JP2012148920A - Low valence titanium oxide composition, and method for producing the same - Google Patents

Abstract

Disclosed is a finely divided low-valent titanium oxide composition suitable for producing a low-valent titanium oxide-doped zinc oxide target that does not cause abnormal discharge during sputtering, and the low-valent titanium oxide composition Provided is a manufacturing method that can be manufactured at low cost.
In an X-ray diffraction profile, a fine low-valent titanium oxide composition having a plurality of low-valent titanium oxide peaks whose titanium valence is lower than tetravalent and a primary particle diameter of 50 nm to 1 μm. A mixture of titanium dioxide and carbon is manufactured through a step of firing at 1000 to 1500 ° C. in an air current in a closed container having a function of releasing the internal gas to the outside when the internal pressure is increased. Can do.
[Selection] Figure 1

Description

  The present invention relates to a particulate low-valent titanium oxide composition and a method for producing the same, and more specifically, a particulate low-valent titanium oxide composition that can be used as a dopant source for a zinc oxide-based transparent conductive material at low cost, and It relates to a production method capable of mass production.

  Transparent conductive films that combine electrical conductivity and light transmission have been used as electrodes in solar cells, liquid crystal display elements, and other various light receiving elements, as well as automotive window and heat ray reflective films for buildings, It is used for a wide range of applications such as anti-static films and transparent heating elements for anti-fogging in frozen showcases. In particular, it is known that a transparent conductive film having low resistance and excellent conductivity is suitable for a solar cell, a liquid crystal display element such as a liquid crystal, organic electroluminescence, and inorganic electroluminescence, a touch panel, and the like.

Conventionally, as the transparent conductive film, for example, a tin oxide (SnO ₂ ) -based thin film such as an antimony-doped tin oxide (ATO) film, a zinc oxide (ZnO) -based thin film such as an aluminum-doped zinc oxide (AZO) film, tin-doped An indium oxide (In ₂ O ₃ ) -based thin film such as an indium oxide (ITO) film is known.
Among them, the most industrially used is an indium oxide-based transparent conductive film, and in particular, an ITO film is widely used because of its low resistance and excellent conductivity.

  However, an indium oxide-based transparent conductive film such as an ITO film is expensive and may be depleted of resources because In (indium), which is an essential raw material, is a rare metal, and has toxicity and is harmful to the environment and the human body. It may have an adverse effect on it. Therefore, in recent years, an industrially versatile transparent conductive film that can be substituted for an ITO film has been demanded. Under such circumstances, a zinc oxide-based transparent conductive film that can be industrially manufactured by a sputtering method has attracted attention, and research is being conducted to improve its conductive performance.

  Non-Patent Document 1 reports an attempt to dope various dopants into ZnO in order to increase conductivity.

  Further, the present inventors have newly found that low-valent titanium oxides such as titanium (II) oxide and titanium (III) oxide are effective dopants for the zinc oxide-based transparent conductive film. This zinc oxide-based transparent conductive film doped with low-valent titanium oxide realizes low resistance, excellent chemical durability, and high transmittance in the near infrared region suitable for transparent conductive films for solar cells. Have.

Low-valent titanium oxides such as TiO (II), Ti ₂ O ₃ (III), Ti ₆ O ₁₁ , Ti ₅ O ₉ and Ti ₈ O ₁₅ are used as dopants for such zinc oxide-based transparent conductive films. Although used, to date, low-valent titanium oxides such as particulate titanium (II) oxide and titanium (III) oxide have not been obtained on an industrial scale. This is based on the fact that it is difficult to industrially produce fine particulate low-valent titanium oxide by reducing titanium dioxide (TiO ₂ ) as described below.

The following various methods (A) to (D) are known as conventional methods for reducing titanium dioxide (TiO ₂ ) for industrially producing low-valent titanium oxide.
(A) A hydrogen reduction method in which titanium dioxide powder is fired at a high temperature in a hydrogen stream (see, for example, Patent Document 1).
(B) An ammonia reduction method in which titanium dioxide powder is calcined at a high temperature in an ammonia (+ hydrogen) stream (see, for example, Patent Document 2).
(C) A homogenization reaction with metal titanium powder that is uniformly mixed with metal titanium powder and titanium dioxide powder and then fired at a high temperature in a reducing atmosphere (see, for example, Patent Document 3).
(D) A method of reducing and firing titanium dioxide together with a hydride such as sodium borohydride (see, for example, Patent Document 4).

