ZnO varistor uniformly doped with Y element and sol-gel preparation method thereof
By employing the sol-gel method and molecular-level mixing technology, the problem of uneven Y element doping in ZnO varistors was solved, achieving efficient uniform doping and grain refinement, thus improving electrical performance and stability. This makes it suitable for overvoltage protection in high-voltage electrical appliances and electronic circuits.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-29
- Publication Date
- 2026-03-13
AI Technical Summary
Existing ZnO varistors suffer from uneven distribution and agglomeration during rare earth element Y doping, leading to deterioration in electrical performance, especially poor overvoltage protection in high-voltage electrical appliances and electronic circuits.
The sol-gel method, combined with a citric acid complexation system and PEG-2000 dispersant, was used to achieve uniform doping of Y element in ZnO varistors through pH gradient control and ultrasonic dispersion. Citric acid forms a chelate structure with Y3+, polyethylene glycol inhibits nanoparticle aggregation, and graded drying and step calcination ensure grain refinement and uniform bismuth oxide encapsulation.
Uniform doping of Y element in ZnO varistors was achieved, which improved the nonlinear coefficient and stability, reduced leakage current, and enhanced the overvoltage protection capability of high-voltage electrical appliances and electronic circuits.
Abstract
Description
Technical Field
[0001] This invention relates to the field of electronic ceramic materials technology, specifically to a uniformly Y-doped ZnO varistor and its sol-gel preparation method. This ZnO varistor is suitable for overvoltage protection of high-voltage electrical appliances, surge absorption of electronic circuits, and other scenarios. Background Technology
[0002] Zinc oxide (ZnO) varistors are widely used in overvoltage protection of high-voltage electrical appliances, surge absorption of electronic circuits, new energy power generation systems, and lightning protection of communication equipment. They are key nonlinear resistive devices that ensure the safe operation of power systems and electronic equipment. Their core performance parameters include the nonlinear coefficient α, varistor voltage gradient, leakage current, and current carrying capacity.
[0003] Appropriate doping of rare earth element Y can improve the voltage gradient and nonlinear coefficient of ZnO varistors. Currently, most ZnO varistors are produced using the traditional solid-state sintering method. However, this method faces the challenge of uneven doping when using yttrium oxide as a raw material. Yttrium oxide, being a water-insoluble solid particle, exhibits uneven doping due to mechanical mixing. 3+ Uneven distribution of rare earth ions makes them prone to agglomeration, leading to localized deterioration of electrical properties. Summary of the Invention
[0004] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a ZnO varistor uniformly doped with Y and its sol-gel preparation method. The sol-gel method combines a citric acid complex system with a PEG-2000 dispersant, and solves the technical bottlenecks of easy aggregation of Y and uneven grain size in traditional processes through pH gradient control and ultrasonic dispersion.
[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A sol-gel preparation method for a uniformly Y-doped ZnO varistor, the method comprising the following steps: (1) Preparation of raw materials for ZnO varistors: Weigh each component according to the composition of ZnO varistors. The raw materials for ZnO varistors are composed of ZnO, Bi2O3, Sb2O3, NiO, Mn3O4, Co3O4, Cr2O3 and Y(NO3)3·6H2O. The raw materials contain 0.5-1.8wt.% Y(NO3)3•6H2O. (2) Preparation of precursor solution: Dissolve Y(NO3)3·6H2O in deionized water to prepare a yttrium nitrate solution with a concentration of 0.5-2 g / L; under stirring conditions, add citric acid solution dropwise to the yttrium nitrate solution until the pH value of the solution is adjusted to 3.0-5.0, then add polyethylene glycol, and sonicate for 5-10 minutes to obtain the precursor solution; (3) Sol preparation and mixing: Place the precursor solution obtained in step (2) in a constant temperature stirrer at 50-70℃, and slowly add ammonia water with a concentration of 0.5-5g / L until the pH value rises to 5-6 under stirring conditions (stirring at a speed of 200-500rpm) to form a transparent sol; pour Bi2O3 powder into the sol and continue stirring for 4-10 hours to achieve uniform dispersion of Bi2O3 powder in the sol; (4) Aging and gelation: The sol containing Bi2O3 powder obtained in step (3) is left to stand at room temperature for 24-48 hours so that the wet gel formed by the sol reaction is uniformly coated on the surface of Bi2O3 powder. (5) Drying and calcination: The wet gel containing Bi2O3 powder obtained in step (4) is dried at 50-70℃ for 12-24 hours, and then heated to 80-100℃ for 4-8 hours to obtain dry gel blocks; the dry gel blocks are ground through a 30-200 mesh sieve and then subjected to a two-stage calcination treatment to obtain Y-Bi2O3 composite powder; (6) Preparation of total slurry: The Y-Bi2O3 composite powder obtained in step (5) is mixed with ZnO, Sb2O3, NiO, Cr2O3, Mn3O4, Co3O4, and Cr2O3. Then Al(NO3)3•9H2O, dispersant, binder, and deionized water are added. The mixture is then ball-milled and passed through a 100-200 mesh sieve to obtain the total slurry for later use. (7) Green body preparation: The total slurry obtained in step (6) is spray granulated and aged in sequence, and then pressed into a green body; (8) Sintering: After the blank obtained in step (7) is debinded, it is calcined at high temperature. The sample obtained after calcination is then post-processed to obtain the ZnO varistor uniformly doped with Y element.
