Method for manufacturing tungsten carbide

Abstract

To suppress an increase in the amount of carbon as a raw material.SOLUTION: A method for producing tungsten carbide includes a mixing step (S01) for mixing carbon with a specific surface area of less than 10 m2 / g with tungsten oxide to yield a mixture and a carbonizing step for heating the mixture in an inert gas atmosphere, to carbonize the tungsten oxide, preparing tungsten carbide (S05).SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

[0003] In the reduction process of (A), CO is released and W is produced. In the carbonization process, as in (B) and (C), W and C react and produce WC.

[0004] Patent Document 1 describes a method for carrying out the above reaction by heating and reducing a mixed powder of tungsten trioxide powder and carbon powder in a hydrogen atmosphere to perform the first stage of carbonization, and then heating it in a hydrogen atmosphere or an inert atmosphere to perform the second stage of carbonization to produce tungsten carbide. Patent Document 2 also describes a method for carrying out a mixed powder of tungsten oxide powder and carbon powder by heating it in a nitrogen atmosphere to perform the first stage of carbonization, and then heating it in a hydrogen atmosphere to perform the second stage of carbonization to produce tungsten carbide. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2005-335997 [Patent Document 2] Japanese Patent Publication No. 2018-165233 [Overview of the initiative]

Problems to be Solved by the Invention

[0006] However, carbon powder may contain oxygen as an impurity. When the oxygen content increases, carbon reacts with the oxygen in the impurities, consuming extra carbon. Therefore, in order to achieve a sufficient carbonization rate, the mixing ratio (C / W) when mixing tungsten oxide powder and carbon powder needs to be increased, resulting in the need for a large amount of carbon powder. Accordingly, it is required to suppress an increase in the amount of carbon as a raw material.

[0007] The present invention has been made in view of the above, and an object thereof is to provide a method for producing tungsten carbide capable of suppressing an increase in the amount of carbon as a raw material.

Means for Solving the Problems

[0008] The method for producing tungsten carbide according to the present disclosure includes a mixing step of mixing carbon having a specific surface area of less than 10 m / g and tungsten oxide to obtain a mixture, and a carbonization step of carbonizing tungsten oxide by heating the mixture in an inert gas atmosphere to produce tungsten carbide.

Effects of the Invention

[0009] The method for producing tungsten carbide according to the present invention can suppress an increase in the amount of carbon as a raw material.

Brief Description 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 table showing the evaluation results of each example. [Figure 4] FIG. 4 is a table showing the evaluation results of the water addition rate of each example. [Modes for carrying out the invention]

[0011] Below, a method for producing tungsten carbide powder, which is one embodiment of the present invention, will be described in detail with reference to the attached drawings. This embodiment of the method for producing tungsten carbide powder is used, for example, to produce tungsten carbide powder used as a raw material for cutting tools and wear-resistant tools made of cemented carbide, but the use of the tungsten carbide powder may be arbitrary. The present invention is not limited to the embodiments described below. Furthermore, the components in the embodiments below include those that can be easily imagined by those skilled in the art, those that are substantially the same, and those that are equivalent. In addition, the components disclosed in the embodiments below can be combined as appropriate.

[0012] The method for producing tungsten carbide powder in this embodiment is a so-called direct carbonization method, in which tungsten oxide and carbon are mixed and heat-treated, as shown in equation (1) below, to obtain tungsten carbide by continuously carrying out the reduction reaction of tungsten oxide and the carbonization reaction of the tungsten metal obtained from the reduction reaction. Note that a in equation (1) may be any positive number. WO3+(4-a)C→WC+(3-2a)CO+aCO2···(1)

[0013] (1) Equation (1) is the reaction equation 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 any tungsten oxide of any composition. In other words, W xa O ya It may be tungsten oxide represented by the chemical formula (where xa and ya are any positive numbers). Similarly, the tungsten carbide produced in this embodiment is not limited to WC but may be tungsten carbide of any composition, in other words, W xb C yb It may be tungsten carbide represented by the chemical formula (where xb and yb are any positive numbers).

[0014] Using FIG. 1, the manufacturing method of tungsten carbide will be described. FIG. 1 is a flowchart showing the manufacturing method of tungsten carbide.

