JP2020026384A - Method for producing composite tungsten oxide particle - Google Patents

Abstract

To provide a method for producing composite tungsten oxide particles by which equipment with a low introduction cost can be used and the number of steps is small.SOLUTION: There is provided a method for producing composite tungsten oxide particles represented by the general formula: MWO(where the M element is one or more elements selected from an alkali metal, an alkaline earth metal, a rare earth element and others, 0.001≤x/y≤1, 2.2≤z/y≤3.0). The method comprises a droplet formation step of forming droplets of a raw material mixed solution containing a tungsten source and the M element source which are treatment targets; a heat treatment step of heat-treating the treatment targets at 500°C or higher; and a reduction treatment step of reducing the particles obtained in the heat treatment step at a temperature in the range of higher than 400°C and lower than 700°C in an atmosphere containing a reducing gas.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a method for producing composite tungsten oxide particles.

  Various techniques have been proposed as near-infrared shielding techniques for reducing solar radiation transmittance while maintaining good transparency with good visible light transmittance. Above all, near-infrared shielding technology using inorganic conductive particles is superior to other technologies in near-infrared shielding characteristics, is low in cost, has radio wave permeability, and has high weather resistance. There are advantages.

For example, in Patent Document 1, a general formula M _x W _y O _z (where M is H, He, an alkali metal, an alkaline earth metal, a rare earth element, Mg, Zr, Cr, Mn, Fe, Ru, Co, Rh , Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb, B, F, P, S, Se, Br, Te , Ti, Nb, V, Mo, Ta, Re, Be, Hf, Os, Bi, I, at least one element selected from the group consisting of W, tungsten, O, oxygen, 0.001 ≦ x / y ≦ 1, 2.2 ≦ z / y ≦ 3.0) infrared ray shielding material fine particle dispersion in which composite tungsten oxide fine particles expressed as infrared ray shielding material fine particles are dispersed in a medium such as a resin that transmits visible light. Technology related to a method for producing the infrared shielding material fine particles has been developed. It is. Patent Literature 1 discloses an example in which an infrared shielding film, which is a thin film-shaped infrared shielding material fine particle dispersion, is manufactured.

  According to Patent Literature 1, an infrared shielding material fine particle dispersion having excellent optical properties, such as efficiently shielding sunlight, particularly light in the near infrared region, and simultaneously maintaining transmittance in the visible light region is produced. It is said that it will be possible. For this reason, application of the infrared ray shielding material fine particle dispersion disclosed in Patent Document 1 to various uses such as window glass has been studied.

  Various studies have been made on a method for producing composite tungsten oxide particles useful as a near-infrared shielding material.

For example, in Non-Patent Document 1, the inventor of Patent Document 1 proposes a method of synthesizing Cs _0.32 WO ₃ nanoparticles by a solid phase method. However, in the synthesis method disclosed in Non-Patent Document 1, the particle diameter is large, and a pulverization process is required to convert the particles into nanoparticles. For this reason, the number of process steps may increase.

Non-Patent Document 2 discloses a method for synthesizing Cs _x WO ₃ by a hydrothermal synthesis method. However, the hydrothermal synthesis method requires several tens of hours or more of synthesis time. In addition, the hydrothermal synthesis method has a problem that the number of steps such as a post-treatment step is large.

  Non-Patent Document 3 discloses a synthesis method based on an inductively coupled thermal plasma technique. However, such a synthesizing method requires the introduction of an inductively coupled thermal plasma apparatus, which has increased the cost.

Patent Document 2 discloses a process for preparing potassium-cesium-tungsten bronze solid solution particles represented by the chemical formula K _x Cs _y WO _z , wherein x + y ≦ 1 and 2 ≦ z ≦ 3, Combining a suitable tungsten source with a potassium salt and a cesium salt to form a powder mixture and exposing the powder mixture to a plasma torch under a reducing atmosphere, preferably a sheath gas comprising a hydrogen / rare gas mixture. A process is disclosed, provided by:

  However, also in Patent Document 2, it is necessary to use plasma, and the cost is increased due to introduction of a plasma device. Further, according to the manufacturing method disclosed in Patent Document 2, it is also disclosed that metal tungsten is mixed as an impurity.

Takeda Hiromitsu, and Kenji Adachi, "Near infrared absorption of tungsten oxide nanoparticle dispersions." Journal of the American Ceramic Society, 2007, Vol.90, Issue 12, P.4059-4061 Guo Chongshen, et al., "Novel synthesis of homogenous CsxWO3 nanorods with excellent NIR shielding properties by a water controlled-release solvothermal process." Journal of Materials Chemistry, 2010, Vol. 20, Issue 38, P. 8227-8229. Mamak Marc, et al., "Thermal plasma synthesis of tungsten bronze nanoparticles for near infra-red absorption applications." Journal of Materials Chemistry, 2010, Vol.20, Issue44, P.9855-9857.

Japanese Patent No. 4096205 JP 2012-532822 A

  As described above, composite tungsten oxide particles are useful as near-infrared shielding materials. Therefore, there is a need for a method for producing composite tungsten oxide particles that can be produced at low cost and with few steps.

  However, the conventionally disclosed method for producing composite tungsten oxide particles has problems such as the necessity of introducing a special high-cost apparatus and the necessity of many steps as described above.

  In view of the above problems of the related art, it is an object of one aspect of the present invention to provide a method for producing composite tungsten oxide particles that can use equipment with low introduction cost and has a small number of steps.

In order to solve the above-described problems, in one aspect of the present invention,
Formula _M x _W y _{O z} (where, M element, an alkali metal, alkaline earth metal, rare earth elements, Mg, Zr, Cr, Mn , Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb, B, F, P, S, Se, Br, Te, Ti, Nb, V, Mo, At least one element selected from Ta, Re, Be, Hf, Os, Bi and I, W is tungsten, O is oxygen, 0.001 ≦ x / y ≦ 1, 2.2 ≦ z / y ≦ 3.0), wherein the composite tungsten oxide particles are represented by the following formula:
A droplet forming step of forming a droplet of a raw material mixed solution including a tungsten source and the M element source, which is an object to be processed;
A heat treatment step of heat treating the object to be processed at 500 ° C. or higher;
A reduction treatment step of reducing the particles obtained in the heat treatment step at a temperature in a range of higher than 400 ° C. and lower than 700 ° C. in an atmosphere containing a reducing gas, and a method for producing composite tungsten oxide particles. provide.

  According to one aspect of the present invention, equipment with low introduction cost can be used, and a method for producing composite tungsten oxide particles with a small number of steps can be provided.

FIG. 1 is a schematic diagram of a composite material manufacturing apparatus that can be suitably used in the method for manufacturing composite tungsten oxide particles of the present embodiment. FIG. 1 is a schematic diagram of a reduction treatment apparatus that can be suitably used in the method for producing composite tungsten oxide particles of the present embodiment. 9 shows the temperature distribution measurement results of the reaction section of the composite material manufacturing apparatus used in Reference Example 1. XRD diffraction patterns of composite tungsten oxide particles obtained in Reference Example 1, Examples 1, 2 and Comparative Example 1, and masses of Cs _0.32 WO ₃ phase and Cs ₂ O phase obtained by Rietveld analysis Percentage. Lattice constant of Cs _0.32 WO ₃ phase obtained by Rietveld analysis for the composite tungsten oxide particles obtained in Reference Example 1, Examples 1, 2 and Comparative Example 1. The occupancy of tungsten at the tungsten sites in the composite tungsten oxide phase of the composite tungsten oxide particles obtained in Reference Example 1, Examples 1, 2, and Comparative Example 1. 5 is an SEM image of the composite tungsten oxide particles obtained in Reference Example 1. 4 is a TEM image of the composite tungsten oxide particles obtained in Reference Example 1. 5 is a mapping image of the composite tungsten oxide particles obtained in Reference Example 1 using TEM-EDS. 7 is an XPS spectrum of W4f and Cs3d of the composite tungsten oxide particles obtained in Reference Example 1. XPS spectrum of O1s of composite tungsten oxide particles obtained in Reference Example 1 9 shows high-angle angular dark-field images and contrast intensity of the composite tungsten oxide particles obtained in Reference Example 1. 7 shows the calculation results of the radial distribution function of the composite tungsten oxide particles obtained in Reference Example 1 and Example 2 using XAFS. 9 is an XRD diffraction pattern of the composite tungsten oxide particles obtained in Reference Examples 1 to 5. SEM images of the composite tungsten oxide particles obtained in Reference Examples 1 to 5. 5 is an SEM image of the composite tungsten oxide particles obtained in Example 2. 5 is a mapping image of the composite tungsten oxide particles obtained in Example 2 using TEM-EDS. 7 is an XPS spectrum of W4f and Cs3d of the composite tungsten oxide particles obtained in Example 2. 13 is an XPS spectrum of O1s of the composite tungsten oxide particles obtained in Example 2. 5 shows high-angle angular dark-field images of the composite tungsten oxide particles obtained in Example 2 and contrast intensity. 3 shows absorption spectra of the composite tungsten oxide particles obtained in Reference Example 1, Examples 1, 2 and Comparative Example 1.

A specific example of a method for producing composite tungsten oxide particles according to an embodiment of the present disclosure (hereinafter, referred to as “the present embodiment”) will be described below with reference to the drawings. It should be noted that the present invention is not limited to these examples, but is indicated by the claims, and is intended to include all modifications within the scope and meaning equivalent to the claims.
[Method for producing composite tungsten oxide particles]
Hereinafter, one configuration example of the method for producing composite tungsten oxide particles of the present embodiment will be described.

