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

Abstract

The invention discloses a high-power pulse magnetron cathode heater assembly, a preparation method and an application. The preparation method comprises the following steps: winding a tungsten filament, and sequentially carrying out primary high-temperature shaping, insulating layer coating and secondary high-temperature sintering to prepare a required heater; preparing a cathode blank with a tantalum sponge body; preparing a cathode prefabricated part with the tantalum sponge body; coating the composite rare earth oxide turbid liquid, and sintering in a high-temperature vacuum furnace to obtain the required cathode; and assembling the cathode and the heater, filling the space between the cathode and the heater with a heat-conducting and electric-conducting material, and sintering in a vacuum furnace to prepare the cathode and heater assembly. The cathode heater assembly has high heat emission and secondary electron emission, has good electron and ion bombardment resistance, prolongs the service life, and can adapt to the working environment of a high-power pulse magnetron; and the device also has the characteristics of low cathode heating power, high thermal emission current density and the like, and can be quickly started.

Description

Technical Field

[0001] The 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] At present, the cathodes commonly used in high-power magnetrons are mainly alkaline earth metal oxide cathodes, barium tungsten cathodes, thorium tungsten cathodes, etc. 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 weak resistance to electron and ion bombardment, and low secondary emission coefficient. It is necessary to increase the back bombardment to obtain sufficient current multiplication, which is not conducive to quick oscillation. The manufacturing process of this cathode is more complicated and the cost is higher; while thorium tungsten cathodes have good resistance to electron bombardment, but thorium is a radioactive element.

[0003] The resistivity of the oxide coating of the existing common oxide cathode is relatively high. When there is an intermediate layer between the base metal and the coating, the coating resistance has a very bad effect on the use; especially when the high-power pulse magnetron is used, the heat generated by the resistance in the coating destroys the thermal balance of the cathode, and the electric field generated is one of the main reasons for the occurrence of electric sparks. Therefore, in order to avoid the generation of the intermediate resistance layer and increase the conductivity of the coating, nickel powder is currently sintered on the nickel sleeve to form a nickel sponge, and then coated with ternary carbonate, but this can only be adapted to low-power vacuum devices. Summary of the invention

[0004] The purpose of the present invention is to solve the above-mentioned technical problems and to 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 high-power pulse magnetron cathode thermal subassembly, comprising the following steps:

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

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

[0008] Assembly: Assemble the cathode and the heater, fill the space between the cathode and the heater with heat-conducting and electrically-conductive materials, and then send them into a vacuum furnace for sintering to prepare a cathode-heater assembly.

[0009] Furthermore, the tungsten wire is of 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 insulating layer is coated by cathode electrophoresis, the electrophoresis voltage is 30-100V, and the thickness of the 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.

[0011] Furthermore, in the step a), the purified tantalum powder is screened and coated multiple times until the weight of the purified tantalum powder meets the requirements; the temperature of vacuum degassing is 1400-1600°C and the time is 30-60 minutes; the temperature of baking the mold on the cathode sleeve is 80-100°C; the specific process of purifying the tantalum powder in the step a) is: put the pure tantalum powder that meets the national standard into a glass bottle, immerse it completely with butyl acetate, and then seal and roll for 30-60 minutes, pour out the residual liquid after precipitation, immerse it in ethanol, dry it, and boil it with distilled water for 3-5 times, each time for 5-10 minutes; dehydrate and dry it with anhydrous ethanol, send it into a hydrogen burning furnace, control the temperature at 650-850°C, and the time is 10-15 minutes; after cooling, crush it to obtain the purified tantalum powder.

[0012] Furthermore, the specific process of placing the cathode blank with tantalum sponge in the 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 supply, 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 percentage, and the average particle size of Y2O3 is 5-10 μM.

[0014] Furthermore, in 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 cool; before each heating and during the heating process, 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 the nickel powder and the molybdenum powder are both sieved with a 200-mesh molecular sieve.

[0016] A cathode thermal sub-assembly is also provided, and the cathode thermal sub-assembly is the cathode thermal sub-assembly prepared by the above preparation method.

[0017] Finally, an application of a cathode thermal subassembly prepared by the above preparation method is provided, wherein the cathode thermal subassembly 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 subassembly 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 the high-power pulse magnetron of the present invention is as follows:

[0020] Preparation of the heater: Tungsten wire is wound and formed, and then high-temperature shaping, insulation layer coating and secondary high-temperature sintering are performed in sequence to make the required heater. The cold-measured resistance of the heater is 0.1 to 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 the tungsten wire is wound into a spiral, the deformation of the tungsten wire material is large at the turning point, resulting in a certain plastic deformation. Therefore, when winding, the annealing temperature is 850±20℃ (lower than the optimal annealing temperature of the tungsten wire) to obtain the temperature of maximum elongation; when the annealing temperature is lower than the optimal annealing temperature of the tungsten wire, there are still dislocations and distorted and broken grains formed during deformation in the tungsten wire. After annealing, the elongation of the tungsten wire is small, and the 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 the tungsten wire, due to collective recrystallization, the plasticity and strength of the tungsten wire become worse, the original properties of the overheated tungsten wire cannot be restored, it is fragile, the yield rate is very low, and there are many scraps.

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

[0024] The coating insulation layer adopts cathode electrophoresis, the electrophoresis voltage is 30-100V, the thickness of electrophoretic alumina powder is 0.02-0.04mm; the secondary high-temperature sintering is carried out in a hydrogen furnace, the sintering temperature is 1400±20℃, and the time is 3-5 minutes. It is ensured that when the heater is powered on, the coils and other metals will not touch each other and cause short circuit.

