A pressure-sensitive ceramic and a method for preparing and using the same

Abstract

The application belongs to the technical field of piezoelectric ceramic material preparation, and particularly relates to a piezoelectric ceramic, a preparation method and application thereof. The preparation method comprises (1) obtaining a granulating material containing zinc oxide, pre-pressing forming to obtain a green body; the granulating material containing zinc oxide further comprises Bi2O3, Sb2O3 and SiO2; (2) the green body is sequentially subjected to glue removal sintering, first sintering, second sintering, third sintering and cooling; wherein the first sintering comprises heating at a heating rate of 80-100 ℃ / h to 650-850 ℃ and then keeping for 1-3 h; the second sintering is at a temperature of 1100-1200 ℃; and the third sintering is at a temperature of 800-900 ℃. The application controls the first sintering process, which is conducive to improving the comprehensive performance of the zinc oxide resistor disc.

Description

Technical Field

[0001] This invention belongs to the field of pressure-sensitive ceramic material preparation technology, and particularly relates to a pressure-sensitive ceramic, its preparation method and application. Background Technology

[0002] Zinc oxide varistors, as components in the field of lightning surge protection, have a strong structure-property relationship between their electrical performance parameters and microstructure characteristics. This relationship directly determines the reliability of the components in power system overvoltage protection.

[0003] In zinc oxide varistors, the Zn₂Sb₂O₇ and Zn₂SiO₄ spinel phases are key second phases in the ceramic system. Their role is to hinder the abnormal growth of the zinc oxide main grains through a "pinning effect." Therefore, it is necessary to control the particle size of the spinel phase and ensure its uniform distribution at the grain boundaries. Traditional sintering processes result in insufficient nucleation density and uncontrolled growth rate of the spinel phase, ultimately forming coarse particles. This abnormal growth causes the spinel phase to lose its pinning ability, failing to inhibit the abnormal growth of the zinc oxide main grains. This allows the zinc oxide main grains to continue growing at high temperatures, resulting in uneven grain size distribution and reduced thermal conductivity. When subjected to high current flow or impact, localized heat concentration can easily occur, leading to grain boundary breakdown or grain fragmentation. Furthermore, Bi₂O₃, a key sintering aid and grain boundary modifier in zinc oxide varistors, is continuously volatilized in traditional processes before fully participating in grain boundary construction, resulting in a volatilization rate exceeding 15%. The large loss of Bi2O3 leads to an imbalance in the composition of the grain boundary phase, which in turn causes a significant increase in leakage current. At the same time, the nonlinear coefficient also decreases significantly as the potential barrier decreases, severely weakening the overvoltage response sensitivity of the device. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a pressure-sensitive ceramic, its preparation method, and its application.

[0005] In a first aspect, the present invention provides a method for preparing piezoresistive ceramics, comprising the following steps: (1) Obtain granules containing zinc oxide, pre-press them to obtain a green body; the granules containing zinc oxide also include Bi2O3, Sb2O3 and SiO2; (2) The blank is sequentially subjected to debinding sintering, first sintering, second sintering and third sintering, and then cooled down; wherein, the first sintering includes heating to 650℃~850℃ at a heating rate of 80℃ / h~100℃ / h and then holding at that temperature for 1~3h; the temperature of the second sintering is 1100℃~1200℃; and the temperature of the third sintering is 800℃~900℃.

[0006] As an optional implementation, the temperature of the first sintering is 720~780℃.

[0007] As an optional implementation, the heating rate of the second sintering is 50℃ / h to 70℃ / h.

[0008] As an optional implementation, the third sintering includes cooling to 800℃~900℃ at a cooling rate of 50℃ / h~70℃ / h and then holding at that temperature for 6h~10h. As an optional implementation, the cooling includes cooling to room temperature at a cooling rate of 30°C / h to 50°C / h.

[0009] As an optional implementation, the debinding sintering includes heating to 250℃~350℃ at a heating rate of 100℃ / h~200℃ / h, then heating to 400℃~500℃ at a heating rate of 40℃ / h~80℃ / h, holding at that temperature for 2h~4h, and then cooling down with the furnace.

