A method for preparing a high-life doped tungsten bar

Abstract

This invention relates to the field of metallurgical processing technology, specifically to a method for preparing long-life doped tungsten strips. This invention overcomes the problem of short service life in existing tungsten strips. After adding dopant and composite surfactant to blue tungsten oxide and mixing them uniformly, hydrogen reduction is performed followed by the addition of a combined binder. Layered pressing is then carried out using a layered filling and multi-point filling method to obtain a green compact. This compact is then subjected to staged high-temperature sintering and acid washing. Alumina is coated onto the surface of the acid-washed semi-finished product using trimethylaluminum and oxygen as raw materials to obtain a long-life doped tungsten strip. This invention improves the density and high-temperature oxidation resistance of the doped tungsten strip by changing the amount of blue tungsten oxide added, the component ratio of the dopant, the amount of dopant, the combined binder, and the composite surfactant, adjusting the pressing pressure, the temperature and time of different stages of high-temperature sintering, and the deposition temperature and time during alumina coating, thereby extending the service life of the doped tungsten strip.

Description

Technical Field

[0001] This invention relates to the field of metallurgical processing technology, specifically to a method for preparing high-lifetime doped tungsten bars. Background Technology

[0002] Tungsten-doped bars play a crucial role in the lighting and heating industries. In electric arc furnaces, melting furnaces, glass melting furnaces, electron beam welding, and vacuum melting and casting processes, the operating temperature of tungsten-doped bars reaches over 1500℃. To ensure that the tungsten-doped bars maintain a low oxidation rate during prolonged high-temperature operation, they need excellent high-temperature oxidation resistance to extend their service life and reduce operating costs. To improve the high-temperature oxidation resistance of tungsten-doped bars, the traditional preparation method involves adding dopant elements to tungsten oxide, then preparing doped tungsten powder through hydrogen reduction and acid leaching, and finally obtaining the tungsten-doped bars through pressing and sintering. The uniformity and adhesion between the raw tungsten oxide and the dopant affect the density of the resulting tungsten-doped bar, thus influencing its high-temperature oxidation resistance. Generally, higher density provides better high-temperature oxidation resistance. In the aforementioned application scenarios, tungsten bars can take various shapes, including not only strips and rods, but also plates, blocks, and meshes. Conventional pressing methods often result in poor density uniformity when preparing tungsten bars with complex shapes, leading to cracking and oxidation at high temperatures. Doped tungsten bars prepared by vertical melting sintering show limited improvement in oxidation resistance at high temperatures and cannot effectively extend their service life. Medium-frequency sintering technology can achieve uniform heating within the material and has a precise temperature control device that can accurately control the temperature during the sintering process, reducing the risk of over- or under-burning. It is characterized by high efficiency, energy saving, and environmental friendliness.

[0003] To extend the service life of doped tungsten strips, a method for preparing long-life doped tungsten strips is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing long-life doped tungsten strips. This invention overcomes the problem of short service life of existing tungsten strips. After adding dopant and composite surfactant to blue tungsten oxide and mixing them evenly, hydrogen reduction is performed followed by the addition of a combined binder. A layered pressing process using layered filling and multi-point filling methods is employed to obtain a green compact. This compact is then subjected to staged high-temperature sintering and acid washing. Alumina is coated onto the surface of the acid-washed semi-finished product using trimethylaluminum and oxygen as raw materials, resulting in a long-life doped tungsten strip. This invention improves the density and high-temperature oxidation resistance of the doped tungsten strip by changing the amount of blue tungsten oxide added, the component ratio of the dopant, the amount of dopant, the combined binder, and the composite surfactant, adjusting the pressing pressure, the temperature and time of different stages of high-temperature sintering, and the deposition temperature and time during alumina coating, thereby extending the service life of the doped tungsten strip.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing a high-lifetime doped tungsten strip, comprising the following steps, by weight:

[0007] S1 mixes 95.2-98.6 parts of blue tungsten oxide, 2.6-4.8 parts of dopant and 0.23-0.59 parts of composite surfactant, and then ball-mills for 30 minutes to obtain doped tungsten oxide; the dopant is silicon dioxide, aluminum oxide, potassium oxide and rare earth element oxide; the rare earth element oxide is lanthanum oxide;

[0008] S2 preheats the doped tungsten oxide at 400℃ for 3 hours, then reduces it at 900-1100℃ for 3 hours under a hydrogen atmosphere at a rate of 10℃ / min. After slow cooling, 1.1-2.7 parts of combined binder are added to granulate the tungsten doped particles.

[0009] S3 fills the doped tungsten particles into the container using layered filling and multi-point filling methods, and then uses cold isostatic pressing to form a doped tungsten strip green blank; the doped tungsten strip green blank is placed in a medium-frequency sintering furnace for high-temperature sintering to obtain a sintered doped tungsten strip semi-finished product, which is then cooled with the furnace and acid-washed with a mixed acid solution, cleaned with deionized water and ethanol solvent, and then dried to obtain an acid-washed doped tungsten strip semi-finished product.

