U.S. patent application number 10/584069 was filed with the patent office on 2007-07-19 for process for producing microparticles and apparatus therefor.
Invention is credited to Seiichiro Takahashi, Hiroshi Watanabe.
Application Number | 20070163385 10/584069 |
Document ID | / |
Family ID | 34746853 |
Filed Date | 2007-07-19 |
United States Patent
Application |
20070163385 |
Kind Code |
A1 |
Takahashi; Seiichiro ; et
al. |
July 19, 2007 |
Process for producing microparticles and apparatus therefor
Abstract
The invention provides a process for producing microparticles,
which process enables production of microparticles such as oxide
microparticles by means of a simple apparatus at low cost and which
is suitable for producing ITO powder, and an apparatus for
producing the microparticles. In the process for producing
microparticles, a raw material in the form of a liquid stream,
liquid droplets, or powder is fed into a heat source; the formed
product in the form of microparticles is captured by means of an
atomized liquid fluid; and the microparticles in the form of slurry
are collected through gas-liquid separation.
Inventors: |
Takahashi; Seiichiro;
(Ageo-shi, JP) ; Watanabe; Hiroshi; (Ageo-shi,
JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Family ID: |
34746853 |
Appl. No.: |
10/584069 |
Filed: |
December 24, 2004 |
PCT Filed: |
December 24, 2004 |
PCT NO: |
PCT/JP04/19354 |
371 Date: |
June 22, 2006 |
Current U.S.
Class: |
75/346 |
Current CPC
Class: |
B22F 9/082 20130101;
B22F 2998/00 20130101; C01B 21/06 20130101; B01J 2219/00123
20130101; B01J 2219/00159 20130101; C01B 13/34 20130101; B01J
2219/00112 20130101; C01B 13/322 20130101; C01G 19/00 20130101;
B01J 8/0055 20130101; C01B 13/326 20130101; B01J 2219/0877
20130101; C01G 1/02 20130101; B22F 9/026 20130101; B22F 9/082
20130101; B22F 2202/13 20130101; B22F 9/026 20130101; B01J
2219/00114 20130101; B22F 2998/00 20130101; B01J 2219/0879
20130101; B01J 2219/0894 20130101; C01P 2002/72 20130101; C01B
21/0821 20130101; B01J 2219/00108 20130101; B01J 19/088
20130101 |
Class at
Publication: |
075/346 |
International
Class: |
C22B 5/20 20060101
C22B005/20; C22C 1/04 20060101 C22C001/04; C21B 15/04 20060101
C21B015/04; B22F 1/00 20060101 B22F001/00; B22F 9/00 20060101
B22F009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 25, 2003 |
JP |
2003-431586 |
Claims
1. A process for producing microparticles, characterized in that
the process comprises feeding into a heat source a raw material in
the form of a liquid stream, liquid droplets, or powder; capturing
the formed product in the form of microparticles by means of an
atomized liquid fluid; and collecting the microparticles in the
form of slurry through gas-liquid separation.
2. A process for producing microparticles according to claim 1,
wherein the raw material to be fed into the heat source is provided
through forming a molten material into a liquid stream or liquid
droplets.
3. A process for producing microparticles according to claim 1,
wherein the raw material to be fed into the heat source is in the
form of atomized powder.
4. A process for producing microparticles according to claim 1,
wherein the gas-liquid separation is performed by means of a
cyclone separator.
5. A process for producing microparticles according to claim 1,
wherein the heat source is acetylene flame or DC plasma flame.
6. A process for producing microparticles according to claim 1,
wherein the liquid fluid is water.
7. A process for producing microparticles according to claim 1,
wherein the raw material is at least one member selected from among
metals, alloys, oxides, nitrides, and oxide nitrides.
8. A process for producing microparticles according to claim 1,
wherein the heat source is an oxidizing atmosphere or a nitrifying
atmosphere, whereby oxide microparticles, nitride microparticles,
or oxide nitride microparticles are produced.
9. A process for producing microparticles according to claim 1,
wherein the raw material is an In--Sn alloy or ITO powder, from
which indium oxide-tin oxide powder is produced.
10. A process for producing microparticles according to claim 9,
which produces indium oxide-tin oxide powder having a tin content
of 2.3 to 45 mass % as calculated on the basis of SnO.sub.2.
11. A process for producing microparticles according to claim 1,
wherein the product flows at a maximum speed of 150 m/sec or less,
when the product is captured by means of the liquid fluid.
12. An apparatus for producing microparticles, characterized in
that the apparatus comprises an inlet for introducing, into the
inside of the apparatus, a gas fluid and a product obtained through
feeding a raw material in the form of a liquid flow, liquid
droplets, or powder into a heat source; a fluid jetting means for
jetting an atomized liquid fluid to the introduced product; a first
gas-liquid separation means for subjecting, to gas-liquid
separation, microparticles captured by the liquid fluid, to thereby
form a slurry of the microparticles; and a first circulating means
for returning a part of an atmosphere fluid containing
microparticles that have not been captured by the liquid fluid to a
position where the fluid jetting means is disposed.
