A method for low temperature preparation of coarse-grained tungsten carbide powder

Abstract

The application relates to the field of powder metallurgy tungsten carbide production, and discloses a method for preparing coarse-grained tungsten carbide powder at low temperature, which comprises the following steps: S1, providing a mixture, wherein the mixture comprises fine-grained tungsten powder and fine-grained carbon black, the average particle size of the fine-grained tungsten powder is 0.2-8 mu m, the average particle size of the fine-grained carbon black is 0.5-5 mu m, and the fine-grained tungsten powder and the fine-grained carbon black are mixed at a mass ratio of 10:1; and S2, adding an activator to the mixture, wherein the activator is composed of cobalt powder and zinc powder, the average particle size of the cobalt powder and the zinc powder is 1-5 mu m, the total adding amount of the activator is 1%-10% of the mass of the tungsten powder, and the adding ratio of the cobalt powder to the zinc powder is 1:1 to 1:3. In a traditional high-temperature solid-phase growth method, the production of coarse-grained tungsten carbide usually needs to be carried out at a high temperature of 1500 DEG C or above, which not only puts forward higher requirements on the heat resistance of production equipment, but also leads to high production cost due to large energy consumption; the low-temperature growth method is adopted in the application, energy consumption is greatly reduced, and production cost is directly reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of powder metallurgy tungsten carbide production, in particular to a method for preparing coarse-grained tungsten carbide powder at low temperature. BACKGROUND

[0002] In modern industrial production, cemented carbide is highly valued for its excellent wear resistance, toughness, and resistance to thermal shock and thermal fatigue. Coarse-grained tungsten carbide is one of the key raw materials for preparing coarse-grained cemented carbide, which is widely used in various high-strength and high-wear-resistant mining tools, such as oil drilling, rock drilling tools, coal cutting machine teeth, road cold milling machine teeth, and shield cutter. These application fields have very high requirements for the performance of the material, so the quality of coarse-grained tungsten carbide is directly related to the service life and mining efficiency of the mining tools.

[0003] Traditional methods for producing coarse-grained tungsten carbide powder mainly include the following: high-temperature hydrogen reduction to prepare coarse-grained tungsten powder, followed by high-temperature carbonization to obtain coarse-grained tungsten carbide powder; adding various additives to promote the growth of tungsten powder particles to obtain coarse-grained tungsten powder, and then performing carbonization treatment to prepare tungsten carbide powder; or increasing the water pressure during the hydrogen reduction process to promote the growth of tungsten powder particles, and then producing tungsten carbide powder through carbonization reaction. However, these methods have a series of problems. First of all, they all rely on high-temperature conditions, resulting in a significant increase in production cost and a negative impact on economic benefits. Secondly, the obtained coarse-grained tungsten carbide is not a single grain growth, but a group of tungsten carbide particles agglomerated to form pseudo-particles, which is not conducive to the production of cemented carbide. The tungsten carbide powder with such pseudo-particle structure will affect the performance of the final cemented carbide product, especially in terms of wear resistance and toughness.

[0004] Therefore, the present application proposes a method for preparing coarse-grained tungsten carbide powder at low temperature to solve the problems of the prior art. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a method for preparing coarse-grained tungsten carbide powder at low temperature, which can effectively produce single-grain coarse-grained tungsten carbide powder at a lower temperature. Compared with the prior art, the method of the present application can significantly reduce production cost and significantly improve the performance of cemented carbide, especially in terms of wear resistance, toughness, and resistance to thermal shock and thermal fatigue. This breakthrough will bring major progress to the cemented carbide industry and is expected to lead the field to higher efficiency and better performance.

[0006] To achieve the above-mentioned purposes, the present application is implemented by the following technical solution: a method for preparing coarse-grained tungsten carbide powder at low temperature, comprising the following steps:

[0007] S1, providing a mixture including fine tungsten powder and fine carbon black, wherein the average particle size of the fine tungsten powder is 0.2-8 μm, the average particle size of the fine carbon black is 0.5-5 μm, and the fine tungsten powder and the fine carbon black are mixed at a mass ratio of 10:1;

[0008] S2, adding an activator to the mixture, the activator being composed of cobalt powder and zinc powder, the average particle size of the cobalt powder and the zinc powder being 1-5 μm, the total amount of the activator being 1%-10% of the mass of the tungsten powder, and the addition ratio of the cobalt powder to the zinc powder being 1:1 to 1:3;

