Additive and preparation method thereof, insulating oil and application

Abstract

The invention provides an additive, a preparation method thereof, insulating oil and application. The additive is prepared by carrying out amidation reaction on a nano metal oxide with amino on the surface and a carboxylic acid compound in a mass ratio of 1: (1-4); wherein the nano metal oxide with the amino group on the surface is prepared from the following raw materials: nano metal oxide and an amino silane coupling agent in a mass ratio of 1: (2-4). According to the additive used in the invention, amino is grafted on the surface of nano cobalt oxide and then further reacts with a carboxylic acid compound to form an amide compound, so that the compatibility between the nano cobalt oxide and the carboxylic acid compound is effectively improved, and the final additive increases the number of tiny interfaces in the insulating oil; the interfaces can prevent current from directly passing through, so that the alternating-current insulating strength of the insulating oil is improved.

Description

Technical Field

[0001] The present application relates to the technical field of insulating oil additives, and in particular to an additive and a preparation method thereof, insulating oil, and applications thereof. Background Art

[0002] The electrical strength of transformer insulating oil is a core indicator for ensuring equipment insulation reliability. This requirement stems from the stringent safety and stability demands of power systems. As the primary insulating medium within transformers, insulating oil must form a stable insulation barrier in high-voltage electric fields, withstanding both the long-term effects of power frequency voltage and transient overvoltages such as lightning strikes. Insufficient electrical strength can easily lead to partial discharge or penetrating breakdown in the oil, causing serious accidents such as winding short circuits and arc explosions, threatening the safe operation of the power grid. For example, trace contaminants in the oil (such as moisture and metal particles) can significantly degrade its dielectric properties: when the moisture content exceeds 0.01%, the breakdown voltage can drop by over 35%. Furthermore, the acidic substances and oil sludge produced by oxidation accelerate the aging of the insulating cardboard, forming conductive paths.

[0003] Modified materials, such as surface-modified titanium dioxide nanosieves, are commonly used. These polarize under the action of an electric field, creating a large number of traps that capture free electrons in the oil. This delays the formation of discharge channels, increases the oil's breakdown voltage, and effectively improves the electrical strength of mineral insulating oil. However, when faced with electrical equipment operating at higher voltage levels and in more complex operating environments, the potential for improving the AC insulation performance of insulating oil may be limited. Summary of the Invention

[0004] Based on this, it is necessary to provide an additive with good AC insulation performance, a preparation method thereof, insulating oil and applications thereof.

[0005] The present application provides an additive, which is prepared by amidation reaction of a nano-metal oxide having amino groups on the surface and a carboxylic acid compound in a mass ratio of 1:(1-4);

[0006] The raw materials of the nano-metal oxide having amino groups on the surface include nano-metal oxide and aminosilane coupling agent in a mass ratio of 1:(2-4).

[0007] In one embodiment, one or more of the following conditions are met:

[0008] (1) The particle size of the nano metal oxide is 50nm~150nm;

[0009] (2) The pore size of the nano-metal oxide surface is 5 nm to 15 nm;

[0010] (3) The nano metal oxide includes one or more of nano cobalt oxide, nano iron oxide, nano copper oxide, nano titanium dioxide and nano zinc oxide;

[0011] (4) The aminosilane coupling agent includes one or more of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltriisopropoxysilane and 3-aminopropyltriacetoxysilane;

[0012] (5) The carboxylic acid compound includes one or both of arachidonic acid and oleic acid.

[0013] The present application also provides a method for preparing an additive, comprising the following steps:

[0014] Mixing a nano-metal oxide having an amino group on the surface and a carboxylic acid compound in a mass ratio of 1:(1-4), and performing an amidation reaction to prepare the additive;

[0015] The raw materials for preparing the nano metal oxide having amino groups on the surface are mixed with nano metal oxide and aminosilane coupling agent in a mass ratio of 1:(2-4).

