U.S. patent application number 11/660057 was filed with the patent office on 2008-10-23 for fine particulate titanium dioxide, and production process and use thereof.
This patent application is currently assigned to SHOWA DENKO K.K.. Invention is credited to Susumu Kayama, Hisao Kogoi, Jun Tanaka.
Application Number | 20080260625 11/660057 |
Document ID | / |
Family ID | 35355488 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080260625 |
Kind Code |
A1 |
Kogoi; Hisao ; et
al. |
October 23, 2008 |
Fine Particulate Titanium Dioxide, and Production Process and Use
Thereof
Abstract
A high-purity ultrafine particulate titanium dioxide with a
reduced fluctuation of the adsorbed water content which is a large
mass fluctuation factor in a fine particulate powder body, is
provided. The fine particulate titanium dioxide has a BET specific
surface area of 10 to 200 m.sup.2/g, wherein when a powder of the
titanium dioxide in an amount of 2 to 5 g is spread in a 10
cm-diameter glass-made Petri dish to a uniform thickness and left
standing in an environment at 20.degree. C. and a relative humidity
of 80% for 5 hours, the rate of change of mass based on the mass
before standing is from -5 mass % to 5 mass %. The process for
producing the fine particulate titanium dioxide comprises a first
step of high-temperature oxidizing a titanium
tetrachloride-containing gas with use of an oxidative gas to
produce a titanium dioxide powder, and a second step of contacting
water vapor with the titanium dioxide powder while rolling the
powder in a heating furnace, thereby effecting dechlorination and
at the same time, increasing the adsorbed water.
Inventors: |
Kogoi; Hisao; (Toyama,
JP) ; Kayama; Susumu; (Toyama, JP) ; Tanaka;
Jun; (Tokyo, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
SHOWA DENKO K.K.
Tokyo
JP
|
Family ID: |
35355488 |
Appl. No.: |
11/660057 |
Filed: |
August 11, 2005 |
PCT Filed: |
August 11, 2005 |
PCT NO: |
PCT/JP2005/015039 |
371 Date: |
February 19, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60602649 |
Aug 19, 2004 |
|
|
|
Current U.S.
Class: |
423/610 ;
428/402 |
Current CPC
Class: |
B01J 35/1019 20130101;
C09C 1/3607 20130101; Y10T 428/2982 20150115; B01J 21/063 20130101;
C01G 23/075 20130101; H01G 9/2031 20130101; B01J 35/004 20130101;
B01J 35/1014 20130101; C01G 23/07 20130101; C01P 2004/62 20130101;
C01P 2006/80 20130101; Y02E 10/542 20130101; C01P 2006/82 20130101;
C01G 23/047 20130101; A61K 8/29 20130101; A61Q 17/04 20130101; C01P
2006/12 20130101 |
Class at
Publication: |
423/610 ;
428/402 |
International
Class: |
C01G 23/047 20060101
C01G023/047 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 11, 2004 |
JP |
2004-234764 |
Claims
1. A fine particulate titanium dioxide having a BET specific
surface area of 10 to 200 m.sup.2/g, wherein when a powder of the
titanium dioxide in an amount of 2 to 5 g is spread in a 10
cm-diameter glass-made Petri dish to a uniform thickness and left
standing in an environment at 20.degree. C. and a relative humidity
of 80% for 5 hours, the rate of change of mass based on the mass
before standing is from -5 mass % to 5 mass %.
2. The fine particulate titanium dioxide according to claim 1,
wherein the 90% cumulative mass-particle size distribution diameter
(hereinafter denoted as "D90") is 2.2 .mu.m or less.
3. The fine particulate titanium dioxide according to claim 1,
wherein the distribution constant n according to the Rosin-Rammler
formula represented by the following formula (1) is from 1.7 to
3.5: R=100exp(-bD.sup.n) (1) wherein D is a particle diameter, R is
a mass percentage of particles larger than D (particle diameter)
based on the mass of all particles, and n is a distribution
constant.
4. A fine particulate titanium dioxide wherein, assuming that the
BET specific surface area is .alpha. (m.sup.2/g) and the mass
decrement when the powder is ignited in an electric furnace kept at
900.degree. C. for 1 hour (hereinafter this decrement is called a
loss on ignition) is X (mass %), the loss on ignition X is present
in the range represented by formula (2):
2.1.times.{.alpha./(6.times.14).times.18+(.alpha.-.beta.)/(6.times.-
10.sup.4).times.9}.times.100.gtoreq.X.gtoreq.0.25.times.{.alpha./(6.times.-
10.sup.4).times.18+(.alpha.-.beta.)/(6.times.10.sup.4).times.9}.times.100
(2) herein .beta. is a BET specific surface area (m.sup.2/g) after
the powder is ignited in an electric furnace kept at 900.degree. C.
for 1 hour.
5. A fine particulate titanium dioxide wherein, assuming that the
BET specific surface area is .alpha. (m.sup.2/g) and the mass
decrement when the powder is ignited in an electric furnace kept at
900.degree. C. for 1 hour (hereinafter this decrement is called a
loss on ignition) is X (mass %), the loss on ignition X is present
in the range represented by formula (2'):
1.3.times.{.alpha./(6.times.10.sup.4).times.18+(.alpha.-.beta.)/(6-
.times.10.sup.4).times.9}100.gtoreq.X.gtoreq.0.7.times.{.alpha./(6.times.1-
0.sup.4).times.18+(.alpha.-.beta.)/(6.times.10.sup.4).times.9}.times.100
(2') wherein .beta. is a BET specific surface area (m.sup.2/g)
after the powder is ignited in an electric furnace kept at
900.degree. C. for 1 hour.
6. A fine particulate titanium dioxide wherein, assuming that the
BET specific surface area is .alpha. (m.sup.2/g) and the mass
decrement when the powder is ignited in an electric furnace kept at
900.degree. C. for 1 hour (hereinafter this decrement is called
"loss on ignition") is X (mass %), the loss on ignition X is
present in the range represented by formula (3):
1.5.times.{.alpha./(6.times.10.sup.4).times.18+(.alpha.-.beta.)/(6.-
times.10.sup.4).times.9}.times.100.gtoreq.X.gtoreq.0.85.times.{.alpha./(6.-
times.10.sup.4).times.18+(.alpha.-.beta.)/(6.times.10.sup.4).times.9}.time-
s.100 (3) wherein .beta. is a BET specific surface area (m.sup.2/g)
after the powder is ignited in an electric furnace kept at
900.degree. C. for 1 hour.
7. A fine particulate titanium dioxide wherein, assuming that the
BET specific surface area is .alpha. (m.sup.2/g) and the mass
decrement when the powder is ignited in an electric furnace kept at
900.degree. C. for 1 hour (hereinafter this decrement is called
"loss on ignition") is X (mass %), the loss on ignition X is
present in the range represented by formula (3'):
1.15.times.{.alpha./(6.times.10.sup.4).times.18+(.alpha.-.beta.)/(-
6.times.10.sup.4).times.9}.times.100.gtoreq.X.gtoreq.0.85.times.{.alpha./(-
6.times.10.sup.4).times.18+(.alpha.-.beta.)/(6.times.10.sup.4).times.9}.ti-
mes.100 (3') wherein .beta. is a BET specific surface area
(m.sup.2/g) after the powder is ignited in an electric furnace kept
at 900.degree. C. for 1 hour.
8. The fine particulate titanium dioxide according to claim 1,
wherein the Fe, Al and S contents each is 10 ppm by mass or
less.
9. The fine particulate titanium dioxide according to claim 1,
wherein the content of Cl in the powder body is 50 mass % or less
of the loss on ignition.
10. A process for producing a fine particulate titanium dioxide,
comprising a first step of high-temperature oxidizing a titanium
tetrachloride-containing gas with use of an oxidative gas to
produce a titanium dioxide powder, and a second step of contacting
water vapor with the titanium dioxide powder while rolling the
powder in a heating furnace, thereby effecting dechlorination and
at the same time, increasing the adsorbed water.
11. The process for producing a fine particulate titanium dioxide
according to claim 10, wherein the oxidative gas is water
vapor.
12. The process for producing a fine particulate titanium dioxide
according to claim 11, wherein the amount of water vapor contacted
is from 2 to 30 mol per mol of the titanium tetrachloride gas.
13. The process for producing a fine particulate titanium dioxide
according to claim 10, wherein the titanium
tetrachloride-containing gas and the oxidative gas supplied to the
reaction tube each is preheated at a temperature of 600.degree. C.
to less than 1,100.degree. C.
14. The process for producing a fine particulate titanium dioxide
according to claim 10, wherein in the second step, the water vapor
and the powder body are counter-currently contacted by introducing
the water vapor into the heating furnace at a ratio of 1 to 60 mass
% based on the titanium dioxide powder.
15. The process for producing a fine particulate titanium dioxide
according to claim 10, wherein in the second step, the water vapor
and the powder body are counter-currently contacted by introducing
the water vapor into the heating furnace to occupy a ratio of 1 to
50 mass % based on the titanium dioxide powder.
16. The process for producing a fine particulate titanium dioxide
according to claim 10, wherein in the second step, the titanium
dioxide is heated at 150 to 500.degree. C.
17. The process for producing a fine particulate titanium dioxide
according to claim 10, wherein in the second step, the residence
time of the powder in the heating furnace is from 0.5 hours to less
than 3 hours.
18. A process for producing a fine particulate titanium dioxide,
comprising spraying water droplets having a liquid droplet diameter
of 5 to 500 .mu.m at the time of packing the powder in a resin bag,
and closing and then storing the bag.
19. A fine particulate titanium dioxide produced by the process
described in claim 10.
20. A perovskite compound using the fine particulate titanium
dioxide described in claim 1 as a part of the raw materials.
21. A dielectric raw material comprising the titanium dioxide
powder described in claim 1.
22. A slurry comprising the titanium dioxide powder described in
claim 1.
23. A composition comprising the titanium dioxide powder described
in claim 1.
