Active substance for dipping diffusion cathode, dipping diffusion cathode and preparation method of dipping diffusion cathode

Abstract

The invention provides an active substance for a dipping diffusion cathode, the dipping diffusion cathode and a preparation method of the dipping diffusion cathode, and relates to the technical field of dipping diffusion cathode active materials and vacuum electronic device manufacturing. The preparation method of the active substance for dipping the diffusion cathode comprises the following steps: preparing an aqueous solution by taking at least one of water-soluble acetate, nitrate, gluconate, formate and lactate of barium, calcium, aluminum and cerium elements in a molar ratio of (25-40): (2-20): (10-25): (5-20) as a raw material; drying the aqueous solution to obtain a precursor powder material; placing the precursor powder in a protective atmosphere, and heating for 1-4 hours in an environment of 800-1000 DEG C; the invention further provides the active material for the impregnated diffusion cathode, the impregnated diffusion cathode and a preparation method of the impregnated diffusion cathode.

Description

Technical Field

[0001] The present disclosure relates to the technical field of impregnated diffusion cathode active materials and vacuum electronic device manufacturing, and more specifically, to an active material for an impregnated diffusion cathode that can work in a low vacuum environment and has excellent anti-poisoning performance, an impregnated diffusion cathode, and a preparation method thereof. Background Art

[0002] Vacuum electron devices (VEDs) possess unique advantages in high-power, high-frequency applications and are difficult to replace with other devices. They are currently widely used in high-tech fields such as radar, communications, medical treatment, and accelerators. In vacuum electron devices, the cathode provides the necessary electron beam for device operation. Immersed diffusion cathodes, as highly efficient electron sources, are widely used in the manufacture of vacuum electron devices such as klystrons, traveling wave tubes, gyrotrons, and X-ray tubes. When the cathode is heated to high temperatures, the immersed active material reacts with the base metal, producing active elements carrying free electrons that migrate to the cathode surface and adsorb there, resulting in efficient electron emission.

[0003] The impregnated diffusion cathode has undergone nearly 70 years of development. Over the years, in order to meet the development needs of low-power devices to high-power devices, most of the research work has been carried out around how to improve the electron emission capability of the impregnated diffusion cathode, and good results have been achieved. The cathode emission current density has gradually increased from the early 1~5A / cm² to the current 20~50A / cm², and the pulse emission current density has even exceeded 100A / cm². In theory, the electron emission capability of the impregnated diffusion cathode has basically met the needs of existing vacuum device design and manufacturing.

[0004] However, when the cathode is actually applied to devices, especially high-power devices, the cathode emission capability is insufficient. Taking a high-power klystron as an example, as the device duty cycle increases and the pulse width increases, the measured cathode emission value will be lower than the design value. Summary of the Invention

[0005] In view of the above problems, the present disclosure provides an active material for an impregnated diffusion cathode, an impregnated diffusion cathode and a preparation method thereof to improve the low vacuum poisoning resistance, so as to meet the design and manufacturing requirements of the above vacuum electronic devices.

[0006] According to a first aspect of the present disclosure, a method for preparing an active material for an impregnated diffusion cathode is provided, comprising the following steps: preparing an aqueous solution containing at least one of water-soluble acetates, nitrates, gluconates, formates, and lactates of barium, calcium, aluminum, and cerium in a molar ratio of 25-40:2-20:10-25:5-20 as raw materials; drying the aqueous solution to obtain a precursor powder material; and heating the precursor powder under a protective atmosphere at 800-1000°C for 1-4 hours.

[0007] According to an embodiment of the present disclosure, a method includes semi-sealing a precursor powder in a heating dish using a heat-resistant porous material.

[0008] Another aspect of the embodiments of the present disclosure provides an active material for an impregnated diffusion cathode. The active material comprises calcium barium aluminate and barium ceria, and the active material is prepared by the above-mentioned method for preparing the active material for an impregnated diffusion cathode.

[0009] Another aspect of the embodiments of the present disclosure provides an impregnated diffusion cathode, comprising: a substrate and an active material prepared from the above-mentioned active material for the impregnated diffusion cathode; the substrate comprises pores, and the active material is impregnated in the pores of the substrate.

[0010] According to an embodiment of the present disclosure, the substrate is a tungsten sponge substrate, and the porosity of the tungsten sponge substrate is in the range of 22%-25%.

[0011] According to an embodiment of the present disclosure, the surface of the immersion diffusion cathode is covered with a metal film layer and / or an alloy film layer different from the matrix element.

