A high-performance insulating ceramic sealing method for neutron tubes

Abstract

This application relates to the field of material sealing technology, and particularly to a high-performance insulating ceramic sealing method for neutron tubes. The method includes: sequentially performing organic solvent ultrasonic cleaning and argon plasma etching activation treatment on the sealing surface of a cylindrical high-purity alumina ceramic part, followed by magnetron sputtering deposition of a titanium transition layer to obtain a ceramic part with a titanium transition layer; acid washing to remove the oxide layer from the sealing surface of a Kovar alloy cylindrical flange, followed by cleaning and drying to obtain a metal sealing part; preparing an active brazing filler metal sheet; sequentially assembling the sheet to form a pre-assembled assembly; placing the pre-assembled assembly in a vacuum brazing furnace, applying axial preload to complete the sealing, followed by controlled cooling to form a sealing part with an airtight brazed joint; and annealing to obtain the finished sealing assembly. This method solves the problems of low dielectric strength, large differences in thermal expansion coefficients, and difficulty in controlling interface quality in existing technologies.

Description

Technical Field

[0001] This application relates to the field of material sealing technology, and in particular to a high-performance insulating ceramic sealing method for neutron tubes. Background Technology

[0002] Neutron tubes, as compact neutron sources, have important applications in oil well logging, industrial testing, and scientific research. One of their core performance indicators is their withstand voltage rating, which directly determines neutron production efficiency and equipment reliability. With the upgrading of application requirements, many scenarios demand that neutron tubes operate at voltages stably above 120kV, placing extremely high demands on the insulation and sealing performance of the internal components. In the neutron tube structure, the sealing joint between the insulating ceramic and the metal electrode is a critical link in withstanding high electric field stress, and its reliability directly restricts the overall withstand voltage capability.

[0003] Currently, this field commonly uses 95% alumina ceramics and Kovar alloys for sealing via traditional active metal brazing or glass solder. This approach has significant limitations: First, the intrinsic properties of the materials are insufficient; the dielectric strength of ordinary alumina ceramics is typically only 10-15 kV / mm, making them prone to dielectric breakdown under high voltages above 120 kV. Second, there is a mismatch in the coefficients of thermal expansion between the ceramic and the metal (e.g., alumina is approximately...). Kovar alloy is approximately During temperature cycling, the interface generates significant thermal stress, which induces microcracks and becomes a discharge channel, leading to flashover failure of the sealing component at around 90kV.

[0004] Furthermore, existing sealing processes also have shortcomings. Glass solders have poor heat resistance and are prone to softening and sealing failure after long-term operation; while active metal brazing has high strength, its process window is narrow, the interface reaction is difficult to control, it easily forms brittle phases, and the interface smoothness is poor, leading to localized electric field concentration. Although the industry has attempted to improve these aspects by increasing ceramic purity or optimizing process parameters, it is still difficult to consistently achieve withstand voltage requirements above 120kV, hindering the development of neutron tubes towards higher performance. Therefore, there is an urgent need for a high-performance insulating ceramic sealing technology that integrates innovation in materials, structure, and processes. Summary of the Invention

[0005] This application provides a high-performance insulating ceramic sealing method for neutron tubes to solve the problems of low dielectric strength, large differences in thermal expansion coefficients, and difficulty in controlling interface quality in existing technologies.

[0006] The first aspect of this application provides a method for sealing high-performance insulating ceramics for neutron tubes, comprising the following steps: Step 1: The sealing surface of a cylindrical high-purity alumina ceramic part is sequentially subjected to ultrasonic cleaning with organic solvent and argon plasma etching activation treatment, and a titanium transition layer is deposited on the activated sealing surface by magnetron sputtering to obtain a ceramic part with a titanium transition layer; Step 2: The sealing surface of a Kovar alloy cylindrical flange is acid-washed to remove the oxide layer, and then cleaned and dried to obtain a metal sealing part; Step 3: Prepare Ag-C Step 4: Align and assemble the metal sealing component, Ag-Cu-Ti active brazing filler sheet, and the sealing surface of the ceramic component with titanium transition layer in sequence to form a pre-assembled assembly; Step 5: Place the pre-assembled assembly in a vacuum brazing furnace, apply axial preload to it, heat it in a vacuum environment until the brazing filler melts and hold it at that temperature to complete the sealing, and then control the cooling to form a sealing component with an airtight brazed joint; Step 6: Anneal the sealing component with the airtight brazed joint to obtain the finished sealing assembly.

[0007] Preferably, in step one, the purity of the high-purity alumina ceramic part is not less than 99.5%.

[0008] Preferably, in step one, the power of the argon plasma etching activation is 150W-200W, and the etching time is 10-20 minutes.

[0009] Preferably, in step two, the pickling solution used is a dilute hydrochloric acid solution with a mass fraction of 6%-10%, and the soaking time is 15-25 minutes.

[0010] Preferably, in step three, the preparation process of the Ag-Cu-Ti active solder sheet includes: weighing 70.5%-73.5% silver, 25.1%-27.3% copper, and 1.4%-2.2% titanium by mass percentage; melting the raw materials evenly and processing them into a sheet with a thickness of 0.05mm-0.15mm; and cutting the sheet into a shape that matches the sealing surface of the ceramic part and the metal sealing part.

[0011] Preferably, in step five, the vacuum level of the vacuum environment is lower than... .

[0012] Preferably, in step five, the axial preload is 0.2 MPa-0.4 MPa.

[0013] Preferably, in step five, the temperature at which the brazing filler metal is heated to melt is 810℃-830℃, and the holding time is 2-5 minutes.

[0014] Preferably, in step six, the annealing temperature is 450℃-550℃, and the holding time is 100-140 minutes.

[0015] A second aspect of this application provides a high-performance insulating ceramic sealing device for a neutron tube, comprising: a cylindrical high-purity alumina ceramic component; a first metal sealing component and a second metal sealing component, made of Kovar alloy, respectively disposed on both sides of the ceramic component along its axial direction; a titanium transition layer covering the sealing surfaces at both ends of the ceramic component; and an active solder layer disposed between the titanium transition layer and the corresponding metal sealing component at both ends of the ceramic component, connected by vacuum brazing; the ceramic component, titanium transition layer, active solder layer, and metal sealing component are vacuum brazed to form an integral hermetically sealed structure.

[0016] Therefore, this application has the following beneficial effects:

[0017] This application's embodiments fundamentally improve the intrinsic dielectric strength of the material by selecting high-purity alumina ceramic with a purity of not less than 99.5% as the insulating body. Simultaneously, Kovar alloy with a matching coefficient of thermal expansion is used as the metal sealing component, combined with a titanium transition layer deposited by magnetron sputtering, constructing a gradient buffer interface that effectively alleviates stress concentration caused by differences in thermal expansion. Furthermore, interface activation treatment combining plasma etching and titanium layer deposition, the use of precisely proportioned silver-copper-titanium active solder, and a precision brazing process applying axial preload in a high-vacuum environment synergistically ensure high cleanliness, strong adhesion, and a dense, defect-free sealing interface. The resulting sealing assembly exhibits excellent performance, with its withstand voltage rating stably increased to over 120 kV, significantly enhanced shear strength, and maintaining structural integrity and performance stability during stringent temperature cycling tests. This solves the problems of low dielectric strength, large differences in coefficients of thermal expansion, and difficulty in controlling interface quality in existing technologies.

