Carbon nanotube field emission cathode and method for manufacturing the same

Abstract

The application provides a manufacturing method of a carbon nanotube field emission cathode and the carbon nanotube field emission cathode. In the carbon nanotube paste, adhesive particles and conductive metal particles are introduced. After high-temperature annealing treatment, the carbon nanotube roots are embedded into the matrix formed by the adhesive particles and the conductive metal particles to form a firm combination and have good conductivity, so that the opening electric field of the carbon nanotube cathode is reduced, and the carbon nanotube cathode can stably emit at a higher current, and the emission current density of the cathode is greatly improved.

Description

Technical Field

[0001] This application relates to the field of field emission technology, and in particular to a carbon nanotube field emission cathode and its preparation method. Background Technology

[0002] Electron emission cathodes are core components of vacuum electronic devices such as X-ray tubes, microwave tubes, and traveling wave tubes, and currently, metal thermionic cathodes, such as tungsten filaments, are mainly used. During operation, the thermionic cathode is heated to over 2000 degrees Celsius by an electric current. Electrons in the cathode overcome the surface potential barrier of the material and escape into the vacuum, forming an emission current. Thermionic cathodes suffer from drawbacks such as large size, high power consumption, long on-time, and material evaporation at high temperatures. Recently, field emission cold cathodes, represented by carbon nanotubes, have received widespread attention and research. Electrons at their nanoscale tips can undergo quantum tunneling under an electric field, forming a very large current. Carbon nanotube cold cathodes have advantages such as room temperature operation, low on-time, fast switching, low power consumption, and miniaturization. Their application in vacuum electronic devices can simplify the structure and achieve excellent power and frequency characteristics. Currently, the fabrication of carbon nanotube cold cathodes mainly employs two methods: chemical vapor deposition and screen printing. The general process of screen printing involves uniformly mixing carbon nanotubes, organic solvents, various binders, and conductive particles to form a paste, which is then printed onto a substrate. After thermal annealing and surface treatment, a carbon nanotube cathode is formed. Compared to chemical vapor deposition (CVD), screen printing for preparing carbon nanotube cold cathodes offers advantages such as simpler process, lower cost, higher controllability, and better repeatability, making it highly promising for applications. Currently, the main problem with screen-printed carbon nanotube cathodes is the poor bonding strength and conductivity between the carbon nanotubes and the substrate. This makes the carbon nanotubes easily detach from the substrate under applied voltage, significantly reducing the cathode's emission current density and stability, thus failing to meet the requirements of high-performance devices. Summary of the Invention

[0003] Therefore, it is necessary to provide a carbon nanotube field emission cathode with high cathode emission current density, good stability, and that can meet the requirements of high-performance devices, as well as its preparation method, to address the shortcomings of existing technologies.

[0004] To solve the above problems, this application adopts the following technical solution:

[0005] One of the objectives of this application is to provide a method for manufacturing a carbon nanotube field emission cathode, comprising the following steps:

[0006] A carbon nanotube slurry is prepared, comprising carbon nanotubes, nanoparticle fillers, organic powder, and solvent. The nanoparticle fillers include binder particles and conductive metal particles. The binder particles include at least one of silicon carbide, alumina, titanium dioxide, zirconium oxide, zirconium carbide, and tungsten carbide. The conductive metal particles include nickel, cobalt, silver, titanium, copper, aluminum, and their alloys.

[0007] The carbon nanotube paste is printed onto a conductive substrate to obtain a carbon nanotube film.

[0008] The surface of the carbon nanotube film is treated so that the carbon nanotubes are vertically aligned perpendicular to the surface of the conductive substrate to obtain the carbon nanotube field emission cathode.

[0009] In some embodiments, the step of preparing the carbon nanotube slurry specifically includes the following steps:

[0010] The conductive metal particles are added to the solvent and ultrasonically dispersed to obtain a first slurry. The ultrasonic power is 100-150W and the ultrasonic time is 45-60min.

[0011] The adhesive particles are added to the solvent and dispersed by ball milling to obtain a second slurry. The ball milling power is 550–650W and the ball milling time is 40–90min.

