High-voltage-resistant PTC thermosensitive ceramic material, preparation method and application thereof

Abstract

The application relates to the field of ceramic materials, and provides a high-pressure-resistant PTC (Positive Temperature Coefficient) thermosensitive ceramic material, a preparation method and application, aiming to improve the pressure resistance and PTC effect stability of the thermosensitive ceramic. The material is composed of alumina-coated manganese-doped barium titanate nanorods, hollow silica microspheres and glass phase sintering aids, a core-shell structure and a three-dimensional composite system are constructed, and the electric heating performance and microstructure stability are optimized. The structure of raw materials is precisely controlled through a hydrothermal method and a sol-gel method, alcohol dispersion, flow casting and weak oxidation atmosphere sintering are combined, and the ceramic density and consistency are ensured. The material is suitable for high-voltage temperature control elements and overcurrent protection devices, and is widely applied to the fields of over-temperature protection of new energy automobile battery packs, current limiting elements of high-voltage power equipment and industrial automation temperature control switches.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ceramic materials, in particular to a high-voltage-resistant PTC thermosensitive ceramic material, a preparation method and applications. BACKGROUND

[0002] In modern power electronic systems, automotive electronic control devices and smart home products, PTC (Positive Temperature Coefficient) thermosensitive ceramic materials are playing an increasingly important role as key temperature control and overcurrent protection elements. Especially in high-voltage power modules, electric vehicle battery management systems and high-speed motor drivers, these materials need to operate in high-voltage, high-temperature and strong electromagnetic interference environments for a long time, which puts forward more stringent requirements for their voltage resistance and PTC effect stability. High voltage resistance can effectively prevent electrical breakdown and ensure safe operation of the system, while the stability of the PTC effect is the core basis for achieving high-sensitivity temperature control response and long-term reliable protection function. Therefore, developing thermosensitive ceramic materials with excellent high-voltage resistance and long-term stable PTC effect not only helps to improve the response speed and safety level of the device, but also expands its application range in high-voltage and high-power systems, promoting the development of related industries towards high performance and high reliability. Under this background, exploring new PTC ceramic materials with structure design and microstructure control synergistic optimization has become an important research direction in the field of material science and engineering technology, and has significant application value and industrial prospect.

[0003] Although there are many current studies on PTC thermosensitive ceramic materials, trying to improve their overall performance, there are still obvious deficiencies in high-voltage resistance and PTC effect stability, and there is no systematic and effective solution. For example, Chinese patent CN104844196A discloses a high-Tc lead-free PTC thermosensitive ceramic material, which shows certain temperature response characteristics under normal working conditions, but is prone to electrical breakdown in high-voltage environments, and the PTC effect shows significant drift as the number of cycles increases, making it difficult to meet the requirements of long-term stable operation. The main reason is that the material system lacks effective microstructure control mechanisms, making it difficult to improve electrical insulation while maintaining the thermal regulation function of the current-carrying channel; at the same time, the interface between ceramic grains lacks sufficient energy buffering and electric field homogenization ability, leading to local electric field concentration and inducing breakdown or effect instability. In addition, the existing preparation process has limited control precision of the microstructure, resulting in microcracks or inhomogeneous distribution in the ceramic, further weakening its voltage resistance and effect stability. Therefore, it is necessary to start from material composition, structure construction and sintering process, etc., to propose new design and synergistic control strategies to systematically solve the problem of high-voltage resistance and PTC effect synergistic optimization. SUMMARY

[0004] (1) Technical problems solved

[0005] The application aims to provide a high-voltage PTC thermosensitive ceramic material, a preparation method and an application, and solve the problems of insufficient high-voltage performance and PTC effect stability of the current thermosensitive ceramic material.

[0006] (2) Technical scheme

[0007] In order to achieve the above-mentioned purpose, the application provides the following technical scheme:

[0008] The preparation raw material of the high-voltage PTC thermosensitive ceramic material comprises the following raw materials in parts by weight: 100.0-120.0 parts of alumina / doped barium titanate nanorods, 5-15 parts of hollow silica microspheres, 4-8 parts of glass phase sintering agent, 1.0-2.0 parts of polyvinyl alcohol binder, 0.5-2.0 parts of polyacrylamide dispersant, and 5.0-10.0 parts of anhydrous ethanol.

[0009] The alumina / doped barium titanate nanorod is of a core-shell structure, the shell layer is alumina, and the core part is manganese-doped barium titanate nanorod; the chemical general formula of the manganese-doped barium titanate is BaTi 1-x Mn x O3, wherein x=0.05-0.20, and manganese elements realize lattice doping by replacing titanium sites. Further, the preparation method of the alumina / doped barium titanate nanorod is as follows: 20-40 parts by weight of doped barium titanate nanorods are dispersed in 50-80 parts of ethanol for ultrasonic treatment for 10-30 min to form a uniform suspension, 5-15 parts of aluminum nitrate and 30-50 parts of ethanol are mixed, 1-5 parts of acetylacetone is added, and the reaction is carried out at 40-60 DEG C for 60-120 min under the condition of a stirring rate of 300-500 rpm to form an aluminum precursor sol, then the suspension is injected into the aluminum precursor sol at a rate of 1-3 mL / min, the pH is adjusted to 4.0-5.5, and the temperature is maintained at 50-70 DEG C to continue stirring for 120-180 min to complete the hydrolysis and polycondensation reaction, the obtained mixed system is subjected to suction filtration through a filter membrane with a pore size of 0.22-0.45 mu m to retain the solid phase components, the gel-coated nanorod precursor is obtained by drying at 80-100 DEG C for 120-240 min, the precursor is calcined in an air atmosphere at a temperature rising rate of 2-5 DEG C / min to 500-700 DEG C for 120-240 min to form an alumina coating layer, the oxygen partial pressure in the furnace during the calcination stage is controlled to be 0.1-0.3 MPa, the solid phase product is retained after the final product is separated by centrifugation at a centrifugal rate of 8000-12000 rpm for 10-30 min, then the product is washed with ethanol for 3-5 times to remove the unreacted aluminum source and by-products, and the product is dried at 60-80 DEG C under a vacuum degree of 0.01-0.05 MPa for 60-120 min to obtain the alumina / doped barium titanate nanorod.

[0010] Further, the preparation method of the doped barium titanate nanorods is as follows: 122-145 parts of barium nitrate hexahydrate is dissolved in 200-300 parts of deionized water to form a first solution, 100 parts of tetrabutyl titanate is mixed with 50-80 parts of ethanol and 2-20 parts of manganese nitrate tetrahydrate is added to form a second solution, the first solution is added dropwise into the second solution at a rate of 2-5 mL / min, and the mixture is stirred at a rate of 300-500 rpm for 30-90 min to obtain a suspension, then 30-50 parts of citric acid is added, and the stirring is continued at 90-120 °C for 120-180 min until a viscous gel is formed, the gel is placed in a muffle furnace and heated at a rate of 10-15 °C / min to 250-300 °C for 20-40 min to complete the self-ignition reaction, the obtained precursor powder is sintered at a rate of 5-8 °C / min to 1050-1150 °C for 300-420 min in a nitrogen atmosphere, and after the furnace is cooled to room temperature, the particles with a particle size greater than 500 nm are removed by ethanol dispersion and centrifugal separation, and finally the doped barium titanate nanorods are obtained.

