Preparation method of metal porous tungsten filter element

Abstract

The invention discloses a preparation method of a metal porous tungsten filter element, and relates to the technical field of powder metallurgy and refractory metal preparation, the preparation method comprises the following steps: dispersing raw material tungsten powder into nearly spherical narrow-particle-size-distribution standby tungsten powder through a jet mill; the tungsten powder to be used is put into a sheath, and a packaging body is obtained through compaction treatment and vacuumizing treatment; carrying out hot isostatic pressing sintering molding on the packaging body, cooling to room temperature, releasing pressure, and demolding to obtain a sintered body; blowing the sintered body through nitrogen to remove impurities and floating powder on the surface of the sintered body; the blown sintered body is cleaned through an ultrasonic overflow method, and the cleaned sintered body is dried; and carrying out secondary sintering on the dried sintered body in a hydrogen atmosphere to obtain the porous tungsten filter element. The high-quality porous tungsten filtering element which is high in purity, cleanliness and strength, low in oxygen content and uniform in pore diameter distribution can be prepared.

Description

Technical Field

[0001] The invention relates to the technical field of powder metallurgy and refractory metal preparation, and in particular to a method for preparing a metal porous tungsten filter element. Background Art

[0002] Metal tungsten has high melting point, high strength, low vapor pressure, good corrosion resistance, low thermal expansion coefficient, thermal conductivity and electrical conductivity, so it is widely used in aerospace, military, nuclear power, energy and mechanical electronics industries. Porous tungsten has both structural and functional characteristics, and is mainly used in various types of high-temperature filter materials, electronic cathode materials and ionizer materials, such as: used as the base material of the reserve diffusion tungsten hot cathode, and used as a micro tungsten filter for mercury gas-liquid separation in ion rocket engines.

[0003] With the continuous advancement of filtering equipment, more stringent requirements are also placed on the performance of materials. Traditional porous tungsten preparation mostly requires the addition of additives such as adhesives, pore formers, and lubricants. After the tungsten powder is formed and sintered at high temperature, as the additives evaporate, irregular and uneven pores will be formed; some residual impurities form a solid solution with the tungsten powder, and the solid solution will react chemically with the corrosive filtering liquid or gas under high temperature environment, causing the filter element's own particles to loosen and fall off, making the filter element's filtration efficiency low, the filtration performance unstable, and the service life shortened. In order to prepare high-quality tungsten filter elements with high efficiency, stable performance, and long service life, it is necessary to explore a porous tungsten filter element with high purity, high cleanliness, high strength, low oxygen content, and uniformly distributed pore size. Summary of the invention

[0004] The invention provides a method for preparing a metal porous tungsten filter element. The method can prepare a porous tungsten filter element with high purity, high cleanliness, high strength, low oxygen content and uniformly distributed pore diameters.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme:

[0006] In a first aspect, the present invention provides a method for preparing a metal porous tungsten filter element, the method comprising:

[0007] The raw tungsten powder is dispersed by air jet mill to obtain the ready-to-use tungsten powder with nearly spherical narrow particle size distribution;

[0008] The tungsten powder to be used is placed in a package, and subjected to a compaction treatment and a vacuum treatment to obtain a package body;

[0009] The package body is subjected to hot isostatic pressing sintering, and after cooling to room temperature, the package body is depressurized and demolded to obtain a sintered body;

[0010] Purging the sintered body with nitrogen to remove impurities and floating powder on the surface of the sintered body;

[0011] Cleaning the purged sintered body by ultrasonic overflow method, and drying the cleaned sintered body;

[0012] The dried sintered body is subjected to secondary sintering in a hydrogen atmosphere to obtain a porous tungsten filter element.

[0013] In a possible implementation, the package body is subjected to hot isostatic pressing sintering, and after cooling to room temperature, the package body is depressurized and demolded to obtain a sintered body, which specifically includes:

[0014] The package is placed in a hot isostatic press, and maintained at a pressure of 205-220 MPa and a temperature of 1100-1200° C. for 300-360 minutes to sinter the tungsten powder to be used;

[0015] The hot isostatic press was controlled to have a pressure reduction rate of 10 MPa / min and a temperature reduction rate of 5°C / min, and the mold was removed after cooling to room temperature to obtain a sintered body.

