WO2024005017A1

WO2024005017A1 - Tungsten carbide powder

Info

Publication number: WO2024005017A1
Application number: PCT/JP2023/023813
Authority: WO
Inventors: 貴彦牧野; 志賢青木; 直樹岩井
Original assignee: 京セラ株式会社
Priority date: 2022-06-30
Filing date: 2023-06-27
Publication date: 2024-01-04

Abstract

This tungsten carbide powder includes a powder containing, as a main ingredient, tungsten carbide crystal grains. In addition, when a region down to 5 (nm) in the depth direction from the outermost surface of the tungsten carbide crystal grains is analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS), the intensity ratio (SUM/W) of the total value (SUM) of secondary ion intensities of metal elements belonging to groups 4a, 5a, and 6a of the periodic table but excluding tungsten, chromium, and vanadium, with respect to the secondary ion intensity (W) of tungsten is 0.03 or more.

Description

tungsten carbide powder

The disclosed embodiments relate to tungsten carbide powder.

In recent years, the development of recycling technology for metals or metal compounds has been progressing. For example, tungsten carbide is a component of superhard alloys such as cemented carbide, is used together with cobalt, niobium, etc., and is often used in cutting tools and the like.

In addition, since the metal tungsten contained in tungsten carbide has a high melting point, it 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, and heat dissipation materials. ing. In order to effectively utilize these resources, a method of recycling tungsten from waste materials (scrap) has been devised (see Patent Document 1).

Japanese Patent Application Publication No. 2004-2927

The tungsten carbide powder according to one aspect of the embodiment includes powder whose main component is tungsten carbide crystal grains. Furthermore, when analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS) in a region up to 5 (nm) in the depth direction from the outermost surface of the tungsten carbide crystal grains, tungsten, chromium, and vanadium are excluded. The intensity ratio (SUM/W) between the sum of the secondary ion strengths (SUM) of metal elements in groups 4a, 5a, and 6a of the periodic table and the secondary ion strength (W) of tungsten is 0.03 or more.

FIG. 1 is a diagram showing the structure of tungsten carbide crystal grains according to an embodiment. FIG. 2 is a flowchart illustrating an example of the procedure of the tungsten carbide production process according to the embodiment. FIG. 3 is a flowchart illustrating an example of a procedure of a tungsten carbide generation process in a reference example. Figure 4 is a diagram showing the depth distribution of the intensity ratio (SUM/W) between the total value (SUM) of the secondary ion intensity of specific metal elements and the secondary ion intensity (W) of tungsten in tungsten carbide powder. be.

Hereinafter, embodiments of the tungsten carbide powder disclosed in the present application will be described with reference to the accompanying drawings. Note that the present invention is not limited to the embodiments described below.

In addition, since the metal tungsten contained in tungsten carbide has a high melting point, it 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, and heat dissipation materials. ing. In order to effectively utilize these resources, methods have been devised to recycle tungsten from waste materials (scrap).

On the other hand, in the above-mentioned conventional technology, when tungsten carbide powder produced by recycling technology is used, there is room for further improvement in terms of efficiently producing cemented carbide. Therefore, it is expected that a technology that can solve the above problems and efficiently produce cemented carbide will be realized.

The tungsten carbide powder according to the embodiment includes powder whose main component is tungsten carbide crystal grains 1 (see FIG. 1). For example, the tungsten carbide powder according to the embodiment includes powder consisting of tungsten carbide crystal grains 1 and inevitable impurities.

In the embodiment, a region from the outermost surface 1a (see FIG. 1) to 5 (nm) in the depth direction of the tungsten carbide crystal grains 1 was analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS). In this case, the intensity ratio (SUM/ W) may be 0.03 or more.

In the present disclosure, metal elements in groups 4a, 5a, and 6a of the periodic table (i.e., titanium, zirconium, hafnium, niobium, tantalum, and molybdenum) excluding tungsten, chromium, and vanadium are collectively referred to as "specific metal elements." To call.

In this way, the presence of a relatively large amount of specific metal elements that are highly soluble in cobalt on the surface of tungsten carbide powder increases the affinity between cobalt, which is used as a binder in cemented carbide, and tungsten carbide powder ( wettability).

