JP2012158493A - Fine particle low valence niobium oxide composition, and method for producing the same - Google Patents

Abstract

A fine particle low valence niobium oxide composition suitable for producing a low valence niobium oxide doped zinc oxide target that does not cause abnormal discharge during sputtering, and the fine particle low valence niobium oxide composition is extremely inexpensive. A manufacturing method capable of being manufactured is provided.
A fine-particle low-valence niobium oxide composition having a peak of low-valence niobium oxide whose niobium valence is lower than pentavalent in an X-ray diffraction profile and having a primary particle diameter of 50 nm to 1 μm. A mixture of niobium oxide and carbon can be manufactured through a step of firing at 1000 to 1600 ° C. in an air-containing gas stream in a closed container having a function of releasing the internal gas to the outside when the internal pressure is increased. .
[Selection] Figure 1

Description

  The present invention relates to a fine particle low-valent niobium oxide composition and a method for producing the same, and more specifically, a fine particle low-valent niobium oxide composition that can be used as a dopant source for a zinc oxide-based transparent conductive material and its mass production. It relates to a manufacturing method.

  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 Indium oxide (In ₂ O ₃ ) -based thin films such as indium oxide (ITO) films are 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.

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

To date, low-valence niobium oxides such as NbO (II), Nb ₂ O ₃ (III), and NbO ₂ (IV) have not been obtained on an industrial scale. As described below, this is based on the fact that niobium oxide (Nb ₂ O ₅ ) is reduced and it is difficult to industrially produce fine-particle low-valent niobium oxide.
As a method for producing low-valence niobium oxide, Nb ₂ O ₅ (V) is generally prepared by firing in a strong reducing atmosphere, and is reduced in incandescent hydrogen (see Non-Patent Document 2). ). Therefore, for safety, hydrogen requiring attention to handling is essential, and there is a problem that the manufacturing process becomes expensive.
Therefore, it is difficult to obtain fine-particle low-valence niobium oxide on an industrial scale, and production of a fine-particle low-valence niobium oxide composition on an industrial scale has not yet been performed.

Monthly Display, September 1999, p10 “Trends in ZnO-based transparent conductive films” “Iwanami Physical and Chemical Dictionary”, 3rd edition, Iwanami Shoten, p517 “Niobium Oxide”

The above-described zinc oxide-based transparent conductive film using low-valent niobium oxide as a dopant is prepared by using various vacuum processes (sputtering method, sputtering) using a target (sintered body) made of zinc oxide powder and low-valent niobium 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 niobium 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-valence niobium oxide obtained by the conventional manufacturing method is at least 40 μm or more, and the order of the primary particle diameters of the two is different, so that the film raw material is not uniformly solid-phase sintered. Therefore, the target obtained by sintering has voids generated due to low sintering density, and unreacted low-valence niobium oxide having high resistance.
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-valence niobium oxide can be as small as possible. It is preferable to use zinc oxide powder and low-valence niobium oxide that are not different, that is, have the same size.

  Therefore, an object of the present invention is to prepare a fine particle low-valence niobium oxide composition suitable for producing a low-valence niobium oxide-doped zinc oxide target in which abnormal discharge does not occur during sputtering, and the niobium oxide composition. An object of the present invention is to provide a manufacturing method that can be manufactured 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) Fine particle low-valence niobium oxide composition having a low-valence niobium oxide peak having a niobium valence lower than pentavalent in the X-ray diffraction profile and a primary particle diameter of 50 nm to 1 μm object.
(2) The fine-particle low-valence niobium oxide composition according to (1), comprising a mixture of low-valence niobium oxide selected from NbO (II), Nb ₂ O ₃ (III) and NbO ₂ (IV).
(3) including a step of firing a mixture of niobium oxide and carbon in an oxygen-containing gas stream at 1000 to 1600 ° C. in a closed container having a function of releasing an internal gas to the outside when the internal pressure increases. (1) A method for producing a fine particle low valence niobium oxide composition according to (1) or (2), wherein the fine particle low valence niobium oxide composition is produced.
(4) The method for producing a fine particle low-valence niobium oxide composition according to (3), wherein the carbon is a powder having a particle size of 50 nm to 150 μm.

When the fine particle low-valence niobium 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 to do.
Further, according to the production method of the present invention, since the fine particle low-valence niobium oxide composition can be produced at low cost, it can be produced (mass produced) on an industrial scale and is extremely useful industrially. It is.

(A) is a diagram showing the X-ray diffraction measurement results of the niobium oxide obtained in Example 1, (b), said measurements from above, is a diagram showing a peak list of NbO _2. 2 is an identification pattern list of niobium oxide obtained in Example 1.

  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 fine particle low valence niobium oxide of the present invention has a low valence niobium oxide peak in the X-ray diffraction profile and a primary particle diameter within a predetermined range, and a mixture of niobium oxide (V) and carbon is used. It is obtained through a reduction process of niobium oxide with carbon, which is baked under a predetermined condition in a predetermined closed system container.

