Preparation method of Ni electrode strontium titanate toroidal varistor

Abstract

This invention discloses a method for preparing a Ni-electrode strontium titanate toroidal varistor, specifically including: 1) dry pressing strontium titanate powder into a strontium titanate toroidal varistor green ceramic sheet; 2) removing the binder from the green ceramic sheet and pre-firing it; 3) sintering the removed-bind green ceramic sheet in a reducing atmosphere of a mixed gas of equal volumes of nitrogen and hydrogen to form a ceramic substrate; 4) subjecting the ceramic substrate to an oxidation heat treatment to form an oxide film on the surface; 5) screen printing a first layer of nickel paste onto the ceramic sheet, drying it, then screen printing a second layer of silver paste, drying it, and then firing it in an air atmosphere. In this invention, Ni paste is used instead of ohmic silver paste, and sintering is performed in air, which significantly reduces the cost compared to ohmic silver paste, resulting in lower subsequent production costs; at the same time, the nickel paste can form a strong bond with the ceramic substrate, thus giving the nickel paste better adhesion to the ceramic substrate, good stability, and less tendency to delamination.

Description

Technical Field

[0001] This invention relates to the field of toroidal varistor fabrication technology, specifically to a method for fabricating a Ni electrode strontium titanate toroidal varistor. Background Technology

[0002] Strontium titanate toroidal varistors are electronic components used in miniature DC motors to absorb sparks, suppress surges, and eliminate noise.

[0003] In existing processes for manufacturing strontium titanate toroidal varistors, silver is primarily used as the electrode. The manufacturing process involves: first, screen printing a first layer of ohmic silver paste and drying it at 100℃-200℃; then, screen printing a second layer of silver paste and drying it at 100℃-200℃; finally, the two layers of silver paste are subjected to silver reduction by calcination at 580℃-680℃. The reason for printing the silver paste twice is that silver paste is a non-ohmic material. A varistor with only silver paste has an oxygen barrier between the silver layer and the ceramic body. After being subjected to a certain level of pulse voltage impact or solder thermal shock, the varistor voltage will drop significantly, resulting in a significant decrease in resistance. Therefore, before printing the silver paste, a layer of paste with ohmic contact (Ag-Zn) needs to be printed first; however, this ohmic paste itself has almost no solderability, so a second layer of solderable silver paste is also required.

[0004] In view of this, it is indeed necessary to provide a new type of toroidal varistor that uses Ni paste instead of ohmic silver paste (Ag-Zn) as the paste for forming ohmic contacts, and has good adhesion and stability. Summary of the Invention

[0005] To address the problems existing in the prior art, the purpose of this invention is to provide a method for preparing a Ni electrode strontium titanate ring varistor.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] The fabrication method of a Ni electrode strontium titanate toroidal varistor includes the following steps:

[0008] 1) Use a servo molding machine to dry press strontium titanate powder into strontium titanate ring varistor green ceramic sheets;

[0009] 2) Remove the glue and pre-fire the raw ceramic pieces from step 1) at 1000-1200℃;

[0010] 3) The pre-fired raw ceramic sheet from step 2) is sintered in a reducing atmosphere of a mixed gas consisting of equal volumes of nitrogen and hydrogen to produce a ceramic substrate.

[0011] 4) The ceramic substrate from step 3) is subjected to an oxidation heat treatment at 800-1000℃ to form an oxide film on the surface;

[0012] 5) The ceramic tile from step 4) is screen-printed with the first layer of nickel paste and dried at 100-200℃. Then, the second layer of silver paste is screen-printed and dried at 100-200℃. Finally, it is fired in an air atmosphere at 600-800℃.

[0013] As a further preferred embodiment of the present invention, the nickel paste is made from the following raw materials in parts by weight: 70-95 parts nickel powder, 5-30 parts powder, 8-13 parts organic carrier, and 2-6 parts composite nanomaterials;

[0014] The preparation method of the nickel paste is as follows: the ingredients of the organic carrier are heated in a water bath at 90-93℃ to form a uniform solution. Then, nickel powder, powder and composite nanomaterials are added to the organic carrier and stirred. The paste is then ground by a three-roll mill until the particle size of the paste is less than 10μm. Finally, it is filtered through a 300-mesh nylon screen.

