Zinc oxide varistor and method for manufacturing the same

Abstract

This invention relates to the field of varistor materials technology, and particularly to a zinc oxide varistor sheet and its preparation method. The zinc oxide varistor sheet has the following composition by molar parts: ZnO 85-94 parts, Bi2O3 0.5-2.0 parts, Sb2O3 0.5-2.0 parts, Ho2O3 0.23-0.54 parts, Eu2O3 0.1-0.2 parts, Nb2O5 0.02-0.2 parts, Co2O3 0.2-1.5 parts, MnO2 0.2-1.5 parts, Cr2O3 0.1-1.0 parts, and Al2O3 0.005-0.1 parts. This invention utilizes two rare earth oxides, Ho2O3 and Eu2O3. 3+ During sintering, ions tend to segregate at ZnO grain boundaries, which can inhibit abnormal grain growth, thereby increasing the number of grain boundaries per unit thickness and improving the voltage gradient of the varistor. 3+ Ions can increase the density of state at grain boundaries, improve the height of grain boundaries, improve the nonlinear coefficient and reduce leakage current. By controlling the ratio of these two rare earth oxides, the varistor can obtain a higher voltage gradient and nonlinear coefficient while maintaining a lower leakage current.

Description

Technical Field

[0001] This invention relates to the field of varistor materials technology, and in particular to a zinc oxide varistor sheet and its preparation method. Background Technology

[0002] Zinc oxide (ZnO) varistors are nonlinear resistive elements made primarily of ZnO with the addition of various metal oxide additives, through ceramic processes such as mixing, molding, and high-temperature sintering. Their voltage-current characteristics exhibit an extremely high nonlinear coefficient in the breakdown region; that is, the resistance drops sharply after the voltage across them exceeds a certain threshold, thus clamping overvoltages and absorbing surge energy. Based on this characteristic, ZnO varistors are widely used in power system surge arresters, communication base station surge protectors, rail transit traction power supply systems, and overvoltage protection in various household electronic products.

[0003] However, as electronic devices evolve towards miniaturization, integration, and high reliability, higher demands are placed on the core performance of varistor chips. Existing ZnO varistor chips still suffer from the following shortcomings in practical applications: First, the voltage gradient (varistor voltage per unit thickness) is relatively low, resulting in a larger component thickness for the same voltage level, which is detrimental to miniaturization design; second, there is a restrictive relationship between the nonlinear coefficient and leakage current, often increasing the leakage current while increasing the nonlinear coefficient, reducing the energy efficiency and stability of the equipment in long-term standby states; third, the impact aging performance is insufficient, with significant varistor voltage drift after multiple lightning or operational overvoltage impacts, affecting protection reliability. Furthermore, problems such as uneven additive dispersion and rough sintering process control in traditional manufacturing processes also limit the consistency of product performance and yield.

[0004] Therefore, developing a zinc oxide varistor and its preparation method through reasonable component matching and process optimization, improving the voltage gradient, nonlinear coefficient and aging stability of the zinc oxide varistor, while maintaining low leakage current and good process repeatability, is a technical problem that those skilled in the art have been continuously concerned about and urgently need to solve. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a zinc oxide varistor and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A zinc oxide varistor, in molar amounts, comprises: 85-94 parts ZnO, 0.5-2.0 parts Bi₂O₃, 0.5-2.0 parts Sb₂O₃, 0.23-0.54 parts Ho₂O₃, 0.1-0.2 parts Eu₂O₃, 0.02-0.2 parts Nb₂O₅, 0.2-1.5 parts Co₂O₃, 0.2-1.5 parts MnO₂, 0.1-1.0 parts Cr₂O₃, and 0.005-0.1 parts Al₂O₃.

[0007] This invention, by simultaneously adding two rare earth oxides, Ho2O3 and Eu2O3, to the formulation, and using Nb2O5 as a grain boundary modifier, utilizes the differential distribution of the two at the grain boundaries to effectively improve the voltage gradient and nonlinear coefficient of the varistor, while maintaining a low leakage current.

[0008] Based on the above technical solutions, preferably, the molar ratio of Ho2O3 to Eu2O3 is 2.3-2.7:1.

