High dielectric breakdown strength nanostructured aluminum oxide insulating coating and method of making same

Abstract

The application discloses a kind of high dielectric breakdown strength nanostructure alumina insulation coating, the preparation steps of the nanostructure alumina insulation coating are as follows: one, in ball mill, deionized water, grinding ball, dispersing agent, submicron alumina powder, nano alumina powder, binder and defoaming agent are ball milled, to obtain slurry;Two, the slurry is carried out spray granulation, to obtain alumina agglomerated powder;Three, alumina agglomerated powder is carried out solid phase sintering, by screening to the powder after solid phase sintering, to obtain nanostructure alumina feed powder;Four, the nanostructure alumina feed powder is carried out atmospheric plasma spraying, to prepare the nanostructure alumina insulation coating with high dielectric breakdown strength.The method utilizes the high sintering activity of nanoscale size alumina, so that more nanoscale powder is retained in the powder as much as possible, thereby effectively improving the dielectric breakdown strength of the prepared coating.

Description

Technical Field

[0001] This invention relates to a method for preparing an insulating coating, specifically to a high dielectric breakdown strength nanostructured alumina insulating coating and its preparation method. Background Technology

[0002] Due to its excellent insulation, high hardness, high rigidity, high chemical stability, and good biocompatibility, alumina ceramic coatings are widely used in the preparation of insulating coatings in electronics, aerospace, automotive, high-speed rail, wind power, and medical devices. The principle of insulating coatings is to form an insulating film or coating on the surface of an object, giving it excellent insulating properties. This effectively isolates current, prevents current leakage and arc discharge, and blocks current from passing through the object's surface, thus achieving the purpose of insulation. In the electronics field, insulating coatings can be applied to circuit boards, electronic components, etc., protecting electronic equipment from moisture, dust, and chemical corrosion, improving the service life and reliability of electronic equipment. In the aerospace field, insulating coatings can be applied to aircraft, missiles, etc., improving the aircraft's high-temperature resistance, corrosion resistance, and lightning protection capabilities. In the automotive field, insulating coatings can be applied to automotive wiring harnesses, batteries, etc., increasing the stability and safety of automotive electrical systems. In the high-speed rail, wind power, and new energy fields, insulating coatings can be applied to motor bearings, motor end covers, etc., extending the service life of motor bearings and improving motor stability. In the medical device field, such as pacemakers, defibrillators, and electrosurgical units, insulating coatings can ensure electrical isolation between the device surface and the patient, reducing the risk of electric shock. Therefore, with the development of industries such as electronics, aerospace, automobiles, high-speed rail, wind power, and medical devices, the requirements for insulating coatings are becoming increasingly stringent.

[0003] Currently, atmospheric plasma spraying is an effective method for preparing alumina ceramic insulating coatings. However, coatings prepared using existing alumina powders via plasma spraying do not meet the electrical breakdown strength requirements of high-voltage electrical insulation applications such as high-speed rail, rail transit, and wind power. Therefore, there is an urgent need to develop alumina ceramic coatings with higher dielectric breakdown strength. Summary of the Invention

[0004] To address the shortcomings of traditional micron-sized alumina feed powder with large grain size and low dielectric breakdown strength in the prepared insulating coating, this invention provides a high dielectric breakdown strength nanostructured alumina insulating coating and its preparation method. This method involves adding a small amount of submicron-sized alumina to the nano-alumina powder raw material. Utilizing the high sintering activity of nano-sized alumina, the method retains as many nano-sized particles as possible within the powder, thereby effectively improving the dielectric breakdown strength of the coating.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A nanostructured alumina feed powder is prepared from submicron alumina powder and nano alumina powder, wherein: the amount of submicron alumina is 10-30 wt% of the total alumina powder; the particle size of the nano alumina powder is 10-80 nm, and the particle size of the submicron alumina powder is 200-800 nm.

[0007] A method for preparing the above-mentioned nanostructured alumina feed powder includes the following steps:

[0008] Step 1: Add deionized water and grinding balls to a ball mill, then add a dispersant and stir until fully dissolved. Next, add submicron and nano-alumina powders in batches, ball milling to ensure uniform dispersion. Finally, add a binder and defoamer to obtain the slurry required for spray granulation, wherein:

[0009] The amount of deionized water used is 45-75 wt% of the total alumina powder, the amount of dispersant used is 0.5-5 wt% of the total alumina powder, the amount of binder used is 0.1-10 wt% of the total alumina powder, and the amount of defoamer used is 0.2-5 ml / kg of the total alumina powder.

