A PTC ceramic material with uniform fine-grain structure and its preparation method and application

Abstract

The application discloses a PTC ceramic material with a uniform fine-grain structure and a preparation method and application thereof, and belongs to the technical field of PTC ceramic materials. The application guarantees growth continuity by accurately supplying growth kinetic energy of crystal grains, improves growth consistency by regulating and controlling synchronous growth of crystal grains in the whole region, and inhibits abnormal growth of the crystal grains by controlling sintering temperature and sintering time, so that the PTC ceramic material finally forms a fine-grain structure with uniform micro-grain size and regular grain boundary distribution. The PTC ceramic material can not only meet the basic demand of low resistivity of the PTC ceramic material, but also can significantly improve the voltage resistance capacity per unit thickness and the high-energy impact resistance of the material, and effectively avoids problems such as delamination failure, edge sparking and arc flying and breakdown that are prone to occur in traditional materials.

Description

Technical Field

[0001] This application belongs to the field of PTC ceramic materials technology, specifically relating to a PTC ceramic material with a uniform fine-grained structure, its preparation method, and its application. Background Technology

[0002] PTC (Positive Temperature Coefficient) ceramic materials are widely used in overcurrent protection, surge current suppression, self-limiting heating, and temperature sensing due to their unique resistance-temperature characteristics. Currently, mature PTC ceramic materials have switching temperatures ranging from -20℃ to +320℃ and resistance values ​​from 0.1Ω to 100KΩ. To achieve excellent electrical performance and reliability, PTC ceramic materials need to possess low resistivity and a uniform microstructure. Among these, the grain size is one of the key factors affecting material performance. Research shows that the grain size of PTC ceramic materials typically needs to be controlled at 5μm or larger. If the grain size is too small (e.g., less than 5μm), the resistivity of the material will increase significantly, making it difficult to achieve semiconductivity and thus failing to meet the basic requirements of the PTC effect.

[0003] In the preparation process of PTC ceramic materials, sintering is the core process that determines its final microstructure and properties. Traditional PTC ceramic material processes typically include steps such as secondary wet ball milling, pre-sintering to synthesize the main crystalline phase, secondary ball milling followed by drying, granulation with binder, molding, and sintering. Its processes (such as...) Figure 1 As shown, there are significant defects (using a fixed maximum temperature and holding time can easily cause the grain size distribution to become wider and the microstructure to be uneven), making it difficult to obtain a uniform fine-grained structure. It will also amplify the asynchronous growth of grains in different regions, thus leading to abnormal growth problems.

[0004] Therefore, traditional sintering methods cannot effectively control the uniformity of grain growth, making it difficult to prepare high-performance PTC ceramic materials that combine low resistivity and uniform fine-grained structure, thus limiting their further development in high-end application fields. Summary of the Invention

[0005] The purpose of this application is to provide a PTC ceramic material with a uniform fine-grained structure, its preparation method and application, which can effectively suppress abnormal grain growth, achieve microstructure uniformity, and thus improve the overall performance of PTC ceramic materials.

[0006] To achieve the above objectives, this application provides a method for preparing a PTC ceramic material with a uniform fine-grained structure, comprising the following steps: Weigh the raw materials according to the preset ratio, mix them evenly, and then dry them to obtain the mixture. After pre-sintering the mixture, it is ball-milled a second time, dried and granulated to obtain the pre-treated raw material. PTC ceramic materials are prepared by molding and sintering pretreated raw materials. The sintering process includes the following stages: heating stage, glass phase melting stage, highest temperature sintering stage and cooling stage. The sintering atmosphere is neutral. The highest temperature sintering stage adopts continuous heating to provide stable kinetic energy for grain growth by continuously increasing the temperature. The micrograin size of the PTC ceramic material is 1.8 μm to 2.2 μm.

[0007] Furthermore, the heating phase includes: heating to 580℃~620℃ at a rate of 290℃ / h~310℃ / h, and holding at that temperature for 25min~35min.

[0008] Furthermore, the glass phase melting section includes: heating to 1150℃~1300℃ at a rate of 270℃ / h~290℃ / h to accelerate melting and form a glass phase.

[0009] Furthermore, the highest temperature sintering section includes: The temperature is continuously increased to 1300℃~1325℃ over a period of 10min~30min for the first sintering treatment; The temperature is continuously increased to 1325℃~1340℃ over a period of 30min~90min for the second sintering treatment.

[0010] Furthermore, the cooling section includes: a first cooling section that cools down to 800°C at a rate of 100°C / h to 240°C / h, and a second cooling section that cools the waste heat down to room temperature using natural cooling or air cooling.

[0011] Furthermore, the raw materials include ceramic phase materials, semiconductor agents, glass phase materials, and manganese nitrate solution, wherein the formulation of the ceramic phase material is (Ba... 1-x-y-z Sr x Pb y Ca z For TiO3, the value of x ranges from 0.01 to 0.045, the value of y ranges from 0.06 to 0.10, and the value of z ranges from 0.12 to 0.22. The molar ratio of the semiconductor agent to titanium dioxide in the ceramic phase material is 0.15%~0.25%; The amount of glass phase material added is 0.8wt%~1.3wt% of the ceramic phase material; The concentration of manganese nitrate solution is 0.4 mol / L to 0.6 mol / L, and the ratio of manganese nitrate solution to ceramic phase material is (0.25 mL to 0.6 mL): 100 g.

[0012] Furthermore, the pre-sintering treatment includes the following steps: heating to 1100℃~1200℃ in an air atmosphere at a rate of 4℃ / min~5℃ / min, holding at that temperature for 120min~160min; cooling to 800℃ at a rate of 3℃ / min~4℃ / min, and then naturally cooling to room temperature.

[0013] Furthermore, during the drying and granulation process, the drying temperature is 140℃~160℃, and the drying time is 1.5h~2.5h. The granulation method includes adding 12mL~18mL of PVA solution with a concentration of 10wt%~20wt% to every 100g of dry powder, mixing evenly, sieving, and drying at a temperature of 110℃~130℃ for 25min~35min.

[0014] This application also provides a PTC ceramic material obtained by the above preparation method.

[0015] This application also provides an application of PTC ceramic material in the preparation of electrode materials, wherein the preparation of electrode materials includes the following steps: A nickel layer is sputtered onto the surface of a PTC ceramic material using a magnetron sputtering process to serve as the bottom electrode. Silver paste is printed onto the surface of PTC ceramic material using a printing and sintering process to serve as a surface electrode.

