Tungsten Oxide Powder

Abstract

This tungsten oxide powder comprises a powder containing tungsten oxide crystal grains as a main component. When the pore size distribution of the powder is measured by mercury porosimetry, the cumulative pore volume of the powder is 0.35 (ml / g) to 0.45 (ml / g), the bulk density of the powder is 1.7 (g / ml) to 2.1 (g / ml), and the average pore radius of the powder is 0.2 (μm) or more. When the powder is measured by a BET method, the specific surface area of the powder is 3 (m2 / g) to 5.5 (m2 / g).

Description

[Technical Field]

[0001] Disclosed embodiments relate to tungsten oxide powder. [Background technology]

[0002] In recent years, the development of recycling technologies for metals and metal compounds has been progressing. For example, tungsten is a component of cemented carbide and cermet, and is used together with cobalt and niobium in cutting tools and other applications.

[0003] Furthermore, due to its high melting point, tungsten is used in a variety of applications, such as heating elements, structural members, catalysts for the petrochemical industry, environmental equipment, wiring for ceramic wiring boards, heat dissipation members, etc. In order to make effective use of these resources, a method for recycling tungsten from waste materials (scrap) has been devised (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-002927 Summary of the Invention

[0005] The tungsten oxide powder of the present disclosure includes a powder whose main component is tungsten oxide crystal grains. Furthermore, when the pore size distribution of the powder is measured by mercury intrusion porosimetry, the cumulative pore volume of the powder is 0.35 (ml / g) to 0.45 (ml / g), the bulk density of the powder is 1.7 (g / ml) to 2.1 (g / ml), and the average pore radius of the powder is 0.2 (μm) or more. Furthermore, when the specific surface area of ​​the powder is measured by the BET method, it is 3 (m 2 / g)~5.5(m 2 / g). [Brief explanation of the drawings]

[0006] [Figure 1]FIG. 1 is a flowchart showing an example of the procedure for producing tungsten oxide powder and tungsten carbide powder according to an embodiment. [Figure 2] FIG. 2 is a flow chart showing an example of the procedure for producing tungsten oxide powder and tungsten carbide powder in a reference example. [Figure 3] FIG. 3 is a diagram showing the results of pore size distribution measurement by mercury intrusion porosimetry of a tungsten oxide powder according to an embodiment. [Figure 4] FIG. 4 is a diagram showing the results of pore size distribution measurement of a tungsten oxide powder in a reference example by mercury intrusion porosimetry. [Figure 5] FIG. 5 is a view showing an SEM observation photograph of the tungsten oxide powder according to the embodiment. [Figure 6] FIG. 6 is a view showing an SEM photograph of the tungsten oxide powder in the reference example. DETAILED DESCRIPTION OF THE INVENTION

[0007] In the prior art, there was room for further improvement in the tungsten recycling process in terms of efficiently producing tungsten carbide, which is a raw material for cemented carbide, from tungsten oxide powder, which is an intermediate product.

[0008] Therefore, there is a need for a technology that can solve the above problems and provide a tungsten oxide powder that can efficiently produce tungsten carbide.

[0009] Hereinafter, embodiments of the tungsten oxide powder disclosed in the present application will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described below.

[0010] The tungsten oxide powder according to the embodiment includes a powder mainly composed of tungsten oxide crystal grains. For example, the tungsten oxide powder according to the embodiment includes a powder composed of tungsten oxide crystal grains and inevitable impurities.

[0011] The powder contained in the tungsten oxide powder according to the embodiment may have a cumulative pore volume of 0.35 (ml / g) to 0.45 (ml / g).

[0012] In this way, by making the tungsten oxide powder into a powder with a cumulative pore volume of 0.35 (ml / g) or more, it is possible to promote the diffusion of hydrogen gas into the powder in the hydrogen reduction treatment that produces metallic tungsten, which is an intermediate when producing tungsten carbide from the tungsten oxide powder.

[0013] That is, in the embodiment, the tungsten oxide powder can be efficiently reduced, and therefore, according to the embodiment, tungsten carbide can be efficiently produced from the tungsten oxide powder.

[0014] Furthermore, by making the tungsten oxide powder into a powder with a cumulative pore volume of 0.45 (ml / g) or less, it is possible to reduce the possibility that the metallic tungsten produced by the reduction treatment will spontaneously combust and return to tungsten oxide, which would otherwise be caused by the powder being too fine.

[0015] Therefore, according to the embodiment, tungsten carbide can be stably produced from tungsten oxide powder.

