A low secondary electron emission coefficient collector electrode surface treatment method

Abstract

The application relates to the technical field of surface treatment of collecting electrode, and provides a low secondary electron emission coefficient collecting electrode surface treatment method, which comprises the following steps: processing a graphite-doped metal into a collecting electrode part through a mechanical processing mode; removing the impurities remaining on the surface of the collecting electrode part after processing through an acetone ultrasonic cleaning mode; performing hydrogen burning purification treatment on the collecting electrode part; performing copper plating treatment on the welding area of the graphite-doped metal material; and assembling the collecting electrode by using a low-vapor-pressure gold-based alloy solder as filling solder for an electric vacuum device. Compared with the collecting electrode prepared from oxygen-free copper in the prior art, the low secondary electron emission coefficient and the weight of the electrode are reduced by adopting the lightweight new material graphite-doped metal. The connection between the lead wire of the collecting electrode and the collecting electrode is realized through local copper plating and vacuum heat treatment on the graphite-doped metal collecting electrode part, so that the power supply requirement of each electrode of the collecting electrode is met.

Description

Technical Field

[0001] This invention relates to the field of surface treatment technology for collecting electrodes, specifically a method for surface treatment of collecting electrodes with low secondary electron emission coefficient. Background Technology

[0002] High-power millimeter-wave traveling wave tubes (TWTs) are indispensable core components in high-precision millimeter-wave radar systems, serving as microwave power amplifiers. Radar systems have extremely high requirements for the efficiency and signal quality of TWTs, with efficiency directly affecting the radar system's payload. As the important component for collecting residual electrons within the TWT, improving the efficiency of the collector is crucial.

[0003] like Figure 1 As shown, given a fixed collector electrode structure design, obtaining a high-efficiency collector electrode requires consideration of materials and processes. This can be achieved by selecting materials with low secondary electron emission coefficients as the collector electrode or by modifying the electrode surface. However, surface modification technology currently suffers from unstable processes and high processing costs, hindering engineering applications. Therefore, directly changing the material is the most direct and effective way to improve recovery efficiency. This invention proposes a surface treatment method for a collector electrode with a low secondary electron emission coefficient, which can significantly reduce the secondary electrons generated during the operation of the traveling wave tube. While meeting the requirements of good processing performance, low outgassing, and high welding quality for thin-walled collector electrodes, it improves the collector electrode efficiency and reduces the overall tube weight, thus meeting the requirements of radar systems for high-power millimeter-wave traveling wave tube payloads. Summary of the Invention

[0004] This invention provides a surface treatment method for a collector electrode with a low secondary electron emission coefficient, and studies a matching surface treatment method to meet the welding requirements of the collector components, so as to solve the problem that the high secondary emission coefficient of the collector electrode of a high-power millimeter-wave traveling wave tube made of oxygen-free copper material in the prior art limits the improvement of the overall tube efficiency.

[0005] The technical solution of this invention is as follows:

[0006] A method for treating the surface of a collecting electrode with a low secondary electron emission coefficient includes the following steps:

[0007] S1: Graphite-doped metal is processed into collecting electrode parts through mechanical processing;

[0008] S2: Use acetone ultrasonic cleaning to remove residual debris or particles from the surface of the collecting electrode parts after processing;

[0009] S3: The collecting electrode components are kept at 700℃ for 10 minutes for hydrogen purification treatment;

[0010] S4: The welding area of ​​the graphite-doped metal material is plated with copper and then kept at 900℃-950℃ in a vacuum furnace for 20 minutes.

[0011] S5: The collector electrode is assembled using a low vapor pressure gold-based alloy brazing filler metal for vacuum electronic devices, and then welded into a collector electrode component in a vacuum furnace.

[0012] Preferably, the graphite content in the graphite-doped metal in S1 is 80%-90%.

[0013] Preferably, the machining methods in S1 include turning, washing, grinding, and electrical discharge machining.

[0014] Preferably, alcohol is used as a coolant during machining in step S1.