[0016] In one embodiment, the method for preparing the nano metal oxide comprises the following steps:

[0017] The metal salt is placed in a first organic solvent with a pH value of 7.5 to 8.5 for hydrolysis reaction to prepare a colloid;

[0018] placing the colloid at a first temperature and stirring for a first time to form a gel;

[0019] The gel is dried and calcined.

[0020] In one embodiment, one or more of the following conditions are met:

[0021] (1) The first temperature is 40°C to 50°C;

[0022] (2) The first time is 12 hours to 24 hours;

[0023] (3) The drying temperature is 50℃~70℃;

[0024] (4) Drying time is 20h~30h;

[0025] (5) The calcination temperature is 850℃~950℃;

[0026] (6) The calcination time is 3h~4h.

[0027] In one embodiment, the method for preparing the nano metal oxide having amino groups on the surface comprises the following steps:

[0028] The nano metal oxide and the aminosilane coupling agent are mixed according to a mass ratio, and modified at a temperature of 70° C. to 90° C. and a humidity of 50% to 70%.

[0029] In one embodiment, the amidation reaction satisfies one or both of the following conditions:

[0030] (1) Temperature is 70℃~90℃;

[0031] (2) The time is 10h~14h.

[0032] Furthermore, the present application also provides an insulating oil, comprising a natural ester oil and a modified substance in a volume ratio of 1:(0.05~0.3), wherein the modified substance comprises the additive as described above or the additive prepared by the preparation method as described above.

[0033] In one embodiment, the natural ester oil includes one or more of FR3 insulating oil, palm oil and rapeseed oil.

[0034] Furthermore, the present application also provides the use of the above-mentioned additive or the additive prepared by the above-mentioned preparation method or the above-mentioned insulating oil in power equipment.

[0035] The additive used in this application effectively improves the compatibility between nano-metal oxides and carboxylic acid compounds by grafting amino groups on the surface of nano-metal oxides and further reacting with carboxylic acid compounds. The final additive increases the number of tiny interfaces in the insulating oil, which can hinder the direct passage of current, thereby improving the AC insulation strength of the insulating oil. DETAILED DESCRIPTION

[0036] In order to facilitate understanding of the present application, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0037] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In the description of this application, the meaning of "several" is at least one, such as one, two, etc., unless otherwise clearly and specifically defined.

[0038] The words "preferably", "more preferably", etc. in this application refer to embodiments of the present application that may provide certain benefits under certain circumstances. However, other embodiments may also be preferred under the same circumstances or other circumstances. In addition, the description of one or more preferred embodiments does not imply that other embodiments are not applicable, nor is it intended to exclude other embodiments from the scope of this application.

[0039] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein are understood to include any and all subranges subsumed therein.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0041] The present application provides an additive, which is prepared by amidation reaction of a nano-metal oxide having amino groups on the surface and a carboxylic acid compound in a mass ratio of 1:(1-4);

[0042] The raw materials of the metal oxide with amino groups on the surface include nano-metal oxide and aminosilane coupling agent in a mass ratio of 1:(2-4).

[0043] The additive used in this application effectively improves the compatibility between nano-metal oxides and carboxylic acid compounds by grafting amino groups on the surface of nano-metal oxides and further reacting with carboxylic acid compounds. The final additive increases the number of tiny interfaces in the insulating oil, which can hinder the direct passage of current, thereby improving the AC insulation strength of the insulating oil.

[0044] In a specific example, the particle size of the nano-metal oxide is 50 nm to 150 nm. Specifically, the particle size of the nano-metal oxide can be, but is not limited to, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, or 150 nm.

[0045] In a specific example, the pore size of the nano-metal oxide surface is 5 nm to 15 nm. Specifically, the pore size of the nano-metal oxide surface can be, but is not limited to, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, or 15 nm.

[0046] In a specific example, the nano metal oxide includes one or more of nano cobalt oxide, nano iron oxide, nano copper oxide, nano titanium dioxide, and nano zinc oxide.

[0047] In a specific example, the aminosilane coupling agent includes one or more of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltriisopropoxysilane, and 3-aminopropyltriacetoxysilane.

[0048] In a specific example, the carboxylic acid compound includes one or both of arachidonic acid and oleic acid.

