A method for preparing tungsten carbide powder by microwave carbon thermal reduction

Abstract

The invention belongs to the technical field of microwave synthesis of tungsten carbide and discloses a method for preparing tungsten carbide powder by microwave carbon thermal reduction. The method comprises the following steps: tungsten trioxide powder and carbon powder are mixed in proportion, ball-milled and mixed in a planetary ball mill, the mixed powder is dried and pre-pressed into a blank, the blank is placed in a crucible, and subjected to a carbon-embedded and aluminum oxide powder composite coating structure treatment, the crucible is then placed in a heat-insulating structure and placed in a microwave sintering furnace, microwave sintered within a temperature range of 1100-1300°C, and heat-insulated to synthesize tungsten carbide powder. The method optimizes the microwave sintering process, accurately controls process parameters, reduces the reaction temperature, effectively inhibits abnormal grain growth, obtains submicron-level uniform grains, and synthesizes tungsten carbide powder with uniform particle size, good dispersibility and high purity at low temperature and high efficiency in a short time, thereby saving energy and reducing emissions. The obtained tungsten carbide micropowder has a small and uniform particle size and a low free carbon content, and is suitable for high-end fields such as cemented carbide cutting tools and wear-resistant coatings.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave synthesis of tungsten carbide, and particularly relates to a method for preparing tungsten carbide powder by a microwave carbon thermal reduction method. Background Art

[0002] As an important raw material for cemented carbide, tungsten carbide (WC) powder has shown important application value in many fields. It has the characteristics of high hardness, high wear resistance, good chemical stability and high melting point, and is widely used in industries such as cutting tools, wear-resistant materials, cemented carbide and electronic devices. The traditional method of producing tungsten carbide is to react metallic tungsten and carbon in the solid state at a relatively high temperature for a long time. However, this method requires high costs and has problems in controlling particle size and carbon content, such as high carbonization temperature, long time, coarse particles and complex process, which limit the further application and development of tungsten carbide powder. In order to solve the above problems, researchers are constantly exploring new preparation technologies, such as carbon thermal method (direct carburizing of tungsten powder), mechanical alloying method, carbon thermal reduction of tungsten oxide, etc.

[0003] Microwave sintering, as an emerging preparation technology, has garnered widespread attention in recent years. Microwave heating offers advantages such as internal heating, selective heating, and rapid heating rates, significantly shortening reaction times and reducing energy consumption. In the microwave field, reactant molecules directly absorb microwave energy, stimulating their vibration and rotation, enabling the reaction to proceed rapidly at lower temperatures. Furthermore, microwave heating promotes sufficient contact between reactants, improving reaction uniformity, thereby increasing carbonization efficiency and shortening carbonization time. This facilitates the preparation of tungsten carbide ceramic powders with uniform particle size and high purity.

[0004] However, the current process for applying microwave sintering technology to the carbon thermal reduction method to prepare tungsten carbide ceramic powder is still imperfect. Problems include low microwave-material coupling efficiency, difficulty in accurately controlling process parameters, and unstable product quality. Therefore, developing an efficient and stable technology for preparing tungsten carbide powder using microwave heating and carbon thermal reduction has important practical significance and broad application prospects for promoting the development of cemented carbide materials. Summary of the Invention

[0005] To address the above-mentioned technical problems, the present invention provides a method for preparing tungsten carbide powder using microwave carbon thermal reduction. This method addresses the issues of high carbonization temperature, high energy consumption, and uneven product particle size that exist in traditional tungsten carbide powder preparation processes. By optimizing the microwave sintering process, high-efficiency synthesis is achieved at low temperature. By precisely controlling process parameters, this method improves the coupling efficiency between microwaves and the material, enhancing the effects of microwave coupling thermal effects and electric field directional effects during microwave heating, thereby addressing the issue of unstable product quality. Ultimately, tungsten carbide powder with uniform particle size, good dispersion, and high purity can be synthesized in a short period of time.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: a method for preparing tungsten carbide powder by microwave carbon thermal reduction method, comprising the following steps:

[0007] Step 1: Prepare the sintering precursor: Mix tungsten trioxide powder (WO3) and carbon powder in proportion, mill the mixture in a planetary ball mill, and dry the milled mixed powder;

[0008] Step 2: Pre-pressing the mixed powder into a green body: Press the mixed powder after drying in step 1 into a disc-shaped green body that meets the requirements;

[0009] Step 3: Microwave sintering: Place the green body prepared in step 2 in a crucible and perform carbon embedding treatment, that is, lay a layer of carbon powder around and on the green body, and then lay a layer of alumina powder on the carbon powder. Place the crucible in a heat-insulating structure and then put it into a microwave sintering furnace. Microwave sintering is performed in the temperature range of 1100-1300°C, and heat-insulating treatment is performed to synthesize tungsten carbide (WC) powder.

[0010] Step 4: Ball mill the microwave-sintered tungsten carbide powder until it is below 325 mesh, place it in a sintering furnace, heat it to 200-500°C, and keep it warm for 6-24 hours to perform carbon removal treatment to further reduce the free carbon content.

[0011] Furthermore, high-purity tungsten trioxide (WO3) powder and carbon powder are selected as raw materials. The diameter of the tungsten trioxide powder raw material is 1 μm, and the diameter of the carbon powder raw material is 1 μm. The average particle size of the mixed powder after ball milling is 0.5-1 μm.

[0012] Furthermore, the molar ratio of tungsten trioxide to carbon powder in step 1 is 1:3-3.5, and the raw materials are accurately weighed to achieve the best synthesis effect.

[0013] Furthermore, tungsten trioxide and carbon powder are mixed by wet planetary ball milling, with anhydrous ethanol as the wet mixing medium. The grinding balls are not limited to alumina grinding balls. The grinding balls are graded, and the volume ratio of the added anhydrous ethanol and grinding balls to the total mixed powder is 0.5-1.5:1. The mass ratio of the grinding balls to the mixed powder is 2-10:1. The rotation speed of the planetary ball mill is 150-300 r / min, and the ball milling time is 8-10 hours to ensure that the raw materials are fully mixed.

[0014] Furthermore, in step 1, the mixed powder is dried at a temperature of 80-110° C. and a drying time of 10-12 h.

[0015] Furthermore, in step 2, the precursor powder mixture is pre-pressed into a green sheet by placing the mixed powder into a cylindrical tableting mold and maintaining the pressure at 3 MPa for 1 minute. The green sheet produced by dry pressing has a diameter of 30 mm and a thickness of 3 mm. This pre-pressing of the precursor powder mixture strengthens the bond between the carbon powder and the tungsten trioxide powder. Furthermore, it prevents the gas generated during microwave heating from escaping, generating microwave plasma that promotes temperature rise and intensifies the synthesis reaction.

[0016] Furthermore, in step 3, the prefabricated body is placed in a corundum crucible to complete the microwave sintering process. Before microwave heating preparation, the body is subjected to a carbon-alumina composite powder embedding treatment. First, carbon is embedded around and above the body to prevent oxidation of the body during sintering. Then, a layer of 0.4-0.6 cm thick alumina powder is laid on top of the carbon powder to play an anti-oxidation, heat insulation and protective role, performing a double-layer embedding. The thickness of the alumina powder should be neither too thick nor too thin. If it is too thin, it will not have an anti-oxidation effect. If it is too thick, the temperature detection will be inaccurate, affecting the effective control of the sintering process.

[0017] Furthermore, the frequency of the microwave treatment is 2450 MHz-300 GHz, the power is continuously adjustable from 0 to 15 kW, and the input power rate is 100 to 1000 w / min.

[0018] Furthermore, the time for heating from room temperature to microwave sintering temperature is 16-25 minutes, the microwave heat preservation treatment time is 5-10 minutes, and the material is cooled to room temperature after natural cooling.

[0019] Furthermore, the particle size of the tungsten carbide micropowder prepared after crushing, grinding and screening is 0.1-5µm.