Method for producing a composite tungsten oxide particles of the present embodiment relates to a method of manufacturing a composite tungsten oxide particles expressed by the general formula M _x W _y O _z, it may have the following steps.

  The M element in the above general formula is an alkali metal, an alkaline earth metal, a rare earth element, Mg, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb, B, F, P, S, Se, Br, Te, Ti, Nb, V, Mo, Ta, Re, One or more elements selected from Be, Hf, Os, Bi, and I can be used. W represents tungsten, O represents oxygen, and x, y, and z preferably satisfy 0.001 ≦ x / y ≦ 1, 2.2 ≦ z / y ≦ 3.0, respectively.

A droplet forming step of forming droplets of a raw material mixed solution containing a tungsten source and an M element source, which are to be processed;
A heat treatment step of heat treating the object to be processed at 500 ° C. or higher;
A reduction treatment step of subjecting the particles obtained in the heat treatment step to a reduction treatment in an atmosphere containing a reducing gas at a temperature higher than 400 ° C. and lower than 700 ° C.

  First, the composite tungsten oxide particles produced by the method for producing composite tungsten oxide particles of the present embodiment will be described.

Composite tungsten oxide contained in the composite tungsten oxide particles are expressed by the general formula M _x W _y O _z as described above. Since the M element, W, O, and x, y, and z in the formula have already been described, their description is omitted here.

  The composite tungsten oxide can have a tungsten bronze-type crystal structure of, for example, any of tetragonal, cubic, and hexagonal. The crystal structure of the composite tungsten oxide contained in the composite tungsten oxide particles of the present embodiment is not particularly limited, and can have one or more crystal structures selected from tetragonal, cubic, and hexagonal.

  However, when the composite tungsten oxide has a hexagonal crystal structure, the transmittance of light in the visible light region and the absorption of light in the near infrared region of the composite tungsten oxide particles are particularly improved, which is preferable. Therefore, the composite tungsten oxide particles preferably include a composite tungsten oxide having a hexagonal crystal structure. When at least one element selected from Cs, Rb, K, Tl, Ba, and In is used as the M element, a hexagonal crystal is easily formed. For this reason, the M element preferably contains at least one selected from Cs, Rb, K, Tl, Ba, and In.

  Here, how to arrange the M element when the composite tungsten oxide has a hexagonal crystal structure will be described.

  An octahedron formed with W and six Os as a unit, that is, an octahedron in which O atoms are arranged at the vertices and W atoms are arranged in the center, and six octahedrons are formed of O atoms by assembling six A rectangular void (tunnel) is formed. Then, the M element is arranged in the space to form one unit, and a large number of the one unit are assembled to form a hexagonal crystal structure. When the composite tungsten oxide having a hexagonal crystal structure has a uniform crystal structure, the addition amount of the M element is preferably 0.2 or more and 0.5 or less in terms of x / y, more preferably 0.33 or less. It is. When z / y = 3, when the value of x / y is 0.33, it is considered that the M element is arranged in all the hexagonal voids.

  Similarly, when z / y = 3, each of the cubic and tetragonal composite tungsten oxides also has an upper limit of the amount of the M element derived from the structure, and the maximum amount of the M element added to 1 mol of tungsten. Is about 1 mol in the case of cubic and about 0.5 mol in the case of tetragonal. The maximum amount of the M element added to 1 mol of tungsten in the case of tetragonal crystal varies depending on the type of the M element, but the industrially easy production is about 0.5 mol as described above. However, it is difficult to simply define these structures, and since the range is an example showing a particularly basic range, the present invention is not limited to this.

  Also, by adding a very small amount of the M element, free electrons are generated in the composite tungsten oxide, and a desired infrared absorption effect can be obtained. Therefore, it is preferable that x / y satisfies 0.001 ≦ x / y ≦ 1.

Further, the composite tungsten oxide has a composition in which an M element is added to tungsten trioxide (WO ₃ ). Tungsten trioxide does not contain effective free electrons, so that the infrared absorption effect cannot be exhibited unless the ratio of oxygen to 1 mol of tungsten is less than 3. However, in the composite tungsten oxide, free electrons are generated by adding the M element, and an infrared absorption effect can be obtained. Therefore, the ratio of oxygen to 1 mol of tungsten can be set to 3 or less. However, the crystal phase of WO ₂ causes absorption or scattering of light in the visible light region, and may reduce the absorption of light in the near infrared region. For this reason, from the viewpoint of suppressing the generation of WO ₂ , the ratio of oxygen to 1 mol of tungsten is preferably larger than 2.

  Therefore, it is preferable that 2.2 ≦ z / y ≦ 3.0 be satisfied as described above.

  The particle diameter of the composite tungsten oxide particles produced by the method for producing composite tungsten oxide particles of the present embodiment is not particularly limited, and can be selected according to the purpose of use and the like.

  For example, when used for applications requiring transparency, it is preferable to have a particle size of 800 nm or less. This is because particles having a particle size of 800 nm or less do not completely block light due to scattering, can maintain high visibility in the visible light region, and can efficiently maintain transparency at the same time. In particular, when importance is placed on transparency in the visible light region, it is preferable to further consider scattering by particles.

  When emphasis is placed on the reduction of scattering by such particles, the particle diameter is preferably 200 nm or less, more preferably 100 nm or less.

  This is because, when the particle diameter is small, the scattering of light in the visible light region having a wavelength of 400 nm to 780 nm due to geometrical scattering or Mie scattering is reduced, and as a result, the infrared shielding film becomes like frosted glass and clear transparency. This is because it is possible to avoid becoming impossible to obtain. When the particle diameter is 200 nm or less, the geometric scattering or the Mie scattering is reduced, and the region becomes a Rayleigh scattering region. This is because, in the Rayleigh scattering region, the scattered light is reduced in proportion to the sixth power of the particle diameter, so that the scattering is reduced and the transparency is improved as the particle diameter decreases. Further, when the particle diameter is 100 nm or less, scattered light is very small, which is preferable. From the viewpoint of avoiding light scattering, it is preferable that the particle diameter is small.

  For this reason, the particle diameter of the composite tungsten oxide particles produced by the method for producing composite tungsten oxide particles of the present embodiment can be selected according to the intended use. For example, when high visibility in the visible light region is required to be maintained as described above, the particle diameter is preferably 800 nm or less, more preferably 200 nm or less, and further preferably 100 nm or less. preferable. Although the lower limit of the particle size of the composite tungsten oxide particles produced by the method for producing composite tungsten oxide particles of the present embodiment is not particularly limited, it can be, for example, 1 nm or more.

  The particle diameter of the composite tungsten oxide particles obtained by the method for producing composite tungsten oxide particles of the present embodiment is obtained by observing the particles with, for example, an SEM or a TEM and drawing a minimum circumscribed circle circumscribing the particles. It can be a diameter.

  Note that the particle size of the obtained composite tungsten oxide particles can be selected by, for example, adjusting the size and the like of the droplet formed in the droplet forming step described later.

  Since the infrared shielding material containing the composite tungsten oxide particles obtained by the method for producing composite tungsten oxide particles of the present embodiment largely absorbs light in the near-infrared region, particularly near the wavelength of 1000 nm, the transmission color tone is blue. There are many things that turn greenish.

  Although the lattice constant of the composite tungsten oxide particles obtained by the method for producing composite tungsten oxide particles of the present embodiment, specifically, the composite tungsten oxide contained in the composite tungsten oxide particles is not particularly limited, the a-axis Is preferably not less than 7.37 ° and not more than 7.42 °, the c-axis is preferably not less than 7.58 ° and not more than 7.70 °, the a-axis is not less than 7.38 ° and not more than 7.42 °, and the c-axis is not less than 7.58 ° and not more than 7.69 °. Is more preferable.

  This is because a crystal structure without W (tungsten) deficiency is formed by setting the lattice constant of the composite tungsten oxide within the above range.

  The method for calculating the lattice constant is not particularly limited, and can be calculated from the powder X-ray diffraction pattern measured for the obtained composite tungsten oxide particles.

  The composite tungsten oxide particles of the present embodiment may contain an unavoidable component such as an oxide of element M, for example. In this case, the lattice constant of the crystal phase of the composite tungsten oxide can be used as the lattice constant of the composite tungsten oxide particles.

  Next, the method for producing composite tungsten oxide particles of the present embodiment will be specifically described.

  In the method for producing composite tungsten oxide particles of the present embodiment, a droplet containing a tungsten source and an M element source is supplied together with a gas stream to an atmosphere at or above the thermal decomposition temperature of the raw material, and the solvent is evaporated and thermally decomposed. This is a spray pyrolysis method for obtaining composite tungsten oxide particles.

Therefore, the method for producing composite tungsten oxide particles according to the present embodiment includes, as described above, a droplet forming step of forming droplets of a raw material mixed solution containing a tungsten source and an M element source, which are to be processed. Can be provided. In addition, the method may include a heat treatment step of heat-treating the droplet as the object to be processed at 500 ° C. or higher.
(Droplet forming step)
In the droplet forming step, droplets of the raw material mixed solution containing the tungsten source and the M element source, which are the objects to be processed, can be formed.

  Specific means for forming a droplet in the droplet forming step is not particularly limited. For example, a method of forming droplets of a solution containing a tungsten source and an M element source by using a spray nozzle, and a method of forming droplets by irradiating a solution containing a tungsten source and an M element source with ultrasonic waves And a method of forming droplets using a two-fluid nozzle, and a method of forming droplets using various atomizers such as a centrifugal atomizer.

