High-power pulse magnetron cathode heater assembly, preparation method and application

Abstract

The present invention discloses a cathode heater assembly for a high-power pulse magnetron, a preparation method, and applications. The assembly comprises a tungsten wire wound into a desired shape, followed by a primary high-temperature shaping step, an insulating layer coating, and a secondary high-temperature sintering step to produce the desired heater. A cathode blank with a tantalum sponge is prepared; a cathode preform with a tantalum sponge is coated with a composite rare earth oxide suspension and sintered in a high-temperature vacuum furnace to produce the desired cathode. The cathode and heater are assembled, and the space between the cathode and heater is filled with a thermally conductive and electrically conductive material before being sintered in a vacuum furnace to produce the cathode heater assembly. The cathode heater assembly of the present invention exhibits high thermal emission and secondary electron emission, and good resistance to electron and ion bombardment, thereby extending its service life while adapting to the operating environment of a high-power pulse magnetron. The assembly also features low cathode heating power, high thermal emission current density, and rapid startup.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-power microwave vacuum electronic devices, and in particular relates to a high-power pulse magnetron cathode heater assembly, a preparation method and an application thereof. Background Art

[0002] Currently, the cathodes commonly used in high-power magnetrons include alkaline earth metal oxide cathodes, barium tungsten cathodes, and thoriated tungsten cathodes. Alkaline earth metal oxide cathodes have a large secondary electron emission coefficient, but their resistance to electron and ion bombardment is poor, and the cathode is prone to "sparking" discharge under high voltage. Barium tungsten cathodes have good high-voltage resistance, but are weak to electron and ion bombardment and have a low secondary emission coefficient. Increased backbombardment is required to achieve sufficient current multiplication, which is not conducive to rapid oscillation. This cathode is complex to manufacture and has high cost. Thorium tungsten cathodes have good resistance to electron bombardment, but thorium is a radioactive element.

[0003] The oxide coating of conventional oxide cathodes has a relatively high resistivity. When an intermediate layer exists between the base metal and the coating, the coating resistance negatively impacts operation. This is particularly true in high-power pulsed magnetrons, where resistive heating within the coating disrupts the cathode's thermal balance. The resulting electric field is a primary cause of sparking. Therefore, to avoid the formation of this intermediate resistance layer and increase the coating's conductivity, nickel powder is currently sintered onto a nickel sleeve to form a nickel sponge, which is then coated with a ternary carbonate. However, this is only suitable for low-power vacuum devices. Summary of the Invention

[0004] The purpose of the present invention is to solve the above technical problems and provide a high-power pulse magnetron cathode thermal subassembly, a preparation method and an application. The prepared cathode thermal subassembly has high thermal emission and secondary electron emission, and has good resistance to electron and ion bombardment, and can adapt to the working environment of the high-power pulse magnetron.

[0005] To achieve the above object, the present invention provides a method for preparing a cathode heater assembly of a high-power pulsed magnetron, comprising the following steps:

[0006] Preparation of heater: After winding tungsten wire into shape, high-temperature shaping, insulation coating and secondary high-temperature sintering are carried out in sequence to produce the required heater;

[0007] Preparation of the cathode: a) forming a tantalum-niobium alloy strip into a cathode sleeve and then vacuum degassing the sleeve, baking the cathode sleeve mold, and then evenly spraying cotton glue onto the emitting surface of the cathode sleeve. Purified tantalum powder is evenly sieved on the cotton glue surface, and finally cotton glue is sprayed on the surface of the purified tantalum powder and dried to obtain a cathode blank with a tantalum sponge. b) placing the cathode blank with the tantalum sponge in a tantalum skin vacuum furnace and sintering at high temperature to obtain a cathode preform with a tantalum sponge. c) coating the surface of the tantalum sponge of the cathode preform with the tantalum sponge with a composite rare earth oxide suspension and drying or air-drying. d) repeating step c) until the pores of the tantalum sponge are filled with the composite rare earth oxide. e) placing the cathode coated with the composite rare earth oxide in a high-temperature vacuum furnace and sintering to obtain the desired cathode.

