Piezoresistor composite raw material powder as well as preparation method and application thereof

Abstract

The invention relates to piezoresistor composite raw material powder as well as a preparation method and application thereof, belongs to the technical field of piezoresistors, and aims at solving the problems that the microstructure of the piezoresistor composite raw material powder prepared by the existing method is not uniform; and the prepared piezoresistor has at least one of the problems of unstable performance, poor consistency, low voltage gradient, low nonlinear coefficient and the like. According to the preparation method of the piezoresistor composite raw material powder, ZnO powder coated by a sol coating method is homogenized, so that sol aggregates which are not dispersed in a stirring process are dispersed in a high-pressure and high-speed fluid of a homogenizer, an additive is dispersed around the ZnO powder at a molecular level, and the ZnO powder is uniformly dispersed in the high-pressure and high-speed fluid of the homogenizer. According to the homogenizing treatment disclosed by the invention, the stability, the consistency, the voltage gradient and the nonlinear coefficient of the piezoresistor can be remarkably improved by optimizing a microstructure, controlling particle size distribution, reducing defects, optimizing an interface and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of varistor, and in particular to a varistor composite raw material powder and a preparation method and application thereof. Background Art

[0002] ZnO varistors are widely used in electronic power systems due to their excellent nonlinear ohmic characteristics and large energy absorption capacity. Traditional preparation methods such as solid phase method have problems such as uneven distribution of additive components and uneven microstructure, which affect the performance of varistors.

[0003] The existing method can only ensure the uniformity of the oxide additives of the varistor. The additives are still mixed with ZnO through the traditional ball milling method. This method will also cause problems such as uneven microstructure of the varistor composite raw material powder, poor consistency of the prepared varistor, low voltage gradient, and low nonlinear coefficient. Summary of the invention

[0004] In view of the above analysis, the present invention aims to provide a varistor composite raw material powder and a preparation method and application thereof, so as to solve at least one of the problems of uneven microstructure of the varistor composite raw material powder prepared by the existing method, unstable performance of the prepared varistor, poor consistency, low voltage gradient, low nonlinear coefficient, etc.

[0005] In a first aspect, the present invention provides a method for preparing a varistor composite raw material powder, the method comprising: coating ZnO powder by a sol coating method, homogenizing to obtain a wet sol, and sequentially drying, roasting, and grinding the wet sol to obtain a varistor composite raw material powder.

[0006] Furthermore, the homogenization pressure is 20-50 MPa, the homogenization time is 10-60 min, and the homogenization flow rate is 200-1000 mL / min.

[0007] Furthermore, the drying temperature is 80-105° C., and the drying time is 7-9.5 h.

[0008] Furthermore, the calcination temperature is 700-1000° C., and the calcination time is 2.5-3 h.

[0009] Furthermore, when the ZnO powder is coated by the sol coating method, bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate are selected as precursors.

[0010] Furthermore, the coating of ZnO powder by the sol coating method specifically includes the following: dissolving the precursor in dilute nitric acid to obtain reagent A, dissolving citric acid in deionized water to obtain reagent B, slowly dripping the reagent A into reagent B, stirring to obtain reagent C, slowly dripping ethanolamine into reagent C until the pH value is 6.0-9.5, to obtain reagent D, and adding ZnO slurry to reagent D.

[0011] Furthermore, according to the mass percentage, bismuth nitrate: 2.8-4.5%, cobalt nitrate: 1.5-3.6%, manganese nitrate: 1.5-3.6%, nickel nitrate: 1.5-3.6%, ZnO powder: 85.5-90.5%.

[0012] Furthermore, the mass concentration of the dilute nitric acid is 28-32%, and the mass ratio of the dilute nitric acid to the precursor is 1-2:1.

[0013] Furthermore, the mass ratio of citric acid to the total mass of bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate is 2-3:1.

[0014] Furthermore, the mass fraction of citric acid in deionized water is 28-32%.

[0015] In a second aspect, the present invention provides a varistor composite raw material powder prepared by the above method.

[0016] In a third aspect, the present invention provides a varistor, wherein the raw material of the varistor is the above-mentioned varistor composite raw material powder.

[0017] Furthermore, the raw materials of the varistor also include a dispersant and a binder.