[0010] As an optional implementation, the zinc oxide-containing granulated material includes zinc oxide, dopants, and additives; As an optional implementation, the zinc oxide has a particle size of 0.2 μm to 0.5 μm; As an optional implementation, the dopant includes at least one of Bi2O3, Sb2O3, Ga2O3, NiO, SiO2, MnO2, Cr2O3, Co2O3, Al(NO3)3·9H2O, and silver glass powder; As an optional implementation, the additives include at least one of dispersants, defoamers, and binders.

[0011] As an optional implementation, the molar ratio of zinc oxide, Bi2O3, Sb2O3, Ga2O3, NiO, SiO2, MnO2, Cr2O3, Co2O3, Al(NO3)3·9H2O, and silver glass powder is (88.0~96.0):(0.5~2.5):(0.2~2.5):(0.1~1.0):(0.3~1.5):(0.3~1.2):(0.2~1.5):(0.2~1.0):(0.5~2.0):(0.05~0.3):(0.01~0.30). As an optional implementation, based on the mass of zinc oxide as 100%, the amount of dispersant added is 0.5wt% to 1.5wt%, the amount of defoamer added is 0.1wt% to 1wt%, and the amount of binder added is 5wt% to 6wt%.

[0012] As an optional implementation, the granulated powder has a mesh size of 80 to 200 mesh; As an optional implementation, the parameters for the pre-compression molding include: pressure of 100MPa~200MPa, holding time of 5s~30s, and molding density of 3.0g / cm³. 3 ~3.6g / cm 3 .

[0013] Secondly, the present invention provides a pressure-sensitive ceramic prepared by the above-described preparation method.

[0014] Secondly, the present invention provides the application of the varistor ceramic prepared by the above preparation method in lightning protection insulators or overvoltage protection of power equipment.

[0015] The technical solution provided by the embodiments of the present invention has the following advantages compared with the prior art: 1. The present invention provides a method for preparing pressure-sensitive ceramics, comprising (1) obtaining granules containing zinc oxide, pre-pressing them to obtain a green body; wherein the granules containing zinc oxide further include Bi2O3, Sb2O3 and SiO2; (2) the green body is subjected to debinding sintering, first sintering, second sintering and third sintering in sequence, and then cooled; wherein the first sintering includes heating to 650℃~850℃ at a heating rate of 80℃ / h~100℃ / h and holding for 1~3h; the temperature of the second sintering is 1100℃~1200℃; and the temperature of the third sintering is 800℃~900℃. This invention introduces a first sintering step in the preparation of zinc oxide varistors. On the one hand, it regulates the nucleation and initial growth of the spinel phases Zn2Sb2O7 and Zn2SiO4 to ensure appropriate particle size, thus solving the problems of excessively large spinel particle size and uncontrolled growth in traditional processes. On the other hand, the spinel phase can be evenly distributed at the grain boundaries to exert optimal pinning effect, thereby regulating the zinc oxide grains, inhibiting abnormal growth of the main zinc oxide grains, improving the thermal conductivity of the zinc oxide varistors, reducing local heat concentration when encountering large current flow or impact, and preventing grain boundary breakdown or grain fragmentation. On the other hand, Bi₂O₃ has a melting point close to 825℃. The first sintering can reduce the high-temperature volatilization of Bi₂O₃, allowing it to fully participate in grain boundary construction, effectively ensuring the integrity and uniformity of the grain boundary phase composition, improving grain boundary stability, preventing the collapse of the grain boundary barrier due to Bi element loss, improving aging performance, and suppressing problems such as a significant increase in leakage current, a decrease in nonlinear coefficient, and weakened overvoltage response sensitivity of components. Simultaneously, the reduced Bi₂O₃ volatilization also helps suppress spinel phase agglomeration, thereby improving the spinel pinning effect and inhibiting excessively large zinc oxide grain size. In summary, heating to 650℃~850℃ at a heating rate of 80℃ / h~100℃ / h followed by holding for 1~3 hours, this sintering temperature is within the optimal range for zinc oxide lattice activation and slow ion diffusion, which can promote Sb³⁺ ion diffusion. + Si 4+By gradually penetrating the zinc oxide lattice, uniform spinel phase nuclei of the smallest scale are formed through solid solution-desolution reaction. During subsequent sintering, these nuclei can refine the zinc oxide grains to 4.93 μm through the "pinning effect", which significantly reduces the standard deviation of grain size distribution. They can also promote the formation of a low-melting-point eutectic phase between Bi2O3 and zinc oxide and spinel phase, which encapsulates the zinc oxide particles and minimizes the volatilization of Bi element (volatilization amount <3%). Moreover, the eutectic phase can spread into a continuous and uniform grain boundary insulating layer at high temperature, making the electric field distribution more uniform and thus improving the overall performance of zinc oxide resistor sheet.

