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

Abstract

The invention belongs to the technical field of tungsten carbide microwave synthesis, and discloses a method for preparing tungsten carbide powder by a microwave carbon thermal reduction method, which comprises the following steps: mixing tungsten trioxide powder and carbon powder in proportion, carrying out ball-milling mixing in a planetary ball mill, drying the mixed powder, pre-pressing into a blank, putting the blank into a crucible, and carrying out vacuum drying to obtain the tungsten carbide powder. The preparation method comprises the following steps: performing carbon burying and alumina powder composite coating structure treatment on a crucible, putting the crucible into a heat preservation structure, putting the crucible into a microwave sintering furnace, performing microwave sintering at the temperature of 1100-1300 DEG C, and performing heat preservation treatment to synthesize tungsten carbide powder. The method has the advantages of simple process, low cost, effective inhibition of the abnormal growth of crystal grains, obtaining of submicron uniform crystal grains, efficient synthesis of tungsten carbide powder with uniform particle size, good dispersibility and high purity at low temperature in a short time, energy saving and emission reduction, small and uniform particle size of the obtained tungsten carbide micro powder, low free carbon content, and suitableness for the high-end fields of hard alloy cutters, wear-resistant coatings and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave synthesis of tungsten carbide, and in particular relates to a method for preparing tungsten carbide powder by microwave carbon thermal reduction. 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 cutting tools, wear-resistant materials, cemented carbide and electronic devices. The traditional method of producing tungsten carbide is that metal tungsten and carbon react for a long time in the solid state at a relatively high temperature. 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] As an emerging preparation technology, microwave sintering has received widespread attention in recent years. Microwave heating has the advantages of internal heating, selective heating, and fast heating speed, which can significantly shorten the reaction time and reduce energy consumption. In the microwave field, the reactant molecules can directly absorb microwave energy, thereby stimulating the vibration and rotation of the molecules, allowing the reaction to proceed rapidly at a lower temperature. In addition, microwave heating can also promote full contact between the reactants, improve the uniformity of the reaction, thereby improving the carbonization efficiency and shortening the carbonization time. It is conducive to the preparation of tungsten carbide ceramic powder with uniform particle size and high purity.

[0004] However, the current process of applying microwave sintering technology to the carbon thermal reduction method to prepare tungsten carbide ceramic powder is still imperfect, and there are problems such as low microwave-material coupling efficiency, difficulty in accurately controlling process parameters, and unstable product quality. Therefore, the development of an efficient and stable technology for preparing tungsten carbide powder by 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] In order to solve the above technical problems, the present invention provides a method for preparing tungsten carbide powder by microwave carbon thermal reduction. In view of the problems of high carbonization temperature, high energy consumption, and uneven product particle size in the traditional tungsten carbide powder preparation process, the microwave sintering process is optimized to achieve low-temperature and efficient synthesis. The method can improve the coupling efficiency of microwaves and materials by accurately controlling the process parameters, strengthen the effects of microwave coupling thermal effects and electric field direction effects on them during microwave heating, solve the problem of unstable product quality, and finally synthesize tungsten carbide powder with uniform particle size, good dispersibility, and high purity in a short 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: Step 1: Prepare 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; Step 2: Pre-pressing the mixed powder into a green body: Pressing the mixed powder after drying in step 1 into a disc-shaped green body that meets the requirements; Step 3, microwave sintering: Place the green body prepared in step 2 in a crucible and perform carbon burying 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 preservation structure and then put it in a microwave sintering furnace. Perform microwave sintering in the temperature range of 1100-1300°C and perform heat preservation treatment to synthesize tungsten carbide (WC) powder.

[0007] Step 4: ball-mill the microwave-sintered tungsten carbide powder to less than 325 mesh, place it in a sintering furnace, heat it to 200-500°C, keep it warm for 6-24 hours, and perform carbon removal treatment to further reduce the free carbon content.

[0008] Furthermore, high-purity tungsten trioxide (WO3) powder and carbon powder are selected as raw materials, wherein 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.