[0015] In the manufacturing method of tungsten carbide of the present embodiment, tungsten carbide is manufactured by processing carbon and tungsten oxide as raw materials. The manufacturing method of tungsten carbide includes a mixing step of mixing carbon and tungsten oxide to obtain a mixture, and a carbonization step of carbonizing tungsten oxide by heating the mixture in an inert gas atmosphere to manufacture tungsten carbide. More specifically, in the present embodiment, as shown in FIG. 1, a mixing step S01 of mixing carbon and tungsten oxide to obtain a mixture, a kneading step S02 of adding water to the obtained mixture and kneading to obtain a wet powder, a forming 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 heating the dried granulated product to carbonize the granulated product are included.

[0016] (Mixing step S01) In the mixing step, carbon and tungsten oxide are mixed. The mixing method of carbon and tungsten oxide may be arbitrary. As the mixer, in addition to a general mixer with blades, media mixing, for example, using a ball mill or the like, may be used for mixing.

[0017] The carbon used in the mixing step (the carbon mixed with tungsten oxide) is in powder form and can also be called carbon powder. As the carbon used in the mixing step, carbon black, graphite carbon, etc. can be used. The carbon used in the mixing step has a specific surface area of less than 10 m 2 / g, preferably 1 m 2 / g or more and 10 m 2 / g or less, and more preferably 5 m 2 / g or more and 10 m 2It is more preferable that the specific surface area is less than or equal to / g. By using carbon with a specific surface area within this range, for example, it is possible to suppress the amount of oxygen adsorbed on the carbon surface, thereby suppressing an increase in oxygen content and thus suppressing the amount of carbon used in the mixture. The specific surface area can be measured by the gas adsorption method.

[0018] The tungsten oxide used in the mixing process (tungsten oxide mixed with carbon) is in powder form and can also be called tungsten oxide powder. For example, powder obtained by calcining ammonium paratungstate (APT) can be used as the tungsten oxide used in the mixing process. The tungsten oxide used in the mixing process has a specific surface area of ​​1 m². 2 / g or more 10m 2 It is preferable that the specific surface area is less than or equal to / g. By using tungsten oxide with a specific surface area within this range, reactivity can be improved and tungsten carbide can be produced appropriately.

[0019] The mixing ratio of tungsten oxide powder to carbon powder is preferably such that the molar ratio of carbon to tungsten oxide (C / W) is close to 4. For example, it is preferable that the molar ratio of carbon (C / W) be 4.00 or less, more preferably between 3.50 and 4.00, and even more preferably between 3.60 and 3.70. By setting the C / W within this range, it is possible to appropriately carbonize the tungsten while suppressing the use of excessive amounts of carbon.

[0020] (Kneading process S02) Next, a kneading step is performed in which water is supplied to the mixture of carbon and tungsten oxide mixed in mixing step S01 to obtain a hydrated mixture (wet powder). Specifically, pure water is added to the mixed powder of tungsten oxide and carbon obtained in mixing step S01 and kneaded to obtain a hydrated mixture. Here, pure water is water with an electrical conductivity of 1 mS / m or less. The method of water purification is not limited, and distillation, ion exchange, membrane treatment, etc., can be applied. In the mixing process S02, it is preferable to adjust the amount of water supplied to achieve a predetermined hydration rate. Specifically, it is preferable that the hydration rate be 5 mass% or more and 15 mass% or less, more preferably 8 mass% or more and 12 mass% or less, even more preferably 11 mass% or less, and even more preferably 9 mass% or more and 11 mass% or less. Here, the hydration rate (mass%) can be calculated as (amount of water added (kg)) × 100 / (amount of tungsten oxide added (kg) + amount of carbon added (kg)). If the water content is below the lower limit, insufficient moisture may prevent granulation to the desired particle size. If it exceeds the upper limit, excessive moisture will cause the wet powder to adhere to the inner walls of the equipment, which can reduce manufacturing efficiency and is undesirable. In this embodiment, since the specific surface area of ​​carbon is within the above range, it is possible to properly granulate even with a small amount of water supplied, thus shortening the time required for subsequent drying processes, for example. Methods for adding pure water include dropping it dropwise into a mixture of tungsten oxide powder and carbon powder. Alternatively, kneading after adding pure water can produce a uniformly moistened powder.

