Hot cathode for vacuum device as well as preparation method and application of hot cathode

Abstract

The invention discloses a hot cathode for a vacuum device and a preparation method and application of the hot cathode. The structure of the hot cathode comprises a cathode substrate and an emission active material combined on the cathode substrate; wherein the cathode substrate is of a porous structure, and the cathode substrate is made of a mixture of chromic oxide and tungsten; and the emission active material is scandium-containing barium aluminate. According to the scheme, the problem that the requirement of a current high-power vacuum electronic device for a low-working-temperature and high-emission-current-density electron source cannot be met is well solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of vacuum electron devices. More particularly, it relates to a hot cathode for vacuum devices and a preparation method and application thereof. BACKGROUND

[0002] A vacuum electron device is a kind of device that realizes specific functions through electron movement in a vacuum or near-vacuum environment. It is widely used in the fields of aviation, communication, etc. The cathode is the core component in a vacuum device, which provides electrons, also known as an electron source. The electrons emitted by the cathode move under the action of electric field and magnetic field, and are finally received by the anode or other electrodes, during which various functions of the device are realized. As can be seen from the working principle of the above-mentioned vacuum device, the ability of the cathode to emit electrons is the core ability of the cathode and is also the main indicator for measuring the performance of the cathode. The main challenge in current cathode research is to improve the emission current.

[0003] The widely used large current density cathodes at present include film diffusion cathodes and scandium-containing cathodes. The emission current density of the film diffusion cathodes cannot meet the requirements of high-power devices, and the ordinary scandium-containing cathodes have problems such as poor resistance to poisoning and process stability, and low engineering level. Therefore, the above-mentioned two kinds of cathodes cannot fully meet the needs of actual devices. SUMMARY

[0004] Based on the above background, the purpose of the present application is to provide a hot cathode for vacuum devices and a preparation method and application thereof, so as to solve the problem that the current demand for low working temperature and high emission current density electron source of high-power vacuum electron devices cannot be met.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: On the one hand, the present application provides a hot cathode for vacuum devices, the structure of the hot cathode comprising a cathode base and an emission active material combined on the cathode base; wherein, The cathode base is a porous structure, and the material of the cathode base is a mixture of chromium oxide and tungsten; The emission active material is scandium-containing barium aluminate.

[0006] Further, the emission active material is located at least in the pores of the cathode base.

[0007] Further, the emission active material is impregnated in the pores of the cathode base.

[0008] Further, in the hot cathode, the mass fraction of the emission active material is 4-10wt%.

[0009] Further, the molar ratio of tungsten to chromium oxide is (9.0-13.0):(0.09-0.75), and the volume percentage of pores in the cathode substrate is 10-45%.

[0010] In a second aspect, the present application provides a preparation method of the hot cathode as described in the first aspect above, which comprises the following steps: mixing chromium oxide powder and tungsten powder uniformly to obtain mixed substrate powder; pressing and forming the mixed substrate powder and performing sintering to obtain a cathode substrate; combining scandium-containing barium aluminate with the cathode substrate by a heat treatment method to obtain the hot cathode.

[0011] Further, the sintering temperature is 1400-1900℃, and the sintering time is 10-50 minutes.

[0012] Further, the average particle size of the tungsten powder is 0.5-7.5μm, and the purity of the chromium oxide powder is ≥99.9%.

[0013] Further, the pressing and forming method uses die pressing or isostatic pressing.

[0014] Further, the heat treatment method is: melting the scandium-containing barium aluminate at high temperature in a hydrogen atmosphere, and impregnating into the pores of the cathode substrate by capillary action.

[0015] Further, the impregnation temperature is 1550-1750℃, and the impregnation time is 0.5-5 minutes.

[0016] Further, the scandium-containing barium aluminate is prepared by a coprecipitation method, and the specific preparation steps include: dissolving soluble barium salt (for example, barium nitrate), calcium salt (for example, calcium nitrate), aluminum salt (for example, aluminum nitrate), and scandium salt (for example, scandium nitrate) in deionized water to prepare a mixed salt solution (the solution concentration is preferably 0.5-2.0mol / L); dissolving ammonium carbonate ((NH4)2CO3) in deionized water to obtain a carbonate solution; mixing the above mixed salt solution and the carbonate solution (the volume ratio of the mixed salt solution to the carbonate solution is preferably 1:1-1:4), and the reaction generates a precipitate, and the product is dried to obtain the scandium-containing barium aluminate.

[0017] Further, the molar ratio of the soluble barium salt, the calcium salt, the aluminum salt, and the scandium salt is 2-5:0.5-2:1.5-4:0.2-1.0.

