Carbon nanotube cold cathode and method of making same, x-ray tube

Abstract

The application provides a carbon nanotube cold cathode, a preparation method thereof and an X-ray tube. The preparation method comprises the following steps: ball milling agglomerated carbon nanotubes to obtain carbon nanotube powder; mixing the carbon nanotube powder with a first solvent and an electrolyte solution, and then performing ultrasonic oscillation to obtain a suspension; placing a metal substrate in the suspension to perform electrophoretic deposition, thereby obtaining a carbon nanotube film cold cathode; coating a curing agent on the carbon nanotube film cold cathode to perform cross-linking and curing, thereby obtaining a cured carbon nanotube cold cathode; using a high-energy ion beam to form a tip of the carbon nanotube in the cured carbon nanotube cold cathode; and using a high-strength electric field to make the carbon nanotube stand upright, thereby obtaining an activated carbon nanotube cold cathode.

Description

Technical Field

[0001] This application relates to the fields of nanomaterials and radiation technology, and in particular to carbon nanotube cold cathodes and their preparation methods, and X-ray tubes. Background Technology

[0002] Since its discovery by Sumio Iijima in 1991, carbon nanotubes (CNTs) have become a core material in the field of field emission due to their unique structure and properties. CNTs possess excellent electrical conductivity, and their tip surface area is close to the theoretical limit, allowing for the formation of highly concentrated local electric fields that facilitate electron escape through the tunneling effect. Simultaneously, CNTs exhibit extremely low field emission threshold voltages (typically less than 100 volts), enabling extremely high current densities, and demonstrate excellent long-term operational stability. These characteristics make them an ideal choice for cold cathode field emission materials, showing significant application potential in fields such as vacuum electron sources and field emission displays.

[0003] Compared to traditional tungsten filament hot cathode X-ray tubes, carbon nanotube cold cathode X-ray tubes represent a fundamental technological breakthrough. Traditional hot cathodes require high-temperature heating (typically thousands of degrees Celsius) to excite electrons, resulting in drawbacks such as long heating times, high power consumption, easy filament wear, and short lifespan. Furthermore, they are prone to motion artifacts during rotating imaging. In contrast, carbon nanotube cold cathodes, based on the field emission principle, can achieve electron emission at room temperature through grid electric field modulation. They feature rapid start-up, low power consumption, and are compact and easily integrated. More importantly, they can be fabricated into multi-focal-spot array sources for static CT imaging, significantly improving imaging resolution and efficiency. They can also withstand higher electric field forces, producing higher doses of X-rays, and offer superior heat dissipation and operational reliability, making them urgently needed in high-end fields such as medical diagnostics and industrial inspection.

[0004] The basis for electron emission in CNTs is that electron emission occurs under the field emission principle when the CNT tip is subjected to a strong electric field. However, the CNT materials currently prepared are usually lying on the substrate surface and do not form an upright state. Therefore, the high aspect ratio characteristics of slender CNTs are not utilized, and the CNT tip is difficult to form a field strength enhancement effect similar to that of a "lightning rod", making it difficult to achieve stable emission of large current.

[0005] The information disclosed in this section is only used to understand the background of the inventive concept of this application. Therefore, the above information may include information that does not constitute prior art. Summary of the Invention

[0006] To address at least one aspect of the above-mentioned problems, embodiments of this application provide a carbon nanotube cold cathode and its preparation method, as well as an X-ray tube.

[0007] One aspect of this application provides a method for preparing a carbon nanotube cold cathode, the method comprising: ball milling aggregated carbon nanotubes to obtain carbon nanotube powder; mixing the carbon nanotube powder with a first solvent and an electrolyte solution and then subjecting the mixture to ultrasonic oscillation to obtain a suspension; placing a metal substrate in the suspension for electrophoretic deposition to obtain a carbon nanotube thin film cold cathode; coating a curing agent onto the carbon nanotube thin film cold cathode for cross-linking and curing to obtain a cured carbon nanotube cold cathode; using a high-energy ion beam to form tips on the carbon nanotubes in the cured carbon nanotube cold cathode, and using a high-intensity electric field to make the carbon nanotubes stand upright to obtain an activated carbon nanotube cold cathode.

[0008] According to some exemplary embodiments, the crosslinking and curing of the curing agent applied to the carbon nanotube film cold cathode includes: spraying the curing agent onto the surface of the carbon nanotube film cold cathode using a spray gun, or brushing the curing agent onto the surface of the carbon nanotube film cold cathode using a brush or roller.

[0009] According to some exemplary embodiments, the curing agent includes one of polyphenylsiloxane solution and conductive silver paste; the thickness of the curing agent coating is 500-3000 nm.

[0010] According to some exemplary embodiments, the process of coating the curing agent onto the carbon nanotube film cold cathode for crosslinking and curing includes: dissolving polyphenylsiloxane in a second solvent to obtain a mixture; spraying the mixture onto the surface of the carbon nanotube film cold cathode using a spray gun; and heating and curing the carbon nanotube film cold cathode to obtain a cured carbon nanotube cold cathode.

[0011] According to some exemplary embodiments, the second solvent includes one of toluene, xylene, and chloroform, and the concentration of the mixture is 5-15 wt%; the temperature for heat curing is 80-150°C, and the duration of heat curing is 6-10 h.

[0012] According to some exemplary embodiments, the heating and curing of the carbon nanotube film cold cathode includes: placing the carbon nanotube film cold cathode in a ventilation chamber to allow the second solvent to evaporate; placing the carbon nanotube film cold cathode in a heating chamber, heating the heating chamber to a first temperature, and holding it at the first temperature for 1-3 hours; heating the heating chamber to a second temperature, and holding it at the second temperature for 3-5 hours; heating the heating chamber to a third temperature, and holding it at the third temperature for 0.5-2 hours; wherein the first temperature is lower than the second temperature, the second temperature is lower than the third temperature, and the range of the first temperature, the second temperature, and the third temperature is 50-200°C.

[0013] According to some exemplary embodiments, the ball milling of the aggregated carbon nanotubes includes: loading the aggregated carbon nanotubes into a ball mill for ball milling, wherein the rotation speed of the ball mill is 100-300 rpm and the ball milling time is 5-15 min.

[0014] According to some exemplary embodiments, each carbon nanotube in the aggregated state includes at least two graphene layers, each graphene layer being a hollow tubular structure, and the at least two graphene layers are nested sequentially, arranged according to the diameter of the hollow tubular structure; the number of graphene layers is between 2 and 5, and the purity of the aggregated state carbon nanotube is greater than or equal to 99.9%.

[0015] According to some exemplary embodiments, the step of mixing the carbon nanotube powder with a first solvent and an electrolyte solution and then subjecting it to ultrasonic oscillation includes: preparing an electrolyte solution, wherein the electrolyte includes one or more of magnesium chloride, magnesium nitrate, aluminum chloride, and aluminum nitrate; and mixing the carbon nanotube powder, the first solvent, the electrolyte solution, and deionized water and then subjecting it to ultrasonic oscillation to obtain a suspension.