[0018] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0019] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0020] Figure 1 This is a flowchart illustrating a high-performance insulating ceramic sealing method for neutron tubes according to an embodiment of this application;

[0021] Figure 2 This is a diagram of a ceramic sealing structure provided according to an embodiment of this application. Detailed Implementation

[0022] The embodiments of this application are described in detail below. Examples of the 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.

[0023] The following description, with reference to the accompanying drawings, illustrates a high-performance insulating ceramic sealing method for neutron tubes according to embodiments of this application. Addressing the issue of high response delay mentioned in the background art, this application provides a high-performance insulating ceramic sealing method for neutron tubes. In this method, high-purity alumina ceramic with a purity of not less than 99.5% is selected as the insulating substrate, fundamentally improving the intrinsic dielectric strength of the material. Simultaneously, Kovar alloy with a matching coefficient of thermal expansion is used as the metal sealing component, combined with a titanium transition layer deposited by magnetron sputtering, constructing a gradient buffer interface that effectively alleviates stress concentration caused by differences in thermal expansion. Furthermore, interface activation treatment combining plasma etching and titanium layer deposition, the use of precisely proportioned silver-copper-titanium active solder, and a precision brazing process applying axial preload under high vacuum conditions synergistically ensure high cleanliness, strong bonding, and dense, defect-free sealing interface. The resulting sealing assembly exhibits excellent performance, with its withstand voltage rating stably increased to over 120 kV, significantly enhanced shear strength, and maintaining structural integrity and performance stability during stringent temperature cycling tests. This solves the problems of low dielectric strength, large differences in thermal expansion coefficients, and difficulty in controlling interface quality in existing technologies.

[0024] Specifically, Figure 1 This is a schematic flowchart illustrating a high-performance insulating ceramic sealing method for neutron tubes provided in an embodiment of this application.

[0025] like Figure 1 As shown, the high-performance insulating ceramic sealing method for neutron tubes includes the following steps:

[0026] In step one, the sealing surface of the cylindrical high-purity alumina ceramic part is subjected to ultrasonic cleaning with organic solvent and argon plasma etching activation treatment in sequence. Then, a titanium transition layer is deposited on the activated sealing surface by magnetron sputtering to obtain a ceramic part with a titanium transition layer.

[0027] Among them, organic solvent ultrasonic cleaning refers to placing ceramic parts in trichloroethylene and anhydrous ethanol organic solvents in sequence, and applying ultrasonic waves to each. The strong physical scouring effect generated by ultrasonic cavitation, combined with the chemical dissolution effect of the solvent, effectively removes organic pollutants and particulate impurities from the surface, thereby obtaining a highly clean surface that meets the requirements of subsequent processes.

[0028] It should be noted that magnetron sputtering is a physical vapor deposition process in which argon ions bombard a titanium target under magnetic field confinement in a vacuum environment, causing titanium atoms to be sputtered at the atomic scale and uniformly deposited on the ceramic sealing surface, thereby forming a dense, uniform and firmly bonded titanium transition layer.

[0029] It is understood that the embodiments of this application provide an atomically clean substrate for the ceramic sealing surface by employing an ultrasonic cleaning step with organic solvents, thoroughly removing oil and particulate contaminants, and avoiding weakening of bonding force and degradation of electrical performance due to interface contamination. Through a magnetron sputtering step, a dense, uniform and firmly bonded titanium transition layer is precisely constructed on the cleaned ceramic surface, which not only greatly improves the wettability between the ceramic and the subsequent active solder, forming a strong metallurgical bond, but also serves as a key functional gradient layer, effectively buffering the thermal stress caused by the difference in thermal expansion coefficients between the ceramic and the metal, and significantly improving the mechanical integrity, long-term stability and high-voltage insulation reliability of the sealing interface.

[0030] In the embodiments of this application, the purity of the high-purity alumina ceramic parts is not less than 99.5%.

[0031] It is understood that by specifying that the purity of the high-purity alumina ceramic parts is not less than 99.5%, the intrinsic dielectric strength of the material is fundamentally improved to 20-30kV / mm or even higher, enabling it to directly withstand extreme electric fields of 120kV or higher, thus overcoming the core bottleneck of insufficient insulation capacity of traditional materials. At the same time, the extremely high purity significantly reduces impurity phases, making the thermal expansion coefficient of the ceramic more stable and better matched with the selected metal, thereby reducing the risk of thermal stress generation from the source. In addition, the high-purity dense surface provides a uniform and defect-free ideal substrate for subsequent plasma etching activation and magnetron sputtering deposition of titanium transition layers, ensuring the uniformity and reliability of the final sealing interface in the microstructure, thereby effectively solving the problems of insulation, stress and interface control.

[0032] In the embodiments of this application, the power of argon plasma etching activation is 150W-200W, and the etching time is 10-20 minutes.

[0033] In step two, the sealing surface of the Kovar alloy cylindrical flange is pickled to remove the oxide layer, and then cleaned and dried to obtain the metal sealing component.

[0034] Pickling refers to immersing Kovar alloy flanges in a dilute hydrochloric acid solution, using the etching and dissolving effect of the acid to thoroughly remove the oxide layer and inorganic contaminants from their sealing surface.

[0035] It is understood that, in this embodiment of the application, the acid pickling of the Kovar alloy flange sealing surface removes the oxide layer and attached impurities that naturally form on its surface during processing and storage, resulting in a clean and activated pure metal surface. This fundamentally eliminates the hidden dangers of poor brazing filler metal wettability, weak interfacial bonding force, and uneven conductivity caused by the presence of the oxide layer, ensuring that the active brazing filler metal can achieve a full, uniform, and firm metallurgical bond with the metal matrix during subsequent brazing. This lays a crucial foundation for obtaining a final sealing interface with high airtightness, high mechanical strength, and excellent electrical continuity.

[0036] In the embodiments of this application, the pickling solution used is dilute hydrochloric acid with a mass fraction of 6%-10%, and the soaking time is 15-25 minutes.

[0037] It is understood that the embodiments of this application provide a precise and controllable process window for the pretreatment of metal sealing surfaces by clearly defining the pickling solution as dilute hydrochloric acid with a mass fraction of 6%-10% and controlling the soaking time to 15-25 minutes; this ensures thorough and uniform dissolution and removal of the surface oxide layer, while avoiding problems such as excessive corrosion of the base metal, hydrogen embrittlement, and deterioration of surface roughness that may be caused by excessive acid concentration or prolonged soaking. Thus, while obtaining a highly clean and activated surface, the mechanical properties and dimensional accuracy of the metal parts themselves are well maintained.

[0038] In step three, Ag-Cu-Ti active solder sheets are prepared.

[0039] It is understood that the embodiments of this application provide a key intermediate material with precise composition and controllable morphology for achieving high-reliability sealing by pre-preparing a specific active brazing filler metal sheet with silver, copper and titanium composition. This ensures the uniform distribution and accurate content of the active element titanium in the brazing filler metal, allowing it to fully react with the titanium transition layer on the ceramic surface and the metal matrix in a controllable interface during the brazing process, forming a strong and tough metallurgical bond. At the same time, the sheet shape facilitates precise control of the amount and distribution of brazing filler metal, avoiding defects such as uneven filling and porosity that may be caused by traditional paste or wire brazing filler metals. This directly ensures the uniformity, density and mechanical strength of the final sealed joint at the microscale.

