How tungsten carbide is produced

Abstract

To provide a method for manufacturing tungsten carbide that can manufacture tungsten carbide with a high yield while simplifying the carbonization process.SOLUTION: A method for manufacturing tungsten carbide includes: a granulation step of mixing carbon and tungsten carbide to produce granules; and a carbonization step S05 of charging the produced granules into a heat treatment furnace, heating the produced granules while supplying an inert gas to a reaction region of the heat treatment furnace, and carbonizing the tungsten oxide to produce tungsten carbide. In the carbonization process S05, a flow rate of the inert gas to be supplied is set to 0.1 m / min or less when a temperature in the reaction region is less than 1500°C, and the flow rate of the inert gas to be supplied is set to 0.4 m / min or less when the temperature in the reaction region is 1500°C or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing tungsten carbide. [Background technology]

[0002] Tungsten carbide can be produced by reacting carbon with tungsten oxide, specifically by reducing and carbonizing tungsten oxide. When WO3 is used as tungsten oxide and WC is produced as tungsten carbide by the direct carbonization method, WO3 is reduced and carbonized to WC according to the following formula: WO3+3C→ W+3CO (A) 2W+C→W2C (B) W2C+C→2WC (C)

[0003] In the reduction process (A), CO is released to produce W. In the carbonization process (B) and (C), W reacts with C to produce WC.

[0004] Patent Document 1 describes a two-stage rotary carbonization furnace that performs the above reaction, with the first stage of carbonization being carried out in a nitrogen atmosphere (1300°C to 1600°C), followed by the second stage of carbonization in a hydrogen atmosphere (1400°C to 1700°C) to produce WC. Patent Document 2 describes a method for producing tungsten carbide by vapor-phase carburization, in which WO3 is carbonized to WC by CO. In vapor-phase carburization, WO3 and CO are reacted over a time period in a CO2 atmosphere (800°C to 1000°C) to produce WC. Patent Documents 3-5 also describe the production of WC by a first stage of carbonization in an inert gas atmosphere and a second stage of carbonization in a hydrogen atmosphere. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 2617140 [Patent Document 2] Patent No. 3963649 [Patent Document 3] Japanese Patent Application Publication No. 03-208811 [Patent Document 4] Japanese Patent Application Laid-Open No. 2005-335997 [Patent Document 5] Japanese Patent Application Laid-Open No. 2006-176405 Summary of the Invention [Problem to be solved by the invention]

[0006] The methods described in Patent Documents 1, 3-5 can produce tungsten carbide, but after carbonization in a nitrogen atmosphere, further carbonization is performed in a hydrogen atmosphere. Carbonization in a nitrogen atmosphere alone makes it difficult for steps (B) and (C) to proceed, resulting in a carbide that is a mixture of WC and WC, resulting in only a carbide with a low WC carbonization rate. By performing a second carbonization step in a hydrogen atmosphere on the carbide obtained in the first step, steps (B) and (C) are promoted, increasing the WC carbonization rate. This results in a two-step carbonization process, and requires additional equipment for carbonization in a hydrogen atmosphere. Furthermore, the use of hydrogen gas increases running costs. The vapor-phase carburization method described in Patent Document 2 requires a long production time due to the low-temperature reaction.

[0007] The present invention has been made in view of the above, and an object of the present invention is to provide a method for producing tungsten carbide that can produce tungsten carbide with a high yield while simplifying the carbonization process. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems and achieve the objects, the method for producing tungsten carbide according to the present disclosure includes a granulation step of mixing carbon and tungsten oxide to produce granules, and a carbonization step of charging the produced granules into a heat treatment furnace and heating them while supplying an inert gas to a reaction zone of the heat treatment furnace to carbonize the tungsten oxide to produce tungsten carbide, wherein in the carbonization step, when the temperature in the reaction zone is less than 1500°C, the flow rate of the inert gas supplied is 0.1 m / min or less, and when the temperature in the reaction zone is 1500°C or higher, the flow rate of the inert gas supplied is 0.4 m / min or less. [Effects of the Invention]

[0009] The method for producing tungsten carbide according to the present invention has the effect of simplifying the carbonization process and producing tungsten carbide with a high yield. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a flowchart showing a method for producing tungsten carbide. [Figure 2] FIG. 2 is a schematic diagram showing an example of a carbonization apparatus including a rotary kiln. [Figure 3] FIG. 3 is a graph showing an example of the weight change of WO3 depending on the temperature. [Figure 4] FIG. 4 is a graph showing an example of the measurement results of the sieve particle size and the total carbon content of the granulated product. [Figure 5] FIG. 5 is a table showing the test results of the examples. [Figure 6] FIG. 6 is a table showing the results of another experimental example. [Figure 7] FIG. 7 is a graph showing the results of another experimental example. [Figure 8] FIG. 8 is a graph showing the results of another experimental example. [Figure 9] FIG. 9 is a graph showing the results of another experimental example. DETAILED DESCRIPTION OF THE INVENTION

[0011] A method for producing tungsten carbide powder according to one embodiment of the present invention will be described in detail below with reference to the accompanying drawings. The method for producing tungsten carbide powder according to this embodiment is intended to produce tungsten carbide powder for use as a raw material for cutting tools and wear-resistant tools made of cemented carbide, for example. However, the tungsten carbide powder may be used for any purpose. The present invention is not limited to the following detailed description of the invention (hereinafter referred to as the "embodiment"). Furthermore, the components in the following embodiments include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that fall within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be combined as appropriate.