[0016] In summary, this application has the following advantages: To address the shortcomings of traditional PTC ceramic sintering processes, such as insufficient grain growth kinetic energy, asynchronous regional growth, and abnormal growth, this application improves the sintering process. Through multiple safeguards including continuous kinetic energy supply, synchronous growth across the entire region, and suppression of abnormal growth, PTC ceramic materials can ultimately form a fine-grained structure with uniform microstructure and regular grain boundary distribution (e.g., this application can stably achieve a uniform grain size of approximately 2 μm). This fine-grained structure not only meets the fundamental requirement of low resistivity for PTC ceramic materials but also significantly improves the voltage withstand capability per unit thickness and resistance to high-energy impacts. It effectively avoids problems such as delamination failure, edge arcing, and breakdown that are prone to occur in traditional materials, providing key process support for the preparation of high-performance PTC ceramic materials. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the temperature curve for a traditional sintering method. Figure 2 This is a schematic diagram of the sintering temperature curve involved in Embodiment 1 of this application; Figure 3 A photograph of ceramic slabs obtained by traditional sintering methods, magnified 400 times under an optical microscope; Figure 4A photograph of the ceramic piece prepared for Example 1 of this application, magnified 400 times under an optical microscope. Detailed Implementation

[0018] The principles and features of this application are described below with reference to embodiments. The examples are for illustrative purposes only and are not intended to limit the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0019] PTC (Positive Temperature Coefficient) ceramic materials are widely used in overcurrent protection, surge current suppression, self-limiting heating, and temperature sensing due to their unique resistance-temperature characteristics. Currently, mature PTC ceramic materials have switching temperatures ranging from -20℃ to 320℃ and resistance values ​​from 0.1Ω to 100KΩ. To achieve excellent electrical performance and reliability, PTC ceramic materials need to possess low resistivity and a uniform microstructure. Among these, the grain size is one of the key factors affecting material performance. Research shows that the grain size of PTC ceramic materials typically needs to be controlled at 5μm or larger. If the grain size is too small (e.g., less than 5μm), the resistivity of the material will increase significantly, making it difficult to achieve semiconductivity and thus failing to meet the basic requirements of the PTC effect.

[0020] In the preparation process of PTC ceramic materials, sintering is the core process that determines its final microstructure and properties. The traditional process for PTC ceramic materials typically includes steps such as secondary wet ball milling, pre-sintering to synthesize the main crystalline phase, drying after secondary ball milling, adding binder for granulation, molding, and sintering. Among these, the sintering process generally employs a staged heating method, such as... Figure 1 As shown: First, the temperature is raised to around 600℃ at a certain heating rate and held for a period of time to fully remove volatile substances such as binders and moisture from the green body (i.e., the debinding process). Then, the temperature is raised to the highest sintering temperature (usually above 1300℃) and held at this temperature for 1 to 2.5 hours to complete the grain growth, ceramic densification, and semiconductorization processes. Finally, sintering is completed by controlling the cooling rate. During the sintering process, as the temperature rises, the glassy phase material in the green body gradually melts and disperses uniformly, which plays a role in lowering the sintering temperature, absorbing harmful impurities, and promoting semiconductorization. After entering the high-temperature stage, grain growth proceeds rapidly, and small grains gradually disappear and aggregate into micro-grains of the target size (the initial powder micro-size is about 0.6μm, with high activity and a fast initial grain growth rate).

[0021] However, traditional sintering methods have significant drawbacks, mainly in the difficulty of obtaining a uniform fine-grained structure. The specific reasons are as follows: (1) Uneven sintering kinetic energy and abnormal grain growth. During the holding period at the highest sintering temperature, the sintering kinetic energy of different regions of the ceramic body shows a non-uniform decay trend over time. In some regions, due to the higher sintering kinetic energy, grain growth continues; while in other regions, due to the decrease in sintering kinetic energy, grain growth slows down or stops. This difference between regions leads to inconsistent grain growth rates, which can easily cause abnormal grain growth (i.e., some grain sizes significantly exceed the average level), destroying the uniformity of the microstructure. (2) The inherent contradiction between temperature and time parameters. The grain growth process depends on both temperature and time: higher temperatures can provide greater sintering kinetic energy and promote grain growth, but excessively high temperatures will significantly increase the risk of abnormal grain growth; although extending the high-temperature holding time can compensate for insufficient temperature, it will exacerbate the difference in sintering kinetic energy in different regions of the ceramic body, resulting in excessive grain growth in some regions and insufficient growth in others. The traditional process mode of fixing the maximum temperature and the holding time is difficult to balance this contradiction, which easily leads to the widening of grain size distribution and uneven microstructure. (3) Regional temperature difference and activity decay. In the early stage of sintering, the powder activity is high (initial powder size is about 0.6μm) and the grain growth rate is fast; however, as the holding time increases, the overall activity of the material decreases, and there is a temperature gradient between the center and the surface of the ceramic body due to the difference in heat transfer, which further amplifies the asynchronous growth of grains in different regions and exacerbates the abnormal growth problem.

[0022] The aforementioned microstructural inhomogeneity directly leads to the deterioration of PTC ceramic material performance, manifesting macroscopically as: reduced breakdown voltage (decreased voltage withstand capability per unit thickness), and susceptibility to ceramic delamination, breakdown, and edge arcing under high-energy impacts, severely affecting product reliability and service life. Therefore, traditional sintering methods, unable to effectively control the uniformity of grain growth, struggle to produce high-performance PTC ceramic materials with both low resistivity and a uniform fine-grained structure, limiting their further development in high-end applications. Based on this, this application provides a PTC ceramic material with a uniform fine-grained structure, its preparation method, and its application. Through improvements in raw materials, formulation, and processes, PTC ceramic materials with low resistivity and a uniform fine-grained structure (microscopic grain size controlled at approximately 2 μm) can be obtained, thereby improving the material's resistance to energy impacts.

[0023] In a first aspect, this application provides a method for preparing a PTC ceramic material with a uniform fine-grained structure, comprising the following steps: S1. Weigh the raw materials according to the preset ratio, mix them evenly, and then dry them to obtain the mixture.

[0024] In a specific embodiment, the raw materials include ceramic phase material, semiconductor agent, glass phase material, and manganese nitrate solution, wherein the formulation of the ceramic phase material is (Ba 1-x-y-zSr x Pb y Ca z The values ​​of x, y, and z in TiO3 range from 0.01 to 0.045, 0.06 to 0.10, and 0.12 to 0.22, respectively. The molar ratio of the semiconductor agent to titanium dioxide in the ceramic phase material is 0.15% to 0.25%. The amount of glass phase material added is 0.8 wt% to 1.3 wt% of the ceramic phase material. The concentration of manganese nitrate solution is 0.4 mol / L to 0.6 mol / L, and the ratio of manganese nitrate solution to ceramic phase material is (0.25 mL to 0.6 mL): 100 g. Preferably, the raw materials are weighed according to a preset ratio. That is, the high-purity materials used are determined according to the target product, and the precise mass of each raw material required is calculated according to its stoichiometric ratio, and then accurately weighed.

[0025] This application employs a strontium-lead-calcium co-addition formulation system as the main component system. Strontium (Sr), lead (Pb), and calcium (Ca) are combined with titanium (Ti) to form the main crystalline framework. Through the synergistic effect of these three elements, a stable crystal structure foundation is provided for the material. Furthermore, by adjusting the ratio of these three elements, the lattice parameters of the main crystalline phase can be initially controlled, reserving adjustment space for subsequent semiconductorization and performance optimization. Transition metal oxides such as Nb₂O₅, Y₂O₃, La₂O₃, and Sm₂O₃ are used as key semiconductorization aids, either individually or in various combinations. Their core function is to enter the main crystalline phase lattice through ion doping, controlling lattice defects and carrier concentration, thereby promoting the material's semiconductorization. Appropriate addition of components such as SiO₂, Al₂O₃, Li₂CO₃, and BN allows these substances to melt and form a glassy phase during sintering, playing a dual role in sintering aid and impurity control. A small amount of manganese ions (Mn) is also added. 2+ By precisely controlling the amount of manganese ions added, the positive temperature coefficient effect of the material is optimized in a targeted manner, thereby further improving the material's temperature sensitivity and electrical performance stability.

