High gradient ZnO voltage-dependent resistor ceramic and simple low-temperature sintering method

Abstract

The application discloses a ZnO pressure-sensitive ceramic and a simple low-temperature sintering method. The composition of the ZnO pressure-sensitive ceramic is [100-(a+b+c+d+e)] mol% ZnO+amol% Bi2O3+bmol% Co3O4+cmol% Mn2O3+dmol% Cr2O3+emol% SnO2, wherein 2.1<=a+b+c+d+e<=7.5. The ceramic is sintered at a sintering temperature of 800-1000 DEG C, and the voltage gradient E of the ZnO pressure-sensitive ceramic is 1529-2362 V / mm, the nonlinear coefficient a is 63-86, the leakage current density I is 0.2-0.7 mu A / cm b , and the performance is better than that of the commercially available ZnO pressure-sensitive ceramic at the present stage, and the performance requirement of the pressure-sensitive ceramic in actual production can be met. L 2 ​​

Description

Technical Field

[0001] This invention belongs to the field of ceramic production technology, and specifically relates to a high-performance ZnO varistor ceramic and a simple low-temperature sintering method. Background Technology

[0002] ZnO-based varistors are important semiconductor ceramics, primarily composed of ZnO powder, with their performance optimized by incorporating metal oxides. Due to their excellent electrical properties, ZnO varistors are widely used in various technological fields, including communications, power systems, traffic control, industrial automation, automotive electronics, and home appliances. They possess high nonlinear coefficients, low leakage current, fast response times, and excellent resistance to high-current surges. With the rapid development of high-voltage AC / DC transmission lines and the trend towards integration and miniaturization in electronic devices, the market demand for ZnO varistors with high breakdown voltages is constantly increasing. The voltage gradient of these varistors is one of their key performance indicators, directly affecting their reliability in high-voltage applications. However, currently commercially available ZnO varistors generally exhibit low voltage gradients (<400V / mm), making it difficult for them to meet the requirements for miniaturization and high breakdown voltage.

[0003] Currently, the high-temperature solid-state sintering method used in the production of commercial ZnO varistors typically operates at temperatures exceeding 1000℃. However, this process has revealed several significant drawbacks in modern applications. First, during high-temperature sintering, Bi₂O₃ (melting point approximately 825℃) undergoes severe volatilization, leading to a significant decrease in the nonlinear IV characteristics of the ZnO varistor and reducing its electrical performance. Second, high-temperature sintering also results in excessive ZnO grain growth, which not only affects the voltage gradient of the varistor but also reduces its nonlinear coefficient, making it difficult for traditional methods to meet miniaturization requirements.

[0004] To address these challenges, researchers have begun exploring more advanced sintering processes to lower the sintering temperature of ZnO varistors, thereby controlling grain growth and improving material performance. Emerging sintering technologies such as selective laser sintering (SLS), flash sintering (FS), and spark plasma sintering (SPS) have been proposed as improvement solutions. These advanced sintering processes can effectively increase the densification of materials at lower temperatures, thereby controlling grain growth and ultimately improving the electrical properties and voltage gradient of ZnO varistors. For example, selective laser sintering uses laser energy to locally heat the material, enabling rapid densification at lower temperatures. Flash sintering promotes densification through short-duration high-energy pulse heating, while spark plasma sintering uses the high temperatures generated by electric arc discharge to accelerate the sintering process. Despite these significant advantages, these advanced sintering technologies also face several challenges. First, the equipment required for these technologies is typically expensive and complex, significantly increasing production costs. Second, operating this advanced equipment requires a high level of technical expertise and experience, increasing the difficulty of production. Therefore, although these sintering technologies have shown great potential in laboratory research, they are currently mainly still in the laboratory research stage and have not been widely applied in actual production due to their high cost and complex operation.