[0011] Further, the mass ratio of aluminum oxide and doped barium titanate in the aluminum oxide / doped barium titanate nanorods is 1:12-1:18;

[0012] Further, the average length of the aluminum oxide / doped barium titanate nanorods is 800-1200 nm, and the aspect ratio is controlled to be 4.5:1-10:1;

[0013] Further, the thickness of the aluminum oxide is 10-20 nm;

[0014] The application adopts the design of alumina / doped barium titanate nanorod, mainly for enhancing the comprehensive performance of high voltage resistance performance and PTC effect stability, the core of which is to realize the synergistic optimization between material structure and performance by constructing functional nanorod with core-shell structure. The doped barium titanate nanorod as the core phase endows the material with good PTC effect response ability, and at the same time, the current carrying mechanism and energy band structure are adjusted through manganese element doping, so as to improve the thermal sensitivity stability; and the alumina shell layer has excellent electrical insulation and thermal stability, which can effectively inhibit the local electric field concentration and electrical breakdown phenomenon under high voltage stress, and significantly enhance the voltage resistance of the material. The construction of the core-shell structure adopts the combination of sol-gel method and calcination process, so that the alumina is uniformly coated on the surface of the doped barium titanate in nanoscale, the shell thickness and interface quality are effectively controlled, the balanced distribution of interface electric field is promoted and the overall thermal conductivity is improved, so as to realize the dual stability of thermal field and electric field while maintaining the sensitivity of PTC effect. In addition, by adjusting the mass ratio of alumina and doped barium titanate, the length-diameter ratio of rod-shaped particles and the shell thickness, the packing structure between particles and the ceramic density can be further optimized, the microcrack generation and stress concentration phenomenon can be inhibited, and the reliability and service life of the material under complex working conditions can be enhanced. The above design not only realizes the functional complementation between structural units, but also realizes the synergistic regulation of thermal and electrical characteristics at the micro level, so as to significantly improve the comprehensive performance of the material under high voltage and alternating stress conditions, and provides an effective structure and process solution for the development of high-performance PTC thermosensitive ceramic materials.

[0015] Further, the preparation method of the hollow silica microspheres is as follows: 1.0-1.2 parts by weight of monohydrated glucose is dissolved in 18-22 parts of deionized water to form a first solution, and 0.28-0.32 parts of sodium silicate nonahydrate is dissolved in 9-11 parts of deionized water to form a second solution; the two solutions are mixed at a stirring speed of 200-500 rpm, and citric acid is used to adjust the pH to 2.5-3.5 during the mixing process; then the mixture is transferred to a sealed reaction container and subjected to hydrothermal reaction at 160-200 DEG C for 20-28 hours, with the reaction pressure being maintained at 0.5-2.0 MPa; after the reaction is completed, the solid-liquid mixture is filtered through a filter membrane with a pore size of 0.22 microns; the retained solid product is washed with 20-30 parts of deionized water and 15-25 parts of anhydrous ethanol for 3-5 times respectively to remove soluble ions and organic residues; then the silica-carbon composite is dried under a vacuum degree of -0.08 to -0.10 MPa and a temperature of 55-65 DEG C for 4-6 hours; finally, the silica-carbon composite is placed in a muffle furnace and subjected to programmed heating at a heating rate of 3-8 DEG C / min to a temperature of 500-600 DEG C, and calcined in an air atmosphere for 4-6 hours to completely remove the carbon core, thereby obtaining the hollow silica microspheres.

[0016] Further, the average diameter of the hollow silica microspheres is 300-600 nm.

[0017] This invention employs alumina / doped barium titanate nanorods primarily to enhance structural stability and dielectric uniformity, thereby improving high voltage withstand performance and PTC effect stability. By introducing hollow silica microspheres, the microstructure and dielectric environment of the ceramic material are further optimized, achieving a synergistic enhancement effect among multiple components. Hollow silica microspheres possess excellent size controllability and a hollow structure. Their introduction into the material system not only helps disperse the framework structure formed by the nanorods and improve overall density but also effectively alleviates stress concentration problems caused by uneven thermal expansion during high-temperature sintering or operation, thus improving the structural integrity and long-term stability of the ceramic body. Their hollow nature creates micron-scale buffer cavities within the material, providing additional energy release space under thermal excitation or electrical stress, reducing the risk of localized heat accumulation and electric field concentration, thus contributing to improved overall voltage withstand performance. Simultaneously, hollow silica microspheres exhibit excellent electrical insulation properties. Their uniform distribution within the ceramic matrix helps improve the local dielectric environment, achieving a more stable electric field distribution and temperature response behavior, thereby enhancing the stability of the PTC effect. Furthermore, the specific surface area advantage provided by the hollow structure also helps to enhance the physical bonding and thermal conductivity between micro-interfaces, further promoting the synergistic regulation of thermoelectric properties. By organically integrating hollow silica microspheres with alumina / doped barium titanate nanorods, this invention forms a composite ceramic system with a layered structure, thermal insulation, and electrical uniformity. While maintaining the PTC functional response, it significantly enhances the overall structural stability and reliability under extreme conditions, demonstrating the significant advantages of multiphase materials in functional complementarity and synergistic enhancement.

[0018] Furthermore, the glass phase sintering aid is mainly composed of B2O3, Li2O and SiO2. By mass percentage, the content of B2O3 in the sintering aid is 30% to 60%, the content of Li2O is 5% to 20%, and the content of SiO2 is 20% to 50%.

[0019] This invention also provides a method for preparing a high-pressure-resistant PTC thermistor ceramic material, comprising the following steps:

[0020] S1. Alumina / doped barium titanate nanorods are added to anhydrous ethanol and treated with ultrasonic oscillation for 10–30 min at an ultrasonic frequency of 40–60 kHz to form a nanorod ethanol dispersion. Hollow silica microspheres are then slowly added to the dispersion and stirred continuously for 20–40 min at a magnetic stirring rate of 300–500 rpm to ensure that the microspheres are uniformly distributed in the nanorod matrix. Glass phase sintering aid is added to the system in batches, and the stirring rate is controlled at 400–600 rpm for 30–60 min to form a premixed slurry with a three-dimensional composite structure.

[0021] S2. Polyvinyl alcohol binder and ammonium polyacrylate dispersant are added sequentially to the premixed slurry, with the binder added first and then the dispersant. The stirring speed is 300-500 rpm and the stirring time is 30-60 min to obtain a ceramic slurry with stable viscosity. The slurry is placed in a constant temperature water bath and heated to 40-60℃. The stirring speed is controlled at 200-400 rpm and the holding time is 30-60 min to complete the solvent evaporation control and rheological property optimization. The casting process is adopted, with the pressure set at 10-30 MPa and the holding time at 5-10 min to prepare the green body.

[0022] S3. Place the green body in a hot air circulating drying oven and pre-dry it at 80-100℃ for 120-240 min to make the moisture content ≤0.5wt%. After drying, transfer the green body to a muffle furnace and heat it to a sintering temperature of 1000-1150℃ at a heating rate of 2-5℃ / min under a weak oxidizing atmosphere with an oxygen content ≤5%. Hold the temperature for 300-420 min to achieve grain densification. Cool to room temperature to obtain a high pressure resistant PTC thermistor ceramic material.

[0023] This invention employs a multi-component synergistic construction of a three-dimensional composite structure, primarily designed to enhance the density and structural stability of high-pressure-resistant PTC thermistor ceramic materials. The technical solution rationally integrates alumina / doped barium titanate nanorods, hollow silica microspheres, and a glassy sintering aid, optimizing microstructure distribution while achieving synergistic regulation of thermal, electrical, and mechanical properties. Firstly, during preparation, the alumina / doped barium titanate nanorods are ultrasonically dispersed to form a stable alcohol dispersion system, providing a uniform framework for subsequent microstructure construction. The introduction of hollow silica microspheres, while maintaining the overall lightweight structure, improves the uniformity of nanorod distribution and the three-dimensional support effect, effectively alleviating uneven shrinkage and stress concentration during sintering. The gradual addition of the glassy sintering aid promotes interfacial wetting and sintering activity between components, achieving effective densification between grains by lowering the sintering temperature, thus enhancing the overall structural integrity of the ceramic body. During the molding stage, the synergistic use of polyvinyl alcohol binder and ammonium polyacrylate dispersant not only ensured the rheological stability of the ceramic slurry but also improved the uniformity of particle distribution and molding quality. The use of a constant-temperature water bath treatment achieved a dynamic balance between solvent evaporation and internal stress regulation, thus providing a good foundation for subsequent tape casting. Finally, under a weakly oxidizing atmosphere, controlled heating rate and holding time achieved grain densification, forming a compact ceramic microstructure with clean interfaces, effectively improving high pressure resistance and the stability of the PTC effect. This preparation process, through the synergistic effect of multiple components and precise multi-stage control, achieved an organic unity between raw material structure and final performance, fully demonstrating the core value of material design and process optimization in improving the comprehensive performance of functional ceramics.

