Method for preparing ultra-fine tungsten powder with ultra-low carbon content based on carbon thermal reduction of tungsten oxide

Abstract

The invention provides a method for preparing ultra-fine tungsten powder with ultra-low carbon content based on carbon thermal reduction of tungsten oxide, which comprises the following steps: 1) by using tungsten oxide as a tungsten source, carrying out ball milling and refining on the tungsten oxide to enable the particle size D50 of the tungsten oxide to be less than 1 mu m; 2) uniformly mixing the ball-milled tungsten oxide with nano carbon black with the particle size of 100-200 nm, and carrying out carbon thermal pre-reduction at 950-1050 DEG C in an inert atmosphere under the carbon-deficient condition that the molar ratio of the carbon black to the tungsten oxide is 1.0-1.7; and (3) the pre-reduced tungsten powder is placed in a wet hydrogen atmosphere with the dew point ranging from-20 DEG C to 20 DEG C, further treatment is conducted at the temperature ranging from 750 DEG C to 850 DEG C, deep decarburization is achieved, and residual oxygen is synchronously removed. The purity of the ultra-low-carbon-content superfine tungsten powder reaches 99.9% or above, the particle size distribution is smaller than 100 nm, the carbon content is smaller than 50 ppm, and the carbon impurity control level of the hydrogen reduction process is achieved in the carbon thermal reduction process.

Description

Technical Field

[0001] This invention relates to the field of tungsten powder preparation and powder metallurgy, specifically to a method for preparing ultrafine tungsten powder with ultra-low carbon content. Background Technology

[0002] Tungsten powder, as an important basic raw material in the field of powder metallurgy, is widely used in cemented carbide, tungsten-based high-temperature structural materials, W-Cu composite materials, and high-power electronic devices. As related applications develop towards high power density, high reliability, and multi-physics coupled service conditions, more stringent requirements have been placed on the particle size, purity, and impurity control of tungsten powder. In particular, the limit on carbon impurity content has been further tightened from the traditional level of hundreds of ppm to tens of ppm or even lower.

[0003] In existing technologies, industrial tungsten powder is typically obtained by hydrogen reduction of tungsten oxide or through multi-stage reduction of intermediate oxides. While these methods are mature, they generally suffer from the following drawbacks when preparing ultrafine or submicron-sized tungsten powder: Firstly, as particle size decreases, the specific surface area of ​​the powder increases significantly, making it highly sensitive to reduction kinetics and atmosphere control. This can easily introduce residual oxygen or lead to abnormal grain growth, making it difficult to achieve a stable balance between refinement and purity. Secondly, the reduction rate of a single hydrogen reduction pathway is limited at low temperatures, while at high temperatures it easily induces particle sintering and agglomeration, which is not conducive to obtaining ultrafine tungsten powder with uniform particle size. To overcome the kinetic bottleneck of pure hydrogen reduction, carbothermic reduction, as a reduction method with strong reaction driving force, has been used for the reduction preparation of tungsten powder. However, traditional carbothermic reduction generally uses carbon content close to or higher than the theoretical stoichiometry. Although complete reduction can be achieved, free carbon residue or trace carbide phases are prone to appear in the later stages of the reaction, making it difficult to effectively control the carbon content of the final tungsten powder.

[0004] Chinese invention patent CN108500283B discloses a low-cost two-stage reduction method for preparing nano-tungsten powder, and further discloses the following steps: (1) Tungsten trioxide and carbon are mixed evenly under insufficient carbon ratio, and a first-stage reduction is carried out under an inert atmosphere. Under carbon deficiency, most of the tungsten trioxide is reduced to nano-tungsten powder, and a small amount of oxygen is retained in the product; (2) The pre-reduced nano-tungsten powder obtained in step (1) is subjected to a second-stage reduction under a hydrogen atmosphere to remove the remaining small amount of oxygen, and a nano-tungsten powder with high purity is obtained; the average particle size of the nano-tungsten powder can reach 40 nm. Although this method can obtain nano-tungsten powder with a low particle size, it does not effectively control the residual carbon content in the tungsten powder. The residual carbon content of the tungsten powder prepared according to the above scheme is basically above 150 ppm.