[0012] 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 produce tungsten carbide by continuously reducing the tungsten oxide and carbonizing the tungsten metal obtained by the reduction reaction, as shown in the following formula (1): a in formula (1) may be any positive number. WO3+(4-a)C→WC+(3-2a)CO+aCO2···(1)

[0013] Formula (1) is a reaction formula when WO3 is used as tungsten oxide and WC is obtained as tungsten carbide. However, the tungsten oxide used in this embodiment is not limited to WO3 and may be tungsten oxide of any composition. In other words, W xa O ya (xa and ya are any positive numbers). Similarly, the tungsten carbide produced in this embodiment is not limited to WC and may be tungsten carbide of any composition. In other words, W xb C yb The tungsten carbide may be represented by the chemical formula (xb, yb are any positive numbers).

[0014] The method for producing tungsten carbide will be described with reference to Fig. 1. Fig. 1 is a flowchart showing the method for producing tungsten carbide.

[0015] The method for producing tungsten carbide according to this embodiment produces tungsten carbide by processing carbon and tungsten oxide as raw materials. The method includes a granulation step of mixing carbon and tungsten oxide to produce granules, and a carbonization step of introducing the produced granules into a heat treatment furnace and heating the granules while supplying an inert gas to a reaction zone of the heat treatment furnace to carbonize the tungsten oxide to produce tungsten carbide. 1, the present embodiment includes a mixing step S01 of mixing tungsten oxide powder and carbon powder to obtain a mixed powder, a kneading step S02 of adding water to the obtained mixed powder and kneading the mixture to obtain a wet powder, a molding step S03 of granulating the obtained wet powder to obtain a granulated product, a drying step S04 of drying the obtained granulated product, and a carbonization step (heat treatment step) S05 of heat-treating the dried granulated product to carbonize it, as shown in FIG. 1. In this embodiment, the mixing step S01, the kneading step S02, the molding step S03, and the drying step S04 correspond to the above-mentioned granulation step, and the carbonization step S05 corresponds to the above-mentioned carbonization step.

[0016] (granulation process) (Mixing process S01) In the mixing step, the tungsten oxide powder and the carbon powder are mixed together. The mixing ratio of tungsten oxide powder and carbon powder is preferably such that the molar ratio C / W of carbon to tungsten oxide is close to 4, more preferably in the range of 3.50 to 4.00, and even more preferably in the range of 3.70 to 3.90. If it is less than 3.50, there will be too little carbon, and insufficiently carbonized WC may be mixed into the WC powder, while if it exceeds 4.00, there will be too much carbon, and excess C may be mixed into the WC powder, which is not preferable. The tungsten oxide powder used as the raw material can be, for example, a powder obtained by calcining ammonium paratungstate (APT). Carbon powder can be, for example, carbon black or graphite carbon. Furthermore, the mixer can be a general mixer with blades, or a media mixer such as a ball mill.

[0017] (Kneading process S02) Next, a kneading step is carried out in which water is supplied to the carbon and tungsten oxide mixed in the mixing step S01 to form a mixture (wet powder). Specifically, pure water is added to the mixed powder of tungsten oxide powder and carbon powder obtained in the mixture mixing step S01 and kneaded to obtain a mixture. Here, pure water is water with an electrical conductivity of 1 mS / m or less. There are no particular restrictions on the method of purifying the water, and distillation, ion exchange, membrane treatment, etc. can be applied. In the kneading step S02, it is preferable to adjust the amount of water supplied to a predetermined water content. Specifically, the water content is preferably 25 mass% or more and 30 mass% or less, more preferably 26.5 mass% or more and 29.2 mass% or less, and even more preferably 27.8 mass% or more and 29.2 mass% or less. Here, the water content (mass%) can be calculated by (amount of water added (kg)) × 100 / (amount of tungsten oxide added (kg) + amount of carbon added (kg)). The amount of pure water added may vary depending on the specific surface area of ​​the carbon. 2 In the case of carbon of 10 m / g or more, it is desirable that the weight of the mixed powder of tungsten oxide powder and carbon powder is 0.25 times or more and 0.35 times or less. 2 / g or more, 30m 2 In 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. 2In the case of carbon of less than 1 / g, the water content is preferably 0.05 to 0.15 times the weight of the mixed powder of tungsten oxide powder and carbon powder. If the water content or amount of water added is below the lower limit, the amount of water added may be too little and granulation to the desired particle size may not be possible, whereas if the water content exceeds the upper limit, the amount of water added may be too much, causing the wet powder to adhere to the inner walls of the apparatus, which may reduce production efficiency, and is therefore undesirable. The pure water can be added dropwise to the mixture of tungsten oxide powder and carbon powder. Alternatively, after adding the pure water, the mixture can be kneaded to form a uniformly wet powder.

[0018] The conditions for mixing and kneading the powders in the mixing step S01 and the kneading step S02 may be arbitrary. For example, the peripheral speed (peripheral velocity) of the rotating part of the mixer is preferably 5.9 m / s to 10 m / s, and more preferably 5.9 m / s to 8 m / s. The peripheral speed of the rotating part can be calculated as follows: Peripheral velocity (m / s) = outer diameter (mm) of chopper (rotating part) × 3.14 × rotation speed (rpm) of chopper (rotating part) / 1000 / 60. For example, if the rotation speed of the chopper of the mixer is 1400 rpm to 2400 rpm and the chopper outer diameter is 80 mm, the peripheral velocity can be 5.9 m / s to 10 m / s. If the rotation speed is less than 5.9 m / s, mixing and kneading may be insufficient. If the rotation speed is more than 10 m / s, mixing and kneading will not be improved and will become inefficient, which is not preferable. The above-mentioned conditions for mixing and kneading can be applied regardless of the type of granulation method (for example, extrusion granulation or stirring granulation) described below.