[0024] This invention also discloses the application of a high-pressure-resistant PTC thermistor ceramic material in over-temperature protection of new energy vehicle battery packs, self-resetting current-limiting elements for high-voltage power equipment, and temperature control switches for industrial automation.

[0025] (3) Beneficial technical effects

[0026] 1. This invention achieves a synergistic improvement in pressure resistance and PTC effect by constructing a core-shell structure of alumina / doped barium titanate nanorods, significantly improving thermoelectric stability and structural compactness, solving the problems of electrical breakdown and response instability under high voltage conditions, and is suitable for high-reliability temperature control devices with broad application prospects.

[0027] 2. This invention achieves dense ceramic structure, uniform stress distribution, and stable thermoelectric properties through the synergistic construction of nanorod framework, lightweight microspheres, and sintering aid, significantly improving reliability and safety under high pressure conditions, solving the problems of uneven sintering and effect drift in traditional PTC materials, and possessing excellent engineering application potential. Attached Figure Description

[0028] Figure 1 Transmission electron microscopy and elemental linear scanning distribution of alumina / doped barium titanate nanorods prepared in Example 1 of this invention.

[0029] Figure 2 The image shows the morphology of the alumina / doped barium titanate nanorods prepared in Example 1 of this invention.

[0030] Figure 3 This is a transmission electron microscope (TEM) image of the hollow silica microspheres prepared in Example 1 of the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0032] Example 1

[0033] A high-pressure-resistant PTC thermistor ceramic material comprises the following raw materials in parts by weight: 100.0 parts of alumina / doped barium titanate nanorods, 5 parts of hollow silica microspheres, 4 parts of glass phase sintering aid; 1.0 part of polyvinyl alcohol binder, 0.5 parts of ammonium polyacrylate dispersant, and 5.0 parts of anhydrous ethanol.

[0034] The alumina / doped barium titanate nanorods have a core-shell structure, with an alumina shell and a barium titanate-doped core; the doped barium titanate is manganese-doped barium titanate; the general chemical formula of the manganese-doped barium titanate is BaTi. 1-x Mn x O3, where x = 0.05, is a lattice doping process in which manganese is substituted for titanium sites.

[0035] The preparation method of alumina / doped barium titanate nanorods in this embodiment is as follows: 20 parts by weight of doped barium titanate nanorods are dispersed in 50 parts by weight of ethanol and ultrasonically treated for 10 min to form a uniform suspension. 5 parts by weight of aluminum nitrate are mixed with 30 parts by weight of ethanol, and 1 part by weight of acetylacetone is added. The mixture is reacted at 40°C for 60 min under a stirring rate of 300 rpm to form an aluminum precursor sol. Subsequently, the suspension is injected into the aluminum precursor sol at a rate of 1 mL / min. The pH is adjusted to 4.0, and the temperature is maintained at 50°C while stirring is continued for 120 min to complete the hydrolysis-condensation reaction. The resulting mixture is then analyzed through a pore size of 0. After filtration through a .22 μm filter membrane, the solid phase was retained and dried at 80 °C for 120 min to obtain a gel-coated nanorod precursor. The precursor was then calcined in air at 500 °C for 120 min at a rate of 2 °C / min to form an alumina coating layer. The oxygen partial pressure in the furnace was controlled at 0.1 MPa during the calcination stage. The final product was separated by centrifugation at 8000 rpm for 10 min, and the solid phase was retained. The product was then washed three times with ethanol to remove unreacted aluminum source and byproducts. The product was then dried at 60 °C for 60 min under a vacuum of 0.01 MPa to obtain alumina / doped barium titanate nanorods.

[0036] The preparation method of the doped barium titanate nanorods in this embodiment is as follows: 122 parts by weight of barium nitrate hexahydrate are dissolved in 200 parts of deionized water to form a first solution. 80 parts of tetrabutyl titanate and 50 parts of ethanol are mixed and 4 parts of manganese nitrate tetrahydrate are added to form a second solution. The first solution is added dropwise to the second solution at a rate of 2 mL / min. The mixture is stirred at a stirring rate of 300 rpm for 30 min to obtain a suspension. Then, 30 parts of citric acid are added, and the mixture is stirred continuously at 90°C for 120 min until a viscous gel is formed. The gel is placed in a muffle furnace and heated to 250°C at 10°C / min and maintained for 20 min to complete the auto-ignition reaction. The resulting precursor powder is sintered in a nitrogen atmosphere at 1050°C at 5°C / min for 300 min. After cooling to room temperature in the furnace, particles larger than 500 nm are removed by ethanol dispersion and centrifugation to finally obtain the doped barium titanate nanorods.

[0037] In this embodiment, the mass ratio of alumina to barium titanate in the alumina / doped barium titanate nanorods is 1:12.

[0038] The alumina / doped barium titanate nanorods in this embodiment have an average length of 800 nm and an aspect ratio controlled at 4.5:1.

[0039] The thickness of the alumina in this embodiment is 10 nm.

[0040] The preparation method of hollow silica microspheres in this embodiment is as follows: 1.2 parts by weight of glucose monohydrate are dissolved in 22 parts of deionized water to form a first solution, and 0.32 parts of sodium silicate nonahydrate are dissolved in 11 parts of deionized water to form a second solution. The two solutions are mixed at a stirring speed of 500 rpm. During the mixing process, the pH is adjusted to 3.5 with citric acid. Then, the mixture is transferred to a sealed reaction vessel and subjected to a hydrothermal reaction at 200°C for 28 hours, with the reaction pressure maintained at 2.0 MPa. After the reaction is completed, the solid-liquid mixture is separated. The mixture was filtered through a 0.22 μm pore size filter membrane. The retained solid product was washed five times with 30 parts of deionized water and 25 parts of anhydrous ethanol to remove soluble ions and organic residues. Then, it was dried for 6 h under a vacuum of -0.10 MPa and a temperature of 65 °C to obtain a silicon-carbon composite. Finally, the silicon-carbon composite was placed in a muffle furnace and heated to 600 °C at a programmed heating rate of 8 °C / min. It was then calcined in air for 6 h to completely remove the carbon core, obtaining hollow silica microspheres.

[0041] The average diameter of the hollow silica microspheres in this embodiment is 600 nm.

[0042] The glass phase sintering aid in this embodiment is mainly composed of B2O3, Li2O and SiO2. By mass percentage, the content of B2O3 in the sintering aid is 60%, the content of Li2O is 20% and the content of SiO2 is 20%.

[0043] This embodiment describes a method for preparing a high-pressure-resistant PTC thermistor ceramic material, comprising the following steps:

[0044] S1. Alumina / doped barium titanate nanorods were added to anhydrous ethanol and treated with ultrasonic oscillation for 30 min at an ultrasonic frequency of 60 kHz to form a nanorod ethanol dispersion. Hollow silica microspheres were then slowly added to the dispersion and stirred continuously for 40 min at a magnetic stirring rate of 500 rpm to ensure that the microspheres were uniformly distributed in the nanorod matrix. Glass phase sintering aid was added to the system in batches, and the stirring rate was controlled at 600 rpm for 60 min to form a premixed slurry with a three-dimensional composite structure.