[0012] Another aspect of an embodiment of the present disclosure provides a method for preparing an impregnated diffusion cathode, comprising the following steps: impregnating a substrate into a molten active material under a hydrogen atmosphere; the active material is prepared by the above-mentioned method for preparing an active material for an impregnated diffusion cathode.

[0013] According to an embodiment of the present disclosure, before the step of immersing the substrate in the molten active material, the method includes placing the substrate in an environment of 1600° C. to 1800° C. under a hydrogen atmosphere for 0.5 to 2 hours.

[0014] According to an embodiment of the present disclosure, after the step of immersing the substrate in the molten active material, the method further includes: chemically cleaning the surface of the immersed diffusion cathode.

[0015] According to an embodiment of the present disclosure, the substrate is a tungsten sponge substrate, which is obtained by removing copper from a tungsten copper substrate.

[0016] One or more of the above embodiments have the following beneficial effects:

[0017] The active material component system of the disclosed embodiment enhances the cathode surface stability. The embodiment of the application introduces the rare earth element cerium (Ce) into the traditional barium aluminate system and strictly designs the stoichiometric ratio of each element (molar ratio 25~40:2~20:10~25:5~20) to form a mixture containing barium cerate (BaCeO3) and barium calcium aluminate (Ba5CaAl4O 12 ) composite active material. By comparing the data of Example 1 and Example 2 (vacuum degree 3.5×10 -5Pa, the emission current decreased by 2.3% vs. 27.2%, respectively. This shows that the introduction of cerium enables the active material to react with the tungsten matrix to form more stable atomic groups (such as Ce-O bonds) on the cathode surface, significantly inhibiting the adsorption of impurity gases on active elements (such as Ba), enhancing the surface emission layer's resistance to gas poisoning, and solving the problem of a sudden drop in emission current in traditional cathodes under low vacuum.

[0018] 2. Optimization of the active material synthesis process to enhance its activity: A semi-sealed synthesis process (precursor powders are placed in a high-purity ceramic jar, and the CO2 / NO2 generated by the decomposition of the raw materials is used as the synthesis atmosphere) effectively avoids impurity contamination compared to traditional synthesis methods (the current in Example 3 decreased by 13.6% vs. 2.3% in Example 1). This also promotes the directional formation of calcium barium aluminate and barium ceramate. Combined with a freeze-drying method to prepare a highly dispersible precursor, the activity of the emissive material is increased. After the active elements on the cathode surface are adsorbed by impurities, a replacement reaction can be rapidly completed within the matrix and replenished through pore diffusion (for example, in Example 1, a current of 208 mA was maintained even when the vacuum deteriorated).

[0019] 3. Synergistic effect of matrix treatment, impregnation process and surface cleaning process: The tungsten matrix is ​​purified by high temperature of 1600~1800℃ under hydrogen atmosphere, combined with 1550~1750℃ melt impregnation process to ensure that the active material in the pores of the tungsten matrix is ​​fully impregnated, and the surface chemical cleaning is used to remove floating salt ( Figure 4 The microscopic morphology shows that the pores are fully exposed), which makes the diffusion path of active materials unobstructed, not only improving the cathode activity, but also improving the uniformity of cathode electron emission.

[0020] 4. The embodiments of the present disclosure increase the wettability of the active material to the substrate after melting by selecting a suitable high-temperature purification temperature and atmosphere for the tungsten sponge substrate, lower the impregnation temperature, formulate a melt impregnation process method for the cerium-containing cathode active material, and combine it with chemical cleaning of the cathode surface to reduce the cathode activity loss.

[0021] 5. The embodiments of the present disclosure, through the combined implementation of the above technical solutions, obtain a new impregnated diffusion cathode that exhibits superior anti-poisoning capabilities under low vacuum conditions than traditional impregnated diffusion cathodes, meeting the stringent requirements of devices such as high-power klystrons and space ion thrusters. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above contents and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0023] Figure 1 A flow chart schematically illustrates a method for preparing an active material for an impregnated diffusion cathode according to an embodiment of the present disclosure;

[0024] Figure 2 A flow chart schematically illustrates a method for preparing an impregnated diffusion cathode according to an embodiment of the present disclosure;

[0025] Figure 3 A flow chart schematically illustrates another method for preparing an impregnated diffusion cathode according to an embodiment of the present disclosure;

[0026] Figure 4 This is a surface electron microscopic morphology image of the impregnated diffusion cathode of the disclosed embodiment;

[0027] Figure 5 The XRD spectrum of the cathode active material prepared by the method in Example 1 of the present invention;

[0028] Figure 6 This is a curve showing the emission current of the low vacuum anti-poisoning impregnated diffusion cathode as the vacuum degree decreases in Example 1 of the present invention;

