Manufacturing method of tungsten carbide powder

Abstract

To provide a method for producing tungsten carbide powder by which the particle size of tungsten carbide powder produced by a direct carbonization method can be controlled.SOLUTION: A mixture of tungsten oxide powder and carbon powder is granulated and the resulting granules are heat-treated in an inert gas atmosphere at a heating temperature of 1,400°C or more to obtain tungsten carbide powder by reduction and carbonization reactions. Tungsten carbide powder with a particle size of Y1±10% of tungsten carbide is produced from a mixture of tungsten oxide and carbon powder with a tapping density X1 corresponding to a target tungsten carbide particle size Y1 based on a proportional relation Y=aX+b (a and b are each a constant) of a tapping density X (g / cm3) of the carbon powder and a particle size Y (μm) of tungsten carbide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing tungsten carbide powder that is capable of controlling the particle size of the tungsten carbide powder when produced by a direct carbonization method. [Background technology]

[0002] The above-mentioned tungsten carbide powder is mainly used as a raw material for WC-Co based cemented carbide (hereinafter referred to as cemented carbide). Cemented carbide is used for cutting tools, wear-resistant tools, wear-resistant parts, etc., and in order to achieve various properties such as hardness, strength, toughness, wear resistance, fracture resistance, and chipping resistance depending on the application, it is necessary to optimize the particle size of the tungsten carbide powder, the amount of cobalt added, the amount of grain growth inhibitor added, etc. In particular, the particle size of the tungsten carbide powder has a significant effect on the alloy properties, and in order to exhibit alloy properties suitable for each application, it is necessary to strictly control the particle size of the tungsten carbide powder.

[0003] Generally, tungsten carbide powder is synthesized by hydrogen reduction of a tungsten-containing compound such as tungsten oxide powder (WO3 powder) to produce tungsten powder, which is then mixed with carbon and carbonized. Since the particle size of tungsten carbide powder is strongly dependent on the tungsten powder, controlling the particle size of its precursor, tungsten powder, is important for controlling the particle size of the tungsten carbide powder. Therefore, in the hydrogen reduction process of a tungsten-containing compound, it is necessary to combine a complex number of operating factors that affect the particle size of the tungsten powder, such as the hydrogen flow rate, the partial pressure of the generated water vapor, and the reduction temperature, which makes the manufacturing process complicated and increases the manufacturing cost. Furthermore, since tungsten powder and hydrogen are flammable and explosive, there are safety concerns in this manufacturing process.

[0004] Here, for example, in the direct carbonization method shown in Patent Document 1, tungsten oxide powder and carbon powder are directly mixed and heated, for example, in a nitrogen atmosphere at 1050-1200°C, and then in a hydrogen atmosphere at 900-1300°C for a predetermined time, thereby synthesizing tungsten carbide powder by successively reducing the tungsten oxide powder to tungsten powder and carbonizing the tungsten powder to tungsten carbide powder. The direct carbonization method is a method that has succeeded in shortening the reduction and carbonization steps required in conventional methods, and has significant advantages in terms of production cost and safety. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-335997 Summary of the Invention [Problem to be solved by the invention]

[0006] However, as described in Patent Document 1, the tungsten carbide powder obtained by the direct carbonization method can only be an ultrafine powder of 100 nm or less, and in addition, particle size control requires a complex and strict set of conditions, as the starting materials, heating furnace, atmosphere, heating temperature, and crushing method must be appropriately combined. Other methods for particle size control include extending the heating time or increasing the heating temperature, but these increase the manufacturing lead time and energy consumption, which raises concerns about poor economic efficiency. Therefore, if a direct carbonization technique can be acquired that can produce tungsten carbide powder of desired particle size easily and at low cost, the direct carbonization method will be able to replace conventional methods as a new production process for tungsten carbide powder that is superior in terms of economy, safety, and ease of particle size control.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing tungsten carbide powder that is capable of controlling the particle size of the tungsten carbide powder produced by the direct carbonization method. [Means for solving the problem]

