High-voltage-resistant PTC thermal sensitive ceramic material, preparation method and application

Abstract

The invention relates to the field of ceramic materials, provides a high-voltage-resistant PTC (Positive Temperature Coefficient) thermal sensitive ceramic material as well as a preparation method and application thereof, and aims to improve the voltage resistance and PTC effect stability of thermal sensitive ceramic. The material is composed of aluminum oxide-coated manganese-doped barium titanate nanorods, hollow-core silicon dioxide microspheres and a glass phase sintering aid, and the electric heating performance and the microstructure stability are optimized by constructing a core-shell structure and a three-dimensional composite system. A hydrothermal method and a sol-gel method are adopted to precisely control a raw material structure, and alcohol dispersion, tape casting and weak oxidizing atmosphere sintering are combined, so that the compactness and consistency of the ceramic are ensured. The material is suitable for high-voltage temperature control elements and over-current protection devices, and is widely applied to the fields of new energy automobile battery pack over-temperature protection, high-voltage power equipment current limiting elements, industrial automatic temperature control switches and the like.

Description

Technical Field

[0001] The present invention relates to the field of ceramic materials, and particularly to a high-voltage-resistant PTC thermistor ceramic material, a preparation method and an application thereof. Background Art

[0002] In modern power electronics systems, automotive electronic control devices and smart home products, PTC (positive temperature coefficient) thermistor ceramic materials, as key temperature control and overcurrent protection components, are playing an increasingly important role. Especially in complex working conditions such as high-voltage power modules, electric vehicle battery management systems and high-speed motor drives, these materials need to operate in an environment of high voltage, high temperature and strong electromagnetic interference for a long time, posing more stringent requirements on their high-voltage resistance performance and the stability of the PTC effect. High-voltage resistance performance can effectively suppress the risk of electric breakdown and ensure the 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-lasting and reliable protection functions. Therefore, developing thermistor 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 devices, but also can expand their application scope in high-voltage and high-power systems, promoting the development of related industries towards high performance and high reliability. In this context, exploring new PTC ceramic materials with coordinated optimization of structural design and microstructural regulation has become an important research direction in the field of materials science and engineering technology, with significant application value and industrial prospects.

[0003] Although there have been many studies on PTC thermistor ceramic materials to improve their comprehensive performance, there are still obvious deficiencies in high-voltage resistance performance and the stability of the PTC effect, and no systematic and effective solution path has been formed. For example, Chinese Patent No. CN104844196A discloses a high-Tc lead-free PTC thermistor ceramic material, which shows certain temperature response characteristics under normal working conditions, but is prone to electric breakdown in a high-voltage environment, and with the increase of the number of cycles, the PTC effect shows significant drift, making it difficult to meet the requirements of long-term stable operation. The main reason is that there is a lack of an effective microstructure regulation mechanism in the material system, making it difficult to maintain the thermal regulation function of the current-carrying channels while improving electrical insulation; at the same time, the grain boundaries of the ceramic lack sufficient energy buffering and electric field homogenization capabilities, resulting in local electric field concentration, which induces breakdown or effect instability. In addition, the existing preparation process has limited control precision over the microstructure, resulting in microcracks or inhomogeneous distribution inside the ceramic, further weakening its high-voltage resistance and effect stability. Therefore, it is urgent to start from multiple aspects such as material composition, structure construction and sintering process, and propose new design and coordinated regulation strategies to systematically solve the problem of coordinated optimization of high-voltage resistance and PTC effect. Summary of the Invention

[0004] (1) Technical Problems to be Solved

[0005] The object of the present invention is to provide a high-voltage-resistant PTC thermosensitive ceramic material, a preparation method and an application, so as to solve the problems of insufficient high-voltage resistance performance and PTC effect stability of current thermosensitive ceramic materials.

[0006] (2) Technical solution

[0007] In order to achieve the above object, the present invention provides the following technical solution:

[0008] The raw materials for preparing the high-voltage-resistant PTC thermosensitive ceramic material include, 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 aids; 1.0-2.0 parts of polyvinyl alcohol binder, 0.5-2.0 parts of ammonium polyacrylate dispersant, 5.0-10.0 parts of absolute ethanol;

[0009] The alumina / doped barium titanate nanorods have a core-shell structure, the shell layer is alumina, and the core part is manganese-doped barium titanate nanorods; the chemical general formula of the manganese-doped barium titanate is BaTi 1-x Mn x O3, where x = 0.05-0.20, and the manganese element realizes lattice doping by substituting the titanium site. Further, the preparation method of the alumina / doped barium titanate nanorods is as follows: by weight, 20-40 parts by weight of doped barium titanate nanorods are dispersed in 50-80 parts of ethanol and ultrasonically treated 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 are added, and the reaction is carried out at 40-60 °C for 60-120 min at a stirring rate of 300-500 rpm to form an aluminum precursor sol. Subsequently, 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 °C and stirring is continued for 120-180 min to complete the hydrolysis and polycondensation reaction. The obtained mixed system is filtered through a filter membrane with a pore size of 0.22-0.45 μm to retain the solid phase component, dried at 80-100 °C for 120-240 min to obtain a gel-coated nanorod precursor, and the precursor is calcined in an air atmosphere at a heating rate of 2-5 °C / min to 500-700 °C for 120-240 min to form an alumina coating layer. The oxygen partial pressure in the furnace during the calcination stage is controlled at 0.1-0.3 MPa. The final product is separated by centrifugation at a centrifugal rate of 8000-12000 rpm for 10-30 min to retain the solid phase product, and then the product is washed with ethanol 3-5 times to remove unreacted aluminum sources and by-products, and dried at 60-80 °C under a vacuum of 0.01-0.05 MPa for 60-120 min to obtain alumina / doped barium titanate nanorods.

[0010] Further, the preparation method of the doped barium titanate nanorods is as follows: by weight, 122-145 parts 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 2-20 parts of manganese nitrate tetrahydrate are added to form a second solution. The first solution is dropped into the second solution at a rate of 2-5 mL / min, and the mixture is stirred at a stirring rate of 300-500 rpm for 30-90 min to obtain a suspension. Subsequently, 30-50 parts of citric acid are added, and the mixture is continuously stirred 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 a rate of 10-15 °C / min and maintained for 20-40 min to complete the self-combustion reaction. The obtained precursor powder is heated to 1050-1150 °C at a rate of 5-8 °C / min in a nitrogen atmosphere and sintered for 300-420 min. After cooling to room temperature with the furnace, particles with a particle size larger than 500 nm are removed by ethanol dispersion and centrifugal separation, and finally doped barium titanate nanorods are obtained.