[0018] Furthermore, the dispersant is sodium polyacrylate, and the binder is polyvinyl alcohol.

[0019] In a fourth aspect, the present invention provides a method for preparing the above-mentioned varistor, comprising: mixing the raw materials of the varistor and water, spray drying, granulating, pressing, calcining, and grinding to obtain the varistor.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: (1) The preparation method of the composite raw material powder of the varistor of the present invention is to homogenize the ZnO powder coated by the sol coating method, so that the sol agglomerates that are not dispersed in the stirring process are dispersed in the high-pressure and high-speed fluid of the homogenizer, so that the additives are dispersed around the ZnO powder at the molecular level. The homogenization treatment of the present invention can significantly improve the stability, consistency, voltage gradient and nonlinear coefficient of the varistor by optimizing the microstructure, controlling the particle size distribution, reducing defects and optimizing the interface; (2) The homogenization pressure within the scope of the present invention can control the growth of grains, making them finer and more uniform. Fine grains can increase the number of grain boundaries and increase the height of the grain boundary barrier, thereby improving the voltage gradient, nonlinear coefficient and consistency of the varistor; the homogenization time within the scope of the present invention can reduce the defect density in the material. Too short a homogenization time may cause insufficiently mixed areas in the material, forming defects and affecting the electrical properties. A longer homogenization time can effectively reduce these defects and optimize the voltage gradient, nonlinear coefficient and consistency. The homogenization flow rate within the scope of the present invention can better disperse the particles in the sol and prevent particle agglomeration. This helps to form fine and uniform particles and improve the voltage gradient, nonlinear coefficient and consistency of the varistor; (3) The present invention selects specific homogenization treatment conditions, reduces the drying temperature and increases the calcination temperature, only requires one step of drying, shortens the calcination time, shortens the process flow, and improves production efficiency. The present invention, through the synergistic effect of the above conditions, not only improves the uniformity of the powder, but also improves the crystallinity and density of the material, and significantly improves the stability, consistency, voltage gradient and nonlinear coefficient of the varistor; (4) The present invention adopts specific raw materials and a sol-gel method to achieve the preparation of high-performance varistor composite raw material powder at a lower temperature, thereby reducing energy consumption and cost; and the method of the present invention improves the uniformity of the varistor composite material, and the prepared varistor has better consistency, higher voltage gradient and nonlinear coefficient, and improved stability and reliability of the varistor; (5) The voltage gradient of the varistor prepared by the present invention is 230~240V / mm, preferably, 234~236V / mm, the standard deviation of the voltage gradient is 0.99~1.03, the nonlinear coefficient is 75~78, the standard deviation of the nonlinear coefficient is 3.56~3.85, the residual voltage ratio of 10kA 8 / 20 lightning wave pulse current is 1.62~1.67, and the standard deviation of the residual voltage ratio of 10kA 8 / 20 lightning wave pulse current is 0.006~0.008.

[0021] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings are only used for the purpose of illustrating specific embodiments and are not to be considered as limiting the present invention. In the entire drawings, the same reference symbols represent the same components; Figure 1 The particle size distribution diagram of the varistor composite raw material powder prepared in Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0023] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0024] A specific embodiment of the present invention discloses a method for preparing a composite raw material powder of a varistor, the method comprising: coating ZnO powder by a sol coating method, homogenizing to obtain a wet sol, and sequentially drying, roasting, and grinding the wet sol to obtain a composite raw material powder of a varistor.

[0025] Compared with the prior art, the preparation method of the composite raw material powder of the varistor of the present invention homogenizes the ZnO powder coated by the sol coating method, so that the sol agglomerates that are not dispersed in the stirring process are dispersed in the high-pressure and high-speed fluid of the homogenizer, so that the additives are dispersed around the ZnO powder at the molecular level. The homogenization treatment of the present invention can significantly improve the stability, consistency, voltage gradient and nonlinear coefficient of the varistor by optimizing the microstructure, controlling the particle size distribution, reducing defects and optimizing the interface.