[0016] In a possible implementation, after the package is placed in a hot isostatic press, the hot isostatic press increases the pressure to 205-220 MPa at a pressure increase rate of 10 MPa / min, and increases the temperature to 1100-1200° C. at a heating rate of 5° C. / min.

[0017] In a possible implementation, the purged sintered body is cleaned by an ultrasonic overflow method, and the cleaned sintered body is dried, which specifically includes:

[0018] placing the purged sintered body in an isopropyl alcohol cleaning agent, and performing a first cleaning on the sintered body by an ultrasonic overflow method;

[0019] Removing the cleaning agent residue on the sintered body after the first cleaning by circulating deionized water to obtain a sintered body after the second cleaning;

[0020] The sintered body after the second cleaning is dried at a constant temperature.

[0021] In a possible implementation, the isopropyl alcohol cleaning agent is electronic grade isopropyl alcohol with a purity higher than 99.9%;

[0022] The ultrasonic overflow time of the ultrasonic overflow method is 20 to 45 minutes, and the water resistance is greater than 15 MΩ·cm;

[0023] The constant temperature drying is carried out at a temperature of 80 to 90° C. and the drying time is 3 to 4 hours.

[0024] In a possible implementation, the dried sintered body is subjected to secondary sintering in a hydrogen atmosphere to obtain a porous tungsten filter element, which specifically includes:

[0025] The dried sintered body is placed in a tungsten wire sintering furnace, and kept at 1700-1900° C. for 6-8 hours in a hydrogen atmosphere to perform secondary sintering on the sintered body;

[0026] The tungsten wire sintering furnace is taken out of the furnace after the temperature of the furnace drops to room temperature, thereby obtaining a porous tungsten filter element.

[0027] In a possible implementation, before the sintered body is subjected to secondary sintering at 1700-1900° C. for 6-8 hours in a hydrogen atmosphere, the method further comprises:

[0028] The hydrogen entering the tungsten wire sintering furnace is purified to remove moisture and oxygen in the hydrogen and reduce the dew point of the hydrogen to below -90°C.

[0029] In a possible implementation, the purity of the tungsten powder to be used is 99.99%, and the average particle size is 4-6 μm.

[0030] In a possible implementation, in the jet mill dispersion process, the jet mill is a fluidized bed jet mill;

[0031] The rotation speed of the fluidized bed jet mill is 0-3600 rpm, the feed in each batch is 2-4 kg, and the grinding air pressure is 0.2-0.6 MPa.

[0032] In a possible implementation, the roughness of the inner wall of the sheath is less than 0.1.

[0033] In practical applications, the preparation method of the metal porous tungsten filter element provided by the embodiment of the present invention is as follows: first, the raw tungsten powder is dispersed by air flow milling to be a standby tungsten powder with a nearly spherical narrow particle size distribution. In this step, no adhesive, pore-forming agent or lubricant is added to the raw tungsten powder, thereby ensuring the high purity, pollution-free and corrosion resistance of the raw tungsten powder and simplifying the manufacturing process; secondly, the standby tungsten powder is placed in a package, and a package body is obtained by vibration and vacuum treatment; thirdly, the package body is hot isostatic pressing sintering to obtain a sintered body. This step adopts hot isostatic pressing. The method is used to make the tungsten powder to be used be subjected to the combined effects of high temperature and high pressure at the same time, thereby strengthening the pressing and sintering process, significantly reducing the sintering temperature of the tungsten powder, improving the strength of the tungsten powder material, and simplifying the process flow; then, impurities and floating powder on the surface of the sintered body are removed by nitrogen purging, and loose particles and other impurity particles on the sintered body are removed by ultrasonic overflow method to improve the cleanliness of the sintered body; finally, the dried sintered body is subjected to secondary sintering in a hydrogen atmosphere to prepare a porous tungsten filter element with high purity, high cleanliness, high strength, low oxygen content and uniformly distributed pore size. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A flowchart of a method for preparing a metal porous tungsten filter element provided by an embodiment of the present invention;

