Tungsten carbide powder

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 (V / W) of the secondary ion intensity (V) of vanadium to the secondary ion intensity (W) of tungsten is 0.05 or more.

Description

Technical Field

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[0001] The disclosed embodiments relate to tungsten carbide powder.

Background Art

[0002] In recent years, the development of recycling technologies for metals or metal compounds has been underway. For example, tungsten carbide is a component constituting cemented carbides such as superhard alloys, and is used together with cobalt, niobium, etc., and is widely used in cutting tools and the like.

[0003] Moreover, since the metal tungsten contained in tungsten carbide has a high melting point, it is used in various applications such as heating elements, structural members, catalysts for petrochemical industries, environmental equipment, wiring of ceramic wiring boards, heat dissipation members, etc. In order to effectively utilize 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

Summary of the Invention

[0005] The tungsten carbide powder of the present disclosure contains a powder mainly composed of tungsten carbide crystal grains. Further, in the region from the outermost surface of the tungsten carbide crystal grains to a depth of 5 (nm) in the depth direction, when analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS), the intensity ratio (V / W) of the secondary ion intensity (V) of vanadium to the secondary ion intensity (W) of tungsten is 0.05 or more.

Brief Description of the Drawings

[0006] [Figure 1] FIG. 1 is a diagram showing the structure of tungsten carbide crystal grains according to an embodiment. [Figure 2]Figure 2 is a flowchart showing an example of the procedure for the tungsten carbide production process according to this embodiment. [Figure 3] Figure 3 is a flowchart showing an example of the procedure for the tungsten carbide production process in a reference example. [Figure 4] Figure 4 shows the depth-direction distribution of the intensity ratio (V / W) between the secondary ionic intensity of vanadium (V) and the secondary ionic intensity of tungsten (W) in tungsten carbide powder. [Modes for carrying out the invention]

[0007] The embodiments of the tungsten carbide powder disclosed herein will be described below with reference to the attached drawings. However, the embodiments described below are not the sole limiting factor of this disclosure.

[0008] In recent years, the development of recycling technologies for metals and metal compounds has been progressing. For example, tungsten carbide is a component of cemented carbide alloys and is used together with cobalt, niobium, etc., and is widely used in cutting tools and other applications.

[0009] Furthermore, due to its high melting point, metallic tungsten contained in tungsten carbide is used in a variety of applications, including heating elements, structural components, catalysts for the petrochemical industry, environmental equipment, wiring for ceramic circuit boards, and heat dissipation components. To effectively utilize these resources, methods for recycling tungsten from waste materials (scrap) have been devised.

[0010] On the other hand, the conventional technology described above had room for further improvement in terms of efficiently producing cemented carbide when using tungsten carbide powder generated by recycling technology. Therefore, there is a need to realize a technology that can solve the above problems and efficiently produce cemented carbide.

[0011] The tungsten carbide powder according to this embodiment includes a powder mainly composed of tungsten carbide crystal grains 1 (see Figure 1). For example, the tungsten carbide powder according to this embodiment includes a powder consisting of tungsten carbide crystal grains 1 and unavoidable impurities.

[0012] Furthermore, in the embodiment, when the region from the outermost surface 1a (see Figure 1) of the tungsten carbide crystal grain 1 to a depth of 5 nm is analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS), the intensity ratio (V / W) of the secondary ion intensity of vanadium (V) to the secondary ion intensity of tungsten (W) may be 0.05 or greater.

[0013] Thus, the relatively high solubility of vanadium in cobalt on the surface of tungsten carbide powder increases the affinity (wettability) between cobalt, which is used as a binder in cemented carbide, and tungsten carbide powder.

[0014] As a result, when producing cemented carbide by firing a mixed powder of tungsten carbide powder and cobalt powder, the liquefied cobalt in the temperature range where the liquid phase of cobalt begins to appear smoothly wets and diffuses on the surface of the tungsten carbide powder, which contains a relatively large amount of vanadium.