[0021] In addition, the conditions for mixing and kneading the powder in the mixing process S01 and the kneading process S02 may be arbitrary, but it is preferable, for example, to set the peripheral speed of the rotating part of the mixer to 5.9 m / s or more and 10 m / s or less, and more preferably to 5.9 m / s or more and 8 m / s or less. The peripheral speed of the rotating part can be calculated as follows: Peripheral speed (m / s) = Outer diameter of chopper (rotating part) (mm) × 3.14 × Rotational speed of chopper (rotating part) (rpm) / 1000 / 60. For example, if the rotational speed of the chopper of the mixer is set to 1400 rpm or more and 2400 rpm or less, and the outer diameter of the chopper is 80 mm, the peripheral speed can be set to 5.9 m / s to 10 m / s. If it is less than 5.9 m / s, mixing and kneading may be insufficient, and if it exceeds 10 m / s, there will be no further improvement in mixing and kneading and it will become inefficient, so it is undesirable. Furthermore, the above conditions for mixing and kneading can be applied regardless of the type of granulation method described later (e.g., extrusion granulation or agitation granulation).

[0022] (Molding process S03) Next, a molding process is performed to granulate the mixture obtained in the kneading process S02 and produce granules. Here, the size of the granules is preferably set appropriately considering the ease of handling in subsequent processes. For example, in this embodiment, the size of the granules may be set within the range of 0.5 mm to 3.0 mm. The granulation method can be extrusion granulation or agitation granulation. If the size is less than 0.5 mm, the fluidity of the granules in the furnace may not improve in the subsequent carbonization process, and stable processing may not be possible. If it exceeds 3.0 mm, carbonization may be insufficient in the subsequent carbonization process, which is undesirable. The size of the granules here may refer to, for example, the maximum distance between any two points on the outer circumference of the granules, or, for example, the diameter of the granules if the granules are spherical.

[0023] In extrusion granulation, for example, the mixture obtained in the kneading step S02 is pressed towards a member with an opening, the mixture is extruded through the opening, and the rod-shaped mixture extruded from the opening is cut to obtain granular granules. By applying extrusion granulation, the size of the granules can be made more uniform, which enables a uniform reaction in the subsequent carbonization step. The equipment used to pressurize the mixture can be any type, such as a screw, plunger, or roller. The member from which the extrusion opening is formed can also be any type, such as a plate-shaped member with multiple openings, and the size of the extrusion opening can be set according to the desired size of the granules.

[0024] When performing stirring granulation, for example, after stopping the addition of water to the mixture obtained in the kneading step S02, stirring with a chopper for a predetermined time, for example, 3 minutes to 10 minutes, preferably 5 minutes to 8 minutes, can produce granulated material from the mixture. If the stirring time is less than 3 minutes, granulation may be insufficient, and if it exceeds 10 minutes, the granules may become too large, which is undesirable.

[0025] (Drying process S04) Next, drying is performed to remove moisture contained in the granules obtained in the molding process S03. There are no particular restrictions on the type of dryer used, but in order to suppress the collapse of the granules in the drying process S04, a belt conveyor type dryer, which does not move the granules, is preferable. In addition, the drying temperature is preferably 110°C or higher, and more preferably 120°C or higher.

[0026] Furthermore, when performing agitation granulation, for example, it is preferable to perform a sieving step to separate the dried granules. In the sieving step, a sieve with a mesh size of 0.1 mm may be used to sieve the granules into those smaller than 0.1 mm and those larger than 0.1 mm. Granules smaller than 0.1 mm have a lower carbon content than granules larger than 0.1 mm, and if granules containing granules smaller than 0.1 mm are carbonized in the carbonization step, the carbonization will be uneven. However, the threshold size of the granules in the sieving step is not limited to 0.1 mm and may be set arbitrarily according to the desired granule size. That is, in the sieving step, the obtained granules may be sieved into those smaller than a predetermined size and those larger than a predetermined size. Also, the sieving step is not limited to agitation granulation, but may be applied to any granulation method, such as extrusion granulation. Conversely, the sieving step is not essential and may not be applied even in the case of agitation granulation.

