Method for preparing diffusion cathode based on corner stacking of refractory metal net

Abstract

The invention discloses a method for preparing a diffusion cathode based on corner stacking of refractory metal nets, and belongs to the field of diffusion cathodes. The multiple layers of tungsten mesh wafers are loaded into a mold in an angle-rotating stacking mode, two-way pressing forming is carried out, and a cathode green body is obtained; then sintering in a pure hydrogen atmosphere of a high-temperature tungsten mesh hydrogen furnace; and sintering and salt leaching are carried out in a pure hydrogen atmosphere, and finally the cathode is obtained. According to the cathode prepared by the method, different porosities and pore structures can be set or adjusted according to needs, so that the diffusion cathode is large in impregnation amount and good in emission performance.

Description

Technical Field

[0001] The invention relates to the technical field of vacuum electronic device manufacturing, and is a method for preparing a novel diffusion cathode. Background Art

[0002] Vacuum electronic devices play an important role in information systems and daily life. They are the "heart" of radar, communication, electronic countermeasures, telemetry and remote control, and precision guidance equipment; in information systems, they are widely used in our work and life as the transmission source of radio and television stations, the repeater of microwave communication and satellite communication, and various display devices for displaying images.

[0003] High frequency, high power and small volume are the development trends of modern microwave vacuum electronic devices. At present, microwave vacuum electronic devices are gradually expanding towards the millimeter wave, submillimeter wave and even terahertz regions. As the core component of such devices, the cathode is required to provide the highest possible current emission density at a suitable operating temperature. The high current density hot cathode is based on a diffusion cathode, and the active material in the diffusion cathode needs to diffuse to the cathode surface through the pores in the cathode. Traditional methods for regulating porosity, such as powder metallurgy, are limited by factors such as powder particle size and morphology, and the resulting cathode porosity is not large. The porosity and pore structure will affect the impregnation amount and diffusion channel of the active material, further affecting the life and emission performance of the cathode. Therefore, the present invention uses a fiber sintering method to stack tungsten meshes with different numbers of layers and different rotation angles to obtain different pore structures with large porosity, and obtains different porosities by controlling the pressing pressure and sintering process.

[0004] In summary, by changing the tungsten mesh rotation angle, sintering process, pressing pressure and other methods to control the cathode porosity and pore structure, the impregnation amount of cathode active material and the diffusion channel of the active material are affected, which affects the emission life and emission performance of the cathode, which is of great significance for the diffusion cathode. Summary of the invention

[0005] The present invention provides a novel preparation method of a diffusion cathode, which utilizes tungsten meshes stacked at different rotation angles to obtain different pore structures, and controls different sintering methods, pressing pressures and other conditions to obtain different porosities and pore structures. A diffusion cathode with high porosity, large impregnation volume and good emission performance is successfully prepared.

[0006] The present invention provides a simple preparation method for preparing a diffusion cathode based on a corner stacking method, which is achieved by:

[0007] A. Cut the tungsten mesh into discs, clean and dry them;

[0008] B. The discs in step A are loaded into a mold in a stacked manner by rotating the angles, and are pressed in two directions to obtain a cathode green body;

[0009] C. sintering the cathode green body obtained in step B in a high temperature tungsten mesh hydrogen furnace in a pure hydrogen atmosphere;

[0010] D. performing an impregnation pretreatment on the sample sintered in step C;

[0011] E. The cathode pre-treated by immersion in step D is sintered and salted in a high-temperature tungsten mesh hydrogen furnace in a pure hydrogen atmosphere to finally obtain a cathode.

[0012] In step A of the above method, a tungsten mesh with a mesh size of 20 to 300, a wire diameter of 60 to 100 μm, and a pore size of 0.1 mm to 1.17 mm is used, ultrasonic cleaning is performed for 5 to 15 minutes, and dehydration is performed by anhydrous ethanol;

[0013] In step B of the above method, the angle stacking refers to the coaxial stacking of multiple layers of discs, with an angle formed between the warps of the tungsten mesh of two adjacent layers of discs; 10 to 60 layers of discs are stacked into a mold, with the angle between the two adjacent layers being plus or minus 0-90°, and bidirectional compression molding is performed with a pressing pressure of 0.2 to 1t, with a holding time of 30 to 60s. After demolding, a cathode green body is obtained, and the surface of the cathode green body is flat, and there is no obvious edge falling phenomenon for the next step of processing; the angle of plus or minus 0-90° means that the angle between the warp of the upper disc and the warp of the lower disc is 0-90° clockwise or 0-90° counterclockwise, and all the warp lines of the upper and lower discs do not completely overlap, and the angle can be adjusted as needed.