[0008] In order to solve the above problems, the method for producing tungsten carbide powder of the present invention comprises granulating a mixed powder of tungsten oxide powder and carbon powder, heat-treating the resulting granules in an inert gas atmosphere at a heating temperature of 1400°C or higher, and obtaining tungsten carbide powder through a reduction reaction and a carbonization reaction, and the tapping density X (g / cm) of the carbon powder is 3 The method is characterized in that tungsten carbide powder with a tungsten carbide particle size of Y1±10% is produced from a mixed powder of tungsten oxide and carbon powder with a tapping density X1 corresponding to the target tungsten carbide particle size Y1, based on the proportional relationship Y=aX+b (a and b are constants) between the tapping density X1 and the tungsten carbide particle size Y (μm). Here, tungsten oxide refers to WO3 (Yellow Tungsten Oxide), WO 2.9 The stoichiometric ratio of tungsten and oxygen is not limited.

[0009] Here, if the tapping density of the carbon powder is high, the voids in the granules will be reduced, and the distance between the tungsten oxide and the carbon will be reduced, which will promote the grain growth of the tungsten carbide produced by the progress of the reduction reaction and the carbonization reaction, resulting in coarsening of the grain size of the tungsten carbide powder. Therefore, by determining the relationship between the tapping density of carbon powder and the particle size of tungsten carbide for a given heating temperature and a given holding time in the heating furnace, and adjusting the tapping density of the carbon powder used based on this relationship, it is possible to control the particle size of the tungsten carbide powder produced. From a mixed powder of carbon powder with a tapping density of X1 corresponding to the target tungsten carbide particle size Y1, the particle size of the tungsten carbide powder can be produced within a range of ±10% of Y1, taking into account variations in particle size during production.

[0010] In the method for producing tungsten carbide powder of the present invention, when the heating temperature of the heating furnace is 1600°C and the holding time is 30 minutes, the tapping density X (g / cm 3 The method is characterized in that tungsten carbide powder with a tungsten carbide particle size of Y1±10% is produced from a mixed powder of tungsten oxide and carbon powder with a tapping density X1 corresponding to the target tungsten carbide particle size Y1, based on the relational equation Y=0.40X+0.10 between the tapping density X1 and the tungsten carbide particle size Y (μm). In this case, when the heating temperature of the heating furnace is 1600°C and the holding time is 30 minutes, the tapping density of the carbon powder is X (g / cm 3 The tapping density of the carbon powder used is adjusted based on the relational expression Y=0.40X+0.10 between the tapping density of the carbon powder and the particle size Y (μm) of the tungsten carbide, so that the particle size of the produced tungsten carbide powder can be stably controlled.

[0011] In the method for producing tungsten carbide powder of the present invention, the tapping density of the carbon powder is set to 0.15 g / cm 3 More than 0.50g / cm 3 It is preferable to set it within the following range. In this case, the tapping density of the carbon powder is 0.15 g / cm 3 Since the tapping density of the carbon powder is set to 0.50 g / cm or more, the reduction reaction and the carbonization reaction can be sufficiently promoted, and the tungsten carbide powder can be efficiently produced. 3 Since the above conditions are satisfied, it is possible to prevent the granulated material from hanging, etc., and it is possible to stably produce tungsten carbide powder. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a method for producing tungsten carbide powder that is capable of controlling the particle size of the tungsten carbide powder produced by the direct carbonization method. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a flow diagram of a method for producing a tungsten carbide powder according to an embodiment of the present invention. [Figure 2] FIG. 2 is an explanatory diagram illustrating the grain growth process of tungsten carbide. [Figure 3] 1 is a graph showing the relationship between the tapping density of carbon powder and the average particle size of tungsten carbide powder. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, a method for producing tungsten carbide powder according to one embodiment of the present invention will be described in detail with reference to the accompanying drawings. The method for producing tungsten carbide powder according to this embodiment is for producing tungsten carbide powder that is used as a raw material for cutting tools, wear-resistant tools, and the like made of cemented carbide.