[0016] The cumulative pore volume is the value obtained by integrating the volume of pores having a size equal to or larger than a predetermined size (pore diameter). For example, the cumulative pore volume for a pore diameter of 0.1 μm is the value obtained by integrating the volume of pores having a pore diameter of 0.1 μm or larger.

[0017] Since tungsten oxide powder contains pores of various sizes, the smaller the set pore diameter, the larger the cumulative pore volume. However, since there is a physical lower limit to the pore size, the smaller the set pore diameter, the more the cumulative pore volume converges to a specific value.

[0018] In addition, in an embodiment, the bulk density of the powder contained in the tungsten oxide powder may be 1.7 (g / ml) to 2.1 (g / ml).

[0019] In this way, by making the tungsten oxide powder into a powder with a small bulk density of 2.1 (g / ml) or less and large voids, it is possible to promote the diffusion of hydrogen gas into the powder during the hydrogen reduction process that produces metallic tungsten from the tungsten oxide powder.

[0020] That is, in the embodiment, the tungsten oxide powder can be efficiently reduced, and therefore, according to the embodiment, tungsten carbide can be efficiently produced from the tungsten oxide powder.

[0021] If the powder has too many gaps, the surface area of ​​the metallic tungsten tends to increase, and the metallic tungsten produced by the reduction treatment may easily ignite spontaneously and return to tungsten oxide. If the tungsten oxide powder has a bulk density of 1.7 (g / ml) or more, the gaps in the powder can be reduced.

[0022] Therefore, according to the embodiment, tungsten carbide can be stably produced from tungsten oxide powder.

[0023] In addition, in the embodiment, the porosity of the powder contained in the tungsten oxide powder may be 65(%) to 85(%).

[0024] In this way, by making the tungsten oxide powder a powder with a high porosity of 65% or more and large gaps, it is possible to promote the diffusion of hydrogen gas into the powder during the hydrogen reduction process that produces metallic tungsten from the tungsten oxide powder.

[0025] That is, in the embodiment, the tungsten oxide powder can be efficiently reduced, and therefore, according to the embodiment, tungsten carbide can be efficiently produced from the tungsten oxide powder.

[0026] Furthermore, by making the tungsten oxide powder a powder with a porosity of 85% or less, it is possible to prevent the surface area of ​​the tungsten oxide powder from becoming excessively large, and the metallic tungsten produced by the reduction treatment is less likely to return to tungsten oxide.

[0027] Therefore, according to the embodiment, tungsten carbide can be stably produced from tungsten oxide powder.

[0028] In an embodiment, the average pore radius of the powder contained in the tungsten oxide powder may be 0.2 (μm) or more.

[0029] By making the tungsten oxide powder into a powder with an average pore radius of 0.2 μm or more, the diffusion of hydrogen gas into the powder can be promoted in the hydrogen reduction process for producing metallic tungsten from the tungsten oxide powder. Furthermore, when the tungsten oxide powder is directly reduced and carbonized with carbon powder, an efficient solid-state reaction can be easily achieved.

[0030] That is, in the embodiment, the tungsten oxide powder can be efficiently reduced, and therefore, according to the embodiment, tungsten carbide can be efficiently produced from the tungsten oxide powder.

[0031] In addition, in an embodiment, the most frequent pore size in the powder contained in the tungsten oxide powder may be 0.01 (μm) to 1 (μm).

[0032] In this way, by making the tungsten oxide powder into a powder with a mode pore size of 1 μm or less, it is possible to promote the diffusion of hydrogen gas into the powder in the hydrogen reduction process that produces metallic tungsten from the tungsten oxide powder.

[0033] That is, in the embodiment, the tungsten oxide powder can be efficiently reduced, and therefore, according to the embodiment, tungsten carbide can be efficiently produced from the tungsten oxide powder.

[0034] Furthermore, by making the tungsten oxide powder a powder with a mode pore size of 0.01 (μm) or more, it is possible to reduce the possibility that the metallic tungsten produced by the reduction treatment will spontaneously combust within the pores and return to tungsten oxide, which would otherwise be caused by the pores being too small.

[0035] Therefore, according to the embodiment, tungsten carbide can be stably produced from tungsten oxide powder.

[0036] In an embodiment, the specific surface area of ​​the powder contained in the tungsten oxide powder is 3 (m 2 / g)~5.5(m 2 / g). The specific surface area of ​​the powder in the present disclosure is determined by the BET method.

