A method for producing refractory tungsten having a uniform microstructure

Abstract

The present application relates to the field of powder injection molding, and particularly relates to a preparation method of refractory tungsten with uniform microporous structure. The preparation method mixes tungsten nanopowder with a binder to granulate, and then injection molds the treated powder to obtain a green body with uniform microporous structure; a sectional sintering method is used to pre-coarsen to control the uniformity of the structure and pores, and then further control the grain size and pore size, so that the prepared porous tungsten material has fine and uniformly distributed grain structure and pores, the porosity is 20%-50%, the average grain size is less than 1 mu m, the pore size is less than or equal to 0.5 mu m, and the variance is not more than 0.4. The method solves the problems of coarse grains, uneven pore size and pore distribution in the porous tungsten material prepared by the traditional method.

Description

Technical Field

[0001] This invention relates to the field of powder injection molding, and more specifically to a method for preparing refractory tungsten metal with a uniform microporous structure. Background Technology

[0002] Porous metallic structures possess low density, large specific surface area, and high specific strength, exhibiting excellent permeability, shock absorption, energy absorption, and filtration properties, making them a high-performance structural-functional integrated material. In recent years, they have been widely used in electrode materials, energy-absorbing materials, and catalyst supports. Tungsten, as a refractory metal, possesses excellent high-temperature performance, and porous tungsten, in particular, has important applications in electron emitters. The pore structure of the porous tungsten matrix plays a crucial role in the diffusion of active materials, placing high demands on the pore size, pore distribution uniformity, and porosity of porous tungsten.

[0003] Traditional methods for preparing porous tungsten often involve adding pore-forming agents or etchants to create pores, or adjusting the powder particle size and performing low-temperature sintering to create pores. However, these methods often fail to simultaneously meet the requirements for grain size, porosity, and fine and uniform pore size in the sintered products. Summary of the Invention

[0004] This invention discloses a method for preparing refractory tungsten metal with a uniform microporous structure, in order to solve any of the above-mentioned and other potential problems in the prior art.

[0005] To achieve the above objectives, the technical solution of the present invention is: a method for preparing refractory tungsten metal with a uniform microporous structure, the preparation method specifically including the following steps:

[0006] S1) Using nano-tungsten powder as raw material, adding PVA solution, and mixing to obtain granular feed;

[0007] S2) The pellets obtained from S1) are fed into the feedstock and then molded using injection molding to obtain a green body;

[0008] S3) The green body obtained in S2) is degreased by a combination of solvent degreasing and thermal degreasing to obtain a degreased green body;

[0009] S4) The degreased blank treated by S3) is sintered and shaped under a protective atmosphere using a segmented sintering method to obtain refractory tungsten metal with a uniform microporous structure.

[0010] Furthermore, the specific steps of S1) are as follows:

[0011] S1.1) Select nano-tungsten powder of a certain diameter and mix it with PVA solution to prepare a slurry. Under vacuum drying conditions, use a centrifugal spray granulator to prepare the slurry into micron-sized granulated powder; while retaining the sintering activity of nano-powder, improve the powder flowability.

[0012] S1.2) The granulated powder is then mixed evenly with the polymer organic binder, cooled, crushed, and granulated to produce granular feed for injection molding.

[0013] Furthermore, the nano-tungsten powder in S1.1) has a particle size of 50-400 nm and a purity greater than 99.9%.

[0014] The concentration of the PVA solution is 10-30%; the mass fraction of tungsten powder in the slurry is 70-85%.

[0015] Furthermore, the mass fraction of each component in the PVA solution is as follows: PVA mass fraction is 5-20%, dispersant mass fraction is 0.2-5%, and the remainder is deionized water;

[0016] The mass fraction of each component of the polymeric organic binder described in S1.2) is: 60-70% paraffin wax, 10-20% polyethylene, 10-15% polypropylene, and 1-5% stearic acid.

[0017] Furthermore, in S2), the injection pressure for injection molding is 100-150 MPa, and the feeding heating temperature is 80-200℃.

[0018] Furthermore, the specific process of S3) is as follows: First, the paraffin binder is removed in trichloroethane for 4-10 hours to form certain pore channels; then, thermal degreasing is performed to remove the remaining binder cleanly. The thermal degreasing temperature is 300-800℃, the heating rate is 1-5℃ / min, and the holding time is 1-3 hours.

[0019] Furthermore, the specific process of S4 is as follows:

[0020] S4.1) First, perform low-temperature sintering;

[0021] S4.2) Then, high-temperature and long-term dense sintering is carried out to prepare refractory tungsten metal with a uniform microporous structure.

