Tungsten Oxide Powder

Abstract

This tungsten oxide powder includes a powder body having a tungsten oxide crystal grain as a main component. The tungsten oxide crystal grain contains sodium and potassium. In addition, the tungsten oxide crystal grain has a composition in which the sodium concentration is higher than the potassium concentration throughout the depth direction.

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] A tungsten oxide powder according to one embodiment includes a powder mainly composed of tungsten oxide crystal grains, the tungsten oxide crystal grains containing sodium and potassium, and the tungsten oxide crystal grains have a higher sodium concentration than potassium concentration throughout the entire depth direction. [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 depth distribution of sodium and potassium in a tungsten oxide powder according to an embodiment. [Figure 4] FIG. 4 is a diagram showing the depth distribution of sodium and potassium in the tungsten oxide powder of 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, it is desired to realize 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. Furthermore, the tungsten oxide crystal grains according to the embodiment are not composed only of tungsten oxide, but also contain sodium and potassium.

[0011] In the embodiment, the tungsten oxide crystal grains contained in the tungsten oxide powder have a sodium concentration higher than a potassium concentration throughout the entire depth direction.

[0012] This makes it possible to enhance the reaction promotion effect in the hydrogen reduction treatment for producing metallic tungsten, which is an intermediate in producing tungsten carbide from tungsten oxide powder, compared to when the potassium concentration is higher than the sodium concentration. The reason for this is explained below.

[0013] The melting point of sodium is 98°C and the boiling point is 883°C, while the melting point of potassium is 64°C and the boiling point is 759°C. The treatment temperature when reducing tungsten oxide powder to metallic tungsten with hydrogen gas is generally 800°C to 950°C.

[0014] As described above, the temperature during hydrogen reduction of tungsten oxide powder is 800°C to 950°C, which is close to the boiling point of sodium. Meanwhile, potassium reaches its boiling point during hydrogen reduction, causing it to volatilize and disappear during the process. Therefore, due to the influence of the heat of vaporization generated when potassium volatilizes, sodium volatilization is suppressed even at temperatures close to the boiling point of sodium. For these reasons, sodium tends to exist in a molten state during hydrogen reduction of tungsten oxide powder.

[0015] In this embodiment, the molten state of sodium allows the reduction treatment to proceed in a state in which adjacent particles are bonded together, and as a result, grain growth of metallic tungsten can be achieved with less energy (i.e., lower temperature and shorter time) compared to when only sodium is contained without potassium.

[0016] Furthermore, according to the embodiment, the sodium concentration in the powder is higher than the potassium concentration. Because the sodium concentration is relatively high, the effect of bonding adjacent particles together due to the molten state of sodium is strong. Also, because the potassium concentration is relatively small but not zero, the effect of bonding adjacent particles together due to the molten state of sodium is strong, while simultaneously suppressing the volatilization of sodium.

[0017] Furthermore, according to the embodiment, the tungsten oxide crystal grains are configured such that the sodium concentration is higher than the potassium concentration throughout the entire depth direction. In such a case, the production of metallic tungsten is likely to proceed not only on the surface of the powder but also throughout the entire powder toward the center. This improves the efficiency of producing metallic tungsten. Therefore, tungsten carbide can be efficiently produced from tungsten oxide powder.

[0018] In an embodiment, a region having a higher sodium concentration than the interior of the tungsten oxide crystal grains may be formed on the surface of the tungsten oxide crystal grains, which further promotes the reduction treatment in the state where adjacent particles are bonded together, thereby achieving grain growth of metallic tungsten with even lower energy.

[0019] Therefore, according to the embodiment, tungsten carbide can be produced more efficiently from tungsten oxide powder.

[0020] In an embodiment, the high sodium concentration regions formed on the surfaces of the tungsten oxide crystal grains may be present at a depth of up to 100 nm from the surfaces of the tungsten oxide crystal grains, which further promotes the reduction treatment in the state where adjacent particles are bonded together, thereby achieving grain growth of metallic tungsten with even lower energy.

[0021] Therefore, according to the embodiment, tungsten carbide can be produced more efficiently from tungsten oxide powder.

[0022] In addition, in an embodiment, the tungsten oxide crystal grains may have a sodium concentration of 5 (ppm) to 100 (ppm), and preferably have a sodium concentration of 20 (ppm) to 100 (ppm).

[0023] This further accelerates the reduction process while maintaining the adhesion of adjacent particles, thereby achieving grain growth of the tungsten metal with even lower energy. Therefore, according to the embodiment, tungsten carbide can be produced more efficiently from the tungsten oxide powder.

[0024] The sodium contained in the tungsten oxide crystal grains is decomposed and disappears when exposed to high temperatures of 1200°C or higher during the carbonization process that produces tungsten carbide from metallic tungsten. Therefore, even if the tungsten oxide crystal grains themselves contain sodium, this does not pose any particular problem to the quality of the tungsten carbide.

[0025] Furthermore, in the embodiment, regions having a higher sodium concentration than the interior of the tungsten oxide crystal grains are formed on the surfaces of the tungsten oxide crystal grains, which facilitates decomposition and dissipation of sodium during the carbonization process, thereby enabling the production of high-quality tungsten carbide. [Example]

[0026] 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.

[0027] Cemented carbide, a type of cemented carbide, is primarily composed of composite carbides such as metallic tungsten or tungsten carbide, with iron, nickel, cobalt, etc. as a binder phase, and optionally containing additive components such as TiC, TaC, NbC, VC, Cr3C2, etc. The scrap in the examples further contains sodium and potassium in addition to these additive components.

[0028] 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.).