[0026] Since gel is obtained after coating ZnO powder by sol-gel coating method, gel is a material with a three-dimensional mesh structure, which can contain various particles or liquids inside it. The gel itself has certain viscosity and structure, and it is easy to form agglomerates or uneven distribution during the dispersion process. Gels usually have high viscosity and elasticity, which makes it difficult to achieve uniform dispersion in traditional mixing processes. When preparing gel for particle dispersion, traditional stirring methods may cause uneven distribution of particles in the gel, affecting the performance of the final product. This makes it difficult for technicians in this field to think of solving the gel dispersion problem through homogenization. The present invention has found through a large number of experiments that the stability, consistency, voltage gradient and nonlinear coefficient of the pressure resistor can be improved by homogenizing the gel under specific pressure, time and flow.

[0027] Specifically, the homogenization pressure is 20-50MPa (for example, 20MPa, 25MPa, 30MPa, 35MPa, 40MPa, 45MPa, 50MPa), the homogenization time is 10-60min (for example, 10min, 15min, 20min, 25min, 30min, 35min, 40min, 45min, 50min, 55min, 60min), and the homogenization flow rate is 200-1000mL / min (for example For example, 200mL / min, 250mL / min, 300mL / min, 350mL / min, 400mL / min, 450mL / min, 500mL / min, 550mL / min, 600mL / min, 650mL / min, 700mL / min, 750mL / min, 800mL / min, 850mL / min, 900mL / min, 950mL / min, 1000mL / min).

[0028] It should be noted that the homogenization pressure within the scope of the present invention can control the growth of grains, making them smaller and more uniform. Fine grains can increase the number of grain boundaries and increase the height of the grain boundary barrier, thereby improving the voltage gradient, nonlinear coefficient and consistency of the varistor. The homogenization time within the scope of the present invention can reduce the defect density in the material. Too short homogenization time may cause insufficiently mixed areas in the material, forming defects and affecting the electrical properties. A longer homogenization time can effectively reduce these defects and optimize the voltage gradient, nonlinear coefficient and consistency. The homogenization flow rate within the scope of the present invention can better disperse the particles in the sol and prevent particle agglomeration. This helps to form fine and uniform particles and improve the voltage gradient, nonlinear coefficient and consistency of the varistor.

[0029] Specifically, the drying temperature is 80-105°C (for example, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C), and the drying time is 7-9.5h (for example, 7.2h, 7.4h, 7.6h, 7.8h, 8h, 8.2h, 8.4h, 8.6h, 8.8h, 9.0h, 9.2h, 9.4h).

[0030] It should be noted that the drying temperature and time directly affect the rate and degree of water removal in the sol. A lower drying temperature can avoid thermal decomposition or crystal transformation of the material during the drying process, while an appropriate drying time ensures that the water is fully removed. This helps to maintain the chemical composition and structural stability of the material, providing a good foundation for subsequent roasting. Too high a drying temperature or too long a drying time causes excessive shrinkage of the material surface, forming a dense shell, which hinders the further removal of internal water and affects the uniformity and density of the material. Reasonable drying conditions help to form a uniform microstructure and improve the electrical properties of the material.

[0031] Specifically, the calcination temperature is 700-1000°C (for example, 700°C, 720°C, 740°C, 760°C, 780°C, 800°C, 820°C, 840°C, 860°C, 880°C, 900°C, 920°C, 940°C, 960°C, 980°C, 1000°C), and the calcination time is 2.5-3h (for example, 2.6h, 2.7h, 2.8h, 2.9h).

[0032] It should be noted that the calcination temperature is a key factor affecting the grain growth and densification of the material. Appropriate calcination temperature can promote grain growth and material densification, and improve the mechanical strength and electrical properties of the material. Higher calcination temperatures are conducive to grain growth and the reduction of grain boundaries, thereby improving the voltage gradient and nonlinear coefficient of the material. Phase changes may occur in the material during the calcination process, and the diffusion and solid solution of the doping elements are also closely related to the calcination temperature. By precisely controlling the calcination temperature and time, the distribution and solid solubility of the doping elements can be optimized, further improving the electrical properties of the material and improving its consistency.

[0033] The present invention selects specific homogenization treatment conditions, reduces the drying temperature and increases the roasting temperature, only requires one step of drying, shortens the roasting time, shortens the process flow, and improves production efficiency. The homogenization treatment of the present invention provides a good foundation for subsequent drying and roasting, and drying and roasting further consolidate and optimize the effect of the homogenization treatment. The present invention, through the synergistic effect of the above conditions, not only improves the uniformity of the powder, but also improves the crystallinity and density of the material, and significantly improves the stability, consistency, voltage gradient and nonlinear coefficient of the varistor.