[0035] Figure 2 A 1000-fold scanning image of a porous tungsten filter element prepared by a method for preparing a metal porous tungsten filter element provided in Example 1 of the present invention;

[0036] Figure 3 A 1000-fold scanning image of a porous tungsten filter element prepared by a method for preparing a metal porous tungsten filter element provided in Example 2 of the present invention;

[0037] Figure 4 This is a 1000x scan image of a porous tungsten filter element prepared by the method for preparing a metal porous tungsten filter element provided in Example 3 of the present invention. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] In the following, the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present disclosure, unless otherwise specified, "multiple" means two or more. In addition, the use of "based on" or "according to" means openness and inclusiveness, because the process, steps, calculations or other actions "based on" or "according to" one or more of the conditions or values ​​may be based on additional conditions or values ​​beyond the described values ​​in practice.

[0040] In order to prepare a porous tungsten filter element with high purity, high cleanliness, high strength, low oxygen content and uniform pore size distribution, an embodiment of the present invention provides a method for preparing a metal porous tungsten filter element.

[0041] like Figure 1 As shown, an embodiment of the present invention provides a method for preparing a metal porous tungsten filter element, the method comprising:

[0042] Step 101: The raw tungsten powder is dispersed by a jet mill to obtain a nearly spherical tungsten powder with a narrow particle size distribution for use.

[0043] Among them, the raw material tungsten powder is non-spherical tungsten powder. Airflow mill dispersion treatment is a technology that uses high-speed airflow to grind and disperse materials. Its core principle is to spray dry, oil-free compressed air or superheated steam through a nozzle at high speed to form a high-speed jet, which drives the material to move at high speed, causing collision and friction between the materials and crushing. The crushed material arrives at the grading area with the airflow, and the material that meets the fineness requirements is collected by the collector, and the material that does not meet the requirements is returned to the crushing chamber for continued crushing until the required fineness is reached. Compared with traditional grinding methods, the energy consumption of airflow mills is reduced by an average of 30% to 40%, and its efficient working method reduces unnecessary energy consumption.

[0044] Furthermore, the purity of the tungsten powder to be used is 99.99%, and the average particle size is 4-6 μm.

[0045] Furthermore, in the jet mill dispersion process, the jet mill is a fluidized bed jet mill.

[0046] The rotation speed of the fluidized bed jet mill is 0-3600rpm, the feed in each batch is 2-4kg, and the grinding air pressure is 0.2-0.6MPa.

[0047] In an embodiment of the present invention, a fluidized bed air flow mill is used to grade non-spherical tungsten powder, and high-purity nitrogen is used as a jet carrier to carry the tungsten powder. Each batch of feed is 2 to 4 kg, the grinding gas pressure is 0.2 to 0.6 MPa, and the rotation speed is 0 to 3600 rpm. Finally, a nearly spherical polyhedral high-purity tungsten powder with a purity of 99.99% is obtained, and the average particle size of the tungsten powder is distributed between 4 and 6 μm.

[0048] Step 102: put the tungsten powder to be used into the package, and obtain a package body through vibration and vacuum treatment.

[0049] In this embodiment, the sleeve is made of 45 steel, with a wall thickness of 2 mm, an inner diameter of 28 mm, and a length of 50 mm. The inner positioning ring of the sleeve is made of 304L, with a diameter of 15 mm and a length of 45 mm. The inner wall of the sleeve and the inner positioning ring are mechanically mirror polished and then chemically mirror polished to ensure that the contact surface between the inner wall of the sleeve, the positioning ring and the tungsten powder is flat, bright, traceless, pit-free, and free of metal disturbance layers.

[0050] 348-365 g of the tungsten powder to be used is loaded into the package, and then the tungsten powder to be used is compacted by mechanical vibration for 120-180 seconds, and finally the package is vacuumed.