[0006] Further, in step (1), the raw material composition of the ZnO varistor, by weight percentage, is as follows: ZnO 83-93 wt.%, Bi2O3 2-5 wt.%, Sb2O3 1-4 wt.%, NiO 1-3 wt.%, Mn3O4 0.5-3 wt.%, Co3O4 0.5-3 wt.%, Cr2O3 0.5-3 wt.%, and Y(NO3)3·6H2O 0.5-1.8 wt.%.
[0007] Further, in the precursor solution described in step (2), the content of polyethylene glycol (PEG-2000) is 0.5-2 wt.%.
[0008] Further, in step (5), the two-stage calcination process is as follows: first, the temperature is raised to 400-550℃ at a heating rate of 1.5-2.5℃ / min and held for 2-4 hours to remove organic matter from the dry gel block; then, the temperature is raised to 700-800℃ at a heating rate of 4-6℃ / min and held for 2-4 hours, and then naturally cooled to obtain Y-Bi2O3 composite powder.
[0009] Further, in step (6), the dispersant is polyvinyl alcohol (PVA), polyacrylamide, or sodium carboxymethyl cellulose, and the amount of dispersant added is 0.3-1.5% of the weight of solid powder in the total slurry; the binder is polyvinyl alcohol, and the amount of binder added is 0.3-1.5% of the weight of solid powder in the total slurry; the amount of Al(NO3)3•9H2O added is 0.01-0.03% of the weight of solid powder in the total slurry.
[0010] Further, in step (6), the spray granulation process is as follows: the total slurry is spray granulated using a spray dryer with an inlet temperature of 150-250℃ and an atomizing disc speed of 8000-16000 rpm.
[0011] Further, in step (6), the aging process is as follows: after mixing the granulated material obtained by spray granulation with deionized water and release agent stearic acid, the resulting mixture is left to stand for 24-48 hours at room temperature and under sealed conditions; the moisture content of the mixture is 1.0-1.5 wt.% and the stearic acid content is 0.8-1.5 wt.%.
[0012] Further, in step (6), the pressing molding is to press the aged granulated material into a blank using a hydraulic press, and adjust the pressure to control the density of the cylindrical blank to 3.1-3.4 g / cm³, and the blank diameter to 35-150 mm.
[0013] Further, in step (6), the debinding process is as follows: the blank obtained in step (3) is placed in a ventilated electric furnace for debinding, the temperature is controlled at 380-520℃, the organic matter in the blank is burned off, and the debinding process is completed; the high temperature calcination temperature is 1000-1300℃, and the heat preservation time is 0.5-3 hours.
[0014] Furthermore, the sample obtained after high-temperature calcination is subjected to double-sided grinding, ultrasonic cleaning, and drying. Then, a metal electrode is prepared on the surface of the obtained resistor blank to obtain the finished ZnO varistor.
