Scandate active substance with high Sc2O3 content and application of scandate active substance in impregnated diffusion cathode
By optimizing the Sc2O3 content in an impregnated scandium-containing diffused cathode and using ion beam etching technology, the problems of low Sc2O3 content and pore blockage were solved, achieving efficient electron emission and improved stability.
Patent Information
- Application Number
- CN202511799024.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-02
- Publication Date
- 2026-02-10
AI Technical Summary
The existing impregnated scandium diffusion cathode has a low Sc2O3 content, which leads to reduced emission performance. Pore blockage affects the diffusion of active materials, and pore blockage caused by mechanical polishing or processing is difficult to remove effectively.
Scandium salt active material with high Sc2O3 content is used, and the composition ratio is optimized by combining surface etching technology. The cathode surface is treated by ion beam etching to eliminate pore blockage and promote the diffusion of active material.
It significantly improves the electron emission efficiency and stability of the cathode, increases the emission current density and operational stability, and enhances the emission performance of the cathode.
Smart Images
Figure CN121494548A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of manufacturing technology of thermal diffusion cathodes for vacuum electronic devices, specifically relating to a scandium active material with high Sc2O3 content and its application in impregnation-type diffusion cathodes. Background Technology
[0002] With the continuous development of vacuum electronic devices, higher requirements are being placed on cathode emission performance, including higher current density, lower operating temperature, and longer service life. Impregnated scandium-containing diffused cathodes can achieve high current density electron emission at lower temperatures and are considered one of the most promising cathode types for future vacuum electronic devices.
[0003] Impregnated scandium-containing diffused cathodes possess advantages such as good machinability, stable processing, and reliable emission performance, making them a commonly used cathode structure in high-power vacuum electronic devices. These cathodes typically use a porous tungsten substrate as a framework, impregnated with scandium-containing active materials under high-temperature conditions. These active materials are generally obtained by sintering a mixture of BaCO3, CaCO3, Al2O3, and Sc2O3 in a specific ratio. At high temperatures, the active material decomposes or reacts, generating components that promote electron emission. These components diffuse through the pores to the cathode surface, forming an emission layer with low work function, thereby achieving stable electron emission performance.
[0004] The active material used in traditional impregnated scandium diffusion cathodes is generally prepared by adding a certain amount (usually 3-5 wt.%) of Sc2O3 to an aluminate formulation (BaO:CaO:Al2O3 molar ratio of 6:1:2 or 4:1:1). For example, the molar ratio of BaO:CaO:Al2O3:Sc2O3 is 6:1:2:0.3. However, further increasing the amount of Sc2O3 will generate a larger amount of the non-emissive BaAl2O4 phase (Qiang Zheng et al., Ceramics International, 2021, 47: 18831–18837). Therefore, there is an urgent need to design a scandium-containing active material with a high Sc2O3 content and a low amount of BaAl2O4 non-emissive phase to further improve the cathode's emission performance.
[0005] Furthermore, the pore structure of the surface of the impregnated scandium-containing diffusion cathode has a significant impact on its emission performance. Higher porosity provides more channels for the storage and migration of active materials, promoting the continuous diffusion of active materials to the surface, thereby forming a stable and uniform active layer. When the porosity is low, the release and replenishment of active materials are limited, easily leading to uneven distribution of the surface active layer, which in turn affects the emission stability and service life of the cathode. In the manufacturing process of the impregnated scandium-containing diffusion cathode, after the active material impregnation process is completed, surface mechanical polishing or secondary processing is usually required to remove residual impregnation salts and meet design dimensional requirements. However, mechanical friction or cutting can cause plastic deformation of the tungsten metal particles on the surface, covering some of the pores on the substrate surface, thereby limiting the effective diffusion of active materials during operation and reducing electron emission efficiency. In addition, polishing or machining may also introduce impurities such as metal debris, non-metallic particles, or grease that are difficult to completely remove, easily causing "poisoning" of the cathode surface and resulting in emission performance degradation.