[0051] Furthermore, the roughness of the inner wall of the sleeve is less than 0.1.

[0052] Specifically, the surface roughness of the inner wall of the sleeve is polished to less than 0.1 by mechanical mirror polishing.

[0053] In order to further improve the cleanliness of the porous tungsten filter element, before the tungsten powder to be used is loaded into the sleeve, an isopropyl alcohol cleaning agent is used, and the sleeve is cleaned by ultrasonic cleaning, and the cleaned sleeve is dried.

[0054] Step 103 , hot isostatic pressing and sintering are performed on the package body, and after cooling to room temperature, the package body is depressurized and demolded to obtain a sintered body.

[0055] Specifically, by means of hot isostatic pressing, the tungsten powder to be used is gradually nucleated and crystallized under high temperature and high pressure to form a sintering neck.

[0056] Further, the package body is subjected to hot isostatic pressing sintering, and after cooling to room temperature, the package body is depressurized and demolded to obtain a sintered body, which specifically includes:

[0057] The package is placed in a hot isostatic press, and maintained at a pressure of 205-220 MPa and a temperature of 1100-1200° C. for 300-360 minutes to sinter the tungsten powder to be used.

[0058] The hot isostatic press was controlled to have a pressure reduction rate of 10 MPa / min and a temperature reduction rate of 5°C / min, and the mold was released after cooling to room temperature to obtain a sintered body.

[0059] Furthermore, after the package is placed in a hot isostatic press, the hot isostatic press increases the pressure to 205-220 MPa at a pressure increase rate of 10 MPa / min, and increases the temperature to 1100-1200° C. at a heating rate of 5° C. / min.

[0060] Step 104 , purge the sintered body with nitrogen to remove impurities and floating powder on the surface of the sintered body.

[0061] Since impurities and residual floating powder are introduced during the demolding process of the sintered body, the impurities and floating powder on the surface of the sintered body can be removed by purging the sintered body with nitrogen.

[0062] Step 105 , cleaning the purged sintered body by ultrasonic overflow method, and drying the cleaned sintered body.

[0063] Furthermore, step 105 specifically includes:

[0064] The purged sintered body is placed in an isopropyl alcohol cleaning agent, and the sintered body is first cleaned by an ultrasonic overflow method;

[0065] Residues of cleaning agent on the sintered body after the first cleaning are removed by circulating deionized water to obtain a sintered body after the second cleaning;

[0066] The sintered body after the second cleaning is dried at a constant temperature.

[0067] Further, the isopropyl alcohol cleaning agent is electronic grade isopropyl alcohol with a purity higher than 99.9%;

[0068] The ultrasonic overflow time of the ultrasonic overflow method is 20 to 45 minutes, and the water resistance is greater than 15MΩ·cm;

[0069] The drying temperature of constant temperature drying is 80-90℃, and the drying time is 3-4h.

[0070] Step 106: Under a hydrogen atmosphere, the dried sintered body is subjected to secondary sintering to obtain a porous tungsten filter element.

[0071] Furthermore, step 106 specifically includes:

[0072] The dried sintered body is placed in a tungsten wire sintering furnace and kept at 1700-1900°C for 6-8 hours in a hydrogen atmosphere to perform secondary sintering on the sintered body;

[0073] After the temperature of the tungsten wire sintering furnace drops to room temperature, the tungsten wire is taken out of the furnace to obtain a porous tungsten filter element.

[0074] In order to further reduce the oxygen content of the porous tungsten material and provide a good sintering atmosphere, the method further includes: keeping the temperature at 1700-1900°C for 6-8 hours in a hydrogen atmosphere before the secondary sintering of the sintered body:

[0075] The hydrogen entering the tungsten wire sintering furnace is purified to remove moisture and oxygen from the hydrogen and reduce the dew point of the hydrogen to below -90°C.

