A varistor composite raw material powder, its preparation method and application

Abstract

The present invention relates to a varistor composite raw material powder and a preparation method and application thereof, belonging to the technical field of varistors, and is used to solve at least one of the problems such as the uneven microstructure of the varistor composite raw material powder prepared by the existing method, the unstable performance, poor consistency, low voltage gradient, and low non-linear coefficient of the prepared varistor. The preparation method of the varistor composite raw material powder of the present invention homogenizes the ZnO powder coated by the sol coating method, so that the sol aggregates that are not dispersed in the stirring process are dispersed in the high-pressure and high-speed fluid of the homogenizer, and 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 non-linear coefficient of the varistor by optimizing the microstructure, controlling the particle size distribution, reducing defects, and optimizing the interface, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of varistors, and particularly 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 non-linear Ohmic characteristics and large energy absorption capacity. Traditional preparation methods such as the solid-phase method have problems such as uneven distribution of additive components and non-uniform microstructure, which affect the performance of varistors.

[0003] Existing methods can only ensure the uniformity of varistor oxide additives, and the additives are still mixed with ZnO by the traditional ball milling method. This method will also cause problems such as non-uniform microstructure of the varistor composite raw material powder, poor consistency of the prepared varistors, low voltage gradient, and low non-linear 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 such as non-uniform microstructure of the varistor composite raw material powder prepared by the existing method, unstable performance, poor consistency, low voltage gradient, and low non-linear coefficient of the prepared varistors.

[0005] In a first aspect, the present invention provides a preparation method of a varistor composite raw material powder, the method comprising: coating ZnO powder by a sol coating method, performing homogenization treatment to obtain a wet sol, and sequentially drying, calcining, and grinding the wet sol to obtain the varistor composite raw material powder.

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

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

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

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

[0010] Further, the coating of ZnO powder by the sol coating method specifically includes the following steps: Dissolve the precursor in dilute nitric acid to obtain reagent A, dissolve citric acid in deionized water to obtain reagent B, slowly drop reagent A into reagent B and stir to obtain reagent C, slowly drop ethanolamine into reagent C until the pH value is 6.0 - 9.5 to obtain reagent D, and add ZnO slurry to reagent D.

[0011] Further, by 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] Further, 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] Further, 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] Further, 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, and the raw material of the varistor is the above varistor composite raw material powder.

[0017] Further, the raw materials of the varistor further include a dispersant and a binder.

[0018] Further, 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 varistor, including: 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:

[0021] (1)The preparation method of the varistor composite raw material powder of the present invention homogenizes the ZnO powder coated by the sol coating method, so that the sol aggregates that are not dispersed in the stirring process are dispersed in the high-pressure and high-speed fluid of the homogenizer, enabling the additives to be 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, etc.;

[0022] (2)The homogenization pressure within the scope of the present invention can control the growth of grains, making them finer and more uniform. The fine grains can increase the number of grain boundaries and improve the height of the grain boundary barrier, thereby increasing 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 result in areas in the material that are not fully mixed, forming defects and affecting the electrical properties. While 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 aggregation. This helps to form fine and uniform particles, increasing the voltage gradient, nonlinear coefficient, and consistency of the varistor;

[0023] (3)By selecting specific homogenization treatment conditions, reducing the drying temperature, and increasing the calcination temperature, the present invention only requires one-step drying, shortens the calcination time, shortens the process flow, and improves the production efficiency. Through the synergistic effect of the above conditions, the present invention not only improves the uniformity of the powder but also improves the crystallinity and density of the material, significantly increasing the stability, consistency, voltage gradient, and nonlinear coefficient of the varistor;

[0024] (4)The present invention uses specific raw materials and the sol-gel method to achieve the preparation of high-performance varistor composite raw material powder at a lower temperature, reducing energy consumption and costs; moreover, through the method of the present invention, the uniformity of the varistor composite material is improved, and the prepared varistor has better consistency, higher voltage gradient and nonlinear coefficient, improving the stability and reliability of the varistor;

[0025] (5)The voltage gradient of the varistor prepared by the present invention is 230~240 V / mm, preferably 234~236 V / 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 10 kA 8 / 20 lightning wave impulse current residual voltage ratio is 1.62~1.67, and the standard deviation of the 10 kA 8 / 20 lightning wave impulse current residual voltage ratio is 0.006~0.008.