[0009] Specifically, you can choose 2.3:1, 2.4:1, 2.5:1, 2.6:1, or 2.7:1, but you are not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0010] Both Ho₂O₃ and Eu₂O₃, two rare earth oxides, are added to the zinc oxide varistor. Ho... 3+ During sintering, ions tend to segregate at ZnO grain boundaries, effectively suppressing abnormal grain growth, thereby increasing the number of grain boundaries per unit thickness and improving the voltage gradient of the varistor. Eu 3+ Rare earth ions can increase the density of states at grain boundaries, raise the grain boundary barrier height, improve the nonlinear coefficient, and reduce leakage current. When the molar ratio of Ho₂O₃ to Eu₂O₃ is controlled within the range of 2.3–2.7:1, the proportion of the two rare earth ions at the grain boundary is most harmonious, which can fully utilize the Ho₂O₃ content. 3+ It inhibits grain growth while ensuring Eu 3+ Sufficient interface state density is provided to achieve a better balance between overall performance such as voltage gradient, nonlinear coefficient, and leakage current. If the ratio is too low, Eu... 3+ An excessive number of ions and a high grain boundary barrier may lead to an abnormally high leakage current; if the proportion is too high, Ho 3+ An excessive number of ions may lead to over-refinement of grains, an increase in grain boundary defects, or inhomogeneity of grain boundary phases, thereby causing a decrease in the nonlinear coefficient.

[0011] This invention also provides a method for preparing a zinc oxide varistor, comprising the following steps: S1. Weigh out Ho2O3 and Eu2O3 powders in molar amounts, add them to an organic solvent, and ball mill them under microwave radiation to obtain a rare earth pre-dispersion slurry. S2. Weigh out ZnO, Bi2O3, Sb2O3, Nb2O5, Co2O3, MnO2, Cr2O3, and Al2O3 in molar amounts and mix them with the rare earth pre-dispersed slurry. Add deionized water and dispersant, and ball mill to obtain a mixed slurry. S3. The mixed slurry is dried, sieved, and a binder is added. After granulation, it is pressed into green sheets. S4. Heat the green sheet to 450-600℃ at a rate of 0.5-2℃ / min, hold for 2-5 hours, and then remove the binder. S5. Segmented sintering: First, in an oxygen-nitrogen mixed atmosphere, heat the temperature to 980-1050℃ at 3-6℃ / min and hold for 1-3 hours. Then, in an air atmosphere or a pure oxygen atmosphere, continue to heat the temperature to 1080-1150℃ at 1-3℃ / min and hold for 2-5 hours. S6. After sintering, first cool to 900-950℃ at 4-8℃ / min, hold for 0.5-1h, then cool to 600-700℃ at 0.5-2℃ / min, and then let it cool naturally to room temperature with the furnace to obtain zinc oxide varistor sheet.

[0012] Based on the above technical solutions, preferably, in step S1, the power of the microwave radiation is 300-600W, the ball-to-material ratio of the ball mill is 3-10:1, the ball milling speed is 200-500r / min, and the ball milling time is 2-8h.

[0013] Specifically, microwave radiation enables rare earth particles to rapidly absorb energy, causing a rapid increase in surface temperature and generating thermal stress within the particles, thus accelerating particle breakage and refinement. Simultaneously, microwave radiation helps reduce the agglomeration tendency of refined nanoparticles, improving the dispersion uniformity of rare earth elements in solvents. Through the synergistic effect of microwave and mechanical ball milling, a well-dispersed rare earth pre-dispersion slurry with a small average particle size can be obtained in a relatively short time.

[0014] Based on the above technical solutions, preferably, in step S1, the organic solvent is anhydrous ethanol, methanol, or isopropanol.

[0015] Based on the above technical solutions, preferably, in step S2, the dispersant is an ammonium salt dispersant, and the amount of the dispersant added is 0.2%-2.0% of the mass of ZnO.

[0016] Based on the above technical solution, preferably, in step S2, the Al2O3 is introduced in the form of Al(NO3)3·9H2O.

[0017] Based on the above technical solutions, preferably, in step S2, the ball-to-material ratio of the ball mill is 2-6:1, the ball milling speed is 150-400 r / min, and the ball milling time is 4-12 h.

[0018] Based on the above technical solutions, preferably, in step S3, the adhesive is polyvinyl alcohol, and the amount of adhesive added is 0.5%-2.0% of the mass of ZnO.

[0019] Based on the above technical solutions, preferably, in step S5, the oxygen volume concentration in the oxygen-nitrogen mixed atmosphere is 10%-30%.