As a result, when a mixed powder of tungsten carbide powder and cobalt powder is fired to produce cemented carbide, the liquefied cobalt in the temperature range where the liquid phase of cobalt starts to appear has a relatively large amount of specific metal elements. The surface of the tungsten carbide powder wets and spreads smoothly.

Therefore, according to the embodiment, since it is possible to generate cemented carbide by low-temperature firing, cemented carbide can be efficiently produced. Further, in the embodiment, since the crystals are finely densified when producing the cemented carbide, a cemented carbide with a small amount of deformation can be obtained.

In addition, in the embodiment, when analyzed by TOF-SIMS in a region from the outermost surface 1a of tungsten carbide crystal grains 1 to 5 (nm) in the depth direction, the total value of secondary ion intensities of specific metal elements ( The intensity ratio (SUM/W) between the tungsten secondary ion strength (SUM) and the tungsten secondary ion strength (W) may be 0.1 or more.

As a result, when sintering a mixed powder of tungsten carbide powder and cobalt powder to produce cemented carbide, the liquefied cobalt in the temperature range where the liquid phase of cobalt starts to appear becomes carbonized with a large amount of specific metal elements. Wet and spread even more smoothly on the surface of tungsten powder.

Therefore, according to the embodiment, cemented carbide can be produced more efficiently. Furthermore, in the embodiment, a cemented carbide with even less deformation can be obtained.

FIG. 1 is a diagram showing the structure of tungsten carbide crystal grains 1 according to an embodiment. In the embodiment, as shown in FIG. 1, a powder mainly composed of tungsten carbide crystal grains 1 includes a combined body 2 having a plurality of tungsten carbide crystal grains 1.

In the embodiment, in the grain boundaries 1b of the plurality of tungsten carbide crystal grains 1 in the combined body 2, the total value of the atomic ratios of the specific metal elements may be 1 (at%) or less.

In this way, by reducing the uneven distribution of specific metal elements at the grain boundaries 1b, the temperature of the mixed powder is raised to 1400 (°C) to 1600 (°C) and two-stage firing is performed in the manufacturing process of cemented carbide. In some cases, a mixed structure of coarse grains and fine grains can be easily formed. The reason is as follows.

Tungsten carbide crystal grains 1 have the property that grain growth is reduced in areas where the content of specific metal elements is high, but by creating a structure in which there is no segregation of specific metal elements at grain boundaries 1b of tungsten carbide crystal grains 1. , the grain boundaries 1b tend to become starting points for grain growth.

On the other hand, since the outermost surface 1a of the tungsten carbide crystal grains 1 has a relatively high content of the specific metal element as described above, it is difficult to become a starting point for grain growth.

In this way, in the embodiment, the combined body 2 has a mixture of places that are likely to become the starting point of grain growth and places that are difficult to start grain growth. When producing , a mixed structure of coarse grains and fine grains is likely to be formed.

That is, in the embodiment, by reducing the uneven distribution of the specific metal element at the grain boundaries 1b, a mixed structure of coarse grains and fine grains is more likely to be formed, so that a tough cemented carbide can be produced. .

Examples of the present disclosure will be specifically described below. FIG. 2 is a flowchart illustrating an example of the procedure of the tungsten carbide powder production process according to the embodiment. As shown in FIG. 2, in the process of producing tungsten carbide powder according to the embodiment, scraps of cemented carbide were first prepared.

Cemented carbide, which is a type of superhard alloy, is mainly composed of composite carbides such as tungsten metal and tungsten carbide, and has a binder phase of iron, nickel, cobalt, etc., and optionally contains TiC, TaC, NbC, etc. as additive components. Contains VC, _Cr3C2 _{, etc.}

Materials to be treated containing cemented carbide include, 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.).

Next, the prepared cemented carbide scrap was oxidized and roasted to obtain a mixture of tungsten oxide (WO ₃ ) and cobalt tungstate (CoWO ₄ ). Then, the obtained mixture was refluxed with an aqueous sodium hydroxide (NaOH) solution and extracted, thereby obtaining 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 cause tungsten compound ions to be adsorbed to lysine (denoted as lysine-WO ₄ in the figure).