[0076] By using the preparation method of the present invention, a porous tungsten filter element can be prepared with an average pore size of 0.8 to 1 μm, a porosity of 20 to 25%, and various impurity contents less than 5 ppm. The porous tungsten filter element can filter highly corrosive liquids and gases and work continuously for 300 hours without deformation or particle shedding.

[0077] Furthermore, the preparation method of the present invention needs to be carried out in a clean room, and the hot isostatic pressing sintering and secondary sintering need to be carried out in a Class 10,000 clean room, and the remaining steps need to be carried out in a Class 100 clean room.

[0078] In practical applications, the preparation method provided by the embodiment of the present invention is firstly subjected to a dispersion treatment of the raw tungsten powder by a jet mill to obtain a standby tungsten powder with a nearly spherical narrow particle size distribution. In this step, no adhesive, pore-forming agent or lubricant is added to the raw tungsten powder, thereby ensuring the high purity, pollution-free and corrosion-resistant properties of the raw tungsten powder and simplifying the manufacturing process.

[0079] Secondly, the tungsten powder to be used is put into the package, and a package body is obtained through vibration and vacuum treatment.

[0080] Next, the package body is subjected to hot isostatic pressing and sintering to obtain a sintered body. This step adopts hot isostatic pressing to subject the tungsten powder to be used to the combined effects of high temperature and high pressure, thereby strengthening the pressing and sintering process, significantly reducing the sintering temperature of the tungsten powder, improving the strength of the tungsten powder material, and simplifying the process flow.

[0081] Afterwards, impurities and floating powder on the surface of the sintered body are removed by nitrogen purging, and loose particles and other impurity particles on the sintered body are removed by ultrasonic overflow method to improve the cleanliness of the sintered body.

[0082] Finally, the dried sintered body is subjected to secondary sintering in a hydrogen atmosphere, thereby preparing a porous tungsten filter element with high purity, high cleanliness, high strength, low oxygen content and uniformly distributed pore size.

[0083] Example 1

[0084] In Example 1 of the present invention, a method for preparing a metal porous tungsten filter element specifically includes:

[0085] Step 101: The raw tungsten powder is dispersed by a jet mill to obtain a nearly spherical tungsten powder with a narrow particle size distribution for use.

[0086] The purity of the tungsten powder to be used is 99.99%, and the average particle size is 4.9 μm; the air flow mill dispersion treatment is achieved by a fluidized bed air flow mill, and the rotation speed of the fluidized bed air flow mill is 3000 rpm, the feed per batch is 2.2 kg, and the grinding air pressure is 0.4 MPa.

[0087] Step 102: put the tungsten powder to be used into the package, and obtain a package body through vibration and vacuum treatment.

[0088] Among them, the sleeve is made of 45 steel, with a wall thickness of 2mm, an inner diameter of 28mm and a length of 50mm. The internal positioning ring of the sleeve is made of 304L, with a diameter of 15mm and a length of 45mm. The inner wall of the sleeve and the internal positioning ring are first mechanically mirror polished to make the roughness of the inner wall of the sleeve less than 0.1, and then chemical solution mirror polishing is performed to ensure that the contact surface between the inner wall of the sleeve, the positioning ring and the tungsten powder is flat, bright, traceless, pit-free, and free of metal disturbance layer.

[0089] Before loading the tungsten powder to be used into the sheath, the sheath is cleaned with isopropyl alcohol cleaning agent and ultrasonic cleaning, and the cleaned sheath is dried.

[0090] 350 g of tungsten powder to be used was loaded into the package, and then the tungsten powder to be used was compacted by mechanical vibration for 150 seconds, and finally the package was vacuumed.

[0091] Step 103, placing the package body in a hot isostatic press, maintaining the pressure and temperature at 205 MPa and 1100°C for 360 minutes, so that the tungsten powder to be used is sintered and formed; then controlling the hot isostatic press to reduce the pressure at a rate of 10 MPa / min and a temperature at a rate of 5°C / min, and demolding after cooling to room temperature to obtain a sintered body.

[0092] Step 104 , purge the sintered body with nitrogen to remove impurities and floating powder on the surface of the sintered body.