[0015] As a further preferred embodiment of the present invention, the powder includes one or more of glass powder, silicate, silicon dioxide, boron trioxide, bismuth trioxide, and boron powder;

[0016] The organic carrier is composed of ethyl cellulose, terpineol, dibutyl phthalate, and oleic acid in a mass ratio of (10-18):(30-50):(38-42):(0.5-1.2).

[0017] As a further preferred embodiment of the present invention, the method for preparing the composite nanomaterial is as follows:

[0018] 1) The porous nanomaterials were ultrasonically cleaned with acetone, distilled water and ethanol for 30-50 minutes respectively. After cleaning, they were dried to obtain pretreated porous nanomaterials.

[0019] 2) Dissolve cobalt nitrate hexahydrate in the mixed solution, stir thoroughly, add the pretreated porous nanomaterials, and then put them into the reaction vessel. React at 120-126℃ for 5-10 hours. After the reaction is completed, cool to room temperature, rinse, dry and then bake for later use.

[0020] 3) Place the above-mentioned spare product in a tube furnace, heat it to 700-750℃ under a nitrogen atmosphere, and hold it at that temperature for 90-120 minutes. After cooling to room temperature, react the obtained product with sufficient thioacetamide at 100-110℃ for 3-5 hours. After cooling, cleaning and drying, the composite nanomaterial can be obtained.

[0021] As a further preferred embodiment of the present invention, the ratio of cobalt nitrate hexahydrate, mixed solution and pretreated porous nanomaterial is (3-7)g:(120-180)mL:(5-13)g;

[0022] The mixed solution is composed of N,N-dimethylformamide and methanol in a volume ratio of 1:(2-3).

[0023] As a further preferred embodiment of the present invention, the heating rate is 5-7°C / min.

[0024] As a further preferred embodiment of the present invention, the method for preparing the porous nanomaterial is as follows:

[0025] 1) Dissolve nickel nitrate in deionized water, add sodium oxalate and hexamethylenetetramine, react at room temperature for 4-6 hours, centrifuge, wash repeatedly with ethanol and deionized water, and dry to obtain nanorod precursor;

[0026] 2) Place the nanorod precursor in a tube furnace, introduce nitrogen gas, heat to 350-380℃ and maintain for 4-6 hours. After naturally cooling to room temperature, put the obtained product and sodium hypophosphite into a tube furnace at a mass ratio of 1:(10-13), heat to 300-320℃ and maintain for 2-3 hours. After naturally cooling to room temperature, take it out, wash by centrifugation and dry to obtain porous nanorods.

[0027] 3) Disperse titanium dioxide nanowires in deionized water to obtain a dispersion. Then place porous nanorods in a vacuum impregnation container and evacuate to 50-80 Pa. Then inject the dispersion into the vacuum impregnation tank at a solid-liquid ratio of 1 g: (10-20) mL. Keep it under ultrasonic treatment for 30-50 min. After the treatment is completed, take out the product, centrifuge, wash and dry it to obtain porous nanomaterials.

[0028] As a further preferred embodiment of the present invention, the ratio of nickel nitrate, deionized water, sodium oxalate, and hexamethylenetetramine is (2-5)g:(260-400)mL:(1.3-1.8)g:(1.4-2.0)g.

[0029] As a further preferred embodiment of the present invention, the heating rate is 1-3°C / min.

[0030] As a further preferred embodiment of the present invention, the solid content of the dispersion is 1-3 wt%;

[0031] The power of the ultrasound is 150-200W.

