal"
boron nitride obtained by the aggregation of scaly primary
particles from boric acid and melamine has been proposed in the art
(Patent Publication 1).
[0012] However, the aggregate particle diameter of boron nitride
prepared by this method is greater than 50 .mu.m; in other words,
it is difficult to prepare boron nitride fine particles of the
submicron order--the object of the invention.
[0013] On the other hand, there have been reports (Patent
Publications 2, 3 and 4) about how to obtain boron nitride fine
particles by a vapor-phase synthesis process.
[0014] However, boron nitride fine particles obtained by these
methods, because of having low crystallinity, are found to be less
than satisfactory in terms of boron nitride's characteristics:
lubrication capability and high thermal conductivity.
PRIOR ARTS
Patent Publications
[0015] Patent Publication 1: JP(A) 09-202663 [0016] Patent
Publication 2: JP(A) 2000-327312 [0017] Patent Publication 3: JP(A)
2004-182572 [0018] Patent Publication 4: JP(A) 2010-180066
SUMMARY OF THE INVENTION
Objects of the invention
[0019] An object of the invention is to provide a submicron-order
spherical boron nitride fine particle having a high sphericity.
EMBODIMENTS OF THE INVENTION
[0020] To achieve the aforesaid object, the present invention is
embodied as follows. [0021] (1) A spherical boron nitride fine
particle, characterized by having an average particle diameter of
0.01 to 1.0 .mu.m, an orientation index of 1 to 15, a boron nitride
purity of 98.0% by mass or greater, and an average circularity of
0.80 or greater. [0022] (2) A method of producing a spherical boron
nitride fine particle, characterized by reacting ammonia with an
alkoxide borate at an ammonia/alkoxide borate molar ratio of 1 to
10 in an inert gas stream at 750.degree. C. or higher within 30
seconds, then applying heat treatment to a reaction product in an
atmosphere of ammonia gas or a mixed gas of ammonia gas and an
inert gas at 1,000 to 1,600.degree. C. for at least 1 hour, and
further firing the reaction product in an inert gas atmosphere at
1,800 to 2,200.degree. C. for at least 0.5 hour.
ADVANTAGES OF THE INVENTION
[0023] According to the invention, it is possible to provide a
submicron-order spherical boron nitride fine particle having a high
sphericity.
BRIEF EXPLANATION OF THE DRAWINGS
[0024] FIG. 1 is a schematic view of the apparatus of producing
boron nitride fine particles under firing condition 1.
[0025] FIG. 2 is a schematic view of the apparatus of producing
boron nitride fine particles under firing condition 2.
[0026] FIG. 3 is an electron micrograph taken of spherical boron
nitride fine particles according to an example of the
invention.
[0027] FIG. 4 is an electron micrograph taken of spherical boron
nitride fine particles according to a comparative example of the
invention.
MODES FOR CARRYING OUT THE INVENTION
[0028] In the invention described here, a tubular furnace 3 is
first used in an inert gas stream for a so-called gas phase
reaction between a vaporized alkoxide borate and ammonia thereby
continuously synthesizing a white powder (firing condition 1).
Then, this white powder is fired in the tubular furnace 3
(resistance heating furnace) (firing condition 2). Finally, the
fired product is charged in a boron nitride crucible that is then
transferred to an induction heating furnace in which the fired
product is further fired into a boron nitride fine particle (firing
condition 3).
[0029] It is here to be noted that unless otherwise specified, % is
given on the mass basis.
[0030] As described above, there are three firing conditions used
in the invention: in firing temperature ascending order, firing
condition 1 of at least 750.degree. C., firing condition 2 of 1,000
to 1,600.degree. C., and firing condition 3 of 1,800 to
2,200.degree. C. Under firing conditions 1 and 2 the tubular
furnace 3 may be used in the resistance heating mode, and under
firing condition 3 an electric furnace may be used as the tubular
furnace 3 in the induction heating mode. Of course, there is no
problem at all with the use of the induction heating mode of
electric furnace under firing conditions 1 and 2.