[0026] In specific embodiments, the semiconductor agent includes at least one selected from Nb₂O₅ (niobium pentoxide), Y₂O₃ (yttrium oxide), La₂O₃ (lanthanum oxide), and Sm₂O₃ (samarium oxide), and the glass phase material includes at least one selected from TiO₂ (titanium dioxide), SiO₂ (silicon dioxide), Al₂O₃ (aluminum oxide), Li₂CO₃ (lithium carbonate), and BN (boron nitride). Among these, the transition metal oxides selected in this application exhibit excellent semiconductor properties, and the Y₂O₃ in these oxides... 3+ La 3+ and Sm 3+ +3 valent ions, replacing A-site ions (Ba) in the perovskite structure (main crystal phase). 2+ 、Sr 2+ Pb2+ and Ca 2+ ) or Nb 5+ Replacing B-site titanium ions in the perovskite structure (main crystal phase) with 5+ valent ions effectively increases the carrier concentration in the lattice, driving the material to transition from an insulating state to a semiconducting state. At the same time, the combined use of multiple transition metal oxides can reduce lattice distortion or doping saturation problems that may occur with single impurity doping through ion synergistic doping, ensuring a uniform distribution of carrier concentration and avoiding resistivity fluctuations caused by excessively high or low local carrier concentrations, thus ensuring the stability and consistency of the material's semiconducting performance. The added glass phase forming material plays a key auxiliary role in the sintering process: First, the melting temperature of this material is lower than the sintering temperature of the main crystalline phase. In the high-temperature sintering stage, it can melt in advance to form a fluid glass phase, which fills the gaps between the main crystalline phase particles, reduces the sintering activation energy of the main crystalline phase, and achieves a low-temperature sintering aid effect. This can reduce the excessive promotion of grain growth by high-temperature sintering and improve the density of the ceramic body. Second, the glass phase has a strong impurity adsorption capacity, which can wrap and fix the residual harmful impurities (such as alkali metal ions and heavy metal impurities) in the material at the grain boundaries, preventing impurities from entering the main crystalline phase and affecting the semiconductor effect. At the same time, the purified grain boundaries can form a more stable barrier structure, which provides a guarantee for the full play of the PTC effect. In addition, the addition of boron nitride can further optimize the dispersion of the glass phase and avoid the uneven grain boundary performance caused by local aggregation of the glass phase.

[0027] In specific embodiments, the raw materials for the ceramic phase material can be selected from: barium carbonate, strontium carbonate, calcium carbonate, lead oxide, and titanium dioxide. In this application, manganese ions are added in the form of manganese nitrate solution; the addition of a small amount of manganese ions is key to optimizing the PTC effect of the material. As acceptor impurities, manganese ions can selectively adsorb at the grain boundaries of the main crystal phase, and interact with donor ions (such as Nb) at the grain boundaries. 5+ The manganese ions form charge compensation, regulate the height of the grain boundary barrier, and thus significantly enhance the positive temperature coefficient effect of the material (i.e., the characteristic of the resistivity increasing sharply when the temperature rises). At the same time, manganese ions can also inhibit defect migration at the grain boundary, reduce the deterioration of the grain boundary structure under high temperature working environment, improve the electrical performance stability of the material in long-term temperature cycling, reduce the risk of product failure caused by PTC effect decay, and further ensure the application reliability of the material.

[0028] In a specific embodiment, the method of mixing raw materials includes: mixing the raw materials with pure water and milling media (preferably agate balls) in a mass ratio of 1:1.3:3, and then milling them on a planetary ball mill at a speed of 420 Hz for 4 hours.

[0029] In a specific embodiment, the drying temperature is 140℃~160℃, and the drying time is 1.5h~2.5h.

[0030] S2. After pre-sintering the mixture, it is ball-milled a second time and dried and granulated to obtain the pre-treated raw material.

[0031] In a specific embodiment, the pre-sintering treatment includes the following steps: heating to 1100℃~1200℃ in an air atmosphere at a rate of 4℃ / min~5℃ / min, holding at that temperature for 120min~160min; cooling to 800℃ at a rate of 3℃ / min~4℃ / min, and then naturally cooling to room temperature.

[0032] In a specific embodiment, the secondary ball milling method includes: mixing the pre-sintered material with pure water and ball milling media (preferably agate balls) in a mass ratio of 1:0.8:3 and then performing wet ball milling for 4 hours at a speed of 420 Hz.

[0033] In a specific embodiment, drying includes: drying temperature of 140℃~160℃ and drying time of 1.5h~2.5h.

[0034] In a specific embodiment, the granulation method includes: adding 12 mL to 18 mL of a PVA solution with a concentration of 10 wt% to 20 wt% to every 100 g of dry powder, mixing evenly, sieving, and drying at a temperature of 110°C to 130°C for 25 min to 35 min. Preferably, the degree of polymerization of the PVA material is 500.

[0035] S3. The pretreated raw materials are subjected to molding and sintering processes to obtain PTC ceramic materials. Sintering refers to the densification process in which the green body of PTC ceramic powder, after being formed, undergoes high-temperature action, through interparticle bonding and mass transfer, eliminating pores, shrinking volume, and increasing strength, gradually transforming into a dense sintered body with a certain geometric shape and solidity. This process is also known as the semiconductorization process of PTC functional materials.

[0036] In a specific embodiment, the molding process includes: placing the granulated pretreated raw material in a single punch press to obtain a green blank with dimensions of φ (18mm~20mm, diameter) × (2mm~3mm, thickness) and a weight of 2.93g~2.97g.

[0037] In a specific embodiment, the sintering process includes the following stages: a heating stage, a glass phase melting stage, a maximum temperature sintering stage, and a cooling stage. The sintering atmosphere is a neutral atmosphere (i.e., natural environment), and the maximum temperature sintering stage is carried out by continuous heating. The sintering atmosphere affects the performance of PTC ceramics by influencing the chemical reactions and microstructure of the material. PTC ceramic functional materials need to avoid interference with semiconductor properties from oxidation or reduction reactions; therefore, this application prioritizes sintering in a neutral atmosphere. For large sintering equipment such as tunnel furnaces, this application further optimizes the atmosphere control strategy by using inlet exhaust and tail-end air supply. On the one hand, exhaust removes gases volatilized from the green body during the heating stage, preventing residual gases from affecting sintering; on the other hand, air supply introduces fresh air with a suitable oxygen content into the furnace, optimizing the electrical properties of the material. Furthermore, tail-end air supply can transfer heat dissipated at the tail end to the front end, achieving heat recovery and energy saving.

[0038] In a specific embodiment, the heating stage includes: heating to 580℃~620℃ at a rate of 290℃ / h~310℃ / h, and holding at that temperature for 25min~35min. The heating rate in this application balances sintering efficiency and the integrity of the green body, and is preferably 300℃ / h under normal circumstances. This rate is dynamically adjusted based on the green body size; for larger green bodies, the heating rate needs to be appropriately reduced to ensure sufficient exhaust of internal gases; for smaller green bodies, the heating rate can be moderately increased to improve production efficiency while ensuring quality. The 580℃~620℃ stage is the binder removal stage, the core objective of which is to completely remove the binder from the green body to prevent its carbonization at high temperatures from adversely affecting sintering. This application utilizes a constant temperature environment of approximately 600℃ to fully combust, decompose, and completely volatilize the PVA, clearing impurities for subsequent high-temperature sintering and ensuring the structural stability of the green body at high temperatures.