[0019] (Molding process S03) Next, a molding step is carried out in which the mixture obtained in the kneading step S02 is granulated to produce granulated material. Here, it is preferable to set the size of the granules appropriately, taking into consideration the ease of handling in subsequent steps. For example, in this embodiment, the size of the granules may be set within the range of 0.5 mm or more and 3.0 mm or less. The granulation method may be extrusion granulation, stirring granulation, or the like. If the size is less than 0.5 mm, the flowability of the granules in the furnace in the subsequent carbonization step may not be improved, and stable processing may not be possible. If the size exceeds 3.0 mm, carbonization may be insufficient in the subsequent carbonization step, which is not preferable.

[0020] When performing extrusion granulation, for example, the mixture obtained in the kneading step S02 is pressed toward a member having an opening, extruding the mixture through the opening of the member, and the rod-shaped mixture extruded from the opening is cut to obtain granular granules. By using extrusion granulation, the size of the granules can be made more uniform, which enables a uniform reaction in the subsequent carbonization step. Any device may be used to pressurize the mixture, and for example, a screw, plunger, roller, etc. may be used. Furthermore, the member having an opening for extrusion may also be any device, and for example, a plate-shaped member having multiple openings may be used, and the size of the opening for extrusion may be set according to the desired size of the granules.

[0021] When stirring and granulation is performed, for example, the mixture obtained in the kneading step S02 is stirred with a chopper for a predetermined time, for example, from 3 to 10 minutes, preferably from 5 to 8 minutes, after the addition of water is stopped, thereby producing a granulated product by granulating the mixture. If the stirring time is less than 3 minutes, the granulation may be insufficient, and if the stirring time is more than 10 minutes, the granulated product may become too large, which is not preferable.

[0022] (Drying process S04) Next, the granules obtained in the molding step S03 are dried to remove the moisture contained therein. There are no particular restrictions on the dryer used, but in order to prevent the granules from collapsing in the drying step S04, a belt conveyor type dryer, which does not move the granules, is preferred. The drying temperature is preferably 110°C or higher, and more preferably 120°C or higher.

[0023] For example, when performing agitation granulation, it is preferable to perform a sieving process in which the dried granules are sieved. In the sieving process, a sieve with 0.1 mm openings may be used to sieve the granules into those less than 0.1 mm and those greater than 0.1 mm. Granules less than 0.1 mm have a lower carbon content than granules greater than 0.1 mm, and carbonizing the granules containing granules less than 0.1 mm in the carbonization process will result in uneven carbonization. However, the threshold size of the granules in the sieving process is not limited to 0.1 mm and may be set arbitrarily according to the desired size of the granules. That is, in the sieving process, the obtained granules may be sieved into those less than a predetermined size and those greater than a predetermined size. Furthermore, the sieving process is not limited to being applied only to agitation granulation, but may also be applied to any granulation method, such as extrusion granulation. Conversely, the sieving process is not essential and may not be applied to agitation granulation.

[0024] When the sieving step is performed, a TC measurement is performed to measure the total carbon (TC) content of the under-sieve granules classified as smaller than a predetermined size (here, 0.1 mm), and the ratio of carbon to tungsten oxide is calculated from the measured total carbon content. The components are adjusted based on the calculated ratio, and the under-sieve granules are then fed back into the mixer for the mixing step. This allows the under-sieve granules to be granulated again, allowing for efficient use of the materials. Next, a TC measurement is performed to measure the total carbon content of the sieved granules classified into a predetermined size (here, 0.1 mm) or larger in the sieving step, and the ratio of carbon to tungsten oxide is calculated from the measured total carbon content. Once it is confirmed that the predetermined ratio is achieved, the granulation step can be terminated. In other words, the sieved granules whose TC has been measured are used as granules to proceed to the heat treatment step. In other words, the sieved granules may be used as granules to be used in the production of tungsten carbide.

[0025] (Carbonization process S05) Next, the carbonization step (heat treatment step) will be described. In the carbonization step, the dried granules are charged into a heat treatment furnace and subjected to heat treatment, whereby the reduction reaction of tungsten oxide and the carbonization reaction of the tungsten metal obtained by the reduction reaction proceed continuously, as shown in the above formula (1), to obtain tungsten carbide. In this embodiment, tungsten carbide can be obtained in a single carbonization step S05 under an inert gas atmosphere, and the WC carbonization rate can be increased without performing a second or subsequent carbonization step.

[0026] (Configuration of heat treatment furnace) In this embodiment, a rotary kiln is used as the heat treatment furnace. An example of a carbonization apparatus used in the heat treatment step will be described with reference to Fig. 2. Fig. 2 is a schematic diagram showing an example of a carbonization apparatus including a rotary kiln. The carbonization apparatus 10 shown in Fig. 2 includes a rotary kiln 11, a material charging device 18, a gas supply device 20, and an exhaust pipe 24.

[0027] The rotary kiln 11 includes a kiln body 12, a heater 14, and a drive unit 16. The kiln body 12 is a hollow, cylindrical member, into which granulated material is introduced by a material introduction device 18. The kiln body 12 is preferably arranged such that the central axis of the cylindrical shape is horizontal and the end where the material is introduced is tilted relative to the horizontal so that it is vertically higher than the other end. The heater 14 heats the kiln body 12. The heater 14 may be configured to heat the outer periphery of the kiln body 12, and a configuration in which the kiln body 12 is heated by a heating device may be used. A heating device using a burner may also be used as a supplement. The heater 14 can heat the kiln body 12 to a temperature range of 1300°C to 2000°C. The heater 14 is positioned within a distance L excluding both ends of the cylindrical shape of the kiln body 12. The range within the distance L where the heater 14 is positioned is the heating region. The range of distance L within which the heater 14 is arranged is a reaction region where WO3 is carbonized.

