Method for preparing nano tungsten carbide powder by dynamic vacuum carbon thermal reduction-carbonization method

Abstract

The invention belongs to the technical field of nano materials, and particularly relates to a method for preparing nano tungsten carbide powder through a dynamic vacuum carbon thermal reduction-carbonization method. The designed preparation method comprises the following steps: mixing micron tungsten oxide and nano carbon black according to a set proportion to obtain mixed powder; and carrying out dynamic vacuum carbon thermal reduction-carbonization reaction in a vacuum atmosphere to obtain the nano tungsten carbide powder. The prepared tungsten carbide powder is high in purity, uniform and fine in particle and large in specific surface area, the technological process is simple, production continuity is high, controllability is high, the requirement for equipment is low, and wide application prospects are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanomaterials, and particularly relates to a method for preparing nano tungsten carbide powder by dynamic vacuum carbothermal reduction-carbidization method. Background Art

[0002] WC-Co cemented carbide has excellent physical properties such as high hardness, high melting point, high wear resistance and low friction coefficient, and has been widely used in cutting tools, metal processing tools, mining, oil drilling and other fields, and is known as the "teeth of industry". With the rapid development of modern industry, the performance of WC-Co cemented carbide with ordinary grain size can no longer meet the requirements. Generally speaking, the performance of WC-Co cemented carbide depends to a large extent on the grain size of WC. As the grain size of WC decreases, the hardness of the alloy increases significantly, but the fracture toughness decreases sharply. Nano-crystalline WC-Co cemented carbide has both high hardness and fracture toughness at the same time. Therefore, the preparation of high-performance nano-crystalline cemented carbide has become a research hotspot in the field of cemented carbide in recent years.

[0003] One of the keys to preparing nano-crystalline WC-Co cemented carbide lies in the preparation of nano WC powder. At present, the method for preparing nano WC powder industrially at home and abroad is hydrogen reduction-carbidization method. This method is mainly divided into two steps: First, tungsten oxide is reduced to tungsten in a hydrogen atmosphere; second, tungsten is carbonized into tungsten carbide by carbon black. It is found that during the hydrogen reduction process, the gaseous product water vapor formed by the combination of hydrogen atoms and oxygen atoms will react with tungsten oxide and deposit on the W crystal nucleus in the form of a ternary gaseous tungsten compound (WO2(OH)2), resulting in abnormal growth of W particles; in the subsequent carbonization process, a higher carbonization temperature and a longer carbonization time must be adopted to make the carburization reaction proceed fully, and finally it is difficult to obtain nano-scale WC powder.

[0004] It is found through investigation that some scholars have prepared nano WC powder by vacuum reduction-carbidization method. For example, Qianyu Wang et al. prepared pure nano WC powder with a specific surface area of 3.839 m 2 / g, an average particle size of about 100 nm and no carbon-deficient phase by vacuum reduction-carbidization method at 1100 °C in a hot press sintering furnace. However, when the preparation temperature is increased to 1300 °C, the specific surface area of the WC powder rapidly decreases to 1.554 m 2 / g, the average particle size increases to about 247 nm, and a carbon-deficient phase appears in the product again. Summary of the Invention

[0005] Aiming at the deficiencies existing in the prior art, on the basis of the existing vacuum reduction-carbonization method, the present invention for the first time attempts to use a reaction method of rotating or agitating powder to prepare nano WC powder with a larger specific surface area and a smaller average particle size.

[0006] The present invention relates to a method for preparing nano tungsten carbide powder by dynamic vacuum carbothermal reduction-carbonization. This method directly reduces and carbonizes micron-sized / submicron-sized raw materials into nano-sized WC powder through a continuously rotating reduction-carbonization reaction in a vacuum atmosphere, and there is no need to crush the powder. This method uses solid carbon black as a reducing agent and a carbonizing agent, which can effectively avoid the problem of product particle growth caused by the gas-phase transport mechanism during hydrogen reduction; compared with an argon atmosphere, using a vacuum atmosphere can greatly increase the reaction rate; adopting a dynamic rotation reaction method can make the reaction proceed more uniformly, which is more conducive to preparing nano WC powder with a high specific surface area and a small average particle size. Compared with the traditional process, it has the advantages of simple process, low production cost, and high production efficiency.