[0010] S4 uses vapor deposition to coat the surface of acid-washed doped tungsten strip semi-finished product with an aluminum oxide film, thus obtaining a high-lifetime doped tungsten strip.

[0011] Preferably, the dopant is obtained by mixing silicon dioxide, aluminum oxide, potassium oxide and lanthanum oxide in a ratio of 0.8:0.6-2.7:0.85:1.2 by mass.

[0012] Preferably, the composite surfactant is obtained by mixing polyethylene glycol and 3-aminopropyltriethoxysilane in a mass ratio of 3.1:2.3.

[0013] Preferably, the combined binder is obtained by mixing paraffin wax and stearic acid in a mass ratio of 7.4:2.8.

[0014] Preferably, the combined operation steps of layered filling and multi-point filling are as follows: First filling: 1 / 3 of the mass of doped tungsten particles is filled at the top, bottom, left, right and center points of the bottom of the container, respectively, and after being spread evenly, it is compacted by cold isostatic pressing under a pressure of 350-580 MPa; Second filling: 1 / 3 of the mass of doped tungsten particles is filled, and the steps of the first filling are repeated, and after being spread evenly, it is compacted by cold isostatic pressing under a pressure of 220-470 MPa; Third filling: 1 / 3 of the mass of doped tungsten particles is filled, and the steps of the first filling are repeated, and after being spread evenly, it is compacted by cold isostatic pressing under a pressure of 130-390 MPa.

[0015] Preferably, the S3 high-temperature sintering is carried out in a hydrogen atmosphere.

[0016] Preferably, the S3 high-temperature sintering is divided into a preheating stage, a sintering stage, and a tempering stage. The preheating stage has a heating rate of 10℃ / min, and after heating to 850℃, it is held for 1.5-3.0h. The sintering stage is as follows: after the preheating stage, the temperature is increased to 1850-2260℃ at 8℃ / min and held for 4-12h to obtain sintered tungsten bars. The tempering stage is as follows: after the sintering stage, the sintered tungsten bars are cooled to 1380℃ at 5℃ / min and held for 4-8h, and then cooled to room temperature with the furnace to obtain sintered doped tungsten bar semi-finished product.

[0017] Preferably, the S3 pickling operation steps are as follows: immerse the sintered doped tungsten strip semi-finished product in the mixed acid solution for 30 minutes, take it out, rinse it with pure water and dry it to obtain the pickled doped tungsten strip semi-finished product; the mixed acid solution is obtained by mixing nitric acid and hydrofluoric acid in a volume ratio of 6.4:3.6.

[0018] Preferably, the method for coating with an alumina film is as follows: Acid-washed and doped tungsten strip semi-finished product is placed on a support in the vapor deposition reaction chamber. After evacuation, the heating system is turned on, and the deposition temperature in the vapor deposition reaction chamber is 850-1150℃. Aluminum precursor gas and oxygen source gas are introduced into the reaction chamber, and the reaction chamber pressure is 5×10⁻⁶. -2 The deposition time is 45-75 minutes; the heating system is turned off, and the reaction chamber is allowed to cool naturally to room temperature to obtain high-lifetime doped tungsten strips.

[0019] Preferably, the aluminum precursor gas is trimethylaluminum, and the flow rate of trimethylaluminum is 50 cm³ / s. 3 / min; the oxygen source gas is oxygen, and the oxygen flow rate is 150 cm³ / min. 3 / min.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. Silica, potassium oxide, aluminum oxide, and rare earth element oxides, as additives in the preparation of long-life doped tungsten strips, have a significant impact on the oxidation resistance of the doped tungsten strips. They can lower the melting point of tungsten, improve thermal stability and densification of the tungsten strips, saving energy while enhancing wear resistance and high-temperature oxidation resistance, thus extending the lifespan of the doped tungsten strips. Alumina and lanthanum oxide form a composite oxide, lanthanum aluminate, which acts as a grain boundary strengthening agent in the doped tungsten strips. At high temperatures, alumina and silica react to form an aluminum silicate phase, promoting the densification process of the doped tungsten strips. This phase acts as a liquid phase to promote particle bonding, helping to eliminate porosity during sintering. The aluminum silicate phase can also lower the sintering temperature of the doped tungsten strips, thereby reducing energy consumption and shortening sintering time. Adding a surfactant can ensure uniform distribution of the dopant in the system, preventing agglomeration and ensuring uniform distribution of the aluminum silicate phase and lanthanum aluminate. By changing the proportion of aluminum oxide in the dopant, and the amounts of blue tungsten oxide, dopant, lanthanum oxide, and composite surfactant, a high-lifespan doped tungsten strip with a density of 16.9 g / cm³ was obtained. 3 The weight gain due to high-temperature oxidation was 20.1 g / cm³. 2 .