[0026] In the present invention, the above 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 specification. Moreover, some advantages can be made obvious from the specification or understood by implementing the present invention. The objectives and other advantages of the present invention can be realized and obtained from the content specifically pointed out in the specification and the drawings. Description of the Drawings

[0027] The drawings are only for the purpose of showing specific embodiments and are not considered as limiting the present invention. Throughout the drawings, the same reference signs denote the same components.

[0028] Figure 1 It is the particle size distribution diagram of the composite raw material powder of the varistor prepared in Example 1 and Comparative Example 1 of the present invention. Detailed Embodiments

[0029] The following will specifically describe the preferred embodiments of the present invention in conjunction with the drawings. The drawings form a part of the present invention and are used together with the embodiments of the present invention to explain the principle of the present invention, rather than to limit the scope of the present invention.

[0030] A specific embodiment of the present invention discloses a method for preparing a composite raw material powder of a varistor. The method includes: coating ZnO powder by a sol coating method, performing a homogenization treatment to obtain a wet sol, and sequentially drying, roasting, and grinding the wet sol to obtain the composite raw material powder of the varistor.

[0031] Compared with the prior art, the method for preparing the composite raw material powder of the varistor of the present invention performs a homogenization treatment on the ZnO powder coated by the sol coating method, so that the sol aggregates that are not dispersed in the stirring process are dispersed in the high-pressure and high-speed fluid of the homogenizer, and the additives are dispersed around the ZnO powder at the molecular level. Through optimizing the microstructure, controlling the particle size distribution, reducing defects, and optimizing the interface, etc., the homogenization treatment of the present invention can significantly improve the stability, consistency, voltage gradient, and nonlinear coefficient of the varistor.

[0032] Since a gel is obtained after coating ZnO powder by the sol coating method, the gel is a material with a three-dimensional mesh structure that can contain various particles or liquids inside. The gel itself has a certain viscosity and structure and is prone to forming aggregates or uneven distribution during the dispersion process. Gels usually have relatively high viscosity and elasticity, which makes it difficult to achieve uniform dispersion in traditional mixing processes. When preparing gels for particle dispersion, traditional stirring methods may result in uneven distribution of particles in the gel, affecting the performance of the final product. This makes it not easy for those skilled in the art to think of solving the gel dispersion problem through homogenization treatment. Through a large number of experiments, the present invention discovers that by subjecting the gel to homogenization treatment at specific pressure, time, and flow rate, the stability, consistency, voltage gradient, and non-linear coefficient of the piezoresistance can be improved.

[0033] Specifically, the pressure for homogenization treatment is 20 - 50 MPa (for example, 20 MPa, 25 MPa, 30 MPa, 35 MPa, 40 MPa, 45 MPa, 50 MPa), the homogenization time is 10 - 60 min (for example, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min), and the flow rate for homogenization is 200 - 1000 mL / min (for example, 200 mL / min, 250 mL / min, 300 mL / min, 350 mL / min, 400 mL / min, 450 mL / min, 500 mL / min, 550 mL / min, 600 mL / min, 650 mL / min, 700 mL / min, 750 mL / min, 800 mL / min, 850 mL / min, 900 mL / min, 950 mL / min, 1000 mL / min).

[0034] It should be noted that the homogenization pressure within the scope of the present invention can control the growth of crystal grains, making them finer and more uniform. Finer crystal grains can increase the number of grain boundaries and the height of the grain boundary barrier, thereby increasing the voltage gradient, non-linear coefficient, and consistency of the varistor. The homogenization time within the scope of the present invention can reduce the defect density in the material. An overly short homogenization time may result in regions in the material where there is insufficient mixing, forming defects and affecting the electrical properties. A longer homogenization time can effectively reduce these defects and optimize the voltage gradient, non-linear 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 aggregation. This helps to form finer and more uniform particles and improve the voltage gradient, non-linear coefficient, and consistency of the varistor.