[0007] The method for preparing nano tungsten carbide powder by dynamic vacuum carbothermal reduction-carbonization of the present invention has the following process flow:

[0008] Fully mix tungsten oxide and carbon black powder to obtain a mixed powder; under a vacuum atmosphere, perform dynamic rotation reduction-carbonization on the mixed powder to obtain nano tungsten carbide powder; the particle size of the tungsten oxide is 20-100 μm; the particle size of the carbon black is 20-60 nm; during reduction-carbonization, control the temperature at 1000-1300 °C, the rotation speed at 2-10 r / min, preferably 2-5 r / min.

[0009] Preferably, the molar ratio of carbon black to tungsten oxide in the mixed powder is 3.5-4.5.

[0010] The vacuum degree, rotation speed, and reaction temperature of the present invention must be controlled in a coordinated manner, otherwise it is very difficult to obtain ultra-fine nano powder with a super high specific surface area.

[0011] As a further preference, the molar ratio of carbon black to tungsten oxide in the mixed powder is 3.72-4.0.

[0012] Preferably, the tungsten oxide is at least one of yellow tungsten (WO3), blue tungsten (WO 2.9 ) and purple tungsten (WO 2.72 ), and the particle size of the tungsten oxide is 20-100 μm, preferably yellow tungsten. In the present invention, the selection of raw materials is also crucial, otherwise it is very difficult to further refine the particle size of the product and further increase the specific surface area.

[0013] Preferably, the mixing is carried out in a V-type mixer, a three-dimensional mixer or a ball mill.

[0014] As a further preference, when ball milling, the rotation speed is controlled to be 150 - 250 r / min, the time is 2 - 20 h, and more preferably 4 - 10 h.

[0015] Preferably, the reaction temperature is 1000 - 1300 °C, preferably 1050 - 1150 °C, and the heat preservation time is 100 - 300 min, more preferably 120 - 180 min.

[0016] The vacuum degree in the furnace is controlled to be 0.1 - 50 Pa, preferably 5 - 50 Pa. The present invention can be implemented under the condition of a vacuum degree of 5 - 50 Pa (including 10 - 50 Pa) and achieve good effects. Compared with the prior art, the requirement for the vacuum degree of the equipment in the present invention is significantly reduced. This provides a necessary condition for industrial application.

[0017] A method for preparing nano tungsten carbide powder by a dynamic vacuum carbothermal reduction - carbonization method of the present invention includes the following steps:

[0018] Step 1: Obtaining a mixed powder using a ball mill

[0019] According to the mass ratio, 82.8 g of yellow tungsten is matched with 17.2 g of carbon black; yellow tungsten with an average particle size of 20 - 100 μm and carbon black with an average particle size of 20 - 60 nm are weighed; the prepared powder is loaded into a tungsten carbide ball mill for ball milling. The ball milling time is 10 h, and the rotation speed of the ball mill is 200 r / min to obtain a mixed powder;

[0020] Step 2: Preparation of nano tungsten carbide powder

[0021] The obtained mixed powder is put into a rotary furnace, and a dynamic rotary reduction - carbonization reaction is carried out in a vacuum atmosphere. The vacuum degree is 10 Pa, the temperature is 1100 °C, the rotation speed is 2 r / min, and the heat preservation time is 180 min to obtain nano WC powder.

[0022] In the present invention, the obtained product is nano tungsten carbide powder with an average particle size of 69 - 128 nm and a specific surface area of 3.01 - 5.57 m 2 / g. Through optimization, the present invention first adopts a dynamic reduction - carbonization method to obtain nano tungsten carbide powder with a particle size of 70 - 80 nm and a specific surface area of 4.7 - 5.45 m 2 / g.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. Compared with the traditional two-step preparation process of first reduction and then carbonization, the present invention adopts a one-step heating method to make the reduction reaction and carbonization reaction proceed continuously, avoiding the problem of particle size growth of powder particles during multiple heating and heat preservation processes, simplifying the process flow, shortening the production cycle, and greatly improving the continuity of industrial production.

[0025] 2. The method for preparing nano tungsten carbide by the dynamic vacuum reduction-carbonization method of the present invention uses solid carbon black as a reducing agent and a carbonizing agent, avoiding the problem of coarse powder particle size caused by traditional hydrogen reduction. Using a vacuum atmosphere reduces the reaction temperature, increases the reaction rate, and shortens the reaction time. The dynamic rotation reaction method enables the reaction to proceed more evenly, thereby preparing nano WC powder with a large specific surface area and a small average particle size. After optimization, the average particle size of the nano WC powder is 70-80 nm and the specific surface area is 4.7-5.45 m 2 / g. Description of the Drawings

[0026] Figure 1 It is the microscopic morphology diagram of the nano tungsten carbide powder prepared in Example 3, Example 4 and Example 5.