[0015] The method for producing tungsten carbide powder according to this embodiment is a so-called direct carbonization method, in which tungsten oxide and carbon are mixed and heat-treated to successively reduce the tungsten oxide and carbonize the tungsten obtained by the reduction reaction, thereby obtaining tungsten carbide. As an example, the reaction formula when WO3 is used as tungsten oxide is shown in formula (1) below. WO3+(4-a)C→WC+(3-2a)CO+aCO2···(1)

[0016] As shown in FIG. 1, this embodiment includes a mixing step S01 in which tungsten oxide powder and carbon powder are mixed to obtain a mixed powder, a kneading step S02 in which water is added to the obtained mixed powder and kneaded to obtain a wet powder, a granulation step S03 in which the obtained wet powder is granulated to obtain a granulated product, a drying step S04 in which the obtained granulated product is dried, and a heat treatment step S05 in which the dried granulated product is heat treated.

[0017] (Mixing process S01) First, tungsten oxide powder and carbon powder are mixed together. Here, the mixing ratio of the tungsten oxide powder and the carbon powder is preferably such that the molar ratio C / W of tungsten oxide to carbon is in the range of 3.50 to 4.00. By setting the molar ratio of tungsten oxide to carbon (C / W) to 3.50 or higher, the amount of carbon is secured and the inclusion of insufficiently carbonized WC in the WC powder can be prevented. On the other hand, by setting the molar ratio of tungsten oxide to carbon (C / W) to 4.00 or lower, the inclusion of excess C in the WC powder can be prevented. The tungsten oxide powder used as the raw material may be, for example, a powder obtained by calcining ammonium paratungstate (APT), and the carbon powder may be, for example, carbon black or graphite carbon. Furthermore, as the mixer, in addition to a general mixer with blades, a media mixer such as a ball mill can be used.

[0018] (Kneading process S02) Next, pure water is added to the mixed powder of tungsten oxide powder and carbon powder obtained in the mixing step S01 and kneaded to obtain a wet powder. Here, pure water is water with an electrical conductivity of 1 mS / m or less. There are no limitations on the method for purifying the water, and distillation, ion exchange, membrane treatment, etc. can be applied. The amount of pure water added varies depending on the specific surface area of ​​the carbon. 2 In the case of carbon having a content of 10 ... 2 / g or more, 30m 2In the case of carbon of less than 10000000 / g, the weight of the mixed powder of tungsten oxide powder and carbon powder is preferably 0.15 to 0.25 times. 2 In the case of carbon of less than 1 / g, it is desirable that the carbon content be 0.05 times or more and 0.15 times or less the weight of the mixed powder of tungsten oxide powder and carbon powder. By setting the amount of pure water to be equal to or greater than the lower limit, it is possible to ensure sufficient moisture and ensure granulation to the desired particle size. Furthermore, by setting the amount of pure water to be equal to or less than the upper limit, it is possible to prevent excess moisture, prevent the wet powder from adhering to the inner wall surfaces of the apparatus, and prevent a decrease in production efficiency. The pure water may be added dropwise to a mixture of tungsten oxide powder and carbon powder. After adding pure water, the mixture is kneaded to form a uniform wet powder.

[0019] (Pelletization process S03) Next, the wet powder obtained in the kneading step S02 is granulated to produce a granulated product. Here, it is preferable to set the size of the granules appropriately taking into consideration ease of handling in subsequent steps. In this embodiment, the size of the granules is set within the range of 0.5 mm to 3.0 mm. By making the size of the granules 0.5 mm or more, the fluidity of the granules in the furnace in the subsequent heat treatment step is improved, enabling stable heat treatment.On the other hand, by making the size of the granules 3.0 mm or less, it is possible to reliably carbonize the granules in the subsequent heat treatment step. The granulation method may be extrusion granulation, stirring granulation, or the like.