[0005] In summary, as a promising semiconductor ceramic device, the improvement of ZnO varistors' manufacturing process is crucial to meeting the demands of modern electronic devices for high breakdown voltage and miniaturization. Future research will continue to explore more efficient and economical sintering processes to drive the upgrading of commercial ZnO varistors and realize their widespread application in various technological fields. Summary of the Invention

[0006] To address the aforementioned problems in existing technologies, the present invention aims to develop a high-gradient ZnO varistor ceramic and a simple low-temperature sintering method.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A ZnO varistor ceramic, the composition formula of which is:

[0009] [100-(a+b+c+d+e)]mol%ZnO+amol%Bi2O3+bmol%Co3O4+cmol%Mn2O3+dmol%Cr2O3+emol%SnO2, where 2.1≤a+b+c+d+e≤7.5. The ceramic is sintered at a sintering temperature of 800–1000℃ to obtain the voltage gradient E of the ZnO varistor ceramic. b The leakage current density is 1529–2362 V / mm, the nonlinear coefficient α is 63–86, and the leakage current density I is...L It ranges from 0.2 to 0.7 μA / cm. 2 Its performance is superior to that of commercially available ZnO varistors, and it can meet the performance requirements of varistors in actual production processes.

[0010] A simple low-temperature sintering method for ZnO varistors includes the following steps:

[0011] S1: Mixing: Take the raw powder according to the above proportions and place it in a ball mill jar. Use anhydrous ethanol zirconium balls as the medium to ball mill and mix thoroughly. Remove the mixed powder, dry it, and sieve it through a 60-mesh sieve for later use. Specifically, weigh the raw powder according to the proportions and place it in a ball mill jar. Use anhydrous ethanol or deionized water or other polar solutions as the medium to ball mill and mix evenly. After mixing, remove the mixed powder and dry it in an oven. Finally, sieve it through a 60-mesh sieve to obtain a uniformly mixed ceramic powder with a suitable particle size.

[0012] S2: Powder solid-phase reaction: The dried mixed powder from S1 is placed in a high-temperature crucible and then placed in a muffle furnace, and reacted at 800-1000℃ for 1-3 hours to obtain fully reacted ZnO-based varistor ceramic powder.

[0013] S3: Secondary mixing: Grind the ZnO-based pressure-sensitive ceramic powder in S2 into fine powder, and then put it into a ball mill jar again. Use anhydrous ethanol as the medium for ball milling for 8-24 hours. After ball milling, dry it in an oven and pass it through a 100-mesh sieve to obtain ZnO-based pressure-sensitive ceramic powder with uniform particle size.

[0014] S4: Molding: Weigh an appropriate amount of ZnO-based varistor ceramic powder from S3, use acetic acid solution of 15-30 wt% of the ZnO-based varistor ceramic powder as a wetting agent to uniformly wet the ZnO-based varistor ceramic powder, grind it thoroughly and evenly, transfer the ZnO-based varistor ceramic powder into a mold, apply a pressure of 200-500 MPa, and heat it to 200-400℃ and keep it at that temperature for 30 min-2 h to obtain a pre-densified ZnO varistor ceramic green body.

[0015] S5: Sintering: The ZnO varistor ceramic green body is placed in a muffle furnace and sintered at 800-1000℃ for 2-5 hours to obtain the ZnO varistor ceramic product. A sintering temperature of only 800-1000℃ is sufficient to obtain a potential gradient, nonlinear coefficient, and leakage current density that are far superior to varistors produced by commercial methods.

[0016] Furthermore, in S1, the mass ratio of powder, zirconium balls, and ball milling liquid media is 1:10:1.5, wherein the mass ratio of zirconium balls is 2:1:1 with a diameter of 1 cm, a diameter of 0.5 cm, and a diameter of 0.2 cm, and the high-energy ball mill speed is 380 r / min.

[0017] Furthermore, in S1, the original ZnO powder has a particle size of ~500nm, and the original Bi2O3, Co3O4, Mn2O3, Cr2O3 and SnO2 powders have particle sizes of ~100nm, ~200nm, 100~300nm, ~200nm and <250nm, respectively.

[0018] Furthermore, the ZnO varistor ceramic green body in S4 has a compaction density of over 90%.