[0009] S3, mixing the tungsten powder, the carbon black, the cobalt powder and the zinc powder at a ratio of the total weight to ensure uniformity and completeness of the carbonization reaction;

[0010] S4, placing the mixture in a ball mill for ball milling treatment, alloy steel balls being used in the ball milling, the volume ratio of the balls to the material being 1:1 to 6:1, and the ball milling time being set to 5-60 hours to ensure that the mixture is fully mixed and homogenized;

[0011] S5, carbonizing the mixture after the ball milling in a carbonization furnace at 1200-1450°C, the carbonization time being set to 20-200 minutes, and the hydrogen flow rate being controlled at 100-500 ml / min as a protective gas, the control of the flow rate of the protective gas being helpful to the carbonization reaction and the property control of the coarse-grained tungsten carbide powder;

[0012] S6, after the coarse-grained tungsten carbide powder after carbonization is cooled to room temperature, wet grinding and sieving treatment are performed, deionized water or ethanol being used as the medium for the wet grinding, and a screen with a pore size of 50-500 μm being used for the sieving treatment to remove unreacted tungsten powder and carbon black, thereby obtaining coarse-grained tungsten carbide powder with uniform particle size;

[0013] S7, using a 3%-37% concentration of hydrochloric acid solution to treat the coarse-grained tungsten carbide powder after carbonization to remove cobalt powder and zinc powder and other possible metal impurities therein;

[0014] S8, drying the treated tungsten carbide powder in a hot air circulating oven at 100-150°C for 1-4 hours to ensure that the moisture in the powder is completely removed, thereby obtaining dry coarse-grained tungsten carbide powder.

[0015] Preferably, the fine tungsten powder has high purity, the purity being ≥99.9%, and the impurity content in the tungsten powder being controlled to be below 0.1%, the impurities including but not limited to iron, nickel, and aluminum metal elements.

[0016] Preferably, the addition amount of the activator cobalt powder and zinc powder is adjusted according to the particle size of the coarse-grained tungsten carbide powder required to achieve the directional preparation of tungsten carbide powder with different particle sizes, and the addition amount of the activator is increased to promote particle growth when preparing tungsten carbide powder with larger particle sizes.

[0017] Preferably, in the S4 step, the ball milling process adopts dry ball milling technology, and the temperature inside the ball mill is controlled at 50-80℃ to prevent overheating of the material and maintain the stability of the chemical composition.

[0018] Preferably, in the S5 step, the carbonization process is carried out in a graphite boat, and the graphite boat cover is provided with adjustable gas discharge holes to control the gas pressure in the boat and promote the growth of tungsten carbide particles, while allowing the escape of tungsten carbide gas and other byproduct gases to avoid excessive pressure in the reaction chamber.

[0019] Preferably, the carbonized tungsten carbide powder is subjected to wet grinding treatment in the S6 step for 1-5 hours, and the grinding medium used is anisotropic abrasive with a particle size of 1-3mm to improve the purity and uniformity of the powder.

[0020] Preferably, at least two sieves with different pore sizes are used in series in the S6 step, the first sieve has a larger pore size to remove larger unreacted particles, and the second sieve has a smaller pore size to ensure the consistency of the product particle size.

[0021] Preferably, in the S7 step, the hydrochloric acid treatment time is 1-3 hours, and the treatment process is continuously stirred to ensure the complete dissolution and removal of metal impurities, and the treated waste liquid is treated and neutralized.

[0022] Preferably, the S8 step adopts vacuum drying technology, and the vacuum degree is maintained at -0.08 to -0.095MPa during the drying process to accelerate the evaporation of water and prevent the oxidation of the powder.

[0023] Preferably, the average particle size of the coarse-grained tungsten carbide powder is 10-50μm, and the particles have a highly spherical morphology, the particle surface is smooth, and the particle size distribution consistency between particles is higher than 90%, the coarse-grained tungsten carbide powder is suitable for the production of hard alloys, wear-resistant materials and high-density alloys.

[0024] The present application provides a low-temperature preparation method of coarse-grained tungsten carbide powder.

[0025] 1. In traditional high-temperature solid-state growth methods, the production of coarse-grained tungsten carbide typically requires temperatures above 1500°C. This not only places higher demands on the heat resistance of the production equipment but also results in high production costs due to significant energy consumption. In contrast, this invention employs a low-temperature growth method, which greatly reduces energy consumption and directly lowers production costs. Furthermore, the requirements for equipment are relatively lower under low-temperature conditions, thereby reducing equipment investment and maintenance costs.

