Composite film layer M-type thermionic cathode and preparation method thereof

Abstract

The invention provides a composite film M-type hot cathode and a preparation method thereof. The composite film layer M-type hot cathode comprises a barium tungsten cathode substrate, a Re3W alloy phase barrier layer and a noble metal surface layer, and the Re3W alloy phase barrier layer is formed between the barium-tungsten cathode substrate and the noble metal surface layer. The composite film layer M-type thermionic cathode can effectively prevent alloying between the tungsten substrate and the precious metal film layer, so that the emission capability of the cathode is improved, and the service life of the cathode is prolonged.

Description

Technical Field

[0001] This invention relates to the field of vacuum electronic device manufacturing technology, and in particular to a composite film M-type hot cathode and its preparation method. Background Technology

[0002] Vacuum electronic devices, such as traveling wave tubes and magnetrons, are the core of modern radar, communication, and electronic warfare systems. The performance and lifespan of these devices largely depend on the performance of their electron emission material (cathode). As the "heart" of the electron source, the cathode needs to possess high emission current density, good stability, long operating life, and uniform emission characteristics.

[0003] Among numerous cathode materials, barium tungsten cathodes are widely used due to their excellent electron emission capabilities. To further enhance their performance, M-type cathodes have been developed. An M-type cathode is a standard barium tungsten cathode with a thin film of a noble metal (such as osmium, iridium, rhenium, or their alloys) coated on its emitting surface. This structural design offers significant advantages: the noble metal film effectively resists ion bombardment from residual gas within the device, improving the cathode's durability; simultaneously, it improves the uniformity of the emission current and significantly increases the cathode's emission current density, enabling it to meet the demands of higher-power devices.

[0004] Despite the superior performance of M-type cathodes, several key technical challenges remain during long-term operation. To optimize performance, existing technologies primarily employ several approaches: for example, replacing single-metal films with noble metal alloy films to optimize film performance; adjusting the composition of internal active emitting materials (such as barium calcium aluminate) to enhance electron emission; or improving processes to reduce the evaporation rate of active materials and extend lifespan. However, these improvements do not fundamentally solve the inherent problems of M-type cathodes.

[0005] Among them, the most prominent problems include: 1. Interdiffusion between the film and the substrate: At operating temperatures, significant interdiffusion occurs between the tungsten substrate of the cathode and the noble metal film on its surface. This not only leads to changes in the composition and structural degradation of the noble metal film, but also causes tungsten to diffuse to the surface, forming high work function materials, thereby reducing the emission performance of the cathode.

[0006] 2. Film adhesion and stability issues: Due to factors such as thermal stress and material mismatch, the precious metal film may have insufficient adhesion to the substrate, which may lead to peeling and detachment of the film, resulting in cathode failure.

[0007] 3. Emission performance degradation: The interdiffusion and film instability mentioned above together lead to long-term degradation of the cathode emission current, limiting further improvement of its working life.

[0008] In view of this, the present application is proposed. SUMMARY

[0009] The present application aims to provide a composite film layer M-type thermionic cathode and a preparation method thereof, which solves at least one problem raised by the background art.

[0010] In a first aspect, the present application provides a composite film layer M-type thermionic cathode, comprising a barium-tungsten cathode base, a Re3W alloy phase barrier layer and a noble metal surface layer; the Re3W alloy phase barrier layer is formed between the barium-tungsten cathode base and the noble metal surface layer.

[0011] According to some embodiments, the noble metal surface layer is one or both of an osmium film layer and an iridium film layer.

[0012] According to some embodiments, the thickness of the Re3W alloy phase barrier layer and the noble metal surface layer is 150-250 nm respectively, and the thickness of the barium-tungsten cathode base is 2.5-3.5 mm.

[0013] In a second aspect, the present application provides a preparation method of the composite film layer M-type thermionic cathode described above, comprising the following steps: Step S1. A tungsten base is obtained by pressing tungsten powder and then performing active salt impregnation; Step S2. The barium-tungsten cathode obtained in step S1 is treated by rhenium film coating and then heat treated, to obtain a barium-tungsten cathode with a Re3W alloy phase film layer on the surface; Step S3. The barium-tungsten cathode with the Re3W alloy phase film layer obtained in step S2 is treated by noble metal film coating again, to obtain a composite film layer M-type thermionic cathode.

[0014] According to some embodiments, the particle size of the tungsten powder is 4-6 μm, and the pressing is performed by a die pressing method; preferably, the pressure of the die pressing is 0.2-1 MPa, and the pressure holding time is 30-60 s.