[0022] 2. Paraffin wax exhibits good fluidity at room temperature, acting as a bridge between tungsten powder particles to enhance interparticle bonding and facilitate molding into doped tungsten strips of the desired shape. Stearic acid, a fatty acid, acts as a binder and lubricant, helping to fill the gaps between tungsten powder particles during pressing, thereby reducing the porosity of the final product. Furthermore, paraffin wax and stearic acid readily volatilize and decompose during sintering, promoting densification and reducing deformation and cracking. The two complement each other, contributing to an increased lifespan of the doped tungsten strips. By varying the amount of the combined binder added, a high-lifespan doped tungsten strip with a density of 17.2 g / cm³ was obtained. 3 No deformation or cracking was observed.

[0023] 3. In the process of pressing doped tungsten particles into green blanks, layered and multi-point filling methods are used to fill the container with doped tungsten particles. Each layer is pressed separately to improve the uniform density of the pressed green blanks with complex shapes. By changing the pressure of each pressing, the density of the pressed green blank is increased, and the density of the high-lifetime doped tungsten strips obtained is 17.6 g / cm³. 3 .

[0024] 4. The high-temperature sintering process plays a crucial role in the performance of the doped tungsten strips. This invention involves three stages of high-temperature sintering: preheating, sintering, and tempering. The preheating stage allows the binder to volatilize and decompose; the sintering stage improves the high-temperature oxidation resistance of the doped tungsten strips; and the tempering stage eliminates stress in the doped tungsten strips, extending their lifespan. Using a hydrogen atmosphere for sintering removes residual carbon black from the binder. By changing the temperature and time of the high-temperature sintering process, the high-lifespan doped tungsten strips achieved a high-temperature oxidation weight gain of 13.2 g / cm³. 2 .

[0025] 5. Using trimethylaluminum and oxygen as raw materials, alumina is obtained by reacting the two through vapor deposition. This alumina is then coated onto the surface of doped tungsten strips, effectively improving high-temperature oxidation resistance and extending service life. By changing the heating temperature and deposition time, the high-temperature oxidation rate of the resulting long-life doped tungsten strips reached 7.2 g / cm³. 2 . Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the high-temperature oxidation weight gain of Examples 52, 55-63 and Comparative Example 9 of the present invention. Detailed Implementation

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0028] Please see Figure 1 This invention provides a method for preparing high-lifetime doped tungsten strips, the technical solution of which is as follows:

[0029] The material information involved in this invention is as follows:

[0030] Blue tungsten oxide CAS: 1314-35-8; Potassium oxide CAS: 12136-45-7; Aluminum oxide CAS: 11092-32-3; Cerium oxide CAS: 1306-38-3; Polyethylene glycol CAS: 25322-68-3; 3-Aminopropyltriethoxysilane CAS: 919-30-2; Paraffin wax CAS: 68476-81-3; Stearic acid CAS: 57-11-4; Hydrogen CAS: 1333-74-0; Nitric acid CAS: 7697-37-2; Hydrofluoric acid CAS: 7664-39-3; Trimethylaluminum CAS: 75-24-1; Oxygen CAS: 7782-44-7.

[0031] Example 1

[0032] SiO2, silica, alumina, potassium oxide, and lanthanum oxide were mixed in a mass ratio of 0.8:0.6:0.85:1.2 to obtain a dopant; polyethylene glycol and 3-aminopropyltriethoxysilane were mixed in a mass ratio of 3.1:2.3 to obtain a composite surfactant. 95.2 parts of blue tungsten oxide, 2.6 parts of the dopant, and 0.23 parts of the composite surfactant were mixed and then ball-milled at high energy for 30 min to obtain doped tungsten oxide.

[0033] S2 mixes paraffin and stearic acid in a mass ratio of 7.4:2.8 to obtain a combined binder; preheats doped tungsten oxide at 400℃ for 3 hours, then reduces it at 1050℃ for 3 hours under a hydrogen atmosphere at a rate of 10℃ / min, and after slow cooling, adds 1.1 parts of the combined binder to granulate and obtain doped tungsten particles.

[0034] S3 fills the container with doped tungsten particles using a layered and multi-point filling method. The first filling consists of 1 / 3 of the mass of doped tungsten particles: 1 / 15 of the mass of doped tungsten particles are filled at the top, bottom, left, right, and center points of the bottom of the container, spread evenly, and then compacted under cold isostatic pressing at a pressure of 350 MPa. The second filling consists of 1 / 3 of the mass of doped tungsten particles, repeating the steps of the first filling, spreading evenly, and then compacted under cold isostatic pressing at a pressure of 220 MPa. The third filling consists of 1 / 3 of the mass of doped tungsten particles, repeating the steps of the first filling, spreading evenly, and then compacted under cold isostatic pressing at a pressure of 130 MPa.