[0027] Figure 2 It is the XRD phase diagram of the nano tungsten carbide powder prepared in Example 3, Example 4 and Example 5.

[0028] Figure 3 It is the microscopic morphology diagram of the nano tungsten carbide powder prepared in Comparative Example 1, Comparative Example 2 and Comparative Example 3.

[0029] Figure 4 It is the XRD diagram of the nano tungsten carbide powder prepared in Comparative Example 1, Comparative Example 2 and Comparative Example 3.

[0030] Figure 1 Consists of Figure 1 (a), Figure 1 (b) and Figure 1 (c). Among them Figure 1 (a) is the microscopic morphology of the nano tungsten carbide powder prepared in Example 3, Figure 1 (b) is the microscopic morphology of the nano tungsten carbide powder prepared in Example 4, Figure 1 (c) is the morphology of the nano tungsten carbide powder prepared in Example 5. It can be seen from Figure 1 that the nano tungsten carbide powder particles prepared by the dynamic vacuum carbothermal reduction-carbonization method adopted by the present invention are nearly spherical in shape and have uniform and fine particle sizes.

[0031] It can be seen from Figure 2 that the powder phase prepared by the vacuum carbothermal reduction-carbonization method adopted by the present invention is a single WC phase and the powder purity is high.

[0032] Figure 3 Consisting of Figure 3 (a), Figure 3 (b) and Figure 3 (c). Among them Figure 3 (a) is the microscopic morphology of the powder prepared in Comparative Example 1, Figure 3 (b) is the microscopic morphology of the powder prepared in Comparative Example 2, Figure 3 (c) is the powder morphology prepared in Comparative Example 3. It can be seen from Figure 3 that the powder morphology prepared in the comparative example under an argon atmosphere consists of spherical particles and rod-shaped particles, and the particle size uniformity of the powder is poor.

[0033] It can be seen from Figure 4 that the powder phase of the powder prepared in the comparative example under an argon atmosphere consists of WC, W2C and W phases, and the powder purity is poor. Specific embodiments

[0034] The following combines examples to describe the process of the present invention in detail, rather than limiting the present invention.

[0035] Exploration Example 1

[0036] The detailed steps of a method for preparing nano tungsten carbide powder in this example are as follows.

[0037] Step 1: Obtain a mixed powder using a ball mill

[0038] Weigh 82.8 g of yellow tungsten with an average particle size of 20 - 100 μm; 17.2 g of carbon black with an average particle size of 20 - 60 nm. Put the above powders into a tungsten carbide ball mill tank for ball milling. The ball milling time is 10 h, and the rotational speed of the ball mill is 200 r / min to obtain a mixed powder.

[0039] Step 2: Preparation of nano tungsten carbide powder

[0040] Put the obtained mixed powder into a rotary furnace and carry out a reduction-carbide reaction under a vacuum atmosphere. The vacuum degree is 10 Pa, the temperature is 1100 °C, the rotational speed is 0 r / min, and the heat preservation time is 120 min to obtain nano WC powder.

[0041] After XRD and BET specific surface area tests, the powder phase of the powder prepared in this example is WC, W2C and W. Due to the short reaction time, there is still a carbon-deficient phase in the product, and the phase is impure.

[0042] Example 2

[0043] The detailed steps of a method for preparing nano tungsten carbide powder in this example are as follows.

[0044] Step 1: Obtain a mixed powder using a ball mill

[0045] Weigh 82.8 g of yellow tungsten with an average particle size of 20 - 100 μm; weigh 17.2 g of carbon black with an average particle size of 20 - 60 nm. Load the above powders into a tungsten carbide ball mill jar for ball milling. The ball milling time is 10 h, and the rotational speed of the ball mill is 200 r / min to obtain a mixed powder.

[0046] Step 2: Preparation of nano tungsten carbide powder

[0047] Put the obtained mixed powder into a rotary furnace and carry out a reduction - carbonization reaction under a vacuum atmosphere. The vacuum degree is 10 Pa, the temperature is 1100 °C, the rotational speed is 0 r / min, and the heat preservation time is 180 min to obtain nano WC powder.

[0048] After XRD and BET specific surface area tests, the powder phase prepared in this example is a single WC phase, and the specific surface area is 5.40 m 2 / g, and the average particle size is about 70 nm.

[0049] Example 3

[0050] Other conditions are the same as those in Example 2, except that: the rotational speed is 2 r / min. After XRD and BET specific surface area tests, the powder phase prepared in this example is a single WC phase, and the specific surface area is 5.57 m 2 / g, and the average particle size is about 69 nm.