[0005] Therefore, there is an urgent need to develop a new method for preparing tungsten powder that can achieve deep and stable control of carbon content while ensuring ultrafine powder, so as to meet the urgent demand of high-end application fields for low-carbon, high-purity, ultrafine tungsten powder. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a method for preparing ultra-low carbon content ultrafine tungsten powder based on carbothermic reduction of tungsten oxide. The aim is to achieve stable control of the carbon content of the finished product below 50 ppm while ensuring particle refinement (less than 100 nm) through synergistic regulation of raw material particle size, carbon black ratio, reduction temperature range, and hydrogen dew point.

[0007] According to one aspect of the present invention, a method for preparing ultrafine tungsten powder with ultra-low carbon content based on carbothermic reduction of tungsten oxide is provided, comprising the following steps:

[0008] 1) Tungsten oxide is ball-milled to obtain fine tungsten oxide powder;

[0009] 2) Mix the tungsten oxide powder obtained in step 1) with nano-carbon black evenly, and perform carbon-deficient carbothermal pre-reduction under an inert atmosphere to obtain pre-reduced tungsten powder. The molar ratio of the tungsten oxide powder to the nano-carbon black is 1:1 to 1:1.7.

[0010] 3) The pre-reduced tungsten powder obtained in step 2) is placed in a humid hydrogen atmosphere to react and obtain ultra-low carbon content ultrafine tungsten powder, wherein the humid hydrogen dew point is -20~20 ℃.

[0011] As a preferred embodiment of the method for preparing ultra-low carbon content ultrafine tungsten powder based on carbothermic reduction of tungsten oxide according to the present invention, in step 1), the tungsten oxide includes one or more of yellow tungsten, blue tungsten, and purple tungsten, and the particle size D50 of the tungsten oxide powder is ≤1 μm.

[0012] As a preferred embodiment of the method for preparing ultra-low carbon content ultrafine tungsten powder based on carbothermic reduction of tungsten oxide according to the present invention, in step 1), the ball milling is a planetary ball mill, the ball milling medium is cemented carbide balls, the ball-to-material ratio is 5:1 to 20:1, and the ball milling time is 6 to 24 h.

[0013] As a preferred embodiment of the method for preparing ultra-low carbon content ultrafine tungsten powder based on carbothermic reduction of tungsten oxide according to the present invention, in step 2), the particle size of the nano carbon black is 100~200 nm.

[0014] As a preferred embodiment of the method for preparing ultra-low carbon content ultrafine tungsten powder based on carbothermic reduction of tungsten oxide according to the present invention, in step 2), the mixing is carried out using a three-dimensional mixer for a mixing time of 6-12 h, so that the nano carbon black forms a continuous dispersion coating on the surface of tungsten oxide.

[0015] As a preferred embodiment of the method for preparing ultra-low carbon content ultrafine tungsten powder based on carbothermic reduction of tungsten oxide according to the present invention, in step 2), the pre-reduction temperature is 950~1050 ℃, and the inert atmosphere is argon or nitrogen.

[0016] As a preferred embodiment of the method for preparing ultra-low carbon content ultrafine tungsten powder based on carbothermic reduction of tungsten oxide according to the present invention, in step 3), the wet hydrogen dew point is -20~20 ℃ and the reaction temperature is 750~850 ℃.

[0017] Based on another objective of the present invention, an ultra-low carbon content ultrafine tungsten powder prepared by any of the above methods is also provided, wherein the ultra-low carbon content ultrafine tungsten powder has a purity of 99.9% or higher, a carbon content of less than 50 ppm, and a particle size of less than 100 nm.

[0018] This invention employs wet hydrogen as the reaction condition to perform deep decarburization treatment on porous tungsten powder obtained by carbothermic pre-reduction. The appropriate partial pressure of water vapor in the wet hydrogen atmosphere promotes the migration of residual carbon to the gas phase and its discharge in gaseous form, while simultaneously reducing tungsten oxide. This process improves the purity of the tungsten powder while maintaining its fine grain structure. This process avoids the particle sintering and coarsening problems caused by simply increasing the reduction temperature, thus establishing an effective balance between particle size control and impurity removal, ultimately obtaining ultrafine tungsten powder with extremely low carbon content and stable particle size.

