Multi-element doped ZnO voltage-sensitive ceramic as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of voltage-sensitive ceramic material preparation, and particularly relates to multi-element doped ZnO voltage-sensitive ceramic as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) mixing a gallium source, a nickel source, a zirconium source, aluminum nitrate and a solvent, and adjusting the pH value to 7-8 to obtain a mixed solution; the gallium source comprises gallium nitrate and / or gallium acetate; the nickel source comprises nickel nitrate and / or nickel acetate; the zirconium source comprises zirconium nitrate and / or zirconium acetate; the molar ratio of the gallium source to the nickel source to the zirconium source is (0.2-1.5): (0.5-1.8): (0.2-1); and (2) mixing the mixed solution with the remaining raw materials to obtain a mixture, granulating and forming to obtain a green body, and sintering. The gallium source, the nickel source and the zirconium source are used as raw materials in the form of salt at the same time, the prepared ZnO voltage-sensitive ceramic has large discharge-current capacity, high voltage gradient, low leakage current and low residual voltage ratio, the comprehensive performance meets the ionization protection requirement, for example, the ZnO voltage-sensitive ceramic is used for overvoltage protection of lightning protection insulators and ionization equipment.

Description

Technical Field

[0001] This invention belongs to the field of varistor ceramic material preparation technology, and particularly relates to a multi-element doped ZnO varistor ceramic, its preparation method and application. Background Technology

[0002] Zinc oxide varistors, as core components for lightning surge protection, require electrical properties such as high voltage gradient, low leakage current and residual voltage ratio, and large current capacity. These properties are highly correlated with the microstructure, including dopant dispersion, grain size, and grain boundary barriers. Traditional methods for preparing zinc oxide varistors present the following challenges: First, the raw material for the donor doping element Ga is mostly Ga2O3. This oxide is prone to agglomeration in the slurry, leading to Ga... 3+ Inhomogeneous solid solution in the ZnO lattice and local donor concentration imbalance ultimately result in a high residual voltage ratio in varistor ceramics, making it difficult to meet the low residual voltage requirements of high-end power equipment.

[0003] Secondly, the raw material for Ni, a grain boundary barrier control element, is mainly NiO. The density difference between NiO and ZnO particles is significant, making them prone to stratification during mixing, which leads to Ni… 2+ Uneven segregation at grain boundaries and uneven distribution of grain boundary barriers lead to a decrease in nonlinear coefficient and an increase in leakage current. The overall performance of ZnO varistors still cannot meet the requirements of high-end applications such as distribution network lightning protection insulators.

[0004] Third, Zr, an element for grain refinement and grain boundary stabilization, is often used as a raw material for ZrO2. ZrO2 has a high melting point and its particles are prone to agglomeration, which leads to Zr… 4+ It is difficult to distribute evenly in the ZnO matrix, thus failing to fully exert its role in refining grains and suppressing the volatilization of Bi2O3 grain boundaries. It also exacerbates the heterogeneity of the grain boundary phase composition, further weakening the current carrying capacity and varistor voltage stability.

[0005] Improving the voltage gradient and current carrying capacity of zinc oxide varistors, and reducing leakage current and residual voltage ratio have a significant impact on their applications. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a multi-element doped ZnO varistor ceramic, its preparation method, and its application.

[0007] In a first aspect, the present invention provides a method for preparing multi-element doped ZnO varistors, comprising the following steps: (1) gallium source, nickel source, zirconium source, aluminum nitrate and solvent are mixed, and pH is adjusted to 7-8 to obtain a mixed solution; the gallium source includes gallium nitrate and / or gallium acetate; the nickel source includes nickel nitrate and / or nickel acetate; the zirconium source includes zirconium nitrate and / or zirconium acetate; the molar ratio of the gallium source, nickel source and zirconium source is (0.2-1.5):(0.5-1.8):(0.2-1); (2) the mixed solution is mixed with the remaining raw materials to obtain a mixture, and the mixture is granulated and molded to obtain a green body, which is sintered.

[0008] As an optional embodiment, in the step (1), a pH adjusting agent is added to adjust pH to 7.4-7.6. Preferably, the pH adjusting agent includes ammonia.

[0009] As an optional embodiment, the step (2) includes: Bi2O3, Sb2O3, MnCO3, Cr2O3, Co2O3, SiO2, silver glass powder are added to the mixed solution, and first grinding is performed; ZnO and an additive are added, and second grinding is performed to obtain a mixture, which is sintered.

[0010] As an optional embodiment, based on the total molar amount of Bi2O3, Sb2O3, MnCO3, Cr2O3, Co2O3, SiO2, ZnO, silver glass powder, gallium source, nickel source, zirconium source and aluminum nitrate being 100%, the content of the gallium source is 0.2-1.5%; and / or, the content of the nickel source is 0.5-1.8%; and / or, the content of the zirconium source is 0.2-1%.