[0020] In the first stage of this invention, sintering is carried out in a low-oxygen atmosphere with an oxygen concentration of 10%-30% to suppress abnormal growth of ZnO grains and promote uniform spreading of Bi2O3 liquid phase; in the second stage, the atmosphere is switched to air or pure oxygen to promote oxygen vacancy filling and reduce leakage current.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention optimizes the formulation of the zinc oxide varistor, particularly by adding two rare earth oxides, Ho2O3 and Eu2O3. 3+ During sintering, ions tend to segregate at ZnO grain boundaries, which can inhibit abnormal grain growth, thereby increasing the number of grain boundaries per unit thickness and improving the voltage gradient of the varistor. 3+ Ions can increase the density of state at grain boundaries, improve the height of grain boundaries, improve the nonlinear coefficient, and reduce leakage current. By using the ratio of these two rare earth oxides, the varistor can obtain a higher voltage gradient and nonlinear coefficient while maintaining a lower leakage current.

[0022] (2) This invention controls the molar ratio of Ho2O3 to Eu2O3 to achieve the most harmonious ratio of the two rare earth ions at the grain boundary, thus fully utilizing the Ho2O3 content. 3+ It inhibits grain growth while ensuring Eu 3+ Sufficient interface state density is provided to achieve a better balance between overall performance such as voltage gradient, nonlinear coefficient, and leakage current. If the ratio is too low, Eu... 3+ An excessive number of ions and a high grain boundary barrier may lead to an abnormally high leakage current; if the proportion is too high, Ho 3+ An excessive number of ions may lead to over-refinement of grains, an increase in grain boundary defects, or inhomogeneity of grain boundary phases, thereby causing a decrease in the nonlinear coefficient.

[0023] (3) In the preparation process, the rare earth raw materials are pretreated by microwave-assisted ball milling, and combined with two-step sintering with variable oxygen concentration and segmented temperature control cooling process, which is conducive to refining ceramic grains and promoting uniform distribution of grain boundary phase, thereby improving the impact resistance and long-term working stability of the varistor sheet. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] It should be noted that, unless otherwise specified, all chemical reagents involved in this invention are purchased through commercial channels or synthesized from raw materials purchased through commercial channels.

[0026] Example 1 This embodiment provides a method for preparing a zinc oxide varistor, characterized by comprising the following steps: S1. Weigh 0.4 parts of Ho2O3 and 0.16 parts of Eu2O3 powder (molar ratio of Ho2O3 to Eu2O3 is 2.5:1) according to molar ratio, add them to anhydrous ethanol, the amount of anhydrous ethanol added is 1.2 times the total mass of powder, and ball mill under microwave radiation. The microwave radiation power is 450W, the ball-to-powder ratio is 6:1, the ball milling speed is 350r / min, and the ball milling time is 5 hours to obtain rare earth pre-dispersion slurry. S2. Weigh out 89.5 parts ZnO, 1.25 parts Bi2O3, 1.25 parts Sb2O3, 0.11 parts Nb2O5, 0.85 parts Co2O3, 0.85 parts MnO2, 0.55 parts Cr2O3, and 0.05 parts Al2O3 (introduced in the form of Al(NO3)3·9H2O) according to the molar ratio and mix them with the rare earth pre-dispersed slurry. Add deionized water and ammonium polyacrylate. The amount of deionized water added is 1.0 times the total mass of the powder, and the amount of ammonium polyacrylate added is 1.0% of the mass of ZnO. Then, perform ball milling once with a ball-to-material ratio of 4:1, a ball milling speed of 250 r / min, and a ball milling time of 8 hours to obtain a uniform mixed slurry. S3. Dry the mixed slurry at 100℃ for 12 hours, pass it through an 80-mesh sieve, add the binder polyvinyl alcohol, mix, and then granulate through a 40-mesh sieve. The polyvinyl alcohol is added in the form of a 5wt% aqueous solution, and the amount of solid polyvinyl alcohol added is 1.25% of the mass of ZnO. After granulation, dry at 60℃ for 2 hours, and then press it into green sheets under a pressure of 20MPa. S4. Heat the green sheet to 525℃ at a rate of 1℃ / min, hold for 3.5h, and remove the binder polyvinyl alcohol. S5. Segmented sintering: First, in an oxygen-nitrogen mixed atmosphere with an oxygen volume concentration of 20%, the temperature is increased to 1020℃ at 4.5℃ / min and held for 2 hours. Then, in a pure oxygen atmosphere, the temperature is increased to 1120℃ at 2℃ / min and held for 3.5 hours. S6. After sintering, first cool to 925℃ at 6℃ / min, hold for 0.75h, then cool to 650℃ at 1℃ / min, and then let it cool naturally to room temperature with the furnace to obtain zinc oxide varistor sheet.