13. An apparatus for producing microparticles according to claim
12, which further comprises, on the downstream side of the first
gas-liquid separation means, a second gas-liquid separation means,
the second gas-liquid separation means being provided for
introducing a part of an atmosphere fluid containing microparticles
that have not been captured by the liquid fluid, for jetting an
atomized liquid fluid to the atmosphere fluid, and for performing
gas-liquid separation, to thereby obtain a slurry of the
microparticles.
14. An apparatus for producing microparticles according to claim
13, which apparatus further comprises, on the downstream side of
the second gas-liquid separation means, a second circulating means
for returning a part of an atmosphere fluid containing
microparticles that have not been captured by the liquid fluid to
the inlet of the second gas-liquid separation means.
15. An apparatus for producing microparticles according to claim
12, wherein the first or second gas-liquid separation is a cyclone
separator.
16. An apparatus for producing microparticles according to claim
12, wherein the particles flow at a maximum speed of 150 m/sec or
less, when the microparticles are captured by the liquid fluid
jetted by means of the fluid jetting means.
Description
TECHNICAL FIELD
[0001] The present invention relates to a process for producing
microparticles of a material such as indium oxide-tin oxide powder,
and to an apparatus for producing the microparticles.
BACKGROUND ART
[0002] Sputtering is a generally known technique for forming thin
film. In the sputtering technique, a thin film is formed by
sputtering a sputtering target. The sputtering technique is
employed in industrial processes, since a thin film of large
surface area can be readily formed, and a high-performance film can
be formed at high efficiency. In recent years, various sputtering
techniques have been known, such as reactive sputtering; i.e.,
sputtering in a reactive gas, and magnetron sputtering, which
realizes high-speed thin film formation by placing a magnet on the
backside of a target.
[0003] Among thin film products obtained through sputtering, indium
oxide-tin oxide (In.sub.2O.sub.3--SnO.sub.2 compound oxide,
hereinafter abbreviated to as ITO) film is a transparent conductive
film which has high optical transparency with respect to visible
light and high conductivity and which, therefore, finds a wide
variety of uses such as for a liquid crystal display, a
heat-generating film for defogging a glass panel, and an
IR-reflecting film.
[0004] Thus, in order to produce thin films with higher efficiency
and lower cost, modification and improvement of sputtering
conditions and sputtering apparatuses are required and are now
under way, and effective operation of sputtering apparatuses is
essential. In the production of ITO film through sputtering, the
period from setting of a new sputtering target to termination of
initial arc (anomalous discharge); i.e., the period required for
initiating formation of thin films, is preferably as short as
possible, and assessing the sputter-enabling period of a target
from the setting thereof (cumulative sputtering time: target life)
is a key issue.
[0005] The aforementioned sputtering target for forming an ITO film
is produced through mixing indium oxide powder and tin oxide powder
at a predetermined ratio, molding under dry or wet conditions, and
sintering the molded product (Patent Document 1). In this
connection, highly-dispersible indium oxide powder has been
proposed for producing high-density sintered ITO (see, for example,
Patent Documents 2, 3, and 4).
[0006] Another known method includes sintering an ITO powder
synthesized through the co-precipitation method under wet
conditions (see, for example Patent Document 5). Similarly, a
variety of wet-synthesis methods for producing ITO powder have been
proposed for producing high-density sintered ITO (see, for example,
Patent Documents 6 to 9).
[0007] Yet another method for producing ITO powder has been
proposed in which an indium-tin alloy is reacted with oxygen in
plasma arc, followed by cooling the reaction product at a
predetermined cooling rate or faster by means of a gas flow at a
Mach number of .gtoreq.1 (see Patent Document 10). However, use of
a high-speed gas flow at a Mach number of >1 requires large
facilities, problematically impeding production of ITO powder at
low cost and with high efficiency.
[0008] Besides the ITO powder production methods, the following
methods for producing metal oxide microparticles have been
proposed. For example, there have been proposed a variety of
methods including feeding a metal powder into a burner flame, to
thereby produce oxide ultra-microparticles, followed by solid-gas
separation (see, for example, Patent Documents 11 to 16). There has
also been proposed a method including spraying a gas to a molten
metal, to thereby form a powder of the metal; conveying the powder
by gas; and feeding the powder into a liquid where reaction such as
chemical reaction or concentration is performed, thereby forming a
micropowder (see patent Document 17). Furthermore, there have been
proposed methods for forming ultra-microparticles including
applying plasma arc to a source such as bulk metal or a metal oxide
rod, to thereby melt and evaporate the source, and spraying a
reaction/cooling gas to the vaporized gas (see Patent Documents 18
to 20).
[0009] However, the above dry-synthesis methods may be unsuitable
for producing ITO powder. Thus, currently, dry-synthesis of ITO
powder is not carried out on an industrial scale. [0010] Patent
Document 1: Japanese Patent Application Laid-Open (kokai) No.