[0016] According to some exemplary embodiments, the concentration of carbon nanotubes in the suspension is 0.001-0.01 g / ml; the concentration of deionized water in the suspension is 1%-10% vol; the concentration of electrolyte in the suspension is 0.002-0.01 g / ml; the first solvent includes anhydrous ethanol; and the duration of ultrasonic oscillation is 3-5 h.

[0017] According to some exemplary embodiments, the step of placing the metal substrate in the suspension for electrophoretic deposition includes: connecting the metal substrate to a first electrode of a power source and connecting a second metal plate to a second electrode of the power source; placing the metal substrate and the second metal plate in the suspension for electrophoretic deposition; and drying the metal substrate with the deposited carbon nanotube film to obtain a carbon nanotube film cold cathode.

[0018] According to some exemplary embodiments, the electric field strength in the suspension is 5-80V / cm, the electrophoretic deposition time is 20-200s, the drying temperature is 70-100℃, and the drying time is 0.1-1h.

[0019] According to some exemplary embodiments, the process of forming tips on carbon nanotubes in a solidified carbon nanotube cold cathode using a high-energy ion beam includes: cleaning the surface of the solidified carbon nanotube cold cathode with plasma; bombarding the surface of the solidified carbon nanotube cold cathode with a first high-energy ion beam for a first duration; bombarding the surface of the solidified carbon nanotube cold cathode with a second high-energy ion beam for a second duration; and bombarding the surface of the solidified carbon nanotube cold cathode with a third high-energy ion beam, observing the surface at third intervals, and stopping bombardment if uniform and dense tips are formed on the surface, otherwise continuing to bombard the surface with the third high-energy ion beam; wherein the energy and beam current density of the first high-energy ion beam are lower than those of the second high-energy ion beam, and the energy and beam current density of the second high-energy ion beam are lower than those of the third high-energy ion beam.

[0020] According to some exemplary embodiments, the energy of the first high-energy ion beam is 500-700 eV, and the beam current density is 5-15 μA / cm. 2 The first duration is 10-30 s; the energy of the second high-energy ion beam is 700-900 eV, and the beam current density is 15-25 μA / cm. 2 The second duration is 10-30 s; the energy of the third high-energy ion beam is 900-1200 eV, and the beam current density is 25-35 μA / cm. 2 The third duration is 10-30 seconds.

[0021] According to some exemplary embodiments, the step of using a high-intensity electric field to make the carbon nanotubes stand upright includes: placing the carbon nanotube cold cathode in a high-intensity electric field for activation, wherein the electric field strength of the high-intensity electric field is 1-10V / µm, and the activation time is 30-120min.

[0022] In another aspect of the embodiments of this application, a carbon nanotube cold cathode is provided, which is prepared according to the preparation method described above.

[0023] According to some exemplary embodiments, the carbon nanotube cold cathode includes a metal substrate and carbon nanotubes, wherein the carbon nanotubes are located on a first surface of the metal substrate, and the height of the carbon nanotubes is 4-15 μm; the angle between the extension direction of the carbon nanotubes and the first surface is 75-90°; and the density of the carbon nanotubes within their distribution range is 100-200 nanotubes / μm. 2 .

[0024] In another aspect of the embodiments of this application, an X-ray tube is provided, the X-ray tube comprising a carbon nanotube cold cathode according to the above description.

[0025] According to some exemplary embodiments, the X-ray tube further includes a gate, the carbon nanotube cold cathode is spaced 215 μm from the gate, and the X-ray tube is configured such that, in response to a control voltage of 1600 V on the gate, the emission current of the carbon nanotube cold cathode is greater than or equal to 350 mA.

[0026] In the embodiments of this application, a carbon nanotube thin film cold cathode is prepared by electrophoretic deposition. The carbon nanotubes are cured with a curing agent to improve the bonding force between the carbon nanotubes and the metal substrate and improve the emission stability of the cold cathode. The carbon nanotubes are activated by a high-energy ion beam and a high-intensity electric field to form a uniform and dense upright tip structure of the carbon nanotube cold cathode. The upright tip structure of the carbon nanotubes can form an electric field enhancement effect, which can emit at low voltage and easily form a large current emission. Attached Figure Description

[0027] Other objects and advantages of this application will become apparent from the following description of the application with reference to the accompanying drawings, and will help to provide a comprehensive understanding of the application.

[0028] Figure 1 A flowchart illustrating a method for preparing a carbon nanotube cold cathode according to some exemplary embodiments of this application is shown schematically.

[0029] Figure 2 The schematic diagram illustrates a process flow diagram of a method for preparing a carbon nanotube cold cathode according to some exemplary embodiments of this application;

[0030] Figure 3 This schematically illustrates a process flow diagram of a method for crosslinking and curing a curing agent coated on a carbon nanotube thin film cold cathode according to some exemplary embodiments of this application;

[0031] Figure 4 The schematic diagram shows a partially magnified scanning electron microscope image of a solidified carbon nanotube cold cathode obtained in some exemplary embodiments according to this application;

[0032] Figure 5 The schematic diagram illustrates the structure of an electrophoretic deposition apparatus according to some exemplary embodiments of this application;

[0033] Figure 6A The illustration shows a physical image of an activated carbon nanotube cold cathode obtained according to some exemplary embodiments of this application;

[0034] Figure 6B The illustration schematically shows a partially magnified scanning electron microscope image of an activated carbon nanotube cold cathode obtained according to some exemplary embodiments of this application;

[0035] Figure 7The schematic diagram shows partially magnified scanning electron microscope images of carbon nanotube cold cathodes obtained in some exemplary comparative examples according to this application;

[0036] Figure 8 The schematic diagram illustrates a structural schematic of an X-ray tube including a carbon nanotube cold cathode according to some exemplary embodiments of this application;

[0037] Figure 9 The diagram illustrates the relationship between field voltage and emission current when a carbon nanotube cold cathode is applied in an X-ray tube according to some exemplary embodiments of this application.

[0038] Figure 10 The illustration schematically shows a lifetime test diagram of a carbon nanotube cold cathode when applied to an X-ray tube according to some exemplary embodiments of the present application.

[0039] It should be noted that, for clarity, the dimensions of layers, structures, or regions in the drawings used to describe embodiments of this application may be enlarged or reduced, i.e., these drawings are not drawn to actual scale. Detailed Implementation

[0040] The technical solution of this application will be further described in detail below through embodiments and in conjunction with the accompanying drawings. In the specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of this application with reference to the accompanying drawings is intended to explain the overall inventive concept of this application and should not be construed as a limitation of this application.