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

[0012] Further, the average length of the alumina / 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 alumina is 10-20 nm;

[0014] The design of the present invention using alumina / doped barium titanate nanorods is mainly used to enhance the comprehensive performance of high breakdown voltage performance and PTC effect stability. The core lies in realizing the synergistic optimization between the material structure and performance by constructing functional nanorods with a core-shell structure. The doped barium titanate nanorods serve as the core phase, endowing the material with good PTC effect response ability. At the same time, the doping of manganese elements adjusts its carrier mechanism and energy band structure, thereby improving its thermal sensitivity stability. The alumina shell layer has excellent electrical insulation and thermal stability, and can effectively suppress local electric field concentration and electric breakdown phenomena under high voltage stress, significantly enhancing the breakdown voltage ability of the material. The construction of this core-shell structure combines the sol-gel method and the calcination process, enabling alumina to uniformly coat the surface of doped barium titanate at the nanoscale, effectively controlling the shell thickness and interface quality, promoting the balanced distribution of the interface electric field and increasing the overall thermal conductivity, thereby achieving the dual stability of the thermal field and the electric field while maintaining the sensitivity of the PTC effect. In addition, by regulating the mass ratio of alumina to doped barium titanate, the aspect ratio of the rod-shaped particles, and the shell thickness, the packing structure between particles and the ceramic densification can be further optimized, inhibiting the generation of microcracks and stress concentration phenomena, and enhancing the reliability and service life of the material under complex working conditions. The above design not only realizes the functional complementarity between structural units, but also realizes the synergistic regulation of thermal and electrical properties at the microscopic level, thereby significantly improving the comprehensive performance of the material under high voltage and alternating stress conditions, providing an effective structural and technological solution for the development of high-performance PTC thermosensitive ceramic materials.

[0015] Further, the preparation method of the hollow silica microspheres is as follows: Dissolve 1.0 - 1.2 parts by weight of glucose monohydrate in 18 - 22 parts of deionized water to form a first solution, and dissolve 0.28 - 0.32 parts of sodium silicate nonahydrate in 9 - 11 parts of deionized water to form a second solution. The two solutions are mixed at a stirring rate of 200 - 500 rpm, and the pH is adjusted to 2.5 - 3.5 with citric acid during the mixing process. Then, it is transferred to a closed reaction vessel and hydrothermally reacted at 160 - 200 °C for 20 - 28 h, and the reaction pressure is 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 μm. The retained solid product is washed 3 - 5 times with 20 - 30 parts of deionized water and 15 - 25 parts of absolute ethanol respectively to remove soluble ions and organic residues. Subsequently, it is dried at a vacuum degree of -0.08 - -0.10 MPa and a temperature of 55 - 65 °C for 4 - 6 h to obtain a silicon-carbon composite. Finally, the silicon-carbon composite is placed in a muffle furnace and heated at a heating rate of 3 - 8 °C / min to 500 - 600 °C, and calcined in an air atmosphere for 4 - 6 h to completely remove the carbon core, obtaining hollow silica microspheres.

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

[0017] The present invention adopts the design of alumina / doped barium titanate nanorods mainly to enhance the structural stability and dielectric uniformity of high withstand voltage performance and PTC effect stability. By introducing hollow silica microspheres on this basis, the microstructure and dielectric environment of the ceramic material are further optimized to achieve a synergistic enhancement effect between multiple components. Hollow silica microspheres have good size controllability and hollow structural characteristics. Their introduction in the material system not only helps to disperse the skeleton structure formed by the nanorods and improve the overall density, but also effectively alleviates the stress concentration problem caused by uneven thermal expansion during high-temperature sintering or operation, thereby improving the structural integrity and long-term stability of the ceramic body. Its hollow feature forms a micron-scale buffer cavity inside the material, which can provide additional energy release space under thermal excitation or electrical stress, reduce local heat accumulation and electric field concentration risks, and thus help to improve the overall withstand voltage performance. At the same time, hollow silica microspheres have excellent electrical insulation properties, and their uniform distribution in the ceramic matrix helps to improve the local dielectric environment, achieve a more stable electric field distribution and temperature response behavior, thereby improving the stability of the PTC effect. In addition, the specific surface area advantage brought by the hollow structure also helps to enhance the physical bonding and heat conduction efficiency between micro-interfaces, further promoting the coordinated regulation of thermal-electrical performance. By organically integrating hollow silica microspheres with alumina / doped barium titanate nanorods, the present invention forms a composite ceramic system with a layered structure, thermal insulation and electrical uniformity. On the basis of maintaining the PTC functional response, the overall structural stability and reliability under extreme working conditions are significantly enhanced, reflecting 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] The present invention also provides a method for preparing a high-voltage PTC thermistor ceramic material, comprising the following steps:

[0020] S1. Alumina / doped barium titanate nanorods are added to anhydrous ethanol, and ultrasonic oscillation is performed for 10 to 30 minutes at an ultrasonic frequency of 40 to 60 kHz to form a nanorod alcohol dispersion, and then hollow silica microspheres are slowly added to the dispersion, and the magnetic stirring rate is continuously stirred for 20 to 40 minutes at a rate of 300 to 500 rpm to make the microspheres evenly distributed in the nanorod matrix, and a glass phase sintering aid is added to the system in batches, and the stirring rate is controlled to be 400 to 600 rpm for a stirring time of 30 to 60 minutes to form a premixed slurry with a three-dimensional composite structure;

[0021] S2. Add polyvinyl alcohol binder and ammonium polyacrylate dispersant to the premixed slurry in sequence. The feeding order is binder first and then dispersant. The stirring rate is 300 - 500 rpm, and the stirring time is 30 - 60 min to obtain a ceramic slurry with stable viscosity. Place the slurry in a constant temperature water bath and heat it to 40 - 60 °C. Control the stirring rate at 200 - 400 rpm, and the heat preservation time is 30 - 60 min to complete the control of solvent volatilization and rheological property optimization. Adopt the tape casting process, set the pressure at 10 - 30 MPa, and the pressure holding time is 5 - 10 min to prepare a green body.

[0022] S3. Place the green body in a hot air circulation drying oven and pre-dry it at 80 - 100 °C for 120 - 240 min to make the moisture content ≤ 0.5 wt%. Transfer the dried embryo to a muffle furnace. Under a weak oxidation atmosphere with an oxygen content ≤ 5%, raise the temperature to the sintering temperature of 1000 - 1150 °C at a heating rate of 2 - 5 °C / min, and keep it warm for 300 - 420 min to achieve grain densification. Cool it to room temperature to obtain a high-voltage-resistant PTC thermosensitive ceramic material.

