High-gradient voltage-sensitive ceramic powder, voltage-sensitive ceramic and preparation method of high-gradient voltage-sensitive ceramic powder

Abstract

The invention discloses high-gradient voltage-sensitive ceramic powder, voltage-sensitive ceramic and a preparation method of the high-gradient voltage-sensitive ceramic powder. The invention provides voltage-sensitive ceramic powder which takes ZnO as a main component and contains other dopants, and the voltage-sensitive ceramic powder is prepared by burning a precursor prepared from salt solutions of Zn, Bi, Co, Mn, Cr, Ni and Sb which are mixed in proportion in a muffle furnace. According to the voltage-sensitive ceramic powder, good control over components and uniform distribution between ZnO and dopants are achieved. In addition, the invention provides a method for sintering the voltage-sensitive ceramic at low temperature by taking the voltage-sensitive ceramic powder as original powder, and the method realizes the optimization of the microstructure of the voltage-sensitive ceramic through two-step low-temperature densification.

Description

Technical Field

[0001] The invention relates to varistor ceramic powder, varistor ceramic and methods for preparing the varistor ceramic powder and varistor ceramic, belonging to the technical field of varistor ceramic materials. Background Art

[0002] ZnO varistors are an important polycrystalline electronic device widely used for sensing and limiting transient voltage surges. ZnO varistors are increasingly being used in technology due to their excellent nonlinear electrical properties and high energy handling capabilities. Although varistors based on materials such as tin oxide (SnO2), titanium oxide (TiO2), perovskite (SrTiO3) and tungsten oxide (WO3) are being studied to replace ZnO-based varistors, ZnO varistors still dominate in a variety of applications from low-current electronic circuits to high-current transmission lines because their voltage-current characteristics exhibit excellent non-ohmic behavior.

[0003] The traditional manufacturing method of ZnO varistor ceramics involves mixing ZnO powder with various additives (such as bismuth oxide, antimony oxide and various transition metal oxides such as cobalt, manganese, chromium, nickel, etc.) into a uniform mixture, followed by pressing and molding, and finally sintering at a high temperature of 1200℃-1300℃. The average grain size of commercial ZnO varistor ceramics is usually in the range of 10μm-25μm, and its potential gradient and nonlinear coefficient are 200V / mm-400V / mm and 30-50, respectively. Studies have shown that reducing the grain size can improve the performance of ZnO varistor ceramics because it increases the number of grain boundaries per unit volume, thereby increasing the potential gradient. In addition, ensuring the uniform distribution of dopants in the grain boundaries is also a key factor in achieving high-performance varistor ceramics.

[0004] In order to achieve high-performance ZnO varistor ceramics, fine powders (such as nanopowders) are required as starting materials in order to retain smaller grains and uniform doping distribution after sintering. High-energy ball milling has been used to produce fine ZnO and doped powders, but its cost is relatively high. With the development of nanotechnology, a variety of technologies for preparing nanocrystalline ZnO powders have been developed, including sol-gel method, coprecipitation method, enhanced mechanical grinding method, microemulsion method, organometallic method, spray pyrolysis method, solution coating method and combustion synthesis method. Among these methods, combustion synthesis method has become the first choice because of its advantages in large-scale economic production of nanopowders.

[0005] Studies have shown that pure ZnO and doped ZnO nanopowders synthesized by combustion method have good control over composition, but research on their electrical properties is still insufficient. Hwang et al. used combustion synthesis method to produce ZnO nanopowder with glycerol as fuel, and studied its performance in varistor ceramic applications, reporting a potential gradient of 205V / mm and a nonlinear coefficient of 42. However, the varistor ceramics made with this ZnO nanopowder are not significantly better than traditional commercial varistor ceramics in terms of potential gradient, nonlinear coefficient and leakage current. Therefore, there is an urgent need to explore cost-effective methods to manufacture new varistor ceramics with better performance than traditional varistor ceramics. Summary of the invention

[0006] In view of the above problems existing in the prior art, the technical problem to be solved by the present invention is: the purpose of the present invention is to provide an advanced varistor ceramic powder, which improves the distribution of dopants in ZnO. In addition, the present invention provides a varistor ceramic with a potential gradient greater than 1000V / mm. The present invention further provides a method for manufacturing the ceramic powder and the varistor ceramic.

[0007] To solve the above technical problems, the present invention adopts the following technical solution: a ceramic powder for manufacturing varistor ceramics, comprising: ZnO and other dopants. ZnO is the main component, which is obtained by calcining and decomposing a metal salt of Zn.

[0008] The other dopants are obtained by calcining and decomposing precursors prepared in proportion such as metal carbonates, metal acetates, metal citrates, metal nitrates, etc., and include at least one compound containing Bi as a metal element, at least one compound containing Co as a metal element, at least one compound containing Mn as a metal element, at least one compound containing Cr as a metal element, at least one compound containing Ni as a metal element, and at least one compound containing Sb as a metal element.

[0009] Calculated by element molar ratio, the content of the ceramic powder is as follows:

[0010] 87mol%≤a≤96.9mol%

[0011] 0.5mol%≤b≤3mol%

[0012] 0.5mol%≤c≤2.5mol%

[0013] 0.5mol%≤d≤1.5mol%

[0014] 0.1mol%≤e≤1.5mol%

[0015] 0.5mol%≤f≤1.5mol%

[0016] 1mol%≤g≤3mol%

[0017] wherein a represents the ratio of the amount of Zn calculated as a metal salt of Zn, b represents the ratio of the amount of Bi calculated as a metal salt of Bi, c represents the ratio of the amount of Co calculated as a metal salt of Co, d represents the ratio of the amount of Mn calculated as a metal salt of Mn, e represents the ratio of the amount of Cr calculated as a metal salt of Cr, f represents the ratio of the amount of Ni calculated as a metal salt of Ni, and g represents the ratio of the amount of Sb calculated as a metal salt of Sb, wherein the total molar ratio content of Zn, Bi, Co, Mn, Cr, Ni and Sb is 100%.