[0041] Furthermore, in the following detailed description, numerous specific details are set forth for ease of explanation to provide a thorough understanding of the embodiments disclosed herein. However, it will be apparent that one or more embodiments may be practiced without these specific details.

[0042] It should be understood that although the terms first, second, etc., may be used herein to describe different elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of the exemplary embodiments, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0043] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that when the terms “comprising” and / or “including” are used herein, it indicates the presence of the stated features, integrals, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or combinations thereof.

[0044] Currently, five main technical approaches are used for carbon nanotube cold cathodes designed for high current output: direct growth, slurry printing, electrophoretic deposition, barcode paper composite process, and cold pressing.

[0045] Direct growth refers to the in-situ growth of vertically aligned carbon nanotube arrays on a metal or silicon substrate using chemical vapor deposition. While this method can yield well-oriented structures, it still faces challenges in practical fabrication, such as uneven catalyst distribution, entanglement and agglomeration at the array tops, and poor planarity at the roots. Furthermore, the high density of carbon nanotubes causes the distance between adjacent tips to be significantly smaller than their height, leading to a severe "field shielding effect" that weakens the local electric field enhancement. This not only necessitates applying higher driving voltages but also increases the overall system cost and the risk of dielectric breakdown.

[0046] The paste printing method involves mixing carbon nanotubes with organic binders, metal powders, and other materials to form a paste, which is then coated onto a substrate using screen printing technology and sintered. This method is relatively simple and suitable for large-area fabrication, but it also has some drawbacks: carbon nanotubes tend to agglomerate in the paste and their orientation is random; a large number of carbon nanotubes are encapsulated by the insulating binder, resulting in the proportion of effective carbon nanotubes participating in electron emission typically being less than 30%; during sintering, carbon nanotubes are difficult to keep upright and mostly lie in a creeping state, failing to fully utilize the "lightning rod effect" brought about by their high aspect ratio.

[0047] Electrophoretic deposition uses an electric field to drive charged carbon nanotubes to migrate directionally in a solvent and deposit them on the surface of a conductive substrate. Although it can form a relatively uniform coating, traditional electrophoretic processes lack effective control over the orientation, density, and interfacial bonding strength of carbon nanotubes. This results in the carbon nanotubes in the deposited layer being flatly stacked with their tips not effectively exposed, thus limiting their field emission performance.

[0048] The buckypaper composite process involves cutting a pre-fabricated carbon nanotube film (buckypaper) and bonding it to a metal substrate. While this method can achieve a high carbon nanotube loading, it is prone to problems such as film edge breakage and poor interfacial contact during the cutting and bonding process. Furthermore, because the carbon nanotubes maintain a horizontal orientation, it is difficult to achieve efficient vertical electron emission, resulting in the need for a high control voltage, high control costs, and a relatively low emission current.

[0049] Cold pressing directly deposits carbon nanotube powder onto the surface of a metal substrate (such as tin) without the need for non-conductive additives such as binders, solvents, or surfactants. However, this method has the following problems: the orientation of carbon nanotubes is difficult to control, with most falling onto the substrate surface, making it difficult to obtain the field strength enhancement effect, resulting in low emission current; the uneven distribution of carbon nanotubes affects the stability and uniformity of current emission; the bonding strength between carbon nanotubes and the metal substrate is weak and difficult to control, making them prone to detachment and failure under high voltage or long-term operation, resulting in insufficient long-term device reliability and difficulty in meeting the requirements of high current (such as 50mA) and patterned applications.

[0050] The inventors' research revealed that although the aforementioned methods, such as direct growth, slurry printing, electrophoretic deposition, buckypaper composite process, and cold pressing, have been extensively studied, the carbon nanotube cold cathodes prepared by these methods still generally suffer from several problems: low material utilization, with a large number of carbon nanotubes unable to participate in effective emission due to encapsulation, breakage, or poor orientation; poor emission uniformity, with excessively high local current density forming hot spots that limit the overall current increase; insufficient uprightness of the carbon nanotubes, with flat or tilted orientation weakening the tip electric field enhancement effect; weak field strength enhancement effect, either due to dense shielding (such as in the direct growth method) or poor orientation (such as in other methods), making it difficult to achieve efficient, low-voltage emission; and high interfacial contact resistance, with a lack of good electrical connection between the carbon nanotubes and the metal substrate, resulting in significant Joule heating under high current, which easily leads to failure. For the reasons mentioned above, most X-ray tubes currently made using carbon nanotube cold cathodes have an operating current of less than 10mA. There are no high-current carbon nanotube cold cathode X-ray tubes that can operate stably for a long time, especially models with an operating current of 100mA or more. This seriously restricts the practical application range of carbon nanotube cold cathode X-ray tubes.

[0051] To address at least one of the above problems, embodiments of this application provide a carbon nanotube cold cathode and its preparation method, as well as an X-ray tube.

[0052] Figure 1 A flowchart illustrating a method for preparing a carbon nanotube cold cathode according to some exemplary embodiments of this application is shown schematically. Figure 2The illustration shows a schematic flowchart of a method for preparing a carbon nanotube cold cathode according to some exemplary embodiments of this application.

[0053] In some embodiments of this application, reference is made to Figure 1 and Figure 2 A method for preparing a carbon nanotube cold cathode includes: S100, ball milling aggregated carbon nanotubes 21 to obtain carbon nanotube powder; S200, mixing the carbon nanotube powder with a first solvent and an electrolyte solution and then ultrasonically vibrating to obtain a suspension 31, which includes dispersed carbon nanotubes 22; S300, placing a metal substrate 10 in the suspension 31 for electrophoretic deposition to obtain a carbon nanotube thin film cold cathode 43, which includes deposited carbon nanotubes 23; S400, coating a curing agent 32 onto the carbon nanotube thin film cold cathode 43 for cross-linking and curing to obtain a cured carbon nanotube cold cathode 44, which includes cured carbon nanotubes 24; S500, using a high-energy ion beam to form tips on the carbon nanotubes in the cured carbon nanotube cold cathode 44, and using a high-intensity electric field to make the carbon nanotubes stand upright to obtain an activated carbon nanotube cold cathode 45, which includes activated carbon nanotubes 25.

[0054] The preparation method of the embodiments of this application is based on electrophoretic deposition. Electrophoretic deposition is a technique that uses an electric field to drive the directional migration of charged particles in a suspension and deposit them on the surface of an electrode with opposite charge. It includes two steps: electrophoresis and deposition. Electrophoresis, also known as electromigration, refers to the physicochemical phenomenon in which charged particles move directionally in a medium under the influence of an electric field. Deposition refers to the process in which the charged particles that have migrated to the electrode surface gradually aggregate to form a thin film or bulk structure.