[0035] Specifically, the drying temperature is 80 - 105 °C (e.g., 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, 105 °C), and the drying time is 7 - 9.5 h (e.g., 7.2 h, 7.4 h, 7.6 h, 7.8 h, 8 h, 8.2 h, 8.4 h, 8.6 h, 8.8 h, 9.0 h, 9.2 h, 9.4 h).

[0036] It should be noted that the drying temperature and time directly affect the removal rate and degree of moisture in the sol. A lower drying temperature can avoid thermal decomposition or crystal form transformation of the material during drying, while an appropriate drying time ensures sufficient removal of moisture. This helps to maintain the chemical composition and structural stability of the material, providing a good foundation for subsequent calcination. Excessively high drying temperature or too long drying time can lead to excessive surface shrinkage of the material, forming a dense shell, which hinders further removal of internal moisture and affects the uniformity and denseness of the material. Reasonable drying conditions, on the other hand, contribute to the formation of a uniform microstructure and improve the electrical properties of the material.

[0037] Specifically, the calcination temperature is 700 - 1000 °C (e.g., 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 - 3 h (e.g., 2.6 h, 2.7 h, 2.8 h, 2.9 h).

[0038] It should be noted that the calcination temperature is a key factor affecting grain growth and densification of the material. An appropriate calcination temperature can promote grain growth and densification of the material, improving the mechanical strength and electrical properties of the material. A higher calcination temperature is beneficial to grain growth and reduction of grain boundaries, thereby increasing the voltage gradient and non - linear coefficient of the material. Phase transformation may occur during the calcination process, and the diffusion and solid solution of doping elements are also closely related to the calcination temperature. By precisely controlling the calcination temperature and time, the distribution and solid solubility of doping elements can be optimized, further improving the electrical properties of the material and enhancing its consistency.

[0039] By selecting specific homogenization treatment conditions, reducing the drying temperature, and increasing the calcination temperature, the present invention only requires one - step drying, shortens the calcination time, shortens the process flow, and improves production efficiency. The homogenization treatment of the present invention provides a good foundation for subsequent drying and calcination, while drying and calcination further consolidate and optimize the effect of homogenization treatment. Through the synergistic effect of the above - mentioned various conditions, the present invention not only improves the uniformity of the powder, but also improves the crystallinity and denseness of the material, significantly enhancing the stability, consistency, voltage gradient, and non - linear coefficient of the varistor.

[0040] Specifically, when coating ZnO powder by the sol coating method, bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate are selected as precursors.

[0041] Specifically, the coating of ZnO powder by the sol coating method specifically includes the following steps: dissolving the above-mentioned precursors in dilute nitric acid to obtain reagent A, dissolving citric acid in deionized water to obtain reagent B, slowly dropping reagent A into reagent B, and stirring to obtain reagent C, slowly dropping ethanolamine into reagent C until the pH value is 6.0 - 9.5 to obtain reagent D, and adding ZnO slurry to reagent D.

[0042] Specifically, a method for preparing a varistor composite raw material powder of the present invention includes the following steps:

[0043] (1) Weigh bismuth nitrate, cobalt nitrate, manganese nitrate, nickel nitrate and ZnO powder respectively according to mass percentages, wherein bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate are used as precursors;

[0044] (2) Dissolve the above-mentioned precursors in dilute nitric acid to obtain reagent A;

[0045] (3) Dissolve citric acid in deionized water to obtain reagent B;

[0046] (4) Slowly drop reagent A into reagent B and stir to obtain reagent C;

[0047] (5) Slowly drop ethanolamine into reagent C until the pH value is 6.0 - 9.5 to obtain reagent D;

[0048] (6) Add ZnO slurry to reagent D, stir, pour it into a homogenizer for homogenization treatment to obtain a wet sol;

[0049] (7) Let the wet sol stand in the air to form a gel, dry, calcine, and grind to obtain the varistor composite raw material powder.

[0050] Compared with the prior art, the present invention uses specific raw materials and the sol-gel method to achieve the preparation of high-performance varistor composite raw material powder at a lower temperature (room temperature), reducing energy consumption and cost; and through the method of the present invention, the uniformity of the varistor composite material is improved, and the consistency of the prepared varistor is better, the voltage gradient and the non-linear coefficient are higher, improving the stability and reliability of the varistor.