62-21751 [0011] Patent Document 2: Japanese Patent Application
Laid-Open (kokai) No. 5-193939 [0012] Patent Document 3: Japanese
Patent Application Laid-Open (kokai) No. 6-191846 [0013] Patent
Document 4: Japanese Patent Application Laid-Open (kokai) No.
2001-261336 [0014] Patent Document 5: Japanese Patent Application
Laid-Open (kokai) No. 62-21751 [0015] Patent Document 6: Japanese
Patent Application Laid-Open (kokai) No. 9-221322 [0016] Patent
Document 7: Japanese Patent Application Laid-Open (kokai) No.
2000-281337 [0017] Patent Document 8: Japanese Patent Application
Laid-Open (kokai) No. 2001-172018 [0018] Patent Document 9:
Japanese Patent Application Laid-Open (kokai) No. 2002-68744 [0019]
Patent Document 10: Japanese Patent Application Laid-Open (kokai)
No. 11-11946 [0020] Patent Document 11: Japanese Patent Publication
(kokoku) No. 1-55201 [0021] Patent Document 12: Japanese Patent
Publication (kokoku) No. 5-77601 [0022] Patent Document 13:
Japanese Patent No. 3253338 [0023] Patent Document 14: Japanese
Patent No. 3253339 [0024] Patent Document 15: Japanese Patent No.
3229353 [0025] Patent Document 16: Japanese Patent No. 3225073
[0026] Patent Document 17: Japanese Patent Application Laid-Open
(kokai) No. 60-71037 [0027] Patent Document 18: Japanese Patent
Application Laid-Open (kokai) No. 2002-253953 [0028] Patent
Document 19: Japanese Patent Application Laid-Open (kokai) No.
2002-253954 [0029] Patent Document 20: Japanese Patent Application
Laid-Open (kokai) No. 2002-263474
DISCLOSURE OF THE INVENTION
[0029] Problems to be Solved by the Invention
[0030] Under such circumstances, an object of the present invention
is to provide a process for producing microparticles, which process
enables production of microparticles such as oxide microparticles
by means of a simple apparatus at low cost and which is suitable
for producing ITO powder. Another object of the invention is to
provide an apparatus for producing the microparticles.
Means for Solving the Problems
[0031] In a first mode of the present invention for attaining the
aforementioned objects, there is provided a process for producing
microparticles, characterized in that the process comprises feeding
into a heat source a raw material in the form of a liquid stream,
liquid droplets, or powder; capturing the formed product in the
form of microparticles by means of a fluid of atomized liquid
(hereinafter referred to as atomized liquid fluid); and collecting
the microparticles in the form of slurry through gas-liquid
separation.
[0032] According to the first mode, the product obtained through
feeding the raw material into the heat source is effectively
captured in the form of microparticles by means of the atomized
liquid fluid, and the microparticles are effectively collected in
the form of slurry through gas-liquid separation.
[0033] A second mode of the present invention is drawn to a
specific embodiment of the process of the first mode, wherein the
raw material to be fed into the heat source is provided through
forming a molten material into a liquid stream or liquid
droplets.
[0034] According to the second mode, the raw material in the form
of a liquid stream or liquid droplets formed from a molten material
such as a metal or an alloy may be converted to an oxide thereof in
the heat source, and the oxide can be captured in the form of
microparticles by means of the atomized liquid fluid.
[0035] A third mode of the present invention is drawn to a specific
embodiment of the process of the first mode, wherein the raw
material to be fed into the heat source is in the form of atomized
powder.
[0036] According to the third mode, the raw material in the form of
atomized powder formed from a raw material such as a metal or an
alloy is fed into the heat source, whereby the microparticles
thereof are formed.
[0037] A fourth mode of the present invention is drawn to a
specific embodiment of the process of any of the first to third
modes, wherein the gas-liquid separation is performed by means of a
cyclone separator.
[0038] According the fourth mode, the microparticles are
effectively collected with the liquid fluid in the form of slurry
through gas-liquid separation performed by means of a cyclone
separator.
[0039] A fifth mode of the present invention is drawn to a specific
embodiment of the process of any of the first to fourth modes,
wherein the heat source is acetylene flame or DC plasma flame.
[0040] According to the fifth mode, the raw material is formed into
microparticles thereof by acetylene flame or DC plasma flame.
[0041] A sixth mode of the present invention is drawn to a specific
embodiment of the process of any of the first to fifth modes,
wherein the liquid fluid is water.
[0042] According the sixth mode, the product is captured by water,
and the product-water slurry is collected.
[0043] A seventh mode of the present invention is drawn to a
specific embodiment of the process of any of the first to sixth
modes, wherein the raw material is at least one member selected
from among metals, alloys, oxides, nitrides, and oxide
nitrides.
[0044] According the seventh mode, the raw material such as metal,
alloy, oxide, nitride, or oxide nitride is formed into
microparticles thereof.