[0015] Preferably, the vacuum degree inside the vacuum furnace in S4 and S5 shall not be lower than 10. -4 Pa.

[0016] Preferably, the copper layer thickness in S4 is 7-8 μm.

[0017] Preferably, the gold-based alloy brazing filler metal in S5 includes Au-Cu and Au-Ni.

[0018] Preferably, the Au-Cu welding temperature is 910-930℃, the Au-Ni welding temperature is 950-1000℃, and the heating rate is 10℃ / min.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. This invention utilizes lightweight novel material graphite-doped metal, which, compared to the previous oxygen-free copper-based collecting electrode, reduces the secondary electron emission coefficient and weight of the electrode itself. Alcohol is used as the coolant. Through machining and ultrasonic cleaning with acetone, the invention effectively solves the problem of severe material outgassing caused by improper processing while meeting the precision requirements of the collecting electrode. This contributes to improving the vacuum level inside the traveling wave tube and enhancing the consistency of electrical parameters such as the spiral current.

[0021] 2. This invention improves the bonding strength between the copper plating layer and the graphite-doped metal substrate by locally plating copper onto the graphite-doped metal collecting electrode parts and performing vacuum heat treatment. This also improves the wetting performance of the brazing filler metal on the graphite-doped metal surface, realizes the connection between the collecting electrode lead and the collecting electrode, and meets the power requirements of each collecting electrode. Attached Figure Description

[0022] Figure 1 This is a structural diagram of the collecting electrode of the present invention;

[0023] Figure 2 This is a physical image of the graphite-doped metal collecting electrode of the present invention;

[0024] Figure 3 This is a physical image of the graphite-doped metal collecting electrode of the present invention;

[0025] Figure 4 This is a flowchart of the surface treatment method of the present invention. Detailed Implementation

[0026] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0027] Example 1:

[0028] A method for treating the surface of a collecting electrode with a low secondary electron emission coefficient includes the following steps:

[0029] S1: The graphite-doped metal with a graphite content of 80% is processed into the required collecting electrode parts through turning, washing, grinding, and electrical discharge machining. In order to meet the vacuum hygiene requirements of the traveling wave tube, the collecting electrode parts are processed by machining with alcohol as the coolant to avoid problems such as gas release from the collecting electrode caused by the incomplete removal of coolant residue.

[0030] S2: Acetone ultrasonic cleaning is used to remove residual debris or particles on the surface of the collecting electrode parts after processing, so as to avoid the formation of excess material after the tube is assembled, which may cause problems such as arcing in the traveling wave tube.

[0031] S3: To remove copper oxides that appear on the surface of the parts during processing, the collecting electrode parts are placed in a sealed container, high-purity hydrogen gas is introduced into the container, and the mixture is heated to 700°C for 10 minutes; the processed collecting electrode is as follows: Figure 2 As shown;

[0032] S4: To accommodate different voltages at each electrode, external leads need to be welded to the collecting electrode. To ensure reliable welding of the graphite-doped metal, a copper plate is used as the cathode, and the welded area of ​​the graphite-doped metal serves as the anode, at a potential of 0.5V and an A / cm² voltage of 1.5-2.5A. 2 At a current density, copper ions are reduced from the electrolyte through an electrolytic reaction and deposited on the graphite surface to achieve a copper layer thickness of 7 μm. Then, a vacuum degree of not less than 10... -4 The copper layer is held at 900℃-950℃ for 20 minutes in a vacuum furnace to improve the bonding strength between the copper layer and the graphite-doped metal matrix, while effectively removing residual gas molecules inside the material.

[0033] S5: Use a low vapor pressure gold-based alloy solder (Au-Cu or Au-Ni) for vacuum electronic devices as filler solder to fix it at a predetermined position on the collecting electrode, and then place it in a vacuum furnace to maintain a temperature not lower than 10°C. -4 A vacuum level of Pa is maintained, and the temperature is kept at 910-930℃ or 950-1000℃, while simultaneously increasing the temperature at a rate of 10℃ / min. The temperature is kept constant while the gold-based alloy brazing filler metal melts, ensuring a thorough bond between the gold-based alloy brazing filler metal and the collecting electrode assembly. The collecting electrode assembly brazed with gold-based solder wire is as follows: Figure 3 As shown.