[0019] The heating rates in S4 and S5 are 5-20℃ / min and 0.5-2℃ / min, respectively.

[0020] This invention involves three key temperatures: the first is the S2 powder solid-state reaction temperature, the second is the S4 ZnO varistor ceramic greening temperature, and the third is the S5 ceramic sintering temperature. The functions of these three temperatures are as follows:

[0021] 1. Powder Solid-Phase Reaction Temperatures: The reaction temperatures of oxides such as ZnO, Bi₂O₃, Co₃O₄, Mn₂O₃, Cr₂O₃, and SnO₂ mainly depend on the type of chemical reaction and the required activation energy. Different oxides have different reaction temperature ranges; therefore, when discussing their reaction temperatures, the following aspects can be considered:

[0022] 1) Formation temperature of Bi-rich phase: Reaction of ZnO with Bi₂O₃: ① The reaction temperature of ZnO and Bi₂O₃ is relatively low, usually between 800-900℃. At higher temperatures, they may form complex oxides such as Bi₂ZnO₄ (bismuth zinc oxide). ② The reaction of Cr₂O₃ with other oxides usually occurs above 900℃, especially when Cr₂O₃ interacts with oxides such as ZnO and Bi₂O₃, which often requires higher temperatures. This is because chromium oxide has strong chemical activity at higher temperatures and can form different chromium-based oxides or solid solutions with other metal oxides.

[0023] 2) Formation temperature of spinel phase: The reaction temperature between Co3O4 and Mn2O3 is relatively high, usually requiring 900℃ or above. Cobalt oxide and manganese oxide can undergo oxygen exchange reaction at high temperatures to form complexes such as cobalt-manganese oxides (e.g., CoMn2O4), which requires high temperatures to drive the reaction.

[0024] 3) Reactions of SnO2 with other oxides: Reactions with other metal oxides typically occur at higher temperatures, usually between 800-1000℃. At higher temperatures, tin oxide readily forms solid solutions or complexes with other oxides. For example, the reaction of SnO2 with ZnO or Bi2O3 may form perovskite-structured oxides.

[0025] In summary, relatively high temperatures are typically required to promote the reactions among these oxides. Generally, the reaction temperature range is approximately 800-1000℃, with the specific temperature depending on the specific reaction ratios and the types of oxides involved.

[0026] 2. ZnO Pressure-Sensitive Ceramic Green Forming Temperature: Traditionally, polyvinyl alcohol (PVA) is often added as a binder during ceramic forming. This necessitates the complete removal of PVA during sintering, otherwise it may affect the density and properties of the final ceramic. Furthermore, the addition of PVA can lead to cracks or pores during forming, especially at high temperatures. Additionally, improper use of PVA as a binder can result in insufficient uniformity of the formed body. This invention overcomes these drawbacks by introducing an acetic acid solution as a transient liquid phase, allowing for pressing at 300°C. This eliminates the need for binder addition and granulation, making the process simpler, more efficient, and eliminating the pre-firing and binder removal step in the subsequent sintering process.

[0027] 3. Ceramic sintering temperature: The sintering temperature of ZnO varistors is usually higher than 1100℃. However, this invention can significantly reduce the sintering temperature to below 1000℃ by sintering a high-density (>90%) original preform, which effectively controls the abnormal growth of grains and optimizes electrical performance.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. The preparation process of this invention has precise control over the stoichiometry, is relatively simple, and uses inexpensive equipment, which can significantly improve production efficiency;

[0030] 2. The molding method of the present invention eliminates the steps of adding binders and granulation in the traditional sintering method, consumes less raw materials, and reduces the cost in the production and manufacturing process;

[0031] 3. The relative density of the preform during molding of this invention is higher than 90%, which is much higher than that of the preform prepared by traditional molding methods (the relative density is usually 60%-80%). The extremely high initial density can result in a lower final sintering temperature, which can significantly reduce sintering energy consumption and is conducive to energy conservation, emission reduction and reduction of industrial production costs.