[0029] Figure 7 The XRD spectrum of the cathode active material prepared by the method in Example 2 of the present invention;

[0030] Figure 8 This is a curve showing the emission current of the conventional 612-type impregnated diffusion cathode as the vacuum degree decreases in Example 2 of the present invention;

[0031] It should be noted that, for the sake of clarity, in the drawings used to describe the embodiments of the present disclosure, the sizes of the overall / local structures or overall / local areas may be enlarged or reduced, that is, these drawings are not drawn according to the actual scale. DETAILED DESCRIPTION

[0032] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present disclosure. In the detailed description below, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0033] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise," "include," etc. used herein indicate the presence of the features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0034] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0035] When expressions such as "at least one of A, B, and C, etc." are used, they should generally be interpreted in accordance with the meaning commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0036] Existing impregnated diffusion cathodes have an emission capacity exceeding 100A / cm², which theoretically meets the design and manufacturing requirements of existing vacuum devices. However, when the cathodes are actually used in devices and the operating voltage is increased, the measured cathode emission current density falls below the theoretical design value. This is particularly true in high-power microwave devices, where cathode emission performance is significantly compromised. This is directly related to the rapid deterioration of the device's internal vacuum environment at high output power. The cathode's insufficient resistance to low-vacuum poisoning is a key reason why its ultimate performance fails to meet device requirements.

[0037] In addition, in some emerging engineering fields, such as space ion thrusters, open X-ray tubes, high-power magnetrons and other new devices, most of them require the cathode to work at 10 -5 Pa~10 -3 Vacuum environments with a Pa-level vacuum or even lower place very high demands on the cathode's anti-poisoning capabilities. Traditional impregnated diffusion cathodes lack low-vacuum anti-poisoning capabilities, leading to the following issues during operation: slow cathode startup and long device warm-up times; lower-than-normal cathode emission current density during operation, requiring elevated cathode temperatures for normal device operation; poor electron beam focusing, impacting device performance output; and significantly shortened cathode lifespan. These issues arise from the following: Normal device operation comes at the expense of elevated cathode temperatures, shortening device lifespan.

[0038] In order to solve the problem of insufficient anti-poisoning ability of traditional impregnated diffusion cathodes, the embodiments of the present disclosure propose a new impregnated diffusion cathode that can work stably in a lower vacuum environment and can adapt to the application requirements of special devices such as high-power microwave devices and electric propulsion systems.

[0039] Figure 1 The flowchart of a method for preparing an active material for an impregnated diffusion cathode according to an embodiment of the present disclosure is schematically shown.

[0040] like Figure 1 As shown, this embodiment includes:

[0041] In operation S110 , an aqueous solution is prepared using at least one of water-soluble acetate, nitrate, gluconate, formate, and lactate containing barium, calcium, aluminum, and cerium elements in a molar ratio of 25-40:2-20:10-25:5-20 as a raw material.

[0042] In this embodiment, nitrates containing barium, calcium, aluminum, and cerium in a molar ratio of 25:2:10:5, i.e., barium nitrate, calcium nitrate, aluminum nitrate, and cerium nitrate, can be used as raw materials. This embodiment can also use multiple salts of the four elements as raw materials. For example, one embodiment uses barium acetate, calcium nitrate, aluminum gluconate, and cerium formate containing barium, calcium, aluminum, and cerium in a molar ratio of 40:20:25:20 as raw materials. One embodiment uses barium nitrate, calcium gluconate, aluminum formate, and cerium lactate containing barium, calcium, aluminum, and cerium in a molar ratio of 30:5:15:10 as raw materials. One embodiment uses barium acetate, calcium acetate, aluminum nitrate, and cerium nitrate containing barium, calcium, aluminum, and cerium in a molar ratio of 35:10:20:15 as raw materials. More than one salt of the same element can also be used as a raw material. For example, one embodiment uses barium acetate, barium nitrate, calcium nitrate, aluminum nitrate, and cerium nitrate in a molar ratio of 40:20:10:5 for barium, calcium, aluminum, and cerium as raw materials. Another embodiment uses barium acetate, calcium acetate, aluminum nitrate, cerium formate, cerium acetate, and cerium lactate in a molar ratio of 25:2:25:20 for barium, calcium, aluminum, and cerium as raw materials.

[0043] In operation S120 , the aqueous solution is dried to obtain a precursor powder material.

[0044] In this embodiment, the aqueous solution can be dried to obtain the precursor powder material by spray drying, vacuum drying, freeze drying or the like.