[0010] The mass ratio of the grinding balls to the total amount of alumina powder is 1 to 4:1;

[0011] The diameter of the grinding ball is 3-10 mm;

[0012] The ball milling time is 4–10 hours, and the rotation speed is 200–800 r / min;

[0013] The submicron alumina powder and nano alumina powder are added as follows: first, the submicron alumina is added to deionized water, and then the nano alumina powder is added to the deionized water in 3 to 5 portions, with an interval of 5 to 20 minutes between each addition.

[0014] The dispersant is one or more of sodium tripolyphosphate, sodium hexametaphosphate, isobutanol, ethylene glycol, ammonium citrate, and sodium citrate.

[0015] The binder includes one or more of PVA, PEO, PEG, starch, cellulose and gum arabic;

[0016] The defoamer includes one or more of the following: tributyl phosphate, polysiloxane, dimethyl silicone oil, polyether defoamer, and silicone polyether defoamer;

[0017] Step 2: Spray granulation is performed on the slurry obtained in Step 1 to obtain alumina agglomerates with micron-scale, wherein:

[0018] The parameters for the spray granulation are: inlet air temperature of 200-260℃, outlet air temperature of 80-120℃, needle frequency of 3-20 times / minute, and peristaltic pump speed of 30-45 r / min.

[0019] Step 3: Solid-state sintering of alumina agglomerates with a particle size less than 150 mesh is performed, followed by furnace cooling to room temperature. The sintered powder is then sieved to obtain nanostructured alumina feed powder with particle size, flowability, and density that meet the requirements for atmospheric plasma spraying.

[0020] The solid-state sintering is carried out in an atmospheric environment. The solid-state sintering process is as follows: the temperature is raised to 260-350℃ at a rate of 1-10℃ / min and held for 0.5-3.5h; then the temperature is raised to 550-700℃ at a rate of 1-10℃ / min and held for 0.5-3.5h; finally, the temperature is raised to 1000-1300℃ at a rate of 5-10℃ / min and held for 0.5-2h.

[0021] The screening method is as follows: the powder after solid-phase sintering is screened using a vibrating screen with a mesh size of 200 to 600.

[0022] A method for preparing a high dielectric breakdown strength nanostructured alumina insulating coating involves using the aforementioned nanostructured alumina feed powder to prepare a coating with a nanostructure, thereby achieving high dielectric breakdown strength in the alumina coating. The specific steps are as follows:

[0023] A nanostructured alumina feed powder was subjected to atmospheric plasma spraying to prepare a nanostructured alumina insulating coating with high dielectric breakdown strength, wherein:

[0024] The parameters for atmospheric plasma spraying are as follows: spraying voltage of 50-65V, spraying current of 500-650A, powder feeding speed of 15-30g / min, spraying distance of 80-120mm, gun movement speed of 400-800mm / s; main gas flow rate of 55-110SCFH, auxiliary gas flow rate of 3-15SCFH, and spraying thickness of 50-1000μm.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. By controlling the ratio of nano- and submicron-sized alumina powders, different microstructures can be constructed within the feed powder. Furthermore, the price of submicron alumina powder is lower than that of nanostructures. Appropriately introducing submicron-sized powders during the preparation process can reduce the use of nanostructure raw materials. The final feed powder preparation process is relatively simple and has strong applicability. Therefore, the cost of this invention is relatively low, the process is simple, and it is easy to mass-produce.

[0027] 2. In the preparation process of this invention, due to the introduction of some submicron particles, the number of particles is reduced under the same solid content conditions, and the use of some dispersants and binders is reduced. Therefore, the impact of the addition of organic matter on the purity of raw materials can be appropriately reduced, thereby ensuring that the prepared powder has high purity.