[0032] The beneficial effects of this invention are as follows:

[0033] In this invention, a rod-shaped nanorod precursor is first synthesized via room-temperature precipitation. Then, after calcination in a nitrogen atmosphere, phosphating is used to prepare porous nanorods assembled from nanoparticles. These porous nanorods have a rich pore structure and a rough surface. Using vacuum impregnation, the porous nanorods are physically structured with titanium dioxide nanowires. Under ultrasonic treatment, the titanium dioxide nanowires embed into the pores of the porous nanorods, connecting them together. Furthermore, due to the relatively smooth surface of the titanium dioxide nanowires, some of the interconnected nanowires loosen under ultrasonic treatment. Therefore, after ultrasonic treatment... Vacuum impregnation under acoustic effects creates a wire-rod connection between titanium dioxide nanowires and porous nanorods, resulting in porous nanomaterials. To enhance the bonding strength between the wires and rods, this invention involves repeatedly washing and drying the porous nanomaterials, then depositing nanosheets on their surface using hydrothermal and high-temperature calcination methods. These deposited nanosheets not only cover and fill the connection points between the wires and rods, strengthening the bond, but also increase the surface roughness of the nanowires, resulting in a larger contact area between the nanowires and the substrate, leading to a more robust bond.

[0034] In this invention, Ni paste is used instead of ohmic silver paste as the paste for forming ohmic contacts. Sintering in air significantly reduces costs compared to ohmic silver paste, resulting in lower subsequent production costs. Simultaneously, a composite nanomaterial is introduced into the nickel paste. This composite nanomaterial has a rod-like structure at its ends, a large surface area, and a larger contact area with the nickel paste, resulting in greater frictional force between them. Therefore, the composite nanomaterial can be better embedded in the nickel paste, is less prone to migration, and can be stably embedded in the nickel paste. Furthermore, because its front end has a linear structure, it is easily exposed from the nickel paste, and its rough surface provides a large contact area with the ceramic substrate, allowing for better contact and a strong bond. This results in better adhesion, stability, and reduced delamination of the nickel paste on the ceramic substrate. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] In this embodiment of the invention, the powder is glass powder; the organic carrier is composed of ethyl cellulose, terpineol, dibutyl phthalate and oleic acid mixed in a mass ratio of 13:42:40:0.9.

[0037] Example 1

[0038] The fabrication method of a Ni electrode strontium titanate toroidal varistor includes the following steps:

[0039] 1) Use a servo molding machine to dry press strontium titanate powder into strontium titanate ring varistor green ceramic sheets;

[0040] 2) Remove the glue and pre-fire the raw ceramic pieces from step 1) at 1000℃;

[0041] 3) The pre-fired raw ceramic sheet from step 2) is sintered in a reducing atmosphere of a mixed gas consisting of equal volumes of nitrogen and hydrogen to produce a ceramic substrate.

[0042] 4) The ceramic substrate from step 3) is subjected to an oxidation heat treatment at 800℃ to form an oxide film on the surface;

[0043] 5) The ceramic tile from step 4) is screen-printed with the first layer of nickel paste and dried at 100°C. Then, the second layer of silver paste is screen-printed and dried at 100°C. The tile is then fired in an air atmosphere at 600°C.

[0044] The nickel paste is made from the following raw materials in parts by weight: 70 parts nickel powder, 5 parts powder, 8 parts organic carrier, and 2 parts composite nanomaterials.

[0045] The preparation method of nickel paste is as follows: the ingredients of the organic carrier are heated in a water bath at 90°C to dissolve ethyl cellulose into a uniform solution. Then, nickel powder, powder and composite nanomaterials are added to the organic carrier and stirred. The paste is then ground by a three-roll mill until the particle size of the paste is less than 10μm. Finally, it is filtered through a 300-mesh nylon screen.