[0027] If a sieving process is performed, the total carbon content (TC) of the sieved granules classified as being smaller than a predetermined size (in this case, 0.1 mm) is measured. The ratio of carbon to tungsten oxide is calculated from the measured total carbon content, and the components are adjusted based on the calculated ratio before the sieved granules are put back into the mixer in the mixing process. This allows the sieved granules to be granulated again, enabling efficient use of the material. Next, a TC measurement is performed to measure the total carbon content of the sieved granules that have been classified to a predetermined size (in this case, 0.1 mm) or larger during the sieving process. The ratio of carbon to tungsten oxide is calculated from the measured total carbon content, and after confirming that the ratio is as determined, the granulation process may be terminated. In other words, the sieved granules from which the TC has been measured are used as the granules that proceed to the heat treatment process. That is, the sieved granules may be used as the granules for the production of tungsten carbide.

[0028] (Carbonization process S05) Next, the carbonization process (heat treatment process) will be described. In the carbonization process, the dried granules are charged into a heat treatment furnace and heat-treated, thereby allowing the reduction reaction of tungsten oxide and the carbonization reaction of the tungsten metal obtained from the reduction reaction to proceed in succession, as shown in equation (1) above, in order to obtain tungsten carbide. In this embodiment, it is possible to obtain tungsten carbide in a single carbonization process S05 under an inert gas atmosphere, and the WC carbonization rate can be increased without performing subsequent carbonization processes. In this embodiment, the granules obtained through the kneading, molding, and drying processes are carbonized in the carbonization process. However, the kneading, molding, and drying processes are not essential. In this case, for example, the mixture obtained in the mixing process may be carbonized in the carbonization process.

[0029] In the carbonization process, tungsten oxide is carbonized by heating the granules in an inert gas atmosphere at a temperature of 1600°C to 2000°C to produce tungsten carbide. The heat treatment furnace used in the carbonization process and the detailed processing conditions of the carbonization process will be described below. In this embodiment, the inert gas used is nitrogen, but it is not limited to nitrogen; for example, a noble gas such as argon may also be used.

[0030] (Configuration of a 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 process will be explained with reference to Figure 2. Figure 2 is a schematic diagram showing an example of a carbonization apparatus including a rotary kiln. The carbonization apparatus 10 shown in Figure 2 includes a rotary kiln 11, a material input device 18, a gas supply device 20, and a discharge pipe 24.

[0031] 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 fed by a material feeding device 18. Preferably, the kiln body 12 is inclined with respect to the horizontal direction such that the central axis of its cylindrical shape is aligned horizontally, and the end into which the material is fed is vertically higher than the other end. The heater 14 heats the kiln body 12. The structure may include heating the outer circumference of the kiln body 12 with the heater 14, or a structure in which the kiln body 12 is heated by a heating device. A heating device using a burner may be used supplementarily. The heater 14 can heat the kiln body 12 in a range of 1300°C to 2000°C. The heater 14 is positioned within a distance L of the kiln body 12, excluding both ends of the cylindrical shape. The distance L in which the heater 14 is positioned becomes the heating area. The area where the heater 14 is located, at a distance L, is the reaction region where WO3 is carbonized.

[0032] The drive unit 16 rotates the kiln body 12 around a cylindrical central axis. 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 from the drive source 30 to the kiln body 12. The transmission mechanism 32 is, for example, an endless belt stretched over both the drive source 30 and the kiln body 12. A structure combining gears can also be used as the transmission mechanism 32.

[0033] The material input 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.

[0034] 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 supply source that supplies 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 the end of the kiln body 12 opposite to the end to which the supply pipe 22 is connected. The discharge pipe 44 is connected to the end of the kiln body 12 to which the supply pipe 22 that supplies granules is connected.

[0035] The discharge pipe 24 is connected to the end of the kiln body 12 opposite to the end to which the supply pipe 22 is connected. The discharge pipe 24 allows the carbonized material to pass through the kiln body 12 and be discharged.

[0036] The carbonization apparatus 10 supplies granules from the material input device 18 to the kiln body 12. The kiln body 12 is heated by the heater 14 and rotated in the rotational direction 54 by the drive unit 16. The granules supplied to the kiln body 12 move along the transport path 52 from the supply pipe 22 to the discharge pipe 24 due to the rotation of the kiln body 12. The granules moving along the transport path 52 are heated over a distance L. The carbonization apparatus 10 also supplies nitrogen from the gas supply device 20 to the kiln body 12 in the direction of nitrogen gas flow 60, that is, in the opposite direction to the transport path 52. The carbonization apparatus 10 discharges the carbonized char that has passed through the kiln body 12 from the discharge pipe 24 and recovers it. The gas from the kiln body 12 is discharged from the discharge pipe 44.