[0016] Compared to resistors produced by traditional processes, this invention can simultaneously optimize the performance indicators of zinc oxide resistors, such as voltage gradient, nonlinear coefficient, and square wave current capacity. The leakage current and residual voltage ratio are significantly reduced, and the performance stability is good after being subjected to strong impacts. This indicates that zinc oxide resistors have better overvoltage protection, lower operating losses, and stronger anti-aging capabilities, making them suitable for scenarios with extremely high reliability requirements. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 These are X-ray diffraction patterns of zinc oxide resistor sheets obtained in Examples 1-3 and Comparative Examples 1-2 of the present invention; Figure 2 These are microscopic morphology diagrams and grain size distribution diagrams of the zinc oxide resistor sheets obtained in Embodiment 1 and Comparative Examples 1-2 of the present invention. Figure 3 These are voltage-current characteristic curves of the zinc oxide resistive sheets obtained in Examples 1-3 and Comparative Examples 1-2 of the present invention; Figure 4 These are DC aging curves of zinc oxide resistors obtained in Examples 1-3 and Comparative Examples 1-2 of the present invention. Detailed Implementation

[0020] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0021] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0022] In a first aspect, the present invention provides a method for preparing pressure-sensitive ceramics, comprising the following steps: (1) Obtain granules containing zinc oxide, pre-press them to obtain a green body; the granules containing zinc oxide also include Bi2O3, Sb2O3 and SiO2; (2) The blank is sequentially subjected to debinding sintering, first sintering, second sintering and third sintering, and then cooled down; wherein, the first sintering includes heating to 650℃~850℃ at a heating rate of 80℃ / h~100℃ / h and then holding at that temperature for 1~3h; the temperature of the second sintering is 1100℃~1200℃; and the temperature of the third sintering is 800℃~900℃.

[0023] This invention introduces a first sintering step in the preparation of zinc oxide varistors. On the one hand, it regulates the nucleation and initial growth of the spinel phases Zn2Sb2O7 and Zn2SiO4 to ensure appropriate particle size, thus solving the problems of excessively large spinel particle size and uncontrolled growth in traditional processes. On the other hand, the spinel phase can be evenly distributed at the grain boundaries to exert optimal pinning effect, thereby regulating the zinc oxide grains, inhibiting abnormal growth of the main zinc oxide grains, improving the thermal conductivity of the zinc oxide varistors, reducing local heat concentration when encountering large current flow or impact, and preventing grain boundary breakdown or grain fragmentation. On the other hand, Bi₂O₃ has a melting point close to 825℃. The first sintering can reduce the high-temperature volatilization of Bi₂O₃, allowing it to fully participate in grain boundary construction, effectively ensuring the integrity and uniformity of the grain boundary phase composition, improving grain boundary stability, preventing the collapse of the grain boundary barrier due to Bi element loss, improving aging performance, and suppressing problems such as a significant increase in leakage current, a decrease in nonlinear coefficient, and weakened overvoltage response sensitivity of components. Simultaneously, the reduced Bi₂O₃ volatilization also helps suppress spinel phase agglomeration, thereby improving the spinel pinning effect and inhibiting excessively large zinc oxide grain size. In summary, heating to 650℃~850℃ at a heating rate of 80℃ / h~100℃ / h followed by holding for 1~3 hours, this sintering temperature is within the optimal range for zinc oxide lattice activation and slow ion diffusion, which can promote Sb³⁺ ion diffusion. + Si 4+By gradually penetrating the zinc oxide lattice, uniform spinel phase nuclei of the smallest scale are formed through solid solution-desolution reaction. During subsequent sintering, these nuclei can refine the zinc oxide grains to 4.93 μm through the "pinning effect", which significantly reduces the standard deviation of grain size distribution. They can also promote the formation of a low-melting-point eutectic phase between Bi2O3 and zinc oxide and spinel phase, which encapsulates the zinc oxide particles and minimizes the volatilization of Bi element (volatilization amount <3%). Moreover, the eutectic phase can spread into a continuous and uniform grain boundary insulating layer at high temperature, making the electric field distribution more uniform and thus improving the overall performance of zinc oxide resistor sheet.