24. A photocatalyst material comprising the titanium dioxide powder
described in claim 1.
25. A cosmetic material comprising the titanium dioxide powder
described in claim 1.
26. A solar cell material comprising the titanium dioxide powder
described in claim 1.
27. An additive for silicone rubber, comprising the titanium
dioxide powder described in claim 1.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is an application filed under 35 U.S.C.
.sctn.111(a) claiming benefit pursuant to 35 U.S.C. .sctn.119(e)(1)
of the filing date of the Provisional Application No. 60/602,649
filed on Aug. 19, 2004, pursuant to 35 U.S.C. .sctn.111(b).
TECHNICAL FIELD
[0002] The present invention relates to a fine particulate titanium
dioxide (TiO.sub.2) and a production process thereof. More
specifically, the present invention relates to a fine particulate
titanium dioxide, obtained by a vapor phase process starting from
titanium tetrachloride, which ensures a small rate of change of
mass and is suitable for photocatalysts, solar cells, additives and
dielectric raw materials, and also relates to a production process
and uses thereof.
BACKGROUND ART
[0003] A fine particulate titanium dioxide has been heretofore used
in various applications such as a UV-shielding material, an
additive to silicone rubber, a dielectric raw material and a
cosmetic material. In recent years, application to photocatalysts,
solar cells and the like is attracting much attention.
[0004] As for the crystal form of titanium dioxide, three types of
rutile, anatase and brookite, are present and among these, anatase
or brookite titanium dioxide more excellent in the
photoelectrochemical activity than the rutile is used in the fields
of photocatalyst and solar cell.
[0005] The photocatalytic activity of titanium dioxide is utilized,
for the decomposition of organic materials, as antimicrobial tiles,
self-cleaning building materials and deodorant fibers, and the
mechanism thereof is understood to be as follows. The titanium
dioxide absorbs ultraviolet light and generates an electron and a
hole in the inside thereof. The hole reacts with the adsorbed water
of titanium dioxide to produce a hydroxy radical and, by the effect
of this radical, the organic material adsorbed to the surface of
the titanium dioxide particles is decomposed into carbonic acid gas
or water (Akira Fujishima, Kazuhito Hashimoto and Toshiya Watanabe,
Hikari Clean Kakumei (Light Clean Revolution), CMS (1997)).
[0006] That is, the conditions required of the titanium dioxide
having strong photocatalytic activity are to readily generate a
hole and to allow the hole to easily reach the titanium dioxide
surface. Examples of the titanium dioxide having high
photocatalytic activity include those of anatase type, those having
a small number of crystal defects, and those of giving a small
particle having a large specific surface area (Kazuhito Hashimoto
and Akira Fujishima (compilers), Sannka Titan Hikari Shokubai no
Subete (All About Titanium Oxide Photocatalyst), CMC (1998)).
[0007] In practice, titanium dioxide is fixed to the surface of a
substrate with a binder and when light is irradiated onto that
layer, a catalytic activity is realized. Transparency of a
photo-catalytic layer is demanded for the aesthetic reasons.
Accordingly, when titanium dioxide is supported on a substrate, the
amount of titanium dioxide and dispersibility of the powder are
very important.
[0008] As for the application to solar cells, a dye-sensitized
solar cell comprising a combination of a titanium dioxide and a
ruthenium-base dye was reported in 1991 by Graetzel et al. of
EPFL-Lausanne and, since this discovery, studies are being made
thereon (M. Graezel, Nature, 353, 737 (1991)).
[0009] In the dye-sensitized solar cell, the titanium dioxide plays
the role of a support for the dye as well as of an n-type
semiconductor and is used as a dye electrode bound to an
electrically conducting glass electrode. The dye-sensitized solar
cell has a structure where an electrolytic layer is sandwiched by a
dye electrode and a counter electrode, where the dye absorbs light
and thereby generates an electron and a hole. The electron
generated is transferred to the electrically conducting glass
electrode through the titanium dioxide layer and taken outside. On
the other hand, the generated hole is transferred to the counter
electrode through the electrolytic layer and combines with an
electron supplied through the electrically conducting glass
electrode. One of the factors for improving the characteristic
feature of a dye-sensitized solar cell is that the titanium dioxide
and the dye are easily combined. As for the crystal form of
titanium dioxide which can be easily combined with the dye, for
example, JP-A-10-255863 (the term "JP-A" as used herein means an
"Japanese Unexamined Patent Publication (Kokai)") describes use of
an anatase type, and JP-A-2000-340269 states that a brookite type
is suitable for dye-sensitized solar cells.
[0010] To bring out the function of titanium dioxide, good
dispersibility is important. For example, when the titanium dioxide
is used as a photocatalyst, if the dispersibility is bad, the
covering property is intensified and the usable application is
restricted. A titanium dioxide having bad dispersibility hardly
transmits light and, therefore, also in the field of solar cells,
the amount of titanium dioxide capable of contributing to the light
absorption is limited and the photoelectric conversion efficiency
decreases. In general, it is considered that light scattering
(covering power) becomes maximum when the particle diameter is
about a half of the visible light wavelength, and as the particle
size becomes smaller, the light scattering is weakened (Manabu
Kiyono, Sannka-Titan (Titanium Oxide), p. 129, Gihodo-Shuppan
(1991)).
[0011] The primary particle diameter of the titanium dioxide used
in the above-described field is from several nm to tens of nm in
many cases and, therefore, as long as the dispersibility is good,
the effect on the light scattering is small. If the titanium
dioxide has poor dispersibility and gives an aggregated particle
having a large diameter, light scattering is intensified.
Therefore, the particle having good dispersibility can be said to
be a particle which is free from aggregation and can be stably
present in a state close to a primary particle in a solvent.
[0012] The titanium dioxide is an indispensable material as a
high-performance dielectric raw material. The dielectric material,
for example, BaTiO.sub.3 is obtained by the following reaction
under heating:
BaCO.sub.3+TiO.sub.2.fwdarw.BaTiO.sub.3+CO.sub.2
[0013] In order to enhance the dielectric property of BaTiO.sub.3,
the BaTiO.sub.3 particle must be pulverized. The reaction above is
a solid phase reaction and it is said that BaCO.sub.3 is first
decomposed at a high temperature to produce BaO, and the BaO is
diffused and solid-dissolved in the TiO.sub.2 particle and becomes
BaTiO.sub.3. Accordingly, the size of the BaTiO.sub.3 particle is
governed by the size of the TiO.sub.2 particle. The chlorine
contained in the TiO.sub.2 particle is present by adsorbing on an
extreme surface layer of the particle and reacts with BaO produced
during heating to produce BaCl.sub.2. This BaCl.sub.2 is melted and
acts as a flux to bring about aggregation of TiO.sub.2 particles or
BaTiO.sub.3 particles. Also, the melted flux is readily localized
and many aggregations occur in the localized portion, as a result,
the quality differs from other portions. In addition, when the
particles are aggregated, the BaTiO.sub.3 particle crystal grows
into an abnormal particle and thus decreases the dielectric
property of BaTiO.sub.3. during the synthesis of a high-performance
dielectric material, the ratio of BaO and TiO.sub.2 must be
strictly controlled to be 1:1, but the presence of chlorine causes
deviation from the compositional ratio.
[0014] Furthermore, fluctuation of the adsorbed water on the
particle surface gives rise to a problem greater than the
above-described impurity. In use of a titanium dioxide, it is
required in many cases to very strictly control the blended Ti
content. Particularly, in the case of using the titanium dioxide as
the dielectric raw material, the blended components must be
controlled even to the ppm order. However, in industrial use,
strict control of raw materials is not easy, because the water is a
substance present in the atmosphere where the raw materials are
handled, and great difficulties are involved in the control of the
amount of chemically adsorbed water and physically adsorbed water
on the particle surface.
[0015] The titanium oxide surface is fundamentally covered with an
OH group chemically bonded to a Ti atom or an O atom, and a water
molecule is physically adsorbed to this OH group in many layers by
hydrogen bonding and forms a water content measured as the loss on
drying (Manabu Kiyono, Sannka Titan (Titanium Oxide), p. 54, Gihodo
Shuppan (1991)).
[0016] However, this water content is readily affected by the
season or weather because moisture is repeatedly absorbed or
released according to the ambient humidity. Therefore, in order to
strictly control the ratio of BaO and TiO.sub.2, the materials must
be bone-dry and weighed immediately before the synthesis and this
imposes an large load in view of equipment and expense.
Furthermore, as the particle is finer, the surface area per unit
mass, namely, the specific surface area is larger and therefore,
the amount of water adsorbed and the quantitative fluctuation of
the raw material charged are larger. Combined with recent tendency
toward fine particle formulation, the fluctuation of the charged
amount and in turn, the reduction of the yield cannot be
avoided.
[0017] The production process of titanium dioxide is roughly
classified into a liquid phase process of hydrolyzing titanium
tetrachloride or titanyl sulfate, and a vapor phase process of
reacting titanium tetrachloride with an oxidative gas such as
oxygen or water vapor. According to the liquid phase process, a
titanium dioxide comprising anatase as the main phase can be
obtained but this is in a sol or slurry state. In the case of using
the titanium dioxide in this state, the application is limited. For
using the titanium dioxide as a powder, the sol or slurry must be
dried, but when dried, intensive aggregation generally results
(Shinnroku Saito (superviser), Cho-Biryushi Handbook (Handbook of
Ultrafine Particles), p. 388, Fuji-Technosystem Corporation,
(1990)).
[0018] In the case of using this titanium dioxide as a
photocatalyst or the like, the titanium oxide must be strongly
cracked or ground so as to elevate the dispersibility, but this may
cause problems such as mingling of abraded materials attributable
to the grinding treatment or the like, and a non-uniform particle
size distribution.
[0019] On the other hand, the titanium dioxide by a vapor phase
process is excellent in the dispersibility as compared with that
obtained by a liquid phase process, because a solvent is not used
(Shinnroku Saito (superviser), Cho-Biryushi Handbook (Handbook of
Ultrafine Particles), p. 388, Fuji-Technosystem Corporation,
(1990)).