[0039] In a specific embodiment, the glass phase melting section includes: heating to 1150℃~1300℃ at a rate of 270℃ / h~290℃ / h to accelerate the melting and formation of the glass phase. This glass phase melting section is the key melting zone for the glass phase-forming material in the PTC ceramic formulation. Its core function is to achieve low-temperature sintering aid through glass phase formation and create conditions for subsequent uniform grain growth. As the sintering temperature rises, the atomic diffusion rate intensifies, ceramic particles shift from point contact to surface contact, voids gradually shrink and form closed, isolated pores, small particles begin to disappear, and grain boundaries move and grains gradually grow. Simultaneously, glass phase forming agents such as silica, alumina, lithium carbonate, and boron nitride added to the formulation melt within this temperature range to form a fluid glass phase. The core functions of the glass phase in this application are mainly reflected in two aspects: first, filling the interparticle gaps, reducing the sintering activation energy of the main crystalline phase, achieving low-temperature sintering aid, and avoiding excessive high-temperature promotion of grain growth; second, adsorbing harmful impurities in the material, providing a clean environment for the material's semiconductorization. To ensure rapid and uniform melting of the glass phase and its encapsulation of nascent small particles, this application employs a rapid heating strategy, controlling the heating rate in the 600℃~(1150℃~1300℃) range at 270℃ / h~290℃ / h. By rapidly traversing the glass phase melting range, local glass phase aggregation is reduced, ensuring uniform distribution of the glass phase within the preform and laying the foundation for subsequent uniform grain growth.

[0040] In a specific embodiment, the highest temperature sintering section includes: continuously raising the temperature to 1300℃~1325℃ for 10min~30min for the first sintering treatment; and continuously raising the temperature to 1325℃~1340℃ for 30min~90min for the second sintering treatment. Specifically, this application divides the highest sintering temperature of 1300℃~1340℃ into two segments for temperature control, providing stable kinetic energy for grain growth by continuously increasing the temperature. The first stage (1300℃~1325℃): the holding time is set to 10min~30min. This stage mainly provides initial kinetic energy for grain growth, propelling the grains into the early stage of rapid growth and ensuring that grains in each region start growing synchronously. The second stage (1325℃~1340℃): the holding time is set to 30min~90min. This stage is the critical period for grain growth and has a significantly greater impact on the material resistivity than the first stage. By adjusting the holding time in this stage, precise control of the material resistivity can be achieved. Through a two-stage process, this application can ensure that the temperature rises slowly and continuously within the high-temperature range, providing a continuous source of kinetic energy for grain growth in all regions of the green body (including the center and surface), avoiding regional growth differences, and ultimately achieving uniform grain growth and overall uniformity of the ceramic body.

[0041] In a specific embodiment, the cooling section includes: a first cooling section that cools to 800℃ at a rate of 100℃ / h to 240℃ / h, and a second cooling section that uses natural cooling or air cooling to dissipate residual heat. Specifically, this application controls the cooling rate to be between 100℃ / h and 240℃ / h, which can be dynamically adjusted based on the target room temperature resistance value. For example, if the room temperature resistance value needs to be increased, the cooling rate is reduced; if the room temperature resistance value needs to be decreased, the cooling rate is appropriately increased. Simultaneously, a lower limit for the cooling temperature is set at 800℃. Above 800℃, controlled cooling is used; below 800℃, natural cooling can be selected, or cooling can be accelerated by blowing a controlled amount of air into the furnace from the tail of the furnace, thus ensuring both performance and cooling efficiency.

[0042] Secondly, based on a general inventive concept, this application also provides a PTC ceramic material obtained by the above preparation method, wherein the microcrystalline grain size of the PTC ceramic material is 1.8 μm to 2.2 μm.

[0043] Among them, the microstructure of PTC ceramic materials obtained by traditional sintering methods is basically around 5μm. It can be seen from the microstructure that the significant increase in the number of grains directly leads to a multiple increase in the number of grain boundaries. As the key structural unit of PTC ceramic materials, the number and distribution of grain boundaries have a decisive influence on the electrical properties, mechanical stability and failure resistance of the materials, laying the microstructure foundation for subsequent performance optimization. For example (1): In the application of PTC ceramic materials, after applying voltage, the voltage will be distributed between the grains along the thickness direction. The voltage division value of a single grain directly affects the voltage effect of the material (manifested as parameters such as inrush current and maximum input power). The voltage effect is the core cause of problems such as material delamination failure, edge arcing, and breakdown. Therefore, the smaller the maximum input power, the lower the failure probability. The single grain voltage of the fine-grained material of 1.8μm~2.2μm in this application is only 40% of that of traditional materials. According to the electrical characteristics of PTC ceramic materials, the lower the partial voltage of a single grain, the smaller the decrease in grain resistance caused by voltage, which in turn significantly reduces the maximum input power of the material, fundamentally reducing the risk of failure such as delamination, arcing, and breakdown caused by high power impact. For example (2): the optimization of voltage effect also has a positive impact on the working equilibrium temperature of PTC ceramic materials. Under high voltage, traditional coarse-grained materials have a higher partial voltage of a single grain, resulting in a more significant voltage effect, a greater decrease in resistance, and greater energy consumption inside the material, which easily leads to an increase in working equilibrium temperature; while the fine-grained material of about 2μm in this application has a lower partial voltage of a single grain, a weaker voltage effect, and reduced energy loss, so that the equilibrium temperature of the material under high voltage conditions shows a low-level stable trend. From the perspective of material aging mechanism, working equilibrium temperature is the key factor affecting aging performance. The lower the equilibrium temperature, the slower the thermal degradation rate of the internal microstructure of the material, and the smaller the decay of core performance such as grain boundary stability and resistivity consistency, thereby greatly extending the service life of the material and improving long-term working reliability. For example (3): From the perspective of material aging mechanism, the working equilibrium temperature is the key factor affecting aging performance. The lower the equilibrium temperature, the slower the thermal degradation rate of the internal microstructure of the material, and the smaller the attenuation of core performance such as grain boundary stability and resistivity consistency, thereby significantly extending the service life of the material and improving long-term working reliability. For example (4): When PTC ceramic materials are subjected to energy impact, micro-defects (such as microcracks) will be generated inside them. The propagation speed and path of the defects directly determine the impact resistance of the material. Studies have shown that the minimum defect size of PTC ceramic materials is comparable to the micro-grain size. Therefore, reducing the grain size can optimize the energy impact resistance performance from two dimensions. The minimum defect size of the fine-grained material of about 2μm in this application is much smaller than that of the traditional coarse-grained material of about 5μm. The expansion size of defects caused by energy impact at the micro level is limited to a smaller range, avoiding macroscopic failure caused by rapid defect expansion.Meanwhile, since the number of grains around 2μm is about 15 times that of grains around 5μm, defects need to cross more grain boundaries during propagation, significantly lengthening the path. Assuming that the defect propagation scale caused by each energy impact is at the single grain size level, the grain boundary resistance that defects need to overcome in fine-grained materials is greater, and the propagation speed is slower, thus greatly improving the material's resistance to energy impacts.