[0028] 3. The dielectric breakdown strength of the coating prepared by the feed powder of this invention exceeds 10 kV / mm after spraying, without any post-treatment. Compared with the coating breakdown strength of less than 8 kV / mm reported in the literature (Effect of Melting Behavior of Al2O3 Powder on the Structure and Dielectric Properties of Plasma-Sprayed Coatings), the dielectric breakdown strength of the coating prepared using nanostructured feed powder can be increased by 2 kV / mm. Therefore, the preparation of coatings using nanostructured alumina feed powder can effectively improve the dielectric breakdown strength of the coating, and the introduction of the nanoscale enables the coating to have a high dielectric breakdown strength. Attached Figure Description

[0029] Figure 1 The preparation process of nanostructured alumina powder and coating;

[0030] Figure 2 XRD pattern of nanostructured alumina feed powder;

[0031] Figure 3 The surface morphology of nanostructured alumina feed powder;

[0032] Figure 4 XRD pattern of nanostructured alumina insulating coating;

[0033] Figure 5 The surface morphology of the nanostructured alumina insulating coating;

[0034] Figure 6 The cross-sectional morphology of the nanostructured alumina insulating coating is shown. Detailed Implementation

[0035] The technical solution of the present invention will be further described below with reference to the embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0036] Example 1:

[0037] This embodiment provides a method for preparing a high dielectric breakdown strength nanostructured alumina insulating coating, such as... Figure 1 As shown, the specific steps are as follows:

[0038] (1) Preparation of slurry: First, weigh 9 kg of alumina grinding balls and place them in a ball mill jar. Then, weigh 15 g of ammonium citrate, dissolve it in 2 L of deionized water, and transfer it to the ball mill jar. Weigh 0.5 kg of alumina raw material with a D50 value of 200 nm and add it to the ball mill jar. Then, add 2.5 kg of alumina raw material with a D50 value of 30 nm (20-80 nm) to the ball mill jar in 5 portions, with an interval of 10 min between each addition. After all the slurry has been added, adjust the ball mill speed to 600 r / min and stir for 6 h. Then, add 15 g of PVA and 10 ml of tributyl phosphate, and continue stirring at a stirring speed of 600 r / min for 30 min to ensure that the PVA and raw materials are mixed evenly, thus obtaining the slurry required for spray granulation.

[0039] (2) Spray granulation is performed on the slurry obtained in step (1) to obtain the required feed powder. The spray granulation parameters are: inlet air temperature is 245℃, outlet air temperature is 90℃, needle frequency is 15 times / minute, and peristaltic pump speed is 42r / min.

[0040] (3) Solid-state sintering is performed on the powder obtained in step (2). The sintering parameters are as follows: first, the temperature is raised to 330℃ at a rate of 5℃ / min and held for 2h; then, the temperature is raised to 600℃ at a rate of 8℃ / min and held for 1h; finally, the temperature is raised to 1150℃ at a rate of 10℃ / min and held for 1h; then, the powder is cooled to room temperature by furnace cooling. The solid-state sintered powder is sieved to a size range of -48 to +13μm to meet the requirements of atmospheric plasma spraying.

[0041] (4) First, the GCr15 bearing steel substrate was sandblasted, then ultrasonically cleaned in alcohol for 15 min, and finally atmospheric plasma spraying was performed on the powder obtained in step (3) to prepare a nanostructured alumina insulating coating with high dielectric breakdown strength. The atmospheric plasma spraying parameters were: spraying voltage of 60V, spraying current of 650A, powder feeding speed of 20g / min, spraying distance of 100mm, gun moving speed of 400mm / s; main gas flow rate of 100SCFH, auxiliary gas flow rate of 10SCFH, and spraying thickness of 350±25μm.

[0042] (5) The dielectric breakdown strength of the coating prepared in step (4) was tested according to the national standard. The test result was 11.3kV / mm.

[0043] The XRD results of the nanostructured alumina feed powder after solid-state sintering are as follows: Figure 2As shown, by Figure 2 It can be seen that the phase structure of the nanostructured alumina feed powder prepared in this embodiment is mainly α phase, with a small amount of θ phase; the surface morphology of the nanostructured alumina feed powder after solid-state sintering is as follows: Figure 3 As shown, according to Figure 3 The surface morphology shown indicates that nanoparticles are retained in the nanostructured alumina feed powder; the coating phase structure prepared using the nanostructured feed powder is as follows: Figure 4 As shown, by Figure 2 It can be seen that the coating mainly consists of α and γ phases, with the α phase being the dominant phase; the surface morphology of the coating prepared using nanostructure feedstock is as follows. Figure 5 As shown, according to Figure 5 The surface morphology shows that the coating has obvious molten and unmelted areas, exhibiting a typical dual-modal morphology of nanostructures; the cross-sectional morphology of the coating prepared using nanostructure feedstock is as follows. Figure 6 As shown, by Figure 6 As can be seen, the coating thickness meets the design requirements, and although there are a few pores in the cross-sectional area, the overall coating is relatively dense, thus the coating has a high dielectric breakdown strength.