[0051] Specifically, in step (1), by mass percentage, bismuth nitrate: 2.8 - 4.5% (for example, 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% (for example, 1.5%, 1.7%, 1.9%, 2.1%, 2.3%, 2.5%, 2.7%), manganese nitrate: 1.5 - 3.6% (for example, 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% (for example, 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% (for example, 85.5%, 86%, 8.65%, 87%, 87.5%, 88%, 88.5%, 89%, 89.5%, 90%, 90.5%).

[0052] It should be noted that in the present invention, bismuth nitrate, cobalt nitrate, manganese nitrate, nickel nitrate and ZnO powder act together. By adjusting the height of the grain boundary potential barrier and the density of interface states, the voltage gradient and non - linear coefficient of the varistor can be significantly improved. At the same time, these additives can reduce the defects of the grain boundary, improve the uniformity and compactness of the grain boundary, thereby improving the stability and reliability of the component.

[0053] In the present invention, by precisely controlling the mass ratio of each raw material, it can be ensured that during the sol - gel process, various metal ions can be uniformly dispersed in the ZnO matrix. This uniform dispersion helps to form a consistent microstructure, reduce the defects and stress concentration inside the material, thereby improving the consistency of the material.

[0054] Specifically, in step (2), the mass concentration of 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).

[0055] 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%).

[0056] It should be noted that using the above range for the mass ratio 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, forming smaller particles. Excessive or insufficient citric acid may lead to uneven or overly large particle sizes, affecting the densification and electrical consistency of the varistor.

[0057] In addition, improper proportioning may cause 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 the voltage gradient.

[0058] Furthermore, the ratio of citric acid to metal nitrates has an important impact on the formation and characteristics of the grain boundary barrier. Appropriate proportioning can promote the formation and stability of the grain boundary barrier, thereby increasing the non-linear coefficient of the varistor. The grain boundary barrier is an important source of the non-linear characteristics of the varistor. A higher non-linear coefficient means that the varistor can more effectively limit the current under overvoltage conditions, providing better protection performance. Appropriate proportioning can optimize the energy band structure and electron state density of the material, improving the migration and transition characteristics of electrons at different voltages, thus increasing the non-linear coefficient.

[0059] The present invention realizes the fine regulation of the microstructure and electrical properties of the varistor material by precisely controlling the ratio of citric acid to metal nitrates.

[0060] Specifically, in step (6), the ZnO slurry is a suspension formed by dissolving ZnO powder in water with a solid content of 20-30% (for example, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%).

[0061] In the process of forming the sol-gel of the present invention, after the precursor solution combines with citric acid and ethanolamine, by controlling conditions such as pH value and stirring, a uniform sol can be formed, and then a uniform gel can be produced. This uniformity helps to improve the consistency of the microstructure of the varistor material, thereby improving its electrical properties.

[0062] In addition, by precisely controlling the chemical reaction conditions and raw material ratios in the sol-gel process, the microstructure and grain boundary distribution of the varistor material can be optimized. By controlling the type and content of dopants, the characteristics of the grain boundary layer can be adjusted, thereby increasing the voltage gradient and nonlinear coefficient of the material. An increase in the voltage gradient means that the material can maintain stable resistance characteristics at higher voltages, while an increase in the nonlinear coefficient helps to better suppress overvoltage.

[0063] Specifically, in step (7), the standing time is 3 - 6 h (for example, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h).

[0064] It should be noted that by using the standing time of the present invention, the solvent in the wet sol can be fully evaporated, promoting the mutual connection between sol particles and forming a uniform and dense gel structure. This structure helps the material to shrink and densify uniformly during subsequent drying and calcination processes, thereby improving the consistency of the material. It can reduce the stress concentration and defect generation inside the gel, making the material less likely to have defects such as cracks during subsequent heat treatment processes, and contributing to maintaining the integrity and electrical properties of the material.

[0065] Another specific embodiment of the present invention discloses a varistor composite raw material powder prepared by the above method.