[0015] According to some embodiments, the process of the active salt impregnation is as follows: the tungsten base formed by pressing is heated to 800-900℃ within 25-35 min in a reactive gas atmosphere or vacuum state, and then heated to 1500-1700℃ at a heating rate of 5-15℃ / min for impregnation of the barium-containing active salt; preferably, the reactive gas is hydrogen; preferably, the active salt is a mixture of BaO, CaO and Al2O3; preferably, the molar ratio of BaO, CaO and Al2O3 is 3-5:1:1, preferably 4:1:1.

[0016] According to some embodiments, the rhenium film in step S2 and the noble metal film in step S3 are formed by magnetron sputtering; preferably, the process parameters of the magnetron sputtering are as follows: the sputtering power is 80-120 W, the voltage is 420-450 V, the cavity is connected to argon, the argon flow rate is 70-180 sccm, and the vacuum degree is kept at 0.1-0.8 Pa; preferably, the argon flow rate and the vacuum degree in step S3 are greater than those in step S2.

[0017] According to some embodiments, the thickness of the rhenium film in step S2 and the thickness of the noble metal film in step S3 are each 150-250 nm; preferably, step S2 further comprises a step of forming a tungsten film before forming the rhenium film, and the thickness of the tungsten film layer is 50-100 nm; preferably, the tungsten film is formed by magnetron sputtering; preferably, the process parameters of the magnetron sputtering are as follows: the sputtering power is 80-120 W, the voltage is 420-450 V, the cavity is connected to argon, the argon flow rate is 70-180 sccm, and the vacuum degree is kept at 0.1-0.8 Pa. Preferably, the argon flow rate and the vacuum degree in step S3 are greater than those in step S2.

[0018] According to some embodiments, the heat treatment in step S2 is performed in a tube furnace; preferably, the process of the heat treatment is as follows: heating to 1000-1200℃ at a heating rate of 10-15℃ / min in a reactive gas atmosphere or under vacuum, and keeping the temperature for 480-720 min, and then cooling with the furnace; preferably, the reactive gas is hydrogen; preferably, the flow rate of the reactive gas during the heat treatment is 40-50 mL / min.

[0019] According to some embodiments, the noble metal in step S3 is one or both of osmium and iridium.

[0020] The present application has at least the following beneficial effects: 1. The M-type cathode film layer obtained by the present application has a Re3W alloy phase barrier layer between the film layer and the substrate.

[0021] 2. The cathode obtained by the present application has a Re3W alloy phase barrier layer on the surface, and no alloy compound of the tungsten substrate and the osmium film is found on the surface of the cathode compared with the cathode directly coated with a rhenium film and an osmium film.

[0022] 3. The cathode obtained by the present application has the characteristics of low temperature and large current, which hinders the alloying process between the film layer and the substrate, solves the problems of film layer falling off and film layer composition deterioration during long-term use of the M-type cathode, and thus ensures the service life and stability of the cathode and increases the emission current density of the cathode.

[0023] 4. Compared with the tungsten-rhenium-osmium ternary mixed-based diffusion cathode, this cathode material has lower production costs, is easier to operate, and is more conducive to industrial application, while having similar performance. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the composite film layer M-type hot cathode in an embodiment of the present invention; Figure 2 This is a flowchart illustrating the formation of the composite film layer M-type in an embodiment of the present invention; Figure 3 This is a morphological diagram of the barium tungsten cathode obtained in step S1 of Embodiment 1 of the present invention; Figure 4 This is a morphology diagram of the material after rhenium film coating treatment in step S2 of Embodiment 1 of the present invention but before heat treatment; Figure 5 This is a morphology diagram of the material after heat treatment in step S2 of Embodiment 1 of the present invention to generate the Re3W alloy phase; Figure 6 This is a morphological diagram of the composite film layer M-type hot cathode finally obtained in step S3 of Embodiment 1 of the present invention; Figure 7 The XRD pattern of the material after heat treatment in step S2 of Embodiment 1 of this invention to generate the Re3W alloy phase; Figure 8 The XRD patterns of the materials prepared in Example 1 and Comparative Example 1 after thermal emission are shown. Figure 9 This is a graph showing the emission performance of the composite film layer M-type cathode prepared in Example 1 of the present invention; Figure 10 The emission performance diagram of the cathode prepared in Comparative Example 1 is shown. Figure 11 This is an accelerated lifetime diagram of the composite film layer M-type cathode prepared in Example 1 of the present invention; Figure 12 This is an accelerated lifetime diagram of the cathode prepared in Comparative Example 1. Detailed Implementation

[0026] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0027] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form includes the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0028] It should be noted that if the text uses terms such as "first" or "second", these terms are only used to distinguish similar objects and should not be interpreted as indicating or implying their relative importance, order of precedence, or implicitly indicating the number of technical features indicated. It should be understood that the data in the descriptions of "first" and "second" can be interchanged where appropriate.