[0024] Compared to resistors produced by traditional processes, this invention can simultaneously optimize the performance indicators of zinc oxide resistors, such as voltage gradient, nonlinear coefficient, and square wave current capacity. The leakage current and residual voltage ratio are significantly reduced, and the performance stability is good after being subjected to strong impacts. This indicates that zinc oxide resistors have better overvoltage protection, lower operating losses, and stronger anti-aging capabilities, making them suitable for scenarios with extremely high reliability requirements.

[0025] For example, the first sintering temperature is 650°C, 680°C, 700°C, 720°C, 750°C, 780°C, 800°C, 820°C, 850°C, or any value within this range. The second sintering temperature is 1100°C, 1120°C, 1140°C, 1160°C, 1180°C, 1200°C, or any value within this range. The third sintering temperature is 800°C, 820°C, 840°C, 860°C, 880°C, 1000°C, or any value within this range.

[0026] As an optional implementation, the first sintering temperature is 720℃~780℃. Controlling the first sintering temperature within this range is more conducive to optimizing zinc oxide grains, reducing Bi volatilization, and further improving the overall performance of the zinc oxide resistor sheet.

[0027] As an optional implementation, the heating rate of the second sintering is 50℃ / h~70℃ / h, which is beneficial to further control the zinc oxide grains and their density, reduce porosity, and improve grain boundary uniformity, thereby further improving the electrical properties of the zinc oxide resistor sheet, such as varistor voltage, leakage current and current carrying capacity.

[0028] As an optional implementation, the third sintering includes cooling to 800℃~900℃ at a cooling rate of 50℃ / h~70℃ / h and then holding at that temperature for 6h~10h. This is beneficial for controlling the size of zinc oxide grains and the distribution of grain boundaries, the number of grain boundary defects, reducing internal stress, and optimizing the uniformity of grain boundary barriers, thereby improving leakage current, aging performance and potential gradient.

[0029] As an optional implementation, the cooling includes cooling to room temperature at a cooling rate of 30°C / h to 50°C / h.

[0030] As an optional implementation, the debinding sintering includes heating to 250℃~350℃ at a heating rate of 100℃ / h~200℃ / h, then heating to 400℃~500℃ at a heating rate of 40℃ / h~80℃ / h, holding at that temperature for 2h~4h, and then cooling down with the furnace.

[0031] As an optional implementation, the zinc oxide-containing granulated material includes zinc oxide, dopants, and additives; Preferably, the zinc oxide has a particle size of 0.2 μm to 0.5 μm; Preferably, the dopant includes at least one of Bi2O3, Sb2O3, Ga2O3, NiO, SiO2, MnO2, Cr2O3, Co2O3, Al(NO3)3·9H2O, and silver glass powder; Preferably, the additives include at least one of dispersants, defoamers, and binders.

[0032] As an optional implementation, the molar ratio of zinc oxide, Bi2O3, Sb2O3, Ga2O3, NiO, SiO2, MnO2, Cr2O3, Co2O3, Al(NO3)3·9H2O, and silver glass powder is (88.0~96.0):(0.5~2.5):(0.2~2.5):(0.1~1.0):(0.3~1.5):(0.3~1.2):(0.2~1.5):(0.2~1.0):(0.5~2.0):(0.05~0.3):(0.01~ 0.30); For example, the molar ratio is 88:2.5:0.2:1:0.3:1.2:0.2:1:0.5:0.3:0.01, 96:0.5:2.4:0.11:1.4:0.3:1.5:0.2:2:0.05:0.3, 92:1.5:1.5:0.5:0.9:0.8:0.8:0.6:1.2:0.17:0.16, 90:1:2:0.8:0.5:0.5:1:0.8:0.8:0.2:0.1 or any ratio within this range.