However, each of these methods has the following problems.
(A) In the hydrogen reduction method, since the reduction treatment is performed at a high temperature in a hydrogen stream, the problem in terms of safety is great and the manufacturing process becomes expensive.
(B) Since the ammonia reduction method is a reduction treatment method using active hydrogen, nitrogen, and radicals generated by a decomposition reaction in a high-temperature atmosphere, the oxygen vacancies generated by the reduction treatment are replaced with nitrogen, titanium oxynitride ( TiO _x N _y ) is produced. In addition, since the decomposition of ammonia starts at about 500 ° C., the product becomes a mixture with unreduced titanium dioxide. Therefore, it is inevitable that the mixture becomes a mixture of low-valent titanium oxide and titanium oxynitride.
(C) In the homogenization reaction with titanium metal, it is possible to obtain ultrafine titanium dioxide powder, but metal titanium can only be obtained with a particle size larger than titanium dioxide powder. As a result, it is difficult to obtain fine particle titanium monoxide.
(D) The hydride reduction reaction uses a hydride that is easier to handle than gaseous hydrogen, so it is highly safe, but the hydride starts decomposing at about several hundred degrees Celsius. Therefore, it is unavoidable to be a mixture of low-valent titanium oxide obtained by reduction and unreduced titanium dioxide.

In addition, any of the above methods (A) to (D) has a problem that the atmosphere needs to be a reducing atmosphere, resulting in a high-cost process.
Therefore, it is difficult to obtain fine particle low-valent titanium oxide on an industrial scale, and production of a fine particle low-valent titanium oxide composition on an industrial scale has not yet been performed.

JP-A-61-56710 JP-A-5-25812 JP 59-199530 A Japanese Patent Laid-Open No. 5-193942

Monthly Display, September 1999, p10 “Trends in ZnO-based transparent conductive films”

The above-described zinc oxide-based transparent conductive film using low-valent titanium oxide as a dopant uses various vacuum processes (sputtering method, sputtering) using a target (sintered body) using zinc oxide powder and low-valent titanium oxide as film raw materials. The ion plating method, the pulse laser deposition (PLD) method, the electron beam (EB) vapor deposition method, etc.).
However, when zinc oxide powder, which is a film raw material, and low-valent titanium oxide obtained by a conventional manufacturing method are sintered, the primary particle diameter of zinc oxide powder is from about several tens of nanometers to about 1 μm. The primary particle diameter of the low-valent titanium oxide obtained by the conventional production method is at least 10 μm or more, and the order of the primary particle diameters of both are different, so that the film raw material is not uniformly solid-phase sintered. Therefore, in the target obtained by sintering, voids are generated because the sintered density is low.
In sputtering using a target having such a low sintered density and voids, the impedance of the discharge system including the target changes due to fluctuations during sputtering, so abnormal discharge frequently occurs in the sputtering apparatus. However, it has been difficult to stably form a zinc oxide-based transparent conductive film.
In order to suppress this abnormal discharge, it is necessary to solid-phase-sinter the film raw material uniformly to suppress the generation of vacancies. For this purpose, the primary particle diameter of zinc oxide powder and low-valent titanium oxide can be as small as possible. It is preferred that there is no difference, ie the same size.

  Accordingly, an object of the present invention is to provide a particulate low-valent titanium oxide composition suitable for producing a low-valent titanium oxide-doped zinc oxide target that does not cause abnormal discharge during sputtering, and the titanium oxide composition. An object of the present invention is to provide a production method capable of producing a product at an industrial level at low cost.

  As a result of various studies to solve the above problems, the present inventors have completed the present invention.