[0037] Furthermore, the configuration of the carbonization apparatus 10 used for the production of tungsten carbide is not limited to the above and may be arbitrary.

[0038] (Processing conditions for the carbonization process) Next, the processing conditions for the carbonization process will be explained. In the carbonization process, the carbonization treatment is performed 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 of the reaction region). The nitrogen gas flow velocity inside the furnace is the flow velocity of nitrogen flowing through the kiln body 12 of the rotary kiln 11, and can be said to be the flow velocity of nitrogen gas (inert gas) supplied to the reaction area. The nitrogen gas flow velocity inside 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 velocity inside the furnace (m / min) = flow rate of N2 (L / min) × 10 / cross-sectional area of ​​the kiln body 12 (cm²) 2 ) is calculated as follows. In this embodiment, since the inside of the kiln body 12 is the reaction region, the nitrogen gas flow rate inside the furnace can be said to be calculated as the amount of nitrogen gas supplied from the gas supply device 20 divided by the cross-sectional area of ​​the reaction region as viewed from the direction in which the nitrogen gas flows. The cross-sectional area of ​​the reaction region here may be the average value of the cross-sectional area at each position of the reaction region as viewed from the direction in which the nitrogen gas flows. However, the nitrogen gas flow rate inside the furnace is not limited to being calculated in this way and may be obtained by any method, for example, by measuring it using a flowmeter. The heating temperature (temperature of the reaction region) refers to the temperature within the reaction region during the carbonization process, and may be measured, for example, by a thermometer installed in the reaction region. In this embodiment, the reaction region is the space within the distance L in the kiln body 12 where the heater 14 is located, as described above. However, the reaction region is not limited to this, and may refer to the space within the heat treatment furnace (rotary kiln 11 in this embodiment) during the carbonization process that is heated to a temperature at which tungsten oxide can be carbonized (for example, 1300°C).

[0039] In this embodiment, it is preferable to set the heating temperature when heating the granules to 1600°C or higher and 2000°C or lower. By setting the heating temperature within this range, the carbonization process can be reduced to, for example, one stage, simplifying the carbonization process while ensuring proper carbonization. For example, if the heating temperature is below the lower limit, the carbonization reaction may not proceed sufficiently, and if it exceeds the upper limit, power consumption increases, which is undesirable as it increases production costs.

[0040] In this embodiment, the holding time at the above heating temperature is preferably 10 minutes or more and 90 minutes or less, and more preferably 30 minutes or more and 60 minutes or less. By setting the holding time within this range, the carbonization process can be simplified while ensuring proper carbonization. For example, if the holding time is below the lower limit, the carbonization reaction may not proceed sufficiently, and if it exceeds the upper limit, productivity will decrease, which is undesirable.

[0041] In this embodiment, the nitrogen gas flow rate in the furnace (the flow rate of the inert gas supplied to the reaction region) is preferably 0.4 m / min or less, and more preferably 0.1 m / min or more and 0.4 m / min or less. By setting the flow rate within this range, the carbonization process can be simplified while ensuring proper carbonization. For example, if the flow rate exceeds the upper limit, the reduction effect of CO gas cannot be utilized, and the carbonization reaction may not proceed sufficiently, which is undesirable. Furthermore, it is preferable that the inert gas is supplied in the opposite direction to the direction of granulation (counterflow).

[0042] In the carbonization process of this embodiment, more preferably, when the heating temperature (temperature of the reaction region) is less than 1500°C, the nitrogen gas flow rate in the furnace is 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 0.4 m / min or less. By adjusting the combination of nitrogen gas flow rate in the furnace and the temperature of the reaction region in this way, a high WC carbonization rate can be achieved in a single carbonization treatment, simplifying the carbonization process and enabling the production of tungsten carbide with a high yield. Furthermore, when producing tungsten carbide, CO gas is generated by the reaction shown in equation (1), but by suppressing the gas flow rate of the inert gas in the furnace as in this embodiment, the emission of CO gas can be suppressed, and the CO gas can be used as a reducing agent, further promoting the reaction shown in equation (1). As shown in equation (1), CO and CO2 are generated as post-reaction gases, and the proportion of CO gas increases with higher temperatures. Therefore, at temperatures above 1500°C, the nitrogen gas flow rate can be increased compared to when the temperature is below 1500°C. It is preferable that the inert gas flows in the opposite direction to the direction of granulation (counterflow).