[0006] Therefore, there is an urgent need for a method that can effectively improve the emission capability of the cathode and remove the pores blocking the cathode surface, so as to improve the electron emission performance of the impregnated scandium diffused cathode. Summary of the Invention
[0007] To address the problems of low Sc content in existing scandium active materials, pore blockage on the surface of impregnated scandium-containing diffusion cathodes, reduced emission performance, and limited diffusion of active materials, this invention provides a scandium active material with high Sc2O3 content and its application in impregnated diffusion cathodes. By optimizing the component ratio, the Sc2O3 content of the scandium active material is increased to improve the emission performance of the impregnated diffusion cathode. Furthermore, surface etching technology is used to modify the cathode surface to effectively eliminate pore blockage caused by mechanical polishing or processing, thereby significantly improving the electron emission efficiency and stability of the cathode.
[0008] The technical solution adopted in this invention is as follows:
[0009] A scandium salt active material with high Sc2O3 content is obtained by mixing BaCO3, CaCO3, Al2O3 and Sc2O3 in a molar ratio of 12:2:3:1, grinding and pressing into sheets, sintering at 1100~1150 ℃ in air for 24~48 h, and then cooling and grinding.
[0010] The present invention also proposes the application of the scandium active material with high Sc2O3 content in an impregnated diffusion cathode.
[0011] A high-emission impregnated scandium-containing diffusion cathode is obtained by coating a porous tungsten substrate with a scandium active material of high Sc2O3 content, heating it to 1650~1700 °C in a hydrogen atmosphere, and holding it at that temperature until the scandium active material of high Sc2O3 content melts and impregnates into the porous tungsten substrate.
[0012] Furthermore, the heat preservation time is 3-5 minutes.
[0013] Furthermore, the surface of the high-emission impregnated scandium-containing diffusion cathode obtained by impregnation is polished, cleaned and dried, and then heated to 1100 °C in a hydrogen atmosphere and held for 8~15 min.
[0014] Furthermore, the polishing process uses 400-1000 grit sandpaper.
[0015] Furthermore, the specific cleaning process is as follows: first, ultrasonic cleaning with detergent, followed by repeated rinsing with deionized water.
[0016] Furthermore, the detergent is an aqueous solution of ethylenediaminetetraacetic acid (EDTA).
[0017] Furthermore, after polishing, a surface machining process is also included to process high-emission impregnated scandium-containing diffused cathodes into different shapes to meet different practical application requirements.
[0018] Furthermore, the obtained high-emission impregnated scandium-containing diffused cathode was placed in a vacuum chamber, and the vacuum level was evacuated to 5.0 × 10⁻⁻⁻⁶. 4 Below Pa, ion source gas is introduced into the vacuum chamber to maintain a working pressure of 3.0×10⁻² Pa. Then, ion beam etching is performed on the surface of the high-emission impregnated scandium-containing diffusion cathode to obtain a high-emission impregnated scandium-containing diffusion cathode with a high porosity surface.
[0019] Furthermore, the ion source gas is not limited to an argon ion source.
[0020] Furthermore, during the ion beam etching process, the ion energy was set to 1000 eV and the ion beam current to 70 mA. After the ion source was running stably, the high-emission impregnated scandium-containing diffusion cathode was placed 15-20 cm directly above the ion source and etched continuously for 60-120 min.
[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0022] 1. This invention proposes a scandium active material with high Sc2O3 content and its application in an impregnated diffusion cathode. By optimizing the composition ratio, a scandium active material with a Sc2O3 molar percentage of more than 5.5% is obtained, and it does not contain the ineffective active material BaAl2O4, so as to improve the emission performance of the impregnated diffusion cathode.
[0023] 2. Preferably, the present invention combines surface etching technology to modify the surface of the immersion-type diffusion cathode, so as to effectively eliminate the pore blockage caused by mechanical polishing or processing, promote the diffusion and regeneration of active materials, and thus achieve simultaneous improvement of cathode emission current density and working stability. Attached Figure Description
[0024] Figure 1 The X-ray diffraction (XRD) spectra of scandium powder prepared in Comparative Example 1 with a molar ratio of BaO:CaO:Al2O3:Sc2O3 of 6:1:2:0.3 are shown.
[0025] Figure 2 The X-ray diffraction pattern is that of scandium powder with a molar ratio of BaO:CaO:Al2O3:Sc2O3 of 12:2:3:1 prepared in Example 1.