That is, this invention consists of the following structures.
(1) The X-ray diffraction profile has a plurality of low-valent titanium oxide peaks whose titanium valence is lower than tetravalent, and the primary particle diameter is 50 nm to 1 μm, and the particulate low Valence titanium oxide composition.
(2) The low valence titanium oxide composition according to (1), comprising a mixture of a plurality of low valence titanium oxides represented by the general formula: TiO _2-X (X = 0.1-1).
(3) At least two kinds selected from the group consisting of TiO (II), Ti ₂ O ₃ (III), Ti ₃ O ₅ , Ti ₄ O ₇ , Ti ₆ O ₁₁ , Ti ₅ O ₉ and Ti ₈ O ₁₅ The low-valent titanium oxide composition according to the above (1) or (2), comprising a mixture of titanium oxide.
(4) including a step of firing a mixture of titanium dioxide and carbon at 1000 to 1500 ° C. in an oxygen-containing gas stream in a closed container having a function of releasing an internal gas to the outside when the internal pressure is increased. (1) A method for producing a low-valent titanium oxide composition, comprising producing the particulate low-valent titanium oxide composition according to any one of (1) to (3).
(5) The method for producing a low-valent titanium oxide composition according to (4), wherein the carbon is carbon powder having a particle diameter of 50 nm to 150 μm.

When the low-valence titanium oxide composition of the present invention is used, a target capable of stably forming a film without causing abnormal discharge by sputtering, ion plating, PLD, EB vapor deposition or the like is produced. It becomes possible.
In addition, according to the production method of the present invention, since the low-valent titanium oxide composition can be produced at a low cost, it can be produced (mass produced) on an industrial scale and is extremely useful industrially. is there.

(A) is a diagram showing the X-ray diffraction measurement results of the titanium oxide obtained in Example 1, (b), said measurements from _{above, Ti 6 O 11, Ti 5} O 9, Ti 8 O FIG. ₁₅ is a diagram showing a peak list of each of ₁₅ . 2 is an identification pattern list of titanium oxide obtained in Example 1. FIG.

  Hereinafter, although one embodiment of the present invention is described in detail, the present invention is not limited by the following description unless it departs from the gist of the present invention.

  The low-valent titanium oxide composition of the present invention has a plurality of low-valent titanium oxide peaks in the X-ray diffraction profile, and has a primary particle diameter in a predetermined range, and includes titanium (IV), carbon, Is obtained through a reduction process of titanium dioxide with carbon, which is baked under a predetermined condition in a predetermined closed system container.

  As starting material titanium dioxide (IV), any of anatase type titanium dioxide, rutile type titanium dioxide, amorphous titanium dioxide, etc. can be used. It is preferred to use any of titanium or a mixture thereof.

  The particle diameter of titanium dioxide is not particularly limited, but in order to obtain a fine particle low-valence titanium oxide composition having a small particle diameter, titanium dioxide having a smaller particle diameter is preferable. For example, laser diffraction / scattering method, etc. From the measurement of the particle size distribution, the average primary particle size is preferably 1 μm or less, and the above-mentioned average primary particle size is preferably 50 nm or more and 800 nm or less in consideration of handleability.

  Further, the carbon in the present invention may be any carbon as long as it is made of carbon, for example, carbon black, carbon diamond, graphite, ronsdaylite, fullerene, amorphous carbon (activated carbon, carbon black), carbon nanotube, graphene, carbon Any material can be applied as long as the material is mainly composed of carbon such as fiber. Among these, it is preferable to use amorphous carbon (activated carbon, carbon black), graphite or the like that can be obtained at a low cost.

The carbon is preferably in a powder state, and the particle size may be 50 nm to 150 μm, preferably 100 nm to 100 μm, more preferably 200 nm to 50 μm. When the particle size is too small, the handleability is deteriorated, so that it is desirable that the particle size is within the above range.
Moreover, it is not preferable to use granular carbon having a particle size exceeding 150 μm. Although it is possible to proceed the reduction reaction of titanium dioxide even if granular carbon is used, there is a possibility that titanium dioxide cannot be sufficiently reduced by touching part of the air because titanium dioxide cannot be sufficiently coated. Because there is.
The particle size distribution of the powdered carbon is not particularly specified, but even if it is not all in the above particle size range, 80% by mass or more, particularly 90% by mass or more may be in the above range.

  In the present invention, the titanium dioxide and carbon are mixed in advance. The titanium dioxide to be used may be in powder form, but it is preferable that the titanium dioxide powder is preliminarily formed into a predetermined shape by pressurization or the like for easy separation from the carbon powder. The shape may be any shape such as a tablet shape. Further, the size of the molded product is not particularly limited as long as it can be covered with carbon powder.