[0020] A large number of methods are known for obtaining ultrafine
particulate titanium dioxide by a vapor phase process. For example,
a process of producing a titanium dioxide by hydrolyzing titanium
tetrachloride in flame is disclosed, wherein the reaction is
performed by adjusting the molar ratio of oxygen, titanium
tetrachloride and hydrogen to obtain a titanium dioxide having a
high rutile content (JP-A-03-252315). Also, a process of producing
a crystalline titanium dioxide powder by hydrolyzing titanium
tetrachloride in a high-temperature vapor phase and rapidly cooling
the reaction produce is disclosed, wherein the flame temperature
and the titanium concentration in the raw material gas are
specified to obtain a crystalline transparent titanium dioxide
having an average primary particle diameter of 40 to 150 nm
(JP-A-7-316536).
[0021] As for the process of producing a titanium dioxide
comprising anatase as the main phase by a vapor phase process, for
example, a production process where the rutile content ratio is
adjusted by changing the ratio of hydrogen in an oxygen/hydrogen
mixed gas in the vapor phase reaction is disclosed and a titanium
dioxide having a rutile content of 9% is described, but the
particle diameter of the titanium dioxide described is from 0.5 to
0.6 .mu.m and coarser than the particle diameter range of particles
generally called an ultrafine particle (JP-A-3-252315).
[0022] In the case of using a titanium dioxide for a photocatalyst
or a solar cell, the fluctuation of loss on drying of titanium
dioxide causes change in the formulation and this gives rise to
fluctuation of quality and reduction of performance and yield.
[0023] Also, impurities such as Fe, Al, Si and S in the titanium
dioxide give rise to a fluctuation in quality and reductions of
performance and yield and therefor, their content is preferably
reduced. For example, when Fe is present in titanium dioxide,
coloration is caused and the titanium dioxide is not suited for
usage where transparency is required. Also, when a component such
as Al and S is present inside the titanium dioxide particle,
crystal defects are generated and the function as a photocatalyst
or a solar cell may be deteriorated.
[0024] As for the production process of titanium dioxide, when a
titanium dioxide is produced by a vapor phase process starting from
titanium tetrachloride, an ultrafine particle may be readily
obtained but chlorine originated in the raw material often remains
in the titanium dioxide and dechlorination by heating, water
washing or the like is required. The method for this treatment such
as heating or water washing greatly affects the amount of water or
hydroxyl group chemically adsorbing to the titanium dioxide
particle surface. Such surface properties of titanium dioxide,
including the residual chlorine, have a great effect not only on
the amount of adsorbed water but also on the sintering or
aggregation behavior of particles with each other at the heating in
use of the titanium dioxide. Particularly, as the titanium dioxide
particle is finer, the ratio of atoms present on the surface
increases and the effect of the surface state becomes greater.
[0025] The present invention has been made to solve the
above-described problems and an object of the present invention is
to provide a fine particulate titanium dioxide with reduced
fluctuation of the adsorbed water content which is a great mass
fluctuation factor in a fine particulate powder body, more
preferably a high-purity ultrafine particulate titanium dioxide and
a production process thereof.
DISCLOSURE OF THE INVENTION
[0026] As a result of intensive investigations to solve those
problems, the present inventors have found that when the conditions
for the synthesis and high-purity formulation in the vapor phase
process are adjusted, the amount of the hydroxyl group present on
the titanium dioxide surface can be made sufficiently large and in
turn, an ultrafine particulate titanium dioxide hardly undergoing
fluctuation of mass in any environment can be produced. The
above-described object can be attained based on this finding.
[0027] That is, in a preferred embodiment of the present invention,
a fine particulate titanium dioxide stabilized in the loss on
ignition and mass fluctuation in a normal environment, and an
ultrafine particulate titanium dioxide having specific features in
view of the particle size distribution and the coarse particle are
provided, which are obtained by a vapor phase process of reacting a
titanium tetrachloride-containing gas with an oxidative gas (water
vapor or a mixed gas containing oxygen and water vapor), wherein
the raw material gases are reacted while controlling the heating
temperature of these gases and the kind and amount of the oxidative
gas and, then, the heating temperature and the amount of water
vapor added at the dechlorination treatment by heating are
controlled. Also, a production process thereof is provided.
[0028] The present invention includes the following matters.
[0029] [1] A fine particulate titanium dioxide having a BET
specific surface area of 10 to 200 m.sup.2/g, wherein when a powder
of the titanium dioxide in an amount of 2 to 5 g is spread in a 10
cm-diameter glass-made Petri dish to a uniform thickness and left
standing in an environment at 20.degree. C. and a relative humidity
of. 80% for 5 hours, the rate of change of mass based on the mass
before standing is from -5 mass % to 5 mass %.
[0030] [2] The fine particulate titanium dioxide as described in
[1] above, wherein the 90% cumulative mass-particle size
distribution diameter (hereinafter denoted as "D90") is 2.2 .mu.m
or less.
[0031] [3] The fine particulate titanium dioxide as described in
[1] or [2] above, wherein the distribution constant n according to
the Rosin-Rammler formula represented by the following formula (1)
is from 1.7 to 3.5:
R=100exp(-bD.sup.n) (1)
wherein D is a particle diameter, R is a mass percentage of
particles larger than D (particle diameter) based on the mass of
all particles, and n is a distribution constant.
[0032] [4] A fine particulate titanium dioxide wherein, assuming
that the BET specific surface area is .alpha. (m.sup.2/g) and the
mass decrement when the powder is ignited in an electric furnace
kept at 900.degree. C. for 1 hour (hereinafter this decrement is
called a loss on ignition) is X (mass %), the loss on ignition X is
present in the range represented by formula (2):
2.1.DELTA.{.alpha./(6.times.10.sup.4).times.18+(.alpha.-.beta.)/(6.times-
.10.sup.4).times.9}.times.100.gtoreq.X.gtoreq.0.25.times.{.alpha./(6.times-
.10.sup.4).times.18+(.alpha.-.beta.)/(6.times.10.sup.4).times.9}.times.100
(2)
wherein .beta. is a BET specific surface area (m.sup.2/g) after the
powder is ignited in an electric furnace kept at 900.degree. C. for
1 hour.
[0033] [5] A fine particulate titanium dioxide, wherein assuming
that the BET specific surface area is .alpha.(m.sup.2/g) and the
mass decrement when the powder is ignited in an electric furnace
kept at 900.degree. C. for 1 hour (hereinafter this decrement is
called a loss on ignition) is X (mass %), the loss on ignition X is
present in the range represented by formula (2'):
1.3.times.{.alpha./(6.times.10.sup.4).times.18+(.alpha.-.beta.)/(6.times-
.10.sup.4).times.9}.times.100.gtoreq.X.gtoreq.0.7.times.{.alpha./(6.times.-
10.sup.4).times.18+(.alpha.-.beta.)/(6.times.10.sup.4).times.9}.times.100
(2')
wherein .beta. is a BET specific surface area (m.sup.2/g) after the
powder is ignited in an electric furnace kept at 900.degree. C. for
1 hour.
[0034] [6] A fine particulate titanium dioxide, wherein assuming
that the BET specific surface area is .alpha. (m.sup.2/g) and the
mass decrement when the powder is ignited in an electric furnace
kept at 900.degree. C. for 1 hour (hereinafter this decrement is
called a loss on ignition) is X (mass %), the loss on ignition X is
present in the range represented by formula (3):
1.5.times.{.alpha./(6.times.10.sup.4).times.18+(.alpha.-.beta.)/(6.times-
.10.sup.4).times.9}.times.100.gtoreq.X.gtoreq.0.85.times.{.alpha./(6.times-
.10.sup.4).times.18+(.alpha.-.beta.)/(6.times.10.sup.4).times.9}.times.100
(3)
wherein .beta. is a BET specific surface area (m.sup.2/g) after the
powder is ignited in an electric furnace kept at 900.degree. C. for
1 hour.
[0035] [7] A fine particulate titanium dioxide, wherein assuming
that the BET specific surface area is .alpha.(m.sup.2/g) and the
mass decrement when the powder is ignited in an electric furnace
kept at 900.degree. C. for 1 hour (hereinafter this decrement is
called a loss on ignition) is X (mass %), the loss on ignition X is
present in the range represented by formula (3'):
1.15.times.{.alpha./(6.times.10.sup.4).times.18+(.alpha.-.beta.)/(6.time-
s.10.sup.4).times.9}.times.100.gtoreq.X.gtoreq.0.85.times.{.alpha./(6.time-
s.10.sup.4).times.18+(.alpha.-.beta.)/(6.times.10.sup.4).times.9}100
(3')
wherein .beta. is a BET specific surface area (m.sup.2/g) after the
powder is ignited in an electric furnace kept at 900.degree. C. for
1 hour.
[0036] [8] The fine particulate titanium dioxide as described in
any one of [1] to [7] above, wherein the Fe, Al and S contents each
is 10 ppm by mass or less.
[0037] [9] The fine particulate titanium dioxide as described in
any one of [1] to [8] above, wherein the content of Cl in the
powder body is 50 mass % or less of the loss on ignition.
[0038] [10] A process for producing a fine particulate titanium
dioxide, comprising a first step of high-temperature oxidizing a
titanium tetrachloride-containing gas with use of an oxidative gas
to produce a titanium dioxide powder, and a second step of
contacting water vapor with the titanium dioxide powder while
rolling the powder in a heating furnace, thereby effecting
dechlorination and at the same time, increasing the adsorbed
water.
[0039] [11] The process for producing a fine particulate titanium
dioxide as described in [10] above, wherein the oxidative gas is
water vapor.
[0040] [12] The process for producing a fine particulate titanium
dioxide as described in [11] above, wherein the amount of water
vapor contacted is from 2 to 30 mol per mol of the titanium
tetrachloride gas.
