A ceramic material for PTC thermistors and its preparation method

Abstract

This application relates to the field of ceramic materials technology, specifically disclosing a ceramic material for PTC thermistors and its preparation method. The ceramic material for PTC thermistors includes the following raw materials: barium titanate, silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder, rare earth oxides, alumina, ammonium polyacrylate, and polyvinyl alcohol. This application adds the silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder to the ceramic material. The alumina directionally coats the lead tetroxide, effectively suppressing the volatilization of lead vapor during high-temperature sintering and improving the environmental friendliness of the ceramic material. Simultaneously, the in-situ composite bonding of lead tetroxide and silicon boride, combined with silane modification, improves the interfacial bonding ability between the composite powder and the barium titanate matrix, reducing internal stress during ceramic sintering and improving the mechanical properties of the ceramic material.

Description

Technical Field

[0001] This application relates to the field of ceramic materials technology, and more specifically, to a ceramic material for PTC thermistors and a method for preparing the same. Background Technology

[0002] PTC thermistors, with their unique positive temperature coefficient effect, play an irreplaceable role in overcurrent protection, temperature control, and self-limiting heating, and are widely used in electronic equipment, new energy vehicles, smart homes, aerospace, and other industries. The ceramic material used to manufacture PTC thermistors is the core substrate that determines their performance. Among them, barium titanate-based polycrystalline ceramics have become the most mainstream PTC ceramic system in industrial applications due to their excellent PTC effect, controllable Curie temperature, and good high-temperature resistance.

[0003] Since the Curie temperature of pure barium titanate is approximately 120°C, it cannot meet the diverse temperature threshold requirements of different application scenarios. Strontium and lead ions, due to their similar ionic radii to barium ions in the barium titanate lattice, can successfully dissolve into the perovskite lattice to form a substituted solid solution. By altering the intensity of polarization and the phase transition energy barrier within the crystal, the Curie temperature can be precisely adjusted. Lead doping, in particular, can fine-tune the Curie temperature within a certain range and broaden the control interval, thereby meeting the requirements of different scenarios for the PTC effect triggering temperature. For example, patent application CN121248281A discloses a PTC ceramic material and its preparation method. The PTC ceramic material, by weight, is composed of the following components: 50-65 parts The application describes a method for improving the overall performance of PTC ceramic materials by combining barium titanate, 12-16 parts lead tetroxide, 0.1-0.3 parts yttrium oxide, 0.1-0.3 parts lanthanum oxide, 6-15 parts modified silicon boride, 4-10 parts alumina, 1-3 parts ammonium polyacrylate, and 3-6 parts polyvinyl alcohol. However, during the high-temperature sintering stage of PTC ceramic material preparation, lead tetroxide releases lead vapors, which directly harm the health of production operators and adhere to the inner walls of sintering and other production equipment, causing heavy metal pollution and increasing the cost of environmental cleaning and maintenance. Furthermore, the volatilized lead vapors enter the atmosphere, causing atmospheric heavy metal pollution. Summary of the Invention

[0004] To improve the environmental friendliness of ceramic materials used in PTC thermistors, this application provides a ceramic material for PTC thermistors and a method for preparing the same.

[0005] In a first aspect, this application provides a ceramic material for PTC thermistors, employing the following technical solution: A ceramic material for PTC thermistors comprises the following raw materials in parts by weight: 60-68 parts barium titanate, 28-32 parts silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder, 0.4-0.6 parts rare earth oxides, 9-11 parts alumina, 1-2 parts ammonium polyacrylate, and 4-6 parts polyvinyl alcohol. The preparation method of the silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder includes the following steps: (1) Add 10 parts by weight of lead tetroxide and 8-12 parts by weight of silicon boride to 140-160 parts by weight of deionized water and disperse by ultrasonication to obtain a suspension; add the suspension to 29-34 parts by weight of 15wt% hydrogen peroxide and stir at 200-300r / min at room temperature for 15-25min to obtain a reaction solution. (2) Add 1-1.4 parts by weight of aluminum nitrate to the reaction solution, stir for 8-12 min, adjust the pH to 8-8.5 with ammonia water, stir at a water bath temperature of 55-65℃ for 2 h to obtain the coating; (3) Dissolve 1-2 parts by weight of silane coupling agent in ethanol to form a solution, drop it into the coating, heat to 60-70℃, stir and react for 2h; after the reaction is completed, filter, wash and dry, calcine at 380-420℃ for 2h, cool and sieve to obtain the silane modified alumina coated lead tetroxide-silicon boride in-situ composite powder; The silane coupling agent is one or both of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane.

