CN110993465A - High-current repetition frequency strontium titanate-carbon nanotube medium cathode and preparation method thereof - Google Patents
High-current repetition frequency strontium titanate-carbon nanotube medium cathode and preparation method thereof Download PDFInfo
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- CN110993465A CN110993465A CN201911348633.0A CN201911348633A CN110993465A CN 110993465 A CN110993465 A CN 110993465A CN 201911348633 A CN201911348633 A CN 201911348633A CN 110993465 A CN110993465 A CN 110993465A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
- H01J1/02—Main electrodes
- H01J1/30—Cold cathodes, e.g. field-emissive cathode
- H01J1/304—Field-emissive cathodes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
- H01J9/02—Manufacture of electrodes or electrode systems
- H01J9/022—Manufacture of electrodes or electrode systems of cold cathodes
- H01J9/025—Manufacture of electrodes or electrode systems of cold cathodes of field emission cathodes
Abstract
The invention discloses a high-current repetition frequency strontium titanate-carbon nanotube dielectric cathode, which comprises a cathode body made of SrTiO3 ceramic, wherein an emission layer made of carbon nanotubes is attached to the side surface of the cathode body, and the cathode body and the emission layer are formed by co-sintering. By adopting the strontium titanate-carbon nanotube medium cathode with high current repetition frequency and the preparation method thereof, the cathode emission threshold is low and uniform, and the emission life is prolonged.
Description
Technical Field
The invention relates to a high-current repetition frequency strontium titanate-carbon nanotube medium cathode and a preparation method thereof, belonging to the technical field of relativistic electric vacuum devices.
Background
Relativistic electric vacuum devices are developing towards high power, high repetition frequency, miniaturization and long service life. The electron beam is a beam and wave interaction energy source, and the requirements of uniform and stable emission and electron beam density at least greater than 1kA/cm2 are met under a certain repetition frequency, and the high-current cold cathode which directly emits electrons under the drive of a high-voltage pulse power supply, has a low emission threshold and is stable in performance is required. The common strong current cathode is a field explosion emission cathode, whiskers on the surface of the cathode are subjected to field induced emission under the action of electric field enhancement, the whiskers are rapidly heated, plasma is generated by combining thermal field emission whisker explosion, and electron beams are pulled out from the surface plasma under the action of the electric field to generate new whiskers, so that the emission threshold and the electron temperature are relatively high, the plasma expansion speed is high, under the influence of electric field shielding and uneven distribution of new and old whiskers, the electron emission is uneven, local ablation is easily caused, and the emission stability is influenced.
In addition to explosive emissions, a flashover plasma cathode along the surface is an important direction of development. The plasma is generated primarily due to ionization of the desorbed gas under initial field-emitted electrons. The high-current carbon nano tube has a hollow structure and a large specific surface area, is easy to adsorb gas molecules, is easy to release after being bombarded by electrons, increases the flashover probability along the surface, and reduces the electron temperature and the plasma speed. In addition, the quasi-one-dimensional geometrical characteristics (large length-diameter ratio) can provide a large electric field enhancement coefficient, so that the carbon nanotube cathode has the advantage of high power application.
The electric field enhancement is a dielectric enhancement in addition to a geometric enhancement. In order to further improve the cathode flashover probability, increasing the dielectric constant of the carbon nanotube substrate is an effective means. However, the electric field enhancement coefficient is too large, and the deformation recovery of the carbon nano tube is influenced by the stress release under the action of the electric field. In the conventional process, the carbon nanotube film cathode has poor emission stability of the high-current repetition frequency due to the interface bonding force, and the emission times are extremely limited. The strontium titanate ceramic has moderate dielectric constant and good temperature stability.
Disclosure of Invention
The invention aims to: aiming at the problems, the invention provides the strontium titanate-carbon nanotube medium cathode with high current repetition frequency and the preparation method thereof.
The technical scheme adopted by the invention is as follows:
a strontium titanate-carbon nanotube dielectric cathode with high current repetition frequency comprises a cathode body made of SrTiO3 ceramic, wherein an emission layer made of carbon nanotubes is attached to the side surface of the cathode body, and the cathode body and the emission layer are formed in a co-sintering mode.