[0015] A uniformly Y-doped ZnO varistor was prepared using the above method. The varistor has a varistor voltage gradient ≥195V / mm and a leakage current <0.90μA. After withstanding 20 lightning surges of 20kA 8 / 20μs, 2 lightning surges of 40kA 8 / 20μs, and 2 lightning surges of 60kA 8 / 20μs, the varistor voltage change rate is less than 10%.
[0016] The design mechanism and beneficial effects of this invention are as follows: 1. This invention achieves uniform doping of Y element in ZnO varistors through the sol-gel method, leveraging its molecular-level mixing advantage. This significantly improves the nonlinear coefficient and stability of ZnO varistors, making them suitable for overvoltage protection needs in high-voltage electrical appliances, electronic circuits, and other fields. It has significant technological advancements and industrial application value.
[0017] 2. Uniform doping mechanism of the present invention: Citric acid reacts with Y through the carboxyl group. 3+ By forming a chelate structure, polyethylene glycol (PEG-2000) inhibits the aggregation of nanoparticles through steric hindrance, achieving atomic-level uniform distribution of Y element in the ZnO lattice.
[0018] 3. This invention optimizes the gelation and post-treatment process: The sol containing Bi2O3 powder is aged at room temperature for 24-48 hours to ensure that the formed wet gel uniformly coats the surface of the Bi2O3 powder; cracking is avoided by staged drying (50-70℃ / 12-24 hours, 80-100℃ / 4-8 hours), followed by a stepped temperature increase of 400-550℃ / 2-4 hours to remove organic matter and calcination at 700-800℃ / 2-4 hours to ensure grain refinement (350-800nm) and the effect of bismuth oxide on Y. 3+ The melting and encapsulation of ions.
[0019] 4. Grain boundary control effect of the present invention: Y 3+ with Bi 3+ The synergistic effect enhances the grain boundary barrier height, reduces leakage current (≤1μA), and improves the stability of the varistor after lightning surge.
[0020] 5. Process optimization of this invention: pH gradient control combined with ultrasonic treatment controls the sol particle size to 20-50nm. The calcination process adopts a two-stage heating rate to avoid abnormal grain growth and ensure electrical performance stability. Detailed Implementation
[0021] To further illustrate the technical solution of the present invention, the present invention will be further described below through embodiments.
[0022] In the following embodiments, in step 6, the dispersant is polyacrylamide, and the amount of dispersant added is 0.8% of the total solid powder weight in the slurry; the binder is polyvinyl alcohol, and the amount of binder added is 0.8% of the total solid powder weight in the slurry; the amount of Al(NO3)3•9H2O added is 0.02% of the total solid powder weight in the slurry. The polyethylene glycol used is PEG-2000. The concentration of the citric acid solution is 192 g / L. Example 1:
[0023] This embodiment describes the preparation of a uniformly Y-doped ZnO varistor using a sol-gel method. The specific process is as follows: 1. Preparation of raw materials for preparing resistor sheets: Weigh each raw material according to the raw material composition of the ZnO varistor; the raw material composition of the ZnO varistor is (wt.%): ZnO 89.5wt.%, Bi2O3 3.5wt.%, Sb2O3 1.8wt.%, NiO 1.2wt.%, Mn3O4 0.8wt.%, Co3O4 1.5wt.%, Cr2O3 0.7wt.%, Y(NO3)3•6H2O 1.0wt.
[0024] 2. Preparation of precursor solution: Y(NO3)3•6H2O was dissolved in deionized water to prepare a 1 g / L yttrium nitrate solution. Citric acid solution was added dropwise to the yttrium nitrate solution under stirring until the pH was adjusted to 3.5. Polyethylene glycol was then added, and the solution was sonicated for 6 minutes to promote dispersion, yielding the precursor solution. The polyethylene glycol content in the obtained precursor solution was 1.2 wt.%. In this step, citric acid reacts with Y... 3+ The appropriate ratio and addition of PEG-2000 stabilize Y through chelation. 3+ To avoid agglomeration; pH value is controlled to ensure the uniformity of subsequent sol preparation.