[0018] Furthermore, the other dopants are derived from metal salts, specifically selected from metal carbonates, metal acetates, metal citrates, metal nitrates or other soluble metal salt compounds.

[0019] A method for preparing the above-mentioned ceramic powder for manufacturing varistor ceramics comprises the following steps:

[0020] S1: Weigh Zn, Bi, Co, Mn, Cr, Ni and Sb metal salts according to the ratio specified in claim 1, dissolve them in a solvent, and prepare solution ①.

[0021] S2: adding a fuel additive to the solution ① of step S1 to obtain a mixed solution ②, wherein the amount of the fuel additive added is 5%-30% of the total mass of the solution ①.

[0022] S3: Place the mixed solution ② in step S2 in an oil bath at 120°C-300°C and stir until the solvent is completely evaporated to obtain a mixed powder.

[0023] S4: calcining the mixed powder in step S3 at 500° C.-800° C. to prepare ceramic powder for manufacturing varistor ceramics.

[0024] Furthermore, the solvent in S1 includes deionized water, alcohols, ethers, ammonia water or acid solutions.

[0025] Furthermore, the fuel additive in S2 is sucrose, polyvinyl alcohol, urea, glycerol or ammonia.

[0026] A varistor ceramic is prepared by using the above-mentioned ceramic powder, wherein the voltage gradient of the varistor ceramic is greater than 1000V / mm and the nonlinear coefficient is greater than 70.

[0027] A method for preparing the above-mentioned varistor ceramic comprises the following steps:

[0028] A1: Prepare a formic acid solution with a concentration of 1-7 mol / L. The formic acid solution used is slightly acidic and can ionize hydrogen ions to partially dissolve the varistor ceramic powder and enhance the fluidity between particles.

[0029] A2: Weigh ceramic powder and mix it with 20wt% formic acid solution in A1, so that the ceramic powder is evenly wetted by the formic acid solution. The amount of ceramic powder depends on the size of the sample. For example, for small-sized varistor ceramics with a diameter of 2mm, the amount of powder used is usually 1 to 4g. For lightning arrester valve plates with a diameter of 40mm, the amount of powder used is usually greater than 40g.

[0030] A3: Pour the wet powder in A2 into a steel mold and press it under an automatic press for at least 1 hour. The applied pressure and temperature are 50-800 MPa and 150-300°C respectively.

[0031] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered into a dense ceramic body, wherein the sintering temperature is 750° C.-1000° C. and the sintering time is 1-12 hours.

[0032] A5: The ceramic body sintered in A4 is ground and polished to obtain a varistor ceramic, and metal electrodes are sprayed on the upper and lower surfaces of the sample to test the relevant electrical properties.

[0033] Compared with the prior art, the present invention has at least the following advantages:

[0034] 1. In the method of ceramic powder, the present invention overcomes the shortcomings existing in the preparation of traditional ZnO varistor ceramics, proposes a new doping method of doping with dopants, utilizes liquid phase conditions to evenly mix the dopant with ZnO, and then obtains the varistor ceramic powder by low-temperature calcination, so that the doping elements are easier to achieve precise control.

[0035] The benefits of using metal salts instead of metal oxides are mainly reflected in improving mixing uniformity, improving particle dispersion, reducing particle wear, supporting the processing of reactive materials, optimizing particle morphology, controlling particle size distribution, etc. It is suitable for production processes that require high uniformity and dispersion, especially in applications such as chemical reactions, dissolution or forming.

[0036] First, in the liquid phase mixing method of the present invention, acetate will dissolve in the liquid medium, making it easier to disperse in the ZnO matrix during the mixing process.

[0037] Secondly, the addition of the combustion agent in the present invention not only provides the necessary heat to promote the reduction reaction between the reactants, but also improves the morphology, particle size, purity and other properties of the product. By accurately controlling the amount of the combustion agent added and the reaction conditions, the effect of the solid phase reaction can be optimized and the quality and performance of the final powder can be improved.

[0038] Then, in the present invention, oil bath evaporation provides precise temperature control, slow solvent evaporation rate and uniform heating effect in the powder preparation process, which can effectively improve the quality, morphology, purity and preparation efficiency of the powder. Especially in experiments that need to control particle morphology, reduce overheating and solvent residue, oil bath is an ideal heating method.

[0039] Finally, the solid phase reaction temperature of 500-800°C used in the present invention can not only ensure the decomposition of various additives, but also effectively control the size and shape of the particles, improve the purity and uniformity of the composite powder, while reducing energy consumption and side reactions and simplifying the process. These advantages make low-temperature solid phase reaction an important means for preparing high-quality composite powder materials, especially in the preparation of environmentally friendly, energy-saving and high-performance materials. It has a wide range of application prospects.

[0040] 2. The doping of metal elements and their dosage play a key role in the preparation process of varistor ceramics, affecting the conductivity, nonlinear IV characteristics, polarization, stability and high voltage resistance of the ceramics. The mechanism of action of each element is as follows:

[0041] Bismuth (Bi): Increases the grain boundary resistance and nonlinear coefficient of ceramics and improves high temperature stability.