[0035] The doped tungsten bar green billet was placed in a medium-frequency sintering furnace and sintered at high temperature in a hydrogen atmosphere. The high-temperature sintering was divided into a preheating stage, a sintering stage, and a tempering stage. In the preheating stage, the heating rate was 10℃ / min, and the temperature was raised to 850℃ and held for 1.5h. In the sintering stage, after the preheating stage, the temperature was raised to 1850℃ at 8℃ / min and held for 4h to obtain sintered tungsten bars. In the tempering stage, after the sintering stage, the sintered tungsten bars were cooled to 1380℃ at 5℃ / min and held for 4h. The temperature was then cooled to room temperature with the furnace to obtain a sintered doped tungsten bar semi-finished product. Nitric acid and hydrofluoric acid were mixed at a volume ratio of 6.4:3.6 to obtain a mixed acid solution. The sintered doped tungsten bar semi-finished product was immersed in the mixed acid solution for 30min, then rinsed with pure water and dried to obtain an acid-washed doped tungsten bar semi-finished product.

[0036] S4 places the acid-washed, doped tungsten strip semi-finished product on a support in the vapor deposition reaction chamber. After evacuation, the heating system is turned on to set the deposition temperature in the reaction chamber to 850°C. Trimethylaluminum and oxygen are introduced into the reaction chamber at a flow rate of 50 cm³ / h. 3 / min; oxygen flow rate is 150cm 3 / min. The reaction chamber pressure is 5×10 -2The deposition time was 45 minutes; the heating system was turned off, and the reaction chamber was allowed to cool naturally to room temperature to obtain a high-lifetime doped tungsten strip.

[0037] Example 2-19

[0038] The reaction parameters and conditions are the same as those in Example 1, as shown in Table 1.

[0039] Table 1 Reaction parameters and conditions for Examples 1-19

[0040]

[0041] Comparative Example 1

[0042] The reaction parameters and conditions were the same as in Example 1, except that alumina was not added.

[0043] Comparative Example 2

[0044] The reaction parameters and conditions were the same as in Example 1, except that no dopant was added.

[0045] Comparative Example 3

[0046] The reaction parameters and conditions were the same as in Example 1, except that no composite surfactant was added.

[0047] Example 20 Density and High-Temperature Oxidation Weight Gain Test

[0048] The high-lifetime doped tungsten bars of Examples 1-19 and Comparative Examples 1-3 were weighed at room temperature using a precision balance. The initial weight was recorded, and the bars were placed in a quartz boat and then heated to 1500°C in a high-temperature furnace. After the temperature stabilized, timing was started. The furnace atmosphere was pure oxygen. After 1 hour, the heating was turned off, and the high-lifetime doped tungsten bars were allowed to cool naturally to room temperature inside the furnace. The oxidized weight of the samples was then recorded. Oxidation weight gain was calculated: the ratio of the weight difference before and after oxidation to the surface area of ​​each high-lifetime doped tungsten bar was calculated, i.e., the high-temperature oxidation weight gain. The density of the high-lifetime doped tungsten bars of Examples 1-19 and Comparative Examples 1-3 was determined using the Archimedes displacement method. The results are shown in Table 2.

[0049] Table 2 Density and High-Temperature Oxidation Weight Gain of Examples 1-19 and Comparative Examples 1-3

[0050]