[0031] The invention will now be explained with reference to the
accompanying drawings.
[0032] An apparatus used under firing condition 1 to prepare boron
nitride fine particles comprises a tubular furnace 3 (resistance
heating furnace), a reaction tube (quartz tube) 2, an alkoxide
borate feeder vessel 1, an alkoxide borate inlet pipe 4, an ammonia
gas inlet pipe 5, a sample recovery vessel 6, etc.
[0033] The spherical boron nitride fine particles of the invention
are continuously synthesized by the so-called gas-phase reaction
between a vaporized alkoxide borate and ammonia. This requires the
use of an apparatus capable of continuous synthesis, and an
apparatus using such a tubular furnace 3 as shown typically in FIG.
1 is preferably used under firing condition 1.
[0034] While there is no particular limitation on the tubular
furnace 3, it is preferable to use an easy-to-handle electric
furnace.
[0035] An electric furnace operates on the basic principle that a
heating element or the like forming a furnace generates heat by the
passage of electric current for heating of the interior of the
furnace, and is specialized on the basis of heating modes and
heating element materials.
[0036] Generally, heating up to nearly 1,700.degree. C. may be
carried out in the resistance heating mode using a heating element,
but for heating up to nearly 2,000.degree. C. there is a coil
induction heating mode in need.
[0037] By way of example but not by way of limitation, the heating
element may be formed of a material such as silicon carbide or
carbon.
[0038] Although there is no particular limitation on the material
of the reaction tube 2 used herein, it is preferable to make use of
alumina or quartz having chemical stability and good heat
resistance.
[0039] Reference is now made to FIG. 1 that is a schematic view of
firing condition 1 where a quartz tube is used as the reaction tube
2 and trimethyl borate is used as the alkoxide borate.
[0040] The quartz tube 2 is placed in the resistance heating
furnace 3 that is heated up to a given temperature. Then, trimethyl
borate is placed in the feeder vessel 1 and introduced together
with nitrogen into the quartz tube 2 by way of the inlet pipe 4. In
the meantime, ammonia is also introduced into the quartz tube 2 by
way of the inlet pipe 5. The introduced trimethyl borate and
ammonia react with each other in the heated quartz tube 2, yielding
white powders (firing condition 1). Some white powders adhere to
the interior of the quartz tube 2, but the rest is all delivered to
the recovery vessel 6 together with nitrogen and unreacted ammonia.
The white powder product (product 7) is recovered in the recovery
vessel 6.
[0041] The temperature of the tubular furnace 3 is preferably
750.degree. C. or higher. At lower than 750.degree. C., the
resultant boron nitride fine particles often come to have an
average particle diameter of greater than 1.0 .mu.m.
[0042] The reaction between trimethyl borate and ammonia gets done
within 30 seconds. Exceeding 30 seconds may possibly cause the
boron nitride fine particles to have an average particle diameter
of greater than 1.0 .mu.m.
[0043] The alkoxide borate used herein includes trimethyl borate,
triethyl borate and tri-isopropyl borate, among which the trimethyl
borate is preferred because of its high reactivity with ammonia and
its availableness. The trimethyl borate is available as reagents
from many companies in general, and in the form of a reagent under
the trade name of "TMB" from Tama Chemicals Corporate in
particular.
[0044] While there is also no particular limitation on the ammonia
used herein, it is preferable to use a so-called impurity-free
"high-purity" type.
[0045] While there is no particular limitation on the inert gas
used herein, there is the mention of less chemical reactive gases,
for instance, noble or rare gases such as helium, neon and argon,
and nitrogen.
[0046] The ammonia and alkoxide borate are fed at a molar ratio of
1 to 10. As the ammonia/alkoxide borate molar ratio is less than 1,
it is likely that the boron nitride fine particles may have a
purity of lower than 98.0%, and as that molar ratio is greater than
10, it is likely that the boron nitride fine particles may have an
average particle diameter of less than 0.01 .mu.m.