[0012] The carbon nanotubes are added to the second slurry and dispersed by ball milling to obtain the third slurry. The ball milling power is 400-500W and the ball milling time is 30-50min.

[0013] The first slurry is added to the third slurry and mixed by ball milling to obtain the fourth slurry. The ball milling power is 300W and the ball milling time is 10–20min.

[0014] Organic powder is added to the fourth slurry and ball-milled to obtain the carbon nanotube slurry. The ball milling power is 300W and the ball milling time is 10-20min.

[0015] In some embodiments, the carbon nanotubes are single-walled or multi-walled carbon nanotubes, the length of the carbon nanotubes is 5–20 μm, and the diameter of the multi-walled carbon nanotubes is 3–10 nm.

[0016] In some embodiments, the nanoparticle filler has a size of 10–50 nm.

[0017] In some embodiments, the organic powder is ethyl cellulose; the solvent is terpineol.

[0018] In some embodiments, the mass ratio of the carbon nanotubes, the adhesive particles, the conductive metal particles, the organic powder, and the solvent is 1-2:3-6:1-2.5:2-3:3-5.

[0019] In some embodiments, the step of printing the carbon nanotube paste onto a conductive substrate to obtain a carbon nanotube film specifically includes the following steps:

[0020] The carbon nanotube paste is uniformly printed onto a conductive substrate using screen printing equipment to form the desired pattern. The paste is then dried and annealed to obtain the carbon nanotube film.

[0021] In some embodiments, the drying temperature is 90°C and the drying time is 30 min; the annealing process is as follows: under a nitrogen protective atmosphere, annealing is performed at 300–400°C for 180 min; then the temperature is raised to 750–850°C and annealed for 60–90 min; and then naturally cooled to obtain the carbon nanotube film.

[0022] In some embodiments, the conductive substrate comprises iron, nickel, cobalt, iron-nickel alloy, or iron-nickel-cobalt alloy, and the conductive substrate further includes the following pretreatment step before use:

[0023] The conductive substrate surface is polished with abrasive paper to remove the surface oxide layer, and then ultrasonically cleaned with ethanol and deionized water in sequence. The cleaned conductive substrate is then immersed in an acid solution for acid treatment, and then cleaned with deionized water to remove residual acid solution from the surface. The acid solution includes hydrochloric acid, sulfuric acid and nitric acid, and the concentration of the acid solution is 0.2–2 mol / L. The acid treatment time is 1–10 min.

[0024] In some embodiments, the step of treating the surface of the carbon nanotube film to align the carbon nanotubes vertically perpendicular to the surface of the conductive substrate to obtain the carbon nanotube field emission cathode specifically includes the following steps:

[0025] The surface of the carbon nanotube film is treated with a low-viscosity silicone roller to remove loosely adhered particles and to align the carbon nanotubes vertically perpendicular to the substrate surface, thereby activating the carbon nanotube cathode.

[0026] The second objective of this application is to provide a carbon nanotube field emission cathode, which is prepared by the method for manufacturing the carbon nanotube field emission cathode.

[0027] The present application adopts the above technical solution, and its beneficial effects are as follows:

[0028] The method for manufacturing a carbon nanotube field emission cathode and the carbon nanotube field emission cathode provided in this application involve introducing binder particles and conductive metal particles into a carbon nanotube slurry. After high-temperature annealing, the roots of the carbon nanotubes are embedded in the matrix formed by the binder particles and conductive metal particles, forming a strong bond and exhibiting good conductivity. This reduces the turn-on electric field of the carbon nanotube cathode and enables stable emission at higher currents, greatly improving the emission current density of the cathode.

[0029] In addition, the method for manufacturing carbon nanotube field emission cathode provided in this application introduces micro-nano structures on the surface of the conductive substrate by pre-treating the substrate, which greatly increases the specific surface area and wettability with the slurry, thereby increasing the interfacial bonding force between the carbon nanotubes and the substrate. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 A flowchart illustrating the steps of a method for manufacturing a carbon nanotube field emission cathode provided in an embodiment of this application.

