Ultrafine tungsten carbide powder, its preparation method and use

Abstract

This application belongs to the field of metallurgical technology, specifically relating to an ultrafine tungsten carbide powder, its preparation method, and its application. The preparation method includes the following steps: S1, obtaining carbon slurry, hydrochloric acid, and ammonium tungstate solution; subjecting the carbon slurry and hydrochloric acid to a first ultrasonic stirring to obtain a first mixture; subjecting the ammonium tungstate solution and the first mixture to a second ultrasonic stirring to obtain a second mixture; washing the second mixture with pure water and drying it to obtain a tungsten acid + carbon precursor mixture; S2, calcining the tungsten acid + carbon precursor mixture to obtain a tungsten oxide + carbon mixture; S3, subjecting the tungsten oxide + carbon mixture to a first carbonization, crushing, and sieving to obtain a first tungsten carbide powder; S4, co-firing the first tungsten carbide powder with carbon to obtain a second tungsten carbide powder; subjecting the second tungsten carbide powder to a second carbonization, crushing, and sieving to obtain ultrafine tungsten carbide powder. This application uses carbothermal reduction and stepwise carbonization to prepare tungsten carbide powder with a specific surface area of ​​2.0-3.0 m². 2 / g, tungsten carbide powder with 6.10-6.11wt% combined carbon and 0.03-0.04wt% free carbon.

Description

Technical Field

[0001] This application relates to the field of metallurgical technology, specifically to an ultrafine tungsten carbide powder, its preparation method, and its application. Background Technology

[0002] Ultrafine tungsten carbide, with its high hardness, high strength, excellent wear resistance, and high temperature stability brought about by the Hall-Petch effect, has become a core raw material for high-end cemented carbide and is widely used in high-speed cutting tools, precision components of 3C electronics, key components of aerospace, medical devices, and other fields. Its compatibility with PVD coating processes further improves the processing efficiency and product precision of high-end manufacturing.

[0003] Current research focuses on improving material properties by optimizing preparation and sintering processes. For example, liquid-phase precursor methods are used to reduce the free carbon content in powders, or inhibitors such as tantalum carbide are introduced to suppress grain coarsening during sintering. However, several prominent issues remain: first, precisely controlling the particle size of ultrafine powders, preventing agglomeration, and reducing free carbon content during preparation present technical challenges; second, high temperatures during sintering densification can easily lead to excessive grain growth, thereby compromising the performance advantages of the ultrafine structure. Therefore, effectively reducing free carbon and increasing the combined carbon content in the preparation of ultrafine powders is a key future technological challenge. To address the critical technical problem of high free carbon and generally low combined carbon content in the current preparation of ultrafine tungsten carbide powder, a method for preparing ultrafine tungsten carbide powder and its applications are urgently needed. Summary of the Invention

[0004] To solve the above-mentioned technical problems, this application provides a method for preparing ultrafine tungsten carbide powder, comprising the following steps: S1, obtaining carbon slurry, hydrochloric acid and ammonium tungstate solution, subjecting the carbon slurry and hydrochloric acid to first ultrasonic stirring to obtain a first mixture, subjecting the ammonium tungstate solution and the first mixture to second ultrasonic stirring to obtain a second mixture, washing the second mixture with pure water and drying it to obtain a tungstic acid + carbon precursor mixture, wherein the molar ratio of carbon in the carbon slurry, hydrogen ions in the hydrochloric acid and tungstate ions in the ammonium tungstate solution is (1.5-2.5):(4.9-5.2):1; S2, calcining the tungstic acid + carbon precursor mixture to obtain a tungsten oxide + carbon mixture; S3, subjecting the tungsten oxide + carbon mixture to first carbonization, crushing and sieving to obtain first tungsten carbide powder; S4, carbonizing the first tungsten carbide powder to obtain a second tungsten carbide powder, subjecting the second tungsten carbide powder to second carbonization, crushing and sieving to obtain ultrafine tungsten carbide powder.

[0005] In a preferred embodiment of the method for preparing ultrafine tungsten carbide powder according to this application, in step S1, the carbon content in the carbon slurry is 17-19 wt%, the concentration of hydrochloric acid is 15-20 wt%, and the content of tungstate ions in the ammonium tungstate solution is 220-260 g / L.

[0006] As a preferred embodiment of the method for preparing ultrafine tungsten carbide powder according to this application, in step S1, the frequency of the first ultrasonic stirring is 80-100Hz, the time of the first ultrasonic stirring is 10-20min, the frequency of the second ultrasonic stirring is 10-30Hz, and the time of the second ultrasonic stirring is 40-80min.

[0007] In a preferred embodiment of the method for preparing ultrafine tungsten carbide powder according to this application, in step S2, the calcination is carried out in a nitrogen atmosphere, the calcination temperature is 600-700℃, and the calcination time is 1-2 hours.