[0044] Thirdly, based on a general inventive concept, this application also provides the application of PTC ceramic materials in the preparation of electrode materials, wherein the preparation of electrode materials includes the following steps: S101. A nickel layer is sputtered onto the surface of a PTC ceramic material using a magnetron sputtering process to serve as the bottom electrode.

[0045] In a specific implementation, the PTC ceramic material needs to be cleaned and dried before preparing the electrode material. The cleaning is carried out using an ultrasonic cleaning device at a frequency of 20 kHz for 12 to 20 minutes. The drying temperature is 175°C to 185°C and the drying time is 3.5 to 4.5 hours.

[0046] In a specific implementation, the target current for the magnetron sputtering process is 23A~27A, and the vacuum level is 5×10⁻⁶. -3 Pa, the thickness of the nickel layer is ≥0.3μm.

[0047] S102. Silver paste is printed on the surface of PTC ceramic material using a printing and sintering process to serve as a surface electrode.

[0048] In the specific implementation, the silver paste is a PTC-specific silver paste with a solid content of 80%, the screen mesh number of the printing and sintering process is 180 mesh, the sintering temperature is 550℃~580℃, the holding time is 15min~25min, and the silver paste thickness is preferably 3.5μm~6.5μm.

[0049] In this application, a composite electrode structure is formed by a bottom nickel electrode and a surface silver electrode. The presence of the nickel layer can improve the bonding force between the electrode and the ceramic substrate, buffer thermal stress, and prevent the surface silver from diffusing into the ceramic (avoiding the impact on the PTC effect). The surface silver electrode, with its high conductivity, ensures efficient current conduction. The combination of the two not only solves the problems of insufficient conductivity of a single nickel electrode, the inability of a single silver electrode to achieve ohmic contact with the ceramic body, and poor electrode reliability, but also achieves comprehensive optimization of electrode performance (conductivity, bonding force, and stability) through pretreatment processes and precise parameter control, ultimately ensuring the reliability and consistency of PTC ceramic electrode products during long-term use.

[0050] In summary, this application has at least the following beneficial effects: (1) This application breaks through the limitation of fixed temperature in the high-temperature stage of traditional sintering process. It scientifically divides the high-temperature sintering temperature range of PTC ceramic materials into segments and matches different heating rates to the grain growth requirements of different temperature segments. Through a slow and orderly sintering temperature increase, it continuously and stably supplies sintering kinetic energy for the grain growth process. Compared with the problem of the gradual decrease of kinetic energy in the high-temperature stage of traditional process as the holding time goes by, the sintering method of this application can avoid the stagnation of grain growth caused by interruption or insufficient kinetic energy supply, and ensure that the grain can obtain sufficient energy support throughout the high-temperature sintering stage, laying the foundation for subsequent uniform growth.

[0051] (2) Based on the synergistic effect of segmented temperature control and differentiated heating rate, this application can effectively solve the problem of uneven sintering kinetic energy in different regions of the ceramic body in traditional processes. By precisely controlling the heating rhythm of each temperature segment, the temperature field distribution in each region (including the central region and the surface region) of the ceramic body can be made more uniform, thereby allowing the grains in different regions to obtain similar growth environment and kinetic energy conditions at the same sintering stage, and promoting the synchronous growth of grains in the entire ceramic body. This completely changes the imbalance state in traditional processes where grain growth in some regions has slowed down or stopped, while some regions are still growing rapidly, greatly improving the spatial consistency of grain growth and fundamentally reducing the problem of uneven microstructure caused by regional growth differences.

[0052] (3) This application achieves dual precise control of key parameters in the sintering process by segmenting the temperature and using differentiated heating rates for coordinated regulation: on the one hand, through segmented temperature design, the maximum temperature threshold of each stage can be reasonably controlled according to the grain growth rate characteristics of different temperature ranges, avoiding excessive grain growth caused by continuous high temperature; on the other hand, by optimizing the heating rate of each temperature range, the actual effective holding time at different temperatures can be indirectly limited, preventing grain size imbalance caused by excessive holding time in a certain temperature range. The above dual control mechanism can effectively suppress the core conditions for abnormal grain growth and eliminate the phenomenon of uneven grain size distribution and abnormally large grains caused by unreasonable temperature or time parameter settings in traditional processes.

[0053] The technical solutions described above in this application will be explained in detail below with reference to specific embodiments.

[0054] The raw materials and equipment involved in the following embodiments include: Barium carbonate (BaCO3), with a purity of 99.5%, is produced by Sichuan Mianyang Yuanda New Materials Co., Ltd.

[0055] Strontium carbonate (SrCO3), with a purity of 99.5%, is produced by Chongqing Dazu Hongdie Strontium Industry Co., Ltd.

[0056] Calcium carbonate (CaCO3), with a purity of 99.3%, is manufactured by Shandong Dongying New Century Optoelectronic Materials Co., Ltd.

[0057] Lead oxide (PbO), with a purity of 99.5%, is produced by Guangdong Whale Shark Chemical Co., Ltd.

[0058] Titanium dioxide (TiO2), with a purity of 99.9%, is manufactured by Hubei Tianci Electronic Materials Co., Ltd.

[0059] Lanthanum trioxide (La2O3), 3N standard, manufactured by Jiangxi Zhongli Tantalum & Niobium Co., Ltd.

[0060] Samarium oxide (Sm2O3), 3N standard, is manufactured by Jiangxi Zhongli Tantalum-Niobium Co., Ltd.

[0061] Niobium pentoxide (Nb2O5), 4N standard, manufactured by Jiangxi Zhongli Tantalum-Niobium Co., Ltd.

[0062] Silicon dioxide (SiO2), AR standard, manufactured by Xilong Scientific Co., Ltd.

[0063] Aluminum oxide (Al2O3), AR standard, manufactured by Sinopharm Chemical Reagent Co., Ltd.

[0064] Lithium carbonate (Li2CO3), AR standard, manufactured by Sinopharm Chemical Reagent Co., Ltd.

[0065] Boron nitride (BN), with a purity of 99.9%, is manufactured by Hebei Keze Metal Materials Co., Ltd.

[0066] Manganese nitrate (Mn(NO3)2), AR standard, manufactured by Chongqing Chuandong Chemical Co., Ltd.

[0067] Electric heating drying oven TDB-216SCBF, Chengdu Xingtianyu Experimental Instrument Co., Ltd.

[0068] DMM6500 ohmmeter, KEITHEY.

[0069] High-temperature box-type resistance furnace ZZ-6-14, Chengdu Langchen Electronics Co., Ltd.

[0070] JL-1155 Laser Particle Size Analyzer, Chengdu Jingxin Powder Testing Equipment Co., Ltd.

[0071] SFJ-160KN powder tablet press, manufactured by Jiangsu Wujiang Chaoyu Press.

[0072] Electronic balance (620g / 0.01g), Sartorius Industrial Technology GmbH, Germany.

[0073] Planetary ball mill YXQM-4L, Changsha Miqi Instrument Equipment Co., Ltd.

[0074] HJ1 optical microscope, Nanjing Nanpai Technology Co., Ltd.

[0075] Example 1 This embodiment provides a PTC ceramic material with a uniform fine-grained structure, which is prepared by the following method: (1) Weigh the raw materials It includes 107.64g barium carbonate, 0.55g strontium carbonate, 14.32g calcium carbonate, 17.17g lead oxide, 61.68g titanium dioxide, 0.24g yttrium trioxide, 0.22g niobium pentoxide, 0.82g silicon dioxide, 0.12g lithium carbonate, 0.25g boron nitride, and 0.85mL manganese nitrate solution (0.5mol / L).