[0022] Furthermore, the low-temperature sintering process in S4.1) is as follows: the temperature is slowly raised to 900-1100℃ at a heating rate of 4-5℃ / min, and held for 4-8 hours. A segmented sintering method is adopted, firstly performing low-temperature sintering to achieve pre-coarsening and homogenize the microstructure and pores. Then, high-temperature, long-time sintering is performed to improve sintering density and meet porosity requirements.

[0023] S4.2) The specific process of dense sintering is as follows: heat up to 1400-1800℃ at a rate of 10-15℃ / min and hold for 1-2 hours.

[0024] Furthermore, the protective atmosphere in S4) is hydrogen.

[0025] Furthermore, the refractory tungsten metal with a uniform microporous structure has a porosity of 20%-50%, an average grain size of less than 1 μm, a pore diameter of ≤0.5 μm, and a variance of no more than 0.4.

[0026] The beneficial effects of this invention are as follows:

[0027] (1) Using nanoparticles for granulation not only ensures the activity of the nanoparticles, which can reduce the sintering temperature, but also obtains a fine and uniform grain structure, thereby improving the performance of the sintered products. At the same time, it avoids the problems of agglomeration and poor flowability that occur when nanoparticles are directly used for injection molding, and improves its formability and the uniformity of pores.

[0028] (2) The segmented sintering method is used to prepare porous tungsten. First, the pre-coarsening treatment can obtain uniform pores, avoiding the large grains from engulfing the small grains and forming pore structures of different sizes or closed pores caused by direct sintering. At the same time, this sintering method can obtain fine and uniform grain structure. This preparation method can obtain porous tungsten products with a grain size of less than 1 μm and a pore size of less than 0.5 μm.

[0029] (3) Injection molding can be used to prepare porous tungsten, which can directly form irregular parts, avoid or reduce processing steps, and solve the problem of difficult processing of refractory metal tungsten. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a process flow diagram of a method for preparing refractory tungsten metal with a uniform microporous structure according to the present invention. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0033] like Figure 1 As shown, the present invention discloses a method for preparing refractory tungsten metal with a uniform microporous structure, the preparation method specifically including the following steps:

[0034] S1) Using nano-tungsten powder as raw material, adding PVA solution, and mixing to obtain granular feed;

[0035] S2) The pellets obtained from S1) are fed into the feedstock and then molded using injection molding to obtain a green body;

[0036] S3) The green body obtained in S2) is degreased by a combination of solvent degreasing and thermal degreasing to obtain a degreased green body;

[0037] S4) The degreased blank treated by S3) is sintered and shaped under a protective atmosphere using a segmented sintering method to obtain refractory tungsten metal with a uniform microporous structure.

[0038] The specific steps of S1) are as follows:

[0039] S1.1) Select nano-tungsten powder of a certain diameter and mix it with PVA solution to prepare a slurry. Under vacuum drying conditions, use a centrifugal spray granulator to prepare the slurry into micron-sized granulated powder; while retaining the sintering activity of nano-powder, improve the powder flowability.

[0040] S1.2) The granulated powder is then mixed evenly with the polymer organic binder, cooled, crushed, and granulated to produce granular feed for injection molding.

[0041] The nano-tungsten powder in S1.1) has a particle size of 50-400 nm and a purity greater than 99.9%.

[0042] The concentration of the PVA solution is 10-30%; the mass fraction of tungsten powder in the slurry is 70-85%.

[0043] The mass fractions of each component in the PVA solution are as follows: PVA 5-20%, dispersant 0.2-5%, and the remainder is deionized water;

[0044] The mass fraction of each component of the polymeric organic binder described in S1.2) is: 60-70% paraffin wax, 10-20% polyethylene, 10-15% polypropylene, and 1-5% stearic acid.

[0045] The injection pressure in S2) is 100-150MPa, and the feeding heating temperature is 80-200℃.

[0046] The specific process of S3 is as follows: First, the paraffin binder is removed in trichloroethane for 4-10 hours to form certain pore channels; then, thermal degreasing is performed to remove the remaining binder cleanly. The thermal degreasing temperature is 300-800℃, the heating rate is 1-5℃ / min, and the holding time is 1-3 hours.

[0047] The specific process of S4 is as follows:

[0048] S4.1) First, perform low-temperature sintering;

[0049] S4.2) Then, high-temperature and long-term dense sintering is carried out to prepare refractory tungsten metal with a uniform microporous structure.