[0034] Specifically, when the ZnO powder is coated by the sol coating method, bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate are selected as precursors.

[0035] Specifically, the coating of ZnO powder by the sol coating method specifically includes the following: dissolving the precursor in dilute nitric acid to obtain reagent A, dissolving citric acid in deionized water to obtain reagent B, slowly dripping the reagent A into reagent B, stirring to obtain reagent C, slowly dripping ethanolamine into reagent C until the pH value is 6.0-9.5, to obtain reagent D, and adding ZnO slurry to reagent D.

[0036] Specifically, a method for preparing a varistor composite raw material powder of the present invention comprises the following steps: (1) Weighing bismuth nitrate, cobalt nitrate, manganese nitrate, nickel nitrate and ZnO powder respectively according to mass percentage, wherein bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate are used as precursors; (2) dissolving the precursor in dilute nitric acid to obtain reagent A; (3) Dissolve citric acid in deionized water to obtain reagent B; (4) slowly dripping the reagent A into the reagent B and stirring to obtain the reagent C; (5) Slowly add ethanolamine dropwise to reagent C until the pH value is 6.0-9.5 to obtain reagent D; (6) Add ZnO slurry to reagent D, stir, and pour into a homogenizer for homogenization to obtain a wet sol; (7) The wet sol is allowed to stand in air to generate a gel, which is then dried, calcined, and ground to obtain the varistor composite raw material powder.

[0037] Compared with the prior art, the present invention adopts specific raw materials and a sol-gel method to achieve the preparation of high-performance varistor composite raw material powder at a relatively low temperature (room temperature), thereby reducing energy consumption and cost; and the method of the present invention improves the uniformity of the varistor composite material, and the prepared varistor has better consistency, higher voltage gradient and nonlinear coefficient, thereby improving the stability and reliability of the varistor.

[0038] Specifically, in step (1), by mass percentage, bismuth nitrate: 2.8-4.5% (e.g., 2.8%, 3.0%, 3.2%, 3.4%, 3.6%, 3.8%, 4.0%, 4.2%, 4.4%, 4.5%), cobalt nitrate: 1.5-3.6% (e.g., 1.5%, 1.7%, 1.9%, 2.1%, 2.3%, 2.5%, 2.7%), manganese nitrate: 1.5-3.6% (e.g., 1.5%, 1.7%, 1.9%, 2.1%, 2.3%, 2.5%, 2.7%, 2.9%, 3.1%, 3.3%, 3.5%, 3.6%), Nickel nitrate: 1.5-3.6% (e.g., 1.5%, 1.7%, 1.9%, 2.1%, 2.3%, 2.5%, 2.7%, 2.9%, 3.1%, 3.3%, 3.5%, 3.6%), ZnO powder: 85.5-90.5% (e.g., 85.5%, 86%, 8.65%, 87%, 87.5%, 88%, 88.5%, 89%, 89.5%, 90%, 90.5%).

[0039] It should be noted that the bismuth nitrate, cobalt nitrate, manganese nitrate, nickel nitrate and ZnO powder of the present invention work together to significantly improve the voltage gradient and nonlinear coefficient of the varistor by adjusting the grain boundary barrier height and interface state density. At the same time, these additives can reduce the defects of the grain boundary, improve the uniformity and density of the grain boundary, and thus improve the stability and reliability of the component.

[0040] In the present invention, by precisely controlling the mass ratio of each raw material, it can be ensured that various metal ions can be uniformly dispersed in the ZnO matrix during the sol-gel process. This uniform dispersion helps to form a consistent microstructure, reduce defects and stress concentration inside the material, and thus improve the consistency of the material.

[0041] Specifically, in step (2), the mass concentration of the dilute nitric acid is 28-32% (for example, 28%, 28.5%, 29%, 29.5%, 30%, 30.5%, 31%, 31.5%, 32%), and the mass ratio of the dilute nitric acid to the precursor is 1-2:1 (for example, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1).