[0051] Silica, potassium oxide, aluminum oxide, and rare earth element oxides, as additives in the preparation of long-life doped tungsten strips, have a significant impact on the oxidation resistance of the doped tungsten strips. Alumina can promote the bonding between tungsten particles, improve the overall structural strength and oxidation resistance of the doped tungsten strip, and enhance the structural and oxidation resistance of the tungsten strip by changing the sintering behavior of tungsten powder, thereby improving the overall performance and lifespan of the doped tungsten strip. Simultaneously, the doping of aluminum oxide can increase the density of the doped tungsten strip, resulting in a higher density. As shown in Tables 1 and 2, in Examples 1-5, increasing the proportion of aluminum oxide in the dopant improved the density and high-temperature oxidation resistance of the high-life doped tungsten strips. Silica plays a stabilizing and improving role in the preparation process, enhancing the structural and oxidation resistance of the doped tungsten strip, thereby improving its stability and lifespan under high-temperature conditions. The addition of potassium oxide can improve high-temperature deformation performance. Before hydrogen reduction of tungsten, the addition of potassium oxide can improve the stability of the doped tungsten strip under high-temperature conditions, reducing sagging and deformation caused by thermal expansion. Under high-temperature conditions, the addition of lanthanum oxide can reduce the growth rate of the oxide film on the surface of the doped tungsten strip, inhibiting the oxidation reaction by altering oxidation kinetics, thereby improving the high-temperature oxidation resistance of the doped tungsten strip. Alumina and lanthanum oxide form a composite oxide, lanthanum aluminate, which acts as a grain boundary strengthening agent in the doped tungsten strip. At high temperatures, alumina and silica react to form an aluminum silicate phase, promoting the densification process of the doped tungsten strip. This phase acts as a liquid phase to promote particle bonding, helping to eliminate porosity during sintering. The aluminum silicate phase can also lower the sintering temperature of the doped tungsten strip, thereby reducing energy consumption and shortening sintering time. In Examples 6-9, by increasing the amount of dopant added to increase the amounts of silica, potassium oxide, and lanthanum oxide, the density of the high-lifespan doped tungsten strips increased, and the weight gain from high-temperature oxidation decreased, indicating improved high-temperature oxidation resistance and contributing to extended service life. The higher the amount of blue tungsten oxide added, the higher the purity of tungsten in the product and the better its high-temperature resistance. In Examples 10-14, increasing the amount of blue tungsten oxide helps improve the density of the high-lifetime doped tungsten strips, increasing both density and high-temperature oxidation resistance. Polyethylene glycol and 3-aminopropyltriethoxysilane, as surfactants, improve the dispersibility of the dopant, ensuring uniform distribution of the aluminosilicate and lanthanum aluminate phases and preventing agglomeration of components. In Examples 15-19, increasing the amount of composite surfactant improves the overall uniformity of the doped tungsten strips, helping each component to fully function. In Example 18, the mass ratio of silicon dioxide, alumina, potassium oxide, and lanthanum oxide in the dopant was 0.8:2.1:0.85:1.2; the dopant addition amount was 4.3 parts by mass; the blue tungsten oxide addition amount was 98.0 parts by mass; and the composite surfactant addition amount was 0.53 parts by mass. This resulted in the highest-performance high-lifetime doped tungsten strip with a density of 16.9 g / cm³.3 High-temperature oxidation resulted in a weight gain of 20.1 mg / cm³. 2 In Comparative Example 1, the density of the high-lifetime doped tungsten strip prepared without the addition of alumina was 15.5 g / cm³. 3 High-temperature oxidation resulted in a weight gain of 34.8 mg / cm³. 2 In Comparative Example 2, the density of the high-lifetime doped tungsten strip prepared without added dopant was 14.1 g / cm³. 3 High-temperature oxidation resulted in a weight gain of 40.1 mg / cm³. 2 In Comparative Example 3, without the addition of a composite surfactant, the density of the high-lifetime doped tungsten strip was 15.8 g / cm³. 3 High-temperature oxidation resulted in a weight gain of 38.2 mg / cm³. 3 .

[0052] Examples 21-24

[0053] The reaction parameters and conditions of Example 18 are different as shown in Table 3.

[0054] Comparative Example 4

[0055] The reaction parameters and conditions were the same as in Example 18, except that stearic acid was not added.

[0056] Comparative Example 5

[0057] The reaction parameters and conditions were the same as in Example 18, except that no combined adhesive was added.

[0058] Example 25: Density Test and Appearance

[0059] The density of the high-lifetime doped tungsten strips in Examples 18, 21-24, and Comparative Examples 4-5 was determined by Archimedes' displacement method, and their appearance was observed. The results are shown in Table 3.

[0060] Table 3. Density and appearance of Examples 18, 21-24, and Comparative Examples 4-5

[0061]

[0062] In the preparation process, paraffin wax and stearic acid play complementary roles. During the pressing stage: Paraffin wax, with its good fluidity at room temperature, acts as a bridge between tungsten powder particles, enhancing interparticle bonding and reducing friction. This makes the tungsten powder flow more easily and distributes more evenly during pressing, contributing to the formation of a uniform green body. Stearic acid acts as a binder, helping the powder particles to bond better. During the high-temperature sintering stage: The volatilization of paraffin wax may lead to pore formation, while the liquid phase produced by the decomposition of stearic acid helps the sintering and densification of tungsten particles, reducing porosity. In summary, paraffin wax and stearic acid, in the preparation of doped tungsten strips, influence the pressing and sintering behavior of the powder, thereby improving the density and appearance of the doped tungsten strips and extending their service life. As shown in Table 3, an appropriate amount of combined binder can improve density and appearance; in Example 23, adding 2.3 parts by weight of the combined binder resulted in a high-lifespan doped tungsten strip with a density of 17.2 g / cm³. 3 No deformation or cracking was observed. However, paraffin wax volatilizes during sintering. If volatilization is incomplete or excessive, it may leave pores inside the doped tungsten strip, thereby reducing its density and causing defects on the surface of the sintered doped tungsten strip. As shown in Comparative Example 4, without the addition of stearic acid, the high-lifetime doped tungsten strip prepared by paraffin wax bonding had a density of 15.8 g / cm³. 3 Slight deformation and cracks were observed; in Comparative Example 5, without the addition of a binder, the density of the high-lifetime doped tungsten strip was 15.4 g / cm³. 3 Deformation and cracking occurred.