[0029] Throughout the accompanying drawings, identical elements are represented by the same or similar reference numerals. Conventional structures or configurations may be omitted where they might cause confusion in understanding the invention. Furthermore, the shapes, dimensions, and positional relationships of the components in the drawings do not reflect actual size, scale, or actual positional relationships. Additionally, any reference symbols placed within parentheses in this invention should not be construed as limiting the scope of the invention.

[0030] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] This invention relates to the field of vacuum electronic device manufacturing technology, and mainly to microwave devices such as space traveling wave tubes and high-power klystrons that use coated diffused cathodes.

[0032] Figure 1 This is a schematic diagram of the structure of the composite film layer M-type hot cathode in an embodiment of the present invention.

[0033] One aspect of the present invention provides a composite film layer M-type thermocathode, such as Figure 1 As shown, the composite film M-type hot cathode includes a barium-tungsten cathode substrate 10, a Re3W alloy phase barrier layer 20, and a noble metal surface layer 30. The Re3W alloy phase barrier layer 20 is formed between the barium-tungsten cathode substrate 10 and the noble metal surface layer 30.

[0034] Electron emission materials (cathodes) are core components of vacuum electronic devices, significantly impacting their performance and lifespan. M-type cathodes are ordinary barium-tungsten cathodes coated with a thin film of noble metal. Compared to ordinary barium-tungsten cathodes, these cathodes exhibit stronger resistance to ion bombardment, better emission uniformity, and higher emission current density.

[0035] Previous studies have found that cathode emission performance can be improved by replacing single-layer films with alloy films, improving the composition of the emission material (active salt), and reducing the evaporation rate of the active salt. However, this method still cannot avoid problems such as poor stability of the formed cathode material, film peeling, diffusion of tungsten substrate into the noble metal film, and changes in surface composition.

[0036] Through in-depth research, the inventors of this invention discovered that by setting a rhenium tritungsten (Re3W) film layer between the barium tungsten cathode substrate and the noble metal surface layer, a novel high-temperature hot cathode-composite film layer M-type cathode is formed. This can slow down the alloying process between the film layer (i.e., the noble metal surface layer) and the substrate, avoid uncontrollable performance and changes in film composition during long-term use of the cathode, thereby extending the service life of the cathode and enhancing its emission performance. In some embodiments, the noble metal surface layer is one or both of osmium film and iridium film. Using such a metal surface material, especially an osmium film, in combination with a rhenium tritungsten phase film, enables the cathode to have excellent emission performance.

[0037] To ensure excellent emission performance of the cathode material, in some embodiments, the thicknesses of the Re3W alloy phase barrier layer and the noble metal surface layer can each be 150–250 nm, for example, 170 nm, 190 nm, 220 nm, 245 nm, etc., and the thickness of the barium-tungsten cathode substrate can be 2.5–3.5 mm, for example, 2.7 mm, 2.9 mm, 3.1 mm, 3.4 mm, etc. The thicknesses of the Re3W alloy phase barrier layer and the noble metal surface layer can be the same or different, depending on the actual situation or requirements.

[0038] Another aspect of the present invention provides a method for preparing the above-mentioned composite film layer M-type hot cathode, such as... Figure 2 As shown, the preparation method includes the following steps: Step S1. Tungsten powder is pressed into a tungsten matrix and then impregnated with active salt to obtain a barium tungsten cathode; Step S2. The barium tungsten cathode obtained in step S1 is heat-treated after being coated with a rhenium film to obtain a barium tungsten cathode with a Re3W alloy phase film layer on its surface. Step S3. The barium tungsten cathode coated with Re3W alloy phase film obtained in step S2 is subjected to noble metal film coating treatment again to obtain composite film layer M-type hot cathode.

[0039] As mentioned above, in view of the shortcomings of the prior art, the inventors have discovered through in-depth research that by pretreatment before coating the M-type cathode with a noble metal film, a Re3W phase alloy film layer can be generated on the surface of the barium tungsten cathode, which can slow down the alloying process between the film and the substrate, thereby enhancing the emission performance of the cathode.

[0040] Specifically, the present invention provides a method for preparing a composite film layer M-type hot cathode with a barrier effect. The present invention involves covering the surface of a diffusing cathode with a rhenium film layer before coating the M-type cathode with a noble metal film, and then heat-treating it to form a Re3W alloy phase barrier layer, which effectively prevents alloying between the tungsten substrate and the noble metal film layer, thereby improving the cathode emission capability.

[0041] Studies have found that if the tungsten powder particles are too large or too small, the porosity of the tungsten matrix will not meet the standard, affecting the amount of subsequent active salt impregnation, and thus affecting the emission performance of the cathode material. Therefore, in some embodiments, in step S1, the particle size of the tungsten powder can be 4~6 μm, for example, 4.5 μm, 5 μm, 5.6 μm, etc., and pressing can be carried out by molding.