[0014] In step C of the above method, the sintering step is to first heat up, linearly heat from room temperature to 1700±50°C over 30 to 90 minutes, keep warm for 30 to 40 minutes, and then cool down, linearly cool from 1700±50°C to room temperature over 30-90 minutes, and the high-purity hydrogen concentration of the pure hydrogen atmosphere is 99.999%.

[0015] In step D of the above method, the salt selected for impregnation is "411" barium aluminate salt (the molar ratio of BaO:CaO:Al2O3 is 4:1:1) or "612" barium aluminate salt (the molar ratio of BaO:CaO:Al2O3 is 6:1:2), and the impregnation is to mix the salt with the binder and stir them evenly, evenly apply them on the cathode surface, or immerse them in a mixed solution of the salt and the binder.

[0016] In step E of the above method, the salt immersion sintering temperature is 1670±10°C and the temperature is kept for 30 to 60 seconds.

[0017] Advantages of the present invention: The cathode prepared by the method of the present invention can be set or adjusted with different porosities and pore structures as required, thereby making the diffusion cathode have a large impregnation amount and good emission performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the process roadmap for cathode preparation;

[0019] Figure 2 This is a schematic diagram of the stacking of tungsten mesh corner angles;

[0020] Figure 3 This is the SEM image of the tungsten mesh and cathode after pressing;

[0021] Figure 4 The pulse emission current density IV characteristic curve of the cathode after immersion in Example 1;

[0022] Table 1 shows the cathode DC emission current density. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with examples, but the present invention is not limited to the following examples.

[0024] Example 1

[0025] A tungsten mesh with 80 mesh and a wire diameter of 40 μm was cut into small discs with a diameter of 3 mm. The small discs were ultrasonically cleaned in deionized water, dehydrated with anhydrous ethanol, and placed on absorbent paper to dry. The adjacent tungsten mesh layers were rotated clockwise at an angle of about 60° and stacked for 10 layers. Figure 2 (b) The cathode green body is loaded into a mold and molded by bidirectional compression molding with a pressing pressure of 0.3t and a holding time of 1min. After demolding, a cathode green body with a flat surface and a height of about 1mm is obtained. The green body is sintered in a high-temperature tungsten mesh hydrogen furnace in a pure hydrogen atmosphere at 1700℃ for 30min to obtain a cathode matrix. The microscopic morphology of the cathode matrix is ​​as follows: Figure 3 (a) is shown. The previously ground "411" barium calcium aluminate salt (BaO:CaO:Al2O3 molar ratio is 4:1:1) is mixed with the binder and stirred evenly, and evenly coated on the cathode surface, placed in a high-temperature hydrogen furnace in a hydrogen atmosphere, and salted at 1670°C for 30 seconds. Subsequently, annealing treatment is carried out in a reducing atmosphere to obtain a diffusion cathode impregnated with alkaline earth metal aluminate. The cathode micromorphology is shown in FIG. Figure 3 As shown in (e), the test results obtained after the cathode was subjected to the DC emission test are as follows Figure 4 .

[0026] Example 2

[0027] The 20-mesh tungsten mesh with a wire diameter of 100 μm was cut into small discs with a diameter of 3 mm. The small discs were placed in deionized water for ultrasonic cleaning. After cleaning, they were dehydrated with anhydrous ethanol and placed on absorbent paper to dry. The adjacent tungsten mesh layers were stacked at an angle of about 60° for 15 layers, loaded into the mold, and molded in two directions with a pressing pressure of 0.5t. The holding time was 1min. After demolding, a cathode green body with a flat surface and a height of about 1mm was obtained. The green body was sintered in a pure hydrogen atmosphere of a high-temperature tungsten mesh hydrogen furnace. The sintering process was 1700℃ for 30min to obtain a cathode matrix. The "411" barium calcium aluminate salt (BaO:CaO:Al2O3 molar ratio of 4:1:1) ground into powder in advance was mixed with a binder and stirred evenly, evenly coated on the cathode surface, placed in a high-temperature hydrogen furnace in a hydrogen atmosphere, and salted at 1670℃ for 30s. Subsequently, an annealing treatment was performed in a reducing atmosphere to obtain a diffusion cathode impregnated with alkaline earth metal aluminate. The test results of the cathode after a DC emission test are shown in Table 1.