[0045] S2. Polyvinyl alcohol binder and ammonium polyacrylate dispersant are added to the premixed slurry in sequence, with the binder added first and then the dispersant. The stirring speed is 500 rpm and the stirring time is 60 min to obtain a ceramic slurry with stable viscosity. The slurry is placed in a constant temperature water bath and heated to 60℃. The stirring speed is controlled at 400 rpm and the holding time is 60 min to complete the solvent evaporation control and rheological property optimization. The casting process is adopted, with the pressure set at 30 MPa and the holding time at 10 min to prepare the green body.

[0046] S3. Place the green body in a hot air circulating drying oven and pre-dry it at 100℃ for 240 min to make the moisture content ≤0.5wt%. After drying, transfer the green body to a muffle furnace and heat it to the sintering temperature of 1150℃ at a heating rate of 5℃ / min under a weak oxidizing atmosphere with an oxygen content ≤5%, and hold it for 420 min to achieve grain densification. Cool it to room temperature to obtain a high pressure resistant PTC thermistor ceramic material.

[0047] Combination Figure 1 , Figure 2 and Figure 3 The structural characterization results demonstrate that the material design strategy employed in this invention possesses clear structural controllability and interface construction advantages, wherein... Figure 1 The transmission electron microscope and elemental line scan images clearly show that the alumina / doped barium titanate nanorods have a typical core-shell structure, with aluminum elements uniformly distributed on the surface of the rods to form a continuous and dense coating layer, which effectively improves the interfacial insulation and grain boundary barrier. Figure 2 This further demonstrates that nanorods have a good aspect ratio and dispersibility, which is beneficial for forming oriented structures in ceramic matrices, enhancing compactness and thermal response uniformity; Figure 3 The hollow silica microspheres shown exhibit a regular spherical cavity structure and a uniform particle size distribution, providing the ceramic material with electric field modulation and thermal stress buffering functions. They can construct a stable three-dimensional composite network at the microscale. In summary, this invention fully demonstrates that by introducing structurally ordered nanorods and hollow microspheres to synergistically construct a multi-scale interface modulation mechanism, it achieves significant improvements in the PTC effect, insulation performance, and thermal cycling stability of the thermosensitive ceramic material.

[0048] Example 2

[0049] A high-pressure-resistant PTC thermistor ceramic material comprises the following raw materials in parts by weight: 106 parts of alumina / doped barium titanate nanorods, 8 parts of hollow silica microspheres, 5 parts of glass phase sintering aid; 1.3 parts of polyvinyl alcohol binder, 1.0 part of ammonium polyacrylate dispersant, and 6.5 parts of anhydrous ethanol.

[0050] The alumina / doped barium titanate nanorods described herein have a core-shell structure, with an alumina shell and a manganese-doped barium titanate core; the chemical formula of the manganese-doped barium titanate is BaTi. 1-x Mn xO3, where x = 0.1, is used for lattice doping by manganese substitution of titanium sites. The preparation method of the alumina / doped barium titanate nanorods in this embodiment is as follows: 26 parts by weight of doped barium titanate nanorods are dispersed in 59 parts by weight of ethanol and ultrasonically treated for 16 min to form a uniform suspension. 8 parts by weight of aluminum nitrate are mixed with 36 parts by weight of ethanol, and 2 parts by weight of acetylacetone are added. The mixture is reacted at 46°C for 78 min under a stirring rate of 360 rpm to form an aluminum precursor sol. The suspension is then injected into the aluminum precursor sol at a rate of 1.6 mL / min. The pH is adjusted to 4.5, and the temperature is maintained at 56°C. Stirring continues for 138 min to complete the hydrolysis-condensation reaction. The resulting mixture is then analyzed through a pore size of 0. After filtration through a .29 μm filter membrane, the solid phase was retained and dried at 86 °C for 156 min to obtain a gel-coated nanorod precursor. The precursor was then calcined in air at 560 °C for 156 min at a rate of 3 °C / min to form an alumina coating layer. The oxygen partial pressure in the furnace was controlled at 0.16 MPa during the calcination stage. The final product was separated by centrifugation at 9200 rpm for 16 min, and the solid phase was retained. The product was then washed four times with ethanol to remove unreacted aluminum source and byproducts. The product was then dried at 66 °C for 78 min under a vacuum of 0.02 MPa to obtain alumina / doped barium titanate nanorods.

[0051] The preparation method of the doped barium titanate nanorods in this embodiment is as follows: 127.8 parts by weight of barium nitrate hexahydrate are dissolved in 230 parts of deionized water to form a first solution. 86 parts of tetrabutyl titanate and 59 parts of ethanol are mixed and 8.2 parts of manganese nitrate tetrahydrate are added to form a second solution. The first solution is added dropwise to the second solution at a rate of 3 mL / min. The mixture is stirred at a stirring rate of 360 rpm for 48 min to obtain a suspension. Then, 36 parts of citric acid are added, and the mixture is stirred continuously at 99°C for 138 min until a viscous gel is formed. The gel is placed in a muffle furnace and heated to 265°C at 12°C / min and maintained for 26 min to complete the auto-ignition reaction. The resulting precursor powder is sintered in a nitrogen atmosphere at 1080°C at 6°C / min for 336 min. After cooling to room temperature in the furnace, particles larger than 500 nm are removed by ethanol dispersion and centrifugation to finally obtain the doped barium titanate nanorods.

[0052] In this embodiment, the mass ratio of alumina to barium titanate in the alumina / doped barium titanate nanorods is 1:14.

[0053] The alumina / doped barium titanate nanorods in this embodiment have an average length of 920 nm and an aspect ratio controlled at 6.2:1.

[0054] The thickness of the alumina in this embodiment is 13 nm;

[0055] The preparation method of hollow silica microspheres in this embodiment is as follows: 1.1 parts by weight of glucose monohydrate are dissolved in 20 parts of deionized water to form a first solution, and 0.30 parts of sodium silicate nonahydrate are dissolved in 10 parts of deionized water to form a second solution. The two solutions are mixed at a stirring speed of 380 rpm. During the mixing process, the pH is adjusted to 3.1 with citric acid. Then, the mixture is transferred to a sealed reaction vessel and subjected to a hydrothermal reaction at 184°C for 25 hours, with the reaction pressure maintained at 1.4 MPa. After the reaction is completed, the solid and liquid are mixed. The material was filtered through a 0.22 μm pore size filter membrane. The retained solid product was washed four times with 26 parts of deionized water and 21 parts of anhydrous ethanol to remove soluble ions and organic residues. Then, it was dried for 5.2 h under a vacuum of -0.09 MPa and a temperature of 61 °C to obtain a silicon-carbon composite. Finally, the silicon-carbon composite was placed in a muffle furnace and heated to 560 °C at a programmed heating rate of 6 °C / min, and calcined in air for 5.2 h to completely remove the carbon core, obtaining hollow silica microspheres.

[0056] The average diameter of the hollow silica microspheres in this embodiment is 480 nm.

[0057] The glass phase sintering aid in this embodiment is mainly composed of B2O3, Li2O and SiO2. By mass percentage, the content of B2O3 in the sintering aid is 48%, the content of Li2O is 14% and the content of SiO2 is 38%.

[0058] This embodiment describes a method for preparing a high-pressure-resistant PTC thermistor ceramic material, comprising the following steps:

[0059] S1. Alumina / doped barium titanate nanorods were added to anhydrous ethanol and treated with ultrasonic oscillation for 22 min at an ultrasonic frequency of 52 kHz to form a nanorod ethanol dispersion. Hollow silica microspheres were then slowly added to the dispersion and stirred continuously for 32 min at a magnetic stirring rate of 420 rpm to ensure that the microspheres were uniformly distributed in the nanorod matrix. Glass phase sintering aid was added to the system in batches, and the stirring rate was controlled at 520 rpm for 48 min to form a premixed slurry with a three-dimensional composite structure.