[0037] In this way, tungsten oxide powder with a specific surface area of ​​3 (m 2 / g) or more, contact between the powder and hydrogen gas can be promoted in the hydrogen reduction treatment for producing metallic tungsten from the tungsten oxide powder.

[0038] That is, in the embodiment, the tungsten oxide powder can be efficiently reduced, and therefore, according to the embodiment, tungsten carbide can be efficiently produced from the tungsten oxide powder.

[0039] In addition, tungsten oxide powder with a specific surface area of ​​5.5 (m 2 / g) or less, it is possible to reduce the spontaneous combustion of metallic tungsten produced by the reduction treatment and its reversion to tungsten oxide.

[0040] Therefore, according to the embodiment, tungsten carbide can be stably produced from tungsten oxide powder.

[0041] In addition, in an embodiment, the average particle size of the powder contained in the tungsten oxide powder may be 100 (nm) to 1000 (nm).

[0042] In this way, by making the tungsten oxide powder into a fine powder with an average particle size of 1000 (nm) or less, contact between the powder and hydrogen gas can be promoted in the hydrogen reduction process for producing metallic tungsten from the tungsten oxide powder.

[0043] That is, in the embodiment, the tungsten oxide powder can be efficiently reduced, and therefore, according to the embodiment, tungsten carbide can be efficiently produced from the tungsten oxide powder.

[0044] Furthermore, by making the tungsten oxide powder a powder with an average particle size of 100 nm or more, the specific surface area tends to be small, which reduces the risk of the metallic tungsten produced in the reduction treatment spontaneously combusting and returning to tungsten oxide, which would otherwise occur if the powder were too fine.

[0045] Therefore, according to the embodiment, tungsten carbide can be stably produced from tungsten oxide powder. [Example]

[0046] Examples of the present disclosure will be described in detail below. Fig. 1 is a flowchart showing an example of the steps of producing tungsten oxide powder and tungsten carbide according to an embodiment. As shown in Fig. 1, in the steps of producing tungsten oxide powder and tungsten carbide according to an embodiment, first, scrap of cemented carbide was prepared.

[0047] Cemented carbide, a type of hard alloy, is mainly composed of composite carbides such as metallic tungsten or tungsten carbide, with iron, nickel, cobalt, etc. as the binder phase, and optionally containing TiC, TaC, NbC, VC, Cr3C2, etc. as additive components.

[0048] The target materials containing cemented carbide include, for example, cutting tools (cutting inserts, drills, end mills, etc.), molds (forming rolls, forming dies, etc.), and civil engineering and mining tools (oil drilling tools, rock crushing tools, etc.).

[0049] Next, the prepared cemented carbide scrap was oxidized and roasted to obtain a mixture of tungsten oxide (WO3) and cobalt tungstate (CoWO4).The mixture was then refluxed with an aqueous sodium hydroxide (NaOH) solution and extracted to obtain a tungsten compound solution containing sodium tungstate (Na2WO4).

[0050] Next, an adsorbent containing lysine was added to the obtained tungsten compound solution, and the tungsten compound ions were adsorbed onto the lysine (shown as lysine-WO4 in the figure).

[0051] The adsorbent according to the present disclosure is not limited to containing lysine, and may also contain at least one first amino acid selected from alanine, cystine, methionine, tyrosine, valine, glutamic acid, histidine, proline, threonine, asparagine, glycine, isoleucine, ornithine, arginine, serine, citrulline, and cystathionine.

[0052] In such an adsorption treatment, for example, the total amount of the salt of the first amino acid added to the adsorbent is added in a content ratio of 0.2 (mol) to 1.1 (mol) per 1 (mol) of the metal component of the tungsten compound, which allows a large amount of the tungsten compound to be adsorbed with a small amount of the adsorbent.

[0053] The total amount of the first amino acid salt added is, for example, 10 (g / L) to 300 (g / L) relative to the tungsten compound solution. This prevents the viscosity of the solution from increasing, and the recovery efficiency of the metal compound from decreasing. In particular, when the adsorbent is made of an amino acid salt, the viscosity of the solution is less likely to increase, and workability is good.

[0054] The temperature can be adjusted depending on the activity of the free amino acid, and is usually room temperature. The tungsten compound solution to which the adsorbent has been added may be adjusted using hydrochloric acid or the like so that the zeta potential of the free amino acid becomes positive. This allows the adsorbent to adsorb anionic tungsten compound ions.

[0055] The pH of the solution may be less than 7 (acidic). When the free amino acids are lysine and arginine, the pH is preferably 4 or less, more preferably 0.5 to 3, and even more preferably 0.8 to 2.3. When the free amino acid is glutamic acid, the pH is preferably 1.5 or less.