[0076] (2) First ball milling After weighing and mixing the raw materials, mix them with pure water and agate balls in a mass ratio of 1:1.3:3 and wet ball mill them at 420 Hz for 4 hours. After ball milling, transfer the mixture to a clean enamel pan and place it in an electric heating drying oven at 150 ℃ for 2 hours to obtain the mixture.

[0077] (3) Pre-sintering The mixture is placed in a corundum-mullite sagger, covered, and pre-sintered in an air atmosphere. Among other things, such as... Figure 1 As shown, the pre-sintering process includes: the first stage involves heating the material at a constant rate from room temperature to 1150℃ for 270 minutes; then holding the material at 1150℃ for 150 minutes; next, reducing the temperature from 1150℃ to 800℃ over 90 minutes; and finally, reducing the temperature to room temperature over 60 minutes to obtain the pre-sintered material.

[0078] (4) Secondary ball milling and drying granulation The pre-sintered material was mixed with pure water and agate balls in a mass ratio of 1:0.8:3 and then ball-milled at 420 Hz for 4 hours in a planetary ball mill. After ball milling, the slurry was transferred to a clean enamel pan and dried in an electric heating drying oven to obtain dry powder at 150℃ for 2 hours.

[0079] Add 15 mL of PVA solution (concentration of 17 wt%, degree of PVA polymerization of 500) to every 100 g of dry powder, mix evenly in a mortar, pass through a 40-mesh sieve, and then dry at 120℃ for 0.5 h to obtain pretreated raw material.

[0080] (5) Molding The pretreated raw material is placed in a single-press press and pressed into a green blank with a diameter of 18.68 mm, a thickness of 2.98 mm, and a weight of 2.97 g.

[0081] (6) Sintering The green blank is placed on a V-groove, which is then placed inside a high-alumina sagger and covered. The high-alumina sagger is placed on the furnace base of a bell-type furnace. An automatic lifting device moves the furnace base into the hood, and the two are sealed tightly to ensure no air convection occurs between the sealed area and the outside (all embodiments and comparative examples in this application use a V-groove + high-alumina sagger + bell-type furnace sintering method during the sintering process). The high-alumina sagger has dimensions of 170mm × 170mm × 45mm (length × width × height), a wall thickness of 10mm, and venting notches of 30mm width and 5mm depth on all four sides of the sagger opening. The V-groove is 53mm long, 18mm wide, and 3mm thick, made of yttrium-stabilized zirconia, and fired at temperatures above 1600℃. The inner wall of the bell-type furnace is made of lightweight high-alumina fiber, which is lightweight, heat-resistant, and has excellent heat insulation properties. The bell-type furnace consists of two parts: the furnace hood and the product-supporting furnace base. The furnace hood is fixed in place.

[0082] The sintering process involves introducing a neutral atmosphere, such as... Figure 2 As shown, the sintering curves include: Heat to 600℃ at a rate of 300℃ / h, hold for 30 minutes, and then remove the adhesive. The heating rate was then controlled at 280℃ / h and the temperature was continuously increased to 1300℃ to promote the formation of the glass phase. The temperature is then continuously increased to 1325℃ over 30 minutes, and then to 1335℃ over 45 minutes to continuously provide kinetic energy for sintering and ensure uniform grain growth in each region. After heating, the material was cooled to 800℃ at a rate of 130℃ / h, and then allowed to cool naturally to room temperature to obtain PTC ceramic material (plain sheet). A 400x magnified photograph of this material under an optical microscope is shown below. Figure 4 As shown.

[0083] This embodiment also provides a method for preparing a PTC ceramic material electrode, including: The obtained PTC ceramic material was ultrasonically cleaned for 15 minutes using an ultrasonic frequency of 20kHz and a pure water ultrasonic medium. It was divided into four cleaning tanks and cleaned with running water to clean the surface. Then it was dried at 180℃ for 4 hours.

[0084] A 0.35 μm thick nickel layer was sputtered onto the cleaned PTC ceramic material surface using magnetron sputtering to serve as an ohmic electrode. The target current for the magnetron sputtering process was 25 A, and the vacuum level was 5 × 10⁻⁶. -3 Pa.

[0085] After nickel electrode sputtering, PTC ceramic material electrode surfaces are printed with PTC-specific silver paste (80% solid content) using a printing-sintering process, with a printing thickness of 3.5 μm, serving as the surface silver electrode. The printing-sintering process uses a 180-mesh screen, a sintering temperature of 560℃, and a holding time of 20 min.

[0086] Example 2 This embodiment provides a PTC ceramic material with a uniform fine-grained structure, which is prepared by the following method: (1) Weigh the raw materials It includes 107.64g barium carbonate, 0.55g strontium carbonate, 14.32g calcium carbonate, 17.17g lead oxide, 61.68g titanium dioxide, 0.24g yttrium trioxide, 0.22g niobium pentoxide, 0.82g silicon dioxide, 0.12g lithium carbonate, 0.25g boron nitride, and 0.85mL manganese nitrate solution (0.5mol / L).

[0087] (2) First ball milling After weighing and mixing the raw materials, mix them with pure water and agate balls in a mass ratio of 1:1.3:3 and wet ball mill them at 420 Hz for 4 hours. After ball milling, transfer the mixture to a clean enamel pan and place it in an electric heating drying oven at 150 ℃ for 2 hours to obtain the mixture.

[0088] (3) Pre-sintering The mixture was placed in a corundum-mullite sagger, covered, and pre-sintered in an air atmosphere. The pre-sintering process included: first, a uniform temperature rise from room temperature to 1150℃ over 270 minutes; then, a holding temperature of 1150℃ for 150 minutes; next, a temperature reduction from 1150℃ to 800℃ over 90 minutes; and finally, a temperature reduction to room temperature over 60 minutes to obtain the pre-sintered material.

[0089] (4) Secondary ball milling and drying granulation The pre-sintered material was mixed with pure water and agate balls in a mass ratio of 1:0.8:3 and then ball-milled at 420 Hz for 4 hours in a planetary ball mill. After ball milling, the slurry was transferred to a clean enamel pan and dried in an electric heating drying oven to obtain dry powder at 150℃ for 2 hours.

[0090] Add 15 mL of PVA solution (concentration of 13 wt%, degree of polymerization of 500) to every 100 g of dry powder, mix evenly in a mortar, pass through a 40-mesh sieve, and then dry at 120℃ for 0.5 h to obtain the pretreated raw material.

[0091] (5) Molding The pre-treated raw material is placed in a single-press press and pressed into a green blank with a diameter of 18mm, a thickness of 2.95mm, and a weight of 2.95g.

[0092] (6) Sintering The sintering process is carried out in a neutral atmosphere, and the sintering curves include: Heat to 600℃ at a rate of 290℃ / h, hold for 30 minutes, and then remove the adhesive. The heating rate was then controlled at 280℃ / h and the temperature was continuously increased to 1280℃ to promote the formation of the glass phase. The temperature is then continuously increased to 1325℃ over 30 minutes, and then to 1340℃ over 45 minutes to continuously provide kinetic energy for sintering and ensure uniform grain growth in each region. After the heating is completed, the temperature is cooled to 800℃ at a rate of 130℃ / h, and then naturally cooled to room temperature to obtain PTC ceramic material (plain sheet).