[0093] Step 105 , cleaning the purged sintered body by ultrasonic overflow method, and drying the cleaned sintered body.

[0094] Specifically, the purged sintered body is placed in an electronic grade isopropyl alcohol cleaning agent with a purity higher than 99.9%, and the sintered body is cleaned for the first time by an ultrasonic overflow method; wherein the ultrasonic overflow time for the first cleaning is 30 minutes, and the water resistance is 18 MΩ·cm.

[0095] The cleaning agent residue on the sintered body after the first cleaning is removed by circulating deionized water to obtain the sintered body after the second cleaning; wherein the ultrasonic overflow time of the second cleaning is 20 minutes, and the water resistance is 18 MΩ·cm.

[0096] The sintered body after the second cleaning is dried at a constant temperature; wherein the drying temperature of the constant temperature drying is 80° C., and the drying time is 4 hours.

[0097] Step 106, placing the dried sintered body in a tungsten wire sintering furnace, keeping it at 1700°C for 8 hours in a hydrogen atmosphere, and performing secondary sintering on the sintered body; then, after the temperature of the tungsten wire sintering furnace drops to room temperature, taking it out of the furnace to obtain a porous tungsten filter element.

[0098] Among them, before the secondary sintering, the hydrogen entering the tungsten wire sintering furnace needs to be purified to remove moisture and oxygen in the hydrogen and reduce the dew point of the hydrogen to below -90°C.

[0099] Example 2

[0100] The difference between Example 2 of the present invention and Example 1 is that:

[0101] In step 101, the purity of the tungsten powder to be used is 99.99%, and the average particle size is 5.2 μm; the rotation speed of the fluidized bed jet mill is 3400 rpm, the feed per batch is 3.0 kg, and the grinding pressure is 0.5 MPa.

[0102] In step 102, 358 g of tungsten powder to be used is loaded into the package, and then the loaded tungsten powder to be used is compacted by mechanical vibration for 160 seconds, and finally the package is vacuumed.

[0103] In step 103, the pressure and temperature are maintained at 215 MPa and 1150° C. for 340 minutes to sinter the tungsten powder to be used.

[0104] In step 105, the purged sintered body is placed in an electronic grade isopropyl alcohol cleaning agent with a purity higher than 99.9%, and the sintered body is cleaned for the first time by an ultrasonic overflow method; wherein the ultrasonic overflow time for the first cleaning is 30 minutes, and the water resistance is 17 MΩ·cm.

[0105] The cleaning agent residue on the sintered body after the first cleaning is removed by circulating deionized water to obtain the sintered body after the second cleaning; wherein the ultrasonic overflow time of the second cleaning is 30 minutes, and the water resistance is 17 MΩ·cm.

[0106] The sintered body after the second cleaning is dried at a constant temperature; wherein the drying temperature of the constant temperature drying is 85° C., and the drying time is 3.5 hours.

[0107] In step 106, the dried sintered body is placed in a tungsten wire sintering furnace and kept at 1800° C. for 7 hours in a hydrogen atmosphere to perform secondary sintering on the sintered body.

[0108] Example 3

[0109] The difference between Example 3 of the present invention and Example 1 is that:

[0110] In step 101, the purity of the tungsten powder to be used is 99.99%, and the average particle size is 6 μm; the rotation speed of the fluidized bed jet mill is 3600 rpm, the feed per batch is 4 kg, and the grinding pressure is 0.6 MPa.

[0111] In step 102, 365 g of tungsten powder to be used is loaded into the package, and then the loaded tungsten powder to be used is compacted by mechanical vibration for 180 seconds, and finally the package is vacuumed.

[0112] In step 103, the pressure and temperature are maintained at 220 MPa and 1200° C. for 300 minutes to sinter the tungsten powder to be used.

[0113] In step 105, the purged sintered body is placed in an electronic grade isopropyl alcohol cleaning agent with a purity higher than 99.9%, and the sintered body is cleaned for the first time by an ultrasonic overflow method; wherein the ultrasonic overflow time for the first cleaning is 45 minutes, and the water resistance is 16 MΩ·cm.

