Hollow cathode and method of processing the same

Abstract

The application relates to the technical field of space electric propulsion, in particular to a hollow cathode and a processing method thereof, which comprises a composite substrate; the composite substrate is provided with a cathode salt; the preparation material of the composite substrate comprises tungsten carbide and lanthanum hexaboride; the application discloses a hollow cathode; the tungsten carbide and the lanthanum hexaboride are mixed and used, so that the hollow cathode disclosed by the application can not only ensure a low working temperature, but also ensure the current density emitted by the hollow cathode.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of space electric propulsion technology, in particular to a hollow cathode and a processing method thereof. BACKGROUND

[0002] In space thrusters, electric propulsion technology has the characteristics of high specific impulse, small thrust, long life, and convenient adjustment, and is widely used in space propulsion, such as spacecraft attitude adjustment control, position keeping, orbit maneuvering, and interstellar flight. Its principle is to ionize gaseous working medium and accelerate positive ions to be emitted under the action of a strong electric field, thereby propelling the satellite to perform attitude adjustment or orbit transfer tasks through the reaction force. It is the main direction of the development of current space thrusters.

[0003] Compared with traditional chemical thrusters, electric thrusters require less working medium mass, and are the most suitable for long-distance navigation among the already practical propulsion technologies.

[0004] When the electric thruster is working, the working gas needs to be ionized into plasma, and a reaction force is obtained by emitting positively charged ions, thereby propelling the spacecraft to run. Generally, electrons are emitted by the cathode to ionize the inert gas into plasma. Since positively charged ions repel each other, the ion emission shape is in a divergent state, which reduces the efficiency of the ion engine. At this time, electrons need to be added to the positive ions to offset the repulsive force between the positive ions, ensure the electrical neutrality of the ions, ensure the emission shape of the positive ions, and improve the efficiency of the ion thruster. At the same time, since the spacecraft is in an isolated and insulated state in space, the surface of the spacecraft will accumulate negative charges due to the emission of positive charges, and the more negative charges accumulate, the more the spacecraft will be in a negative electric field state, and the positive ion charge will be affected by the negative electric field and will not be normally emitted. At this time, an electron emission source is needed to emit electrons from the surface of the spacecraft to neutralize the positive ions, so that the spacecraft is in a positive and negative charge balance state, so that the thruster can continuously work and the spacecraft can continuously run.

[0005] In the ion thruster, the cathode has two functions, one is to ionize gas molecules into plasma, and the other is to emit electrons to neutralize positive ions and maintain the electrical neutrality of the spacecraft. In the Hall thruster, a cathode can ionize gas molecules into plasma, and can also emit electrons to neutralize positive ions and maintain the electrical neutrality of the spacecraft. The cathode plays a very important role in electric propulsion, and its performance, reliability, and life have a particularly important influence on the thruster, and even play a key role.

[0006] At present, there are two kinds of conventional cathodes:

[0007] Barium tungsten cathode and lanthanum hexaboride cathode.

[0008] The barium tungsten cathode has the advantages of low working temperature (about 1000℃), long service life, and the disadvantages of small emission current density and great influence of atmosphere environment (water vapor, oxygen, etc.) on the cathode; the lanthanum hexaboride cathode has the advantages of large emission current density and insensitivity to atmosphere environment, and the disadvantages of high working temperature (about 1600℃) and short service life. SUMMARY

[0009] The present application aims to provide a new hollow cathode with low working temperature and large emission current density.

[0010] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0011] A hollow cathode, comprising a composite substrate, wherein the composite substrate is provided with a cathode salt, and the preparation material of the composite substrate comprises tungsten carbide and lanthanum hexaboride.

[0012] A processing method of a hollow cathode, comprising the following steps:

[0013] Step 1: taking tungsten carbide and lanthanum hexaboride powders;

[0014] Step 2: after the completion of Step 1, the tungsten carbide and lanthanum hexaboride powders are stirred and mixed;

[0015] Step 3: after the completion of Step 2, the mixed tungsten carbide and lanthanum hexaboride powders are pressed into a required cathode shape;

[0016] Step 4: after the completion of Step 3, sintering is performed in a vacuum furnace or a hydrogen furnace to obtain a composite substrate;

[0017] Step 5: after the completion of Step 4, the sintered composite substrate is processed into a required shape.

[0018] In Step 1, the mass ratio of the tungsten carbide and the lanthanum hexaboride powders is required to be 1:1.

[0019] The tungsten carbide can be replaced by tantalum carbide, zirconium carbide and titanium carbide.

[0020] In Step 3, the porosity of the pressed cathode shape is required to be 20% to 30%.

[0021] In Step 5, the sintering temperature is required to be 1300 to 1600℃.

[0022] In Step 2, when the tungsten carbide and the lanthanum hexaboride powders are mixed, aluminum oxide powder and paraffin are added into the mixture of the tungsten carbide and the lanthanum hexaboride.

