Coating for inhibiting secondary electron emission of aluminum oxide ceramic as well as preparation method and application of coating

Abstract

The invention discloses a coating for inhibiting secondary electron emission of aluminum oxide ceramic as well as a preparation method and application of the coating, and belongs to the technical field of processing of aluminum oxide ceramic shells for X-ray tubes. Comprising the following steps: mixing quartz, potassium feldspar, calcium carbonate, kaolin and borax according to a specific ratio, melting, performing water quenching, grinding and sieving to obtain an activating agent; mixing the activating agent and chromium oxide powder according to the weight ratio of (15%-25%): (75%-85%), grinding and sieving to obtain coating powder; the coating powder and water are mixed according to the weight ratio of 50%-80%: 20%-50% and then ground and sieved, and coating slurry is obtained; and spraying the coating slurry on the inner surface of the aluminum oxide ceramic by using a spraying method to form the chromium oxide coating. And after the chromium oxide coating is sprayed, sintering in an inert gas atmosphere at 700-900 DEG C to obtain the aluminum oxide ceramic containing the chromium oxide coating. According to the invention, the interface thermal stress can be effectively relieved, the coating stripping caused by thermal mismatch in the thermal-thermal cycling process is avoided, and the long-term reliability requirement of a high-temperature application scene is met.

Description

Technical Field

[0001] The invention belongs to the technical field of processing alumina ceramic shells for X-ray tubes and relates to a coating for suppressing secondary electron emission of alumina ceramics and a preparation method and application thereof. Background Art

[0002] Alumina ceramics have long been used as the core material for X-ray tube insulation housings due to their excellent insulation properties, high mechanical strength, and good chemical stability. However, under the high electric field and complex operating conditions of X-ray tubes, the inherent characteristics of alumina ceramics gradually exposed key defects: First, the secondary electron emission coefficient (δ) of alumina ceramics is usually as high as 1.5-2.5. When a high-energy electron beam bombards the inner surface of the tube shell, a large number of secondary electrons are excited and migrate to the ceramic surface, forming charge accumulation; second, its surface resistivity (ρs) is generally at The above characteristics work together to form local electric field distortion on the inner surface of ceramics under the conditions of vacuum environment and strong electric field coupling. When the electric field strength exceeds the critical value (usually ), surface flashover will occur.

[0003] The reduction of surface flashover voltage directly threatens the operational reliability of X-ray tubes. Experimental data show that under continuous working conditions, the surface flashover voltage of traditional alumina ceramic tube shells may decrease, resulting in a significant increase in the probability of discharge breakdown. This failure mode manifests itself in two typical paths: one is that the accumulation of surface charge triggers local electric field concentration, leading to the formation of micro-discharge channels; the other is that the spatial electric field generated by charge rearrangement is superimposed on the external electric field, inducing dendritic discharge trajectories. In the existing technology, although attempts have been made to improve conductivity through coating, it is easy to fall off due to thermal stress and there is a risk of high-temperature failure. In addition, traditional processes cannot achieve precise control of surface conductivity while ensuring the insulation performance of the ceramic body, resulting in a contradiction between the modification effect and the insulation requirements. Summary of the Invention

[0004] The purpose of the present invention is to solve the technical problem in the prior art that the traditional coating process cannot achieve precise control of the surface conductivity while ensuring the insulation performance of the ceramic body, and to provide a coating for suppressing the secondary electron emission of alumina ceramics and its preparation method and application.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention discloses a method for preparing a coating for suppressing secondary electron emission of alumina ceramics, comprising: The activator is obtained by mixing quartz, potassium feldspar, calcium carbonate, kaolin and borax in a specific ratio, melting them, quenching them with water, grinding and sieving them; The activator and chromium oxide powder are mixed in a weight ratio of 15%-25%:75%-85%, and then ground and sieved to obtain a coating powder; The coating powder and water are mixed in a weight ratio of 50%-80%:20%-50%, and then ground and sieved to obtain a coating slurry; The coating slurry is sprayed on the inner surface of the alumina ceramic by a spraying method to form a chromium oxide coating.

[0006] Further improvements are: After the chromium oxide coating is sprayed, it is sintered in an inert gas atmosphere at 700°C-900°C to obtain an alumina ceramic containing a chromium oxide coating.

[0007] The quartz, potassium feldspar, calcium carbonate, kaolin and borax are specifically as follows according to specific proportions: By weight, quartz 20% to 40%, potassium feldspar 15% to 35%, calcium carbonate 10% to 20%, kaolin 10% to 20%, and borax 10% to 20%.

