WO2023145521A1

WO2023145521A1 - Tungsten oxide powder

Info

Publication number: WO2023145521A1
Application number: PCT/JP2023/001052
Authority: WO
Inventors: 志賢青木; 貴彦牧野; 直樹岩井
Original assignee: 京セラ株式会社
Priority date: 2022-01-28
Filing date: 2023-01-16
Publication date: 2023-08-03

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

tungsten oxide powder

The disclosed embodiments relate to tungsten oxide powder.

In recent years, the development of recycling technology for metals or metal compounds has progressed. For example, tungsten is a component that constitutes cemented carbide and cemented carbide such as cermet, and is used together with cobalt, niobium, etc., and is widely used in cutting tools and the like.

In addition, since tungsten has a high melting point, it is used in various applications such as heating elements, structural members, catalysts for the petrochemical industry, environmental equipment, wiring for ceramic wiring boards, and heat dissipation members. In order to effectively utilize these resources, a method of recycling tungsten from waste materials (scrap) has been devised (see Patent Document 1).

JP 2004-002927 A

The tungsten oxide powder of the present disclosure includes a powder mainly composed of tungsten oxide crystal grains. Further, when the pore distribution of the powder is measured by a mercury intrusion method, the cumulative pore volume of the powder is 0.35 (ml / g) to 0.45 (ml / g), and the powder 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. Further, the specific surface area of the powder measured by the BET method is 3 (m ² /g) to 5.5 (m ² /g).

FIG. 1 is a flow chart showing an example of a procedure for producing tungsten oxide powder and tungsten carbide according to an embodiment. FIG. 2 is a flow chart showing an example of a procedure for producing tungsten oxide powder and tungsten carbide in a reference example. FIG. 3 is a diagram showing the results of pore size distribution measurement of the tungsten oxide powder according to the embodiment by mercury porosimetry. FIG. 4 is a diagram showing the results of pore size distribution measurement by mercury porosimetry of tungsten oxide powder in Reference Example. FIG. 5 is a diagram showing an SEM observation photograph of the tungsten oxide powder according to the embodiment. FIG. 6 is a diagram showing an SEM observation photograph of tungsten oxide powder in Reference Example.

With the conventional technology, there is room for further improvement in terms of efficiently producing tungsten carbide, which is a raw material for cemented carbide, from the intermediate tungsten oxide powder in the tungsten recycling process.

Therefore, it is expected to realize a technology that can solve the above problems and provide tungsten oxide powder that can efficiently produce tungsten carbide.

Hereinafter, embodiments of the tungsten oxide powder disclosed in the present application will be described with reference to the accompanying drawings. In addition, this invention is not limited by embodiment shown below.

The tungsten oxide powder according to the embodiment contains powder containing tungsten oxide crystal grains as a main component. For example, the tungsten oxide powder according to the embodiment contains powder composed of tungsten oxide crystal grains and unavoidable impurities.

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).

Thus, by making the tungsten oxide powder a powder having a cumulative pore volume of 0.35 (ml/g) or more, metal tungsten, which is an intermediate in producing tungsten carbide from the tungsten oxide powder, is produced. In the hydrogen reduction treatment, diffusion of hydrogen gas into the powder can be promoted.

That is, in the embodiment, tungsten oxide powder can be efficiently reduced. Therefore, according to the embodiment, tungsten carbide can be efficiently produced from tungsten oxide powder.

In addition, by making the tungsten oxide powder a powder having a cumulative pore volume of 0.45 (ml / g) or less, the metal tungsten generated by the reduction treatment spontaneously ignites due to the powder being too fine. can be reduced to return to tungsten oxide.

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

It should be noted that the cumulative pore volume is a value obtained by accumulating the volume of pores having a size equal to or larger than a predetermined size (pore diameter). For example, the cumulative pore volume at a pore diameter of 0.1 μm is a value obtained by accumulating the volume of pores having a pore diameter of 0.1 μm or more.

Since there are pores of various sizes in the tungsten oxide powder, the smaller the set value of the pore diameter, the larger the cumulative pore volume. However, since there is a physical lower limit to the pore size, the cumulative pore volume converges to a specific value as the set value of the pore diameter is decreased.

Further, in the embodiment, the bulk density of the powder contained in the tungsten oxide powder may be 1.7 (g/ml) to 2.1 (g/ml).