[0033] As an optional implementation, based on the mass of zinc oxide as 100%, the amount of dispersant added is 0.5wt% to 1.5wt%, the amount of defoamer added is 0.1wt% to 1wt%, and the amount of binder added is 5wt% to 6wt%. Exemplarily, the dispersant is a known dispersant in the art, such as ammonium polymethacrylate; the defoamer is a known defoamer in the art, such as tributyl phosphate; and the binder is a known binder in the art, such as a polyvinyl alcohol (PVA) solution with a concentration of 5wt%.

[0034] As an optional implementation, the granulated powder has a mesh size of 80 to 200 mesh.

[0035] As an optional implementation method, the zinc oxide-containing granules can be prepared in-house or purchased commercially; optionally, the steps for obtaining zinc oxide-containing granules include: mixing raw materials to obtain a slurry; and granulating by spray drying, wherein the spray drying parameters include: an inlet temperature of 200℃~250℃, an outlet temperature of 120℃~150℃, and a rotation speed of 7000rpm~10000rpm.

[0036] As an optional implementation, the raw material mixing includes primary sand milling and secondary sand milling. The primary sand milling speed is 1500 rpm to 3000 rpm and the time is 5 min to 15 min. The secondary sand milling speed is 1500 rpm to 3000 rpm and the time is 30 min to 60 min.

[0037] As an optional implementation, the particle size of the slurry is no greater than 0.5 μm.

[0038] As an optional implementation, the parameters for the pre-compression molding include: pressure of 100MPa~200MPa, holding time of 5s~30s, and molding density of 3.0g / cm³. 3 ~3.6g / cm 3 .

[0039] As an optional implementation, the cooling process also includes steps such as grinding, heat treatment, and aluminum electrode spraying. Optionally, the heat treatment step includes heating to 500℃~600℃ at a heating rate of 80℃ / h~100℃ / h, holding at that temperature for 2h~4h, and then cooling to 150℃~250℃ at a cooling rate of 20℃ / h~40℃ / h, with the furnace being cooled.

[0040] The method for preparing zinc oxide resistor sheets provided by this invention has strong industrial adaptability. By adding a first sintering step to the traditional sintering process, the process stability and repeatability are outstanding. Compared with the chemical coprecipitation method, which requires a large amount of acid-base regulators and generates heavy metal waste liquid, the preparation method of this invention is more environmentally friendly.

[0041] Secondly, the present invention provides a pressure-sensitive ceramic prepared by the above-described preparation method.

[0042] Thirdly, the present invention provides the application of the varistor ceramic prepared by the above-mentioned method in lightning protection insulators or overvoltage protection of power equipment.

[0043] The zinc oxide varistor ceramic of this invention can be applied to high-end scenarios such as lightning protection insulators for distribution networks and overvoltage protection for power equipment, meeting the requirements of these scenarios for ceramics to be impact-resistant, have low leakage current, and have a high nonlinear coefficient.

[0044] In this invention, room temperature is typically expressed as 25±2℃, and all pressures are gauge pressures.

[0045] The raw materials used in the following examples and comparative examples are all commercially available.

[0046] Example 1 This embodiment provides a method for preparing pressure-sensitive ceramics, including the following steps: (1) SiO2 is milled to a median particle size D50 of 0.3μm-0.4μm and then set aside.

[0047] Bi₂O₃, Sb₂O₃, Ga₂O₃, NiO, MnO₂, Cr₂O₃, Co₂O₃, Al(NO₃)₃·9H₂O, and silver glass powder were mixed, water was added, and then milled SiO₂ was added. The mixture was ultrasonically dispersed at 300W for 20 min, followed by a first milling at 1500 rpm for 10 min, with a solid-liquid ratio of approximately 1:1. Zinc oxide (particle size 0.2 μm~0.5 μm), ammonium polymethyl methacrylate, tributyl phosphate, PVA solution, and water were then added, followed by a second milling at 3000 rpm for 30 min, with a solid-liquid ratio of approximately 1:1. After the second milling, a slurry with a particle size not exceeding 0.5 μm was obtained.