[0044] Example 2:

[0045] (1) Slurry preparation: First, weigh 9 kg of alumina grinding balls and place them in a ball mill jar. Then, weigh 25 g of ammonium citrate, dissolve it in 2.5 L of deionized water, and transfer it to the ball mill jar. Weigh 1 kg of alumina raw material with a D50 value of 500 nm and add it to the ball mill jar. Then, add 3 kg of alumina raw material with a D50 value of 30 nm in 5 portions to the ball mill jar, with an interval of 10 min between each addition. After all the slurry has been added, adjust the ball mill speed to 400 r / min and stir for 6 h. Then, add 20 g of PVA and 10 ml of tributyl phosphate, and continue stirring at a stirring speed of 400 r / min for 30 min to ensure that the PVA and raw materials are mixed evenly, thus obtaining the slurry required for spray granulation.

[0046] (2) Spray granulation is performed on the slurry obtained in step (1) to obtain the required feed powder. The spray granulation parameters are: inlet air temperature is 240℃, outlet air temperature is 80℃, needle frequency is 15 times / minute, and peristaltic pump speed is 42r / min.

[0047] (3) Solid-state sintering is performed on the powder obtained in step (2). The sintering parameters are as follows: first, the temperature is raised to 350℃ at a rate of 5℃ / min and held for 2h; then, the temperature is raised to 550℃ at a rate of 8℃ / min and held for 1h; finally, the temperature is raised to 1100℃ at a rate of 10℃ / min and held for 1h; then, the powder is cooled to room temperature by furnace cooling. The solid-state sintered powder is sieved to a size range of -48 to +20μm to meet the requirements of atmospheric plasma spraying.

[0048] (4) First, the GCr15 bearing steel substrate was sandblasted, then the substrate was transferred to alcohol for ultrasonic cleaning for 15 min. Finally, the powder obtained in step (3) was used for atmospheric plasma spraying to prepare a nanostructured alumina insulating coating with high dielectric breakdown strength. The atmospheric plasma spraying parameters were: spraying voltage of 65V, spraying current of 650A, powder feeding speed of 25g / min, spraying distance of 100mm, gun moving speed of 400mm / s; main gas flow rate of 100SCFH, auxiliary gas flow rate of 12SCFH, and spraying thickness of 350±25μm.

[0049] (5) The dielectric breakdown strength of the coating prepared in step (4) was tested according to the national standard. The test result was 10.8kV / mm.

[0050] Example 3:

[0051] (1) Preparation of slurry: First, weigh 9 kg of alumina grinding balls and place them in a ball mill jar. Then, weigh 25 g of ammonium citrate, dissolve it in 2.5 L of deionized water, and transfer it to the ball mill jar. Weigh 1 kg of alumina raw material with a D50 value of 300 nm and add it to the ball mill jar. Then, add 3 kg of alumina raw material with a D50 value of 50 nm to the ball mill jar in 5 portions, with an interval of 10 min between each addition. After all the slurry has been added, adjust the ball mill speed to 500 r / min and stir for 6 h. Then, add 20 g of PVA and 10 ml of tributyl phosphate, and continue stirring at a stirring speed of 500 r / min for 30 min to ensure that the PVA and raw materials are mixed evenly, thus obtaining the slurry required for spray granulation.

[0052] (2) Spray granulation is performed on the slurry obtained in step (1) to obtain the required feed powder. The spray granulation parameters are: inlet air temperature is 240℃, outlet air temperature is 80℃, needle frequency is 15 times / minute, and peristaltic pump speed is 42r / min.

[0053] (3) Solid-state sintering is performed on the powder obtained in step (2). The sintering parameters are as follows: first, the temperature is raised to 350℃ at a rate of 5℃ / min and held for 2h; then, the temperature is raised to 550℃ at a rate of 8℃ / min and held for 1h; finally, the temperature is raised to 1130℃ at a rate of 10℃ / min and held for 1h; then, the powder is cooled to room temperature by furnace cooling. The solid-state sintered powder is sieved to obtain a size range of -48 to +13μm to meet the requirements of atmospheric plasma spraying.