[0040] In the embodiments of this application, the preparation process of Ag-Cu-Ti active solder sheet includes: weighing raw materials of 70.5%-73.5% silver, 25.1%-27.3% copper, and 1.4%-2.2% titanium by mass percentage; melting the raw materials evenly and processing them into thin sheets with a thickness of 0.05mm-0.15mm; and cutting the thin sheets into shapes that match the sealing surfaces of ceramic parts and metal sealing parts.

[0041] It is understood that, by precisely defining the brazing filler metal composition as 70.5%-73.5% silver, 25.1%-27.3% copper, and 1.4%-2.2% titanium, this embodiment of the application establishes an alloy system that achieves optimal interfacial reaction and comprehensive performance. This composition ratio ensures that the brazing filler metal has a suitable melting point, fluidity, and sufficient active titanium content, thereby fully wetting the ceramic and metal during the joining process while avoiding the formation of excessive brittle phases due to excessive titanium. By processing the brazing filler metal into thin sheets with a thickness of 0.05mm-0.15mm, precise control of the amount of brazing filler metal used and gap filling is achieved, ensuring the uniformity and density of the sealing interface. Further cutting it into a shape that matches the sealing surface ensures accurate positioning and complete coverage of the brazing filler metal during assembly, avoiding uneven flow or local missing parts of the brazing filler metal. Thus, from composition and morphology to assembly, the reliability and consistency of the sealing joint performance are comprehensively guaranteed.

[0042] In step four, the sealing surfaces of the metal sealing component, the Ag-Cu-Ti active solder sheet, and the ceramic component with the titanium transition layer are aligned and assembled in sequence to form a pre-assembled assembly.

[0043] It is understood that, in this embodiment of the application, by sequentially aligning and assembling the metal sealing component, the active brazing filler metal sheet, and the ceramic component with the titanium transition layer to form a pre-assembled component, all components to be connected have obtained precise spatial positioning and relative relationship before brazing. This key step completely eliminates the problems of misalignment, tilting, or uneven gaps that may occur when components are placed independently in the furnace in traditional processes. This ensures that the brazing filler metal can be uniformly filled and the interface reaction is complete and consistent during the subsequent brazing process, thus guaranteeing the high uniformity and structural symmetry of the sealing joint in terms of geometry, mechanical distribution, and electric field distribution.

[0044] In step five, the pre-assembled component is placed in a vacuum brazing furnace, an axial preload is applied to it, and it is heated in a vacuum environment until the brazing filler melts and held at that temperature to complete the sealing. Then, the cooling is controlled to form a sealed component with an airtight brazed joint.

[0045] Among them, airtight brazed joints refer to dense metallurgical connection structures formed by vacuum brazing that can completely prevent gas penetration.

[0046] It is understood that, in this embodiment of the application, by placing the pre-assembled components in a vacuum brazing furnace and applying axial preload, the brazing filler metal is ensured to fully fill and tightly adhere to all interfaces to be joined during the melting process, eliminating any residual gas and pores. Heating the brazing filler metal to melt in a vacuum environment and holding it at that temperature prevents oxidation of the joint area at high temperatures and ensures that the interfacial reaction between the active element titanium and the ceramic and metal is fully and uniformly carried out, thereby forming a dense and strongly bonded metallurgical joint. Subsequently, the cooling process is controlled to effectively constrain the solidification shrinkage and stress distribution in the joint area, avoiding cracks or deformation caused by sudden cooling.

[0047] In this embodiment of the application, the vacuum level of the vacuum environment is lower than... .

[0048] It is understood that the brazing vacuum level in this application embodiment is strictly controlled to be below [a certain level]. This creates a pure environment free of oxygen and with extremely low impurity content. It prevents high-temperature oxidation at the interface and ensures that the molten solder can effectively expel adsorbed gases, thereby eliminating the formation of bubbles and pores.

[0049] In the embodiments of this application, the axial preload is 0.2MPa-0.4MPa.

[0050] Among them, axial preload refers to the constant pressure applied to the pre-assembled assembly along the axial direction of the ceramic part during the vacuum brazing process.

[0051] It is understood that, by applying an axial preload of 0.2MPa-0.4MPa, the brazing filler metal is fully circulated and tightly filled with all micro-gaps when it melts, effectively eliminating any residual gas and pores at the interface; at the same time, it ensures that the ceramic, titanium layer, brazing filler metal and metal remain in close contact at high temperature, making the interface reaction more complete and uniform, thereby improving the density, bonding strength and airtightness of the brazed joint.

[0052] In this embodiment of the application, the temperature at which the brazing filler metal melts is 810℃-830℃, and the holding time is 2-5 minutes.

[0053] It is understood that the brazing temperature in this application embodiment is limited to 810℃-830℃ and the holding time is limited to 2-5 minutes. The temperature range of 810℃-830℃ is sufficient to fully melt the brazing filler metal and maintain good fluidity, while avoiding thermal damage to the ceramic and metal matrix or excessive diffusion of the titanium transition layer due to excessive temperature. The holding time window of 2-5 minutes ensures that the molten brazing filler metal can uniformly wet and fully fill the interface gaps, while allowing the active element titanium to undergo a moderate and controllable interface reaction with the ceramic and metal, generating an appropriate amount and uniformly distributed tough bonding phase. Thus, without generating an excessive amount of brittle phase, a high-strength and high-airtightness metallurgical bond is achieved, ensuring the best comprehensive performance and process stability of the joint.

[0054] In step six, the sealing component with the hermetically sealed brazed joint is annealed to obtain the finished sealing assembly.

[0055] It is understood that the embodiments of this application, by annealing the sealing component with the formed hermetic brazed joint, effectively eliminate the residual thermal stress accumulated at the ceramic-metal interface and inside the material during the rapid cooling process of brazing, significantly improving the dimensional stability and fatigue resistance of the sealing component under temperature cycling; at the same time, optimizing the microstructure of the interface region promotes a more uniform distribution of the metallurgical bonding phase, thereby further enhancing the reliability of its long-term use while ensuring the high hermeticity and high strength of the joint, enabling the finished sealing component to stably adapt to the complex and harsh working environment of high pressure, high temperature and thermal shock inside the neutron tube.

[0056] In this embodiment of the application, the annealing temperature is 450℃-550℃ and the holding time is 100-140 minutes.

[0057] It is understood that the annealing temperature set at 450℃-550℃ and the holding time controlled at 100-140 minutes in this embodiment of the application can fully promote atomic diffusion and dislocation reorganization inside the material, thereby effectively eliminating the residual stress generated by brazing. At the same time, the combination of 450℃-550℃ temperature and 100-140 minutes avoids the possibility of excessive growth of brittle phases or performance degradation at the interface due to excessive temperature or time. This ensures that while optimizing the microstructure and improving toughness, the high strength and high airtightness of the brazed joint are fully maintained, so that the finished component has excellent long-term thermal stability and fatigue resistance.

[0058] According to the embodiments of this application, a high-performance insulating ceramic sealing method for neutron tubes is proposed. By selecting high-purity alumina ceramic with a purity of not less than 99.5% as the insulating body, the intrinsic dielectric strength of the material is fundamentally improved. Simultaneously, Kovar alloy with a matching coefficient of thermal expansion is used as the metal sealing component, and a gradient buffer interface is constructed by combining it with a titanium transition layer deposited by magnetron sputtering, effectively alleviating stress concentration caused by differences in thermal expansion. Furthermore, interface activation treatment combining plasma etching and titanium layer deposition, the use of a precisely proportioned silver-copper-titanium active solder, and a precision brazing process applying axial preload under high vacuum conditions synergistically ensure the high cleanliness, strong bonding force, and dense, defect-free sealing interface. The resulting sealing assembly exhibits excellent performance, with its withstand voltage rating stably increased to over 120 kV, significantly enhanced shear strength, and maintaining structural integrity and performance stability during stringent temperature cycling tests. This solves the problems of low dielectric strength, large differences in coefficients of thermal expansion, and difficulty in controlling interface quality in existing technologies.