[0041] [13] The process for producing a fine particulate titanium
dioxide as described in any one of [10] to [12] above, wherein the
titanium tetrachloride-containing gas and the oxidative gas
supplied to the reaction tube each is preheated at a temperature of
600.degree. C. to less than 1,100.degree. C.
[0042] [14] The process for producing a fine particulate titanium
dioxide as described in any one of [10] to [13] above, wherein in
the second step, the water vapor and the powder body are
counter-currently contacted by introducing the water vapor into the
heating furnace to occupy a ratio of 1 to 50 mass % based on the
titanium dioxide powder.
[0043] [15] The process for producing a fine particulate titanium
dioxide as described in any one of [10] to [14] above, wherein in
the second step, the water vapor and the powder body are
counter-currently contacted by introducing the water vapor into the
heating furnace to occupy a ratio of 1 to 50 mass % based on the
titanium dioxide powder.
[0044] [16] The process for producing a fine particulate titanium
dioxide as described in any one of [10] to [15] above, wherein in
the second step, the titanium dioxide is heated at 150 to
500.degree. C.
[0045] [17] The process for producing a fine particulate titanium
dioxide as described in any one of [10] to [16] above, wherein in
the second step, the residence time of the powder in the heating
furnace is from 0.5 hours to less than 3 hours.
[0046] [18] A process for producing a fine particulate titanium
dioxide, comprising spraying water droplets having a liquid droplet
diameter of 5 to 500 .mu.m at the time of packing the powder in a
resin bag, and closing and then storing the bag.
[0047] [19] A fine particulate titanium dioxide produced by the
process described in any one of [10] to [18] above.
[0048] [20] A perovskite compound using the fine particulate
titanium dioxide described in any one of [1] to [9] and [19] above
as a part of the raw materials.
[0049] [21] A dielectric raw material comprising the titanium
dioxide powder described in any one of [1] to [9] and [19]
above.
[0050] [22] A slurry comprising the titanium dioxide powder
described in any one of [1] to [9] and [19] above.
[0051] [23] A composition comprising the titanium dioxide powder
described in any one of [1] to [9] and [19] above.
[0052] [24] A photocatalyst material comprising the titanium
dioxide powder described in any one of [1] to [9] and [19]
above.
[0053] [25] A cosmetic material comprising the titanium dioxide
powder described in any one of [1] to [9] and [19] above.
[0054] [26] A solar cell material comprising the titanium dioxide
powder described in any one of [1] to [9] and [19] above.
[0055] [27] An additive for silicone rubber, comprising the
titanium dioxide powder described in any one of [1] to [9] and [19]
above.
[0056] According to a preferred production process of the present
invention, a fine particulate titanium dioxide reduced in the
change of mass and an ultrafine particulate titanium dioxide having
specific features in view of the particle size distribution and the
coarse particle are obtained.
[0057] As a result, in the industrial use of titanium dioxide, a
titanium dioxide which can dispense with a step of strictly
measuring the Ti content in advance by the measurement of loss on
ignition or the like can be obtained, so that not only the
production cost can be reduced but also the amount of the titanium
dioxide blended can be controlled with good precision.
[0058] The thus-produced fine particulate titanium dioxide is,
despite its large specific surface area, reduced in the
quantitative fluctuation of the raw material charged, so that in
uses as a pigment of various compositions, a UV-shielding material,
an additive to silicone rubber, clothes, a dielectric raw material
or a raw material of a cosmetic material, a photocatalyst, a solar
cell or the like, a remarkable effect of less causing fluctuation
of quality, reduction of performance and decrease of yield is
exerted.
BRIEF DESCRIPTION OF THE DRAWING
[0059] FIG. 1 is a graph showing the BET specific surface area and
the loss on ignition of fine particulate titanium oxide produced in
Examples and Comparative Examples.
BEST MODE FOR CARRYING OUT THE INVENTION
[0060] The present invention is described in detail below.
[0061] Usually, when using a titanium dioxide in an industrial
scale, the charged amount of the raw material component is strictly
controlled and, for this purpose, the loss on ignition, loss on
drying and the like are measured and based on the measured values,
the charged amount is correctly modified. However, the
adsorption/release of moisture rapidly proceeds and the amount of
water adsorbed in the time period from analysis to measurement of
the charged amount gives rise to an error in the amount charged.
Therefore, even when the charged amount is correctly modified, it
is very difficult to strictly control the charged amount of the Ti
content.
[0062] An ultrafine particulate titanium dioxide (the titanium
dioxide as used in the present invention includes all of those
which are simply referred to as "titanium oxide") as a preferred
embodiment of the present invention is reduced in the change of
mass. In a normal titanium dioxide, an OH group is chemically
bonded to a Ti atom on the surface, and a water molecule is bonded
to the OH group in many layers by hydrogen bonding to form
physically adsorbed water layers. The bonding of this physically
adsorbed water is considered to be weaker as the layer is remoter
from the titanium dioxide surface, that is, on the outer side.
Therefore, as the number of constituted layers is larger, the mass
is more susceptible to the environment and more fluctuates. In the
titanium dioxide as a preferred embodiment of the present
invention, the stratum allowing for adsorption of water is
considered to be low in layer number and the fluctuation of the
mass is small.
[0063] More specifically, the titanium dioxide as a preferred
embodiment of the present invention is characterized in that when
the powder in an amount of 2 to 5 g is spread in a 10 cm-diameter
glass-made Petri dish to a uniform thickness and left standing in
an environment at 20.degree. C. and a relative humidity of 80% for
5 hours, the rate of change of mass based on the mass before
standing is from -5 mass % to 5 mass %, preferably from -4.5 mass %
to 4.5 mass %, more preferably from -4 mass % to 4 mass %, further
preferably from -2.5 mass % to 2.5 mass %.
[0064] In this fine particulate titanium dioxide powder, the
specific surface area of the powder body as measured by the BET
method is from 10 to 200 m.sup.2/g, preferably from 20 to 180
m.sup.2/g, and at the same time, the 90% cumulative mass-particle
size distribution diameter D90 is preferably 2.2 .mu.m or less.
This means that coarse particles are less present and the powder is
suitable for usage where a fine particle is required. Also, in the
particle size distribution, the distribution constant n according
to the Rosin-Rammler formula represented by the following formula
(1) is preferably from 1.7 to 3.5. The distribution constant n
shows the degree of uniformity of the particle size and as the
numerical value of n is larger, the particle size uniformity is
judged to be more excellent.
R=100exp(-bD.sup.n) (1)
[0065] In formula (1), D is a particle diameter, R is a mass
percentage of particles larger than D based on the mass of all
particles, n is a distribution constant, and b is a factor showing
the particle size property. The Rosin-Rammler formula is described
in Ceramic Kogaku Handbook (Ceramic Engineering Handbook), compiled
by Nippon Ceramics Kyokai, 1st ed., pp. 596-598, Gihodo-Shuppan
(1989).
[0066] Furthermore, a fine particulate titanium dioxide powder, in
which assuming that the specific surface area of the powder body as
measured by the BET method is a (m.sup.2/g) and the mass decrement
when the powder is ignited in an electric furnace kept at
900.degree. C. for 1 hour (hereinafter this decrement is called a
loss on ignition) is X (mass %), the loss on ignition X is
preferably present in the range represented by formula (2):
2.1.times.{.alpha./(6.times.10.sup.4).times.18+(.alpha.-.beta.)/(6.times-
.10.sup.4).times.9}.times.100.gtoreq.X.gtoreq.0.25.times.{.alpha./(6.times-
.10.sup.4).times.18+(.alpha.-.beta.)/(6.times.10.sup.4).times.9}.times.100
(2)
more preferably by formula (2'):
1.3.times.{.alpha./(6.times.10.sup.4).times.18+(.alpha.-.beta.)/(6.times-
.10.sup.4).times.9}.times.100.gtoreq.X.gtoreq.0.7.times.{.alpha./(6.times.-
10.sup.4).times.18+(.alpha.-.beta.)/(6.times.10.sup.4).times.9}.times.100
(2'),
or preferably, in the range represented by formula (3):
1.5.times.{.alpha./(6.times.10.sup.4).times.18+(.alpha.-.beta.)/(6.times-
.10.sup.4).times.9}.times.100.gtoreq.X.gtoreq.0.85.times.{.alpha./(6.times-
.10.sup.4).times.18+(.alpha.-.beta.)/(6.times.10.sup.4).times.9}.times.100
(3),
more preferably by formula (3'):
1.15.times.{.alpha./(6.times.10.sup.4).times.18+(.alpha.-.beta.)/(6.time-
s.10.sup.4).times.9}.times.100.gtoreq.X.gtoreq.0.85.times.{.alpha./(6.time-
s.10.sup.4).times.18+(.alpha.-.beta.)/(6.times.10.sup.4).times.9}.times.10-
0 (3')
is reduced in the rate of change of mass as compared with
conventional titanium dioxide powders and is suitable for a raw
material required to assure a precise charged amount. In formulae
(2), (2'), (3) and (3'), .beta. is a specific surface area
(m.sup.2/g) of powder body measured by the BET method after the
powder is ignited in an electric furnace kept at 900.degree. C. for
1 hour.
[0067] Meanings of formulae (2), (2'), (3) and (3') are described
below. These two formulae are based on the following formula (4),
where .alpha. and .beta. have the same meanings as in formula (2),
(2'), (3) or (3').
{.alpha..times.10.times.10.sup.8)/(6.times.10.sup.23).times.18+{(.alpha.-
-.beta.).times.10.times.10.sup.18}/(6.times.10.sup.23).times.0.5.times.18
(4)
[0068] This formula is divided into the following two formulae:
{.alpha.[m.sup.2/g].times.10.times.10.sup.18[pieces/m.sup.2]}/(6.times.1-
0.sup.23)[pieces/mol].times.18[g/mol] (5)
{(.alpha.-.beta.)[m.sup.2/g].times.10.times.10.sup.18[pieces/m.sup.2]}/(-
6.times.10.sup.23)[pieces/mol].times.0.5.times.18 [g/mol] (6)
[0069] It is said that on the surface of titanium dioxide particle,
about 10.times.10.sup.18 [pieces/m.sup.2] of OH is present in the
case of rutile and about 13.times.10.sup.18 [pieces/m.sup.2] of OH
is present in the case of anatase [Manabu Kiyono, Sannka Titan
(Titanium Oxide), p. 54, Gihodo-Shuppan (1991))]. Each of this
number of OH groups on the rutile particle surface is bonded to one
H.sub.2O molecule and, considering that these are eliminated as
water due to heating at the measurement of loss on ignition, the
mass ratio of water eliminated from the particle is represented by
formula (5).