[0063] Examples 26-38

[0064] The reaction parameters and conditions of Example 23 are different as shown in Table 4.

[0065] Comparative Example 6

[0066] Referring to the parameters and conditions in Example 23, the difference is that the doped tungsten particles are filled in one go, and after being flattened, they are cold isostatically pressed at a pressure of 550 MPa to obtain tungsten strip green blanks.

[0067] Example 39 Density Test

[0068] The density of the high-lifetime doped tungsten strips in Examples 23, 26-38 and Comparative Example 6 was determined using the Archimedes displacement method, and the data were recorded. The results are shown in Table 4.

[0069] Table 4 Densities of Examples 23, 26-38, and Comparative Example 6

[0070]

[0071] Multi-layer, multi-point packing and pressing helps improve the density uniformity of doped tungsten strips because the pressure of each layer can be controlled individually, resulting in a more uniform density distribution throughout the volume. Higher density usually leads to better mechanical properties. By precisely controlling the pressing pressure, multi-layer, multi-point packing can produce tungsten strips with higher density, which helps to extend the service life of the doped tungsten strips. Simultaneously, uniform pressing leads to a more uniform grain structure, thus affecting the sintering behavior and final properties of the doped tungsten strips. A higher pressure is typically required during the first packing to ensure good densification of the bottom powder, which contributes to the stability of the entire pressed body. As shown in Table 4, in Examples 23 and 26-29, increasing the pressing pressure of the first packing resulted in an increasing density of the doped tungsten strips. In Example 28, when the first pressing pressure was 530 MPa, the density of the high-lifespan doped tungsten strip was 17.3 g / cm³. 3 The pressure of the intermediate layer is slightly lower than that of the bottom layer because the bottom layer already provides stable support. In Examples 29-34, the second pressing pressure is 220-470 MPa. In Example 33, when the second pressing pressure is 420 MPa, the density of the high-lifetime doped tungsten strip is 17.5 g / cm³. 3 The top layer only needs to ensure the densification of the top powder, and does not need to provide support like the bottom layer. The pressure is between 130-390 MPa. In Example 37, the third filling and pressing pressure was 330 MPa, and the resulting high-lifetime doped tungsten strip had a density of 17.6 g / cm³. 3 In the comparative example, the tungsten bar green blank was prepared using a one-time filling and pressing method, resulting in poor pressing effect and a high-lifetime doped tungsten bar density of 16.1 g / cm³. 3 .

[0072] Examples 40-53

[0073] The reaction parameters and conditions of Example 37 are different, as shown in Table 5.

[0074] Comparative Example 7

[0075] The reaction parameters and conditions were the same as in Example 37, except that the preheating stage was not performed on the tungsten strip green billet.

[0076] Comparative Example 8

[0077] The reaction parameters and conditions were the same as in Example 37, except that the sintered tungsten strips were not subjected to a tempering stage.

[0078] Example 54 High-Temperature Oxidation Weight Gain Test

[0079] The high-lifetime doped tungsten bars of Examples 37, 40-53, and Comparative Examples 7-8 were weighed at room temperature using a precision balance. The initial weight was recorded, and the bars were placed in a quartz boat and then heated to 1500°C in a high-temperature furnace. After the temperature stabilized, timing was started. The furnace atmosphere was pure oxygen. After 1 hour, the heating was turned off, and the high-lifetime doped tungsten bars were allowed to cool naturally to room temperature inside the furnace. The samples were then removed, and their post-oxidation weight was measured and recorded. Oxidation weight gain was calculated: the ratio of the weight difference before and after oxidation to the surface area of ​​each high-lifetime doped tungsten bar was calculated, i.e., the high-temperature oxidation weight gain. The results are shown in Table 5.

[0080] Table 5. Weight gain due to high-temperature oxidation in Examples 37, 40-53, and Comparative Examples 7-8

[0081]

