A nano-tungsten carbide and its preparation method
By calcining ammonium paratungstate to form purple tungsten and oxidizing it to yellow tungsten, combined with ball milling and carbonization, the problem of powder coarsening caused by hydrogen reduction of purple tungsten was solved, achieving the preparation of finer nano-tungsten carbide powder and cost reduction.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- WENZHOU HONGFENG ALLOY CO LTD
- Filing Date
- 2024-03-27
- Publication Date
- 2026-05-26
AI Technical Summary
In existing methods for producing nano WC powder, the hydrogen reduction process of purple tungsten leads to the volatilization and deposition of hydrated tungsten, resulting in powder coarsening. Furthermore, the carbon reduction process of yellow tungsten requires high-end equipment and is difficult to reduce in cost.
Ammonium paratungstate was calcined to form purple tungsten, which was then oxidized to yellow tungsten in pure oxygen. After being mixed with carbon, the mixture was ball-milled and isostatically pressed. Subsequently, carbon reduction and carbonization were carried out under a slightly positive pressure N2 atmosphere to avoid the purple tungsten stage and directly prepare nano-tungsten carbide.
Finer nano-tungsten carbide powder was prepared, reducing equipment requirements and manufacturing costs, breaking through the 200nm particle size limitation, and simplifying the process.
Smart Images
Figure CN118221119B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of powder metallurgy technology, specifically to a nano-tungsten carbide and its preparation method. Background Technology
[0002] Nanocrystalline WC-Co cemented carbide possesses both high strength and high toughness, making it an indispensable component of machining tools in high-end machine tools. The preparation of nano-tungsten carbide (WC) powder is the key and prerequisite for the production of nanocrystalline WC-Co cemented carbide materials.
[0003] There are many existing methods for producing nano-WC powder, such as high-energy ball milling, tungsten oxide reduction-carbonization, spray conversion, and chemical vapor phase reaction synthesis. The mainstream industrial production of nano-WC powder both domestically and internationally mainly uses the tungsten oxide reduction-carbonization method.
[0004] Tungsten oxide reduction-carburization can be further divided into blue / violet tungsten hydrogen reduction-carburization and yellow tungsten carbon reduction-carburization. The key process lies in the formation of a special intermediate phase, violet tungsten (WO3), during the reduction of tungsten oxide to tungsten powder. 2.72 Control of ) . Theoretical calculations show that the reduction of tungsten to form W powder must go through the processes of tungsten (WO3) and blue tungsten (WO4). 2.9 The process involves the reduction of tungsten oxide to W powder, specifically through stages of wollastonite (WO2) and tungsten powder production. During this process, except for tungsten ore, the particle shape remains relatively stable with minimal variation in particle size, exhibiting a "hereditary" characteristic in particle shape. Tungsten ore, however, requires specific hydrogen-to-water ratio reduction conditions and is a high aspect ratio needle / rod-shaped crystalline structure (high bulk density) of tungsten oxide. The porous structure of tungsten ore facilitates hydrogen entry and rapid water vapor escape during reduction, contributing to the preparation of nano-W powder. Therefore, the ammonium paratungstate (APT) / wollastonite-wollastonite-tungsten powder reduction technology route can theoretically achieve a significant transformation in the particle size and morphology of the raw material powder, reducing the difficulty of preparing nano-W powder.