[0060] S2. Polyvinyl alcohol binder and ammonium polyacrylate dispersant are added to the premixed slurry in sequence, with the binder added first and then the dispersant. The stirring speed is 420 rpm and the stirring time is 48 min to obtain a ceramic slurry with stable viscosity. The slurry is placed in a constant temperature water bath and heated to 52℃. The stirring speed is controlled at 320 rpm and the holding time is 48 min to complete the solvent evaporation control and rheological property optimization. The casting process is adopted, with the pressure set at 22 MPa and the holding time at 8 min to prepare the green body.

[0061] S3. Place the green body in a hot air circulating drying oven and pre-dry it at 92℃ for 192 min to make the moisture content ≤0.5wt%. After drying, transfer the green body to a muffle furnace and heat it to the sintering temperature of 1090℃ at a rate of 3.8℃ / min under a weak oxidizing atmosphere with an oxygen content ≤5%, and hold it for 372 min to achieve grain densification. Cool it to room temperature to obtain a high pressure resistant PTC thermistor ceramic material.

[0062] Example 3

[0063] A high-pressure-resistant PTC thermistor ceramic material comprises the following raw materials in parts by weight: 120.0 parts of alumina / doped barium titanate nanorods, 15 parts of hollow silica microspheres, 8 parts of glass phase sintering aid; 2.0 parts of polyvinyl alcohol binder, 2.0 parts of ammonium polyacrylate dispersant, and 10.0 parts of anhydrous ethanol.

[0064] The alumina / doped barium titanate nanorods described herein have a core-shell structure, with an alumina shell and a manganese-doped barium titanate core; the chemical formula of the manganese-doped barium titanate is BaTi. 1-x Mn x O3, where x = 0.20, is used for lattice doping by manganese substitution of titanium sites. The preparation method of alumina / doped barium titanate nanorods in this embodiment is as follows: 40 parts by weight of doped barium titanate nanorods are dispersed in 80 parts by weight of ethanol and ultrasonically treated for 30 min to form a uniform suspension. 15 parts by weight of aluminum nitrate are mixed with 50 parts by weight of ethanol, and 5 parts by weight of acetylacetone are added. The mixture is reacted at 60°C for 120 min under a stirring rate of 500 rpm to form an aluminum precursor sol. Subsequently, the suspension is injected into the aluminum precursor sol at a rate of 3 mL / min. The pH is adjusted to 5.5, and the temperature is maintained at 70°C while stirring is continued for 180 min to complete the hydrolysis-condensation reaction. The resulting mixed system is then analyzed through a pore size of 0. After filtration through a 45 μm filter membrane, the solid phase was retained and dried at 100 °C for 240 min to obtain a gel-coated nanorod precursor. The precursor was then calcined in air at 700 °C for 240 min at a rate of 5 °C / min to form an alumina coating layer. The oxygen partial pressure in the furnace was controlled at 0.3 MPa during the calcination process. The final product was separated by centrifugation at 12000 rpm for 30 min, and the solid phase was retained. The product was then washed five times with ethanol to remove unreacted aluminum source and byproducts. Finally, it was dried at 80 °C for 120 min under a vacuum of 0.05 MPa to obtain alumina / doped barium titanate nanorods.

[0065] The preparation method of the doped barium titanate nanorods in this embodiment is as follows: 145 parts by weight of barium nitrate hexahydrate are dissolved in 300 parts of deionized water to form a first solution. 100 parts of tetrabutyl titanate and 80 parts of ethanol are mixed and 20 parts of manganese nitrate tetrahydrate are added to form a second solution. The first solution is added dropwise to the second solution at a rate of 5 mL / min. The mixture is stirred at a stirring rate of 500 rpm for 90 min to obtain a suspension. Then, 50 parts of citric acid are added, and the mixture is stirred continuously at 120°C for 180 min until a viscous gel is formed. The gel is placed in a muffle furnace and heated to 300°C at 15°C / min and maintained for 40 min to complete the auto-ignition reaction. The resulting precursor powder is sintered in a nitrogen atmosphere at 1150°C at 8°C / min for 420 min. After cooling to room temperature in the furnace, particles larger than 500 nm are removed by ethanol dispersion and centrifugation to finally obtain the doped barium titanate nanorods.

[0066] In this embodiment, the mass ratio of alumina to barium titanate in the alumina / doped barium titanate nanorods is 1:18.

[0067] The alumina / doped barium titanate nanorods in this embodiment have an average length of 1200 nm and an aspect ratio controlled at 10:1.

[0068] The thickness of the alumina in this embodiment is 20 nm;

[0069] The preparation method of hollow silica microspheres in this embodiment is as follows: 1.1 parts of glucose monohydrate are dissolved in 19 parts of deionized water to form a first solution, and 0.29 parts of sodium silicate nonahydrate are dissolved in 10 parts of deionized water to form a second solution. The two solutions are mixed at a stirring rate of 290 rpm. During the mixing process, the pH is adjusted to 2.8 with citric acid. Then, the mixture is transferred to a sealed reaction vessel and subjected to a hydrothermal reaction at 172°C for 22 hours, with the reaction pressure maintained at 0.95 MPa. After the reaction is completed, the solid-liquid mixture is subjected to... The solid product was filtered through a 0.22 μm pore size membrane and washed four times with 23 parts deionized water and 18 parts anhydrous ethanol to remove soluble ions and organic residues. It was then dried for 4.6 h under a vacuum of -0.09 MPa and a temperature of 58 °C to obtain a silicon-carbon composite. Finally, the silicon-carbon composite was placed in a muffle furnace and heated to 530 °C at a programmed heating rate of 4.5 °C / min and calcined in air for 4.6 h to completely remove the carbon core, resulting in hollow silica microspheres.

[0070] The average diameter of the hollow silica microspheres in this embodiment is 390 nm.

[0071] The glass phase sintering aid in this embodiment is mainly composed of B2O3, Li2O and SiO2. By mass percentage, the content of B2O3 in the sintering aid is 40%, the content of Li2O is 10% and the content of SiO2 is 50%.

[0072] This embodiment describes a method for preparing a high-pressure-resistant PTC thermistor ceramic material, comprising the following steps:

[0073] S1. Alumina / doped barium titanate nanorods were added to anhydrous ethanol and treated with ultrasonic oscillation for 16 min at an ultrasonic frequency of 46 kHz to form a nanorod ethanol dispersion. Hollow silica microspheres were then slowly added to the dispersion and stirred continuously for 26 min at a magnetic stirring rate of 360 rpm to ensure that the microspheres were uniformly distributed in the nanorod matrix. Glass phase sintering aid was added to the system in batches, and the stirring rate was controlled at 460 rpm for 39 min to form a premixed slurry with a three-dimensional composite structure.

[0074] S2. Polyvinyl alcohol binder and ammonium polyacrylate dispersant are added to the premixed slurry in sequence, with the binder added first and then the dispersant. The stirring speed is 360 rpm and the stirring time is 39 min to obtain a ceramic slurry with stable viscosity. The slurry is placed in a constant temperature water bath and heated to 46℃. The stirring speed is controlled at 260 rpm and the holding time is 39 min to complete the solvent evaporation control and rheological property optimization. The casting process is adopted, with the pressure set at 16 MPa and the holding time at 6.5 min to prepare the green body.

[0075] S3. Place the green body in a hot air circulating drying oven and pre-dry it at 86℃ for 156 min to make the moisture content ≤0.5wt%. After drying, transfer the green body to a muffle furnace and heat it to the sintering temperature of 1045℃ at a heating rate of 2.9℃ / min under a weak oxidizing atmosphere with an oxygen content ≤5%, and hold it for 336 min to achieve grain densification. Cool it to room temperature to obtain a high pressure resistant PTC thermistor ceramic material.