[0056] This can increase the recovery rate of the tungsten compound. Note that the order of the step of adjusting the pH of the solution and the step of adding the adsorbent to the solution containing the metal compound does not matter.

[0057] When the adsorbent is a salt of the first amino acid, the recovery efficiency of the adsorbent is higher if the adsorption reaction is within one hour. In other words, if the adsorption reaction exceeds one hour, some of the adsorbed metal compound may be desorbed from the free amino acid.

[0058] Following the lysine adsorption step, the adsorbent with adsorbed tungsten compound ions was dehydrated by centrifugation or other means. Then, if necessary, the adsorbent was washed in this order: with acid and then with pure water. Instead of acid washing, washing with warm water at 40°C or higher was also possible. Impurities were then removed by washing with pure water until the electrical conductivity of the washing filtrate reached 500 μS / m or less. This allowed the tungsten compound to be recovered at a high quality.

[0059] Next, the adsorbent with the adsorbed tungsten compound ions was incinerated in the atmosphere at a temperature of 300°C or higher to oxidize the tungsten compounds and remove organic components including the adsorbent, thereby obtaining a tungsten oxide powder (WO) according to the embodiment.

[0060] As shown in Figure 1, the obtained tungsten oxide powder is heat-treated in a reducing atmosphere (for example, a hydrogen gas atmosphere) at a temperature of 800°C to 950°C to reduce the tungsten oxide compound. This allows metallic tungsten (W) to be obtained. The obtained metallic tungsten can then be carbonized to obtain tungsten carbide (WC), which is a raw material for cemented carbide.

[0061] Fig. 2 is a flow chart showing an example of the procedure of the process for producing tungsten oxide powder and tungsten carbide in the reference example. As shown in Fig. 2, in the process for producing tungsten oxide powder and tungsten carbide in the reference example, first, scrap of cemented carbide was prepared.

[0062] Next, the prepared cemented carbide scrap was oxidized and roasted to obtain a mixture of tungsten oxide (WO3) and cobalt tungstate (CoWO4). The obtained mixture was then extracted with a sodium hydroxide (NaOH) solution to obtain a tungsten compound solution containing sodium tungstate (Na2WO4). Since each step up to this point is the same as in the above-mentioned embodiment, detailed explanations will be omitted.

[0063] Next, the resulting tungsten compound solution was subjected to ion exchange using an ion exchange resin or the like to produce an aqueous solution of ammonium tungstate ((NH4)2WO4).The resulting aqueous solution was then heated and concentrated to crystallize the tungsten compound as ammonium paratungstate (APT).

[0064] Next, the obtained APT was oxidized by thermal decomposition to obtain tungsten oxide powder (WO3) of the reference example.

[0065] As shown in Figure 2, the obtained tungsten oxide powder is heat-treated in a reducing atmosphere to reduce the tungsten oxide compound, thereby obtaining metallic tungsten (W).Then, by carbonizing the obtained metallic tungsten, tungsten carbide (WC), which is a raw material for cemented carbide, can be obtained.

[0066] Next, the pore size distribution of the obtained tungsten oxide powders of the embodiment and the reference example was measured by mercury intrusion porosimetry. The measurement conditions for the pore size distribution measurement by mercury intrusion porosimetry were as follows.

[0067] As a pretreatment, the sample was dried at a constant temperature of 120°C for 4 hours. After that, the pore size distribution was determined using mercury intrusion porosimetry, with a pore size range of approximately 0.0018 μm to 100 μm. The measurement device used was an Autopore V9620 (manufactured by Micromeritics). The pore size was calculated using the Washburn equation below. Washburn's formula: PD=-4σ cosθ P: Pressure D: pore diameter σ: Surface tension of mercury (480 (dynes / cm)) θ: Contact angle between mercury and sample (140°)

[0068] Fig. 3 shows the results of pore size distribution measurement by mercury intrusion porosimetry for a tungsten oxide powder according to an embodiment, and Fig. 4 shows the results of pore size distribution measurement by mercury intrusion porosimetry for a tungsten oxide powder in a reference example.

[0069] Table 1 also shows the cumulative pore volume, average pore radius, bulk density and porosity of the tungsten oxide powder determined by the mercury intrusion method.

[0070] [Table 1]

[0071] 3 and 4 and Table 1, the powder contained in the tungsten oxide powder according to the embodiment has a cumulative pore volume of 0.42 (mL / g), which is larger than that of the reference example. This result is also supported by SEM observation photographs of the tungsten oxide powders according to the embodiment and the reference example shown in FIGS. 5 and 6.