[0093] This embodiment also provides a method for preparing a PTC ceramic material electrode, including: The obtained PTC ceramic material was ultrasonically cleaned for 15 minutes using an ultrasonic frequency of 20kHz and a pure water ultrasonic medium. It was divided into four cleaning tanks and cleaned with running water to clean the surface. Then it was dried at 180℃ for 4 hours.

[0094] A 0.4 μm thick nickel layer was sputtered onto the cleaned PTC ceramic material surface using magnetron sputtering to serve as an ohmic electrode. The magnetron sputtering process used a target current of 25 A and a vacuum level of 5 × 10⁻⁶. -3 Pa.

[0095] After nickel electrode sputtering, PTC ceramic material electrode surfaces are printed with PTC-specific silver paste (80% solid content) using a printing-sintering process, with a printing thickness of 5 μm, serving as the surface silver electrode. The printing-sintering process uses a 180-mesh screen, a sintering temperature of 560℃, and a holding time of 20 min.

[0096] Example 3 This embodiment provides a PTC ceramic material with a uniform fine-grained structure, which is prepared by the following method: (1) Weigh the raw materials It includes 107.64g barium carbonate, 0.55g strontium carbonate, 14.32g calcium carbonate, 17.17g lead oxide, 61.68g titanium dioxide, 0.24g yttrium trioxide, 0.22g niobium pentoxide, 0.82g silicon dioxide, 0.12g lithium carbonate, 0.25g boron nitride, and 0.85mL manganese nitrate solution (0.5mol / L).

[0097] (2) First ball milling After weighing and mixing the raw materials, mix them with pure water and agate balls in a mass ratio of 1:1.3:3 and wet ball mill them at 420 Hz for 4 hours. After ball milling, transfer the mixture to a clean enamel pan and place it in an electric heating drying oven at 150 ℃ for 2 hours to obtain the mixture.

[0098] (3) Pre-sintering The mixture was placed in a corundum-mullite sagger, covered, and pre-sintered in an air atmosphere. The pre-sintering process included: first, a uniform temperature rise from room temperature to 1150℃ over 270 minutes; then, a holding temperature of 1150℃ for 150 minutes; next, a temperature reduction from 1150℃ to 800℃ over 90 minutes; and finally, a temperature reduction to room temperature over 60 minutes to obtain the pre-sintered material.

[0099] (4) Secondary ball milling and drying granulation The pre-sintered material was mixed with pure water and agate balls in a mass ratio of 1:0.8:3 and then ball-milled at 420 Hz for 4 hours in a planetary ball mill. After ball milling, the slurry was transferred to a clean enamel pan and dried in an electric heating drying oven to obtain dry powder at 150℃ for 2 hours.

[0100] Add 15 mL of PVA solution (concentration of 13 wt%, degree of polymerization of 500) to every 100 g of dry powder, mix evenly in a mortar, pass through a 40-mesh sieve, and then dry at 120℃ for 0.5 h to obtain the pretreated raw material.

[0101] (5) Molding The pretreated raw material is placed in a single-press press and pressed into a green blank with a diameter of 18.68 mm, a thickness of 2.98 mm, and a weight of 2.97 g.

[0102] (6) Sintering The sintering process is carried out in a neutral atmosphere, and the sintering curves include: Heat to 600℃ at a rate of 305℃ / h, hold for 30 minutes, and then remove the adhesive. The heating rate was then controlled at 280℃ / h and the temperature was continuously increased to 1305℃ to promote the formation of the glass phase. The temperature is then continuously increased to 1325℃ over 30 minutes, and then to 1335℃ over 45 minutes to continuously provide kinetic energy for sintering and ensure uniform grain growth in each region. After the heating is completed, the temperature is cooled to 800℃ at a rate of 130℃ / h, and then naturally cooled to room temperature to obtain PTC ceramic material (plain sheet).

[0103] This embodiment also provides a method for preparing a PTC ceramic material electrode, including: The obtained PTC ceramic material was ultrasonically cleaned for 15 minutes using an ultrasonic frequency of 20kHz and a pure water ultrasonic medium. It was divided into four cleaning tanks and cleaned with running water to clean the surface. Then it was dried at 180℃ for 4 hours.

[0104] A 0.5 μm thick nickel layer was sputtered onto the cleaned PTC ceramic material surface using magnetron sputtering to serve as an ohmic electrode. The target current for the magnetron sputtering process was 27 A, and the vacuum level was 5 × 10⁻⁶. -3 Pa.

[0105] After nickel electrode sputtering, PTC ceramic material electrode surfaces are printed with PTC-specific silver paste (80% solid content) using a printing-sintering process, with a printing thickness of 6.5 μm, serving as the surface silver electrode. The printing-sintering process uses a 180-mesh screen, a sintering temperature of 560℃, and a holding time of 20 min.

[0106] Comparative Example 1 This comparative example provides a method for preparing PTC ceramic material, which differs from Example 1 in that: the sintering process uses a traditional sintering curve, heating to 1330℃ and holding for 75 min, then cooling to 800℃ at a rate of 120℃ / h, and finally allowing it to cool naturally to room temperature to obtain a raw sheet. Its 400x magnified photograph under an optical microscope is shown below. Figure 3 As shown.

[0107] The remaining steps are the same.

[0108] Comparative Example 2 This comparative example provides a method for preparing PTC ceramic materials, which differs from Example 1 in that: (1) Adjustment of raw material dosage and selection: The dosage of strontium carbonate is 1.54g, calcium carbonate is 14.21g, lead oxide is 15.58g, niobium pentoxide is 0.25g, silicon dioxide is 0.95g, lithium carbonate is 0.08g, and manganese nitrate is 0.6mL. Yttrium oxide and boron nitride are not added, but 0.12g of lanthanum oxide and 0.3g of aluminum oxide are added.

[0109] (2) The sintering process adopts the traditional sintering curve, heating to 1330℃ and holding for 95 minutes, then cooling down to 800℃ at a rate of 135℃ / h, and then naturally cooling to room temperature to obtain raw sheet.

[0110] The remaining steps are the same.

[0111] Comparative Example 3 This comparative example provides a method for preparing PTC ceramic materials, which differs from Example 1 in that: (1) Adjustment of raw material dosage and selection: The dosage of barium carbonate is 108.88g, strontium carbonate is 0.56g, lead oxide is 15.67g, niobium pentoxide is 0.32g, silicon dioxide is 0.88g, lithium carbonate is 0.07g, boron nitride is 0.35g, and manganese nitrate is 0.6mL. Yttrium oxide and lanthanum oxide are not added, and 0.35g of aluminum oxide is added in addition.

[0112] (2) The sintering process adopts the traditional sintering curve, heating to 1330℃ and holding for 120 min, then cooling to 800℃ at a rate of 110℃ / h, and then naturally cooling to room temperature to obtain raw sheet.

[0113] The remaining steps are the same.

[0114] The raw materials and amounts used in Example 1 and Comparative Examples 1-3 are shown in Table 1, and the performance parameters of the obtained PTC ceramic materials and electrode materials are shown in Table 2.