[0026] 2. In this invention, the selected activator effectively reduces the activation energy of the reaction, allowing fine tungsten carbide particles to dissolve rapidly in the activator melt and precipitate quickly on the surface of coarse tungsten carbide particles. This dissolution-precipitation mechanism greatly accelerates the growth rate of coarse particles, thereby improving production efficiency.

[0027] 3. The operation process of this invention is very simple. First, fine tungsten powder and carbon black are mixed in a certain proportion, and then an appropriate amount of activator is added. Under low temperature conditions, the mixture is heated until the activator melts, and then maintained for a certain period of time to promote the growth of tungsten carbide. Throughout the process, only the type and content of the activator and the reaction temperature and time need to be controlled to precisely control the particle size and morphology of the final product. This easy-to-control feature makes scale-up from laboratory to industrial production possible.

[0028] 4. The growth process of tungsten carbide particles under the method of the present invention is uniform and controllable. Therefore, the coarse tungsten carbide particles prepared have better particle size uniformity and morphological regularity. These particles can provide better performance in applications such as cemented carbide, such as higher hardness, better toughness and stronger wear resistance, which is crucial for improving the market competitiveness of the final product.

[0029] 5. The method of the present invention is simple, easy to implement and control. It can seamlessly transition from small-scale laboratory operation to large-scale industrial production. In the industrial production process, a high-efficiency production process can be achieved through continuous or batch production, which is of great significance for meeting the market demand for tungsten carbide quickly. Attached Figure Description

[0030] Figure 1 The morphology image obtained by scanning electron microscopy in Embodiment 1 of the present invention shows the regular polyhedral shape of the particles;

[0031] Figure 2 The morphology image obtained by scanning electron microscopy in Embodiment 2 of the present invention shows the regular polyhedral shape of the particles;

[0032] Figure 3 The morphology image obtained by scanning electron microscopy in Embodiment 3 of the present invention shows the regular polyhedral shape of the particles;

[0033] Figure 4 The SEM image of the embodiment four of the present application shows that the particles have regular polyhedral shape. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the specification of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0035] Please refer to the drawings in the specification of the present application Figure 1 - the drawings Figure 4 :

[0036] Embodiment:

[0037] Embodiment one:

[0038] Preparation of raw materials for experiment:

[0039] Tungsten powder with Fisher particle size of 0.8 μm

[0040] Cobalt powder with Fisher particle size of 1.2 μm

[0041] Zinc powder with Fisher particle size of 1.8 μm

[0042] Carbon black with Fisher particle size of 1.2 μm

[0043] Concentrated hydrochloric acid with mass fraction of 36%

[0044] Experimental steps:

[0045] Batching: first, prepare 1 kg of mixed raw materials according to the proportions of total carbon content of 6.14%, cobalt powder content of 1% and zinc powder content of 1%, i.e. 10 g of cobalt powder, 10 g of zinc powder, 61.4 g of carbon black and 918.6 g of tungsten powder.

[0046] Ball-milling mixing: after the prepared raw materials are mixed uniformly, put them into a 1-liter ball-milling cylinder, add 5 kg of milling rods, and set the rolling-milling time to 30 hours to ensure sufficient mixing.

[0047] Discharge treatment: after the rolling-milling is completed, take out the mixed materials from the ball-milling cylinder.

[0048] Carbonization process: The milled mixture was transferred to a graphite boat with a lid and placed in a molybdenum wire furnace. Under the protection of hydrogen gas, the hydrogen flow was set to 8 liters per minute, and then carbonization was carried out according to the following temperature program: first at 900°C for 50 minutes, then at 1100°C for 50 minutes, and finally at 1400°C for 60 minutes.

[0049] Post-processing: After carbonization, the mixture was allowed to cool naturally to room temperature, and then crushing and sieving were carried out to remove unreacted raw materials and large pieces formed during carbonization.

[0050] Acid washing and filtration: The carbonized material was immersed in 36% concentrated hydrochloric acid for 4 hours to remove excess cobalt, zinc and other impurities.

[0051] Cleaning and drying: The filtered tungsten carbide was thoroughly washed with deionized water to remove residual hydrochloric acid and soluble impurities, and then dried in an oven at 105°C to constant weight.