[0043] Below, the conditions for the carbonization process when the heating temperature is less than 1500°C will be referred to as Condition 1, and the conditions for the carbonization process when the heating temperature is 1500°C or higher will be referred to as Condition 2. Conditions 1 and 2 will be explained in more detail.

[0044] (Condition 1) Under the first condition, it is preferable to keep the nitrogen gas flow rate in the furnace at 0.1 m / min or less. Exceeding this limit is undesirable because it may prevent the carbonization reaction from proceeding sufficiently due to the inability to utilize the reduction effect that converts to CO gas. Furthermore, under the first condition, it is preferable to set the temperature within the reaction region to 1300°C or higher and less than 1500°C. A temperature below the lower limit is undesirable because the carbonization reaction may not proceed sufficiently. Furthermore, under the first condition, it is preferable that the holding time, which is the time the granules are held at the heating temperature, be between 10 minutes and 90 minutes. Note that the holding time may refer to the time during which the granules remain present in the reaction region heated to the heating temperature while nitrogen gas is supplied. If the holding time is below the lower limit, the carbonization reaction may not proceed sufficiently, and if it exceeds the upper limit, productivity will decrease, which is undesirable. By setting the first condition in this way, a high WC carbonization rate can be achieved in a single carbonization treatment, simplifying the carbonization process while producing tungsten carbide with a high yield.

[0045] (Second condition) Under the second condition, it is preferable to keep the nitrogen gas flow rate inside the furnace at 0.4 m / min or less. Exceeding this limit is undesirable because it may prevent the carbonization reaction from proceeding sufficiently due to the inability to utilize the reduction effect that converts to CO gas. Furthermore, under the second condition, it is preferable to set the temperature within the reaction region to 1500°C or higher and 2000°C or lower, and more preferably to 1700°C or higher and 2000°C or lower. If the temperature is below the lower limit, the carbonization reaction may not proceed sufficiently, and if it exceeds the upper limit, power consumption will increase, which is undesirable as it will increase production costs. Furthermore, under the second condition, it is preferable to set the holding time to 10 minutes or more and 90 minutes or less. If it is below the lower limit, the carbonization reaction may not proceed sufficiently, and if it exceeds the upper limit, productivity will decrease, which is undesirable. By setting the second condition in this way, a high WC carbonization rate can be achieved in a single carbonization treatment, simplifying the carbonization process while producing tungsten carbide with a high yield. For example, by setting the heating temperature to 1700°C or higher and the holding time to 10 minutes or more, the grain growth of the primary tungsten carbide particles produced is promoted, making it possible to appropriately obtain tungsten carbide powder with an average particle size exceeding 0.6 μm.

[0046] In this embodiment, by performing the carbonization process under the above conditions, a high WC carbonization rate can be achieved in a single carbonization treatment. Specifically, the carbonization rate can be set to, for example, 99.5% or higher.

[0047] The carbonization rate is determined by measuring the intensity at the peak position of each component (I) of the W, W2C, and WC by performing X-ray diffraction analysis (XRD) on the manufactured carbide. W、 I W2C、 I WC The ) 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 (%) is (I WC / ( I W +I W2C +I WC It can be calculated by multiplying by )) × 100.

[0048] By achieving a carbonization rate of 99.5% or higher, it is now possible to achieve a WC carbonization rate equivalent to that of a manufacturing method that includes a two-stage carbonization process, where carbonization is performed in a nitrogen atmosphere followed by further carbonization in a hydrogen atmosphere, using only primary carbonization. Furthermore, since direct carbonization using a rotary kiln can be performed in primary carbonization alone, the number of furnace facilities can be reduced, and costs can be lowered because H2 is not used.