[0042] In order to ensure the strength of the cathode material and to ensure the appropriate amount of impregnation in the future, in some embodiments, the molding pressure can be 0.2~1 MPa, such as 0.4 MPa, 0.6 MPa, 0.8 MPa, etc., and the holding time can be 30~60 s, such as 35 s, 42 s, 50 s, 57 s, etc.

[0043] In some embodiments, the active salt impregnation process can be as follows: The pressed tungsten substrate is heated to 800-900°C (e.g., 820°C, 850°C, 880°C, 895°C) within 25-35 minutes, for example, 28 minutes, 30 minutes, or 33 minutes, under a reactive gas atmosphere or vacuum. Then, it is heated to 1500-1700°C (e.g., 1550°C, 1600°C, 1680°C) at a heating rate of 5-15°C / min (e.g., 8°C / min, 10°C / min, 13°C / min) to impregnate it with a barium-containing active salt. Studies have found that the above impregnation process results in a more suitable amount of active salt, thereby optimizing the electron emission performance of the prepared cathode material.

[0044] In some embodiments, the reactive gas may be hydrogen. In some embodiments, the active salt may be a mixture of BaO, CaO and Al2O3.

[0045] To further optimize the emission performance of the cathode material, in some embodiments, the molar ratio of BaO, CaO and Al2O3 can be 3 to 5:1:1, for example 3.3:1:1, 3.7:1:1, 4.1:1:1, 4.5:1:1, preferably 4:1:1.

[0046] For example, the active salt impregnation process can be specifically as follows: a porous tungsten substrate is heated to 850°C within 30 minutes under a hydrogen atmosphere, and then heated to 1600°C at a heating rate of 10°C / min for active salt impregnation; the active salt is a mixture of BaO, CaO, and Al2O3 in a molar ratio of 4:1:1. This impregnation process can optimize the emission performance of the prepared cathode material to the greatest extent.

[0047] In some embodiments, the rhenium coating in step S2 and the noble metal coating in step S3 can be performed by magnetron sputtering.

[0048] In some embodiments, the process parameters for magnetron sputtering can be: sputtering power of 80~120 W, such as 90 W, 105 W, 115 W, etc.; voltage of 420~450 V, such as 425 V, 433 V, 440 V, 447 V, etc.; argon gas is introduced into the cavity at a flow rate of 70~180 sccm, such as 80 sccm, 95 sccm, 115 sccm, 130 sccm, 150 sccm, 170 sccm, etc.; and the vacuum level is maintained at 0.1~0.8 Pa, such as 0.2 Pa, 0.4 Pa, 0.6 Pa, 0.75 Pa, etc. Studies have found that using sputtering power, sputtering voltage, hydrogen flow rate, and vacuum level within the above range for magnetron sputtering results in a more uniform film thickness during the coating process and reduces the likelihood of oxidation.

[0049] In some embodiments, the argon gas flow rate and vacuum level during the coating of the noble metal film in step S3 are greater than those during the coating of the rhenium film in step S2.

[0050] In some embodiments, specifically, during step S3, when coating with a noble metal film, the argon gas flow rate can be 140-180 sccm, and the vacuum degree can be 0.4-0.8 Pa; while during step S2, when coating with a rhenium film, the argon gas flow rate can be 70-150 sccm, and the vacuum degree can be 0.1-0.1 Pa. Under these conditions, coating with rhenium and noble metal films can minimize oxidation, thereby resulting in a more uniform film thickness.

[0051] In some embodiments, the thickness of the rhenium coating in step S2 and the noble metal coating in step S3 can each be 150~250 nm, for example, 170 nm, 190 nm, 220 nm, 245 nm, etc. Similarly, the thickness of the rhenium coating and the noble metal coating can be the same or different, depending on the actual situation or needs. For example, the thickness of the rhenium coating and the noble metal coating can both be 200 nm, or the rhenium coating can be 180 nm and the noble metal coating can be 220 nm, etc.

[0052] In some embodiments, step S2 further includes a tungsten film coating step before the rhenium film coating, wherein the thickness of the tungsten film layer is 50-100 nm. Coating with a tungsten film before rhenium film coating can effectively control the amount and uniformity of the Re3W alloy phase barrier layer, further improving the emission performance of the final cathode material.