[0008] In a preferred embodiment of the method for preparing ultrafine tungsten carbide powder according to this application, in step S3, the first carbonization is carried out in an argon atmosphere with a flow rate of 0.5-2 L / min, the temperature of the first carbonization is 1000-1100℃, and the time of the first carbonization is 0.5-1.5 h.

[0009] As a preferred embodiment of the preparation method of ultrafine tungsten carbide powder described in this application, in step S4, the carbon addition method is specifically as follows: the total carbon content of the first tungsten carbide powder is detected, and carbon is added to the first tungsten carbide powder according to the detection result to obtain the second tungsten carbide powder, wherein the total carbon content of the second tungsten carbide powder is 6.28-6.30 wt%.

[0010] In a preferred embodiment of the method for preparing ultrafine tungsten carbide powder according to this application, in step S4, the second carbonization is carried out in a hydrogen atmosphere with a flow rate of 4-8 L / min, the temperature of the second carbonization is 1100-1200℃, and the time of the second carbonization is 1-2 h.

[0011] This application also provides an ultrafine tungsten carbide powder, which is prepared by the above-described method for preparing ultrafine tungsten carbide powder.

[0012] As a preferred embodiment of the ultrafine tungsten carbide powder described in this application, the specific surface area of ​​the ultrafine tungsten carbide powder is 2.0-3.0 m². 2 / g, the content of compound carbon in the ultrafine tungsten carbide powder is 6.10-6.11wt%, and the content of free carbon in the ultrafine tungsten carbide powder is 0.03-0.04wt%.

[0013] This application also provides an application of the above-mentioned ultrafine tungsten carbide powder in cemented carbide.

[0014] The beneficial effects of this application are as follows:

[0015] This application provides an ultrafine tungsten carbide powder, its preparation method, and its application. The research found that carbon powder, due to its large surface area and high activity, is prone to agglomeration, especially in solution where its dispersibility is poor and it easily agglomerates upon contact with liquid. Therefore, carbon slurry, which has better carbon dispersion uniformity, is used to replace carbon powder, and high-frequency ultrasound is employed for dispersion, further improving the dispersibility of carbon in the carbon slurry in solution. In the preparation of tungstic acid, lowering the ultrasonic frequency can promote uniform mixing of tungstic acid particles and carbon while ensuring carbon dispersibility. Simultaneously, high-frequency dispersion is used when adding carbon slurry to improve dispersion uniformity; too low an ultrasonic frequency results in poor dispersion, while too high an ultrasonic frequency places high demands on equipment and increases costs. Low-frequency ultrasound is used in the preparation of tungstic acid to promote uniform mixing of tungstic acid particles and carbon while ensuring carbon dispersibility; both excessively high and low frequencies reduce the uniformity of mixing between tungstic acid and carbon. Too low an ammonium tungstate concentration affects the efficiency of tungstic acid preparation and results in a lower specific surface area; too high an ammonium tungstate concentration can easily lead to the instantaneous precipitation of paratungstate due to localized over-acidification, affecting the preparation of tungstic acid and the uniformity of mixing.

[0016] This application utilizes carbothermal reduction and stepwise carbonization to prepare ultrafine tungsten carbide powder with high combined carbon and low free carbon. A nitrogen atmosphere is used to calcine the tungstic acid + carbon precursor, ensuring no carbon loss during the calcination of tungstic acid to tungsten oxide. If the carbon content in the tungsten oxide + carbon precursor is too low, there will be more uncarbonized tungsten particles during the first carbonization process. During the second carbonization, the carbonization path increases, leading to secondary sintering and growth between tungsten particles, which easily reduces the degree of carbonization and increases free carbon. If the carbon content is too high, tungsten carbide is easily formed, resulting in severe solid-phase sintering and particle agglomeration during the second carbonization. If the calcination temperature is too low or the time is too short, the tungstic acid will not be completely calcined, resulting in incomplete development of nano-tungsten oxide particles with excessively high activity. This leads to easy solid-phase sintering and growth during subsequent carbonization, which is detrimental to subsequent carbonization. If the calcination temperature is too high or the time is too long, partial carbonization reactions are likely to occur, which is not conducive to subsequent carbon control.

[0017] The first carbonization is carried out in an argon atmosphere to ensure that the particles do not grow due to the volatilization-deposition effect during the reduction process, thus ensuring particle uniformity. If the first carbonization temperature is too low, the carbonization effect will be poor, and tungsten dicarbide will not be fully formed, resulting in a large number of tungsten particles. If the temperature is too high, solid-state sintering will be severe, and particle growth will be excessive, which is not conducive to carbonization. If the argon flow rate is too high, it will easily carry away the carbon atmosphere, which is not conducive to carbon control. If the flow rate is too low, the exhaust will be poor, which is also not conducive to carbon control. If the holding time is too short, the reaction will be incomplete. If the holding time is too long, sintering and growth will be easy, resulting in low efficiency.