[0018] Further, the concentration of the carbonate solution is 0.1-0.5mol / L.

[0019] In a third aspect, the application provides a use of the thermionic cathode as described in the first aspect above in the manufacture of a vacuum device.

[0020] Further, the vacuum device is a high power (preferably a power above 1 kW) vacuum electron device.

[0021] Further, the vacuum device is a vacuum electron device with an electron source of high current density (50 A / cm 2 above, preferably 70 A / cm 2 above).

[0022] Unless otherwise defined, all ranges recited in the application include the endpoints and any and all intervening values between the endpoints, as well as any and all sub-ranges between the endpoints.

[0023] The application has the following advantages: The thermionic cathode provided in the application can provide an emission current density above 60 A / cm 2 at 1000℃. In the thermionic cathode of the application, the chromium oxide can act as a reducing agent to react with the emission material to generate active barium element and improve the generation efficiency of barium during the operation of the cathode. On the other hand, the chromium can combine with the tungsten element to form a more stable emission surface structure, thereby helping to improve the stability and reliability of the cathode operation. The thermionic cathode has the characteristics of low operating temperature and high emission current density, and provides a vacuum electron device with an electron source of high current density, effectively solving various problems caused by insufficient emission during the development of the vacuum device. BRIEF DESCRIPTION OF DRAWINGS

[0024] The specific embodiments of the application will be further described in detail below with reference to the accompanying drawings.

[0025] Figure 1 An SEM picture of the mixed base powder prepared in Example 1 of the application is shown; Figure 2 An SEM picture of the surface of the chromium oxide-tungsten porous cathode base prepared in Example 1 of the application is shown; Figure 3 An SEM picture of the surface element type and distribution of the thermionic cathode prepared in Example 1 of the application is shown; Figure 4 A comparison chart of the emission performance of the thermionic cathode prepared in Example 1 of the application and a common pure tungsten base scandium-containing thermionic cathode is shown. DETAILED DESCRIPTION

[0026] In order to make the present application clearer, further description will be made to the present application with preferred embodiments and accompanying drawings. Like components are denoted by like reference numerals in the accompanying drawings. Those skilled in the art should understand that the specific description below is illustrative rather than limiting, and the scope of protection of the present application should not be limited thereby.

[0027] In the present application, unless otherwise specified, all conventional methods are used, and the raw materials used can be obtained from public commercial channels unless otherwise specified.

[0028] Example 1 A hot cathode for a vacuum device, the specific preparation method comprising the following steps: Tungsten powder (average particle size 3.0±0.5μm) and chromium oxide powder (purity >99.9%, green flocculent) are weighed in a molar ratio of 9.8:0.12 and mechanically mixed in a universal ball mill to prepare a chromium oxide-tungsten mixed matrix powder; the scanning electron microscope picture of the obtained mixed matrix powder is shown in Figure 1 ; The mixed matrix powder is pressed into a cylindrical porous body by a molding method; The pressed porous body is sintered in a hydrogen atmosphere, the sintering temperature is 1620℃, and the holding time is 30 minutes, to prepare a chromium oxide-tungsten porous cathode matrix, the total porosity of the cathode matrix is 24-29%, and the diameter is 3.1-3.6mm, the surface SEM picture of the chromium oxide-tungsten porous cathode matrix is shown in Figure 2 ; The above-mentioned scandium-containing barium aluminate is high-temperature melted in a hydrogen furnace and impregnated into the chromium oxide-tungsten porous cathode matrix, the impregnation temperature is 1600℃, and the time is 3 minutes to prepare the hot cathode. After impregnation, the mass fraction of the emission active material in the hot cathode is in the range of 6-8wt%.

[0029] The scandium-containing barium aluminate is prepared by a coprecipitation method, specifically comprising the following steps: Barium nitrate, calcium nitrate, aluminum nitrate, and scandium nitrate are weighed and mixed in a molar ratio of 3.25:0.85:1.87:0.35, dissolved in deionized water to prepare a mixed nitrate solution, and the concentration of the solution is 1.25mol / L; Ammonium carbonate ((NH4)2CO3) is dissolved in deionized water to prepare a solution with a concentration of 0.25mol / L; The mixed nitrate solution and the ammonium carbonate solution are mixed in a volume ratio of 1:1.75, and stirred thoroughly, then left to stand and filtered, the precipitate is washed in deionized water, left to stand and filtered, and the filtered precipitate is baked at 150℃ for 6 hours to obtain the scandium-containing barium aluminate.

[0030] The types and distribution of elements on the surface of the hot cathode are shown in Figure 3The emission surface of the hot cathode comprises the base elements W, Cr, O and the impregnated material elements Ba, Sc, Ca, Al, O.