[0053] In some embodiments, the tungsten-coated film is also produced using magnetron sputtering. The magnetron sputtering process parameters can also be as follows: sputtering power of 80-120 W, voltage of 420-450 V, argon gas introduced into the cavity at a flow rate of 70-180 sccm, and vacuum maintained at 0.1-0.8 Pa. Of course, the magnetron sputtering process parameters for tungsten-coated films do not necessarily have to be exactly the same as those for rhenium-coated films; they can be appropriately adjusted within the above ranges according to actual conditions.

[0054] In some embodiments, the heat treatment in step S2 can be performed in a tube furnace.

[0055] In some embodiments, the heat treatment process may be as follows: heating to 1000-1200°C, such as 1050°C, 1100°C, or 1170°C, at a heating rate of 10-15°C / min, for example 12°C / min or 14°C / min, under a reactive gas atmosphere or vacuum, and holding at this temperature for 480-720 min, for example 500 min, 550 min, 600 min, 660 min, or 710 min, followed by furnace cooling. Based on the physical mechanism of rhenium-tungsten formation, these treatment conditions facilitate the formation of a rhenium-tungsten alloy phase film. For example, the heat treatment process can be as follows: heat to 1100℃ at a heating rate of 10~15℃ / min, hold at 1100℃ for 480~720 min, and then cool with the furnace.

[0056] In some embodiments, the reactive gas may be hydrogen. To avoid oxidation of the rhenium-coated film during heat treatment and the introduction of other impurities, in some embodiments, the flow rate of the reactive gas during heat treatment can be set to 40-50 mL / min, for example, 42 mL / min, 45 mL / min, 48 mL / min, etc.

[0057] In some embodiments, the precious metal in step S3 is one or both of osmium and iridium.

[0058] The technical solution of the present invention will be described in detail below through specific embodiments, but the present invention is not limited to the following embodiments.

[0059] Example 1 S1. Weigh 0.125 g of tungsten powder with a particle size of 5 μm, load it into a mold with an inner diameter of 3 mm, and use a powder press to form a bidirectional molding process. Hold the pressure at 0.8 MPa for 35 s to obtain a sintered green compact. Place the porous tungsten green compact in a hydrogen furnace, heat it to 850℃ within 30 min, and then heat the sample to 1600℃ at a heating rate of 10℃ / min to complete the impregnation with 411 active salt (BaO:CaO:Al2O3 molar ratio 4:1:1) to obtain a barium tungsten cathode material, the morphology of which is shown in the figure below. Figure 3 As shown.

[0060] S2. The barium-tungsten cathode material was sequentially coated with a tungsten film and then with a rhenium film using a magnetron sputtering system. During both coating processes, the magnetron sputtering power was maintained at 100 W, the voltage at 430 V, and argon gas was introduced into the magnetron sputtering chamber at a flow rate of 100 sccm while maintaining a vacuum of 2.5E⁻¹ Pa. The coating thicknesses of the tungsten and rhenium films were approximately 80 nm and 200 nm, respectively, and their morphologies are shown in the figures below. Figure 4 As shown. The obtained tungsten-coated and rhenium-coated cathodes were subjected to heat treatment. The heat treatment conditions were: heating to 1100℃ at a rate of 10~15℃ / min, holding at that temperature for 600 min, and then cooling with the furnace. The hydrogen gas flow rate during the process was 50 mL / min. The morphology of the material after heat treatment is shown in the figure. Figure 5 As shown, the XRD pattern is as follows Figure 7 As shown. From Figure 7 It can be seen that after this heat treatment step, a Re3W alloy phase is formed in the material.

[0061] S3. The cathode with the generated Re3W alloy phase was coated with an osmium film using a magnetron sputtering system. The magnetron sputtering power was maintained at 120 W, the voltage at 420 V, and argon gas was introduced into the magnetron sputtering chamber at a flow rate of 160 sccm with a vacuum of 4.5E-1 Pa. The coating thickness was approximately 200 nm. The resulting sample is a composite film M-type thermocathode with a barrier effect, and its morphology is shown in the figure below. Figure 6 As shown.

[0062] Example 2 S1. Weigh 0.125 g of tungsten powder with a particle size of 5 μm, load it into a mold with an inner diameter of 3 mm, and mold it using a powder press in a bidirectional manner. Hold the pressure at 0.8 MPa for 35 s to obtain a sintered green compact. Place the porous tungsten green compact in a hydrogen furnace, heat it to 850℃ within 30 min, and then heat the sample to 1600℃ at a heating rate of 10℃ / min to complete the impregnation with 411 active salt (BaO:CaO:Al2O3 molar ratio 4:1:1) to obtain barium tungsten cathode material.