[0005] A search revealed a Chinese invention patent with publication number CN1593822A, which uses APT (Alternating Current Processing) to directly calcine needle-shaped tungsten, then reduces the tungsten to nano-sized W powder in a high-flow-rate dry hydrogen environment, and finally combines the W powder with carbon to prepare nano-sized WC powder. However, the hydrogen reduction process inevitably generates water vapor, which reacts with tungsten oxide to form hydrated tungsten. The volatilization and deposition of hydrated tungsten on the surface of tungsten particles are the main reasons for powder growth. Therefore, the particle size limit of WC powder produced stably in industrial batches by this method is around 200 nm. Tokyo Tungsten Co., Ltd., in collaboration with Sumitomo Electric Industries, Ltd., uses a tungsten carbide reduction-carburization method to prepare nano-sized WC [Particle size of fine grain WC by the continuous direct carburizing process]. Tungsten powder undergoes a staged transformation in a continuous rotary kiln, from tungsten carbide to blue tungsten, purple tungsten, brown tungsten, to tungsten powder, and finally carburizes to obtain WC powder of 200 nm and finer. The WC prepared by this method has lower sintering sensitivity and higher powder uniformity. However, due to the complex reactions that the powder undergoes in the furnace (from yellow tungsten to purple tungsten to WC in one step), and the special reduction environment required for the transformation from yellow / blue tungsten to purple tungsten during the reduction process, strict control of the furnace atmosphere is required. This results in extremely high requirements for continuous rotary kiln equipment and difficulties in reducing the manufacturing cost of nano WC powder. Summary of the Invention
[0006] In view of the deficiencies in the prior art, the purpose of this invention is to provide nano-tungsten carbide and its preparation method.
[0007] According to one aspect of the present invention, a method for preparing nano-tungsten carbide is provided, the method comprising:
[0008] Ammonium paratungstate is provided, and the ammonium paratungstate is calcined to form purple tungsten;
[0009] The purple tungsten is oxidized in pure oxygen to form yellow tungsten;
[0010] The tungsten was mixed with carbon and then ball-milled, then isostatically pressed into a block, and subsequently carbon-reduced to obtain a tungsten-carbon mixed block.
[0011] The tungsten-carbon mixed block is carbonized and then crushed to obtain nano-tungsten carbide powder.
[0012] Further, the ammonium paratungstate is calcined to form purple tungsten, wherein: calcination is carried out at 800-900℃ for 10-20 minutes.
[0013] Further, the purple tungsten is oxidized in pure oxygen, wherein: oxidation is carried out in a pure oxygen environment at 500-600℃ for 30-60 minutes.
[0014] Further, the tungsten is ball-milled after being mixed with carbon, wherein the tungsten is mixed with carbon black at an atomic ratio of 1:4 to 1:4.02.
[0015] Further, the tungsten carbide is ball-milled with carbon, including: ball milling in a drum ball mill for 2-4 hours at a speed of 40-60 r / min.
[0016] Furthermore, the tungsten carbide is ball-milled with carbon, wherein the specific surface area of the tungsten carbide after ball milling is 7.7–7.8 m². 2 / g, with a particle size of 70-150nm.
[0017] Furthermore, the carbon reduction yields a tungsten-carbon mixed block, wherein carbon reduction is performed at 900-1000℃ for 3-4 hours.
[0018] Furthermore, the tungsten-carbon mixed block is subjected to a carbonization treatment, wherein the carbonization is carried out at 1200-1400℃ for 30-60 minutes.
[0019] Furthermore, both the carbon reduction and carbonization processes are carried out under a slightly positive pressure N2 atmosphere.
[0020] According to another aspect of the present invention, a nano-tungsten carbide is provided, which is prepared by the above-described method for preparing nano-tungsten carbide, and the nano-tungsten carbide is in powder form with a specific surface area of 3.1 to 3.2 m². 2 / g, with a particle size of 150-200nm.
[0021] Compared with the prior art, the present invention has at least one of the following beneficial effects:
[0022] 1. This invention employs a process route of calcining ammonium paratungstate to form purple tungsten, then using the purple tungsten to form nano-yellow tungsten, and finally forming nano-yellow tungsten carbide. Compared to the hydrogen reduction-carbide process of purple tungsten, this invention avoids the problem of powder coarsening caused by hydrated tungsten formed during the hydrogen reduction process of purple tungsten, and can prepare finer tungsten carbide powder with a particle size of 150-200 nm, breaking through the 200 nm particle size limitation of industrial production of nano-tungsten carbide.