[0011] As an optional embodiment, based on the total molar amount of Bi2O3, Sb2O3, MnCO3, Cr2O3, Co2O3, SiO2, ZnO, silver glass powder, gallium source, nickel source, zirconium source and aluminum nitrate being 100%, the content of ZnO is 87.0-95.0%, the content of Bi2O3 is 0.7-2.5%, the content of Sb2O3 is 0.2-2.5%, the content of MnCO3 is 0.2-1.0%, the content of Cr2O3 is 0.1-0.7%, the content of Co2O3 is 0.1-1.2%, the content of SiO2 is 0.3-1.0%, the content of silver glass powder is 0.001-0.10%, and the content of aluminum nitrate is 0.005-0.01%. As an optional implementation, the auxiliary agent comprises ammonium polymethacrylate, tributyl phosphate, and PVA solution, and the mass ratio of the ammonium polymethacrylate, tributyl phosphate, PVA solution to ZnO is (0.3-1.0):(0.1-0.8):(4-6):100, and the concentration of the PVA solution is 70-80 g / L; preferably, the mass ratio of the ammonium polymethacrylate, tributyl phosphate, PVA solution to ZnO is 1:0.5:5:100.

[0012] As an optional implementation, in the first grinding, the solid-liquid ratio is 1:(1-2), the rotating speed is 1500-3000 r / min, and the time is 10-30 min. And / or, in the second grinding, the solid-liquid ratio is 1:(1-2), the rotating speed is 1500-3000 r / min, and the time is 30-60 min.

[0013] As an optional implementation, after the mixture is granulated, granulated material is obtained, and the granulated material is sieved to obtain powder, and the mesh number of the powder is 80-200 mesh. As an optional implementation, the sintering comprises degreasing, first sintering, and second sintering. As an optional implementation, after the sintering, the method further comprises the steps of adhering insulating material to at least part of the surface of the green body to form an insulating layer, and then performing heat treatment.

[0014] As an optional implementation, the specific steps of the degreasing comprise the following steps: increasing the temperature from room temperature to 300-350℃ at a temperature increasing rate of 120-180℃ / h, continuously increasing the temperature to 400-450℃ at a temperature increasing rate of 40-80℃ / h, keeping the temperature for 2-4 h, and decreasing the temperature with the furnace; As an optional implementation, the specific steps of the first sintering comprise the following steps: increasing the temperature from room temperature to 600-800℃ at a temperature increasing rate of 60-90℃ / h, and keeping the temperature for 1.5-2.5 h; preferably, the specific steps of the first sintering comprise the following steps: increasing the temperature from room temperature to 600℃ at a temperature increasing rate of 90℃ / h, and keeping the temperature for 2 h; As an optional implementation, the specific steps of the second sintering comprise the following steps: increasing the temperature to 1100-1200℃ at a temperature increasing rate of 60-80℃ / h, decreasing the temperature to 800-900℃ at a temperature decreasing rate of 60-80℃ / h, keeping the temperature for 7-9 h, and decreasing the temperature with the furnace; preferably, the specific steps of the second sintering comprise the following steps: increasing the temperature to 1150℃ at a temperature increasing rate of 60℃ / h, decreasing the temperature to 850℃ at a temperature decreasing rate of 60℃ / h, keeping the temperature for 8 h, and decreasing the temperature with the furnace. As an optional implementation, the insulating material is adhered to at least part of the surface of the green body by using an adhesive; preferably, the adhesive comprises ethanol, butyl carbitol and ethyl cellulose in a ratio of 100: (5-15): (1-4), preferably 100:10:2.5, in units of ml:ml:g; As an optional implementation, the specific step of the heat treatment comprises: heating from room temperature to 500-550 DEG C at a heating rate of 90-180 DEG C / h, holding for 2-4 h, and then cooling to 200 DEG C at a cooling rate of 10-50 DEG C / h, and cooling down with the furnace.

[0015] In a second aspect, the present application provides a ZnO pressure-sensitive ceramic prepared by the above preparation method.

[0016] In a third aspect, the present application provides a lightning protection device comprising the ZnO pressure-sensitive ceramic prepared by the above preparation method.