[0028] The drive unit 16 rotates the kiln body 12 around the central axis of the cylindrical shape. The drive unit 16 includes a drive source 30 and a transmission mechanism 32. The drive source 30 is a device that generates rotational force, such as a motor. The transmission mechanism 32 transmits the amount of rotation of the drive source 30 to the kiln body 12. The transmission mechanism 32 is, for example, an endless belt that is wound around both the drive source 30 and the kiln body 12. The transmission mechanism 32 may also be a structure that combines gears.

[0029] The material charging device 18 includes a material storage section 21 and a supply pipe 22. The material storage section 21 stores the granulated material produced in the granulation process. The supply pipe 22 connects the material storage section 21 to the kiln body 12 and supplies the granulated material from the material storage section 21 to the kiln body 12.

[0030] The gas supply device 20 includes a gas supply source 40, a supply pipe 42, and a discharge pipe 44. The gas supply source 40 is a source that supplies an inert gas. The inert gas is, for example, nitrogen (N2). In the following description, the inert gas will be referred to as nitrogen gas. The supply pipe 42 connects the gas supply source 40 to the kiln body 12. The supply pipe 42 is connected to an end of the kiln body 12 opposite to the end to which the supply pipe 22 that supplies the gas is connected. The discharge pipe 44 is connected to the end of the kiln body 12 to which the supply pipe 22 that supplies the granulated material is connected.

[0031] The discharge pipe 24 is connected to the end opposite to the end to which the supply pipe 22 of the kiln body 12 is connected. The discharge pipe 24 passes through the kiln body 12 and discharges the carbonized material.

[0032] The carbonization apparatus 10 supplies granulated material from the material feeding device 18 to the kiln body 12. The kiln body 12 is heated by the heater 14 and rotated in a rotation direction 54 by the drive unit 16. The granulated material supplied to the kiln body 12 moves along the conveying path 52 from the supply pipe 22 toward the discharge pipe 24 as the kiln body 12 rotates. The granulated material moving along the conveying path 52 is heated within a range of a distance L. In addition, in the carbonization apparatus 10, nitrogen is supplied from the gas supply device 20 to the kiln body 12 in the nitrogen gas flow direction 60, i.e., in the opposite direction to the conveying path 52. The carbonization apparatus 10 discharges the carbonized material that has passed through the kiln body 12 from the discharge pipe 24 and collects it. In addition, the gas from the kiln body 12 is discharged from the discharge pipe 44.

[0033] The configuration of the carbonization apparatus 10 used to produce tungsten carbide is not limited to the above and may be any configuration.

[0034] (Treatment conditions for carbonization process) Next, the processing conditions required for the carbonization step will be explained. In the carbonization step, the carbonization process is carried out in the carbonization apparatus 10 while satisfying the following processing conditions. The processing conditions are a combination of the nitrogen gas flow rate in the furnace and the heating temperature (temperature in the reaction area). The nitrogen gas flow rate in the furnace is the flow rate of nitrogen flowing through the kiln body 12 of the rotary kiln 11, and can be said to be the flow rate of nitrogen gas (inert gas) supplied to the reaction zone. The nitrogen gas flow rate in the furnace is calculated from the cross-sectional area of ​​the kiln body 12 and the amount of nitrogen gas supplied from the gas supply device 20. Specifically, the nitrogen gas flow rate in the furnace (m / min) = N2 flow rate (L / min) × 10 / cross-sectional area of ​​the kiln body 12 (cm 2 ) In this embodiment, since the reaction zone is inside the kiln body 12, the nitrogen gas flow rate in the furnace can be calculated as the amount of nitrogen gas supplied from the gas supply device 20 divided by the cross-sectional area of ​​the reaction zone as viewed from the direction of nitrogen gas flow. The cross-sectional area of ​​the reaction zone here may be the average value of the cross-sectional areas at each position in the reaction zone as viewed from the direction of nitrogen gas flow. However, the nitrogen gas flow rate in the furnace is not limited to being calculated in this way and may be obtained by any method, for example, it may be measured using a flow meter or the like. The heating temperature (temperature of the reaction zone) refers to the temperature in the reaction zone during the carbonization step, and may be measured, for example, by a thermometer installed in the reaction zone. In this embodiment, the reaction zone is the space within the distance L in which the heater 14 is disposed in the kiln body 12, as described above. However, the reaction zone is not limited thereto, and may refer to a space in a heat treatment furnace (rotary kiln 11 in this embodiment) during the carbonization step that is heated to a temperature at which tungsten oxide can be carbonized (for example, 1300°C) or higher.

[0035] In the carbonization process of this embodiment, when the heating temperature (temperature of the reaction zone) is less than 1500°C, the nitrogen gas flow rate in the furnace is set to 0.1 m / min or less, and when the heating temperature is 1500°C or higher, the nitrogen gas flow rate in the furnace is set to 0.4 m / min or less. By adjusting the combination of the nitrogen gas flow rate in the furnace and the temperature in the reaction zone in this manner, a high WC carbonization rate can be achieved in a single carbonization process, simplifying the carbonization process and producing tungsten carbide with a high yield. Furthermore, when producing tungsten carbide, CO gas is generated by the reaction shown in formula (1). However, by reducing the inert gas flow rate in the furnace as in this embodiment, CO gas emissions can be suppressed and CO gas can be used as a reducing agent, further promoting the reaction shown in formula (1). As shown in formula (1), CO and CO2 are generated as gases after the reaction, and the higher the temperature, the higher the proportion of CO gas. Therefore, at temperatures above 1500°C, the nitrogen gas flow rate can be increased compared to temperatures below 1500°C. It is preferable that the inert gas flows in the opposite direction (countercurrent) to the direction of travel of the granulated material.