[0027] Example 2 This embodiment provides a method for preparing a zinc oxide varistor, characterized by comprising the following steps: S1. Weigh 0.23 parts of Ho2O3 and 0.1 parts of Eu2O3 powder (molar ratio of Ho2O3 to Eu2O3 is 2.3:1) according to molar ratio, add them to anhydrous ethanol, the amount of anhydrous ethanol added is 1.2 times the total mass of powder, and ball mill under microwave radiation. The microwave radiation power is 300W, the ball-to-powder ratio is 3:1, the ball milling speed is 200r / min, and the ball milling time is 2 hours to obtain rare earth pre-dispersion slurry. S2. Weigh out 85 parts ZnO, 0.5 parts Bi2O3, 0.5 parts Sb2O3, 0.02 parts Nb2O5, 0.2 parts Co2O3, 0.2 parts MnO2, 0.1 parts Cr2O3, and 0.005 parts Al2O3 (introduced in the form of Al(NO3)3·9H2O) according to the molar ratio and mix them with the rare earth pre-dispersed slurry. Add deionized water and ammonium polyacrylate. The amount of deionized water added is 1.0 times the total mass of the powder, and the amount of ammonium polyacrylate added is 0.2% of the mass of ZnO. Then, perform ball milling once with a ball-to-material ratio of 2:1, a ball milling speed of 150 r / min, and a ball milling time of 4 hours to obtain a uniform mixed slurry. S3. Dry the mixed slurry at 100℃ for 12 hours, pass it through an 80-mesh sieve, add the binder polyvinyl alcohol, mix, and then granulate through a 40-mesh sieve. The polyvinyl alcohol is added in the form of a 5wt% aqueous solution, and the amount of solid polyvinyl alcohol added is 0.5% of the mass of ZnO. After granulation, dry at 60℃ for 2 hours, and then press it into green sheets under a pressure of 20MPa. S4. Heat the green sheet to 450℃ at a rate of 0.5℃ / min, keep it at that temperature for 2 hours, and then remove the adhesive polyvinyl alcohol. S5. Segmented sintering: First, in an oxygen-nitrogen mixed atmosphere with an oxygen volume concentration of 10%, the temperature is increased to 980℃ at 3℃ / min and held for 1 hour. Then, in a pure oxygen atmosphere, the temperature is increased to 1080℃ at 1℃ / min and held for 2 hours. S6. After sintering, first cool to 900℃ at 4℃ / min, hold for 0.5h, then cool to 600℃ at 0.5℃ / min, and then let it cool naturally to room temperature with the furnace to obtain zinc oxide varistor sheet.

[0028] Example 3 This embodiment provides a method for preparing a zinc oxide varistor, characterized by comprising the following steps: S1. Weigh 0.54 parts of Ho2O3 and 0.2 parts of Eu2O3 powder (molar ratio of Ho2O3 to Eu2O3 is 2.7:1) according to molar ratio, add them to anhydrous ethanol, the amount of anhydrous ethanol added is 1.2 times the total mass of powder, and ball mill under microwave radiation. The microwave radiation power is 600W, the ball-to-powder ratio is 10:1, the ball milling speed is 500r / min, and the ball milling time is 8 hours to obtain rare earth pre-dispersion slurry. S2. Weigh out 94 parts ZnO, 2 parts Bi2O3, 2 parts Sb2O3, 0.2 parts Nb2O5, 1.5 parts Co2O3, 1.5 parts MnO2, 1.0 parts Cr2O3, and 0.1 parts Al2O3 (introduced in the form of Al(NO3)3·9H2O) according to the molar ratio and mix them with the rare earth pre-dispersed slurry. Add deionized water and ammonium polyacrylate. The amount of deionized water added is 1.0 times the total mass of the powder, and the amount of ammonium polyacrylate added is 2.0% of the mass of ZnO. Then, perform ball milling once with a ball-to-material ratio of 6:1, a ball milling speed of 400 r / min, and a ball milling time of 12 hours to obtain a uniform mixed slurry. S3. Dry the mixed slurry at 100℃ for 12 hours, pass it through an 80-mesh sieve, add the binder polyvinyl alcohol, mix, and then granulate through a 40-mesh sieve. The polyvinyl alcohol is added in the form of a 5wt% aqueous solution, and the amount of solid polyvinyl alcohol added is 2.0% of the mass of ZnO. After granulation, dry at 60℃ for 2 hours, and then press it into green sheets under a pressure of 20MPa. S4. Heat the green sheet to 600℃ at 2℃ / min, keep it at that temperature for 5 hours, and then remove the binder polyvinyl alcohol. S5. Segmented sintering: First, in an oxygen-nitrogen mixed atmosphere with an oxygen volume concentration of 30%, the temperature is increased to 1050℃ at 6℃ / min and held for 3h. Then, in a pure oxygen atmosphere, the temperature is increased to 1150℃ at 3℃ / min and held for 5h. S6. After sintering, first cool to 950℃ at 8℃ / min, hold for 1 hour, then cool to 700℃ at 2℃ / min, and then let it cool naturally to room temperature with the furnace to obtain zinc oxide varistor sheet.