[0046] The preparation methods for composite nanomaterials are as follows:

[0047] 1) Dissolve 2g of nickel nitrate in 260mL of deionized water, add 1.3g of sodium oxalate and 1.4g of hexamethylenetetramine, react at room temperature for 4h, centrifuge, wash repeatedly with ethanol and deionized water, and dry to obtain nanorod precursor;

[0048] 2) The nanorod precursor was placed in a tube furnace, nitrogen gas was introduced, and the temperature was heated to 350°C at 1°C / min and held for 4 hours. After naturally cooling to room temperature, the obtained product and sodium hypophosphite were placed in a tube furnace at a mass ratio of 1:10 and heated to 300°C at 1°C / min and held for 2 hours. After naturally cooling to room temperature, the product was removed, centrifuged, washed, and dried to obtain porous nanorods.

[0049] 3) Titanium dioxide nanowires were dispersed in deionized water to obtain a dispersion with a solid content of 1 wt%. Then, porous nanorods were placed in a vacuum impregnation container and evacuated to 50 Pa. The dispersion was then injected into the vacuum impregnation tank at a solid-liquid ratio of 1 g: 10 mL. The mixture was kept under ultrasonic treatment at 150 W for 30 min. After the treatment was completed, the product was taken out, centrifuged, washed and dried to obtain porous nanomaterials.

[0050] 4) The porous nanomaterials were ultrasonically cleaned with acetone, distilled water and ethanol for 30 min each. After cleaning, they were dried to obtain pretreated porous nanomaterials.

[0051] 5) Dissolve 3g of cobalt nitrate hexahydrate in 120mL of a mixed solution of N,N-dimethylformamide and methanol in a volume ratio of 1:2. After stirring thoroughly, add 5g of pretreated porous nanomaterials and then put them into a reaction vessel. React at 120℃ for 5h. After the reaction is completed, cool to room temperature, rinse, dry and then bake for later use.

[0052] 6) Place the above-mentioned spare product in a tube furnace, heat it to 700°C at 5°C / min under a nitrogen atmosphere, hold it at that temperature for 90 min, cool it to room temperature, and then react the obtained product with 0.13 mol of thioacetamide at 100°C for 3 h. After cooling, cleaning and drying, the composite nanomaterial can be obtained.

[0053] Example 2

[0054] The fabrication method of a Ni electrode strontium titanate toroidal varistor includes the following steps:

[0055] 1) Use a servo molding machine to dry press strontium titanate powder into strontium titanate ring varistor green ceramic sheets;

[0056] 2) Remove the glue and pre-fire the raw ceramic pieces from step 1) at 1100℃;

[0057] 3) The pre-fired raw ceramic sheet from step 2) is sintered in a reducing atmosphere of a mixed gas consisting of equal volumes of nitrogen and hydrogen to produce a ceramic substrate.

[0058] 4) The ceramic substrate from step 3) is subjected to an oxidation heat treatment at 900℃ to form an oxide film on the surface;

[0059] 5) The ceramic tile from step 4) is screen-printed with the first layer of nickel paste and dried at 150°C. Then, the second layer of silver paste is screen-printed and dried at 150°C. The tile is then fired in an air atmosphere at 700°C.

[0060] The nickel paste is made from the following raw materials in parts by weight: 85 parts nickel powder, 20 parts powder, 10 parts organic carrier, and 5 parts composite nanomaterials.

[0061] The preparation method of nickel paste is as follows: the ingredients of the organic carrier are heated in a water bath at 92°C to dissolve ethyl cellulose into a uniform solution. Then, nickel powder, powder and composite nanomaterials are added to the organic carrier and stirred. The paste is then ground by a three-roll mill until the particle size of the paste is less than 10μm. Finally, it is filtered through a 300-mesh nylon screen.

[0062] The preparation methods for composite nanomaterials are as follows:

[0063] 1) Dissolve 3g of nickel nitrate in 350mL of deionized water, add 1.5g of sodium oxalate and 1.8g of hexamethylenetetramine, react at room temperature for 5h, centrifuge, wash repeatedly with ethanol and deionized water, and dry to obtain nanorod precursor;

[0064] 2) The nanorod precursor was placed in a tube furnace, nitrogen gas was introduced, and the temperature was heated to 365°C at 2°C / min and held for 5 hours. After naturally cooling to room temperature, the obtained product and sodium hypophosphite were placed in a tube furnace at a mass ratio of 1:12 and heated to 310°C at 2°C / min and held for 2.5 hours. After naturally cooling to room temperature, the product was removed, centrifuged, washed, and dried to obtain porous nanorods.