[0032] Figure 2 This is a flowchart illustrating the steps involved in preparing the carbon nanotube slurry provided in this embodiment.

[0033] Figure 3 This is a schematic diagram of the current density-electric field strength working curve of the carbon nanotube cathode provided in Example 1 of this application.

[0034] Figure 4 This is a schematic diagram of the emission current stability curve of the carbon nanotube cathode provided in Example 1 of this application.

[0035] Figure 5 This is a schematic diagram of the current density-electric field strength working curve of the carbon nanotube cathode provided in this embodiment 2.

[0036] Figure 6 This is a schematic diagram of the emission current stability curve of the carbon nanotube cathode provided in this embodiment 2.

[0037] Figure 7 This is a schematic diagram of the current density-electric field strength working curve of the carbon nanotube cathode provided in this embodiment 3.

[0038] Figure 8 This is a schematic diagram of the emission current stability curve of the carbon nanotube cathode provided in this embodiment 3. Detailed Implementation

[0039] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0040] In the description of this application, it should be understood that the terms "upper", "lower", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0041] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0042] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments.

[0043] Please see Figure 1 This application provides a flowchart of a method for manufacturing a carbon nanotube field emission cathode according to an embodiment, including the following steps S110 to S130. The implementation of each step is described in detail below.

[0044] Step S110: Prepare carbon nanotube slurry, wherein the carbon nanotube slurry comprises carbon nanotubes, nanoparticle fillers, organic powder and solvent, wherein the nanoparticle fillers comprise binder particles and conductive metal particles, wherein the binder particles comprise at least one of silicon carbide, alumina, titanium dioxide, zirconium oxide, zirconium carbide and tungsten carbide, and wherein the conductive metal particles comprise nickel, cobalt, silver, titanium, copper, aluminum and their alloys.

[0045] In this embodiment, the carbon nanotube is a single-walled or multi-walled carbon nanotube, the length of the carbon nanotube is 5–20 μm, and the diameter of the multi-walled carbon nanotube is 3–10 nm.

[0046] In this embodiment, the size of the nanoparticle filler is 10–50 nm.

[0047] In this embodiment, the organic powder is ethyl cellulose; the solvent is terpineol.

[0048] In this embodiment, the mass ratio of the carbon nanotubes, the adhesive particles, the conductive metal particles, the organic powder, and the solvent is 1-2:3-6:1-2.5:2-3:3-5.

[0049] Please see Figure 2 The preparation of carbon nanotube slurry includes steps S111 to S115, and the implementation of each step is described in detail below.

[0050] Step S111: Add the conductive metal particles to the solvent and disperse them by ultrasonication to obtain a first slurry. The ultrasonic power is 100-150W and the ultrasonic time is 45-60min.

[0051] Step S112: Add the adhesive particles to the solvent and disperse them by ball milling to obtain a second slurry. The ball milling power is 550–650W and the ball milling time is 40–90min.

[0052] Step S113: Add the carbon nanotubes to the second slurry, disperse them by ball milling, and obtain the third slurry. The ball milling power is 400-500W and the ball milling time is 30-50min.

[0053] Step S114: The first slurry is added to the third slurry and ball-milled to obtain the fourth slurry. The ball mill has a power of 300W and a milling time of 10–20 minutes.

[0054] Step S115: Add the organic powder to the fourth slurry and ball mill to mix, thereby obtaining the carbon nanotube slurry. The ball milling power is 300W and the ball milling time is 10-20min.

[0055] The invention described in the above embodiments employs an optimized multi-step method to prepare carbon nanotube slurry, which significantly reduces the damage to the carbon nanotube crystal structure caused by the ball milling process, allowing the carbon nanotubes to maintain their excellent electrical and thermal conductivity. On the one hand, the excellent electrical conductivity of carbon nanotubes results in extremely high electron conduction and emission efficiency, increasing the field emission current density; on the other hand, the excellent thermal conductivity of carbon nanotubes can rapidly conduct the Joule heat generated by field emission to the substrate, reducing the damage to the carbon nanotube structure caused by high-temperature heat and improving the stability of the field emission current.

