Process for the production of a coating-modified alumina insulator and insulator

Abstract

The application provides a preparation method of a coating modified alumina insulator and the insulator, and can solve the problems of low pressure resistance improvement range, easy peeling of the coating, and the coating being mostly a polymer coating, which cannot meet the high-temperature baking and gas removal sealing requirements of the alumina insulator. The method comprises the following steps: respectively weighing tetraethyl orthosilicate, dimethyldiethoxysilane and X triethoxysilane, and mixing to obtain an organosilane reaction reagent; adding isopropyl alcohol into a reaction container, and then adding the organosilane reaction reagent and deionized water into the reaction container under stirring to obtain a reaction liquid; adjusting the pH of the reaction liquid, and reacting until the reaction liquid is in a clear and transparent state, and then cooling to room temperature to obtain a polyorganosilica sol; coating the polyorganosilica sol on the surface of a pre-prepared alumina insulator body, and then drying in air, and then undergoing a dehydration condensation reaction to obtain the coating modified alumina insulator.

Description

Technical Field

[0001] This invention relates to an insulator and its preparation method, specifically to a method for preparing a coating-modified alumina insulator and the insulator itself. Background Technology

[0002] Alumina, as a common vacuum insulating material, can be used as an insulator for pulsed power systems, high-power microwave (HPM) transmission windows, klystron transmission windows, and other high-voltage insulating devices. Because alumina has a high secondary electron emission coefficient, at low voltages, the interface between the alumina insulator and the vacuum will experience breakdown discharge, resulting in a low overall withstand voltage performance of the system. During operation, breakdown discharge is likely to occur, and the system cannot achieve higher technical specifications, posing a significant risk to the system's operation (see: Mingdong Zhu, Falun Song and Fei Li et al., "Surface insulating properties of titanium implanted alumina ceramics by plasma immersion ion implantation," Nuclear Instruments & Methods in Physics Research 407(sep.15), 155-159(2017). YJLei, BHTang and XJHuang et al., "Effects of bulk doping on surface insulating performance of alumina ceramic in vacuum," IEEE Transactions on Dielectrics & Electrical Insulation 18(6), 2103-2107(2012).).

[0003] Studies have shown that preparing a coating on the surface of alumina insulators is an effective method to reduce secondary electron emission and increase the surface flashover voltage of alumina insulators. However, current methods for preparing coatings on the surface of alumina insulators have the following problems: the withstand voltage increase is not high, the coating is easy to fall off, and most coatings are polymer coatings, which cannot meet the requirements of high-temperature baking and degassing sealing of alumina insulators (see: YJLei and DQXiao, "Influence of Cr2O3 and MnO additives on the surface properties of alumina insulators", IEEE Transactions on Dielectrics & Electrical Insulation 13(1), 93-97 (2006).). Summary of the Invention

[0004] The purpose of this invention is to solve the technical problems of existing methods for preparing coatings on the surface of alumina insulators, such as low withstand voltage improvement, easy coating peeling, and most coatings being polymer coatings that cannot meet the requirements of high-temperature baking and degassing sealing of alumina insulators. The invention provides a method for preparing a coating-modified alumina insulator and an insulator.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a coating-modified alumina insulator, characterized by the following steps:

[0007] Step 1: Weigh tetraethyl orthosilicate, dimethyldiethoxysilane, and X-triethoxysilane according to a molar ratio of 10-6:2:2-4, and mix them to obtain an organosilane reaction reagent; wherein, X is a high-pressure-resistant molecular group that can improve the vacuum surface pressure resistance performance.

[0008] Step 2: Add isopropanol, which is 2 to 4 times the volume of the organosilane reaction reagent, to the reaction vessel; under stirring, add the organosilane reaction reagent and deionized water, which is 1 to 2 times the volume of the organosilane reaction reagent, to the reaction vessel in sequence, and mix to obtain a reaction solution;

[0009] Step 3: Adjust the pH of the reaction solution to 4-5, react at 50℃-60℃ for 3-6 hours, and then let the reaction solution become clear and transparent. Cool it to room temperature to obtain polyorganosilicon sol.