[0034] Example 2:

[0035] S1: The graphite-doped metal with a graphite content of 85% is processed into the required collecting electrode parts through turning, washing, grinding, and electrical discharge machining. In order to meet the vacuum hygiene requirements of the traveling wave tube, the collecting electrode parts are processed by using alcohol as a coolant to avoid problems such as gas release from the collecting electrode caused by the incomplete removal of coolant residue.

[0036] S2: Acetone ultrasonic cleaning is used to remove residual debris or particles on the surface of the collecting electrode parts after processing, so as to avoid the formation of excess material after the tube is assembled, which may cause problems such as arcing in the traveling wave tube.

[0037] S3: To remove copper oxides that appear on the surface of the parts during processing, the collecting electrode parts are placed in a sealed container, high-purity hydrogen gas is introduced into the container, and the mixture is heated to 700°C for 10 minutes; the processed collecting electrode is as follows: Figure 2 As shown;

[0038] S4: To accommodate different voltages at each electrode, external leads need to be welded to the collecting electrode. To ensure reliable welding of the graphite-doped metal, a copper plate is used as the cathode, and the welded area of ​​the graphite-doped metal serves as the anode, at a potential of 0.5V and an A / cm² voltage of 1.5-2.5A. 2 At a current density, copper ions are reduced from the electrolyte through an electrolytic reaction and deposited on the graphite surface to achieve a copper layer thickness of 7.5 μm. Then, a vacuum degree of not less than 10... -4 The copper layer is held at 900℃-950℃ for 20 minutes in a vacuum furnace to improve the bonding strength between the copper layer and the graphite-doped metal matrix, while effectively removing residual gas molecules inside the material.

[0039] S5: Use a low vapor pressure gold-based alloy solder (Au-Cu or Au-Ni) for vacuum electronic devices as filler solder to fix it at a predetermined position on the collecting electrode, and then place it in a vacuum furnace to maintain a temperature not lower than 10°C. -4A vacuum level of Pa is maintained, and the temperature is kept at 910-930℃ or 950-1000℃, while simultaneously increasing the temperature at a rate of 10℃ / min. The temperature is kept constant while the gold-based alloy brazing filler metal melts, ensuring a thorough bond between the gold-based alloy brazing filler metal and the collecting electrode assembly. The collecting electrode assembly brazed with gold-based solder wire is as follows: Figure 3 As shown.

[0040] Example 3:

[0041] A method for treating the surface of a collecting electrode with a low secondary electron emission coefficient includes the following steps:

[0042] S1: The graphite-doped metal with a graphite content of 90% is processed into the required collecting electrode parts through turning, washing, grinding, and electrical discharge machining. In order to meet the vacuum hygiene requirements of the traveling wave tube, the collecting electrode parts are processed by machining with alcohol as the coolant to avoid problems such as gas release from the collecting electrode caused by the incomplete removal of coolant residue.

[0043] S2: Acetone ultrasonic cleaning is used to remove residual debris or particles on the surface of the collecting electrode parts after processing, so as to avoid the formation of excess material after the tube is assembled, which may cause problems such as arcing in the traveling wave tube.

[0044] S3: To remove copper oxides that appear on the surface of the parts during processing, the collecting electrode parts are placed in a sealed container, high-purity hydrogen gas is introduced into the container, and the mixture is heated to 700°C for 10 minutes; the processed collecting electrode is as follows: Figure 2 As shown;

[0045] S4: To accommodate different voltages at each electrode, external leads need to be welded to the collecting electrode. To ensure reliable welding of the graphite-doped metal, a copper plate is used as the cathode, and the welded area of ​​the graphite-doped metal serves as the anode, at a potential of 0.5V and an A / cm² voltage of 1.5-2.5A. 2 At a current density, copper ions are reduced from the electrolyte through an electrolytic reaction and deposited on the graphite surface to achieve a copper layer thickness of 8 μm. Then, a vacuum degree of not less than 10... -4 The copper layer is held at 900℃-950℃ for 20 minutes in a vacuum furnace to improve the bonding strength between the copper layer and the graphite-doped metal matrix, while effectively removing residual gas molecules inside the material.