[0025] 3. Sol Preparation and Mixing: The obtained precursor solution was placed in a 55℃ constant-temperature stirrer and stirred at 300 rpm. Ammonia solution with a concentration of 1.5 g / L was slowly added dropwise until the pH reached 5.5, forming a transparent sol. Bi2O3 powder was then added to the sol, and stirring was continued for 6 hours to ensure thorough mixing and uniform dispersion of Bi2O3 powder in the sol, with a particle size of 20-50 nm. In this step, the pH was controlled by adding ammonia solution dropwise, and the formation of a transparent sol promoted the uniform coating and mixing of the Bi2O3 powder.
[0026] 4. Aging and gelation: The obtained sol containing Bi2O3 powder was aged at room temperature for 36 hours, and the wet gel formed by the sol reaction was uniformly coated on the surface of Bi2O3 powder.
[0027] 5. Drying and calcination: The wet gel containing Bi2O3 powder obtained in step 4 is dried at 60℃ for 16 hours, and then heated to 85℃ for 6 hours to obtain a dry gel block. The dry gel block is ground through a 200-mesh sieve and then subjected to a two-stage calcination treatment: first, the temperature is raised to 450℃ at a heating rate of 2℃ / min and held for 2.5 hours to remove organic matter, and then the temperature is raised to 750℃ at a heating rate of 5℃ / min and held for 3 hours. After natural cooling, Y-Bi2O3 composite powder with a particle size of 350-800nm is obtained.
[0028] 6. Preparation of total slurry: The Y-Bi2O3 composite powder obtained in step 5 is mixed with ZnO, Sb2O3, NiO, Cr2O3, Mn3O4, Co3O4, and Cr2O3. Then Al(NO3)3·9H2O, dispersant, binder, and deionized water are added. The mixture is then added to a ball mill for mixing and grinding. The resulting slurry is passed through a 100-mesh sieve to obtain the total slurry. 7. Green body preparation: The total slurry obtained in step 6 is sequentially subjected to spray granulation and aging treatment, and then pressed into green bodies; the process is as follows: (a) Spray granulation: The prepared total slurry is spray granulated using a spray dryer; the inlet temperature is 200℃ and the atomizing disc speed is 10000rpm.
[0029] (b) Aging: The granulated material obtained by spray granulation is mixed with deionized water and release agent stearic acid, and the resulting mixture is left to stand for 26 hours at room temperature and under sealed conditions; the moisture content of the mixture is 1.2 wt.% and the stearic acid content is 1.0 wt.%.
[0030] (c) Molding: The aged granules are pressed into blanks using a hydraulic press. The pressure is adjusted to control the density of the blanks at 3.3 g / cm³. The blanks are square sheets of 40 mm × 40 mm.
[0031] 8. Sintering: The blank obtained in step 7 is subjected to a debinding process. The process is as follows: the blank is placed in a ventilated electric furnace and heated to 480℃ to ablate the organic matter in the blank, thus completing the debinding process. After the debinding process, it is calcined at 1100℃ for 2 hours. After calcination, the resulting sample is double-sided ground, ultrasonically cleaned, and dried. Then, a metal electrode is prepared on the surface of the treated resistor blank to obtain the finished cerium-doped ZnO varistor.
[0032] The performance test results of the ZnO varistor obtained in this embodiment are as follows: The ZnO varistor prepared by the method in this embodiment is a 33.5mm×33.5mm square sheet with a varistor voltage gradient of 205V / mm, a nonlinear coefficient of 58, and a leakage current of 0.64μA. After being subjected to 20 lightning surges of 20kA 8 / 20μs, 2 lightning surges of 40kA 8 / 20μs, and 2 lightning surges of 60kA 8 / 20μs, the varistor voltage change rate is 7.2%, which is less than 10%. Example 2:
[0033] This embodiment describes the preparation of a uniformly Y-doped ZnO varistor using a sol-gel method. The specific process is as follows: 1. Preparation of raw materials for preparing resistor sheets: Weigh each raw material according to the raw material composition of the ZnO varistor; the raw material composition of the ZnO varistor is (wt.%): ZnO 89.8wt.%, Bi2O3 3.5wt.%, Sb2O3 1.8wt.%, NiO 1.2wt.%, Mn3O4 0.8wt.%, Co3O4 1.5wt.%, Cr2O3 0.7wt.%, Y(NO3)3•6H2O 0.7wt.