[0045] In operation S130 , the precursor powder is placed in a protective atmosphere and heated at 800 to 1000° C. for 1 to 4 hours.

[0046] In this embodiment, the protective atmosphere can be a reducing atmosphere (such as hydrogen, CO gas), an inert gas (helium, argon), nitrogen, carbon dioxide, nitrogen dioxide gas, a mixed gas of carbon dioxide and nitrogen dioxide, etc. The precursor powder can also be semi-sealed in a heating dish using a heat-resistant porous material. During the heating process, the carbon dioxide and / or nitrogen dioxide gas generated by the decomposition of the precursor powder can serve as a protective atmosphere.

[0047] In this embodiment, in order to further synthesize the precursor powder into an active emissive material, the precursor powder is preferably semi-sealed in a heating dish using a heat-resistant porous material. Specifically, before high-temperature synthesis, permeable alumina powder, expanded perlite, alumina-silica aerogel, foam ceramics, alkali-activated foam materials, etc. can be used to semi-seale the precursor powder in the heating dish. For example, the prepared precursor powder is placed in a high-purity alumina ceramic jar, and a mixed slurry of nitre-cotton solution and alumina powder is evenly applied between the alumina ceramic jar and the ceramic lid as a temporary adhesive (the ceramic container used is not limited to alumina materials, and high-temperature resistant materials such as zirconium oxide and yttrium oxide can also be used). The concentration of the nitre-cotton solution is 1% to 5%, and the particle size of the alumina powder is 25 to 40 μm. The active material precursor powder is semi-sealed in the ceramic jar.

[0048] The precursor is semi-sealed in a heating dish to slow the rate of gas evolution during heating, prevent excess gas from inhibiting the decomposition of the raw materials, and avoid inadequate decomposition of the precursor powder. In this embodiment, the active material precursor is semi-sealed in a clean heating dish before undergoing high-temperature synthesis. This, on the one hand, avoids contamination of the equipment or atmosphere with impurities during the synthesis process, thereby improving product purity. On the other hand, it cleverly utilizes the carbon dioxide and / or nitrogen dioxide atmosphere generated by the high-temperature decomposition of the raw materials to promote the formation of the active materials, calcium barium aluminate and barium cerate, thereby enhancing product activity.

[0049] In this embodiment, the active material synthesis can be a one-step synthesis in a muffle furnace, with a synthesis temperature of 800-1000°C and a holding time of 1-4 hours. The reaction is sufficient and the product is highly active. Specifically, it can be heated in an 800°C environment for 4 hours, or it can be heated at 900°C for 2 hours. Depending on the amount of precursor material used, it can also be heated in an 800°C environment for 1 hour. The synthesis temperature of 800-1000°C and the holding time of 1-4 hours significantly improve the purity and activity of the product. It can also be a step-by-step synthesis, for example, first holding in an 800°C environment for 2 hours, and then holding in a 1000°C environment for 2 hours.

[0050] The effective components of the active material in this embodiment include: cerium, barium, calcium, aluminum, and oxygen elements. By strictly designing and controlling their ratios in the system, the active material immersed in the matrix can react with the matrix to form stable atomic groups on the cathode surface, thereby weakening the binding of impurity gas elements on the cathode surface to the emission-active elements, maintaining the emission capability of the cathode in a low vacuum environment, and improving the anti-poisoning capability.

[0051] In some embodiments of the present disclosure, an aqueous solution can be prepared with a raw material to water mass ratio of 1:7 to 10; for example, the raw material to water mass ratio can be 1:7, 1:10, 1:8, or other intermediate values. The prepared aqueous solution can be freeze-dried to prepare an active material precursor powder. The precursor powder obtained using this method has good uniformity, providing the basic conditions for uniformity and consistency in the preparation of the active material.

[0052] Based on the above-mentioned preparation method of the active material for the impregnated diffusion cathode, the present disclosure also provides an active material for the impregnated diffusion cathode, the active material comprises barium calcium aluminate (Ba5CaAl4O 12 ) and barium cerate (BaCeO3), the active material is prepared by the above-mentioned method for preparing the active material for the impregnation diffusion cathode.

[0053] Based on the above-mentioned method for preparing the active material for the impregnated diffusion cathode, the present disclosure also provides an impregnated diffusion cathode.