[0019] This invention uses nano-carbon black as the carbon source for carbothermic reduction. While participating in the tungsten oxide reduction reaction, its nanoparticle characteristics provide nucleation sites during the reaction, effectively reducing the particle size of tungsten powder. Furthermore, compared to conventional micron-sized carbon sources, nano-carbon black with a particle size of 100-200 nm can achieve a uniform distribution of refined tungsten oxide particles during the mixing stage, effectively shortening the solid-solid reaction diffusion distance, improving the overall uniformity of the reduction reaction, and thus effectively reducing the residual carbon content.

[0020] This invention achieves a continuous and dispersed coating of nano-carbon black on the surface of tungsten oxide by uniformly mixing nano-carbon black with oxide. The nano-carbon black and submicron-sized tungsten oxide form a highly dispersed reaction interface at high temperature, which facilitates the full reaction, effectively reduces residual carbon content, and improves the yield and purity of tungsten powder.

[0021] Under carbon-deficient conditions, the present invention allows for the continuous release of CO and CO2 gases during the transformation of tungsten oxide into tungsten, which causes the original dense tungsten oxide particles to form a loose and porous structure, providing sufficient reaction conditions for subsequent steps.

[0022] In the technical solution of this invention, process parameters adapted to the characteristics of the raw materials further ensure the stable preparation of high-purity, low-carbon-content ultrafine tungsten powder. For example, the selection of carbon black ratio and carbothermal pre-reduction temperature aims to achieve the reduction of tungsten oxide under carbon-deficient conditions, accompanied by gas release, to destroy the original crystal structure and form a loose and porous tungsten particle skeleton. Based on this, the appropriate carbon black / oxide molar ratio is 1.0~1.7, and the carbothermal pre-reduction temperature range is 950~1050℃, to avoid significant sintering and grain growth of tungsten particles. The selection of wet hydrogen treatment temperature and dew point aims to achieve the synergistic removal of residual carbon and residual oxygen without causing grain coarsening. Based on this, the treatment temperature is controlled at 750~850℃, and the hydrogen dew point is controlled within the range of -20~20℃, thereby ensuring the controllability and effectiveness of the decarburization process.

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

[0024] 1. The present invention uses a process route that combines carbon-deficient carbon thermal pre-reduction of nano-carbon black with deep decarburization by wet hydrogen to prepare ultra-low carbon content ultrafine tungsten powder with a total carbon content that is consistently below 50 ppm, which is significantly better than conventional carbothermal reduction or single hydrogen reduction methods.

[0025] 2. By synergistically controlling the particle size of raw materials, the size of carbon source and key heat treatment parameters, this invention effectively suppresses the sintering and agglomeration of tungsten powder during the reduction process, resulting in tungsten powder with fine particle size (average particle size <100nm), uniform distribution and high purity (>99.9%). Detailed Implementation

[0026] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1

[0028] A method for preparing low-carbon content ultrafine tungsten powder based on carbothermic reduction of tungsten oxide includes the following steps:

[0029] 1) High-purity tungsten trioxide raw material was ball-milled to achieve a particle size D50 of 0.9 μm;

[0030] 2) The ball-milled tungsten trioxide was mixed evenly with nano carbon black with a particle size of 100 nm. The molar ratio of carbon black to tungsten trioxide, C / WO3, was controlled to be 1.3. The mixed powder was placed in an argon protective atmosphere, heated to 1050 °C and held for 3 h for carbothermic pre-reduction to obtain pre-reduced tungsten powder with a residual carbon content of 90 ppm.

[0031] 3) The pre-reduced tungsten powder is transferred into a wet hydrogen atmosphere, the hydrogen dew point is controlled at 0°C, and it is treated at 800°C for 2 hours to complete the deep decarburization process, and ultrafine tungsten powder with uniform distribution, an average particle size of about 90 nm, and a carbon content of 35 ppm is obtained.