[0023] The design of using multi-component synergistic construction of a three-dimensional composite structure in the present invention is mainly used to enhance the densification and structural stability of the high-voltage-resistant PTC thermosensitive ceramic material. Its technical solution realizes the synergistic regulation of multiple properties such as heat, electricity, and force while optimizing the microstructure distribution by reasonably integrating alumina / doped barium titanate nanorods, hollow silica microspheres, and glass-phase sintering aids. First, during the preparation process, the alumina / doped barium titanate nanorods form a stable alcohol dispersion system through ultrasonic dispersion, providing a uniform framework basis for subsequent microstructure construction. The introduction of hollow silica microspheres improves the distribution uniformity and three-dimensional support effect among the nanorods while maintaining the lightness of the overall structure, effectively alleviating the uneven shrinkage and stress concentration during the sintering process. The gradual addition of the glass-phase sintering aid promotes the interfacial wetting and sintering activity among the components, realizes effective densification between grains while reducing the sintering temperature, and enhances the overall structural integrity of the ceramic body. In the forming stage, the synergistic use of polyvinyl alcohol binder and ammonium polyacrylate dispersant not only ensures the rheological stability of the ceramic slurry but also improves the distribution uniformity and forming quality among the particles. Assisted by constant temperature water bath treatment, the dynamic balance of solvent volatilization and internal stress adjustment is achieved, thus providing a good forming basis for subsequent tape casting. Finally, grain densification is realized by controlling the heating rate and heat preservation time under a weak oxidation atmosphere, forming a ceramic microstructure with a compact structure and clean interface, effectively improving the high-voltage-resistant performance and the stability of the PTC effect. This preparation process realizes the organic unity of the raw material structure and the final performance through multi-component synergistic action and multi-stage precise control, fully reflecting the core value of material design and process optimization in improving the comprehensive performance of functional ceramics.

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

[0025] (3) Beneficial technical effects

[0026] 1. By constructing a core-shell structure of alumina / doped barium titanate nanorods, the present invention realizes the synergistic improvement of voltage resistance and PTC effect, significantly improves the thermoelectric stability and structural compactness, solves the problems of electric breakdown and response instability in high-voltage environments, is applicable to highly reliable temperature control devices, and has broad application prospects.

[0027] 2. Through the synergistic construction of nanorod skeletons, lightweight microspheres and sintering aids, the present invention realizes a dense ceramic structure, uniform stress distribution and stable thermoelectric performance, significantly improves the reliability and safety in high-voltage environments, solves the problems of uneven sintering and effect drift of traditional PTC materials, and has excellent engineering application potential. Description of the drawings

[0028] Figure 1 It is the transmission electron microscope and elemental line scan distribution diagram of the alumina / doped barium titanate nanorods prepared in Example 1 of the present invention.

[0029] Figure 2 It is the morphology diagram of the alumina / doped barium titanate nanorods prepared in Example 1 of the present invention.

[0030] Figure 3 It is the transmission electron microscope morphology diagram of the hollow silica microspheres prepared in Example 1 of the present invention. Detailed implementation manners

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

[0032] Example 1

[0033] A high-voltage-resistant PTC thermistor ceramic material, including 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 part of ammonium polyacrylate dispersant, 5.0 parts of absolute ethanol;

[0034] The alumina / doped barium titanate nanorods have a core-shell structure, the shell layer is alumina, and the core part is doped barium titanate nanorods; the doped barium titanate is manganese-doped barium titanate; the chemical general formula of the manganese-doped barium titanate is BaTi 1-x Mn x O3, where x = 0.05, and the manganese element realizes lattice doping by substituting the titanium site.

[0035] The preparation method of the alumina / doped barium titanate nanorods in this embodiment is as follows: by weight, 20 parts of doped barium titanate nanorods are dispersed in 50 parts of ethanol and ultrasonically treated for 10 min to form a uniform suspension. 5 parts of aluminum nitrate is mixed with 30 parts of ethanol, 1 part of acetylacetone is added, and the reaction is carried out at 40 °C for 60 min at 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 and stirring is continued for 120 min to complete the hydrolysis and polycondensation reaction. The obtained mixed system is filtered through a filter membrane with a pore size of 0.22 μm, and the solid-phase component is retained. It is dried at 80 °C for 120 min to obtain a nanorod precursor coated with gel. The precursor is calcined in an air atmosphere at a heating rate of 2 °C / min to 500 °C for 120 min to form an alumina coating layer. The oxygen partial pressure in the furnace during the calcination stage is controlled at 0.1 MPa. The final product is separated by centrifugation at a rate of 8000 rpm for 10 min, and the solid-phase product is retained. Then the product is washed 3 times with ethanol to remove the unreacted aluminum source and by-products, and 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: by weight, 122 parts of barium nitrate hexahydrate is dissolved in 200 parts of deionized water to form a first solution. 80 parts of tetrabutyl titanate is mixed with 50 parts of ethanol and 4 parts of manganese nitrate tetrahydrate is added to form a second solution. The first solution is added dropwise to the second solution at a rate of 2 mL / min, and the mixture is stirred at a rate of 300 rpm for 30 min to obtain a suspension. Subsequently, 30 parts of citric acid is added, and stirring is continued at 90 °C for 120 min until a viscous gel is formed. The gel is placed in a muffle furnace and heated at a rate of 10 °C / min to 250 °C and maintained for 20 min to complete the self-ignition reaction. The obtained precursor powder is sintered in a nitrogen atmosphere at a heating rate of 5 °C / min to 1050 °C for 300 min. After cooling to room temperature with the furnace, particles with a particle size greater than 500 nm are removed by ethanol dispersion and centrifugal separation, and finally doped barium titanate nanorods are obtained.

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

[0038] The average length of the alumina / doped barium titanate nanorods of this embodiment is 800 nm, and the aspect ratio is controlled to be 4.5:1;

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

[0040] The preparation method of the hollow silica microspheres in this embodiment is as follows: Dissolve 1.2 parts by weight of glucose monohydrate in 22 parts of deionized water to form a first solution, and dissolve 0.32 parts of sodium silicate nonahydrate in 11 parts of deionized water to form a second solution. The two solutions are mixed at a stirring rate of 500 rpm, and the pH is adjusted to 3.5 with citric acid during the mixing process. Then, it is transferred to a closed reaction vessel and subjected to hydrothermal reaction at 200 °C for 28 h, and the reaction pressure is maintained at 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 μm. The retained solid product is washed 5 times with 30 parts of deionized water and 25 parts of absolute ethanol respectively to remove soluble ions and organic residues. Subsequently, it is dried at a vacuum degree of -0.10 MPa and a temperature of 65 °C for 6 h to obtain a silicon-carbon composite. Finally, the silicon-carbon composite is placed in a muffle furnace and heated at a heating rate of 8 °C / min to 600 °C, and calcined in an air atmosphere 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] The preparation method of a high-voltage-resistant PTC thermistor ceramic material in this embodiment includes the following steps:

[0044] S1. Add alumina / doped barium titanate nanorods into absolute ethanol and perform ultrasonic oscillation treatment for 30 min at an ultrasonic frequency of 60 kHz to form a nanorod alcohol dispersion. Subsequently, slowly add the hollow silica microspheres into the dispersion and continuously stir at a magnetic stirring rate of 500 rpm for 40 min to make the microspheres evenly distributed in the nanorod matrix. Add the glass-phase sintering aid to the system in batches, control the stirring rate at 600 rpm, and stir for 60 min to form a premixed slurry with a three-dimensional composite structure;