[0015] Therefore, according to the embodiment, cemented carbide can be produced by low-temperature firing, allowing for efficient production of cemented carbide. Furthermore, in the embodiment, the crystals are neatly densified during the production of the cemented carbide, resulting in a cemented carbide with minimal deformation.

[0016] Furthermore, in the embodiment, when the region from the outermost surface 1a of the tungsten carbide crystal grain 1 to a depth of 5 nm is analyzed by TOF-SIMS, the intensity ratio (V / W) of the secondary ionic intensity of vanadium (V) to the secondary ionic intensity of tungsten (W) may be 0.30 or higher.

[0017] As a result, when sintering a mixed powder of tungsten carbide powder and cobalt powder to produce a cemented carbide, the liquefied cobalt in the temperature range where the liquid phase of cobalt starts to appear wets and diffuses more smoothly on the surface of the tungsten carbide powder with a high vanadium content.

[0018] Therefore, according to the embodiment, a cemented carbide can be produced more efficiently. Further, in the embodiment, a cemented carbide with less deformation can be obtained.

[0019] FIG. 1 is a diagram showing the structure of tungsten carbide crystal grains 1 according to the embodiment. In the embodiment, as shown in FIG. 1, a powder mainly composed of tungsten carbide crystal grains 1 includes an aggregate 2 having a plurality of tungsten carbide crystal grains 1.

[0020] And in the embodiment, at the grain boundaries 1b of the plurality of tungsten carbide crystal grains 1 in the aggregate 2, the atomic ratio of vanadium may be 1 (at%) or less.

[0021] Thus, by reducing the uneven distribution of vanadium at the grain boundaries 1b, when the mixed powder is heated to 1400 (°C) to 1600 (°C) and two-stage sintering is performed in the manufacturing process of the cemented carbide, it is possible to easily form a mixed structure of coarse grains and fine grains. The reason is as follows.

[0022] The tungsten carbide crystal grains 1 have the property that grain growth is reduced in places with a high vanadium content. However, by adopting a structure in which there is no segregation of vanadium at the grain boundaries 1b of the tungsten carbide crystal grains 1, the grain boundaries 1b are likely to become the starting points of grain growth.

[0023] On the other hand, since the outermost surface 1a of the tungsten carbide crystal grains 1 has a relatively high vanadium content as described above, it is difficult to become the starting point of grain growth.

[0024] Thus, in the embodiment, since locations where grain growth is likely to occur and locations where it is unlikely to occur are mixed in the combined body 2, when firing a mixed powder of tungsten carbide powder and cobalt powder to produce a cemented carbide, a mixed structure of coarse grains and fine grains is likely to be formed.

[0025] That is, in the embodiment, since the uneven distribution of vanadium at the grain boundaries 1b is reduced, a mixed structure of coarse grains and fine grains is likely to be formed, so that a tough cemented carbide can be produced.

Example

[0026] Hereinafter, examples of the present disclosure will be specifically described. FIG. 2 is a flowchart showing an example of the procedure of the production process of tungsten carbide powder according to the embodiment. As shown in FIG. 2, in the production process of tungsten carbide powder according to the embodiment, first, cemented carbide scrap was prepared.

[0027] Cemented carbide, which is a type of hard alloy, mainly consists of composite carbides such as metallic tungsten and tungsten carbide, has iron, nickel, cobalt, etc. as binding phases, and contains TiC, TaC, NbC, VC, Cr3C2, etc. as additive components as required.

[0028] The workpiece containing the target cemented carbide is, for example, a cutting tool (cutting insert, drill, end mill, etc.), a mold (forming roll, mold, etc.), a tool for civil engineering and mining (tool for oil drilling, tool for rock crushing, etc.).

[0029] Next, the prepared cemented carbide scrap was oxidatively roasted to obtain a mixture of tungsten oxide (WO3) and cobalt tungstate (CoWO4). Then, after refluxing the obtained mixture with an aqueous sodium hydroxide (NaOH) solution and extracting, a tungsten compound solution containing sodium tungstate (Na2WO4) was obtained.