[0065] 3) Titanium dioxide nanowires were dispersed in deionized water to obtain a dispersion with a solid content of 2wt%. Then, porous nanorods were placed in a vacuum impregnation container and evacuated to 70Pa. The dispersion was then injected into the vacuum impregnation tank at a solid-liquid ratio of 1g:15mL. The mixture was kept under ultrasonic treatment at 180W for 40min. After the treatment was completed, the product was taken out, centrifuged, washed and dried to obtain porous nanomaterials.

[0066] 4) The porous nanomaterials were ultrasonically cleaned with acetone, distilled water and ethanol for 40 min respectively. After cleaning, they were dried to obtain pretreated porous nanomaterials.

[0067] 5) Dissolve 5g of cobalt nitrate hexahydrate in 160mL of a mixed solution consisting of N,N-dimethylformamide and methanol in a volume ratio of 1:2.5. After stirring thoroughly, add 9g of pretreated porous nanomaterials and then place them together in a reaction vessel. React at 125℃ for 7h. After the reaction is complete, cool to room temperature, rinse, dry and then bake for later use.

[0068] 6) Place the above-mentioned spare product in a tube furnace, heat it to 720°C at 6°C / min under a nitrogen atmosphere, hold it at that temperature for 100 min, cool it to room temperature, and then react the obtained product with 0.15 mol of thioacetamide at 105°C for 4 h. After cooling, cleaning and drying, the composite nanomaterial can be obtained.

[0069] Example 3

[0070] The fabrication method of a Ni electrode strontium titanate toroidal varistor includes the following steps:

[0071] 1) Use a servo molding machine to dry press strontium titanate powder into strontium titanate ring varistor green ceramic sheets;

[0072] 2) Remove the glue and pre-fire the raw ceramic pieces from step 1) at 1200℃;

[0073] 3) The pre-fired raw ceramic sheet from step 2) is sintered in a reducing atmosphere of a mixed gas consisting of equal volumes of nitrogen and hydrogen to produce a ceramic substrate.

[0074] 4) The ceramic substrate from step 3) is subjected to an oxidation heat treatment at 1000℃ to form an oxide film on the surface;

[0075] 5) The ceramic tile from step 4) is screen-printed with the first layer of nickel paste and dried at 200°C. Then, the second layer of silver paste is screen-printed and dried at 200°C. The tile is then fired in an air atmosphere at 800°C.

[0076] The nickel paste is made from the following raw materials in parts by weight: 95 parts nickel powder, 30 parts powder, 13 parts organic carrier, and 6 parts composite nanomaterials.

[0077] The preparation method of nickel paste is as follows: the ingredients of the organic carrier are heated in a water bath at 93°C to dissolve ethyl cellulose into a uniform solution. Then, nickel powder, powder and composite nanomaterials are added to the organic carrier and stirred. The paste is then ground by a three-roll mill until the particle size of the paste is less than 10μm. Finally, it is filtered through a 300-mesh nylon screen.

[0078] The preparation methods for composite nanomaterials are as follows:

[0079] 1) Dissolve 5g of nickel nitrate in 400mL of deionized water, add 1.8g of sodium oxalate and 2.0g of hexamethylenetetramine, react at room temperature for 6h, centrifuge, wash repeatedly with ethanol and deionized water, and dry to obtain nanorod precursor;

[0080] 2) The nanorod precursor was placed in a tube furnace, nitrogen gas was introduced, and the temperature was heated to 380°C at 3°C / min and held for 6 hours. After naturally cooling to room temperature, the obtained product and sodium hypophosphite were placed in a tube furnace at a mass ratio of 1:13 and heated to 320°C at 3°C / min and held for 3 hours. After naturally cooling to room temperature, the product was removed, centrifuged, washed, and dried to obtain porous nanorods.

