Method for preparing tungsten carbide through dynamic reduction

Abstract

According to the preparation method, the carbonization reaction rate and the grain growth rate are dynamically matched through periodic high-methane atmosphere regulation and control, carbon source supply is accelerated in the key stage, generation of a WC phase is promoted, the methane content is reduced in the later stage, grain growth is effectively inhibited, and the yield of the tungsten carbide is improved. And fine particle size and concentrated distribution of the powder are ensured. The tungsten carbide powder obtained through the technical scheme is small in particle size, narrow in distribution, high in purity and suitable for the fields of high-end hard alloy, micro devices and the like.

Description

Technical Field

[0001] This invention belongs to the field of alloy material manufacturing technology, specifically relating to a method for preparing tungsten carbide by dynamic reduction. Background Technology

[0002] Tungsten carbide powder is widely used in high-end manufacturing fields such as cemented carbide, cermets, precision tools, and micro-devices. With the continuous upgrading of industrial technology, downstream industries are placing higher demands on the purity, particle size, and uniformity of particle size distribution of tungsten carbide powder. Fine-grained, concentrated tungsten carbide powder helps improve the density and mechanical properties of alloys, expanding its application scope in high-end fields such as aerospace, electronics, and medical.

[0003] Current mainstream methods for preparing tungsten carbide mostly employ a two-step process: first, tungsten oxide is reduced to tungsten powder at high temperature, and then it is mixed with carbon black and carbonized at high temperature to obtain tungsten carbide. This method suffers from problems such as high energy consumption, large and wide particle size distribution, and difficulty in controlling carbon content, making it difficult to meet the performance requirements of high-end applications. Further reducing the particle size of tungsten carbide powder and improving the uniformity of particle size distribution has become a key focus of the industry.

[0004] However, existing processes struggle to simultaneously control the carbonization reaction rate and grain growth rate. Simply lowering the temperature can suppress grain growth, but the reaction is incomplete, resulting in low product quality. Increasing the temperature leads to larger particle size and wider particle size distribution. Problems such as a single atmosphere composition and slow cooling rate also limit the industrial preparation of ultrafine, highly uniform tungsten carbide powder.

[0005] Therefore, there is an urgent need for a dynamic reduction method for preparing tungsten carbide with high product purity, fine particle size, and uniform particle size distribution. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for preparing tungsten carbide by dynamic reduction. By periodically controlling the high-methane atmosphere, the carbonization reaction rate and the grain growth rate are dynamically matched. The carbon source supply is accelerated in the critical stage to promote the formation of the WC phase, and the methane content is reduced in the later stage to effectively inhibit grain growth, ensuring that the powder has a small particle size and concentrated distribution. The rapid cooling immediately after the carburizing reaction further shortens the high-temperature residence time, greatly inhibits the migration and agglomeration of particles in the high-temperature stage, and prevents secondary grain growth in the cooling stage. The tungsten carbide powder obtained in the end has the advantages of small particle size, narrow distribution and high purity, and is suitable for high-end cemented carbide, micro-devices and other fields.

[0007] To achieve the above and other related objectives, the present invention provides a method for preparing tungsten carbide by dynamic reduction, specifically comprising the following steps:

[0008] Tungsten source and carbon source are mixed in a molar ratio of 1:2.9 to 1:3.3, and a combination of dry mixing and wet ball milling is used to obtain a uniformly mixed raw material powder.

[0009] The raw material powder was subjected to carbothermal reduction at 900-1300℃ under an inert atmosphere to obtain the carbothermal reduction product.

[0010] The carbothermic reduction product was subjected to a carburizing reaction at 800-1100℃ in a methane / hydrogen mixed gas atmosphere. During the carburizing process, the volume fraction of methane changed periodically, ranging from 3% to 20%, and the carburizing reaction time was 1-5 hours.

[0011] After the carburizing reaction is completed, a low-temperature airflow cooling method is immediately used to reduce the powder temperature to below 80°C within 5 minutes;

[0012] The obtained powder is dried and sieved to obtain tungsten carbide powder.

[0013] Furthermore, the temperature of the carbothermic reduction step is 1100-1250℃, and the holding time is 1-3 hours. This temperature range helps to achieve sufficient reduction while avoiding excessively high temperatures that could lead to particle size growth.