[0020] (Drying process S04) Next, the granulated material obtained in the granulation step S03 is dried to remove moisture contained therein. There are no particular restrictions on the dryer used, but in order to prevent the granules from collapsing during the drying process, a belt conveyor type dryer that does not move the granules is preferable. The drying temperature should be 120°C or higher.

[0021] (Heat treatment process S05) The dried granules are then charged into a heating furnace and subjected to heat treatment, whereby the reduction reaction of tungsten oxide and the carbonization reaction of the tungsten obtained by the reduction reaction proceed, as shown in the above formula (1), to obtain tungsten carbide. In this embodiment, a rotary kiln is used as the heating furnace. In this embodiment, the heating temperature is set to 1400° C. or higher, and the holding time at the heating temperature is set to 5 minutes or longer. By setting these conditions, the reaction shown in formula (1) can be promoted.

[0022] The lower limit of the heating temperature in the heat treatment step S05 is preferably 1600°C or higher. On the other hand, there is no particular upper limit to the heating temperature in the heat treatment step S05, but from the viewpoint of energy saving, it is preferably 2000°C or lower. By setting the temperature to 1600°C or higher, the particle size of the tungsten carbide can be increased to 0.1 μm or more. Furthermore, the lower limit of the holding time at the heating temperature in the heat treatment step S05 is preferably 15 minutes or more. On the other hand, there is no particular upper limit to the holding time at the heating temperature in the heat treatment step S05, but from the viewpoint of energy saving, it is preferably 60 minutes or less. By holding the heating temperature for 15 minutes or more, the particle size of the tungsten carbide can be increased to 0.1 μm or more.

[0023] The inside of the heating furnace must be an inert atmosphere, and examples of the inert gas that can be used include nitrogen gas and argon gas. Furthermore, it is preferable that the inert gas flows in the opposite direction (countercurrent) to the direction of travel of the granules, and that the gas flow rate in the kiln is 0.4 m / min or less. The gas flow rate in the kiln is calculated as follows: Gas flow rate in the kiln (m / min) = N2 flow rate (L / min) / cross-sectional area of ​​the rotary kiln (m 2 ) x 10 -3 CO gas is produced by the reaction shown in formula (1), but by suppressing the flow rate of the inert gas inside the furnace and thereby suppressing the emission of CO gas, CO gas can be used as a reducing agent, further promoting the reaction shown in formula (1). It is more preferable that the inert gas flow rate inside the furnace is 0.1 m / min or less.

[0024] In this embodiment, the particle size of the produced tungsten carbide powder is controlled by adjusting the tapping density of the carbon powder used in the mixing step S01. In a granulated product obtained by granulating a mixed powder of tungsten oxide powder and carbon powder, the higher the tapping density of the carbon powder, the higher the density of the granulated product. In high-density granules, the voids within the granules are reduced, bringing the tungsten oxide powder and the carbon powder closer together. As a result, heat transfer from the furnace and mass transfer of chemical species (tungsten oxide, carbon, etc.) during heat treatment are facilitated, promoting the reduction reaction and carbonization reaction by the solid carbon, which is thought to result in the rapid completion of the production of tungsten carbide.

[0025] A schematic diagram of grain growth is shown in Figure 2. Grain growth occurs when powder particles come into contact with each other and bond together. Therefore, the closer the particles are to each other and the larger the contact surface, the more favorable it is for grain growth. When high-density granules are heated, the carbonization reaction is completed early in the heating process, compared to when low-density granules are heated for the same time and at the same temperature, allowing the remaining heating time to be used for tungsten carbide grain growth. Furthermore, the arrangement of the resulting tungsten carbide particles inherits the arrangement of the tungsten oxide powder and carbon powder during granulation. Therefore, when high-density granules are used, the tungsten carbide particles are closer to each other, resulting in a larger contact surface. As a result, grain growth is promoted, and the final particle size of the tungsten carbide increases.