[0050] The low-temperature sintering process in S4.1) is as follows: The temperature is slowly raised to 900-1100℃ at a heating rate of 4-5℃ / min, and held for 4-8 hours. A segmented sintering method is used. First, low-temperature sintering is performed to achieve pre-coarsening, resulting in a more uniform microstructure and pore size. Then, high-temperature, long-time sintering is performed to improve sinter density and meet porosity requirements.

[0051] S4.2) The specific process of dense sintering is as follows: heat up to 1400-1800℃ at a rate of 10-15℃ / min and hold for 1-2 hours.

[0052] The protective atmosphere in S4 is hydrogen.

[0053] The refractory tungsten metal with a uniform microporous structure has a porosity of 20%-50%, an average grain size of less than 1 μm, a pore diameter of ≤0.5 μm, and a variance of no more than 0.4.

[0054] Example 1

[0055] (1) The powder raw material is commercially available tungsten powder with a particle size of 50 nm and a purity of more than 99.9%.

[0056] (2) Powder granulation: The nanoparticles are mixed evenly with polyvinyl alcohol (PVA) solution to form a slurry, and then spray-dried to prepare micron-sized granulated powder.

[0057] (3) Preparation of feed: The granulated powder and organic binder are mixed evenly in a mixer, cooled, crushed and granulated to obtain granular feed for injection molding, wherein the volume fraction of powder particles is 50%.

[0058] (4) Injection molding: The feed material is injected into the mold to prepare the green blank. The injection pressure is 100MPa and the feed heating temperature is 155℃.

[0059] (5) Degreasing: First, solvent degreasing is used to remove paraffin components by soaking in trichloroethane for 6 hours. Then, thermal degreasing is carried out by heating to 300℃ at a heating rate of 1℃ / min and holding for 0.5 hours, then heating to 600℃ at a heating rate of 3℃ / min and holding for 1 hour, and then heating to 700℃ and holding for 0.5 hours.

[0060] (6) A segmented sintering process was adopted. The first step was to perform a pre-coarsening treatment, slowly heating to 900℃ at a heating rate of 4-5℃ / min and holding for 5 hours. The second step was to heat to 1600℃ at a rate of 10-15℃ / min and hold for 1 hour. Hydrogen gas was used for protection during the sintering process. The final sintered product had a porosity of 20%, an average pore size of 0.34μm, and an average grain size of 0.75μm.

[0061] Example 2:

[0062] (1) Powder raw materials: 200nm commercially available tungsten powder with a purity greater than 99.9%.

[0063] (2) Powder granulation: The nanoparticles are mixed evenly with polyvinyl alcohol (PVA) solution to form a slurry, and then spray-dried to prepare micron-sized granulated powder.

[0064] (3) Preparation of feed: The granulated powder and organic binder are mixed evenly in a mixer, cooled, crushed and granulated to obtain granular feed for injection molding, wherein the volume fraction of powder particles is 55%.

[0065] (4) Injection molding: The feed material is injected into the mold to prepare the green blank. The injection pressure is 120MPa and the feed heating temperature is 160℃.

[0066] (5) Degreasing: First, solvent degreasing is used to remove paraffin components by soaking in trichloroethane for 6 hours. Then, thermal degreasing is carried out by heating to 300℃ at a heating rate of 1℃ / min and holding for 0.5 hours, then heating to 600℃ at a heating rate of 3℃ / min and holding for 1 hour, and then heating to 700℃ and holding for 1 hour.

[0067] (6) A segmented sintering process was adopted. The first step was to perform a pre-coarsening treatment, slowly heating to 1000℃ at a heating rate of 4-5℃ / min and holding for 5 hours. The second step was to heat to 1700℃ at a rate of 10-15℃ / min and hold for 1 hour. Hydrogen gas was used for protection during the sintering process. The final sintered product had a porosity of 25%, an average pore diameter of 0.4μm, and an average grain size of 0.8μm.

[0068] Example 3

[0069] (1) The powder raw material is commercially available tungsten powder with a particle size of 400 nm and a purity of more than 99.9%.

[0070] (2) Powder granulation: The nanoparticles are mixed evenly with polyvinyl alcohol (PVA) solution to form a slurry, and then spray-dried to prepare micron-sized granulated powder.

[0071] (3) Preparation of feed: The granulated powder and organic binder are mixed evenly in a mixer, cooled, crushed and granulated to obtain granular feed for injection molding, wherein the volume fraction of powder particles is 55%.

[0072] (4) Injection molding: The feed material is injected into the mold to prepare the green blank. The injection pressure is 120MPa and the feed heating temperature is 160℃.