In this way, by making the tungsten oxide powder a powder with a low bulk density of 2.1 (g/ml) or less and large gaps, in the hydrogen reduction treatment for producing metal tungsten from the tungsten oxide powder, of hydrogen gas can be promoted.

If there are too many gaps in the powder, the surface area of the metallic tungsten tends to increase, and there is a risk that the metallic tungsten produced by the reduction treatment will spontaneously ignite and easily return to tungsten oxide. When the tungsten oxide powder has a bulk density of 1.7 (g/ml) or more, the gaps in the powder can be reduced.

In addition, in the embodiment, the powder contained in the tungsten oxide powder may have a porosity of 65(%) to 85(%).

In this way, by making the tungsten oxide powder a powder with a large porosity of 65 (%) or more and large gaps, in the hydrogen reduction treatment for producing metal tungsten from the tungsten oxide powder, hydrogen gas is introduced into the powder. Diffusion can be facilitated.

In addition, by making the tungsten oxide powder a powder having a porosity of 85 (%) or less, excessive increase in the surface area of the tungsten oxide powder can be avoided, and metallic tungsten produced by the reduction treatment returns to tungsten oxide. hard to get rid of.

In addition, in the embodiment, the powder contained in the tungsten oxide powder may have an average pore radius of 0.2 (μm) or more.

In this way, by making the tungsten oxide powder into a powder having an average pore radius of 0.2 (μm) or more, in the hydrogen reduction treatment for producing metal tungsten from the tungsten oxide powder, diffusion of hydrogen gas into the powder can promote In addition, when the tungsten oxide powder is directly reduced and carbonized with the carbon powder, an efficient solid-phase reaction tends to occur.

In addition, in the embodiment, the pore diameter with the highest frequency in the powder contained in the tungsten oxide powder may be 0.01 (μm) to 1 (μm).

Thus, by making the tungsten oxide powder a powder having a mode pore diameter of 1 (μm) or less, in the hydrogen reduction treatment for producing metal tungsten from the tungsten oxide powder, diffusion of hydrogen gas into the powder is promoted. can do.

In addition, by making the tungsten oxide powder a powder having a mode pore diameter of 0.01 (μm) or more, the pores inside the powder are too fine, resulting in metal tungsten generated by the reduction treatment. , spontaneous ignition in the pores and returning to tungsten oxide can be reduced.

Further, in embodiments, the specific surface area of the powder contained in the tungsten oxide powder may be 3 (m ² /g) to 5.5 (m ² /g). In addition, the specific surface area of the powder in the present disclosure is the specific surface area determined by the BET method.

Thus, by making the tungsten oxide powder a powder having a specific surface area of 3 (m ² /g) or more, contact between the powder and hydrogen gas can be prevented in the hydrogen reduction treatment for producing metallic tungsten from the tungsten oxide powder. can be promoted.

In addition, by making the tungsten oxide powder a powder having a specific surface area of 5.5 (m ² /g) or less, it is possible to reduce the spontaneous ignition of metal tungsten generated by the reduction treatment and return to tungsten oxide. be able to.

Further, in the embodiment, the average particle size of the powder contained in the tungsten oxide powder may be 100 (nm) to 1000 (nm).

In this way, by making the tungsten oxide powder into a fine powder having an average particle size of 1000 (nm) or less, the contact between the powder and hydrogen gas is promoted in the hydrogen reduction treatment for producing metal tungsten from the tungsten oxide powder. can do.

Also, by making the tungsten oxide powder a powder having an average particle size of 100 (nm) or more, the specific surface area tends to be small. Therefore, it is possible to reduce the spontaneous ignition of metal tungsten produced in the reduction treatment and return to tungsten oxide due to too fine powder.

Examples of the present disclosure will be specifically described below. FIG. 1 is a flow chart showing an example of a procedure for producing tungsten oxide powder and tungsten carbide according to an embodiment. As shown in FIG. 1, in the step of producing tungsten oxide powder and tungsten carbide according to the embodiment, first, cemented carbide scrap was prepared.

Cemented carbide, which is a kind of cemented carbide, is mainly composed of composite carbides such as metal tungsten and tungsten carbide, and has iron, nickel, cobalt, etc. as a binding phase, and if necessary, as additive components TiC, TaC, NbC, VC, Cr ₃ C ₂ and the like.