[0008] Assembly: Assemble the cathode and heater, fill the space between the cathode and heater with thermally conductive material, and then sinter them in a vacuum furnace to prepare a cathode-heater assembly.

[0009] Furthermore, the tungsten wire is of the brand WK80G; the annealing temperature of the tungsten wire during winding is 850±20°C; the high temperature setting temperature is 1200±50°C and the time is 10 to 15 minutes; the thermal cold measurement resistance is 0.1 to 0.119Ω.

[0010] Furthermore, the coating insulation layer adopts cathode electrophoresis method, the electrophoresis voltage is 30-100V, and the thickness of electrophoretic alumina powder is 0.02-0.04 mm; the secondary high-temperature sintering is carried out in a hydrogen furnace, the sintering temperature is 1400±20°C, and the time is 3-5 minutes.

[0011] Furthermore, in step a), the purified tantalum powder is screen-coated multiple times until the weight of the purified tantalum powder meets the requirements; the vacuum degassing temperature is 1400-1600°C and the time is 30-60 minutes; the mold on the cathode sleeve is baked at a temperature of 80-100°C; the specific process of purifying the tantalum powder in step a) is as follows: pure tantalum powder that meets national standards is placed in a glass bottle, completely immersed in butyl acetate, and then sealed and rolled for 30-60 minutes. After precipitation, the residual liquid is poured out, the powder is immersed in ethanol, dried, and washed with distilled water for 3-5 times, each time for 5-10 minutes; it is dehydrated and dried with anhydrous ethanol, and sent to a hydrogen burning furnace, the temperature is controlled at 650-850°C, and the time is 10-15 minutes; after cooling, it is crushed to obtain the purified tantalum powder.

[0012] Furthermore, the specific process of placing the cathode blank with tantalum sponge into a tantalum skin vacuum furnace for high temperature sintering in step b) is as follows: when the vacuum degree P is less than 3×10 -3Pa, start heating, when the temperature rises to 600-800℃, keep it warm for 30-60 minutes; when the temperature rises to 1200-1400℃, keep it warm for 60-90 minutes; and the vacuum degree is always kept at 5×10 -3 Pa~6×10 -3 Pa; cool down to zero position of the voltage regulator twice, turn off the heating power, and take out the cathode preform with tantalum sponge after it cools down.

[0013] Furthermore, in step d), the composite rare earth oxide comprises 90-80% Y2O3 and 10-20% ZrO2 by mass, and the average particle size of Y2O3 is 5-10 μM.

[0014] Furthermore, in step e), the cathode coated with composite rare earth oxide is placed in a high temperature vacuum furnace for sintering. The specific process is as follows: when the vacuum degree P is less than 3×10 -3 Pa, start heating, when the temperature rises to 400-500℃, keep it warm for 30-60 minutes; when the temperature rises to 1050-1100℃, keep it warm for 50-80 minutes; when the temperature rises to 1200-1300℃, keep it warm for 10-20 minutes, and then cool; the vacuum degree is always kept at 5×10 -3 Pa~6×10 -3 Pa.

[0015] Furthermore, during the assembly process, the vacuum furnace sintering temperature is 1200-1400° C. and the time is 10-15 minutes; the thermally conductive and electrically conductive material includes 60-50% nickel powder and 40-50% molybdenum powder by weight, and both the nickel powder and the molybdenum powder are sieved with a 200-mesh molecular sieve.

[0016] A cathode heater assembly is also provided, which is prepared by the above preparation method.

[0017] Finally, an application of a cathode heater assembly prepared by the above preparation method is provided, wherein the cathode heater assembly is heated by a direct current power supply.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: the cathode thermal sub-assembly of the present invention has higher thermal emission and secondary electron emission, and has good resistance to electron and ion bombardment, which increases the service life, while being able to adapt to the working environment of high-power pulse magnetrons; it also has the characteristics of low cathode heating power, large thermal emission current density, and can start quickly. DETAILED DESCRIPTION

[0019] The method for preparing the cathode heater assembly of a high-power pulse magnetron according to the present invention is as follows:

[0020] Preparation of heater: Tungsten wire is wound and formed, and then high-temperature shaping, insulation layer coating and secondary high-temperature sintering are carried out in sequence to make the required heater. The cold-measured resistance of the heater is 0.1~0.119Ω.