[0081] 3) Titanium dioxide nanowires were dispersed in deionized water to obtain a dispersion with a solid content of 3wt%. Then, porous nanorods were placed in a vacuum impregnation container and evacuated to 80Pa. The dispersion was then injected into the vacuum impregnation tank at a solid-liquid ratio of 1g:20mL. The mixture was kept under ultrasonic treatment at 200W for 50min. After the treatment was completed, the product was taken out, centrifuged, washed and dried to obtain porous nanomaterials.

[0082] 4) The porous nanomaterials were ultrasonically cleaned with acetone, distilled water and ethanol for 50 min each. After cleaning, they were dried to obtain pretreated porous nanomaterials.

[0083] 5) Dissolve 7g of cobalt nitrate hexahydrate in 180mL of a mixed solution of N,N-dimethylformamide and methanol in a volume ratio of 1:3. After stirring thoroughly, add 13g of pretreated porous nanomaterials and then put them into a reaction vessel. React at 126℃ for 10h. After the reaction is completed, cool to room temperature, rinse, dry and then bake for later use.

[0084] 6) Place the above-mentioned spare product in a tube furnace, heat it to 750°C at 7°C / min under a nitrogen atmosphere, hold it at that temperature for 120 min, cool it to room temperature, and then react the obtained product with 0.17 mol of thioacetamide at 110°C for 5 h. After cooling, cleaning and drying, the composite nanomaterial can be obtained.

[0085] Comparative Example 1: This comparative example is basically the same as Example 1, except that it does not contain composite nanomaterials.

[0086] Comparative Example 2: This comparative example is basically the same as Example 1, except that steps 1)-2) are omitted in the preparation of the composite nanomaterial.

[0087] Comparative Example 3: This comparative example is basically the same as Example 1, except that step 3 is omitted in the preparation of the composite nanomaterial.

[0088] Comparative Example 4: This comparative example is basically the same as Example 1, except that step 4 is omitted in the preparation of the composite nanomaterial.

[0089] Comparative Example 5: This comparative example is basically the same as Example 1, except that steps 5)-6) are omitted in the preparation of the composite nanomaterial.

[0090] Test experiment:

[0091] Following the methods provided in Examples 1-3 and Comparative Examples 1-5, nickel paste was printed onto a 15mm×20mm×6mm ceramic substrate, dried at 100°C for 10 minutes, and then calcined in air at 600°C for 90 minutes. Test samples were prepared and tested, and the results are shown in Table 1.

[0092] Table 1

[0093] Example 1 Example 2 Example 3 Comparative Example 1 Adhesion / kg 9.6 9.8 9.5 3.7 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Adhesion / kg 5.2 5.8 7.1 6.3

[0094] As shown in Table 1, the nickel paste in this invention has a strong adhesion to the ceramic substrate, can firmly adhere to the ceramic substrate, has a stable structure, and is not easy to detach.