[0055] For example, firstly, dispersed carbon nanotubes 22 are deposited on a metal substrate 10 via electrophoretic deposition to obtain a carbon nanotube thin-film cold cathode 43, which includes deposited carbon nanotubes 23. Then, the deposited carbon nanotubes 23 are cured using a curing agent to form cured carbon nanotubes 24, thereby enhancing the bonding force between the carbon nanotubes and the metal substrate 10 and improving the emission stability of the cold cathode. Next, the cured carbon nanotubes 24 are activated using a high-energy ion beam and a high-intensity electric field, resulting in a uniform and dense upright tip structure on the surface of the cold cathode. This upright tip structure can effectively leverage the electric field enhancement effect, achieving efficient electron emission at lower voltages and possessing the potential for high-current emission. By synergistically controlling the physical behavior of carbon nanotubes in multiple stages—aggregated, dispersed, deposited, cured, and activated—high-density, high-uprightness, and high-conductivity directional assembly of activated carbon nanotubes 25 on the metal substrate 10 is achieved, providing key technological support for next-generation high-power carbon nanotube cold cathodes.

[0056] According to some exemplary embodiments, crosslinking and curing the curing agent applied to the carbon nanotube film cold cathode 43 includes: spraying the curing agent onto the surface of the carbon nanotube film cold cathode 43 using a spray gun, or brushing the curing agent onto the surface of the carbon nanotube film cold cathode 43 using a brush or roller.

[0057] For example, coating the curing agent onto the carbon nanotube film cold cathode 43 includes spraying and brushing methods. Spraying involves using a spray gun to uniformly spray the curing agent onto the surface of the carbon nanotube cold cathode, while brushing involves using a brush or roller to apply the curing agent to the surface of the carbon nanotube film. Both methods allow the curing agent to fully penetrate the gaps between the carbon nanotubes, forming a cross-linked network during subsequent curing. This fixes the cured carbon nanotubes 24 onto the metal substrate 10, thereby enhancing the bonding force between the cured carbon nanotubes 24 and the metal substrate 10 and improving the emission stability of the cold cathode.

[0058] According to some exemplary embodiments, the curing agent includes one of a polyphenylsiloxane solution and a conductive silver paste; the thickness of the curing agent coating is 500-3000 nm.

[0059] For example, polyphenylsilsesquioxane (PPSQ) is an organosilicon polymer including phenyl side chains, whose solution can form a cross-linked network structure during curing. The PPSQ solution possesses good wettability and flowability, allowing it to penetrate deep into the gaps between carbon nanotubes. After curing, a stable three-dimensional cross-linked framework is formed between the cured carbon nanotubes 24 and the metal substrate 10, enhancing the bonding force between the cured carbon nanotubes 24 and the metal substrate 10. Conductive silver paste is a functional adhesive material in which micron or nano-sized silver particles are dispersed in an organic resin system. The cured conductive silver paste forms an adhesive layer with certain strength and toughness, effectively anchoring the cured carbon nanotubes 24, enhancing the adhesion of the cured carbon nanotubes 24 to the metal substrate 10, and reducing the risk of carbon nanotube breakage or detachment under high electric fields.

[0060] For example, controlling the coating thickness within the range of 500-3000 nm ensures that the curing agent fully wets the gaps between the carbon nanotubes, while avoiding excessive thickness that would cause the cured carbon nanotubes 24 to be encapsulated, or excessive thinness that would result in weak bonding between the cured carbon nanotubes 24 and the metal substrate 10. Within this optimized thickness range, the curing agent can form a stable bonding layer between the cured carbon nanotubes 24 and the metal substrate 10, effectively improving the mechanical adhesion strength of the cured carbon nanotube cold cathode 44.

[0061] Figure 3 The diagram illustrates a process flow chart of a method for crosslinking and curing a curing agent coated on a carbon nanotube thin film cold cathode according to some exemplary embodiments of the present application.

[0062] According to some exemplary embodiments, refer to Figure 3 The method of coating the curing agent onto the carbon nanotube thin film cold cathode 43 for cross-linking and curing includes the following steps S410 to S430.

[0063] In step S410, polyphenylsiloxane is dissolved in a second solvent to obtain a mixture.

[0064] In step S420, the mixture is sprayed onto the surface of the carbon nanotube thin film cold cathode 43 using a spray gun.

[0065] In step S430, the carbon nanotube film cold cathode 43 is heated and cured to obtain a cured carbon nanotube cold cathode 44.

[0066] For example, in step S410, the second solvent includes one of toluene, xylene, and chloroform, such as toluene or xylene. The concentration of the mixture is 5-15 wt%, for example, 6-10 wt%. For example, the step of obtaining the mixture includes: weighing 40 g of polyphenylsiloxane solution into a 1 L glass beaker, adding 460 g of toluene solution, stirring at a rate of 100-300 rpm for 10-20 min, and letting it stand for 5-10 min after stirring to form a bubble-free homogeneous mixture.

[0067] For example, in step S420, the removed metal substrate 10 is fixed in a dedicated spraying fixture. After covering the non-deposition area, a finely atomized precision spray gun, for example, with a nozzle diameter of 0.3-1.2 mm, is used to uniformly spray a layer of polyphenylsiloxane (PPSQ) curing agent on the exposed deposition area surface, controlling the spraying thickness to be between 500-3000 nm.

[0068] For example, in step S430, the carbon nanotube film cold cathode 43 coated with the curing agent is subjected to heat curing treatment to transform it into a structurally stable cured carbon nanotube cold cathode 44. For example, the heat curing temperature is 80-150°C, and the heat curing time is 6-10 hours. Through heat treatment, the curing agent can fully crosslink and form a stable three-dimensional network structure, thereby significantly enhancing the bonding strength between the cured carbon nanotubes 24 and the metal substrate 10, and forming a good electrical connection between the cured carbon nanotubes 24 and the metal substrate 10.

[0069] Figure 4 The illustration schematically shows a partially magnified scanning electron microscope image of a solidified carbon nanotube cold cathode obtained in some exemplary embodiments according to this application.

[0070] According to some exemplary embodiments, heating and curing the carbon nanotube film cold cathode 43 includes: placing the carbon nanotube film cold cathode 43 in a ventilation chamber to allow the second solvent to evaporate; placing the carbon nanotube film cold cathode 43 in a heating chamber, heating the heating chamber to a first temperature, and holding it at the first temperature for 1-3 hours; heating the heating chamber to a second temperature, and holding it at the second temperature for 3-5 hours; heating the heating chamber to a third temperature, and holding it at the third temperature for 0.5-2 hours; wherein the first temperature is lower than the second temperature, the second temperature is lower than the third temperature, and the range of the first temperature, the second temperature, and the third temperature is 50-200°C.