[0070] At the measurement of loss on ignition, the heating is
performed at 900.degree. C. When heated, the titanium dioxide
undergoes particle growth and is decreased in the specific surface
area. This decrement is represented by (.alpha.-.beta.)
[m.sup.2/g]. That is, a route allowing for elimination of the OH
group due to decrease in the specific surface area during heating
may also be considered. At this time, one molecular of water is
produced from two molecules of OH group on the titanium dioxide
surface and therefore, in formula (6), 0.5 is multiplied.
[0071] Accordingly, the mass ratio of water which is eliminated
resulting from decrease in the surface area is represented by
formula (6).
[0072] The eliminated water measured as a loss on ignition is the
sum of formulae (5) and (6), that is, formula (4). Then, a certain
range is imparted to formula (4) and this is formula (2), (2'), (3)
or (3').
[0073] In the fine particulate titanium dioxide as a preferred
embodiment of the present invention, the contents of Fe, Al and S
each is preferably 10 ppm by mass or less. The titanium dioxide
obtained by the vapor phase process uses a high-purity titanium
tetrachloride as the raw material and therefore, mingling of
impurities can be suppressed. The concentration of such an impurity
is preferably lower but in view of the apparatus material, raw
material purity and the like, higher purity incurs higher cost. In
the industrial use, the lower limit of each substance is actually
about 2 ppm by mass.
[0074] The titanium dioxide as a preferred embodiment of the
present invention is characterized by high dispersibility. This is
considered to result because the reaction at the particle
production is performed in an atmosphere rich in water vapor and
therefore, the particle surface is fully covered with a water
molecule or an OH group. In the present invention, a particle size
distribution is measured as an index of dispersibility by employing
a laser diffraction-type particle size distribution measuring
method. According to Shinroku Saito (supervisor), Cho-Biryushi
Handbook (Handbook of Ultrafine Particles), page 93,
Fujitechnosystem Corporation (1990), the measuring method for
dispersibility includes a precipitation method, a microscope
method, a light scattering method, a direct counting method and the
like and out of these, the precipitation method and the direct
counting method are not suitable for the measurement of
dispersibility of ultrafine particles, because the measurable
particle diameter is hundreds of nm or more. In the microscope
method, the measured value may fluctuate according to sampling of
the objective sample or pretreatment of the sample, and this method
is also not preferred. On the other hand, the light-scattering
method can measure a particle diameter in the range from several nm
to several .mu.m and is suitable for the measurement of ultrafine
particles. The dispersibility is preferably measured by a particle
size distribution measurement method using a laser diffraction
particle size distribution measuring apparatus. For example,
Microtrac HRA (Nikkiso Co. Ltd.) or ALD-2000J (Shimadzu
Corporation) can be used for the measurement. The procedure for
measuring the particle size distribution is described below.
[0075] A slurry obtained by adding 50 ml of pure water and 100
.mu.l of an aqueous 10% sodium hexametaphosphate solution to 0.05 g
of titanium dioxide is irradiated with an ultrasonic wave (46 KHz,
65 W) for 3 minutes. Then, this slurry is measured of the particle
size distribution by a laser diffraction-type particle size
measuring apparatus (SALD-2000J, manufactured by Shimadzu
Corporation). As the D90 value in the thus-measured particle size
distribution is smaller, the dispersibility in a hydrophilic
solvent is judged higher. The 50% cumulative mass-particle size
distribution diameter may also be used as an index of
dispersibility, but it is difficult to detect an aggregated
particle of which dispersibility is bad.
[0076] In the ultrafine particle titanium dioxide of the present
invention, D90 is preferably 2.2 .mu.m or less.
[0077] The production process is described below.
[0078] A general production process of titanium dioxide by a vapor
phase process is known, where titanium tetrachloride is oxidized by
using an oxidative gas such as oxygen or water vapor under the
reaction condition of about 1,000.degree. C. to obtain a fine
particulate titanium dioxide.
[0079] In a preferred embodiment of the present invention, a vapor
phase process of high-temperature oxidizing a titanium
tetrachloride-containing gas with an oxidative gas to produce a
titanium dioxide is employed. Preferably, a titanium
tetrachloride-containing gas heated to 600.degree. C. to less than
1,100.degree. C. and an oxidative gas (preferably water vapor)
heated to 600.degree. C. to less than 1,100.degree. C. are supplied
to a reaction tube. More preferably, the titanium dioxide obtained
by the reaction is allowed to reside in the reaction tube under the
temperature condition of 800.degree. C. to less than 1,100.degree.
C. and then dechlorinated while counter-currently contacting an
oxidative gas with the powder body under the condition of 150 to
500.degree. C., whereby an ultrafine particulate titanium dioxide
reduced in the change of mass, and in which water is satisfactorily
and stably bound to the titanium dioxide surface, is obtained.
[0080] The dechlorination includes a dry process and a wet process,
but here a dry dechlorination method is described. For example, a
method where titanium dioxide is heated by using a heating
apparatus such as cylindrical rotary heating furnace, hot-air
circulation heating furnace, fluidized drying furnace and
stir-drying furnace, and the surface water content is stabilized
while removing chlorine. However, the present invention is not
limited to these heating devices. For example, a wet dechlorination
method of suspending titanium dioxide in pure water and separating
chlorine, having transferred to the liquid phase, out of the system
may also be used. In view of stabilization of water content, a dry
dechlorination method is preferred.
[0081] The temperature in a reaction tube into which the titanium
tetrachloride-containing gas or water vapor is introduced is
preferably from 800.degree. C. to less than 1,100.degree. C., more
preferably from 900.degree. C. to less than 1,000.degree. C. By
elevating the temperature in the reaction tube, the reaction is
completed at the same time with mixing, so that generation of
uniform nuclei can be promoted and also the reaction zone can be
made small. If the temperature in the reaction tube is less than
800.degree. C., a titanium dioxide having a high anatase content is
readily obtained, but the reaction may proceed unsatisfactorily to
cause chlorine to remain inside the titanium dioxide particle,
whereas if the temperature in the reaction tube becomes
1,100.degree. C. or more, transition to rutile or particle growth
tends to proceed, failing in obtaining a low-rutile type ultrafine
particle.
[0082] When the raw material gases are introduced and the reaction
proceeds, this reaction is an exothermic reaction and therefore,
there is present a reaction zone where the reaction temperature
exceeds 1,100.degree. C. Although the heat is more or less released
from the apparatus, unless the titanium dioxide particle is rapidly
cooled, the particle continues growing and the crystal structure
may be transformed up into rutile. Therefore, in a preferred
embodiment of the present invention, the high-temperature residence
time at 800.degree. C. to less than 1,100.degree. C. is preferably
set to 0.1 second or less, more preferably 0.05 seconds or less. If
the high-temperature residence time exceeds 0.1 second, transition
to rutile, or sintering of the particles, tends to proceed.
[0083] The means for rapid cooling is not particularly limited but
for example, a method of introducing a large amount of a cooling
air or a gas such as nitrogen into the reaction mixture, or a
method of spraying water may be employed.
[0084] By controlling the temperature in the reaction tube to
800.degree. C. to less than 1,100.degree. C., an ultrafine particle
having a low chlorine content inside the particle can be obtained
and furthermore, by controlling the high-temperature residence time
to 0.1 second or less, a transition to rutile and particle growth
can be prevented.
[0085] In order to set the temperature in the reaction tube to
800.degree. C. to less than 1,100.degree. C., the temperature of
raw material gases is preferably adjusted to 600 to 1,100.degree.
C. The heated raw material gases react in the reaction tube to
generate heat, but if the raw material gas temperature is less than
600.degree. C., the temperature in the reaction tube can be hardly
elevated to 800.degree. C. or more, whereas if the raw material gas
temperature exceeds 1,100.degree. C., the temperature in the
reaction tube readily exceeds 1,100.degree. C. despite a release of
heat from the apparatus.
[0086] As for the composition of the titanium
tetrachloride-containing raw material gas, the inert gas preferably
occupies from 0.1 to 20 mol, more preferably from 4 to 20 mol, per
mol of the titanium tetrachloride gas. If the inert gas content is
less than this range, the density of titanium dioxide particles in
the reaction zone increases and aggregation or sintering readily
occurs, as a result, a fine particulate titanium dioxide can be
hardly obtained. If the inert gas content exceeds the
above-described range, the reactivity decreases and the recovery
percentage as a titanium dioxide may decrease.
[0087] The amount of the water vapor reacted with the titanium
tetrachloride-containing raw material gas is preferably from 2 to
30 mol, more preferably from 5 to 25 mol, per mol of titanium
tetrachloride. If the ratio of the water vapor is less than this
range, a water content is not satisfactorily bound to the surface
of the produced titanium dioxide particle and when stored for a
long time, a reaction of the titanium dioxide particle surface with
the water content gradually proceeds and this gives rise to
fluctuation of the mass. When the ratio exceeds the above-described
range, the number of nuclei generated is increased and an ultrafine
particle is readily obtained but even if it exceeds 30 mol, the
effect of increasing the number of nuclei generated is scarcely
obtained. Even when the amount of water vapor exceeds 30 mol, the
properties of the titanium dioxide are not affected, but this upper
limit is specified from the economical viewpoint. On the other
hand, if the amount of the water vapor based on the titanium
tetrachloride is insufficient, the titanium dioxide obtained tends
to have many oxygen defects and be colored.
