Hollow cathode armored heater based on carbon nanotube macroscopic body

Abstract

The invention relates to the technical field of spaceflight electric propulsion systems, in particular to a hollow cathode armored heater based on a carbon nanotube macroscopic body. Comprising a refractory metal armor shell, an insulating heat-insulating layer and a carbon nanotube macroscopic body heating module which is composed of an insulating ceramic framework and a carbon nanotube macroscopic body heating wire wound on the insulating ceramic framework, and the refractory metal armor shell is of a cylinder structure with an interlayer. The carbon nano tube macroscopic body heating module and the insulating thermal-protective coating are sequentially sleeved in an interlayer of the refractory metal armored shell from inside to outside, and the carbon nano tube macroscopic body heating module is used for heating an emitter in the hollow cathode tube; the tail end of the carbon nanotube macroscopic body heating wire is connected with an outer lead, and the outer lead and the refractory metal armored shell are connected with the positive electrode and the negative electrode of a power source respectively to form a heating loop. The device has the advantages of light weight, low power consumption, high energy efficiency and excellent high-temperature stability, is suitable for a thermal control device of a spacecraft attitude and orbit control thruster, and remarkably improves the service life and reliability of a system.

Description

Technical Field

[0001] This invention relates to the field of aerospace electric propulsion system technology, specifically to a hollow cathode armored heater based on a carbon nanotube macrostructure. Background Technology

[0002] With the deepening of human exploration of space and the increasing reliance on satellite orbit control, electric propulsion technology has been widely used in spacecraft propulsion systems. In electric propulsion systems, the hollow cathode is one of the core components, undertaking the crucial functions of providing an electron source and maintaining the discharge. The startup and stable operation of the hollow cathode depend on an external heater heating the launcher to a sufficient operating temperature. Therefore, the high-temperature heater, as a critical component of the electric propulsion system, directly affects the system's lifespan and reliability.

[0003] Currently, commonly used hollow cathode materials are mainly barium tungsten and lanthanum hexaboride, among which lanthanum hexaboride has superior electron emission capability and resistance to poisoning compared to barium tungsten. However, lanthanum hexaboride has a high electron work function, and its thermionic emission requires a relatively high operating temperature, typically above 1500℃, which places very high demands on the performance of the external heater.

[0004] Traditional refractory metal heating elements (such as tantalum, tungsten and their alloys) have long dominated key components such as spacecraft electric propulsion systems and thermal control devices. However, traditional refractory metal heating elements have poor high-temperature stability, and are prone to mechanical property degradation, recrystallization brittle fracture, and continuous evaporation at high temperatures (see Pattee HE, Evans R M. Brazing and bonding of columbium, molybdenum, tantalum, tungsten, and graphite [M]. Battelle Memorial Institute, Defense Metals Information Center, 1962.). Refractory metals are also prone to reacting with insulating materials at high temperatures (see Tighe W, Freick K, Chien K R. Performance evaluation and life test of the XIPS hollow cathode heater [C] / / 41st AIAA / ASME / SAE / ASEE Joint Propulsion Conference & Exhibit. 2005:4066.), leading to short circuits and open circuits. Refractory metals themselves have a high density, relatively low resistivity, relatively large temperature coefficient of resistance, and slow thermal response, which makes it difficult to meet the stringent requirements of modern aerospace equipment for low power consumption, lightweight, and high energy efficiency. In recent years, research on the application of graphite high-temperature heaters in aerospace electric propulsion systems has made progress (see Wordingham CJ, Taunay PYC, Choueiri E. Multiple-kilowatt-class graphite heater for large hollow cathode ignition[C] / / 51st AIAA / SAE / ASEE Joint Propulsion Conference.2015:4010, CN114360985B). Their lightweight nature, excellent thermal shock resistance, and good compatibility with insulating ceramic materials at high temperatures are significantly superior to traditional refractory metals such as tungsten and tantalum. However, the inherent brittleness of graphite materials makes their resistance to mechanical impact insufficient, making it difficult to withstand the micro-vibration loads and attitude adjustment impacts during spacecraft operation in orbit. Furthermore, graphite heating elements are typically large in size, significantly exceeding the current requirements for miniaturization and lightweighting of electric thrusters, becoming a key factor restricting their widespread application.