[0071] For example, the carbon nanotube film cold cathode 43, after being coated with the curing agent, is placed in a quartz boat and left to stand at room temperature in a fume hood for, for example, 1 hour, to allow the second solvent to fully evaporate. Subsequently, the quartz boat is transferred to a tube furnace and cured by a stepped temperature increase procedure as follows: for example, the temperature is increased from room temperature to 80°C over 30 minutes and held at 80°C for 2 hours; then increased to 100°C over 4 minutes and cured at that temperature for 4 hours; subsequently increased to 120°C over 4 minutes and cured at that temperature for 1 hour; finally, the temperature is slowly decreased to room temperature over 30 minutes. This stepped temperature increase procedure aims to gradually remove residual solvent and promote full cross-linking of the curing agent, thereby forming a structurally stable cured carbon nanotube cold cathode 44. A locally magnified scanning electron microscope image of the cured carbon nanotube cold cathode 44 after the above curing treatment is shown below. Figure 4 As shown, at this time, the solidified carbon nanotubes 24 are firmly bonded to the metal substrate 10, and most of the solidified carbon nanotubes 24 are in a flat stacked state.

[0072] According to some exemplary embodiments, ball milling of aggregated carbon nanotubes 21 includes: loading aggregated carbon nanotubes 21 into a ball mill for ball milling, wherein the rotation speed of the ball mill is 100-300 rpm and the ball milling time is 5-15 min.

[0073] For example, the aggregated carbon nanotube 21 film can be cut into small pieces and placed in a ball mill jar along with milling balls. The pieces are then ground using a ball mill at a low rotation speed to obtain carbon nanotube powder. The rotation speed of the ball mill is controlled within the range of 100-300 rpm: too low a speed may result in insufficient deagglomeration, while too high a speed can easily damage the carbon nanotube structure. The milling time is controlled within 5-15 minutes: too short a time will also affect the deagglomeration effect, while too long a time will increase the risk of carbon nanotube structural damage. The main purpose of this step is to achieve preliminary deagglomeration of the carbon nanotubes.

[0074] According to some exemplary embodiments, each carbon nanotube in the aggregated carbon nanotube 21 includes at least two graphene layers, each graphene layer being a hollow tubular structure, with the at least two graphene layers nested sequentially and arranged in order of the diameter of the hollow tubular structure; the number of graphene layers is between 2 and 5, and the purity of the aggregated carbon nanotube 21 is greater than or equal to 99.9%.

[0075] In carbon nanotube materials, the number of graphene layers and their nesting structure jointly determine the material's performance. A graphene layer count between 2 and 5 layers facilitates the fabrication of carbon nanotubes of a single type, avoiding the mixing of carbon nanotubes with different properties. Carbon nanotubes with a 2-5 layer structure exhibit excellent mechanical and electrical properties, better withstanding high-current and high-energy electron emission processes while maintaining high stability, thus extending the lifespan of carbon nanotube cold cathodes. Aggregated carbon nanotubes with a purity greater than or equal to 99.9% are beneficial for simultaneous electron emission performance, increasing emission current and improving the output power and operating efficiency of the carbon nanotube cold cathode.

[0076] According to some exemplary embodiments, the process of mixing carbon nanotube powder with a first solvent and an electrolyte solution and then subjecting it to ultrasonic vibration includes: preparing an electrolyte solution, wherein the electrolyte includes one or more of magnesium chloride, magnesium nitrate, aluminum chloride, and aluminum nitrate; mixing the carbon nanotube powder, the first solvent, the electrolyte solution, and deionized water and then subjecting the mixture to ultrasonic vibration to obtain a suspension. The concentration of carbon nanotubes in the suspension is 0.001-0.01 g / ml; the concentration of deionized water in the suspension is 1%-10% vol; the concentration of electrolyte in the suspension is 0.002-0.01 g / ml; the first solvent includes anhydrous ethanol; and the duration of ultrasonic vibration is 3-5 hours.

[0077] For example, the preparation of the electrolyte solution includes: using magnesium nitrate hexahydrate (Mg(NO3)2·6H2O) as the electrolyte and anhydrous ethanol as the solvent to prepare a magnesium nitrate solution with a concentration of 0.1 g / ml. For instance, 34.56 g of Mg(NO3)2·6H2O is weighed and placed in a 500 ml glass bottle, 200 ml of anhydrous ethanol solution is added, and the mixture is shaken and sonicated for 30 minutes to obtain a homogeneous electrolyte solution with a Mg(NO3)2 concentration of 0.1 g / ml.

[0078] For example, the preparation of the electrophoresis buffer includes the following: the main components of the electrophoresis buffer are carbon nanotube powder, deionized water, anhydrous ethanol, and electrolyte, wherein the concentration range of each component is as follows: the concentration of carbon nanotubes is 0.001 g / ml-0.01 g / ml, for example, 0.003-0.008 g / ml; the volume content of deionized water is 1%-10% vol, for example, 2%-6% vol; and the amount of Mg(NO3)2 electrolyte solution added is 50-150 ml, for example, 80-120 ml. For example, 1600 ml of anhydrous ethanol, 40 ml of deionized water, 8 g of carbon nanotube powder, and 80 ml of 0.1 g / ml Mg(NO3)2 electrolyte solution are respectively added to a 2 L glass bottle, and the mixed solution is ultrasonically vibrated for 4 h to uniformly disperse the carbon nanotubes in the solution, forming a dispersed suspension. The main purpose of this step is to achieve uniform dispersion of carbon nanotubes in the solvent, providing a uniform and stable electrophoretic buffer for subsequent electrophoretic deposition.

[0079] Figure 5 The schematic diagram illustrates the structure of an electrophoretic deposition apparatus according to some exemplary embodiments of this application.

[0080] According to some exemplary embodiments, electrophoretic deposition of a metal substrate 10 in a suspension 31 includes: connecting the metal substrate 10 to a first terminal of a DC power supply, and connecting a second metal plate 522 to a second terminal of the DC power supply; placing the metal substrate 10 and the second metal plate 522 in the suspension 31 for electrophoretic deposition; and drying the metal substrate 10 with the deposited carbon nanotube film to obtain a carbon nanotube film cold cathode 43. The electric field strength in the suspension 31 is 5-80 V / cm, the electrophoretic deposition time is 20-200 s, the drying temperature is 70-100°C, and the drying time is 0.1-1 h. Exemplarily, the first terminal is the negative electrode, and the second terminal is the positive electrode.

[0081] Reference Figure 5The metal substrate 10 is mounted on an insulating mask fixture 51 designed according to the shape of the deposition area. The mask fixture 51 is fixed to the first metal plate 521 and connected to the negative terminal of the deposition power supply DC. Simultaneously, the second metal plate 522 is connected to the positive terminal of the deposition power supply DC, serving as the counter electrode paired with the metal substrate 10, and both are immersed in the suspension 31. The electric field strength within the suspension 31 is 6.7-80 V / cm. This range helps to avoid excessively low field strength, which would result in a slow carbon nanotube deposition rate and insufficient film density; at the same time, it prevents excessively high field strength, which would cause the carbon nanotubes to impact the substrate too quickly, leading to decreased adhesion or film detachment. For example, the distance between the two metal plates 52 is set to 5-15 cm, a DC voltage of 100-400 V is applied between the electrodes, and the electrophoresis time is 20-200 s. Under the influence of an electric field, the dispersed carbon nanotubes 22 in the suspension 31 migrate together with charged ions and gradually deposit on the surface of the metal substrate 10, forming a deposited carbon nanotube film cold cathode 43. The main purpose of this step is to form a uniformly distributed and densely structured carbon nanotube film on the surface of the metal substrate 10.