[0010] Step 4: Coat the prepared alumina insulator body surface with the polysilicon sol, air dry it in the air, and then allow it to undergo a dehydration condensation reaction at 120℃~150℃ for 2h~4h to obtain the coated alumina insulator.

[0011] Furthermore, in step 1, the high-pressure-resistance molecular group is a long-chain alkyl group, a fluorocarbon group, or a delocalized electron group;

[0012] In step 2, under stirring conditions, the organosilane reaction reagent is first added to the reaction vessel dropwise, and then deionized water with a volume of 1 to 2 times that of the organosilane reaction reagent is added to the reaction vessel.

[0013] Furthermore, step 3 specifically involves:

[0014] The pH of the reaction solution was adjusted to 4-5 using an acid solution of 0.1 mol / L to 1 mol / L. After reacting at 50℃ to 60℃ for 3-6 hours, the reaction solution was allowed to become clear and transparent. It was then cooled to room temperature and allowed to stand for 24-48 hours to precipitate, thus obtaining polyorganosilicon sol.

[0015] Furthermore, step 4 specifically involves:

[0016] The prepared alumina insulator body is immersed in the polysilicon sol. The polysilicon sol is coated on the surface of the alumina insulator body by a pulling method with a pulling speed controlled at 0.1 mm / min to 1 mm / min. After being dried in the air, a dehydration condensation reaction is carried out at 120℃ to 150℃ for 2 to 4 hours to obtain a coated alumina insulator.

[0017] Furthermore, step 4 specifically involves:

[0018] Polysilicon sol was brushed onto the surface of the pre-prepared alumina insulator body. After being air-dried, the alumina insulator underwent a dehydration condensation reaction at 120℃~150℃ for 2h~4h to obtain a coated alumina insulator.

[0019] Furthermore, in step 3, the acid solution is a hydrochloric acid solution, a sulfuric acid solution, or a nitric acid solution.

[0020] Furthermore, step 1 specifically includes:

[0021] According to a molar ratio of 10:2:3, tetraethyl orthosilicate, dimethyldiethoxysilane and perfluorophenyltriethoxysilane were weighed and mixed to obtain an organosilane reaction reagent.

[0022] Step 2 specifically involves adding isopropanol, which has a volume twice that of the organosilane reaction reagent, into the reaction vessel; under stirring conditions, the organosilane reaction reagent is first added to the reaction vessel dropwise, and then deionized water, which has a volume once that of the organosilane reaction reagent, is added to the reaction vessel, and the mixture is then mixed to obtain the reaction solution.

[0023] Furthermore, step 3 specifically involves:

[0024] The pH of the reaction solution was adjusted to 4.5 using a 1 mol / L sulfuric acid solution. After reacting at 60°C for 3 hours, the reaction solution was allowed to become clear and transparent. It was then cooled to room temperature and allowed to stand for 24 hours to settle, resulting in polyorganosilicon sol.

[0025] Furthermore, step 4 specifically involves:

[0026] The pre-prepared alumina insulator body was immersed in the polysilicon sol. The polysilicon sol was coated on the surface of the alumina insulator body by using a pull-up method with a pull-up speed of 1 mm / min. After being dried in the air, a dehydration condensation reaction was carried out at 150°C for 2 hours to obtain a coated alumina insulator.

[0027] Meanwhile, the present invention also provides a coating-modified alumina insulator, which is special in that it is prepared by the above-mentioned preparation method of coating-modified alumina insulator.

[0028] The beneficial effects of this invention are:

[0029] 1. This invention provides a method for preparing a coated alumina insulator and an insulator thereof. The main component of the coating is an organosilicon copolymer. The high-voltage-resistance molecular groups in the copolymer have a low secondary electron emission coefficient, which imparts high vacuum surface withstand voltage characteristics to the copolymer coating. The silicon-oxygen molecular chains and silicon-oxygen nanogroups in the copolymer impart high-temperature resistance to the copolymer coating. Applying this coating to the surface of the alumina insulator reduces the secondary electron emission coefficient of the insulator surface and inhibits the vacuum flashover development process on the insulator surface, thereby significantly improving the surface withstand voltage level of the insulator. Simultaneously, it meets the requirements for high-temperature baking and degassing sealing of the insulator, and can withstand high-temperature baking of 200℃ to 400℃. Compared with traditional polymer-coated modified alumina insulators, the alumina insulator of this invention has a wider range of applications.