[0005] Macroscopic assemblies of carbon nanotubes (CNTs), such as fibers and fiber bundles, inherit the intrinsic properties of single tubes, exhibiting excellent high-temperature stability, low density, tunable resistivity, and extremely fast thermal response, demonstrating great potential in high-temperature electrothermal applications. However, in extreme scenarios such as aerospace electric propulsion systems requiring ultra-high temperatures, strong vibrations, and long lifespans, there are no publicly reported technical approaches using continuous macroscopic CNTs as core heating elements. Summary of the Invention

[0006] The purpose of this invention is to address the technical problems existing in the background art described above, and to provide a hollow cathode armored heater based on carbon nanotube macrostructures. Through specific structural design and material selection, this heater exhibits excellent thermal stability and electrical performance at a high temperature of 1600℃. This heater can be applied to hollow cathode systems in electric propulsion vehicles, effectively extending the system's service life.

[0007] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0008] This invention provides a hollow cathode armored heater based on a carbon nanotube macrostructure, comprising a refractory metal shell, a carbon nanotube macrostructure heating module, and an insulating layer. The refractory metal shell is a cylindrical structure with a sandwich structure. The carbon nanotube macrostructure heating module and the insulating layer are sequentially fitted into the sandwich structure of the refractory metal shell from the inside out. The carbon nanotube macrostructure heating module is used to heat the emitter inside the hollow cathode tube, and the insulating layer is used for insulation.

[0009] The carbon nanotube macrobody heating module includes a cylindrical insulating ceramic skeleton and a carbon nanotube macrobody heating wire wound on the insulating ceramic skeleton.

[0010] One end of the refractory metal shell is provided with a lead wire hole. The tail end of the carbon nanotube macrobody heating wire is led out from the lead wire hole and connected to the external lead wire through a wiring structure. The external lead wire and the refractory metal shell are respectively connected to the positive and negative terminals of the power supply to form a heating circuit.

[0011] The carbon nanotube macrostructure heating wire is a high-quality carbon nanotube fiber bundle assembled from carbon nanotubes.

[0012] The carbon nanotube fiber bundles were continuously prepared from a high-quality liquid crystal solution, and the Raman spectrum I... G / I D ≥80, filament diameter 50~400μm, resistivity greater than 10 -7 Ω·m, with a maximum tensile strength of 4 GPa.

[0013] The insulating and heat-insulating layer is a heat-insulating ceramic cylinder.

[0014] The insulating ceramic skeleton is made of aluminum nitride ceramic or hexagonal boron nitride ceramic; the heat-insulating ceramic cylinder is made of alumina ceramic; the external lead wire is Pt wire; and the insulating ceramic powder is alumina ceramic powder.

[0015] The wiring structure includes a refractory metal thin-walled tube fixed at the lead hole of the refractory metal shell. The tail end of the carbon nanotube macrobody heating wire is connected to the external lead wire through high-temperature resistant inorganic adhesive inside the refractory metal thin-walled tube. The middle gap of the refractory metal thin-walled tube is filled with insulating ceramic powder.

[0016] The refractory metal shell and the refractory metal thin-walled tube are made of the same material, namely, any one of tungsten, molybdenum, tantalum, and niobium, or an alloy containing any one of tungsten, molybdenum, tantalum, and niobium.

[0017] The refractory metal shell includes a small refractory metal cylinder, a large refractory metal cylinder, and two refractory metal rings. The large refractory metal cylinder is fitted outside the small refractory metal cylinder, and an annular cavity for forming the interlayer is left between the large refractory metal cylinder and the small refractory metal cylinder. The two ends of the annular cavity are sealed by the two refractory metal rings respectively.

[0018] One of the refractory metal rings is provided with a lead hole for the tail end of the carbon nanotube macrobody heating wire to pass through; the other refractory metal ring is connected to the head end of the carbon nanotube macrobody heating wire, and the head end of the carbon nanotube macrobody heating wire is reserved with a relaxation section to buffer stress.

[0019] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0020] 1. The heating element of the present invention adopts a carbon nanotube macrostructure, which has low density, low coefficient of thermal expansion, low temperature coefficient of resistance, fast thermal response, high mechanical strength, and excellent thermal conductivity, electrical conductivity and chemical stability, which can effectively improve the performance and reliability of the heater.

[0021] 2. The diameter and resistivity of the heating element of the present invention can be flexibly adjusted to adapt to different application scenarios.

[0022] 3. The integrated armored heater of this invention has a more compact structure and is easier to install.

[0023] 4. The electrical insulation, thermal shielding, armor protection, and circuit connection of this invention are reasonable and meet the overall requirements of low power consumption, lightweight, and high energy efficiency for aerospace thermal control. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of a hollow cathode armored heater based on a carbon nanotube macrostructure according to the present invention;

[0025] Figure 2 This is a schematic diagram of the structure of the lead-out portion of the armored heater of the present invention;

[0026] Figure 3 The Raman spectrum of the carbon nanotube fiber bundle prepared in Example 1 of this invention;

[0027] In the figure, the horizontal axis represents the Raman shift (cm). -1 The vertical axis, Intensity, represents the relative intensity (au).