  Since the mixing ratio of carbon with respect to titanium dioxide affects the reducing power, it is preferable that titanium dioxide: carbon = 1: 10 to 1: 1000 in weight ratio so as to cover the titanium dioxide with carbon as much as possible. If the mixing amount of carbon is too small, the reduction reaction of titanium dioxide does not proceed sufficiently, and the target low-valent titanium oxide composition may be difficult to obtain. If the mixing amount of carbon is too large, titanium dioxide This reduction reaction is too rapid, and metal titanium is produced or unreacted carbon remains, which may be not economical.

  If the mixing ratio of carbon in the mixture is within the above range, the carbon dioxide can be sufficiently covered with carbon. Therefore, during the titanium dioxide reduction reaction, the carbon is consumed by the reduction reaction or by reacting with oxygen in the air. However, it suffices that an amount sufficiently coated with titanium oxide is present even after the reduction reaction of titanium dioxide is completed. It is preferable to add a large amount in advance assuming that carbon is consumed by the reduction reaction. In this way, even when baked in the atmosphere, titanium dioxide is not oxidized and low-valent titanium oxide can be produced. Therefore, titanium dioxide (IV) can be reduced without using reducing gas in a large inert atmosphere furnace by covering carbon powder densely with titanium dioxide (IV) in a normal atmospheric furnace. It becomes possible to produce low-valence titanium oxide at low cost.

In the present invention, the mixture is placed in a reaction vessel and the reduction reaction of titanium dioxide proceeds. As the reaction vessel, it is preferable to use a closed vessel having a function of lowering the pressure inside the vessel by releasing the gas inside the vessel to the outside when the pressure inside the vessel rises. As described above, the use of a closed container having a function of releasing the gas inside the container to the outside when the internal pressure is increased is because the reaction rapidly proceeds when the reduction reaction of titanium dioxide by carbon starts, and the temperature rises accordingly. Then, the gas inside the container expands, which may cause a risk of rupture of the container, and when the pressure inside the container rises, release the gas inside the container This is to reduce the pressure and secure safety.
In addition, it is thought that the gas generated in the closed vessel during the reduction reaction of titanium dioxide is mainly carbon dioxide and carbon monoxide based on the consideration of the reduction mechanism described later.

In addition, the closed system container is a function that prevents the reactant from reacting with oxygen in the atmosphere and reducing and reducing low-valent titanium oxide to be further oxidized and returned to the original titanium dioxide. It has a function of suppressing the inflow of oxygen into the system container.
The closed system in a closed container means that the container may be completely sealed, or even if it is not completely sealed, it is only necessary to suppress exposure to the air to some extent, and it is closed when necessary. In other words, the closed system can be canceled when filling the mixture or taking out the reactant.
Thus, in the present invention, in the step of firing the mixture, the carbon covers titanium dioxide (IV) densely in the closed container, and the closed container can suppress the inflow of oxygen into the container. Even if the mixture is fired therein, the reduced titanium dioxide can be prevented from being further oxidized.

The firing in the present invention is performed by placing a predetermined closed system container filled with the mixture in a firing furnace. It does not specifically limit as a baking furnace, For example, various baking furnaces, such as an electric furnace, are mentioned.
The firing temperature for generating the low-valent titanium oxide composition, that is, the temperature at the time of the reduction reaction of titanium dioxide with carbon (hereinafter sometimes simply referred to as “the above reduction reaction” or “reduction reaction”), The temperature is 1000 ° C. or higher and 1500 ° C. or lower, preferably 1100 ° C. or higher and 1400 ° C. or lower. When the firing temperature is lower than 1000 ° C, there is a possibility that the reduction action of carbon may not be exhibited. When the firing temperature is higher than 1500 ° C, the sintering proceeds and becomes dense, and the obtained low-valent titanium oxide is not mechanically pulverized. There is a possibility that it cannot be crushed and fine particles cannot be obtained.
The firing time, that is, the reduction reaction time, may be appropriately adjusted depending on the firing temperature, the amount of titanium dioxide and the like, and is usually 30 minutes to 4 hours, more preferably about 1 hour to 2 hours.

As a reduction mechanism, carbon directly reacts with titanium dioxide (IV) to reduce titanium dioxide (IV), carbon becomes carbon dioxide, and carbon is oxidized to oxygen in the atmosphere. It is considered that two types of reactions, ie, a reaction in which carbon oxide reacts with titanium oxide (IV) and titanium dioxide (IV) is reduced, mainly proceed.
Further, the latter reaction utilizes the reducing ability of carbon monoxide, and it is necessary to perform it in an air atmosphere in order to convert carbon to carbon monoxide.