[0066] Another specific embodiment of the present invention discloses a varistor made from the above varistor composite raw material powder.

[0067] Specifically, the raw materials of the varistor further include a dispersant and a binder.

[0068] Specifically, the dispersant is sodium polyacrylate, and the binder is polyvinyl alcohol.

[0069] Another specific embodiment of the present invention discloses a method for preparing the above varistor, including: mixing the raw materials of the varistor and water, spray drying, granulating, pressing, calcining, and grinding to obtain the varistor.

[0070] The voltage gradient of the varistor prepared by the present invention is 230 - 240 V / mm, preferably 234 - 236 V / 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 10 kA 8 / 20 lightning wave impulse current residual voltage ratio is 1.62 - 1.67, and the standard deviation of the 10 kA 8 / 20 lightning wave impulse current residual voltage ratio is 0.006 - 0.008.

[0071] It should be noted that the consistency in the present invention refers to the standard deviation in multiple groups of tests. The smaller the standard deviation, the better the consistency. The following further explains the technical solution of the present invention in combination with specific embodiments.

[0072] Example 1

[0073] A preparation method of a varistor composite raw material powder body in this embodiment includes the following steps:

[0074] (1) Weigh bismuth nitrate: 3.1%, cobalt nitrate: 2.2%, manganese nitrate: 1.8%, nickel nitrate: 2.8% and ZnO powder: 90.1% respectively according to mass percentage. Among them, bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate are used as precursors;

[0075] (2) Under stirring, dissolve the above-mentioned precursors in dilute nitric acid with a mass concentration of 30% according to a mass ratio of 1:1 to obtain reagent A;

[0076] (3) Dissolve citric acid in deionized water. Among them, 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;

[0077] (4) Drop the reagent A into reagent B and stir for 20 min to make the two reagents fully mixed to obtain reagent C;

[0078] (5) Under stirring conditions, slowly drop ethanolamine into reagent C until the pH value is 6.0 - 9.5 and stop dropping ethanolamine to obtain reagent D;

[0079] (6) Add ZnO slurry with a solid content of 25% to reagent D, stir, pour it into a homogenizer for homogenization treatment. The pressure of the homogenizer is 35 MPa, the homogenization time is 35 min, and the homogenization flow rate is 600 mL / min to obtain a wet sol;

[0080] (7) Let the wet sol stand in the air for 5 h to form a gel, put it into an oven for drying. The drying temperature is 92 °C and the drying time is 8.2 h. Roast it in a muffle furnace at 850 °C for 2.75 h and grind it to obtain the varistor composite raw material powder body.

[0081] The particle size distribution diagram of the varistor composite raw material powder body prepared in this embodiment is shown in Figure 1 , and it can be seen that the particle size distribution curve of the composite raw material powder body has two peaks. The peak with a smaller particle size is the peak formed by non-agglomerated particles, and the peak with a larger particle size is the peak formed by agglomerated particles. The left peak with a smaller particle size is significantly higher, indicating that the vast majority of particles are not agglomerated.

[0082] Example 2

[0083] A preparation method of a varistor composite raw material powder in this embodiment includes the following steps:

[0084] (1) Weigh bismuth nitrate: 2.8%, cobalt nitrate: 3.6%, manganese nitrate: 3.6%, nickel nitrate: 3.6% and ZnO powder: 86.4% respectively according to mass percentage. Among them, bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate are used as precursors;

[0085] (2) Under stirring, dissolve the above-mentioned precursors in dilute nitric acid with a mass concentration of 30% according to a mass ratio of 1:2 to obtain reagent A;

[0086] (3) Dissolve citric acid in deionized water. 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;

[0087] (4) Drop reagent A into reagent B and stir for 15 min to make the two reagents fully mixed to obtain reagent C;

[0088] (5) Under the condition of stirring, slowly drop ethanolamine into reagent C until the pH value is 6.0 - 9.5 and then stop dropping ethanolamine to obtain reagent D;

[0089] (6) Add ZnO slurry with a solid content of 20% to reagent D, stir, pour it into a homogenizer for homogenization treatment. The pressure of the homogenizer is 20 MPa, the homogenization time is 60 min, and the homogenization flow rate is 1000 mL / min to obtain a wet sol;

[0090] (7) Let the wet sol stand in the air for 3 h to form a gel, put it into an oven for drying. The drying temperature is 80 °C and the drying time is 9.5 h. Then calcine it in a muffle furnace at 700 °C for 3 h and grind it to obtain the varistor composite raw material powder.