[0028] Figure 4 The image shows a scanning electron microscope (SEM) image of the carbon nanotube fiber bundles prepared in Example 1 of this invention, with a scale bar of 50 μm.

[0029] Figure 5 This is a cross-sectional microscopic image of a carbon nanotube fiber bundle installed in high-temperature insulating powder in Embodiment 1 of the present invention. The scale bar is 50 μm.

[0030] In the diagram: 1-Cathode tube; 2-Emitter; 3-Small refractory metal cylinder; 4-Refractory metal ring; 5-Refractory metal thin-walled tube; 6-Insulating ceramic skeleton; 7-Carbon nanotube macroscopic heating wire; 8-Heat-insulating ceramic cylinder; 9-High temperature resistant inorganic adhesive; 10-External lead wire; 11-Insulating ceramic powder; 12-Large refractory metal cylinder. Detailed Implementation

[0031] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] See Figure 1 and Figure 2 As shown, the present invention provides a hollow cathode armored heater based on a carbon nanotube macrobody, comprising a refractory metal shell, a carbon nanotube macrobody heating module, and an insulating layer. The refractory metal shell is a cylindrical structure with a sandwich structure. The carbon nanotube macrobody heating module and the insulating layer are sequentially fitted into the sandwich structure of the refractory metal shell from the inside to the outside. The carbon nanotube macrobody heating module is used to heat the emitter 2 inside the hollow cathode tube 1, and the insulating layer is used for insulation and heat insulation.

[0033] See Figure 1As shown, in an embodiment of the present invention, the refractory metal shell includes a small refractory metal cylinder 3, a large refractory metal cylinder 12, and two refractory metal rings 4. The large refractory metal cylinder 12 is fitted on the outside of the small refractory metal cylinder 3, and an annular cavity for forming a sandwich is left between the large refractory metal cylinder 12 and the small refractory metal cylinder 3. The two ends of the annular cavity are sealed by the two refractory metal rings 4 respectively.

[0034] See Figure 1 As shown, in an embodiment of the present invention, the carbon nanotube macroscopic heating module includes a cylindrical insulating ceramic skeleton 6 and a carbon nanotube macroscopic heating wire 7 wound around the insulating ceramic skeleton 6; one end of the refractory metal sheath is provided with a lead hole, and the tail end of the carbon nanotube macroscopic heating wire 7 is led out from the lead hole and connected to an external lead wire 10 through a wiring structure. The external lead wire 10 and the refractory metal sheath are respectively connected to the positive and negative terminals of a power supply to form a heating circuit. The outer circumference of the insulating ceramic skeleton 6 has a threaded groove feature, and the carbon nanotube macroscopic heating wire 7 is wound in the groove.

[0035] Specifically, a refractory metal ring 4 is provided with a lead hole for the tail end of the carbon nanotube macro-body heating wire 7 to pass through; another refractory metal ring 4 is connected to the head end of the carbon nanotube macro-body heating wire 7, and a relaxation section is reserved at the head end of the carbon nanotube macro-body heating wire 7 to buffer stress.

[0036] In this embodiment of the invention, the macroscopic carbon nanotube heating wire 7 is a high-quality carbon nanotube fiber bundle assembled from carbon nanotubes. The carbon nanotube fiber bundle is continuously prepared from a high-quality liquid crystal solution, and the Raman spectrum is shown in Figure I. G / I D ≥80, filament diameter 50~400μm, resistivity greater than 10 -7 The resistivity and diameter of carbon nanotube fiber bundles can be controlled by adjusting the liquid crystal solution and the pore size of the spinneret. After annealing at 400℃ for 10 hours, the carbon nanotube fiber bundles were subjected to compatibility tests with various insulating ceramics at high temperatures of 1200-1600℃, and the properties of the carbon nanotube fiber bundles remained stable.

[0037] Furthermore, the insulating and heat-insulating layer is an insulating ceramic cylinder 8. Specifically, the insulating ceramic cylinder 8 is made of alumina ceramic with a thermal conductivity of 30 W / (m·K); the insulating ceramic skeleton 6 is made of aluminum nitride ceramic or hexagonal boron nitride ceramic, with thermal conductivity of 320 W / (m·K) and 200 W / (m·K) respectively; the external lead wire 10 is Pt wire, and the insulating ceramic powder 11 is alumina ceramic powder.