Niobium oxide (V) is used as the starting material niobium oxide.
The particle diameter of niobium oxide is not particularly limited, but niobium oxide (V) having a smaller particle diameter is preferable for obtaining fine particle low-valence niobium oxide having a small particle diameter, for example, by laser diffraction / scattering method or the like. From the measurement of the particle size distribution, those having an average primary particle diameter of 1 μm or less are preferable. In consideration of handleability, those having an average primary particle diameter of 50 nm to 800 nm are preferable.

  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, coke, amorphous carbon (activated carbon, carbon black), carbon nanotube, graphene Any carbon allotrope may be used as long as the main component is composed of such a carbon allotrope. Of these, amorphous carbon (activated carbon, carbon black) and graphite are preferably used from the viewpoint of availability at 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. In addition, it is not preferable to use granular carbon having a particle size exceeding 150 μm. Even if such granular carbon is used, the reduction reaction of niobium oxide can proceed, but niobium oxide cannot be covered sufficiently, and the niobium oxide is sufficiently reduced by touching part of the air. This is because there is a possibility that it cannot be done.
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 niobium oxide and carbon are mixed in advance. The niobium oxide to be used may be in the form of powder, but it is preferable that the niobium oxide powder is formed into a predetermined shape by pressurization or the like in advance 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 to niobium oxide (V) affects the reducing power, it is preferable that niobium oxide: carbon = 1: 5 to 1:50 by weight ratio so that niobium oxide is covered with carbon as much as possible. . If the amount of carbon mixed is too small, the reduction reaction of niobium oxide may not proceed sufficiently, making it difficult to obtain the desired low-valence niobium oxide composition. If the amount of carbon mixed is excessive, Therefore, there is a possibility that metal niobium is generated or unreacted carbon remains, which is not economical.

  If the mixing ratio of the carbon in the mixture is within the above range, the niobium oxide can be sufficiently covered with the carbon. Therefore, during the reduction reaction of niobium oxide, the carbon is consumed by reacting with the reduction reaction or oxygen in the air. However, it suffices that there is a sufficient amount of niobium oxide after the reduction reaction of niobium oxide. It is preferable to add a large amount in advance assuming that carbon is consumed by the reduction reaction. By doing so, even when baked in the air, niobium oxide is not oxidized and low-valence niobium oxide can be produced. Therefore, niobium oxide (V) can be reduced without using a large inert atmosphere furnace or reducing gas by densely covering the carbon powder with niobium oxide (V) in a normal air atmosphere furnace. It becomes possible to produce low-valence niobium oxide at a low cost.

In the present invention, the mixture is placed in a reaction vessel and the reduction reaction of niobium oxide (V) 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. In this way, the use of a closed container having a function of releasing the gas inside the container to the outside when the internal pressure rises causes the reduction reaction to proceed rapidly when the carbon reduction reaction starts, and the temperature rises accordingly. The gas inside the container expands, which may cause a risk of rupture of the container, so that the gas inside the container is released to the outside when the pressure inside the container rises. This is to reduce safety and ensure safety.
The gas generated in the closed vessel during the reduction reaction of niobium oxide is considered to be mainly carbon dioxide and carbon monoxide based on the consideration of the reduction mechanism described later.

In addition, the closed system vessel prevents the reactant from reacting with oxygen in the atmosphere and reducing the low-valent niobium oxide, which is produced by further reduction, to return to the original niobium oxide (V). That is, it has a function of suppressing the inflow of oxygen into the closed 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.
As described above, in the present invention, in the step of firing the mixture, the carbon covers niobium oxide densely in the closed container and the inflow of oxygen into the container can be suppressed by the closed container. Even if calcined, the reduced niobium oxide 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 fine particle low-valent niobium oxide, that is, the temperature during the reduction reaction with carbon (hereinafter sometimes referred to simply as “the above reduction reaction” or “reduction reaction”) is 1000 ° C. or higher and 1600 ° C. The temperature is preferably 1 ° C. or lower, particularly 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 1600 ° C, the sintering proceeds and becomes dense, and the obtained low-valence niobium oxide is not obtained by mechanical grinding. 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 niobium oxide, 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 niobium oxide (V) to reduce niobium oxide (V), 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 niobium oxide (V) and reduces niobium oxide (V) 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 reaction product is taken out from the reaction vessel and finally cooled to room temperature, and then carbon and low-valent niobium oxide are separated.
The method for separating carbon and low-valent niobium oxide is not particularly limited. For example, when a mixture of niobium oxide in tablet form is used, a method of 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 niobium oxide may be pulverized.
The method of pulverization is not particularly limited as long as it can be pulverized within the range of the primary particle diameter of the fine particle low-valence niobium oxide composition described later. For example, when using media, a bead mill, a ball mill, a planetary mill, Examples thereof include a method using a pulverizer equipped with an apparatus such as a sand grinder, a vibration mill, or an attritor; a method using a wet ultrahigh pressure atomizer such as a jet mill, nanomizer, or starburst that does not use media.