[0018] Secondary carbonization in a hydrogen atmosphere promotes complete carbonization and effectively reduces free carbon in the powder. If the secondary carbonization temperature is too low or the holding time is too short, incomplete carbonization and excessive free carbon will result. If the temperature is too high or the holding time is too long, the particles are prone to solid-state sintering and growth, resulting in a low specific surface area. If the hydrogen flow rate is too low, the carbonization-promoting effect is not significant, and the free carbon content is too high; if the hydrogen flow rate is too high, excessive carbon consumption is detrimental to carbon atmosphere control. The specific surface area of ​​the ultrafine tungsten carbide powder prepared in this application is 2.0-3.0 m². 2 / g, with combined carbon of 6.10-6.11wt% and free carbon of 0.03-0.04wt%. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0020] Figure 1 This is an electron microscope image of the ultrafine tungsten carbide powder prepared in Example 4;

[0021] Figure 2 The image shows the metallographic structure of the cemented carbide prepared in Example 4.

[0022] Figure 3 The image shows an electron microscope image of the ultrafine tungsten carbide powder prepared in Comparative Example 1.

[0023] Figure 4 The image shows the metallographic diagram of the cemented carbide prepared in Comparative Example 1.

[0024] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0025] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0026] This application provides a method for preparing ultrafine tungsten carbide powder, comprising the following steps: S1, obtaining carbon slurry, hydrochloric acid and ammonium tungstate solution, subjecting the carbon slurry and hydrochloric acid to first ultrasonic stirring to obtain a first mixture, subjecting the ammonium tungstate solution and the first mixture to second ultrasonic stirring to obtain a second mixture, washing the second mixture with pure water and drying it to obtain a tungstic acid + carbon precursor mixture, wherein the molar ratio of carbon in the carbon slurry, hydrogen ions in the hydrochloric acid and tungstate ions in the ammonium tungstate solution is (1.5-2.5):(4.9-5.2):1;

[0027] The carbon slurry contains 17-19 wt% carbon, the hydrochloric acid contains 15-20 wt% hydrochloric acid, and the ammonium tungstate solution contains 220-260 g / L of tungstate ions. The frequency of the first ultrasonic stirring is 80-100 Hz, the duration of the first ultrasonic stirring is 10-20 min, the frequency of the second ultrasonic stirring is 10-30 Hz, and the duration of the second ultrasonic stirring is 40-80 min.

[0028] S2. The tungstic acid + carbon precursor mixture is calcined to obtain tungsten oxide + carbon mixture;

[0029] The calcination is carried out in a nitrogen atmosphere at a temperature of 600-700℃ for 1-2 hours.

[0030] Specifically, the calcination temperature is any one or any two of 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, 690℃, and 700℃; the calcination time is any one or any two of 1h, 1.5h, and 2h.

[0031] S3. The tungsten oxide + carbon mixture is subjected to first carbonization, crushing and sieving to obtain first tungsten carbide powder;

[0032] The first carbonization is carried out in an argon atmosphere with a flow rate of 0.5-2 L / min, the temperature of the first carbonization is 1000-1100℃, and the time of the first carbonization is 0.5-1.5 h;

[0033] Specifically, the temperature of the first carbonization is within the range of any one or any two of 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, 1050℃, 1060℃, 1070℃, 1080℃, 1090℃, and 1100℃; the time of the first carbonization is within the range of any one or any two of 0.5h, 1h, and 1.5h.

[0034] S4. The first tungsten carbide powder is carbonized to obtain the second tungsten carbide powder, and the second tungsten carbide powder is subjected to a second carbonization, crushing, and sieving to obtain ultrafine tungsten carbide powder.

[0035] The specific carbon addition method is as follows: the total carbon content of the first tungsten carbide powder is detected, and carbon is added to the first tungsten carbide powder according to the detection result to obtain the second tungsten carbide powder, wherein the total carbon content of the second tungsten carbide powder is 6.28-6.30 wt%; the second carbonization is carried out in a hydrogen atmosphere with a flow rate of 4-8 L / min, the temperature of the second carbonization is 1100-1200℃, and the time of the second carbonization is 1-2 h;

[0036] Specifically, the second carbonization temperature is any one or any two of 1100℃, 1110℃, 1120℃, 1130℃, 1140℃, 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, and 1200℃; the second carbonization time is any one or any two of 1h, 1.5h, and 2h.

[0037] This application also provides an ultrafine tungsten carbide powder with a specific surface area of ​​2.0-3.0 m². 2 / g, the content of compound carbon in the ultrafine tungsten carbide powder is 6.10-6.11wt%, and the content of free carbon in the ultrafine tungsten carbide powder is 0.03-0.04wt%.

[0038] This application also provides an application of the above-mentioned ultrafine tungsten carbide powder in cemented carbide.

[0039] The technical solution of this application will be further described below with reference to specific embodiments.