[0030] Next, an adsorbent containing lysine was added to the obtained tungsten compound solution to adsorb the tungsten compound ions onto the lysine (labeled as lysine-WO4 in the figure).

[0031] Furthermore, the adsorbent in this disclosure is not limited to containing lysine, but may also contain at least one first amino acid from among alanine, cystine, methionine, tyrosine, valine, glutamic acid, histidine, proline, threonine, asparagine, glycine, isoleucine, ornithine, arginine, serine, citrulline, and cystathionine.

[0032] In this adsorption treatment, for example, the total amount of salt of the first amino acid in the adsorbent is added at a content ratio of 0.2 to 1.1 moles per mole of the metal component of the tungsten compound. This makes it possible to adsorb a large amount of tungsten compound with a small amount of adsorbent.

[0033] Furthermore, 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, thus minimizing the decrease in the recovery efficiency of the metal compound. In particular, when the adsorbent consists of an amino acid salt, the viscosity of the solution does not increase easily, resulting in good workability.

[0034] The temperature can be adjusted according to the activity of the free amino acids, and is usually fine at room temperature. The tungsten compound solution with the adsorbent added may also be adjusted using hydrochloric acid or the like so that the zeta potential of the free amino acids becomes positive. This allows the tungsten compound ions, which are anions, to be adsorbed onto the adsorbent.

[0035] Furthermore, the pH of the solution may be less than 7 (acidic). When the free amino acids are lysine and arginine, the preferred pH is 4 or less, preferably 0.5 to 3.0, and more preferably pH = 0.8 to 2.3. When the free amino acid is glutamic acid, the preferred pH is 1.5 or less.

[0036] This increases the recovery rate of tungsten compounds. Note that the order of the steps—adjusting the pH of the solution and adding the adsorbent to the solution containing the metal compound—does not matter.

[0037] When the adsorbent is a salt of the first amino acid, the recovery efficiency of the adsorbent is higher if the adsorption reaction is completed within one hour. In other words, if the adsorption reaction exceeds one hour, some of the adsorbed metal compound may detach from the free amino acid.

[0038] Following the adsorption process onto lysine, the adsorbent containing the adsorbed tungsten compound ions was filtered using a filter or other means.

[0039] Next, the filtered adsorbent was washed with acid and then pure water, as needed. Alternatively, the filtered adsorbent could be washed with hot water at 40°C or higher instead of acid. Then, impurities were removed by washing with pure water until the electrical conductivity of the washing filtrate was 500 μS / m or less. This process allowed for the recovery of high-grade tungsten compounds.

[0040] Next, the washed adsorbent was compressed using a press or similar means. Then, the required amount of ammonium vanadate powder was added to the compressed adsorbent. The amount of ammonium vanadate powder added is preferably 0.1 (wt%) to 10.0 (wt%) relative to the dry weight of the tungsten-containing adsorbent. However, if the raw material, cemented carbide scrap, contains the required amount of vanadium, the addition of ammonium vanadate powder may be omitted.

[0041] Furthermore, it is desirable that the water absorption rate of the adsorbent after pressing be 40% or higher. By allowing the adsorbent to contain a large amount of moisture in this way, the ammonium vanadate powder added to the adsorbent after pressing can be dissolved well in the adsorbent.

[0042] Next, the adsorbent on which tungsten compound ions were adsorbed was dried, and then, for example, it was incinerated in air at a temperature of 300°C or higher to oxidize the tungsten compound and remove organic components including the adsorbent and additives. This yielded tungsten oxide powder (WO3).

[0043] Next, the obtained tungsten oxide powder was 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 yielded metallic tungsten (W). Finally, the obtained metallic tungsten was carbonized to obtain tungsten carbide powder (WC) according to the embodiment.

[0044] Figure 3 is a flowchart showing an example of the procedure for producing tungsten carbide powder in the reference example. As shown in Figure 3, in the tungsten carbide powder production process in the reference example, cemented carbide scrap was first prepared.