[0051] Example 4

[0052] Other conditions are the same as those in Example 2, except that: the rotational speed is 5 r / min. After XRD and BET specific surface area tests, the powder phase prepared in this example is a single WC phase, and the specific surface area is 5.42 m 2 / g, and the average particle size is about 71 nm.

[0053] Example 5

[0054] Other conditions are the same as those in Example 2, except that: the rotational speed is 10 r / min. After XRD and BET specific surface area tests, the powder phase prepared in this example is a single WC phase, and the specific surface area is 5.32 m 2 / g, and the average particle size is about 72 nm.

[0055] Example 6

[0056] Other conditions are the same as those in Example 2, except that: the temperature is 1200 °C. After XRD and BET specific surface area tests, the powder phase prepared in this example is a single WC phase, and the specific surface area is 3.64 m 2 / g, and the average particle size is about 105 nm.

[0057] Example 7

[0058] Other conditions are the same as those in Example 2, except that the temperature is 1300 °C. After XRD and BET specific surface area tests, the powder prepared in this example has a single WC phase, and the specific surface area is 3.01 m 2 / g, and the average particle size is about 128 nm.

[0059] Example 8

[0060] Other conditions are the same as those in Example 3, except that the raw materials are blue tungsten and carbon black, and the molar ratio of the two is 1:3.9. After XRD and BET specific surface area tests, the powder prepared in this example has a single WC phase, and the specific surface area is 3.97 m 2 / g, and the average particle size is about 96 nm.

[0061] Example 9

[0062] Other conditions are the same as those in Example 3, except that the raw materials are blue tungsten and carbon black, and the molar ratio of the two is 1:3.72. After XRD and BET specific surface area tests, the powder prepared in this example has a single WC phase, and the specific surface area is 3.71 m 2 / g, and the average particle size is about 103 nm.

[0063] Comparative Example 1

[0064] Weigh 82.8 g of yellow tungsten with an average particle size of 20 - 100 μm; 17.2 g of carbon black with an average particle size of 20 - 60 nm. Put the above powders into a tungsten carbide ball mill jar for ball milling. The ball milling time is 10 h, and the ball mill rotation speed is 200 r / min to obtain a mixed powder.

[0065] Put the obtained mixed powder into a tubular furnace and carry out reduction - carbonization reaction under an argon atmosphere. The temperature is 1100 °C and it is not rotated, and the holding time is 300 min.

[0066] After testing, the powder phase prepared in this example is WC, W2C and W phases, and the average particle size is about 198 nm.

[0067] Comparative Example 2

[0068] Other conditions are the same as those in Comparative Example 1, except that the temperature is 1200 °C. After testing, the powder phase prepared in this example is WC, W2C and W phases, and the average particle size is about 229 nm.

[0069] Comparative Example 3

[0070] Other conditions are the same as those in Comparative Example 1, except that: the temperature is 1300 °C. After testing, the phases of the powder prepared in this example are WC, W2C and W phases, and the average particle size is about 312 nm.

[0071] Comparative Example 4

[0072] According to the report of Qianyu Wang et al. in the paper "Study on influencing factors and mechanism of high-quality tungsten carbide nanopowders synthesized via carbothermal reduction": Tungsten yellow with an average particle size of 38 μm and a content of 82.8 wt% and carbon black powder with a particle size of 30 - 40 nm and a content of 17.2 wt% were ball-milled for 15 h at a ball-milling speed of 180 rpm to obtain a mixed powder.

[0073] The obtained mixed powder was put into a hot press sintering furnace, and a reduction-carbide reaction was carried out under a vacuum atmosphere at a temperature of 1100 °C for 180 min.

[0074] The specific surface area of the WC powder prepared is 3.839 m 2 / g, and the average particle size is about 100 nm.

[0075] Comparative Example 5

[0076] According to the report of Qianyu Wang et al. in the paper "Study on influencing factors and mechanism of high-quality tungsten carbide nanopowders synthesized via carbothermal reduction": Tungsten yellow with an average particle size of 38 μm and a content of 82.8 wt% and carbon black powder with a particle size of 30 - 40 nm and a content of 17.2 wt% were ball-milled for 15 h at a ball-milling speed of 180 rpm to obtain a mixed powder.

[0077] The obtained mixed powder was put into a hot press sintering furnace, and a reduction-carbide reaction was carried out under a vacuum atmosphere at a temperature of 1200 °C for 180 min.