[0045] S2. Add a polyvinyl alcohol binder and an ammonium polyacrylate dispersant to the premixed slurry in sequence. The feeding order is the binder first and then the dispersant. The stirring rate is 500 rpm, and the stirring time is 60 min to obtain a ceramic slurry with stable viscosity. Heat the slurry in a constant-temperature water bath to 60 °C, control the stirring rate at 400 rpm, and keep it warm for 60 min to complete the control of solvent evaporation and the optimization of rheological properties. Use the tape casting process, set the pressure at 30 MPa, and keep the pressure for 10 min to prepare a green body;

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

[0047] Combined with Figure 1 、 Figure 2 and Figure 3 The structural characterization results can prove that the material design strategy adopted in the present invention has clear structural controllability and interface construction advantages. Among them, Figure 1 The transmission electron microscope and elemental line scan diagrams shown clearly show that the alumina / doped barium titanate nanorods have a typical core-shell structure, and aluminum elements are evenly distributed on the surface of the rod body, forming a continuous and dense coating layer, effectively improving the interface insulation and grain boundary barrier; Figure 2 Furthermore, it shows that the nanorods have good aspect ratio and dispersibility, which is beneficial to form an oriented arrangement structure in the ceramic matrix, enhancing densification and thermal response uniformity; Figure 3 The hollow silica microspheres shown present a regular spherical cavity structure and uniform particle size distribution, providing electric field regulation and thermal stress buffering functions for the ceramic material, and being able to construct a stable three-dimensional composite network at the microscale. In summary, it can fully prove that the present invention realizes a significant improvement in the PTC effect, insulation performance, thermal cycle stability, etc. of the thermosensitive ceramic material by introducing structurally ordered nanorods and hollow microspheres to synergistically construct a multi-scale interface regulation mechanism.

[0048] Example 2

[0049] A high-voltage-resistant PTC thermosensitive ceramic material, including 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, 6.5 parts of absolute ethanol;

[0050] The alumina / doped barium titanate nanorods are of core-shell structure, the shell layer is alumina, and the core part is manganese-doped barium titanate nanorods; the chemical general formula of the manganese-doped barium titanate is BaTi 1-x Mn xO3, where x = 0.1, and the manganese element realizes lattice doping by substituting the titanium sites. The preparation method of the alumina / doped barium titanate nanorods in this example is as follows: By weight, 26 parts of doped barium titanate nanorods are dispersed in 59 parts of ethanol and ultrasonically treated for 16 min to form a homogeneous suspension. 8 parts of aluminum nitrate are mixed with 36 parts of ethanol, 2 parts of acetylacetone are added, and the reaction is carried out at 46 °C for 78 min at a stirring rate of 360 rpm to form an aluminum precursor sol. Subsequently, the suspension is 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 and stirring is continued for 138 min to complete the hydrolysis and polycondensation reaction. The obtained mixed system is filtered through a filter membrane with a pore size of 0.29 μm to retain the solid-phase component, dried at 86 °C for 156 min to obtain a gel-coated nanorod precursor. The precursor is calcined in an air atmosphere at a heating rate of 3 °C / min to 560 °C for 156 min to form an alumina coating layer. The oxygen partial pressure in the furnace during the calcination stage is controlled at 0.16 MPa. The final product is separated by centrifugation at a rate of 9200 rpm for 16 min to retain the solid-phase product. Then the product is washed 4 times with ethanol to remove the unreacted aluminum source and by-products, and dried at 66 °C under a vacuum of 0.02 MPa for 78 min to obtain alumina / doped barium titanate nanorods.

[0051] The preparation method of the doped barium titanate nanorods in this example is as follows: By weight, 127.8 parts of barium nitrate hexahydrate are dissolved in 230 parts of deionized water to form a first solution. 86 parts of tetrabutyl titanate are mixed with 59 parts of ethanol and 8.2 parts of manganese nitrate tetrahydrate are added to form a second solution. The first solution is dropped into the second solution at a rate of 3 mL / min, and the mixture is stirred at a rate of 360 rpm for 48 min to obtain a suspension. Subsequently, 36 parts of citric acid are added, and stirring is continued at 99 °C for 138 min until a viscous gel is formed. The gel is placed in a muffle furnace and heated at a rate of 12 °C / min to 265 °C and maintained for 26 min to complete the self-ignition reaction. The obtained precursor powder is sintered in a nitrogen atmosphere at a heating rate of 6 °C / min to 1080 °C for 336 min, cooled to room temperature with the furnace, and the particles with a particle size greater than 500 nm are removed by ethanol dispersion and centrifugal separation. Finally, doped barium titanate nanorods are obtained.

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

[0053] The average length of the alumina / doped barium titanate nanorods in this example is 920 nm, and the aspect ratio is controlled at 6.2:1;

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

[0055] The preparation method of the hollow silica microspheres in this example is as follows: Dissolve 1.1 parts by weight of glucose monohydrate in 20 parts of deionized water to form a first solution, and dissolve 0.30 parts of sodium silicate nonahydrate in 10 parts of deionized water to form a second solution. The two solutions are mixed at a stirring rate of 380 rpm. During the mixing process, the pH is adjusted to 3.1 with citric acid, and then transferred to a sealed reaction vessel. Hydrothermal reaction is carried out at 184 °C for 25 h, and the reaction pressure is maintained at 1.4 MPa. After the reaction is completed, the solid-liquid mixture is filtered through a filter membrane with a pore size of 0.22 μm. The retained solid product is washed 4 times with 26 parts of deionized water and 21 parts of absolute ethanol respectively to remove soluble ions and organic residues. Subsequently, it is 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 is placed in a muffle furnace and heated from room temperature to 560 °C at a heating rate of 6 °C / min, and calcined in an air atmosphere 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 example is 480 nm;

[0057] The glass phase sintering aid in this example 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] The preparation method of a high-voltage-resistant PTC thermistor ceramic material in this example includes the following steps:

[0059] S1. Add alumina / doped barium titanate nanorods into absolute ethanol, and perform ultrasonic oscillation treatment for 22 min at an ultrasonic frequency of 52 kHz to form a nanorod alcohol dispersion. Subsequently, slowly add the hollow silica microspheres into the dispersion, and continuously stir at a magnetic stirring rate of 420 rpm for 32 min to make the microspheres evenly distributed in the nanorod matrix. Add the glass phase sintering aid to the system in batches, control the stirring rate at 520 rpm, and the stirring time at 48 min to form a premixed slurry with a three-dimensional composite structure;

[0060] S2. Add polyvinyl alcohol binder and ammonium polyacrylate dispersant to the premixed slurry in sequence. The feeding order is binder first and then dispersant. The stirring rate is 420 rpm, and the stirring time is 48 min to obtain a ceramic slurry with stable viscosity. Heat the slurry in a constant temperature water bath to 52 °C, control the stirring rate at 320 rpm, and the heat preservation time at 48 min to complete the control of solvent volatilization and the optimization of rheological properties. Use the tape casting process, set the pressure at 22 MPa, and the pressure holding time at 8 min to prepare a green body;

[0061] S3. Place the green body in a hot air circulation drying oven and pre-dry it at 92 °C for 192 min to make the moisture content ≤ 0.5 wt%. After drying, transfer the embryo to a muffle furnace and raise the temperature to the sintering temperature of 1090 °C at a heating rate of 3.8 °C / min in a weakly oxidizing atmosphere with an oxygen content ≤ 5%, and hold for 372 min to achieve grain densification; cool to room temperature to obtain a high-voltage-resistant PTC thermistor ceramic material.