  Particularly, since a fine droplet can be stably formed, it is preferable to form a droplet by irradiating a solution containing a tungsten source and an M element source with ultrasonic waves. That is, a droplet forming method using ultrasonic waves can be suitably used.

  In addition, a solution containing a tungsten source and a solution containing an M element source are separately prepared, and are mixed, for example, immediately before supply to a droplet forming section (droplet forming means) or in the droplet forming section. It is preferable to form a solution containing and M element source. That is, in the droplet forming step, it is preferable that the solution containing the tungsten source and the solution containing the M element source are mixed to form a raw material mixed solution. After the formation of the raw material mixed solution, it is preferable to continuously form droplets using the raw material mixed solution.

  The specific method of mixing both solutions in the droplet forming step is not particularly limited. For example, a solution containing a tungsten source and a solution containing an M element source are separately introduced into an ultrasonic spraying device (ultrasonic irradiation device) which is a droplet forming portion, and both solutions are mixed in the device to mix raw materials. It is preferable to form a solution and form droplets. That is, in the case where droplets of the raw material mixed solution are formed using an ultrasonic spraying device in the droplet forming process, the solution including the tungsten source and the solution including the M element source are mixed in the ultrasonic spraying device. Then, it is preferable to form a raw material mixed solution. As described above, the solution containing the tungsten source and the solution containing the M element source are separately prepared, and mixed by, for example, an ultrasonic spraying device, so that the raw material mixed solution is formed and then formed into droplets. The time can be particularly shortened. Therefore, it is possible to particularly suppress the tungsten source from reacting with the M element source due to the neutralization reaction and to cause precipitation or the like in the raw material mixed solution.

The tungsten source is not particularly limited, and a tungsten salt or the like can be used. For example, ammonium paratungstate can be preferably used. Ammonium tungstate pentahydrate (ATP) can be represented by, for example, (NH ₄ ) ₁₀ (W ₁₂ O ₄₁ ) · 5H ₂ O.

  In the ammonium paratungstate, elements other than tungsten are N (nitrogen), H (hydrogen), and O (oxygen), and are discharged out of the system in a temperature raising step and a heat treatment step described later. Therefore, by using it as a solute of a solution containing a tungsten source, it is possible to obtain composite tungsten oxide particles in which impurities are suppressed from being mixed, so that it is preferably used.

  As the solution containing a tungsten source, an aqueous solution containing a tungsten source can be suitably used from the viewpoint of easy handling. Therefore, a water-soluble salt can be suitably used as the tungsten source. Ammonium paratungstate can be preferably used because it is easily dissolved in water and can easily form a solution containing a tungsten source using water as a solvent.

  As the solution containing the M element source, for example, a salt solution containing the M element can be used. The kind of the salt of the M element which is the M element source is not particularly limited, and for example, one or more kinds selected from carbonate, acetate, nitrate, hydroxide and the like of the M element can be used.

  As the solution containing the M element source, an aqueous solution containing the M element source can be suitably used from the viewpoint of easy handling. Therefore, a water-soluble salt can be suitably used as the salt of the element M.

  For example, when the element M is cesium, one or more selected from carbonates, acetates, nitrates, hydroxides, and the like can be used, but carbonates can be particularly preferably used. This is because cesium carbonate is easily dissolved in water.

  The ratio of the M element to 1 mol of tungsten in the obtained composite tungsten oxide, that is, the doping amount is determined by the ratio of the tungsten source and the M element source when forming the raw material mixed solution. Therefore, it can be controlled by, for example, the concentration of the solution containing the tungsten source, the concentration of the solution containing the M element source, and the like.

  The concentration of the tungsten source contained in the solution containing the tungsten source is not particularly limited. For example, it is preferable that the solution containing the tungsten source has a tungsten concentration of 0.12 mol / L or more and 120 mol / L or less. This is because, by setting the tungsten concentration of the solution containing the tungsten source to 0.12 mol / L or more, a sufficient production amount of the composite tungsten oxide particles per unit time can be secured. For example, a sufficient amount is collected by a filter or the like. This is because productivity can be increased. Further, by setting the tungsten concentration of the solution containing the tungsten source to 120 mol / L or less, it is possible to suppress the generated particles from agglomerating, and to suppress, for example, mixing of coarse composite tungsten oxide particles of several μm or more. Because.

  For example, when an aqueous solution of ammonium paratungstate is used as the solution containing the tungsten source, the concentration of ammonium paratungstate is 0.01 mol / L or more and 10 mol / L or less because ammonium paratungstate contains 12 tungsten atoms in the molecule. Is preferred.

  Also, the concentration of the M element contained in the solution containing the M element source is not particularly limited, and the desired composition of the composite tungsten oxide particles to be produced and the concentration of the tungsten source contained in the solution containing the tungsten source It can be selected according to the like.

  Any component other than the solution containing the tungsten source and the solution containing the M element source can be added to the raw material mixed solution. For example, ammonia can be added as a reducing agent to promote the reduction of the composite tungsten oxide particles. When the above-mentioned aqueous solution of ammonium paratungstate is used as the solution containing the tungsten source, the above-mentioned ammonia can be added, for example, to the aqueous solution of ammonium paratungstate.

  The size of the droplet formed in the droplet forming step is not particularly limited, but the diameter of the droplet is preferably 100 μm or less, more preferably 10 μm or less, and still more preferably 5 μm or less. By setting the diameter of the droplet to 100 μm or less, it is possible to prevent the obtained composite tungsten oxide particles from becoming coarse, and to obtain nanometer-order composite tungsten oxide particles. The lower limit of the size of the droplet formed in the droplet forming step is not particularly limited. However, since it is difficult to form an excessively small droplet and the productivity may be reduced, for example, the thickness is preferably 1 μm or more.

The droplets formed in the droplet forming step can be transported by, for example, a carrier gas and subjected to a heat treatment step or a temperature raising step.
(Heat treatment process)
In the heat treatment step, the object can be heat-treated at 500 ° C. or higher.

  The solvent contained in the droplets of the raw material mixed solution containing the tungsten source and the M element source, which are the objects to be processed, evaporates in the course of being heated to 500 ° C., and the tungsten source and the M element source are further decomposed. Then, in the decomposition process, tungsten reacts with the element M to form a composite tungsten oxide.

  When the droplet is heated in a heat treatment step or the like and the solvent contained in the droplet is water, it is estimated that the evaporation of the water occurs in a range of 50 ° C. or more and 120 ° C. or less. Further, it is estimated that decomposition of the tungsten source and the M element source occurs, for example, in a range of 120 ° C. or more and 500 ° C. or less.

  Then, it is considered that the tungsten and the M element react with each other at the process of decomposition of the tungsten source and the M element source and at a higher temperature to form a composite tungsten oxide.

  Therefore, in order to sufficiently promote the decomposition of the tungsten source or the M element source and to suppress the contamination of the composite tungsten oxide with impurities, the heat treatment is performed at a temperature higher than the decomposition temperature of the tungsten source or the M element source. Is preferred. As described above, it is considered that the decomposition of the tungsten source or the M element source usually occurs at 500 ° C. or lower. For this reason, in the heat treatment step, heat treatment can be performed on the droplet to be processed at 500 ° C. or higher.

  According to the study of the inventors of the present invention, the heat treatment temperature also affects the particle diameter of the obtained composite tungsten oxide particles. According to further studies by the inventors of the present invention, there is a tendency that as the heat treatment temperature increases, the particle diameter of the obtained composite tungsten oxide particles tends to decrease.

  An example will be described in which cesium-doped tungsten oxide particles are manufactured using an aqueous solution of ammonium paratungstate as a solution of a tungsten source and an aqueous solution of cesium carbonate as a solution of an M element source. In this case, when the heat treatment temperature was 500 ° C. or more and less than 1000 ° C., the particle diameter of the cesium-doped tungsten oxide particles was reduced from 100 nm to less than 1 μm. Further, when the temperature was further increased to 1000 ° C. or higher, the particle diameter of the cesium-doped tungsten oxide particles sometimes became less than 100 nm.

  This is presumably because when the heat treatment temperature is increased, thermal energy is used for sublimation of the generated composite tungsten oxide particles, and the sublimation causes the particles to pop, thereby obtaining particles having a fine particle diameter.

  It was confirmed that the same tendency was observed in the production of composite tungsten oxide particles having other compositions. For this reason, in order to obtain composite tungsten oxide particles, which are particularly fine nanoparticles, the heat treatment temperature is preferably set to 1000 ° C. or higher. That is, when the purpose is to obtain particularly fine nanoparticles, it is preferable that the object to be processed is heat-treated at 1000 ° C. or more in the heat treatment step.

  The upper limit of the heat treatment temperature of the object to be treated in the heat treatment step is not particularly limited. However, if the temperature is excessively increased, the cost of the heating device may be increased.

  In the case where the object is to produce composite tungsten oxide particles of nanoparticles having a particle diameter of less than 100 nm, in addition to heat-treating the object to be processed to 1000 ° C. or more in the heat treatment step, a heat treatment temperature of 1000 ° C. or more Is preferably 1 second or more, more preferably 3 seconds or more. This is because, by setting the heat treatment time at a heat treatment temperature of 1000 ° C. or more to 1 second or more, sufficient thermal energy is given to the generated composite tungsten oxide particles to cause sublimation, and for example, the particle diameter is more reliably reduced. This is because the nanoparticles can be smaller than 100 nm.