[0032] 4. The ZnO varistor ceramic prepared by this invention has excellent electrical properties and good repeatability, and can meet all the requirements for the preparation of commercial surge protection devices. Attached Figure Description

[0033] Figure 1 This is a microscopic morphology diagram of a specific embodiment of the low-temperature sintered ZnO varistor ceramic of the present invention.

[0034] Figure 2The diagram shows the nonlinear JE characteristics of a specific embodiment of the low-temperature sintered ZnO varistor ceramic of the present invention. Detailed Implementation

[0035] The present invention will be further described in detail below through specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0036] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can understand other advantages and effects of the present invention from its content. The present invention can also be applied through different implementations, and the details in this specification can be modified or adjusted according to different viewpoints and applications without changing the basic spirit of the present invention.

[0037] Please note that any process equipment or apparatus not specifically described in the following embodiments uses conventional equipment or apparatus in the art. All pressure values ​​and ranges refer to relative pressure, and the raw materials used are also conventionally used materials in the art.

[0038] Example 1: A simple low-temperature sintering method for high-gradient ZnO varistors, comprising the following steps:

[0039] (1) Mixing: According to the composition formula [100-(a+b+c+d+e)]mol% ZnO+amol% Bi2O3+bmol% Co3O4+cmol% Mn2O3+dmol% Cr2O3+emol% SnO2, where 2.1≤a+b+c+d+e≤7.5, 30g of the original powder was weighed using a precision electronic analytical balance and placed into a ball mill jar. The proportion of ZnO was 97.9mol%, and the proportions of Bi2O3, Co3O4, Mn2O3, Cr2O3 and SnO2 were 0.5mol%, 0.5mol%, 0.5mol%, 0.1mol% and 0.5mol%, respectively. Then, 300g of zirconium balls were added and 45g of anhydrous ethanol was used as the ball milling medium. The mixture was ball milled and mixed evenly in a high-energy ball mill at a speed of 380r / min. After the ball milling was completed, the mixed powder was taken out and dried in an 80℃ oven. Finally, it was sieved through a 60-mesh sieve to obtain a uniformly mixed ceramic powder with a suitable particle size.

[0040] (2) Powder solid-phase reaction: The dried mixed ceramic powder in (1) was placed in a high-temperature crucible and then placed in a muffle furnace and reacted at 800℃ for 1h to obtain fully reacted ZnO-based pressure-sensitive ceramic powder.

[0041] (3) Secondary mixing: The ZnO-based pressure-sensitive ceramic powder in (2) is ground into fine powder in a mortar and then put into a ball mill jar again and ball milled for 8 hours with anhydrous ethanol as the medium. After ball milling, it is dried in an oven and passed through a 100-mesh sieve to obtain ZnO-based pressure-sensitive ceramic powder with uniform particle size.

[0042] (4) Molding: Weigh an appropriate amount of powder from (3), use acetic acid solution of 15wt% of powder mass as wetting agent to uniformly wet the powder, grind it evenly, transfer the powder into a ceramic mold, apply uniaxial pressure of 200MPa through a manual tablet press, and apply a temperature of 400℃ to the mold through a heating jacket. The heating rate is 20℃ / min. After holding the temperature for 30min, a cylindrical ceramic green body with a diameter of 12.7mm and a height of 2mm is obtained.

[0043] (5) Sintering: The ceramic green body is placed in a muffle furnace and heated to 1000℃ at a heating rate of 2℃ / min. It is sintered for 2h to obtain ZnO varistor ceramic product.

[0044] (6) Sample testing: Through relevant tests on the ZnO varistor ceramic product in (5), the final product can achieve a relative density of 98.74% and has excellent electrical properties, voltage gradient E b The voltage is 1858.93 V / mm, the nonlinear coefficient α is 56.45, and the leakage current density I... L 0.63 μA / cm 2 .