[0023] 2. Compared with the yellow tungsten carbide reduction technology, this invention adopts a nanoscale yellow tungsten reduction process, which does not require the purple tungsten stage. No special reduction environment needs to be created in the furnace. The operation is simple. By utilizing the genetic characteristics of yellow tungsten reduction, it can be easily reduced into nano tungsten powder. This can significantly reduce the difficulty of controlling the reaction atmosphere in the furnace, greatly reduce the equipment requirements and the difficulty of subsequent preparation of nano tungsten carbide powder, thereby reducing the manufacturing cost of nano tungsten carbide. Attached Figure Description
[0024] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:
[0025] Figure 1 This is a schematic flowchart of a method for preparing nano-tungsten carbide in one embodiment of the present invention;
[0026] Figure 2 The scanning electron microscope (SEM) characterization results of purple tungsten in Example 1 (1000x magnification) are shown.
[0027] Figure 3 The scanning electron microscope (SEM) characterization results of purple tungsten in Example 1 (10000x) are shown.
[0028] Figure 4 The scanning electron microscope (SEM) characterization results (10000x) of the tungsten in Comparative Example 1 are shown.
[0029] Figure 5 The scanning electron microscope (SEM) characterization results of thyrite in Comparative Example 3 are shown (10,000x magnification). Detailed Implementation
[0030] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.
[0031] Reference Figure 1 As shown, an embodiment of the present invention provides a method for preparing nano-tungsten carbide, comprising the following steps:
[0032] S1. Provide ammonium paratungstate (APT), and calcine the ammonium paratungstate to form purple tungsten;
[0033] S2. Oxidize purple tungsten in pure oxygen to form yellow tungsten;
[0034] S3. After mixing tungsten with carbon, ball mill it, then press it into a block by isostatic pressing, and then reduce it with carbon to obtain a tungsten-carbon mixed block.
[0035] S4. The tungsten-carbon mixed block is carbonized and then crushed to obtain nano-tungsten carbide powder.
[0036] In some embodiments, in step S, ammonium paratungstate powder is placed in a calcining furnace and calcined at 800-900°C for 10-20 minutes to obtain needle-shaped tungsten. 800-900°C is the theoretically calculated temperature range for the formation of tungsten; exceeding this temperature range easily leads to the formation of blue tungsten or a mixture of blue and tungsten. Calcination for 10-20 minutes ensures the formation of needle-shaped tungsten particles, preventing coarsening of the tungsten. This needle-shaped tungsten retains the large particle shape of ammonium paratungstate, with an internal hollow morphology of stacked needle-shaped particles.
[0037] In order to ensure that tungsten can be completely oxidized to form tungsten, and to avoid sintering and powder coarsening of tungsten at excessively high temperatures, in some embodiments, in step S2, tungsten is oxidized in a dry pure oxygen environment at 500-600°C for 30-60 minutes to form tungsten.
[0038] During the preparation process, it was found that when purple tungsten is oxidized in air or in an oxygen-rich environment, hydrated tungsten is formed on the surface of the purple tungsten, causing the oxidized tungsten to coarsen and adhere. However, when purple tungsten is calcined in pure oxygen, the resulting tungsten retains the nanoscale needle-like microstructure of the purple tungsten.
[0039] In some embodiments, in step S3, tungsten and carbon black are mixed in an atomic ratio of 1:4 to 1:4.02. This carbon ratio is set according to the ratio of oxygen to carbon atoms in tungsten. A slight excess of carbon helps to reduce the amount of unreacted tungsten oxide or W powder residue.