[0063] S2. The barium-tungsten cathode material was sequentially coated with a tungsten film and then with a rhenium film using a magnetron sputtering apparatus. During the tungsten and rhenium film coating processes, the magnetron sputtering power was maintained at 100 W and the voltage at 430 V. Argon gas was introduced into the magnetron sputtering chamber at a flow rate of 100 sccm and the vacuum degree was maintained at 2.5E-1 Pa. The coating thicknesses of the tungsten film and the rhenium film were approximately 60 nm and 200 nm, respectively. The resulting coated cathode was then subjected to heat treatment. The heat treatment conditions were: heating to 1100 °C at a rate of 10–15 °C / min and holding at that temperature for 480 min, followed by furnace cooling. During the process, the hydrogen gas flow rate was 50 mL / min.

[0064] S3. The cathode with the generated Re3W alloy phase was coated with osmium film in a magnetron sputtering instrument. The magnetron sputtering power was maintained at 120 W, the voltage was maintained at 420 V, the magnetron sputtering chamber was purged with argon gas at a flow rate of 160 sccm and the vacuum degree was maintained at 4.5E-1 Pa. The coating thickness was about 200 nm. The resulting sample is the M-type hot cathode with a composite film layer and barrier effect.

[0065] Example 3 S1. Weigh 0.125 g of tungsten powder with a particle size of 5 μm, load it into a mold with an inner diameter of 3 mm, and mold it using a powder press in a bidirectional manner. Hold the pressure at 0.8 MPa for 35 s to obtain a sintered green compact. Place the porous tungsten green compact in a hydrogen furnace, heat it to 850℃ within 30 min, and then heat the sample to 1600℃ at a heating rate of 10℃ / min to complete the impregnation with 411 active salt (BaO:CaO:Al2O3 molar ratio 4:1:1) to obtain barium tungsten cathode material.

[0066] S2. The barium-tungsten cathode material was sequentially coated with tungsten and then with rhenium films using a magnetron sputtering system. During both coating processes, the magnetron sputtering power was maintained at 100 W and the voltage at 430 V. Argon gas was introduced into the magnetron sputtering chamber at a flow rate of 100 sccm, and the vacuum level was maintained at 2.5E⁻¹ Pa. The coating thicknesses of the tungsten and rhenium films were approximately 70 nm and 200 nm, respectively. The resulting coated cathode was then subjected to heat treatment. The heat treatment conditions were: heating to 1100 °C at a rate of 10–15 °C / min, holding at that temperature for 540 min, followed by furnace cooling. During this process, the hydrogen gas flow rate was 50 mL / min.

[0067] S3. The cathode with the generated Re3W alloy phase was coated with osmium film in a magnetron sputtering instrument. The magnetron sputtering power was maintained at 120 W, the voltage was maintained at 420 V, the magnetron sputtering chamber was purged with argon gas at a flow rate of 160 sccm and the vacuum degree was maintained at 4.5E-1 Pa. The coating thickness was about 200 nm. The resulting sample is the M-type hot cathode with a composite film layer and barrier effect.

[0068] Example 4 S1. Weigh 0.125 g of tungsten powder with a particle size of 5 μm, load it into a mold with an inner diameter of 3 mm, and mold it using a powder press in a bidirectional manner. Hold the pressure at 0.8 MPa for 35 s to obtain a sintered green compact. Place the porous tungsten green compact in a hydrogen furnace, heat it to 850℃ within 30 min, and then heat the sample to 1600℃ at a heating rate of 10℃ / min to complete the impregnation with 411 active salt (BaO:CaO:Al2O3 molar ratio 4:1:1) to obtain barium tungsten cathode material.

[0069] S2. The barium-tungsten cathode material was coated with rhenium using a magnetron sputtering system. The magnetron sputtering power was maintained at 100 W, the voltage at 430 V, and argon gas was introduced into the magnetron sputtering chamber at a flow rate of 100 sccm with a vacuum of 2.5E-1 Pa. The coating thickness was approximately 200 nm. The resulting coated cathode was then heat-treated under the following conditions: heating to 1100 °C at a rate of 10 °C / min and holding at that temperature for 660 min, followed by furnace cooling. During this process, the hydrogen gas flow rate was 50 mL / min.

[0070] S3. The cathode with the generated Re3W alloy phase was coated with osmium film in a magnetron sputtering instrument. The magnetron sputtering power was maintained at 120 W, the voltage was maintained at 420 V, the magnetron sputtering chamber was purged with argon gas at a flow rate of 160 sccm and the vacuum degree was maintained at 4.5E-1 Pa. The coating thickness was about 200 nm. The resulting sample is the M-type hot cathode with a composite film layer and barrier effect.