[0042] Specifically, in step (3), the mass ratio of citric acid to the total mass of bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate is 2-3:1 (for example, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3:1), and the mass fraction of citric acid in deionized water is 28-32% (for example, 28%, 28.5%, 29%, 29.5%, 30%, 30.5%, 31%, 31.5%, 32%).

[0043] It should be noted that the above-mentioned range of the ratio of the mass of citric acid to the total mass of bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate can promote the complexation and precipitation of metal ions to form smaller particles, while excessive or insufficient citric acid may cause uneven or excessively large particle size, affecting the density and electrical consistency of the varistor.

[0044] In addition, improper ratios may lead to changes in the defect density in the material. Excessive citric acid may introduce too many impurity defects, while insufficient citric acid may lead to the generation of lattice defects. These defects will affect the electrical properties of the varistor and thus affect the voltage gradient.

[0045] Again, the ratio of citric acid to metal nitrate has an important influence on the formation and characteristics of grain boundary barriers. Appropriate ratio can promote the formation and stability of grain boundary barriers, thereby improving the nonlinear coefficient of the varistor. Grain boundary barriers are an important source of nonlinear characteristics of varistors. A higher nonlinear coefficient means that the varistor can more effectively limit current under overvoltage conditions and provide better protection performance. Appropriate ratio can optimize the material's band structure and electronic state density, so that the migration and transition characteristics of electrons at different voltages are improved, thereby improving the nonlinear coefficient.

[0046] The present invention achieves fine regulation of the microstructure and electrical properties of the varistor material by precisely controlling the ratio of citric acid to metal nitrate.

[0047] Specifically, in step (6), the ZnO slurry is a suspension formed by dissolving ZnO powder in water and having a solid content of 20-30% (e.g., 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%).

[0048] In the sol-gel formation process of the present invention, after the precursor solution is combined with citric acid and ethanolamine, a uniform sol can be formed by controlling conditions such as pH value and stirring, and then a uniform gel is produced. This uniformity helps to improve the consistency of the microstructure of the varistor material, thereby improving its electrical properties.

[0049] In addition, the microstructure and grain boundary distribution of the varistor material can be optimized by precisely controlling the chemical reaction conditions and raw material ratios in the sol-gel process. By controlling the type and content of dopants, the characteristics of the grain boundary layer can be adjusted, thereby improving the voltage gradient and nonlinear coefficient of the material. The increase in voltage gradient means that the material can maintain stable resistance characteristics at higher voltages, while the increase in nonlinear coefficient helps to better suppress overvoltage.

[0050] Specifically, in step (7), the standing time is 3-6 h (e.g., 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h).

[0051] It should be noted that the standing time of the present invention can fully evaporate the solvent in the wet sol, promote the interconnection between the sol particles, and form a uniform and dense gel structure. This structure helps the uniform shrinkage and densification of the material during the subsequent drying and roasting process, thereby improving the consistency of the material. It can reduce stress concentration and defect generation inside the gel, making it less likely for the material to have defects such as cracks during the subsequent heat treatment process, which helps to maintain the integrity and electrical properties of the material.

[0052] Another specific embodiment of the present invention discloses a varistor composite raw material powder prepared by the above method.

[0053] Another specific embodiment of the present invention discloses a varistor made using the above-mentioned varistor composite raw material powder.

[0054] Specifically, the raw materials of the varistor also include a dispersant and a binder.

[0055] Specifically, the dispersant is sodium polyacrylate, and the binder is polyvinyl alcohol.

[0056] Another specific embodiment of the present invention discloses a method for preparing the above-mentioned varistor, comprising: mixing the raw materials of the varistor and water, spray drying, granulating, pressing, calcining, and grinding to obtain the varistor.

[0057] The voltage gradient of the varistor prepared by the present invention is 230~240V / mm, preferably 234~236V / mm, the standard deviation of the voltage gradient is 0.99~1.03, the nonlinear coefficient is 75~78, the standard deviation of the nonlinear coefficient is 3.56~3.85, the residual voltage ratio of 10kA 8 / 20 lightning wave pulse current is 1.62~1.67, and the standard deviation of the residual voltage ratio of 10kA 8 / 20 lightning wave pulse current is 0.006~0.008.