[0056] Step S120: Print the carbon nanotube paste onto a conductive substrate to obtain a carbon nanotube film.

[0057] In this embodiment, the step of printing the carbon nanotube paste onto a conductive substrate to obtain a carbon nanotube film specifically includes the following steps:

[0058] The carbon nanotube paste is uniformly printed onto a conductive substrate using screen printing equipment to form the desired pattern. The paste is then dried and annealed to obtain the carbon nanotube film.

[0059] Furthermore, the drying temperature is 90℃ and the drying time is 30 min; the annealing process is as follows: under a nitrogen protective atmosphere, anneal at 300–400℃ for 180 min; then heat to 750–850℃ for annealing for 60–90 min; and then cool naturally to obtain the carbon nanotube film.

[0060] In this embodiment, the conductive substrate includes iron, nickel, cobalt, iron-nickel alloy, and iron-nickel-cobalt alloy. The conductive substrate further includes the following pretreatment step before use:

[0061] The conductive substrate surface is polished with abrasive paper to remove the surface oxide layer, and then ultrasonically cleaned with ethanol and deionized water in sequence. The cleaned conductive substrate is then immersed in an acid solution for acid treatment, and then cleaned with deionized water to remove residual acid solution from the surface. The acid solution includes hydrochloric acid, sulfuric acid and nitric acid, and the concentration of the acid solution is 0.2–2 mol / L. The acid treatment time is 1–10 min.

[0062] It is understood that this embodiment pre-treats the conductive substrate and introduces micro-nano structures on the substrate surface, which greatly increases the specific surface area and wettability with the slurry, and increases the interfacial bonding force between the carbon nanotubes and the substrate.

[0063] Step S130: The surface of the carbon nanotube film is treated so that the carbon nanotubes are vertically arranged perpendicular to the surface of the conductive substrate to obtain the carbon nanotube field emission cathode.

[0064] In this embodiment, the step of treating the surface of the carbon nanotube film to make the carbon nanotubes vertically aligned with the surface of the conductive substrate to obtain the carbon nanotube field emission cathode specifically includes the following steps: using a low-viscosity silicone roller to treat the surface of the carbon nanotube film to remove loosely adhered particles and make the carbon nanotubes vertically aligned with the substrate surface to activate the carbon nanotube cathode.

[0065] The method for manufacturing a carbon nanotube field emission cathode and the carbon nanotube field emission cathode provided in this application involve introducing binder particles and conductive metal particles into a carbon nanotube slurry. After high-temperature annealing, the roots of the carbon nanotubes are embedded in the matrix formed by the binder particles and conductive metal particles, forming a strong bond and exhibiting good conductivity. This reduces the turn-on electric field of the carbon nanotube cathode and enables stable emission at higher currents, significantly improving the emission current density of the cathode. Furthermore, by pretreating the conductive substrate and introducing micro-nano structures on the substrate surface, the specific surface area and wettability with the slurry are greatly increased, enhancing the interfacial bonding force between the carbon nanotubes and the substrate. This further reduces the turn-on electric field of the carbon nanotube cathode and enables stable emission at higher currents, significantly improving the emission current density of the cathode.

[0066] The technical solutions described above in this application will be explained in detail below with reference to specific embodiments.

[0067] Example 1:

[0068] (1) Pretreatment of conductive substrate

[0069] The substrate can be a metal substrate such as iron, nickel, cobalt, iron-nickel alloy, or iron-nickel-cobalt alloy. The surface of the conductive substrate is polished with abrasive paper to remove the surface oxide layer, and then ultrasonically cleaned sequentially with ethanol and deionized water. The cleaned conductive substrate is then immersed in an acid solution, which can be hydrochloric acid, sulfuric acid, or nitric acid, with a concentration of 0.2–2 mol / L, for 1–10 minutes. After acid treatment, it is rinsed with deionized water to remove any residual acid solution from the surface.

[0070] (2) Preparation of carbon nanotube slurry.