[0006] This application utilizes alumina to directionally coat lead tetroxide, effectively suppressing the volatilization of lead vapor during high-temperature sintering and reducing the harm of lead pollution to human health, equipment, and the atmosphere, while retaining the core function of lead ions in regulating Curie temperature. Lead tetroxide and silicon boride are combined in situ, and silane modification enhances the interfacial bonding between the composite powder and the barium titanate matrix, reducing internal stress during ceramic sintering. The trace amounts of alumina adsorbed on the silicon boride surface form an inorganic bridging phase, further improving the interfacial bonding tightness, buffering thermal expansion differences, and synergistically enhancing the density and mechanical properties of the ceramic material, thus improving the environmental friendliness and overall performance of the ceramic material used in PTC thermistors.

[0007] Specifically, in this application, the silane coupling agent undergoes a grafting reaction, whereby the silanol groups form Si-O-Al covalent bonds with the alumina coating layer, thereby activating the powder surface and inhibiting powder agglomeration. Subsequently, during calcination, the silane organic segments completely decompose and volatilize, and the silicon element is transformed into amorphous silicon-oxygen species and condenses to form a Si-O-Si network, filling the nanoscale pores of the alumina coating layer. This creates a dual dense structure of alumina coating and silicon-oxygen network filling, which not only enhances the lead vapor suppression effect but also provides inorganic bonding sites for the bonding of the composite powder with the barium titanate matrix. Finally, during the high-temperature sintering stage of the ceramic, the silicon-oxygen network fuses with the inorganic bonds of the barium titanate and alumina matrix, eliminating interfacial gaps, reducing sintering internal stress, and ultimately improving the interfacial bonding ability and the mechanical properties of the ceramic.

[0008] Preferably, in step (1), 10 parts by weight of lead tetroxide and 8-12 parts by weight of silicon boride are added to 140-160 parts by weight of deionized water and ultrasonically dispersed to obtain a suspension; the suspension is added to 29-34 parts by weight of 15wt% hydrogen peroxide and stirred at a rate of 200-300r / min at room temperature for 15-25min, and then 0.08-0.12 parts by weight of trisodium citrate is added and stirred to obtain a reaction solution.

[0009] By adopting the above technical solution, in step (1), after activation with hydrogen peroxide, trisodium citrate is introduced. As a chelating water-soluble dispersant, it can be effectively adsorbed on the surface of lead tetroxide and silicon boride powder, improving the dispersion uniformity of the two in the weakly alkaline aqueous system, avoiding powder agglomeration, laying the foundation for the subsequent directional and dense coating of lead tetroxide by alumina, and ensuring the stability of the lead vapor suppression effect. At the same time, its chelating groups can form a weak chelating effect with rare earth oxides and rare earth ions in the ceramic formula, effectively preventing rare earth doping in the subsequent ceramic preparation process. The aggregation of impurities improves the doping uniformity of rare earth ions in the barium titanate lattice and optimizes the grain boundary barrier structure. Furthermore, trisodium citrate is compatible with the weakly alkaline aqueous phase system of this process and does not undergo side reactions with reagents such as hydrogen peroxide and aluminum nitrate. It can be completely decomposed without residue in the subsequent calcination stage, which does not interfere with the subsequent core processes such as silane modification of silicon boride and alumina coating formation. It can also indirectly improve the interfacial compatibility between the composite powder and organic molding aids such as ammonium polyacrylate and polyvinyl alcohol, improve the formability of ceramic blanks, and reduce cracking problems during the molding process.

[0010] Preferably, in step (2), 0.05-0.1 parts by weight of nano-zirconia are added to the reaction solution, ultrasonically dispersed, and then 1-1.4 parts by weight of aluminum nitrate are added. After stirring for 8-12 minutes, the pH is adjusted to 8-8.5, and the mixture is stirred in a water bath at 55-65°C for 2 hours to obtain the coating.