[0058] It should be noted that the consistency of the present invention refers to the standard deviation in multiple groups of tests, and the smaller the standard deviation, the better the consistency. The technical solution of the present invention is further explained below in conjunction with specific embodiments.

[0059] Example 1 A method for preparing a varistor composite raw material powder in this embodiment includes the following steps: (1) Weighing 3.1% bismuth nitrate, 2.2% cobalt nitrate, 1.8% manganese nitrate, 2.8% nickel nitrate and 90.1% ZnO powder respectively according to mass percentage, wherein bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate are used as precursors; (2) dissolving the precursor in dilute nitric acid with a mass concentration of 30% at a mass ratio of 1:1 under stirring to obtain reagent A; (3) dissolving citric acid in deionized water, wherein the mass ratio of citric acid to the total mass of bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate is 3:1, and the mass fraction of citric acid in deionized water is 30%, to obtain reagent B; (4) Add reagent A dropwise into reagent B and stir for 20 minutes to completely mix the two reagents to obtain reagent C; (5) Slowly add ethanolamine dropwise to reagent C under stirring until the pH value reaches 6.0-9.5, and then stop adding ethanolamine to obtain reagent D; (6) Add ZnO slurry with a solid content of 25% to reagent D, stir, and pour into a homogenizer for homogenization. The homogenizer pressure is 35 MPa, the homogenization time is 35 min, and the homogenization flow rate is 600 mL / min to obtain a wet sol; (7) The wet sol is allowed to stand in air for 5 hours to generate a gel, which is then placed in an oven for drying at 92° C. for 8.2 hours, calcined in a muffle furnace at 850° C. for 2.75 hours, and ground to obtain the varistor composite raw material powder.

[0060] The particle size distribution diagram of the varistor composite raw material powder prepared in this embodiment is shown in Figure 1 It can be seen that the particle size distribution curve of the composite raw material powder has two peaks. The peak with smaller particle size is formed by unagglomerated particles, and the peak with larger particle size is formed by agglomerated particles. The left peak with smaller particle size is obviously higher, indicating that most of the particles are not agglomerated.

[0061] Example 2 A method for preparing a varistor composite raw material powder in this embodiment includes the following steps: (1) Weighing 2.8% bismuth nitrate, 3.6% cobalt nitrate, 3.6% manganese nitrate, 3.6% nickel nitrate and 86.4% ZnO powder respectively according to mass percentage, wherein bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate are used as precursors; (2) dissolving the precursor in dilute nitric acid with a mass concentration of 30% at a mass ratio of 1:2 under stirring to obtain reagent A; (3) dissolving citric acid in deionized water, wherein the mass ratio of citric acid to the total mass of bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate is 2.5:1, and the mass fraction of citric acid in deionized water is 28%, to obtain reagent B; (4) Add reagent A dropwise into reagent B and stir for 15 minutes to completely mix the two reagents to obtain reagent C; (5) Slowly add ethanolamine dropwise to reagent C under stirring until the pH value reaches 6.0-9.5, and then stop adding ethanolamine to obtain reagent D; (6) Add ZnO slurry with a solid content of 20% to reagent D, stir, and pour into a homogenizer for homogenization. The homogenizer pressure is 20 MPa, the homogenization time is 60 min, and the homogenization flow rate is 1000 mL / min to obtain a wet sol; (7) The wet sol is allowed to stand in air for 3 hours to generate a gel, which is then placed in an oven for drying at 80° C. for 9.5 hours, calcined in a muffle furnace at 700° C. for 3 hours, and ground to obtain the varistor composite raw material powder.

[0062] The varistor composite raw material powder prepared in the embodiment was tested in the embodiment 1, and the results were basically consistent. Due to limited space, they are not listed one by one.