  The upper limit of the heat treatment time at a heat treatment temperature of 1000 ° C. or more is not particularly limited. However, if the heat treatment temperature is excessively long, the size of the heat treatment furnace becomes large, and the productivity may be reduced. Otherwise, it may fall into the inside of the piping of the reaction part and be blocked. Therefore, the heat treatment time at a heat treatment temperature of 1000 ° C. or more is preferably, for example, 100 seconds or less.

  The droplet formed in the droplet forming step is transported to an electric furnace or the like by a carrier gas, for example, and the above-described heat treatment step can be performed. Therefore, for example, by controlling the flow rate of the carrier gas or the like, the time of the heat treatment step can be adjusted.

  Note that the method for producing composite tungsten oxide particles of the present embodiment may further include a temperature raising step before the heat treatment step.

  In the temperature raising step, for example, a step of raising the temperature of a droplet to be processed to 500 ° C. can be performed. Further, for example, in the case where nanoparticles having a particularly small particle size are used as described above, the temperature raising step can be a step of raising the temperature of a droplet as an object to be processed to 1000 ° C.

  After the temperature raising step, a heat treatment can be performed in a heat treatment step. In the heat treatment step, the temperature can be raised to a predetermined temperature as needed.

  The time required for the temperature raising step is not particularly limited, and can be arbitrarily selected.

As described above, the solvent contained in the droplets of the raw material mixed solution containing the tungsten source and the M element source, which are the objects to be processed, evaporates in the course of increasing the temperature in the temperature increasing step. The source and the M element source decompose. Then, in the decomposition process, the tungsten reacts with the element M to form a composite tungsten oxide.
(Reduction process)
Particles obtained through the heat treatment step, specifically, composite tungsten oxide particles sometimes did not exhibit infrared absorption characteristics. Therefore, the inventors of the present invention have studied and found that by further performing a reduction treatment step of performing a reduction treatment on the composite tungsten oxide particles obtained through the heat treatment step, the composite tungsten oxide particles are infrared rays It has been found that absorption characteristics can be exhibited.

  For this reason, the method for producing composite tungsten oxide particles of the present embodiment can include a reduction treatment step of reducing the particles obtained in the heat treatment step in an atmosphere containing a reducing gas.

  The conditions for the reduction treatment are not particularly limited. However, when the composite tungsten oxide particles after the reduction treatment are analyzed by an X-ray diffraction pattern, the crystal structure does not change before and after the reduction treatment step, and metal tungsten or the like precipitates. It is preferable to select the conditions of the reduction treatment so as not to cause the reduction.

  In the reduction treatment step, the composite tungsten oxide obtained in the heat treatment step can be reduced by raising and lowering the temperature in a reducing atmosphere containing a reducing gas, that is, by performing a heat treatment.

  During the reduction treatment step, the composite tungsten oxide particles may be stirred or allowed to stand, and the handling of the composite tungsten oxide particles in the reduction treatment step can be appropriately selected, but is handled so that metal tungsten does not precipitate. It is preferable to select the conditions.

  The temperature of the reduction treatment (reduction treatment temperature) is higher than 400 ° C. and less than 700 ° C., preferably 500 ° C. or more and less than 700 ° C., and more preferably 600 ° C. or more and less than 700 ° C. After the temperature is raised from room temperature to the temperature of the reduction treatment, the temperature can be lowered again to room temperature.

  By setting the temperature of the reduction treatment to be higher than 400 ° C., the reduction treatment is performed on the composite tungsten oxide particles, and the infrared absorption characteristics can be more reliably exhibited. Further, by setting the temperature to be lower than 700 ° C., it is possible to prevent the composite tungsten oxide particles from being reduced to metallic tungsten.

The reducing atmosphere is preferably an atmosphere of a mixed gas of an inert gas such as argon and a reducing gas such as H ₂ gas (hydrogen gas), and the reducing gas is preferably H ₂ gas.

When H ₂ gas is used as the reducing gas, the content of H ₂ gas in the reducing atmosphere can be appropriately selected, but the content of H ₂ gas is preferably in the range of 0.1% to 10% by volume. Preferably, the range is 2% or more and 10% or less. Care must be taken when reducing in an atmosphere containing only a reducing gas, because the reduction reaction may proceed excessively and metal tungsten may be deposited.

  It is desirable that the time of the reduction treatment step be 30 minutes or more over the entire time from temperature rise to temperature fall. The upper limit of the time of the reduction treatment step is not particularly limited, and for example, it is preferable to select by conducting a preliminary test or the like so that the reduction does not proceed excessively. Here, the total time from the temperature rise to the temperature decrease means the time from the start of the temperature rise from the room temperature to the time when the temperature reaches the reduction treatment temperature and is cooled to the room temperature. In addition, it is preferable that the composite tungsten oxide particles be placed in the above-described reducing atmosphere for such a time.

  By performing the reduction treatment step in this way, an undesired heterophase of the composite tungsten oxide particles obtained after the heat treatment step can be converted into a target composite tungsten oxide phase. And the deficiency rate of tungsten atoms in the tungsten atom site in the composite tungsten oxide phase of the composite tungsten oxide particles can be reduced, that is, the occupancy rate of tungsten atoms can be increased.

For example, in Examples 1 and 2 described below, it is presumed that the reaction represented by the following chemical formulas (1) and (2) has progressed in the reduction treatment step. As shown by the following chemical formulas (1) and (2), for example, in Examples 1 and 2 in which the element M is Cs, a heterogeneous Cs ₂ O phase, (H ₂ O) It is estimated that the reaction in which the _0.33 WO ₃ phase and the like disappear, the tungsten atoms are reduced, Cs penetrates into the Cs atom sites in the composite tungsten oxide particles, and the tungsten deficiency is reduced simultaneously. Note that Cs _x WO ₃ in the following chemical formula (1) means a compound in which Cs, which is an M element, is deficient from the target composition.

The tungsten atom occupancy in the tungsten atom sites in the composite tungsten oxide phase of the composite tungsten oxide particles obtained after the reduction treatment step is preferably high, for example, preferably 90% or more, and more preferably 95% or more. Is more preferred. This is because, as described above, the higher the occupancy of tungsten atoms in the tungsten atom sites in the composite tungsten oxide phase, the lower the heterophase, and the greater the proportion of the composite tungsten oxide phase that can exhibit infrared absorption characteristics. This is because it can be done. The upper limit of the occupancy of W atoms in the tungsten atom sites in the composite tungsten oxide phase of the composite tungsten oxide particles is not particularly limited, but can be 100% or less.

  The occupancy of tungsten atoms in the tungsten atom sites in the composite tungsten oxide phase of the composite tungsten oxide particles can be determined by performing Rietveld analysis on the XRD pattern of the composite tungsten oxide particles as a sample. The sum of the occupancy rate and the deficiency rate of tungsten atoms at the tungsten atom site is 100%.

  In addition, the deficiency of the M element or the tungsten atom in the composite tungsten oxide particles can be confirmed by STEM observation. FIGS. 12 (A), 12 (B), and 12 (D), which are STEM observation results of the composite tungsten oxide particles obtained in Reference Example 1 described later, and Example 2 in which the reduction process was performed. 20 (A), FIG. 20 (B), and FIG. 20 (D) which are STEM observation results of the obtained composite tungsten oxide particles. It can be confirmed that there is no defect.

  As described above, by performing the reduction treatment step, the hetero-phase that does not significantly contribute to the infrared absorption characteristics can be used as the target phase capable of exhibiting the infrared absorption characteristics. It becomes possible to obtain particles.

By eliminating the deficiency of the M element and the tungsten atom in the composite tungsten oxide particles that have undergone the reduction treatment step, high infrared absorption characteristics can be exhibited.
[Composite material production equipment, reduction treatment equipment]
A configuration example of a composite material manufacturing apparatus and a reduction processing apparatus that can be suitably used in the method for manufacturing composite tungsten oxide particles of the present embodiment will be described below.
(Composite material manufacturing equipment)
FIG. 1 is a diagram schematically illustrating a composite material manufacturing apparatus 10.

  The composite material manufacturing apparatus 10 can include a droplet forming unit 11, a transporting unit 12, a reaction unit 13, and a collecting unit 14, and perform the droplet forming step, the temperature increasing step, and the heat treatment step described above. Can be implemented.

  As shown in FIG. 1, it is preferable that the droplet forming section 11, the transport section 12, the reaction section 13, and the recovery section 14 are connected by a pipe.

  Ancillary equipment can be connected to the droplet forming unit 11 as needed. For example, a first storage unit 151 for storing a solution containing a tungsten source, which is a raw material solution, and a second storage unit 152 for storing a solution containing a M element source can be connected to the droplet forming unit 11. . For example, pumps 151A and 152A are provided in the pipe between the first storage unit 151 and the droplet forming unit 11 and the pipe between the second storage unit 152 and the droplet forming unit 11, respectively. Each solution can be supplied to the droplet forming unit 11 at a desired flow rate. Further, a carrier gas tank 16 containing a carrier gas for transporting the droplets formed by the droplet forming unit 11 to the transport unit 12 or the like can be connected.

  The solution containing the tungsten source and the solution containing the M element source supplied to the droplet forming unit 11 from the first storage unit 151 and the second storage unit 152 are supplied to the droplet forming unit in the apparatus shown in FIG. The mixture is mixed at the upper part in 11 to form a raw material mixed solution. Next, droplets are formed by the droplet forming unit 11 using the formed raw material mixed solution.