[0040] Example 1

[0041] An ultrafine tungsten carbide powder and its preparation method, comprising:

[0042] S1. Obtain carbon slurry, hydrochloric acid, and ammonium tungstate solution. Perform a first ultrasonic stirring of the carbon slurry and hydrochloric acid to obtain a first mixture. Perform a second ultrasonic stirring of the ammonium tungstate solution and the first mixture to obtain a second mixture. Wash the second mixture with pure water and dry it to obtain a tungstic acid + carbon precursor mixture.

[0043] The molar ratio of carbon in the carbon slurry, hydrogen ions in hydrochloric acid, and tungstate ions in the ammonium tungstate solution is 1.6:5.0:1; the carbon content in the carbon slurry is 17wt%, the hydrochloric acid concentration is 15wt%, and the tungstate ion content in the ammonium tungstate solution is 240g / L; the frequency of the first ultrasonic stirring is 80Hz, the duration of the first ultrasonic stirring is 10min, the frequency of the second ultrasonic stirring is 10Hz, and the duration of the second ultrasonic stirring is 60min.

[0044] S2. Calcining the mixture of tungstic acid and carbon precursor yields a mixture of tungsten oxide and carbon.

[0045] The calcination was carried out in a nitrogen atmosphere at a temperature of 600℃ for 1 hour.

[0046] S3. The tungsten oxide + carbon mixture is subjected to first carbonization, crushing and sieving to obtain first tungsten carbide powder;

[0047] The first carbonization was carried out in an argon atmosphere with a flow rate of 0.5 L / min, at a temperature of 1000 °C, and for a time of 0.5 h.

[0048] S4. The first tungsten carbide powder is carbonized to obtain the second tungsten carbide powder. The second tungsten carbide powder is then subjected to a second carbonization, crushed, and sieved to obtain ultrafine tungsten carbide powder.

[0049] The carbon addition method is as follows: the total carbon content of the first tungsten carbide powder is detected, and carbon is added to the first tungsten carbide powder according to the detection results to obtain the second tungsten carbide powder, wherein the total carbon content of the second tungsten carbide powder is 6.29 wt%; the second carbonization is carried out in a hydrogen atmosphere with a flow rate of 4 L / min, the temperature of the second carbonization is 1100℃, and the time of the second carbonization is 1 h.

[0050] The ultrafine tungsten carbide powder prepared in Example 1 was tested, and the results showed that the specific surface area of ​​the ultrafine tungsten carbide powder was 2.84 m². 2 / g, the content of compound carbon in ultrafine tungsten carbide powder is 6.10wt%, and the content of free carbon in ultrafine tungsten carbide powder is 0.04wt%.

[0051] Example 2

[0052] An ultrafine tungsten carbide powder and its preparation method, comprising:

[0053] S1. Obtain carbon slurry, hydrochloric acid, and ammonium tungstate solution. Perform a first ultrasonic stirring of the carbon slurry and hydrochloric acid to obtain a first mixture. Perform a second ultrasonic stirring of the ammonium tungstate solution and the first mixture to obtain a second mixture. Wash the second mixture with pure water and dry it to obtain a tungstic acid + carbon precursor mixture.

[0054] The molar ratio of carbon in the carbon slurry, hydrogen ions in hydrochloric acid, and tungstate ions in the ammonium tungstate solution is 1.6:4.9:1; the carbon content in the carbon slurry is 18wt%, the hydrochloric acid concentration is 20wt%, and the tungstate ion content in the ammonium tungstate solution is 250g / L; the frequency of the first ultrasonic stirring is 100Hz, the duration of the first ultrasonic stirring is 15min, the frequency of the second ultrasonic stirring is 30Hz, and the duration of the second ultrasonic stirring is 40min.

[0055] S2. Calcining the mixture of tungstic acid and carbon precursor yields a mixture of tungsten oxide and carbon.

[0056] The calcination was carried out in a nitrogen atmosphere at a temperature of 700℃ for 2 hours.

[0057] S3. The tungsten oxide + carbon mixture is subjected to first carbonization, crushing and sieving to obtain first tungsten carbide powder;

[0058] The first carbonization was carried out in an argon atmosphere with a flow rate of 2 L / min, at a temperature of 1100℃, and for a time of 1.5 h.

[0059] S4. The first tungsten carbide powder is carbonized to obtain the second tungsten carbide powder. The second tungsten carbide powder is then subjected to a second carbonization, crushed, and sieved to obtain ultrafine tungsten carbide powder.

[0060] The carbon addition method is as follows: the total carbon content of the first tungsten carbide powder is detected, and carbon is added to the first tungsten carbide powder according to the detection results to obtain the second tungsten carbide powder, wherein the total carbon content of the second tungsten carbide powder is 6.30 wt%; the second carbonization is carried out in a hydrogen atmosphere with a flow rate of 8 L / min, the temperature of the second carbonization is 1200℃, and the time of the second carbonization is 2 h.