[0031] The hot cathode was tested for emission performance in a close-spaced diode system. A comparison of the U-J curve of the hot cathode obtained in this embodiment with that of a pure tungsten-based (without chromium oxide) scandium-containing hot cathode sample is shown in FIG. 2. Figure 4 The results show that the emission current density of the hot cathode in this embodiment can reach 79.4 A / cm 2 under the same test conditions. The typical emission current density of a pure tungsten-based scandium-containing hot cathode impregnated with the same formula emission material prepared in the same batch is 52.2 A / cm 2 The emission current density of the hot cathode prepared in this embodiment is 52.1% higher than that of a conventional tungsten-based cathode under the same test conditions.

[0032] Embodiment 2 A hot cathode for a vacuum device, the specific preparation method comprising the following steps: The tungsten powder (average particle size 3.5±0.5 μm) and chromium oxide powder (purity > 99.9%, green flocculent) are weighed according to a molar ratio of 12.0:0.45 and then mixed to form a chromium oxide-tungsten mixed base powder; The mixed base powder is pressed into a cylindrical porous body by a die pressing method; The pressed porous body is sintered in a hydrogen atmosphere at a sintering temperature of 1580°C for 24 minutes to form a chromium oxide-tungsten porous cathode base, and the total porosity of the cathode base is 27-30% and the diameter is 3.17±0.05 mm; The scandium-containing barium aluminate is melted at high temperature in a hydrogen furnace and impregnated into the chromium oxide-tungsten porous cathode base at an impregnation temperature of 1600°C for 3 minutes to obtain the hot cathode. The mass fraction of the emission active material in the impregnated hot cathode is in the range of 5-7 wt%.

[0033] The scandium-containing barium aluminate is prepared by a co-precipitation method, specifically comprising the following steps: Barium nitrate, calcium nitrate, aluminum nitrate and scandium nitrate are weighed and mixed according to a molar ratio of 2.7:1.3:2.5:0.2, dissolved in deionized water to obtain a mixed nitrate solution, and the concentration of the solution is 1.65 mol / L; Ammonium carbonate ((NH4)2CO3) is dissolved in deionized water to obtain a solution with a concentration of 0.32 mol / L; The mixed nitrate solution and the ammonium carbonate solution are mixed at a volume ratio of 1:2.15, and after being stirred thoroughly, the precipitate is filtered after standing, the precipitate is washed in deionized water, and after standing and filtering, the filtered precipitate is baked at 150°C for 7 hours to obtain the scandium-containing barium aluminate.

[0034] The hot cathode is tested for emission performance in a close-spaced diode system, and the results show that in this embodiment, the hot cathode has an emission current density of 79.1 A / cm 2 under the same test conditions. The scandium-containing hot cathode prepared in this embodiment has an emission current density that is 47.0% higher than that of a conventional tungsten-based cathode under the same test conditions. 2

[0035] Example 3 A hot cathode for a vacuum device, the specific preparation method comprising the following steps: The tungsten powder (average particle size 4.5±0.5 μm) and the chromium oxide powder (purity >99.9%, green flocculent) are weighed at a molar ratio of 12.5:0.67 and mixed to form a chromium oxide-tungsten mixed matrix powder; The mixed matrix powder is pressed into a cylindrical porous body by a pressing method; The pressed porous body is sintered in a hydrogen atmosphere at a sintering temperature of 1650°C for 30 minutes to form a chromium oxide-tungsten porous cathode matrix, and the total porosity of the cathode matrix is 26-29%, and the diameter is 3.2±0.05 mm; The scandium-containing barium aluminate is melted at high temperature in a hydrogen furnace and impregnated into the chromium oxide-tungsten porous cathode matrix at an impregnation temperature of 1600°C for 3 minutes to form the hot cathode. After impregnation, the mass fraction of the emission active material in the hot cathode is in the range of 4-7wt%.

[0036] The scandium-containing barium aluminate is prepared by a coprecipitation method, specifically comprising the following steps: Barium nitrate, calcium nitrate, aluminum nitrate, and scandium nitrate are weighed and mixed at a molar ratio of 2.5:1.5:2.0:0.32, dissolved in deionized water to form a mixed nitrate solution, and the concentration of the solution is 0.95 mol / L; Ammonium carbonate ((NH4)2CO3) is dissolved in deionized water to form a solution with a concentration of 0.40 mol / L; The mixed nitrate solution and the ammonium carbonate solution are mixed at a volume ratio of 1:3, and after being stirred thoroughly, the precipitate is filtered after standing, the precipitate is washed in deionized water, and after standing and filtering, the filtered precipitate is baked at 150°C for 7 hours to obtain the scandium-containing barium aluminate.