  The droplet forming unit 11 shown in FIG. 1 shows an example of an ultrasonic spraying device. For example, ultrasonic waves are irradiated to the raw material mixed solution by the ultrasonic irradiation unit 111 to form droplets. .

  As described above, the carrier gas tank 16 filled with a carrier gas can be connected to the droplet forming unit 11, and the carrier gas is supplied from the carrier gas tank 16 to the droplet forming unit 11. The droplet formed by the droplet forming unit 11 is transported by the carrier gas and supplied to the reaction unit 13 via the transport unit 12.

  The transport unit 12 connects the droplet forming unit 11 and the reaction unit 13, and can supply the droplet formed by the droplet forming unit 11 to the reaction unit 13. It is preferable that the droplets passing through the transport unit 12 are preliminarily heated so that the inside of the transport unit 12 can be heated so that the temperature of the reaction unit 13 does not decrease. Specifically, for example, it is preferable that a heater is wound around the outside of the transporting section 12 and installed, and the temperature inside the transporting section 12 is maintained at 30 ° C. or more and 80 ° C. or less.

  In the reaction section 13, the above-described temperature raising step and heat treatment step can be performed. For this reason, the reaction section 13 can have, for example, a heat-resistant pipe 131 and a heater 132 for heating the pipe 131 as shown in FIG.

  As the pipe 131, for example, a ceramic pipe can be used.

  The length of the reaction section 13 is not particularly limited, and is preferably selected so that the reaction section 13 can be heated to a predetermined temperature in the temperature raising step and the heat treatment step, and the time for the heat treatment step can be sufficiently secured.

  The length of the pipe 131 of the reaction section 13 is preferably 1 m or more from the viewpoint of heating to a predetermined temperature and sufficiently securing the time of the heat treatment step. The upper limit of the length of the pipe 131 is not particularly limited. However, if the length is excessively long, a large amount of carrier gas is required, and the size of the apparatus is increased.

  The diameter (inner diameter) of the pipe 131 is not particularly limited, but is preferably 2 cm or more from the viewpoint of productivity. The upper limit of the diameter (inner diameter) of the pipe 131 is not particularly limited, but is preferably selected so that the temperature difference between the center part and the wall part does not become excessively large. The diameter of the pipe 131 is, for example, 20 cm or less. Preferably, there is.

  The pipe 131 of the reaction section 13 usually has a temperature gradient along its longitudinal direction. For example, the temperature at the reaction section inlet 131A side is low, and the temperature rises toward the reaction section outlet 131B.

  For this reason, it is preferable to set various conditions so that a temperature region where the temperature becomes 500 ° C. or higher can be formed in the vicinity of the reaction section outlet 131B.

  In particular, when the object to be processed is heat-treated at a temperature of 1000 ° C. or more in the heat treatment step described above, various conditions are set so that a temperature region where the temperature becomes 1000 ° C. or more can be formed near the reaction part outlet 131B. Is preferred. Further, in the heat treatment step, for example, when the heat treatment time at a temperature of 1000 ° C. or more is 1 second or more, the time for the object to pass through the temperature region of 1000 ° C. or more in the reaction unit 13 is 1 second or more. Therefore, it is preferable to set various conditions. Specifically, for example, it is preferable to measure the temperature distribution in the pipe 131 in advance and adjust the supply speed of the carrier gas and the like.

  The recovery unit 14 can recover the composite tungsten oxide particles generated in the reaction unit 13. The configuration of the recovery unit 14 is not particularly limited, and can be selected according to the particle size of the composite tungsten oxide particles to be manufactured. As the collection unit 14, for example, various filters can be used. Alternatively, an electrostatic collector can be used. Note that a heating unit such as a heater may be disposed around the collection unit 14 and heated so that the liquid or the like contained in the solution containing the tungsten source or the like does not precipitate in the collection unit 14.

It is preferable that the inside of the composite material manufacturing apparatus 10 is sealed, and a gas flow is configured so that gas flows into the droplet forming unit 11 from the carrier gas tank 16 and flows out of the recovery unit 14.
(Reduction treatment device)
In the reduction processing device, the above-described reduction processing step can be performed.

  The reduction treatment device is not particularly limited as long as it can be configured to perform the reduction treatment step described above. For example, a container for storing composite tungsten oxide particles which are particles obtained by the above-described composite material manufacturing apparatus, a gas pipe for supplying a mixed gas as a reducing atmosphere into the container, and a heat source for heating the container Should be provided.

  Note that a mixed gas serving as a reducing atmosphere may be introduced and exhausted into the container, and the composite tungsten oxide particles to be processed may be placed under a gas flow of the mixed gas. In this case, a supply pipe for mixed gas and an exhaust pipe can be provided as gas pipes so that such an airflow can be formed.

  Further, a stirring blade for stirring the composite tungsten oxide particles in the container may be used in combination.

  FIG. 2 is a diagram schematically illustrating a configuration example of the reduction processing apparatus, and is a cross-sectional view of a plane passing through the central axis of the reaction tube 21 of the reduction processing apparatus 20.

  The reduction treatment apparatus 20 is a horizontal tubular furnace, and can be used by attaching a gas introduction pipe (not shown) to one port 21A of the reaction tube 21 and a gas exhaust pipe (not shown) to the other port 21B of the tubular furnace. . Then, by supplying the mixed gas to be the reducing atmosphere from the one port 21A side, the inside of the reaction tube 21 can be set to the reducing atmosphere.

  A heater 22 can be provided around the reaction tube 21. The composite tungsten oxide particles are placed in a ceramic container 23 such as a boat and placed in a position corresponding to the heater 22 in the reaction tube 21 of the tubular furnace. Can be placed.

  By using such a reduction treatment device 20 and setting the inside of the reaction tube 21 to a reduction atmosphere and heating the reaction tube 21 to a desired temperature by the heater 22, the reduction treatment of the composite tungsten oxide particles 24 placed in the container 23 can be performed.

  According to the method for producing composite tungsten oxide particles of the present embodiment described above, it is possible to use equipment with a low introduction cost such as a droplet forming unit and a heater. Further, composite tungsten oxide particles, which are near-infrared absorbing particles, can be directly obtained without going through a process such as pulverization, and the number of steps can be reduced. Therefore, composite tungsten oxide particles can be easily produced.

  Furthermore, by performing the reduction treatment step, infrared absorption characteristics can be reliably exhibited, and even if a different phase is contained in the composite tungsten oxide particles synthesized in the heat treatment step, the different phase can be reduced or removed. Therefore, the method for producing composite tungsten oxide particles of the present embodiment has high industrial utility value.

Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to these examples.
[Reference Example 1]
Using the composite material manufacturing apparatus 10 shown in FIG. 1, Cs _0.32 WO ₃ particles were manufactured as composite tungsten oxide particles, and evaluation was performed. Hereinafter, specific conditions will be described.

  The composite material manufacturing apparatus 10 illustrated in FIG. 1 includes a droplet forming unit 11, a transporting unit 12, a reaction unit 13, and a collecting unit 14, and includes a droplet forming unit 11, a transporting unit 12, , The reaction unit 13 and the recovery unit 14 are connected by piping.

  The droplet forming unit 11 has a first storage unit 151 for storing a solution containing a tungsten source, which is a raw material solution, a second storage unit 152 for storing a solution containing a M element source, and a liquid formed by the droplet forming unit 11. A carrier gas tank 16 containing a carrier gas for transporting the droplets to the transport unit 12 and the like was connected.

First, as a solution containing a tungsten source, ammonium paratungstate (ATP) represented by (NH ₄ ) ₁₀ (W ₁₂ O ₄₁ ) · 5H ₂ O (purity: 88 to 90%, manufactured by Kanto Chemical Co.) and ultrapure An aqueous solution of 10 mmol / L ammonium paratungstate was prepared using water. The aqueous solution of ammonium paratungstate was placed in the first storage unit 151, and was configured to be continuously supplied by the pump 151A to the droplet forming unit 11 connected to the first storage unit 151 by a pipe.

  As a solution containing the M element source, a cesium carbonate aqueous solution of 19.2 mmol / L was prepared using cesium carbonate (manufactured by Sigma-Aldrich) and ultrapure water. Then, the cesium carbonate aqueous solution is placed in the second storage section 152, and is configured to be continuously supplied by the pump 152A to the droplet forming section 11 connected to the second storage section 152 by a pipe.

  As described above, the respective solutions are supplied at a constant flow rate from the first storage unit 151 and the second storage unit 152 to the droplet forming unit 11 via the pipes by the pumps 151A and 152A, and It is configured such that the two solutions are mixed at the upper portion inside to form a raw material mixed solution. Then, the supply rate and the concentration of each solution were adjusted so that the ratio of the number of moles of cesium to 1 mole of tungsten in the raw material mixed solution formed in the droplet forming section 11 was 0.32. The raw material mixed solution contains 5 mmol / L ammonium paratungstate and 9.6 mmol / L cesium carbonate.

  A carrier gas tank 16 was connected to the droplet forming unit 11, and an air cylinder was used as the carrier gas tank 16. During the production of the composite tungsten oxide particles, air was supplied as a carrier gas to the droplet forming section 11 at a flow rate of 5 L / min.

  The droplet forming unit 11 is provided with an ultrasonic irradiation unit 111, which irradiates the raw material mixed solution formed by the droplet forming unit 11 with ultrasonic waves to form droplets having a diameter of 1 μm or more and 5 μm or less. The output of the ultrasonic wave was adjusted so that it could be formed. In addition, as the droplet forming part 11, an ultrasonic nebulizer (model: NE-U17 ultrasonic transmission frequency 1.7 MHz, manufactured by OMRON Healthcare Co., Ltd.) was used.