[0061] The ultrafine tungsten carbide powder prepared in Example 2 was tested, and the results showed that the specific surface area of ​​the ultrafine tungsten carbide powder was 2.0 m². 2 / g, the content of compound carbon in ultrafine tungsten carbide powder is 6.10wt%, and the content of free carbon in ultrafine tungsten carbide powder is 0.04wt%.

[0062] Example 3

[0063] An ultrafine tungsten carbide powder and its preparation method, comprising:

[0064] S1. Obtain carbon slurry, hydrochloric acid, and ammonium tungstate solution. Perform a first ultrasonic stirring of the carbon slurry and hydrochloric acid to obtain a first mixture. Perform a second ultrasonic stirring of the ammonium tungstate solution and the first mixture to obtain a second mixture. Wash the second mixture with pure water and dry it to obtain a tungstic acid + carbon precursor mixture.

[0065] The molar ratio of carbon in the carbon slurry, hydrogen ions in hydrochloric acid, and tungstate ions in the ammonium tungstate solution is 2.3:5.2:1; the carbon content in the carbon slurry is 18wt%, the concentration of hydrochloric acid is 18wt%, and the tungstate ion content in the ammonium tungstate solution is 260g / L; the frequency of the first ultrasonic stirring is 90Hz, the duration of the first ultrasonic stirring is 20min, the frequency of the second ultrasonic stirring is 20Hz, and the duration of the second ultrasonic stirring is 70min.

[0066] S2. Calcining the mixture of tungstic acid and carbon precursor yields a mixture of tungsten oxide and carbon.

[0067] The calcination was carried out in a nitrogen atmosphere at a temperature of 650℃ for 1.5 hours.

[0068] S3. The tungsten oxide + carbon mixture is subjected to first carbonization, crushing and sieving to obtain first tungsten carbide powder;

[0069] The first carbonization was carried out in an argon atmosphere with a flow rate of 1 L / min, at a temperature of 1050 °C, and for a time of 1 h.

[0070] S4. The first tungsten carbide powder is carbonized to obtain the second tungsten carbide powder. The second tungsten carbide powder is then subjected to a second carbonization, crushed, and sieved to obtain ultrafine tungsten carbide powder.

[0071] The carbon preparation method is as follows: the total carbon content of the first tungsten carbide powder is detected, and carbon is added to the first tungsten carbide powder according to the detection results to obtain the second tungsten carbide powder, wherein the total carbon content of the second tungsten carbide powder is 6.28 wt%; the second carbonization is carried out in a hydrogen atmosphere with a flow rate of 6 L / min, the temperature of the second carbonization is 1150℃, and the time of the second carbonization is 1.5 h.

[0072] The ultrafine tungsten carbide powder prepared in Example 3 was tested, and the results showed that the specific surface area of ​​the ultrafine tungsten carbide powder was 2.46 m². 2 / g, the content of compound carbon in ultrafine tungsten carbide powder is 6.10wt%, and the content of free carbon in ultrafine tungsten carbide powder is 0.04wt%.

[0073] Example 4

[0074] An ultrafine tungsten carbide powder, its preparation method, and its applications include:

[0075] S1. Obtain carbon slurry, hydrochloric acid, and ammonium tungstate solution. Perform a first ultrasonic stirring of the carbon slurry and hydrochloric acid to obtain a first mixture. Perform a second ultrasonic stirring of the ammonium tungstate solution and the first mixture to obtain a second mixture. Wash the second mixture with pure water and dry it to obtain a tungstic acid + carbon precursor mixture.

[0076] The molar ratio of carbon in the carbon slurry, hydrogen ions in hydrochloric acid, and tungstate ions in the ammonium tungstate solution is 1.9:5.1:1; the carbon content in the carbon slurry is 19wt%, the hydrochloric acid concentration is 20wt%, and the tungstate ion content in the ammonium tungstate solution is 230g / L; the frequency of the first ultrasonic stirring is 80Hz, the duration of the first ultrasonic stirring is 20min, the frequency of the second ultrasonic stirring is 10Hz, and the duration of the second ultrasonic stirring is 60min.

[0077] S2. Calcining the mixture of tungstic acid and carbon precursor yields a mixture of tungsten oxide and carbon.

[0078] The calcination was carried out in a nitrogen atmosphere at a temperature of 600℃ for 1 hour.

[0079] S3. The tungsten oxide + carbon mixture is subjected to first carbonization, crushing and sieving to obtain first tungsten carbide powder;

[0080] The first carbonization was carried out in an argon atmosphere with a flow rate of 0.5 L / min, at a temperature of 1000℃, and for a time of 1 hour.

[0081] S4. The first tungsten carbide powder is carbonized to obtain the second tungsten carbide powder. The second tungsten carbide powder is then subjected to a second carbonization, crushed, and sieved to obtain ultrafine tungsten carbide powder.