[0073] (5) Degreasing: First, solvent degreasing is used to remove paraffin components by soaking in trichloroethane for 7 hours. Then, thermal degreasing is carried out by heating to 300℃ at a heating rate of 1℃ / min and holding for 0.5 hours, then heating to 600℃ at a heating rate of 2℃ / min and holding for 1 hour, and then heating to 700℃ and holding for 1 hour.

[0074] (6) A segmented sintering process was adopted. The first step was to perform a pre-coarsening treatment, and the temperature was slowly raised to 1100℃ at a heating rate of 4-5℃ / min and held for 6 hours. The second step was to raise the temperature to 1800℃ at a rate of 10-15℃ / min and hold for 1 hour. Hydrogen gas was used for protection during the sintering process. The final sintered product had a porosity of 24%, an average pore size of 0.43μm, and an average grain size of 0.89μm.

[0075] This invention employs nanoparticle granulation technology to pretreat powder, obtaining micron-sized powder. This ensures the activity of the nanoparticles, resulting in a fine grain structure after sintering, while also giving the powder a certain degree of fluidity, preventing nanoparticle agglomeration and uneven pore distribution. Injection molding is used to achieve good forming performance. By controlling the injection molding pressure and temperature, a green body with a certain powder loading is obtained, resulting in fine pores after sintering. Finally, segmented sintering and pre-coarsening treatment control the grain size, pore size, and uniform distribution during sintering.

[0076] The foregoing has provided a detailed description of a refractory tungsten metal with a uniform microporous structure and its preparation method, as provided in the embodiments of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of this application; furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

[0077] Certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The terms "comprising" and "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising / including but not limited to". "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error. The following descriptions in the specification are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of illustrating the general principles of this application and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0078] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes said element.

[0079] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0080] The foregoing description illustrates and describes several preferred embodiments of this application. However, as previously stated, it should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the application concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be within the protection scope of the appended claims.

Claims

1. A method for preparing refractory tungsten metal with a uniform microporous structure, characterized in that, The preparation method specifically includes the following steps: S1) Using nano-tungsten powder as raw material, adding PVA solution, and mixing to obtain granular feed; The specific steps are as follows: S1.1) Select nano-tungsten powder of a certain diameter and mix it with PVA solution to prepare a slurry. Under vacuum drying conditions, use a centrifugal spray granulator to prepare the slurry into micron-sized granulated powder. The concentration of the PVA solution is 10-30%; the mass fraction of tungsten powder in the slurry is 70-85%. S1.2) The granulated powder is then mixed evenly with a high-molecular organic binder, cooled, crushed, and granulated to produce granular feedstock for injection molding; the nano-tungsten powder has a particle size of 50-400 nm and a purity greater than 99.9%; S2) The granules obtained from S1) are fed into the feedstock and then injection molded to obtain a green body; S3) The green body obtained in S2) is degreased by a combination of solvent degreasing and thermal degreasing to obtain a degreased green body; S4) The degreased blank treated by S3) is sintered and shaped under a protective atmosphere using a segmented sintering method to obtain refractory tungsten metal with a uniform microporous structure. The specific process is as follows: S4.1) First, perform low-temperature sintering; The low-temperature sintering process is as follows: slowly heat to 900-1100℃ at a heating rate of 4-5℃ / min, and hold for 4-8 hours; S4.2) Then, high-temperature and long-term dense sintering is carried out to prepare refractory tungsten metal with a uniform microporous structure; The specific process for dense sintering is as follows: heat to 1400-1800℃ at a rate of 10-15℃ / min and hold for 1-2 hours; The protective atmosphere is hydrogen; the refractory tungsten metal with a uniform microporous structure has a porosity of 20%-50%, an average grain size of less than 1 μm, a pore diameter of ≤0.5 μm, and a variance of no more than 0.

4.

2. The preparation method according to claim 1, characterized in that, The mass fractions of each component in the PVA solution are as follows: PVA 5-20%, dispersant 0.2-5%, and the remainder is deionized water. S1.2) The mass fraction of each component of the polymeric organic binder is: 60-70% paraffin wax, 10-20% polyethylene, 10-15% polypropylene, and 1-5% stearic acid.

3. The preparation method according to claim 1, characterized in that, The injection pressure in S2) is 100-150MPa, and the feeding heating temperature is 80-200℃.

4. The preparation method according to claim 1, characterized in that, The specific process of S3 is as follows: First, the paraffin binder is removed in trichloroethane for 4-10 hours to form certain pore channels; then, thermal degreasing is performed to completely degrease the remaining binder. The thermal degreasing temperature is 300-800℃, the heating rate is 1-5℃ / min, and the holding time is 1-3 hours.

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