[0026] In this embodiment, the tapping density X (g / cm 3 Based on the proportional relationship Y=aX+b (where a and b are constants) between the tapping density X1 and the particle size Y (μm) of tungsten carbide, tungsten carbide powder with a particle size of Y1±10% is produced from a mixed powder of tungsten oxide and carbon powder with a tapping density X1 that corresponds to the target particle size Y1 of tungsten carbide.

[0027] In this embodiment, when the heating temperature of the heating furnace in the heat treatment step S05 is 1600°C and the holding time is 30 minutes, the tapping density X (g / cm 3 It is preferable to control the particle size of the tungsten carbide powder based on the tapping density of the carbon powder, based on the relational expression Y=0.40X+0.10 between the tapping density of the carbon powder and the particle size Y (μm) of the tungsten carbide.

[0028] In this embodiment, the tapping density of the carbon powder is 0.15 g / cm 3 More than 0.50g / cm 3 It is preferable to set it within the following range. The tapping density of the carbon powder is 0.15 g / cm 3 By setting the tapping density of the carbon powder at 0.50 g / cm or more, it is possible to form granules with a sufficiently high density, and it is possible to promote the reaction shown in formula (1). 3 By setting the following, it is possible to prevent the occurrence of hanging of the granulated material.

[0029] According to the method for producing tungsten carbide powder of this embodiment configured as described above, a mixed powder of tungsten oxide powder and carbon powder is granulated, and the granulated product is heat-treated to obtain tungsten carbide powder. The tapping density X (g / cm 3 The tapping density of the carbon powder used is adjusted based on the proportional relationship Y=aX+b (where a and b are constants) between the density of the granulated material and the particle size Y (μm) of the tungsten carbide. Therefore, the degree of particle growth of the produced tungsten carbide changes depending on the density of the granulated material, making it possible to control the particle size of the produced tungsten carbide powder.

[0030] In the method for producing tungsten carbide powder according to the present embodiment, when the heating temperature of the heating furnace is 1600°C and the holding time is 30 minutes, if the tapping density of the carbon powder used is adjusted based on the relational expression Y = 0.40X + 0.10, it is possible to control the particle size of the produced tungsten carbide powder.

[0031] In the method for producing tungsten carbide powder according to the present embodiment, the tapping density of the carbon powder is set to 0.15 g / cm 3 When the tapping density of the carbon powder is set to 0.50 g / cm or more, the reduction reaction and the carbonization reaction can be sufficiently promoted, and tungsten carbide powder can be efficiently produced. 3 When the above conditions are met, it is possible to prevent the granulated material from hanging, etc., and it is possible to stably produce tungsten carbide powder.

[0032] Although the embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate within the scope of the technical idea of ​​the invention. For example, in the present embodiment, a rotary kiln furnace is used as the heating furnace, but the present invention is not limited to this, and heating furnaces of other structures may also be used. [Example]

[0033] The results of confirmation experiments conducted to confirm the effectiveness of the present invention will be described below.

[0034] Tungsten oxide powder and carbon powder were mixed to obtain a mixed powder, and pure water was added to this mixed powder to make a wet powder, which was then extruded and granulated to produce granules with a particle size of 1.0 to 1.5 mm. The above granulated material was charged into a rotary kiln furnace in a nitrogen atmosphere and subjected to heat treatment under the conditions shown in Table 1 to produce tungsten carbide powder.