In the invention, the SrTiO3 ceramic medium has enhanced electric field, insulating property and carbon nanotube adsorption and desorption properties, so that the surface flashover probability is greatly improved, and the electron temperature and the plasma expansion speed are reduced; the SrTiO3 has moderate dielectric constant and good temperature stability, so that the cathode emission of the invention is more stable compared with other carbon nanotube medium cathodes; the carbon nano tubes are anchored on the cathode body by co-sintering the emission layer and the SrTiO3 ceramic cathode body, and the carbon nano tubes are uniformly and stably distributed on the side surface of the cathode body to form a stable carbon nano tube emission layer, so that the stable emission performance and the emission life of the high-current repetition frequency of the conventional carbon nano tube film cathode are higher than those of the conventional carbon nano tube film cathode.
Preferably, a glass phase ceramic additive is further added into the emission layer, and the addition amount of the glass phase ceramic additive is 0.3-0.7% of the mass of the carbon nano tube; further, the glass phase ceramic additive is SiO2-B2O-ZnO glass powder.
The addition of the glass phase ceramic additive leads the carbon nano tube to be better anchored on the SrTiO3 ceramic cathode body, and leads the surface resistance of an emitting layer formed by the carbon nano tube to be obviously improved, thus greatly improving the surface flashover probability and reducing the electron temperature and the plasma expansion speed; the heat conduction coefficients of the ceramic and the carbon nano tube are different, the sintered emission layer is easy to crack, and the emission layer formed by the carbon nano tube is not cracked in the sintering process after the glass phase ceramic additive is added.
The invention also comprises a preparation method of the high-current repetition frequency strontium titanate-carbon nano tube medium cathode, which comprises the following steps:
step a, preparing emission layer slurry containing carbon nano tubes and a SrTiO3 ceramic cathode body;
coating the emission layer slurry on the side surface of the cathode body;
c, putting the cathode body coated with the emission layer slurry on the side surface into a sintering furnace for sintering;
and d, cooling to obtain a finished product.
The preparation method comprises the steps of preparing emission layer slurry containing carbon nanotubes and a SrTiO3 ceramic cathode body, coating the emission layer slurry on the side surface of the cathode body, and carrying out co-sintering to uniformly and stably distribute the carbon nanotubes on the side surface of the cathode body to form the stable carbon nanotube emission layer.
Preferably, in step a, the emission layer slurry containing the carbon nanotubes is prepared by the following method: mixing the carbon nano tube with the adhesive, and grinding to prepare first slurry; mixing the glass phase ceramic additive and the adhesive, and grinding to prepare second slurry; and mixing the first slurry and the second slurry, and grinding to obtain the emitting layer slurry.
In the scheme, the carbon nano tube and the glass phase ceramic additive are ground separately and then ground together, and because the carbon nano tube and the glass phase ceramic additive have different fineness and require different grinding time, the carbon nano tube can be ground better only by separate grinding, so that the grinding fineness of the carbon nano tube is smaller and more uniform. In the scheme, the planetary ball mill is used for ball milling, the planetary ball mill can achieve better grinding fineness, the fineness of the finally ball-milled carbon nano tubes is less than 10 microns, the carbon nano tubes are less prone to agglomeration when the fineness of the carbon nano tubes is smaller, and the electron emission of the prepared emission layer is more uniform.
Preferably, the carbon nanotubes are subjected to a carboxylation-enhancing activity treatment using a strong acid. The carbon nano tube can be enhanced in electronegativity after being subjected to carboxylation enhancing activity treatment, so that the carbon nano tube can be combined with other materials more easily.
Preferably, the strong acid is concentrated sulfuric acid, concentrated nitric acid or diluted hydrochloric acid.
Preferably, a dispersant is further added to the first slurry. The dispersing agent is added to enhance the dispersibility of the carbon nanotubes and prevent the carbon nanotubes from agglomerating.
Preferably, the dispersant is ethyl cellulose, and the addition amount of the dispersant is 0.1-1% of the mass of the carbon nanotubes.
Preferably, the glass phase ceramic additive is glass powder, and further is SiO2-B2O-ZnO glass powder.
Preferably, the mass fraction of the glass phase ceramic additive in the emission layer slurry is 0.3-0.7%.