[0045] An eighth mode of the present invention is drawn to a
specific embodiment of the process of any of the first to seventh
modes, wherein the heat source is an oxidizing atmosphere or a
nitrifying atmosphere, whereby oxide microparticles, nitride
microparticles, or oxide nitride microparticles are produced.
[0046] According to the eighth mode, the raw material is converted
to oxide microparticles, nitride microparticles, or oxide nitride
microparticles in an oxidizing atmosphere or a nitrifying
atmosphere serving as a heat source.
[0047] A ninth mode of the present invention is drawn to a specific
embodiment of the process of any of the first to seventh modes,
wherein the raw material is an In--Sn alloy or ITO powder, from
which indium oxide-tin oxide powder is produced.
[0048] According to the ninth mode, a slurry of ITO powder is
produced from an In--Sn alloy or ITO powder.
[0049] A tenth mode of the present invention is drawn to a specific
embodiment of the process of the ninth mode, which process produces
indium oxide-tin oxide powder having a tin content of 2.3 to 45
mass % as calculated on the basis of SnO.sub.2.
[0050] According to the tenth mode, the produced ITO maintains
conductivity by virtue of a predetermined amount of tin oxide.
[0051] An eleventh mode of the present invention is drawn to a
specific embodiment of the process of any of the first to tenth
modes, wherein the product flows at a maximum speed of 150 m/sec or
less, when the product is captured by means of the liquid
fluid.
[0052] According to the eleventh mode, microparticles can be
produced at a relatively slow flow speed of the product.
[0053] In a twelfth mode of the present invention, there is
provided an apparatus for producing microparticles, characterized
in that the apparatus comprises an inlet for introducing, into the
inside of the apparatus, a gas fluid and a product obtained through
feeding a raw material in the form of a liquid flow, liquid
droplets, or powder into a heat source;
[0054] a fluid jetting means for jetting an atomized liquid fluid
to the introduced product;
[0055] a first gas-liquid separation means for subjecting, to
gas-liquid separation, microparticles captured by the liquid fluid,
to thereby form a slurry of the microparticles; and
[0056] a first circulating means for returning a part of an
atmosphere fluid containing microparticles that have not been
captured by the liquid fluid to a position where the fluid jetting
means is disposed.
[0057] According to the twelfth mode, the product obtained through
feeding a raw material into a heat source is captured in the form
of microparticles by means of an atomized liquid fluid, followed by
gas-liquid separation, and at least a part of the atmosphere fluid
is circulated through the circulating means, followed by another
gas-liquid separation. Thus, the microparticles can be effectively
collected.
[0058] A thirteenth mode of the present invention is drawn to a
specific embodiment of the apparatus of the twelfth mode, which
apparatus further comprises, on the downstream side of the first
gas-liquid separation means, a second gas-liquid separation means,
the second gas-liquid separation means being provided for
introducing a part of an atmosphere fluid containing microparticles
that have not been captured by the liquid fluid, for jetting an
atomized liquid fluid to the atmosphere fluid, and for performing
gas-liquid separation, to thereby obtain a slurry of the
microparticles.
[0059] According to the thirteenth mode, the microparticles that
have not been collected can be effectively collected through the
second gas-liquid separation means.
[0060] A fourteenth mode of the present invention is drawn to a
specific embodiment of the apparatus of the thirteenth mode, which
apparatus further comprises, on the downstream side of the second
gas-liquid separation means, a second circulating means for
returning a part of an atmosphere fluid containing microparticles
that have not been captured by the liquid fluid to the inlet of the
second gas-liquid separation means.
[0061] According to the fourteenth mode, the atmosphere gas which
has not provided a slurry through the second gas-liquid separation
means is further subjected to gas-liquid separation, whereby
microparticles are effectively collected.
[0062] A fifteenth mode of the present invention is drawn to a
specific embodiment of the apparatus of any of the twelfth to
fourteenth modes, wherein the first or second gas-liquid separation
is a cyclone separator.
[0063] According to the fifteenth mode, gas-liquid separation can
be performed continuously and effectively by means of a cyclone
separator.
[0064] A sixteenth mode of the present invention is drawn to a
specific embodiment of the apparatus of any of the twelfth to
fifteenth modes, wherein the particles flow at a maximum speed of
150 m/sec or less, when the microparticles are captured by the
liquid fluid jetted by means of the fluid jetting means.
[0065] According to the sixteenth mode, microparticles can be
produced at a relatively slow flow speed.
EFFECTS OF THE INVENTION
[0066] As described hereinabove, according to the present
invention, a raw material metal or alloy in the form of a liquid
stream, liquid droplets, or powder is fed into a heat source, and
the formed product in the form of microparticles is captured by
means of an atomized liquid fluid. Thus, microparticles can be
effectively produced in a simple manner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0067] [FIG. 1] Schematic configuration of an embodiment of the
apparatus of the present invention for producing
microparticles.
[0068] [FIG. 2] An X-ray diffraction chart of ITO powder produced
in Example 1 of the present invention.
[0069] [FIG. 3] An X-ray diffraction chart of ITO powder produced
in Example 2 of the present invention.