[0040] In some embodiments, tungsten is ball-milled after being mixed with carbon, including: ball milling in a drum ball mill for 2-4 hours at a speed of 40-60 r / min. The drum ball mill is mainly used to disperse tungsten. Because tungsten oxidized from purple tungsten has a very loose structure, it can be broken down and refined without long-term ball milling or high-energy grinding. The specific surface area of the tungsten after ball milling is 7.7-7.8 m². 2 / g, with a particle size of 70-150nm. Due to the "inherited" characteristic of particle shape in the reduction of tungsten carbide, the particle size variation is relatively small. Therefore, during the reduction and carbonization process, the particle size parameter of tungsten carbide after ball milling is directly related to the final prepared nano-WC particle size. This particle size after ball milling of tungsten carbide is beneficial for preparing finer tungsten carbide powder. The mixture is then pressed into blocks in an isostatic press.
[0041] Following the aforementioned oxidation process of purple tungsten, the resulting tungsten particles can be ball-milled in a drum mill for 2-4 hours to obtain uniformly dispersed tungsten powder with a particle size of approximately 200 nm. During the preparation process, it was found that if purple tungsten is directly used for ball milling, due to its high hardness and brittleness, large, hard, and brittle agglomerates are easily formed during the milling process, making it difficult to disperse and form uniformly loose nano-tungsten oxide, which is detrimental to subsequent carbon addition and uniformity control. Furthermore, tungsten formed by directly calcining ammonium paratungstate inherits the morphological characteristics of ammonium paratungstate, primarily consisting of solid particles with a particle size of 30-50 μm. Even after 50 hours of drum milling, this type of tungsten powder still has a particle size of 3-7 μm, making it difficult to directly form dispersed and uniformly sized nano-tungsten. Therefore, it is essential to use ammonium paratungstate to calcine purple tungsten, followed by oxidation in pure oxygen, to easily prepare nano-tungsten oxide.
[0042] In some embodiments, in step S3, after the mixture is pressed into blocks in an isostatic press, it is carbon-reduced at 900-1000°C for 3-4 hours to obtain a mixed block of W and C. If the carbon reduction temperature is lower than this temperature or the carbon reduction time is shorter, unreacted brown tungsten is likely to remain; if the temperature is higher than this range or the carbon reduction time is longer, the W powder is prone to growth and coarsening, both of which are detrimental to the subsequent preparation of nano-tungsten carbide powder.
[0043] In some embodiments, in step S4, the mixed block of W and C is carbonized at 1200-1400℃ for 30-60 minutes, and then crushed to obtain nano-sized WC powder. If the carbonization process is carried out at a temperature lower than this range or for a shorter time, unreacted W and W2C are likely to remain in the tungsten carbide product; if the temperature is higher than this range or the carbonization time is longer, the tungsten carbide particles are likely to grow larger and coarser, both of which are not conducive to the preparation of finer tungsten carbide powder.
[0044] In the above embodiments, the carbon reduction and carbonization processes are carried out under a slightly positive pressure N2 atmosphere. N2 mainly plays a protective role and can prevent the powder from being oxidized.
[0045] In the above embodiments of the present invention, nano-sized tungsten and carbon powder are mixed, isostatically pressed into blocks, and then carbon reduced at 900-1000℃ to obtain W and C mixed blocks. Further, the W and C mixed blocks are carbonized at 1200-1400℃ to obtain WC blocks. Both the carbon reduction and carbonization processes are conducted under a slightly positive pressure N2 atmosphere. After the WC blocks are broken, nano-WC powder is obtained. During the preparation process, it was found that due to the complex atmosphere and difficulty in temperature control during calcination of tungsten, a blue / purple tungsten mixture (WO3) is easily formed. 3-x(x = 0.9–0.72). Therefore, directly using tungsten powder to prepare carbon can easily result in either excess or insufficient carbon, requiring multiple subsequent carbon measurements and additional ball milling to supplement carbon. In contrast, the tungsten to oxygen stoichiometric ratio in thyrite (WO3) is stable, making the carbon preparation using nano-thyrite more precise. This allows for accurate carbon preparation in a single step during the reduction and carbonization process, eliminating the need for subsequent carbon supplementation. Furthermore, by using nano-sized thyrite to react with carbon, and leveraging the genetic characteristics of tungsten oxide particle morphology during the reduction stage, the tungsten powder stage can be skipped directly to prepare nano-W and WC powders. This significantly simplifies furnace reaction and atmosphere control, reducing preparation difficulty and cost.