[0021] Specifically: the tungsten wire used is brand WK80G. The WK80G tungsten wire is doped with trace elements such as potassium oxide, aluminum oxide, silicon oxide, etc. It is shock-resistant, anti-sagging, and has good high-temperature performance.

[0022] When tungsten wire is wound into a spiral, the deformation of the tungsten wire material is very large at the turning point, resulting in a certain amount of plastic deformation. Therefore, when winding, the annealing temperature is 850±20℃ (lower than the optimal annealing temperature of tungsten wire) to obtain the temperature of maximum elongation; when the annealing temperature is lower than the optimal annealing temperature of tungsten wire, dislocations, distortion and broken grains formed during deformation still remain in the tungsten wire. After annealing, the elongation of the tungsten wire is small. Under-annealed tungsten wire can be well annealed by reheating to the corresponding temperature. If the annealing temperature is higher than the optimal annealing temperature of tungsten wire, the plasticity and strength of the tungsten wire will become worse due to collective recrystallization. The original properties of the overheated tungsten wire cannot be restored, it is brittle, the yield rate is very low, and there is a lot of waste.

[0023] After the tungsten wire material is formed, it must be "set" before the external force is removed. Therefore, high-temperature setting is carried out at 1200±50℃ for 10 to 15 minutes. Tungsten wire setting is actually a stage before the recrystallization process in heat treatment, generally called the recovery stage. It can reduce the elastic distortion ability of the tungsten wire, greatly weaken the mutual restraint between grains and crystal blocks, greatly reduce the microscopic internal stress, and restore various mechanical properties to a certain extent, so that the shape of the heat element can be stabilized.

[0024] The insulating layer is coated using cathodic electrophoresis, with a voltage of 30-100V and an alumina powder thickness of 0.02-0.04mm. Secondary high-temperature sintering is performed in a hydrogen furnace at 1400±20°C for 3-5 minutes. This ensures that when the heater is powered on, coils and other metals will not collide and short-circuit.

[0025] Preparation of the cathode: a) A tantalum-niobium alloy strip is formed into a cathode sleeve and then vacuum degassed at 1400-1600°C for 30-60 minutes. The upper mold of the cathode sleeve is baked at 80-100°C for several minutes, and then cotton glue is evenly sprayed onto the emission surface of the cathode sleeve. Purified tantalum powder is then evenly sieved onto the surface of the cotton glue. The sieve-coating of the purified tantalum powder is repeated multiple times until the weight of the purified tantalum powder meets the requirements. Finally, cotton glue is sprayed onto the surface of the purified tantalum powder and dried to produce a cathode blank with a tantalum sponge. The addition of tantalum powder increases the conductivity and mechanical strength of the coating, thereby improving the DC emission capability of the magnetron.

[0026] The specific process of purifying tantalum powder is as follows: put pure tantalum powder that meets national standards into a glass bottle, immerse it completely with butyl acetate, then seal and roll grind for 30 to 60 minutes, pour out the residual liquid after precipitation, soak it in ethanol, dry it, boil it with distilled water and wash it 3 to 5 times, each time for 5 to 10 minutes; dehydrate and dry it with anhydrous ethanol, send it into a hydrogen burning furnace, control the temperature at 650 to 850 degrees Celsius, and the time is 10 to 15 minutes; after cooling, crush it to obtain the purified tantalum powder.

[0027] b) placing the cathode blank with the tantalum sponge into a tantalum skin vacuum furnace and sintering at high temperature to obtain a cathode preform with the tantalum sponge;

[0028] Since the melting point of tantalum is 2996℃ and the density is 16.5×10 3 Kg / m 3 The conductivity is 6 times that of mercury. Tantalum will react with hydrogen at room temperature, making the material brittle. Therefore, it cannot be treated with high-temperature hydrogen burning. Therefore, the cathode blank with tantalum sponge is placed in a tantalum skin vacuum furnace and gradually evacuated. When the vacuum degree P≤3×10 -3 Pa, start heating, when the temperature rises to 600-800℃, keep it warm for 30-60 minutes; when the temperature rises to 1200-1400℃, keep it warm for 60-90 minutes; and the vacuum degree is always kept at 5×10 -3 Pa~6×10 -3 Pa; cool down to zero position of voltage regulator twice, turn off heating power, take out cathode preform with tantalum sponge after cooling, and require tantalum sponge and base metal to be free of oxidation, cracks, powder loss and firm and reliable.