[0042] Manganese (Mn): Enhances the electrical conductivity and nonlinear response of ceramics and improves their ability to resist voltage shocks.

[0043] Cobalt (Co): Improves the nonlinear characteristics of current response and enhances the varistor characteristics of ceramics.

[0044] Nickel (Ni): Improves electrical conductivity and nonlinear characteristics, and enhances high-voltage stability.

[0045] Chromium (Cr): affects electrical properties and enhances redox stability.

[0046] Antimony (Sb): Improves electrical conductivity and nonlinear characteristics, and enhances breakdown resistance.

[0047] In order to optimize the performance of varistor ceramics, it is usually necessary to reasonably select and control the type and doping amount of metal elements according to application requirements. In actual production, reasonable doping amount and element combination can improve the varistor characteristics, stability and reliability of varistor ceramics.

[0048] 3. In the method for preparing varistor ceramics of the present invention, the present invention uses formic acid solution as an auxiliary liquid phase to dissolve and rearrange the varistor ceramic powder in a tablet press to obtain a microstructured and uniform embryo, which is then highly sintered at a sintering temperature far lower than that of the traditional method. The sintering temperature of the present invention is low, which avoids the volatilization of doping elements, and the microstructure of the material is more uniform and dense. The ZnO varistor ceramics prepared by the present invention not only have significantly improved comprehensive electrical properties, but also have an ultra-high potential gradient that is conducive to the miniaturization design of commercial devices. The present invention has a simple process and a short processing time, and is suitable for industrial-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is the XRD diagram of the varistor ceramic powder of Example 11.

[0050] Figure 2 This is a microstructure diagram of the varistor ceramic of Example 11, wherein the diagram on the left is a microstructure diagram of the varistor ceramic when initially pressed in a steel mold, and the diagram on the right is a microstructure diagram of the varistor ceramic when subsequently sintered in a muffle furnace. DETAILED DESCRIPTION

[0051] The content of the present invention is further described below in conjunction with specific examples, but it should not be construed as limiting the present invention. If not specifically indicated, the technical means used in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0052] Embodiment 1:

[0053] Preparation of ceramic powder:

[0054] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=96.9:0.5:0.5:0.5:0.1:0.5:1, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0055] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0056] S3: placing the mixed solution ② in step S2 in an oil bath at 120° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0057] S4: calcining the mixed precursor powder in step S3 at 500° C. to prepare varistor ceramic powder.

[0058] Preparation of varistor ceramics:

[0059] A1: Prepare 1 mol / L formic acid solution for later use;

[0060] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0061] A3: Pour the wet powder in A2 into a steel mold, apply 300 MPa pressure for 1 hour by an automatic press, and apply 300°C temperature to assist the pressing. After the pressing is completed, take out the sample from the mold for use;

[0062] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 750°C for 3 hours to form a dense ceramic body;

[0063] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test the performance. The measured potential gradient of the varistor ceramic was 2581 and the nonlinear coefficient was 18.

[0064] Embodiment 2:

[0065] Preparation of ceramic powder:

[0066] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=94:1:1:1:0.5:1:1.5, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0067] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0068] S3: placing the mixed solution ② in step S2 in an oil bath at 180° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0069] S4: calcining the mixed precursor powder in step S3 at 600° C. to prepare varistor ceramic powder.

[0070] Preparation of varistor ceramics:

[0071] A1: Prepare 1 mol / L formic acid solution for later use;

[0072] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0073] A3: Pour the wet powder in A2 into a steel mold, apply 300 MPa pressure for 1 hour by an automatic press, and apply 300°C temperature to assist the pressing. After the pressing is completed, take out the sample from the mold for use;

[0074] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 750° C. for 12 hours to form a dense ceramic body;

[0075] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test the performance. The measured potential gradient of the varistor ceramic was 2981V / mm and the nonlinear coefficient was 25.

[0076] Example 3: Preparation of ceramic powder:

[0077] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=91:2:2:1:1:1:2, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0078] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0079] S3: placing the mixed solution ② in step S2 in an oil bath at 250° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0080] S4: calcining the mixed precursor powder in step S3 at 700° C. to prepare a varistor ceramic powder.

[0081] Preparation of varistor ceramics:

[0082] A1: Prepare 1 mol / L formic acid solution for later use;

[0083] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0084] A3: Pour the wet powder in A2 into a steel mold, apply 300 MPa pressure for 1 hour by an automatic press, and apply 300°C temperature to assist the pressing. After the pressing is completed, take out the sample from the mold for use;

[0085] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 750°C for 9 hours to form a dense ceramic body;

[0086] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test the performance. The measured potential gradient of the varistor ceramic was 3244V / mm and the nonlinear coefficient was 28.

[0087] Embodiment 4:

[0088] Preparation of ceramic powder:

[0089] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=87:3:2.5:1.5:1.5:1.5:3, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0090] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0091] S3: placing the mixed solution ② in step S2 in an oil bath at 300° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0092] S4: calcining the mixed precursor powder in step S3 at 800° C. to prepare a varistor ceramic powder.

[0093] Preparation of varistor ceramics:

[0094] A1: Prepare 1 mol / L formic acid solution for later use;

[0095] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0096] A3: Pour the wet powder in A2 into a steel mold, apply 300 MPa pressure for 1 hour by an automatic press, and apply 300°C temperature to assist the pressing. After the pressing is completed, take out the sample from the mold for use;

[0097] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 750°C for 6 hours to form a dense ceramic body;

[0098] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test the performance. The measured potential gradient of the varistor ceramic was 3569V / mm and the nonlinear coefficient was 29.