[0026] Figure 3 The image shows a scanning electron microscope (SEM) image of the cathode of the scandium powder obtained in Example 1, which was impregnated with sandpaper in Example 2, after polishing.
[0027] Figure 4 The image shows a scanning electron microscope image of the cathode of Example 3, which was impregnated with the scandate powder obtained in Example 1, after sandpaper polishing and argon ion etching.
[0028] Figure 5 The images shown are scanning electron microscope images of the cathode of the scandium powder obtained in Example 1, which was impregnated with sandpaper and polished, under different argon ion etching times.
[0029] Figure 6 The DC emission current density J (unit A / cm²) of the cathode in Example 5 after impregnation with the scandate powder obtained in Example 1, followed by sandpaper polishing and argon ion etching. 2 A graph showing the relationship between the logarithm of the anode voltage U (in V).
[0030] Figure 7 The graph shows the relationship between the logarithm of the DC emission current density J and the logarithm of the anode voltage U after the cathode of Comparative Example 2, which is impregnated with scandate powder obtained in Comparative Example 1, is polished with sandpaper and etched with argon ions.
[0031] Figure 8The temperature T (in °C) of the cathode in Example 6 after being polished with sandpaper with the scandate powder obtained in Example 1 is shown in Example 6. b The relationship between () and normalized current density;
[0032] Figure 9 The graph shows the relationship between the temperature T and the normalized current density of the cathode after sandpaper polishing and argon ion etching of the scandium powder obtained in Example 1 in Example 7. Detailed Implementation
[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.
[0034] Comparative Example 1
[0035] This comparative example prepared a scandium salt powder with a molar ratio of BaO:CaO:Al2O3:Sc2O3 of 6:1:2:0.3. The specific process is as follows:
[0036] Weigh dry BaCO3, CaCO3, Al2O3, and Sc2O3 powders in a molar ratio of 6:1:2:0.3, grind them thoroughly in an agate mortar for at least 30 minutes to ensure uniform mixing, press the resulting powder mixture into 10 mm diameter discs, and place them in a corundum crucible. Place the crucible in a muffle furnace and heat it to 1150 °C at a rate of 2 °C / min. Calcinate the mixture in air for 24 h, then cool it to room temperature with the furnace to obtain scandate powder with a molar ratio of BaO:CaO:Al2O3:Sc2O3 of 6:1:2:0.3. In the obtained scandate powder, the molar ratio of alkaline earth metal oxides (BaO and CaO) to light metal oxides (Al2O3 and Sc2O3) is 7:2.3, and the molar percentage of Sc2O3 is 3.2%.
[0037] Figure 1 The X-ray diffraction pattern of the scandate powder obtained in this comparative example is shown. By comparing it with the standard card in the International Centre for Diffraction Data (ICDD), it can be seen that the scandate powder obtained in this comparative example contains three compounds: Ba3Al2O6 (PDF# 25-0075), BaAl2O4 (PDF# 17-0306), and β-phase Ba2ScAlO5 (PDF# 43-0078), among which BaAl2O4 is an inactive substance.
[0038] Example 1
[0039] This embodiment prepared a scandium salt powder with a molar ratio of BaO:CaO:Al2O3:Sc2O3 of 12:2:3:1. The specific process is as follows:
[0040] Weigh dry BaCO3, CaCO3, Al2O3, and Sc2O3 powders in a molar ratio of 12:2:3:1, grind them thoroughly in an agate mortar for at least 30 minutes to ensure uniform mixing, press the resulting powder mixture into 10 mm diameter discs, and place them in a corundum crucible. Place the crucible in a muffle furnace and heat it to 1150 °C at a rate of 2 °C / min. Calcinate the mixture in air for 24 h, then cool it to room temperature with the furnace to obtain scandate powder with a molar ratio of BaO:CaO:Al2O3:Sc2O3 of 12:2:3:1. In the obtained scandate powder, the molar ratio of alkaline earth metal oxides (BaO and CaO) to light metal oxides (Al2O3 and Sc2O3) is 14:4 = 7:2, and the molar percentage of Sc2O3 is 5.5%.