  And the heater was arrange | positioned outside the transport part 12, and it comprised so that the temperature inside the transport part 12 might be maintained at 70 degreeC.

  The reaction section 13 is provided with a pipe 131, and a cylindrical pipe made of ceramic having a length of 1.3 m and an inner diameter of 28.5 mm is used as the pipe 131.

  The reaction section 13 is configured to be heated from outside the pipe 131 by a heater 132, and the temperature is set so that the temperature increases from the reaction section inlet 131A toward the reaction section outlet 131B.

  In the present reference example, the temperature of the heater 132 was set such that the maximum temperature near the outlet 131B of the reaction section was 1200 ° C. FIG. 3 shows the temperature distribution of the reaction section used in this example. FIG. 3 shows a temperature distribution curve obtained by measuring the temperature with a thermocouple every 2 cm along the length direction of the pipe 131. In addition, the temperature of a part of the pipe between the pipe 131 and the collection unit 14 is also measured. The horizontal axis in FIG. 3 indicates the position (distance) x (cm) of the measurement point along the length direction of the pipe 131 from the reaction unit inlet 131A when the position of the reaction unit inlet 131A is set to 0. I have. The vertical axis in FIG. 3 indicates the furnace temperature at each position in the length direction of the pipe 131.

  As shown in FIG. 3, it was confirmed that the temperature distribution was formed such that the temperature gradually increased from the reaction section inlet 131A toward the reaction section outlet 131B, and a temperature region where the temperature became 1000 ° C. or higher was also set. it can.

  A bag filter was arranged in the collecting section 14, and the temperature rising step and the heat treatment step were completed in the reaction section 13, so that the formed composite tungsten oxide particles could be collected. In order to collect the powder in a dried state, the periphery of the glass filter was lined with a glass fiber tape and heated to 120 ° C. If not heated, evaporated droplets may be deposited.

  Under the above conditions, composite tungsten oxide particles were produced.

  Specifically, in the droplet forming section 11, droplets of a raw material mixed solution of an aqueous solution of ammonium paratungstate and an aqueous solution of cesium carbonate were formed (droplet forming step), and the furnace body temperature was set to 1200 ° C. The droplets were supplied to the reaction unit 13 by a carrier gas, and a temperature raising step and a heat treatment step were performed. Since the inside of the pipe 131 of the reaction unit 13 has the temperature distribution shown in FIG. 3 and the flow rate of the carrier gas is set to 5 L / min, the temperature of the droplet is raised to 1000 ° C. (temperature raising step), The heat treatment is performed at the above heat treatment temperature for 3.0 seconds (heat treatment step).

The following evaluation was performed on the composite tungsten oxide particles collected by the collection unit 14.
(1) Powder X-ray diffraction The obtained composite tungsten oxide particles were subjected to measurement of a powder X-ray diffraction pattern (XRD pattern) using a powder X-ray diffractometer (Model: D2 PHASER manufactured by Bruker). The powder X-ray diffraction pattern was measured at a tube voltage of 40 kV and a tube current of 30 mA using CuKα radiation as a radiation source.

The obtained XRD pattern is shown in FIG. As shown in FIG. 4A, from the XRD pattern, the obtained composite tungsten oxide particles show that the 2θ peak of the Cs ₂ O phase is around 26 °, and (H ₂ O) _{0.33 is around} 18 °. Although the peak of WO ₃ phase was confirmed, it was confirmed that the single phase was almost Cs _0.32 WO ₃ . The proportion of Cs _0.32 WO ₃ phase calculated by Rietveld analysis was 81% by mass. FIG. 4B shows the ratio of the Cs _0.32 WO ₃ phase, the Cs ₂ O phase, and the (H ₂ O) _0.33 WO ₃ phase.

Also, when the lattice constant of Cs _0.32 WO ₃ phase, which is a composite tungsten oxide, was calculated by Rietveld analysis, a = 7.38 ° and c = 7.71 °. FIG. 5 shows the relationship between the lattice constant a axis and the lattice constant c axis.

Further, in the Rietveld analysis, the calculation was performed using the occupancy of tungsten atoms at tungsten atom sites in the Cs _0.32 WO ₃ phase of the composite tungsten oxide particles as a parameter. FIG. 6 shows the occupancy of tungsten atoms in the tungsten atom sites in the Cs _0.32 WO ₃ phase calculated by Rietveld analysis. The occupancy of tungsten atoms in the tungsten atom sites in the Cs _0.32 WO ₃ phase in the particles was 60%. Since the sum of the occupancy and the vacancy rate is 100%, the value obtained by subtracting the occupancy value from 100% is interpreted as the vacancy rate of tungsten atoms at the tungsten atom sites in the Cs _0.32 WO ₃ phase. . That is, the defect rate of tungsten atoms at the tungsten atom sites in the Cs _0.32 WO ₃ phase in the present particles is 40%.
(2) Observation of SEM image The obtained composite tungsten oxide particles were observed using a field emission scanning electron microscope (FE-SEM: Model S-5200 manufactured by Hitachi High-Technologies Corporation). Was. The observation was performed with an applied voltage of 5 to 20 kV.

  FIGS. 7A and 7B show the obtained SEM images. FIG. 7B is an SEM image showing a part of FIG. 7A further enlarged.

From the SEM images shown in FIGS. 7A and 7B, as the obtained composite tungsten oxide particles, coarse particles are partially observed, but fine particles of 200 nm or less are obtained. I was able to confirm that.
(3) TEM Image Observation Obtained composite tungsten oxide particles were observed using a transmission electron microscope (TEM: Transmission Electron Microscope, model: JEM-3000F, manufactured by JEOL Ltd.). The observation was performed at an applied voltage of 297 kV.

  FIG. 8 shows the obtained TEM image.

  As shown in FIG. 8, it was confirmed from the TEM image that fine particles of 200 nm or less were obtained. It was also confirmed that square particles having a size of several tens nm were obtained.

  FIG. 9 shows a mapping image using TEM / EDS. 9 (A) is a TEM observation image, FIG. 9 (B) is a Cs image, FIG. 9 (C) is a W image, and FIG. 9 (D) is an O mapping image. 9 (B) to 9 (D) indicate the presence of each element. As is clear from the comparison of FIGS. 9A to 9D, it can be confirmed that Cs, W, and O are substantially uniformly dispersed throughout the obtained composite tungsten oxide particles. Further, from FIG. 9B, it was confirmed that Cs was present inside the fine particles.

(4) XPS measurement FIGS. 10A and 10B show measurement results of the spectrum of 4f of W atom and 3d of Cs atom using XPS. Note that ESCA-3400 manufactured by Shimadzu Corporation was used for the measurement. The second embodiment also uses a simultaneous device. FIG. 10A shows the result of W atom 4f, and FIG. 10B shows the result of Cs 3d. The measurement result of W atom at 4f has peaks at 37.8 eV and 35.7 eV, and it is considered that these peaks are derived from W ⁶⁺ .

  On the other hand, in the case of Cs 3d, peaks derived from CsOH (724 ± 0.2 eV) and Csmetal (726 ± 0.3 eV) are considered, but the present composite tungsten oxide particles have a peak at 723.9 eV. Was confirmed. This is monovalent. From the above results, it is considered that W and Cs in the composite tungsten oxide particles prepared in the present reference example are both oxidized.

FIG. 11 shows the result of the XPs spectrum of 1 s of the O atom of the composite tungsten oxide particles obtained in Reference Example 1. When the obtained spectrum was subjected to peak separation, the spectrum shift of the O atom bonded to the W atom (WO ₃ in the figure) and the shift of the spectrum caused by the attachment of the H atom to the O atom bonded to the W atom. (OH, OH ₂ in the figure) was confirmed. The shift of the spectrum due to Si atoms (SiO ₂ in the figure) is due to impurities adhering to the composite tungsten oxide particles obtained in Reference Example 1.

(5) STEM observation FIG. 12A, FIG. 12B and FIG. 12D show high-angle angular dark-field images (HAADF) observed using JEOL STEM (model: JEM-ARM200F). An image is shown. In the HAADF image, the heavier atoms show brighter contrast, so the brightest contrast is W, the brightest contrast is Cs, and O cannot be confirmed.

  FIGS. 12A and 12B are HAADF images at the time of 001 incidence, and FIG. 12B is an enlarged view of the square frame of FIG. A streak-like defect in the directions of 100, 010, and 110 was confirmed at the location of the arrow in FIG. This streak-like defect exists along a row in which W and Cs are alternately arranged. FIG. 12C shows the contrast within the defect surrounded by the frame in FIG. The contrast was found to be missing at the W site. FIG. 12D shows a HAADF image at 010 incidence.

  Since a defect of about 10 nm can be confirmed even when observed from a direction different by 90 °, it is considered that the present W defect exists in a planar shape. In addition, the schematic diagrams of the crystal structures in FIGS. 12B and 12D show surfaces on which STEM observation is performed. Note that the defects observed in FIGS. 12A, 12B, and 12D were similarly observed in other visual fields.