[0082] The carbon preparation method is as follows: the total carbon content of the first tungsten carbide powder is detected, and carbon is added to the first tungsten carbide powder according to the detection results to obtain the second tungsten carbide powder, wherein the total carbon content of the second tungsten carbide powder is 6.30 wt%; the second carbonization is carried out in a hydrogen atmosphere with a flow rate of 6 L / min, the temperature of the second carbonization is 1150℃, and the time of the second carbonization is 1.5 h.

[0083] For the testing of the ultrafine tungsten carbide powder prepared in Example 4, please refer to [link / reference needed]. Figure 1 , Figure 1 The image shows an electron microscope (EM) image of the ultrafine tungsten carbide powder prepared in Example 4; the results indicate that the specific surface area of ​​the ultrafine tungsten carbide powder is 3.0 m². 2 / g, the content of compounded carbon in ultrafine tungsten carbide powder is 6.11wt%, and the content of free carbon in ultrafine tungsten carbide powder is 0.03wt%;

[0084] Using the ultrafine tungsten carbide powder prepared in Example 4 as raw material, cobalt powder, paraffin wax, alcohol, etc. were added in proportion, wet-milled, spray-dried, pressed into shape, and sintered at 1420℃ for 1 hour to obtain cemented carbide. Please refer to Figure 2 , Figure 2The image shows the metallographic structure of the cemented carbide prepared in Example 4. The cemented carbide has a uniform metallographic structure, a hardness of HRA92.5, and a bending strength of 4350 MPa.

[0085] Comparative Example 1

[0086] The difference between this comparative example and Example 4 is that toner is used instead of carbon paste in step S1, while the other steps are the same as in Example 4.

[0087] For the analysis of the ultrafine tungsten carbide powder prepared in Comparative Example 1, please refer to [link / reference needed]. Figure 3 , Figure 3 The image shows an electron microscope (EM) image of the ultrafine tungsten carbide powder prepared in Comparative Example 1. The results indicate that the ultrafine tungsten carbide powder has poor particle uniformity and exhibits carbon aggregation, leading to high local carbon content. The specific surface area of ​​the ultrafine tungsten carbide powder is 2.73 m². 2 / g, the content of compound carbon in ultrafine tungsten carbide powder is 6.05wt%, and the content of free carbon in ultrafine tungsten carbide powder is 0.08wt%.

[0088] Please see Figure 4 , Figure 4 The image shows the metallographic diagram of the cemented carbide prepared in Comparative Example 1. The cemented carbide contains abnormally large particles. The hardness of the cemented carbide is HRA92.1 and the bending strength is 3340 MPa.

[0089] Comparative Example 2

[0090] The difference between this comparative example and Example 4 is that stirring is used instead of ultrasonic stirring in step S1, while the other steps are the same as in Example 4.

[0091] The ultrafine tungsten carbide powder prepared in Comparative Example 2 was tested, and the results showed that the specific surface area of ​​the ultrafine tungsten carbide powder was 2.80 m². 2 / g, the content of compound carbon in ultrafine tungsten carbide powder is 6.06wt%, and the content of free carbon in ultrafine tungsten carbide powder is 0.06wt%.

[0092] Comparative Example 3

[0093] The difference between this comparative example and Example 4 is that the carbonization step is carried out under a hydrogen atmosphere at a temperature of 1150°C for 2 hours and a flow rate of 6 L / min, instead of steps S3 and S4. All other steps are the same as in Example 4.

[0094] The ultrafine tungsten carbide powder prepared in Comparative Example 3 was tested, and the results showed that the specific surface area of ​​the ultrafine tungsten carbide powder was 1.80 m². 2 / g, the content of compound carbon in ultrafine tungsten carbide powder is 5.96wt%, and the content of free carbon in ultrafine tungsten carbide powder is 0.03wt%.

[0095] Comparative Example 4

[0096] The difference between this comparative example and Example 4 is that an argon atmosphere is used instead of a hydrogen atmosphere in step S4, while the other steps are the same as in Example 4.

[0097] The ultrafine tungsten carbide powder prepared in Comparative Example 4 was tested, and the results showed that the specific surface area of ​​the ultrafine tungsten carbide powder was 2.85 m². 2 / g, the content of compound carbon in ultrafine tungsten carbide powder is 6.05wt%, and the content of free carbon in ultrafine tungsten carbide powder is 0.07wt%.

[0098] Comparative Example 5

[0099] The difference between this comparative example and Example 4 is that the frequency of the first ultrasound in step S1 is 10Hz, while the other steps are the same as in Example 4.

[0100] The ultrafine tungsten carbide powder prepared in Comparative Example 5 was tested, and the results showed that the specific surface area of ​​the ultrafine tungsten carbide powder was 1.47 m². 2 / g, the content of compound carbon in ultrafine tungsten carbide powder is 6.08wt%, and the content of free carbon in ultrafine tungsten carbide powder is 0.06wt%.