[0008] The particle size of the chromium oxide powder is 1-3 μm.

[0009] The coating slurry is sprayed on the inner surface of the alumina ceramic to form a chromium oxide coating by spraying: The specific gravity of the coating slurry is 1.5 g / cm3~2.5g / cm3, the spray gun pressure is 0.3 MPa~0.6MPa, the distance between the spray gun and the inner surface of the alumina ceramic is 50 mm~200 mm, the number of spraying times is 2~6 times, and the coating thickness is 0.05 mm~0.3 mm.

[0010] The grinding was performed using a ball mill; and the screening was performed through a 400-mesh sieve.

[0011] The melting is carried out by keeping the temperature in a crucible for more than 1 hour; the holding temperature is 1000°C to 1300°C.

[0012] Before spraying the chromium oxide coating on the inner surface of the alumina ceramic using a spraying method, the inner surface of the alumina ceramic is subjected to plasma pretreatment with a processing power of 300 W-500 W and a time of 60 s-120 s to improve the interface roughness to Ra≥1.5 μm.

[0013] In a second aspect, the present invention discloses a coating for suppressing secondary electron emission of alumina ceramics, which is prepared using the above-mentioned method for preparing a coating for suppressing secondary electron emission of alumina ceramics.

[0014] In a third aspect, the present invention discloses an application of the above-mentioned coating for suppressing secondary electron emission of alumina ceramics, wherein the coating for suppressing secondary electron emission of alumina ceramics is used for an alumina ceramic housing for an X-ray tube.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a method for preparing a coating that suppresses secondary electron emission from alumina ceramics. Through the combined action of a chromium oxide coating and a specific activator, a composite structure with both electron capture and conduction functions is constructed on the surface of the alumina ceramic. The semiconductor properties of chromium oxide can effectively suppress surface charge accumulation, while the glass phase component in the activator forms a dense interface layer during the sintering process. The synergistic effect of the two can significantly reduce the tendency of secondary electron emission, which is better than the performance of a single-component coating. A composite ratio design of activator and chromium oxide is adopted to form a resistivity gradient structure in the coating. The activator component close to the ceramic substrate side realizes interface strengthening through chemical bonding, and the surface chromium oxide component constructs a conductive network, so that the coating has both low resistivity characteristics and interface bonding strength, effectively solving the problem of insufficient conductivity of traditional high-resistance ceramic materials. The rheological properties are optimized through slurry formula design, so that the slurry viscosity is adapted to the requirements of the spraying process. Particle size distribution control ensures that the slurry can form a uniform and dense coating under the spraying pressure, avoiding performance fluctuations caused by local defects and significantly improving the controllability of the coating quality. The activator is prepared using low-cost mineral raw materials, replacing traditional high-priced additives, significantly reducing raw material costs. The combination of a water-quenching batch preparation process and the high raw material utilization of the spray coating process enables industrial-scale production while maintaining performance, offering significant economic advantages. The high chromium oxide content (75-85%) in the coating effectively reduces the secondary electron emission rate on the inner surface of the X-ray tube.

[0016] Furthermore, a high-temperature sintering method is used to obtain a chromium oxide coating, which is sintered onto the inner surface of the alumina ceramic substrate, providing a tight bond and preventing peeling. The high-temperature sintering temperature employed is higher than the exhaust temperature of the X-ray tube, ensuring that subsequent manufacturing processes of the X-ray tube will not affect the coating or alter its performance. The glass-ceramic component in the activator forms a microcrystalline network during the sintering process, achieving thermal expansion coefficient matching between the coating and the alumina ceramic substrate. This invention can effectively alleviate interfacial thermal stress, preventing coating peeling due to thermal mismatch during hot and cold cycles, and meeting the long-term reliability requirements of high-temperature applications.

[0017] Furthermore, chromium oxide with a particle size of 1 to 3 microns is used, the activator is fully filled in the chromium oxide, the coating is dense and has no pores, and the vacuum degree of the X-ray tube is not affected during the preparation process of the X-ray tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 The present invention is a flowchart of a method for preparing a coating for suppressing secondary electron emission of alumina ceramics in an embodiment of the present invention. DETAILED DESCRIPTION

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0021] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0022] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0023] The present invention is described in further detail below with reference to the accompanying drawings: See also Figure 1 The present invention discloses a method for preparing a coating for suppressing secondary electron emission of alumina ceramics, comprising: S1. Mix 20% to 40% quartz, 15% to 35% potassium feldspar, 10% to 20% calcium carbonate, 10% to 20% kaolin, and 10% to 20% borax by weight, melt the mixture, quench with water, grind, and sieve to obtain an activator; the melting step is performed by holding the mixture in a crucible for more than 1 hour; and the holding temperature is 1000° C. to 1300° C.