[0036] Below, the conditions for the carbonization process when the heating temperature is less than 1500°C are referred to as the first conditions, and the conditions for the carbonization process when the heating temperature is 1500°C or higher are referred to as the second conditions, and the first and second conditions will be explained in more detail.

[0037] (First condition) In the first condition, the nitrogen gas flow rate in the furnace is preferably 0.1 m / min or less. If the flow rate exceeds the upper limit, the reduction effect to CO gas cannot be utilized and the carbonization reaction may not proceed sufficiently, which is undesirable. In the first condition, the temperature in the reaction zone is preferably 1300° C. or higher and lower than 1500° C. If the temperature is lower than the lower limit, the carbonization reaction may not proceed sufficiently, which is undesirable. In the first condition, the holding time, which is the time for which the granules are held at the heating temperature, is preferably 10 minutes or more and 90 minutes or less. The holding time may refer to the time for which the granules remain in the reaction zone heated to the heating temperature while nitrogen gas is being supplied. If the holding time is less than the lower limit, the carbonization reaction may not proceed sufficiently, while if the holding time is more than the upper limit, productivity decreases, which is undesirable. By setting the first condition in this way, a high WC carbonization rate can be achieved in a single carbonization treatment, and tungsten carbide can be produced with a high yield while simplifying the carbonization process.

[0038] (Second condition) In the second condition, the nitrogen gas flow rate in the furnace is preferably 0.4 m / min or less. If the flow rate exceeds the upper limit, the reduction effect to CO gas cannot be utilized, and the carbonization reaction may not proceed sufficiently, which is undesirable. In addition, under the second condition, the temperature in the reaction zone is preferably 1500° C. or higher and 2000° C. or lower, and more preferably 1700° C. or higher and 2000° C. or lower. If the temperature is lower than the lower limit, the carbonization reaction may not proceed sufficiently, while if the temperature is higher than the upper limit, power consumption increases, which undesirably increases production costs. In the second condition, the holding time is preferably 10 minutes or more and 90 minutes or less. If it is less than the lower limit, the carbonization reaction may not proceed sufficiently, and if it is more than the upper limit, the productivity decreases, which is not preferable. By setting the second condition in this way, a high WC carbonization rate can be achieved in a single carbonization treatment, and tungsten carbide can be produced with a high yield while simplifying the carbonization process. For example, by setting the heating temperature to 1700°C or higher and the holding time to 10 minutes or longer, the grain growth of the primary particles of the generated tungsten carbide is promoted, making it possible to appropriately obtain tungsten carbide powder with an average particle size exceeding 0.6 μm.

[0039] (Effects of this embodiment) In this embodiment, by performing the carbonization process under the above conditions, a high WC carbonization rate can be achieved in a single carbonization process. Specifically, the carbonization rate can be set to 99.5% or more.

[0040] The manufacturing method according to this embodiment includes a granulation step in which carbon and tungsten oxide are mixed to produce granules, and a carbonization step in which the granules are introduced into a heat treatment furnace and heated while supplying an inert gas to a reaction zone of the heat treatment furnace to carbonize the tungsten oxide to produce tungsten carbide. In the carbonization step, the flow rate of the inert gas is set to 0.1 m / min or less when the temperature in the reaction zone is less than 1500°C, and set to 0.4 m / min or less when the temperature in the reaction zone is 1500°C or higher. In this embodiment, the inert gas flow rate into the heat treatment furnace is set to a predetermined value or less, thereby preventing CO gas generated by the reaction represented by formula (1) from being discharged from the heat treatment furnace. This CO gas acts as a reducing agent to promote the reduction reaction of tungsten oxide, enabling efficient production of tungsten carbide powder. Furthermore, since this embodiment includes a granulation step in which a mixture of tungsten oxide powder and carbon powder is granulated, the granulated material can be handled relatively easily in the carbonization step, and tungsten carbide powder can be produced even more efficiently.

[0041] In the carbonization step, when the temperature in the reaction zone is below 1500°C, the flow rate of the inert gas is preferably 0.1 m / min or less, and when the temperature in the reaction zone is above 1500°C, the flow rate of the inert gas is preferably 0.4 m / min or less. By adjusting the flow rate of the inert gas within this range depending on the temperature, tungsten carbide powder can be produced efficiently.

[0042] In the carbonization step, the temperature in the reaction zone is preferably set to 1700° C. or higher and 2000° C. or lower. Setting the heating temperature within this range promotes grain growth of the primary particles of tungsten carbide produced by the reaction shown in formula (1), making it possible to appropriately obtain tungsten carbide powder with an average particle size exceeding 0.6 μm.

[0043] In addition, in this embodiment, a rotary kiln is used as the heat treatment furnace, which allows stable heat treatment under high-temperature conditions. Furthermore, the mixed powder of tungsten oxide powder and carbon powder can be efficiently heated, which promotes the reaction shown in formula (1), allowing for more efficient production of tungsten carbide powder.

[0044] The carbonization rate was measured by measuring the intensity (I) at the peak positions of each component of W, WC, and WC by X-ray diffraction analysis (XRD) on the produced carbide. W、 I W2C、 I WC ) was calculated, and the carbonization rate was calculated based on the intensity. 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 WC carbonization rate (%) was calculated by (I WC / (I W +I W2C +I WC )) x 100.