[0017] Compared with the prior art, the technical scheme provided by the embodiments of the present application has the following advantages: 1. The preparation method of the multi-element doped ZnO pressure-sensitive ceramic provided by the present application comprises (1) mixing a gallium source, a nickel source, a zirconium source, aluminum nitrate and a solvent, and adjusting the pH to 7-8 to obtain a mixed solution; the gallium source comprises gallium nitrate and / or gallium acetate; the nickel source comprises nickel nitrate and / or nickel acetate; the zirconium source comprises zirconium nitrate and / or zirconium acetate; the molar ratio of the gallium source, the nickel source and the zirconium source is (0.2-1.5):(0.5-1.8):(0.2-1); (2) mixing the mixed solution with the remaining raw materials to obtain a mixed material, and then granulating and molding to obtain a green body, and then sintering. In the present application, the gallium source comprises gallium nitrate and / or gallium acetate, the nickel source comprises nickel nitrate and / or nickel acetate, and the zirconium source comprises zirconium nitrate and / or zirconium acetate, which are in the form of salt as raw materials, which is beneficial to realizing molecular-level dispersion of Ga, Ni and Zr elements for doping, and improving the dispersion uniformity of the doped elements; Ga ions can be uniformly solid-solved into the ZnO crystal lattice, Ga acts as a donor doping component to provide carriers, thereby reducing the grain resistance and residual voltage; Ni ions can be uniformly diffused to the grain boundaries to regulate the height of the grain boundary barrier and improve the nonlinear coefficient; Zr ions realize grain refinement and inhibit the volatilization of Bi2O3 at the grain boundaries, which is beneficial to improving the current flow capacity and the stability of the pressure-sensitive voltage; Al ions and Ga ions form a synergistic effect to inhibit the volatilization of Bi2O3 during the sintering process, and ensure the uniformity of the grain boundaries. In the present application, the gallium source, the nickel source and the zirconium source are simultaneously used in the form of salt as raw materials, and the ZnO pressure-sensitive ceramic prepared has large current flow capacity, high voltage gradient, low leakage current and low residual voltage ratio, and the comprehensive performance meets the demand of ionization protection, for example, can be applied to lightning protection insulators and overvoltage protection of ionization equipment. BRIEF DESCRIPTION OF DRAWINGS

[0018] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate preferred embodiments of the present application and, together with the description, serve to explain the principles of the application.

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, for those skilled in the art, other drawings can also be obtained based on these drawings without any creative effort.

[0020] Figure 1 is the SEM image and particle size distribution diagram of the ZnO varistor disc prepared in Example 1 of the present application; Figure 2 is the SEM image and particle size distribution diagram of the ZnO varistor disc prepared in Comparative Example 4 of the present application; Figure 3 is the current density of the ZnO varistor disc prepared in Example 1 and Comparative Examples 1-4 of the present application. DETAILED DESCRIPTION

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, for those skilled in the art, other drawings can also be obtained based on these drawings without any creative effort.

[0022] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in a variety of ways beyond the specific details set forth herein without departing from the spirit of the present application. It will be apparent that the present application, as described in the specification, is only a part of the embodiments of the present application, not all the embodiments.

[0023] In a first aspect, the present application provides a preparation method of a multi-element doped ZnO varistor ceramic, comprising the following steps: (1) After mixing gallium source, nickel source, zirconium source, aluminum nitrate and solvent, the pH is adjusted to 7-8 to obtain a mixed solution; the gallium source includes gallium nitrate and / or gallium acetate; the nickel source includes nickel nitrate and / or nickel acetate; the zirconium source includes zirconium nitrate and / or zirconium acetate; the molar ratio of the gallium source, nickel source and zirconium source is (0.2-1.5):(0.5-1.8):(0.2-1); wherein the solvent is a conventional solvent in the art, which can dissolve the gallium source, nickel source, zirconium source and aluminum nitrate, and can use a single solvent or a compounded solvent, including but not limited to water, ethanol, etc.; (2) After mixing the mixed solution with the remaining raw materials, a mixed material is obtained, and after granulation and molding, a green body is obtained, which is sintered.

[0024] The ZnO pressure sensitive ceramic prepared by the preparation method has the advantages that Ga, Ni and Zr elements are doped in a molecular level, the dispersion uniformity of the doped elements is improved, Ga ions can be uniformly solid-solved into the ZnO crystal lattice, Ga as a donor doping component provides carriers, thereby reducing the grain resistance and residual voltage value, Ni ions can be uniformly diffused to the grain boundary to regulate the grain boundary barrier height and improve the nonlinear coefficient, Zr ions realize grain refinement and inhibit the volatilization of Bi2O3 at the grain boundary, which is beneficial to improve the through-flow capacity and stability of the pressure sensitive voltage, and Al ions and Ga ions form a synergistic effect to inhibit the volatilization of Bi2O3 in the sintering process and ensure the uniformity of the grain boundary. The ZnO pressure sensitive ceramic prepared by the method has large through-flow capacity, high voltage gradient, low leakage current and low residual voltage ratio, and the comprehensive performance meets the demand of ionization protection, for example, can be applied to lightning insulation sub, ionization equipment overvoltage protection.

[0025] The method of the application can slow down the over-acidity or over-alkalinity of the mixed system by mixing the gallium source, nickel source, zirconium source and aluminum nitrate with a solvent and then regulating the pH, so as to prevent the doped elements from preforming precipitates or agglomerates under over-acid or over-alkaline conditions, thereby improving the dispersion of the doped elements and the through-flow capacity and voltage gradient of the ZnO pressure sensitive ceramic, reducing the leakage current and residual voltage ratio.

[0026] As an optional embodiment, the step (1) comprises adding a pH regulator to regulate the pH to 7.4-7.6, and the effect is better.

[0027] Preferably, the pH regulator comprises ammonia water.