[0034] 2. Preparation of precursor solution: Y(NO3)3•6H2O was dissolved in deionized water to prepare a 1 g / L yttrium nitrate solution. Citric acid solution was added dropwise to the yttrium nitrate solution under stirring until the pH value of the solution was adjusted to 3.0. Polyethylene glycol was then added, and the solution was sonicated for 6 minutes to promote dispersion, thus obtaining the precursor solution. The polyethylene glycol content in the obtained precursor solution was 1.2 wt.%.
[0035] 3. Sol preparation and mixing: The obtained precursor solution was placed in a 55℃ constant temperature stirrer and stirred at 300 rpm. Ammonia water with a concentration of 1.5 g / L was slowly added dropwise until the pH rose to 5.0 to form a transparent sol. Bi2O3 powder was poured into the sol and stirred for 6 hours to mix thoroughly, so as to achieve uniform dispersion of Bi2O3 powder in the sol.
[0036] 4. Aging and gelation: The obtained sol containing Bi2O3 powder was aged at room temperature for 36 hours, and the wet gel formed by the sol reaction was uniformly coated on the surface of Bi2O3 powder.
[0037] 5. Drying and calcination: The wet gel containing Bi2O3 powder obtained in step 4 is dried at 60℃ for 16 hours, and then heated to 85℃ for 6 hours to obtain a dry gel block. The dry gel block is ground through a 200-mesh sieve and then subjected to a two-stage calcination treatment: first, the temperature is increased to 450℃ at a heating rate of 2℃ / min and held for 2.5 hours to remove organic matter, and then the temperature is increased to 750℃ at a heating rate of 5℃ / min and held for 3 hours. After natural cooling, Y-Bi2O3 composite powder is obtained.
[0038] 6. Preparation of total slurry: The Y-Bi2O3 composite powder obtained in step 5 is mixed with ZnO, Sb2O3, NiO, Cr2O3, Mn3O4, Co3O4, and Cr2O3. Then Al(NO3)3·9H2O, dispersant, binder, and deionized water are added. The mixture is then added to a ball mill for mixing and grinding. The resulting slurry is passed through a 100-mesh sieve to obtain the total slurry. 7. Green body preparation: The total slurry obtained in step 6 is sequentially subjected to spray granulation and aging treatment, and then pressed into green bodies; the process is as follows: (a) Spray granulation: The prepared total slurry is spray granulated using a spray dryer; the inlet temperature is 200℃ and the atomizing disc speed is 10000rpm.
[0039] (b) Aging: The granulated material obtained by spray granulation is mixed with deionized water and release agent stearic acid, and the resulting mixture is left to stand for 26 hours at room temperature and under sealed conditions; the moisture content of the mixture is 1.2 wt.% and the stearic acid content is 1.0 wt.%.
[0040] (c) Molding: The aged granules are pressed into blanks using a hydraulic press. The pressure is adjusted to control the density of the blanks at 3.3 g / cm³. The blanks are square sheets of 40 mm × 40 mm.
[0041] 8. Sintering: The blank obtained in step 7 is subjected to a debinding process. The process is as follows: the blank is placed in a ventilated electric furnace and heated to 480℃ to ablate the organic matter in the blank, thus completing the debinding process. After the debinding process, it is calcined at 1100℃ for 2 hours. After calcination, the resulting sample is double-sided ground, ultrasonically cleaned, and dried. Then, a metal electrode is prepared on the surface of the treated resistor blank to obtain the finished cerium-doped ZnO varistor.
[0042] The performance test results of the ZnO varistor obtained in this embodiment are as follows: The ZnO varistor prepared by the method in this embodiment is a 33.5mm×33.5mm square sheet with a varistor voltage gradient of 196V / mm, a nonlinear coefficient of 54, and a leakage current of 0.86μA. After being subjected to 20 lightning surges of 20kA 8 / 20μs, 2 lightning surges of 40kA 8 / 20μs, and 2 lightning surges of 60kA 8 / 20μs, the varistor voltage change rate is 8.9%, which is less than 10%. Example 3:
[0043] This embodiment describes the preparation of a uniformly Y-doped ZnO varistor using a sol-gel method. The specific process is as follows: 1. Preparation of raw materials for preparing resistor sheets: Weigh each raw material according to the raw material composition of the ZnO varistor; the raw material composition of the ZnO varistor is (wt.%): ZnO 89.3wt.%, Bi2O3 3.5wt.%, Sb2O3 1.8wt.%, NiO 1.2wt.%, Mn3O4 0.8wt.%, Co3O4 1.5wt.%, Cr2O3 0.7wt.%, Y(NO3)3•6H2O 1.2wt.%.