[0045] Example 2: A simple low-temperature sintering method for high-gradient ZnO varistors, comprising the following steps:

[0046] (1) Mixing: According to the composition formula [100-(a+b+c+d+e)]mol% ZnO+amol% Bi2O3+bmol% Co3O4+cmol% Mn2O3+dmol% Cr2O3+emol% SnO2, where 2.1≤a+b+c+d+e≤7.5, 30g of the original powder was weighed using a precision electronic analytical balance and placed into a ball mill jar. The proportion of ZnO was 96.7mol%, and the proportions of Bi2O3, Co3O4, Mn2O3, Cr2O3 and SnO2 were 1.0mol%, 0.5mol%, 0.5mol%, 0.3mol% and 1.0mol%, respectively. Then, 300g of zirconium balls were added and 45g of anhydrous ethanol was used as the ball milling medium. The mixture was ball milled and mixed evenly in a high-energy ball mill at a speed of 380r / min. After the ball milling was completed, the mixed powder was taken out and dried in an 80℃ oven. Finally, it was sieved through a 60-mesh sieve to obtain a uniformly mixed ceramic powder with a suitable particle size.

[0047] (2) Powder solid-phase reaction: The dried mixed ceramic powder in (1) was placed in a high-temperature crucible and then placed in a muffle furnace and reacted at 850°C for 2 hours to obtain fully reacted ZnO-based pressure-sensitive ceramic powder.

[0048] (3) Secondary mixing: The ZnO-based pressure-sensitive ceramic powder in (2) is ground into fine powder in a mortar and then put into a ball mill jar again and ball milled for 16 hours with anhydrous ethanol as the medium. After ball milling, it is dried in an oven and passed through a 100-mesh sieve to obtain ZnO-based pressure-sensitive ceramic powder with uniform particle size.

[0049] (4) Molding: Weigh an appropriate amount of powder from (3), use acetic acid solution of 20wt% of powder mass as wetting agent to uniformly wet the powder, grind it evenly, transfer the powder into a ceramic mold, apply uniaxial pressure of 300MPa through a manual tablet press, and apply a temperature of 400℃ to the mold through a heating jacket. The heating rate is 15℃ / min. After holding for 2 hours, a cylindrical ceramic green body with a diameter of 12.7mm and a height of 2mm is obtained.

[0050] (5) Sintering: The ceramic green body is placed in a muffle furnace and heated to 850°C at a heating rate of 2°C / min. It is sintered for 3 hours to obtain ZnO varistor ceramic products.

[0051] (6) Sample testing: Through relevant tests on the ZnO varistor ceramic product in (5), the final product can achieve a relative density of 98.65% and has excellent electrical properties, voltage gradient E b The voltage is 2232.48 V / mm, the nonlinear coefficient α is 60.81, and the leakage current density I... L 0.66 μA / cm 2 .

[0052] Example 3: A simple low-temperature sintering method for high-gradient ZnO varistors, comprising the following steps:

[0053] (1) Mixing: According to the composition formula [100-(a+b+c+d+e)]mol% ZnO+amol% Bi2O3+bmol% Co3O4+cmol% Mn2O3+dmol% Cr2O3+emol% SnO2, where 2.1≤a+b+c+d+e≤7.5, 30g of the original powder was weighed using a precision electronic analytical balance and placed into a ball mill jar. The proportion of ZnO was 94.75mol%, and the proportions of Bi2O3, Co3O4, Mn2O3, Cr2O3 and SnO2 were 1.5mol%, 1.0mol%, 0.75mol%, 0.5mol% and 1.5mol%, respectively. Then, 300g of zirconium balls were added and 45g of anhydrous ethanol was used as the ball milling medium. The mixture was ball milled and mixed evenly in a high-energy ball mill at a speed of 380r / min. After the ball milling was completed, the mixed powder was taken out and dried in an 80℃ oven. Finally, it was sieved through a 60-mesh sieve to obtain a uniformly mixed ceramic powder with a suitable particle size.