[0076] Example 4

[0077] A high-pressure-resistant PTC thermistor ceramic material comprises the following raw materials in parts by weight: 112 parts of alumina / doped barium titanate nanorods, 11 parts of hollow silica microspheres, 6 parts of glass phase sintering aid; 1.6 parts of polyvinyl alcohol binder, 1.4 parts of ammonium polyacrylate dispersant, and 8.0 parts of anhydrous ethanol.

[0078] The alumina / doped barium titanate nanorods described herein have a core-shell structure, with an alumina shell and a manganese-doped barium titanate core; the chemical formula of the manganese-doped barium titanate is BaTi. 1-x Mn xO3, where x = 0.14, is used for lattice doping by manganese substitution of titanium sites. The preparation method of the alumina / doped barium titanate nanorods in this embodiment is as follows: 32 parts by weight of doped barium titanate nanorods are dispersed in 68 parts by weight of ethanol and ultrasonically treated for 22 min to form a uniform suspension. 11 parts by weight of aluminum nitrate are mixed with 42 parts by weight of ethanol, and 3 parts by weight of acetylacetone are added. The mixture is reacted at 52°C for 96 min under a stirring rate of 420 rpm to form an aluminum precursor sol. Subsequently, the suspension is injected into the aluminum precursor sol at a rate of 2.2 mL / min, the pH is adjusted to 4.9, and the temperature is maintained at 62°C while stirring is continued for 156 min to complete the hydrolysis-condensation reaction. The resulting mixed system is then analyzed through a pore size of 0. After filtration through a 0.36 μm filter membrane, the solid phase was retained and dried at 92 °C for 192 min to obtain a gel-coated nanorod precursor. The precursor was then calcined in air at 620 °C for 192 min at a rate of 4 °C / min to form an alumina coating layer. The oxygen partial pressure in the furnace was controlled at 0.22 MPa during the calcination stage. The final product was separated by centrifugation at 10400 rpm for 22 min, and the solid phase was retained. The product was then washed four times with ethanol to remove unreacted aluminum source and byproducts. The product was then dried at 72 °C for 96 min under a vacuum of 0.03 MPa to obtain alumina / doped barium titanate nanorods.

[0079] The preparation method of the doped barium titanate nanorods in this embodiment is as follows: 134 parts by weight of barium nitrate hexahydrate are dissolved in 260 parts of deionized water to form a first solution. 92 parts of tetrabutyl titanate and 68 parts of ethanol are mixed and 12 parts of manganese nitrate tetrahydrate are added to form a second solution. The first solution is added dropwise to the second solution at a rate of 4 mL / min. The mixture is stirred at a stirring rate of 420 rpm for 66 min to obtain a suspension. Then, 42 parts of citric acid are added, and the mixture is stirred continuously at 108°C for 156 min until a viscous gel is formed. The gel is placed in a muffle furnace and heated to 280°C at 13°C / min and maintained for 32 min to complete the auto-ignition reaction. The resulting precursor powder is sintered in a nitrogen atmosphere at 1110°C at 7°C / min for 372 min. After cooling to room temperature in the furnace, particles larger than 500 nm are removed by ethanol dispersion and centrifugation to finally obtain the doped barium titanate nanorods.

[0080] In this embodiment, the mass ratio of alumina to barium titanate in the alumina / doped barium titanate nanorods is 1:16.

[0081] The alumina / doped barium titanate nanorods in this embodiment have an average length of 1040 nm and an aspect ratio controlled at 7.8:1.

[0082] The thickness of the alumina in this embodiment is 16 nm;

[0083] The preparation method of hollow silica microspheres in this embodiment is as follows: 1.0 part by weight of glucose monohydrate is dissolved in 18 parts of deionized water to form a first solution, and 0.28 parts of sodium silicate nonahydrate is dissolved in 9 parts of deionized water to form a second solution. The two solutions are mixed at a stirring speed of 200 rpm. During the mixing process, the pH is adjusted to 2.5 with citric acid. Then, the mixture is transferred to a sealed reaction vessel and subjected to a hydrothermal reaction at 160°C for 20 hours, with the reaction pressure maintained at 0.5 MPa. After the reaction is completed, the solid-liquid mixture is... The compound was filtered through a 0.22 μm pore size filter membrane. The retained solid product was washed three times with 20 parts of deionized water and 15 parts of anhydrous ethanol to remove soluble ions and organic residues. Then, it was dried for 4 h under a vacuum of -0.08 MPa and a temperature of 55 °C to obtain a silicon-carbon composite. Finally, the silicon-carbon composite was placed in a muffle furnace and heated to 500 °C at a programmed heating rate of 3 °C / min. It was then calcined in air for 4 h to completely remove the carbon core, obtaining hollow silica microspheres.

[0084] The average diameter of the hollow silica microspheres in this embodiment is 300 nm.

[0085] The glass phase sintering aid in this embodiment is mainly composed of B2O3, Li2O and SiO2. By mass percentage, the content of B2O3 in the sintering aid is 60%, the content of Li2O is 5%, and the content of SiO2 is 35%.

[0086] This embodiment describes a method for preparing a high-pressure-resistant PTC thermistor ceramic material, comprising the following steps:

[0087] S1. Alumina / doped barium titanate nanorods were added to anhydrous ethanol and treated with ultrasonic oscillation for 10 min at an ultrasonic frequency of 40 kHz to form a nanorod ethanol dispersion. Hollow silica microspheres were then slowly added to the dispersion and stirred continuously for 20 min at a magnetic stirring rate of 300 rpm to ensure that the microspheres were uniformly distributed in the nanorod matrix. Glass phase sintering aid was added to the system in batches, and the stirring rate was controlled at 400 rpm for 30 min to form a premixed slurry with a three-dimensional composite structure.

[0088] S2. Polyvinyl alcohol binder and ammonium polyacrylate dispersant are added sequentially to the premixed slurry, with the binder added first and then the dispersant. The stirring speed is 300 rpm and the stirring time is 30 min to obtain a ceramic slurry with stable viscosity. The slurry is placed in a constant temperature water bath and heated to 40℃. The stirring speed is controlled at 200 rpm and the holding time is 30 min to complete the solvent evaporation control and rheological property optimization. The casting process is adopted, with the pressure set at 10 MPa and the holding time at 5 min to prepare the green body.

[0089] S3. Place the green body in a hot air circulating drying oven and pre-dry it at 80℃ for 120 min to make the moisture content ≤0.5wt%. After drying, transfer the green body to a muffle furnace and heat it to the sintering temperature of 1000℃ at a rate of 2℃ / min under a weak oxidizing atmosphere with an oxygen content ≤5%, and hold it for 300 min to achieve grain densification. Cool it to room temperature to obtain a high pressure resistant PTC thermistor ceramic material.

[0090] Comparative Example 1

[0091] It is basically the same as Example 1, except that the amount of alumina / doped barium titanate nanorods used is 90.0 parts.

[0092] Comparative Example 2

[0093] It is basically the same as Example 1, except that the amount of hollow silica microspheres used is 3 parts.

[0094] Comparative Example 3

[0095] Example 1 is basically the same, except that the stirring rate of the aluminum precursor sol reaction is 200 rpm.

[0096] Comparative Example 4

[0097] It is basically the same as Example 1, except that the calcination temperature of the alumina coating is 750°C.

[0098] Comparative Example 5

[0099] It is basically the same as Example 1, except that the sintering temperature of the barium titanate nanorods for the auto-ignition reaction is 1000℃.

[0100] Comparative Example 6

[0101] It is basically the same as Example 1, except that the mass ratio of alumina to barium titanate is 1:20.