[0038] See Figure 2As shown, in an embodiment of the present invention, the wiring structure includes a refractory metal thin-walled tube 5 fixed at the lead hole of the refractory metal shell, and the tail end of the carbon nanotube macrobody heating wire 7 inside the refractory metal thin-walled tube 5 is connected to the external lead wire 10 through high-temperature resistant inorganic adhesive 9. The middle gap of the refractory metal thin-walled tube 5 is filled with insulating ceramic powder 11.

[0039] Furthermore, the tail end of the carbon nanotube macroscopic heating wire 7 and the external lead wire 10 are wound together to form a wound joint, and then coated with high-temperature resistant inorganic adhesive 9.

[0040] Specifically, the refractory metal shell and the refractory metal thin-walled tube 5 are made of the same material, namely, any one of tungsten, molybdenum, tantalum, and niobium, or an alloy containing any one of tungsten, molybdenum, tantalum, and niobium. The joints of the small refractory metal cylinder 3, the large refractory metal cylinder 12, the refractory metal ring 4, and the refractory metal thin-walled tube 5 are welded by pulsed laser.

[0041] This invention provides a hollow cathode armored heater based on carbon nanotube macrostructures, which uses carbon nanotube macrostructure heating wires. These wires have low density, low coefficient of thermal expansion, low temperature coefficient of resistance, fast thermal response, high mechanical strength, and excellent thermal conductivity, electrical conductivity, and chemical stability, effectively improving the performance and reliability of the heater. This invention can be applied to thermal control devices used in spacecraft and orbital thrusters.

[0042] Example 1

[0043] See Figure 1 and Figure 2 As shown, this invention provides a hollow cathode armored heater based on a carbon nanotube macrostructure, comprising two armored cylinders of different sizes made of refractory metal, namely a small refractory metal cylinder 3 and a large refractory metal cylinder 12; two refractory metal rings 4 connecting the two armored cylinders; one of the refractory metal rings 4 having a lead hole for leading out a refractory metal thin-walled tube 5; a threaded insulating ceramic skeleton 6 fitted onto the small refractory metal cylinder 3; a carbon nanotube macrostructure heating wire 7 wound around the insulating ceramic skeleton 6; and a heat-insulating ceramic cylinder 8 fitted over the carbon nanotube macrostructure heating wire 7. Both the refractory metal armor and the refractory metal thin-walled tube 5 are made of tantalum. The armor shells are connected by pulsed laser welding. The insulating ceramic skeleton 6 is made of aluminum nitride, and the ceramic heat-insulating cylinder 8 is made of high-purity α-Al₂O₃. The carbon nanotube macrostructure heating wire 7 is continuously prepared from a high-quality liquid crystal solution, and its Raman spectroscopy... G / I D The ratio is 90, the diameter is approximately 70 μm, and the resistivity is >10. -7 Ω·m, tensile breaking strength is 4GPa, such as Figures 3 to 5As shown, carbon nanotube bundles are wound around an insulating ceramic skeleton 6. The first end of the bundle is connected to a refractory metal ring 4 using a high-temperature resistant inorganic adhesive, with a 1mm relaxation section left to buffer stress. The tail end of the carbon nanotube bundle is connected to an external lead 10 within a refractory metal thin-walled tube 5 using a high-temperature resistant inorganic adhesive 9. The gap in the middle is filled with insulating ceramic powder 11, which is alumina ceramic powder with a particle size ≤5μm. The high-temperature resistant inorganic adhesive 9 is a commercially available high-temperature resistant inorganic adhesive with a long-term operating temperature ≥1800℃. The Pt material external lead 10 and the refractory metal shell are connected to the positive and negative terminals of the power supply, respectively, forming a heating circuit.

[0044] This invention provides a hollow cathode armored heater based on a carbon nanotube macrostructure, used to heat the emitter inside the hollow cathode tube, solving the problems of poor high-temperature stability, high density, and slow thermal response of traditional refractory metal heating elements. The heating wire is composed of high-quality carbon nanotube fiber bundles, and its resistivity and diameter can be adjusted by controlling the liquid crystal solution and the spinneret orifice size. It exhibits Raman spectroscopy. G / I D ≥80, resistivity >10 -7 It possesses properties such as Ω·m and tensile strength up to 4 GPa, and exhibits excellent compatibility with insulating ceramics after high-temperature annealing. The armor shell is made of tungsten, molybdenum, tantalum, or their alloys, with interfaces welded by pulsed laser. The external leads are Pt wires, and insulating ceramic powder fills the gaps to form a stable heating circuit. This invention combines lightweight design, low power consumption, high energy efficiency, and excellent high-temperature stability, making it suitable for thermal control devices of spacecraft attitude and orbital control thrusters, significantly improving system lifespan and reliability.