[0041] Figure 2 The X-ray diffraction pattern of the scandate powder obtained in this embodiment, when compared with the standard card in the International Diffraction Data Center, shows that the scandate powder obtained in this embodiment contains two effective active substances: Ba4Al2O7 (PDF# 28-0119) and β-phase Ba2ScAlO5 (PDF# 43-0078), and does not contain the non-effective active substance BaAl2O4 (PDF# 17-0306).
[0042] Compared to Comparative Example 1, the scandium powder obtained in this embodiment has a significantly increased Sc2O3 content and does not contain the non-effective active material BaAl2O4, which helps to improve the cathode emission performance.
[0043] Example 2
[0044] This embodiment prepares an impregnated diffusion cathode based on the scandium powder obtained in Example 1, and performs surface sandpaper polishing treatment. The specific process is as follows:
[0045] Tungsten-copper rods with a porosity of 23-25% were processed into cylinders with a diameter of 3.0 mm and a thickness of 2.5 mm. These cylinders were then immersed in sufficient concentrated nitric acid for chemical copper removal, with the nitric acid being replaced every 24 hours until the solution became colorless and transparent. Next, the tungsten substrate was subjected to high-temperature (1400 °C) vacuum copper removal using a high-frequency induction heating device. This heating and cooling process was repeated 3-5 times until no copper metal vapor evaporated. The copper-removed porous tungsten substrate and a molybdenum support cylinder were welded together using Mo-Ru solder at a welding temperature of 1950 °C. A wound tungsten wire heat exchanger was then inserted into the molybdenum support cylinder, and alumina powder was added to prevent short circuits. The heat exchanger assembly was then sintered in a hydrogen furnace for 8-15 minutes at a sintering temperature of 1700 °C. Scandium powder obtained in Example 1 was then coated around the porous tungsten substrate and placed in a high-temperature tungsten mesh hydrogen furnace at 1650 °C. High-temperature impregnation was performed at ℃ to obtain an impregnated diffusion cathode; residual salt on the cathode surface was removed using a carbide blade, and then the cathode surface was polished sequentially using 400-mesh, 800-mesh and 1000-mesh metallographic sandpaper to obtain a sandpaper-polished surface impregnated scandium-containing diffusion cathode.
[0046] Figure 3 This is a scanning electron microscope image of the cathode of the scandium powder obtained in Example 1 after sandpaper polishing. Obvious scratches are visible on the cathode surface after sandpaper polishing, but the original porous structure is obscured or blocked due to the deformation of the tungsten particles. Figure 3 The black area represents holes, and the calculated hole density is approximately 1300 holes / mm². 2 The opening size is relatively low.
[0047] Example 3
[0048] In this embodiment, the impregnated diffusion cathode prepared based on the scandium powder obtained in Example 1 is subjected to surface polishing with sandpaper and argon ion etching in sequence. The specific process is as follows:
[0049] The impregnated diffusion cathode obtained in Example 2, after being polished with sandpaper, was placed in an ethylenediaminetetraacetic acid solution and ultrasonically cleaned at a frequency of 40 kHz for 3-5 min, while maintaining the temperature at 25 ℃. It was then rinsed three times with deionized water and dried. Next, the cathode was heated to 1100 ℃ in a hydrogen atmosphere and held at that temperature for 8-15 min. Finally, the treated cathode was placed in a high-vacuum chamber, and its surface was bombarded and etched using an argon ion beam, with a base vacuum level not less than 5.0 × 10⁻⁻⁻⁻⁶. 4 High-purity argon gas is introduced into the chamber and the working pressure is maintained at 3.0×10⁻² Pa. An argon ion beam is generated using a Kaufman-type ion source with an ion energy of 1000 eV and an ion beam current of 70 mA. The bombardment etching lasts for 120 min, and finally, an impregnated scandium-containing diffusion cathode after argon ion etching is obtained.
[0050] Figure 4 This is a scanning electron microscope image of the cathode impregnated with the scandium powder obtained in Example 1, after sandpaper polishing and argon ion etching. It can be seen that after argon ion etching, the pores on the cathode surface are clearly visible after sandpaper polishing, the previously blocked pores are opened, and surface contaminants are effectively removed. Figure 4 The black area represents holes, and the calculated hole density is approximately 9300 holes / mm². 2 The porosity is significantly improved.