[0020] The present invention uses common raw materials and does not require expensive additives, thus reducing raw material costs. Microwave sintering can penetrate deep into the material and evenly heat it, avoiding local temperature differences, so that the tungsten carbide grains grow evenly, with a narrow particle size distribution and good dispersion. It effectively solves the problems of uneven powder size, agglomeration, and high impurities caused by the traditional carbon thermal reduction method. At the same time, short-term sintering and special protection reduce the introduction of impurities and improve purity. Uniform particle size and high purity improve the hardness, wear resistance and other properties of tungsten carbide ceramic powder, and the tool parts made from it have a longer service life.

[0021] This method uses a carbon thermal reduction method to mix tungsten trioxide (WO3) with carbon powder, followed by carbonization at high temperature to produce tungsten carbide. Planetary ball milling parameters are optimized to ensure uniform mixing of the precursors, providing a homogeneous foundation for subsequent reactions. Prior to microwave heating, the precursor powder undergoes a double-layer carbon-alumina composite buried powder treatment. This carbon burial and combined alumina powder layer provide protection, maintaining a reducing atmosphere while preventing excessive carbon volatilization, providing antioxidant, thermal insulation, and protection. By enhancing the effects of microwave coupling thermal effects and electric field directional effects during microwave heating, high-purity WC powder with micron-sized particles can be synthesized in a short period of time. Due to the selective heating characteristics of microwaves, the reaction temperature is reduced by 200-300°C compared to conventional carbonization processes, effectively suppressing abnormal grain growth and producing uniform submicron-sized grains.

[0022] The present invention adopts microwave heating, which has a fast heating speed, short preparation time and no pollution. The reaction can be completed within 40 minutes, which is much shorter than the several hours or even dozens of hours of traditional methods. It complies with the national energy conservation and environmental protection policies and guidelines. In addition, the process is easy to realize continuous production, further improving production scale and efficiency, and providing a new approach and idea for the industrial microwave heating preparation of WC powder.

[0023] The present invention has the following beneficial effects: simple raw materials, simple preparation steps, clear operation methods, and high production efficiency. By optimizing the microwave sintering process, it achieves low-temperature, high-efficiency synthesis of tungsten carbide powder. This process can improve the coupling efficiency between microwaves and materials, precisely control process parameters, and enhance the effects of microwave coupling thermal effects and electric field direction effects during microwave heating. Ultimately, tungsten carbide powder with uniform particle size, good dispersibility, and high purity can be synthesized in a short period of time. Compared with traditional processes, this method saves energy and reduces emissions. The resulting tungsten carbide powder has a smaller and more uniform particle size, a lower free carbon content, and a low oxygen content, making it suitable for high-end applications such as cemented carbide cutting tools and wear-resistant coatings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the XRD pattern of the WC material prepared by microwave sintering in Example 1 of the present invention;

[0025] Figure 2 This is a temperature rise curve diagram of WC powder prepared by microwave sintering in Example 1 of the present invention;

[0026] Figure 3 This is a scanning electron microscope image of the tungsten carbide powder synthesized in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below with reference to specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0028] It should be noted that the experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials used are commercially available unless otherwise specified. The tungsten trioxide used in the examples has a purity of ≥99.97%, and the raw material tungsten trioxide powder has a diameter of 1 μm, and the raw material carbon powder has a diameter of 1 μm.

[0029] Example 1

[0030] A method for preparing tungsten carbide powder by microwave carbon thermal reduction method comprises the following steps:

[0031] Step 1. Prepare the sintering precursor: Mix tungsten trioxide powder (WO3) and carbon powder in a molar ratio of 1:3, put them into a planetary ball mill, add anhydrous ethanol at a volume ratio of 1.5:1 between anhydrous ethanol and grinding balls and the total volume of the mixed powder, and use wet planetary ball milling to mix the materials. The mass ratio of grinding balls to mixed powder is 2:1, and alumina grinding balls are used. The speed of the planetary ball mill is 300r / min and the ball milling time is 10h. The average particle size of the mixed powder after ball milling is 0.5-1μm. The mixed powder after ball milling is dried at a drying temperature of 80℃ and a drying time of 12h.