[0047] The feeding of alkoxide borate and ammonia is put off, and
the tubular furnace 3 is powered off to recover the white powders
synthesized under firing condition 1. Then, firing is carried out
by the apparatus shown typically in FIG. 2 under firing condition
2.
[0048] The apparatus used under firing condition 2 is built up of a
resistance heating furnace 3' and a reaction tube 2' formed of
alumina. The white powder product (product 7) synthesized under
fining condition 1 is filled in the middle of the reaction tube
that is then placed in the resistance heating furnace 3'. After
that, nitrogen is introduced from an inlet pipe 4' and ammonia is
introduced from an inlet pipe 5'. After heated to a given
temperature, the white powder product is fired for a given period
of time. After the completion of firing, the resistance heating
furnace 3' is cooled down for recovery of the fired product.
[0049] Under firing condition 2 an induction heating furnace may be
used instead.
[0050] The temperature of the resistance heating furnace 3 is in
the range of 1,000 to 1,600.degree. C. Out of this range, the boron
nitride fine particles are likely to have an orientation index of
greater than 15.
[0051] The reaction time under firing condition 2 is 1 hour or
longer. In less than 1 hour, the boron nitride fine particles are
likely to have an orientation index of greater than 15 and a scaly
shape having a lower circularity.
[0052] The atmosphere used under fining condition 2 is preferably
ammonia gas or an ammonia gas/inert gas mixture. In the absence of
ammonia gas, the boron nitride fine particles are likely to have an
orientation index of greater than 15 or a purity of less than
98.0%, and to take a scaly shape having a lower average
circularity.
[0053] After the completion of the reaction under firing condition
2, the electric furnace is powered off and the introduction of
nitrogen or ammonia is put off, followed by cooling.
[0054] The fired product obtained under firing condition 2 is
placed in a boron nitride crucible, and then further fired under
firing condition 3 in an induction heating furnace at a given
temperature, in which furnace a nitrogen atmosphere prevails.
[0055] It is here to be noted that the firing temperature is as
high as about 2,000.degree. C.; so it is preferable to use the
induction heating furnace as the firing furnace.
[0056] The temperature under firing condition 3 is 1,800 to
2,200.degree. C. At lower than 1,800.degree. C., the boron nitride
fine particles are likely to have a purity of lower than 98.0%, and
at higher than 2,200.degree. C., the boron nitride fine particles
are likely to break down.
[0057] The reaction time under fining condition 3 is 0.5 hour or
longer. In less than 0.5 hour, the boron nitride fine particles are
likely to have a purity of lower than 98.0%.
[0058] The boron nitride fine particles of the invention have an
average particle diameter of 0.05 to 1.0 .mu.m. Out of this range,
there is poor dispersability in resins, failing to obtain smooth
surfaces, or upon dispersed in a resin, there are hard spots
appearing in the resin, often making it impossible to keep the
strength of the resin layer high.
[0059] The orientation index of the boron nitride fine particles of
the invention, represented by a ratio (I.sub.002/I.sub.100) between
the diffraction line intensity I.sub.002 of the (002) plane and the
diffraction line intensity I.sub.100 of the (100) plane as measured
by powder X-ray diffractometry, should be 1 to 15 so as to obtain
high thermal conductivity.
[0060] The boron nitride fine particles of the invention should
have a boron nitride purity of at least 98.0% so as to obtain high
thermal conductivity.
[0061] The boron nitride fine particles of the invention should
have an average circularity of at least 0.80 so as to obtain high
thermal conductivity.
EXAMPLES
[0062] The present invention will now be explained in further
details with reference to experimental runs.
Experimental Run 1
Firing Condition 1
[0063] The quartz tube 2 was placed in the resistance heating
furnace 3 that was then heated to a given temperature. Trimethyl
borate was introduced from the feeder vessel 1 together with
nitrogen into the quartz tube 2 by way of the inlet pipe 4. In the
meantime, ammonia was also introduced into the quartz tube 2 by way
of the inlet pipe 5. The introduced trimethyl borate and ammonia
reacted with each other in the heated quartz tube 2, yielding a
white power product. The resultant white powder product was
recovered in the recovery vessel 6.