Materials to be treated containing cemented carbide are, for example, cutting tools (cutting inserts, drills, end mills, etc.), molds (forming rolls, molds, etc.), civil engineering and mining tools (oil drilling tools, rock crushing tools, etc.).

The prepared cemented carbide scrap was then oxidatively roasted to obtain a mixture of tungsten oxide (WO ₃ ) and cobalt tungstate (CoWO ₄ ). Then, the resulting mixture was refluxed with an aqueous sodium hydroxide (NaOH) solution and then extracted to obtain a tungsten compound solution containing sodium tungstate (Na ₂ WO ₄ ).

Next, an adsorbent containing lysine was added to the obtained tungsten compound solution to adsorb tungsten compound ions to lysine (denoted as lysine-WO ₄ in the figure).

Note that the adsorbent in the present disclosure is not limited to containing lysine, Alanine, Cystine, Methionine, Tyrosine, Valine, Glutamic acid, Histidine ( Histidine, Proline, Threonine, Asparagine, Glycine, Isoleucine, Ornithine, Arginine, Serine, Citrulline and Cystathionine ( Cystathionine).

In such adsorption treatment, for example, the total addition amount of the salt of the first amino acid in the adsorbent is 0.2 (mol) to 1.1 (mol) with respect to 1 (mol) of the metal component of the tungsten compound. Add in proportion. As a result, a large amount of tungsten compound can be adsorbed with a small amount of adsorbent.

Also, the total added amount of the salt of the first amino acid is, for example, 10 (g/l) to 300 (g/l) with respect to the tungsten compound solution. As a result, the viscosity of the solution does not increase, and the recovery efficiency of the metal compound is less likely to decrease. In particular, when the adsorbent consists of an amino acid salt, the viscosity of the solution is less likely to increase, resulting in good workability.

The temperature may be adjusted according to the activity of free amino acids, and usually room temperature is fine. 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 free amino acids is positive. This allows the adsorbent to adsorb tungsten compound ions, which are anions.

Also, the pH of the solution may be less than 7 (acidic). When the free amino acids are lysine and arginine, a suitable pH is 4 or less, preferably 0.5-3, desirably pH=0.8-2.3. When the free amino acid is glutamic acid, the preferred pH is 1.5 or less.

By doing so, it is possible to increase the recovery rate of the tungsten compound. Either the step of adjusting the pH of the solution or the step of adding the adsorbent to the solution containing the metal compound may be performed first.

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 1 hour. That is, when the adsorption reaction exceeds 1 hour, part of the adsorbed metal compound may be desorbed from the free amino acid.

Following the adsorption step to lysine, the adsorbent with the tungsten compound ions adsorbed was dehydrated by centrifugation or other means. Then, if necessary, the adsorbent is washed in the order of acid washing and pure water washing. Instead of acid cleaning, hot water of 40 (° C.) or more may be used for cleaning. Impurities were removed by washing with pure water until the electric conductivity of the washing filtrate became 500 (μS/m) or less. As a result, the tungsten compound can be improved in quality and recovered.

Next, the adsorbent with the tungsten compound ions adsorbed thereon was incinerated, for example, at a temperature of 300 (° C.) or higher in the atmosphere to oxidize the tungsten compound and remove organic components including the adsorbent. As a result, a tungsten oxide powder (WO ₃ ) according to the embodiment was obtained.

Note that, as shown in FIG. 1, the obtained tungsten oxide powder is heat-treated at a temperature of 800 (° C.) to 950 (° C.) in a reducing atmosphere (eg, hydrogen gas atmosphere) to reduce the tungsten oxide compound. Thereby, metallic tungsten (W) can be obtained. By carbonizing the obtained metal tungsten, it is possible to obtain tungsten carbide (WC) as a raw material of cemented carbide.

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

The prepared cemented carbide scrap was then oxidatively roasted to obtain a mixture of tungsten oxide (WO ₃ ) and cobalt tungstate (CoWO ₄ ). Then, the resulting mixture was extracted with an aqueous sodium hydroxide (NaOH) solution to obtain a tungsten compound solution containing sodium tungstate (Na2WO ₄ ). Since each process up to this point is the same as the above-described embodiment, detailed description thereof is omitted.