[0054] (2) Powder solid-phase reaction: The dried mixed ceramic powder in (1) was placed in a high-temperature crucible and then placed in a muffle furnace and reacted at 900℃ for 2h to obtain fully reacted ZnO-based pressure-sensitive ceramic powder;

[0055] (3) Secondary mixing: The ZnO-based pressure-sensitive ceramic powder in (2) is ground into fine powder in a mortar and then put into a ball mill jar again and ball milled for 16 hours with anhydrous ethanol as the medium. After ball milling, it is dried in an oven and passed through a 100-mesh sieve to obtain ZnO-based pressure-sensitive ceramic powder with uniform particle size.

[0056] (4) Molding: Weigh an appropriate amount of powder from (3), use acetic acid solution of 20wt% of powder mass as wetting agent to uniformly wet the powder, grind it evenly, transfer the powder into a ceramic mold, apply uniaxial pressure of 300MPa through a manual tablet press, and apply a temperature of 300℃ to the mold through a heating jacket. The heating rate is 10℃ / min. After holding for 1h, a cylindrical ceramic green body with a diameter of 12.7mm and a height of 2mm is obtained.

[0057] (5) Sintering: The ceramic green body is placed in a muffle furnace and heated to 900°C at a heating rate of 1°C / min. It is sintered for 3 hours to obtain ZnO varistor ceramic products.

[0058] (6) Sample testing: Through relevant tests on the ZnO varistor ceramic product in (5), the final product can achieve a relative density of 97.95% and has excellent electrical properties, voltage gradient E b The voltage is 1943.53 V / mm, the nonlinear coefficient α is 73.42, and the leakage current density I... L 0.31 μA / cm 2 .

[0059] Example 4: A simple low-temperature sintering method for high-gradient ZnO varistors, comprising the following steps:

[0060] (1) Mixing: According to the composition formula [100-(a+b+c+d+e)]mol% ZnO+amol% Bi2O3+bmol% Co3O4+cmol% Mn2O3+dmol% Cr2O3+emol% SnO2, where 2.1≤a+b+c+d+e≤7.5, 30g of the original powder was weighed using a precision electronic analytical balance and placed into a ball mill jar. The proportion of ZnO was 93.75mol%, and the proportions of Bi2O3, Co3O4, Mn2O3, Cr2O3 and SnO2 were 2.0mol%, 1.5mol%, 0.75mol%, 0.5mol% and 1.5mol%, respectively. Then, 300g of zirconium balls were added and 45g of anhydrous ethanol was used as the ball milling medium. The mixture was ball milled and mixed evenly in a high-energy ball mill at a speed of 380r / min. After the ball milling was completed, the mixed powder was taken out and dried in an 80℃ oven. Finally, it was sieved through a 60-mesh sieve to obtain a uniformly mixed ceramic powder with a suitable particle size.

[0061] (2) Powder solid-phase reaction: The dried mixed ceramic powder in (1) was placed in a high-temperature crucible and then placed in a muffle furnace and reacted at 950°C for 3 hours to obtain fully reacted ZnO-based pressure-sensitive ceramic powder.

[0062] (3) Secondary mixing: The ZnO-based pressure-sensitive ceramic powder in (2) is ground into fine powder in a mortar and then put into a ball mill jar again and ball milled for 24 hours with anhydrous ethanol as the medium. After ball milling, it is dried in an oven and passed through a 100-mesh sieve to obtain ZnO-based pressure-sensitive ceramic powder with uniform particle size.

[0063] (4) Molding: Weigh an appropriate amount of powder from (3), use acetic acid solution of 30wt% of powder mass as wetting agent to uniformly wet the powder, grind it evenly, transfer the powder into a ceramic mold, apply uniaxial pressure of 400MPa through a manual tablet press, and apply a temperature of 300℃ to the mold through a heating jacket. The heating rate is 10℃ / min. After holding for 2 hours, a cylindrical ceramic green body with a diameter of 12.7mm and a height of 2mm is obtained.

[0064] (5) Sintering: The ceramic green body is placed in a muffle furnace and heated to 800°C at a heating rate of 1°C / min. It is sintered for 5 hours to obtain ZnO varistor ceramic products.