[0049] The present application also provides a method for preparing an additive, comprising the following steps:

[0050] Mixing a nano-metal oxide having amino groups on its surface and a carboxylic acid compound in a mass ratio of 1:(1-4), and performing an amidation reaction to prepare an additive;

[0051] The raw materials for preparing the nano-metal oxide with amino groups on the surface are mixed with nano-metal oxide and aminosilane coupling agent in a mass ratio of 1:(2-4).

[0052] In a specific example, the method for preparing nano metal oxide includes the following steps:

[0053] The metal salt is placed in a first organic solvent with a pH value of 7.5 to 8.5 for hydrolysis reaction to prepare a colloid;

[0054] placing the colloid at a first temperature and stirring for a first time to form a gel;

[0055] The gel is dried and calcined.

[0056] It can be understood that the nano-metal oxides prepared by the above sol-gel method generally have a molecular sieve structure, have a more uniform particle size and a more precise pore size distribution, and have higher chemical purity and better structural stability.

[0057] Furthermore, the pH value of the first organic solvent may be, but is not limited to, 7.5, 8 or 8.5.

[0058] In a specific example, the first temperature is 40°C to 50°C. Specifically, the first temperature may be, but is not limited to, 40°C, 42°C, 44°C, 46°C, 48°C or 50°C.

[0059] In a specific example, the first time is 12h~24h. Specifically, the first time can be but is not limited to 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h or 24h.

[0060] In a specific example, the drying temperature is 50°C to 70°C. Specifically, the drying temperature may be, but is not limited to, 50°C, 55°C, 60°C, 65°C or 70°C.

[0061] In a specific example, the drying time is 20 hours to 30 hours. Specifically, the drying time can be, but is not limited to, 20 hours, 21 hours, 22 hours, 23 hours, 24 hours, 25 hours, 26 hours, 27 hours, 28 hours, 29 hours or 30 hours.

[0062] In a specific example, the calcination temperature is 850°C to 950°C. Specifically, the calcination temperature can be, but is not limited to, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C or 950°C.

[0063] In a specific example, the calcination time is 3 h to 4 h. Specifically, the calcination time can be, but is not limited to, 3 h, 3.5 h or 4 h.

[0064] It can be understood that the calcination is carried out in an atmosphere of an inert gas, and the inert gas may be, but is not limited to, argon.

[0065] In a specific example, the preparation method of the nano metal oxide having amino groups on the surface includes the following steps:

[0066] The nano-metal oxide and the aminosilane coupling agent are mixed according to a mass ratio and modified at a temperature of 70° C. to 90° C. and a humidity of 50% to 70%.

[0067] In a specific example, the temperature of the amidation reaction is 70°C to 90°C. The temperature of the amidation reaction can be, but is not limited to, 70°C, 75°C, 80°C, 85°C or 90°C.

[0068] In a specific example, the amidation reaction time is 10 h to 14 h. The amidation reaction time can be, but is not limited to, 10 h, 11 h, 12 h, 13 h or 14 h.

[0069] Furthermore, the present application provides an insulating oil comprising a natural ester oil and a modified substance in a volume ratio of 1:(0.05-0.3), wherein the modified substance comprises the aforementioned additive or the additive prepared by the aforementioned preparation method. Furthermore, the volume ratio of the natural ester oil to the aforementioned additive or the additive prepared by the aforementioned preparation method in the insulating oil can be, but is not limited to, 1:0.05, 1:0.1, 1:0.15, 1:0.2, 1:0.25, or 1:0.3.

[0070] In a specific example, the natural ester oil includes one or more of FR3 insulating oil, palm oil, and rapeseed oil.

[0071] Furthermore, the present application also provides the use of the above-mentioned additive or the additive prepared by the above-mentioned preparation method or the above-mentioned insulating oil in power equipment.

[0072] The present application will be further described in detail below with reference to specific examples. It should be understood that these examples are intended to illustrate the present application only and are not intended to limit the scope of the present application. For experimental methods in the following examples where specific conditions are not specified, reference should be made to the instructions provided in this application, or to experimental manuals or conventional conditions in the art, or to conditions recommended by the manufacturer, or to experimental methods known in the art.