[0028] As an optional embodiment, the step (2) comprises: adding Bi2O3, Sb2O3, MnCO3, Cr2O3, Co2O3, SiO2 and silver glass powder to the mixed solution, grinding once, adding ZnO and additives, and grinding twice to obtain a mixed material, and then sintering.

[0029] As an optional embodiment, the total mole amount of Bi2O3, Sb2O3, MnCO3, Cr2O3, Co2O3, SiO2, ZnO, silver glass powder, gallium source, nickel source, zirconium source and aluminum nitrate is 100% as a basis, the content of the gallium source is 0.2-1.5%; and / or, the content of the nickel source is 0.5-1.8%; and / or, the content of the zirconium source is 0.2-1%. As an example, the content of the gallium source is any one of 0.2%, 0.5%, 0.8%, 1%, 1.2% and 1.5%; the content of the nickel source is any one of 0.5%, 0.8%, 1%, 1.3%, 1.5% and 1.8%; and the content of the zirconium source is any one of 0.2%, 0.5%, 0.8% and 1%.

[0030] The content of gallium, nickel and zirconium is regulated, which is beneficial to improve the pressure-sensitive characteristic and stability of the pressure-sensitive ceramic. If the content of gallium is too high, the carrier concentration is too high, the pressure-sensitive voltage is significantly reduced, the design voltage requirement cannot be met, Ga2O3 second phase is easily formed, the combination between zinc oxide grains is cut off, the mechanical strength and heat conductivity of the device are reduced, the leakage current is greatly increased, the device power consumption is increased, the aging speed is accelerated during long-term work, and the service life is shortened. If the content of nickel is too high, the zinc oxide grain growth is inhibited, the grains are excessively refined and the size is uneven, the pressure-sensitive voltage discreteness is large, NiO second phase is formed, the uniformity of the grain boundary barrier is destroyed, the nonlinear coefficient is reduced, the current-carrying capacity and surge resistance are weakened, and thermal breakdown or permanent failure is easily caused when a large instantaneous current is encountered. If the content of zirconium is too high, the grains are excessively refined and the sintering densification is hindered, the porosity of the device is increased, the insulation performance is reduced, ZrO2 hard brittle phase is generated, the impact resistance of the device is reduced and the temperature dependence of the leakage current is increased, the grain boundary resistance is abnormally increased, the response speed of the pressure-sensitive resistance is slow, and the instantaneous overvoltage cannot be quickly responded.

[0031] As an optional embodiment, the total mole amount of Bi2O3, Sb2O3, MnCO3, Cr2O3, Co2O3, SiO2, ZnO, silver glass powder, gallium source, nickel source, zirconium source and aluminum nitrate is 100% as a basis, the content of the ZnO is 87.0-95.0%, the content of the Bi2O3 is 0.7-2.5%, the content of the Sb2O3 is 0.2-2.5%, the content of the MnCO3 is 0.2-1.0%, the content of the Cr2O3 is 0.1-0.7%, the content of the Co2O3 is 0.1-1.2%, the content of the SiO2 is 0.3-1.0%, the content of the silver glass powder is 0.001-0.10%, and the content of the aluminum nitrate is 0.005-0.01%.

[0032] As an optional implementation, the auxiliary agent comprises ammonium polymethacrylate, tributyl phosphate and PVA solution, the mass ratio of the ammonium polymethacrylate, the tributyl phosphate and the PVA solution to ZnO is (0.3-1.0):(0.1-0.8):(4-6):100, and the concentration of the PVA solution is 70-80 g / L; preferably, the mass ratio of the ammonium polymethacrylate, the tributyl phosphate, the PVA solution to ZnO is 1:0.5:5:100.

[0033] The ammonium polymethacrylate, the tributyl phosphate and the PVA are a functional complementary auxiliary agent system in the zinc oxide varistor, the ammonium polymethacrylate can disintegrate the powder agglomeration, reduce the slurry viscosity to improve the fluidity, the tributyl phosphate can break the slurry bubbles to avoid the appearance of pore cracks in the device after sintering, and the PVA can bond the powder to give the green body strength, has low residue during sintering and assists densification, and the synergistic effect of the three can guarantee the slurry stability, reduce the green body defects, and finally improve the performance consistency and reliability of the finished product varistor.

[0034] As an optional implementation, in the first grinding, the solid-liquid ratio is 1:(1-2), the rotation speed is 1500-3000 r / min, and the time is 10-30 min. As an optional implementation, in the second grinding, the solid-liquid ratio is 1:(1-2), the rotation speed is 1500-3000 r / min, and the time is 30-60 min. The parameters of the first grinding and the second grinding are regulated and controlled in the application, so that the grinding can be sufficient and the agglomeration can be reduced.

[0035] As an optional implementation, the mixed material is granulated to obtain granulated material, and the granulated material is sieved to obtain powder, and the mesh number of the powder is 80-200 mesh; optionally, in the granulation, the granulated material is obtained by using a spray granulation mode, the inlet temperature is 200-250 DEG C, the outlet temperature is set to 120-150 DEG C, the rotation speed is 7000-10000 r / min, the mass ratio of D90 to D10 in the granulated material is 1-3:1, and D50 is 30-40 mu m.