[0070] [FIG. 4] An X-ray diffraction chart of ITO powder produced
in Comparative Example 1 of the present invention.
[0071] [FIG. 5] An X-ray diffraction chart of ITO powder produced
in Comparative Example 2 of the present invention.
[0072] [FIG. 6] An X-ray diffraction chart of ITO powder produced
in Comparative Example 3 of the present invention.
[0073] [FIG. 7] An X-ray diffraction chart of ITO powder produced
in Example 3 of the present invention.
[0074] [FIG. 8] An X-ray diffraction chart of ITO powder produced
in Comparative Example 4 of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0075] According to the process of the present invention for
producing microparticles, a raw material in the form of a liquid
stream, liquid droplets, or powder is fed into a heat source.
[0076] The raw material is, for example, metal or alloy, and
specific examples include metals such as Mg, Al, Zr, Fe, Si, In,
and Sn, and alloys thereof. The raw material may be any of the
aforementioned oxides, nitrides, and oxide nitrides of the metal or
alloy. As used herein, the "oxides" include compound oxides, and
the "nitrides" include complex nitrides.
[0077] The raw material to be fed may be melted to form a liquid
stream or liquid droplets, or may be powder. In other words, a
molten metal may be continuously poured from a tank in the form of
a liquid stream or liquid droplets. Alternatively, the raw material
to be fed may be formed into atomized powder.
[0078] In the case where an In--Sn alloy is employed as a raw
material, an ITO powder can be produced. Furthermore, when an ITO
powder is employed as a raw material, a different type of ITO
material can be produced.
[0079] The heat source may be an oxidizing atmosphere or a
nitrifying atmosphere, and specific examples include acetylene
flame and DC plasma flame. No particular limitation is imposed on
the temperature of the heat source, so long as the heat source can
melt metal, alloy, oxide, nitride, or oxide nitride and can
sufficiently oxidize or nitrify the raw material. Conceivably, the
temperature is at least some thousands of degrees Celsius in the
case of acetylene flame, and at least some ten-thousands of degrees
Celsius in the case of DC plasma flame.
[0080] When a raw material in the form of a liquid stream, liquid
droplets, or powder is fed into the above acetylene flame or DC
plasma flame, a gas flow of a raw material itself, of the
corresponding oxide, of the corresponding nitride, or of the
corresponding oxide nitride is yielded as a product. The product
may be a raw material itself (i.e., metal or alloy) or the
corresponding oxide, nitride, or oxide nitride, depending on the
flame conditions. In other words, when the flame is an oxidizing
atmosphere, an oxide or oxide nitride of the metal or alloy is
formed, whereas when the flame is a nitrifying atmosphere, a
nitride or oxide nitride of the metal or alloy is formed.
Alternatively, when an oxide, nitride, or oxide nitride is employed
as a raw material, a different type of oxide, nitride, or oxide
nitride may be formed.
[0081] According to the present invention, the formed product is
captured by means of an atomized liquid fluid. Specifically, an
atomized liquid fluid, preferably atomized water, is jetted to the
product carried by a jet generated from the acetylene flame or DC
plasma flame. By the mediation of the atomized liquid fluid, the
product is quenched to form microparticles, and a slurry containing
the microparticles in the jetted liquid is produced.
[0082] No particular limitation is imposed on the type of the
atomized liquid fluid to be fed, so long as the fluid can capture
and cool the product. For example, when water is employed, water
(preferably pure water) at ambient temperature is used.
Alternatively, chilled water may also be used.
[0083] The product flows at a maximum speed of, for example, 150
m/sec or less, preferably about 100 m/sec or less, when the product
is captured in the form of microparticles.
[0084] According to the present invention, the liquid fluid
containing the microparticles captured by means of the jetted
liquid fluid is subjected to gas-liquid separation, whereby the
microparticles are collected in the form of slurry. No particular
limitation is imposed on the method of collecting the slurry, and a
cyclone separator is preferably employed.
[0085] According to the method of the present invention, when an
In--Sn alloy or ITO powder is employed as a raw material, an indium
oxide-tin oxide (ITO) powder can be produced. The thus-produced ITO
powder contains a large amount of a SnO.sub.2 solid solution
component dissolved in In.sub.2O.sub.3. Therefore, the ITO exhibits
high sinterability and readily provides high-density sintered ITO.
As a result, a long-life sputtering target can be produced. When an
ITO powder produced through any of various production methods or an
ITO powder obtained by pulverizing sintered ITO is employed as a
raw material, a different type of ITO powder having characteristics
different from those of the raw material and containing a large
amount of a SnO.sub.2 solid solution component dissolved in
In.sub.2O.sub.3 may be produced.
[0086] The above ITO powder may be employed as a material for an
ITO sputtering target. The ITO sputtering target material
preferably has a tin content, as calculated on the basis of
SnO.sub.2, of 2.3 to 45 mass %.
EXAMPLES
[0087] An embodiment of the apparatus for producing microparticles
of the present invention will next be described with reference to
FIG. 1.