[0054] In some embodiments of the present disclosure, the impregnated diffusion cathode comprises: a substrate and an active material prepared by the above-mentioned method for preparing the active material for the impregnated diffusion cathode. The substrate comprises pores, and the active material is impregnated in the pores of the substrate. The substrate of the impregnated diffusion cathode is generally a tungsten substrate. Tungsten has the advantages of high melting point, high hardness, low vapor pressure and good electron emission performance, and is suitable as a substrate material for the impregnated diffusion cathode. In addition to the tungsten substrate, substrates of other materials are also used for the impregnated diffusion cathode, such as a mixed substrate containing tungsten. The mixed substrate is formed by sintering precious metal particles and tungsten particles together.

[0055] The active material immersed in the cathode matrix of this embodiment can react with the matrix and form more stable atomic groups on the cathode surface to weaken the binding of impurity gas elements to the emission-active elements on the cathode surface. The active material of this embodiment has high activity. During the operation of the cathode, once the active elements on the cathode surface are adsorbed by the impurity gas, the active elements can continuously complete the replacement reaction inside the tungsten sponge matrix and quickly diffuse through the pores of the matrix to the cathode surface for replenishment, thereby improving the cathode's anti-poisoning ability. The preparation method of the active material used in this embodiment enhances the reaction between the components and improves the purity and activity of the material.

[0056] In some embodiments of the present disclosure, the substrate is a tungsten sponge substrate, and the porosity of the tungsten sponge substrate is in the range of 22%-25%.

[0057] In some embodiments of the present disclosure, the surface of the impregnated diffusion cathode can be covered with a metal film layer and / or alloy film layer that is different from the matrix element, depending on the emission performance requirements of the device. For example, it can be a single metal film layer or alloy layer of Ir, Os, Pt, etc.; or it can include a single metal film layer and an alloy layer, such as an Ir layer and an Os / Pt alloy layer. After the matrix is ​​impregnated with the above-mentioned active material to form an impregnated diffusion cathode, it is covered with a metal film layer and / or alloy film layer that is different from the matrix element. The emission performance of the impregnated diffusion cathode is further optimized by coating the cathode surface.

[0058] Based on the above-mentioned method for preparing the active material for the impregnated diffusion cathode, the present disclosure also provides a method for preparing the impregnated diffusion cathode.

[0059] In some embodiments of the present disclosure, the active material obtained by the above-described method for preparing an impregnated diffusion cathode active material is used. A substrate is embedded in the active material under a reducing hydrogen atmosphere, and the active material is melt-impregnated. The specific impregnation temperature can be 1550°C to 1750°C. The active material is then impregnated into the porous substrate to form a cathode emitter. The matrix to active material mass ratio can be 20% to 40%. In this embodiment, a reducing hydrogen atmosphere is used as the shielding gas.

[0060] In some embodiments of the present disclosure, before the step of impregnating the substrate with the molten active material, the step includes: placing the substrate in a hydrogen atmosphere at 1600°C to 1800°C and keeping it warm for 0.5 to 2 hours. Before using the active material to impregnate the substrate, the substrate is purified to remove substrate impurities and surface oxidation, thereby improving the subsequent wettability of the active material and the substrate. The purification temperature can be 1600°C, a heating rate of 10°C / min, and a holding time of 2 hours; it can also be 1800°C, a heating rate of 40°C / min, and a holding time of 0.5 hours; or a temperature of 1700°C.

[0061] In some embodiments of the present disclosure, after the substrate is immersed in the molten active material, the process includes chemically cleaning the surface of the impregnated diffusion cathode. This chemical cleaning removes floating salts from the surface and surface pores, allowing the surface pores to leak out, thereby facilitating the diffusion of the active material. The cleaning agent used for chemical cleaning can include acidic cleaning agents (such as hydrochloric acid and nitric acid), alkaline cleaning agents (such as sodium hydroxide solution and sodium carbonate solution), or organic solvent cleaning agents (such as ethanol and acetone). The specific cleaning agent selected depends on the cathode material and the composition of the floating salts.

[0062] In some embodiments of the present disclosure, the substrate is a tungsten sponge substrate, which is obtained by removing copper from a tungsten-copper substrate. For example, the tungsten-copper substrate can be subjected to high-frequency heating and vacuum evaporation at a temperature of 1300°C to 1600°C to obtain a porous tungsten sponge substrate. Alternatively, chemical copper removal methods such as nitric acid, a mixture of nitric acid and tantalum, or high-temperature copper removal in a hydrogen atmosphere can be used to obtain the tungsten sponge substrate.

[0063] Figure 2 A flow chart schematically illustrates a method for preparing an impregnated diffusion cathode according to an embodiment of the present disclosure;

[0064] like Figure 2 As shown, the preparation method of the impregnated diffusion cathode of this embodiment includes:

[0065] In operation S210, the substrate is placed in a hydrogen atmosphere at 1600° C. to 1800° C. for 0.5 to 2 hours.