Note that the adsorbent in the present disclosure is not limited to containing lysine, and may also include alanine, cystine, methionine, tyrosine, valine, glutamic acid, and histidine. Histidine), Proline, Threonine, Asparagine, Glycine, Isoleucine, Ornithine, Arginine, Serine, Citrulline and Cystathionine ( Cystathionine).

In such adsorption treatment, for example, the total amount of the first amino acid salt added in the adsorbent is 0.2 (mol) to 1.1 (mol) per 1 (mol) of the metal component of the tungsten compound. Add in proportions. This allows a large amount of tungsten compounds to be adsorbed with a small amount of adsorbent.

Further, the total amount of the first amino acid salt added is, for example, 10 (g/l) to 300 (g/l) with respect to the tungsten compound solution. This prevents the viscosity of the solution from increasing, making it difficult for the recovery efficiency of the metal compound to decrease. In particular, when the adsorbent is made of an amino acid salt, the viscosity of the solution does not increase easily and the workability is good.

The temperature may be adjusted depending on the activity of the free amino acid, and usually room temperature is sufficient. The tungsten compound solution containing the adsorbent 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 tungsten compound ions, which are anions.

Additionally, 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 0.5-3.0, desirably pH=0.8-2.3. When the free amino acid is glutamic acid, the preferred pH is 1.5 or less.

Thereby, the recovery rate of the tungsten compound can be increased. Note that either the step of adjusting the pH of the solution or the step of adding an adsorbent into 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 takes place within 1 hour. That is, if the adsorption reaction exceeds 1 hour, part of the adsorbed metal compound may be desorbed from the free amino acid.

Following the adsorption step onto lysine, the adsorbent on which the tungsten compound ions were adsorbed was filtered using a means such as a filter.

Next, the filtered adsorbent was washed in the order of acid washing and pure water washing as necessary. Note that the filtered adsorbent may be washed with warm water of 40 (° C.) or higher instead of acid washing. Then, impurities were removed by washing with pure water until the electrical conductivity of the washing filtrate became 500 (μS/m) or less. This makes it possible to improve the quality of the tungsten compound and recover it.

Next, the washed adsorbent was compressed by means such as a compressor. Then, a required amount of at least one of titanium alkoxide compound powder, zirconium alkoxide compound powder, niobium oxalate powder, ammonium molybdate powder, and tantalum oxalate powder was added to the compressed adsorbent.

The amount of the titanium alkoxide compound powder added is preferably 0.3 (wt%) to 33 (wt%) based on the dry weight of the adsorbent containing tungsten, and the amount of the zirconium alkoxide compound powder added is, for example, It is preferably 0.1 (wt%) to 20.0 (wt%) based on the dry weight of the adsorbent containing tungsten.

For example, the amount of niobium oxalate powder added is preferably 0.1 (wt%) to 20.0 (wt%) based on the dry weight of the adsorbent containing tungsten, and the amount of ammonium molybdate powder added is , for example, preferably 0.1 (wt%) to 20.0 (wt%) based on the dry weight of the adsorbent containing tungsten. The amount of tantalum oxalate powder added is preferably, for example, 0.1 (wt%) to 12.0 (wt%) based on the dry weight of the tungsten-containing adsorbent.

Furthermore, the water absorption rate of the adsorbent after pressing is preferably 40 (%) or more. In this way, by including a large amount of water in the adsorbent, each powder added to the compressed adsorbent can be well dissolved in the adsorbent.

Next, the adsorbent on which the tungsten compound ions have been adsorbed is dried and further incinerated at a temperature of 300 (℃) or higher in the air to oxidize the tungsten compound and remove organic components including the adsorbent and additives. did. As a result, tungsten oxide powder (WO ₃ ) was obtained.

Next, the obtained tungsten oxide powder was heat treated at a temperature of 800 (°C) to 950 (°C) in a reducing atmosphere (for example, hydrogen gas atmosphere) to reduce the tungsten oxide compound. As a result, metallic tungsten (W) was obtained. Finally, the obtained tungsten metal was carbonized to obtain tungsten carbide powder (WC) according to the embodiment.

FIG. 3 is a flowchart illustrating an example of a procedure for producing tungsten carbide powder in a reference example. As shown in FIG. 3, in the step of producing tungsten carbide powder in the reference example, scraps of cemented carbide were first prepared.