[0032] Step 2: Pre-press the mixed powder into a green body: Take 6 g of the mixed powder obtained after ball milling and drying, place it in a mold with a diameter of 30 mm and a height of 120 mm, press it at a pressure of 3 MPa and hold the pressure for 1 minute, and press the mixed powder into a disc-shaped green body with a thickness of 3 mm.

[0033] Step 3: Microwave Sintering: The green body prepared in Step 2 is placed in a corundum crucible and carbonized. This involves applying a layer of carbon powder around and above the green body, followed by a 0.5cm thick layer of alumina powder above the carbon powder. The crucible is then placed inside a fiber insulation product and placed in a microwave sintering furnace. Heating is performed at a microwave input power rate of 0.2kW / min. During sintering, the temperature is steadily increased at a rate of 20-100°C / min to reach a microwave sintering temperature of 1300°C. The temperature is then held for 10 minutes to synthesize tungsten carbide (WC) powder. The microwave frequency is 100GHz, and the microwave power is continuously adjustable from 0-5kW. The entire process takes approximately 30 minutes, significantly reducing preparation time compared to traditional WC powder preparation methods.

[0034] Step 4: Ball mill the microwave-sintered tungsten carbide powder to below 325 mesh, place it in a sintering furnace, heat it to 300°C, keep it warm for 16 hours, and then cool it naturally before crushing, grinding, and screening to obtain tungsten carbide micropowder with an average particle size of 0.1-0.5µm, a free carbon content of 0.08%, and an oxygen content of 0.2%.

[0035] Example 2

[0036] A method for preparing tungsten carbide powder by microwave carbon thermal reduction method comprises the following steps:

[0037] Step 1. Prepare the sintering precursor: Mix tungsten trioxide powder (WO3) and carbon powder in a molar ratio of 1:3, put them into a planetary ball mill, add anhydrous ethanol in a ratio of 1:1 between the volume of anhydrous ethanol and the volume of grinding balls and the total volume of the mixed powder, and use wet planetary ball milling to mix the materials. The ball-to-material mass ratio is 5:1, the speed of the planetary ball mill is 200r / min, and the ball milling time is 9h. The average particle size of the mixed powder after ball milling is 0.5-1μm. The mixed powder after ball milling is dried at a drying temperature of 100℃ and a drying time of 11h.

[0038] Step 2: Pre-press the mixed powder into a green body: Take 6 g of the mixed powder obtained after ball milling and drying, place it in a mold with a diameter of 30 mm and a height of 120 mm, press it at a pressure of 3 MPa and hold the pressure for 1 minute, and press the mixed powder into a disc-shaped green body with a thickness of 3 mm.

[0039] Step 3: Microwave sintering: The green body prepared in step 2 is placed in a corundum crucible for carbon embedding treatment, i.e., a layer of carbon powder is laid around and on the green body, and then a layer of 0.4 cm thick alumina powder is laid on the carbon powder. The crucible is placed in an insulation structure and then placed in a microwave sintering furnace. It is heated at a microwave input power rate of 0.1 kW / min. During the sintering process, the temperature is steadily increased at a heating rate of 20-100°C / min to reach a microwave sintering temperature of 1200°C. The heat preservation treatment is carried out for 8 minutes to synthesize tungsten carbide (WC) powder. The microwave frequency is 2450 MHz, and the microwave power is continuously adjustable from 0 to 10 kW. The whole process takes about 40 minutes, which greatly shortens the preparation time compared to the traditional WC powder preparation method.

[0040] Step 4: Ball mill the microwave-sintered tungsten carbide powder to below 325 mesh, place it in a sintering furnace, heat it to 200°C, keep it warm for 24 hours, and then cool it naturally before crushing, grinding, and screening to obtain tungsten carbide micropowder with an average particle size of 0.5-1µm, a free carbon content of 0.12%, and an oxygen content of 0.24%.