[0066] In operation S220 , the substrate is immersed in the molten active material under a hydrogen atmosphere.

[0067] In operation S230, after the active material is impregnated, the surface of the impregnated diffusion cathode is chemically cleaned. Specific steps can be referred to the above embodiment and will not be described in detail here.

[0068] Figure 3 A flow chart of another method for preparing an impregnated diffusion cathode according to an embodiment of the present disclosure is schematically shown.

[0069] like Figure 3 As shown, the preparation method of the impregnated diffusion cathode of this embodiment includes:

[0070] In operation S11, a rare earth cerium-containing active material precursor is prepared. A precision balance is used to weigh chemical raw material reagents such as barium acetate, calcium acetate, aluminum nitrate, and cerium nitrate. The reagents are of analytical purity and are weighed in a molar ratio of 25~40:2~20:10~25:5~20. The raw material reagents are prepared into an aqueous solution with a mass ratio of raw material to water of 1:7~10. The prepared solution is freeze-dried to prepare an active material precursor powder material.

[0071] In operation S12, the active material precursor powder is semi-sealed in a container. The precursor powder prepared in step S11 is further synthesized into an active emitting material. Unlike conventional synthesis methods, before high-temperature synthesis, the prepared precursor powder is placed in a high-purity alumina ceramic jar, and a mixed slurry of nitre-cotton solution and alumina powder is used as a temporary adhesive material to be evenly applied between the alumina ceramic jar and the ceramic cover (the ceramic container used is not limited to alumina materials, and high-temperature resistant materials such as zirconium oxide and yttrium oxide can also be used). The concentration of the nitre-cotton solution is 1% to 5%, and the particle size of the alumina powder is 25 to 40 μm. The active material precursor powder is semi-sealed in the ceramic jar.

[0072] In operation S13, the precursor material is synthesized at high temperature to obtain a cerium-containing active material. The active material synthesis is performed in a muffle furnace in one step at a synthesis temperature of 800-1000°C for 1-4 hours. The reaction is sufficient and the obtained product is highly active.

[0073] In operation S21, the cathode substrate is de-coppered to obtain a tungsten sponge substrate. The processed 2.5mm tungsten copper substrate is subjected to high-frequency heating and vacuum evaporation to remove copper at a heating temperature of 1300°C to 1600°C to obtain a porous tungsten sponge substrate with a porosity range of 22%-25%.

[0074] In operation S22, the tungsten sponge substrate is purified at high temperature. The porous tungsten sponge substrate in step S21 is purified at high temperature to remove impurities and surface oxidation from the substrate and improve the wettability of the substrate with the subsequent active material. The high-temperature purification of the tungsten sponge substrate is carried out in a hydrogen atmosphere furnace at a purification temperature of 1600°C to 1800°C, a heating rate of 10°C to 40°C / min, and a holding time of 0.5 to 2 hours.

[0075] In operation S31, the cerium-containing active material is melted at high temperature and impregnated into the pores of the tungsten sponge matrix to obtain a composite emitter. The cerium-containing active material synthesized in step S12 is impregnated into the porous tungsten sponge matrix in step S22 to impregnate the emitting active material. The cathode matrix is ​​buried in the active material at a mass ratio of 20% to 40% of the cathode tungsten sponge matrix to the active material. Under a reducing gas hydrogen atmosphere, the active material is melted and impregnated at a temperature of 1550°C to 1750°C. The active material is impregnated into the porous matrix to obtain a cathode emitter.

[0076] In operation S32, the emitter surface is chemically cleaned to remove the floating salt in the surface pores to obtain the target cathode. The cathode emitter prepared in step S31 is chemically cleaned to remove the floating salt on the surface and the surface pores of the cathode emitter, so that the surface pores are leaked, which is conducive to the diffusion of active substances. Thus, an impregnated diffusion cathode (target cathode) with excellent anti-poisoning performance under low vacuum is obtained. The electron microscopic morphology of the cathode surface is as follows: Figure 4 ,from Figure 4It can be seen that the pores are fully exposed. This cathode can also be used as a film-coated cathode by coating the cathode surface with a metal or alloy film that is beneficial to emission, depending on the device's emission performance requirements. During cathode preparation, it is necessary to minimize cathode activity loss. To this end, this embodiment utilizes a method that involves high-temperature purification of the tungsten sponge substrate, melt impregnation of the cathode active material in a reducing atmosphere, and chemical cleaning of the cathode surface to ensure cathode performance.

[0077] The preparation of the impregnated diffusion cathode and the verification of its technical effect will be further introduced below in combination with specific embodiments.