The obtained reactant is taken out from the reaction vessel and finally cooled to room temperature, and then carbon and low-valent titanium oxide are separated.
The method for separating carbon and low-valent titanium oxide is not particularly limited. For example, when a mixture of titanium dioxide in tablet form is used, a method for selectively removing tablets; a method using a sieve; For example, a method by air classification in which fine powder is separated by a blown air flow and collected by a cyclone, a bag filter, or the like.

The separated low valence titanium oxide may be subjected to a grinding treatment.
The pulverization method is not particularly limited as long as it can be pulverized within the range of the primary particle diameter of low-valent titanium oxide described later. For example, as a pulverizer, for example, when using media, a bead mill, a ball mill And a method using a pulverizer equipped with an apparatus such as a planetary mill, a sand grinder, a vibration mill or an attritor, and a method using a wet ultrahigh pressure atomizer such as a jet mill without using media, a nanomizer, or a starburst.

Thus, the obtained low valence titanium oxide has a plurality of low valence titanium oxide peaks in the X-ray diffraction profile.
The above-mentioned low-valence titanium oxide does not include TiO ₂ (IV), and includes not only those having an integer valence of TiO (II) and Ti ₂ O ₃ (III), but also Ti ₃ O ₅ and Ti _{4. O 7, Ti 6 O 11,} Ti 5 O 9, Ti 8 O 15 and the like including, but in the range represented by the general formula _{TiO 2-X (X = 0.1~1} ).
The low-valent titanium oxide in the present invention is a novel low-valent titanium oxide represented by a chemical formula of the general formula TiO _{2 -X} . The crystal structure of this low-valence titanium oxide can be confirmed by the results of instrumental analysis using an X-ray diffraction device (X-Ray Diffraction, XRD), an X-ray photoelectron spectrometer (XPS), or the like. .

  In the present invention, the target is a fine particle low-valence titanium oxide composition, which is not a single-component oxide consisting only of oxides having the same titanium valence, but a mixture of oxides having different titanium valences. That is, it is a mixture of low-valent titanium oxide.

The primary particle diameter of the low-valent titanium oxide composition of the present invention is 50 nm to 1 μm, preferably 100 nm to 700 nm, as measured by particle size distribution by a laser diffraction / scattering method. When the primary particle size is smaller than 50 nm, it is necessary to make the primary particle size of titanium dioxide, which is a raw material, smaller than 50 nm. It becomes a sintered body that is substantially coarse particles that cannot be crushed by mechanical pulverization or the like. Therefore, in the present invention, it is not possible to obtain a fine particle low-valence titanium oxide having a primary particle diameter of less than 50 nm.
If the primary particle diameter is larger than 1 μm, the sintering density of the target (sintered body) obtained by sintering may be reduced when used as a dopant.
If the primary particle diameter is within the above range, mechanical pulverization is possible.

The low-valent titanium oxide composition of the present invention is a fine particle suitable for producing a low-valent titanium oxide-doped zinc oxide-based transparent conductive film target in which abnormal discharge does not occur during sputtering, as described above. In addition, it can be manufactured at an industrial level at a very low cost using titanium dioxide as a raw material.
The low-valent titanium oxide of the present invention is also suitably used for black paint as a black pigment, black matrix (BM) for liquid crystal color filters, and the like.

  Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the examples illustrated in the examples.

  About the measurement of each physical property in an Example and a comparative example, it carried out with the following method.

(Specific surface area)
The specific surface area was measured by a nitrogen adsorption method using “BELSORP-mini” manufactured by Nippon Bell Co., Ltd.

(X-ray diffraction analysis)
X-ray diffraction analysis for obtaining an X-ray diffraction profile was performed using an X-ray diffractometer “X'Pert PRO” (trade name) manufactured by Spectris Co., Ltd. using a CuK X-ray with an applied voltage of 45 kV and an applied current of 40 mA. , Θ-2θ method.

(Primary particle size measurement)
The primary particle size of the low valent titanium oxide was determined by placing the low valent titanium oxide in a sodium hexametaphosphate solution with a Microtrac particle size distribution meter (“MT-3000II” manufactured by Nikkiso Co., Ltd.) and using a homogenizer for 10 minutes. The dispersed sample was irradiated with a laser beam and its diffraction (scattering) was measured.