[0099] Embodiment 5:

[0100] Preparation of ceramic powder:

[0101] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=96.9:0.5:0.5:0.5:0.1:0.5:1, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0102] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0103] S3: placing the mixed solution ② in step S2 in an oil bath at 120° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0104] S4: calcining the mixed precursor powder in step S3 at 500° C. to prepare varistor ceramic powder.

[0105] Preparation of varistor ceramics:

[0106] A1: Prepare 1 mol / L formic acid solution for later use;

[0107] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0108] A3: Pour the wet powder in A2 into a steel mold, apply 300 MPa pressure for 1 hour by an automatic press, and apply 300°C temperature to assist the pressing. After the pressing is completed, take out the sample from the mold for use;

[0109] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 800°C for 3 hours to form a dense ceramic body;

[0110] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test the performance. The measured potential gradient of the varistor ceramic was 2499 and the nonlinear coefficient was 34.

[0111] Embodiment 6:

[0112] Preparation of ceramic powder:

[0113] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=93:2:1:1:0.5:1.5:1, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0114] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0115] S3: placing the mixed solution ② in step S2 in an oil bath at 180° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0116] S4: calcining the mixed precursor powder in step S3 at 600° C. to prepare varistor ceramic powder.

[0117] Preparation of varistor ceramics:

[0118] A1: Prepare 1 mol / L formic acid solution for later use;

[0119] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0120] A3: Pour the wet powder in A2 into a steel mold, apply 300 MPa pressure for 1 hour by an automatic press, and apply 300°C temperature to assist the pressing. After the pressing is completed, take out the sample from the mold for use;

[0121] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 800°C for 1 hour to form a dense ceramic body;

[0122] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test their performance. The measured potential gradient of the varistor ceramic was 2633 V / mm and the nonlinear coefficient was 44.

[0123] Embodiment 7:

[0124] Preparation of ceramic powder:

[0125] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=91:2:2:1:1:1:2, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0126] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0127] S3: placing the mixed solution ② in step S2 in an oil bath at 250° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0128] S4: calcining the mixed precursor powder in step S3 at 700° C. to prepare a varistor ceramic powder.

[0129] Preparation of varistor ceramics:

[0130] A1: Prepare 1 mol / L formic acid solution for later use;

[0131] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0132] A3: Pour the wet powder in A2 into a steel mold, apply 300 MPa pressure for 1 hour by an automatic press, and apply 300°C temperature to assist the pressing. After the pressing is completed, take out the sample from the mold for use;

[0133] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 800°C for 3 hours to form a dense ceramic body;

[0134] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test the performance. The measured potential gradient of the varistor ceramic was 2829V / mm and the nonlinear coefficient was 47.

[0135] Embodiment 8:

[0136] Preparation of ceramic powder:

[0137] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=87:3:2.5:1.5:1.5:1.5:3, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0138] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0139] S3: placing the mixed solution ② in step S2 in an oil bath at 300° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0140] S4: calcining the mixed precursor powder in step S3 at 800° C. to prepare a varistor ceramic powder.

[0141] Preparation of varistor ceramics:

[0142] A1: Prepare 1 mol / L formic acid solution for later use;

[0143] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0144] A3: Pour the wet powder in A2 into a steel mold, apply 300 MPa pressure for 1 hour by an automatic press, and apply 300°C temperature to assist the pressing. After the pressing is completed, take out the sample from the mold for use;

[0145] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 800°C for 3 hours to form a dense ceramic body;

[0146] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test the performance. The measured potential gradient of the varistor ceramic was 2889V / mm and the nonlinear coefficient was 48.

[0147] Embodiment 9:

[0148] Preparation of ceramic powder:

[0149] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=96.9:0.5:0.5:0.5:0.1:0.5:1, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0150] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0151] S3: placing the mixed solution ② in step S2 in an oil bath at 120° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0152] S4: calcining the mixed precursor powder in step S3 at 500° C. to prepare varistor ceramic powder.

[0153] Preparation of varistor ceramics:

[0154] A1: Prepare 1 mol / L formic acid solution for later use;

[0155] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0156] A3: Pour the wet powder in A2 into a steel mold, apply 300 MPa pressure for 1 hour by an automatic press, and apply 300°C temperature to assist the pressing. After the pressing is completed, take out the sample from the mold for use;

[0157] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 850°C for 3 hours to form a dense ceramic body;

[0158] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test their performance. The measured potential gradient of the varistor ceramic was 2046 and the nonlinear coefficient was 54.

[0159] Embodiment 10:

[0160] Preparation of ceramic powder:

[0161] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=94:1:1:1:0.5:1:1.5, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0162] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0163] S3: placing the mixed solution ② in step S2 in an oil bath at 180° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0164] S4: calcining the mixed precursor powder in step S3 at 600° C. to prepare varistor ceramic powder.

[0165] Preparation of varistor ceramics:

[0166] A1: Prepare 1 mol / L formic acid solution for later use;

[0167] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0168] A3: Pour the wet powder in A2 into a steel mold, apply 300 MPa pressure for 1 hour by an automatic press, and apply 300°C temperature to assist the pressing. After the pressing is completed, take out the sample from the mold for use;

[0169] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 850°C for 3 hours to form a dense ceramic body;

[0170] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test the performance. The measured potential gradient of the varistor ceramic was 2291V / mm and the nonlinear coefficient was 78.