[0065] (6) Sample testing: Through relevant tests on the ZnO varistor ceramic product in (5), the final product can achieve a relative density of 97.95% and has excellent electrical properties, voltage gradient Eb The voltage is 2035.82 V / mm, the nonlinear coefficient α is 85.61, and the leakage current density I... L 0.23 μA / cm 2 .

[0066] Example 5: A simple low-temperature sintering method for high-gradient ZnO varistors, comprising the following steps:

[0067] (1) Mixing: According to the composition formula [100-(a+b+c+d+e)]mol% ZnO+amol% Bi2O3+bmol% Co3O4+cmol% Mn2O3+dmol% Cr2O3+emol% SnO2, where 2.1≤a+b+c+d+e≤7.5, 30g of the original powder was weighed using a precision electronic analytical balance and placed into a ball mill jar. The proportion of ZnO was 92.5mol%, and the proportions of Bi2O3, Co3O4, Mn2O3, Cr2O3 and SnO2 were 2.0mol%, 1.5mol%, 1.0mol%, 1.0mol%, and 2.0mol%, respectively. Then, 300g of zirconium balls were added and 45g of anhydrous ethanol was used as the ball milling medium. The mixture was ball milled and mixed evenly in a high-energy ball mill at a speed of 380r / min. After the ball milling was completed, the mixed powder was taken out and dried in an 80℃ oven. Finally, it was sieved through a 60-mesh sieve to obtain a uniformly mixed ceramic powder with a suitable particle size.

[0068] (2) Powder solid-phase reaction: The dried mixed ceramic powder in (1) was placed in a high-temperature crucible and then placed in a muffle furnace and reacted at 1000℃ for 2h to obtain fully reacted ZnO-based pressure-sensitive ceramic powder;

[0069] (3) Secondary mixing: The ZnO-based pressure-sensitive ceramic powder in (2) is ground into fine powder in a mortar and then put into a ball mill jar again and ball milled for 24 hours with anhydrous ethanol as the medium. After ball milling, it is dried in an oven and passed through a 100-mesh sieve to obtain ZnO-based pressure-sensitive ceramic powder with uniform particle size.

[0070] (4) Molding: Weigh an appropriate amount of powder from (3), use acetic acid solution of 30wt% of powder mass as wetting agent to uniformly wet the powder, grind it evenly, transfer the powder into a ceramic mold, apply uniaxial pressure of 500MPa through a manual tablet press, and apply a temperature of 200℃ to the mold through a heating jacket. The heating rate is 5℃ / min. After holding the temperature for 30min, a cylindrical ceramic green body with a diameter of 12.7mm and a height of 2mm is obtained.

[0071] (5) Sintering: The ceramic green body is placed in a muffle furnace and heated to 900°C at a heating rate of 0.5°C / min. It is sintered for 3 hours to obtain ZnO varistor ceramic products.

[0072] (6) Sample testing: Through relevant tests on the ZnO varistor ceramic product in (5), the final product can achieve a relative density of 97.95% and has excellent electrical properties, voltage gradient E b The value is 1600.53 V / mm, the nonlinear coefficient α is 74.72, and the leakage current density I... L 0.45 μA / cm 2 .

[0073] Table 1 Performance parameters of ZnO varistors under different conditions and formulations

[0074]

[0075]

[0076] See Figure 1 , Figure 2 Based on the experimental results described in Table 1, we can identify the following experimental patterns:

[0077] 1) The voltage gradient of ZnO varistors decreases continuously with increasing sintering temperature. As the sintering temperature rises, the grain growth rate accelerates, leading to an increase in grain size. According to the conductivity mechanism of varistors, a larger grain size reduces the number of grain boundaries, thereby lowering the grain boundary barrier and making it easier for electrons to cross the grain boundaries, thus resulting in a decrease in the voltage gradient.

[0078] 2) The nonlinear coefficient of ZnO varistors decreases with increasing sintering temperature. As the sintering temperature rises, the growth of ZnO grains and the volatilization of some dopants (bismuth oxide has a melting point of 825℃) lead to changes in the grain boundary structure. Grain boundaries are key regions determining the nonlinear characteristics of varistors. At high temperatures, changes in defect concentration and grain boundary phase composition at grain boundaries lower the grain boundary barrier, thus reducing the nonlinear coefficient.