[0014] Furthermore, the tungsten source is tungsten trioxide, the carbon source is carbon black, and the wet ball milling media is an alcohol solvent; even further, the media is ethanol. Using tungsten trioxide and carbon black as raw materials ensures the controllability of the reaction and the high purity of the final product, and the raw materials are widely available, facilitating industrial-scale application. Ethanol, as the ball milling media, effectively disperses the powder, prevents agglomeration, improves mixing uniformity, and promotes the uniformity of subsequent reactions.

[0015] Furthermore, during the carburizing reaction, the methane volume fraction is periodically adjusted as follows: 3%-7% in the initial stage, increased to 10%-20% in the intermediate stage, and reduced back to 3%-7% in the final stage. The carburizing reaction atmosphere can be dynamically controlled using a mass flow controller and an automatic switching valve. This measure ensures precise control of the atmosphere composition, improving the stability and repeatability of the process.

[0016] Furthermore, the volume fraction of methane is periodically controlled as follows: 5% in the initial stage, increased to 15% in the middle stage, and reduced back to 5% in the final stage. This periodic control method can achieve mild carburization in the early stage of the reaction, accelerate carbon source supply in the middle stage, and inhibit grain growth in the final stage, thereby achieving particle size control and narrowing of distribution.

[0017] Furthermore, the wet ball milling time is 5-15 hours, the ball-to-material ratio is 3:1-8:1, and the ball milling speed is 200-400 rpm.

[0018] Furthermore, the cryogenic airflow cooling method involves introducing dry air, cold nitrogen, or liquid nitrogen at -35°C. Multiple cooling methods are available to suit different conditions, all of which can achieve rapid cooling and inhibit particle growth.

[0019] Furthermore, the drying step is carried out at 60°C, and the powder is sieved using a 200-mesh sieve. Under these conditions, moisture can be effectively removed from the powder, resulting in uniform particle size and facilitating subsequent applications.

[0020] Furthermore, the wet ball milling time is 10 hours, the ball-to-material ratio is 5:1, and the ball milling speed is 300 rpm. This combination of parameters can balance mixing uniformity and particle size refinement.

[0021] The present invention also provides an ultrafine tungsten carbide powder, which is prepared by the method described above.

[0022] The present invention also provides a cemented carbide, which is prepared using ultrafine tungsten carbide powder as described above.

[0023] Due to the adoption of the above technologies, the significant advantages of this invention compared with the prior art are as follows:

[0024] 1) By periodically controlling the high methane atmosphere, the carbonization reaction rate and grain growth rate are dynamically matched to obtain ultrafine tungsten carbide powder with uniform particle size distribution.

[0025] 2) The rapid cooling process significantly inhibits particle migration and agglomeration in the high-temperature stage, prevents secondary growth of grains in the cooling stage, and further narrows the grain size distribution.

[0026] 3) The process of this invention is simple, the raw materials are widely available, and it is easy to promote industrialization. The tungsten carbide powder produced is suitable for high-end cemented carbide, micro-devices and other fields, and has broad application prospects. Detailed Implementation

[0027] To better understand the present invention, the following detailed description is provided in conjunction with specific embodiments. These embodiments are used to illustrate the main reactions and basic features of the present invention and are not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to specific requirements. Implementation conditions not specified are generally those in conventional experiments.

[0028] The present invention will be further described below with reference to the embodiments.

[0029] Example 1

[0030] Raw materials for preparation: 50 g tungsten trioxide (WO3) powder, 8.0 g carbon black (molar ratio 1:3.1), 100 mL ethanol.

[0031] Preparation method: Weigh WO3 and carbon black according to the specified ratio, dry mix for 2 minutes, add ethanol, and ball mill for 10 hours (ball-to-material ratio 5:1, speed 300 rpm). Filter the ball-milled slurry and vacuum dry at 50℃ for 12 hours to obtain a mixed raw material powder. Load the dried mixed powder into a quartz boat, purge with high-purity argon gas at 0.5 L / min, heat to 1200℃, hold for 2 hours, and allow to cool naturally to room temperature. Spread the carbothermic reduction product evenly on the quartz boat, purge with a methane / hydrogen mixed gas at a total flow rate of 0.2 L / min, with the methane volume fraction at 5% for the first 30 minutes, 15% for the middle 60 minutes, and 5% for the last 90 minutes, slowly decreasing to 3%. The carburizing reaction temperature is 1000℃, and the total time is 3 hours. Immediately after the reaction, transfer to a cooling chamber, purge with -35℃ dry air at 1 L / min, and cool to below 80℃ within 5 minutes. Finally, vacuum dry the powder at 60℃ for 2 hours and pass through a 200-mesh sieve.