[0029] Next, the prepared cemented carbide scrap was oxidized and roasted to obtain a mixture of tungsten oxide (WO3) and cobalt tungstate (CoWO4). If the cemented carbide scrap contains only a small amount of sodium and potassium, sodium and potassium may be added when obtaining the mixture. The obtained mixture was then refluxed with an aqueous sodium hydroxide (NaOH) solution and extracted to obtain a tungsten compound solution containing sodium tungstate (Na2WO4).

[0030] 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).

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] Potassium has a higher ionization tendency than sodium. Therefore, when the solution is acidic, potassium ionizes more easily than sodium. In other words, sodium is relatively difficult to ionize and is therefore difficult to remove in the adsorbent washing process described below. For the above reasons, it is possible to increase the sodium concentration in the powder to a level higher than the potassium concentration, as a non-limiting example.

[0037] The above-described steps can increase the recovery rate of tungsten compounds. Note that the steps of adjusting the pH of the solution and adding the adsorbent to the solution containing the metal compounds can be carried out in any order.

[0038] In addition to the above-described process using an acidic solution, it is also possible to increase the sodium concentration in the powder to be higher than the potassium concentration by, for example, adjusting the amounts of sodium and potassium added when obtaining the mixture.

[0039] 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.

[0040] 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.

[0041] 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 (WO3) according to the embodiment.

[0042] 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.

[0043] Fig. 2 is a flow chart showing an example of the procedure for 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. Furthermore, the scrap in the Reference Example also contains sodium and potassium, similar to the scrap in the Examples.

[0044] 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.

[0045] Next, the obtained 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 obtained aqueous solution was then heated and concentrated to crystallize the tungsten compound as ammonium paratungstate (APT). Since the aqueous solution of ammonium tungstate used in the comparative example was not an acidic solution, much of the sodium was removed in the process of crystallizing APT, and the potassium to sodium content ratio was likely to increase.

[0046] Next, the obtained APT was oxidized by thermal decomposition to obtain tungsten oxide powder (WO3) of the reference example.

[0047] 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.

[0048] Next, the obtained tungsten oxide powders of the embodiment and the reference example were analyzed by ToF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry). Specifically, the depth distribution of sodium and potassium in the tungsten oxide powders of the embodiment and the reference example was measured by ToF-SIMS.

[0049] The ToF-SIMS measurement conditions were as follows: The tungsten oxide powders of the embodiment and the reference example were fixed, and the powder surface was measured over a 100 μm square. The measurement device used was a TOF.SIMS5 from ION-TOF, with Bi (bismuth) selected as the primary ion source, and elemental analysis in the depth direction was measured.

[0050] Fig. 3 is a diagram showing the depth distribution of sodium and potassium in the tungsten oxide powder according to the embodiment, and Fig. 4 is a diagram showing the depth distribution of sodium and potassium in the tungsten oxide powder of a reference example.

[0051] As shown in FIG. 3, it can be seen that in the tungsten oxide crystal grains contained in the tungsten oxide powder according to the embodiment, the sodium concentration is higher than the potassium concentration throughout the entire depth direction.

[0052] The tungsten oxide crystal grains contained in the tungsten oxide powder according to the embodiment have a grain size of approximately several tens to several hundreds of nanometers. Therefore, by measuring the depth distribution up to 500 nanometers as shown in FIG. 3, it can be estimated that the sodium concentration is higher than the potassium concentration throughout the entire depth direction.

[0053] On the other hand, as shown in FIG. 4, in the tungsten oxide crystal grains contained in the tungsten oxide powder of the reference example, the potassium concentration is higher than the sodium concentration throughout the entire depth direction.

[0054] Thus, in the embodiment, unlike the reference example, by making the sodium concentration higher than the potassium concentration throughout the entire depth direction, it is possible to efficiently produce tungsten carbide from tungsten oxide powder, as described above. Specifically, the processing temperature can be reduced by about 5% to 10%, which reduces the energy required for production by about 5% to 20%.

[0055] Furthermore, as shown in FIG. 3, in the embodiment, a region having a higher sodium concentration than the inside of the tungsten oxide crystal grain is formed on the surface of the tungsten oxide crystal grain to a depth of about 100 nm from the surface.

[0056] This allows the embodiment to more efficiently produce tungsten carbide from tungsten oxide powder.

[0057] The sodium content of the obtained tungsten oxide powder according to the embodiment was evaluated using an ICP (Inductively Coupled Plasma) emission spectrometer. As a result, it was found that the tungsten oxide crystal grains contained in the tungsten oxide powder according to the embodiment had a sodium content of 5 (ppm) to 100 (ppm).

[0058] This allows the embodiment to produce tungsten carbide from tungsten oxide powder more efficiently, as described above.

[0059] 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.

[0060] 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, The tungsten oxide crystal grains contain sodium and potassium, the tungsten oxide crystal grains have a sodium concentration higher than a potassium concentration throughout the entire depth direction, When a region from the surface of the tungsten oxide crystal grain to a depth of 100 (nm) is defined as a surface region, and a region deeper than the surface region is defined as an internal region, The sodium concentration in the surface region is higher than the sodium concentration in the inner region. Tungsten oxide powder.

2. The sodium concentration in the tungsten oxide crystal grains continuously decreases from the surface toward the interior of the tungsten oxide crystal grains.

2. The tungsten oxide powder according to claim 1.

3. The potassium concentration in the surface region is higher than the potassium concentration in the inner region.

2. The tungsten oxide powder according to claim 1.

4. The tungsten oxide crystal grains contain 5 (ppm) to 100 (ppm) of sodium. The tungsten oxide powder according to any one of claims 1 to 3.

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