[0088] The apparatus has an inlet 10 for introducing, into the
inside of the apparatus, a gas fluid and a product 3 obtained
through feeding of a raw material 2 (e.g., metal or alloy) in the
form of a liquid flow, liquid droplets, or powder into a flame 1
(acetylene flame or DC plasma flame) serving as a heat source that
can provide an oxidizing atmosphere or a nitrifying atmosphere;
fluid jetting means 20 for jetting an atomized liquid fluid to the
introduced microparticles; a cyclone separator 30 serving as
gas-liquid separation means for subjecting, to gas-liquid
separation, the microparticles captured by the liquid fluid, to
thereby form a slurry of the microparticles; and circulating means
40 for returning a part of an atmosphere fluid containing
microparticles that have not been captured by the liquid fluid to a
position where the fluid jetting means is disposed.
[0089] No particular limitation is imposed on the type of the inlet
10, so long as the inlet allows a gas flow containing a product to
feed into the inside of the apparatus. The inlet may be gas-suction
means.
[0090] The fluid jetting means 20 is provided in a conduit 11 on
the downstream side of the inlet 10. The fluid jetting means 20
includes, for example, a plurality of jet nozzles 21 for jetting
water, a pump 22 for feeding fluid to the jet nozzles 21, and a
fluid tank 23 for storing fluid. No particular limitation is
imposed on the jetting direction of the fluid jetted through the
jet nozzles 21. However, the jetting direction is preferably such
that the jetted fluid is merged with a gas flow introduced through
the inlet 10. The product 3 contained in the gas fluid introduced
through the inlet 10 is cooled by means of the atomized liquid
fluid (e.g., water) to form microparticles, and the microparticles
are captured. In the conduit 11, a venturi section 12, where the
flow path is narrowed, is provided on the downstream side of the
jet nozzles 21, so as to prevent reduction in flow rate of a
gas-liquid mixture. Provision of the venturi section 12 is not
obligatory. The jet nozzles 21 and the pump 22 are not necessarily
provided, and instead, the liquid may be jetted on the basis of
suction power generated by flow of gas.
[0091] The conduit 11 provided with the inlet 10 is in
communication with an inlet 31 of the cyclone separator 30 serving
as gas-liquid separation means. A gas-liquid mixture which has been
introduced through the inlet 31 into the cyclone separator 30 forms
a vortex 33 proceeding around the inner wall of a cyclone body 32,
whereby a liquid component is separated from the gas. The liquid
component; i.e., a slurry containing the microparticles, falls down
in the cyclone separator 30, and a gas component is discharged
through a gas-discharge outlet 34.
[0092] In the apparatus of the embodiment, the circulating means 40
is provided so as to communicate with the gas-discharge outlet 34.
In other words, circulation piping 41 is connected to the outlet
34, the circulation piping 41 being in communication with a
position near the inlet 10 of the conduit 11. A blower 42
intervenes in the circulation piping 41. The circulation means 40
consists of the members 41 and 42. Through the circulation means
40, the powder which has not been captured is returned to the
upstream side of the jet nozzles 21, thereby enhancing capturing
efficiency.
[0093] The liquid component which has been separated from the gas
by means of the cyclone separator 30 is discharged through a
water-discharge outlet 36 and stored in the fluid tank 23. The
supernatant water of the slurry stored in the tank 23 is circulated
by means of the circulation means 40, whereby the concentration of
the slurry containing the microparticles gradually increases.
[0094] Most of the discharged gas produced by means of the cyclone
separator 30 is circulated through the gas-discharge outlet 34 to
the circulation piping 41. A part of the discharged gas; for
example, about 1/10 of the amount of the discharge gas, is
discharged through a second gas-discharge outlet 35.
[0095] In the apparatus of the present embodiment, a second cyclone
separator 50 serving as second gas-liquid separation means is
connected to the second gas-discharge outlet 35 via discharge
piping 43. The second cyclone separator 50 has virtually the same
structure as the cyclone separator 30 and serves as gas-liquid
separation means. Specifically, a gas-liquid mixture which has been
introduced through an inlet 51 connected to the discharge piping 43
into the second cyclone separator 50 forms a vortex 53 proceeding
around the inner wall of a cyclone body 52, whereby a liquid
component is separated from the gas. The liquid component; i.e., a
slurry containing the microparticles, falls down in the cyclone
separator 50, and is discharged through a water-discharge outlet 54
and stored in a fluid tank 61. More specifically, a venturi section
44, where the flow path is narrowed, intervenes in the discharge
piping 43, and water circulating piping 62 is provided so as to
maintain communication between the venturi section 44 and the fluid
tank 61. When high-speed gas flow is provided in the venturi
section 44, water contained in the fluid tank 61 is drawn and
jetted into the venturi section 44, whereby microparticles
remaining in the gas phase are captured by water (liquid).