[0029] Comparative Example 1 This comparative example provides a method for preparing a zinc oxide varistor, characterized by comprising the following steps: S1. Weigh 0.48 parts of Ho2O3 and 0.16 parts of Eu2O3 powder (molar ratio of Ho2O3 to Eu2O3 is 3:1) according to the molar ratio, add them to anhydrous ethanol, the amount of anhydrous ethanol added is 1.2 times the total mass of powder, and ball mill under microwave radiation. The microwave radiation power is 450W, the ball-to-powder ratio is 6:1, the ball milling speed is 350r / min, and the ball milling time is 5 hours to obtain rare earth pre-dispersion slurry. S2. Weigh out 89.5 parts ZnO, 1.25 parts Bi2O3, 1.25 parts Sb2O3, 0.11 parts Nb2O5, 0.85 parts Co2O3, 0.85 parts MnO2, 0.55 parts Cr2O3, and 0.05 parts Al2O3 (introduced in the form of Al(NO3)3·9H2O) according to the molar ratio and mix them with the rare earth pre-dispersed slurry. Add deionized water and ammonium polyacrylate. The amount of deionized water added is 1.0 times the total mass of the powder, and the amount of ammonium polyacrylate added is 1.0% of the mass of ZnO. Then, perform ball milling once with a ball-to-material ratio of 4:1, a ball milling speed of 250 r / min, and a ball milling time of 8 hours to obtain a uniform mixed slurry. S3. Dry the mixed slurry at 100℃ for 12 hours, pass it through an 80-mesh sieve, add the binder polyvinyl alcohol, mix, and then granulate through a 40-mesh sieve. The polyvinyl alcohol is added in the form of a 5wt% aqueous solution, and the amount of solid polyvinyl alcohol added is 1.25% of the mass of ZnO. After granulation, dry at 60℃ for 2 hours, and then press it into green sheets under a pressure of 20MPa. S4. Heat the green sheet to 525℃ at a rate of 1℃ / min, hold for 3.5h, and remove the binder polyvinyl alcohol. S5. Segmented sintering: First, in an oxygen-nitrogen mixed atmosphere with an oxygen volume concentration of 20%, the temperature is increased to 1020℃ at 4.5℃ / min and held for 2 hours. Then, in a pure oxygen atmosphere, the temperature is increased to 1120℃ at 2℃ / min and held for 3.5 hours. S6. After sintering, first cool to 925℃ at 6℃ / min, hold for 0.75h, then cool to 650℃ at 1℃ / min, and then let it cool naturally to room temperature with the furnace to obtain zinc oxide varistor sheet.

[0030] The difference between Comparative Example 1 and Example 1 is that the molar ratio of Ho2O3 to Eu2O3 is increased to 3:1.