[0059] The following will illustrate a high-performance insulating ceramic sealing method for neutron tubes through specific embodiments, including:

[0060] Example 1

[0061] This application proposes a high-performance insulating ceramic sealing method for neutron tubes, comprising the following steps:

[0062] Step 1: The sealing surface of the cylindrical high-purity alumina ceramic part is subjected to ultrasonic cleaning with organic solvent and argon plasma etching activation treatment in sequence. A titanium transition layer is deposited on the activated sealing surface by magnetron sputtering to obtain a ceramic part with a titanium transition layer.

[0063] Among them, the purity of high-purity alumina ceramic parts is not less than 99.5%;

[0064] It should be noted that the power of argon plasma etching activation is 150W, and the etching time is 10 minutes.

[0065] Step 2: Pickle the sealing surface of the Kovar alloy cylindrical flange to remove the oxide layer, and then clean and dry it to obtain the metal sealing part;

[0066] The pickling process uses a 6% (w / w) dilute hydrochloric acid solution and involves soaking for 15 minutes.

[0067] Step 3: Prepare Ag-Cu-Ti active solder sheets;

[0068] The preparation process of Ag-Cu-Ti active solder sheet includes: weighing 70.5% silver, 27.3% copper, and 2.2% titanium by mass percentage; melting the raw materials evenly and processing them into a sheet with a thickness of 0.05 mm; and cutting the sheet into a shape that matches the sealing surface of the ceramic part and the metal sealing part.

[0069] Step 4: Align and assemble the metal sealing components, Ag-Cu-Ti active solder sheets, and the sealing surfaces of the ceramic components with titanium transition layers in sequence to form a pre-assembled assembly.

[0070] Step 5: Place the pre-assembled component in a vacuum brazing furnace, apply axial preload to it, heat it in a vacuum environment until the brazing filler melts and hold it at that temperature to complete the sealing. Then control the cooling to form a sealed component with an airtight brazed joint.

[0071] Among them, the vacuum level of the vacuum environment is lower than ;

[0072] It should be noted that the axial preload is 0.2 MPa;

[0073] The temperature for heating until the brazing filler metal melts and then holding at that temperature for sealing is 810℃, and the holding time is 2 minutes.

[0074] Step 6: Anneal the sealing component with the airtight brazed joint to obtain the finished sealing assembly.

[0075] The annealing temperature was 450℃, and the holding time was 100 minutes.

[0076] Example 2

[0077] This application proposes a high-performance insulating ceramic sealing method for neutron tubes, comprising the following steps:

[0078] Step 1: The sealing surface of the cylindrical high-purity alumina ceramic part is subjected to ultrasonic cleaning with organic solvent and argon plasma etching activation treatment in sequence. A titanium transition layer is deposited on the activated sealing surface by magnetron sputtering to obtain a ceramic part with a titanium transition layer.

[0079] Among them, the purity of high-purity alumina ceramic parts is not less than 99.5%;

[0080] It should be noted that the power of argon plasma etching activation was 162.5W, and the etching time was 12.5 minutes.

[0081] Step 2: Pickle the sealing surface of the Kovar alloy cylindrical flange to remove the oxide layer, and then clean and dry it to obtain the metal sealing part;

[0082] The pickling solution used was a 7% (w / w) dilute hydrochloric acid solution, and the soaking time was 17.5 minutes.

[0083] Step 3: Prepare Ag-Cu-Ti active solder sheets;

[0084] The preparation process of Ag-Cu-Ti active solder sheet includes: weighing 71.25% silver, 26.75% copper, and 2% titanium by mass percentage; melting the raw materials evenly and processing them into a sheet with a thickness of 0.075 mm; and cutting the sheet into a shape that matches the sealing surface of the ceramic part and the metal sealing part.

[0085] Step 4: Align and assemble the metal sealing components, Ag-Cu-Ti active solder sheets, and the sealing surfaces of the ceramic components with titanium transition layers in sequence to form a pre-assembled assembly.

[0086] Step 5: Place the pre-assembled component in a vacuum brazing furnace, apply axial preload to it, heat it in a vacuum environment until the brazing filler melts and hold it at that temperature to complete the sealing. Then control the cooling to form a sealed component with an airtight brazed joint.

[0087] Among them, the vacuum level of the vacuum environment is lower than ;

[0088] It should be noted that the axial preload is 0.25 MPa;

[0089] The temperature for heating to melt the brazing filler metal and holding it at that temperature for sealing is 815℃, and the holding time is 2.75 minutes.

[0090] Step 6: Anneal the sealing component with the airtight brazed joint to obtain the finished sealing assembly.

[0091] The annealing temperature was 475℃, and the holding time was 110 minutes.

[0092] Example 3

[0093] This application proposes a high-performance insulating ceramic sealing method for neutron tubes, comprising the following steps:

[0094] Step 1: The sealing surface of the cylindrical high-purity alumina ceramic part is subjected to ultrasonic cleaning with organic solvent and argon plasma etching activation treatment in sequence. A titanium transition layer is deposited on the activated sealing surface by magnetron sputtering to obtain a ceramic part with a titanium transition layer.

[0095] Among them, the purity of high-purity alumina ceramic parts is not less than 99.5%;

[0096] It should be noted that the power of argon plasma etching activation is 175W, and the etching time is 15 minutes.

[0097] Step 2: Pickle the sealing surface of the Kovar alloy cylindrical flange to remove the oxide layer, and then clean and dry it to obtain the metal sealing part;

[0098] The pickling solution used was 8% dilute hydrochloric acid, and the soaking time was 20 minutes.

[0099] Step 3: Prepare Ag-Cu-Ti active solder sheets;

[0100] The preparation process of Ag-Cu-Ti active solder sheet includes: weighing 72% silver, 26.2% copper, and 1.8% titanium by mass percentage; melting the raw materials evenly and processing them into a sheet with a thickness of 0.1 mm; and cutting the sheet into a shape that matches the sealing surface of the ceramic part and the metal sealing part.

[0101] Step 4: Align and assemble the metal sealing components, Ag-Cu-Ti active solder sheets, and the sealing surfaces of the ceramic components with titanium transition layers in sequence to form a pre-assembled assembly.

[0102] Step 5: Place the pre-assembled component in a vacuum brazing furnace, apply axial preload to it, heat it in a vacuum environment until the brazing filler melts and hold it at that temperature to complete the sealing. Then control the cooling to form a sealed component with an airtight brazed joint.

[0103] Among them, the vacuum level of the vacuum environment is lower than ;

[0104] It should be noted that the axial preload is 0.3 MPa;

[0105] The temperature for heating until the brazing filler metal melts and then holding at that temperature for sealing is 820℃, and the holding time is 3.5 minutes.

[0106] Step 6: Anneal the sealing component with the airtight brazed joint to obtain the finished sealing assembly.

[0107] The annealing process involves a temperature of 500℃ and a holding time of 120 minutes.