Gas-discharge piping 71 is connected to a gas-discharge outlet 55,
and a second blower 72 is provided in the gas-discharge piping 71,
such that the gas is discharged through the gas-discharge outlet 55
by the mediation of the second blower 72. Water contained in the
water tank 61 may be jetted into the gas-discharge piping 43 by
means of a pump and jet nozzles as mentioned in relation to the
cyclone separator 30. As also mentioned above, the fluid tank 61
may be provided with a filter and a settling tank for separating
microparticles from the liquid through neutralization. In addition,
a portion of the gas discharged through the gas-discharge outlet 55
may be circulated to the upstream side of the venturi section 44 of
the gas-discharge piping 43, to thereby enhance capturing
efficiency.
[0096] When the cyclone separator 30 provides sufficient
microparticle-capturing efficiency, the second cyclone separator 50
is not necessarily provided. In order to further enhance capturing
efficiency, a plurality of cyclone separators may be linked
together.
[0097] Production Examples of microparticles by means of the
apparatus of the above embodiment will next be described.
EXAMPLE 1
[0098] An atomized powder (mean particle size: 45 .mu.m) of In--Sn
alloy (Sn: 9.6 wt. %) was introduced to acetylene flame, to thereby
synthesize an ITO (In.sub.2O.sub.3:SnO.sub.2=90:10 wt. %) powder
under dry conditions. The powder was collected by means of a bag
filter under dry conditions, to thereby yield an ITO powder of
Example 1.
EXAMPLE 2
[0099] In a manner similar to that of Example 1, an ITO powder was
synthesized by means of acetylene flame under dry conditions. The
powder was collected by jetting water to the powder under wet
conditions, to thereby yield an ITO powder of Example 2.
COMPARATIVE EXAMPLES 1
[0100] An indium oxide powder which had been synthesized under wet
conditions was calcined at 1,000.degree. C. Similarly, a tin oxide
powder which had been synthesized under wet conditions was calcined
at 1,000.degree. C. The thus-calcined indium oxide powder (90 mass
%) and tin oxide powder (10 mass %) were mixed by means of a
mortar, to thereby yield an oxide powder of Comparative Example 1
(Standard Product 1).
COMPARATIVE EXAMPLE 2
[0101] An ITO powder was synthesized through co-precipitation under
wet conditions, to thereby yield an ITO powder of Comparative
Example 2.
[0102] The co-precipitation wet synthesis was performed through the
following procedure. First, In (4N) (20 g) was dissolved in nitric
acid (special-grade reagent, concentration: 60 to 61%) (133 cc) at
ambient temperature, to thereby obtain a solution (pH=-1.5).
Similarly, Sn (4N) (2.12 g) was dissolved in hydrochloric acid
(special-grade reagent, concentration: 35 to 36%) (100 cc) at
ambient temperature, to thereby obtain a solution (pH=-1.9). The
two solutions were mixed, to thereby obtain a mixed-acid solution.
No precipitation was observed during mixing, and the mixed solution
was found to have a pH of -1.5. Subsequently, 25% aqueous ammonia
(special-grade reagent) was added to the acidic solution for
neutralization, to thereby adjust the pH to 6.5, whereby a white
matter was precipitated. Several hours after, the supernatant was
removed, and the precipitate was washed with pure water
(2L.times.3), followed by drying at 80.degree. C., roasting at
600.degree. C. for three hours, and dehydration, to thereby yield
an ITO powder through wet synthesis.
COMPARATIVES EXAMPLE 3
[0103] A mixture (tin oxide content: 10 wt. %) of an indium oxide
powder and a tin oxide powder which had been synthesized under wet
conditions was sintered at 1,550.degree. C. or higher. The sintered
ITO was pulverized, to thereby yield an ITO powder of Comparative
Example 3.
TEST EXAMPLE 1
[0104] Each of the ITO powders of Examples 1 and 2 and Comparative
Examples 1 to 3 was analyzed in terms of SnO.sub.2 solid solution
content. The determination procedure was as follows. Prior to the
test, ITO powders of Examples 1 and 2 and Comparative Examples 2
and 3 were calcined at 1,000.degree. C. for three hours in air so
as to grow precipitated SnO.sub.2 microparticles to SnO.sub.2 large
particles, which are readily detectable.