[0102] Comparative Example 7

[0103] It is basically the same as Example 1, except that the aspect ratio of alumina / doped barium titanate nanorods is 3:1.

[0104] Comparative Example 8

[0105] It is basically the same as Example 1, except that the thickness of the alumina coating layer is 5nm.

[0106] Comparative Example 9

[0107] It is basically the same as Example 1, except that the hydrothermal reaction time of hollow silica is 15 hours.

[0108] Comparative Example 10

[0109] It is basically the same as Example 1, except that the casting pressure is 5MPa.

[0110] Comparative Example 11

[0111] It is basically the same as Example 1, except that the oxygen partial pressure during the calcination stage is 0.05 MPa.

[0112] Comparative Example 12

[0113] It is basically the same as Example 1, except that the doping amount of manganese nitrate tetrahydrate is 0.25 molar ratio.

[0114] Comparative Example 13

[0115] It is basically the same as Example 1, except that the calcination temperature of hollow silica is 650°C.

[0116] Comparative Example 14

[0117] It is basically the same as Example 1, except that no aluminum oxide layer is prepared on the surface of the barium titanate nanorods.

[0118] Comparative Example 15

[0119] The preparation method is basically the same as in Example 1, except that hollow silica microspheres were not added to the thermosensitive ceramic material.

[0120] Performance testing:

[0121] PTC Resistance-Temperature Response Test (RT Curve)

[0122] According to IEC 60738 standard, the thermistor ceramic sample was processed into a disc with a diameter of 10 mm and a thickness of 0.5 ± 0.02 mm. An 8 mm diameter 50 nm platinum electrode was fabricated on the surface by magnetron sputtering. A high-resistivity meter (Keithley 6517B) was used to uniformly heat the sample within the range of 25-180 °C at a rate of 3 °C / min, with each 5 °C increment followed by a 10-minute holding period to eliminate thermal hysteresis. The volume resistance was recorded in real time, and a resistance-temperature (RT) curve was plotted. By analyzing the data in the resistance abrupt change region near the Curie point, the resistance change rate (ΔR / R²⁵ ≥ 10⁻⁶) was calculated. 3 The PTC effect intensity and temperature sensitivity of the material were quantified by using the α coefficient (d(logR) / dT≥0.03℃⁻¹) and repeating the experiment with 5 samples in each group to ensure the coefficient of variation (CV) ≤8%.

[0123] Breakdown voltage test

[0124] Following the ASTM D149 standard, ceramic sheets with a thickness of 0.5±0.05 mm and a surface roughness Ra≤0.2 μm were prepared. In a constant temperature and humidity environment of 25±2℃ and 30±5% RH, the samples were immersed in transformer oil with a dielectric strength ≥30 kV / 2.5 mm. A DC voltage was applied at a constant rate of 1 kV / s until breakdown occurred. The breakdown voltage was recorded, and the breakdown field strength per unit thickness (kV / mm) was calculated. This test directly characterizes the insulation reliability of the material under high electric fields. The breakdown field strength is closely related to the ceramic compactness, defect density, and interface uniformity.

[0125] Thermal cycling stability test

[0126] According to IEC 600-68-2-14 standard, 1000 thermal cycles were performed within a temperature range of -40℃ to 150℃ (heating / cooling rate ≤ 5℃ / min, holding time 30 minutes per temperature zone). After every 100 cycles, the resistivity values ​​at 25℃, 100℃, and 150℃ were measured using the four-probe method (ASTM F1529). By comparing the initial and post-cycle RT curves, the Curie point shift (ΔTc) was statistically analyzed to assess the thermal stability of the material. The smaller the absolute value of ΔTc, the lower the degree of degradation of the grain boundary structure under thermal stress.

[0127] Impedance spectroscopy (grain boundary / grain electrical behavior)

[0128] On a sample with a 100 nm gold electrode (6 mm in diameter) deposited by magnetron sputtering, impedance analysis was performed using a Solartron 1260 at 10 nm. -1 -10 6 Impedance spectrum data were acquired in the Hz frequency range and under a perturbation voltage of 0.1-3Vrms, with a temperature gradient of 25-150℃ (temperature control accuracy ±1℃). Based on the core-shell structure characteristics, an R-(R / / CPE) equivalent circuit model was established (CPE exponent n≥0.9 characterizes interface polarization uniformity). Grain resistance (Rg), grain boundary resistance (Rgb), and polarization capacitance parameters were fitted using ZView software. Finally, the grain boundary resistance change rate (ΔRgb / Rgb_initial) before and after thermal cycling or aging was calculated to quantitatively reveal the correlation between grain boundary degradation mechanism and material lifetime.

[0129] The properties of the thermistor ceramic materials of Examples 1-4 and Comparative Examples 1-15 are summarized in Table 1.

[0130] Table 1. Performance summary of the thermistor ceramic materials in Examples 1-4 and Comparative Examples 1-15

[0131]

[0132]

[0133] As can be seen from the table above, insufficient alumina / doped barium titanate nanorods (as in Comparative Example 1) reduce the coating integrity of ceramic particles, leading to a weakening of the grain boundary barrier, a decrease in the resistivity change rate ΔR / R25 and the α coefficient, thereby weakening the PTC effect. Simultaneously, the breakdown voltage decreases, ΔTc and ΔRgb / Rgb_initial increase, and thermal stability deteriorates. Insufficient or absent hollow silica microspheres (as in Comparative Examples 2 and 15) disrupt the synergistic control ability of the core-shell structure, reduce the uniformity of the electric field distribution, leading to a decrease in the breakdown field strength and accelerated grain boundary degradation after thermal cycling. The low stirring rate of the aluminum precursor sol also contributes to the problem. (As in Comparative Example 3) uneven coating thickness or local defects can occur, affecting insulation and grain boundary structure consistency; excessively high alumina coating calcination temperature (as in Comparative Example 4) can cause sintering densification of the coating layer or even grain boundary reactions, leading to a decrease in breakdown voltage and an aggravation of ΔTc shift; insufficient sintering temperature of the main phase of barium titanate nanorods (as in Comparative Example 5) can cause a decrease in ceramic density and insufficient grain growth, affecting resistivity and breakdown strength; a coating mass ratio deviating from the optimal range (as in Comparative Example 6) can cause the alumina layer to be too thin or too thick, resulting in a decrease in breakdown voltage or an increase in interface resistance, respectively, affecting overall electrical performance; the aspect ratio of the nanorods is not... Insufficient coating thickness (e.g., Comparative Example 7) weakens orientation and film density, leading to a decrease in thermal conductivity and breakdown strength; insufficient coating thickness (e.g., Comparative Example 8) directly affects insulation and grain boundary barrier, thereby reducing the PTC effect and stability; insufficient SiO2 hydrothermal reaction time (e.g., Comparative Example 9) results in incomplete microsphere structure, reduced core-shell composite effect, and affected electric field uniformity; low casting pressure (e.g., Comparative Example 10) reduces ceramic density, leading to lower breakdown voltage and accelerated structural degradation after thermal cycling; insufficient oxygen partial pressure during sintering (e.g., Comparative Example 11) exacerbates oxygen vacancy formation, affecting grain boundary conductivity, reducing α value, and... Excessive manganese doping (e.g., Comparative Example 12) leads to electron trap saturation and grain boundary barrier distortion, resulting in artificially high α values ​​but significantly increased ΔRgb and reduced thermal stability. Excessively high SiO2 calcination temperatures (e.g., Comparative Example 13) destroy the hollow structure, affecting overall dielectric regulation. Lack of alumina coating (e.g., Comparative Example 14) results in extremely low breakdown voltage, significantly increased ΔTc and ΔRgb / Rgb_initial, and severe grain boundary degradation. The absence of hollow silicon oxide (e.g., Comparative Example 15) lacks core-shell structural support, leading to decreased insulation, unstable thermal cycling performance, and accelerated grain boundary degradation. All these factors directly or indirectly affect the intensity of the PTC effect, insulation performance, and thermal cycling stability, determining the overall comprehensive performance of the thermistor ceramic material.