[0082] For example, after electrophoretic deposition, the Mask fixture 51 containing the metal substrate 10 is removed and placed in an oven to dry at 70-100°C for 30 minutes. The main purpose of this step is to remove residual solvent and provide a dry, stable surface for subsequent curing agent spraying. The dried metal substrate 10 is carefully removed from the Mask fixture 51, keeping the surface of the deposition area horizontal and avoiding any scratches or abrasions to protect the integrity of the formed carbon nanotube film structure.

[0083] According to some exemplary embodiments, forming tips on carbon nanotubes in a solidified carbon nanotube cold cathode 44 using a high-energy ion beam includes: cleaning the surface of the solidified carbon nanotube cold cathode 44 with plasma; bombarding the surface of the solidified carbon nanotube cold cathode 44 with a first high-energy ion beam for a first duration; bombarding the surface of the solidified carbon nanotube cold cathode 44 with a second high-energy ion beam for a second duration; and bombarding the surface of the solidified carbon nanotube cold cathode 44 with a third high-energy ion beam, observing the surface at third intervals, and stopping bombardment if uniform and dense tips are formed on the surface, otherwise continuing to bombard the surface with the third high-energy ion beam; wherein the energy and beam current density of the first high-energy ion beam are lower than those of the second high-energy ion beam, and the energy and beam current density of the second high-energy ion beam are lower than those of the third high-energy ion beam.

[0084] For example, the energy of the first high-energy ion beam is 500-700 eV, and the beam current density is 5-15 μA / cm. 2The first high-energy ion beam has a duration of 10-30 seconds; the second high-energy ion beam has an energy of 700-900 eV and a beam current density of 15-25 μA / cm². 2 The second duration is 10-30 seconds; the third high-energy ion beam has an energy of 900-1200 eV and a beam current density of 25-35 μA / cm². 2 The third duration is 10-30 seconds.

[0085] For example, a solidified carbon nanotube cold cathode 44 is placed in a vacuum environment and bombarded with a high-energy ion beam for aging treatment. The main purpose of this step is to induce the exposed or shallow carbon nanotubes to form emission tips, thereby improving the field enhancement factor. The specific aging process is as follows: The surface of the solidified carbon nanotube cold cathode 44 is cleaned using plasma (e.g., argon), for example, with a discharge power of 50W for 30 seconds, to remove contaminants. The distance between the cathode and anode in the ion source is adjusted to 5mm, and a vacuum of 5×10⁻⁶ is applied. -6 Pa, ion source activated. First bombardment aging stage: ion energy set to 600 eV, beam current density to 10 μA / cm², bombardment for 20 seconds. Second bombardment aging stage: ion energy set to 800 eV, beam current density to 20 μA / cm², bombardment for 20 seconds. Third bombardment aging stage: ion energy set to 1000 eV, beam current density to 30 μA / cm², every 20 seconds of bombardment, the surface morphology of the activated carbon nanotube cold cathode 45 is observed using a scanning electron microscope until a uniform, dense tip structure forms on the surface, then bombardment is stopped.

[0086] Figure 6A The illustration shows a physical image of an activated carbon nanotube cold cathode obtained according to some exemplary embodiments of this application; Figure 6B The illustration schematically shows a partially magnified scanning electron microscope image of an activated carbon nanotube cold cathode obtained in some exemplary embodiments according to this application.

[0087] According to some exemplary embodiments, using a high-intensity electric field to make carbon nanotubes stand upright includes: placing a carbon nanotube cold cathode in a high-intensity electric field for activation, wherein the electric field strength of the high-intensity electric field is 1-10V / µm, and the activation time is 30-120min.

[0088] For example, the carbon nanotube cold cathode, after ion bombardment aging treatment, is activated in an electric field of 1-10 V / µm for 30-120 minutes, causing the carbon nanotubes to gradually adjust to an upright and stable activated state. For instance, the activation field strength is 3-5 V / µm, and the activation time is 60 minutes. The main purpose of this step is to make the carbon nanotubes stand upright through the action of a high-intensity electric field, facilitating observation of their morphological evolution under a scanning electron microscope, and effectively avoiding excessive aging or structural damage to the carbon nanotubes due to excessively high field strength or prolonged activation time. The actual image of the activated carbon nanotube cold cathode 45 after the above activation treatment is shown below. Figure 6A As shown, the activated carbon nanotube cold cathode 45 comprises activated carbon nanotubes 25 and a metal substrate 10; a magnified scanning electron microscope image of the activated carbon nanotube cold cathode 45 is shown below. Figure 6B As shown, at this point, a large number of carbon nanotubes remain upright, with their tips effectively exposed and their density distribution uniform. The preparation method provided in the embodiments of this application has comprehensive advantages such as simple process implementation, low cost, easy thickness control, facilitating cathode activation, and suitability for mass production.

[0089] In some embodiments of this application, a carbon nanotube cold cathode is also provided, which is prepared according to the above-described preparation method. According to some exemplary embodiments, the carbon nanotube cold cathode includes a metal substrate 10 and carbon nanotubes, with the carbon nanotubes located on a first surface of the metal substrate 10. The height of the carbon nanotubes is 4-15 μm; the angle between the extension direction of the carbon nanotubes and the first surface is 75-90°; and the density of the carbon nanotubes within their distribution range is 100-200 nanotubes / μm. 2 .

[0090] Continue to refer to Figure 6B The carbon nanotube cold cathode prepared in this embodiment has the following structural features: the carbon nanotubes extend in a direction that is substantially perpendicular to the first surface of the metal substrate 10, and the carbon nanotubes are distributed at an angle of 75-90° to the first surface; the carbon nanotubes have a uniform height, mainly distributed in the range of 4-15 μm; and the carbon nanotubes have a high density, reaching 100-200 nanotubes / μm. 2 The carbon nanotubes exhibit high uniformity, with a distribution non-uniformity of <20%. Testing revealed that the carbon nanotubes have a high bonding strength with the substrate, a long service life, and high reliability. The carbon nanotube cold cathode remained operational after 276,000 cycles, demonstrating that the carbon nanotubes maintained their original position and remained firmly bonded under a high-voltage electric field, without any breakage, adsorption, or loss.