[0063] Example 3 A method for preparing a varistor composite raw material powder in this embodiment includes the following steps: (1) Weighing 4.5% bismuth nitrate, 1.5% cobalt nitrate, 2.5% manganese nitrate, 1.5% nickel nitrate and 90% ZnO powder respectively according to mass percentage, wherein bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate are used as precursors; (2) Under stirring, dissolving the precursor in dilute nitric acid with a mass concentration of 30% at a mass ratio of 1:1.5 to obtain reagent A; (3) dissolving citric acid in deionized water, wherein the mass ratio of citric acid to the total mass of bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate is 2:1, and the mass fraction of citric acid in deionized water is 32%, to obtain reagent B; (4) Add reagent A dropwise into reagent B and stir for 25 minutes to completely mix the two reagents to obtain reagent C; (5) Slowly add ethanolamine dropwise to reagent C under stirring until the pH value reaches 6.0-9.5, and then stop adding ethanolamine to obtain reagent D; (6) Add ZnO slurry with a solid content of 30% to reagent D, stir, and pour into a homogenizer for homogenization. The homogenizer pressure is 50 MPa, the homogenization time is 10 min, and the homogenization flow rate is 200 mL / min to obtain a wet sol; (7) The wet sol is allowed to stand in air for 6 hours to generate a gel, which is then placed in an oven for drying at 105° C. for 7 hours, calcined in a muffle furnace at 1000° C. for 2.5 hours, and ground to obtain the varistor composite raw material powder.

[0064] The varistor composite raw material powder prepared in the embodiment was tested in the embodiment 1, and the results were basically consistent. Due to limited space, they are not listed one by one.

[0065] Comparative Example 1 The preparation method of a composite raw material powder of a varistor in this comparative example is as follows: bismuth trioxide, cobalt trioxide, manganese trioxide, and nickel trioxide are selected as additives. The mass ratio of the four metal oxides to the mass ratio of ZnO powder is 1.7%, 1.5%, 1.8%, 1.7%, and 93.3%, respectively. The above-mentioned bismuth trioxide, cobalt trioxide, manganese trioxide, nickel trioxide and ZnO powder are ground to obtain a composite raw material powder of a varistor.

[0066] The particle size distribution of the powder prepared in this comparative example is as follows Figure 1 As shown, it can be seen from the figure that there are two peaks, and the right peak with a larger particle size is obviously higher. Compared with the method of Example 1, the powder prepared in Comparative Example 1 is more seriously agglomerated.

[0067] Comparative Example 2 The method for preparing a varistor composite raw material powder in this comparative example is the same as that in Example 1, except that in step (6), the homogenization process is removed.

[0068] Comparative Example 3 The method for preparing a varistor composite raw material powder in this comparative example is the same as that in Example 1, except that in step (5), the pH value is 10.

[0069] Comparative Example 4 The method for preparing a varistor composite raw material powder in this comparative example is the same as that in Example 1, except that in step (6), the pressure of the homogenization treatment is 60 MPa.

[0070] Comparative Example 4-1 The method for preparing a varistor composite raw material powder in this comparative example is the same as that in Example 1, except that in step (6), the homogenization time is 5 minutes.

[0071] Comparative Example 4-2 The method for preparing a varistor composite raw material powder in this comparative example is the same as that in Example 1, except that in step (6), the homogenization flow rate is 100 mL / min.

[0072] Comparative Example 5 The method for preparing a varistor composite raw material powder in this comparative example is the same as that in Example 1, except that in step (1), the mass fraction of bismuth nitrate is 1.4%, and the mass fraction of ZnO powder is 87.8%.

[0073] Comparative Example 6 The method for preparing a varistor composite raw material powder in this comparative example is the same as that in Example 1, except that in step (3), the mass ratio of citric acid to the total mass of bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate is 5:1.

[0074] Comparative Example 7 The method for preparing a varistor composite raw material powder in this comparative example is the same as that in Example 1, except that in step (7), the drying temperature is 175° C. and the drying time is 8 h.

[0075] Comparative Example 8 The method for preparing a varistor composite raw material powder in this comparative example is the same as that in Example 1, except that in step (7), the calcination temperature is 580° C. and the calcination time is 2 h.

[0076] Comparative Example 9 The method for preparing a varistor composite raw material powder in this comparative example is the same as that in Example 1, except that in step (7), the standing time is 2 hours.