[0049] (effect) As described above, the manufacturing method according to this embodiment has a specific surface area of ​​10 m². 2 The process includes a mixing step of mixing less than 1g of carbon with tungsten oxide to obtain a mixture, and a carbonization step of heating the mixture in an inert gas atmosphere to carbonize the tungsten oxide and produce tungsten carbide. According to the manufacturing method of this embodiment, the specific surface area is 10 m². 2 By using carbon with a concentration of less than 1g, for example, it is possible to suppress the excessive amount of oxygen adsorbed on the carbon surface, thereby suppressing an increase in oxygen content and thus suppressing the amount of carbon used in the mixture. Furthermore, in the manufacturing method according to this embodiment, it is preferable to heat at a temperature of 1600°C to 2000°C. This allows the carbonization process to be reduced to, for example, one step, thus simplifying the carbonization process.

[0050] In the carbonization process, it is preferable to introduce the mixture into a heat treatment furnace and heat it while supplying an inert gas to the reaction zone of the heat treatment furnace at a flow rate of 0.4 m / min or less. By keeping the flow rate within this range, the carbonization process can be simplified while ensuring proper carbonization.

[0051] In the carbonization process, it is preferable to heat the mixture for a period of 10 minutes or more (holding time) of 90 minutes or less. By setting the holding time within this range, the carbonization process can be simplified while ensuring proper carbonization.

[0052] The manufacturing method according to this embodiment further includes a molding step in which granules are produced by adding water to a mixture and granulating it, and in the carbonization step, tungsten oxide is carbonized by heating the granules to produce tungsten carbide. By carbonizing using granules in this way, the handling of the mixture of carbon and tungsten oxide in the carbonization step becomes relatively easy, and tungsten carbide powder can be produced more efficiently.

[0053] Although this embodiment has 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 this embodiment, the carbonization apparatus 10 uses a gas supply device 20 to supply nitrogen to the rotary kiln 11, but any gas that does not contribute to the reaction between tungsten oxide and carbon may be used, and various inert gases such as argon can be used. Also, for example, in this embodiment, a rotary kiln furnace was used as the heat treatment furnace, but the invention is not limited thereto, and heat treatment furnaces of other structures may be used.

[0054] (Examples) Next, we will describe the examples. Figure 3 is a table showing the evaluation results for each example.

[0055] (Manufacturing conditions) The tungsten oxide powder used as a raw material was obtained by calcining ammonium paratungstate (APT). Carbon was used as carbon black (CB). Four types of carbon with different specific surface areas were prepared: carbon A, carbon B, carbon C, and carbon D. Carbon A had a specific surface area of ​​10 m². 2 Less than / g (9.7m 2 ( / g), and carbon B has a specific surface area of ​​10 m². 2 / g or more 15m 2 / g or less (13.1m 2 ( / g), and carbon C has a specific surface area of ​​30 m². 2 Greater than / g (36.3m 2 ( / g), carbon D has a specific surface area of ​​30 m². 2 / g greater than (63.9m 2 ( / g). Specific surface area was measured by gas adsorption. In each example, the carbon shown in Figure 3 was used, and the tungsten oxide and carbon were mixed in the proportions shown in Figure 3 (molar ratio of carbon to tungsten oxide C / W) to obtain a mixture. Pure water was added to this mixed powder to create a wet powder, and then granules with a particle size of 1.0 to 1.5 mm were produced by extrusion granulation. The prepared granules were placed in a rotary kiln furnace under a nitrogen atmosphere and subjected to heat treatment. The inclination of the rotary kiln 11 was set to 0.5 to 3.0°, and the rotation speed of the kiln body was set to 5 rpm. The nitrogen gas flow rate, heating temperature, and holding time inside the rotary kiln 11 were as shown in Figure 3.

[0056] (evaluation) The carbide content of each example of tungsten carbide produced by the above manufacturing method was evaluated. The carbide content was calculated based on the results measured by XRD as described above. In this experiment, the XRD measurement of the carbide was performed using the Empyrean all-in-one multi-purpose X-ray diffractometer manufactured by PANalytical.

[0057] As shown in Figure 3, in each example, the carbonization rate was 99.5% or higher, while in the comparative example, despite using a similar amount of carbon (C / W) as in each example, the carbonization rate was less than 99.5%. That is, as in the example, the specific surface area was 10 m². 2 It can be seen that by using carbon less than 1g, proper carbonization can be achieved even with a small amount of carbon used in the mixture.