In the scheme, the glass-phase ceramic additive enables the carbon nano tubes to be anchored on the SrTiO3 ceramic cathode body better, and the surface resistance of an emitting layer formed by the carbon nano tubes is obviously improved, so that the surface flashover probability is greatly improved, and the electron temperature and the plasma expansion speed are reduced; the heat conduction coefficients of the ceramic and the carbon nano tube are different, the sintered emission layer is easy to crack, and the emission layer formed by the carbon nano tube is not cracked in the sintering process after the glass phase ceramic additive is added. The addition of the glass phase ceramic additive is 0.3-0.7%, so that the resistance of the emitting layer can be not improved, and the effect of promoting adhesion can be achieved.
Preferably, the binder is terpineol.
Preferably, the mass fraction of the terpineol is 1-5%, which means that the mass fractions of the terpineol in the first paste, the second paste and the emitting layer paste are all 1-5%.
In the scheme, the terpineol plays a role in wetting and dispersing and is used for dispersing the carbon nano tubes and the glass phase ceramic additive, after sintering, the terpineol is volatilized, the carbon nano tubes and the glass phase ceramic additive are easier to grind when the addition amount is less, and the grinding fineness is good so that the carbon nano tubes and the glass phase ceramic additive are not easy to agglomerate.
Preferably, in step a, a green body is prepared from SrTiO3, and then the green body is dried and primarily sintered at 400 ℃ of 200-.
Preferably, in step b, the emission layer paste is coated on the cathode body using a screen printing method.
Preferably, in the step c, after the sintering furnace is vacuumized, protective gas is introduced, and in the process, the protective gas is repeatedly charged and discharged after the sintering furnace is vacuumized, so that oxygen is discharged more thoroughly; further, the protective gas is nitrogen.
Preferably, in step c, the pressure in the sintering furnace is maintained at 2kPa to 200 kPa.
In the scheme, the sintering furnace is vacuumized to discharge oxygen and is filled with nitrogen, so that the carbon nano tubes are prevented from being oxidized and floating upwards is limited.
Preferably, in step c, the sintering furnace is gradually heated to 600-900ssd, and is kept for tens of minutes, and then annealing treatment is performed.
In the scheme, the annealing treatment is carried out, so that the residual stress can be reduced, the size can be stabilized, and the deformation and crack tendency can be reduced.
Preferably, in step c, the rate of temperature rise is less than 10 ℃/min.
In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that: compared with a silk screen cathode and a carbon nano tube film cathode prepared by a vapor deposition method,
1. the high current emission life of the strontium titanate-carbon nanotube medium cathode prepared by the invention is prolonged.
2. The flash emission probability of the strontium titanate-carbon nanotube dielectric cathode prepared by the method is obviously improved, and the reduction of the plasma speed is facilitated.
3. The strontium titanate-carbon nanotube dielectric cathode prepared by the invention has good emission uniformity and stability under a certain repetition frequency.
Drawings
The invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic structural diagram of a strontium titanate-carbon nanotube dielectric cathode;
FIG. 2 is a top view of a strontium titanate-carbon nanotube dielectric cathode;
FIG. 3 is a waveform diagram of a cathode test of a strontium titanate-carbon nanotube medium.
The labels in the figure are: 1-cathode body, 2-emission layer.
Detailed Description
All of the features disclosed in this specification, or all of the steps in any method or process so disclosed, may be combined in any combination, except combinations of features and/or steps that are mutually exclusive.
Any feature disclosed in this specification may be replaced by alternative features serving equivalent or similar purposes, unless expressly stated otherwise. That is, unless expressly stated otherwise, each feature is only an example of a generic series of equivalent or similar features.
Example 1
The strontium titanate-carbon nanotube dielectric cathode with high current repetition frequency comprises a tubular cathode body made of SrTiO3 ceramic, wherein the side surface of the cathode body is a rough surface, an emission layer made of carbon nanotubes is attached to the side surface of the cathode body, the thickness of the emission layer is 0.1mm, SiO2-B2O-ZnO glass powder is added, and the cathode body and the emission layer are formed in a co-sintering mode.