[0045] The above-described embodiments are merely illustrative of certain implementations of the present invention, and are described in a relatively specific and detailed manner. However, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A hollow cathode armored heater based on carbon nanotube macrostructures, characterized in that, It includes a refractory metal shell, a carbon nanotube macro-body heating module, and an insulating heat insulation layer. The refractory metal shell is a cylindrical structure with a sandwich layer. The carbon nanotube macro-body heating module and the insulating heat insulation layer are sequentially fitted into the sandwich layer of the refractory metal shell from the inside to the outside. The carbon nanotube macro-body heating module is used to heat the emitter (2) inside the hollow cathode tube (1), and the insulating heat insulation layer is used for insulation and heat insulation.

2. The hollow cathode armored heater based on carbon nanotube macrostructure according to claim 1, characterized in that, The carbon nanotube macro-body heating module includes a cylindrical insulating ceramic skeleton (6) and a carbon nanotube macro-body heating wire (7) wound on the insulating ceramic skeleton (6); One end of the refractory metal shell is provided with a lead wire hole. The tail end of the carbon nanotube macrobody heating wire (7) is led out from the lead wire hole and connected to the external lead wire (10) through the wiring structure. The external lead wire (10) and the refractory metal shell are respectively connected to the positive and negative terminals of the power supply to form a heating circuit.

3. The hollow cathode armored heater based on carbon nanotube macrostructure according to claim 2, characterized in that, The carbon nanotube macrostructure heating wire (7) is a high-quality carbon nanotube fiber bundle assembled from carbon nanotubes.

4. The hollow cathode armored heater based on carbon nanotube macrostructure according to claim 3, characterized in that, The carbon nanotube fiber bundles were continuously prepared from a high-quality liquid crystal solution, and the Raman spectrum I... G / I D ≥80, filament diameter 50~400μm, resistivity greater than 10 -7 Ω·m, with a maximum tensile strength of 4 GPa.

5. The hollow cathode armored heater based on carbon nanotube macrostructure according to claim 2, characterized in that, The insulating and heat-insulating layer is a heat-insulating ceramic cylinder (8).

6. The hollow cathode armored heater based on carbon nanotube macrostructure according to claim 5, characterized in that, The insulating ceramic skeleton (6) is made of aluminum nitride ceramic or hexagonal boron nitride ceramic; the heat-insulating ceramic cylinder (8) is made of alumina ceramic; the external lead wire (10) is Pt wire; and the insulating ceramic powder (11) is alumina ceramic powder.

7. The hollow cathode armored heater based on carbon nanotube macrostructure according to claim 2, characterized in that, The wiring structure includes a refractory metal thin-walled tube (5) fixed at the lead hole of the refractory metal shell. The tail end of the carbon nanotube macrobody heating wire (7) inside the refractory metal thin-walled tube (5) is connected to the external lead wire (10) through high-temperature resistant inorganic glue (9). The middle gap of the refractory metal thin-walled tube (5) is filled with insulating ceramic powder (11).

8. The hollow cathode armored heater based on carbon nanotube macrostructure according to claim 7, characterized in that, The refractory metal shell and the refractory metal thin-walled tube (5) are made of the same material, namely, any one of tungsten, molybdenum, tantalum, and niobium, or an alloy containing any one of tungsten, molybdenum, tantalum, and niobium.

9. The hollow cathode armored heater based on carbon nanotube macrostructure according to claim 2, characterized in that, The refractory metal shell includes a small refractory metal cylinder (3), a large refractory metal cylinder (12), and two refractory metal rings (4). The large refractory metal cylinder (12) is fitted on the outside of the small refractory metal cylinder (3), and there is an annular cavity between the large refractory metal cylinder (12) and the small refractory metal cylinder (3) for forming the interlayer. The two ends of the annular cavity are sealed by the two refractory metal rings (4).

10. The hollow cathode armored heater based on carbon nanotube macrostructure according to claim 9, characterized in that, One of the refractory metal rings (4) is provided with a lead hole for the tail end of the carbon nanotube macro heating wire (7) to pass through; another refractory metal ring (4) is connected to the head end of the carbon nanotube macro heating wire (7), and the head end of the carbon nanotube macro heating wire (7) is reserved with a relaxation section to buffer stress.

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