[0044] 2. Preparation of precursor solution: Y(NO3)3•6H2O was dissolved in deionized water to prepare a 1 g / L yttrium nitrate solution. Citric acid solution was added dropwise to the yttrium nitrate solution under stirring until the pH value of the solution was adjusted to 3.0. Polyethylene glycol was added, and the solution was sonicated for 6 minutes to promote dispersion, thus obtaining the precursor solution. The polyethylene glycol content in the obtained precursor solution was 1.2 wt.%.
[0045] 3. Sol preparation and mixing: The obtained precursor solution was placed in a 55℃ constant temperature stirrer and stirred at 300 rpm. Ammonia water with a concentration of 1.5 g / L was slowly added dropwise until the pH rose to 5.5 to form a transparent sol. Bi2O3 powder was poured into the sol and stirred for 6 hours to mix thoroughly, so as to achieve uniform dispersion of Bi2O3 powder in the sol.
[0046] 4. Aging and gelation: The obtained sol containing Bi2O3 powder was aged at room temperature for 36 hours, and the wet gel formed by the sol reaction was uniformly coated on the surface of Bi2O3 powder.
[0047] 5. Drying and calcination: The wet gel containing Bi2O3 powder obtained in step 4 is dried at 60℃ for 16 hours, and then heated to 85℃ for 6 hours to obtain a dry gel block. The dry gel block is ground through a 200-mesh sieve and then subjected to a two-stage calcination treatment: first, the temperature is increased to 450℃ at a heating rate of 2℃ / min and held for 2.5 hours to remove organic matter, and then the temperature is increased to 750℃ at a heating rate of 5℃ / min and held for 3 hours. After natural cooling, Y-Bi2O3 composite powder is obtained.
[0048] 6. Preparation of total slurry: The Y-Bi2O3 composite powder obtained in step 5 is mixed with ZnO, Sb2O3, NiO, Cr2O3, Mn3O4, Co3O4, and Cr2O3. Then Al(NO3)3·9H2O, dispersant, binder, and deionized water are added. The mixture is then added to a ball mill for mixing and grinding. The resulting slurry is passed through a 100-mesh sieve to obtain the total slurry. 7. Green body preparation: The total slurry obtained in step 6 is sequentially subjected to spray granulation and aging treatment, and then pressed into green bodies; the process is as follows: (a) Spray granulation: The prepared total slurry is spray granulated using a spray dryer; the inlet temperature is 200℃ and the atomizing disc speed is 10000rpm.
[0049] (b) Aging: The granulated material obtained by spray granulation is mixed with deionized water and release agent stearic acid, and the resulting mixture is left to stand for 26 hours at room temperature and under sealed conditions; the moisture content of the mixture is 1.2 wt.% and the stearic acid content is 1.0 wt.%.
[0050] (c) Molding: The aged granules are pressed into blanks using a hydraulic press. The pressure is adjusted to control the density of the blanks at 3.3 g / cm³. The blanks are square sheets of 40 mm × 40 mm.
[0051] 8. Sintering: The blank obtained in step 7 is subjected to a debinding process. The process is as follows: the blank is placed in a ventilated electric furnace and heated to 480℃ to ablate the organic matter in the blank, thus completing the debinding process. After the debinding process, it is calcined at 1100℃ for 2 hours. After calcination, the resulting sample is double-sided ground, ultrasonically cleaned, and dried. Then, a metal electrode is prepared on the surface of the treated resistor blank to obtain the finished cerium-doped ZnO varistor.