[0054] (4) First, the GCr15 bearing steel substrate was sandblasted, then the substrate was transferred to alcohol for ultrasonic cleaning for 15 min. Finally, the powder obtained in step (3) was used for atmospheric plasma spraying to prepare a nanostructured alumina insulating coating with high dielectric breakdown strength. The atmospheric plasma spraying parameters were: spraying voltage of 65V, spraying current of 650A, powder feeding speed of 25g / min, spraying distance of 100mm, gun moving speed of 400mm / s; main gas flow rate of 100SCFH, auxiliary gas flow rate of 10SCFH, and spraying thickness of 350±25μm.

[0055] (5) The dielectric breakdown strength of the coating prepared in step (4) was tested according to the national standard. The test result was 11.3kV / mm.

[0056] Example 4:

[0057] (1) Preparation of slurry: First, weigh 9 kg of alumina grinding balls and place them in a ball mill jar. Then, weigh 15 g of ammonium citrate, dissolve it in 2 L of deionized water, and transfer it to the ball mill jar. Weigh 0.5 kg of alumina raw material with a D50 value of 200 nm and add it to the ball mill jar. Then, add 2.5 kg of alumina raw material with a D50 value of 40 nm to the ball mill jar in 5 portions, with an interval of 10 min between each addition. After all the slurry has been added, adjust the ball mill speed to 600 r / min and stir for 6 h. Then, add 15 g of PVA and 10 ml of tributyl phosphate, and continue stirring at a stirring speed of 600 r / min for 30 min to ensure that the PVA and raw materials are mixed evenly, thus obtaining the slurry required for spray granulation.

[0058] (2) Spray granulation is performed on the slurry obtained in step (1) to obtain the required feed powder. The spray granulation parameters are: inlet air temperature is 250℃, outlet air temperature is 90℃, needle frequency is 15 times / minute, and peristaltic pump speed is 42r / min.

[0059] (3) Solid-state sintering is performed on the powder obtained in step (2). The sintering parameters are as follows: first, the temperature is raised to 330℃ at a rate of 5℃ / min and held for 2h; then, the temperature is raised to 600℃ at a rate of 8℃ / min and held for 1h; finally, the temperature is raised to 1150℃ at a rate of 10℃ / min and held for 1h; then, the powder is cooled to room temperature by furnace cooling. The solid-state sintered powder is sieved to a size range of -48 to +15μm to meet the requirements of atmospheric plasma spraying.

[0060] (4) First, the GCr15 bearing steel substrate was sandblasted, then ultrasonically cleaned in alcohol for 15 min, and finally atmospheric plasma spraying was performed on the powder obtained in step (3) to prepare a nanostructured alumina insulating coating with high dielectric breakdown strength. The atmospheric plasma spraying parameters were: spraying voltage of 60V, spraying current of 650A, powder feeding speed of 20g / min, spraying distance of 100mm, gun moving speed of 400mm / s; main gas flow rate of 110SCFH, auxiliary gas flow rate of 10SCFH, and spraying thickness of 345±25μm.

[0061] (5) The dielectric breakdown strength of the coating prepared in step (4) was tested according to the national standard. The test result was 12.1 kV / mm.

Claims

1. A nanostructured alumina feed powder, characterized in that... The feed powder is prepared from submicron alumina powder and nano alumina powder, wherein: the amount of submicron alumina is 10~30wt% of the total alumina powder; the particle size of nano alumina powder is 10~80 nm, and the particle size of submicron alumina powder is 200~800 nm. The specific preparation steps are as follows: Step 1: Add deionized water and grinding balls to a ball mill, then add a dispersant and stir to dissolve it in the water. First, add submicron alumina to the deionized water, then add nano alumina powder in 3-5 portions, with an interval of 5-20 minutes between each addition. Ball mill to disperse it evenly. Finally, add a binder and a defoamer to obtain the slurry required for spray granulation. The amount of deionized water is 45-75 wt% of the total alumina powder, the amount of dispersant is 0.5-5 wt% of the total alumina powder, the amount of binder is 0.1-10 wt% of the total alumina powder, and the amount of defoamer is 0.2-5 ml / kg of the total alumina powder. Step 2: Spray granulation is performed on the slurry obtained in Step 1 to obtain alumina agglomerate powder with micron scale. The parameters of the spray granulation are: inlet air temperature of 200~260℃, outlet air temperature of 80~120℃, needle frequency of 3~20 times / minute, and peristaltic pump speed of 30~45r / min. Step 3: Solid-state sintering of alumina agglomerates with a particle size of less than 150 mesh is performed, followed by furnace cooling to room temperature. The solid-state sintered powder is then screened through a 200-600 mesh sieve using a vibrating screen to obtain nanostructured alumina feed powder. The solid-state sintering is carried out in an atmospheric environment. The solid-state sintering process is as follows: heating to 260-350 °C at a rate of 1-10 °C / min and holding for 0.5-3.5 h; then heating to 550-700 °C at a rate of 1-10 °C / min and holding for 0.5-3.5 h; finally heating to 1000-1300 °C at a rate of 5-10 °C / min and holding for 0.5-2 h.