[0077] Test Example 1 The varistor composite raw material powders prepared in Examples 1-3 and Comparative Examples 1-9 were respectively made into varistors. The preparation method of the varistors is as follows: (a) mixing the varistor composite raw material powder, dispersant (sodium polyacrylate), binder (polyvinyl alcohol), and deionized water in a mass ratio of 80.5:1.3:3.2:15, adding the mixture into a ball mill for 8 h, and passing the mixture through a 120-mesh sieve to obtain a mixed slurry; (b) using a spray dryer to spray granulate the mixed slurry to obtain granulated material, and then allowing the granulated material to stand with water, the water content is 1.5%, and the standing time is 12 hours; (c) Pressing the granulated material treated in step (b) into a mold, controlling the pressure so that the density of the molded green body is 3.25 g / cm 3 ; (d) subjecting the green body prepared in step (c) to a debinding treatment at 430° C. to remove organic matter in the green body, and then calcining the green body at 1150° C. for 2 h to obtain a sintered resistor green body; (e) The resistor body is ground and cleaned, and then a metal electrode is prepared on the treated surface of the resistor to obtain a finished varistor.

[0078] The performance of varistors prepared using the raw material powders of Examples 1-3 and Comparative Examples 1-9 were tested respectively. Eight varistors were prepared in each case. The voltage gradient, nonlinear coefficient and 10kA 8 / 20 lightning wave pulse current residual voltage ratio were averaged. The results are shown in Table 1.

[0079]

[0080] It can be seen from Table 1 that the varistor prepared using the composite raw material powder of the present invention has a higher varistor voltage gradient, and its nonlinearity and residual voltage ratio are better than those of other samples. The standard deviation of each performance of the varistor prepared using the composite raw material powder of the present invention is also smaller, indicating better consistency.

[0081] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a varistor composite raw material powder, characterized in that: The method comprises: coating ZnO powder by a sol coating method, homogenizing to obtain a wet sol, and sequentially drying, roasting and grinding the wet sol to obtain a varistor composite raw material powder; The homogenization pressure is 20-50 MPa, the homogenization time is 10-60 min, and the homogenization flow rate is 200-1000 mL / min.

2. The method for preparing a varistor composite raw material powder according to claim 1, characterized in that: The drying temperature is 80-105°C and the drying time is 7-9.5h.

3. The method for preparing a varistor composite raw material powder according to claim 1, characterized in that: The calcination temperature is 700-1000°C and the calcination time is 2.5-3h.

4. The method for preparing a varistor composite raw material powder according to any one of claims 1 to 3, characterized in that: When ZnO powder is coated by the sol coating method, bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate are selected as precursors.

5. The method for preparing a varistor composite raw material powder according to claim 4, characterized in that: The coating of ZnO powder by the sol coating method specifically includes the following steps: dissolving the precursor in dilute nitric acid to obtain reagent A, dissolving citric acid in deionized water to obtain reagent B, slowly dripping the reagent A into reagent B, stirring to obtain reagent C, slowly dripping ethanolamine into reagent C until the pH value is 6.0-9.5 to obtain reagent D, and adding ZnO slurry to reagent D.

6. The method for preparing a varistor composite raw material powder according to claim 5, characterized in that: According to mass percentage, bismuth nitrate: 2.8-4.5%, cobalt nitrate: 1.5-3.6%, manganese nitrate: 1.5-3.6%, nickel nitrate: 1.5-3.6%, ZnO powder: 85.5-90.5%.

7. The method for preparing a varistor composite raw material powder according to claim 5, characterized in that: The mass concentration of the dilute nitric acid is 28-32%, and the mass ratio of the dilute nitric acid to the precursor is 1-2:

1.

8. The method for preparing a varistor composite raw material powder according to claim 5, characterized in that: The mass ratio of citric acid to the total mass of bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate is 2-3:

1.

9. The method for preparing a varistor composite raw material powder according to claim 5, characterized in that: The mass fraction of citric acid in deionized water is 28-32%.

10. A varistor composite raw material powder prepared by the method according to any one of claims 1 to 9.

11. A varistor, characterized in that: The raw material of the varistor includes the varistor composite raw material powder according to claim 10.

12. A varistor according to claim 11, characterized in that: The raw materials of the varistor also include a dispersant and a binder.

13. A varistor according to claim 12, characterized in that: The dispersant is sodium polyacrylate, and the binder is polyvinyl alcohol.

14. A method for preparing a varistor according to any one of claims 11 to 13, characterized in that: include: The raw materials of the varistor are mixed with water, spray-dried, granulated, pressed, calcined, and ground to obtain the varistor.

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