[0082] The high-temperature sintering process plays a crucial role in the performance of the doped tungsten strips. This invention involves high-temperature sintering in three stages: preheating, sintering, and tempering. The preheating stage allows the paraffinic stearic acid in the binder to fully volatilize and decompose. Extending the holding time allows the bubbles generated during this decomposition to fully escape, reducing porosity and making the composition and structure of the doped tungsten strip more uniform, thus increasing density. It also helps the doped tungsten strip material to gradually heat up, reducing thermal stress caused by sudden temperature changes, reducing internal defects, preventing cracks during processing, improving high-temperature oxidation resistance, and extending service life. As shown in Table 5, in Examples 37 and 40-42, extending the preheating stage holding time reduced the high-temperature oxidation weight gain of the high-lifespan doped tungsten strips. In Example 41, when the preheating stage holding time was 2.5 hours, the high-temperature oxidation weight gain of the high-lifespan doped tungsten strip was 16.7 mg / cm³. 2 In Comparative Example 7, without preheating of the doped tungsten strip green billet, the high-lifetime doped tungsten strip exhibited a high-temperature oxidation weight gain of 24.1 mg / cm³. 2 The sintering temperature and holding time are also important factors affecting high-temperature oxidation resistance. Appropriate sintering temperature and time can optimize the mechanical properties and thermal stability of doped tungsten strips, thus improving their high-temperature oxidation resistance. The temperature and time during sintering affect the grain size and shape, thereby influencing the material's microstructure and overall performance. Longer sintering times result in higher densification. However, excessively long sintering times may lead to excessive grain growth, reducing mechanical properties. In Examples 43-51, the sintering temperature and time were adjusted to improve the high-temperature oxidation resistance of the obtained high-lifetime doped tungsten strips; in Example 50, the sintering temperature was 2260℃, the holding time was 10h, and the high-lifetime doped tungsten strips exhibited a high-temperature oxidation weight gain of 14.0 mg / cm³. 2The tempering stage can eliminate the internal stress of the doped tungsten strip, preventing cracking due to stress concentration during use. In Example 52, the holding time during the tempering stage was 6 hours, and the high-lifetime doped tungsten strip obtained had a high-temperature oxidation weight gain of 13.2 mg / cm³. 2 In Comparative Example 8, the sintered tungsten strip was not subjected to a tempering stage, and the high-lifetime doped tungsten strip obtained had a high-temperature oxidation weight gain of 25.9 mg / cm³. 2 .

[0083] Examples 55-63

[0084] The reaction parameters and conditions of Example 52 are different, as shown in Table 6.

[0085] Comparative Example 9

[0086] The reaction parameters and conditions were the same as in Example 52, except that no alumina coating was applied.

[0087] Example 64 High-Temperature Oxidation Weight Gain Test

[0088] The high-lifetime doped tungsten bars of Examples 52, 55-63, and Comparative Example 9 were weighed at room temperature using a precision balance. The initial weight was recorded, and the bars were placed in a quartz boat. They were then placed in a high-temperature furnace and heated to 1500°C. After the temperature stabilized, timing was started. The furnace atmosphere was pure oxygen. After 1 hour, heating was turned off, and the high-lifetime doped tungsten bars were allowed to cool naturally to room temperature inside the furnace. The samples were then removed and weighed after oxidation, and the data was recorded. Oxidation weight gain was calculated: the ratio of the weight difference before and after oxidation to the surface area of ​​each high-lifetime doped tungsten bar was calculated, i.e., the high-temperature oxidation weight gain. The results are shown in Table 6 and... Figure 1 As shown.

[0089] Table 6. Weight gain due to high-temperature oxidation in Examples 52, 55-63, and Comparative Example 9

[0090]

[0091] Trimethylaluminum reacts with oxygen to form alumina, which is deposited on the surface of tungsten strips to increase their high-temperature oxidation resistance. When depositing alumina films on tungsten strips, deposition temperature and time are two key parameters that significantly affect the performance of the final product. Higher deposition temperatures promote the crystallization of the alumina film, forming a film with a good crystalline structure, resulting in better thermal stability of the doped tungsten strip, which helps improve high-temperature oxidation resistance and extend service life. Lower temperatures may lead to the formation of amorphous or microcrystalline structures, which may reduce the film's hardness and thermal stability. However, excessively high temperatures may cause a mismatch in the coefficients of thermal expansion between the alumina film and the tungsten substrate, resulting in significant thermal stress, excessive interfacial reaction between the alumina and tungsten substrates, forming a fragile interfacial layer, reducing adhesion, and leading to film cracking or detachment. (See Table 6 and...) Figure 1 As shown, in Examples 52 and 55-60, increasing the deposition temperature gradually reduced the high-temperature oxidation weight gain of the high-lifetime doped tungsten strips. In Example 59, at a deposition temperature of 1100°C, the high-temperature oxidation weight gain of the high-lifetime doped tungsten strip was 9.6 mg / cm³. 2 The deposition time affects the concentration of gases and the degree of reaction within the reaction chamber, thus influencing the film growth rate and final structure. Extending the deposition time helps improve film uniformity, increase alumina thickness, and enhance its oxidation resistance and mechanical protection. In Example 62, with a deposition time of 65 min, the high-lifetime doped tungsten strip exhibited a high-temperature oxidation weight gain of 7.2 mg / cm³. 2 In Comparative Example 9, without alumina coating, the high-lifetime doped tungsten strip exhibited a high-temperature oxidation weight gain of 16.9 mg / cm³. 2 .