[0025] Preparation of cathode: a) After the tantalum-niobium alloy strip is made into a cathode sleeve, it is vacuum degassed at 1400-1600°C for 30-60 minutes, and 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, and then the purified tantalum powder is evenly sieved on the surface of the cotton glue, and the purified tantalum powder is sieved multiple times until the weight of the purified tantalum powder meets the requirements; finally, cotton glue is sprayed on the surface of the purified tantalum powder and dried to obtain a cathode blank with 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 for 30 to 60 minutes, pour out the residual liquid after precipitation, immerse in ethanol, dry, and wash with distilled water for 3 to 5 times, each time for 5 to 10 minutes; dehydrate and dry with anhydrous ethanol, send it into a hydrogen burning furnace, control the temperature at 650 to 850°C, 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 tantalum sponge into a tantalum skin vacuum furnace and sintering at high temperature to obtain a cathode preform with 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, so 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, and take out the cathode preform with tantalum sponge after cooling. The tantalum sponge and base metal are required to be free of oxidation, cracks, powder loss and firm and reliable.

[0029] c) coating the composite rare earth oxide suspension on the surface of the tantalum sponge of the cathode preform with the tantalum sponge and drying or air-drying, specifically: taking out the composite rare earth oxide suspension that has been ground evenly 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 during repeated coating, coating the composite rare earth oxide suspension on the cathode emission surface while stirring, and drying or drying in the shade;

[0031] The composite rare earth oxide comprises 90-80% Y2O3 and 10-20% ZrO2 by mass percentage, the average particle size of Y2O3 and ZrO2 are both 5-10 μM, and the purity is both 99.9%; Y2O3, ZrO2, acetone, butyl acetate and nitrocellulose solution are put into an agate ball pot, 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 cool; before each heating and during the heating process, 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 is 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. 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°C. 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 impurity semiconductors, and the valence electrons that determine thermal emission are the same. When the crystal structures are the same, the rare earth oxides doped with each other do not cause significant changes in the energy levels inside the lattice. Therefore, the doping between the rare earth oxides does not play a big role in thermal emission. If different groups of transition metal oxides are used to dope the rare earth oxides, the energy levels inside the lattice may be changed, and the cathode surface work function may be reduced. The present invention uses transition metal oxide zirconium oxide (ZrO2) doped with rare earth oxide yttrium oxide (Y2O3), impregnated into tantalum sponge, and uses tantalum-niobium alloy strip as the base metal, thereby obtaining better cathode thermal emission characteristics, work function and electron bombardment resistance, and improving the service life.

[0036] When the magnetron is working normally, the cathode surface is constantly bombarded by electrons. The cathode of a high-power pulse magnetron is bombarded by electrons that account for about 2 to 10% of the output power. Ordinary oxide and barium tungsten cathodes will lose their thermal emission capabilities under this condition. Therefore, the ability to withstand electron bombardment is an important parameter to measure the emission performance of the magnetron cathode. 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 the semiconductor layer improved the conductivity of the cathode surface, reduced the cathode surface work function, and increased the cathode's thermal emission. The B group transition metal oxide ZrO2 doped with the rare earth oxide Y2O3 changed the internal energy level of the lattice, reduced the cathode surface work function, and further increased the cathode's thermal emission.

[0038] Assembly: Assemble the cathode and the heater, fill the space between the cathode and the heater with thermally conductive materials, 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 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 of high power, therefore, the heat-conducting and electric-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 working temperature of the heater is 77-150°C lower than the working temperature of the cathode, the working temperature of the cathode is about 100°C lower than the normal working temperature, and the working start-up time is shortened by about half.

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

[0042] The heater is generally designed to have a high current and low voltage to improve the mechanical strength of the heater. However, due to the interaction between the magnetic field generated by the alternating heater power supply and the axial magnetic field of the magnetron, the heater is subjected to an alternating mechanical force. In order to reduce the influence of the magnetic effect, the cathode heater assembly prepared by the above preparation method is heated by a DC power supply, which reduces the manufacturing cost, increases the life of the heater, and improves the stability of the magnetron.

Claims

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

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, 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, characterized in that: In the step a), the purified tantalum powder is screened and coated for multiple times until the weight of the purified tantalum powder meets the requirements; the temperature of vacuum degassing is 1400-1600°C and the time is 30-60 minutes; the temperature of baking the mold on the cathode sleeve is 80-100°C; the specific process of purifying the tantalum powder in the step a) is as follows: pure tantalum powder that meets national standards is put into a glass bottle, completely immersed in butyl acetate, and then sealed and rolled for 30-60 minutes, and the residual liquid is poured out after precipitation, immersed in ethanol, dried, and boiled and washed with distilled water for 3-5 times, each time for 5-10 minutes; 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, 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 supply, 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 percentage, 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 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 When the temperature reaches 400-500°C, keep it warm for 30-60 minutes; when the temperature reaches 1050-1100°C, keep it warm for 50-80 minutes; when the temperature reaches 1200-1300°C, keep it warm for 10-20 minutes and cool; The vacuum degree was always maintained at 5×10 -3 Pa~6×10 -3 Pa.

8. The method for preparing a high-power pulse 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 the molybdenum powder are both sieved with a 200-mesh molecular sieve.

9. A cathode heater assembly, characterized in that: The cathode thermal subassembly is a cathode thermal subassembly prepared by the preparation method of 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.