Next, the prepared cemented carbide scrap was oxidized and roasted to obtain a mixture of tungsten oxide (WO ₃ ) and cobalt tungstate (CoWO ₄ ). Then, the obtained mixture was extracted with an aqueous sodium hydroxide (NaOH) solution to obtain a tungsten compound solution containing sodium tungstate ( _Na2WO4 ). Each step up to this point is the same as in the above-described embodiment, so detailed explanation will be omitted.

Next, the obtained 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 ). The resulting aqueous solution was then heated and concentrated to crystallize a tungsten compound as ammonium paratungstate (APT).

Next, the obtained APT was oxidized by thermally decomposing it. As a result, tungsten oxide powder (WO ₃ ) was obtained.

Next, the obtained tungsten oxide powder was heat treated in a reducing atmosphere to reduce the tungsten oxide compound. As a result, metallic tungsten (W) was obtained. Finally, the obtained tungsten metal was carbonized to obtain a tungsten carbide powder (WC) as a reference example.

Next, the obtained tungsten carbide powders of the embodiment and reference example were analyzed by TOF-SIMS (Time-Of-Flight Secondary Ion Mass Spectrometry). Specifically, the depth distribution of tungsten and specific metal elements in the tungsten carbide powders of the embodiment and the reference example was measured by TOF-SIMS.

The TOF-SIMS measurement conditions are as follows. The tungsten carbide powders of the embodiment and the reference example were fixed, and the powder surface was measured at a 100 (μm) square. The measuring device is TOF. manufactured by ION-TOF. Using SIMS5, Bi (bismuth) was selected as the primary ion source, and elemental analysis in the depth direction was measured.

In addition, elemental analysis in the depth direction was conducted for Samples 1 and 2, which are tungsten carbide powders according to the embodiment, and Samples 3 and 4, which are tungsten carbide powders in the reference example. Then, for each sample, the depth distribution of the intensity ratio (SUM/W) between the total value (SUM) of the secondary ion intensity of the specific metal element and the secondary ion intensity (W) of tungsten was determined.

Figure 4 is a diagram showing the depth distribution of the intensity ratio (SUM/W) between the total value (SUM) of the secondary ion intensity of specific metal elements and the secondary ion intensity (W) of tungsten in tungsten carbide powder. be.

As shown in FIG. 4, in the tungsten carbide powders (samples 1 and 2) according to the embodiment, all regions from the outermost surface 1a (see FIG. 1) of tungsten carbide crystal grains 1 to 5 (nm) in the depth direction It can be seen that the intensity ratio (SUM/W) is 0.03 or more.

On the other hand, in the tungsten carbide powders in the reference examples (samples 3 and 4), the strength is low in at least a part of the region from the outermost surface 1a (see FIG. 1) of the tungsten carbide crystal grains 1 to 5 (nm) in the depth direction. It can be seen that the ratio (SUM/W) is not 0.03 or more.

As described above, in the embodiment, by increasing the concentration of the specific metal element on the outermost surface 1a of the tungsten carbide crystal grains 1 and in the vicinity thereof, the cemented carbide can be efficiently produced as described above. Further, in the embodiment, by increasing the concentration of the specific metal element at the outermost surface 1a of the tungsten carbide crystal grains 1 and its vicinity, a cemented carbide with a small amount of deformation can be obtained.

Moreover, as shown in FIG. 4, in the tungsten carbide powders (samples 1 and 2) according to the embodiment, all of the tungsten carbide crystal grains 1 from the outermost surface 1a (see FIG. 1) to 5 (nm) in the depth direction It can be seen that the intensity ratio (SUM/W) is 0.1 or more in the region.

On the other hand, in the tungsten carbide powders in the reference examples (samples 3 and 4), the strength is low in at least a part of the region from the outermost surface 1a (see FIG. 1) of the tungsten carbide crystal grains 1 to 5 (nm) in the depth direction. It can be seen that the ratio (SUM/W) is not 0.1 or more.