[0088] Dechlorination by the heating of titanium dioxide is
preferably performed at a heating temperature of 150 to 500.degree.
C. while counter-currently contacting water or water vapor with the
titanium dioxide powder such that the mass ratio of water and
titanium dioxide (=mass of water vapor/mass of titanium dioxide,
hereinafter the same) becomes from 1 to 60 mass %, preferably from
1 to 50 mass %. More preferably, the mass ratio of water and
titanium dioxide is from 5 to 40 mass % and the heating temperature
is from 300 to 450.degree. C. If the heating temperature exceeds
500.degree. C., sintering of titanium dioxide particles proceeds
and particle growth is generated, whereas if the heating
temperature is less than 150.degree. C., the dechlorination
efficiency seriously decreases. Chlorine on the titanium dioxide
surface undergoes a displacement reaction with water in the
vicinity of the particle or with a surface hydroxyl group of an
adjacent particle, whereby dechlorination proceeds. Accordingly, it
is very effective for the dechlorination to add water vapor while
heating, and a displacement reaction between chlorine and water or
OH group is preferably performed. At this time, when chlorine on
the titanium dioxide particle surface is replaced with water,
dechlorination is effected without causing particle growth, but
when chlorine is replaced with a surface hydroxyl group of an
adjacent particle, particle growth is effected simultaneously with
dechlorination. That is, in order to perform the dechlorination
while preventing the particle growth, it is effective to control
the mass ratio of water and titanium dioxide and when the mass
ratio of water and titanium dioxide is 1 mass % or more, the effect
of preventing the particle growth is remarkably recognized and this
is preferred.
[0089] The water vapor put into contact with the titanium dioxide
may be used by mixing it with air. The air plays the role of
efficiently moving the chlorine separated from titanium dioxide,
out of the system. The water vapor is preferably contained in the
air at a concentration of 0.1 vol % or more, more preferably 5 vol
% or more, still more preferably 10 vol % or more. The water
vapor-containing air is preferably heated to 200 to 1,000.degree.
C.
[0090] In the dechlorination step by heating, the residence time of
powder in the rotary furnace is preferably from 0.5 hours to less
than 3 hours, more preferably from 0.5 hours to less than 1 hour.
This is a time period necessary for unfailingly effecting the
dechlorination while preventing the particle growth. If the
residence time is less than this range, insufficient dechlorination
may result, whereas if it exceeds the above-described range,
particle growth may proceed.
[0091] As for the production process of a titanium dioxide reduce
in the rate of change of mass, a process of spraying water droplets
simultaneously at the time of packing the powder in a resin bag,
and closing and then storing the bag may also be used. In this
process, fine water droplets are sprayed on the powder body to
temporarily load water droplets on the particle and the powder body
is stored in a closed packing material relatively impermeable to
water content, such as a resin bag, whereby the temporarily loaded
water droplets are fixed as an adsorbed water. According to this
process, a water droplet can be stabilized in a very short time as
an adsorbed water difficult of desorption. The liquid droplet
diameter is preferably 5 to 500 .mu.M, more preferably 5 to 300
.mu.m. If the water droplet sprayed is large and exceeds 500 .mu.m,
the water content is locally present in the powder bodies and it
takes time for the water content to become uniformly present,
whereas if the water droplet diameter is less than 5 .mu.m, the
loading efficiency is bad and not practical. The water droplet in
the range from 5 to 500 .mu.m is suited for loading on titanium
dioxide at 10 to 200 m.sup.2/g.
[0092] Another method for producing the titanium dioxide is a
method for storing a powder which has been subjected to
dechlorination treatment in a high humidity environment. In this
method, a powder is charged in a moisture vapor permeable package
or the like and allowed to stand in a suitable temperature and high
humidity environment, by which moisture can be adsorbed to a
targeted content and stabilized. The suitable temperature may be an
operable temperature range such as about 20-50.degree. C. and, in
winter, about 5-40.degree. C. The high humidity means a relative
humidity of 60-95%, preferably 60-90%. If the relative humidity
exceeds 95%, moisture is apt to condense by room temperature
change. However, in this method, a long time is required for
stabilization.
[0093] A pressure reduction method, listed as one of titanium oxide
dichlorination methods, can also apply. While the inside of a
container is adjusted to a predetermined temperature, for example,
5-40.degree. C., and water in an amount equal to the amount
necessary to titanium oxide is supplied, a pressure reduction is
then effected. As a result, chlorine is taken out from titanium
oxide to outside the system and, concurrently, water molecules are
adsorbed onto OH groups on the surface of titanium oxide in place
of chlorine, so that the water content adsorbed on titanium oxide
can increase in a relatively short time period. Here, the degree of
pressure reduction is preferably 0.5 kPa or more, more preferably
0.5 kPa to 2 kPa. The degree of pressure reduction is a difference
between the pressure in the container and the atmospheric pressure.
The upper limit of the degree of pressure reduction is not
particularly specified but economical upper limit is 2 kpa since a
large scale pressure reduction apparatus is required if the
pressure reduction degree increases. However, if a large amount of
a powder is treated by this method, an apparatus for maintaining
the reduced pressure during continuous operation and an apparatus
for moving titanium oxide from a container under a reduced pressure
to atmospheric pressure environment are required, which is
disadvantageous from economical viewpoint.
[0094] The characteristics of water to be sprayed are not
particularly limited, but removal of impurity course particles such
as metal particles through a filter is preferred, and pure water in
which impurities have been removed by ion exchange resin, etc. is
more preferred. The temperature of water may be either normal cool
water or warmed water, but warm water at 20-100.degree. C. is
preferred because it is effective in accelerating evaporation and
adsorption to powder of fine water droplets.
[0095] A method for producing and spraying water droplets with a
fine particle size is not particularly limited but, for example, a
method for scattering water vapor using a ultrasonic humidifier or
a heating steam generator, or a spraying method using a one-liquid
or two-liquid spray nozzle may be used. Where a spray nozzle is
used, a preferred nozzle is one which can control the average
particle size of water droplets to 5-500 .mu.m, more preferably
5-300 .mu.m, further preferably 5-50 .mu.m. If the diameter of
water droplets exceeds 500 .mu.m, the possibility that water
unevenly distributes increases and it takes a longer time until
water content distribution becomes uniform. Further, a powder
easily wets and course particles due to aggregation may be formed,
which is not preferred. If the diameter of water droplets is less
than 5 .mu.m, the efficiency of supporting is low and it is not
practical. Water droplets having a diameter of 5-500 .mu.m is very
suitable for supporting on fine titanium oxide of 10-200 m.sup.2/g.
The average particle size of water droplets can be measured by
laser light scattering method, phase Doppler-type laser particle
analysis, or the like.
[0096] When the spray method using a two liquid-type spray nozzle
is used, the properties of air used are not particularly limited,
but it is preferred to remove environmental course particle
impurities through a filter and air in which excess water has been
removed by an air dryer or the like is more preferred. The
temperature of air may be normal temperature but dry air heated to
20-100.degree. C. is preferred because this is effective to
evaporate fine water droplets and adsorb water droplets onto
titanium oxide particles. An uncombustible gas such as nitrogen gas
may be used in place of air. More preferably, simultaneous use of a
combination of warm water heated to 20-100.degree. C. and dry air
or an uncombustible gas such as nitrogen gas heated to
20-100.degree. C. accelerates evaporating fine water droplets and
adsorbing water droplets onto titanium oxide particles, so that it
is effective for water absorption and stabilization in a short
time.
[0097] The thus-produced fine particulate titanium dioxide as a
preferred embodiment of the present invention is a powder body
having a sharp particle size distribution and being free of coarse
particle and reduced in the fluctuation of mass and therefore, can
be suitably used for various uses of fine particulate titanium
dioxide, such as pigment of various compositions, photocatalyst,
UV-shielding cosmetic material, UV-shielding clothing, material for
wet solar cell, deodorant clothing, filler material for UV
shielding, additive for various products (e.g., silicone rubber),
and raw material of dielectric material including perovskite
compound (e.g., barium titanate). The fine particulate titanium
dioxide of the present invention is used as a powder body or a
slurry.
[0098] Representative uses of the perovskite compound are a
piezoelectric ceramic and a pyroelectric ceramic. The piezoelectric
ceramic is used in a piezoelectric actuator and, for example, BT
type, PZT type, PT type and BNT type are known. The pyroelectric
ceramic is used in an infrared sensor or the like and, for example,
PT type is known. In all of these ceramics, titanium oxide is used
as a raw material. The production process of such a ceramic is not
particularly limited and any known method may be employed (see, for
example, "Oyo Gijutsu", Biryushi Kogaku Taikei ("Applied
Technology", Fine Particle Engineering Series), Vol. 2, pp. 27-33
and 190-195). Incidentally, whichever production process is
employed, it is essential to strictly control the atomic
composition.
[0099] The titanium oxide is sometimes used as an abrasive slurry
for hard discs and the like. In this case, the solid concentration
in the abrasive slurry is an important factor governing the
abrasive performance. Also, in terms of dispersion in an aqueous
system, a stable dispersing operation can be achieved when the
adsorbed water is stabilized. Furthermore, in use as a raw material
for cosmetic materials, solar cells, photocatalysts and the like,
the titanium oxide is used also as a dispersion in water, a silicon
rubber-polymer, an organic polymer or the like and in view of
stability in the dispersion step and blending precision determining
the product composition, it is preferred that the adsorbed water
present on the titanium oxide particle surface is stabilized.
EXAMPLES
[0100] The present invention is described in greater detail below
by referring to Examples and Comparative Examples, but the present
invention is not limited thereto.