[0037] ​The hot cathode is tested for emission performance in a close distance diode system, and the results show that in this embodiment, the emission current density of the hot cathode at 1000℃ can reach 68.9A / cm 2 .

[0038] Embodiment 4 A hot cathode for a vacuum device, the specific preparation method comprising the following steps: The tungsten powder (average particle size 5.5±0.5μm) and the chromium oxide powder (purity >99.9%, green flocculent) are weighed and mixed in a ratio of 9.8:0.21 (molar ratio) to form a chromium oxide-tungsten matrix powder; The mixed powder is pressed into a cylindrical porous body by a molding method; The pressed porous body is sintered in a hydrogen atmosphere at a sintering temperature of 1680℃ for 35 minutes to form a chromium oxide-tungsten porous matrix, and the total porosity of the matrix is 23-27%, and the diameter is 3.12±0.05mm; The scandium-containing barium aluminate is melted at high temperature in a hydrogen furnace and impregnated into the chromium oxide-tungsten porous cathode matrix at a temperature of 1600℃ for 3 minutes to obtain the hot cathode. After impregnation, the mass fraction of the emission active material in the hot cathode is in the range of 4-6wt%.

[0039] The scandium-containing barium aluminate is prepared by a co-precipitation method, specifically comprising the following steps: Barium nitrate, calcium nitrate, aluminum nitrate and scandium nitrate are weighed and mixed in a molar ratio of 3.5:1.1:3.2:0.9, dissolved in deionized water to obtain a mixed nitrate solution, and the concentration of the solution is 1.75mol / L; Ammonium carbonate ((NH4)2CO3) is dissolved in deionized water to obtain a solution with a concentration of 0.28mol / L; The mixed nitrate solution and the ammonium carbonate solution are mixed in a volume ratio of 1:3.5 and stirred thoroughly, and after standing, the precipitate is filtered, washed in deionized water, and filtered after standing. The filtered precipitate is baked at 150℃ for 7 hours to obtain the scandium-containing barium aluminate.

[0040] The hot cathode is tested for emission performance in a close distance diode system, and the results show that in this embodiment, the emission current density of the hot cathode at 1000℃ can reach 63.7A / cm 2 .

[0041] Obviously, the above embodiments of the present application are merely exemplary and are not intended to limit the embodiments of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art, and it is impossible to enumerate all the embodiments here. Any obvious changes or variations derived from the technical solutions of the present application are still within the protection scope of the present application.

Claims

1. A hot cathode for a vacuum device, characterized in that, The structure of the hot cathode includes a cathode substrate and an emission-active material bonded to the cathode substrate; wherein... The cathode substrate has a porous structure, and the cathode substrate is made of a mixture of chromium oxide and tungsten. The emission-active material is scandium barium aluminate.

2. The hot cathode according to claim 1, characterized in that, The emission-active material is located at least in the pores of the cathode substrate; Preferably, the mass percentage of the emissive active material in the thermal cathode is 4-10 wt%.

3. The hot cathode according to claim 1, characterized in that, The molar ratio of tungsten to chromium oxide is (9.0-13.0):(0.09-0.75); and / or The volume fraction of pores in the cathode substrate is 10-45%.

4. A method for preparing a hot cathode as described in any one of claims 1-3, characterized in that, The preparation method includes the following steps: Chromium oxide powder and tungsten powder are mixed evenly to obtain a mixed matrix powder; The mixed matrix powder is pressed into shape and sintered to obtain a cathode matrix; The thermal cathode is obtained by bonding scandium barium aluminate to the cathode substrate using a heat treatment method.

5. The preparation method according to claim 4, characterized in that, The tungsten powder has an average particle size of 0.5-7.5 μm, and the chromium oxide powder has a purity of ≥99.9%.

6. The preparation method according to claim 4, characterized in that, The sintering is carried out in a hydrogen atmosphere at a temperature of 1400-1900℃ for 10-50 minutes.

7. The preparation method according to claim 4, characterized in that, The heat treatment method is as follows: scandium barium aluminate is melted at high temperature in a hydrogen atmosphere and impregnated into the pores of the cathode substrate through capillary action; Preferably, the immersion temperature is 1550-1750℃ and the immersion time is 0.5-5min.

8. The application of the hot cathode as described in any one of claims 1-3 in the fabrication of vacuum devices.

9. The application according to claim 8, characterized in that, The vacuum device is a high-power vacuum electronic device.

10. The application according to claim 9, characterized in that, The vacuum device is a vacuum electronic device with a high current density electron source.

Images