[0062] Example 3

[0063] A high-voltage-resistant PTC thermistor ceramic material, including 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, 10.0 parts of anhydrous ethanol;

[0064] The alumina / doped barium titanate nanorods have a core-shell structure, with the shell layer being alumina and the core part being manganese-doped barium titanate nanorods; the chemical general formula of the manganese-doped barium titanate is BaTi 1-x Mn x O3, where x = 0.20, and the manganese element realizes lattice doping by substituting the titanium site. The preparation method of the alumina / doped barium titanate nanorods in this example is: by weight, disperse 40 parts of doped barium titanate nanorods in 80 parts of ethanol and ultrasonically treat for 30 min to form a uniform suspension. Mix 15 parts of aluminum nitrate with 50 parts of ethanol, add 5 parts of acetylacetone, and react at 60 °C for 120 min at a stirring rate of 500 rpm to form an aluminum precursor sol. Then inject the suspension into the aluminum precursor sol at a rate of 3 mL / min, adjust the pH to 5.5, and maintain the temperature at 70 °C and continue stirring for 180 min to complete the hydrolysis and polycondensation reaction. The obtained mixed system is filtered through a 0.45 μm pore size filter membrane and the solid phase component is retained, dried at 100 °C for 240 min to obtain a gel-coated nanorod precursor. The precursor is calcined in an air atmosphere at a heating rate of 5 °C / min to 700 °C for 240 min to form an alumina coating layer. The oxygen partial pressure in the furnace during the calcination stage is controlled at 0.3 MPa. The final product is separated by centrifugation at a rate of 12,000 rpm for 30 min and the solid phase product is retained. Then the product is washed 5 times with ethanol to remove the unreacted aluminum source and by-products, and 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 example is as follows: by weight, 145 parts of barium nitrate hexahydrate are dissolved in 300 parts of deionized water to form a first solution, 100 parts of tetrabutyl titanate are mixed with 80 parts of ethanol and 20 parts of manganese nitrate tetrahydrate are added to form a second solution. The first solution is dropped into the second solution at a rate of 5 mL / min, and the mixture is stirred at a stirring rate of 500 rpm for 90 min to obtain a suspension. Subsequently, 50 parts of citric acid are added, and the mixture is continuously stirred 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 a rate of 15 °C / min and maintained for 40 min to complete the self-combustion reaction. The obtained precursor powder is heated to 1150 °C at a rate of 8 °C / min in a nitrogen atmosphere and sintered for 420 min. After cooling to room temperature with the furnace, particles with a particle size greater than 500 nm are removed by ethanol dispersion and centrifugal separation, and finally doped barium titanate nanorods are obtained.

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

[0067] The average length of the alumina / doped barium titanate nanorods of this example is 1200 nm, and the aspect ratio is controlled to be 10:1;

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

[0069] The preparation method of the hollow silica microspheres in this example is as follows: 1.1 parts of glucose monohydrate are dissolved in 19 parts of deionized water to form a first solution, 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, and the pH is adjusted to 2.8 with citric acid during the mixing process. Then, the mixture is transferred to a sealed reaction vessel and hydrothermally reacted at 172 °C for 22 h, and the reaction pressure is maintained at 0.95 MPa. After the reaction is completed, the solid-liquid mixture is filtered through a filter membrane with a pore size of 0.22 μm. The retained solid product is washed 4 times with 23 parts of deionized water and 18 parts of absolute ethanol respectively to remove soluble ions and organic residues. Subsequently, it is dried at a vacuum degree of -0.09 MPa and a temperature of 58 °C for 4.6 h to obtain a silicon-carbon composite. Finally, the silicon-carbon composite is placed in a muffle furnace and heated to 530 °C at a heating rate of 4.5 °C / min by programmed heating, and calcined in an air atmosphere for 4.6 h to completely remove the carbon core, and hollow silica microspheres are obtained.

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

[0071] The glass co - sintering agent of 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] A preparation method of a high - voltage - resistant PTC thermistor ceramic material in this embodiment includes the following steps:

[0073] S1. Add alumina / doped barium titanate nanorods into absolute ethanol, and perform ultrasonic oscillation treatment for 16 min with an ultrasonic frequency of 46 kHz to form a nanorod alcohol dispersion. Subsequently, slowly add hollow silica microspheres into the dispersion, and continuously stir for 26 min under the condition that the magnetic stirring rate is 360 rpm to make the microspheres evenly distributed in the nanorod matrix. Add the glass co - sintering agent to the system in batches, control the stirring rate at 460 rpm, and the stirring time at 39 min to form a premixed slurry with a three - dimensional composite structure;

[0074] S2. Add a polyvinyl alcohol binder and an ammonium polyacrylate dispersant to the premixed slurry in sequence. The feeding order is binder first and then dispersant. The stirring rate is 360 rpm, and the stirring time is 39 min to obtain a ceramic slurry with stable viscosity. Place the slurry in a constant - temperature water bath and heat it to 46 °C, control the stirring rate at 260 rpm, and the heat - preservation time at 39 min to complete the control of solvent volatilization and the optimization of rheological properties. Use the tape - casting process, set the pressure at 16 MPa, and the pressure - holding time at 6.5 min to prepare a green body;

[0075] S3. Place the green body in a hot - air circulation drying oven and pre - dry it at 86 °C for 156 min to make the moisture content ≤ 0.5 wt%. Transfer the dried embryo to a muffle furnace, and under a weakly oxidizing atmosphere with an oxygen content ≤ 5%, raise the temperature to the sintering temperature of 1045 °C at a heating rate of 2.9 °C / min, and keep it warm for 336 min to achieve grain densification; cool to room temperature to obtain a high - voltage - resistant PTC thermistor ceramic material.