[0029] c) coating the surface of the tantalum sponge of the cathode preform with the tantalum sponge with a composite rare earth oxide suspension and drying or air-drying, specifically: taking out the evenly ground composite rare earth oxide suspension and pouring it into a porcelain crucible, and evenly coating it on the cathode emission surface of the prepared tantalum sponge with a tantalum spoon or a brush, and drying or air-drying;

[0030] d) Repeating step c) until the pores of the tantalum sponge are filled with the composite rare earth oxide, and applying the composite rare earth oxide suspension on the cathode emission surface while stirring during repeated coating, and drying or air-drying;

[0031] The composite rare earth oxide comprises 90-80% Y2O3 and 10-20% ZrO2 by mass, wherein the average particle size of Y2O3 and ZrO2 is 5-10 μM and the purity is 99.9%. Y2O3, ZrO2, acetone, butyl acetate and nitrocellulose solution are placed in an agate ball jar and ball-milled to obtain a composite rare earth oxide suspension.

[0032] e) placing the coated composite rare earth oxide cathode into a high-temperature vacuum furnace for sintering to obtain the desired cathode;

[0033] When the vacuum degree P≤3×10 -3 Pa, start heating, when the temperature rises to 400-500℃, keep it warm for 30-60 minutes; when the temperature rises to 1050-1100℃, keep it warm for 50-80 minutes; when the temperature rises to 1200-1300℃, keep it warm for 10-20 minutes, and then cool; the vacuum degree is always kept at 5×10 -3 Pa~6×10 -3 Pa.

[0034] Although the pulse emission of ordinary oxide cathodes is very large, it can only draw a few hundred mA / cm when used in DC mode. 2 The emission current is very small. When the pulse is used for several microseconds, the emission decays significantly. When it is longer, the waveform of the current pulse becomes extremely poor. In addition, the anti-toxicity of ordinary oxide cathodes is also very poor. After being "poisoned", it can sometimes recover but sometimes cannot. However, the present invention uses a tantalum sponge composite rare earth oxide cathode to test the cathode DC emission characteristics. The results show that the cathode can achieve an emission current density of 1A / cm at 1400℃. 2 This type of cathode is also highly resistant to toxicity and can recover quickly after being "poisoned".

[0035] At high temperatures, rare earth oxides may be impure semiconductors, and the valence electrons that determine thermal emission are the same. When the crystal structure is the same, the mutual doping of rare earth oxides does not cause significant changes in the energy levels within the lattice. Therefore, doping between rare earth oxides does not play a significant role in thermal emission. If rare earth oxides are doped with transition metal oxides from different families, the energy levels within the lattice may be changed, reducing the cathode surface work function. The present invention uses the transition metal oxide zirconium oxide (ZrO2) to dope the rare earth oxide yttrium oxide (Y2O3), impregnates it into a tantalum sponge, and uses a tantalum-niobium alloy strip as the base metal. This achieves better cathode thermal emission characteristics, work function, and electron bombardment resistance, thereby improving service life.

[0036] When the magnetron is working normally, the cathode surface is constantly bombarded by electrons. In high-power pulse magnetrons, the cathode is bombarded by electrons accounting for about 2-10% of the output power. Ordinary oxide and barium tungsten cathodes will lose their thermal emission capabilities under such conditions. Therefore, the ability to withstand electron bombardment is an important parameter to measure the emission performance of magnetron cathodes. The electron bombardment power of the ion source used in this experiment is 10W / cm 2 , the cathode emission effective area is 16.44cm 2 The cathode pulse output power is 3.1MW, the cathode operating temperature is 1500℃, and the initial thermal emission current density is 1.5A / cm 2After 100 hours of electron bombardment, the density of emitted electrons only dropped to 0.5A / cm 2 After stabilization, it can continue to be used, which shows that the cathode of the present invention has strong resistance to electron bombardment.