[0134] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A high-pressure-resistant PTC thermistor ceramic material, characterized in that, The product comprises the following raw materials in parts by weight: 100.0~120.0 parts of alumina / doped barium titanate nanorods, 5~15 parts of hollow silica microspheres, 4~8 parts of glass phase sintering aid; 1.0~2.0 parts of polyvinyl alcohol binder, 0.5~2.0 parts of ammonium polyacrylate dispersant, and 5.0~10.0 parts of anhydrous ethanol. The alumina / doped barium titanate nanorods described herein have a core-shell structure, with an alumina shell and a manganese-doped barium titanate core; the chemical formula of the manganese-doped barium titanate is BaTi. 1-x Mn x O3, where x = 0.05~0.20, is a lattice doping process in which manganese is substituted for titanium sites; The preparation method of the alumina / doped barium titanate nanorods is as follows: 20-40 parts by weight of doped barium titanate nanorods are dispersed in 50-80 parts by weight of ethanol and ultrasonically treated for 10-30 min to form a uniform suspension. 5-15 parts by weight of aluminum nitrate are mixed with 30-50 parts by weight of ethanol, and 1-5 parts by weight of acetylacetone are added. The mixture is reacted at 40-60°C for 60-120 min under a stirring rate of 300-500 rpm to form an aluminum precursor sol. The suspension is then injected into the aluminum precursor sol at a rate of 1-3 mL / min. The pH is adjusted to 4.0-5.5, and the temperature is maintained at 50-70°C. Stirring continues for 120-180 min to complete the hydrolysis-condensation reaction. The resulting mixture is filtered through a 0.22-0.45 μm pore size filter to retain the solid phase components and dried at 80-100°C for 120-240 minutes. A gel-coated nanorod precursor was obtained. The precursor was calcined in air at 500-700°C for 120-240 min at a rate of 2-5°C / min to form an alumina coating layer. The oxygen partial pressure in the furnace was controlled at 0.1-0.3 MPa during the calcination stage. The final product was separated by centrifugation at 8000-12000 rpm for 10-30 min, and the solid phase product was retained. The product was then washed with ethanol 3-5 times to remove unreacted aluminum source and byproducts. The product was dried at 60-80°C for 60-120 min under a vacuum of 0.01-0.05 MPa to obtain alumina / doped barium titanate nanorods. The mass ratio of alumina to barium titanate nanorods in the alumina / doped barium titanate nanorods is 1:12 to 1:

18. The alumina / doped barium titanate nanorods have an average length of 800~1200 nm and an aspect ratio controlled at 4.5:1~10:

1. The thickness of the alumina coating layer is 10~20 nm.

2. The high-pressure-resistant PTC thermistor ceramic material as described in claim 1, characterized in that, The preparation method of the doped barium titanate nanorods is as follows: 122-145 parts by weight of barium nitrate hexahydrate are dissolved in 200-300 parts of deionized water to form a first solution. 100 parts of tetrabutyl titanate are mixed with 50-80 parts of ethanol, and 4-20 parts of manganese nitrate tetrahydrate are added to form a second solution. The first solution is added dropwise to the second solution at a rate of 2-5 mL / min. The mixture is stirred at 300-500 rpm for 30-90 min to obtain a suspension. Then, 30-50 parts of citric acid are added, and the mixture is stirred continuously at 90-120°C for 120-180 min until a viscous gel is formed. The gel is placed in a muffle furnace and heated to 250-300°C at 10-15°C / min, maintained at 20-40 min to complete the auto-ignition reaction. The resulting precursor powder is sintered in a nitrogen atmosphere at 5-8°C / min to 1050-1150°C for 300-420 minutes. After being cooled to room temperature in the furnace, the nanorods were dispersed in ethanol and separated by centrifugation to obtain barium titanate nanorods.

3. The high-pressure-resistant PTC thermistor ceramic material as described in claim 1, characterized in that, The hollow silica microspheres are prepared as follows: 1.0-1.2 parts by weight of glucose monohydrate are dissolved in 18-22 parts by weight of deionized water to form a first solution; 0.28-0.32 parts by weight of sodium silicate nonahydrate are dissolved in 9-11 parts by weight of deionized water to form a second solution. The two solutions are mixed at a stirring rate of 200-500 rpm. During mixing, the pH is adjusted to 2.5-3.5 with citric acid. The mixture is then transferred to a sealed reaction vessel and subjected to a hydrothermal reaction at 160-200°C for 20-28 hours, with the reaction pressure maintained at 0.5-2.0 MPa. After the reaction is complete, the solid-liquid mixture is filtered through a 0.22 μm pore size filter membrane. The retained solid product is washed 3-5 times with 20-30 parts by weight of deionized water and 15-25 parts by weight of anhydrous ethanol to remove soluble ions and organic residues. Subsequently, the mixture is subjected to a vacuum of -0.08 to -0.10 MPa. The silicon-carbon composite was dried at MPa and 55-65°C for 4-6 hours to obtain a silicon-carbon composite. Finally, the silicon-carbon composite was placed in a muffle furnace and heated to 500-600°C at a heating rate of 3-8°C / min. It was then calcined in air for 4-6 hours to completely remove the carbon core and obtain hollow silica microspheres. The hollow silica microspheres have an average diameter of 300~600 nm.

4. The high-pressure-resistant PTC thermistor ceramic material as described in claim 1, characterized in that, The glass phase sintering aid is mainly composed of B2O3, Li2O and SiO2. By mass percentage, the content of B2O3 in the sintering aid is 30% to 60%, the content of Li2O is 5% to 20%, and the content of SiO2 is 20% to 50%.

5. The method for preparing a high-pressure-resistant PTC thermistor ceramic material as described in claim 1, characterized in that, Includes the following steps: S1. Alumina / doped barium titanate nanorods are added to anhydrous ethanol and treated with ultrasonic oscillation for 10-30 min at an ultrasonic frequency of 40-60 kHz to form a nanorod ethanol dispersion. Hollow silica microspheres are then slowly added to the dispersion and stirred continuously for 20-40 min at a magnetic stirring rate of 300-500 rpm to ensure that the microspheres are uniformly distributed in the nanorod matrix. Glass phase sintering aid is added to the system in batches, and the stirring rate is controlled at 400-600 rpm for 30-60 min to form a premixed slurry with a three-dimensional composite structure. S2. Polyvinyl alcohol binder and ammonium polyacrylate dispersant are added sequentially to the premixed slurry, with the binder added first and then the dispersant. The stirring speed is 300~500 rpm and the stirring time is 30~60 min to obtain a ceramic slurry with stable viscosity. The slurry is placed in a constant temperature water bath and heated to 40~60°C. The stirring speed is controlled at 200~400 rpm and the holding time is 30~60 min to complete the solvent evaporation control and rheological property optimization. The casting process is adopted, with the pressure set at 10~30 MPa and the holding time at 5~10 min to prepare the green body. S3. Place the green body in a hot air circulating drying oven and pre-dry it at 80~100°C for 120~240 min to make the moisture content ≤0.5wt%. After drying, transfer the green body to a muffle furnace and heat it to a sintering temperature of 1000~1150°C at a heating rate of 2~5°C / min under a weak oxidizing atmosphere with an oxygen content ≤5%, and hold it for 300~420 min to achieve grain densification. Cool it to room temperature to obtain a high pressure resistant PTC thermistor ceramic material.

6. The application of the high-voltage-resistant PTC thermistor ceramic material as described in claim 1 in self-resetting current-limiting elements of high-voltage power equipment and temperature control switches for industrial automation.

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