[0058] (Evaluation of options) As an evaluation of the options, the water content required to form granules using carbon A to D with different specific surface areas was assessed. Figure 4 is a table showing the evaluation results of the water content for each example.

[0059] In this evaluation, pure water was added to each of the carbon atoms A to D to achieve different hydration rates (mass%) as shown in Figure 4, and granulation was performed on the samples for each hydration rate. The granulation conditions were a C / W range of 3.60 to 4.00 and a hydration rate range of 8% to 34%.

[0060] In this evaluation, granules with a diameter between 0.5 mm and 3.0 mm were marked as "correct," while those outside this range were marked as "incorrect." For example, carbon A is marked as "correct" when the hydration rate is between 9 mass% and 11 mass%. On the other hand, carbons B through D require a higher hydration rate to be marked as "correct" than carbon A. That is, a specific surface area of ​​10 m² is required. 2By using carbon content less than 1 / g, it is possible to produce granulated products appropriately even with a relatively low water content. A lower water content reduces the amount of pure water added, and also shortens the drying time and energy required for drying.

[0061] Although embodiments of the present invention have been described above, the embodiments are not limited to those described herein. Furthermore, the aforementioned components include those that can be easily conceived by those skilled in the art, those that are substantially the same, and those that fall within the so-called equivalent range. Moreover, the aforementioned components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the embodiments described above. [Explanation of Symbols]

[0062] 10 Carbonization apparatus 11 Rotary Kiln 12 Kiln body 14 Heater 60 Nitrogen gas flow direction

Claims

1. Specific surface area is 10 m ２ A mixing step of mixing carbon less than 1g and tungsten oxide to obtain a mixture, The aforementioned mixture is heated in an inert gas atmosphere to carbonize tungsten oxide and produce tungsten carbide in a carbonization step, Includes, In the carbonization process, the material is heated at a temperature of 1600°C to 2000°C. A method for producing tungsten carbide.

2. A mixing step of mixing carbon having a specific surface area of ​​less than 10 m² / g with tungsten oxide to obtain a mixture, The aforementioned mixture is heated in an inert gas atmosphere to carbonize tungsten oxide and produce tungsten carbide in a carbonization step, Includes, In the carbonization step, the mixture is introduced into a heat treatment furnace, and the inert gas is supplied to the reaction region of the heat treatment furnace at a flow rate of 0.4 m / min or less while heating. A method for producing tungsten carbide.

3. A mixing step of mixing carbon having a specific surface area of ​​less than 10 m² / g with tungsten oxide to obtain a mixture, The aforementioned mixture is heated in an inert gas atmosphere to carbonize tungsten oxide and produce tungsten carbide in a carbonization step, Includes, In the carbonization process, the mixture is introduced into a heat treatment furnace, and if the temperature in the reaction region of the heat treatment furnace is less than 1500°C, the flow rate of the supplied inert gas is set to 0.1 m / min or less, and if the temperature in the reaction region is 1500°C or higher, the flow rate of the supplied inert gas is set to 0.4 m / min or less. A method for producing tungsten carbide.

4. The method for producing tungsten carbide according to any one of claims 1 to 3, wherein the mixture has a molar ratio of carbon to tungsten (C / W) of 4.0 or less.

5. A method for producing tungsten carbide according to claim 1 or claim 2, wherein in the carbonization step, the mixture is introduced into a heat treatment furnace, and when the temperature in the reaction region of the heat treatment furnace is less than 1500°C, the flow rate of the supplied inert gas is 0.1 m / min or less, and when the temperature in the reaction region is 1500°C or higher, the flow rate of the supplied inert gas is 0.4 m / min or less.

6. The method for producing tungsten carbide according to any one of claims 1 to 5, wherein the heating time of the mixture in the carbonization step is 10 minutes or more and 90 minutes or less.

7. A method for producing tungsten carbide according to any one of claims 1 to 6, further comprising a molding step of producing granules by adding water to the mixture and granulating it, wherein in the carbonization step, the granules are heated to carbonize tungsten oxide and produce tungsten carbide.

8. The method for producing tungsten carbide according to claim 7, wherein the water content in the molding step is 11 mass% or less.

9. A method for producing tungsten carbide according to any one of claims 1 to 8, wherein the carbonization rate after the carbonization step is 99.5% or more.

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