[0046] S5: Use a low vapor pressure gold-based alloy solder (Au-Cu or Au-Ni) for vacuum electronic devices as filler solder to fix it at a predetermined position on the collecting electrode, and then place it in a vacuum furnace to maintain a temperature not lower than 10°C. -4A vacuum level of Pa is maintained, and the temperature is kept at 910-930℃ or 950-1000℃, while simultaneously increasing the temperature at a rate of 10℃ / min. The temperature is kept constant while the gold-based alloy brazing filler metal melts, ensuring a thorough bond between the gold-based alloy brazing filler metal and the collecting electrode assembly. The collecting electrode assembly brazed with gold-based solder wire is as follows: Figure 3 As shown.

[0047] Comparative Example 1:

[0048] S1: Process multi-level ordinary pressed graphite substrates as needed;

[0049] S2: Use ordinary pressed graphite material to process shielding fixtures to block areas where pyrolytic graphite coatings do not need to be deposited;

[0050] S3: Install the shielding fixture on each graphite substrate and perform a pyrolytic graphite coating treatment with a coating thickness of 10-50μm;

[0051] S4: Metallize the graphite composite electrode obtained in step S3: Use a stainless steel shielding fixture to shield the area on the electrode where the pyrolytic graphite coating is deposited, and perform vacuum ion plating titanium treatment. The thickness of the titanium layer is controlled at 5-15μm.

[0052] S5: Metallization of the welding surface of insulating ceramic parts: Metallization process is carried out using conventional high-temperature molybdenum-manganese method, followed by nickel plating and hydrogen burning;

[0053] S6: Welding;

[0054] S7: After assembling multiple graphite composite electrode units obtained from S6 in axial order, they are fitted with oxygen-free copper or Monel sleeves and welded in a furnace; after being fixed, they are naturally cooled to obtain the finished product.

[0055] The emission coefficient was measured twice in Examples 1 and 2, and Comparative Examples 1 and 2.

[0056] S1: Preparation Phase

[0057] Place the sample to be tested between the collection plates, ensuring that the sample surface is clean and free of contamination, and adjust the electron gun to emit a stable high-energy electron beam.

[0058] S2: Measuring the incident electron beam current

[0059] Without placing the sample to be tested, the electron beam is allowed to pass through the collecting plate and enter the Faraday cup. The current formed by the electron beam entering the Faraday cup is measured using a galvanometer and recorded as I injection current.

[0060] S3: Measure background current

[0061] Short-circuit the collecting plate and apply a 50V voltage between the sample to be tested and the collecting plate to prevent secondary electrons from escaping from the sample. At this time, measure the current between the sample to be tested and the collecting plate. This current is mainly composed of background current (such as instrument noise, leakage current, etc.) and is denoted as I1. Ignore the small changes in the background current and consider I1≈IBG (background current).

[0062] S4: Measuring secondary electron current

[0063] Keep the collecting plate short-circuited, but apply a 20V voltage between the first collecting plate and the sample to be tested. At this time, the secondary electrons emitted by the sample to be tested are collected by the collecting plate, forming a secondary electron current. Use a galvanometer to measure the current between the first collecting plate and the sample to be tested, and record it as I2. This current includes the background current, the current formed by the incident electron beam penetrating the sample (if any), and the secondary electron current.

[0064] According to the formula I2=IBG+Iothers+ISE (where ISE is the secondary electron current), calculate the secondary electron current ISE. Note that due to the measurement of I injection current and I1, the magnitude of I others (other electron currents) can be estimated.

[0065] S5: Calculate the secondary emission coefficient

[0066] The secondary emission coefficient δ is usually defined as the number of secondary electrons excited by a unit incident electron, but in actual measurements, it is often expressed as the current ratio.