[0076] Example 4

[0077] A high - voltage - resistant PTC thermistor ceramic material, by weight, includes: 112 parts of alumina / doped barium titanate nanorods, 11 parts of hollow silica microspheres, 6 parts of glass co - sintering agent; 1.6 parts of polyvinyl alcohol binder, 1.4 parts of ammonium polyacrylate dispersant, 8.0 parts of absolute ethanol;

[0078] The alumina / doped barium titanate nanorods have a core - shell structure, the shell layer is alumina, and the core part is manganese - doped barium titanate nanorods; the chemical general formula of the manganese - doped barium titanate is BaTi 1-x Mn xO3, where x = 0.14, and the manganese element realizes lattice doping by substituting the titanium sites. The preparation method of the alumina / doped barium titanate nanorods in this example is as follows: by weight, 32 parts of doped barium titanate nanorods are dispersed in 68 parts of ethanol and ultrasonically treated for 22 min to form a uniform suspension. 11 parts of aluminum nitrate are mixed with 42 parts of ethanol, 3 parts of acetylacetone are added, and the reaction is carried out at 52 °C for 96 min at 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 and stirring is continued for 156 min to complete the hydrolysis and polycondensation reaction. The obtained mixed system is filtered through a filter membrane with a pore size of 0.36 μm to retain the solid-phase component, dried at 92 °C for 192 min to obtain a nanorod precursor coated with a gel, and the precursor is calcined in an air atmosphere at a heating rate of 4 °C / min to 620 °C for 192 min to form an alumina coating layer. The oxygen partial pressure in the furnace during the calcination stage is controlled at 0.22 MPa. The final product is separated by centrifugation at a centrifugation rate of 10400 rpm for 22 min to retain the solid-phase product, and then the product is washed 4 times with ethanol to remove the unreacted aluminum source and by-products, and 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 example is as follows: by weight, 134 parts of barium nitrate hexahydrate are dissolved in 260 parts of deionized water to form a first solution. 92 parts of tetrabutyl titanate are mixed with 68 parts of ethanol 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, and the mixture is stirred at a stirring rate of 420 rpm for 66 min to obtain a suspension. Subsequently, 42 parts of citric acid are added, and stirring is continued at 108 °C for 156 min until a viscous gel is formed. The gel is placed in a muffle furnace and heated at a heating rate of 13 °C / min to 280 °C and maintained for 32 min to complete the self-ignition reaction. The obtained precursor powder is sintered in a nitrogen atmosphere at a heating rate of 7 °C / min to 1110 °C for 372 min, cooled to room temperature with the furnace, and the particles with a particle size greater than 500 nm are removed by ethanol dispersion and centrifugation separation. Finally, doped barium titanate nanorods are obtained.

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

[0081] The average length of the alumina / doped barium titanate nanorods in this example is 1040 nm, and the aspect ratio is controlled to be 7.8:1;

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

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

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

[0085] The glass-phase sintering aid in this example mainly consists 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] The preparation method of a high-voltage-resistant PTC thermistor ceramic material in this example includes the following steps:

[0087] S1. Add alumina / doped barium titanate nanorods into absolute ethanol, and perform ultrasonic oscillation treatment for 10 min at an ultrasonic frequency of 40 kHz to form a nanorod alcohol dispersion. Subsequently, slowly add the hollow silica microspheres into the dispersion, and continuously stir at a magnetic stirring rate of 300 rpm for 20 min to make the microspheres evenly distributed in the nanorod matrix. Add the glass-phase sintering aid to the system in batches, control the stirring rate at 400 rpm, and the stirring time at 30 min to form a premixed slurry with a three-dimensional composite structure;

[0088] S2. Add a polyvinyl alcohol binder and an ammonium polyacrylate dispersant to the premixed slurry in sequence. The feeding order is the binder first and then the dispersant. The stirring rate is 300 rpm, and the stirring time is 30 min to obtain a ceramic slurry with stable viscosity. Heat the slurry in a constant-temperature water bath to 40 °C, control the stirring rate at 200 rpm, and the holding time at 30 min to complete the control of solvent evaporation and the optimization of rheological properties. Adopt a tape casting process, set the pressure at 10 MPa, and the pressure holding time at 5 min to prepare a green body;

[0089] S3. Place the green body in a hot air circulation drying oven and pre-dry it at 80 °C for 120 min to make the water content ≤ 0.5 wt%. After drying, transfer the green body to a muffle furnace and raise the temperature to the sintering temperature of 1000 °C at a heating rate of 2 °C / min under a weak oxidation atmosphere with an oxygen content ≤ 5%, and hold for 300 min to achieve grain densification; cool to room temperature to obtain a high-voltage-resistant PTC thermistor ceramic material.

[0090] Comparative Example 1

[0091] Basically the same as Example 1, except that the dosage of alumina / doped barium titanate nanorods is 90.0 parts.

[0092] Comparative Example 2

[0093] Basically the same as Example 1, except that the dosage of hollow silica microspheres is 3 parts.

[0094] Comparative Example 3

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

[0096] Comparative Example 4

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

[0098] Comparative Example 5

[0099] Basically the same as Example 1, except that the sintering temperature of the self-combustion reaction of barium titanate nanorods is 1000 °C.

[0100] Comparative Example 6

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

[0102] Comparative Example 7

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

[0104] Comparative Example 8

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

[0106] Comparative Example 9

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

[0108] Comparative Example 10

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

[0110] Comparative Example 11

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

[0112] Comparative Example 12

[0113] 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] Basically the same as Example 1, except that the calcination temperature of hollow silica is 650 °C.

[0116] Comparative Example 14

[0117] Basically the same as Example 1, except that no alumina layer is prepared on the surface of the doped barium titanate nanorods.

[0118] Comparative Example 15

[0119] Basically the same as Example 1, except that hollow silica microspheres are not added in the preparation of the thermosensitive ceramic material.

[0120] Performance test:

[0121] PTC resistance-temperature response test (R-T curve)

[0122] According to the IEC 60738 standard, the thermosensitive ceramic sample is processed into a wafer with a diameter of 10 mm and a thickness of 0.5 ± 0.02 mm, and a 50-nm platinum electrode with a diameter of 8 mm is prepared on the surface by magnetron sputtering. Using a high resistance meter (Keithley6517B), the temperature is increased uniformly at 3 °C / min in the range of 25 - 180 °C, and after stepping at every 5 °C and keeping constant temperature for 10 minutes to eliminate the thermal hysteresis effect, the volume resistance value is recorded in real time and the resistance-temperature (R-T) curve is plotted. By analyzing the data in the resistance mutation region near the Curie point, the resistance change rate (ΔR / R25 ≥ 10 3 ) and the α coefficient (d(logR) / dT ≥ 0.03 °C-1) are calculated. Each group of experiments is repeated to test 5 samples to ensure that the coefficient of variation (CV) ≤ 8%, and the PTC effect intensity and temperature sensitivity of the material are quantified

[0123] Breakdown voltage test

[0124] According to ASTM D149 standard, ceramic wafers 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 °C and humidity 30 ± 5% RH, the samples were immersed in transformer oil with a dielectric strength ≥ 30 kV / 2.5 mm, and a DC voltage was applied at a constant rate of 1 kV / s until breakdown. 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, and the breakdown field strength is closely related to the ceramic densification, defect density, and interface uniformity.