[0078] Example 1

[0079] The low vacuum anti-poisoning impregnated diffusion cathode provided and disclosed in this embodiment has an active material for the impregnated diffusion cathode impregnated inside its substrate. The active material specifically comprises calcium barium aluminate and barium ceria. The specific preparation method is as follows:

[0080] Barium acetate, calcium acetate, aluminum nitrate, and cerium nitrate were weighed in a molar ratio of 32:6:20:11 to prepare a 12% mixed solution. The resulting solution was freeze-dried to prepare an active material precursor powder. The prepared precursor powder was placed in a high-purity alumina ceramic jar. A temporary adhesive mixture of a niter-cotton solution and alumina powder was evenly applied between the jar and the ceramic lid, semi-sealing the active material precursor powder within the jar. An alumina ceramic can is placed in a muffle furnace, and an active material is synthesized at a furnace temperature of 1000°C for a holding time of more than 1 hour to obtain a cerium-containing active material; the synthesized active material is impregnated into a porous tungsten sponge matrix, which has undergone copper removal and purification steps before being impregnated with the active material. The active material is weighed according to a mass ratio of 40% between the cathode tungsten sponge matrix and the active material, and the cathode matrix is ​​buried in the active material. Under a hydrogen atmosphere, the furnace temperature is above 1600°C, and the cathode active material is heated to a molten state. The active material is impregnated into the porous matrix to obtain a cathode emitter; the cathode emitter impregnated with the active material is subjected to surface chemical cleaning to clean excess active material on the surface, and the preparation of the impregnated diffusion cathode is completed.

[0081] The active material prepared in this example was subjected to XRD phase analysis, and the analysis results are as follows: Figure 5 As shown in FIG1 , the active material prepared in this embodiment mainly comprises calcium barium aluminate and barium ceria, which is the key to the excellent anti-poisoning ability of the impregnated diffusion cathode. The prepared impregnated diffusion cathode was loaded into a cathode dynamic test system for degassing, activation and aging. The cathode was then tested at an operating temperature of 1050°C, with an emission current of 213 mA and a system vacuum of 3×10 -6 Pa gradually decreased to 3.5×10 -5Pa, the cathode emission current dropped to 208 mA, with a decrease of only 2.3%, indicating that the new impregnated diffusion cathode has excellent low vacuum anti-poisoning performance. The specific results are as follows Figure 6 shown.

[0082] Example 2

[0083] This embodiment serves as a comparative example of Example 1 and provides a traditional impregnated diffusion cathode impregnated with a 612-type active material. The difference between this embodiment and Example 1 is that the cathode emission active material prepared in this embodiment does not contain cerium elements. Specifically, it is a 612-type cathode active material synthesized according to a molar ratio of 36:6:24 of barium acetate, calcium acetate, and aluminum nitrate. The rest of the cathode preparation path and method are the same as those in Example 1.

[0084] The XRD phase analysis of the 612 type active material in this embodiment is as follows: Figure 7 As shown, the active material prepared in this example is mainly composed of calcium barium aluminate and a small amount of barium carbonate, and does not contain barium cerate. The prepared impregnation diffusion cathode was installed in a cathode dynamic test system, degassed, activated and aged. Then, at an operating temperature of 1050°C, the cathode drew an emission current of 213 mA, and the system vacuum was increased from 3×10 -6 Pa gradually decreased to 3.5×10 -5 Pa, the cathode emission current dropped to 155mA, a decrease of 27.2%. Figure 6 As shown, the decrease is more than 10 times that of the impregnated diffusion cathode in Example 1, indicating that the anti-poisoning performance of the traditional 612 type cathode is much lower than that of the impregnated diffusion cathode in Example 1.

[0085] Example 3

[0086] This embodiment provides and discloses another low-vacuum anti-poisoning impregnated cathode, which is impregnated with active substances including calcium barium aluminate and barium cerate. The difference from Example 1 is that the active substance synthesis method is different from the active substance synthesis method in Example 1. Example 3 adopts the traditional hydrogen atmosphere high-temperature sintering synthesis method. Except for the above differences, the remaining steps of the method for preparing the cathode in this embodiment are the same as those in Example 1.

[0087] The impregnated diffusion cathode prepared by using the active material of Example 3 was loaded into the cathode dynamic test system, and was degassed, activated and aged. Then, the cathode was tested at an operating temperature of 1050°C, with a current draw of 213 mA and a system vacuum degree of 3×10 -6 Pa gradually decreased to 3.5×10 -5 Pa, the cathode emission current dropped to 184 mA, a decrease of 13.6%.