[0045] By achieving a carbonization rate of 99.5% or more, it is now possible to achieve a WC carbonization rate equivalent to that achieved with a manufacturing method that includes a two-stage carbonization process in which carbonization is performed in a nitrogen atmosphere followed by a further carbonization in a hydrogen atmosphere using only the primary carbonization.In addition, because direct carbonization using a rotary kiln can be performed with only the primary carbonization, the number of furnace facilities can be reduced and costs can be reduced because H2 is not used.

[0046] Although the embodiments of the present invention have been described above, the present invention is not limited thereto and can be modified as appropriate without departing from the technical spirit of the invention. For example, in the carbonization apparatus 10 of this embodiment, nitrogen is supplied to the rotary kiln 11 using the gas supply device 20, but any gas that does not contribute to the reaction between tungsten oxide and carbon can be used, and various inert gases such as argon can be used. Furthermore, for example, in this embodiment, a rotary kiln furnace is used as the heat treatment furnace, but this is not limited thereto and heat treatment furnaces of other structures may also be used.

[0047] (Effect of agitation granulation) As a supplement, the effects of performing agitation granulation will be explained. In the granulation process, water is supplied to carbon and tungsten oxide so that the water content is 26.5 mass% or more and 29.2 mass% or less to form a mixture, and the mixture is agitated and granulated to produce granules. It is preferable to sieve the produced granules to remove granules of 0.1 mm or less. By sieving the produced granules while agitating and granulating, the size of the granules can be made closer to uniform, which enables a uniform reaction in the subsequent carbonization process.

[0048] In this embodiment, the water content in the water addition step is adjusted to 26.5 mass% or more and 29.2 mass% or less, preferably 27.8 mass% or more and 29.2 mass% or less, and granules are produced at this water content. This allows for highly efficient (high yield) production of granules with particle sizes of 0.1 mm or more. Specifically, the proportion of granules with particle sizes of 0.1 mm or more in the granulation step can be set to 90% or more, preferably 98 mass% or more. In other words, the proportion of granules with particle sizes less than 0.1 mm produced in the mixing step can be set to less than 10%, preferably less than 2 mass%. This allows for efficient production of granules to be carbonized in the carbonization step, and therefore efficient production of tungsten carbide.

[0049] In this embodiment, the water content is set to 26.5 mass% or more and 29.2 mass% or less, preferably 27.8 mass% or more and 29.2 mass% or less, to prepare granules, and in the sieving step, granules with a particle size of 0.1 mm or more are extracted, and the extracted granules are carbonized in the carbonization step, thereby efficiently producing a large amount of tungsten carbide. Also, in the carbonization step, uncarbonized tungsten can be prevented from adversely affecting the equipment.

[0050] Here, we will explain the effect of extracting granulated material with a particle size of 0.1 mm or more and performing a carbonization process. In the carbonization process, tungsten oxide is heated in a nitrogen atmosphere. Therefore, a BRUKER thermal analyzer was used to measure the sublimation temperature in a nitrogen atmosphere. For the measurement, 25 mg of WO3 was weighed into an alumina dish as sample 1 and placed in the thermal analyzer. Next, while flowing N2 at 100 ml / L into the space of the thermal analyzer, the temperature was raised from room temperature to 1300°C at 10°C / min, and the weight loss of WO3 was measured. The results are shown in Figure 3.

[0051] Figure 3 is a graph showing an example of the weight change of WO3 with temperature. In Figure 3, the horizontal axis is temperature (°C) and the vertical axis is weight change (mg). As shown in Figure 3, it was found that WO3 in N2 suddenly loses weight and sublimes around 1200°C. From this result, if unreacted WO3, that is, WO3 that remains without being carbonized, is present in the tube of the rotary kiln, it may sublime around 1200°C and stick to the wall surface.

[0052] Next, granules were prepared, sieved into particle size ranges, and the total carbon content (TC) of each particle size range was measured. Three samples were prepared, and granules were prepared under the following conditions. For sample 2, the molar ratio (C / W) of carbon to tungsten oxide (WO3) was 3.78, the water content was 27.8 mass%, and the mixing step was carried out for 20 minutes, the water addition step for 37 minutes, the granulation step for 10 minutes, and the drying step for 20 minutes to produce a granulated product. For sample 3, the molar ratio (C / W) of carbon to tungsten oxide (WO3) was 3.75, the water content was 27.8 mass%, and the mixing step was carried out for 5.5 minutes, the water addition step for 23.5 minutes, the granulation step for 13 minutes, and the drying step for 20 minutes to produce a granulated product. For sample 4, the molar ratio (C / W) of carbon to tungsten oxide (WO3) was 3.72, the water content was 27.8 mass%, and the mixing step was carried out for 5.5 minutes, the water addition step for 24.5 minutes, the granulation step for 10 minutes, and the drying step for 20 minutes to produce a granulated product.

[0053] Next, the granules produced from each sample were sieved according to particle size. Specifically, sieves with different mesh sizes were used to separate small granules, resulting in granules with particle sizes between each mesh size. The sieve openings were 0.1 mm, 0.25 mm, 0.5 mm, 1.0 mm, and 1.7 mm. In other words, the granules were classified into the following sizes: less than 0.1 mm, 0.1 mm to less than 0.25 mm, 0.25 mm to less than 0.5 mm, 0.5 mm to less than 1.0 mm, 1.0 mm to less than 1.7 mm, and 1.7 mm or more.