[0031] Comparative Example 2 This comparative example provides a method for preparing a zinc oxide varistor, characterized by comprising the following steps: S1. Weigh 0.32 parts of Ho2O3 and 0.16 parts of Eu2O3 powder (the molar ratio of Ho2O3 to Eu2O3 is 2:1) according to the molar ratio, add them to anhydrous ethanol, the amount of anhydrous ethanol added is 1.2 times the total mass of the powder, and ball mill under microwave radiation. The microwave radiation power is 450W, the ball-to-powder ratio is 6:1, the ball milling speed is 350r / min, and the ball milling time is 5 hours to obtain rare earth pre-dispersion slurry. S2. Weigh out 89.5 parts ZnO, 1.25 parts Bi2O3, 1.25 parts Sb2O3, 0.11 parts Nb2O5, 0.85 parts Co2O3, 0.85 parts MnO2, 0.55 parts Cr2O3, and 0.05 parts Al2O3 (introduced in the form of Al(NO3)3·9H2O) according to the molar ratio and mix them with the rare earth pre-dispersed slurry. Add deionized water and ammonium polyacrylate. The amount of deionized water added is 1.0 times the total mass of the powder, and the amount of ammonium polyacrylate added is 1.0% of the mass of ZnO. Then, perform ball milling once with a ball-to-material ratio of 4:1, a ball milling speed of 250 r / min, and a ball milling time of 8 hours to obtain a uniform mixed slurry. S3. Dry the mixed slurry at 100℃ for 12 hours, pass it through an 80-mesh sieve, add the binder polyvinyl alcohol, mix, and then granulate through a 40-mesh sieve. The polyvinyl alcohol is added in the form of a 5wt% aqueous solution, and the amount of solid polyvinyl alcohol added is 1.25% of the mass of ZnO. After granulation, dry at 60℃ for 2 hours, and then press it into green sheets under a pressure of 20MPa. S4. Heat the green sheet to 525℃ at a rate of 1℃ / min, hold for 3.5h, and remove the binder polyvinyl alcohol. S5. Segmented sintering: First, in an oxygen-nitrogen mixed atmosphere with an oxygen volume concentration of 20%, the temperature is increased to 1020℃ at 4.5℃ / min and held for 2 hours. Then, in a pure oxygen atmosphere, the temperature is increased to 1120℃ at 2℃ / min and held for 3.5 hours. S6. After sintering, first cool to 925℃ at 6℃ / min, hold for 0.75h, then cool to 650℃ at 1℃ / min, and then let it cool naturally to room temperature with the furnace to obtain zinc oxide varistor sheet.

[0032] The difference between Comparative Example 2 and Example 1 is that the molar ratio of Ho2O3 to Eu2O3 was reduced to 2:1.

[0033] Comparative Example 3 This comparative example provides a method for preparing a zinc oxide varistor, characterized by comprising the following steps: S1. Weigh out 89.5 parts ZnO, 1.25 parts Bi2O3, 1.25 parts Sb2O3, 0.11 parts Nb2O5, 0.85 parts Co2O3, 0.85 parts MnO2, 0.55 parts Cr2O3, and 0.05 parts Al2O3 (introduced in the form of Al(NO3)3·9H2O) according to the molar ratio. Add deionized water and ammonium polyacrylate. The amount of deionized water added is 1.0 times the total mass of the powder, and the amount of ammonium polyacrylate added is 1.0% of the mass of ZnO. Then, perform ball milling once with a ball-to-powder ratio of 4:1, a ball milling speed of 250 r / min, and a ball milling time of 8 hours to obtain a uniform mixed slurry. S2. The mixed slurry is dried at 100℃ for 12 hours, passed through an 80-mesh sieve, and then mixed with the binder polyvinyl alcohol. After mixing, it is granulated by passing through a 40-mesh sieve. The polyvinyl alcohol is added in the form of a 5wt% aqueous solution, and the amount of solid polyvinyl alcohol added is 1.25% of the mass of ZnO. After granulation, it is dried at 60℃ for 2 hours, and then pressed into green sheets under a pressure of 20MPa. S3. Heat the green sheet to 525℃ at a rate of 1℃ / min, hold for 3.5h, and remove the binder polyvinyl alcohol; S4. Segmented sintering: First, in an oxygen-nitrogen mixed atmosphere with an oxygen volume concentration of 20%, the temperature is increased to 1020℃ at 4.5℃ / min and held for 2 hours. Then, in a pure oxygen atmosphere, the temperature is increased to 1120℃ at 2℃ / min and held for 3.5 hours. S5. After sintering, first cool to 925℃ at 6℃ / min, hold for 0.75h, then cool to 650℃ at 1℃ / min, and then let it cool naturally to room temperature with the furnace to obtain zinc oxide varistor sheet.

[0034] The difference between Comparative Example 3 and Example 1 is that the formulation does not contain Ho2O3 and Eu2O3.