[0114] The cleaning agent residue on the sintered body after the first cleaning is removed by circulating deionized water to obtain a sintered body after the second cleaning; wherein the ultrasonic overflow time of the second cleaning is 45 minutes, and the water resistance is 16 MΩ·cm.

[0115] The sintered body after the second cleaning is dried at a constant temperature; wherein the drying temperature of the constant temperature drying is 90° C., and the drying time is 3 hours.

[0116] In step 106, the dried sintered body is placed in a tungsten wire sintering furnace and kept at 1900° C. for 6 hours in a hydrogen atmosphere to perform secondary sintering on the sintered body.

[0117] like Figures 2 to 4 As shown, they are 1000 times scanning images of the porous tungsten prepared in Examples 1 to 3. As can be seen from the figure, the pore size and pore distribution of the porous tungsten prepared in Examples 1 to 3 are uniform, and there are no impurities and pollutants. Therefore, the metal porous tungsten filter element prepared by the preparation method of the present invention has high purity, high cleanliness and uniform pore size distribution.

[0118] After testing, the oxygen content of the porous tungsten filter element prepared by the present invention is 0.003%, which is much lower than the surface oxide layer of the traditional chemical filter. Therefore, compared with the existing chemical filter, the oxygen content of the porous tungsten filter element of the present invention is lower, which can effectively reduce the probability of the redox reaction between the filter and the filtered liquid or gas to generate oxides during the filtration process, thereby reducing the risk of filter particles falling off.

[0119] According to "Determination of radial crushing strength of sintered metal bushing (GB / T 6804-2008)", the porous tungsten filter elements prepared by the preparation methods of Examples 1 to 3 were respectively subjected to crushing strength tests to obtain a crushing strength test table, as shown in Table 1:

[0120] Table 1 Crushing strength test table

[0121] serial number Example 1 Example 2 Example 3 Crushing strength (MPa) 301 309 325

[0122] As shown in Table 1, the crushing strength of the filter elements prepared in Examples 1 to 3 of the present invention is above 300 MPa, which is much higher than the actual filtering working pressure. Therefore, when under pressure, the integrity of the filter structure can be guaranteed and the service life of the filter can be extended.

[0123] The porous tungsten filter elements prepared in Examples 1 to 3 were respectively operated for 300 hours under simulated working conditions, and the number of particles of different sizes in every 500 ml of filtrate was detected. Three groups of data were taken for each example to obtain a particle number statistical table, as shown in Table 2:

[0124] Table 2 Particle quantity statistics

[0125]

[0126] It can be seen from Table 2 that after the porous tungsten filter elements prepared in Examples 1 to 3 of the present invention continuously run for 300 hours under simulated working conditions, the number of particles in the filtrate with a particle size ≥ 0.5 μm is relatively large. As the particle size of the detected particles increases, the average number of particles contained in every 500 ml of filtrate gradually decreases, and the number of particles in the filtrate with a particle size ≥ 1 μm is significantly reduced. This shows that the porous tungsten filter elements prepared in Examples 1 to 3 can effectively filter particles of 1 μm and above, and there is almost no particle shedding phenomenon of the filter element itself during the filtration process.

[0127] The preparation method of the porous tungsten filter element of the present invention strictly controls the particle size, morphology and impurity content of the tungsten powder itself, adjusts the processing technology and post-treatment technology while controlling the raw tungsten powder, and prepares high-quality porous tungsten filter elements with high strength, corrosion resistance, low oxidation, no pollution, controllable pore size and porosity, uniform pore distribution, and no particle shedding during the filtration process, thereby realizing independent innovation of the core filtration process and providing excellent filter elements for the preparation of various consumables such as high-purity liquids and gases.