[0171] Embodiment 11:

[0172] Preparation of ceramic powder:

[0173] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=91:2:2:1:1:1:2, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0174] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0175] S3: placing the mixed solution ② in step S2 in an oil bath at 250° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0176] S4: calcining the mixed precursor powder in step S3 at 700° C. to prepare a varistor ceramic powder.

[0177] Preparation of varistor ceramics:

[0178] A1: Prepare 1 mol / L formic acid solution for later use;

[0179] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0180] A3: Pour the wet powder in A2 into a steel mold, apply 300 MPa pressure for 1 hour by an automatic press, and apply 300°C temperature to assist the pressing. After the pressing is completed, take out the sample from the mold for use;

[0181] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 850°C for 3 hours to form a dense ceramic body;

[0182] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test their performance. The measured potential gradient of the varistor ceramic was 2379 V / mm and the nonlinear coefficient was 92.

[0183] Embodiment 12:

[0184] Preparation of ceramic powder:

[0185] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=87:3:2.5:1.5:1.5:1.5:3, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0186] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0187] S3: placing the mixed solution ② in step S2 in an oil bath at 300° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0188] S4: calcining the mixed precursor powder in step S3 at 800° C. to prepare a varistor ceramic powder.

[0189] Preparation of varistor ceramics:

[0190] A1: Prepare 1 mol / L formic acid solution for later use;

[0191] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0192] A3: Pour the wet powder in A2 into a steel mold, apply 300 MPa pressure for 1 hour by an automatic press, and apply 300°C temperature to assist the pressing. After the pressing is completed, take out the sample from the mold for use;

[0193] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 850°C for 3 hours to form a dense ceramic body;

[0194] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test the performance. The measured potential gradient of the varistor ceramic was 2529V / mm and the nonlinear coefficient was 85.

[0195] Embodiment 13:

[0196] Preparation of ceramic powder:

[0197] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=96.9:0.5:0.5:0.5:0.1:0.5:1, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0198] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0199] S3: placing the mixed solution ② in step S2 in an oil bath at 120° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0200] S4: calcining the mixed precursor powder in step S3 at 500° C. to prepare varistor ceramic powder.

[0201] Preparation of varistor ceramics:

[0202] A1: Prepare 1 mol / L formic acid solution for later use;

[0203] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0204] A3: Pour the wet powder in A2 into a steel mold, apply 50MPa pressure for 1h by an automatic press, and apply 300℃ temperature to assist the pressing. After the pressing, take out the sample from the mold for use;

[0205] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 900°C for 3 hours to form a dense ceramic body;

[0206] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test the performance. The measured potential gradient of the varistor ceramic was 1527 and the nonlinear coefficient was 55.

[0207] Embodiment 14:

[0208] Preparation of ceramic powder:

[0209] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=93:2:1:1:0.5:1:1.5, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0210] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0211] S3: placing the mixed solution ② in step S2 in an oil bath at 180° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0212] S4: calcining the mixed precursor powder in step S3 at 600° C. to prepare varistor ceramic powder.

[0213] Preparation of varistor ceramics:

[0214] A1: Prepare 1 mol / L formic acid solution for later use;

[0215] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0216] A3: Pour the wet powder in A2 into a steel mold, apply a pressure of 100 MPa for 1 hour using an automatic press, and apply a temperature of 300°C to assist the pressing. After the pressing is completed, take out the sample from the mold for later use;

[0217] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 900°C for 3 hours to form a dense ceramic body;

[0218] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test the performance. The measured potential gradient of the varistor ceramic was 2692V / mm and the nonlinear coefficient was 73.

[0219] Embodiment 15:

[0220] Preparation of ceramic powder:

[0221] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=91:2:2:1:1:1:2, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0222] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0223] S3: placing the mixed solution ② in step S2 in an oil bath at 250° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0224] S4: calcining the mixed precursor powder in step S3 at 700° C. to prepare a varistor ceramic powder.

[0225] Preparation of varistor ceramics:

[0226] A1: Prepare 1 mol / L formic acid solution for later use;

[0227] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0228] A3: Pour the wet powder in A2 into a steel mold, apply 300 MPa pressure for 1 hour by an automatic press, and apply 300°C temperature to assist the pressing. After the pressing is completed, take out the sample from the mold for use;

[0229] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 900°C for 3 hours to form a dense ceramic body;

[0230] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test the performance. The measured potential gradient of the varistor ceramic was 1829V / mm and the nonlinear coefficient was 63.

[0231] Embodiment 16:

[0232] Preparation of ceramic powder:

[0233] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=87:3:2.5:1.5:1.5:1.5:3, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0234] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0235] S3: placing the mixed solution ② in step S2 in an oil bath at 300° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0236] S4: calcining the mixed precursor powder in step S3 at 800° C. to prepare a varistor ceramic powder.

[0237] Preparation of varistor ceramics:

[0238] A1: Prepare 1 mol / L formic acid solution for later use;

[0239] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0240] A3: Pour the wet powder in A2 into a steel mold, apply 500 MPa pressure for 1 hour by an automatic press, and apply 300°C temperature to assist the pressing. After the pressing is completed, take out the sample from the mold for use;

[0241] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 900°C for 3 hours to form a dense ceramic body;

[0242] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test the performance. The measured potential gradient of the varistor ceramic was 1904V / mm and the nonlinear coefficient was 66.