2. A method for preparing the nanostructured alumina feed powder according to claim 1, characterized in that... The method includes the following steps: Step 1: Add deionized water and grinding balls to a ball mill, then add a dispersant and stir to dissolve it in the water. First, add submicron alumina to the deionized water, then add nano alumina powder in 3-5 portions, with an interval of 5-20 minutes between each addition. Ball mill to disperse it evenly. Finally, add a binder and a defoamer to obtain the slurry required for spray granulation. The amount of deionized water is 45-75 wt% of the total alumina powder, the amount of dispersant is 0.5-5 wt% of the total alumina powder, the amount of binder is 0.1-10 wt% of the total alumina powder, and the amount of defoamer is 0.2-5 ml / kg of the total alumina powder. Step 2: Spray granulation is performed on the slurry obtained in Step 1 to obtain alumina agglomerate powder with micron scale. The parameters of the spray granulation are: inlet air temperature of 200~260℃, outlet air temperature of 80~120℃, needle frequency of 3~20 times / minute, and peristaltic pump speed of 30~45r / min. Step 3: Solid-state sintering of alumina agglomerates with a particle size of less than 150 mesh is performed, followed by furnace cooling to room temperature. The solid-state sintered powder is then screened through a 200-600 mesh sieve using a vibrating screen to obtain nanostructured alumina feed powder. The solid-state sintering is carried out in an atmospheric environment. The solid-state sintering process is as follows: heating to 260-350 °C at a rate of 1-10 °C / min and holding for 0.5-3.5 h; then heating to 550-700 °C at a rate of 1-10 °C / min and holding for 0.5-3.5 h; finally heating to 1000-1300 °C at a rate of 5-10 °C / min and holding for 0.5-2 h.

3. The method for preparing nanostructured alumina feed powder according to claim 2, characterized in that... In step one, the mass ratio of grinding balls to alumina powder is 1~4:1; the diameter of the grinding balls is 3~10 mm.

4. The method for preparing nanostructured alumina feed powder according to claim 2, characterized in that... In step one, the ball milling time is 4~10 h and the rotation speed is 200~800 r / min.

5. The method for preparing nanostructured alumina feed powder according to claim 2, characterized in that... In step one, the dispersant is one or more of sodium tripolyphosphate, sodium hexametaphosphate, isobutanol, ethylene glycol, ammonium citrate, and sodium citrate; the binder includes one or more of PVA, PEO, PEG, starch, cellulose, and gum arabic; and the defoamer includes one or more of tributyl phosphate, polysiloxane, dimethyl silicone oil, polyether defoamer, and silicone polyether defoamer.

6. A method for preparing a high dielectric breakdown strength nanostructured alumina insulating coating, characterized in that... The method includes the following steps: The nanostructured alumina feed powder described in claim 1 is subjected to atmospheric plasma spraying to prepare a nanostructured alumina insulating coating with high dielectric breakdown strength. The parameters of the atmospheric plasma spraying are as follows: spraying voltage of 50~65 V, spraying current of 500~650 A, powder feeding speed of 15~30 g / min, spraying distance of 80~120 mm, gun movement speed of 400~800 mm / s; main gas flow rate of 55~110 SCFH, auxiliary gas flow rate of 3~15 SCFH, and spraying thickness of 50~1000 μm.

7. A high dielectric breakdown strength nanostructured alumina insulating coating prepared by the method of claim 6.

Images