Example 1
20 g of rutile type titanium dioxide (manufactured by Wako Pure Chemical Industries, Ltd.) having an average primary particle diameter of 370 nm converted from the measured value of the specific surface area is placed in a mold, lightly pressurized at 1 MPa, a disk having a diameter of 30 mm and a thickness of 10 mm Molded tablets were obtained.
20 g of the disk-shaped tablet and 100 g of activated carbon (manufactured by Ohira Chemical Industry Co., Ltd., average particle size 20-30 μm) are placed in a stainless steel container, and the container is placed in an electric furnace, and then 1200 ° C. in an air atmosphere. For 2 hours.
After the heat treatment, it was naturally cooled to room temperature. Then, the tablet was taken out, ethanol was added as the tablet, 2 mmΦ zirconia balls and solvent, and the tablet was pulverized to obtain powdered titanium oxide. Next, an X-ray diffraction profile of the obtained titanium oxide was obtained. The results are shown in FIG. 1 and FIG.

  In addition, when the gas inside the container expands due to heating and the pressure rises due to the heating, the lid lifts by the pressure, releases the gas inside the container to the outside, and the pressure inside the container decreases. Since the container body is covered with its own weight, it is a closed container having a function of releasing the gas inside the container to the outside when the internal pressure is increased.

FIG. 1 (a) is a view showing the result of X-ray diffraction measurement of titanium oxide obtained in Example 1, and FIG. 1 (b) shows the result of measurement from above, Ti ₆ O ₁₁ , Ti ₅ O ₉ , Ti _8. is a diagram showing respective peak list O _15. FIG. 2 is an identification pattern list of titanium oxide obtained in Example 1.
As shown in the X-ray diffraction profiles of FIGS. 1 and 2, the titanium oxide composition of Example 1 is a mixture of Ti ₆ O ₁₁ , Ti ₅ O ₉ and Ti ₈ O ₁₅ , that is, a low-valence titanium oxide composition. It was confirmed that.
Moreover, it was 0.5 micrometer when the primary particle diameter of the low valence titanium oxide composition of Example 1 obtained as mentioned above was measured.

  The particle size was small (0.5 μm), and a low-valent titanium oxide composition could be obtained by an extremely simple and inexpensive method using activated carbon in the air atmosphere. The particle size was suitable as a zinc oxide dopant.

(Comparative Example 1)
10 g of rutile type titanium dioxide (manufactured by Wako Pure Chemical Industries, Ltd., average particle size 0.37 μm) having an average primary particle size of 340 nm converted from the measured value of the specific surface area was placed in a mold and lightly pressurized at 1 MPa, A disk-shaped tablet was obtained, and powdered titanium oxide was obtained in the same manner as in Example 1 except that the disk-shaped tablet was placed in a stainless steel container.
Due to firing in the air, the rutile type titanium dioxide remained unchanged.

  As mentioned above, although embodiment of this invention was described, it cannot be overemphasized that this invention is not limited to the said embodiment, A various improvement and change are possible unless it deviates from the summary of this invention. Absent.

Claims (5)

  Fine X-ray diffraction profile characterized by having a plurality of low-valent titanium oxide peaks whose titanium valence is lower than tetravalent in the X-ray diffraction profile and having a primary particle diameter of 50 nm to 1 μm. Titanium composition. The low-valent titanium oxide composition according to claim 1, comprising a mixture of a plurality of low-valent titanium oxides represented by the general formula: TiO _{2 -X} (X = 0.1-1). TiO (II), Ti ₂ O ₃ (III), Ti ₃ O ₅ , Ti ₄ O ₇ , Ti ₆ O ₁₁ , Ti ₅ O ₉ and Ti ₈ O ₁₅ The low-valent titanium oxide composition according to claim 1 or 2, comprising a mixture.   A step of firing a mixture of titanium dioxide and carbon at 1000 to 1500 ° C in an oxygen-containing gas stream in a closed container having a function of releasing an internal gas to the outside when the internal pressure is increased. 4. A method for producing a low-valent titanium oxide composition, comprising producing the particulate low-valent titanium oxide composition according to any one of 3 above.   The method for producing a low-valent titanium oxide composition according to claim 4, wherein the carbon is carbon powder having a particle size of 50 nm to 150 μm.

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