[0243] Embodiment 17:

[0244] Preparation of ceramic powder:

[0245] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=96.9:0.5:0.5:0.5:0.1:0.5:1, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0246] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0247] S3: placing the mixed solution ② in step S2 in an oil bath at 120° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0248] S4: calcining the mixed precursor powder in step S3 at 500° C. to prepare varistor ceramic powder.

[0249] Preparation of varistor ceramics:

[0250] A1: Prepare 1 mol / L formic acid solution for later use;

[0251] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0252] A3: Pour the wet powder in A2 into a steel mold, apply a pressure of 700 MPa for 1 hour using an automatic press, and apply a temperature of 300°C to assist the pressing. After the pressing is completed, take out the sample from the mold for later use;

[0253] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 950°C for 3 hours to form a dense ceramic body;

[0254] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test their performance. The measured potential gradient of the varistor ceramic was 1367 and the nonlinear coefficient was 58.

[0255] Embodiment 18:

[0256] Preparation of ceramic powder:

[0257] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=93:2:1:1:0.5:1:1.5, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0258] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0259] S3: placing the mixed solution ② in step S2 in an oil bath at 180° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0260] S4: calcining the mixed precursor powder in step S3 at 600° C. to prepare varistor ceramic powder.

[0261] Preparation of varistor ceramics:

[0262] A1: Prepare 1 mol / L formic acid solution for later use;

[0263] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0264] A3: Pour the wet powder in A2 into a steel mold, apply 800 MPa pressure for 1 hour by an automatic press, and apply 300°C temperature to assist the pressing. After the pressing is completed, take out the sample from the mold for use;

[0265] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 950°C for 3 hours to form a dense ceramic body;

[0266] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test their performance. The measured potential gradient of the varistor ceramic was 1692V / mm and the nonlinear coefficient was 67.

[0267] Embodiment 19:

[0268] Preparation of ceramic powder:

[0269] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=91:2:2:1:1:1:2, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0270] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0271] S3: placing the mixed solution ② in step S2 in an oil bath at 250° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0272] S4: calcining the mixed precursor powder in step S3 at 700° C. to prepare a varistor ceramic powder.

[0273] Preparation of varistor ceramics:

[0274] A1: Prepare 1 mol / L formic acid solution for later use;

[0275] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0276] A3: Pour the wet powder in A2 into a steel mold, apply 300MPa pressure for 1h by an automatic press, and apply 150℃ temperature to assist the pressing. After the pressing, take out the sample from the mold for use;

[0277] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 950°C for 3 hours to form a dense ceramic body;

[0278] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test the performance. The measured potential gradient of the varistor ceramic was 1882V / mm and the nonlinear coefficient was 68.

[0279] Embodiment 20:

[0280] Preparation of ceramic powder:

[0281] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=87:3:2.5:1.5:1.5:1.5:3, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0282] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0283] S3: placing the mixed solution ② in step S2 in an oil bath at 300° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0284] S4: calcining the mixed precursor powder in step S3 at 800° C. to prepare a varistor ceramic powder.

[0285] Preparation of varistor ceramics:

[0286] A1: Prepare 1 mol / L formic acid solution for later use;

[0287] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0288] A3: Pour the wet powder in A2 into a steel mold, apply 300MPa pressure for 1h by an automatic press, and apply 200℃ temperature to assist the pressing. After the pressing, take out the sample from the mold for use;

[0289] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 950°C for 3 hours to form a dense ceramic body;

[0290] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test the performance. The measured potential gradient of the varistor ceramic was 1897V / mm and the nonlinear coefficient was 77.

[0291] Embodiment 21:

[0292] Preparation of ceramic powder:

[0293] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=96.9:0.5:0.5:0.5:0.1:0.5:1, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0294] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0295] S3: placing the mixed solution ② in step S2 in an oil bath at 120° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0296] S4: calcining the mixed precursor powder in step S3 at 500° C. to prepare varistor ceramic powder.

[0297] Preparation of varistor ceramics:

[0298] A1: Prepare 1 mol / L formic acid solution for later use;

[0299] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0300] A3: Pour the wet powder in A2 into a steel mold, apply 300MPa pressure for 1h by an automatic press, and apply 250℃ temperature to assist the pressing. After the pressing, take out the sample from the mold for use;

[0301] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 1000°C for 3 hours to form a dense ceramic body;

[0302] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test the performance. The measured potential gradient of the varistor ceramic was 987 and the nonlinear coefficient was 49.

[0303] Embodiment 22:

[0304] Preparation of ceramic powder:

[0305] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=93:2:1:1:0.5:1:1.5, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0306] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0307] S3: placing the mixed solution ② in step S2 in an oil bath at 180° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0308] S4: calcining the mixed precursor powder in step S3 at 600° C. to prepare varistor ceramic powder.

[0309] Preparation of varistor ceramics:

[0310] A1: Prepare 1 mol / L formic acid solution for later use;

[0311] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0312] A3: Pour the wet powder in A2 into a steel mold, apply 300 MPa pressure for 1 hour by an automatic press, and apply 300°C temperature to assist the pressing. After the pressing is completed, take out the sample from the mold for use;

[0313] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 1000°C for 3 hours to form a dense ceramic body;

[0314] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test the performance. The measured potential gradient of the varistor ceramic was 1128V / mm and the nonlinear coefficient was 65.

[0315] Embodiment 23:

[0316] Preparation of ceramic powder:

[0317] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=90:3:2:1:1:1:2, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0318] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0319] S3: placing the mixed solution ② in step S2 in an oil bath at 250° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0320] S4: calcining the mixed precursor powder in step S3 at 700° C. to prepare a varistor ceramic powder.