[0125] Thermal cycle stability test

[0126] According to IEC 600-68-2-14 standard, 1000 thermal cycles were performed in the temperature range of -40 °C to 150 °C (heating and cooling rate ≤ 5 °C / min, holding for 30 minutes in each temperature zone). After every 100 cycles, the resistance values at 25 °C, 100 °C, and 150 °C were measured using the four-probe method (ASTM F1529). By comparing the initial and cyclic R-T curves, the Curie point shift (ΔTc) was statistically analyzed to evaluate 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 test (grain boundary / grain electrical behavior)

[0128] On the samples with 100 nm gold electrodes (diameter 6 mm) deposited by magnetron sputtering, impedance spectrum data were collected using an impedance analyzer (Solartron1260) in the frequency range of 10 -1 -10 6 Hz, with a perturbation voltage of 0.1 - 3 Vrms, and a temperature gradient of 25 - 150 °C (temperature control accuracy ± 1 °C). Based on the core-shell structure characteristics, an R-(R / / CPE) equivalent circuit model was established (CPE index n ≥ 0.9 characterizes the interface polarization uniformity). By fitting the grain resistance (Rg), grain boundary resistance (Rgb), and polarization capacitance parameters using ZView software, the change rate of grain boundary resistance (ΔRgb / Rgb_initial) before and after thermal cycling or aging was finally calculated to quantitatively reveal the correlation between the grain boundary degradation mechanism and the material life.

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

[0130] Table 1 Summary of the performances of the thermosensitive ceramic materials in Examples 1 - 4 and Comparative Examples 1 - 15

[0131]

[0132]

[0133] As can be seen from the above table, insufficient dosage of alumina / doped barium titanate nanorods (such as Comparative Example 1) will reduce the coating integrity of ceramic particles, resulting in weakened grain boundary barriers, decreased resistance change rate ΔR / R25 and α coefficient, thereby weakening the PTC effect. At the same time, the breakdown voltage decreases, ΔTc and ΔRgb / Rgb_initial increase, and the thermal stability deteriorates; insufficient or missing dosage of hollow silica microspheres (such as Comparative Examples 2 and 15) will destroy the cooperative regulation ability of the core-shell structure, reduce the uniformity of electric field distribution, resulting in a decrease in breakdown field strength and aggravated grain boundary degradation after thermal cycling; too low stirring rate of aluminum precursor sol (such as Comparative Example 3) will cause uneven coating film thickness or local defects, affecting insulation and the consistency of grain boundary structure; too high calcination temperature of alumina coating (such as Comparative Example 4) will cause sintering densification of the coating layer or even grain boundary reaction, resulting in a decrease in breakdown voltage and aggravated ΔTc deviation; insufficient sintering temperature of the main phase of barium titanate nanorods (such as Comparative Example 5) will cause a decrease in ceramic density and insufficient grain growth, affecting resistivity and breakdown strength; deviation of the coating mass ratio from the optimal range (such as Comparative Example 6) will cause the alumina layer to be too thin or too thick, respectively resulting in a decrease in breakdown voltage or an increase in interface resistance, affecting the overall electrical properties; insufficient aspect ratio of nanorods (such as Comparative Example 7) will weaken orientation and film-forming densification, resulting in a decrease in thermal conductivity and breakdown strength; insufficient coating layer thickness (such as Comparative Example 8) directly affects insulation and grain boundary barriers, thereby reducing the PTC effect and stability; insufficient hydrothermal reaction time of SiO2 (such as Comparative Example 9) will result in incomplete microsphere structure and decreased core-shell composite effect, affecting electric field uniformity; too low tape casting pressure (such as Comparative Example 10) will reduce ceramic density, resulting in a low breakdown voltage and aggravated structural degradation after thermal cycling; insufficient oxygen partial pressure in the sintering stage (such as Comparative Example 11) will exacerbate the formation of oxygen vacancies, affecting grain boundary conductivity characteristics, reducing the α value and aggravating thermal aging; too high manganese doping amount (such as Comparative Example 12) will cause electron trap saturation and grain boundary barrier distortion, manifested as a falsely high α value but a significant increase in ΔRgb, and reduced thermal stability; too high calcination temperature of SiO2 (such as Comparative Example 13) will destroy the hollow structure, affecting the overall dielectric regulation ability; without alumina coating (such as Comparative Example 14) will result in an extremely low breakdown voltage, a large increase in ΔTc and ΔRgb / Rgb_initial, and serious degradation of exposed grain boundaries; without adding hollow silica (such as Comparative Example 15) will lack the support of the core-shell structure, resulting in decreased insulation, unstable thermal cycling performance, and accelerated grain boundary degradation. The above factors all have direct or indirect effects on the PTC effect strength, insulation performance and thermal cycling stability, and determine the overall comprehensive performance of the thermosensitive 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 are not intended to limit it. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that any equivalent structural transformation made under the concept of the present invention using the content of the specification and drawings of the present invention should be covered within the scope of the protection of the claims of the present invention.

Claims

1. A high-voltage-resistant PTC thermistor ceramic material, characterized in that, Comprising, by weight parts: 100.0 to 120.0 parts of alumina / doped barium titanate nanorods, 5 to 15 parts of hollow silica microspheres, 4 to 8 parts of glass phase sintering aid; 1.0 to 2.0 parts of polyvinyl alcohol binder, 0.5 to 2.0 parts of ammonium polyacrylate dispersant, 5.0 to 10.0 parts of absolute ethanol; The alumina / doped barium titanate nanorod is a core-shell structure, with the shell layer being alumina and the core part being a manganese-doped barium titanate nanorod; the chemical general formula of the manganese-doped barium titanate is BaTi 1-x Mn x O3, where x = 0.05 to 0.20, and the manganese element realizes lattice doping by substituting the titanium site.