[0030] 2. In this invention, the silanol groups contained in the coating can undergo a dehydration condensation reaction with the aluminum hydroxyl groups contained in the alumina, and are connected to the surface of the alumina insulator body by forming chemical bonds. Compared with the traditional method of connecting the coating to the surface of the alumina insulator body by intermolecular interaction forces and mechanical riveting, the coating in this invention has a stronger adhesion strength and stability to the alumina insulator body, and the coating is not easy to fall off.

[0031] 3. In this invention, the coating is formed by the dehydration and condensation reaction of liquid polyorganosilicon sol. It can be prepared on the surface of the alumina insulator body by various methods such as impregnation coating and brush coating. It has good flexibility and can be used for insulators of various shapes, with a wide range of applications.

[0032] 4. The preparation method provided by this invention will not damage the bulk structure of the insulator body and can ensure the mechanical strength of the insulator; it only needs to prepare a coating on the surface of the insulator body to play a role, and will not change any structural parameters of the existing insulation system. Attached Figure Description

[0033] Figure 1 This is a synthesis route diagram of polyorganosilica sol in step three of Example 1 of the preparation method of a coating-modified alumina insulator of the present invention. Detailed Implementation

[0034] Example 1

[0035] A method for preparing a coating-modified alumina insulator includes the following steps:

[0036] Step 1: Weigh tetraethyl orthosilicate, dimethyldiethoxysilane, and perfluorophenyltriethoxysilane in a molar ratio of 10:2:3, and mix them to obtain 25 mL of organosilane reaction reagent; wherein, perfluorophenyl is a molecular group with high pressure resistance.

[0037] Step 2: Add 50 mL of isopropanol to a 250 mL three-necked round-bottom flask; under stirring, first add the organosilane reaction reagent dropwise to the round-bottom flask and dissolve it in the isopropanol, then add 25 mL of deionized water to the round-bottom flask and mix to obtain the reaction solution.

[0038] Step 3: Adjust the pH of the reaction solution to 4.5 using a 1 mol / L sulfuric acid solution. After reacting at 60°C for 3 hours, allow the reaction solution to become clear and transparent. Cool to room temperature and allow to stand for 24 hours to settle, thus obtaining polysilicon sol.

[0039] Step 4: Immerse the alumina insulator body with a diameter of 30 mm and a thickness of 10 mm in polysilicon sol. Use the lifting method to control the lifting speed at 0.1 mm / min to coat the surface of the alumina insulator body with polysilicon sol. Place it in the air to dry, so as to promote the gelation of polysilicon sol. Then put it in an oven and carry out a dehydration condensation reaction at 150°C for 2 hours to obtain the coating-modified alumina insulator, which is referred to as "coating-modified alumina insulator 1".

[0040] Figure 1 This is a synthetic route diagram for polyorganosilicone sol. (From...) Figure 1 It is known that tetraethyl orthosilicate, after hydrolysis and polymerization, transforms into silicon-oxygen nanogroups, which can impart certain heat resistance to the coating. Dimethyldiethoxysilane, after hydrolysis and polymerization, transforms into silicon-oxygen molecular chains, which can also impart certain heat resistance to the coating, while simultaneously giving it a certain degree of flexibility and reducing the probability of cracking. Perfluorophenyltriethoxysilane, after hydrolysis and polymerization, has its triethoxysilane end groups transformed into heat-resistant silicon-oxygen nanogroups, and the perfluorophenyl groups enter the coating to form high-pressure-resistant functional groups.

[0041] Example 2

[0042] A method for preparing a coating-modified alumina insulator includes the following steps:

[0043] Step 1: Weigh tetraethyl orthosilicate, dimethyldiethoxysilane, and perfluorodecyltriethoxysilane in a molar ratio of 8:2:4, and mix them to obtain 25 mL of organosilane reaction reagent; wherein, perfluorodecyl is a molecular group with high pressure resistance.

[0044] Step 2: Add 100 mL of isopropanol to a 500 mL three-necked round-bottom flask; under stirring, first add the organosilane reaction reagent dropwise to the round-bottom flask and dissolve it in the isopropanol, then add 50 mL of deionized water to the round-bottom flask and mix to obtain the reaction solution.