[0078] The specific surface area of the WC powder prepared is 2.461 m 2 / g, and the average particle size is about 156 nm.

[0079] Comparative Example 6

[0080] According to the report of Qianyu Wang et al. in the paper "Study on influencing factors and mechanism of high-quality tungsten carbide nanopowders synthesized via carbothermal reduction": Tungsten yellow with an average particle size of 38 μm and a content of 82.8 wt% and carbon black powder with a particle size of 30 - 40 nm and a content of 17.2 wt% were ball-milled for 15 h at a ball-milling speed of 180 rpm to obtain a mixed powder.

[0081] The obtained mixed powder was put into a hot-pressing sintering furnace, and a reduction-carbidization reaction was carried out under a vacuum atmosphere at a temperature of 1300 °C for a holding time of 180 min.

[0082] The specific surface area of the prepared WC powder was 2.461 m 2 / g, and the average particle size was about 247 nm.

Claims

1. A method for preparing nano tungsten carbide powder by dynamic vacuum carbothermal reduction - carbonization, characterized in that: Tungsten oxide and carbon black powders are fully mixed to obtain a mixed powder; in a vacuum atmosphere, the mixed powder is subjected to dynamic rotary reduction - carbonization to obtain nano tungsten carbide powder; the particle size of the tungsten oxide is 20 - 100 μm; the particle size of the carbon black is 20 - 60 nm; during reduction - carbonization, the temperature is controlled at 1000 - 1300 °C, the rotation speed is 2 - 10 r / min, preferably 2 - 5 r / min; The molar ratio of carbon black to tungsten oxide in the mixed powder is 3.5 - 4.5; During the reaction, the vacuum degree in the furnace is controlled at 0.1 - 50 Pa.

2. The method for preparing nano tungsten carbide powder by dynamic vacuum carbothermal reduction - carbonization according to claim 1, characterized in that: The molar ratio of carbon black to tungsten oxide in the mixed powder is 3.72 - 4.

0.

3. The method for preparing nano tungsten carbide powder by dynamic vacuum carbothermal reduction-carbonization according to claim 1, characterized in that: The tungsten oxide is one of yellow tungsten, blue tungsten, and violet tungsten, and the particle size of the tungsten oxide particles is 20 - 100 μm, preferably yellow tungsten.

4. The method for preparing nano tungsten carbide powder by dynamic vacuum carbothermal reduction-carbidization according to claim 1, characterized in that: The mixing is carried out in a V - type mixer, a three - dimensional mixer or a ball mill.

5. The method for preparing nano tungsten carbide powder by dynamic vacuum carbothermal reduction-carbidization according to claim 4, characterized in that: When ball - milling, the rotation speed is controlled at 150 - 250 r / min, the time is 2 - 20 h, and more preferably 4 - 10 h.

6. The method for preparing nano tungsten carbide powder by dynamic vacuum carbothermal reduction-carbidization according to claim 1, characterized in that: The reaction temperature is 1000 - 1300 °C, preferably 1050 - 1150 °C, and the heat - preservation time is 100 - 300 min, further preferably 120 - 180 min.

7. A method for preparing nano tungsten carbide powder by dynamic vacuum carbothermal reduction-carbidization according to claim 1, characterized in that: The vacuum degree in the furnace is controlled at 5 - 20 Pa.

8. A method for preparing nano tungsten carbide powder by a dynamic vacuum carbothermal reduction-carbidization method according to claim 6, characterized in that, It includes the following steps: Step 1: Obtaining a mixed powder using a ball mill According to the mass ratio, 82.8 g of yellow tungsten is mixed with 17.2 g of carbon black; weigh yellow tungsten with an average particle size of 20 - 100 μm and carbon black with an average particle size of 20 - 60 nm; load the weighed powders into a tungsten carbide ball - milling tank for ball - milling. The ball - milling time is 10 h, and the rotation speed of the ball mill is 200 r / min to obtain a mixed powder; Step 2: Preparation of nano tungsten carbide powder Put the obtained mixed powder into a rotary furnace and carry out a dynamic rotary reduction - carbonization reaction in a vacuum atmosphere. The vacuum degree is 10 Pa, the temperature is 1100 °C, the rotation speed is 2 r / min, and the heat - preservation time is 180 min to obtain nano WC powder.

9. A method for preparing nano tungsten carbide powder by dynamic vacuum carbothermal reduction-carbidization according to claim 6, characterized in that, The obtained product has an average particle size of 70 - 80 nm and a specific surface area of 4.7 - 5.45 m 2 / g.

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