[0095] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a Ni electrode strontium titanate toroidal varistor, characterized in that, Specifically, the steps include the following: 1) Use a servo molding machine to dry press strontium titanate powder into strontium titanate ring varistor green ceramic sheets; 2) Remove the glue and pre-fire the raw ceramic pieces from step 1) at 1000-1200℃; 3) The pre-fired raw ceramic sheet from step 2) is sintered in a reducing atmosphere of a mixed gas consisting of equal volumes of nitrogen and hydrogen to produce a ceramic substrate. 4) The ceramic substrate from step 3) is subjected to an oxidation heat treatment at 800-1000℃ to form an oxide film on the surface; 5) The ceramic tile from step 4) is screen-printed with the first layer of nickel paste and dried at 100-200℃. Then, the second layer of silver paste is screen-printed and dried at 100-200℃. The tile is then fired in an air atmosphere at 600-800℃. The nickel paste is made from the following raw materials in parts by weight: 70-95 parts nickel powder, 5-30 parts powder, 8-13 parts organic carrier, and 2-6 parts composite nanomaterials; The preparation method of the nickel slurry is as follows: the ingredients of the organic carrier are heated in a water bath at 90-93℃ to form a uniform solution. Then, nickel powder, powder and composite nanomaterials are added to the organic carrier and stirred. The mixture is then ground by a three-roll mill until the particle size of the slurry is less than 10μm. Finally, it is filtered through a 300-mesh nylon screen. The preparation method of the composite nanomaterial is as follows: 1) The porous nanomaterials were ultrasonically cleaned with acetone, distilled water and ethanol for 30-50 minutes respectively. After cleaning, they were dried to obtain pretreated porous nanomaterials. 2) Dissolve cobalt nitrate hexahydrate in the mixed solution, stir thoroughly, add the pretreated porous nanomaterials, and then put them into the reaction vessel. React at 120-126℃ for 5-10 hours. After the reaction is completed, cool to room temperature, rinse, dry and then bake for later use. 3) Place the above-mentioned spare product in a tube furnace, heat it to 700-750℃ under a nitrogen atmosphere, and keep it at that temperature for 90-120 minutes. After cooling to room temperature, react the obtained product with sufficient thioacetamide at 100-110℃ for 3-5 hours. After cooling, cleaning and drying, the composite nanomaterial can be obtained. The preparation method of the porous nanomaterial is as follows: 1) Dissolve nickel nitrate in deionized water, add sodium oxalate and hexamethylenetetramine, react at room temperature for 4-6 hours, centrifuge, wash repeatedly with ethanol and deionized water, and dry to obtain nanorod precursor; 2) Place the nanorod precursor in a tube furnace, introduce nitrogen gas, heat to 350-380℃ and maintain for 4-6 hours. After naturally cooling to room temperature, put the obtained product and sodium hypophosphite into the tube furnace at a mass ratio of 1:(10-13), heat to 300-320℃ and maintain for 2-3 hours. After naturally cooling to room temperature, take it out, wash by centrifugation and dry to obtain porous nanorods. 3) Disperse titanium dioxide nanowires in deionized water to obtain a dispersion. Then place porous nanorods in a vacuum impregnation container and evacuate to 50-80 Pa. Then inject the dispersion into the vacuum impregnation tank at a solid-liquid ratio of 1 g: (10-20) mL. Keep it under ultrasonic treatment for 30-50 min. After the treatment is completed, take out the product, centrifuge, wash and dry it to obtain porous nanomaterials.

2. The method for preparing the Ni electrode strontium titanate toroidal varistor according to claim 1, characterized in that, The powder includes one or more of glass powder, silicate, silicon dioxide, boron trioxide, bismuth trioxide, and boron powder; The organic carrier is composed of ethyl cellulose, terpineol, dibutyl phthalate, and oleic acid in a mass ratio of (10-18):(30-50):(38-42):(0.5-1.2).

3. The method for preparing the Ni electrode strontium titanate toroidal varistor according to claim 1, characterized in that, The ratio of cobalt nitrate hexahydrate, the mixed solution, and the pretreated porous nanomaterial is (3-7) g: (120-180) mL: (5-13) g; The mixed solution is composed of N,N-dimethylformamide and methanol in a volume ratio of 1:(2-3).

4. The method for preparing the Ni electrode strontium titanate ring varistor according to claim 1, characterized in that, The heating rate is 5-7℃ / min.

5. The method for preparing the Ni electrode strontium titanate toroidal varistor according to claim 1, characterized in that, The ratio of nickel nitrate, deionized water, sodium oxalate, and hexamethylenetetramine used is (2-5) g: (260-400) mL: (1.3-1.8) g: (1.4-2.0) g.

6. The method for preparing a Ni electrode strontium titanate toroidal varistor according to claim 1, characterized in that, The heating rate is 1-3℃ / min.

7. The method for preparing a Ni electrode strontium titanate toroidal varistor according to claim 1, characterized in that, The solid content of the dispersion is 1-3 wt%; The power of the ultrasound is 150-200W.