[0028] Example 3

[0029] The 80-mesh, 40-μm-diameter tungsten mesh was cut into small discs with a diameter of 3 mm. The discs were ultrasonically cleaned in deionized water, dehydrated with anhydrous ethanol, and dried on absorbent paper. The adjacent tungsten mesh layers were stacked at an angle of about 45° for 20 layers. Figure 2 (c) The cathode green body is placed in a mold and molded by bidirectional compression molding with a pressing pressure of 0.3t and a holding time of 1min. After demolding, a cathode green body with a flat surface and a height of about 1mm is obtained. The green body is sintered in a high-temperature tungsten mesh hydrogen furnace in a pure hydrogen atmosphere at 1700℃ for 30min to obtain a cathode matrix. The microscopic morphology of the cathode matrix is ​​as follows: Figure 3 (b) is shown. The previously ground "411" barium calcium aluminate salt (BaO:CaO:Al2O3 molar ratio is 4:1:1) is mixed with the binder and stirred evenly, and evenly coated on the cathode surface, placed in a high-temperature hydrogen furnace in a hydrogen atmosphere, and salted at 1670°C for 30 seconds. Subsequently, annealing treatment is carried out in a reducing atmosphere to obtain a diffusion cathode impregnated with alkaline earth metal aluminate. The test results of the cathode after DC emission test are shown in Table 1.

[0030] Example 4

[0031] The 100 mesh, 50μm wire diameter tungsten mesh was cut into small discs with a diameter of 3mm. The small discs were ultrasonically cleaned in deionized water, dehydrated with anhydrous ethanol, and placed on absorbent paper to dry. The adjacent tungsten mesh layers were stacked at an angle of about 45° for 15 layers, loaded into the mold, and molded by bidirectional compression molding with a pressing pressure of 0.5t. The holding time was 1min. After demolding, a cathode green body with a flat surface and a height of about 1mm was obtained. The green body was sintered in a pure hydrogen atmosphere of a high-temperature tungsten mesh hydrogen furnace. The sintering process was 1700℃ for 30min to obtain a cathode matrix. The "411" barium calcium aluminate salt (BaO:CaO:Al2O3 molar ratio of 4:1:1) ground into powder in advance was mixed with a binder and stirred evenly, evenly coated on the cathode surface, placed in a high-temperature hydrogen furnace in a hydrogen atmosphere, and salted at 1670℃ for 30s. Subsequently, an annealing treatment was performed in a reducing atmosphere to obtain a diffusion cathode impregnated with alkaline earth metal aluminate. The test results of the cathode after a DC emission test are shown in Table 1.

[0032] Example 5

[0033] The 80-mesh, 40-μm-diameter tungsten mesh was cut into small discs with a diameter of 3 mm. The discs were ultrasonically cleaned in deionized water, dehydrated with anhydrous ethanol, and dried on absorbent paper. The adjacent tungsten mesh layers were stacked at an angle of about 30° for 20 layers. Figure 2 (d) The cathode green body is placed in a mold and molded by bidirectional compression molding with a pressing pressure of 0.3t and a holding time of 1min. After demolding, a cathode green body with a flat surface and a height of about 1mm is obtained. The green body is sintered in a high-temperature tungsten mesh hydrogen furnace in a pure hydrogen atmosphere. The sintering process is 2000℃ for 30min to obtain a cathode matrix. The microscopic morphology of the cathode matrix is ​​as follows: Figure 3 (c) As shown. The previously ground "612" barium calcium aluminate salt (BaO:CaO:Al2O3 molar ratio is 6:1:2) is mixed with the binder and stirred evenly, and evenly coated on the cathode surface, placed in a high-temperature hydrogen furnace in a hydrogen atmosphere, and salted at 1670°C for 30 seconds. Subsequently, annealing treatment is carried out in a reducing atmosphere to obtain a diffusion cathode impregnated with alkaline earth metal aluminate. The test results of the cathode after DC emission test are shown in Table 1.

[0034] Example 6

[0035] The 100 mesh, 50μm wire diameter tungsten mesh was cut into small discs with a diameter of 3mm. The small discs were placed in deionized water for ultrasonic cleaning. After cleaning, they were dehydrated with anhydrous ethanol, placed on absorbent paper to dry, stacked in 15 layers, loaded into the mold, and molded by bidirectional compression molding with a pressing pressure of 1t. The holding time was 1min. After demolding, a cathode green body with a flat surface and a height of about 1mm was obtained. The green body was sintered in a pure hydrogen atmosphere of a high-temperature tungsten mesh hydrogen furnace. The sintering process was 2000℃ for 30min to obtain a cathode substrate with a morphology as shown in FIG. Figure 3 (d) is shown. The previously ground "612" barium calcium aluminate salt (BaO:CaO:Al2O3 molar ratio is 6:1:2) is mixed with the binder and stirred evenly, and evenly coated on the cathode surface, placed in a high-temperature hydrogen furnace in a hydrogen atmosphere, and salted at 1670°C for 30 seconds. Subsequently, annealing treatment is carried out in a reducing atmosphere to obtain a diffusion cathode impregnated with alkaline earth metal aluminate. The test results of the cathode after DC emission test are shown in Table 1.