[0079] 3) By comparing the performance data of different formulations at the same or similar sintering temperatures, the contribution of each component to the performance of the varistor ceramic can be evaluated. For example, comparing Examples 3 and 5 (both sintered at 900℃), with the increase of the content of components such as Bi2O3, Cr2O3, and SnO2, the voltage gradient increases, the nonlinear coefficient changes slightly, and the leakage current density increases. This indicates that changes in the content of these components have a significant impact on performance, and the formulation composition can be further optimized according to actual needs to obtain the best performance.

Claims

1. A simplified low-temperature sintering method for high-gradient ZnO varistors, characterized in that, The compositional formula of the ZnO varistor ceramic is: [100-(a+b+c+d+e)]mol%ZnO+amol%Bi2O3+bmol%Co3O4+cmol%Mn2O3+dmol%Cr2O3+emol%SnO2, where 2.1≤a+b+c+d+e≤7.5, and includes the following steps: S1: Mixing: Take the original powder according to the proportion in the composition expression of ZnO varistor ceramic, put it into a ball mill jar, and mix it thoroughly with anhydrous ethanol and zirconium balls as the ball milling medium. Take out the mixed powder and dry it. Then, sieve it through a 60-mesh sieve for later use. S2: Powder solid-state reaction: The mixed powder prepared in S1 is placed in a high-temperature crucible and then placed in a muffle furnace, and reacted at a temperature of 800-1000℃ for 1-3 hours to obtain fully reacted ZnO-based varistor ceramic powder. S3: Secondary mixing: Grind the ZnO-based pressure-sensitive ceramic powder in S2 into fine powder, and then put it into a ball mill jar again. Use anhydrous ethanol as the medium for ball milling for 8-24 hours. After ball milling, dry it in an oven and pass it through a 100-mesh sieve to obtain ZnO-based pressure-sensitive ceramic powder with uniform particle size. S4: Molding: Weigh an appropriate amount of ZnO-based varistor ceramic powder from S3, use an acetic acid solution accounting for 15-30 wt% of the ZnO-based varistor ceramic powder as a wetting agent to uniformly wet the ZnO-based varistor ceramic powder, grind it thoroughly and evenly, transfer the ZnO-based varistor ceramic powder into a mold, apply a pressure of 200-500 MPa, and heat it to 200-400℃ and keep it at that temperature for 30 min-2 h to obtain a pre-densified ZnO varistor ceramic green body; S5: Sintering: Place the ZnO varistor ceramic green body into a muffle furnace and sinter at a sintering temperature of 800-1000℃ for 2-5 hours to obtain the ZnO varistor ceramic product.

2. The simplified low-temperature sintering method for high-gradient ZnO varistors as described in claim 1, characterized in that: In S1, the mass ratio of powder, zirconium balls, and anhydrous ethanol medium is 1:10:1.5, wherein the mass ratio of zirconium balls is 2:1:1 with a diameter of 1 cm, a diameter of 0.5 cm, and a diameter of 0.2 cm, and the high-energy ball mill speed is 380 r / min.

3. The simplified low-temperature sintering method for high-gradient ZnO varistors as described in claim 1, characterized in that: The original ZnO powder in S1 has a particle size of ~500nm, and the original Bi2O3, Co3O4, Mn2O3, Cr2O3 and SnO2 powders have particle sizes of ~100nm, ~200nm, 100~300nm, ~200nm and <250nm, respectively.

4. A simplified low-temperature sintering method for high-gradient ZnO varistors as described in claim 1, characterized in that: The ZnO varistor ceramic green body in S4 has a density of over 90%.

5. A simplified low-temperature sintering method for high-gradient ZnO varistors as described in claim 1, characterized in that: The heating rates in S4 and S5 are 5-20℃ / min and 0.5-2℃ / min, respectively.

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