[0321] Preparation of varistor ceramics:

[0322] A1: Prepare 1 mol / L formic acid solution for later use;

[0323] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0324] A3: Pour the wet powder in A2 into a steel mold, apply 300 MPa pressure for 1 hour by an automatic press, and apply 300°C temperature to assist the pressing. After the pressing is completed, take out the sample from the mold for use;

[0325] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 1000°C for 3 hours to form a dense ceramic body;

[0326] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test their performance. The measured potential gradient of the varistor ceramic was 1256 V / mm and the nonlinear coefficient was 66.

[0327] Embodiment 24:

[0328] Preparation of ceramic powder:

[0329] S1: Weigh the original powder according to the molar mass ratio of Zn(CH3COO)2:Bi(NO3)3:Co(CH3COO)2:Mn(CH3COO)2:Cr(CH3COO)3:Ni(CH3COO)2:Sb(CH3COO)3=87:3:2.5:1.5:1.5:1.5:3, put it into a flask with a magnetic stirrer, use deionized water as solvent, heat and stir to dissolve the original mixed powder, and prepare a mixed solution①;

[0330] S2: adding 5 wt% of the fuel additive sucrose to the solution ① of step S1, and continuously heating and stirring the mixture so that the mixture is uniformly mixed to prepare a mixed solution ②;

[0331] S3: placing the mixed solution ② in step S2 in an oil bath at 300° C. and stirring until the solvent is completely evaporated to obtain a mixed precursor powder;

[0332] S4: calcining the mixed precursor powder in step S3 at 800° C. to prepare a varistor ceramic powder.

[0333] Preparation of varistor ceramics:

[0334] A1: Prepare 1 mol / L formic acid solution for later use;

[0335] A2: Weigh an appropriate amount of the prepared varistor ceramic powder, mix it with a formic acid solution accounting for 20wt% of its mass, and grind it so that the ceramic powder is evenly wetted by the formic acid solution;

[0336] A3: Pour the wet powder in A2 into a steel mold, apply 300 MPa pressure for 1 hour by an automatic press, and apply 300°C temperature to assist the pressing. After the pressing is completed, take out the sample from the mold for use;

[0337] A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered at a sintering temperature of 1000°C for 3 hours to form a dense ceramic body;

[0338] A5: The ceramic body sintered in A4 was polished and ground to make electrodes and test the performance. The measured potential gradient of the varistor ceramic was 1139V / mm and the nonlinear coefficient was 71.

[0339] The performance tests were performed on the ZnO varistor ceramic samples obtained in Examples 1 to 24:

[0340] Table 1 Related parameters of ZnO varistor ceramics under different process conditions

[0341] Sample No. Potential gradient (V / mm) Nonlinear coefficient Example 1 2581 18 Example 2 2981 25 Example 3 3244 28 Example 4 3569 29 Example 5 2499 34 Example 6 2633 44 Example 7 2829 47 Example 8 2889 48 Example 9 2046 54 Example 10 2291 78 Embodiment 11 2379 92 Example 12 2529 85 Embodiment 13 1527 55 Embodiment 14 1692 73 Embodiment 15 1829 63 Example 16 1904 66 Embodiment 17 1367 58 Embodiment 18 1692 67 Embodiment 19 1882 68 Embodiment 20 1897 77 Embodiment 21 987 49 Embodiment 22 1128 65 Embodiment 23 1256 66 Embodiment 24 1139 71

[0342] Through the above experimental results in the present invention, we can find the following experimental rules:

[0343] 1. From the perspective of dopants:

[0344] 1) Insufficient doping and unclear effect: The main function of metal salt dopants is to change the electrical properties of ceramics, such as improving conductivity, enhancing nonlinear IV characteristics, or improving thermal stability. If the dopant content is too small, the structure and electrical properties of the ceramic cannot be significantly changed, resulting in the difficulty in fully exerting the effect of doping. For example, the dopant may not be sufficient to effectively adjust the oxygen vacancy concentration or change the mobility of carriers, so the nonlinear response and conductivity characteristics of the ceramic may be poor. Unable to form an ideal conductive network: For some metal salt dopants (such as Mn, Co, etc.), they enhance conductivity or nonlinearity by introducing oxygen vacancies or changing lattice defects. If the doping amount is too small, the concentration of oxygen vacancies is insufficient, resulting in an unclear conductive path, and the current response of the ceramic may show linear characteristics with a low nonlinear coefficient.

[0345] 2) Effects of excessive doping: Lattice mismatch and structural instability: When the content of dopants is too much, the incorporated metal ions may not match the lattice of the ceramic matrix, resulting in distortion or destruction of the crystal structure, thereby affecting the mechanical and electrical properties of the ceramic. For example, too high a concentration of metal ions may lead to incomplete formation of a solid solution or phase separation, thereby destroying the overall electrical properties of the ceramic. Too high conductivity and weakened nonlinear characteristics: Excessive dopants may significantly increase the conductivity of the ceramic, making the IV characteristics of the ceramic tend to be linear. High-concentration doping may reduce the number of oxygen vacancies, making the nonlinear behavior of electrons less obvious, resulting in a decrease in the nonlinear coefficient of the material and a loss of excellent varistor properties. Reduced breakdown voltage: Excessive doping may lead to electric field concentration in certain areas of the ceramic, reducing the withstand voltage performance of the ceramic. Due to the uneven distribution of dopants in the ceramic, a local electric field concentration effect may occur, causing the ceramic to break down at a lower voltage. Poor thermal stability of ceramics: Excessive dopants may affect the high-temperature performance of the ceramic. Certain dopants may trigger redox reactions in ceramics at high temperatures, causing the stability of the material to decrease and affecting its electrical properties in high-temperature environments.