[0072] By producing a powder with a large cumulative pore volume in this way, it is possible to promote the diffusion of hydrogen gas into the powder during the hydrogen reduction process in which metallic tungsten is produced from the tungsten oxide powder.

[0073] Therefore, according to the embodiment, the tungsten oxide powder can be efficiently reduced, and therefore tungsten carbide can be efficiently produced from the tungsten oxide powder.

[0074] Furthermore, as shown in Figures 3 and 4, the powder contained in the tungsten oxide powder according to the embodiment has a mode pore size (pore size with the largest log differential pore volume) of about 0.2 (μm), which is smaller than that of the reference example.

[0075] By producing powder with a small modal pore size in this way, it is possible to promote diffusion of hydrogen gas into the powder during the hydrogen reduction process for producing metallic tungsten from tungsten oxide powder.

[0076] Therefore, according to the embodiment, the tungsten oxide powder can be efficiently reduced, and therefore tungsten carbide can be efficiently produced from the tungsten oxide powder.

[0077] Furthermore, as shown in Table 1, the powder contained in the tungsten oxide powder according to the embodiment has an average pore radius of 0.26 (μm), which is larger than that of the reference example. By using powder with a larger average pore radius, it is possible to promote the diffusion of hydrogen gas into the powder during the hydrogen reduction process for producing metallic tungsten from the tungsten oxide powder. Furthermore, it is possible to achieve an efficient solid-state reaction when directly reducing and carbonizing the tungsten oxide powder with carbon powder.

[0078] Therefore, according to the embodiment, the tungsten oxide powder can be efficiently reduced, and therefore tungsten carbide can be efficiently produced from the tungsten oxide powder.

[0079] Furthermore, as shown in Table 1, the powder contained in the tungsten oxide powder according to the embodiment has a bulk density of 1.82 (g / mL), which is lower than that of the reference example. In this way, by using a powder with a low bulk density, it is possible to promote the diffusion of hydrogen gas into the powder in the hydrogen reduction process that produces metallic tungsten from the tungsten oxide powder.

[0080] Therefore, according to the embodiment, the tungsten oxide powder can be efficiently reduced, and therefore tungsten carbide can be efficiently produced from the tungsten oxide powder.

[0081] Furthermore, as shown in Table 1, the powder contained in the tungsten oxide powder according to the embodiment has a porosity of 76% which is higher than that of the reference example. In this way, by using a powder with a high porosity, it is possible to promote the diffusion of hydrogen gas into the powder in the hydrogen reduction process that produces metallic tungsten from the tungsten oxide powder.

[0082] Therefore, according to the embodiment, the tungsten oxide powder can be efficiently reduced, and therefore tungsten carbide can be efficiently produced from the tungsten oxide powder.

[0083] 3, the powder contained in the tungsten oxide powder according to the embodiment has a maximum peak of the Log differential pore volume in the pore diameter range of 0.01 μm or more and 1 μm or less. In the embodiment, when the value of this peak is Ip, it can be seen that the value of the Log differential pore volume in the pore diameter range of 1 μm or more and 100 μm or less is 0.1 times or more the peak value Ip.

[0084] 3, in the powder contained in the tungsten oxide powder according to the embodiment, a peak having a Log differential pore volume value of 0.2 (mL / g) or more and 1 (mL / g) or less exists in the pore diameter range of 0.01 (μm) or more and 1 (μm) or less. In the embodiment, it can be seen that the value of the Log differential pore volume in the pore diameter range of 1 (μm) or more and 100 (μm) or less is 0.05 (mL / g) or more.

[0085] The tungsten oxide powder of the present disclosure is characterized by its contribution to an effective synthesis method for synthesizing tungsten carbide, the main raw material for cutting tools. The process for producing tungsten carbide from tungsten oxide powder includes an indirect process in which tungsten oxide is reduced with hydrogen gas and then carbonized with carbon powder, and a direct process in which tungsten oxide is reduced with hydrogen gas and then carbonized with carbon powder.

[0086] Although the indirect process is common in the market, the direct process is an essential technology for synthesizing fine tungsten carbide and has been attracting attention in recent years.

[0087] Since hydrogen reduction treatment in the indirect process is a gas-phase reaction between powder and gas, the higher the gas diffusion rate, the more efficient the reaction. Therefore, it is desirable to have minute pores so that small hydrogen gas molecules can diffuse.