[0032] Example 2

[0033] A method for preparing low-carbon content ultrafine tungsten powder based on carbothermic reduction of tungsten oxide includes the following steps:

[0034] 1) High-purity tungsten trioxide raw material is ball-milled to achieve a particle size D50 = 0.8 μm;

[0035] 2) The ball-milled tungsten trioxide was mixed evenly with nano carbon black with a particle size of 150 nm. The molar ratio of carbon black to tungsten trioxide, C / WO3, was controlled to be 1.6. The mixed powder was placed in an argon protective atmosphere, heated to 1000 ℃ and kept at that temperature for 3 h for carbothermic pre-reduction to obtain pre-reduced tungsten powder containing 100 ppm of residual carbon.

[0036] 3) The pre-reduced tungsten powder is transferred into a wet hydrogen atmosphere, the hydrogen dew point is controlled at -20 °C, and it is treated at 750 °C for 2 h to complete the deep decarburization process, and ultrafine tungsten powder with uniform distribution, an average particle size of about 85 nm, and a carbon content of 48 ppm is obtained.

[0037] Example 3

[0038] A method for preparing low-carbon content ultrafine tungsten powder based on carbothermic reduction of tungsten oxide includes the following steps:

[0039] 1) High-purity tungsten trioxide raw material was ball-milled to achieve a particle size D50 of 0.9 μm;

[0040] The ball-milled tungsten trioxide was mixed evenly with nano-carbon black with a particle size of 120 nm. The molar ratio of carbon black to tungsten trioxide, C / WO3, was controlled to be 1.5. The mixed powder was placed in an argon protective atmosphere, heated to 950 °C and held for 3 h for carbothermic pre-reduction to obtain pre-reduced tungsten powder containing 95 ppm of residual carbon.

[0041] 3) The pre-reduced tungsten powder is transferred into a wet hydrogen atmosphere, the hydrogen dew point is controlled at 20 °C, and it is treated at 850 °C for 2 h to complete the deep decarburization process, and ultrafine tungsten powder with uniform distribution, an average particle size of about 95 nm, and a carbon content of 45 ppm is obtained.

[0042] Comparative Example 1

[0043] A method for preparing low-carbon content ultrafine tungsten powder based on carbothermic reduction of tungsten oxide includes the following steps:

[0044] 1) High-purity tungsten trioxide raw material was ball-milled to achieve a particle size D50 of 0.9 μm;

[0045] 2) The ball-milled tungsten trioxide was mixed evenly with nano carbon black with a particle size of 100 nm. The molar ratio of carbon black to tungsten trioxide, C / WO3, was controlled to be 1.3. The mixed powder was placed in an argon protective atmosphere, heated to 1050 °C and held for 3 h for carbothermic pre-reduction to obtain pre-reduced tungsten powder with a residual carbon content of 90 ppm.

[0046] 3) The pre-reduced tungsten powder is transferred into a hydrogen atmosphere and treated at 800°C for 2 hours to complete the deep decarburization process, resulting in tungsten powder with an average particle size of about 92 nm and a carbon content of 85 ppm.

[0047] Compared with Example 1, this comparative example did not use a wet hydrogen atmosphere, resulting in insufficient water vapor partial pressure in the hydrogen, which significantly affected the removal of residual carbon.

[0048] Comparative Example 2

[0049] A method for preparing low-carbon content ultrafine tungsten powder based on carbothermic reduction of tungsten oxide includes the following steps:

[0050] 1) High-purity tungsten trioxide raw material is ball-milled to achieve a particle size D50 = 0.8 μm;

[0051] 2) The ball-milled tungsten trioxide was mixed evenly with nano carbon black with a particle size of 150 nm. The molar ratio of carbon black to tungsten trioxide, C / WO3, was controlled to be 1.6. The mixed powder was placed in an argon protective atmosphere, heated to 1000 ℃ and kept at that temperature for 3 h for carbothermic pre-reduction to obtain pre-reduced tungsten powder containing 100 ppm of residual carbon.

[0052] 3) The pre-reduced tungsten powder is transferred into a wet hydrogen atmosphere, the hydrogen dew point is controlled at -40 °C, and it is treated at 750 °C for 2 h to complete the deep decarburization process, and ultrafine tungsten powder with an average particle size of about 84 nm and a carbon content of 90 ppm is obtained.

[0053] Compared to Example 2, in this comparative example, the low hydrogen dew point resulted in insufficient water vapor partial pressure in the atmosphere, significantly reducing the decarbonization driving force. This, in turn, significantly affected the removal of residual carbon.