[0346] 3) Optimize the balance of dopant content: In order to obtain excellent varistor ceramic performance, it is necessary to control the appropriate concentration of metal salt dopants. The dopant content should be reasonably adjusted according to the basic composition of the ceramic, the target application and the performance requirements: Improve the nonlinear IV characteristics of the ceramic: The dopant should appropriately increase the oxygen vacancy concentration in the ceramic or change the carrier migration characteristics to improve the nonlinearity of the ceramic. Within a certain doping range, the ceramic exhibits a good current response. Enhance the stability of the ceramic: A reasonable doping amount can improve the ceramic's ability to resist voltage shocks and high temperature stability, but excessive doping may lead to unstable material structure or excessive conductivity. Avoid imbalance in structural and electrical properties: The concentration of the dopant should be appropriate to avoid problems such as uneven distribution, phase separation or lattice mismatch caused by excessive doping.

[0347] 2. From the perspective of sintering temperature:

[0348] 1) The sintering temperature is too low: it leads to incomplete sintering, poor density of the ceramic, pores and defects, and affects the electrical properties and nonlinear characteristics.

[0349] 2) Sintering temperature is too high: it may cause abnormal grain growth, phase separation, uneven composition, abnormal increase in thermal stress, and affect the electrical properties, stability and mechanical properties of the varistor ceramic.

[0350] 3) In order to optimize the comprehensive electrical properties of varistor ceramics, an appropriate sintering temperature must be selected to ensure sufficient densification, appropriate grain size and uniform microstructure, and optimize its varistor characteristics and conductive properties.

Claims

1. A ceramic powder for manufacturing varistor ceramics, characterized in that: Containing: ZnO and other dopants; the other dopants include at least one compound containing Bi as a metal element, at least one compound containing Co as a metal element, at least one compound containing Mn as a metal element, at least one compound containing Cr as a metal element, at least one compound containing Ni as a metal element and at least one compound containing Sb as a metal element; Calculated by element molar ratio, the content of the ceramic powder is as follows: 87mol%≤a≤96.9mol% 0.5mol%≤b≤3mol% 0.5mol%≤c≤2.5mol% 0.5mol%≤d≤1.5mol% 0.1mol%≤e≤1.5mol% 0.5mol%≤f≤1.5mol% 1mol%≤g≤3mol% wherein a represents the ratio of the amount of Zn calculated as a metal salt of Zn, b represents the ratio of the amount of Bi calculated as a metal salt of Bi, c represents the ratio of the amount of Co calculated as a metal salt of Co, d represents the ratio of the amount of Mn calculated as a metal salt of Mn, e represents the ratio of the amount of Cr calculated as a metal salt of Cr, f represents the ratio of the amount of Ni calculated as a metal salt of Ni, and g represents the ratio of the amount of Sb calculated as a metal salt of Sb, wherein the total molar ratio content of Zn, Bi, Co, Mn, Cr, Ni and Sb is 100%.

2. The ceramic powder for manufacturing varistor ceramics according to claim 1, characterized in that: The other dopants are selected from metal carbonates, metal acetates, metal citrates, metal nitrates or other soluble metal salt compounds.

3. A method for preparing the ceramic powder for manufacturing varistor ceramics according to claim 1 or 2, characterized in that: The steps include: S1: Weigh Zn, Bi, Co, Mn, Cr, Ni and Sb metal salts according to the ratio specified in claim 1, dissolve them in a solvent, and prepare solution ①; S2: adding a fuel additive to the solution ① of step S1 to obtain a mixed solution ②, wherein the amount of the fuel additive added is 5%-30% of the total mass of the solution ①; S3: placing the mixed solution ② in step S2 in an oil bath at 120°C-300°C and stirring until the solvent is completely evaporated to obtain a mixed powder; S4: calcining the mixed powder in step S3 at 500° C.-800° C. to prepare ceramic powder for manufacturing varistor ceramics.

4. The method for producing ceramic powder for varistor ceramics according to claim 3, characterized in that: The solvent in S1 includes deionized water, alcohols, ethers, ammonia water or acid solutions.

5. The method for producing ceramic powder for varistor ceramics according to claim 3, characterized in that: The fuel additive in S2 is sucrose, polyvinyl alcohol, urea, glycerol or ammonia.

6. A varistor ceramic, characterized in that: The varistor ceramic is prepared using the ceramic powder according to claim 1 or 2, and has a voltage gradient greater than 1000V / mm and a nonlinear coefficient greater than 70.

7. A method for preparing the varistor ceramic according to claim 6, characterized in that: The steps include: A1: Prepare a formic acid solution with a concentration of 1-7 mol / L; A2: Weigh ceramic powder and mix it with the 20wt% formic acid solution in A1, so that the ceramic powder is evenly wetted by the formic acid solution; A3: Pour the wet powder in A2 into a steel mold and press it in an automatic press for at least 1 hour. The applied pressure and temperature are 50-800 MPa and 150-300°C respectively; A4: The initial embryo body pressed in A3 is placed in a muffle furnace and sintered into a dense ceramic body, wherein the sintering temperature is 750°C-1000°C and the sintering time is 1-12h; A5: The sintered ceramic body in A4 is ground and polished to obtain a varistor ceramic.

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