[0041] Example 3

[0042] A method for preparing tungsten carbide powder by microwave carbon thermal reduction method comprises the following steps:

[0043] Step 1. Prepare the sintering precursor: Mix tungsten trioxide powder (WO3) and carbon powder in a molar ratio of 1:3.5, put them into a planetary ball mill, add anhydrous ethanol at a volume ratio of anhydrous ethanol and grinding balls to the total volume of the mixed powder of 0.5:1, and use wet planetary ball milling to mix the materials. The mass ratio of grinding balls to mixed powder is 10:1, the speed of the planetary ball mill is 150r / min, and the ball milling time is 8h; the average particle size of the mixed powder after ball milling is 0.5-1μm, and the mixed powder after ball milling is dried at a drying temperature of 110℃ and a drying time of 10h.

[0044] Step 2: Pre-press the mixed powder into a green body: Take 6 g of the mixed powder obtained after ball milling and drying, place it in a mold with a diameter of 30 mm and a height of 120 mm, press it at a pressure of 3 MPa and hold the pressure for 1 minute, and press the mixed powder into a disc-shaped green body with a thickness of 3 mm.

[0045] Step 3: Microwave sintering: The green body prepared in step 2 is placed in a corundum crucible for carbon embedding treatment, i.e., a layer of carbon powder is laid around and on top of the green body, and then a layer of 0.6 cm thick alumina powder is laid on top of the carbon powder. The crucible is placed in an insulation structure and then placed in a microwave sintering furnace. A microwave input power rate of 1 kW / min is used for heating. During the sintering process, a stable temperature increase is achieved at a heating rate of 20-100°C / min to reach a microwave sintering temperature of 1100°C. The heat preservation treatment is carried out for 5 minutes to synthesize tungsten carbide (WC) powder. The microwave frequency is 300 GHz, and the microwave power is continuously adjustable from 0 to 15 kW. The whole process takes about 25 minutes, which greatly shortens the preparation time compared to traditional WC powder preparation methods.

[0046] Step 4: Ball mill the microwave-sintered tungsten carbide powder to below 325 mesh, place it in a sintering furnace, heat it to 500°C, keep it warm for 6 hours, and then cool it naturally before crushing, grinding, and screening to obtain tungsten carbide micropowder with an average particle size of 1-5µm, a free carbon content of 0.15%, and an oxygen content of 0.3%.

[0047] The tungsten carbide prepared in Example 1 was tested by XRD using a SmartLab X-ray diffraction analyzer (XRD) from Rigaku Corporation. The test results are shown in Figure 2. Figure 1 shown.

[0048] Depend on Figure 1Peaks of WC, WO3, and C phases can be observed. This observation indicates that the reaction rate at 1100°C is relatively slow and the reaction time is limited, making it difficult for all carbon to participate in the reaction to form products such as tungsten carbide. The remaining carbon will be reflected in the XRD pattern. At 1300°C, the atomic diffusion rate is accelerated, but the sintering time is not long enough, and the diffusion between atoms such as carbon and tungsten is insufficient. Some carbon is still unable to completely combine with tungsten to form tungsten carbide, and then C peaks and WO3 peaks appear in the XRD spectrum. However, with increasing temperature, at 1300°C, the tungsten trioxide peak and C peak decrease, and the WC peak intensity increases, and the diffraction peak becomes sharper. Overall, it shows that the increase in temperature promotes the progress of the carbothermal reduction reaction.

[0049] In order to clarify the effect of the sintering treatment method used in the present invention on the temperature change of the reaction system, the present invention tested the microwave sintering temperature rise curve of tungsten carbide prepared in Example 1. The results are as follows: Figure 2 As shown. Figure 3 As shown, the prepared synthetic tungsten carbide has a uniform grain size distribution. The microwave oven used for sintering in the present invention uses infrared temperature measurement, which is detected by infrared temperature measurement equipment according to the corresponding national standards. Those skilled in the art should know this, so the present invention will not be repeated here.