[0054] Next, the total carbon content (mass%) of each classified granule was measured using a Leco WC-200. The measurement results are shown in Figure 4. Figure 4 is a graph showing an example of the measurement results of the sieve particle size and the total carbon content of the granules. As shown in Figure 4, the granules with a particle size of less than 0.1 mm had a TC value, i.e., a carbon percentage, of 10% or less, with an average value of 8.9 mass% for three samples. In contrast, the granules with a particle size of 0.1 mm or more all had TC values ​​exceeding 15%, with an average value of 16.6 mass%.

[0055] From the above, it can be seen that for all three samples with different molar ratios (C / W), when the particle size is less than 0.1 mm, the carbon content is low. Furthermore, for all three samples with different molar ratios (C / W), when the particle size is 0.1 mm or greater, the molar ratio (C / W) stabilizes and the component ratio corresponds to the molar ratio of the input materials. Therefore, granules with a particle size of less than 0.1 mm have a low carbon content, which means there is insufficient carbon to carbonize the tungsten oxide, resulting in unreacted tungsten oxide during carbonization in the rotary kiln. Therefore, when granules with a particle size less than 0.1 mm are input, the unreacted tungsten oxide sublimes above 1200°C, causing casting inside the furnace.

[0056] As described above, by producing a high proportion of granules with a particle size of 0.1 mm or more, it is possible to prevent sticking in the furnace. Furthermore, by producing a high proportion of granules with a particle size of 0.1 mm or more, it is possible to produce tungsten carbide with a high yield and to prevent the inclusion of unreacted tungsten oxide. Furthermore, by removing granules smaller than 0.1 mm by sieving during the production of granules, it is possible to effectively prevent sticking in the rotary kiln.

[0057] (Example) Next, the method for producing tungsten carbide will be described using specific examples. Figure 5 is a table showing the test results of the examples.

[0058] (Manufacturing conditions) The tungsten oxide powder used as the raw material was a powder obtained by calcining ammonium paratungstate (APT). Carbon black (CB) was used as the carbon. A mixed powder was obtained by mixing tungsten oxide powder and carbon powder in the ratio shown in Figure 5. The higher the heating temperature, the larger the C / W value. This is because the higher the carbonization temperature, the lower the CO2 concentration in the reaction gas in equation (1), i.e., the smaller the value of a in equation (1). Pure water was added to this mixed powder to make it a wet powder, and then extrusion granulation was used to produce granules with a particle size of 1.0 to 1.5 mm. The granulated material was placed in a rotary kiln in a nitrogen atmosphere and heat-treated. The inclination of the rotary kiln 11 was 0.5 to 3.0°, and the rotation speed of the kiln body was 5 rpm. The nitrogen gas flow rate, heating temperature, and retention time in the rotary kiln 11 were as shown in Figure 5.

[0059] (evaluation) The carbonization rate of each tungsten carbide produced by the above-mentioned manufacturing method was evaluated. The carbonization rate was calculated based on the results of the XRD measurement described above. In this experimental example, the XRD measurement of the carbide was performed using an all-in-one multipurpose X-ray diffractometer, Empyrean, manufactured by PANalytical.

[0060] As shown in FIG. 5, in Comparative Example 1, the heating temperature during heat treatment was 1300°C and the nitrogen gas flow rate in the furnace was 0.4 m / min, which are outside the range of this embodiment, and carbonization did not proceed sufficiently, resulting in a carbonization rate of 97.1%. For the same reason, Comparative Examples 2-5 also resulted in a carbonization rate of less than 99.5%. In contrast, in Inventive Examples 1-19, the heating temperature, nitrogen gas flow rate, and holding time during heat treatment were within the range of this embodiment, and carbonization proceeded sufficiently in all cases, resulting in a carbonization rate of 99.5% or more. From the above, it was confirmed that the present invention can provide a method for producing tungsten carbide powder by direct carbonization, which can stably produce tungsten carbide powder with a carbonization rate of 99.5% or more at low cost. Thus, it was found that the present invention can produce tungsten carbide with a high yield.

[0061] (optional evaluation) As an optional evaluation, the average grain size of the tungsten carbide in each example was measured. The average grain size was measured by the Fisher method. 5, in Inventive Examples 5, 8, and 12-18, in which the heating temperature during heat treatment was 1700°C or higher, the average particle size of the produced tungsten carbide powder was 0.6 μm or higher. In other words, it was confirmed that by setting the heating temperature to 1700°C or higher, it is possible to provide a method for producing tungsten carbide powder that can stably produce tungsten carbide powder having an average particle size exceeding 0.6 μm at low cost by direct carbonization.

[0062] (Other experimental examples) Next, a method for producing granules, i.e., a method for producing granules for producing tungsten carbide, will be described using other experimental examples. Fig. 6 is a table showing the results of other experimental examples, and Figs. 7 to 9 are graphs showing the results of other experimental examples. Note that the following experimental examples are experimental examples showing examples of the present invention, and the present invention and embodiments are not limited to the contents thereof.

[0063] (Experimental Example 1) In Experimental Example 1, the relationship between the water content and the particle size distribution of the granulated material was confirmed. In Experimental Example 1, 3.8 kg of WO3 and an amount of carbon black corresponding to the C / WO3 ratio were charged into a kneader, and the mixture was mixed by rotating a chopper at 1400 rpm (circumferential speed 5.9 m / s). The water content was then adjusted to the respective test values, granulated for 10 minutes, and dried at 110°C for 20 minutes. The weight of the dried granulated material was measured, and the granulated material was then sieved through a sieve with 0.1 mm openings to determine the proportion of granulated material with a particle size of less than 0.1 mm and the proportion of granulated material with a particle size of 0.1 mm or more.