[0009] 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 in order to achieve the best synthesis effect.

[0010] Furthermore, the 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 ball grading is set so that 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 150-300r / min, and the ball milling time is 8-10h to ensure that the raw materials are fully mixed and evenly mixed.

[0011] Furthermore, in step one, the mixed powder is dried at a temperature of 80-110° C. and a drying time of 10-12 h.

[0012] Furthermore, in step 2, the mixed powder of the precursor is pre-pressed into a green body, which is to place the mixed powder in a cylindrical tabletting mold and maintain the pressure at 3MPa for 1 minute; the green body obtained by dry pressing is 30mm in diameter and 3mm in thickness. The mixed powder of the precursor is pre-pressed into a green body so that the carbon powder and the tungsten trioxide powder are more tightly combined. In addition, the gas generated during the microwave heating process is not easy to escape, and the microwave plasma generated promotes the temperature rise and intensifies the synthesis reaction.

[0013] 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 burying treatment. First, carbon burying treatment is performed around and above the body to prevent oxidation of the body during sintering, and then a layer of 0.4-0.6cm thick alumina powder is laid on top of the carbon powder to play an anti-oxidation, heat insulation and protection role, and double-layer burying is performed. The thickness of the alumina powder should not be buried too thick or 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, which will affect the effective control of the sintering process.

[0014] 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.

[0015] Furthermore, the time from room temperature to microwave sintering temperature is 16-25 minutes, the microwave heat preservation treatment time is 5-10 minutes, and then it is cooled to room temperature after natural cooling.

[0016] Furthermore, the particle size of the tungsten carbide micropowder prepared after crushing, grinding and screening is 0.1-5µm.

[0017] The present invention uses common raw materials and does not require expensive additives, thus reducing the cost of raw materials. Microwave sintering can heat the material evenly and avoid local temperature differences, so that the tungsten carbide grains grow evenly, with narrow particle size distribution and good dispersibility. It effectively solves the problem that the traditional carbon thermal reduction method easily causes uneven powder particle size, agglomeration and many impurities. At the same time, short-time 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.

[0018] The present invention uses a carbon thermal reduction method to mix tungsten trioxide (WO3) and carbon powder, and then carbonizes them at high temperature to generate tungsten carbide. Planetary ball milling parameters are optimized to ensure that the precursors are mixed evenly, providing a homogeneous basis for subsequent reactions. Before microwave heating preparation, the precursor powder is subjected to a carbon-alumina composite powder burying treatment and double-layer burying. The carbon burying treatment and the alumina powder layer are compositely protected to maintain the reducing atmosphere and prevent excessive carbon volatilization, thereby playing an anti-oxidation, heat insulation and protective role. The microwave coupling thermal effect and electric field direction effect during microwave heating are strengthened, and WC powder with high purity and micron-level particle size can be synthesized in a short time. According to the characteristics of microwave selective heating, the reaction temperature is reduced by 200-300°C compared with the conventional carbonization process, effectively inhibiting abnormal grain growth and obtaining submicron-level uniform grains.

[0019] The present invention adopts microwave heating, which has fast heating speed, short preparation time and no pollution, and can complete the reaction within 40 minutes, which is much shorter than several hours or even dozens of hours of traditional methods, and is in line with the national energy-saving and environmental protection policies and guidelines; and the process is easy to realize continuous production, further improves the production scale and efficiency, and provides a new way and idea for the industrial microwave heating preparation of WC powder.