[0052] Particle size and morphology analysis: The particle size and morphology of tungsten carbide were examined by Fisher particle size analysis and scanning electron microscopy. The average particle size obtained by Fisher particle size analysis was 10.5 μm, and the morphology observed by scanning electron microscopy showed that the particles were regular polyhedral shapes, as shown in Figure 1 .

[0053] The product detection indicators are as follows:

[0054]

[0055] Example Two (comparative experiment, increased content of activator):

[0056] The experimental raw materials were the same as in Example One.

[0057] The experimental steps were the same as in Example One, but the content of cobalt powder and zinc powder was increased to 10% each, and the batching was adjusted to cobalt powder 100g, zinc powder 100g, carbon black 61.4g, tungsten powder 738.6g.

[0058] The experimental results showed that the Fisher particle size of tungsten carbide was 18 μm, and scanning electron microscopy showed that the particle shape remained roughly polyhedral, but the particle size increased significantly, as shown in Figure 2 .

[0059] The product detection indicators are as follows:

[0060]

[0061] Example Three (comparative experiment, increased content of activator, extended holding time):

[0062] The experimental raw materials were the same as in Example One.

[0063] The experimental procedure was the same as in Example 1, but the content of cobalt powder and zinc powder was each 10%, and the cobalt powder was 50 g, the zinc powder was 50 g, the carbon black was 61.4 g, and the tungsten powder was 738.6 g in the ingredients. The holding time at each temperature stage during carbonization was extended to 100 minutes and 120 minutes, respectively.

[0064] The experimental results showed that the Fisher particle size of the tungsten carbide was 32 μm, and the scanning electron microscope observation showed that the particles were more coarse and irregular in shape, as shown in Figure 3. Figure 3 .

[0065] The product detection indexes were as follows:

[0066]

[0067] Example Four (comparative experiment, without adding activator, conventional method):

[0068] The experimental raw materials were tungsten powder with a Fisher particle size of 0.8 μm, and carbon black with a Fisher particle size of 1.2 μm.

[0069] The experimental procedure was the same as in Example 1, but no cobalt powder and zinc powder were added during the ingredient process, and only the carbon black was 61.4 g and the tungsten powder was 938.6 g.

[0070] The experimental results showed that the Fisher particle size of the tungsten carbide was 3.5 μm, and the scanning electron microscope observation showed that the particles were more regular in shape and the particle size distribution was narrower, as shown in Figure 4. Figure 4 .

[0071] The product detection indexes were as follows:

[0072]

[0073] Example Summary:

[0074] Example One: Using the standard content of activator (1% cobalt powder and 1% zinc powder) and the standard holding time, coarse-grained tungsten carbide with an average particle size of 10.5 μm can be prepared, and the particle morphology is a regular polyhedron.

[0075] Example Two: By increasing the content of activator to 10%, under the same carbonization temperature and holding time, larger coarse-grained tungsten carbide can be obtained, with an average particle size of 18 μm, and the morphology still remains a polyhedron.

[0076] Example Three: On the basis of the content of activator being 10%, the holding time at each temperature stage is extended, so that the average particle size of the tungsten carbide is further increased to 32 μm, but the particle morphology becomes irregular.

[0077] Example Four: The conventional method without using activator can prepare tungsten carbide with an average particle size of 3.5 μm, and the particle morphology is relatively regular and the particle size distribution is relatively narrow.

[0078] Summary: The experimental results show that by adjusting the activator content and carbonization holding time, the particle size and morphology of tungsten carbide can be effectively controlled. The addition of activator significantly promotes the growth of tungsten carbide grains, while the extension of holding time further increases the particle size. These findings are of great significance for the preparation of cemented carbide, as the particle size and morphology of tungsten carbide can be tailored according to specific application needs, thereby optimizing the performance of cemented carbide.

[0079] While embodiments of the application have been shown and described, it is to be understood that the application is not limited to the details of the embodiments described, since modifications can be made by those skilled in the art, without departing from the spirit and scope of the application, which are defined by the appended claims and their equivalents.