[0032] Test result: D 50 48 nm, D 90 The wavelength was 59 nm, the standard deviation was 6 nm, and the carbon content was 6.13%.

[0033] Example 2

[0034] Same as Example 1, except that the methane volume fraction is increased to 10% during the intermediate carburizing stage (40-80 minutes), and the other conditions are the same.

[0035] Test result: D 50 61 nm, D 90 The wavelength is 78 nm, the standard deviation is 8 nm, and the carbon content is 6.11%.

[0036] Example 3

[0037] The volume fraction of methane is periodically adjusted (10%→5%→15%→5%), switching every 20 minutes. The total carburizing time is 2 hours, and the rest is the same as in Example 1.

[0038] Test result: D 50 41 nm, D 90 The wavelength is 53 nm, the standard deviation is 5 nm, and the carbon content is 6.15%.

[0039] Example 4

[0040] After carburizing, rapid cooling with liquid nitrogen gas was used, and other processes were the same as in Example 1.

[0041] Test result: D 50 39 nm, D 90 The wavelength is 51 nm, the standard deviation is 4 nm, and the carbon content is 6.12%.

[0042] Example 5

[0043] After carbide diffusion, the carbothermic reduction product is rapidly cooled under vacuum (the reaction chamber is cooled to 0.1 atm while cold nitrogen is introduced), and the temperature is reduced to 50°C within 5 minutes. The rest is the same as in Example 1.

[0044] Test result: D 50 44 nm, D 90 The wavelength is 56 nm, the standard deviation is 5 nm, and the carbon content is 6.13%.

[0045] Example 6

[0046] Microwave-assisted heating was used, periodic atmosphere control was performed during the carburizing process, and airflow cooling was performed after carburizing. The rest was the same as in Example 1.

[0047] Detection results: D50 is 36 nm, D 90 The wavelength was 49 nm, the standard deviation was 4 nm, and the carbon content was 6.14%.

[0048] Example 7

[0049] The tungsten source used was blue tungsten oxide (WO2.9), the carbon source was acetylene black, the molar ratio was 1:3.2, the wet ball milling medium was isopropanol, the ball milling was performed for 8 hours, the carbothermic reduction temperature was 1100℃, the carburizing reaction temperature was 900℃, the volume fraction of methane changed periodically (5%→15%→5%), and the rest was the same as in Example 1.

[0050] Test result: D 50 52 nm, D 90 The wavelength is 65 nm, the standard deviation is 7 nm, and the carbon content is 6.10%.

[0051] Example 8

[0052] The tungsten source was tungsten powder, the carbon source was graphite, the molar ratio was 1:3.0, the wet ball milling medium was propanol, the ball milling was for 12 hours, the carbothermic reduction temperature was 1250℃, the carburizing reaction temperature was 1050℃, and the volume fraction of methane changed periodically (7%→20%→7%), the rest was the same as in Example 1.

[0053] Test result: D 50 55 nm, D 90 The wavelength is 68 nm, the standard deviation is 7 nm, and the carbon content is 6.09%.

[0054] Example 9

[0055] The ball-to-material ratio was 8:1, ball milling was performed for 5 hours, the carbothermic reduction temperature was 1000℃, the carburizing reaction temperature was 800℃, and the methane volume fraction changed periodically (3%→10%→3%), with the rest being the same as in Example 1.

[0056] Test result: D 50For 60 nm, D 90 The wavelength is 73 nm, the standard deviation is 8 nm, and the carbon content is 6.08%.

[0057] Example 10

[0058] The sieve used was 300 mesh, the drying temperature was 80℃, and the rest was the same as in Example 1.

[0059] Test result: D 50 47 nm, D 90 The wavelength is 58 nm, the standard deviation is 5 nm, and the carbon content is 6.12%.

[0060] Comparative Example 1

[0061] This comparative example does not include periodic high-methane atmosphere control.

[0062] During the carburizing stage, the volume fraction of methane was kept constant at 5%, and the rest was the same as in Example 1.

[0063] Test result: D 50 132 nm, D 90 The wavelength is 158 nm, the standard deviation is 19 nm, and the carbon content is 6.19%.

[0064] Comparative Example 2

[0065] This comparative example does not include rapid cooling measures.