[0036] As an optional implementation, the forming step comprises: using a bidirectional floating press of a forming hydraulic machine to press the powder into a green body.

[0037] As an optional implementation, the sintering comprises glue removal, first sintering and second sintering; the first sintering is performed first to promote the formation of stable grain boundaries.

[0038] As an optional implementation, the specific steps of the glue removal include: heating from room temperature to 300-350℃ at a heating rate of 120-180℃ / h, heating to 400-450℃ at a heating rate of 40-80℃ / h, holding for 2-4h, and furnace cooling; As an optional implementation, the specific steps of the first sintering include: heating from room temperature to 600-800℃ at a heating rate of 60-90℃ / h, and holding for 1.5-2.5h; preferably, the specific steps of the first sintering include: heating from room temperature to 600℃ at a heating rate of 90℃ / h, and holding for 2h; As an optional implementation, the specific steps of the second sintering include: heating to 1100-1200℃ at a heating rate of 60-80℃ / h, then cooling to 800-900℃ at a cooling rate of 60-80℃ / h, holding for 7-9h, and furnace cooling; preferably, the specific steps of the second sintering include: heating to 1150℃ at a heating rate of 60℃ / h, then cooling to 850℃ at a cooling rate of 60℃ / h, holding for 8h, and furnace cooling.

[0039] As an optional implementation, after the sintering, the method further includes the steps of adhering an insulating material to at least part of the surface of the body to form an insulating layer, and then performing a heat treatment. Optionally, the insulating material is adhered to the part of the surface of the body by using an adhesive; preferably, the adhesive includes ethanol, butyl carbitol and ethyl cellulose in a ratio of 100:(5-15):(1-4), for example, any one of 100:5:1, 100:5:2, 100:5:4, 100:15:4, 100:15:2, 100:15:1, 100:10:4, 100:10:3, etc., preferably 100:10:2.5, and the ratio unit is ml:ml:g; optionally, the insulating material is a material commonly used in the art, for example, glass glaze. As an optional implementation, the specific steps of the heat treatment include: heating from room temperature to 500-550℃ at a heating rate of 90-180℃ / h, holding for 2-4h, then cooling to 200℃ at a cooling rate of 10-50℃ / h, and furnace cooling. After the heat treatment, the insulating material can be sintered to form ceramic.

[0040] As an optional implementation, after the heat treatment, the method further includes the steps of grinding and spraying an aluminum electrode. It should be noted that the body is in a cylindrical shape, the insulating layer is arranged on the side surface of the cylinder, and the aluminum electrode is arranged on the two circular surfaces of the cylinder. After the grinding and spraying of the aluminum electrode, a varistor disc is obtained.

[0041] In a second aspect, the present application provides a varistor ceramic prepared by the method described above.

[0042] In a third aspect, the embodiments of the present application provide a lightning protection device comprising the ZnO pressure-sensitive ceramic prepared by the method.

[0043] Embodiment 1 The embodiment provides a preparation method of a multi-element doped ZnO pressure-sensitive ceramic, comprising the following steps: (1) mixing gallium acetate, nickel acetate, zirconium acetate, aluminum nitrate and a solvent (specifically including water and ethanol), ultrasonic dispersion, adding ammonia water to adjust pH to 7-8, and standing to obtain a mixed solution.

[0044] (2) adding Bi2O3, Sb2O3, SiO2, MnCO3, Cr2O3, Co2O3 and water in the mixed solution, and performing one-time grinding by using a horizontal sand mill, a solid-liquid ratio during one-time grinding is about 1:1, a grinding speed is 1500 r / min, and a time is 10 min; then adding ZnO, an additive and water, and performing two-time grinding, a solid-liquid ratio during two-time grinding is about 1:1, a grinding speed is 3000 r / min, and a time is 30 min, to obtain a mixed material after grinding. A molar ratio of ZnO, Bi2O3, Sb2O3, SiO2, MnCO3, Cr2O3, Co2O3, gallium acetate, nickel acetate, aluminum nitrate, zirconium acetate and silver glass powder is 92.29:1.8:1:0.8:0.7:0.6:0.5:0.8:1:0.01:0.4:0.1; the additive comprises poly-methyl-acrylic-ammonium, tributyl phosphate and a PVA solution, a mass ratio of poly-methyl-acrylic-ammonium, tributyl phosphate and the PVA solution to ZnO is 1:0.5:5:100, and a concentration of the PVA solution is 73.6 g / L.

[0045] (3) the mixed material is made into granulated material in a spray granulation mode, spray granulation parameters are as follows: an inlet temperature is set to 200-250 DEG C, an outlet temperature is set to 120-150 DEG C, and a rotating speed is 8000 r / min, the mixed material is changed into granulated material under high-speed centrifugation, a D50 of the granulated material is 35 μm, and a mass ratio of D90 and D10 particles is 2:1; the granulated material is screened to obtain a powder, and a screening mesh number is 200 meshes. The powder is pressed into a sheet shape by using a two-way floating press of a molding hydraulic machine, to obtain a molding blank, and the blank is in a cylindrical shape.