As described above, in the embodiment, by further increasing the concentration of the specific metal element at the outermost surface 1a of the tungsten carbide crystal grains 1 and its vicinity, the cemented carbide can be produced more efficiently as described above. . Furthermore, in the embodiment, by further increasing the concentration of the specific metal element at the outermost surface 1a of the tungsten carbide crystal grains 1 and its vicinity, a cemented carbide with a smaller amount of deformation can be obtained.

In addition, in the obtained tungsten carbide powder combined body 2 according to the embodiment, the atomic ratios of various elements within the tungsten carbide crystal grains 1 and the atomic ratios of various elements at the grain boundaries 1b were measured using STEM (Scanning Transmission). Measured using an Electron Microscope (scanning transmission electron microscope).

Specifically, by using STEM, the inside of the tungsten carbide crystal grain 1 was measured at two locations, and the grain boundary 1b of the tungsten carbide crystal grain 1 was measured at three locations, and various elements within the grain and at the grain boundary 1b were measured. The average value of the atomic ratio was determined.

The STEM measurement conditions are as follows. First, as sample pretreatment, the sample was sliced into thin sections using the FIB method (μ-sampling method). Next, the thin sectioned sample was subjected to STEM observation using a scanning transmission electron microscope (JEM-ARM200F manufactured by JEOL Ltd.). The observation conditions were an accelerating voltage of 200 (kV) and a magnification accuracy of ±10 (%).

Then, during STEM observation, elemental analysis (point analysis) was performed by energy dispersive X-ray spectroscopy (EDX) using an elemental analyzer (JED-2300T manufactured by JEOL Ltd.) installed in the STEM microscope. .

The analysis conditions are: acceleration voltage of 200 (kV), beam diameter of approximately 0.1 (nmφ), X-ray detector is a Si drift detector, energy resolution of approximately 140 (eV), and X-ray extraction angle of 21.9. (°), the solid angle was 0.98 (sr), and the acquisition time was 60 (seconds). Table 1 shows the STEM measurement results.

As shown in Table 1, in the tungsten carbide powder according to the embodiment, the specific metal element is It can be seen that the total value of the atomic ratios is 1 (at%) or less.

Note that in Table 1, only molybdenum is listed as a specific metal element, but this is because the atomic ratio of specific metal elements other than molybdenum was less than 0.1 (at%).

In this way, by reducing the uneven distribution of specific metal elements at the grain boundaries 1b, as mentioned above, it is possible to heat the mixed powder to 1400 (°C) to 1600 (°C) in the manufacturing process of cemented carbide. When performing two-stage firing, it is possible to easily form a mixed structure of coarse grains and fine grains. Therefore, according to embodiments, a tough cemented carbide can be produced.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit thereof. For example, in the above embodiment, a case is shown in which tungsten carbide is generated (recycled) from cemented carbide scrap, but the present disclosure is not limited to such an example, and can also be applied to the generation of tungsten carbide from ore. can do.

Further effects and other embodiments 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 shown and described above. Accordingly, various changes may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

1 Tungsten carbide crystal grain 1a Outermost surface 1b Grain boundary 2 Combined body

Claims

Contains powder whose main component is tungsten carbide crystal grains,
When analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS) in a region up to 5 (nm) in the depth direction from the outermost surface of the tungsten carbide crystal grains, the periodic law excluding tungsten, chromium, and vanadium Tungsten carbide powder whose intensity ratio (SUM/W) between the total secondary ion strength (SUM) of metal elements in Groups 4a, 5a, and 6a in Tables 4a, 5a, and 6a and the secondary ion strength (W) of tungsten is 0.03 or more. .
The intensity ratio (SUM/W) between the sum of the secondary ion strengths (SUM) of metal elements in groups 4a, 5a, and 6a of the periodic table excluding tungsten, chromium, and vanadium and the secondary ion strength (W) of tungsten is The tungsten carbide powder according to claim 1, wherein the tungsten carbide powder is 0.1 or more.
The powder includes a combined body having a plurality of the tungsten carbide crystal grains,
In the grain boundaries of the plurality of tungsten carbide crystal grains in the combined body, the total atomic ratio of metal elements of Groups 4a, 5a, and 6a of the periodic table excluding tungsten, chromium, and vanadium is 1 (at%) or less. The tungsten carbide powder according to claim 1 or 2.