[0035] Comparative Example 4 This comparative example provides a method for preparing a zinc oxide varistor, characterized by comprising the following steps: S1. Weigh 0.4 parts of Ho2O3 by molar ratio and add it to anhydrous ethanol. The amount of anhydrous ethanol added is 1.2 times the total mass of the powder. Ball milling is carried out under microwave radiation. The microwave radiation power is 450W, the ball-to-powder ratio is 6:1, the ball milling speed is 350r / min, and the ball milling time is 5 hours to obtain rare earth pre-dispersion slurry. S2. Weigh out 89.5 parts ZnO, 1.25 parts Bi2O3, 1.25 parts Sb2O3, 0.11 parts Nb2O5, 0.85 parts Co2O3, 0.85 parts MnO2, 0.55 parts Cr2O3, and 0.05 parts Al2O3 (introduced in the form of Al(NO3)3·9H2O) according to the molar ratio and mix them with the rare earth pre-dispersed slurry. Add deionized water and ammonium polyacrylate. The amount of deionized water added is 1.0 times the total mass of the powder, and the amount of ammonium polyacrylate added is 1.0% of the mass of ZnO. Then, perform ball milling once with a ball-to-material ratio of 4:1, a ball milling speed of 250 r / min, and a ball milling time of 8 hours to obtain a uniform mixed slurry. S3. Dry the mixed slurry at 100℃ for 12 hours, pass it through an 80-mesh sieve, add the binder polyvinyl alcohol, mix, and then granulate through a 40-mesh sieve. The polyvinyl alcohol is added in the form of a 5wt% aqueous solution, and the amount of solid polyvinyl alcohol added is 1.25% of the mass of ZnO. After granulation, dry at 60℃ for 2 hours, and then press it into green sheets under a pressure of 20MPa. S4. Heat the green sheet to 525℃ at a rate of 1℃ / min, hold for 3.5h, and remove the binder polyvinyl alcohol. S5. Segmented sintering: First, in an oxygen-nitrogen mixed atmosphere with an oxygen volume concentration of 20%, the temperature is increased to 1020℃ at 4.5℃ / min and held for 2 hours. Then, in a pure oxygen atmosphere, the temperature is increased to 1120℃ at 2℃ / min and held for 3.5 hours. S6. After sintering, first cool to 925℃ at 6℃ / min, hold for 0.75h, then cool to 650℃ at 1℃ / min, and then let it cool naturally to room temperature with the furnace to obtain zinc oxide varistor sheet.

[0036] The difference between Comparative Example 4 and Example 1 is that the formulation does not contain Eu2O3.

[0037] Comparative Example 5 This comparative example provides a method for preparing a zinc oxide varistor, characterized by comprising the following steps: S1. Weigh 0.16 parts of Eu2O3 by molar ratio and add it to anhydrous ethanol. The amount of anhydrous ethanol added is 1.2 times the total mass of the powder. Ball milling is carried out under microwave radiation. The microwave radiation power is 450W, the ball-to-powder ratio is 6:1, the ball milling speed is 350r / min, and the ball milling time is 5 hours to obtain rare earth pre-dispersion slurry. S2. Weigh out 89.5 parts ZnO, 1.25 parts Bi2O3, 1.25 parts Sb2O3, 0.11 parts Nb2O5, 0.85 parts Co2O3, 0.85 parts MnO2, 0.55 parts Cr2O3, and 0.05 parts Al2O3 (introduced in the form of Al(NO3)3·9H2O) according to the molar ratio and mix them with the rare earth pre-dispersed slurry. Add deionized water and ammonium polyacrylate. The amount of deionized water added is 1.0 times the total mass of the powder, and the amount of ammonium polyacrylate added is 1.0% of the mass of ZnO. Then, perform ball milling once with a ball-to-material ratio of 4:1, a ball milling speed of 250 r / min, and a ball milling time of 8 hours to obtain a uniform mixed slurry. S3. Dry the mixed slurry at 100℃ for 12 hours, pass it through an 80-mesh sieve, add the binder polyvinyl alcohol, mix, and then granulate through a 40-mesh sieve. The polyvinyl alcohol is added in the form of a 5wt% aqueous solution, and the amount of solid polyvinyl alcohol added is 1.25% of the mass of ZnO. After granulation, dry at 60℃ for 2 hours, and then press it into green sheets under a pressure of 20MPa. S4. Heat the green sheet to 525℃ at a rate of 1℃ / min, hold for 3.5h, and remove the binder polyvinyl alcohol. S5. Segmented sintering: First, in an oxygen-nitrogen mixed atmosphere with an oxygen volume concentration of 20%, the temperature is increased to 1020℃ at 4.5℃ / min and held for 2 hours. Then, in a pure oxygen atmosphere, the temperature is increased to 1120℃ at 2℃ / min and held for 3.5 hours. S6. After sintering, first cool to 925℃ at 6℃ / min, hold for 0.75h, then cool to 650℃ at 1℃ / min, and then let it cool naturally to room temperature with the furnace to obtain zinc oxide varistor sheet.

[0038] The difference between Comparative Example 5 and Example 1 is that the formulation does not contain Ho2O3.