Thus, the obtained fine particle low valence niobium oxide composition has a peak of low valence niobium oxide in the X-ray diffraction profile.
The low-valence niobium oxide composition described above is niobium oxide having a valence of niobium lower than pentavalent, does not include Nb ₂ O ₅ (V), and includes NbO (II), Nb ₂ O ₃ (III), NbO ₂ (IV) and the like can be mentioned, and it is preferably selected from NbO (II), Nb ₂ O ₃ (III) and NbO ₂ (IV). The structure of this low-valence niobium oxide can be confirmed by the results of instrumental analysis such as an X-ray diffraction apparatus (X-Ray Diffraction, XRD) and an X-ray photoelectron spectrometer (X-ray Photoelectron Spectroscopy, XPS).

The primary particle size of the fine particle low-valence niobium 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 diameter is smaller than 50 nm, it is necessary to make the primary particle diameter of niobium oxide (V), which is a raw material, smaller than 50 nm, and niobium oxide is sintered and densified in the reduction reaction process using carbon. Therefore, the sintered body is substantially coarse particles which cannot be crushed by mechanical pulverization or the like. Therefore, in the present invention, the primary particle diameter of the raw material niobium oxide is preferably 50 nm or more from the viewpoint of enabling mechanical pulverization.
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.

The fine particle low-valence niobium oxide composition of the present invention is a fine particle suitable for producing, for example, a low-valence niobium oxide-doped zinc oxide-based transparent conductive film target in which abnormal discharge does not occur during sputtering. As described above, niobium oxide can be produced at an industrial level at a very low cost using niobium oxide as a raw material.
Further, the fine particle low-valence niobium oxide composition of the present invention is also suitably used as a raw material for an antireflection film, taking advantage of the fact that a film having a high refractive index is obtained.

  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.

  The physical properties in Examples and Comparative Examples were evaluated by the following methods.

(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., with an applied voltage of 45 kV and an applied current of 40 mA using CuKα rays. The θ-2θ method was used.

(Primary particle size measurement)
The primary particle size of the low valence niobium oxide was determined by placing the low valence niobium oxide in the sodium hexametaphosphate solution with a microtrack particle size distribution analyzer ("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 niobium oxide (V) (manufactured by Wako Pure Chemical Industries, Ltd., average particle size: 0.5 μm) was placed in a mold and lightly pressurized at 1 MPa to obtain a disk-shaped tablet having a diameter of 30 mm and a thickness of 5 mm.
20 g of the disk-shaped tablet and 200 g of activated carbon (manufactured by Ohira Chemical Sangyo Co., Ltd., average particle size: 20 to 30 μm) were placed in a stainless steel container, and the container was placed in an electric furnace, and then 1200 in the atmosphere. Heat treatment was performed at 2 ° C. 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, a 2 mmφ zirconia ball and a solvent, and the tablet was pulverized to obtain powdered niobium oxide. Next, an X-ray diffraction profile was obtained using the obtained niobium oxide. 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. 1A is a diagram showing the X-ray diffraction measurement result of niobium oxide obtained in Example 1, and FIG. 1B is a diagram showing the measurement result and a peak list of NbO ₂ from above. . FIG. 2 is an identification pattern list of niobium oxide obtained in Example 1.
As shown in the X-ray diffraction profiles of FIGS. 1 and 2, it was confirmed that the niobium oxide of Example 1 was a single phase of NbO ₂ (IV), that is, a low-valence niobium oxide.
The primary particle diameter of NbO ₂ (IV) obtained as described above was measured and found to be 0.67 μm.

  The particle size was small (0.67 μm), and the fine particle low-valence niobium oxide could be obtained by an extremely simple and inexpensive method using activated carbon in the air atmosphere. The particle size was suitable as a dopant for producing a zinc oxide sintered body.

(Comparative Example 1)
20 g of niobium oxide (V) (average particle size 0.5 μm, manufactured by Wako Pure Chemical Industries, Ltd.) was placed in a mold and lightly pressurized at 1 MPa to obtain a disk-shaped tablet in the same manner as in Example 1. Powdered niobium oxide was obtained in the same manner as in Example 1 except that only the tablet of the mold was placed in a stainless steel container.
Since carbon was baked in the air without being placed in a stainless steel container, the white niobium oxide (V) remained unchanged after baking.

  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 (4)

  A fine-particle low-valent niobium oxide composition having a peak of low-valence niobium oxide whose niobium valence is lower than pentavalent in an X-ray diffraction profile and having a primary particle diameter of 50 nm to 1 μm. The fine-particle low-valence niobium oxide composition according to claim 1, comprising a mixture of low-valence niobium oxide selected from NbO (II), Nb ₂ O ₃ (III), and NbO ₂ (IV).   The method comprising firing a mixture of niobium oxide and carbon at 1000 to 1600 ° C in an air stream in a closed container having a function of releasing an internal gas to the outside when the internal pressure is increased. A method for producing a fine particle low valence niobium oxide composition as described above.   The method for producing a fine particle low-valence niobium oxide composition according to claim 3, wherein the carbon is a powder having a particle size of 50 nm to 150 μm.

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