Next, the resulting tungsten compound solution was ion-exchanged with an ion exchange resin or the like to produce an aqueous solution of ammonium tungstate ((NH ₄ ) ₂ WO ₄ ). Then, the resulting aqueous solution was heated and concentrated to crystallize the tungsten compound as ammonium paratungstate (APT).

Next, the obtained APT was thermally decomposed to oxidize the APT, and a tungsten oxide powder (WO ₃ ) of Reference Example was obtained.

As shown in FIG. 2, metal tungsten (W) can be obtained by heat-treating the obtained tungsten oxide powder in a reducing atmosphere to reduce the tungsten oxide compound. By carbonizing the obtained metal tungsten, it is possible to obtain tungsten carbide (WC) as a raw material of cemented carbide.

Next, the obtained tungsten oxide powders of the embodiment and reference example were subjected to pore size distribution measurement by mercury porosimetry. The measurement conditions for pore size distribution measurement by the mercury intrusion method are as follows.

As a pretreatment, constant temperature drying was performed under the conditions of 120 (° C.) and 4 hours. After that, a pore distribution with a pore radius of about 0.0018 (μm) to 100 (μm) was obtained by a mercury intrusion method. Autopore V9620 (manufactured by Micromeritics) was used as a measuring device. The pore diameter was calculated using the following Washburn formula.
Washburn's formula: PD = -4σ · cos θ
P: pressure D: pore diameter σ: surface tension of mercury (480 (dynes/cm))
θ: contact angle between mercury and sample (140 (°))

FIG. 3 is a diagram showing the results of pore distribution measurement of the tungsten oxide powder according to the embodiment by mercury porosimetry. Moreover, FIG. 4 is a view showing the results of pore size distribution measurement by mercury porosimetry of tungsten oxide powder in the reference example.

In addition, Table 1 shows the cumulative pore volume, average pore radius, bulk density and porosity of the tungsten oxide powder obtained by the mercury intrusion method.

　As shown in Figures 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 the SEM observation photographs of the tungsten oxide powder in the embodiment and reference example shown in FIGS.

By making the powder with a large cumulative pore volume in this way, it is possible to promote the diffusion of hydrogen gas into the powder in the hydrogen reduction treatment for producing metal tungsten from the tungsten oxide powder.

Therefore, according to the embodiment, since the tungsten oxide powder can be efficiently reduced, tungsten carbide can be efficiently produced from the tungsten oxide powder.

In addition, as shown in FIGS. 3 and 4, in the powder contained in the tungsten oxide powder according to the embodiment, the mode pore diameter (the pore diameter with the largest log differential pore volume) is 0.2, which is smaller than that of the reference example. (μm).

In this way, by using a powder with a small mode pore diameter, it is possible to promote the diffusion of hydrogen gas into the powder in the hydrogen reduction treatment for producing metal tungsten from the tungsten oxide powder.

Also, 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. In this way, by using a powder having a large average pore radius, it is possible to promote the diffusion of hydrogen gas into the powder in the hydrogen reduction treatment for producing metal tungsten from the tungsten oxide powder. Also, when the tungsten oxide powder is directly reduced and carbonized with the carbon powder, an efficient solid phase reaction can be achieved.

Also, 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 smaller than that of the reference example. In this way, by using a powder having a low bulk density, it is possible to promote the diffusion of hydrogen gas into the powder in the hydrogen reduction treatment for producing metallic tungsten from the tungsten oxide powder.

Also, as shown in Table 1, the porosity of the powder contained in the tungsten oxide powder according to the embodiment is 76 (%), which is higher than that of the reference example. By forming the powder with a large porosity in this way, it is possible to promote the diffusion of hydrogen gas into the powder in the hydrogen reduction treatment for producing metallic tungsten from the tungsten oxide powder.

Further, as shown in FIG. 3, in the powder contained in the tungsten oxide powder according to the embodiment, the maximum peak of the Log differential pore volume is in the range of 0.01 (μm) or more and 1 (μm) or less of the pore diameter. exist. In the embodiment, when the peak value is Ip, 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 of the peak value Ip. I know there is.