[0071] The carbon nanotubes can be single-walled or multi-walled carbon nanotubes, with a length of 5–20 μm. For multi-walled carbon nanotubes, the diameter is preferably 3–10 nm.

[0072] The nanoparticle filler includes binder particles and conductive metal particles. The binder particles may be silicon carbide, alumina, titanium dioxide, zirconium oxide, zirconium carbide, tungsten carbide, etc., and the conductive metal particles may be nickel, cobalt, silver, titanium, copper, aluminum, and their alloys. The size of the nanoparticle filler is 10–50 nm.

[0073] The organic powder is preferably ethyl cellulose, used to adjust the viscosity and flowability of the slurry; the solvent is preferably terpineol.

[0074] Carbon nanotubes, binder particles, conductive metal particles, organic powder, and solvent are uniformly mixed using a ball milling method, with a mass ratio of 1-2:3-6:1-2.5:2-3:3-5. The ball milling process is as follows:

[0075] A. Add conductive metal particles to a solvent and disperse them by ultrasonication at a power of 100-150W for 45-60 minutes.

[0076] B. Add the binder particles to the solvent, then place them in a grinding ball and disperse them by ball milling. The ball milling power is 550–650W, and the ball milling time is 60min.

[0077] C. Add carbon nanotubes to slurry B, disperse by ball milling, ball milling power 400-500W, ball milling time 30-50min;

[0078] D. Add A to slurry C, and ball mill to mix evenly. The ball mill power is 300W, and the ball milling time is 10–20 minutes.

[0079] E. Add the organic powder to slurry D, and ball mill to mix. The ball milling power is 300W and the ball milling time is 10min; to obtain the carbon nanotube slurry with the required viscosity.

[0080] (3) Preparation of carbon nanotube thin films

[0081] Carbon nanotube paste is uniformly printed onto a conductive substrate using screen printing equipment to form the desired pattern, followed by drying and annealing. The drying temperature is 90℃, and the drying time is 30 minutes to allow the solvent to evaporate. The annealing process is as follows: under a nitrogen protective atmosphere, annealing is carried out at 300–400℃ for 180 minutes to fully decompose the organic powder, followed by annealing at 750–850℃ for 60–90 minutes to fully melt and bond the filler. After natural cooling, a carbon nanotube film is obtained.

[0082] (4) Surface treatment of carbon nanotube cathode

[0083] A low-viscosity silicone roller is used to treat the surface of the carbon nanotube cathode, removing loosely adhered particles and aligning the carbon nanotubes vertically perpendicular to the substrate surface, thereby activating the carbon nanotube cathode.

[0084] Example 1:

[0085] (1) Pretreatment of conductive substrate

[0086] The substrate can be an iron-nickel alloy. The surface of the conductive substrate is polished with abrasive paper to remove the surface oxide layer, and then ultrasonically cleaned sequentially with ethanol and deionized water. The cleaned conductive substrate is then immersed in an acid solution, specifically hydrochloric acid, with a concentration of 0.2 mol / L, for 10 minutes. After acid treatment, it is rinsed with deionized water to remove any residual acid solution from the surface.

[0087] (2) Preparation of carbon nanotube slurry.

[0088] The carbon nanotubes are single-walled carbon nanotubes with a length of 5 μm.

[0089] The nanoparticle filler comprises binder particles and conductive metal particles, wherein the binder particles are silicon carbide and the conductive metal particles are nickel. The nanoparticle filler has a size of 10 nm.

[0090] The organic powder is preferably ethyl cellulose, used to adjust the viscosity and flowability of the slurry; the solvent is preferably terpineol.

[0091] Carbon nanotubes, binder particles, conductive metal particles, organic powder, and solvent were uniformly mixed using a ball milling method in a mass ratio of 1:3:1:2:3. The ball milling process was as follows:

[0092] A. Add conductive metal particles to a solvent and disperse them by ultrasonication at a power of 100W for 60 minutes.

[0093] B. Add the adhesive particles to the solvent, then place them in a grinding ball and disperse them by ball milling. The ball milling power is 550W and the ball milling time is 60min.