[0048] The molar ratio of zinc oxide, Bi₂O₃, Sb₂O₃, Ga₂O₃, NiO, SiO₂, MnO₂, Cr₂O₃, Co₂O₃, Al(NO₃)₃·9H₂O, and silver glass powder is 94.8:0.7:0.7:0.25:0.5:1:0.6:0.35:0.85:0.1:0.15. Based on 100wt% zinc oxide, the composition includes 1.0wt% polymethyl methacrylate (HDA-698), 0.2wt% tributyl phosphate, and 5.5wt% PVA solution (5wt% concentration).

[0049] (2) The slurry was granulated by spray drying. The spray drying parameters included an inlet temperature of 220℃±10℃, an outlet temperature of 135℃±10℃, and a rotation speed of 8000rpm. After passing through an 80~200 mesh sieve, granulated powder was obtained. The granulated powder was then pressed into flakes to obtain the green body. The pressing pressure was 150MPa, the holding time was 20s, and the molding density was 3.2g / cm³. 3 .

[0050] (3) The blank is debinded and sintered. The debinding and sintering process includes heating at a rate of 150℃ / h to 300℃, then heating at a rate of 60℃ / h to 450℃, holding for 3h, and then cooling down in the furnace. Then, the blank is heated from room temperature to 750℃ at a rate of 90℃ / h and held for 2h. This process is the first sintering. After holding, the blank is heated at a rate of 60℃ / h to 1150℃. This process is the second sintering. Then, the blank is cooled down to 850℃ at a rate of 60℃ / h and held for 8h. This process is the third sintering. After holding, the blank is cooled down to room temperature at a rate of 40℃ / h.

[0051] (4) Ethanol, butyl carbitol and ethyl cellulose were mixed at a ratio of 100ml:10ml:2.5g to prepare an adhesive for later use. The glass glaze and adhesive were mixed to form a glass glaze slurry. The glass glaze slurry was sprayed onto the side of the sintered blank. Then, the temperature was raised to 550℃ at a heating rate of 90℃ / h and held for 3h. The temperature was then lowered to 200℃ at a cooling rate of 30℃ / h. The furnace was cooled and aluminum electrodes were sputtered to obtain the finished resistor sheet.

[0052] Example 2 This embodiment provides a method for preparing pressure-sensitive ceramics, which is basically the same as that in Embodiment 1, except that the temperature of the first sintering is adjusted to 700°C.

[0053] Example 3 This embodiment provides a method for preparing pressure-sensitive ceramics, which is basically the same as that in Embodiment 1, except that the temperature of the first sintering is adjusted to 800°C.

[0054] Comparative Example 1 This comparative example provides a method for preparing pressure-sensitive ceramics, which is basically the same as that in Example 1, except that the first sintering step is omitted and a second sintering is performed after the binder removal sintering is completed.

[0055] Comparative Example 2 This comparative example provides a method for preparing pressure-sensitive ceramics, which is basically the same as that in Example 1. The main difference is that the first and third sintering steps are omitted, and a second sintering is performed after the binder removal sintering is completed. After the second sintering is completed, the temperature is lowered to room temperature at a rate of 40℃ / h.

[0056] Test case This test example provides the performance test results of the varistors prepared in each embodiment and comparative example. The performance of the zinc oxide resistor was tested according to the IEC61643-11:2011 standard. When testing each performance of the zinc oxide resistor, the number of samples for each performance was 5, and the average value was recorded as the performance result, as follows: Voltage gradient (U) 1mA ): Refer to the above standard and conduct the test using a 1mA voltage testing device.

[0057] Leakage current (I L ), nonlinear coefficient (α), U after 100kA / 4 / 10μs impact 1mA The rate of change and grain size were tested according to the above standards.

[0058] Residual pressure ratio K 10kA Referring to the above standard, a residual voltage test was performed at a nominal discharge current of 10kA for 4 / 10µs to obtain the residual voltage value U of the resistor. 10kA Its relationship with U 1mA The ratio is defined as the residual pressure ratio, denoted as K. 10kA .

[0059] 2ms Square Wave Current Capacity: Each sample undergoes 18 current surges of a 2ms square wave with a specific amplitude. These 18 surges are divided into 6 groups of 3 surges each, with a 60s interval between each surge. The time interval between groups is the time it takes for the sample to cool to room temperature. The oscilloscope simultaneously records the voltage and current waveforms. Only when the sample can withstand all the current surges without cracking, perforation, or flashover is it considered to have passed the 2ms square wave current capacity test for that current amplitude. The current capacity under the 2ms square wave is the maximum current allowed to pass per unit cross-sectional area of ​​the zinc oxide resistive element, expressed in A / cm². 2 .