[0105] 1. Inductively coupled high-frequency plasma spectroscopic
analysis (ICP spectroscopic analysis) was performed. For
calculation, it was assumed that each ITO powder exclusively
consists of In, Sn, and oxygen (O), and that a certain amount of
oxygen may be deficient. The ratio of In to Sn was calculated from
the analytical values, and the ratio by weight of In.sub.2O.sub.3
to SnO.sub.2 was calculated, under the condition that all elemental
In and Sn were converted to In.sub.2O.sub.3 and SnO.sub.2,
respectively. 2. ITO powders of Examples 1 and 2 and Comparative
Examples 1 to 3 were subjected to powder X-ray diffractometry (XRD:
by means of MXP 18II, product of Mac Science), whereby the
precipitated SnO.sub.2 content of each powder was determined. In
each case, the presence of a compound oxide
(In.sub.4Sn.sub.3O.sub.12) was checked from the corresponding
diffraction chart. When the compound oxide was not detected, the
precipitated SnO2 content (mass %) of the ITO powder was determined
from the ratio between integral diffraction intensity attributed to
In.sub.2O.sub.3 (222) and integral diffraction intensity attributed
to SnO.sub.2 (110), with respect to Standard Product 1 of
Comparative Example 1. Specifically, the precipitated SnO.sub.2
content (mass %) is a SnO.sub.2 content obtained from an integral
intensity of X-ray diffraction attributed to SnO.sub.2, assuming
that the SnO.sub.2 component which has not been dissolved in
In.sub.2O.sub.3 and has been grown through calcination at about
1,000.degree. C. exhibits an X-ray diffraction peak attributed to
SnO.sub.2 (110). FIGS. 2 to 6 show the results of X-ray diffraction
analysis.
[0106] 3. On the basis of the results of "1." and "2.," the
SnO.sub.2 solid solution (in In.sub.2O.sub.3) content of each ITO
powder was obtained from the amount of SnO.sub.2 which had been
detected through ICP analysis but which had not been detected as
SnO.sub.2 (110) through X-ray diffraction.
[0107] The results are shown in Table 1.
[0108] The ITO powders of Examples 1 and 2 were found to have a
SnO.sub.2 solid solution content of 2.35 wt. % and 2.42 wt. %,
which are higher than the SnO.sub.2 solid solution content of 2.26
wt. % of the ITO powder of Comparative Example 2 obtained through
wet synthesis. The ITO powder of Comparative Example 3, which had
been produced through pulverizing the sintered product thereof, was
found to form a compound oxide. Therefore, the SnO.sub.2 solid
solution content of the ITO powder of Comparative Example 3 could
not be determined. TABLE-US-00001 TABLE 1 SnO.sub.2 XRD analysis
solid ICP analysis Precipitated solution Sample In Sn
In.sub.2O.sub.3 SnO.sub.2 Compound InO.sub.3 SnO.sub.2 SnO.sub.2
content content No. (wt. %) (wt. %) (wt. %) (wt. %) oxide (222)
(110) (wt. %) (wt. %) Ex. 1 74.1 8.26 89.52 10.48 no 6974596 357821
8.13 2.35 Ex. 2 74.8 7.90 89.92 10.08 no 6875331 331124 7.66 2.42
Comp. 75.1 7.87 90.09 9.91 no 7141621 455777 9.91 0.00 Ex. 1
standard Comp. 76.1 8.03 90.03 9.97 no 7273411 352429 7.71 2.26 Ex.
2 Comp. 74.8 7.90 90.02 9.98 yes 7529677 105639 -- -- Ex. 3
EXAMPLE 3
[0109] An atomized powder (mean particle size: 45 .mu.m) of In--Sn
alloy (Sn: 9.6 wt. %) was introduced to DC plasma flame, to thereby
synthesize an ITO (In.sub.2O.sub.3:SnO.sub.2=90:10 wt. %) powder
under dry conditions. The powder was collected by jetting water to
the powder under wet conditions, to thereby yield an ITO powder of
Example 3.
COMPARATIVE EXAMPLE 4
[0110] Similar to Comparative Example 1, an indium oxide powder
which had been synthesized under wet conditions was calcined at
1,000.degree. C. Similarly, a tin oxide powder which had been
synthesized under wet conditions was calcined at 1,000.degree. C.
The thus-calcined indium oxide powder (90 mass %) and tin oxide
powder (10 mass %) were mixed by means of a mortar, to thereby
yield an oxide powder of Comparative Example 4 (Standard Product
2).
TEST EXAMPLE 2
[0111] Similar to Test Example 1, each of the ITO powders of
Example 3 and Comparative Example 4 was analyzed in terms of
SnO.sub.2 solid solution content. Powder X-ray diffractometry (XRD)
was performed by means of X'PertPRO MPD (product of Spectris Co.,
Ltd.). The results are shown in Table 2. FIGS. 7 and 8 show the
results of X-ray diffraction analysis.
[0112] The ITO powder of Example 3 was found to have a SnO.sub.2
solid solution content of 3.00 wt. %, which is remarkably higher
than the SnO.sub.2 solid solution content of the ITO powder of
Example 2 obtained by means of acetylene flame instead of DC plasma
flame. TABLE-US-00002 TABLE 2 SnO.sub.2 XRD analysis solid ICP
analysis Precipitated solution Sample In Sn In.sub.2O.sub.3
SnO.sub.2 Compound InO.sub.3 SnO.sub.2 SnO.sub.2 content content
No. (wt. %) (wt. %) (Wt. %) (Wt. %) oxide (222) (110) (wt. %) (wt.
%) Ex. 3 73.8 7.46 90.40 9.60 no 691582 31090 6.60 3.00 Comp. 75.1
7.86 90.10 9.90 no 892303 62325 9.90 0.00 Ex. 4
* * * * *