(6) XAFS Measurement FIG. 13 shows the result of performing XAFS measurement using the BL5S1 beam line at the Ichisynchrotron Light Center and calculating the radial distribution function from tungsten. The peak position was 1.35 °. Although this distribution is a spatial average, four oxygens are located in the c-plane around W and two oxygen atoms are located in the c-axis direction, so that the influence of oxygen in the c-plane is strong. . Although this peak position is known to be shorter than the actual interatomic distance, it can be compared with the result of Example 2 in which the reduction step is further performed. The reason why the length is shorter than that of Example 2 is considered that W in the c-plane direction adjacent to the W defect strongly attracts oxygen therebetween due to the W defect. This is consistent with the reason that the value of the a-axis is shorter than that of the second embodiment.

[Reference Example 2]
In Reference Example 2, composite tungsten oxide particles were prepared in the same manner as in Reference Example 1, except that the temperature of the heater 132 was set such that the maximum temperature near the outlet 131B of the reaction section was 1000 ° C. The droplets are heated to 1000 ° C. in the reaction section 13 (heat-up step) and heat-treated at a heat treatment temperature of 1000 ° C. or higher for 3.0 seconds (heat-treatment step).

The powder X-ray diffraction pattern (XRD pattern) of the composite tungsten oxide particles synthesized in this reference example was measured under the same conditions as in reference example 1. FIG. 14 shows the obtained XRD pattern. As shown in FIG. 14, it was confirmed that the XRD pattern of the obtained composite tungsten oxide particles matched the Cs _0.32 WO ₃ phase of JCPDS81-1244 shown in FIG. FIG. 14 also shows the XRD pattern of Reference Example 1 for comparison.

  SEM observation was performed on the obtained composite tungsten oxide particles in the same manner as in Reference Example 1. The obtained SEM image is shown in FIG. As shown in FIG. 15A, it was confirmed that the obtained composite tungsten oxide particles contained hexagonal particles of about 100 nm to 600 nm and fine particles of about 20 nm. For comparison, FIG. 15E also shows an SEM image of Reference Example 1.

[Reference Example 3]
In Reference Example 3, composite tungsten oxide particles were prepared in the same manner as in Reference Example 1, except that the temperature of the heater 132 was set so that the maximum temperature near the outlet 131B of the reaction section was 1100 ° C. The droplets are heated to 1000 ° C. in the reaction section 13 (heat-up step) and heat-treated at a heat treatment temperature of 1000 ° C. or higher for 3.0 seconds (heat-treatment step).

The powder X-ray diffraction pattern (XRD pattern) of the composite tungsten oxide particles synthesized in this reference example was measured under the same conditions as in reference example 1. FIG. 14 shows the obtained XRD pattern. As shown in FIG. 14, it was confirmed that the XRD pattern of the obtained composite tungsten oxide particles matched the Cs _0.32 WO ₃ phase of JCPDS81-1244 shown in FIG.

  SEM observation was performed on the obtained composite tungsten oxide particles in the same manner as in Reference Example 1. The obtained SEM image is shown in FIG. As shown in FIG. 15B, it was confirmed that the obtained composite tungsten oxide particles contained hexagonal particles of about 50 nm to 300 nm and fine particles of about 20 nm.

[Reference Example 4]
In Reference Example 4, composite tungsten oxide particles were prepared in the same manner as in Reference Example 1, except that the temperature of the heater 132 was set so that the maximum temperature near the outlet 131B of the reaction section was 1300 ° C. The droplets are heated to 1000 ° C. in the reaction section 13 (heating step), and are subjected to a heat treatment at a heat treatment temperature of 1000 ° C. or higher for 3.6 seconds (heat treatment step).

The powder X-ray diffraction pattern (XRD pattern) of the composite tungsten oxide particles synthesized in this reference example was measured under the same conditions as in reference example 1. FIG. 14 shows the obtained XRD pattern. As shown in FIG. 14, the XRD pattern of the obtained composite particles of tungsten oxide, the composite tungsten oxide particles according is, JCPDS81-1244 _{Cs 0.32} WO ₃ phase or shown together in Figure 14, Cs It was confirmed that Cubic-HWO _3.5 phase was contained in addition to the ₂ O phase.

  SEM observation was performed on the obtained composite tungsten oxide particles in the same manner as in Reference Example 1. The obtained SEM image is shown in FIG. As shown in FIG. 15C, it was confirmed that the obtained composite tungsten oxide particles contained particles having a square shape of about 20 nm to 80 nm.

[Reference Example 5]
In Reference Example 5, composite tungsten oxide particles were prepared in the same manner as in Reference Example 1, except that the temperature of the heater 132 was set so that the maximum temperature near the outlet 131B of the reaction section was 1400 ° C. The droplets are heated to 1000 ° C. in the reaction section 13 (heating step), and are subjected to a heat treatment at a heat treatment temperature of 1000 ° C. or higher for 3.6 seconds (heat treatment step).

The powder X-ray diffraction pattern (XRD pattern) of the composite tungsten oxide particles synthesized in this reference example was measured under the same conditions as in reference example 1. FIG. 14 shows the obtained XRD pattern. As shown in FIG. 14, the XRD pattern of the obtained composite particles of tungsten oxide, the composite tungsten oxide particles according is, JCPDS81-1244 _{Cs 0.32} WO ₃ phase or shown together in Figure 14, Cs It was confirmed that Cubic-HWO _3.5 phase was contained in addition to the ₂ O phase.

  SEM observation was performed on the obtained composite tungsten oxide particles in the same manner as in Reference Example 1. The obtained SEM image is shown in FIG. As shown in FIG. 15D, it was confirmed that the obtained composite tungsten oxide particles contained particles having a square shape of about 20 nm to 120 nm.

[Example 1]
The composite tungsten oxide particles synthesized in Reference Example 1 were subjected to a reduction treatment using a reduction treatment apparatus 20 shown in FIG. 2 at a reduction treatment temperature of 450 ° C. (reduction treatment step).

  The reduction treatment device 20 is a horizontal tubular furnace in which the composite tungsten oxide particles synthesized in Reference Example 1 are put in a container 23 which is a ceramic boat, and the container 23 is set at the highest temperature in the reaction tube 21, It was arranged at a position where the reduction treatment temperature was reached.

A gas inlet pipe (not shown) was attached to one port 21A of the reaction tube 21, and a gas exhaust pipe (not shown) was attached to the other port 21B of the tubular furnace. Then, a mixed gas containing argon as an inert gas and H ₂ gas as a reducing gas was supplied from one of the ports 21A side to make the inside of the reaction tube 21 a reducing atmosphere. The content of the H ₂ gas in the mixed gas was 5% by volume.

  A heater 22 is provided around the reaction tube 21 and the temperature is raised from room temperature at a rate of temperature increase of 400 ° C./h. Reduction treatment was performed by cooling to room temperature.

FIG. 4A shows an XRD pattern of the obtained composite tungsten oxide particles. It was confirmed that the intensity of the diffraction peak of the Cs ₂ O phase, which is a different phase, was weaker than in the case of Reference Example 1. When the ratio of Cs _0.32 WO ₃ phase was calculated by Rietveld analysis, it was 92.26% by mass, and the ratio of (H ₂ O) _0.33 WO ₃ phase was 2.46% by mass, that of Cs ₂ O phase. The ratio was 5.28% by mass. FIG. 4B shows the ratio of the Cs _0.32 WO ₃ phase, the Cs ₂ O phase, and the (H ₂ O) _0.33 WO ₃ phase.

Also, when the lattice constant of Cs _0.32 WO ₃ phase, which is a composite tungsten oxide, was calculated by Rietveld analysis, the a-axis was 7.39 ° and the c-axis was 7.68 °. FIG. 5 shows the relationship between the lattice constant a axis and the lattice constant c axis.

FIG. 6 shows the occupancy of tungsten atoms in the tungsten atom sites in the Cs _0.32 WO ₃ phase of the composite tungsten oxide particles, calculated by Rietveld analysis. The occupancy of tungsten atoms in the tungsten atom sites in the Cs _0.32 WO ₃ phase in the particles was 95.0%.
[Example 2]
The composite tungsten oxide synthesized in Reference Example 1 was subjected to a reduction treatment at 650 ° C. using the reduction treatment device 20 shown in FIG. 2 (reduction treatment step).

  The reduction treatment step was performed in the same manner as in Example 1 except that the reduction treatment temperature was 650 ° C.

(1) Powder X-ray Diffraction Measurement FIG. 4A shows an XRD pattern of the obtained composite tungsten oxide particles. It was confirmed that the diffraction peak of the Cs ₂ O phase, which was the hetero phase detected in Reference Example 1 and Example 1, disappeared and precipitated as Cs _0.32 WO ₃ single phase particles. The proportion of the Cs _0.32 WO ₃ phase calculated by Rietveld analysis is 97.4% by mass, and the proportion of the (H ₂ O) _0.33 WO ₃ phase is 1.55% by mass, the proportion of the Cs ₂ O phase. The ratio was 1.05% by mass. FIG. 4B shows the ratio of the Cs _0.32 WO ₃ phase, the Cs ₂ O phase, and the (H ₂ O) _0.33 WO ₃ phase.

When the lattice constant of Cs _0.32 WO ₃ phase, which is a composite tungsten oxide, was calculated by Rietveld analysis, the a-axis was 7.42 ° and the c-axis was 7.59 °. FIG. 5 shows the relationship between the lattice constant a axis and the lattice constant c axis.

FIG. 6 shows the occupancy of tungsten atoms in the tungsten atom sites in the Cs _0.32 WO ₃ phase of the composite tungsten oxide particles, calculated by Rietveld analysis. The occupancy of tungsten atoms in the tungsten atom sites in the Cs _0.32 WO ₃ phase in the particles was 100%.