[0091] The varistor composite raw material powder prepared in the example was tested as in Example 1, and the results were basically the same. Due to limited space, they are not listed one by one.

[0092] Example 3

[0093] A preparation method of a varistor composite raw material powder in this embodiment includes the following steps:

[0094] (1) Weigh bismuth nitrate: 4.5%, cobalt nitrate: 1.5%, manganese nitrate: 2.5%, nickel nitrate: 1.5% and ZnO powder: 90% respectively according to mass percentage. Among them, bismuth nitrate, cobalt nitrate, manganese nitrate and nickel nitrate are used as precursors;

[0095] (2) Under stirring, dissolve the above-mentioned precursor in dilute nitric acid with a mass concentration of 30% according to a mass ratio of 1:1.5 to obtain reagent A;

[0096] (3) Dissolve citric acid in deionized water. Among them, 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;

[0097] (4) Drop the above-mentioned reagent A into reagent B and stir for 25 min to completely mix the two reagents to obtain reagent C;

[0098] (5) Under stirring conditions, slowly drop ethanolamine into reagent C until the pH value is 6.0 - 9.5, and stop dropping ethanolamine to obtain reagent D;

[0099] (6) Add ZnO slurry with a solid content of 30% to reagent D, stir, pour it into a homogenizer for homogenization treatment. The pressure of the homogenizer is 50 MPa, the homogenization time is 10 min, and the homogenization flow rate is 200 mL / min to obtain a wet sol;

[0100] (7) Let the above-mentioned wet sol stand in the air for 6 h to form a gel, put it into an oven for drying. The drying temperature is 105 °C, the drying time is 7 h, calcine it in a muffle furnace at a temperature of 1000 °C for 2.5 h, and grind it to obtain the powder of the composite raw material of the varistor.

[0101] The powder of the composite raw material of the varistor prepared in the example was tested in Example 1, and the results were basically the same. Due to space limitations, they are not listed one by one.

[0102] Comparative Example 1

[0103] A preparation method of a powder of a composite raw material of a varistor in this comparative example is as follows: Select bismuth trioxide, cobalt trioxide, manganese trioxide and nickel trioxide as additives. The mass ratios of the four metal oxides to the mass of ZnO powder are 1.7%, 1.5%, 1.8%, 1.7%, and 93.3% respectively. Grind the above-mentioned bismuth trioxide, cobalt trioxide, manganese trioxide, nickel trioxide and ZnO powder to obtain the powder of the composite raw material of the varistor.

[0104] The particle size distribution of the powder prepared in this comparative example is as Figure 1 shown. It can be seen from the figure that there are two peaks, and the right peak with a larger particle size is significantly higher. Compared with the method of Example 1, the powder prepared in Comparative Example 1 has more serious agglomeration.

[0105] Comparative Example 2

[0106] The preparation method of 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 treatment is removed.

[0107] Comparative Example 3

[0108] The preparation method of 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.

[0109] Comparative Example 4

[0110] The preparation method of 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.

[0111] Comparative Example 4-1

[0112] The preparation method of 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 min.

[0113] Comparative Example 4-2

[0114] The preparation method of a varistor composite raw material powder in this comparative example is the same as that in Example 1, except that in step (6), the flow rate of the homogenization is 100 mL / min.

[0115] Comparative Example 5

[0116] The preparation method of 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%.

[0117] Comparative Example 6

[0118] The preparation method of 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.

[0119] Comparative Example 7

[0120] The preparation method of 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.

[0121] Comparative Example 8

[0122] The preparation method of a varistor composite raw material powder in this comparative example is the same as that in Example 1, except that in step (7), the roasting temperature is 580 °C and the roasting time is 2 h.

[0123] Comparative Example 9

[0124] The preparation method of 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 h.