Firing Condition 2
[0064] The white powder product recovered under firing condition 1
was fired in the apparatus shown in FIG. 2.
[0065] The white powder product was filled up in the middle of the
alumina tube 2' that was then placed in the resistance heating
furnace 3', after which nitrogen and ammonia were admitted in from
the inlet pipes 4' and 5', respectively. After heated up to the
given temperatures indicated in Table 1, the white powder product
was fired for a given time, after which the fired product was
cooled down for recovery.
Firing Condition 3
[0066] The fired product obtained under firing condition 2 was
placed in a boron nitride crucible, and further fired at a given
temperature indicated in Table 1 in the induction heating furnace,
in which a nitrogen atmosphere prevailed. The resultant boron
nitride fine particles were measured in terms of average particle
diameter (APD), orientation index (OI), boron nitride purity (BN)
and average circularity (AC). The results are set out in Table
1.
[0067] It is to be noted that the temperature, time and firing
atmosphere under firing conditions 1, 2 and 3 are also
tabulated.
[0068] It is also to be noted that an electron micrograph taken of
an example of the invention is attached hereto as FIG. 3, and an
electron micrograph taken of a comparative example is attached
hereto as FIG. 4.
Materials Used
[0069] Trimethyl Borate (C.sub.3H.sub.9BO.sub.3): Reagent
Trimethoxy Borane made by Wako Pure Chemical Industries, Ltd.
[0070] Ammonia: Commercially available high-purity type
Measuring Methods
[0071] The average particle diameter was measured using a laser
diffraction/scattering particle size distribution analyzer made by
Coulter and available under the trade name of LS-230.
[0072] For the orientation index, an X-ray diffractometry apparatus
(Geiger Flex 2013 Model) made by Rigaku Corporation was used in a
range of 2.theta.=20.degree.-25.degree. to measure the intensity
I.sub.002 of a diffraction line in the vicinity of
2.theta.=27-28.degree. (the plane (002)) and the intensity
I.sub.100 of a diffraction line in the vicinity of
2.theta.=41.degree. (the plane (100)). The orientation index
I.sub.002/I.sub.100 was figured out from the peak intensity ratio
of X-ray diffraction of boron nitride.
[0073] The boron nitride purity was measured by a method in which a
sample was subjected to decomposition with an alkali sodium
hydroxide, and ammonia was distilled out by a steam distillation
process for collection in a boric acid solution. The resultant
solution was titrated with a sulfuric acid normal solution to find
the amount of nitrogen (N), after which the boron nitride purity
(BN) was calculated from BN (%)=N(%).times.1.772.
[0074] For the average circularity, a particle image was taken
using a scanning electron microscope (SEM) or a transmission
electron microscope (TEM), and an image analyzer (for instance,
trade name "MacView" available from Mountech Co., Ltd.) was then
used to measure the projection area (S) and peripheral length (L)
of the particle. The circularity was found by:
Circularity=4.pi.S/L.sup.2
[0075] Arbitrarily selected one hundred particles were measured in
terms of circularity, and the resultant average value was used as
the average circularity for the sample.
TABLE-US-00001 TABLE 1 NH.sub.3/ Firing Firing Firing Run
C.sub.3H.sub.9BO.sub.3 Cond. 1 Cond. 2 Cond. 3 No. (molar ratio)
(.degree. C.) (sec.) (.degree. C.) (hr.) Gas (.degree. C.) (hr.)