Example 1
[0101] 20 kg/hr of titanium tetrachloride diluted with 25
Nm.sup.3/hr (N means that the state is reduced to a standard state
of ideal gas, hereinafter the same) of nitrogen gas was preheated
to 1,100.degree. C. and introduced into a reaction tube. Similarly,
55 Nm.sup.3/hr of water vapor was heated to 1,100.degree. C. and
introduced into the reaction tube and through a reaction with the
titanium tetrachloride gas, fine titanium dioxide particles were
obtained. These fine particles were collected in a
polytetrafluoroethylene-made bag filter and then introduced into an
external heating-type rotary kiln. The external heating-type rotary
kiln had a structure that a stir-up blade for stirring the powder
body was provided in the inside. The rotary kiln was set to a
temperature of 400.degree. C., and the residence time of the powder
body was adjusted to about 1 hour by controlling the length of
high-temperature zone, the rotating speed and the angle at which
the kiln was installed.
[0102] Separately, water vapor in an amount of 20 mass % based on
the mass of titanium dioxide passing through the kiln was
introduced from the outlet for the powder body in the rotary kiln,
thereby counter-currently contacting the powder body and the water
vapor. Incidentally, the water vapor introduced was previously
heated to approximately from 120 to 200.degree. C.
[0103] In the thus-obtained powder body, the BET specific surface
area was 107 m.sup.2/g, the entire chlorine content was 8,000 ppm
by mass, Fe was 2 ppm, Al was 2 ppm or less, and S was 2 ppm or
less. The BET specific surface area was measured by a specific
surface area meter (model: Flow Sorb II, 2300) manufactured by
Shimadzu Corporation.
[0104] On the particle size distribution of the titanium dioxide
powder obtained above, a 90% cumulative mass-particle size
distribution diameter D90 was measured by a laser diffraction-type
particle size distribution measuring method and found to be 0.9
.mu.m.
[0105] Also, 2 g of the powder was spread in a 10 cm-diameter
glass-made Petri dish to a uniform thickness and left standing in
an environment at 20.degree. C. and a relative humidity of 80% for
5 hours, and then the rate of change of mass based on the mass
before standing was measured and found to be 2.3 mass %.
[0106] The mass decrement when the powder was ignited in an
electric furnace kept at 900.degree. C. for 1 hour, that is, the
loss on ignition was 5.0 mass %. The BET specific surface area of
the sample after the measurement of loss on ignition was 6
m.sup.2/g.
[0107] Furthermore, the distribution constant n according to the
Rosin-Rammler formula represented by R=100exp(-bD.sup.n) was
2.7.
Example 2
[0108] 5 kg/hr of titanium tetrachloride diluted with 25
Nm.sup.3/hr of nitrogen gas was preheated to 1,100.degree. C. and
introduced into a reaction tube. Similarly, 55 Nm.sup.3/hr of water
vapor was heated to 1,100.degree. C. and introduced into the
reaction tube and through a reaction with the titanium
tetrachloride gas, fine titanium dioxide particles were obtained.
These fine particles were collected by a
polytetrafluoroethylene-made bag filter and then introduced into an
external heating-type rotary kiln. The external heating-type rotary
kiln had a structure that a stir-up blade for stirring the powder
body was provided in the inside. The rotary kiln was set to a
temperature of 400.degree. C., and the residence time of the powder
body was adjusted to about 1 hour by controlling the length of
high-temperature zone, the rotating speed and the angle at which
the kiln was installed.
[0109] Separately, water vapor in an amount of 30 mass % based on
the mass of titanium dioxide passing through the kiln was
introduced from the outlet for the powder body in the rotary kiln,
thereby counter-currently contacting the powder body and the water
vapor. Incidentally, the water vapor introduced was previously
heated to approximately from 120 to 200.degree. C.
[0110] In the thus-obtained powder body, the BET specific surface
area was 158 m.sup.2/g, the entire chlorine content was 13,000 ppm
by mass, Fe was 2 ppm, Al was 2 ppm or less, and S was 2 ppm or
less. The BET specific surface area was measured by a specific
surface area meter (model: Flow Sorb II, 2300) manufactured by
Shimadzu Corporation.
[0111] On the particle size distribution of the titanium dioxide
powder obtained above, a 90% cumulative mass-particle size
distribution diameter D90 was measured by a laser diffraction-type
particle size distribution measuring method and found to be 0.8
.mu.m.
[0112] Also, 2 g of the powder was spread in a 10 cm-diameter
glass-made Petri dish to a uniform thickness and left standing in
an environment at 20.degree. C. and a relative humidity of 80% for
5 hours, and then the rate of change of mass based on the mass
before standing was measured and found to be 3.6 mass %.
[0113] The mass decrement when the powder was ignited in an
electric furnace kept at 900.degree. C. for 1 hour, that is, the
loss on ignition was 6.5 mass %. The BET specific surface area of
the sample after the measurement of loss on ignition was 3.5
m.sup.2/g.
[0114] Furthermore, the distribution constant n according to the
Rosin-Rammler formula represented by R=100exp(-bD.sup.n) was
3.2.
Example 3
[0115] 150 kg/hr of titanium tetrachloride was preheated to
900.degree. C. and introduced into a reaction tube. Similarly, 30
Nm.sup.3/hr of water vapor was heated to 900.degree. C. and
introduced into the reaction tube and through a reaction with the
titanium tetrachloride gas, fine titanium dioxide particles were
obtained. These fine particles were collected by a
polytetrafluoroethylene-made bag filter and then introduced into an
external heating-type rotary kiln. The external heating-type rotary
kiln had a structure that a stir-up blade for stirring the powder
body was provided in the inside. The rotary kiln was set to a
temperature of 400.degree. C., and the residence time of the powder
body was adjusted to about 45 minutes by controlling the length of
high-temperature zone, the rotating speed and the angle at which
the kiln was installed.
[0116] Separately, water vapor in an amount of 3 mass % based on
the mass of titanium dioxide passing through the kiln was
introduced from the outlet for the powder body in the rotary kiln,
thereby counter-currently contacting the powder body and the water
vapor. Incidentally, the water vapor introduced was previously
heated to approximately from 120 to 200.degree. C.
[0117] In the thus-obtained powder body, the BET specific surface
area was 12 m.sup.2/g, the entire chlorine content was 1,000 ppm by
mass, Fe was 2 ppm, Al was 2 ppm or less, and S was 2 ppm or less.
The BET specific surface area was measured by a specific surface
area meter (model: Flow Sorb II, 2300) manufactured by Shimadzu
Corporation.
[0118] On the particle size distribution of the titanium dioxide
powder obtained above, a 90% cumulative mass-particle size
distribution diameter D90 was measured by a laser diffraction-type
particle size distribution measuring method and found to be 2.2
.mu.m.
[0119] Also, 5 g of the powder was spread in a 10 cm-diameter
glass-made Petri dish to a uniform thickness and left standing in
an environment at 20.degree. C. and a relative humidity of 80% for
5 hours, and then the rate of change of mass based on the mass
before standing was measured and found to be 0.12 mass %.
[0120] The mass decrement when the powder was ignited in an
electric furnace kept at 900.degree. C. for 1 hour, that is, the
loss on ignition was 0.37 mass %. The BET specific surface area of
the sample after the measurement of loss on ignition was 5
m.sup.2/g.
[0121] Furthermore, the distribution constant n according to the
Rosin-Rammler formula represented by R=100exp(-bD.sup.n) was
1.7.
Example 4
[0122] 70 kg/hr of titanium tetrachloride diluted with 20
Nm.sup.3/hr of nitrogen gas was preheated to 900.degree. C. and
introduced into a reaction tube. Similarly, 50 Nm.sup.3/hr of water
vapor was heated to 900.degree. C. and introduced into the reaction
tube and through a reaction with the titanium tetrachloride gas,
fine titanium dioxide particles were obtained. These fine particles
were collected by a polytetrafluoroethylene-made bag filter and
then introduced into an external heating-type rotary kiln. The
external heating-type rotary kiln had a structure that a stir-up
blade for stirring the powder body was provided in the inside. The
rotary kiln was set to a temperature of 450.degree. C., and the
residence time of the powder body was adjusted to about 45 minutes
by controlling the length of high-temperature zone, the rotating
speed and the angle at which the kiln was installed.
[0123] Separately, water vapor in an amount of 10 mass % based on
the mass of titanium dioxide passing through the kiln was
introduced from the outlet for the powder body in the rotary kiln,
thereby counter-currently contacting the powder body and the water
vapor. Incidentally, the water vapor introduced was previously
heated to approximately from 120 to 200.degree. C.
[0124] In the thus-obtained powder body, the BET specific surface
area was 50 m.sup.2/g, the entire chlorine content was 5,000 ppm by
mass, Fe was 2 ppm, Al was 2 ppm or less, and S was 2 ppm or less.
The BET specific surface area was measured by a specific surface
area meter (model: Flow Sorb II, 2300) manufactured by Shimadzu
Corporation.
[0125] On the particle size distribution of the titanium dioxide
powder obtained above, a 90% cumulative mass-particle size
distribution diameter D90 was measured by a laser diffraction-type
particle size distribution measuring method and found to be 1.3
.mu.m.
[0126] Also, 5 g of the powder was spread in a 10 cm-diameter
glass-made Petri dish to a uniform thickness and left standing in
an environment at 20.degree. C. and a relative humidity of 80% for
5 hours, and then the rate of change of mass based on the mass
before standing was measured and found to be 1.8 mass %.
[0127] The mass decrement when the powder was ignited in an
electric furnace kept at 900.degree. C. for 1 hour, that is, the
loss on ignition was 2.40 mass %. The BET specific surface area of
the sample after the measurement of loss on ignition was 5.6
m.sup.2/g.
[0128] Furthermore, the distribution constant n according to the
Rosin-Rammler formula represented by R=100exp(-bD.sup.n) was
1.9.
Example 5
[0129] 160 kg/hr of titanium tetrachloride diluted with 23
Nm.sup.3/hr of nitrogen gas was preheated to 1,050.degree. C. and
introduced into a reaction tube. Similarly, 28 Nm.sup.3/hr of water
vapor was heated to 1,050.degree. C. and introduced into the
reaction tube and through a reaction with the titanium
tetrachloride gas, fine titanium dioxide particles were obtained.