[0036] Table 1

[0037] Examples <![CDATA[1100℃ b Emission current density (A / cm 2 )]]> 1 7.81 2 7.35 3 7.66 4 7.53 5 7.57 6 7.42

[0038] Excellent pore structure is the basis for obtaining high-performance and long-life cathodes. The present invention controls the cathode porosity and pore structure by changing the tungsten mesh rotation angle, sintering process, and pressing pressure, and adjusts the distribution, impregnation amount, and diffusion channel of the cathode active material, thereby adjusting the reaction rate between the active salt and tungsten. In addition, the appropriate porosity and pore structure affect the impregnation of the active material and the evaporation rate of the active material during the cathode operation, thereby improving the cathode emission performance and life, and providing a new way to regulate the porosity and pore structure of the diffusion cathode.

[0039] The above description is only the main implementation scheme of the present invention, but the present invention is not limited thereto. Any modification, equivalent substitution or improvement made without departing from the core of the present invention should be included in the protection scope of the method name.

Claims

1. A method for preparing a diffusion cathode based on corner stacking of refractory metal mesh, characterized in that: The following steps are involved: A. Cut the tungsten mesh into discs, clean and dry them; B. The discs in step A are loaded into a mold in a stacked manner by rotating the angles, and bidirectionally pressed to obtain a cathode green body; C. sintering the cathode green body obtained in step B in a high temperature tungsten mesh hydrogen furnace in a pure hydrogen atmosphere; D. performing an impregnation pretreatment on the sample sintered in step C; E. The cathode pre-treated by immersion in step D is sintered and salted in a high-temperature tungsten mesh hydrogen furnace in a pure hydrogen atmosphere to finally obtain a cathode.

2. A method for preparing a diffusion cathode based on corner stacking of refractory metal mesh according to claim 1, characterized in that: In step A of the above method, a tungsten mesh with a mesh size of 20 to 300, a wire diameter of 60 to 100 μm, and a pore size of 0.1 mm to 1.17 mm is used, ultrasonic cleaning is performed for 5 to 15 minutes, and dehydration is performed using anhydrous ethanol.

3. A method for preparing a diffusion cathode based on corner stacking of refractory metal mesh according to claim 1, characterized in that: In step B of the above method, 10 to 60 layers of stacked discs are loaded into a mold, the angle between two adjacent layers is plus or minus 0-90°, and bidirectional compression molding is performed with a pressing pressure of 0.2 to 1t. The holding time is 30 to 60s. After demolding, a cathode green body is obtained. The surface of the cathode green body is flat, and there is no obvious edge loss for the next step of processing; the angle of plus or minus 0-90° means that the angle between the warp of the upper disc and the warp of the lower disc is 0-90° clockwise or 0-90° counterclockwise, and all the warp lines of the upper and lower discs do not completely overlap, and the angle can be adjusted as needed.

4. A method for preparing a diffusion cathode based on corner stacking of refractory metal mesh according to claim 1, characterized in that: In step C of the above method, the sintering step is to first heat up, linearly heat from room temperature to 1700±50°C over 30 to 90 minutes, keep warm for 30 to 40 minutes, and then cool down, linearly cool from 1700±50°C to room temperature over 30-90 minutes, and the high-purity hydrogen concentration of the pure hydrogen atmosphere is 99.999%.

5. A method for preparing a diffusion cathode based on corner stacking of refractory metal mesh according to claim 1, characterized in that: In step D of the above method, the salt selected for impregnation is "411" barium aluminate salt (the molar ratio of BaO:CaO:Al2O3 is 4:1:1) or "612" barium aluminate salt (the molar ratio of BaO:CaO:Al2O3 is 6:1:2).

6. A method for preparing a diffusion cathode based on corner stacking of refractory metal mesh according to claim 1, characterized in that: In step D of the above method, the impregnation is to mix the salt and the binder and stir them evenly, and evenly apply them on the cathode surface, or immerse them in a mixed solution of the salt and the binder.

7. A method for preparing a diffusion cathode based on corner stacking of refractory metal mesh according to claim 1, characterized in that: In step E of the above method, the salt immersion sintering temperature is 1670±10°C and the temperature is kept for 30 to 60 seconds.

8. A diffusion cathode prepared by corner stacking of refractory metal meshes, prepared according to the method described in any one of claims 1 to 7.

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