1-1 0.8 1,000 10 1,350 5 N.sub.2/NH.sub.3 2,000 4 1-2 1.2 1,000 10
1,350 5 N.sub.2/NH.sub.3 2,000 4 1-3 3.5 1,000 10 1,350 5
N.sub.2/NH.sub.3 2,000 4 1-4 9.7 1,000 10 1,350 5 N.sub.2/NH.sub.3
2,000 4 1-5 10.3 1,000 10 1,350 5 N.sub.2/NH.sub.3 2,000 4 1-6 3.5
720 10 1,350 5 N.sub.2/NH.sub.3 2,000 4 1-7 3.5 760 10 1,350 5
N.sub.2/NH.sub.3 2,000 4 1-8 3.5 1,300 10 1,350 5 N.sub.2/NH.sub.3
2,000 4 1-9 3.5 1,000 25 1,350 5 N.sub.2/NH.sub.3 2,000 4 1-10 3.5
1,000 40 1,350 5 N.sub.2/NH.sub.3 2,000 4 1-11 3.5 1,000 10 950 5
N.sub.2/NH.sub.3 2,000 4 1-12 3.5 1,000 10 1,020 5 N.sub.2/NH.sub.3
2,000 4 1-13 3.5 1,000 10 1,600 5 N.sub.2/NH.sub.3 2,000 4 1-14 3.5
1,000 10 1,630 5 N.sub.2/NH.sub.3 2,000 4 1-15 3.5 1,000 10 1,350
0.5 N.sub.2/NH.sub.3 2,000 4 1-16 3.5 1,000 10 1,350 1 NH.sub.3
2,000 4 1-17 3.5 1,000 10 1,350 5 N.sub.2 2,000 4 1-18 3.5 1,000 10
1,350 5 N.sub.2/NH.sub.3 2,000 4 1-19 3.5 1,000 10 1,350 5
N.sub.2/NH.sub.3 1,750 4 1-20 3.5 1,000 10 1,350 5 N.sub.2/NH.sub.3
1,800 4 1-21 3.5 1,000 10 1,350 5 N.sub.2/NH.sub.3 2,150 4 1-22 3.5
1,000 10 1,350 5 N.sub.2/NH.sub.3 2,230 4 1-23 3.5 1,000 10 1,350 5
N.sub.2/NH.sub.3 2,000 0.4 1-24 3.5 1,000 10 1,350 5
N.sub.2/NH.sub.3 2,000 0.8 Run No. APD (.mu.m) OI BN (%) AC Remarks
1-1 0.20 5.6 97.8 0.90 Comparative 1-2 0.50 6.0 98.3 0.88 Inventive
1-3 0.20 6.0 99.0 0.90 Inventive 1-4 0.05 5.5 99.2 0.90 Inventive
1-5 0.008 4.0 99.2 0.90 Comparative 1-6 1.10 6.0 98.2 0.85
Comparative 1-7 0.50 6.0 98.7 0.87 Inventive 1-8 0.20 8.0 99.1 0.89
Inventive 1-9 0.70 7.0 99.0 0.85 Inventive 1-10 1.20 10.0 98.8 0.87
Comparative 1-11 0.90 18.0 98.3 0.80 Comparative 1-12 0.40 10.0
98.8 0.84 Inventive 1-13 0.30 13.0 99.2 0.82 Inventive 1-14 0.60
16.0 99.1 0.81 Comparative 1-15 1.00 25.0 98.7 * Comparative 1-16
0.20 7.0 98.6 0.85 Inventive 1-17 1.00 22.0 97.0 * Comparative 1-18
0.20 7.0 99.0 0.86 Inventive 1-19 0.20 8.0 97.8 0.88 Comparative
1-20 0.20 6.0 98.4 0.86 Inventive 1-21 0.70 11.0 99.4 0.83
Inventive 1-22 Particle Broken Down Comparative 1-23 0.70 4.5 97.7
0.91 Comparative 1-24 0.20 6.5 98.1 0.89 Inventive *Scaly shape
EXPLANATION OF THE REFERENCE NUMERALS
[0076] 1: Feeder vessel for the alkoxide borate [0077] 2: Reaction
tube (quartz tube) [0078] 2': Reaction tube (alumina tube) [0079]
3, 3': Tubular furnace (resistance heating furnace) [0080] 4:
Alkoxide borate inlet pipe [0081] 4': Nitrogen inlet pile [0082] 5,
5': Ammonia gas inlet pipe [0083] 6: Sample recovery vessel [0084]
7: Product
* * * * *