[0125] Test Example 1

[0126] The varistor composite raw material powders prepared in Examples 1 - 3 and Comparative Examples 1 - 9 were respectively made into varistors, and the preparation method of the varistors is as follows:

[0127] (a) Mix the varistor composite raw material powder, a dispersant (sodium polyacrylate), a binder (polyvinyl alcohol), and deionized water according to a mass ratio of 80.5:1.3:3.2:15, add them to a ball mill for ball milling for 8 h, and pass through a 120 - mesh sieve to obtain a mixed slurry;

[0128] (b) Use a spray dryer to spray - granulate the mixed slurry to obtain granulated material, and then carry out water - containing standing with a water content of 1.5% and a standing time of 12 h;

[0129] (c) Press - mold the granulated material treated by standing in step (b), control the pressure so that the density of the formed green body is 3.25 g / cm 3 ;

[0130] (d) Subject the green body prepared in step (c) to degumming treatment at 430 °C to remove the organic matter in the green body, and then perform high - temperature calcination at 1150 °C for 2 h to obtain a sintered resistor green body;

[0131] (e) Grind and wash the resistor green body, and then prepare metal electrodes on the surface of the treated resistor to obtain a finished varistor chip.

[0132] Test the performance of the varistor chips prepared from the raw material powders of Examples 1 - 3 and Comparative Examples 1 - 9 respectively. 8 resistor chips were prepared for each example, and the voltage gradient, non - linear coefficient, and 10 kA 8 / 20 lightning impulse current residual voltage ratio were all taken as averages. The results are shown in Table 1.

[0133]

[0134] As can be seen from Table 1, the varistors prepared with the composite raw material powder of the present invention have a higher varistor voltage gradient, and both the non-linearity and the residual voltage ratio are better than those of other samples. The standard deviations of the performances of the varistors prepared with the composite raw material powder of the present invention are also smaller, indicating better consistency.

[0135] The above are only the preferred specific embodiments 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 those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A preparation method of a varistor composite raw material powder, characterized in that, The method described above includes: coating ZnO powder by sol coating method, followed by homogenization treatment to obtain wet sol, and then successively drying, calcining, and grinding the wet sol to obtain the varistor composite raw material powder; The pressure for the homogenization treatment is 20 - 45 MPa, the homogenization time is 10 - 60 min, the flow rate for homogenization is 200 - 1000 mL / min, the calcination temperature is 700 - 1000 °C, and the calcination time is 2.5 - 3 h; The homogenization treatment controls the growth of grains. The fine grains increase the number of grain boundaries and raise the height of the grain boundary barrier, thereby enhancing the voltage gradient, non - linear coefficient, and consistency of the varistor; Among them, the specific process of coating ZnO powder by sol coating method is as follows: dissolving the precursor in dilute nitric acid to obtain reagent A, dissolving citric acid in deionized water to obtain reagent B, slowly dropping reagent A into reagent B and stirring to obtain reagent C, slowly dropping ethanolamine into reagent C until the pH value is 6.0 - 9.5 to obtain reagent D, and adding ZnO slurry to reagent D; The precursor is bismuth nitrate, cobalt nitrate, manganese nitrate, and nickel nitrate. By 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%.

2. The preparation method of 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 - 9.5 h.

3. The preparation method of a varistor composite raw material powder according to claim 1, 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.

4. The preparation method of a varistor composite raw material powder according to claim 1, 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.

5. The preparation method of a varistor composite raw material powder according to claim 1, characterized in that, The mass fraction of citric acid in deionized water is 28 - 32%.

6. A varistor composite raw material powder prepared by the method according to any one of claims 1 - 5.

7. A varistor, characterized in that, The raw materials of the varistor include the varistor composite raw material powder according to claim 6.

8. A varistor according to claim 7, characterized in that, The raw materials of the varistor further include a dispersant and a binder.

9. A varistor according to claim 8, characterized in that, The dispersant is sodium polyacrylate, and the binder is polyvinyl alcohol.

10. A method for preparing a varistor according to any one of claims 7-9, characterized in that, It includes: Mixing the raw materials of the varistor and water, followed by spray drying, granulation, pressing, calcining, and wafer grinding to obtain the varistor.

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