[0024] S2. The activator and chromium oxide powder are mixed in a weight ratio of 15%-25%:75%-85%, and the mixture is ground and sieved to obtain a coating powder. The chromium oxide powder has a particle size of 1-3 μm. Using chromium oxide with a particle size of 1-3 μm, the activator is fully filled in the chromium oxide, resulting in a dense, pore-free coating that does not affect the vacuum level of the X-ray tube during the X-ray tube manufacturing process.

[0025] S3, mixing the coating powder with water in a weight ratio of 50%-80%:20%-50%, grinding and sieving to obtain a coating slurry; S4: spraying the coating slurry onto the inner surface of the alumina ceramic to form a chromium oxide coating. The coating slurry has a specific gravity of 1.5 g / cm³ to 2.5 g / cm³, a spray gun pressure of 0.3 MPa to 0.6 MPa, a distance between the spray gun and the inner surface of the alumina ceramic of 50 mm to 200 mm, 2 to 6 spray passes, and a coating thickness of 0.05 mm to 0.3 mm.

[0026] Before spraying the chromium oxide coating on the inner surface of the alumina ceramic using a spraying method, the inner surface of the alumina ceramic is subjected to plasma pretreatment with a processing power of 300 W-500 W and a time of 60 s-120 s to improve the interface roughness to Ra≥1.5 μm.

[0027] S5. After the chromium oxide coating is sprayed, it is sintered in an inert gas atmosphere at 700-900°C to obtain an alumina ceramic containing a chromium oxide coating. The grinding is performed using a ball mill; the screening is performed through a 400-mesh sieve. The sintered chromium oxide coating undergoes laser remelting post-processing, using laser scanning with a pulse width of 0.5-2ms and a power of 50-100W to achieve a surface roughness Ra ≤ 0.15μm. The chromium oxide coating is obtained by a high-temperature sintering method. The chromium oxide coating is sintered to the inner surface of the alumina ceramic substrate, where it is tightly bonded and will not fall off. The high-temperature sintering temperature used is higher than the exhaust temperature of the X-ray tube, and the subsequent manufacturing process of the X-ray tube will not affect the coating or change its performance. The glass-ceramic component in the activator forms a microcrystalline network during the sintering process, which matches the thermal expansion coefficient of the coating with the alumina ceramic substrate. This design effectively alleviates interfacial thermal stress, avoids coating peeling due to thermal mismatch during hot and cold cycles, and meets the long-term reliability requirements of high-temperature applications.

[0028] The present invention discloses a method for preparing a coating that suppresses secondary electron emission from alumina ceramics. Through the combined action of a chromium oxide coating and a specific activator, a composite structure with both electron capture and conduction functions is constructed on the surface of the alumina ceramic. The semiconductor properties of chromium oxide can effectively suppress surface charge accumulation, while the glass phase component in the activator forms a dense interface layer during the sintering process. The synergistic effect of the two can significantly reduce the tendency of secondary electron emission, which is better than the performance of a single-component coating. A composite ratio design of activator and chromium oxide is adopted to form a resistivity gradient structure in the coating. The activator component close to the ceramic substrate side realizes interface strengthening through chemical bonding, and the surface chromium oxide component constructs a conductive network, so that the coating has both low resistivity characteristics and interface bonding strength, effectively solving the problem of insufficient conductivity of traditional high-resistance ceramic materials. The rheological properties are optimized through slurry formula design, so that the slurry viscosity is adapted to the requirements of the spraying process. Particle size distribution control ensures that the slurry can form a uniform and dense coating under the spraying pressure, avoiding performance fluctuations caused by local defects and significantly improving the controllability of the coating quality. The activator is prepared using low-cost mineral raw materials, replacing traditional high-priced additives, significantly reducing raw material costs. The combination of a water-quenching batch preparation process and the high raw material utilization of the spray coating process enables industrial-scale production while maintaining performance, offering significant economic advantages. The high chromium oxide content (75-85%) in the coating effectively reduces the secondary electron emission rate on the inner surface of the X-ray tube.

[0029] Example 1 This embodiment discloses a method for preparing a coating for suppressing secondary electron emission of alumina ceramics, comprising: S1. Mix 20% quartz, 35% potassium feldspar, 20% calcium carbonate, 15% kaolin, and 10% borax by weight, melt the mixture, quench with water, grind, and sieve to obtain an activator; the melting step is performed by holding the mixture in a crucible for more than 1 hour; and the holding temperature is 1000°C.