[0088] Example 4

[0089] This embodiment provides and discloses a low-vacuum anti-poisoning impregnated diffusion cathode, which is impregnated with an active material comprising barium calcium aluminate and barium cerate. The difference from Example 1 is that the proportion of the cerium component in the active material is different, specifically: the molar ratio of barium acetate, calcium acetate, aluminum nitrate and cerium nitrate in the raw materials is 32:6:20:8. Except for the above, the preparation method of the rest of the impregnated diffusion cathode in this embodiment is the same as that in Example 1.

[0090] The prepared impregnated diffusion cathode was placed in the cathode dynamic test system for degassing, activation and aging. Then the cathode was tested at an operating temperature of 1050℃ with a current draw of 213 mA and a system vacuum of 3×10 -6 Pa gradually decreased to 3.5×10 -5 Pa, the cathode emission current dropped to 193 mA, a decrease of 9.4%.

[0091] From the above examples, we can see that: 1. Anti-poisoning performance is improved, and at a vacuum degree of 3.5×10 -5 Under Pa, the cathode emission current of Example 1 decreased by only 2.3%, while that of the traditional cathode (Example 2) decreased by 27.2%; 2. The activity of the active material was enhanced. By comparing the semi-sealed synthesis with the traditional hydrogen atmosphere synthesis (Example 3), the effect of the semi-sealed process on improving the activity of the product was verified; 3. The effect of cerium content on performance. Example 4 showed that the performance deteriorated (current decreased by 9.4%) when the cerium content was reduced (molar ratio 32:6:20:8), indicating that the ratio of cerium is a key parameter.

[0092] Those skilled in the art will appreciate that the features described in the various embodiments of the present disclosure may be combined and / or coupled in various ways, even if such combinations or couplings are not explicitly described in the present disclosure. In particular, the features described in the various embodiments of the present disclosure may be combined and / or coupled in various ways without departing from the spirit and teachings of the present disclosure. All such combinations and / or couplings fall within the scope of the present disclosure.

[0093] The embodiments of the present disclosure are described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Although each embodiment has been described separately above, this does not mean that the measures in each embodiment cannot be used in combination to advantage. The scope of the present disclosure is defined by the appended claims and their equivalents. Without departing from the scope of the present disclosure, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present disclosure.

Claims

1. A method for preparing an active material for an impregnated diffusion cathode, characterized in that: The following steps are involved: preparing an aqueous solution using as a raw material at least one of water-soluble acetate, nitrate, gluconate, formate, and lactate containing barium, calcium, aluminum, and cerium elements in a molar ratio of 25-40:2-20:10-25:5-20; drying the aqueous solution to obtain a precursor powder material; The precursor powder is placed in a protective atmosphere and heated at 800-1000° C. for 1-4 hours.

2. The method for preparing an active material for an impregnated diffusion cathode according to claim 1, wherein: Placing the precursor powder under a protective atmosphere comprises: The precursor powder is semi-sealed in a heating dish using a heat-resistant porous material.

3. An active material for an impregnated diffusion cathode, characterized in that: The active material comprises calcium barium aluminate and barium ceria, and the active material is prepared by the method according to claims 1-2.

4. An impregnated diffusion cathode, characterized in that The invention comprises: a matrix and the active material prepared according to claim 1 to 2; the matrix comprises pores, and the active material is impregnated in the pores of the matrix.

5. The impregnated diffusion cathode according to claim 4, characterized in that The substrate is a tungsten sponge substrate, and the porosity range of the tungsten sponge substrate is 22%-25%.

6. The impregnated diffusion cathode according to claim 4, characterized in that The surface of the immersion diffusion cathode is covered with a metal film layer and / or an alloy film layer that is different from the matrix element.

7. A method for preparing an impregnated diffusion cathode, characterized in that: The following steps are involved: Under a hydrogen atmosphere, the substrate is immersed in a molten active material; the active material is prepared by the method according to claims 1-2.

8. The method for preparing an impregnated diffusion cathode according to claim 7, characterized in that: Before the step of impregnating the substrate into the molten active material, the method comprises: The substrate is placed in a hydrogen atmosphere at 1600° C. to 1800° C. and kept warm for 0.5 to 2 hours.

9. The method for preparing an impregnated diffusion cathode according to claim 7, characterized in that: After the step of impregnating the substrate with the molten active material, the method further comprises: Chemical cleaning of the surface of the impregnated diffusion cathode.

10. The method for preparing an impregnated diffusion cathode according to claim 7, characterized in that: The substrate is a tungsten sponge substrate, which is obtained by removing copper from a tungsten copper substrate.

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