[0060] Aging coefficient (K): Using a resistance aging test apparatus of model Xady-LH35 / 105, in an oven at 130℃, at 0.85U... 1mA Accelerated DC aging was performed for 10 hours under the specified conditions. After the accelerated DC aging test, the samples were removed after cooling to room temperature and left to stand for 48 hours. The aging coefficient was calculated using the formula: k = (U2 × I2) / (U1 × I1), where U1 and I1 are the initial instantaneous voltage and current values, respectively; and U2 and I2 are the instantaneous voltage and current values ​​after the aging test, respectively.

[0061] The test results are shown in Table 1.

[0062] Table 1. Performance test results of the examples and comparative examples.

[0063] As can be seen from the test results in Table 1, compared with Comparative Example 1 which omits the first sintering step, the regulation of the first sintering step in Embodiment 1 of the present invention helps to achieve a zinc oxide resistor sheet that simultaneously possesses high voltage gradient, low leakage current, high nonlinear coefficient, low residual voltage ratio, high current capacity, low impact change rate, small grain size, and high aging coefficient. Compared with Comparative Example 2 which omits the first and third sintering steps, the present invention further regulates the second sintering step, which is beneficial for further improving the voltage gradient of the zinc oxide resistor sheet, reducing leakage current, increasing the nonlinear coefficient, increasing the current capacity, and reducing the grain size. In summary, the regulation of the first sintering step in the present invention can improve the overvoltage protection effect of the zinc oxide resistor sheet, reduce operating losses, and improve its anti-aging ability.

[0064] Compared to the first sintering temperature of 700℃ in Example 2 and 800℃ in Example 3, the zinc oxide resistor sheet prepared by controlling the first sintering temperature to 750℃ in Example 1 of this invention exhibits the best overall performance. The preferred first sintering temperature is 750℃, as this temperature falls within the optimal range for zinc oxide lattice activation and slow ion diffusion, promoting the growth of Sb... 3+ Si 4+ Bi₂O₃ gradually penetrates into the zinc oxide lattice, forming the smallest and most uniform spinel nuclei through a solid solution-desolution reaction. These nuclei refine the zinc oxide grains through a pinning effect during subsequent sintering, significantly reducing the standard deviation of the grain size distribution. This also facilitates the formation of a low-melting-point eutectic phase between Bi₂O₃, zinc oxide, and the spinel phase, minimizing the volatilization of Bi. The eutectic phase spreads into a continuous and uniform grain boundary insulating layer during subsequent sintering, resulting in a more uniform electric field distribution and thus improving the overall performance of the zinc oxide resistor sheet.

[0065] Figure 1 These are X-ray diffraction patterns of zinc oxide resistors obtained in Examples 1-3 and Comparative Examples 1-2. Figure 2 These are microscopic morphology diagrams and grain size distribution diagrams of the zinc oxide resistor sheets obtained in Example 1 and Comparative Examples 1-2. Figure 3 These are voltage-current characteristic curves of the zinc oxide resistive sheets obtained in Examples 1-3 and Comparative Examples 1-2. Figure 4 These are DC aging curves of the zinc oxide resistors obtained in Examples 1-3 and Comparative Examples 1-2. From... Figure 1 It can be seen that the peak intensity of the spinel phase formed in the embodiments of the present invention is significantly higher than that in comparative examples 1-2, and example 1 is superior to examples 2-3. From Figure 2It can be seen that the zinc oxide grains in Example 1 of this invention can be refined to 4.93 μm and are more uniformly distributed. From the voltage-current characteristic curves in Figure 3, it can be seen that the nonlinear characteristics of the curves in Examples 1-3 are significantly better than those in Comparative Examples 1-2. Example 1 has the steepest slope in the nonlinear segment, with a much lower leakage current in the low-voltage region compared to the comparative examples, and a faster and more stable voltage response in the high-voltage impact region. Examples 2 and 3 are slightly inferior, further proving that 750℃ is the optimal temperature for the first sintering. Comparative Example 2, due to the omission of the first and third sintering processes, has the gentlest nonlinear segment. Comparative Examples 1-2 both exhibit small voltage rise amplitude and delayed response in the high-voltage region, resulting in poor overvoltage protection. As can be seen from the DC aging curves in Figure 4, the aging curves of Examples 1-3 are generally more stable, with voltage and current fluctuations much smaller than those of Comparative Examples 1-2. The aging curve of Example 1 shows almost no change, indicating the lowest degree of electrical performance degradation. Examples 2 and 3 have slightly poorer grain boundary stability due to the deviation of the first sintering temperature from the optimal value. Comparative Example 1, due to the omission of the first sintering, has a higher degree of electrical performance degradation than the Examples. Comparative Example 2, by omitting both the first and third sintering processes, has more grain boundary defects and the most severe electrical performance degradation after aging. This fully demonstrates that the segmented temperature-controlled sintering process of the present invention, especially the first sintering step, can significantly improve the nonlinear response characteristics and anti-aging ability of zinc oxide varistors.