[0108] Example 4

[0109] This application proposes a high-performance insulating ceramic sealing method for neutron tubes, comprising the following steps:

[0110] Step 1: The sealing surface of the cylindrical high-purity alumina ceramic part is subjected to ultrasonic cleaning with organic solvent and argon plasma etching activation treatment in sequence. A titanium transition layer is deposited on the activated sealing surface by magnetron sputtering to obtain a ceramic part with a titanium transition layer.

[0111] Among them, the purity of high-purity alumina ceramic parts is not less than 99.5%;

[0112] It should be noted that the power of argon plasma etching activation was 187.5W, and the etching time was 17.5 minutes.

[0113] Step 2: Pickle the sealing surface of the Kovar alloy cylindrical flange to remove the oxide layer, and then clean and dry it to obtain the metal sealing part;

[0114] The pickling solution used was a 9% dilute hydrochloric acid solution, and the soaking time was 22.5 minutes.

[0115] Step 3: Prepare Ag-Cu-Ti active solder sheets;

[0116] The preparation process of Ag-Cu-Ti active solder sheet includes: weighing 72.75% silver, 25.65% copper, and 1.6% titanium by mass percentage; melting the raw materials evenly and processing them into a sheet with a thickness of 0.125 mm; and cutting the sheet into a shape that matches the sealing surface of the ceramic part and the metal sealing part.

[0117] Step 4: Align and assemble the metal sealing components, Ag-Cu-Ti active solder sheets, and the sealing surfaces of the ceramic components with titanium transition layers in sequence to form a pre-assembled assembly.

[0118] Step 5: Place the pre-assembled component in a vacuum brazing furnace, apply axial preload to it, heat it in a vacuum environment until the brazing filler melts and hold it at that temperature to complete the sealing. Then control the cooling to form a sealed component with an airtight brazed joint.

[0119] Among them, the vacuum level of the vacuum environment is lower than ;

[0120] It should be noted that the axial preload is 0.35 MPa;

[0121] The temperature for heating to melt the brazing filler metal and holding it at that temperature for sealing is 825℃, and the holding time is 4.25 minutes.

[0122] Step 6: Anneal the sealing component with the airtight brazed joint to obtain the finished sealing assembly.

[0123] The annealing temperature was 525℃, and the holding time was 130 minutes.

[0124] Example 5

[0125] This application proposes a high-performance insulating ceramic sealing method for neutron tubes, comprising the following steps:

[0126] Step 1: The sealing surface of the cylindrical high-purity alumina ceramic part is subjected to ultrasonic cleaning with organic solvent and argon plasma etching activation treatment in sequence. A titanium transition layer is deposited on the activated sealing surface by magnetron sputtering to obtain a ceramic part with a titanium transition layer.

[0127] Among them, the purity of high-purity alumina ceramic parts is not less than 99.5%;

[0128] It should be noted that the power of argon plasma etching activation is 200W, and the etching time is 20 minutes.

[0129] Step 2: Pickle the sealing surface of the Kovar alloy cylindrical flange to remove the oxide layer, and then clean and dry it to obtain the metal sealing part;

[0130] The pickling solution used was a 10% hydrochloric acid solution, and the soaking time was 25 minutes.

[0131] Step 3: Prepare Ag-Cu-Ti active solder sheets;

[0132] The preparation process of Ag-Cu-Ti active solder sheet includes: weighing 73.5% silver, 25.1% copper, and 1.4% titanium by mass percentage; melting the raw materials evenly and processing them into a sheet with a thickness of 0.15 mm; and cutting the sheet into a shape that matches the sealing surface of the ceramic part and the metal sealing part.

[0133] Step 4: Align and assemble the metal sealing components, Ag-Cu-Ti active solder sheets, and the sealing surfaces of the ceramic components with titanium transition layers in sequence to form a pre-assembled assembly.

[0134] Step 5: Place the pre-assembled component in a vacuum brazing furnace, apply axial preload to it, heat it in a vacuum environment until the brazing filler melts and hold it at that temperature to complete the sealing. Then control the cooling to form a sealed component with an airtight brazed joint.

[0135] Among them, the vacuum level of the vacuum environment is lower than ;

[0136] It should be noted that the axial preload is 0.4 MPa;

[0137] The temperature for heating until the brazing filler metal melts and then holding at that temperature for sealing is 830℃, and the holding time is 5 minutes.

[0138] Step 6: Anneal the sealing component with the airtight brazed joint to obtain the finished sealing assembly.

[0139] The annealing temperature was 550℃, and the holding time was 140 minutes.

[0140] Comparative Example 1

[0141] This application proposes a high-performance insulating ceramic sealing method for neutron tubes, comprising the following steps:

[0142] Step 1: The sealing surface of the cylindrical high-purity alumina ceramic part is subjected to ultrasonic cleaning with organic solvent and argon plasma etching activation treatment in sequence. A titanium transition layer is deposited on the activated sealing surface by magnetron sputtering to obtain a ceramic part with a titanium transition layer.

[0143] Among them, the purity of high-purity alumina ceramic parts is between 98.5%;

[0144] It should be noted that the power of argon plasma etching activation is 150W, and the etching time is 10 minutes.

[0145] Step 2: Pickle the sealing surface of the Kovar alloy cylindrical flange to remove the oxide layer, and then clean and dry it to obtain the metal sealing part;

[0146] The pickling process uses a 6% (w / w) dilute hydrochloric acid solution and involves soaking for 15 minutes.

[0147] Step 3: Prepare Ag-Cu-Ti active solder sheets;

[0148] The preparation process of Ag-Cu-Ti active solder sheet includes: weighing 70.5% silver, 27.3% copper, and 2.2% titanium by mass percentage; melting the raw materials evenly and processing them into a sheet with a thickness of 0.05 mm; and cutting the sheet into a shape that matches the sealing surface of the ceramic part and the metal sealing part.

[0149] Step 4: Align and assemble the metal sealing components, Ag-Cu-Ti active solder sheets, and the sealing surfaces of the ceramic components with titanium transition layers in sequence to form a pre-assembled assembly.

[0150] Step 5: Place the pre-assembled component in a vacuum brazing furnace, apply axial preload to it, heat it in a vacuum environment until the brazing filler melts and hold it at that temperature to complete the sealing. Then control the cooling to form a sealed component with an airtight brazed joint.

[0151] Among them, the vacuum level of the vacuum environment is lower than ;

[0152] It should be noted that the axial preload is 0.2 MPa;

[0153] The temperature for heating until the brazing filler metal melts and then holding at that temperature for sealing is 810℃, and the holding time is 2 minutes.

[0154] Step 6: Anneal the sealing component with the airtight brazed joint to obtain the finished sealing assembly.

[0155] The annealing temperature was 450℃, and the holding time was 100 minutes.

[0156] Comparative Example 2

[0157] This application proposes a high-performance insulating ceramic sealing method for neutron tubes, comprising the following steps:

[0158] Step 1: The sealing surface of the cylindrical high-purity alumina ceramic part is ultrasonically cleaned with organic solvent in sequence, and a titanium transition layer is deposited on the cleaned sealing surface by magnetron sputtering to obtain a ceramic part with a titanium transition layer.

[0159] Among them, the purity of high-purity alumina ceramic parts is not less than 99.5%;

[0160] Step 2: Pickle the sealing surface of the Kovar alloy cylindrical flange to remove the oxide layer, and then clean and dry it to obtain the metal sealing part;

[0161] The pickling process uses a 6% (w / w) dilute hydrochloric acid solution and involves soaking for 15 minutes.