[0064] The proportion (mass%) of granules with a particle size of less than 0.1 mm was calculated by (weight (kg) of granules with a particle size of less than 0.1 mm / weight (kg) of all granules before sieving) × 100. The proportion (mass%) of granules with a particle size of 0.1 mm or more was calculated by (weight (kg) of granules with a particle size of 0.1 mm or more / weight (kg) of all granules before sieving) × 100.

[0065] In Experimental Example 1, three tests were conducted with different hydration rates. Test No. 1 had a hydration rate of 24.5%. Test No. 2 had a hydration rate of 27.8%. Test No. 3 had a hydration rate of 29.0%. Figure 7 shows the ratio of granules with particle sizes of less than 0.1 mm (under 0.1 mm) to those with particle sizes of 0.1 mm or more (over 0.1 mm) in each test.

[0066] (Experimental Example 2) In Experimental Example 2, the chopper rotation speed (peripheral speed) was changed for each test, and the conditions were the same as in Experimental Example 1 except for the granulation time in Test No. 6, except for the water content being 27.8%. In Experimental Example 2, three tests were conducted with different chopper rotation speeds (peripheral speeds). Test No. 4 had a chopper rotation speed of 1400 rpm and a peripheral speed of 5.9 m / s. Test No. 5 had a chopper rotation speed of 1900 rpm and a peripheral speed of 8 m / s. Test No. 6 had a chopper rotation speed of 2400 rpm and a peripheral speed of 10 m / s, and the granulation time was 3 minutes. Figure 8 shows the ratio of granules with particle sizes less than 0.1 mm (under 0.1 mm) to those with particle sizes of 0.1 mm or more (over 0.1 mm) in each test.

[0067] (Experimental Example 3) In Experimental Example 3, the chopper rotation speed (circumferential speed) was set to 1900 rpm (8 m / s), the granulation time was set to 5 minutes, and the water content was changed for each test. Other than this, the conditions were the same as in Experimental Example 1. In Experimental Example 3, three tests were conducted with different water content rates. Test No. 7 had a water content rate of 26.5%. Test No. 8 had a water content rate of 27.8%. Test No. 9 had a water content rate of 29.2%. Figure 9 shows the ratio of granules with particle sizes less than 0.1 mm (under 0.1 mm) to those with particle sizes of 0.1 mm or more (over 0.1 mm) in each test.

[0068] 6 and 7 show that when the water content is 24.5%, the proportion of granules smaller than 0.1 mm exceeds 10 mass%, as shown in Tests No. 1 to No. 3. Furthermore, when the chopper rotation speed is 1400 rpm (circumferential speed 5.9 m / s), by setting the water content between 27.8 mass% and 29.2 mass%, the proportion of granules smaller than 0.1 mm can be reduced to less than 2 mass%, and a high proportion of granules can be produced that can be advanced to the carbonization process.

[0069] 6 and 8 show that the percentage of particles under 0.1 mm is 2.5 mass% or less at any chopper rotation speed or peripheral speed. It is also clear that by setting the chopper rotation speed to 1400 rpm to 1900 rpm (peripheral speed of 5.9 m / s to 8.0 m / s), the percentage of particles under 0.1 mm is 2 mass% or less.

[0070] 6 and 9 show that, as shown in Tests No. 7 to No. 9, when the chopper rotation speed is 1900 rpm (circumferential speed of 8.0 m / s), the proportion of granules smaller than 0.1 mm can be reduced to 4.0 mass% or less by setting the water content between 26.5 mass% and 29.2 mass%. It can also be seen that by setting the water content between 27.8 mass% and 29.2 mass%, the proportion of granules smaller than 0.1 mm can be reduced to less than 2 mass%, enabling a high proportion of granules to be advanced to the carbonization step to be produced.

[0071] From the above, it can be seen that the yield of granulated material can be increased by adjusting the water content. Furthermore, it can be seen that the yield of granulated material can be further increased by adjusting the peripheral speed of the rotating part that rotates for mixing in the kneader in addition to the water content. From the above, it can be seen that the effect can be obtained by carrying out production under the conditions of this embodiment. [Explanation of symbols]

[0072] 10 Carbonization equipment 11 Rotary Kiln 12 Kiln body 14 Heater 16 Drive unit 18 Material feeding device 20 Gas supply equipment 21 Material storage section 22 Supply pipe 30 Power Source 32 Transmission Mechanism 40 Gas Supply Source 42 Supply pipe 44 Discharge pipe 52 Transport Route 54 Rotation direction 60 Nitrogen gas flow direction

Claims

1. a granulation step of mixing carbon and tungsten oxide to produce granules; a carbonization step of charging the produced granules into a heat treatment furnace and heating them while supplying an inert gas into a reaction zone of the heat treatment furnace to carbonize the tungsten oxide and produce tungsten carbide, In the carbonization step, When the temperature in the reaction zone is lower than 1500°C, the flow rate of the inert gas to be supplied is set to 0.1 m / min or less. When the temperature in the reaction zone is 1500°C or higher, the flow rate of the inert gas to be supplied is set to 0.4 m / min or less. How to make tungsten carbide.

2. 2. The method for producing tungsten carbide according to claim 1, wherein the temperature in the reaction zone is set to 1700°C or higher and 2000°C or lower in the carbonization step.

3. The method for producing tungsten carbide according to claim 1 or 2, wherein the granulation step produces the granulated material by extrusion granulation.

4. 3. The method for producing tungsten carbide according to claim 1 or 2, wherein in the granulation step, water is supplied to carbon and tungsten oxide so that the water content is 26.5 mass % or more and 29.2 mass % or less to form a mixture, the mixture is stirred and granulated to produce the granules, and the produced granules are sieved to remove granules having a size of 0.1 mm or less.

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