[0088] On the other hand, in the case of the carbon reduction treatment in the direct process and the carbonization treatment in both processes, since this is a solid-state reaction between powders, minute pores alone do not allow the carbon powder to penetrate properly into the tungsten oxide powder (or metallic tungsten powder), making it difficult to achieve an efficient solid-state reaction.

[0089] Therefore, the tungsten oxide powder according to the embodiment has both fine pores (pore diameter of 0.01 μm or more and 1 μm or less) and relatively large pores (pore diameter of 1 μm or more and 100 μm or less), and thus has the excellent feature of being adaptable to both indirect and direct processes.

[0090] The specific surface area of ​​the tungsten oxide powders obtained in the embodiments and reference examples was measured by the BET method under the following measurement conditions.

[0091] The measurement device used was a Macsorb HM model-1220 manufactured by Mountech Co., Ltd. The measurement conditions were a flow-type BET single-point method (compliant with JIS R 1626-1996), and the sample was heated at 200°C for 10 minutes or more before the measurement was performed. Nitrogen (N2: mixed concentration 30.2%; flow rate 25 ml / min) was used as the adsorption gas.

[0092] Table 2 shows the specific surface areas of the tungsten oxide powders in the embodiments and reference examples determined by the BET method.

[0093] [Table 2]

[0094] As shown in Table 2, the powder contained in the tungsten oxide powder according to the embodiment has a specific surface area of ​​4.22 (m 2 / g).

[0095] By using powder with a large specific surface area in this way, contact between the powder and hydrogen gas can be promoted in the hydrogen reduction process for producing metallic tungsten from tungsten oxide powder.

[0096] Therefore, according to the embodiment, the tungsten oxide powder can be efficiently reduced, and therefore tungsten carbide can be efficiently produced from the tungsten oxide powder.

[0097] The average particle size of the powder contained in the obtained tungsten oxide powder according to the embodiment was evaluated by SEM observation, and it was found that the average particle size of the powder contained in the tungsten oxide powder according to the embodiment was 100 (nm) to 1000 (nm).

[0098] As a result, in this embodiment, the particle size of the reduced metallic tungsten powder becomes appropriately coarse, making it possible to synthesize the desired tungsten carbide without incurring the spontaneous combustion phenomenon that is unique to metal powders.

[0099] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications are possible without departing from the spirit of the present invention. For example, the above embodiments show a case where tungsten oxide powder and tungsten carbide are produced (recycled) from cemented carbide scrap, but the present disclosure is not limited to such an example and can also be applied to the production of tungsten oxide powder and tungsten carbide from ore, etc.

[0100] Further advantages and other aspects may readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Claims

1. It contains a powder whose main component is tungsten oxide crystal grains, When the pore size distribution of the powder was measured by mercury intrusion porosimetry, The cumulative pore volume of the powder is 0.35 (ml / g) to 0.45 (ml / g), The bulk density of the powder is 1.7 (g / ml) to 2.1 (g / ml), The powder has an average pore radius of 0.2 (μm) or more, The specific surface area of ​​the powder measured by the BET method was 3 (m ２ / g) to 5.5 (m ２ / g) Tungsten oxide powder.

2. In a pore distribution curve showing the relationship between pore diameter and log differential pore volume when the pore distribution of the powder is measured by mercury intrusion porosimetry, When the maximum peak of the log differential pore volume exists in the pore diameter range of 0.01 (μm) or more and 1 (μm) or less, and the peak value is designated as Ip, The value of the log differential pore volume in the pore diameter range of 1 (μm) to 100 (μm) is 0.1 times or more the peak value Ip.

2. The tungsten oxide powder according to claim 1.

3. In a pore distribution curve showing the relationship between pore diameter and log differential pore volume when the pore distribution of the powder is measured by mercury intrusion porosimetry, a peak having a log differential pore volume value of 0.2 (mL / g) or more and 1 (mL / g) or less exists in a pore diameter range of 0.01 (μm) or more and 1 (μm) or less; The value of the log differential pore volume in the pore diameter range of 1 (μm) to 100 (μm) is 0.05 (mL / g) or more.

3. The tungsten oxide powder according to claim 1 or 2.

4. When the pore size distribution of the powder was measured by mercury intrusion porosimetry, The porosity of the powder is 65(%) to 85(%), The most frequent pore size in the powder is in the range of 0.01 (μm) to 1 (μm), The average particle size of the powder is 100 (nm) to 1000 (nm).

3. The tungsten oxide powder according to claim 1 or 2.

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