[0023] After the processing of Step 5 is completed, the composite substrate is placed into a hydrogen furnace together with the cathode salt for sintering, so that the cathode salt is impregnated into the substrate.

[0024] The cathode salt comprises calcium oxide, barium oxide and aluminum oxide.

[0025] The finished hollow cathode needs to be assembled into an electron gun for hollow cathode performance testing.

[0026] The advantages of the present application are:

[0027] The present application discloses a kind of hollow cathode;The present application is mixed with tungsten carbide and lanthanum hexaboride, so that the hollow cathode disclosed in the present application can not only ensure low temperature, but also ensure the current density emitted by hollow cathode. BRIEF DESCRIPTION OF DRAWINGS

[0028] The content expressed by each figure of the present application specification is briefly described as follows:

[0029] Figure 1 It is a schematic diagram of cathode structure.

[0030] Figure 2 It is a schematic diagram of electron gun (electron source) structure and performance test principle. DETAILED DESCRIPTION

[0031] The specific embodiment of the present application is further described in detail by comparing the drawings and describing the optimal embodiment.

[0032] A kind of hollow cathode, including composite matrix;The composite matrix is equipped with cathode salt;The preparation material of the composite matrix includes tungsten carbide and lanthanum hexaboride;The present application discloses a kind of hollow cathode;The present application is mixed with tungsten carbide and lanthanum hexaboride, so that the hollow cathode disclosed in the present application can not only ensure low temperature, but also ensure the current density emitted by hollow cathode.

[0033] A processing method of a hollow cathode, the processing method comprises the following steps:

[0034] Step 1: take tungsten carbide and lanthanum hexaboride powder;

[0035] Step 2: after step 1 is completed, tungsten carbide and lanthanum hexaboride powder are stirred and mixed;

[0036] Step 3: after step 2 is completed, the mixed tungsten carbide and lanthanum hexaboride powder is pressed into the required cathode shape;

[0037] Step 4: after step 3 is completed, sintering is carried out in a vacuum furnace or a hydrogen furnace to obtain a composite matrix;

[0038] Step 5: after step 4 is completed, the sintered composite matrix is processed into the required shape.

[0039] The hollow cathode can be processed and produced through the process steps.

[0040] Further, in the application, the mass ratio of tungsten carbide and lanthanum hexaboride powder is 1:1 in step 1; when the mass ratio of tungsten carbide and lanthanum hexaboride powder is 1:1, the porosity of the pressed composite matrix is easily 20% to 30%, and the density is higher.

[0041] Further, in the application, the tungsten carbide can be replaced by tantalum carbide, zirconium carbide and titanium carbide; the types of hollow cathodes are increased, and different types of hollow cathodes can be selected according to needs in subsequent use. In addition, the above-mentioned materials can be used to replace tungsten carbide to avoid the influence of the production of hollow cathodes due to the shortage of tungsten carbide.

[0042] Further, in the application, the porosity of the pressed cathode is 20% to 30% in step 3; through such design, the cathode has a proper number, proper shape and size, uniform dispersion and mutual communication, and no closed pores; that is, through such porosity, the subsequent cathode salt is immersed, the strength of the cathode structure is better ensured, and the service life of the composite matrix in subsequent use is ensured.

[0043] Further, in the application, the sintering temperature is 1300 to 1600 DEG C in step 5; through such temperature limitation, the density of the sintered sintering sample is best.

[0044] Further, in the application, when mixing tungsten carbide and lanthanum hexaboride powder in step 2, alumina powder and paraffin are added to the tungsten carbide and lanthanum hexaboride mixture; through the arrangement of alumina powder and paraffin, the cathode matrix can be better pressed, and the cathode matrix structure is firm and reliable.

[0045] Further, in the application, the composite matrix after step 5 is placed in a hydrogen furnace together with the cathode salt for sintering, so that the cathode salt is impregnated into the matrix; through the setting of the cathode salt, a good protection effect is achieved, and the service life of the cathode is better increased.

[0046] Further, in the application, the cathode salt includes calcium oxide, barium oxide and aluminum oxide; in actual use; the reasonable proportion of BaO, CaO and Al 2O3 in the cathode salt can be adjusted, the content of BaO is increased, the content of CaO is adjusted, and the service life of the cathode can be better ensured.

[0047] Further, in the application, the finished hollow cathode needs to be assembled into an electron gun for hollow cathode performance test; through such setting, the service life and use performance of the hollow cathode can be detected.

[0048] Specifically

[0049] The application discloses a hollow cathode; the hollow cathode is suitable for being used as an electron source in an ion thruster and a Hall thruster.

[0050] In the application, the hollow cathode comprises a composite base body, the preparation material of the composite base body comprises tungsten carbide and lanthanum hexaboride, and in addition, a cathode salt is impregnated on the composite base body, and the cathode salt is composed of a calcium oxide, barium oxide and aluminum oxide mixture.

[0051] In addition, the tungsten carbide and the lanthanum hexaboride are both powder materials with a particle size of 1-5 microns.