[0094] C. Add carbon nanotubes to slurry B, disperse by ball milling, ball milling power 400W, ball milling time 30min;

[0095] D. Add A to slurry C, and ball mill to mix evenly. The ball mill power is 300W and the ball milling time is 10min.

[0096] E. Add the organic powder to slurry D, and ball mill to mix. The ball milling power is 300W and the ball milling time is 10min; to obtain the carbon nanotube slurry with the required viscosity.

[0097] (3) Preparation of carbon nanotube thin films

[0098] Carbon nanotube paste is uniformly printed onto a conductive substrate using screen printing equipment to form the desired pattern, followed by drying and annealing. The drying temperature is 90℃, and the drying time is 30 minutes to allow the solvent to evaporate. The annealing process is as follows: under a nitrogen protective atmosphere, annealing is carried out at 300℃ for 180 minutes to fully decompose the organic powder, followed by heating to 750℃ and annealing for 60 minutes to fully melt and bond the filler. After natural cooling, a carbon nanotube film is obtained.

[0099] (4) Surface treatment of carbon nanotube cathode

[0100] A low-viscosity silicone roller is used to treat the surface of the carbon nanotube cathode, removing loosely adhered particles and aligning the carbon nanotubes vertically perpendicular to the substrate surface, thereby activating the carbon nanotube cathode.

[0101] Please see Figure 3The figure shows the current density-electric field strength operating curve of the carbon nanotube cathode provided in Example 1. Please refer to [link / reference]. Figure 4 The figure shows the emission current stability curve of the carbon nanotube cathode provided in Example 1.

[0102] Example 2:

[0103] (1) Pretreatment of conductive substrate

[0104] The substrate can be an iron-nickel-cobalt alloy. The surface of the conductive substrate is polished with abrasive paper to remove the surface oxide layer, and then ultrasonically cleaned sequentially with ethanol and deionized water. The cleaned conductive substrate is then immersed in an acid solution, which can be sulfuric acid with a concentration of 2 mol / L, for 1 minute. After acid treatment, it is rinsed with deionized water to remove any residual acid solution from the surface.

[0105] (2) Preparation of carbon nanotube slurry.

[0106] The carbon nanotubes are multi-walled carbon nanotubes, and for multi-walled carbon nanotubes, the diameter is preferably 10 nm.

[0107] The nanoparticle filler comprises binder particles and conductive metal particles, wherein the binder particles are aluminum oxide and the conductive metal particles are cobalt. The nanoparticle filler has a size of 50 nm.

[0108] The organic powder is preferably ethyl cellulose, used to adjust the viscosity and flowability of the slurry; the solvent is preferably terpineol.

[0109] Carbon nanotubes, binder particles, conductive metal particles, organic powder, and solvent were uniformly mixed using a ball milling method in a mass ratio of 2:6:2.5:3:3. The ball milling process was as follows:

[0110] A. Add conductive metal particles to a solvent and disperse them by ultrasonication at a power of 150W for 60 minutes.

[0111] B. Add the adhesive particles to the solvent, then place them in a grinding ball and disperse them by ball milling. The ball milling power is 650W and the ball milling time is 60min.

[0112] C. Add carbon nanotubes to slurry B, disperse by ball milling, ball milling power 500W, ball milling time 50min;

[0113] D. Add A to slurry C, and ball mill to mix evenly. The ball mill power is 300W and the ball milling time is 20min.

[0114] E. Add the organic powder to slurry D, and ball mill to mix. The ball milling power is 300W and the ball milling time is 10min; to obtain the carbon nanotube slurry with the required viscosity.

[0115] (3) Preparation of carbon nanotube thin films

[0116] Carbon nanotube paste is uniformly printed onto a conductive substrate using screen printing equipment to form the desired pattern, followed by drying and annealing. The drying temperature is 90℃, and the drying time is 30 minutes to allow the solvent to evaporate. The annealing process is as follows: under a nitrogen protective atmosphere, annealing is carried out at 400℃ for 180 minutes to fully decompose the organic powder, followed by heating to 850℃ and annealing for 90 minutes to fully melt and bond the filler. After natural cooling, a carbon nanotube film is obtained.