[0071] Example 5 S1. Weigh 0.125 g of tungsten powder with a particle size of 5 μm, load it into a mold with an inner diameter of 3 mm, and mold it using a powder press in a bidirectional manner. Hold the pressure at 0.8 MPa for 35 s to obtain a sintered green compact. Place the porous tungsten green compact in a hydrogen furnace, heat it to 850℃ within 30 min, and then heat the sample to 1600℃ at a heating rate of 10℃ / min to complete the impregnation with 411 active salt (BaO:CaO:Al2O3 molar ratio 4:1:1) to obtain barium tungsten cathode material.

[0072] S2. The barium-tungsten cathode material was coated with rhenium using a magnetron sputtering system. The magnetron sputtering power was maintained at 100 W, the voltage at 430 V, and argon gas was introduced into the magnetron sputtering chamber at a flow rate of 100 sccm with a vacuum of 2.5E-1 Pa. The coating thickness was approximately 200 nm. The resulting coated cathode was then heat-treated under the following conditions: heating to 1100 °C at a rate of 12 °C / min, holding at that temperature for 720 min, and then cooling with the furnace. During this process, the hydrogen gas flow rate was 50 mL / min.

[0073] S3. The cathode with the generated Re3W alloy phase was coated with osmium film in a magnetron sputtering instrument. The magnetron sputtering power was maintained at 120 W, the voltage was maintained at 420 V, the magnetron sputtering chamber was purged with argon gas at a flow rate of 160 sccm and the vacuum degree was maintained at 4.5E-1 Pa. The coating thickness was about 200 nm. The resulting sample is the M-type hot cathode with a composite film layer and barrier effect.

[0074] Example 6 S1. Weigh 0.125 g of tungsten powder with a particle size of 5 μm, load it into a mold with an inner diameter of 3 mm, and mold it using a powder press in a bidirectional manner. Hold the pressure at 0.8 MPa for 35 s to obtain a sintered green compact. Place the porous tungsten green compact in a hydrogen furnace, heat it to 850℃ within 30 min, and then heat the sample to 1600℃ at a heating rate of 10℃ / min to complete the impregnation with 411 active salt (BaO:CaO:Al2O3 molar ratio 4:1:1) to obtain barium tungsten cathode material.

[0075] S2. The barium-tungsten cathode material was sequentially coated with tungsten and then with rhenium films using a magnetron sputtering system. During both coating processes, the magnetron sputtering power was maintained at 100 W and the voltage at 430 V. Argon gas was introduced into the magnetron sputtering chamber at a flow rate of 100 sccm, and the vacuum level was maintained at 2.5E-1 Pa. The coating thicknesses of the tungsten and rhenium films were approximately 90 nm and 200 nm, respectively. The resulting coated cathode was then subjected to heat treatment. The heat treatment conditions were: heating at 12 °C / min to 1100 °C, holding at that temperature for 780 min, followed by furnace cooling. During this process, the hydrogen gas flow rate was 50 mL / min.

[0076] S3. The cathode with the generated Re3W alloy phase was coated with osmium film in a magnetron sputtering instrument. The magnetron sputtering power was maintained at 120 W, the voltage was maintained at 420 V, the magnetron sputtering chamber was purged with argon gas at a flow rate of 160 sccm and the vacuum degree was maintained at 4.5E-1 Pa. The coating thickness was about 200 nm. The resulting sample is the M-type hot cathode with a composite film layer and barrier effect.

[0077] Comparative Example 1 The difference from Example 1 is that the barium tungsten cathode material obtained in step S1 is coated with tungsten film and rhenium film and then directly coated with osmium film, that is, no heat treatment step is performed.

[0078] The final products obtained in Examples 1 to 6 and Comparative Example 1 were subjected to a temperature of 1050°C. b The thermal emission current density was tested at (b represents the optical display temperature), and the results are shown in Table 1 below.

[0079] Table 1 Emission Current Density

[0080] As can be seen from the table, the composite film M-type cathode with Re3W phase alloy film prepared in the embodiments of the present invention has a higher current density than the cathode without Re3W phase alloy film.

[0081] The XRD patterns of the materials prepared in Example 1 and Comparative Example 1 after thermal emission were measured, and the results are as follows: Figure 8 As shown, the upper part is the XRD pattern of the material prepared in Example 1 after thermal emission, and the lower part is the XRD pattern of the material prepared in Comparative Example 1 after thermal emission. The comparison in the figures shows that a solid solution reaction occurred between rhenium and osmium in the cathode material prepared in the comparative example, while the rhenium-tungsten barrier layer is stably present in the cathode material prepared in the present invention, preventing the solid solution reaction between rhenium and osmium. The emission performance of the composite film M-type cathode prepared in Example 1 of this invention and the cathode prepared in Comparative Example 1 were tested, and the results are as follows: Figure 9 and Figure 10 As shown in the figure, the current densities shown are at temperatures of 1000℃. b 1050℃ b 1100℃ b The current density measured under [condition]. From [location] Figure 9 and Figure 10 The comparison shows that the current density value measured at the same temperature of the composite film layer M-type cathode of the present invention is significantly higher than that of the cathode of Comparative Example 1 at the corresponding temperature.