[0046] Another embodiment of the present invention provides a nano-tungsten carbide, which is prepared using the preparation method of the nano-tungsten carbide in the above embodiment. The nano-tungsten carbide is in powder form and has a specific surface area of 3.1-3.2 m². 2 / g, with a particle size of 150-200nm.
[0047] The present application's solution will be explained below with reference to specific embodiments and comparative examples. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the application. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained through commercial channels.
[0048] Example 1
[0049] Purple tungsten was formed by calcination at 800℃ for 10 min using APT, and then oxidized in an internal oxidation furnace at 500℃ for 30 min to form yellow tungsten. The yellow tungsten was ball-milled in a drum ball mill for 3 h at a ball milling speed of 45 r / min to obtain nano yellow tungsten. The nano yellow tungsten was mixed with carbon and pressed to obtain a compact. The compact was then heated in an N2 environment at 1000℃ to obtain a W and C mixed compact, which was then carbonized in an N2 environment at 1350℃ to form WC blocks. The WC blocks were crushed to obtain nano WC powder.
[0050] In this embodiment, the morphology of purple tungsten is as follows: Figure 2 and Figure 3 As shown, the large APT particles inherited from purple tungsten exhibit a hollow morphology with needle-like and rod-like stacked structures inside. The specific surface area of the yellow tungsten after ball milling was measured to be 7.75 m². 2 / g, particle size approximately 150nm, nano WC powder specific surface area 3.15m² 2 / g, with a particle size of approximately 150–180 nm.
[0051] Comparative Example 1
[0052] Purple tungsten was formed by calcining with APT at 800℃ for 10 min, and then oxidized in air at 500℃ for 30 min to form yellow tungsten. The yellow tungsten was ball-milled in a drum ball mill for 3 h at a speed of 45 r / min to obtain nano yellow tungsten. The nano yellow tungsten was mixed with carbon and pressed to obtain a compact. The compact was then heated in an N2 environment at 1000℃ to obtain a W and C mixed compact, which was then carbonized in an N2 environment at 1350℃ to form WC blocks. The WC blocks were crushed to obtain nano WC powder.
[0053] In this comparative example, the morphology of oxidized pyrrolidium is as follows: Figure 4 As shown, numerous fine particles formed by the volatilization and deposition of hydrated tungsten accumulate on the surface, with the needle-like tungsten particles gradually agglomerating together. The specific surface area of the tungsten after ball milling was measured to be 5–7 m² / s. 2 / g, with a particle size of 150-300nm, forming nano-WC powder with a specific surface area of 2.85m². 2 / g, with a particle size of approximately 200–350 nm.
[0054] Comparative Example 2
[0055] Purple tungsten was formed by calcining APT at 800℃ for 10 min. The purple tungsten was then ball-milled in a drum ball mill for 3 h at a speed of 45 r / min. The ball-milled purple tungsten was mixed with carbon and pressed to obtain a compact. The compact was then subjected to N2 environment at 1000℃ to obtain a W and C mixed compact, which was subsequently carbonized in N2 environment at 1350℃ to form WC blocks. The WC blocks were crushed to obtain nano WC powder.
[0056] In this comparative example, numerous tungsten atoms formed hard aggregates, resulting in poor mixing uniformity with carbon. The resulting nano-WC powder had a specific surface area of 2.05–2.83 m². 2 / g, with a particle size of 200-400nm.
[0057] Comparative Example 3
[0058] A calcination process using APT at 800℃ for 10 min was used to form tungsten. The tungsten was then ball-milled in a drum ball mill for 60 h at a speed of 45 r / min. The ball-milled tungsten was mixed with carbon and pressed to obtain a compact. The compact was then heated in an N2 environment at 1000℃ to obtain a W and C mixed compact, which was subsequently carbonized in an N2 environment at 1350℃ to form WC blocks. The WC blocks were then crushed to obtain nano WC powder.