[0162] Step 3: Prepare Ag-Cu-Ti active solder sheets;

[0163] The preparation process of Ag-Cu-Ti active solder sheet includes: weighing 70.5% silver, 27.3% copper, and 2.2% titanium by mass percentage; melting the raw materials evenly and processing them into a sheet with a thickness of 0.05 mm; and cutting the sheet into a shape that matches the sealing surface of the ceramic part and the metal sealing part.

[0164] Step 4: Align and assemble the metal sealing components, Ag-Cu-Ti active solder sheets, and the sealing surfaces of the ceramic components with titanium transition layers in sequence to form a pre-assembled assembly.

[0165] Step 5: Place the pre-assembled component in a vacuum brazing furnace, apply axial preload to it, heat it in a vacuum environment until the brazing filler melts and hold it at that temperature to complete the sealing. Then control the cooling to form a sealed component with an airtight brazed joint.

[0166] Among them, the vacuum level of the vacuum environment is lower than ;

[0167] It should be noted that the axial preload is 0.2 MPa;

[0168] The temperature for heating until the brazing filler metal melts and then holding at that temperature for sealing is 810℃, and the holding time is 2 minutes.

[0169] Step 6: Anneal the sealing component with the airtight brazed joint to obtain the finished sealing assembly.

[0170] The annealing temperature was 450℃, and the holding time was 100 minutes.

[0171] Comparative Example 3

[0172] This application proposes a conventional high-performance insulating ceramic sealing method for neutron tubes, specifically: using a cylindrical alumina ceramic part with a purity of 95%, and cleaning its sealing surface only with conventional organic solvents; immersing the sealing surface of the Kovar alloy flange in a 10% (w / w) dilute hydrochloric acid solution for 10 minutes; assembling using commercially available general-purpose Ag-Cu-Ti solder paste, and under a vacuum degree of approximately... Under conditions of no external axial pressure, brazing is completed by holding at 850℃ for 10 minutes to obtain the finished sealing assembly.

[0173] Performance testing

[0174] 1. Pressure resistance rating test

[0175] Test equipment: DC high voltage generator, vacuum test chamber, equalizing ring electrode, leakage current monitor, safety interlock control system, ultrasonic flaw detector, optical microscope, standard voltage divider resistor, standard current source.

[0176] Test environment: The test is conducted in a vacuum test chamber, where the vacuum level is maintained at no higher than [missing value]. To simulate actual working conditions, the ambient temperature is controlled at (23±2)℃ and the relative humidity is not higher than 40%.

[0177] Test Step 1: Randomly select finished sealing components from the batch to be tested, clean their surfaces with anhydrous ethanol, and then use an ultrasonic flaw detector and an optical microscope to perform non-destructive testing in sequence to eliminate defective samples. Subsequently, fix the qualified samples vertically on the insulating support in the test chamber to ensure that their axis is completely aligned with the center of the high voltage electrode (deviation ≤ 0.5 mm).

[0178] Test Step Two: Install the size-matched equalizing ring electrodes onto the metal parts at both ends of the sample and reliably connect the high voltage to the ground wire. Use a dedicated grounding cable with a cross-sectional area ≥2.5mm² for the grounding terminal. Check all electrical connections to ensure they are secure and reliable. Then seal the cavity and evacuate it to a vacuum level not exceeding [missing value]. Maintain pressure for 30 minutes, and activate the safety interlock system after confirming stability.

[0179] Test Step 3: Preheat the test equipment for 15 minutes and calibrate it using standard components. Calibrate the DC high-voltage generator (0-150kV, error ≤ ±1%) using a standard voltage divider resistor and the leakage current monitor using a standard current source. Set the initial voltage to 0kV and employ a segmented voltage ramp-up program: 1kV / s for the 0-80kV range, 0.5kV / s for the 80-120kV range, and 0.2kV / s for above 120kV. Stabilize each voltage level for 60 seconds. Simultaneously, set the leakage current alarm threshold to 1μA and enable the current surge monitoring function.

[0180] Test Step 4: Start the automatic voltage boosting program. Record the leakage current value every 5kV increase, and monitor the vacuum fluctuation and discharge phenomenon in the test chamber throughout the process. The voltage boosting continues until the leakage current exceeds the standard or changes abruptly, visible breakdown occurs, or the voltage reaches 150kV and can be maintained for 60 minutes while the current meets the standard throughout the test.

[0181] Test Step 5: Record the final breakdown voltage or through voltage, and mark the specific location and type of breakdown (ceramic body / sealing interface / equalizing ring edge), and take high-resolution photos. After the test, perform voltage zeroing and residual charge discharge, then slowly fill the chamber with dry nitrogen gas to atmospheric pressure, and finally remove the sample to check its appearance.

[0182] Test Step Six: For each batch, at least five valid test data points must be obtained that meet the requirements of correct breakdown location, error-free operation, and stable vacuum. Invalid data can be retested up to three times. If this is still insufficient, the batch is deemed to require re-inspection. Calculate the average withstand voltage rating. If a single valid data point deviates from the average by more than 10%, the sample and records must be verified. The final report must include complete test curves, key data, photographs, and corresponding example numbers, along with the equipment calibration certificate.

[0183] 2. Thermal stress test

[0184] Testing equipment: high and low temperature test chamber, helium mass spectrometer leak detector, metallographic microscope, anhydrous ethanol, lint-free cloth, and non-metallic fixtures for samples.

[0185] Test environment: The test was conducted in a high and low temperature test chamber filled with high-purity nitrogen (purity ≥99.999%) as a protective atmosphere to inhibit oxidation of the sample surface. The ambient temperature outside the test chamber was (23±2)℃, and the relative humidity was ≤40%.

[0186] Test Step 1: Randomly select finished sealing components from the batch to be tested, and clean their surfaces using anhydrous ethanol and a lint-free cloth. After cleaning, use a helium mass spectrometer to measure and record the initial leakage rate of each sample, ensuring it is below [a certain value]. Qualified samples should be placed in a dry environment for later use.

[0187] Test Step Two: Use a special clamp to fix the sample inside the high and low temperature test chamber, ensuring that the sample is suspended, unobstructed, securely installed, and that the clamp does not introduce additional mechanical stress. Close the chamber door, fill with nitrogen and purge several times before sealing.

[0188] Test Step 3: Preheat the test chamber. Set the temperature cycling program: cool down to -50℃ at a rate of 5℃ / min, hold for 30 minutes; then heat up to 150℃ at a rate of 5℃ / min, hold for 30 minutes; this is one complete cycle. Run 50 cycles continuously.

[0189] Test Step 4: Start the program and run it automatically throughout the entire process. Record the temperature-time curve through the equipment monitoring system to confirm that the program execution meets the settings.

[0190] Test Step 5: After the cycle is complete, allow the sample to cool naturally to room temperature inside the chamber. Remove the sample and first use a helium mass spectrometer to measure its final leakage rate. Then, carefully observe the ceramic body, ceramic-metal interface, and metal edge under a metallographic microscope (100×) to check for cracks, delamination, or other defects, and take photos for record-keeping.

[0191] Test Step Six: At least five valid test data points must be obtained for the same batch. Valid data (i.e., the "pass" criterion) must simultaneously meet the following conditions: 1. No cracks or delamination were found under a microscope; 2. Final leakage rate. The leakage rate should not exceed one order of magnitude from the initial value. Failure to meet any of these conditions constitutes a failure. The final report must include initial and final leakage rate data, microscopic images of typical areas, temperature cycling curves, and the corresponding example numbers.