[0052] The performance test results of the ZnO varistor obtained in this embodiment are as follows: The ZnO varistor prepared by the method in this embodiment is a 33.5mm×33.5mm square sheet with a varistor voltage gradient of 213V / mm, a nonlinear coefficient of 61, and a leakage current of 0.47μA. After being subjected to 20 lightning surges of 20kA 8 / 20μs, 2 lightning surges of 40kA 8 / 20μs, and 2 lightning surges of 60kA 8 / 20μs, the varistor voltage change rate is 6.2%, which is less than 10%.
[0053] Comparative Example 1: The difference between this example and Example 1 is that Y(NO3)3·6H2O in Comparative Example 1 is replaced by Y2O3. Comparative Example 1 does not include step 2, "precursor solution preparation," as in Example 1. In the total slurry preparation step of Comparative Example 1, Y2O3 and bismuth oxide powder are used instead of the Y-Bi2O3 composite powder.
[0054] The performance test results of the ZnO varistor obtained in this example are as follows: The ZnO varistor prepared by this method has a varistor voltage gradient of 214V / mm, a nonlinear coefficient of 47, and a leakage current of 1.21μA. After withstanding 20 lightning surges of 20kA 8 / 20μs, 2 lightning surges of 40kA 8 / 20μs, and 2 lightning surges of 60kA 8 / 20μs, the varistor voltage change rate is 14.7%, which is greater than 10%.
[0055] Comparative Example 2: The difference between this example and Example 1 is that Y element doping was not used in Comparative Example 2.
[0056] The performance test results of the ZnO varistor obtained in this example are as follows: In Comparative Example 2, the varistor has a varistor potential gradient of 184V / mm, a nonlinear coefficient of 62, and a leakage current of 0.44μA. After withstanding 20 lightning surges of 20kA 8 / 20μs, 2 lightning surges of 40kA 8 / 20μs, and 2 lightning surges of 60kA 8 / 20μs, the varistor voltage change rate is 21.7%, which is greater than 10%.
[0057] In summary, this invention employs the sol-gel method, which leverages advantages such as molecular-level mixing, nanoscale particle control, low-temperature synthesis, and structural densification in yttrium oxide dispersion to significantly improve the uniformity, purity, and performance of the material, while simultaneously reducing energy consumption and environmental costs.
[0058] The foregoing has shown and described the main features and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.
Claims
1. A sol-gel preparation method for a uniformly Y-doped ZnO varistor, characterized in that: The method includes the following steps: (1) Preparation of raw materials for ZnO varistors: Weigh each component according to the composition of ZnO varistors. The raw materials for ZnO varistors are composed of ZnO, Bi2O3, Sb2O3, NiO, Mn3O4, Co3O4, Cr2O3 and Y(NO3)3·6H2O. The raw materials contain 0.5-1.8wt.% Y(NO3)3•6H2O. (2) Preparation of precursor solution: Dissolve Y(NO3)3·6H2O in deionized water to prepare a yttrium nitrate solution with a concentration of 0.5-2 g / L; under stirring conditions, add citric acid solution dropwise to the yttrium nitrate solution until the pH value of the solution is adjusted to 3.0-5.0, then add polyethylene glycol, and sonicate for 5-10 minutes to obtain the precursor solution; (3) Sol preparation and mixing: Place the precursor solution obtained in step (2) in a constant temperature stirrer at 50-70℃, and slowly add ammonia water with a concentration of 0.5-5g / L until the pH value rises to 5-6 to form a transparent sol; pour Bi2O3 powder into the sol and continue stirring for 4-10 hours to achieve uniform dispersion of Bi2O3 powder in the sol; (4) Aging and gelation: The sol containing Bi2O3 powder obtained in step (3) is left to stand at room temperature for 24-48 hours so that the wet gel formed by the sol reaction is uniformly coated on the surface of Bi2O3 powder. (5) Drying and calcination: The wet gel containing Bi2O3 powder obtained in step (4) is dried at 50-70℃ for 12-24 hours, and then heated to 80-100℃ for 4-8 hours to obtain dry gel blocks; the dry gel blocks are ground through a 30-200 mesh sieve and then subjected to a two-stage calcination treatment to obtain Y-Bi2O3 composite powder; (6) Preparation of total slurry: The Y-Bi2O3 composite powder obtained in step (5) is mixed with ZnO, Sb2O3, NiO, Cr2O3, Mn3O4, Co3O4, and Cr2O3. Then Al(NO3)3•9H2O, dispersant, binder, and deionized water are added. The mixture is then ball-milled and passed through a 100-200 mesh sieve to obtain the total slurry for later use. (7) Green body preparation: The total slurry obtained in step (6) is spray granulated and aged in sequence, and then pressed into a green body; (8) Sintering: After the blank obtained in step (7) is debinded, it is calcined at high temperature. The sample obtained after calcination is then post-processed to obtain the ZnO varistor uniformly doped with Y element.