[0059] The particle size distribution of the ball-milled thyristor in this comparative example is as follows: Figure 5 As shown, the ball-milled tungsten particles have a diameter between 300 nm and 7 μm and extremely poor uniformity, resulting in WC powder particles with a particle size of 400 nm to 7 μm.
[0060] The above embodiments of the present invention employ a process route of calcining ammonium paratungstate to form purple tungsten, then using purple tungsten to form nano yellow tungsten, and finally forming nano yellow tungsten carbide. Compared with the hydrogen reduction-carbide process of purple tungsten, the embodiments of the present invention avoid the problem of powder coarsening caused by hydrated tungsten formed during the hydrogen reduction process of purple tungsten, and can prepare finer tungsten carbide powder, breaking through the 200nm particle size limitation of industrial production of nano tungsten carbide.
[0061] Compared to the tungsten carbide reduction technology, the embodiments of this invention adopt a nanoscale tungsten carbide reduction process, which does not require the purple tungsten stage and does not require the creation of a special reduction environment in the furnace. The operation is simple, and the tungsten carbide reduction genetic characteristics can be used to easily reduce it into nano tungsten powder. This can significantly reduce the difficulty of controlling the reaction atmosphere in the furnace, greatly reduce the equipment requirements and the difficulty of subsequent preparation of nano tungsten carbide powder, thereby reducing the manufacturing cost of nano tungsten carbide.
[0062] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention. The above preferred features can be used in any combination without conflict.
Claims
1. A method for preparing nano-tungsten carbide, characterized in that, include: Ammonium paratungstate is provided, and the ammonium paratungstate is calcined to form purple tungsten; wherein: calcination at 800-900℃ for 10-20 min yields needle-shaped purple tungsten; The purple tungsten is oxidized in pure oxygen to form yellow tungsten; The tungsten was mixed with carbon and then ball-milled, then isostatically pressed into a block, and subsequently carbon-reduced to obtain a tungsten-carbon mixed block. The tungsten-carbon mixed block is subjected to carbonization treatment, and then crushed to obtain nano-tungsten carbide powder; The carbon reduction and carbonization processes are both carried out under a slightly positive pressure N2 atmosphere, and the carbonization temperature is 1200-1400℃.
2. The method for preparing nano-tungsten carbide according to claim 1, characterized in that, The purple tungsten is oxidized in pure oxygen, wherein the oxidation is carried out in a pure oxygen environment at 500-600℃ for 30-60 minutes.
3. The method for preparing nano-tungsten carbide according to claim 1, characterized in that, The tungsten is ball-milled after being mixed with carbon, wherein the tungsten is mixed with carbon black at an atomic ratio of 1:4 to 1:4.
02.
4. The method for preparing nano-tungsten carbide according to claim 1, characterized in that, The process of ball milling the tungsten carbide with carbon includes: ball milling in a drum ball mill for 2-4 hours at a speed of 40-60 r / min.
5. The method for preparing nano-tungsten carbide according to claim 1, characterized in that, The tungsten carbide is ball-milled with carbon, wherein the specific surface area of the tungsten carbide after ball milling is 7.7~7.8 m². 2 / g, with a particle size of 70-150nm.
6. The method for preparing nano-tungsten carbide according to claim 1, characterized in that, The carbon reduction process yields a tungsten-carbon mixed block, wherein carbon reduction is carried out at 900-1000℃ for 3-4 hours.
7. The method for preparing nano-tungsten carbide according to claim 1, characterized in that, The tungsten-carbon mixed block is subjected to carbonization treatment, wherein the carbonization time is 30-60 minutes.
8. A nano-tungsten carbide, characterized in that, The nano-tungsten carbide was prepared using the method described in any one of claims 1-7, wherein the nano-tungsten carbide is in powder form and has a specific surface area of 3.1~3.2 m². 2 / g, with a particle size of 150-200nm.