[0051] Example 4
[0052] Based on Example 3, this embodiment prepares scandium-containing diffusion cathodes with different argon ion etching times. Specifically, the bombardment etching times in Example 3 are set to 10 min, 60 min, 90 min and 120 min respectively.
[0053] Figure 5 The images shown are scanning electron microscope images of the cathodes impregnated with scandate powder obtained in Example 1 under different argon ion etching durations. It can be seen that when the etching duration is too short (e.g., 10 min), some of the pores on the cathode surface are still blocked. After argon ion etching for 60 min, 90 min and 120 min, the pores on the cathode surface are clearly visible, the original blocked pores are opened, and the surface contaminants are effectively removed.
[0054] Example 5
[0055] This embodiment describes the activation and current-voltage characteristic testing process of an impregnated diffusion cathode prepared based on the scandium powder obtained in Example 1, after surface polishing with sandpaper and argon ion etching.
[0056] Referring to Example 3, a cathode was obtained by impregnating the scandate powder obtained in Example 1 with sandpaper polishing and argon ion etching. The obtained cathode was installed in a water-cooled anode diode testing device. The anode was made of oxygen-free copper with a diameter of 52.0 mm, and the cathode-anode spacing was set to 1.0 mm. The background vacuum of the device was first evacuated to below 5 × 10⁻⁻⁻⁶. 6 Pa, then slowly increase the filament current, during which the vacuum degree does not exceed 5 × 10⁻ 5 Pa; heated to a cathode surface temperature of 1150 ℃ b (Brightness temperature) Gradually increase the voltage between the anode and cathode to 300 V, maintain for 3 h until emission stabilizes, and complete the cathode activation process.
[0057] Next, the current-voltage characteristic test was conducted. Figure 6 The cathode obtained in this embodiment is at 1100 °C bThe double logarithmic graph of emission current density J versus anode voltage U shows that at 1100 ℃... b Below, its deviation point current density J div It is 18.41 A / cm².
[0058] Comparative Example 2
[0059] This comparative example is based on the scandium powder obtained in Comparative Example 1, which is used to prepare an impregnated diffusion cathode. After surface polishing with sandpaper and argon ion etching, the cathode activation and current-voltage characteristic test were performed. The only difference between this example and Example 5 is that the impregnating material was changed to the scandium powder obtained in Comparative Example 1; the other processes remained the same.
[0060] Figure 7 The cathode obtained for this comparative example was at 1100 °C. b The double logarithmic graph of emission current density J versus anode voltage U shows that at 1100 ℃... b Below, its deviation point current density J div With an A / cm² of only 10.98, Example 5 shows a lower deviation point current density J compared to Comparative Example 2. div The increase of about 40% and the relatively fast saturation rate of the current-voltage characteristic curve indicate that the work function distribution on the cathode surface is relatively uniform.
[0061] Example 6
[0062] In this embodiment, the impregnated diffusion cathode prepared based on the scandate powder obtained in Example 1 was subjected to cathode activation and underheating characteristic tests after surface polishing with sandpaper. Specifically:
[0063] Referring to Example 2, a cathode made of scandium powder obtained in Example 1 after being polished with sandpaper was obtained, and the cathode was activated according to Example 5.
[0064] Subsequent underheating characteristic tests were conducted, with the cathode emission fixed at 1 A / cm. 2 2 A / cm 2 4 A / cm 2 and 8A / cm 2 Under the given emission current density, the cathode temperature was gradually reduced, and the emission current value was recorded. Figure 8 The graph shows the relationship between the temperature T and the normalized current density of the cathode after polishing with sandpaper on which the scandate powder obtained in Example 1 was impregnated. It can be seen that the cathode operates at temperatures between 1000 and 1200°C. b The emission density decreases rapidly at 50% emission density, and the interval between each curve at 50% emission density is about 20℃, which is lower than the theoretical value of 40℃. This indicates that there is a region with excessively large differences in the work function on the cathode surface, indicating that the electron emission uniformity of the cathode is poor.