[0092] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-lifetime doped tungsten strip, characterized in that: The method for preparing the high-lifetime doped tungsten strip, by weight, includes the following steps: S1 mixes 95.2-98.6 parts of blue tungsten oxide, 2.6-4.8 parts of dopant, and 0.23-0.59 parts of composite surfactant, and then ball-mills the mixture for 30 minutes to obtain doped tungsten oxide; the dopant is a mixture of silicon dioxide, aluminum oxide, potassium oxide, and rare earth element oxides; the rare earth element oxide is lanthanum oxide; S2 preheats the doped tungsten oxide at 400°C for 3 hours, then raises the temperature to 1050°C at 10°C / min under a hydrogen atmosphere and reduces it for 3 hours. After slow cooling, 1.1-2.7 parts of a combined binder are added to granulate the doped tungsten particles. The combined binder is a mixture of paraffin wax and stearic acid in a mass ratio of 7.4:2.

8. S3 The doped tungsten particles are filled into a container using layered filling and multi-point filling methods, and cold isostatic pressing is used to form a doped tungsten strip green blank; the doped tungsten strip green blank is placed in a medium-frequency sintering furnace for high-temperature sintering to obtain a sintered doped tungsten strip semi-finished product, which is then cooled in the furnace and acid-washed with a mixed acid solution, cleaned with deionized water and ethanol solvent, and dried to obtain an acid-washed doped tungsten strip semi-finished product. The high-temperature sintering process is divided into a preheating stage, a sintering stage, and a tempering stage. The preheating stage involves a heating rate of 10°C / min, heating to 850°C and holding for 1.5-3.0 hours. The sintering stage involves further heating at 8°C / min to 1850-2260°C and holding for 4-12 hours to obtain sintered tungsten bars. The tempering stage involves cooling the sintered tungsten bars at 5°C / min to 1380°C and holding for 4-8 hours, then cooling them to room temperature in the furnace to obtain the sintered doped tungsten bar semi-finished product. S4 uses vapor deposition to coat the surface of the acid-washed doped tungsten strip semi-finished product with an alumina film to obtain the high-lifetime doped tungsten strip.

2. The method for preparing a high-lifetime doped tungsten strip according to claim 1, characterized in that: The dopant is obtained by mixing silicon dioxide, aluminum oxide, potassium oxide and lanthanum oxide in a ratio of 0.8:0.6-2.7:0.85:1.2 by mass.

3. The method for preparing a high-lifetime doped tungsten strip according to claim 1, characterized in that: The composite surfactant is obtained by mixing polyethylene glycol and 3-aminopropyltriethoxysilane in a mass ratio of 3.1:2.

3.

4. The method for preparing a high-lifetime doped tungsten strip according to claim 1, characterized in that: The combined layered filling and multi-point filling operation steps are as follows: First filling: 1 / 3 of the mass of the doped tungsten particles is filled at the top, bottom, left, right and center points of the bottom of the container, respectively, and after being spread evenly, it is compacted under a pressure of 350-580 MPa by cold isostatic pressing; Second filling: 1 / 3 of the mass of the doped tungsten particles is filled, and the first filling steps are repeated, and after being spread evenly, it is compacted under a pressure of 220-470 MPa by cold isostatic pressing; Third filling: 1 / 3 of the mass of the doped tungsten particles is filled, and the first filling steps are repeated, and after being spread evenly, it is compacted under a pressure of 130-390 MPa by cold isostatic pressing.

5. The method for preparing a high-lifetime doped tungsten strip according to claim 1, characterized in that: The high-temperature sintering described in S3 is carried out in a hydrogen atmosphere.

6. The method for preparing a high-lifetime doped tungsten strip according to claim 1, characterized in that: The acid washing operation steps described in S3 are as follows: immerse the sintered doped tungsten strip semi-finished product in the mixed acid solution for 30 minutes, take it out, rinse it with pure water and dry it to obtain the acid-washed doped tungsten strip semi-finished product; the mixed acid solution is obtained by mixing nitric acid and hydrofluoric acid in a volume ratio of 6.4:3.

6.

7. The method for preparing a high-lifetime doped tungsten strip according to claim 1, characterized in that: The method for covering the alumina film is as follows: the acid-washed doped tungsten strip semi-finished product is placed on a support in the vapor deposition reaction chamber, a vacuum is drawn, and the heating system is turned on. The deposition temperature in the vapor deposition reaction chamber is 850-1150℃. Aluminum precursor gas and oxygen source gas are introduced into the reaction chamber, and the reaction chamber pressure is 5×10⁻⁶. -2 The deposition time is 45-75 min; the heating system is turned off, and the reaction chamber is allowed to cool naturally to room temperature to obtain the high-lifetime doped tungsten strip.

8. The method for preparing a high-lifetime doped tungsten strip according to claim 7, characterized in that: The aluminum precursor gas is trimethylaluminum, and the flow rate of trimethylaluminum is 50 cm³. 3 / min; the oxygen source gas is oxygen, and the oxygen flow rate is 150 cm³ / min. 3 / min.

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