  In this example, it is presumed that the following reaction proceeded with the reduction treatment.

(2) SEM Image Observation The observed SEM images are shown in FIGS. 16 (A) and 16 (B). FIG. 16B is a SEM image showing a part of FIG. 16A further enlarged.

(3) Observation of TEM image FIG. 17 shows a mapping image of the obtained composite tungsten oxide particles using TEM / EDS. 17A is a TEM observation image, FIG. 17B is a Cs image, FIG. 17C is a W image, and FIG. 17D is an O mapping image. 17 (B) to 17 (D) indicate the presence of each element. As is clear from the comparison of FIGS. 17A to 17D, it can be confirmed that Cs, W, and O are substantially uniformly dispersed throughout the obtained composite tungsten oxide particles. In addition, from FIG. 17B, it was confirmed that Cs was also present inside the fine particles.

As in the case of Reference Example 1, it was confirmed that square particles having a particle size of several tens nm were obtained. In this example, it was confirmed that sintering and agglomeration of the particles did not proceed even after the reduction treatment was performed.
(4) XPS Measurement FIG. 18 shows the measurement results of the spectrum of 4f of W atoms and 3d of Cs atoms using XPS of the composite tungsten oxide particles obtained in Example 2. FIG. 18A shows the result of 4f of W atom, and FIG. 18B shows the result of 3d of Cs. It is considered that the peaks at 37.6 eV and 35.9 eV in the measurement result of W at 4f shown in FIG. 18A are derived from W ⁶⁺ , and the peaks at 35.0 eV and 33.6 eV are derived from W ^5+. . That is, it was confirmed that W in the particles was partially reduced as compared with the case of Reference Example 1 shown in FIG. On the other hand, in the case of Cs, it was confirmed that it had a peak at 724.0 eV which is almost the same as CsOH (724 ± 0.2 eV). That is, it was confirmed that the valence of Cs after the reduction treatment step was monovalent.

FIG. 19 shows an XPS spectrum result of 1 s of O atoms of the composite tungsten oxide particles obtained in Example 2. When the obtained spectrum was subjected to peak separation, the spectrum shift of the O atom bonded to the W atom (WO ₃ in the figure) and the shift of the spectrum caused by the attachment of the H atom to the O atom bonded to the W atom. (OH, OH ₂ in the figure) was confirmed. The shift in the spectrum due to Si atoms (SiO ₂ in the figure) is due to the fact that impurities were attached to the composite tungsten oxide particles obtained in Example 2.

(5) STEM observation In FIG. 20 (A), FIG. 20 (B), and FIG. 20 (D), high-angle angular dark-field images (HAADF) observed using JEOL STEM (model: JEM-ARM200F). An image is shown. In the HAADF image, the heavier atoms show a brighter contrast, so the brightest contrast is W, the brightest contrast is Cs, and O cannot be confirmed. FIGS. 20 (A) and 20 (B) are HAADF images at the time of incidence of 001, and no defect was observed in the particles. FIG. 20C shows the contrast of the portion surrounded by the frame in FIG. It was confirmed that although the W atom and the Cs atom had a slight contrast difference, their intensities were almost the same. FIG. 20D shows a HAADF image at 010 incidence. No defect was confirmed even when observed from a direction different from 90 °. Note that the schematic diagram of the crystal structure shown in FIGS. 20B and 20D shows a surface on which STEM observation is performed. In addition, in the STEM observation of the composite tungsten oxide particles according to Example 2, no defect was confirmed even when observing another visual field.

(6) XAFS Measurement FIG. 13 shows the result of performing XAFS measurement using the BL5S1 beam line at the Ichisynchrotron Light Center and calculating the radial distribution function from tungsten. The peak position was 1.41 °.

[Comparative Example 1]
The composite tungsten oxide synthesized in Reference Example 1 was subjected to a reduction treatment at 300 ° C. using the reduction treatment device 20 shown in FIG. 2 (reduction treatment step).

  The reduction treatment step was performed in the same manner as in Example 1 except that the reduction treatment temperature was set to 300 ° C.

FIG. 4A shows an XRD pattern of the obtained composite tungsten oxide particles. It was confirmed that the intensity of the diffraction peak of the Cs ₂ O phase, which is a different phase, was almost equal to that of Reference Example 1. The ratio of Cs _0.32 WO ₃ phase calculated by Rietveld analysis is 87.75% by mass, the ratio of (H ₂ O) _0.33 WO ₃ phase is 6.86% by mass, and the ratio of Cs ₂ O phase is The ratio was 5.39% by mass. FIG. 4B shows the proportions of the Cs _0.32 WO ₃ phase, the Cs ₂ O phase, and the (H ₂ O) _0.33 WO ₃ phase.

When the lattice constant of Cs _0.32 WO ₃ phase, which is a composite tungsten oxide, was calculated by Rietveld analysis, the a-axis was 7.38 ° and the c-axis was 7.70 °.

  FIG. 5 shows the relationship between the lattice constant a axis and the lattice constant c axis.

FIG. 6 shows the occupation ratio of the atoms of the composite tungsten oxide particles at the atomic sites of the composite tungsten oxide particles in the Cs _0.32 WO ₃ phase of the composite tungsten oxide particles calculated by Rietveld analysis. The atomic occupancy of the composite tungsten oxide particles in the atomic sites of the composite tungsten oxide particles in the Cs _0.32 WO ₃ phase in the particles was 87.8%.

  A dispersion liquid dispersed in MIBK (methyl isobutyl ketone) such that the concentration of the composite tungsten oxide particles obtained in Reference Example 1, Examples 1, 2 and Comparative Example 1 was 0.02% by mass was 10 mm in optical path length. Was filled into a solution cell to prepare an optical sample. The transmittance of the obtained optical sample was measured with a spectrophotometer (Model: V-670, manufactured by JASCO Corporation) equipped with an integrating sphere in the wavelength range of 300 nm to 21000 nm. The results are shown in FIG.

  From FIG. 21, the composite tungsten oxide particles of Examples 1 and 2 obtained by the method for producing composite tungsten oxide particles according to the present embodiment have lower transmittance in the near infrared region as compared with Reference Example 1 and the like. I was able to confirm that.

  This is presumably because the composite tungsten oxide particles produced in Examples 1 and 2 absorbed infrared light, and the transmittance in the infrared region of 800 nm or more was reduced.

  On the other hand, it was confirmed that the composite tungsten oxide particles obtained in Reference Example 1 in which the reduction treatment was not performed and Comparative Example 1 in which the reduction treatment was insufficient had almost no infrared absorption.

  From the above results, it was confirmed that according to the method for producing composite tungsten oxide particles described above, composite tungsten oxide particles can be produced using equipment having a low introduction cost, such as a droplet forming section and a heater. It was also confirmed that composite tungsten oxide particles, which are near-infrared absorbing particles, can be directly obtained without going through a process such as pulverization, and the number of steps can be reduced.

  Furthermore, by performing the reduction treatment step, infrared absorption characteristics can be reliably exhibited, and even if a heterophase is contained in the composite tungsten oxide particles synthesized in the heat treatment step, the heterophase can be reduced and removed. It could be confirmed.

Claims (8)

Formula _M x _W y _{O z} (where, M element, an alkali metal, alkaline earth metal, rare earth elements, Mg, Zr, Cr, Mn , Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb, B, F, P, S, Se, Br, Te, Ti, Nb, V, Mo, At least one element selected from Ta, Re, Be, Hf, Os, Bi and I, W is tungsten, O is oxygen, 0.001 ≦ x / y ≦ 1, 2.2 ≦ z / y ≦ 3.0), wherein the composite tungsten oxide particles are represented by the following formula:
A droplet forming step of forming a droplet of a raw material mixed solution including a tungsten source and the M element source, which is an object to be processed;
A heat treatment step of heat treating the object to be processed at 500 ° C. or higher;
A reduction treatment step of reducing the particles obtained in the heat treatment step at a temperature higher than 400 ° C. and lower than 700 ° C. in an atmosphere containing a reducing gas, the method comprising the steps of: The method further includes a temperature raising step of raising the temperature of the object to 1000 ° C.
The method for producing composite tungsten oxide particles according to claim 1, wherein in the heat treatment step, the object is heat-treated at 1000 ° C. or higher.   3. The composite tungsten oxide particles according to claim 1, wherein, in the droplet forming step, a solution containing the tungsten source and a solution containing the M element source are mixed to form the raw material mixed solution. 4. Production method. In the droplet forming step, droplets of the raw material mixed solution are formed using an ultrasonic spray device,
The composite according to any one of claims 1 to 3, wherein the ultrasonic atomizer mixes the solution containing the tungsten source and the solution containing the M element source to form the raw material mixed solution. A method for producing tungsten oxide particles. The method for producing composite tungsten oxide particles according to any one of claims 1 to 4, wherein the tungsten source is ammonium paratungstate.   The composite tungsten oxide particles according to any one of claims 1 to 5, wherein the M element source is at least one selected from carbonate, acetate, nitrate, and hydroxide of the M element. Production method.   The lattice constant of the composite tungsten oxide particles has an a-axis of 7.37 ° to 7.42 ° and a c-axis of 7.58 ° to 7.70 °, according to any one of claims 1 to 6. Of producing composite tungsten oxide particles.   The composite tungsten oxide particles according to any one of claims 1 to 7, wherein the occupancy of tungsten atoms in tungsten atom sites in the composite tungsten oxide phase of the composite tungsten oxide particles is 90% or more. Manufacturing method.