[0045] Next, the prepared cemented carbide scrap was oxidized and roasted to obtain a mixture of tungsten oxide (WO3) and cobalt tungstate (CoWO4). Then, the obtained mixture was extracted with an aqueous 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 embodiment described above, a detailed explanation is omitted.

[0046] Next, the obtained tungsten compound solution was subjected to ion exchange using an ion exchange resin to produce an aqueous solution of ammonium tungstate ((NH4)2WO4). Then, the obtained aqueous solution was heated and concentrated to crystallize the tungsten compound as ammonium paratungstate (APT).

[0047] Next, the obtained APT was oxidized by thermal decomposition. This yielded tungsten oxide powder (WO3).

[0048] Next, the obtained tungsten oxide powder was heat-treated in a reducing atmosphere to reduce the tungsten oxide compound. This yielded metallic tungsten (W). Finally, the obtained metallic tungsten was carbonized to obtain tungsten carbide powder (WC), the reference example.

[0049] Next, the tungsten carbide powders of the obtained embodiments and reference examples were analyzed using TOF-SIMS (Time-Of-Flight Secondary Ion Mass Spectrometry). Specifically, the depth distribution of tungsten and vanadium in the tungsten carbide powders of the embodiments and reference examples was measured using TOF-SIMS.

[0050] The measurement conditions for TOF-SIMS were as follows: Tungsten carbide powder from the embodiment and reference example was fixed, and the powder surface was measured at a 100 μm square. The measuring instrument used was ION-TOF's TOF.SIMS5, with Bi (bismuth) selected as the primary ion source, and elemental analysis in the depth direction was measured.

[0051] Furthermore, elemental analysis in the depth direction was performed on samples 1 and 2, which are tungsten carbide powder according to the embodiment, and on samples 3 and 4, which are tungsten carbide powder according to the reference example. Then, the depth direction distribution of the intensity ratio (V / W) of the secondary ionic intensity of vanadium (V) to the secondary ionic intensity of tungsten (W) was determined for each sample.

[0052] Figure 4 shows the depth-direction distribution of the intensity ratio (V / W) between the secondary ionic intensity of vanadium (V) and the secondary ionic intensity of tungsten (W) in tungsten carbide powder.

[0053] As shown in Figure 4, in the tungsten carbide powder (samples 1 and 2) according to the embodiment, the intensity ratio (V / W) is 0.05 or higher in all regions from the outermost surface 1a (see Figure 1) of the tungsten carbide crystal grain 1 to a depth of 5 nm.

[0054] On the other hand, in the tungsten carbide powders in the reference examples (samples 3 and 4), it can be seen that the intensity ratio (V / W) is not 0.05 or higher in at least a portion of the region from the outermost surface 1a (see Figure 1) of the tungsten carbide crystal grain 1 to a depth of 5 nm.

[0055] Thus, in this embodiment, by increasing the vanadium concentration on the outermost surface 1a of the tungsten carbide crystal grains 1 and its vicinity, cemented carbide can be efficiently produced as described above. Furthermore, in this embodiment, by increasing the vanadium concentration on the outermost surface 1a of the tungsten carbide crystal grains 1 and its vicinity, cemented carbide can be obtained with less deformation.

[0056] Furthermore, as shown in Figure 4, in the tungsten carbide powder (samples 1 and 2) according to the embodiment, the intensity ratio (V / W) is 0.30 or higher in all regions from the outermost surface 1a (see Figure 1) of the tungsten carbide crystal grain 1 to a depth of 5 nm.

[0057] On the other hand, in the tungsten carbide powders in the reference examples (samples 3 and 4), it can be seen that the intensity ratio (V / W) is not 0.30 or higher in at least a portion of the region from the outermost surface 1a (see Figure 1) of the tungsten carbide crystal grain 1 to a depth of 5 nm.