The preparation method of the high current repetition frequency strontium titanate-carbon nanotube dielectric cathode of the embodiment comprises the following steps:
step a, carrying out carboxylation activity-enhancing treatment on the carbon nano tube by using concentrated nitric acid, and adding 0.1% of cellulose; mixing carbon nano tubes and 5% terpineol, and grinding to prepare first slurry; mixing SiO2-B2O-ZnO glass powder and 5% terpineol, and grinding to obtain a second slurry; mixing the first slurry and the second slurry, wherein the mixing ratio is 100: 0.5, grinding until the fineness of the carbon nano tube is 8 mu m to prepare emission layer slurry;
preparing a blank by using SrTiO3, drying, and performing primary sintering at 200 to prepare a SrTiO3 ceramic cathode body;
coating the emission layer slurry on the side surface of the cathode body in a screen printing mode;
step c, repeatedly charging and discharging nitrogen after the sintering furnace is vacuumized, keeping the pressure at 100kPa after charging and discharging for many times, heating at the heating rate of 7 ℃/min to 600 ℃, preserving the temperature for 30 minutes, and then carrying out annealing treatment;
and d, naturally cooling to obtain a finished product.
Example 2
The strontium titanate-carbon nanotube dielectric cathode with high current repetition frequency comprises a tubular cathode body made of SrTiO3 ceramic, wherein the side surface of the cathode body is a rough surface, an emission layer made of carbon nanotubes is attached to the side surface of the cathode body, the thickness of the emission layer is 1mm, SiO2-B2O-ZnO glass powder is added, and the cathode body and the emission layer are formed in a co-sintering mode.
The preparation method of the high current repetition frequency strontium titanate-carbon nanotube dielectric cathode of the embodiment comprises the following steps:
step a, carrying out carboxylation activity-enhancing treatment on the carbon nano tube by using concentrated nitric acid, and adding 0.1% of cellulose; mixing carbon nano tubes and 1% terpineol, and grinding to prepare first slurry; mixing SiO2-B2O-ZnO glass powder and 1% terpineol, and grinding to obtain a second slurry; mixing the first slurry and the second slurry, wherein the mixing ratio is 100: 0.7, grinding until the fineness of the carbon nano tube is 8 mu m to prepare emission layer slurry;
preparing a blank body by using SrTiO3, drying, and performing primary sintering at 400 ℃ to prepare a SrTiO3 ceramic cathode body;
coating the emission layer slurry on the side surface of the cathode body in a screen printing mode;
step c, repeatedly charging and discharging nitrogen after vacuumizing the sintering furnace, keeping the pressure at 200kPa after charging and discharging for multiple times, heating at the heating rate of 8 ℃/min to 900 ℃, preserving the temperature for 40 minutes, and then carrying out annealing treatment;
and d, naturally cooling to obtain a finished product.
Example 3
The strontium titanate-carbon nanotube dielectric cathode with high current repetition frequency comprises a tubular cathode body made of SrTiO3 ceramic, wherein the side surface of the cathode body is a rough surface, an emission layer made of carbon nanotubes is attached to the side surface of the cathode body, the thickness of the emission layer is 0.5mm, SiO2-B2O-ZnO glass powder is added, and the cathode body and the emission layer are formed in a co-sintering mode.
The preparation method of the high current repetition frequency strontium titanate-carbon nanotube dielectric cathode of the embodiment comprises the following steps:
step a, carrying out carboxylation activity-enhancing treatment on the carbon nano tube by using concentrated nitric acid, and adding 0.5 percent of cellulose; mixing carbon nano tubes and 3% terpineol, and grinding to prepare first slurry; mixing SiO2-B2O-ZnO glass powder and 3% terpineol, and grinding to obtain a second slurry; mixing the first slurry and the second slurry, wherein the mixing ratio is 100: 0.3, grinding until the fineness of the carbon nano tube is 8 mu m to prepare emission layer slurry;
preparing a blank body by using SrTiO3, drying, and performing primary sintering at 300 ℃ to prepare a SrTiO3 ceramic cathode body;
coating the emission layer slurry on the side surface of the cathode body in a screen printing mode;
step c, repeatedly charging and discharging nitrogen after vacuumizing the sintering furnace, keeping the pressure at 2kPa after charging and discharging for multiple times, heating at the heating rate of 6 ℃/min to 750 ℃, preserving the temperature for 20 minutes, and then carrying out annealing treatment;
and d, naturally cooling to obtain a finished product.