[0050] The above embodiments are merely examples of the explanation, specific embodiments, and implementation effects of the present invention, and are not intended to limit the present invention. Based on the present disclosure, some modifications or improvements without creative contributions may be made thereto, which will be apparent to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present disclosure are intended to fall within the scope of protection claimed in the present disclosure.

Claims

1. A method for preparing tungsten carbide powder by microwave carbon thermal reduction, characterized in that: The following steps are involved: Step 1: Prepare the sintering precursor: Mix tungsten trioxide powder and carbon powder in proportion, and mill the mixture in a planetary ball mill. Dry the milled mixed powder at a temperature of 80-110°C for 10-12 hours. Step 2: Pre-pressing the mixed powder into a green body: Press the mixed powder after the drying treatment in step 1 into a disc-shaped green body that meets the requirements; the precursor mixed powder is pre-pressed into a green body by placing the mixed powder into a cylindrical tableting mold and holding the pressure at 3 MPa for 1 minute; the green body obtained by dry pressing has a diameter of 30 mm and a thickness of 3 mm; Step 3, microwave sintering: The green body prepared in step 2 is placed in a crucible and subjected to carbon embedding treatment, that is, a layer of carbon powder is laid around and on the green body, and then a layer of alumina powder with a thickness of 0.4-0.6 cm is laid on the carbon powder, that is, the green body is subjected to carbon-alumina composite powder embedding treatment before microwave heating preparation; the crucible is placed in an insulation structure and then placed in a microwave sintering furnace, microwave sintering is performed in the temperature range of 1100-1300°C, and insulation treatment is performed, and the green body is placed in a corundum crucible to complete the microwave sintering process to synthesize tungsten carbide powder; Step 4: ball mill the microwave sintered tungsten carbide powder until it is below 325 mesh, place it in a common sintering furnace, heat it to 200-500°C, and keep it warm for 6-24 hours to perform carbon removal treatment; Before microwave heating, the precursor powder is treated with carbon-alumina composite powder embedding to enhance the microwave coupling thermal effect and electric field direction effect during microwave heating. Through the carbon thermal reduction method, tungsten trioxide and carbon powder are mixed and carbonized at high temperature to synthesize WC powder with high purity and micron-level particle size in a short time.

2. The method for preparing tungsten carbide powder by microwave carbon thermal reduction according to claim 1, characterized in that: High-purity tungsten trioxide powder and carbon powder are selected as raw materials. The diameter of the tungsten trioxide powder is 1μm, and the diameter of the carbon powder is 1μm. The average particle size of the mixed powder after ball milling is 0.5-1μm.

3. The method for preparing tungsten carbide powder by microwave carbon thermal reduction according to claim 1, characterized in that: The molar ratio of tungsten trioxide to carbon powder in step 1 is 1:3-3.

5.

4. The method for preparing tungsten carbide powder by microwave carbon thermal reduction according to claim 1, characterized in that: With anhydrous ethanol as the wet mixing medium, tungsten trioxide and carbon powder are mixed by wet planetary ball milling. The volume ratio of the added anhydrous ethanol and grinding balls to the total mixed powder is 0.5-1.5:1, the mass ratio of the grinding balls to the mixed powder is 2-10:1, the speed of the planetary ball mill is 150-300r / min, and the ball milling time is 8-10h.

5. The method for preparing tungsten carbide powder by microwave carbon thermal reduction according to claim 1, characterized in that: The frequency of microwave treatment is 2450MHz-300GHz, the power is continuously adjustable from 0 to 15kW, and the input power rate is 100-1000w / min.

6. The method for preparing tungsten carbide powder by microwave carbon thermal reduction according to claim 1, characterized in that: The time from room temperature to microwave sintering temperature is 16-25 minutes, and the microwave insulation treatment time is 5-10 minutes.

7. The method for preparing tungsten carbide powder by microwave carbon thermal reduction according to claim 1, characterized in that: The particle size of tungsten carbide powder is 0.1-5µm.

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