[0058] Thus, in this embodiment, by further increasing the vanadium concentration on the outermost surface 1a of the tungsten carbide crystal grains 1 and its vicinity, cemented carbide can be produced more efficiently, as described above. Furthermore, in this embodiment, by further increasing the vanadium concentration on the outermost surface 1a of the tungsten carbide crystal grains 1 and its vicinity, cemented carbide can be obtained with less deformation.

[0059] Furthermore, in the tungsten carbide powder composite 2 obtained 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 a STEM (Scanning Transmission Electron Microscope).

[0060] Specifically, using STEM, measurements were taken at two locations within tungsten carbide grain 1, and at three locations along the grain boundary 1b of tungsten carbide grain 1. The average values ​​of the atomic ratios of various elements within the grain and at the grain boundary 1b were then determined.

[0061] The STEM measurement conditions were as follows: First, the sample was thinned using the FIB method (μ-sampling method) as a sample pretreatment. Next, the thinned sample was observed using a scanning transmission electron microscope (JEM-ARM200F, manufactured by JEOL Ltd.). The observation conditions were an acceleration voltage of 200 kV and a magnification accuracy of ±10%.

[0062] During STEM observation, elemental analysis (point analysis) was performed using energy-dispersive X-ray spectroscopy (EDX) with an elemental analyzer (JED-2300T manufactured by JEOL Ltd.) installed on the STEM microscope.

[0063] The analysis conditions were as follows: acceleration voltage of 200 kV, beam diameter of approximately 0.1 nmφ, X-ray detector as a Si drift detector, energy resolution of approximately 140 eV, X-ray extraction angle of 21.9°, solid angle of 0.98 sr, and acquisition time of 60 seconds. The STEM measurement results are shown in Table 1.

[0064] [Table 1]

[0065] As shown in Table 1, in the tungsten carbide powder according to the embodiment, the atomic ratio of vanadium is 1 (at%) or less at the grain boundaries 1b (labeled as "grain boundary" in Table 1) of the multiple tungsten carbide crystal grains 1 within the bond 2.

[0066] Thus, by reducing the uneven distribution of vanadium at the grain boundary 1b, as described above, when the mixed powder is heated to 1400°C to 1600°C and subjected to a two-stage sintering process in the manufacturing process of cemented carbide, it becomes easier to form a mixed structure of coarse and fine grains. Therefore, according to this embodiment, a tough cemented carbide can be produced.

[0067] While embodiments of this disclosure have been described above, this disclosure is not limited to the above embodiments, and various modifications are possible without departing from its spirit. For example, although the above embodiments show the case of producing (recycling) tungsten carbide from cemented carbide scrap, this disclosure is not limited to such examples and can also be applied to the production of tungsten carbide from ore, etc.

[0068] Further effects and other embodiments can be readily derived by those skilled in the art. Therefore, broader embodiments of this disclosure are not limited to the specific details and representative embodiments expressed and described above. Accordingly, various modifications are possible without departing from the spirit or scope of the overall concept of the invention as defined by the appended claims and their equivalents. [Explanation of Symbols]

[0069] 1. Tungsten carbide crystal grains 1a Top surface 1b Grain boundary 2 conjugate

Claims

1. It contains a powder mainly composed of tungsten carbide crystal grains. In the region from the outermost surface of the tungsten carbide crystal grains to a depth of 5 nm, analysis by time-of-flight secondary ion mass spectrometry (TOF-SIMS) reveals that the intensity ratio (V / W) of the secondary ionic intensity of vanadium (V) to the secondary ionic intensity of tungsten (W) is 0.05 or greater. Tungsten carbide powder.

2. The intensity ratio (V / W) of the secondary ionic intensity of vanadium (V) to the secondary ionic intensity of tungsten (W) is 0.30 or higher. The tungsten carbide powder according to claim 1.

3. The powder comprises a composite having a plurality of tungsten carbide crystal grains, In the grain boundaries of the plurality of tungsten carbide crystal grains within the composite body, the atomic ratio of vanadium is 1 (at%) or less. Tungsten carbide powder according to claim 1 or 2.

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