[0067] The secondary emission coefficient δ = ISE / Iinjection current can be calculated based on the secondary electron current ISE and the incident electron beam current Iinjection current.

[0068] When the injected current I is 5.62 × 10 -8 The experimental data obtained at time A are shown in Table 1.

[0069] Table 1: Experimental Data for Secondary Emission Coefficient Measurement

[0070] Example 1 Example 2 Example 3 Comparative Example 1 Secondary emission coefficient 0.62 0.67 0.75 1.32

[0071] As shown in Table 1, the secondary emission coefficient of the collecting electrode made by graphite doping with metal is significantly reduced, and the graphite content of 80%-90% and the copper layer thickness of 7-8μm contribute to the reduction of the secondary emission coefficient.

[0072] Compared to Comparative Example 1, Examples 1, 2, and 3 employ localized copper plating and vacuum heat treatment on the graphite-doped metal collecting electrode components. This enhances the bonding strength between the copper plating layer and the graphite-doped metal substrate, improves the wetting performance of the brazing filler metal on the graphite-doped metal surface, and enables the connection between the collecting electrode leads and the collecting electrode, meeting the power requirements of each collecting electrode. By using lightweight new material, graphite-doped metal, the secondary emission coefficient and weight of the collecting electrode itself are significantly reduced. Furthermore, the collecting electrode components are machined using alcohol as a coolant, avoiding problems such as gas outgassing caused by incomplete removal of coolant residue. The ultrasonic cleaning method using acetone removes residual debris or particles from the surface of the collecting electrode components after machining, preventing arcing in the traveling wave tube caused by excess material after assembly. While meeting the precision requirements for collecting electrode machining, these examples effectively solve the problem of severe gas outgassing in the later stages of material processing caused by improper machining, contributing to the improvement of the vacuum level inside the traveling wave tube and the consistency of solenoid current and other electrical parameters.

[0073] The embodiments of the present invention are given for the purposes of illustration and description. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for surface treatment of a collecting electrode with low secondary electron emission coefficient, characterized in that: Includes the following steps: S1: Graphite-doped metal is processed into collecting electrode parts through mechanical processing; S2: Use acetone ultrasonic cleaning to remove residual debris or particles from the surface of the collecting electrode parts after processing; S3: The collecting electrode components are kept at 700℃ for 10 minutes for hydrogen purification treatment; S4: The welding area of ​​the graphite-doped metal material is plated with copper and then kept at 900℃-950℃ in a vacuum furnace for 20 minutes. S5: The collector electrode is assembled using a low vapor pressure gold-based alloy brazing filler metal for vacuum electronic devices, and then welded into a collector electrode component in a vacuum furnace.

2. The method for treating the surface of a collecting electrode with low secondary electron emission coefficient as described in claim 1, characterized in that: The graphite content in the graphite-doped metal in S1 is 80%-90%.

3. The method for treating the surface of a collecting electrode with low secondary electron emission coefficient as described in claim 1, characterized in that: The machining methods in S1 include turning, washing, grinding, and electrical discharge machining.

4. The method for treating the surface of a collecting electrode with low secondary electron emission coefficient as described in claim 1, characterized in that: In S1, alcohol is used as a coolant during machining.

5. The method for treating the surface of a collecting electrode with low secondary electron emission coefficient as described in claim 1, characterized in that: The vacuum level inside the vacuum furnace in S4 and S5 shall not be lower than 10. -4 Pa.

6. The method for treating the surface of a collecting electrode with low secondary electron emission coefficient as described in claim 1, characterized in that: The copper layer thickness in S4 is 7-8µm.

7. The method for treating the surface of a collecting electrode with low secondary electron emission coefficient as described in claim 1, characterized in that: The gold-based alloy brazing filler metal in S5 includes Au-Cu and Au-Ni.

8. The method for treating the surface of a collecting electrode with low secondary electron emission coefficient as described in claim 7, characterized in that: The Au-Cu welding temperature is 910-930℃, the Au-Ni welding temperature is 950-1000℃, and the heating rate is 10℃ / min.

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