[0037] The elemental composition and content of the surface and cross-section of the cathode of the present invention were analyzed using a scanning electron microscope and an energy spectrum analyzer. The results showed that a layer of n-type Y2O3-Ta semiconductor was formed on the surface of the cathode during the high-temperature activation process. The formation of this semiconductor layer improved the conductivity of the cathode surface, reduced the cathode surface work function, and increased the cathode's thermal emission. The doping of the B group transition metal oxide ZrO2 with the rare earth oxide Y2O3 changed the internal energy levels of the lattice, reduced the cathode surface work function, and further increased the cathode's thermal emission.

[0038] Assembly: Assemble the cathode and heater, fill the space between the cathode and heater with thermally conductive material, and then sinter them in a vacuum furnace to prepare a cathode-heater assembly. The sintering temperature in the vacuum furnace is 1200-1400°C and the sintering time is 10-15 minutes.

[0039] Alumina (Al2O3) powder, a commonly used insulating material, is used as a solid material to fill the space of the cathode heater. Although it has good insulation properties, it has poor conductivity. The operating temperature of the heater is 150℃ to 200℃ lower than that of the cathode. It can only be used in low-power magnetrons and other electric vacuum devices.

[0040] The magnetron of the present invention is high-power. Therefore, the heat-conducting and electrically-conducting materials include 60-50% nickel powder and 40-50% molybdenum powder by weight, and both the nickel powder and the molybdenum powder are sieved with a 200-mesh molecular sieve. The heater operating temperature is 77-150°C lower than the cathode operating temperature. The cathode operating temperature is about 100°C lower than the normal operating temperature, and the operation start-up time is shortened by about half.

[0041] After the cathode thermal subassembly was assembled and the pulse magnetron was tested, the pulse output power was 2.5-3.1MW, the cathode temperature was 1400-1500℃, and the thermal emission current density reached (1.5-4)A / cm3 in continuous wave mode. 2 、The emission current density in pulse condition reaches (60~70)A / cm 2 , lifespan up to thousands of hours, thus improving service life and quick start.

[0042] Heaters are typically designed for high current and low voltage to enhance their mechanical strength. However, the interaction between the magnetic field generated by the alternating heater power supply and the axial magnetic field of the magnetron subjects the heater to an alternating mechanical force. To mitigate the effects of this magnetic force, the cathode heater assembly prepared by the above method utilizes a DC power supply for heating, reducing manufacturing costs, extending heater life, and improving magnetron stability.

Claims

1. A method for preparing a cathode heater assembly for a high-power pulsed magnetron, characterized in that: The steps include: Preparation of heater: After winding tungsten wire into shape, high-temperature shaping, insulation coating and secondary high-temperature sintering are carried out in sequence to produce the required heater; Preparation of the cathode: a) forming a tantalum-niobium alloy strip into a cathode sleeve and then vacuum degassing the sleeve, baking the cathode sleeve mold, and then evenly spraying cotton glue onto the emitting surface of the cathode sleeve. Purified tantalum powder is evenly sieved on the cotton glue surface, and finally cotton glue is sprayed on the surface of the purified tantalum powder and dried to obtain a cathode blank with a tantalum sponge. b) placing the cathode blank with the tantalum sponge in a tantalum skin vacuum furnace and sintering at high temperature to obtain a cathode preform with a tantalum sponge. c) coating the surface of the tantalum sponge of the cathode preform with the tantalum sponge with a composite rare earth oxide suspension and drying or air-drying. d) repeating step c) until the pores of the tantalum sponge are filled with the composite rare earth oxide. e) placing the cathode coated with the composite rare earth oxide in a high-temperature vacuum furnace and sintering to obtain the desired cathode. Assembly: Assemble the cathode and heater, fill the space between the cathode and heater with thermally conductive material, and then sinter them in a vacuum furnace to prepare a cathode-heater assembly.