[0039] Performance testing: A dedicated varistor tester (TTK, Taiwan) was used to test the voltage gradient, nonlinear coefficient, and leakage current of each sample prepared in Examples 1-3 and Comparative Examples 1-5. The ambient temperature during testing was 25±2℃. The test results are shown in Table 1 below.

[0040] Table 1 Performance Test Results As shown in Table 1, the varistor sheets prepared in Examples 1-3 of this application all exhibit excellent comprehensive electrical performance, achieving higher voltage gradients and nonlinear coefficients while maintaining low leakage current. In contrast, the comparative examples with molar ratios deviating from the preferred range show a significant decrease in nonlinear coefficients and a significant increase in leakage current; while the comparative examples using single rare earth elements or no rare earth elements show performance indicators that are comprehensively inferior to the examples. The above results demonstrate that the present invention, by adding Ho₂O₃ and Eu₂O₃ and controlling their molar ratio, enables the varistor sheet to achieve higher voltage gradients and nonlinear coefficients while maintaining low leakage current.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A zinc oxide varistor, characterized in that, Based on molar amounts, its composition is as follows: ZnO 85-94 parts, Bi2O3 0.5-2.0 parts, Sb2O3 0.5-2.0 parts, Ho2O3 0.23-0.54 parts, Eu2O3 0.1-0.2 parts, Nb2O5 0.02-0.2 parts, Co2O3 0.2-1.5 parts, MnO2 0.2-1.5 parts, Cr2O3 0.1-1.0 parts, and Al2O3 0.005-0.1 parts.

2. The zinc oxide varistor sheet according to claim 1, characterized in that: The molar ratio of Ho2O3 to Eu2O3 is 2.3-2.7:

1.

3. A method for preparing the zinc oxide varistor sheet according to claim 1 or 2, characterized in that, Includes the following steps: S1. Weigh out Ho2O3 and Eu2O3 powders in molar amounts, add them to an organic solvent, and ball mill them under microwave radiation to obtain a rare earth pre-dispersion slurry. S2. Weigh out ZnO, Bi2O3, Sb2O3, Nb2O5, Co2O3, MnO2, Cr2O3, and Al2O3 in molar amounts and mix them with the rare earth pre-dispersed slurry. Add deionized water and dispersant, and ball mill to obtain a mixed slurry. S3. The mixed slurry is dried, sieved, and a binder is added. After granulation, it is pressed into green sheets. S4. Heat the green sheet to 450-600℃ at a rate of 0.5-2℃ / min, hold for 2-5 hours, and then remove the binder. S5. Segmented sintering: First, in an oxygen-nitrogen mixed atmosphere, heat the temperature to 980-1050℃ at 3-6℃ / min and hold for 1-3 hours. Then, in an air atmosphere or a pure oxygen atmosphere, continue to heat the temperature to 1080-1150℃ at 1-3℃ / min and hold for 2-5 hours. S6. After sintering, first cool to 900-950℃ at 4-8℃ / min, hold for 0.5-1h, then cool to 600-700℃ at 0.5-2℃ / min, and then let it cool naturally to room temperature with the furnace to obtain zinc oxide varistor sheet.

4. The method for preparing the zinc oxide varistor according to claim 3, characterized in that, In step S1, the power of the microwave radiation is 300-600W, the ball-to-material ratio of the ball mill is 3-10:1, the ball milling speed is 200-500r / min, and the ball milling time is 2-8h.

5. The method for preparing the zinc oxide varistor according to claim 3, characterized in that, In step S1, the organic solvent is anhydrous ethanol, methanol, or isopropanol.

6. The method for preparing the zinc oxide varistor according to claim 3, characterized in that, In step S2, the dispersant is an ammonium salt dispersant, and the amount of the dispersant added is 0.2%-2.0% of the mass of the ZnO.

7. The method for preparing the zinc oxide varistor according to claim 3, characterized in that, In step S2, the Al2O3 is introduced in the form of Al(NO3)3·9H2O.

8. The method for preparing the zinc oxide varistor according to claim 3, characterized in that, In step S2, the ball-to-material ratio of the ball mill is 2-6:1, the ball milling speed is 150-400 r / min, and the ball milling time is 4-12 h.

9. The method for preparing the zinc oxide varistor according to claim 3, characterized in that, In step S3, the binder is polyvinyl alcohol, and the amount of binder added is 0.5%-2.0% of the mass of ZnO.

10. The method for preparing the zinc oxide varistor according to claim 3, characterized in that, In step S5, the oxygen volume concentration in the oxygen-nitrogen mixed atmosphere is 10%-30%.

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