Claims

1. A process for the low temperature preparation of coarse grained tungsten carbide powder, characterized in that, Includes the following steps: S1. A mixture is provided, comprising fine tungsten powder and fine carbon black, wherein the average particle size of the fine tungsten powder is 0.2-8 μm, the average particle size of the fine carbon black is 0.5-5 μm, the fine tungsten powder and fine carbon black are mixed in a mass ratio of 10:1, the fine tungsten powder has high purity, ≥99.9%, and the impurity content in the tungsten powder is controlled below 0.1%, the impurities including iron, nickel and aluminum metal elements; S2. Add an activator to the mixture, the activator being composed of cobalt powder and zinc powder, the average particle size of the cobalt powder and zinc powder being 1-5 μm, the total amount of activator added being 1%-10% of the mass of tungsten powder, and the mass ratio of cobalt powder to zinc powder being 1:1 to 1:

3. S3. Mix tungsten powder, carbon black, cobalt powder and zinc powder according to the total weight ratio to ensure the uniformity and integrity of the carbonization reaction; S4. Place the above mixture in a ball mill for ball milling. The balls used in the ball mill are alloy steel balls, and the volume ratio of balls to material is 1:1 to 6:

1. The ball milling time is set to 5-60 hours to ensure that the mixture is fully mixed and homogenized. In this step, the ball milling process adopts dry ball milling technology. The temperature inside the ball mill is controlled at 50-80℃ to prevent the material from overheating and to maintain the stability of the chemical composition. S5. The ball-milled mixture is carbonized in a carbonization furnace at 1200-1450℃ for 20-200 minutes. The hydrogen flow rate is controlled at 100-500 ml / min as a protective gas. Controlling the protective gas flow rate helps the carbonization reaction to proceed and the characteristics of coarse tungsten carbide powder to be controlled. In this step, the carbonization process is carried out in a graphite boat. The graphite boat cover is provided with adjustable gas exhaust holes to control the gas pressure inside the boat and promote the growth of tungsten carbide particles. At the same time, it allows the escaped tungsten carbide gas and other by-product gases to be discharged to avoid excessive pressure inside the reactor. S6. After the carbonized coarse tungsten carbide powder is cooled to room temperature, it is subjected to wet grinding and sieving. The medium used for wet grinding is deionized water or ethanol. The sieving process uses a sieve with a pore size of 50-500μm to remove unreacted tungsten powder and carbon black, so as to obtain coarse tungsten carbide powder with uniform particle size. S7. Treat the coarse tungsten carbide powder after carbonization with a 3%-37% hydrochloric acid solution to remove cobalt powder, zinc powder and other possible metallic impurities. S8. The treated tungsten carbide powder is dried in a hot air circulating oven at 100-150℃ for 1-4 hours to ensure that the moisture in the powder is completely removed, and dry coarse tungsten carbide powder is obtained.

2. The method of claim 1, wherein the temperature is between 1,000°C and 1,200°C. The amount of cobalt powder and zinc powder added as activators is adjusted according to the particle size of the desired coarse tungsten carbide powder, so as to achieve the directional preparation of tungsten carbide powder with different particle sizes. When preparing tungsten carbide powder with larger particle size, the amount of activator added is increased to promote particle growth.

3. The method of claim 1, wherein the temperature is between 1,000°C and 1,200°C. The carbonized tungsten carbide powder is subjected to wet grinding treatment in the S6 step, the grinding time is 1-5 hours, and the grinding medium is anisotropic abrasive with a particle size of 1-3 mm, so as to improve the purity and uniformity of the powder.

4. The method of claim 1, wherein the temperature is between about 1,000°C and about 1,200°C. In the S6 step, at least two sieves with different aperture sizes are used in series, the first sieve has a larger aperture to remove larger unreacted particles, and the second sieve has a smaller aperture to ensure the consistency of the product particle size.

5. The method of claim 1, wherein the temperature is between about 1,000°C and about 1,200°C. In the S7 step, the hydrochloric acid treatment time is 1-3 hours, and the treatment is continuously stirred to ensure the complete dissolution and removal of metal impurities, and the treated waste liquid is treated and neutralized.

6. The method of claim 1, wherein the temperature is between about 1,000°C and about 1,200°C. In the S8 step, vacuum drying technology is used, and the vacuum degree is maintained at-0.08 to-0.095 MPa during the drying process to accelerate the evaporation of water and prevent the oxidation of the powder.

7. A coarse-grained tungsten carbide powder prepared according to the method of any one of claims 1 to 6, characterized in that, The average particle size of the coarse tungsten carbide powder is 10-50 μm, and it has a highly spherical morphology, the particle surface is smooth, and the particle size distribution consistency between particles is higher than 90%, the coarse tungsten carbide powder is suitable for the production of hard alloy, wear-resistant material and high-density alloy.

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