[0020] The beneficial effects of the present invention are as follows: the raw materials and preparation steps are simple, the operation method is clear, the production efficiency is high, and the low-temperature and efficient synthesis of tungsten carbide powder is achieved by optimizing the microwave sintering process. The process can improve the coupling efficiency of microwaves and materials, accurately control the process parameters, and strengthen the effects of microwave coupling thermal effects and electric field direction effects during microwave heating, and finally synthesize tungsten carbide powder with uniform particle size, good dispersibility and high purity in a short time. Compared with traditional processes, this method saves energy and reduces emissions, and the obtained tungsten carbide powder has a smaller and more uniform particle size, a lower free carbon content, and a low oxygen content, and is suitable for high-end fields such as cemented carbide tools and wear-resistant coatings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the XRD spectrum of the WC material prepared by microwave sintering in Example 1 of the present invention; Figure 2 This is a temperature rise curve diagram of WC powder prepared by microwave sintering in Example 1 of the present invention; Figure 3 This is a scanning electron microscope image of the tungsten carbide powder synthesized in Example 1 of the present invention. DETAILED DESCRIPTION

[0022] 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 in conjunction with specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0023] 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 all commercially available unless otherwise specified. The purity of the tungsten trioxide used in the examples is ≥99.97%, the diameter of the tungsten trioxide powder raw material is 1 μm, and the diameter of the carbon powder raw material is 1 μm.

[0024] Example 1

[0025] A method for preparing tungsten carbide powder by microwave carbon thermal reduction method comprises the following steps: Step 1: Prepare 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 1.5:1 between the volume of anhydrous ethanol and the total volume of grinding balls and the mixed powder, and use wet planetary ball milling to mix the materials. The mass ratio of grinding balls to mixed powders is 2:1. 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 80℃ for 12h.

[0026] Step 2, pre-pressing the mixed powder into a blank: Take 6g of the mixed powder obtained after ball milling and drying, place it in a mold with a diameter of 30mm and a height of 120mm, press it at a pressure of 3MPa and hold the pressure for 1min, and press the mixed powder into a disc-shaped blank with a thickness of 3mm.

[0027] Step 3, microwave sintering: Place the green body prepared in step 2 in a corundum crucible for carbon embedding, that is, lay a layer of carbon powder around and on the green body, and then lay a layer of 0.5cm thick alumina powder on the carbon powder. Place the crucible in a fiber insulation product and then put it in a microwave sintering furnace. Heat it with a microwave input power rate of 0.2kW / min. During the sintering process, the temperature is increased steadily at a heating rate of 20-100℃ / min to reach a microwave sintering temperature of 1300℃. Keep the temperature 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 whole process takes about 30 minutes, which greatly shortens the preparation time compared to the traditional WC powder preparation method.

[0028] Step 4: ball-mill the microwave-sintered tungsten carbide powder to less than 325 mesh, place it in a sintering furnace, heat it to 300°C, keep it warm for 16 hours, and then naturally cool it and crush, grind it, and screen it 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%.

[0029] Example 2

[0030] A method for preparing tungsten carbide powder by microwave carbon thermal reduction method comprises the following steps: Step 1. Prepare 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 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 rotation 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, and the mixed powder after ball milling is dried at a drying temperature of 100℃ and a drying time of 11h.

[0031] Step 2, pre-pressing the mixed powder into a blank: Take 6g of the mixed powder obtained after ball milling and drying, place it in a mold with a diameter of 30mm and a height of 120mm, press it at a pressure of 3MPa and hold the pressure for 1min, and press the mixed powder into a disc-shaped blank with a thickness of 3mm.

[0032] Step 3, microwave sintering: the green body prepared in step 2 is placed in a corundum crucible for carbon embedding treatment, that is, 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 a heat preservation structure and then put into 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 stably increased at a heating rate of 20-100°C / min to reach a microwave sintering temperature of 1200°C. The heat preservation treatment is performed 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.

[0033] Step 4: Ball-mill the microwave-sintered tungsten carbide powder to less than 325 mesh, place it in a sintering furnace, heat it to 200°C, keep it warm for 24 hours, and then naturally cool it and then crush, grind it, and screen it 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%.

[0034] Example 3

[0035] A method for preparing tungsten carbide powder by microwave carbon thermal reduction method comprises the following steps: Step 1: Prepare 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 in a ratio of 0.5:1 between the volume of anhydrous ethanol and the total volume of grinding balls and the mixed powder, and use wet planetary ball milling to mix the materials. The mass ratio of grinding balls to mixed powders 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℃ for 10h.