[0045] Step 3: Adjust the pH of the reaction solution to 5 using 0.1 mol / L nitric acid solution. After reacting at 50°C for 6 hours, allow the reaction solution to become clear and transparent. Cool to room temperature and allow to stand for 48 hours to settle, thus obtaining polysilicon sol.

[0046] Step 4: Apply polysilicon sol to the surface of the alumina insulator body with a diameter of 30 mm and a thickness of 10 mm using a brush, let it air dry to promote the gelation of polysilicon sol, and then put it in an oven at 120°C for 4 hours to undergo a dehydration condensation reaction to obtain a coated alumina insulator, which is called "coated modified alumina insulator 2".

[0047] Example 3

[0048] A method for preparing a coating-modified alumina insulator includes the following steps:

[0049] Step 1: Weigh tetraethyl orthosilicate, dimethyldiethoxysilane, and octadecyltriethoxysilane in a molar ratio of 6:2:2, and mix them to obtain 25 mL of organosilane reaction reagent; wherein, octadecyl is a molecular group with high pressure resistance.

[0050] Step 2: Add 75 mL of isopropanol to a 250 mL three-necked round-bottom flask; under stirring, first add the organosilane reaction reagent dropwise to the round-bottom flask and dissolve it in the isopropanol, then add 37.5 mL of deionized water to the round-bottom flask and mix to obtain the reaction solution.

[0051] Step 3: Adjust the pH of the reaction solution to 4 using 0.5 mol / L hydrochloric acid solution. After reacting at 55°C for 4 hours, allow the reaction solution to become clear and transparent. Cool to room temperature and allow to stand for 30 hours to settle, thus obtaining polyorganosilicon sol.

[0052] Step 4: Immerse the alumina insulator body with a diameter of 30 mm and a thickness of 10 mm in polysilicon sol. Use the lifting method to control the lifting speed at 1 mm / min to coat the surface of the alumina insulator body with polysilicon sol. Place it in the air to dry, so that the polysilicon sol can gel. Then put it in an oven and let it undergo a dehydration condensation reaction at 130°C for 3 hours to obtain the coating-modified alumina insulator, which is called "coating-modified alumina insulator 3".

[0053] Example 4

[0054] The difference between this embodiment and Embodiment 1 is that:

[0055] In step 1, the molecular group with high pressure resistance is a phenyl delocalized electron group.

[0056] In step 4, the pulling speed is 0.5 mm / min, the temperature is 140℃, and the dehydration condensation reaction time is 3 h. The resulting coated alumina insulator is referred to as "coated modified alumina insulator 4".

[0057] The coated alumina insulators prepared in Examples 1 to 4 above, along with the alumina insulator bodies, were subjected to vacuum surface flashover voltage tests on a vacuum surface flashover voltage test bench with a pulse width of 500 ns. The flashover voltage test results are shown in Table 1.

[0058] Table 1

[0059]

[0060]

[0061] Table 1 shows that the flashover voltage of the coated alumina insulator is increased by 90% to 150% compared to the original alumina insulator, indicating that the coating prepared on the surface of the alumina insulator by this invention can effectively improve the flashover voltage. The coated alumina insulators were then heat-treated at 200℃, 300℃, 400℃, and 500℃ for 2 hours, respectively, and the flashover voltage was then tested. The temperature at which a significant decrease in flashover voltage occurred was subtracted by 100℃ and recorded as the coating's temperature resistance strength. Table 1 shows that the temperature resistance strength of the coating prepared by this invention is within the range of 200℃ to 400℃.