[0073] In the following specific examples, the measured parameters of raw material components may have slight deviations within the range of weighing accuracy unless otherwise specified. For temperature and time parameters, acceptable deviations due to instrument testing accuracy or operational accuracy are allowed. "Normal temperature" refers to 25°C; "normal pressure" refers to 100 kPa or 101 kPa.

[0074] Example 1

[0075] A homogeneous solution of 10g of cobalt nitrate (Co(NO3)2) was prepared in 50mL of 60% ethanol by volume. Sodium hydroxide was added to the solution to adjust the pH to 8, triggering a hydrolysis reaction to produce a stable hydroxide colloid. The sol was transferred to a reactor and heated in an oil bath at 50°C with continuous stirring for 12 hours. After the reaction, the resulting gel was vacuum-dried at 60°C for 24 hours and then calcined in a tube furnace at 900°C for 180 minutes under an argon atmosphere. After cooling, the cobalt oxide nanosieve was obtained.

[0076] 10g of KH-550 silane coupling agent (3-aminopropyltriethoxysilane, CAS No. 919-30-2, purchased from Aladdin Reagent Co.) was added to 30ml of acetone and heated to 50°C in a magnetic stirrer with continuous stirring for 1 hour. Meanwhile, impurities on the surface of the cobalt oxide nanosieve were washed with ethanol, and the nanosieve was then dried in a vacuum drying oven at 40°C for 24 hours. The dissolved coupling agent solution was evenly applied to the surface of the cobalt oxide nanosieve by spraying. The nanosieve was then placed in a constant temperature and humidity chamber at 80°C and 60% humidity to allow the coupling agent to react on the surface. After the reaction, the excess coupling agent was washed with ethanol, and the nanosieve was dried in a vacuum drying oven to prepare amino-activated cobalt oxide nanosieve.

[0077] 5 g of amino-activated cobalt oxide nanosieve and 10 g of arachidonic acid were mixed in 50 mL of n-hexane. The solution was heated to 80°C in a magnetic stirrer and stirred continuously for 12 hours to promote amidation between the carboxyl groups of the arachidonic acid and the amino groups on the surface of the cobalt oxide nanosieve. After the reaction, the product was separated from the solution using a centrifuge and washed with an appropriate amount of n-hexane to remove unreacted arachidonic acid and solvent. The washed product was placed in a vacuum desiccator and dried at 30°C for 24 hours to obtain the modified cobalt oxide nanosieve with arachidonic acid grafted on its surface.

[0078] The modified cobalt oxide nanosieve prepared in Example 1 was added to FR3 insulating oil. The modified cobalt oxide nanosieve in the above example accounted for 0.06 vol%, 0.12 vol%, 0.18 vol%, and 0.24 vol% of the total volume of the insulating oil and modified cobalt oxide nanosieve, respectively, as Test Examples 1, 2, 3, and 4. The mixed oil samples were subjected to high-speed dispersion treatment at 1200 rpm for 4 hours. After stirring, they were vacuum dried to obtain cobalt oxide nanosieve natural ester insulating oil with arachidonic acid grafted on its surface. To characterize its AC dielectric strength, the oil samples were subjected to AC breakdown voltage testing and volume resistivity measurements using an LJC-100KV breakdown voltage tester and an insulating oil volume resistivity meter.

[0079] The modified cobalt oxide nanosieve prepared in Example 1 was added to Karamay #25 mineral oil, wherein the nanosieve accounted for 0.06 vol%, 0.12 vol%, and 0.18 vol% of the overall insulating oil volume ratio as Test Example 5, Test Example 6, and Test Example 7, respectively. Subsequently, a high-speed stirrer was used to perform a high-speed dispersion treatment on the mixed oil sample at a speed of 1200 rpm for 4 hours. After stirring, a vacuum drying process was performed to obtain a modified cobalt oxide nanosieve natural ester insulating oil. In order to characterize its AC dielectric strength, an LJC-100KV breakdown voltage tester and an insulating oil volume resistivity meter were used to perform an AC breakdown voltage test and volume resistivity measurement on the oil sample.