[0036] Step 2, pre-pressing the mixed powder into a blank: Take 6g of the mixed powder obtained after ball milling and drying, place it in a mold with a diameter of 30mm and a height of 120mm, press it at a pressure of 3MPa and hold the pressure for 1min, and press the mixed powder into a disc-shaped blank with a thickness of 3mm.

[0037] Step 3, microwave sintering: the green body prepared in step 2 is placed in a corundum crucible for carbon embedding treatment, that is, a layer of carbon powder is laid around and on the green body, and then a layer of 0.6 cm thick alumina powder is laid on the carbon powder. The crucible is placed in a heat preservation structure and then put into a microwave sintering furnace. The microwave input power rate of 1 kW / min is used for heating. During the sintering process, the temperature is stably increased at a heating rate of 20-100°C / min to reach a microwave sintering temperature of 1100°C. The heat preservation treatment is performed 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 with the traditional WC powder preparation method.

[0038] Step 4: Ball-mill the microwave-sintered tungsten carbide powder to less than 325 mesh, place it in a sintering furnace, heat it to 500°C, keep it warm for 6 hours, and then naturally cool it and crush, grind it, and screen it 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%.

[0039] 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 FIG. Figure 1 shown.

[0040] Depend on Figure 1Peaks of WC, WO3, and C phases can be observed. This observation shows that the reaction rate is relatively slow at 1100°C, and the reaction time is limited, so it is difficult for all carbon to participate in the reaction to generate products such as tungsten carbide. The remaining carbon will be reflected in the XRD. 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 still cannot be completely combined with tungsten to form tungsten carbide, and then C peaks and WO3 peaks appear in the XRD spectrum. However, with the increase of temperature, at 1300°C, the tungsten trioxide peak and C peak decrease, and the WC peak intensity increases, and the diffraction peak becomes sharper, which shows that the increase in temperature promotes the carbon thermal reduction reaction.

[0041] 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 grain size distribution of the prepared synthetic tungsten carbide is uniform. The microwave oven used for sintering in the present invention uses infrared temperature measurement, and the infrared temperature measurement equipment is used to perform the detection according to the corresponding national standards. Those skilled in the art should know, so the present invention will not be repeated here.

[0042] The above embodiments are merely examples of the explanation, specific implementation and implementation effect of the present invention, and are not limitations of 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 all belong to 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 a sintering precursor: Mix tungsten trioxide powder and carbon powder in proportion, mill the mixture in a planetary ball mill, and dry the milled mixed powder; Step 2: Pre-pressing the mixed powder into a green body: Pressing the mixed powder after drying in step 1 into a disc-shaped green body that meets the requirements; 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 preservation structure and then put it in a microwave sintering furnace, perform microwave sintering in a temperature range of 1100-1300°C, and perform heat preservation treatment to synthesize tungsten carbide powder; Step 4: ball-mill the microwave-sintered tungsten carbide powder to less than 325 mesh, place it in a common sintering furnace, heat it to 200-500°C, keep it warm for 6-24 hours, and perform carbon removal treatment.

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 raw material is 1μm, and the diameter of the carbon powder raw material 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 rotation 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: In step 1, the mixed powder is dried at a temperature of 80-110° C. and a drying time of 10-12 hours.

6. The method for preparing tungsten carbide powder by microwave carbon thermal reduction according to claim 1, characterized in that: In step 2, the precursor mixed powder is pre-pressed into a green body by placing the mixed powder into a cylindrical tabletting mold and maintaining 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.

7. The method for preparing tungsten carbide powder by microwave carbon thermal reduction according to claim 1, characterized in that: In step three, the green body is placed in a corundum crucible to complete the microwave sintering process, and the green body is subjected to a carbon-alumina composite powder embedding treatment before microwave heating preparation.

8. 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.

9. 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.

10. 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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