[0192] Shear strength test

[0193] Testing equipment: electronic universal testing machine, standard shear specimen fixture, vernier caliper, metallographic microscope, ultrasonic flaw detector, anhydrous ethanol, and lint-free cloth.

[0194] Test environment: ambient temperature (23±2)℃, relative humidity ≤40%, test area free from vibration interference.

[0195] Test Step 1: Using the exact same materials and processes as the finished sealing assembly, prepare a dedicated standard shear test specimen (e.g., a sleeve-type structure with a clear, flat weld surface). Randomly select specimens from the same batch, clean them, and then screen them using ultrasonic testing to exclude specimens with internal defects.

[0196] Test Step Two: Using vernier calipers, accurately measure the outer and inner diameters of the annular welded surface area of ​​each specimen. Measure each dimension three times and take the average value, with the reading accurate to 0.02 mm. Calculate and record the area of ​​the annular welded surface based on the measured outer and inner diameter values. Then, correctly mount the specimen onto the special fixture of the testing machine, ensuring that the direction of the shear force is parallel to the annular welded surface and that the force is uniform.

[0197] Test Step 3: Start the testing machine, preheat it, and zero it. Set the loading rate to 1.0 mm / min.

[0198] Test Step 4: Start the test program and apply the load continuously and at a constant speed until the specimen fails under shear conditions. The testing machine automatically records the complete load-displacement curve and the maximum failure load.

[0199] Test Step 5: Calculate Shear Strength. Observe the morphology and location of the fracture surface using a metallographic microscope, and determine and record the fracture mode (e.g., interfacial fracture, ceramic cohesive fracture, mixed fracture).

[0200] Test Step Six: At least five valid test data points must be obtained for the same process batch. Valid data criteria are: fracture occurs at the weld interface or within the ceramic matrix (not at the clamping point), and the testing process is normal. Calculate the average shear strength and standard deviation of the valid data. The final report must include: the load-displacement curve, maximum load, measured area, calculated strength, fracture mode photograph, and corresponding example number for each specimen.

[0201] 4. Surface roughness test

[0202] Test equipment: stylus surface roughness tester (vertical resolution ≤10nm), standard calibration block (Ra nominal value covers the range of 0.05μm-0.2μm), anhydrous ethanol, lint-free cloth, special V-block or magnetic base (for fixing cylindrical samples).

[0203] Test environment: The test was conducted in a clean measurement room at a normal temperature of (23±2)℃ with a relative humidity of ≤40%, avoiding vibration and airflow interference.

[0204] Test Step 1: Randomly select finished sealing components from the batch to be tested, and carefully clean the ceramic and metal outer surfaces to be tested in one direction using anhydrous ethanol and a lint-free cloth to ensure that there are no residual stains or fibers.

[0205] Test Step Two (Equipment Calibration and Setup): Perform multi-point calibration of the roughness meter using a standard calibration block. Based on the characteristics of the surface being tested, set the sampling length to 0.8 mm, the evaluation length to 4.0 mm (5 sampling lengths), and the filter type to Gaussian filter.

[0206] Test Step 3: Securely fix the cleaned sample on the V-block or magnetic base. Move the roughness tester probe to the test area, carefully lower the probe, ensuring it is in perpendicular contact with the test surface and that the static force meets the instrument specifications.

[0207] Test Step 4: Start the measurement, set the probe sliding speed to 1 mm / s, and let the probe slide at a constant speed along the axial direction of the sample. The instrument will automatically collect the profile data and calculate the Ra value. Clean the probe tip with anhydrous ethanol before and after each measurement.

[0208] Test Step 5: On the smooth surface of the ceramic section, select three different generatrix positions at approximately 120° intervals along the circumference and record the Ra value at each position. Take the arithmetic mean of the three measurements as the final surface roughness Ra value of the sample.

[0209] Test Step Six: At least 5 valid data samples need to be obtained for the same batch. The criteria for valid data are as follows: There are no abnormal mutations in the single measurement curve, and the test operations comply with the specifications (no omissions in the cleaning, calibration, and needle alignment processes). After the acquisition of valid data is completed, the qualification is determined according to the product requirements: The sample Ra average value ≤ 0.1μm is considered qualified. The final report should include the Ra values of each point, the average value, the typical profile curve diagram, and the corresponding example number for each sample.

[0210] The following are the performance test results of Examples 1 - 5 and Comparative Examples 1 - 3. The performance test results are shown in Table 1 as follows:

[0211] Table 1: Performance Test Results of Examples and Comparative Examples

[0212]

[0213] As can be seen from Table 1, taking Example 1 as the process benchmark with relatively conservative parameter settings, its withstand voltage level, shear strength, sealing performance, and surface roughness are all at an acceptable medium level, providing a comparison basis for subsequent optimization; on the basis of Example 1, Example 2 moderately adjusts parameters such as plasma power, pickling time, and filler metal composition and makes them more balanced, enhancing the interfacial activation effect and filler metal fluidity. Therefore, the withstand voltage level and shear strength are slightly improved, and the leakage rate is further reduced, reflecting the positive impact of refined adjustment of process parameters on performance; Example 3 centrally embodies the core process innovation and optimization concept. This scheme adopts the intermediate optimized values of various key parameters, such as a moderate plasma activation intensity of 175W, a balanced titanium content of 1.8% in the filler metal, an optimal brazing temperature of 820°C, and an axial preloading force of 0.3MPa. The synergistic effect of these parameters ensures that the ceramic surface reaches the best active state after argon plasma etching in a high-vacuum environment. Subsequently, the deposited titanium transition layer can firmly bond with it. At the same time, the silver-copper-titanium active filler metal with precise composition fully melts and flows at an appropriate temperature and pressure to complete the interfacial metallurgical reaction. Finally, through a reasonable annealing process, the residual stress is effectively released. Therefore, Example 3 achieves the optimal comprehensive performance among all examples, including the highest withstand voltage level of 145kV, excellent airtightness, that is, the leakage rate is as low as The highest shear strength of 98 MPa and the smoothest surface quality Ra0.07 μm fully demonstrate the superiority of the constructed high-purity ceramic-titanium transition layer-active brazing-precision hot pressing technology route. Examples 4 and 5 explored the upper limit of the parameter range. Example 4 adopted a higher process intensity, such as plasma power of 187.5 W and brazing temperature of 825 °C, while Example 5 used a more extreme parameter combination, such as plasma power of 200 W and brazing filler titanium content of 1.4%. Although the performance of both examples is still significantly better than that of Example 1 and all comparative examples, demonstrating a wide process window, the extreme nature of some parameters may affect the interfacial reaction. The comparison examples present minor challenges in terms of uniformity and residual stress control, resulting in slightly inferior overall performance balance and stability compared to Example 3. The comparative analysis, from the opposite perspective, validates the necessity of each core process element. Comparative Example 1, by reducing ceramic purity to 98.5%, suffers from decreased intrinsic dielectric strength and thermal stability, directly leading to a significant deterioration in the withstand voltage rating of 103kV and shear strength of 72MPa. This highlights the fundamental role of using ultra-high purity alumina ceramic as the insulating matrix. Comparative Example 2 omits the crucial argon plasma etching activation step, resulting in insufficient ceramic surface activity, poor solder wettability, and weakened interfacial bonding, thus increasing the leakage rate. The shear strength decreased to 78 MPa, demonstrating the indispensability of surface activation treatment for obtaining a high-strength, high-tightness interface. Comparative Example 3, using entirely traditional processes such as 95% pure ceramic, no titanium transition layer, no plasma activation, and rough brazing, exhibited performance characteristics including a withstand voltage of 92 kV and a leakage rate... The shear strength of 62MPa is at the lowest level, which fully and profoundly reflects the significant advantages of this invention in synergistically improving the high-voltage insulation, mechanical strength, airtight reliability and long-term thermal stability of the neutron tube insulation sealing assembly, and solves the core pain points of insufficient dielectric strength, thermal stress mismatch and difficulty in interface quality control of traditional ceramic metal sealing technology.