[0082] The emission lifetime of the composite film M-type cathode prepared in Example 1 of this invention and the cathode prepared in Comparative Example 1 were tested, and the results are as follows: Figure 11 and Figure 12 As shown. From Figure 11 and Figure 12 The comparison shows that the emission lifetime of the composite film M-type cathode prepared in Example 1 of the present invention can reach 2800 h, while the emission lifetime of the cathode prepared in Comparative Example 1 is only 1750 h.

[0083] As can be seen from the above comparison, the composite film M-type cathode with Re3W phase alloy film layer of the present invention has a significantly longer service life and better cathode emission performance. The preparation method of the present invention can significantly extend the service life of cathode material and enhance the emission performance of cathode material.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite film M-type thermal cathode, characterized in that, It includes a barium tungsten cathode substrate, a Re3W alloy phase barrier layer, and a noble metal surface layer; The Re3W alloy phase barrier layer is formed between the barium tungsten cathode substrate and the noble metal surface layer.

2. The composite film layer M-type thermal cathode according to claim 1, characterized in that, The precious metal surface layer is one or both of osmium film and iridium film.

3. The composite film layer M-type thermal cathode according to claim 1 or 2, characterized in that, The thickness of the Re3W alloy phase barrier layer and the noble metal surface layer is 150~250 nm, and the thickness of the barium tungsten cathode substrate is 2.5~3.5 mm.

4. A method for preparing a composite film layer M-type hot cathode according to any one of claims 1 to 3, characterized in that, Includes the following steps: Step S1. Tungsten powder is pressed into a tungsten matrix and then impregnated with active salt to obtain a barium tungsten cathode; Step S2. The barium tungsten cathode obtained in step S1 is heat-treated after being coated with a rhenium film to obtain a barium tungsten cathode with a Re3W alloy phase film layer on its surface. Step S3. The barium tungsten cathode coated with Re3W alloy phase film obtained in step S2 is subjected to noble metal film coating treatment again to obtain composite film layer M-type hot cathode.

5. The preparation method according to claim 4, characterized in that, In step S1, the particle size of the tungsten powder is 4~6 μm, and the pressing is carried out by molding. Preferably, the compression molding pressure is 0.2~1MPa and the holding time is 30~60 s.

6. The preparation method according to claim 4 or 5, characterized in that, In step S1, the process of impregnating the active salt is as follows: the tungsten substrate formed by pressing is heated to 800-900°C in a reactive gas atmosphere or vacuum state within 25-35 minutes, and then heated to 1500-1700°C at a heating rate of 5-15°C / min for impregnation with barium-containing active salt. Preferably, the reactive gas is hydrogen. Preferably, the active salt is a mixture of BaO, CaO and Al2O3; Preferably, the molar ratio of BaO, CaO and Al2O3 is 3~5:1:1, and more preferably 4:1:

1.

7. The preparation method according to any one of claims 4 to 6, characterized in that, The rhenium coating in step S2 and the noble metal coating in step S3 are performed by magnetron sputtering. Preferably, the process parameters for magnetron sputtering are: sputtering power of 80~120 W, voltage of 420~450 V, argon gas introduced into the cavity, argon gas flow rate of 70~180 sccm, and vacuum degree maintained at 0.1~0.8 Pa.

8. The preparation method according to any one of claims 4 to 7, characterized in that, The thickness of the rhenium coating in step S2 and the noble metal coating in step S3 are 150~250 nm respectively. Preferably, step S2 further includes a tungsten film coating step before the rhenium film coating, wherein the thickness of the tungsten film layer is 50~100 nm; Preferably, the tungsten coating is applied using magnetron sputtering. Preferably, the process parameters for magnetron sputtering are: sputtering power of 80~120 W, voltage of 420~450 V, argon gas introduced into the cavity, argon gas flow rate of 70~180 sccm, and vacuum degree maintained at 0.1~0.8 Pa.

9. The preparation method according to any one of claims 4 to 8, characterized in that, The heat treatment in step S2 is carried out in a tube furnace; Preferably, the heat treatment process is as follows: heating to 1000-1200°C at a heating rate of 10-15°C / min under a reactive gas atmosphere or vacuum, holding at this temperature for 480-720 min, and then cooling with the furnace. Preferably, the reactive gas is hydrogen. Preferably, the flow rate of the reactive gas during the heat treatment process is 40~50 mL / min.

10. The preparation method according to any one of claims 4 to 9, characterized in that, The precious metal mentioned in step S3 is one or both of osmium and iridium.

Images