[0091] For example, the length of carbon nanotubes (from the substrate to the tip) is approximately 4-10 µm. Within this region, the carbon nanotubes are densely distributed, with a visually estimated linear density of approximately 20-25 nanotubes / 2 µm, corresponding to an areal density of approximately 100-156 nanotubes / µm.2 To further quantify the uniformity of distribution, 3-4 areas with an area of ​​2µm × 2µm (4µm) were randomly selected. 2 Statistical analysis was conducted in the area, and the average density was approximately 529 roots / 4µm. 2 (Approximately 23 roots / 2µm). Density varies across regions: some areas have approximately 441 roots / 4µm. 2 (21 roots / 2µm), with some areas having approximately 625 roots / 4µm. 2 (25 roots / 2µm). The calculated density standard deviation is approximately 92 roots / 4µm. 2 The coefficient of variation for uniformity is approximately 17% (92 ÷ 529 × 100% ≈ 17.4%).

[0092] Figure 7 The illustration schematically shows partially magnified scanning electron microscope images of carbon nanotube cold cathodes obtained in some exemplary comparative examples according to this application.

[0093] For example, a carbon nanotube cold cathode was obtained by electrophoretic deposition in a comparative example, without a curing or activation step, and the process parameters for these steps differed from those in the embodiments of this application. (Refer to...) Figure 7 In the comparative example, the carbon nanotubes are sparsely distributed and skewed, and the number of carbon nanotubes that can effectively participate in electron emission is extremely small.

[0094] Figure 8 The schematic diagram illustrates the structure of an X-ray tube including a carbon nanotube cold cathode according to some exemplary embodiments of this application.

[0095] Embodiments of this application also provide an X-ray tube 1000, which includes a carbon nanotube cold cathode according to the above description.

[0096] Reference Figure 8The X-ray tube 1000 includes an activated carbon nanotube cold cathode 45 prepared according to the above-described method. The activated carbon nanotube cold cathode 45 is located on a substrate 80 and forms a triode electron gun structure with a gate 82 and an anode 83. For example, the distance between the gate 82 and the activated carbon nanotube cold cathode 45 is 150-300 μm. A certain voltage (0-3 kV) is applied to the gate 82 to form a first electric field E1, the magnitude of which is 1-20 V / μm. When the voltage at the gate 82 generates an electric field threshold greater than the threshold for field emission, the activated carbon nanotube cold cathode 45 emits electrons 811. A certain voltage is applied to the anode 83 to form a second electric field E2. The emitted electrons 811 are accelerated under the action of the second electric field E2 and bombard the anode target 84 to generate X-rays 812. X-rays 812 are received by detector 86 after passing through beryllium window 85. They are then processed and analyzed by equipment such as amplifier 87, oscilloscope 88, and computer 89 to achieve imaging or detection of objects.

[0097] In some embodiments of this application, based on Figure 8 Actual tests of the cold cathode X-ray tube show that when the distance between the activated carbon nanotube cold cathode 45 and the gate 82 is 215 μm, the X-ray tube is configured such that, in response to a control voltage of 1600 V for the gate 82, the emission current of the carbon nanotube cold cathode is greater than or equal to 350 mA; and the performance is stable with a lifespan of more than 276,000 cycles per second.

[0098] Figure 9 The diagram illustrates the relationship between field voltage and emission current when a carbon nanotube cold cathode is applied in an X-ray tube according to some exemplary embodiments of this application. Figure 10 The illustration schematically shows a lifetime test diagram of a carbon nanotube cold cathode when applied to an X-ray tube according to some exemplary embodiments of the present application.

[0099] Reference Figure 9 By measuring the emission current under different field voltages, it can be seen that the carbon nanotube cold cathode obtained in the embodiments of this application, with a gate-to-cathode spacing of 215µm and a gate voltage of 1388V, can achieve a maximum emission current of 350mA, corresponding to an emission current density of approximately 7777.8mA / cm². 2 Furthermore, increasing the gate voltage can further increase the emission current, indicating that it has excellent field emission performance. The field emission performance of commercially available carbon nanotubes is relatively poor. When used as cold cathodes in X-ray tubes, the operating current is generally between a few mA and tens of mA, while the maximum short-time pulse emission current disclosed in existing technology is only 200 mA, but the gate control voltage is as high as 1700V or more.

[0100] Reference Figure 10Under operating conditions of 200 mA cathode current, 1 ms current pulse width, and 0.3% duty cycle, after long-term electron emission tests exceeding 5 million cycles, it can be seen that the carbon nanotube cold cathode obtained in the embodiments of this application only increased its voltage from 1342 V to 1372 V during more than 5 million electron emission cycles, an increase of only 30 V. This leaves a growth potential of 1628 V to the allowable gate control voltage of 3000 V. If the gate control voltage maintains the current growth rate in subsequent operations, the number of operating pulses for this cathode can be estimated to reach 2.76 × 10⁻⁶. 8 The total operating time can reach 276,000 seconds (2.76 × 10⁻⁶) times (1628V ÷ 30V × 500 + 5 million times). 8 (1 second × 1 millisecond), which meets the 200,000 seconds lifespan requirement for medical CT tube registration certification, indicating that the carbon nanotube cathode of this application has stable emission performance and a long service life, and can meet the relevant usage requirements in future practical applications.

[0101] In the embodiments of this application, the carbon nanotube cold cathode features high utilization of carbon nanotubes, excellent spatial orientation of carbon nanotubes, high distribution density of carbon nanotubes, and tight bonding between carbon nanotubes and the metal substrate 10. These characteristics significantly improve the performance of the X-ray tube 1000. For example, the operating current of this X-ray tube 1000 is increased by at least one order of magnitude compared to similar technologies, while also exhibiting high stability and long lifespan. These advantages enable the X-ray tube 1000 to successfully transition from the laboratory research stage to large-scale commercial applications, demonstrating enormous potential and value in multiple application areas.

[0102] The X-ray tube 1000 has a wide range of applications. For example, it can be used in medical imaging as a cathode material in X-ray generators for CT scans and radiotherapy. In scientific research equipment, it can serve as an electron source in electron microscopes, providing high-resolution imaging capabilities. In industrial inspection, it can be used in non-destructive testing equipment for examining the internal structure of materials. Finally, it can be used in flat panel displays as an electron source in field emission displays, achieving high brightness and high contrast.

[0103] It should be understood that the X-ray tube 1000 according to some exemplary embodiments of this application has all the features and advantages of the carbon nanotube cold cathode described above, which can be referred to in the above description of the carbon nanotube cold cathode, and will not be repeated here.