Further, as shown in FIG. 3, in the powder contained in the tungsten oxide powder according to the embodiment, the peak value having a log differential pore volume of 0.2 (mL / g) or more and 1 (mL / g) or less exists in the range of pore diameters from 0.01 (μm) to 1 (μm). In the embodiment, the value of the Log differential pore volume is 0.05 (mL/g) or more in the pore diameter range of 1 (μm) or more and 100 (μm) or less.

The tungsten oxide powder of the present disclosure has the characteristic of contributing to an effective synthesis method in synthesizing tungsten carbide, which is the main raw material of cutting tools. The process of producing tungsten carbide from tungsten oxide powder includes an indirect process of reducing with hydrogen gas and then carbonizing with carbon powder, and a direct process of reducing and carbonizing with carbon powder.

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.

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

On the other hand, in the case of the carbon reduction treatment in the direct process and the carbonization treatment in both processes, the solid-phase reaction between the powders causes the carbon powder to successfully enter the inside of the tungsten oxide powder (or metal tungsten powder) with only fine pores. It does not enter, and it is difficult to become an efficient solid-phase reaction.

Therefore, in the tungsten oxide powder according to the embodiment, 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) below), it has the excellent feature of being able to handle both indirect and direct processes.

In addition, the specific surface areas of the tungsten oxide powders in the obtained embodiments and reference examples were measured by the BET method. The measurement conditions of the BET method are as follows.

A Macsorb HM model-1220 manufactured by Mountec was used as a measuring device. The measurement conditions were the BET 1-point method (according to JIS R 1626-1996) using a flow system, and the samples were heated at 200 (° C.) for 10 minutes or longer before being measured. Nitrogen (N ₂ : mixed concentration 30.2 (%) flow rate 25 (ml/min)) was used as the adsorption gas.

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

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), which is larger than that of the reference example.

By making the powder with a large specific surface area in this way, it is possible to promote the contact between the powder and hydrogen gas in the hydrogen reduction treatment for producing metallic tungsten from the tungsten oxide powder.

In addition, the average particle size of the powder contained in the obtained tungsten oxide powder according to the embodiment was evaluated by SEM observation. As a result, 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).

As a result, in the embodiment, the particle size of the metal tungsten powder after reduction becomes moderately coarse, so that the intended tungsten carbide synthesis becomes possible without causing the spontaneous ignition phenomenon peculiar to the metal powder.

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 embodiment shows the case of producing (recycling) tungsten oxide powder and tungsten carbide from cemented carbide scrap, but the present disclosure is not limited to such examples, and tungsten oxide powder and tungsten carbide are produced from ore. It can also be applied when generating

Further effects and other aspects can be easily derived by those skilled in the art. Therefore, the broader aspects of the invention are not limited to the specific details and representative embodiments so shown and described. Accordingly, various changes may be made without departing from the spirit or scope of the general inventive concept defined by the appended claims and equivalents thereof.

Claims

Containing powder mainly composed of tungsten oxide crystal grains,
When the pore distribution of the powder is measured by a mercury intrusion method,
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 average pore radius of the powder is 0.2 (μm) or more,
The tungsten oxide powder has a specific surface area of 3 (m 2 /g) to 5.5 (m 2 /g) when measured by the BET method.
In the pore distribution curve showing the relationship between the pore diameter and the Log differential pore volume when the pore distribution of the powder is measured by the mercury intrusion method,
When the maximum peak of the log differential pore volume exists in the range of pore diameters of 0.01 (μm) or more and 1 (μm) or less, and the peak value is Ip,
The tungsten oxide powder according to claim 1, wherein 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.
In the pore distribution curve showing the relationship between the pore diameter and the Log differential pore volume when the pore distribution of the powder is measured by the mercury intrusion method,
A peak having a log differential pore volume 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 tungsten oxide powder according to claim 1 or 2, wherein the log differential pore volume in a pore diameter range of 1 (μm) or more and 100 (μm) or less is 0.05 (mL/g) or more.
When the pore distribution of the powder is measured by a mercury intrusion method,
The powder has a porosity of 65 (%) to 85 (%),
The pore diameter with the highest frequency in the powder exists in the range of 0.01 (μm) to 1 (μm),
The tungsten oxide powder according to any one of claims 1 to 3, wherein the powder has an average particle size of 100 (nm) to 1000 (nm).