[0080] Example 2

[0081] Using a hydrothermal method, 10g of cobalt nitrate (Co(NO₃)₂) was dissolved in 50mL of deionized water. 20mL of ethylene glycol was added as a reducing agent, and sodium hydroxide was added to adjust the solution's pH to 8. The resulting solution was stirred thoroughly and placed in an autoclave. The solution was then heated in an oil bath at 60°C for 24 hours. The cobalt ions were reduced by the ethylene glycol to cobalt oxide, which precipitated as nanoparticles. After the reaction was complete and allowed to cool to room temperature, the mixture was centrifuged and washed with ethanol. Finally, the solid was dried in a vacuum oven at 60°C for 12 hours to obtain a cobalt oxide nanosieve precursor solid. The nanosieve precursor was then calcined at 900°C for 180 minutes in an argon atmosphere in a tube furnace. After cooling, the cobalt oxide nanosieve was obtained.

[0082] 10g of KH-550 silane coupling agent (3-aminopropyltriethoxysilane, CAS No. 919-30-2, purchased from Aladdin Reagent Co.) was added to 30ml of acetone and heated to 50°C in a magnetic stirrer with continuous stirring for 1 hour. Meanwhile, impurities on the surface of the cobalt oxide nanosieve were washed with ethanol, and the nanosieve was then dried in a vacuum drying oven at 40°C for 24 hours. The dissolved coupling agent solution was evenly applied to the surface of the cobalt oxide nanosieve by spraying. The nanosieve was then placed in a constant temperature and humidity chamber at 80°C and 60% humidity to allow the coupling agent to react on the surface. After the reaction, the excess coupling agent was washed with ethanol, and the nanosieve was dried in a vacuum drying oven to prepare amino-activated cobalt oxide nanosieve.

[0083] 5 g of amino-activated cobalt oxide nanosieve and 10 g of arachidonic acid were mixed in 50 mL of n-hexane. The solution was heated to 80°C in a magnetic stirrer and stirred continuously for 12 hours to promote amidation between the carboxyl groups of the arachidonic acid and the amino groups on the surface of the cobalt oxide nanosieve. After the reaction, the product was separated from the solution using a centrifuge and washed with an appropriate amount of n-hexane to remove unreacted arachidonic acid and solvent. The washed product was placed in a vacuum desiccator and dried at 30°C for 24 hours to obtain the modified cobalt oxide nanosieve with arachidonic acid grafted on its surface.

[0084] The modified cobalt oxide nanosieve prepared by the hydrothermal method obtained in Example 2 above was added to FR3 insulating oil, wherein the nanosieve accounted for 0.06 vol%, 0.12 vol% and 0.18 vol% of the total volume of the insulating oil and the modified cobalt oxide nanosieve, respectively, as Test Example 8, Test Example 9 and Test Example 10. Subsequently, the mixed oil sample was subjected to a high-speed dispersion treatment for 4 hours using a high-speed stirrer at a speed of 1200 rpm. After stirring, it was vacuum dried to obtain a cobalt oxide nanosieve natural ester insulating oil grafted with arachidonic acid on the surface. In order to characterize its AC dielectric strength, the oil sample was subjected to AC breakdown voltage test and volume resistivity measurement using an LJC-100KV breakdown voltage tester and an insulating oil volume resistivity tester.

[0085] Example 3

[0086] A homogeneous solution of 10g of cobalt nitrate (Co(NO3)2) was prepared in 50mL of 60% ethanol by volume. Sodium hydroxide was added to the solution to adjust the pH to 8, triggering a hydrolysis reaction to produce a stable hydroxide colloid. The sol was transferred to a reactor and heated in an oil bath at 50°C with continuous stirring for 12 hours. After the reaction, the resulting gel was vacuum-dried at 60°C for 24 hours and then calcined in a tube furnace at 900°C for 180 minutes under an argon atmosphere. After cooling, the cobalt oxide nanosieve was obtained.