[0046] (4) The temperature is raised from room temperature to 300℃ at a rate of 150℃ / h, and then the temperature is raised to 400℃ at a rate of 60℃ / h, and the temperature is kept for 3h, and the temperature is decreased with the furnace, and the glue of the shaped body is discharged. Then the temperature is raised from room temperature to 600℃ at a rate of 90℃ / h, and the shaped body is sintered for the first time, and the time is 2h; the temperature is continuously raised to 1150℃ at a rate of 60℃ / h, and then the temperature is decreased to 850℃ at a rate of 60℃ / h, and the temperature is kept for 8h, and then the temperature is decreased with the furnace. Ethanol, butyl carbitol and ethyl cellulose are mixed in a ratio of 100:10:2.5 (unit: ml:ml:g) to prepare an adhesive, and the adhesive is used to bond glass glaze on the side surface of the shaped body, and then the temperature is raised from room temperature to 500℃ at a rate of 100℃ / h, and the shaped body is heat-treated for 3h, and then the temperature is decreased to 200℃ at a rate of 20℃ / h, and then the temperature is decreased with the furnace, and after grinding and spraying aluminum electrode, a zinc oxide varistor ceramic resistor sheet is obtained.

[0047] Example 2 The embodiment provides a preparation method of a multi-element doped ZnO varistor ceramic, which is basically the same as that of example 1, and the main difference is that gallium nitrate is used instead of gallium acetate, nickel nitrate is used instead of nickel acetate, and zirconium nitrate is used instead of zirconium acetate, and the molar amounts of gallium element, nickel element and zirconium element are the same as those in example 1.

[0048] Comparative Example 1 The comparative example provides a preparation method of a multi-element doped ZnO varistor ceramic, which is basically the same as that of example 2, and the main difference is that gallium oxide is used instead of gallium nitrate, and the molar amount of gallium element is the same as that in example 1. The molar ratio of ZnO, Bi2O3, Sb2O3, SiO2, MnCO3, Cr2O3, Co2O3, Ga2O3, nickel acetate, aluminum nitrate, zirconium acetate, silver glass powder in the raw material is 92.69:1.8:1:0.8:0.7:0.6:0.5:0.4:1:0.01:0.4:0.1.

[0049] Comparative Example 2 The comparative example provides a preparation method of a multi-element doped ZnO varistor ceramic, which is basically the same as that of example 2, and the main difference is that nickel oxide is used instead of nickel nitrate, and the molar amount of nickel element is the same as that in example 1.

[0050] Comparative Example 3 The comparative example provides a preparation method of a multi-element doped ZnO varistor ceramic, which is basically the same as that of example 2, and the main difference is that zirconium oxide is used instead of zirconium nitrate in an equal molar amount, and the molar amount of zirconium element is the same as that in example 1.

[0051] Comparative Example 4 The comparative example provides a preparation method of a multi-element doped ZnO pressure sensitive ceramic, which is basically the same as that of Example 2, and the main difference is that gallium oxide is used instead of gallium nitrate, nickel oxide is used instead of nickel nitrate, and zirconium oxide is used instead of zirconium nitrate, and the molar amounts of gallium, nickel and zirconium elements are the same as those in Example 1. The molar ratio of ZnO, Bi2O3, Sb2O3, SiO2, MnCO3, Cr2O3, Co2O3, Ga2O3, NiO, aluminum nitrate, ZrO, and silver glass powder is 92.69:1.8:1:0.8:0.7:0.6:0.5:0.4:1:0.01:0.4:0.1.

[0052] Comparative Example 5 The comparative example provides a preparation method of a multi-element doped ZnO pressure sensitive ceramic, which is basically the same as that of Example 1, and the main difference is that the molar ratio of raw materials is different. The amount of raw materials in the comparative example is as follows: the molar ratio of ZnO, Bi2O3, Sb2O3, SiO2, MnCO3, Cr2O3, Co2O3, gallium acetate, nickel acetate, aluminum nitrate, zirconium acetate, and silver glass powder is 92.2:1.8:1:0.8:0.7:0.6:0.5:1.8:0.3:0.1:0.1:0.1.

[0053] Comparative Example 6 The comparative example provides a preparation method of a multi-element doped ZnO pressure sensitive ceramic, which is basically the same as that of Example 1, and the main difference is that the pH value in step (1) is different. In step (1) of the comparative example, ammonia is added to adjust the pH to 9.

[0054] Test Example The test example provides the performance test results of the ZnO pressure sensitive ceramic resistor sheets prepared in each example and comparative example. The performance of the resistor sheet is tested according to the IEC61643-11:2011 standard, and the details are as follows: Voltage gradient U 1mA Test method: According to the above standard, a 1mA voltage test device is used to test the zinc oxide pressure sensitive ceramic, and the voltage gradient U 1mA is calculated, with the unit of V / mm.