[0062] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present invention should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a coating-modified alumina insulator, characterized in that, Includes the following steps: Step 1: Weigh tetraethyl orthosilicate, dimethyldiethoxysilane, and X-triethoxysilane according to a molar ratio of 10-6:2:2-4, and mix them to obtain an organosilane reaction reagent; wherein, X is a high-pressure-resistant molecular group that can improve the vacuum surface pressure resistance performance. Step 2: Add isopropanol, which is 2 to 4 times the volume of the organosilane reaction reagent, to the reaction vessel; under stirring, add the organosilane reaction reagent and deionized water, which is 1 to 2 times the volume of the organosilane reaction reagent, to the reaction vessel in sequence, and mix to obtain a reaction solution; Step 3: Adjust the pH of the reaction solution to 4-5, react at 50℃-60℃ for 3-6 hours, and then let the reaction solution become clear and transparent. Cool it to room temperature to obtain polyorganosilicon sol. Step 4: Coat the prepared alumina insulator body surface with the polysilicon sol, air dry it in the air, and then allow it to undergo a dehydration condensation reaction at 120℃~150℃ for 2h~4h to obtain the coated alumina insulator.

2. The method for preparing the coating-modified alumina insulator according to claim 1, characterized in that: In step 1, the high-pressure-resistance molecular group is a long-chain alkyl group, a fluorocarbon group, or a delocalized electron group; In step 2, under stirring conditions, the organosilane reaction reagent is first added to the reaction vessel dropwise, and then deionized water with a volume of 1 to 2 times that of the organosilane reaction reagent is added to the reaction vessel.

3. The method for preparing the coating-modified alumina insulator according to claim 2, characterized in that, Step 3 specifically involves: The pH of the reaction solution was adjusted to 4-5 using an acid solution of 0.1 mol / L to 1 mol / L. After reacting at 50℃ to 60℃ for 3-6 hours, the reaction solution was allowed to become clear and transparent. It was then cooled to room temperature and allowed to stand for 24-48 hours to precipitate, thus obtaining polyorganosilicon sol.

4. The method for preparing the coating-modified alumina insulator according to claim 3, characterized in that, Step 4 is as follows: The prepared alumina insulator body is immersed in the polysilicon sol. The polysilicon sol is coated on the surface of the alumina insulator body by a pulling method with a pulling speed controlled at 0.1 mm / min to 1 mm / min. After being dried in the air, a dehydration condensation reaction is carried out at 120℃ to 150℃ for 2 to 4 hours to obtain a coated alumina insulator.

5. The method for preparing the coating-modified alumina insulator according to claim 3, characterized in that, Step 4 specifically involves: Polysilicon sol was brushed onto the surface of the pre-prepared alumina insulator body. After being air-dried, the alumina insulator underwent a dehydration condensation reaction at 120℃~150℃ for 2h~4h to obtain a coated alumina insulator.

6. The method for preparing the coating-modified alumina insulator according to claim 4 or 5, characterized in that: In step 3, the acid solution is a hydrochloric acid solution, a sulfuric acid solution, or a nitric acid solution.

7. The method for preparing the coating-modified alumina insulator according to claim 6, characterized in that, Step 1 is as follows: According to a molar ratio of 10:2:3, tetraethyl orthosilicate, dimethyldiethoxysilane and perfluorophenyltriethoxysilane were weighed and mixed to obtain an organosilane reaction reagent. Step 2 specifically involves adding isopropanol, which has a volume twice that of the organosilane reaction reagent, into the reaction vessel; under stirring conditions, the organosilane reaction reagent is first added to the reaction vessel dropwise, and then deionized water, which has a volume once that of the organosilane reaction reagent, is added to the reaction vessel, and the mixture is then mixed to obtain the reaction solution.

8. The method for preparing the coating-modified alumina insulator according to claim 7, characterized in that, Step 3 specifically involves: The pH of the reaction solution was adjusted to 4.5 using a 1 mol / L sulfuric acid solution. After reacting at 60°C for 3 hours, the reaction solution was allowed to become clear and transparent. It was then cooled to room temperature and allowed to stand for 24 hours to settle, resulting in polyorganosilicon sol.

9. The method for preparing the coating-modified alumina insulator according to claim 4, characterized in that, Step 4 specifically involves: The pre-prepared alumina insulator body was immersed in the polysilicon sol. The polysilicon sol was coated on the surface of the alumina insulator body by using a pull-up method with a pull-up speed of 1 mm / min. After being dried in the air, a dehydration condensation reaction was carried out at 150°C for 2 hours to obtain a coated alumina insulator.

10. A coating-modified alumina insulator, characterized in that: It is prepared by the preparation method of the coating modified alumina insulator according to any one of claims 1-9.

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