[0066] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0067] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a pressure-sensitive ceramic, characterized in that, Includes the following steps: (1) Obtain granules containing zinc oxide, pre-press them to obtain a green body; the granules containing zinc oxide also include Bi2O3, Sb2O3 and SiO2; (2) The blank is sequentially subjected to debinding sintering, first sintering, second sintering and third sintering, and then cooled down; wherein, the first sintering includes heating to 650℃~850℃ at a heating rate of 80℃ / h~100℃ / h and then holding at that temperature for 1~3h; the temperature of the second sintering is 1100℃~1200℃; and the temperature of the third sintering is 800℃~900℃.

2. The preparation method according to claim 1, characterized in that, The temperature of the first sintering is 720~780℃.

3. The preparation method according to claim 1 or 2, characterized in that, The heating rate for the second sintering is 50℃ / h to 70℃ / h.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The third sintering process includes cooling to 800℃~900℃ at a cooling rate of 50℃ / h~70℃ / h and then holding at that temperature for 6h~10h. And / or, the cooling includes cooling to room temperature at a cooling rate of 30°C / h to 50°C / h.

5. The preparation method according to any one of claims 1 to 4, characterized in that, The debinding sintering process involves heating to 250℃~350℃ at a heating rate of 100℃ / h~200℃ / h, then heating to 400℃~500℃ at a heating rate of 40℃ / h~80℃ / h, holding at that temperature for 2h~4h, and then cooling down with the furnace.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The zinc oxide-containing granulated material includes zinc oxide, dopants, and additives; Preferably, the zinc oxide has a particle size of 0.2 μm to 0.5 μm; Preferably, the dopant includes at least one of Bi2O3, Sb2O3, Ga2O3, NiO, SiO2, MnO2, Cr2O3, Co2O3, Al(NO3)3·9H2O, and silver glass powder; Preferably, the additives include at least one of dispersants, defoamers, and binders.

7. The preparation method according to claim 6, characterized in that, The molar ratio of zinc oxide, Bi2O3, Sb2O3, Ga2O3, NiO, SiO2, MnO2, Cr2O3, Co2O3, Al(NO3)3·9H2O, and silver glass powder is (88.0~96.0):(0.5~2.5):(0.2~2.5):(0.1~1.0):(0.3~1.5):(0.3~1.2):(0.2~1.5):(0.2~1.0):(0.5~2.0):(0.05~0.3):(0.01~0.30). And / or, based on the mass of zinc oxide as 100%, the amount of the dispersant added is 0.5wt% to 1.5wt%, the amount of the defoamer added is 0.1wt% to 1wt%, and the amount of the binder added is 5wt% to 6wt%.

8. The preparation method according to any one of claims 1 to 7, characterized in that, The granulated powder has a mesh size of 80-200 mesh; Preferably, the parameters for the pre-compression molding include: pressure of 100MPa~200MPa, holding time of 5s~30s, and molding density of 3.0g / cm³. 3 ~3.6g / cm 3 .

9. A pressure-sensitive ceramic prepared by any one of claims 1 to 8.

10. The application of the varistor ceramic prepared by the preparation method according to any one of claims 1 to 9 in lightning protection insulators or overvoltage protection of power equipment.

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