[0087] 10g of KH-550 silane coupling agent (3-aminopropyltriethoxysilane, CAS No. 919-30-2, purchased from Aladdin Reagent Co.) was added to 30ml of acetone and heated to 50°C in a magnetic stirrer with continuous stirring for 1 hour. Meanwhile, impurities on the surface of the cobalt oxide nanosieve were washed with ethanol, and the nanosieve was then dried in a vacuum drying oven at 40°C for 24 hours. The dissolved coupling agent solution was evenly applied to the surface of the cobalt oxide nanosieve by spraying. The nanosieve was then placed in a constant temperature and humidity chamber at 80°C and 60% humidity to allow the coupling agent to react on the surface. After the reaction, the excess coupling agent was washed with ethanol, and the nanosieve was dried in a vacuum drying oven to prepare amino-activated cobalt oxide nanosieve.

[0088] 5 g of amino-activated cobalt oxide nanosieve and 10 g of oleic acid were mixed in 50 mL of n-hexane. The solution was heated to 80°C in a magnetic stirrer and stirred for 12 hours to promote amidation between the carboxyl groups of the oleic acid and the amino groups on the surface of the cobalt oxide nanosieve. After the reaction, the product was separated from the solution using a centrifuge and washed with an appropriate amount of n-hexane to remove unreacted oleic acid and solvent. The washed product was dried in a vacuum desiccator at 30°C for 24 hours to obtain the modified cobalt oxide nanosieve with oleic acid grafted on its surface.

[0089] The modified cobalt oxide nanosieve grafted with oleic acid from Example 3 was added to FR3 insulating oil, with the total volume ratio of insulating oil to modified cobalt oxide nanosieve being 0.06 vol%, 0.12 vol%, and 0.18 vol%, respectively, as Test Examples 11, 12, and 13. Subsequently, the mixed oil sample was subjected to a high-speed dispersion treatment at 1200 rpm for 4 hours. After stirring, it was vacuum-dried to obtain the modified cobalt oxide nanosieve natural ester insulating oil. To characterize its AC dielectric strength, the oil sample was subjected to AC breakdown voltage testing and volume resistivity measurements using an LJC-100KV breakdown voltage tester and an insulating oil volume resistivity meter.

[0090] Example 4

[0091] The surface of commercially available cobalt oxide nanoparticles was activated with amino groups. These nanoparticles were solid particles with a particle size range of 20–100 nm, a specific surface area of ​​25 ± 5 m² / g, and no significant mesoporous structure (pore size < 5 nm). 10 g of KH-550 silane coupling agent (3-aminopropyltriethoxysilane, CAS No. 919-30-2, purchased from Aladdin Reagent Co., Ltd.) was added to 30 ml of acetone and heated to 50°C in a magnetic stirrer with continuous stirring for 1 hour. The dissolved coupling agent solution was evenly applied to the surface of the nanoparticles by spraying. The nanoparticles were then placed in a constant temperature and humidity chamber at 80°C and 60% humidity to allow the coupling agent to react on the surface. After the reaction, the excess coupling agent was washed with ethanol and then dried in a vacuum oven to prepare amino-activated nanoparticles of cobalt oxide.

[0092] 5g of amino-activated nano-cobalt oxide and 10g of arachidonic acid were mixed in 50mL of n-hexane. The solution was heated to 80°C in a magnetic stirrer and stirred continuously for 12 hours to promote the amidation reaction between the carboxyl groups of the arachidonic acid and the amino groups on the surface of the nano-cobalt oxide. After the reaction, the product was separated from the solution using a centrifuge and washed with an appropriate amount of n-hexane to remove unreacted arachidonic acid and solvent. The washed product was placed in a vacuum desiccator at 30°C for 24 hours to obtain modified nano-cobalt oxide with arachidonic acid grafted on its surface.