[0117] (4) Surface treatment of carbon nanotube cathode

[0118] A low-viscosity silicone roller is used to treat the surface of the carbon nanotube cathode, removing loosely adhered particles and aligning the carbon nanotubes vertically perpendicular to the substrate surface, thereby activating the carbon nanotube cathode.

[0119] Please see Figure 5 The figure shows the current density-electric field strength operating curve of the carbon nanotube cathode provided in Example 2. Please refer to [link / reference]. Figure 6 The figure shows the emission current stability curve of the carbon nanotube cathode provided in Example 2.

[0120] Example 3

[0121] (1) Pretreatment of conductive substrate

[0122] The substrate can be an iron substrate. The surface of the conductive substrate is polished with abrasive paper to remove the surface oxide layer, and then ultrasonically cleaned sequentially with ethanol and deionized water. The cleaned conductive substrate is then immersed in an acid solution, which can be nitric acid with a concentration of 1 mol / L, for 5 minutes. After acid treatment, it is rinsed with deionized water to remove any residual acid solution from the surface.

[0123] (2) Preparation of carbon nanotube slurry.

[0124] The carbon nanotubes may be multi-walled carbon nanotubes with a length of 10 μm. For multi-walled carbon nanotubes, the diameter is preferably 6 nm.

[0125] The nanoparticle filler includes binder particles and conductive metal particles. The binder particles are titanium dioxide, and the conductive metal particles can be silver. The size of the nanoparticle filler is 30 nm.

[0126] The organic powder is preferably ethyl cellulose, used to adjust the viscosity and flowability of the slurry; the solvent is preferably terpineol.

[0127] Carbon nanotubes, binder particles, conductive metal particles, organic powder, and solvent were uniformly mixed using a ball milling method in a mass ratio of 1.5:4:2:2.5:4. The ball milling process was as follows:

[0128] A. Add conductive metal particles to a solvent and disperse them by ultrasonication at a power of 120W for 50 minutes.

[0129] B. Add the adhesive particles to the solvent, then place them in a grinding ball and disperse them by ball milling. The ball milling power is 600W and the ball milling time is 60min.

[0130] C. Add carbon nanotubes to slurry B, disperse by ball milling, ball milling power 450W, ball milling time 40min;

[0131] D. Add A to slurry C, and ball mill to mix evenly. The ball mill power is 300W and the ball milling time is 15min.

[0132] E. Add the organic powder to slurry D, and ball mill to mix. The ball milling power is 300W and the ball milling time is 10min; to obtain the carbon nanotube slurry with the required viscosity.

[0133] (3) Preparation of carbon nanotube thin films

[0134] Carbon nanotube paste is uniformly printed onto a conductive substrate using screen printing equipment to form the desired pattern, followed by drying and annealing. The drying temperature is 90℃, and the drying time is 30 minutes to allow the solvent to evaporate. The annealing process involves annealing at 350℃ for 180 minutes under a nitrogen protective atmosphere to fully decompose the organic powder, followed by annealing at 800℃ for 80 minutes to fully melt and bond the filler. Natural cooling yields a carbon nanotube film.

[0135] (4) Surface treatment of carbon nanotube cathode

[0136] A low-viscosity silicone roller is used to treat the surface of the carbon nanotube cathode, removing loosely adhered particles and aligning the carbon nanotubes vertically perpendicular to the substrate surface, thereby activating the carbon nanotube cathode.

[0137] Please see Figure 7 The figure shows the current density-electric field strength operating curve of the carbon nanotube cathode provided in Example 3. Please refer to [link / reference]. Figure 8 The figure shows the emission current stability curve of the carbon nanotube cathode provided in Example 3.