[0030] S2, mixing the activator and chromium oxide powder in a weight ratio of 15%:85%, grinding and sieving to obtain a coating powder; the particle size of the chromium oxide powder is 1 μm.

[0031] S3, mixing the coating powder and water in a weight ratio of 50%:50%, grinding and sieving to obtain a coating slurry; S4, spraying the coating slurry on the inner surface of the alumina ceramic to form a chromium oxide coating. The coating slurry has a specific gravity of 1.5 g / cm 3 , the spray gun pressure is 0.3 MPa, the distance between the spray gun and the inner surface of the alumina ceramic is 50 mm, the number of spraying passes is 2 times, and the coating thickness is 0.05 mm.

[0032] Before spraying a chromium oxide coating on the inner surface of the alumina ceramic using a spraying method, the inner surface of the alumina ceramic is subjected to plasma pretreatment with a treatment power of 300 W and a treatment time of 60 s to improve the interface roughness to Ra ≥ 1.5 μm.

[0033] S5. After the chromium oxide coating is sprayed, the aluminum oxide ceramic is sintered at 700°C in an inert gas atmosphere to obtain a chromium oxide-coated aluminum oxide ceramic. The grinding is performed using a ball mill; the sieving is performed through a 400-mesh sieve. The sintered chromium oxide coating is then laser remelted using a laser scanning method with a pulse width of 0.5-2 ms and a power of 50 W to achieve a surface roughness Ra ≤ 0.15 μm.

[0034] Example 2 This embodiment discloses a method for preparing a coating for suppressing secondary electron emission of alumina ceramics, comprising: S1. Mix 35% quartz, 15% potassium feldspar, 10% calcium carbonate, 20% kaolin, and 20% borax by weight, melt the mixture, quench with water, grind, and sieve to obtain an activator; the melting step is performed by holding the mixture in a crucible for more than 1 hour; and the holding temperature is 1300°C.

[0035] S2, mixing the activator and chromium oxide powder in a weight ratio of 25%:75%, grinding and sieving to obtain a coating powder; the particle size of the chromium oxide powder is 3 μm.

[0036] S3, mixing the coating powder with water in a weight ratio of 80%:20%, grinding and sieving to obtain a coating slurry; S4, spraying the coating slurry on the inner surface of the alumina ceramic to form a chromium oxide coating. The coating slurry has a specific gravity of 2.5 g / cm 3 , the spray gun pressure is 0.6MPa, the distance between the spray gun and the inner surface of the alumina ceramic is 200mm, the number of spraying times is 6 times, and the coating thickness is 0.3mm.

[0037] Before spraying a chromium oxide coating on the inner surface of the alumina ceramic using a spraying method, the inner surface of the alumina ceramic is subjected to plasma pretreatment with a processing power of 500 W and a time of 120 s to improve the interface roughness to Ra≥1.5 μm.

[0038] S5. After the chromium oxide coating is sprayed, the aluminum oxide ceramic is sintered at 900°C in an inert gas atmosphere to obtain an aluminum oxide ceramic containing a chromium oxide coating. The grinding is performed using a ball mill; the screening is performed using a 400-mesh sieve. The sintered chromium oxide coating is then laser remelted using a laser scanning method with a pulse width of 2 ms and a power of 100 W to achieve a surface roughness Ra ≤ 0.15 μm.

[0039] Example 3 This embodiment discloses a method for preparing a coating for suppressing secondary electron emission of alumina ceramics, comprising: S1. Mix 30% quartz, 20% potassium feldspar, 15% calcium carbonate, 20% kaolin, and 15% borax by weight, melt the mixture, quench with water, grind, and sieve to obtain an activator; the melting step is performed by holding the mixture in a crucible for more than 1 hour; and the holding temperature is 1200°C.

[0040] S2, mixing the activator and chromium oxide powder in a weight ratio of 20%:80%, grinding and sieving to obtain a coating powder; the particle size of the chromium oxide powder is 2 μm.

[0041] S3, mixing the coating powder with water in a weight ratio of 30%:70%, grinding and sieving to obtain a coating slurry; S4: Spray the coating slurry onto the inner surface of the alumina ceramic to form a chromium oxide coating. The coating slurry has a specific gravity of 2 g / cm³, the spray gun pressure is 0.5 MPa, the distance between the spray gun and the inner surface of the alumina ceramic is 100 mm, the number of spraying passes is 3, and the coating thickness is 0.1 mm.