2. The high-voltage-resistant PTC thermistor ceramic material according to claim 1, characterized in that, The preparation method of the alumina / doped barium titanate nanorods is as follows: By weight parts, disperse 20 to 40 parts of doped barium titanate nanorods in 50 to 80 parts of ethanol and ultrasonically treat for 10 to 30 min to form a uniform suspension. Mix 5 to 15 parts of aluminum nitrate with 30 to 50 parts of ethanol, add 1 to 5 parts of acetylacetone, and react at 40 to 60 °C for 60 to 120 min under a stirring rate of 300 to 500 rpm to form an aluminum precursor sol. Subsequently, inject the suspension into the aluminum precursor sol at a rate of 1 to 3 mL / min, adjust the pH to 4.0 to 5.5, and maintain the temperature at 50 to 70 °C and continue stirring for 120 to 180 min to complete the hydrolysis and polycondensation reaction. The obtained mixed system is filtered through a filter membrane with a pore size of 0.22 to 0.45 μm to retain the solid phase component, dried at 80 to 100 °C for 120 to 240 min to obtain a gel-coated nanorod precursor. The precursor is heated to 500 to 700 °C at a rate of 2 to 5 °C / min in an air atmosphere and calcined for 120 to 240 min to form an alumina coating layer. The oxygen partial pressure in the furnace during the calcination stage is controlled at 0.1 to 0.3 MPa. The final product is separated by centrifugation at a rate of 8000 to 12000 rpm for 10 to 30 min to retain the solid phase product, and then the product is washed with ethanol 3 to 5 times to remove unreacted aluminum sources and by-products, and dried at 60 to 80 °C under a vacuum of 0.01 to 0.05 MPa for 60 to 120 min to obtain alumina / doped barium titanate nanorods.

3. A high-voltage-resistant PTC thermistor ceramic material according to claim 2, characterized in that, The preparation method of the doped barium titanate nanorods is as follows: By weight parts, dissolve 122 to 145 parts of barium nitrate hexahydrate in 200 to 300 parts of deionized water to form a first solution. Mix 100 parts of tetrabutyl titanate with 50 to 80 parts of ethanol and add 4 to 20 parts of manganese nitrate tetrahydrate to form a second solution. Drop the first solution into the second solution at a rate of 2 to 5 mL / min, and mix for 30 to 90 min under a stirring rate of 300 to 500 rpm to obtain a suspension. Subsequently, add 30 to 50 parts of citric acid, and continuously stir at 90 to 120 °C for 120 to 180 min until a viscous gel is formed. Place the gel in a muffle furnace and heat it to 250 to 300 °C at a rate of 10 to 15 °C / min and maintain for 20 to 40 min to complete the self-ignition reaction. The obtained precursor powder is heated to 1050 to 1150 °C at a rate of 5 to 8 °C / min in a nitrogen atmosphere and sintered for 300 to 420 min. After cooling to room temperature with the furnace, particles with a particle size greater than 500 nm are removed by ethanol dispersion and centrifugation separation, and finally doped barium titanate nanorods are obtained.

4. A high-voltage-resistant PTC thermistor ceramic material according to claim 1, characterized in that, In the described alumina / doped barium titanate nanorods, the mass ratio of alumina to doped barium titanate is 1:12 to 1:

18.

5. A high-voltage-resistant PTC thermistor ceramic material as described in claim 1, characterized in that, The average length of the alumina / doped barium titanate nanorods is 800 - 1200 nm, and the diameter-to-length ratio is controlled to be 4.5:1 to 10:

1.

6. A high-voltage-resistant PTC thermistor ceramic material according to claim 1, characterized in that, The thickness of the described alumina is 10 - 20 nm.

7. A high-voltage-resistant PTC thermistor ceramic material according to claim 1, characterized in that, The preparation method of the hollow silica microspheres is as follows: Dissolve 1.0 - 1.2 parts by weight of glucose monohydrate in 18 - 22 parts by weight of deionized water to form a first solution, and dissolve 0.28 - 0.32 parts of sodium silicate nonahydrate in 9 - 11 parts of deionized water to form a second solution. The two solutions are mixed at a stirring rate of 200 - 500 rpm, and the pH is adjusted to 2.5 - 3.5 with citric acid during the mixing process. Then, it is transferred to a closed reaction vessel and subjected to hydrothermal reaction at 160 - 200 °C for 20 - 28 h, and the reaction pressure is 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 μm. The retained solid product is washed 3 - 5 times with 20 - 30 parts of deionized water and 15 - 25 parts of absolute ethanol respectively to remove soluble ions and organic residues. Subsequently, it is dried at a vacuum degree of -0.08 to -0.10 MPa and a temperature of 55 - 65 °C for 4 - 6 h to obtain a silicon-carbon composite. Finally, the silicon-carbon composite is placed in a muffle furnace and heated at a heating rate of 3 - 8 °C / min to 500 - 600 °C, and calcined in an air atmosphere for 4 - 6 h to completely remove the carbon core to obtain hollow silica microspheres; The average diameter of the described hollow silica microspheres is 300 - 600 nm.

8. A high-voltage-resistant PTC thermistor ceramic material according to claim 1, characterized in that, The glass-phase sintering aid mainly consists of B2O3, Li2O, and SiO2. By mass percentage, the content of B2O3 in the sintering aid is 30% - 60%, the content of Li2O is 5% - 20%, and the content of SiO2 is 20% - 50%.

9. The preparation method of a high-voltage-resistant PTC thermistor ceramic material as claimed in claim 1, characterized in that, It includes the following steps: S1. Add the alumina / doped barium titanate nanorods into absolute ethanol, and perform ultrasonic oscillation treatment for 10 - 30 min with an ultrasonic frequency of 40 - 60 kHz to form a nanorod alcohol dispersion. Subsequently, slowly add the hollow silica microspheres to the dispersion, and continuously stir at a magnetic stirring rate of 300 - 500 rpm for 20 - 40 min to make the microspheres evenly distributed in the nanorod matrix. Add the glass-phase sintering aid to the system in batches, control the stirring rate to be 400 - 600 rpm, and the stirring time to be 30 - 60 min to form a premixed slurry with a three-dimensional composite structure; S2. Add polyvinyl alcohol binder and ammonium polyacrylate dispersant to the premixed slurry in sequence, with the feeding order being binder first and then dispersant. The stirring rate is 300 - 500 rpm, and the stirring time is 30 - 60 min to obtain a ceramic slurry with stable viscosity. Heat the slurry in a constant temperature water bath to 40 - 60 °C, control the stirring rate at 200 - 400 rpm, and the heat preservation time is 30 - 60 min to complete the control of solvent evaporation and the optimization of rheological properties. Use the tape casting process, set the pressure at 10 - 30 MPa, and the pressure holding time is 5 - 10 min to prepare a green body; S3. Place the green body in a hot air circulation drying oven and pre-dry it at 80 - 100 °C for 120 - 240 min to make the moisture content ≤ 0.5 wt%. After drying, transfer the embryo to a muffle furnace, and under a weakly oxidizing atmosphere with an oxygen content ≤ 5%, raise the temperature to the sintering temperature of 1000 - 1150 °C at a heating rate of 2 - 5 °C / min, and keep the temperature for 300 - 420 min to achieve grain densification; cool to room temperature to obtain a high-voltage-resistant PTC thermistor ceramic material.

10. Application of a high-voltage-resistant PTC thermistor ceramic material as described in claim 1 in over-temperature protection of new energy vehicle battery packs, self-restoring current-limiting elements for high-voltage power equipment, and temperature control switches for industrial automation.

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