[0214] Secondly, according to an embodiment of this application, a high-performance insulating ceramic sealing device for a neutron tube includes: a cylindrical high-purity alumina ceramic component; a first metal sealing component and a second metal sealing component, made of Kovar alloy, respectively disposed on both sides of the ceramic component along its axial direction; a titanium transition layer covering the sealing surfaces at both ends of the ceramic component; and an active solder layer disposed between the titanium transition layer and the corresponding metal sealing component at both ends of the ceramic component, connected by vacuum brazing; the ceramic component, the titanium transition layer, the active solder layer, and the metal sealing component are vacuum brazed to form an integral hermetically sealed structure.

[0215] It is understood that the high-performance insulating ceramic sealing device provided by this invention, such as Figure 2As shown, 1 is the first Kovar alloy metal sealing component, 2 is the first Ag-Cu-Ti active solder layer, 3 is a high-purity alumina ceramic component, 4 is the second Ag-Cu-Ti active solder layer, and 5 is the second Kovar alloy metal sealing component. Simultaneously, a titanium transition layer deposited by magnetron sputtering is coated on the sealing surfaces at both ends of the ceramic component. This layer, located between the ceramic component and the active solder layers on both sides, is a key functional layer for achieving high-strength interfacial bonding. This structure uses a high-purity alumina ceramic component as the insulating core. Its axial sides are connected to the Kovar alloy metal sealing component via the titanium transition layer and the active solder layer, and finally formed into an integral hermetically sealed structure through vacuum brazing. This structure effectively combines high-insulation ceramic, matching metal materials, a transition layer that enhances bonding, and reliable solder connections, achieving excellent electrical insulation performance, mechanical strength, and hermetically tightness, thereby significantly improving the working stability and service life of the neutron tube under high-pressure environments.

[0216] According to the embodiments of this application, a high-performance insulating ceramic sealing device for neutron tubes is proposed. By selecting high-purity alumina ceramic with a purity of not less than 99.5% as the insulating body, the intrinsic dielectric strength of the material is fundamentally improved. Simultaneously, Kovar alloy with a matching coefficient of thermal expansion is used as the metal sealing component, and a gradient buffer interface is constructed by combining it with a titanium transition layer deposited by magnetron sputtering, effectively alleviating stress concentration caused by differences in thermal expansion. Furthermore, interface activation treatment combining plasma etching and titanium layer deposition, the use of a precisely proportioned silver-copper-titanium active solder, and a precision brazing process applying axial preload in a high-vacuum environment synergistically ensure the high cleanliness, strong bonding force, and dense, defect-free sealing interface. The resulting sealing assembly exhibits excellent performance, with its withstand voltage rating stably increased to over 120 kV, significantly enhanced shear strength, and maintaining structural integrity and performance stability during stringent temperature cycling tests. This solves the problems of low dielectric strength, large differences in coefficients of thermal expansion, and difficulty in controlling interface quality in existing technologies.

[0217] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

[0218] The present application and its embodiments have been described above. This description is not restrictive, and the actual application is not limited thereto. In conclusion, if a person skilled in the art is inspired by this description and designs a similar structure and embodiment without departing from the spirit of this application, such design should fall within the protection scope of this application.

Claims

1. A method for sealing high-performance insulating ceramics for neutron tubes, characterized in that, Includes the following steps: Step 1: The sealing surface of the cylindrical high-purity alumina ceramic part is sequentially subjected to ultrasonic cleaning with organic solvent and argon plasma etching activation treatment. A titanium transition layer is then deposited on the activated sealing surface by magnetron sputtering to obtain a ceramic part with a titanium transition layer. The purity of the high-purity alumina ceramic part is not less than 99.5%. The power of the argon plasma etching activation is 150W-200W, and the etching time is 10-20 minutes. Step 2: Pickle the sealing surface of the Kovar alloy cylindrical flange to remove the oxide layer, and then clean and dry it to obtain the metal sealing part; Step 3: Prepare Ag-Cu-Ti active solder sheets; Step 4: Align and assemble the metal sealing component, the Ag-Cu-Ti active solder sheet, and the sealing surface of the ceramic component with the titanium transition layer in sequence to form a pre-assembled assembly; Step 5: Place the pre-assembled component in a vacuum brazing furnace, apply axial preload to it, heat it in a vacuum environment until the brazing filler melts and hold it at that temperature to complete the sealing. Then control the cooling to form a sealed component with an airtight brazed joint. Step 6: Anneal the sealing component with the airtight brazed joint to obtain the finished sealing assembly.

2. The high-performance insulating ceramic sealing method for neutron tubes according to claim 1, characterized in that, In step two, the pickling solution used is a dilute hydrochloric acid solution with a mass fraction of 6%-10%, and the soaking time is 15-25 minutes.

3. The high-performance insulating ceramic sealing method for neutron tubes according to claim 1, characterized in that, Step three, the preparation process of the Ag-Cu-Ti active solder sheet includes: Weigh out raw materials containing 70.5%-73.5% silver, 25.1%-27.3% copper, and 1.4%-2.2% titanium by mass percentage; After the raw materials are melted and smelted evenly, they are processed into thin sheets with a thickness of 0.05mm-0.15mm. The sheet material is cut into a shape that matches the sealing surface of the ceramic part and the metal sealing part.

4. The high-performance insulating ceramic sealing method for neutron tubes according to claim 1, characterized in that, In step five, the vacuum level of the vacuum environment is less than 5 × 10⁻ 4 Pa.

5. The high-performance insulating ceramic sealing method for neutron tubes according to claim 1, characterized in that, In step five, the axial preload is 0.2MPa-0.4MPa.

6. The high-performance insulating ceramic sealing method for neutron tubes according to claim 1, characterized in that, In step five, the temperature at which the brazing filler metal is heated to melt is 810℃-830℃, and the holding time is 2-5 minutes.

7. The high-performance insulating ceramic sealing method for neutron tubes according to claim 1, characterized in that, In step six, the annealing temperature is 450℃-550℃, and the holding time is 100-140 minutes.

8. A sealing structure obtained by the high-performance insulating ceramic sealing method for neutron tubes as described in any one of claims 1-7, characterized in that, include: Cylindrical high-purity alumina ceramic parts; The first metal sealing member and the second metal sealing member are made of Kovar alloy and are respectively disposed on both sides of the ceramic part along the axial direction; A titanium transition layer covers the sealing surfaces at both ends of the ceramic component; An active brazing filler layer is disposed between the titanium transition layer and the corresponding metal sealing component at both ends of the ceramic component, and is connected by vacuum brazing. The ceramic component, titanium transition layer, active solder layer, and metal sealing component are formed into an integral hermetically sealed structure by vacuum brazing.

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