[0042] Before spraying a chromium oxide coating on the inner surface of the alumina ceramic using a spraying method, the inner surface of the alumina ceramic is subjected to plasma pretreatment with a processing power of 400 W and a time of 100 s to improve the interface roughness to Ra≥1.5 μm.

[0043] S5. After the chromium oxide coating is sprayed, the aluminum oxide ceramic is sintered at 800°C in an inert gas atmosphere to obtain an aluminum oxide ceramic containing a chromium oxide coating. The grinding is performed using a ball mill; the screening is performed using a 400-mesh sieve. The sintered chromium oxide coating is then laser remelted using a laser scanning process with a pulse width of 1 ms and a power of 80 W to achieve a surface roughness Ra ≤ 0.15 μm.

[0044] Table 1 Performance comparison of the coating prepared by the present invention and conventional coatings

[0045] An embodiment of the present invention further discloses a coating for suppressing secondary electron emission of alumina ceramics and reducing resistivity, which is prepared using the above-mentioned method for preparing the coating for suppressing secondary electron emission of alumina ceramics.

[0046] An embodiment of the present invention further discloses an application of a coating for suppressing secondary electron emission of alumina ceramics and reducing resistivity. The coating for suppressing secondary electron emission of alumina ceramics and reducing resistivity is used for an alumina ceramic housing for an X-ray tube.

[0047] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a coating for suppressing secondary electron emission of alumina ceramics, characterized in that: include: The activator is obtained by mixing quartz, potassium feldspar, calcium carbonate, kaolin and borax in a specific ratio, melting them, quenching them with water, grinding and sieving them; The activator and chromium oxide powder are mixed in a weight ratio of 15%-25%:75%-85%, and then ground and sieved to obtain a coating powder; The coating powder and water are mixed in a weight ratio of 50%-80%:20%-50%, and then ground and sieved to obtain a coating slurry; The coating slurry is sprayed on the inner surface of the alumina ceramic by a spraying method to form a chromium oxide coating.

2. The method for preparing a coating for suppressing secondary electron emission of alumina ceramics according to claim 1, characterized in that: After the chromium oxide coating is sprayed, it is sintered in an inert gas atmosphere at 700°C-900°C to obtain an alumina ceramic containing a chromium oxide coating.

3. The method for preparing a coating for suppressing secondary electron emission of alumina ceramics according to claim 1, characterized in that: The quartz, potassium feldspar, calcium carbonate, kaolin and borax are specifically as follows according to specific proportions: By weight, quartz 20% to 40%, potassium feldspar 15% to 35%, calcium carbonate 10% to 20%, kaolin 10% to 20%, and borax 10% to 20%.

4. The method for preparing a coating for suppressing secondary electron emission of alumina ceramics according to claim 1, characterized in that: The particle size of the chromium oxide powder is 1-3 μm.

5. The method for preparing a coating for suppressing secondary electron emission of alumina ceramics according to claim 1, characterized in that: The coating slurry is sprayed on the inner surface of the alumina ceramic to form a chromium oxide coating by spraying: The specific gravity of the coating slurry is 1.5 g / cm3~2.5g / cm3, the spray gun pressure is 0.3 MPa~0.6MPa, the distance between the spray gun and the inner surface of the alumina ceramic is 50 mm~200 mm, the number of spraying times is 2~6 times, and the coating thickness is 0.05 mm~0.3 mm.

6. The method for preparing a coating for suppressing secondary electron emission of alumina ceramics according to claim 1, characterized in that: The grinding was performed using a ball mill; and the screening was performed through a 400-mesh sieve.

7. The method for preparing a coating for suppressing secondary electron emission of alumina ceramics according to claim 1, characterized in that: The melting is carried out by keeping the temperature in a crucible for more than 1 hour; the holding temperature is 1000°C to 1300°C.

8. The method for preparing a coating for suppressing secondary electron emission of alumina ceramics according to claim 1, characterized in that: Before spraying the chromium oxide coating on the inner surface of the alumina ceramic using a spraying method, the inner surface of the alumina ceramic is subjected to plasma pretreatment with a processing power of 300 W-500 W and a time of 60 s-120 s to improve the interface roughness to Ra≥1.5 μm.

9. A coating for suppressing secondary electron emission of alumina ceramics, characterized in that: The coating for suppressing secondary electron emission of alumina ceramics is prepared using the preparation method of any one of claims 1 to 9.

10. Use of the coating for suppressing secondary electron emission of alumina ceramics according to claim 9, characterized in that: The coating for suppressing secondary electron emission of alumina ceramics is used for an alumina ceramic housing for an X-ray tube.

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