[0052] Of course, tantalum carbide, zirconium carbide and titanium carbide can be used to replace the tungsten carbide.

[0053] The mass ratio of the tungsten carbide to the lanthanum hexaboride is 1:1; the mass ratio can be adjusted appropriately.

[0054] In specific implementation

[0055] The tungsten carbide and the lanthanum hexaboride powder materials are placed together, fully stirred and uniformly mixed. The mixed tungsten carbide and lanthanum hexaboride powder materials are pressed into a cathode shape with a certain porosity, and the porosity is generally 20%-30%, and then the materials are placed in a vacuum furnace or a hydrogen furnace for sintering, and the sintering temperature is generally 1300-1600 DEG C; the porosity of the sintered materials is 15%-25%; and the sintered composite base body is processed into a required shape.

[0056] In order to better press the cathode base body and make the cathode base body structure firm and reliable, a small amount of aluminum oxide powder and paraffin can be appropriately added to the tungsten carbide and lanthanum hexaboride powder.

[0057] In addition, in the application, the cathode salt is composed of calcium oxide, barium oxide and aluminum oxide, and the proportion of the calcium oxide, the barium oxide and the aluminum oxide is a conventional cathode formula: 411 formula (4BaCO3+CaCO3+Al2O3) or 532 formula (5BaCO3+3CaCO3+2Al2O3); other formulas can also be used, such as a scandium salt formed by adding appropriate scandium oxide; through the design, the application avoids the existence of material shortage and can better guarantee actual production.

[0058] Meanwhile, in the specific implementation of the application, the composite base body and the cathode salt (a calcium oxide, barium oxide and aluminum oxide mixture) are placed in a hydrogen furnace for sintering, so that the cathode salt is impregnated into the base body. After the impregnation is completed, the excess cathode salt on the surface of the cathode is removed clean, and the hollow cathode is completed.

[0059] Then the finished hollow cathode is assembled into an electron gun (electron source), and the cathode and electron gun performance is tested according to the drawings; mainly to see whether the performance of the electron gun assembled with the hollow cathode meets the theoretical design requirements and whether the service life of the hollow cathode meets the design requirements.

[0060] The hollow cathode disclosed by the application has the advantages of the barium tungsten cathode and the lanthanum hexaboride cathode: a relatively low working temperature (about 1000℃), a relatively long service life, and insensitivity to the atmosphere, and overcomes the shortcomings of the traditional barium tungsten cathode and the lanthanum hexaboride cathode, and can be widely used in electric propulsion as an electron source emitter.

[0061] Obviously, the specific implementation of the application is not limited by the above-mentioned manner, and various non-essential improvements made by adopting the method concept and technical scheme of the application are within the protection scope of the application.

Claims

1. A method of processing a hollow cathode, characterized by, The hollow cathode comprises a composite base body, and a cathode salt is arranged on the composite base body; The preparation material of the composite base body comprises tungsten carbide and lanthanum hexaboride; The processing method comprises the following steps: Step 1: taking tungsten carbide and lanthanum hexaboride powders; Step 2: after step 1 is completed, the tungsten carbide and lanthanum hexaboride powders are stirred and mixed; Step 3: after step 2 is completed, the mixed tungsten carbide and lanthanum hexaboride powders are pressed into a required cathode shape; Step 4: after step 3 is completed, sintering is performed in a vacuum furnace or a hydrogen furnace to obtain a composite base body; Step 5: after step 4 is completed, the sintered composite base body is processed into a required shape.

2. The method of claim 1, wherein the hollow cathode is formed by a process comprising: In step 1, the mass ratio of the tungsten carbide and lanthanum hexaboride powders is required to be 1:

1.

3. The method of claim 1, wherein the hollow cathode is formed by a process comprising: The tungsten carbide can be replaced by tantalum carbide, zirconium carbide and titanium carbide.

4. The method of claim 1, wherein the hollow cathode is formed by a process comprising: In step 3, the porosity of the pressed cathode shape is required to be 20% to 30%.

5. The method of claim 1, wherein the hollow cathode is formed by a process comprising: In step 5, the sintering temperature is 1300 to 1600 ℃.

6. The method of claim 1, wherein the hollow cathode is formed by a process comprising: In step 2, when the tungsten carbide and lanthanum hexaboride powders are mixed, alumina powder and paraffin are added into the mixture of the tungsten carbide and lanthanum hexaboride.

7. The method of claim 1, wherein the hollow cathode is formed by a process comprising: The composite base body processed in step 5 is placed into a hydrogen furnace together with the cathode salt for sintering, so that the cathode salt is impregnated into the base body.

8. The method of claim 7, wherein the hollow cathode is formed by a process comprising: The cathode salt comprises calcium oxide, barium oxide and alumina.

9. The method of claim 1-8, wherein the method further comprises, The finished hollow cathode needs to be assembled into an electron gun for hollow cathode performance test.

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