[0093] Modified nano-cobalt oxide was added to FR3 insulating oil, with the nanoparticles accounting for 0.06 vol%, 0.12 vol%, and 0.18 vol% of the total volume of the insulating oil and the modified cobalt oxide nanosieve, respectively, as Test Example 14, Test Example 15, and Test Example 16. Subsequently, the mixed oil sample was subjected to a high-speed dispersion treatment at a speed of 1200 rpm using a high-speed blender for 4 hours. After stirring, it was vacuum dried to obtain a modified nano-cobalt oxide natural ester insulating oil. To characterize its AC dielectric strength, the oil samples were subjected to AC breakdown voltage testing and volume resistivity measurements using an LJC-100KV breakdown voltage tester and an insulating oil volume resistivity meter.

[0094] Comparative Example 1

[0095] A homogeneous solution of 10g of cobalt nitrate (Co(NO3)2) was prepared in 50mL of 60% ethanol. Sodium hydroxide was added to the solution to adjust the pH to 8, triggering a hydrolysis reaction to produce a stable hydroxide colloid. The sol was transferred to a reactor and heated in an oil bath at 50°C with continuous stirring for 12 hours. After the reaction, the resulting gel was vacuum-dried at 60°C for 24 hours and then calcined in a tubular furnace at 900°C for 180 minutes under an argon atmosphere. After cooling, the cobalt oxide nanosieve was obtained.

[0096] 5g of cobalt oxide nanosieve and 10g of arachidonic acid were mixed in 50mL of n-hexane. The solution was heated to 80°C in a magnetic stirrer and stirred continuously for 12 hours. After the reaction, the product was separated from the solution using a centrifuge and washed with an appropriate amount of n-hexane to remove unreacted arachidonic acid and solvent. The washed product was then dried in a vacuum desiccator at 30°C for 24 hours. The modified cobalt oxide nanosieve, with arachidonic acid grafted onto its surface, was obtained by physical adsorption.

[0097] The modified cobalt oxide nanosieve of the above-mentioned comparative example 1 that has not been subjected to amino activation treatment was added to FR3 insulating oil, wherein the nanosieve accounted for 0.06 vol%, 0.12 vol%, and 0.18 vol% of the total volume of the insulating oil and the modified cobalt oxide nanosieve, respectively, as test examples 17, 18, and 19. Subsequently, the mixed oil sample was subjected to high-speed dispersion treatment for 4 hours using a high-speed stirrer at a speed of 1200 rpm. After stirring, it was vacuum dried to obtain a modified cobalt oxide nanosieve natural ester insulating oil. In order to characterize its AC insulation strength, the oil sample was subjected to AC breakdown voltage test and volume resistivity measurement using an LJC-100KV breakdown voltage tester and an insulating oil volume resistivity tester.

[0098] The average breakdown voltage and volume resistivity test results of the oil samples in the above embodiments and comparative examples are shown in Table 1 below.

[0099] Table 1

[0100]

[0101] From Table 1 above we can see that:

[0102] (1) The modified cobalt oxide nanosieve prepared by the sol-gel method has a better effect on improving the AC insulation strength of natural ester insulating oil than the modified cobalt oxide nanosieve prepared by the hydrothermal method and solid single crystal nano cobalt oxide. This is because the cobalt oxide nanosieve prepared by the sol-gel method has a more uniform particle size and a more precise pore size distribution, and has higher chemical purity and better structural stability.

[0103] (2) The modified cobalt oxide nanosieve after surface amino activation treatment has a better effect on improving the AC insulation strength of natural ester insulating oil than the modified cobalt oxide nanosieve without surface amino activation treatment. This is because the coupling agent can act as a "molecular bridge" between the nanosieve and arachidonic acid, significantly improving the compatibility between the two.

[0104] (3) The modification effect of using arachidonic acid to graft the surface of cobalt oxide nanosieve is better than that of using oleic acid to graft the surface of cobalt oxide nanosieve.

[0105] (4) When the addition amount of modified cobalt oxide nanosieve is 0.24 vol%, the effect of enhancing the breakdown voltage of FR3 insulating oil is weakened, indicating that too much nanosieve will increase the agglomeration phenomenon, and the contact area between the nanomaterial and the insulating oil will be reduced, which will affect the AC insulation strength of the insulating oil.