[0054] Comparative Example 3

[0055] A method for preparing low-carbon content ultrafine tungsten powder based on carbothermic reduction of tungsten oxide includes the following steps:

[0056] 1) High-purity tungsten trioxide raw material is ball-milled to achieve a particle size D50 = 0.8 μm;

[0057] 2) The ball-milled tungsten trioxide was mixed evenly with nano carbon black with a particle size of 150 nm. The molar ratio of carbon black to tungsten trioxide, C / WO3, was controlled to be 1.6. The mixed powder was placed in an argon protective atmosphere, heated to 1000 ℃ and kept at that temperature for 3 h for carbothermic pre-reduction to obtain pre-reduced tungsten powder containing 100 ppm of residual carbon.

[0058] 3) The pre-reduced tungsten powder is transferred into a wet hydrogen atmosphere, the hydrogen dew point is controlled at 35 °C, and it is treated at 750 °C for 2 h to complete the deep decarburization process, and ultrafine tungsten powder with an average particle size of about 105 nm and a carbon content of 30 ppm is obtained.

[0059] Compared with Example 2, the hydrogen dew point in this comparative example is too high, which leads to a significant increase in the partial pressure of water vapor in the atmosphere. Although this is beneficial for the removal of residual carbon, it also enhances the oxidation tendency of metallic tungsten. Under these conditions, the surface of the pre-reduced tungsten powder is prone to local re-oxidation and repeated reduction processes, which leads to a significant increase in the surface activity of the particles and accelerated sintering and grain growth, thereby weakening the particle size control effect of the ultrafine tungsten powder.

[0060] It should be noted that, based on the above embodiments of the present invention, those skilled in the art can fully realize the scope of the independent claims and dependent claims of the present invention, and the implementation process and methods are the same as those in the above embodiments; and the parts of the present invention not described in detail belong to the well-known technology in the art. However, the protection scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing ultra-low carbon content ultrafine tungsten powder based on carbothermic reduction of tungsten oxide, characterized in that, Includes the following steps: 1) Tungsten oxide is ball-milled to obtain fine tungsten oxide powder; 2) Mix the tungsten oxide powder obtained in step 1) with nano-carbon black evenly, and perform carbon-deficient carbothermal pre-reduction under an inert atmosphere to obtain pre-reduced tungsten powder. The molar ratio of the tungsten oxide powder to the nano-carbon black is 1:1 to 1:1.

7. 3) The pre-reduced tungsten powder obtained in step 2) is placed in a humid hydrogen atmosphere to react and obtain ultra-low carbon content ultrafine tungsten powder, wherein the humid hydrogen dew point is -20~20 ℃.

2. The method as described in claim 1, characterized in that, In step 1), the tungsten oxide includes one or more of yellow tungsten, blue tungsten, and purple tungsten.

3. The method as described in claim 2, characterized in that, In step 1), the particle size D50 of the tungsten oxide powder is ≤1 μm.

4. The method according to any one of claims 1 to 3, characterized in that, In step 1), the ball milling is a planetary ball mill, the ball milling media is cemented carbide balls, the ball-to-material ratio is 5:1 to 20:1, and the ball milling time is 6 to 24 hours.

5. The method as described in any one of claims 4, characterized in that, In step 2), the nano-carbon black has a particle size of 100~200 nm.

6. The method as described in any one of claims 5, characterized in that, In step 2), the mixing is performed using a three-dimensional mixer, and the mixing time is 6-12 hours.

7. The method as described in any one of claims 5, characterized in that, In step 2), the pre-reduction temperature is 950~1050 ℃, and the inert atmosphere is argon or nitrogen.

8. The method according to any one of claims 1-3 and 5-7, characterized in that, In step 3), the wet hydrogen dew point is -20~20 ℃ and the reaction temperature is 750~850 ℃.

9. An ultra-low carbon content ultrafine tungsten powder, characterized in that, The ultra-low carbon content ultrafine tungsten powder is prepared by the method described in any one of claims 1 to 8, and has a purity of 99.9% or higher, a carbon content of less than 50 ppm, and a particle size of less than 100 nm.