[0035] At this time, the carbon powders used were those shown in Table 1. The tapping density of the carbon powder was measured as follows. As a measuring device, the inner diameter is 1.5 cm and the diameter is 0.2 cm. 3 20cm capacity with graduated markings 3A measuring cylinder of 1000 m2 was used. After filling the measuring cylinder to the brim with carbon powder, the excess carbon powder that had accumulated at the top of the container was scraped off. Next, tapping was performed continuously for 2 minutes at a tapping speed of 40 taps / min from a height of 1.5 cm. After that, the weight (m) of the carbon powder was measured using a balance capable of measuring to 0.1 g, and the volume (V) of the carbon powder was read. The carbon tapping density (ρt) was calculated using the following formula. ρt=m / V (2) The reason why the tapping time in this measurement method was set to 2 minutes is that the volume did not decrease even if tapping was continued for longer than that.

[0036] The carbonization rate and average particle size of the obtained tungsten carbide powder were evaluated, and the evaluation results are shown in Table 1. The relationship between the tapping density and average particle size of the carbon powder is shown in Figure 1. Here, the carbonization rate is the intensity (I) at the peak position of each component of W, WC, and WC obtained from X-ray diffraction analysis (XRD) of tungsten carbide powder. W , I W2C , I WC ) to obtain the carbonization rate (%) = (I WC / (I W +I W2C +I WC )) × 100. Here, the peak position (2θ) of W was set to 40.29, the peak position (2θ) of W2C was set to 39.46, and the peak position (2θ) of WC was set to 35.68. The analyzer used was an Ultima IV manufactured by Rigaku.

[0037] The average particle size is shown as the average particle size converted by the BET method, calculated from the BET specific surface area after measuring the BET specific surface area by gas adsorption. The average particle size by the BET method is calculated from the specific surface area, assuming that the particles are uniform and spherical. It can be calculated using the following formula. Here, the theoretical density of tungsten carbide is 15.7 g / cm. 3 is. BET equivalent particle size [μm] = 6 / (theoretical density [g / cm 3 ]×BET specific surface area [m 2 / g])

[0038] [Table 1]

[0039] As shown in Table 1 and Figure 3, a proportional relationship was confirmed between the tapping density of the carbon powder and the average particle size of the produced tungsten carbide powder. Here, if the average particle size of the tungsten carbide powder is Y and the tapping density of the carbon powder is X, this relationship can be expressed by the following formula. By using this formula, it is possible to precisely and easily control the particle size of the tungsten carbide powder. Y=0.40X+0.10

[0040] In addition, the tapping density of the carbon powder was set to 0.15 g / m 3 In the above-described Test Nos. A to D, the carbonization rate exceeded 99.5%, and tungsten carbide powder was able to be produced efficiently.

[0041] From the above, it has been confirmed that the present invention can provide a method for producing tungsten carbide powder that can control the particle size of the tungsten carbide powder produced by the direct carbonization method.

Claims

1. a mixed powder of tungsten oxide powder and carbon powder is granulated, and the resulting granules are heat-treated in an inert gas atmosphere at a heating temperature of 1400°C or higher to obtain tungsten carbide powder through a reduction reaction and a carbonization reaction; Tapping density X (g / cm) of carbon powder ３ ) and the particle size Y (μm) of tungsten carbide Y = aX + b (a and b are constants) tungsten carbide powder having a particle size of Y1±10% is produced from a mixed powder of tungsten oxide and carbon powder having a tapping density X1 corresponding to a target particle size Y1 of tungsten carbide, based on the above.

2. When the heating temperature of the heating furnace is 1600°C and the holding time is 30 minutes, the tapping density X (g / cm ３ ) and the particle size Y (μm) of tungsten carbide 2. The method for producing tungsten carbide powder according to claim 1, characterized in that the tungsten carbide powder has a particle size of Y1±10% from a mixed powder of tungsten oxide and carbon powder having a tapping density X1 corresponding to the target particle size Y1 of tungsten carbide, based on Y=0.40X+0.

10.

3. The tapping density of the carbon powder is 0.15 g / cm ３ 0.50g / cm or more ３ The method for producing tungsten carbide powder according to claim 1 or 2, characterized in that the range is as follows:

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