2. The sol-gel preparation method of uniformly Y-doped ZnO varistor according to claim 1, characterized in that: In step (1), the raw material composition of the ZnO varistor, by weight percentage, is as follows: ZnO 83-93 wt.%, Bi2O3 2-5 wt.%, Sb2O3 1-4 wt.%, NiO 1-3 wt.%, Mn3O4 0.5-3 wt.%, Co3O4 0.5-3 wt.%, Cr2O3 0.5-3 wt.%, and Y(NO3)3·6H2O 0.5-1.8 wt.%.
3. The sol-gel preparation method of uniformly Y-doped ZnO varistor according to claim 1, characterized in that: In step (2), the precursor solution contains 0.5-2 wt.% polyethylene glycol.
4. The sol-gel preparation method of uniformly Y-doped ZnO varistor according to claim 1, characterized in that: In step (5), the two-stage calcination process is as follows: first, the temperature is raised to 400-550℃ at a heating rate of 1.5-2.5℃ / min and held for 2-4 hours to remove organic matter from the dry gel block; then, the temperature is raised to 700-800℃ at a heating rate of 4-6℃ / min and held for 2-4 hours, and then naturally cooled to obtain Y-Bi2O3 composite powder.
5. The sol-gel preparation method of uniformly Y-doped ZnO varistor according to claim 1, characterized in that: In step (6), the dispersant is polyvinyl alcohol (PVA), polyacrylamide, or sodium carboxymethyl cellulose, and the amount of dispersant added is 0.3-1.5% of the weight of solid powder in the total slurry; the binder is polyvinyl alcohol, and the amount of binder added is 0.3-1.5% of the weight of solid powder in the total slurry; the amount of Al(NO3)3•9H2O added is 0.01-0.03% of the weight of solid powder in the total slurry.
6. The sol-gel preparation method of the uniformly Y-doped ZnO varistor according to claim 1, characterized in that: In step (6), the spray granulation process is as follows: the total slurry is spray granulated using a spray dryer with an inlet temperature of 150-250℃ and an atomizing disc speed of 8000-16000 rpm.
7. The sol-gel preparation method of the uniformly Y-doped ZnO varistor according to claim 1, characterized in that: In step (6), the aging process is as follows: after mixing the granulated material obtained by spray granulation with deionized water and release agent stearic acid, the resulting mixture is left to stand for 24-48 hours at room temperature and under sealed conditions; the moisture content of the mixture is 1.0-1.5 wt.% and the stearic acid content is 0.8-1.5 wt.%.
8. The sol-gel preparation method of uniformly Y-doped ZnO varistor according to claim 1, characterized in that: In step (6), the pressing molding is to press the aged granulated material into a blank using a hydraulic press, and adjust the pressure to control the density of the cylindrical blank to 3.1-3.4 g / cm³, and the blank diameter to 35-150 mm.
9. The sol-gel preparation method of the uniformly Y-doped ZnO varistor according to claim 1, characterized in that: In step (6), the debinding process is as follows: the blank obtained in step (3) is placed in a ventilated electric furnace for debinding, the temperature is controlled at 380-520℃, the organic matter in the blank is burned off, and the debinding process is completed; the high temperature calcination temperature is 1000-1300℃, and the holding time is 0.5-3 hours.
10. A ZnO varistor uniformly doped with Y element prepared by the method of claim 1, characterized in that: The ZnO varistor has a varistor voltage gradient ≥195V / mm and a leakage current less than 0.90μA. After withstanding 20 lightning surges of 20kA 8 / 20μs, 2 lightning surges of 40kA 8 / 20μs, and 2 lightning surges of 60kA 8 / 20μs, the varistor voltage change rate is less than 10%.