[0128] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing a metal porous tungsten filter element, characterized in that: include: The raw tungsten powder is dispersed by air jet mill to obtain the ready-to-use tungsten powder with nearly spherical narrow particle size distribution; The tungsten powder to be used is placed in a package, and subjected to a compaction treatment and a vacuum treatment to obtain a package body; The package body is subjected to hot isostatic pressing sintering, and after cooling to room temperature, the package body is depressurized and demolded to obtain a sintered body; Purging the sintered body with nitrogen to remove impurities and floating powder on the surface of the sintered body; Cleaning the purged sintered body by ultrasonic overflow method, and drying the cleaned sintered body; The dried sintered body is subjected to secondary sintering in a hydrogen atmosphere to obtain a porous tungsten filter element.

2. The method for preparing the metal porous tungsten filter element according to claim 1, characterized in that: The package body is subjected to hot isostatic pressing sintering and then, after cooling to room temperature, the package body is depressurized and demolded to obtain a sintered body, which specifically includes: The package is placed in a hot isostatic press, and maintained at a pressure of 205-220 MPa and a temperature of 1100-1200° C. for 300-360 minutes to sinter the tungsten powder to be used; The hot isostatic press was controlled to have a pressure reduction rate of 10 MPa / min and a temperature reduction rate of 5°C / min, and the mold was removed after cooling to room temperature to obtain a sintered body.

3. The method for preparing the metal porous tungsten filter element according to claim 2, characterized in that: After the package is placed in a hot isostatic press, the hot isostatic press increases the pressure to 205-220 MPa at a pressure increase rate of 10 MPa / min, and increases the temperature to 1100-1200° C. at a heating rate of 5° C. / min.

4. The method for preparing the metal porous tungsten filter element according to claim 1, characterized in that: The purged sintered body is cleaned by an ultrasonic overflow method, and the cleaned sintered body is dried, specifically comprising: placing the purged sintered body in an isopropyl alcohol cleaning agent, and performing a first cleaning on the sintered body by an ultrasonic overflow method; Removing the cleaning agent residue on the sintered body after the first cleaning by circulating deionized water to obtain a sintered body after the second cleaning; The sintered body after the second cleaning is dried at a constant temperature.

5. The method for preparing a metal porous tungsten filter element according to claim 4, wherein the isopropyl alcohol cleaning agent is electronic grade isopropyl alcohol with a purity higher than 99.9%; The ultrasonic overflow time of the ultrasonic overflow method is 20 to 45 minutes, and the water resistance is greater than 15 MΩ·cm; The constant temperature drying is carried out at a temperature of 80 to 90° C. and the drying time is 3 to 4 hours.

6. The method for preparing the metal porous tungsten filter element according to claim 1, characterized in that: The dried sintered body is subjected to secondary sintering in a hydrogen atmosphere, specifically comprising: The dried sintered body is placed in a tungsten wire sintering furnace, and kept at 1700-1900° C. for 6-8 hours in a hydrogen atmosphere to perform secondary sintering on the sintered body; The tungsten wire sintering furnace is taken out of the furnace after the temperature thereof drops to room temperature, thereby obtaining a porous tungsten filter element.

7. The method for preparing the metal porous tungsten filter element according to claim 6, characterized in that: Before the sintered body is subjected to secondary sintering at 1700-1900° C. in a hydrogen atmosphere for 6-8 hours, the method further comprises: The hydrogen entering the tungsten wire sintering furnace is purified to remove moisture and oxygen in the hydrogen and reduce the dew point of the hydrogen to below -90°C.

8. The method for preparing the metal porous tungsten filter element according to claim 1, characterized in that: The purity of the tungsten powder to be used is 99.99%, and the average particle size is 4-6 μm.

9. The method for preparing the metal porous tungsten filter element according to claim 1, characterized in that: In the jet mill dispersion process, the jet mill is a fluidized bed jet mill; The rotation speed of the fluidized bed jet mill is 0-3600 rpm, the feed in each batch is 2-4 kg, and the grinding air pressure is 0.2-0.6 MPa.

10. The method for preparing the metal porous tungsten filter element according to claim 1, characterized in that: The roughness of the inner wall of the sheath is less than 0.1.

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