[0065] Example 7
[0066] This embodiment describes the activation and underheating characteristics testing of an impregnated diffusion cathode prepared based on the scandium powder obtained in Example 1, after surface polishing with sandpaper and argon ion etching.
[0067] Referring to Example 3, a cathode made of scandium powder obtained in Example 1 was obtained after sandpaper polishing and argon ion etching, and the cathode was activated according to Example 5.
[0068] Subsequent underheating characteristic tests were conducted, with the cathode emission fixed at 1 A / cm. 2 2 A / cm 2 4 A / cm 2 and 8A / cm 2 Under the given emission current density, the cathode temperature was gradually reduced, and the emission current value was recorded. Figure 9 The cathodes of the scandium powder obtained in Example 1 were polished with sandpaper and etched with argon ions at temperatures T and normalized current densities. It can be seen that the cathodes operate at temperatures between 1000 and 1200°C. b The emission density decreases relatively gently, and the interval between each curve at 50% emission density is about 37 °C, close to the theoretical value of 40 °C, indicating that the emission uniformity of the cathode is significantly improved after argon ion etching.
[0069] In summary, this invention achieves a balance between high porosity of the cathode surface and efficient diffusion of active materials by designing a scandium salt system with high Sc2O3 content and no BaAl2O4 phase, and by combining it with ion surface etching technology. This significantly improves the emission current density and operational stability of the impregnated scandium-containing diffusion cathode.
[0070] It should be noted that the present invention can be modified and varied in various ways. Any modifications, substitutions, improvements, etc., made within the spirit and principle of this application should be included within the scope of the claims of this application.
Claims
1. A scandium salt active material with high Sc2O3 content, characterized in that, BaCO3, CaCO3, Al2O3 and Sc2O3 are mixed in a molar ratio of 12:2:3:1, ground and pressed into sheets, sintered at 1100~1150 ℃ in air for 24~48 h, cooled and ground to obtain the final product.
2. The application of the scandium active material with high Sc2O3 content according to claim 1 in an impregnated diffusion cathode.
3. A high-emission impregnated scandium-containing diffusion cathode, characterized in that, The substrate is obtained by coating the surface of a porous tungsten matrix with the high Sc2O3 content scandate active material as described in claim 1, heating it to 1650~1700 °C in a hydrogen atmosphere, and holding it at that temperature until the high Sc2O3 content scandate active material melts and impregnates into the porous tungsten matrix.
4. The high-emission impregnated scandium-containing diffused cathode according to claim 3, characterized in that, The heat preservation time is 3-5 minutes.
5. The high-emission impregnated scandium-containing diffused cathode according to claim 4, characterized in that, The surface of the high-emission impregnated scandium-containing diffusion cathode obtained by impregnation is polished, cleaned and dried, and then heated to 1100 °C in a hydrogen atmosphere and held for 8~15 min.
6. The high-emission impregnated scandium-containing diffusion cathode according to claim 5, characterized in that, The polishing process uses 400-1000 grit sandpaper.
7. The high-emission impregnated scandium-containing diffused cathode according to claim 5, characterized in that, After polishing, a surface machining process is also included to process high-emission impregnated scandium-containing diffused cathodes into different shapes to meet different practical application requirements.
8. The high-emission impregnated scandium-containing diffused cathode according to claim 5, characterized in that, The resulting high-emission impregnated scandium-containing diffused cathode was then placed in a vacuum chamber, and the vacuum level was evacuated to 5.0 × 10⁻⁻⁻⁶. 4 Below Pa, ion source gas is introduced into the vacuum chamber to maintain a working pressure of 3.0×10⁻² Pa. Then, ion beam etching is performed on the surface of the high-emission impregnated scandium-containing diffusion cathode to obtain a high-emission impregnated scandium-containing diffusion cathode with a high porosity surface.
9. The high-emission impregnated scandium-containing diffused cathode according to claim 8, characterized in that, During the ion beam etching process, the ion energy was set to 1000 eV and the ion beam current to 70 mA. After the ion source was running stably, the high-emission impregnated scandium-containing diffusion cathode was placed 15-20 cm directly above the ion source and etched continuously for 60-120 min.