[0101] Comparative Example 6

[0102] The difference between this comparative example and Example 4 is that the frequency of the second ultrasound in step S1 is 80Hz, while the other steps are the same as in Example 4.

[0103] The ultrafine tungsten carbide powder prepared in Comparative Example 6 was tested, and the results showed that the specific surface area of ​​the ultrafine tungsten carbide powder was 1.82 m². 2 / g, the content of compound carbon in ultrafine tungsten carbide powder is 6.09wt%, and the content of free carbon in ultrafine tungsten carbide powder is 0.05wt%.

[0104] Comparative Example 7

[0105] The difference between this comparative example and Example 4 is that the molar ratio of carbon in the carbon slurry, hydrogen ions in hydrochloric acid, and tungstate ions in the ammonium tungstate solution in step S1 is 3.0:4.5:1. All other steps are the same as in Example 4.

[0106] The ultrafine tungsten carbide powder prepared in Comparative Example 7 was tested, and the results showed that the specific surface area of ​​the ultrafine tungsten carbide powder was 3.51 m². 2 / g, the content of compound carbon in ultrafine tungsten carbide powder is 5.97wt%, and the content of free carbon in ultrafine tungsten carbide powder is 0.27wt%.

[0107] Comparative Example 8

[0108] The difference between this comparative example and Example 4 is that the molar ratio of carbon in the carbon slurry, hydrogen ions in hydrochloric acid, and tungstate ions in the ammonium tungstate solution in step S1 is 1.0:5.5:1. All other steps are the same as in Example 4.

[0109] The ultrafine tungsten carbide powder prepared in Comparative Example 8 was tested, and the results showed that the specific surface area of ​​the ultrafine tungsten carbide powder was 1.51 m². 2 / g, the content of compound carbon in ultrafine tungsten carbide powder is 6.04wt%, and the content of free carbon in ultrafine tungsten carbide powder is 0.08wt%.

[0110] As can be seen from the above examples and comparative examples: Example 4, combined with Comparative Example 1, shows that untreated carbon powder is prone to agglomeration in aqueous solution and is difficult to disperse evenly. Therefore, incomplete carbonization is likely to occur during the carbonization process, resulting in high free carbon and low combined carbon in the produced tungsten carbide. The cemented carbide prepared from it has high local carbon content due to high free carbon, obvious dissolution and exudation mechanism, producing abnormally large particles, and reducing alloy performance. However, using carbon slurry with good dispersibility can effectively avoid the above problems. Example 4, combined with Comparative Example 2, shows that simple stirring is difficult to achieve uniform dispersion of carbon slurry in aqueous solution, resulting in uneven dispersion and agglomeration of carbon in the carbon slurry. This leads to high free carbon and low combined carbon in the produced tungsten carbide. However, the addition of ultrasound can make the carbon slurry and solution uniformly mixed and further disperse the agglomerated carbon in the carbon slurry, improve its dispersibility, and promote the uniform distribution of carbon in the carbon slurry in tungstic acid, increase its effective contact area, thereby increasing the combined carbon and reducing the free carbon in the produced tungsten carbide. Example 4, in conjunction with Comparative Example 3, shows that because the tungstic acid prepared in this application is nanoscale with high surface activity, it remains nanoscale even after calcination to tungsten oxide. Its high activity greatly promotes solid-state sintering during the high-temperature one-step carbonization process, resulting in significant solid-state diffusion of the particles. This leads to particle growth and incomplete carbonization, resulting in a decrease in the specific surface area, combined carbon, and increased free carbon of the prepared tungsten carbide. The two-step carbonization process of this application effectively solves these problems. The first carbonization effectively reduces incomplete carbonization caused by particle growth due to intense solid-state sintering at high temperatures. The second carbonization further precisely controls the carbon content of the tungsten carbide and promotes complete carbonization, thereby increasing the combined carbon and reducing free carbon in the product, resulting in fine tungsten carbide with a high degree of carbonization. Example 4, in conjunction with Comparative Example 4, shows that hydrogen can react with carbon to produce methane, which is then cracked into more reactive carbon, further promoting the carbonization reaction, increasing the combined carbon and reducing free carbon in the tungsten carbide. Argon gas does not participate in the actual reaction; it only serves as a protective atmosphere. Under the temperature conditions of this application, it cannot allow the carbon in the second carbonization process to react completely with the incompletely carbonized products in the first carbonization process, resulting in a decrease in combined carbon and an increase in free carbon. Example 4, combined with Comparative Example 5, shows that the ultrasonic frequency needs to reach a certain level to effectively disperse the carbon in the carbon slurry. A low ultrasonic frequency will not completely disperse the carbon in the slurry and will result in poor mixing uniformity with tungstic acid, leading to high local carbon content. Therefore, incomplete carbonization and severe solid-state sintering are likely to occur during the carbonization process, resulting in tungsten carbide with low specific surface area, high free carbon, and reduced combined carbon. Example 4, combined with Comparative Example 6, shows that the long ultrasonic time in step S2, with its high-frequency ultrasonic vibration, rapidly heats the water and materials, leading to increased activity of tungstic acid micelles and carbon surfaces, and more severe agglomeration. Therefore, incomplete carbonization and severe solid-state sintering are likely to occur during the carbonization process, resulting in tungsten carbide with low specific surface area, high free carbon, and reduced combined carbon.Example 4, in conjunction with Comparative Example 7, shows that excessive carbon and low tungstic acid concentration mean that the carbon powder is difficult to be effectively physically isolated by tungstic acid micelles. This causes the carbon to gradually agglomerate during the dehydration process, making it impossible to disperse and mix evenly with tungstic acid. Furthermore, carbonization cannot be completely effective during the carbonization process, resulting in high free carbon and low combined carbon. Example 4, in conjunction with Comparative Example 8, shows that low carbon content and high ammonium tungstic acid concentration, besides preventing effective physical isolation and causing adhesion between tungstic acid micelles, also leads to larger tungstic acid micelles, preventing the carbon in the carbon slurry from being evenly dispersed and mixed with tungstic acid. Solid-state sintering is significant during carbonization, resulting in incomplete carbonization, high free carbon, low combined carbon, and a reduced specific surface area. Examples 1-4, in conjunction with Comparative Examples 1-8, show that the preparation of ultrafine tungsten carbide particles using this method requires control of multiple influencing factors. Among these, the carbon source, dispersion method, ultrasonic frequency, ultrasonic time, carbonization temperature, carbonization duration, and atmosphere all affect key indicators such as the specific surface area, combined carbon, and free carbon of the final tungsten carbide.