As shown in figure 3, in the strong current and repetition frequency cathode electron emission test, the pulse source voltage is 400kV, the vacuum degree is 1.2 & 10 & 2Pa grade, the cathode form is axial emission, the obtained electron beam intensity is 1.8kA, the equivalent beam density is close to 20kA/cm2, the emission is stable in 3000 cannons at 20Hz, and the carbon nanotube film does not show falling and sputtering.
In the waveform diagram of FIG. 3, the upper row is voltage waveform, 180kV/div, and the lower row is electron beam current waveform, 0.85 kA/div; the beam waveforms are basically consistent, and no obvious positive pulse is seen between pulses, so that the yield of carbon ions is low, and the carbon nano tube is not obviously sputtered.
In conclusion, by adopting the strontium titanate-carbon nanotube medium cathode with the high current repetition frequency, the high current emission life is prolonged; the flashover emission probability is obviously improved, and the reduction of the plasma speed is facilitated; the emission uniformity and stability are good under a certain repetition frequency.
The invention is not limited to the foregoing embodiments. The invention extends to any novel feature or any novel combination of features disclosed in this specification and any novel method or process steps or any novel combination of features disclosed.
Claims (10)
1. A high current repetition frequency strontium titanate-carbon nanotube medium cathode is characterized in that: the cathode comprises a cathode body made of SrTiO3 ceramic, wherein an emission layer made of carbon nanotubes is attached to the side surface of the cathode body, and the cathode body and the emission layer are formed in a co-sintering mode.
2. The high current repetition rate strontium titanate-carbon nanotube dielectric cathode of claim 1, wherein: and a glass phase ceramic additive is also added into the emitting layer.
3. A preparation method of a high-current repetition frequency strontium titanate-carbon nanotube medium cathode is characterized by comprising the following steps: the method comprises the following steps:
step a, preparing emission layer slurry containing carbon nano tubes and a SrTiO3 ceramic cathode body;
coating the emission layer slurry on the side surface of the cathode body;
c, putting the cathode body coated with the emission layer slurry on the side surface into a sintering furnace for sintering;
and d, cooling to obtain a finished product.
4. The method of preparing a high current repetition frequency strontium titanate-carbon nanotube dielectric cathode of claim 4, wherein: in step a, an emitting layer slurry containing carbon nanotubes is prepared by the following method: mixing the carbon nano tube with the adhesive, and grinding to prepare first slurry; mixing the glass phase ceramic additive and the adhesive, and grinding to prepare second slurry; and mixing the first slurry and the second slurry, and grinding to obtain the emitting layer slurry.
5. The method of claim 5, wherein the high current repetition frequency strontium titanate-carbon nanotube dielectric cathode is prepared by the following steps: the carbon nano tube is subjected to carboxylation activity enhancement treatment by adopting strong acid.
6. The method of claim 5, wherein the high current repetition frequency strontium titanate-carbon nanotube dielectric cathode is prepared by the following steps: and a dispersant is also added into the first slurry.
7. The method of claim 5, wherein the high current repetition frequency strontium titanate-carbon nanotube dielectric cathode is prepared by the following steps: the glass phase ceramic additive is SiO2-B2O-ZnO glass powder.
8. The method of claim 2, wherein the high current repetition frequency strontium titanate-carbon nanotube dielectric cathode is prepared by the following steps: the adhesive is terpineol.
9. The method of preparing a high current repetition frequency strontium titanate-carbon nanotube dielectric cathode of claim 4, wherein: and c, vacuumizing the sintering furnace, and introducing protective gas.
10. The method of preparing a high current repetition frequency strontium titanate-carbon nanotube dielectric cathode of claim 4, wherein: in the step c, the temperature of the sintering furnace is gradually increased to 600-900ssd, the temperature is kept for tens of minutes, and then annealing treatment is carried out.
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| US5014289A (en) * | 1989-02-27 | 1991-05-07 | Lasertechnics, Inc. | Long life electrodes for large-area x-ray generators |
| US20050248250A1 (en) * | 2004-05-07 | 2005-11-10 | Steris Inc | Cathode structure for explosive electron emission and method of forming the same |
| CN101093764A (en) * | 2006-06-23 | 2007-12-26 | 清华大学 | Field emission component, and preparation method |
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