[0066] After carburizing, the mixture was allowed to cool naturally, and the rest was the same as in Example 1.

[0067] Test result: D 50 91 nm, D 90 The wavelength is 112 nm, the standard deviation is 13 nm, and the carbon content is 6.17%.

[0068] Comparative Example 3

[0069] This comparative example did not use wet ball milling, but only dry mixing for 2 minutes.

[0070] The rest is the same as in Example 1.

[0071] Test result: D 50 156 nm, D 90 The wavelength is 180 nm, the standard deviation is 22 nm, and the carbon content is 6.21%.

[0072] Examples 1-10 all exhibited extremely small median particle size (D). 50The tungsten carbide powder exhibits a narrower particle size distribution (standard deviation 4-8 nm) and precise carbon content control, significantly outperforming the comparative example. The synergistic effect of periodic high-methane atmosphere regulation and rapid cooling effectively promotes the uniformity of the carbonization reaction, inhibits grain growth and agglomeration, and yields high-purity, ultrafine tungsten carbide powder with uniform particle size distribution.

[0073] Comparative Example 1 lacked periodic atmosphere control, resulting in uneven carburization and large, widely distributed particles. Comparative Example 2 lacked rapid cooling, leading to particle migration and agglomeration at high temperatures, significantly deteriorating both particle size and distribution. Comparative Example 3 lacked wet ball milling, resulting in uneven raw material mixing, incomplete carbonization, and the largest and widest particle size distribution.

[0074] In some examples (such as Examples 2 and 9), the particle size increased slightly due to adjustments in the methane volume fraction or ball milling parameters, but it was still significantly better than the comparative example. Examples 4 and 6, which used liquid nitrogen gas flow or microwave-assisted heating, had the smallest particle size, indicating that the cooling rate and energy input method have a positive effect on powder refinement.

[0075] The above embodiments are merely preferred technical solutions of the present invention and should not be regarded as limitations on the present invention. The scope of protection of the present invention should be the technical solution described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A production method of producing tungsten carbide by dynamic reduction, characterized by, Specifically comprising the following steps: mixing tungsten source and carbon source in a molar ratio of 1:2.9-1:3.3, using dry mixing and wet ball milling in combination to obtain mixed uniform raw material powder; carbothermic reduction of the raw material powder at 900-1300℃ under inert atmosphere to obtain carbothermic reduction product; carburizing reaction of the carbothermic reduction product at 800-1100℃ under methane / hydrogen mixed gas atmosphere, with the methane volume fraction periodically changed in the range of 3%-20% during the carburizing process, and the carburizing reaction time being 1-5 hours; immediately after the carburizing reaction, using low-temperature gas flow cooling method to reduce the powder temperature to below 80℃ within 5 minutes; drying and sieving the obtained powder to obtain product tungsten carbide powder.

2. The production method according to claim 1, wherein The temperature of the carbothermic reduction step is 1100-1250℃, and the holding time is 1-3 hours.

3. The production method according to claim 1, wherein The tungsten source is tungsten trioxide, and the carbon source is carbon black, and the wet ball milling medium is an alcohol solvent; further, the medium is ethanol.

4. The production method according to claim 1, wherein During the carburizing reaction, the methane volume fraction is periodically controlled as follows: 3%-7% in the initial stage, increased to 10%-20% in the intermediate stage, and decreased back to 3%-7% in the final stage. Preferably, the methane volume fraction is periodically controlled as follows: 5% in the initial stage, increased to 15% in the intermediate stage, and decreased back to 5% in the final stage.

5. The production method according to claim 4, wherein The wet ball milling time is 5-15 hours, the ball-to-material ratio is 3:1-8:1, and the ball milling rotation speed is 200-400 rpm.

6. The production method according to claim 1, wherein The low-temperature gas flow cooling method is to pass dry air, cold nitrogen gas or liquid nitrogen gas flow at-35℃.

7. The production method according to claim 1, wherein The drying step is carried out at 60℃, and sieving uses a 200-mesh sieve.

8. The production method according to claim 1, wherein The wet ball milling time is 10 hours, the ball-to-material ratio is 5:1, and the ball milling rotation speed is 300 rpm.

9. An ultrafine tungsten carbide powder, characterized by, The ultrafine tungsten carbide powder is prepared by the method of any one of claims 1-8.

10. A cemented carbide, characterized in that, The cemented carbide is prepared by the ultrafine tungsten carbide powder of claim 9.