[0138] It is understood that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0139] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. A method for manufacturing a carbon nanotube field emission cathode, characterized in that, Includes the following steps: A carbon nanotube slurry is prepared, comprising carbon nanotubes, nanoparticle fillers, organic powder, and solvent. The nanoparticle fillers include binder particles and conductive metal particles. The binder particles include at least one of silicon carbide, alumina, titanium dioxide, zirconium oxide, zirconium carbide, and tungsten carbide. The conductive metal particles include nickel, cobalt, silver, titanium, copper, aluminum, and their alloys. The carbon nanotube paste is printed onto a conductive substrate to obtain a carbon nanotube film. The surface of the carbon nanotube film is treated so that the carbon nanotubes are vertically aligned perpendicular to the surface of the conductive substrate to obtain the carbon nanotube field emission cathode. The preparation of carbon nanotube slurry specifically includes the following steps: The conductive metal particles are added to the solvent and ultrasonically dispersed to obtain a first slurry. The ultrasonic power is 100-150 W and the ultrasonic time is 45-60 min. The adhesive particles are added to the solvent and dispersed by ball milling to obtain a second slurry. The ball milling power is 550–650 W and the ball milling time is 40–90 min. The carbon nanotubes are added to the second slurry and dispersed by ball milling to obtain the third slurry. The ball milling power is 400–500 W and the ball milling time is 30–50 min. The first slurry is added to the third slurry and mixed by ball milling to obtain a fourth slurry. The ball milling power is 300 W and the ball milling time is 10–20 min. Organic powder is added to the fourth slurry and ball-milled to obtain the carbon nanotube slurry. The ball milling power is 300 W and the ball milling time is 10-20 min. The step of printing the carbon nanotube paste onto a conductive substrate to obtain a carbon nanotube film specifically includes the following steps: The carbon nanotube paste is uniformly printed onto a conductive substrate using screen printing equipment to form the desired pattern. The substrate is then dried and annealed to obtain the carbon nanotube film. The drying temperature is 90 °C, and the drying time is 30 min. The annealing process is as follows: annealing at 300–400 °C for 180 min under a nitrogen protective atmosphere; then annealing at 750–850 °C for 60–90 min; and finally, natural cooling to obtain the carbon nanotube film. The mass ratio of the carbon nanotubes, the adhesive particles, the conductive metal particles, the organic powder, and the solvent is 1-2 : 3-6 : 1-2.5 : 2-3 : 3-5; The conductive substrate includes iron, nickel, cobalt, iron-nickel alloy, and iron-nickel-cobalt alloy. Before use, the conductive substrate further includes the following pretreatment steps: The conductive substrate surface is polished with abrasive paper to remove the surface oxide layer, and then ultrasonically cleaned with ethanol and deionized water in sequence. The cleaned conductive substrate is then immersed in an acid solution for acid treatment, and then cleaned with deionized water to remove residual acid solution from the surface. The acid solution includes hydrochloric acid, sulfuric acid and nitric acid, and the concentration of the acid solution is 0.2–2 mol / L. The acid treatment time is 1–10 min.

2. The method for manufacturing a carbon nanotube field emission cathode as described in claim 1, characterized in that, The carbon nanotubes are single-walled or multi-walled carbon nanotubes, with a length of 5–20 μm and a diameter of 3–10 nm for multi-walled carbon nanotubes.

3. The method for manufacturing a carbon nanotube field emission cathode as described in claim 1, characterized in that, The nanoparticle filler has a size of 10–50 nm.

4. The method for manufacturing a carbon nanotube field emission cathode as described in claim 1, characterized in that, The organic powder is ethyl cellulose; the solvent is terpineol.

5. The method for manufacturing a carbon nanotube field emission cathode as described in claim 1, characterized in that, The step of treating the surface of the carbon nanotube film to align the carbon nanotubes vertically perpendicular to the surface of the conductive substrate to obtain the carbon nanotube field emission cathode specifically includes the following steps: The surface of the carbon nanotube film is treated with a low-viscosity silicone roller to remove loosely adhered particles and to align the carbon nanotubes vertically perpendicular to the substrate surface, thereby activating the carbon nanotube cathode.

6. A carbon nanotube field emission cathode, characterized in that, It is prepared by the method for manufacturing carbon nanotube field emission cathode according to any one of claims 1 to 5.

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