[0055] Test method of residual voltage ratio: According to the above standard, the residual voltage test is carried out under the condition of 10kA 4 / 10µs nominal discharge current, and the residual voltage ratio is calculated.

[0056] Leakage current, nonlinearity coefficient, change rate of voltage gradient after 100kA / 4 / 10μs impact (change rate refers to the ratio of voltage gradient after impact to that before impact), grain size, and grain resistance are tested according to the above standard.

[0057] The test method of the through-flow current is as follows: three parallel samples are tested, and the average value is taken after the test; each sample is subjected to 18 current impulses of a certain amplitude of 2ms square wave, the 18 impulses are divided into 6 groups, 3 impulses in each group, the interval between each impulse is 60s, the time interval of each group is the time for the sample to cool to room temperature, and the voltage and current waveforms are recorded by an oscilloscope at the same time. Only when the sample can withstand all the current impulses without damage such as rupture, perforation and flashover, it is considered to pass the 2ms square wave through-flow current capacity test of the current amplitude. The through-flow capacity under 2ms square wave is the maximum current value allowed to pass through per unit area of zinc oxide varistor, and the unit is A / cm 2 .

[0058] Table 1 performance test results of each example and comparative example

[0059] From the above results, it can be seen that the ZnO varistor sheet prepared by the application can simultaneously meet the requirements of large through-flow capacity, high voltage gradient, low leakage current and low residual voltage ratio, and the comprehensive performance meets the ionization protection requirements, for example, can be applied to lightning protection insulator and ionization equipment overvoltage protection. Figure 1 is the SEM image of the zinc oxide varistor ceramic sheet of Example 1, and the particle size distribution is calculated by using proimaging metallographic analysis software, Figure 2 is the SEM image of the zinc oxide varistor ceramic sheet of Comparative Example 4, and the particle size distribution is calculated by using proimaging metallographic analysis software. From Figures 1-2 it can be seen that the zinc oxide varistor ceramic sheet of the application has smaller crystal grains, which is beneficial to improve the voltage gradient. Figure 3 is the current density of the zinc oxide varistor ceramic sheet of Example 1 and Comparative Examples 1-4 of the application, from which it can be seen that the prepared sheet has high potential gradient, low leakage current and high nonlinearity coefficient.

[0060] The application adds soluble salt doping to the zinc oxide base, adjusts the pH and the molar ratio of Ga, Ni and Zr, can effectively inhibit the grain growth and reduce the grain size, and finally obtain the zinc oxide base sheet with small size and good uniformity, which can further improve the zinc oxide base sheet with small size and good uniformity.

[0061] The Ga salt is completely dissolved in the solvent, and can be decomposed into nano-level Ga2O3 with a particle size of less than 50nm during sintering, which can be uniformly solid-solved in the ZnO crystal lattice, significantly improve the donor concentration and reduce the grain resistance, and further realize the improvement of the voltage gradient and the reduction of the residual voltage ratio in application. In Comparative Example 1 using Ga2O3, Ga2O3 is easy to agglomerate and cannot be uniformly solid-solved, resulting in uneven local donor concentration and performance degradation. 2+ The Ni salt is uniformly diffused to the surface of the ZnO grain in the form of Ni2+ The ion radius 0.069nm is close to that of Zn 2+ 0.074nm, which can offset the compressive stress caused by the solid solution of trace Al 3+ (in an ion radius of 0.0535nm) in the raw material, promote the solid solution of Al 3+ and enhance the grain boundary barrier, ultimately achieve reduced leakage current and improved nonlinear coefficient; the comparative example 2 using NiO has a large difference in density between NiO and ZnO, resulting in uneven mixing of the grain boundary barrier and performance degradation; the grain boundary resistance and the grain boundary barrier and nonlinear coefficient have similar trends, and the grain resistance of the example 1 is significantly reduced compared to the comparative examples 1 and 2, which proves that the soluble salt Ga salt can better segregate into the grain than Ga2O3, thereby reducing the residual voltage ratio and improving the overall performance. Zr salt plays an important role in reducing grain size and improving voltage gradient, and the comparative examples 3 and 4 using ZrO2 have a grain size of more than 6μm. The above results all prove that Ga salt, Ni salt and Zr salt play a key role in optimizing the performance of ZnO varistor ceramics.

[0062] It should be noted that, in this text, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another, and do not necessarily require or imply any actual relationship or order between the entities or operations. Moreover, the terms "include", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or device. Without more limitations, the element defined by the statement "including a…" does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0063] The above is only a specific implementation of the present application, which enables those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments described herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for producing a multi-element doped ZnO varistor ceramic, characterized by, It comprises the following steps: (1) After gallium source, nickel source, zirconium source, aluminum nitrate and solvent are mixed, pH is adjusted to 7-8 to obtain a mixed solution; the gallium source comprises gallium nitrate and / or gallium acetate; the nickel source comprises nickel nitrate and / or nickel acetate; the zirconium source comprises zirconium nitrate and / or zirconium acetate; the molar ratio of the gallium source, nickel source and zirconium source is (0.2-1.5):(0.5-1.8):(0.2-1); (2) After the mixed solution is mixed with the remaining raw materials to obtain a mixture, the mixture is granulated and formed to obtain a green body, and then sintered.