[0111] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A method for preparing ultrafine tungsten carbide powder, characterized in that, Includes the following steps: S1. Obtain carbon slurry, hydrochloric acid, and ammonium tungstate solution. Perform a first ultrasonic stirring on the carbon slurry and hydrochloric acid to obtain a first mixture. Perform a second ultrasonic stirring on the ammonium tungstate solution and the first mixture to obtain a second mixture. Wash the second mixture with pure water and dry it to obtain a tungstic acid + carbon precursor mixture. The molar ratio of carbon in the carbon slurry, hydrogen ions in the hydrochloric acid, and tungstate ions in the ammonium tungstate solution is (1.5-2.5):(4.9-5.2):

1. S2. The tungstic acid + carbon precursor mixture is calcined to obtain tungsten oxide + carbon mixture; S3. The tungsten oxide + carbon mixture is subjected to first carbonization, crushing and sieving to obtain first tungsten carbide powder; S4. The first tungsten carbide powder is carbonized to obtain the second tungsten carbide powder, and the second tungsten carbide powder is subjected to a second carbonization, crushing, and sieving to obtain ultrafine tungsten carbide powder. In step S1, the frequency of the first ultrasonic stirring is 80-100Hz, the time of the first ultrasonic stirring is 10-20min, the frequency of the second ultrasonic stirring is 10-30Hz, and the time of the second ultrasonic stirring is 40-80min. In step S3, the first carbonization is carried out in an argon atmosphere with a flow rate of 0.5-2 L / min, the temperature of the first carbonization is 1000-1100℃, and the time of the first carbonization is 0.5-1.5 h. In step S4, the second carbonization is carried out in a hydrogen atmosphere with a flow rate of 4-8 L / min, the temperature of the second carbonization is 1100-1200℃, and the time of the second carbonization is 1-2 h. The specific surface area of ​​the ultrafine tungsten carbide powder is 2.0-3.0 m². 2 / g, the content of compound carbon in the ultrafine tungsten carbide powder is 6.10-6.11wt%, and the content of free carbon in the ultrafine tungsten carbide powder is 0.03-0.04wt%.

2. The method for preparing ultrafine tungsten carbide powder according to claim 1, characterized in that, In step S1, the carbon content in the carbon slurry is 17-19 wt%, the concentration of the hydrochloric acid is 15-20 wt%, and the content of tungstate ions in the ammonium tungstate solution is 220-260 g / L.

3. The method for preparing ultrafine tungsten carbide powder according to claim 1, characterized in that, In step S2, the calcination is carried out in a nitrogen atmosphere, the calcination temperature is 600-700℃, and the calcination time is 1-2 hours.

4. The method for preparing ultrafine tungsten carbide powder according to claim 1, characterized in that, In step S4, the carbon addition method specifically involves: detecting the total carbon content of the first tungsten carbide powder, and adding carbon to the first tungsten carbide powder according to the detection result to obtain the second tungsten carbide powder, wherein the total carbon content of the second tungsten carbide powder is 6.28-6.30 wt%.

5. A type of ultrafine tungsten carbide powder, characterized in that, It is prepared by the method for preparing ultrafine tungsten carbide powder according to any one of claims 1-4.

6. The application of the ultrafine tungsten carbide powder of claim 5 in cemented carbide.

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