[0115] Table 1. Reference Table of Raw Materials and Usage

[0116] Table 2 Performance Parameters

[0117] Table 2 lists the performance and parameter testing methods as follows: (1) The diameter and thickness of the product are measured by micrometer.

[0118] (2) Resistance value at room temperature: Place the product in an environment of 25℃±2℃ for more than 4 hours and then test the resistance value with a resistance meter.

[0119] (3) Switching temperature: A resistance-temperature characteristic testing device is used to automatically test the resistance value corresponding to the temperature range of 25℃ to 250℃. Every 4℃ is a temperature test point. After the temperature is constant, the corresponding resistance value is tested and recorded. After the test is completed, the resistance-temperature characteristic curve is simulated by an algorithm, and the switching temperature value is calculated.

[0120] (4) Breakdown voltage: In a normal temperature environment, use a 50Hz AC power supply, start applying voltage from 0V, apply voltage slowly, the voltage step gradient is 3V for voltages below 10V, the voltage step gradient is 30V for voltages from 10V to 100V, and the voltage step gradient is 50V for voltages above 100V. Apply voltage until the product is damaged, and the maximum test voltage shall not exceed 1200V.

[0121] (5) Dynamic withstand voltage test: In an environment of 25℃±5℃, a 20KVA transformer is used as the voltage source. The PTC thermistor is connected in series with a fixed resistor with a resistance of 25 ohms (power 50W). The initial voltage is 350V, and each voltage value is applied for 5 seconds. Observe whether there is any flashing phenomenon at the moment of power-on. Then disconnect and observe whether the appearance of the PTC thermistor is damaged after cooling for 10 minutes. Test and record the room temperature resistance value of the PTC thermistor. The voltage increase gradient is 20V each time. The method of each step is the same until a product fails. The dynamic withstand voltage value is the test voltage of the failed product minus 20V.

[0122] Depend on Figure 1 and Figure 2 It can be seen that the main difference between the sintering method of this application and the traditional sintering method lies in the high-temperature sintering stage. In traditional sintering methods, the maximum temperature is a fixed value. As the holding time increases, the sintering kinetic energy continuously decreases, leading to uneven grain growth in different regions. This results in uneven grain size and even abnormal grain growth, ultimately degrading the product's performance. In contrast, the high-temperature sintering stage of this application employs a continuous heating method, continuously enhancing the sintering kinetic energy of the material.

[0123] As shown in Table 1, the PTC chip material for motor starting prepared from the PTC ceramic material obtained by the preparation method of Example 1 of this application has a diameter of 15.6 mm, a thickness of 2.5 mm, a switching temperature of 135 °C, and a resistance of 13.5 Ω. Under the same specifications, the withstand voltage of the PTC chip material of Example 1 is 900VAC~950VAC, while the withstand voltage of the PTC chip material obtained by the conventional sintering method is 700VAC~810VAC.

[0124] The PTC chip materials in Table 1 were subjected to a maximum surge current withstand test. The method was as follows: 10 samples were grouped together, and in a room temperature environment, a series resistor of 25Ω was applied. The initial voltage was 350VAC. After energizing for 5 seconds, the samples were cooled for 10 minutes, and the resistance value was measured and the appearance was observed. Then, the voltage was applied again for cyclic testing, with each voltage increase being 20VAC, until a sample failed. The results were as follows: Using the traditional sintering method, the product began to fail at 390VAC (where VAC is the unit of AC voltage, representing the effective value of AC current, V represents volts (a unit of voltage), and AC specifically refers to alternating current). The product sintered in Example 1 of this application did not fail until 470VAC.

[0125] The PTC chip materials in Table 1 were subjected to aging performance tests. The method was as follows: a switching test was conducted at 350VAC with a maximum current not exceeding 8A. After 1000 hours of testing, the resistance change rate of the product in Example 1 of this application (switching temperature of 135℃) was generally in the range of 0% to 5%.

[0126] While specific embodiments of this application have been described in detail, this should not be construed as limiting the scope of protection of this application. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims still fall within the scope of protection of this application.

Claims

1. A method for preparing a PTC ceramic material with a uniform fine-grained structure, characterized in that, Includes the following steps: Weigh the raw materials according to the preset ratio, mix them evenly, and then dry them to obtain the mixture. After the mixture is pre-sintered, it is ball-milled a second time, dried and granulated to obtain the pre-treated raw material. The pretreated raw materials are subjected to molding and sintering processes to obtain PTC ceramic materials. The sintering process includes the following stages: heating stage, glass phase melting stage, highest temperature sintering stage and cooling stage. The atmosphere of the sintering process is a neutral atmosphere. The highest temperature sintering stage adopts a continuous heating method to provide stable kinetic energy for grain growth by continuously increasing the temperature. The micrograin size of the PTC ceramic material is 1.8 μm to 2.2 μm. The highest temperature sintering section includes: The temperature is continuously increased to 1300℃~1325℃ over a period of 10min~30min for the first sintering treatment; The temperature is continuously increased to 1325℃~1340℃ over a period of 30min~90min for the second sintering treatment; The heating section includes: heating to 580℃~620℃ at a rate of 290℃ / h~310℃ / h, and holding at that temperature for 25min~35min; The glass phase melting section includes: heating to 1150℃~1300℃ at a rate of 270℃ / h~290℃ / h to accelerate melting and form a glass phase; The cooling section includes: a first cooling section that cools down to 800°C at a rate of 100°C / h to 240°C / h, and a second cooling section that cools the waste heat down to room temperature by natural cooling or air cooling. The raw materials include ceramic phase materials, semiconductor agents, glass phase materials, and manganese nitrate solution, wherein the formulation of the ceramic phase material is (Ba... 1-x-y-z Sr x Pb y Ca z The values ​​of x, y, and z in TiO3 range from 0.01 to 0.045, 0.06 to 0.10, and 0.12 to 0.22, respectively. The molar ratio of the semiconductor agent to titanium dioxide in the ceramic phase material is 0.15% to 0.25%. The amount of glass phase material added is 0.8 wt% to 1.3 wt% of the ceramic phase material. The concentration of the manganese nitrate solution is 0.4 mol / L to 0.6 mol / L, and the ratio of the manganese nitrate solution to the ceramic phase material is (0.25 mL to 0.6 mL): 100 g.

2. The preparation method according to claim 1, characterized in that, The pre-sintering process includes the following steps: In an air atmosphere, the temperature is increased to 1100℃~1200℃ at a rate of 4℃ / min~5℃ / min, and held for 120min~160min; Cool to 800℃ at a rate of 3℃ / min to 4℃ / min, then allow to cool naturally to room temperature.

3. The preparation method according to claim 1, characterized in that, During the drying and granulation process, the drying temperature is 140℃~160℃, and the drying time is 1.5h~2.5h. The granulation method includes: adding 12mL~18mL of PVA solution with a concentration of 10wt%~20wt% to every 100g of dry powder, mixing evenly, sieving, and drying at a temperature of 110℃~130℃ for 25min~35min.

4. A PTC ceramic material obtained by the preparation method according to any one of claims 1-3.

5. The application of the PTC ceramic material according to claim 4 in the preparation of electrode materials, characterized in that, The preparation of electrode materials includes the following steps: A nickel layer is sputtered onto the surface of the PTC ceramic material using a magnetron sputtering process to serve as the bottom electrode; Silver paste is printed onto the surface of the PTC ceramic material using a printing and sintering process to serve as a surface electrode.

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