[0106] (5) The effect of the nanosieve on improving the breakdown voltage in #25 mineral oil is not as obvious as that in natural ester, which indicates that the modified nanosieve has a higher structural compatibility with natural ester insulating oil. The unique physical and chemical properties of the two make the barrier formed by the nanosieve in natural ester insulating oil to hinder charge migration have a higher blocking effect.

[0107] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0108] The embodiments described above only express several implementation methods of the present application, which are convenient for understanding the technical solutions of the present application in a specific and detailed manner, but they cannot be understood as limiting the scope of protection of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several variations and improvements can be made, which all fall within the scope of protection of the present application. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided in the present application are all within the scope of protection of the claims attached to the present application. Therefore, the scope of protection of the patent of this application shall be based on the content of the attached claims, and the description can be used to interpret the content of the claims.

Claims

1. An additive, characterized in that The method is prepared by amidation reaction of a nano-metal oxide having amino groups on the surface and a carboxylic acid compound in a mass ratio of 1:(1-4); The raw materials of the nano-metal oxide having amino groups on the surface include nano-metal oxide and aminosilane coupling agent in a mass ratio of 1:(2-4).

2. The additive according to claim 1, wherein One or more of the following conditions are met: (1) The particle size of the nano metal oxide is 50nm~150nm; (2) The pore size of the nano-metal oxide surface is 5 nm to 15 nm; (3) The nano metal oxide includes one or more of nano cobalt oxide, nano iron oxide, nano copper oxide, nano titanium dioxide and nano zinc oxide; (4) The aminosilane coupling agent includes one or more of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltriisopropoxysilane and 3-aminopropyltriacetoxysilane; (5) The carboxylic acid compound includes one or both of arachidonic acid and oleic acid.

3. A method for preparing an additive, characterized in that: The following steps are involved: Mixing a nano-metal oxide having an amino group on the surface and a carboxylic acid compound in a mass ratio of 1:(1-4), and performing an amidation reaction to prepare the additive; The raw materials for preparing the nano metal oxide having amino groups on the surface are mixed with nano metal oxide and aminosilane coupling agent in a mass ratio of 1:(2-4).

4. The preparation method according to claim 3, wherein The preparation method of the nano metal oxide comprises the following steps: The metal salt is placed in a first organic solvent with a pH value of 7.5 to 8.5 for hydrolysis reaction to prepare a colloid; placing the colloid at a first temperature and stirring for a first time to form a gel; The gel is dried and calcined.

5. The preparation method according to claim 4, wherein One or more of the following conditions are met: (1) The first temperature is 40°C to 50°C; (2) The first time is 12 hours to 24 hours; (3) The drying temperature is 50℃~70℃; (4) Drying time is 20h~30h; (5) The calcination temperature is 850℃~950℃; (6) The calcination time is 3h~4h.

6. The preparation method according to claim 5, wherein The preparation method of the nano metal oxide having amino groups on the surface comprises the following steps: The nano metal oxide and the aminosilane coupling agent are mixed according to a mass ratio, and modified at a temperature of 70° C. to 90° C. and a humidity of 50% to 70%.

7. The preparation method according to any one of claims 3 to 6, wherein The amidation reaction satisfies one or both of the following conditions: (1) Temperature is 70℃~90℃; (2) The time is 10h~14h.

8. An insulating oil, characterized in that: The invention comprises a natural ester oil and a modified substance in a volume ratio of 1:(0.05-0.3), wherein the modified substance comprises the additive according to claim 1 or 2 or the additive prepared by the preparation method according to any one of claims 3-7.

9. The insulating oil according to claim 8, wherein The natural ester oil includes one or more of FR3 insulating oil, palm oil and rapeseed oil.

10. Use of the additive according to claim 1 or 2, or the additive prepared by the preparation method according to any one of claims 3 to 7, or the insulating oil according to claim 8 or 9 in power equipment.

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