[0104] While some embodiments based on the overall inventive concept of this application have been illustrated and described, those skilled in the art will understand that changes may be made to these embodiments without departing from the principles and spirit of the overall inventive concept of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing a carbon nanotube cold cathode, characterized in that, The preparation method includes: Aggregated carbon nanotubes were ball-milled to obtain carbon nanotube powder. The carbon nanotube powder was mixed with a first solvent and an electrolyte solution and then subjected to ultrasonic vibration to obtain a suspension. A metal substrate is placed in the suspension for electrophoretic deposition to obtain a carbon nanotube thin film cold cathode. The curing agent is coated onto the carbon nanotube film cold cathode and cross-linked and cured to obtain a cured carbon nanotube cold cathode. A high-energy ion beam is used to form the carbon nanotubes in the solidified carbon nanotube cold cathode into tips, and a high-intensity electric field is used to make the carbon nanotubes stand upright, thus obtaining an activated carbon nanotube cold cathode. The step of using a high-energy ion beam to form tips on the carbon nanotubes in the solidified carbon nanotube cold cathode includes: The surface of the solidified carbon nanotube cold cathode was cleaned using plasma. Utilizing energies of 500-700 eV and beam current densities of 5-15 μA / cm 2 The first high-energy ion beam bombards the surface of the solidified carbon nanotube cold cathode for 10-30 seconds; Utilizing energies of 700-900 eV and beam current densities of 15-25 μA / cm² 2 The second high-energy ion beam bombards the surface of the solidified carbon nanotube cold cathode for 10-30 seconds; Utilizing energies of 900-1200 eV and beam current densities of 25-35 μA / cm² 2 The surface of the solidified carbon nanotube cold cathode is bombarded with a third high-energy ion beam for 10-30 seconds. The surface is observed every 10-30 seconds. If uniform and dense tips are formed on the surface, the bombardment is stopped. Otherwise, the surface is bombarded with the third high-energy ion beam. The method of using a high-intensity electric field to make the carbon nanotubes stand upright includes: The carbon nanotube cold cathode is activated by placing it in a high-intensity electric field, wherein the electric field strength of the high-intensity electric field is 1-10V / µm, and the activation time is 30-120min.

2. The preparation method according to claim 1, characterized in that, The process of coating the curing agent onto the carbon nanotube film cold cathode for cross-linking curing includes: The curing agent is sprayed onto the surface of the carbon nanotube film cold cathode using a spray gun, or brushed onto the surface of the carbon nanotube film cold cathode using a brush or roller.

3. The preparation method according to claim 1 or 2, characterized in that, The curing agent includes one of polyphenylsiloxane solution and conductive silver paste; the thickness of the coating with the curing agent is 500-3000 nm.

4. The preparation method according to claim 1, characterized in that, The process of coating the curing agent onto the carbon nanotube film cold cathode for cross-linking curing includes: Polyphenylsiloxane was dissolved in a second solvent to obtain a mixture; The mixture was sprayed onto the surface of the carbon nanotube film cold cathode using a spray gun. The carbon nanotube film cold cathode is heated and cured to obtain a cured carbon nanotube cold cathode.

5. The preparation method according to claim 4, characterized in that, The second solvent includes one of toluene, xylene, and chloroform, and the concentration of the mixture is 5-15 wt%. The temperature for heat curing is 80-150℃, and the duration of heat curing is 6-10 hours.

6. The preparation method according to claim 4 or 5, characterized in that, The step of heating and curing the carbon nanotube film cold cathode includes: The carbon nanotube film cold cathode is placed in a ventilation cavity to allow the second solvent to evaporate; The carbon nanotube film cold cathode is placed in a heating chamber, the heating chamber is heated to a first temperature, and the temperature is maintained at the first temperature for 1-3 hours. The heating chamber is heated to a second temperature and kept at that temperature for 3-5 hours. The heating chamber is heated to a third temperature and held at the third temperature for 0.5-2 hours; wherein the first temperature is lower than the second temperature, the second temperature is lower than the third temperature, and the range of the first temperature, the second temperature and the third temperature is 50-200℃.

7. The preparation method according to claim 1, characterized in that, The process of ball milling aggregated carbon nanotubes includes: The aggregated carbon nanotubes were loaded into a ball mill and milled at a speed of 100-300 rpm for 5-15 minutes.

8. The preparation method according to claim 7, characterized in that, Each carbon nanotube in the aggregated state comprises at least two graphene layers, each graphene layer being a hollow tubular structure, with the at least two graphene layers nested sequentially according to the diameter of the hollow tubular structure; the number of graphene layers is between 2 and 5, and the purity of the aggregated carbon nanotube is greater than or equal to 99.9%.

9. The preparation method according to claim 1, characterized in that, The step of mixing the carbon nanotube powder with a first solvent and an electrolyte solution and then subjecting it to ultrasonic oscillation includes: Prepare an electrolyte solution, wherein the electrolyte comprises one or more of magnesium chloride, magnesium nitrate, aluminum chloride, and aluminum nitrate; The carbon nanotube powder, the first solvent, the electrolyte solution, and deionized water are mixed and then subjected to ultrasonic oscillation to obtain a suspension.

10. The preparation method according to claim 9, characterized in that, The concentration of carbon nanotubes in the suspension is 0.001-0.01 g / ml; the concentration of deionized water in the suspension is 1%-10% vol; the concentration of electrolyte in the suspension is 0.002-0.01 g / ml; the first solvent includes anhydrous ethanol; and the duration of ultrasonic oscillation is 3-5 h.

11. The preparation method according to claim 1, characterized in that, The step of placing the metal substrate in the suspension for electrophoretic deposition includes: The metal substrate is connected to the first terminal of the power supply, and the second metal plate is connected to the second terminal of the power supply. The metal substrate and the second metal plate are placed in the suspension for electrophoretic deposition. The metal substrate on which the carbon nanotube film is deposited is dried to obtain a carbon nanotube film cold cathode.

12. The preparation method according to claim 11, characterized in that, The electric field strength in the suspension is 5-80V / cm, the electrophoretic deposition time is 20-200s, the drying temperature is 70-100℃, and the drying time is 0.1-1h.

13. A carbon nanotube cold cathode, characterized in that, The carbon nanotube cold cathode is prepared by the preparation method according to any one of claims 1 to 12.

14. The carbon nanotube cold cathode according to claim 13, characterized in that, The carbon nanotube cold cathode comprises a metal substrate and carbon nanotubes, wherein the carbon nanotubes are located on a first surface of the metal substrate, and the height of the carbon nanotubes is 4-15 μm; the angle between the extension direction of the carbon nanotubes and the first surface is 75-90°; and the density of the carbon nanotubes within their distribution range is 100-200 nanotubes / μm. 2 .

15. An X-ray tube, characterized in that, The X-ray tube includes a carbon nanotube cold cathode according to claim 13 or 14.

16. The X-ray tube according to claim 15, characterized in that, The X-ray tube also includes a gate, the carbon nanotube cold cathode is spaced 215 μm apart from the gate, and the X-ray tube is configured such that, in response to a control voltage of 1600 V on the gate, the emission current of the carbon nanotube cold cathode is greater than or equal to 350 mA.

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