2. The method for preparing a high-power pulse magnetron cathode heater assembly according to claim 1, characterized in that: The tungsten wire used is tungsten wire with the brand of WK80G; the annealing temperature of the tungsten wire during winding is 850±20°C; the temperature of the high-temperature setting is 1200±50°C and the time is 10 to 15 minutes; the cold measurement resistance of the heater is 0.1 to 0.119Ω.

3. The method for preparing a high-power pulse magnetron cathode heater assembly according to claim 1, characterized in that: The coating insulation layer adopts cathode electrophoresis method, the electrophoresis voltage is 30-100V, and the thickness of electrophoretic aluminum oxide powder is 0.02-0.04 mm; the secondary high-temperature sintering is carried out in a hydrogen furnace, the sintering temperature is 1400±20°C, and the time is 3-5 minutes.

4. The method for preparing a high-power pulse magnetron cathode heater assembly according to claim 1, wherein: In step a), the purified tantalum powder is screen-coated multiple times until the weight of the purified tantalum powder meets the requirements; the vacuum degassing temperature is 1400-1600° C. and the time is 30-60 minutes; the mold on the cathode sleeve is baked at a temperature of 80-100° C.; the specific process of purifying the tantalum powder in step a) is as follows: pure tantalum powder that meets national standards is placed in a glass bottle, completely immersed in butyl acetate, and then sealed and rolled for 30-60 minutes. After precipitation, the residual liquid is poured out, the powder is immersed in ethanol, dried, and washed with distilled water for 3-5 times, each time for 5-10 minutes; dehydrated and dried with anhydrous ethanol, and then sent to a hydrogen burning furnace at a temperature controlled at 650-850° C. for 10-15 minutes; after cooling, the powder is crushed to obtain the purified tantalum powder.

5. The method for preparing a high-power pulse magnetron cathode heater assembly according to claim 1, characterized in that: The specific process of placing the cathode blank with tantalum sponge into a tantalum skin vacuum furnace for high temperature sintering in step b) is as follows: when the vacuum degree P is less than 3×10 -3 Pa, start heating, when the temperature rises to 600-800℃, keep it warm for 30-60 minutes; when the temperature rises to 1200-1400℃, keep it warm for 60-90 minutes; and the vacuum degree is always kept at 5×10 -3 Pa~6×10 -3 Pa; cool down to zero position of the voltage regulator twice, turn off the heating power, and take out the cathode preform with tantalum sponge after it cools down.

6. The method for preparing a high-power pulse magnetron cathode heater assembly according to claim 1, characterized in that: In the step d), the composite rare earth oxide comprises 90-80% Y2O3 and 10-20% ZrO2 by mass, and the average particle size of Y2O3 is 5-10 μM.

7. The method for preparing a high-power pulse magnetron cathode heater assembly according to claim 1, characterized in that: In the step e), the cathode coated with the composite rare earth oxide is placed in a high temperature vacuum furnace for sintering. The specific process is as follows: when the vacuum degree P is less than 3×10 -3 Pa, start heating, when the temperature rises to 400-500℃, keep it warm for 30-60 minutes; when the temperature rises to 1050-1100℃, keep it warm for 50-80 minutes; when the temperature rises to 1200-1300℃, keep it warm for 10-20 minutes, and then cool; The vacuum degree was always kept at 5×10 -3 Pa~6×10 -3 Pa.

8. The method for preparing a high-power pulsed magnetron cathode heater assembly according to claim 1, characterized in that: During the assembly process, the vacuum furnace sintering temperature is 1200-1400° C. and the time is 10-15 minutes; the thermally conductive and electrically conductive material includes 60-50% nickel powder and 40-50% molybdenum powder by weight, and the nickel powder and molybdenum powder are both sieved with a 200-mesh molecular sieve.

9. A cathode heater assembly, characterized in that: The cathode heater assembly is a cathode heater assembly prepared by the preparation method according to claim 1.

10. An application of a cathode heater assembly prepared by the preparation method according to claim 1, characterized in that: The cathode thermal subassembly is heated by a direct current power supply.