2. The production method according to claim 1, characterized by, In the step (1), a pH adjuster is added to adjust the pH to 7.4-7.6; Preferably, the pH adjuster comprises ammonia water.

3. The production method according to claim 1 or 2, characterized by, The step (2) comprises: adding Bi2O3, Sb2O3, MnCO3, Cr2O3, Co2O3, SiO2, silver glass powder to the mixed solution, grinding once, adding ZnO and an additive, grinding twice to obtain a mixture, and then sintering.

4. The production method according to claim 3, characterized by, Based on the total molar amount of Bi2O3, Sb2O3, MnCO3, Cr2O3, Co2O3, SiO2, ZnO, silver glass powder, gallium source, nickel source, zirconium source and aluminum nitrate being 100%, the content of the gallium source is 0.2-1.5%; and / or, the content of the nickel source is 0.5-1.8%; and / or, the content of the zirconium source is 0.2-1%.

5. The production method according to claim 3 or 4, characterized by, Based on the total molar amount of Bi2O3, Sb2O3, MnCO3, Cr2O3, Co2O3, SiO2, ZnO, silver glass powder, gallium source, nickel source, zirconium source and aluminum nitrate being 100%, the content of ZnO is 87.0-95.0%, the content of Bi2O3 is 0.7-2.5%, the content of Sb2O3 is 0.2-2.5%, the content of MnCO3 is 0.2-1.0%, the content of Cr2O3 is 0.1-0.7%, the content of Co2O3 is 0.1-1.2%, the content of SiO2 is 0.3-1.0%, the content of silver glass powder is 0.001-0.10%, and the content of aluminum nitrate is 0.005-0.01%; And / or, the additive comprises poly-methyl-acrylic-ammonium, tributyl phosphate, PVA solution, and the mass ratio of poly-methyl-acrylic-ammonium, tributyl phosphate, PVA solution to ZnO is (0.3-1.0):(0.1-0.8):(4-6):100, and the concentration of the PVA solution is 70-80g / L; preferably, the mass ratio of poly-methyl-acrylic-ammonium, tributyl phosphate, PVA solution to ZnO is 1:0.5:5:

100.

6. The method of any one of claims 1-5, wherein, In the first grinding, the solid-liquid ratio is 1:(1-2), the rotation speed is 1500-3000r / min, and the time is 10-30min; And / or, in the second grinding, the solid-liquid ratio is 1:(1-2), the rotation speed is 1500-3000r / min, and the time is 30-60min.

7. The method of any one of claims 1-6, wherein, After the mixture is granulated, a granulated material is obtained, and the powder is obtained by sieving, and the mesh number of the powder is 80-200 mesh; And / or, sintering comprises glue removal, first sintering and second sintering. And / or, the sintering further comprises a step of adhering an insulating material on at least part of the surface of the green body to form an insulating layer, and then performing a heat treatment.

8. The preparation method according to claim 7, characterized in that, The step of degreasing specifically comprises: heating from room temperature to 300-350℃ at a heating rate of 120-180℃ / h, and then heating to 400-450℃ at a heating rate of 40-80℃ / h, and holding for 2-4h, and furnace cooling; And / or, the first sintering specifically comprises: heating from room temperature to 600-800℃ at a heating rate of 60-90℃ / h, and holding for 1.5-2.5h; preferably, the first sintering specifically comprises: heating from room temperature to 600℃ at a heating rate of 90℃ / h, and holding for 2h; And / or, the second sintering specifically comprises: heating to 1100-1200℃ at a heating rate of 60-80℃ / h, and then cooling to 800-900℃ at a cooling rate of 60-80℃ / h, and holding for 7-9h, and furnace cooling; preferably, the second sintering specifically comprises: heating to 1150℃ at a heating rate of 60℃ / h, and then cooling to 850℃ at a cooling rate of 60℃ / h, and holding for 8h, and furnace cooling; And / or, the insulating material is adhered on at least part of the surface of the green body by using an adhesive; preferably, the adhesive comprises ethanol, butyl carbitol and ethyl cellulose in a ratio of 100:(5-15):(1-4), preferably 100:10:2.5, in units of ml:ml:g; And / or, the heat treatment specifically comprises: heating from room temperature to 500-550℃ at a heating rate of 90-180℃ / h, and holding for 2-4h, and then cooling to 200℃ at a cooling rate of 10-50℃ / h, and furnace cooling.

9. ZnO varistor ceramic prepared by the method of any one of claims 1-8.

10. A lightning protection device, characterized in that, A ZnO varistor ceramic prepared by the method of any one of claims 1-8.

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