These fine particles were collected by a
polytetrafluoroethylene-made bag filter and then introduced into an
external heating-type rotary kiln. The external heating-type rotary
kiln had a structure that a stir-up blade for stirring the powder
body was provided in the inside. The rotary kiln was set to a
temperature of 450.degree. C., and the residence time of the powder
body was adjusted to about 45 minutes by controlling the length of
high-temperature zone, the rotating speed and the angle at which
the kiln was installed.
[0130] Separately, water vapor in an amount of 4 mass % based on
the mass of titanium dioxide passing through the kiln was
introduced from the outlet for the powder body in the rotary kiln,
thereby counter-currently contacting the powder body and the water
vapor. Incidentally, the water vapor introduced was previously
heated to approximately from 120 to 200.degree. C.
[0131] In the thus-obtained powder body, the BET specific surface
area was 30 m.sup.2/g, the entire chlorine content was 2,500 ppm by
mass, Fe was 2 ppm, Al was 2 ppm or less, and S was 2 ppm or less.
The BET specific surface area was measured by a specific surface
area meter (model: Flow Sorb II, 2300) manufactured by Shimadzu
Corporation.
[0132] On the particle size distribution of the titanium dioxide
powder obtained above, a 90% cumulative mass-particle size
distribution diameter D90 was measured by a laser diffraction-type
particle size distribution measuring method and found to be 0.7
.mu.m.
[0133] Also, 5 g of the powder was spread in a 10 cm-diameter
glass-made Petri dish to a uniform thickness and left standing in
an environment at 20.degree. C. and a relative humidity of 80% for
5 hours, and then the rate of change of mass based on the mass
before standing was measured and found to be 1.0 mass %.
[0134] The mass decrement when the powder was ignited in an
electric furnace kept at 900.degree. C. for 1 hour, that is, the
loss on ignition was 1.25 mass %. The BET specific surface area of
the sample after the measurement of loss on ignition was 5.2
m.sup.2/g.
[0135] Furthermore, the distribution constant n according to the
Rosin-Rammler formula represented by R=100exp(-bD.sup.n) was
3.4.
Example 6
[0136] To the titanium dioxide used in Example 4, water droplets
with a liquid diameter of 30 .mu.m were sprayed, and the titanium
dioxide powder was charged and sealed in a resin bag, followed by
storing the powder at a place where the temperature was set at
25.+-.3.degree. C. for 24 hours. 5 g of the powder was then spread
in a 10 cm-diameter glass-made Petri dish to a uniform thickness
and left standing in an environment at 20.degree. C. and a relative
humidity of 80% for 5 hours, and then the rate of change of mass
based on the mass before standing was measured and found to be 1.4
mass %.
Example 7
[0137] To the titanium dioxide used in Example 4, water droplets
with a liquid diameter of 30 .mu.m were sprayed, and the titanium
dioxide powder was charged and sealed in a resin bag, followed by
storing the powder at a place where the temperature was set at
25.+-.3.degree. C. for 24 hours. 5 g of the powder was then spread
in a 10 cm-diameter glass-made Petri dish to a uniform thickness
and left standing in an environment at 20.degree. C. and a relative
humidity of 80% for 5 hours, and then the rate of change of mass
based on the mass before standing was measured and found to be 0.83
mass %.
Example 8
[0138] To the titanium dioxide used in Example 5, water droplets
with a liquid diameter of 30 .mu.m were sprayed, and the titanium
dioxide powder was charged and sealed in a resin bag, followed by
storing the powder at a place where the temperature was set at
25.+-.3.degree. C. for 24 hours. 5 g of the powder was then spread
in a 10 cm-diameter glass-made Petri dish to a uniform thickness
and left standing in an environment at 20.degree. C. and a relative
humidity of 80% for 5 hours, and then the rate of change of mass
based on the mass before standing was measured and found to be 0.74
mass %.
Comparative Example 1
[0139] 180 kg/hr of titanium tetrachloride was preheated to
900.degree. C. and introduced into a reaction tube. Similarly, 30
Nm.sup.3/hr of oxygen was heated to 900.degree. C. and introduced
into the reaction tube and through a reaction with the titanium
tetrachloride gas, fine titanium dioxide particles were obtained.
These fine particles were collected by a
polytetrafluoroethylene-made bag filter and then introduced into an
external heating-type rotary kiln. The external heating-type rotary
kiln had a structure that a stir-up blade for stirring the powder
body was provided in the inside. The rotary kiln was set to a
temperature of 350.degree. C., and the residence time of the powder
body was adjusted to about 50 minutes by controlling the length of
high-temperature zone, the rotating speed and the angle at which
the kiln was installed.
[0140] In the thus-obtained powder body, the BET specific surface
area was 6 m.sup.2/g, the entire chlorine content was 100 ppm by
mass, Fe was 2 ppm, Al was 2 ppm or less, and S was 2 ppm or less.
The BET specific surface area was measured by a specific surface
area meter (model: Flow Sorb II, 2300) manufactured by Shimadzu
Corporation.
[0141] On the particle size distribution of the titanium dioxide
powder obtained above, a 90% cumulative mass-particle size
distribution diameter D90 was measured by a laser diffraction-type
particle size distribution measuring method and found to be 2.6
.mu.m.
[0142] Also, 5 g of the powder was spread in a 10 cm-diameter
glass-made Petri dish to a uniform thickness and left standing in
an environment at 20.degree. C. and a relative humidity of 80% for
5 hours, and then the rate of change of mass based on the mass
before standing was measured and found to be 6 mass %.
[0143] The mass decrement when the powder was ignited in an
electric furnace kept at 900.degree. C. for 1 hour, that is, the
loss on ignition was 0.6 mass %. The BET specific surface area of
the sample after the measurement of loss on ignition was 5
m.sup.2/g.
[0144] Furthermore, the distribution constant n according to the
Rosin-Rammler formula represented by R=100exp(-bD.sup.n) was
1.6.
Comparative Example 2
[0145] 70 kg/hr of titanium tetrachloride diluted with 25
Nm.sup.3/hr of nitrogen gas was preheated to 900.degree. C. and
introduced into a reaction tube. Similarly, 30 Nm.sup.3/hr of water
vapor was heated to 550.degree. C. and introduced into the reaction
tube and through a reaction with the titanium tetrachloride gas,
fine titanium dioxide particles were obtained. These fine particles
were collected by a polytetrafluoroethylene-made bag filter and
then introduced into an external heating-type rotary kiln. The
rotary kiln was set to a temperature of 120.degree. C., and the
residence time of the powder body was adjusted to about 45 minutes
by controlling the length of high-temperature zone, the rotating
speed and the angle at which the kiln was installed.
[0146] In the thus-obtained powder body, the BET specific surface
area was 60 m.sup.2/g, the entire chlorine content was 31,000 ppm
by mass, Fe was 2 ppm, Al was 2 ppm or less, and S was 2 ppm or
less.
[0147] On the particle size distribution of the titanium dioxide
powder obtained above, a 90% cumulative mass-particle size
distribution diameter D90 was measured by a laser diffraction-type
particle size distribution measuring method and found to be 8.8
.mu.m.
[0148] Also, 5 g of the powder was spread in a 10 cm-diameter
glass-made Petri dish to a uniform thickness and left standing in
an environment at 20.degree. C. and a relative humidity of 80% for
5 hours, and then the rate of change of mass based on the mass
before standing was measured and found to be 9 mass %.
[0149] The mass decrement when the powder was ignited in an
electric furnace kept at 900.degree. C. for 1 hour, that is, the
loss on ignition was 5.6 mass %. The BET specific surface area of
the sample after the measurement of loss on ignition was 5.1
m.sup.2/g.
[0150] Furthermore, the distribution constant n according to the
Rosin-Rammler formula represented by R=100exp(-bD.sup.n) was
1.2.
[0151] The results in Examples and Comparative Examples above are
shown together in Table 1 and FIG. 1. In Table 1 and FIG. 1, "LOI
theoretical value" represents a theoretical value of the loss on
ignition and the straight lines of FIG. 1 show a preferred range of
0.25 to 2.1 mass % and a more preferred range of 0.85 to 1.5 mass
%.
TABLE-US-00001 TABLE 1 rate of change of mass based on mass before
standing LOI at 20.degree. C. Theoretical LOI LOI LOI LOI and 80%
RH BET after Value of LOI Theoretical Theoretical Theoretical
Theoretical for 5 BET, Measurement 900.degree. C.-hr, Experimental
Value Value Value Value hours, m.sup.2/g of LOI, m.sup.2/g mass %
Value, mass % *0.85 mass % *1.5 mass % *0.25 mass % *2.1 mass %
mass % Example 1 107 6 4.73 5.00 4.02 7.09 1.18 9.92 2.3 Example 2
158 3.5 7.06 6.50 6.00 10.59 1.76 14.82 3.6 Example 3 12 5 0.47
0.37 0.40 0.70 0.12 0.98 0.12 Example 4 50 5.6 2.17 2.40 1.84 3.25
0.54 4.55 1.8 Example 5 30 5.2 1.27 1.25 1.08 1.91 0.32 2.67 1.0
Example 6 107 6.1 4.73 6.75 4.02 7.09 1.18 9.92 1.4 Example 7 50
5.2 2.17 3.14 1.84 3.25 0.54 4.55 0.83 Example 8 30 5 1.27 1.52
1.08 1.91 0.32 2.67 0.74 Comparative 6 5 0.20 0.60 0.17 0.29 0.05
0.41 6.0 Example 1 Comparative 60 5.1 2.62 5.60 2.23 3.94 0.66 5.51
9.0 Example 2 LOI: Loss on ignition
INDUSTRIAL APPLICABILITY
[0152] The powder body having a narrow particle size distribution
and being free from coarse particle and reduced in the fluctuation
of mass is suitable for various uses. For example, this powder can
be used for a pigment of various compositions, a photocatalyst, an
UV-shielding cosmetic material, an UV-shielding clothing, deodorant
clothing, a filler material for UV shielding, an additive for
various products such as silicone rubber, a dielectric raw
material, or the like.
* * * * *