[0011] By adopting the above technical solution, nano-zirconia is introduced before the addition of aluminum nitrate in step (2). Its nano-sized particles can be rapidly and uniformly dispersed in a weakly alkaline aqueous system without side reactions with the reagents in the system. It will not interfere with the subsequent hydrolysis of aluminum nitrate to form aluminum hydroxide sol and the directional dense coating of lead tetroxide. It can also be pre-dispersed by adhering to the surface of the composite powder in situ during the coating process. Nano-zirconia can form a synergistic effect with rare earth oxides and rare earth dopants in the ceramic formulation to jointly optimize the grain boundary barrier structure of barium titanate lattice and suppress the titanium dioxide in the high-temperature sintering stage of ceramics. The abnormal growth of barium oxide grains improves the drag ratio and electrical performance stability of PTC ceramics under high and low temperature cycling. At the same time, it can complement the alumina coating layer on the surface of lead tetroxide and the alumina reinforcing agent in the original formula, further optimizing the matching of the thermal expansion coefficient of the ceramic system, effectively buffering the internal stress during sintering, reducing the generation of microcracks inside the ceramic, and synergistically improving the mechanical properties of the ceramic material such as density and flexural strength. Moreover, the pre-dispersed nano-zirconia can avoid the agglomeration of this component in the subsequent ceramic preparation, and improve the uniformity of the overall formula components.

[0012] Preferably, in step (3), the silane coupling agent is a mixture of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 1:(0.8-1.2).

[0013] By employing the above technical solution, γ-aminopropyltriethoxysilane (KH550) and γ-glycidoxypropyltrimethoxysilane (KH560) are used in combination. Their functional groups form a synergistic and complementary relationship. The amino group of KH550 can improve the solubility and dispersibility of the coupling agent in the water-alcohol system, promoting its uniform spreading on the surface of the alumina coating layer. The epoxy group of KH560 can accelerate the reaction rate with the hydroxyl groups on the surface of the coating layer and increase the grafting density. The two work together to form a siloxane transition layer. During the subsequent calcination process, the silanol groups formed by hydrolysis of the siloxane groups further condense to form an amorphous Si-O-Si inorganic network, which fills the nanopores of the alumina coating layer in situ. This not only further enhances the lead vapor suppression effect, but also provides uniform inorganic bonding sites for the composite powder, barium titanate matrix, and alumina phase, eliminating interfacial gaps, improving the interfacial bonding strength and the density and mechanical stability of the ceramic material, and ultimately optimizing the interfacial bonding ability between the composite powder and the matrix and the overall performance of the ceramic.

[0014] Preferably, in step (3), 1-2 parts by weight of silane coupling agent are dissolved in ethanol to form a solution, which is then added dropwise to the coating material. The temperature is raised to 60-70℃ and the mixture is stirred for 2 hours. After the reaction is completed, 0.1-0.2 parts by weight of ultrafine silica are added, and after stirring and dispersing, the mixture is filtered, washed, dried, and calcined at 380-420℃ for 2 hours. After cooling and sieving, the silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder is obtained. The silane coupling agent is a mixture of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 1:1.

[0015] By adopting the above technical solution, after the silane modification reaction in step (3), ultrafine silica is introduced. Its ultrafine particle size can be quickly and uniformly dispersed in the system, without interfering with the directional coating of lead tetroxide by alumina and the core reaction of silane modification of silicon boride. It can also adhere to the modified silicon boride and coated lead tetroxide in situ by physical adsorption, realizing the pre-dispersion of the composite powder layer and avoiding the performance inconsistency caused by the agglomeration of this component in the subsequent ceramic preparation. Ultrafine silica can form an Al2O3-SiO2 composite inorganic reinforcing system with alumina in the original formula, efficiently filling the tiny gaps between composite powder particles and improving the powder packing density. When sintered with barium titanate matrix in the future, it further enhances the density, flexural strength and anti-brittleness of the ceramic material. It increases compressive strength and reduces breakage during fine processing. Simultaneously, its surface hydroxyl groups can form weak bonds with the silane-modified layer on the silicon boride surface, improving the structural stability of the composite powder and preventing the modified layer from detaching during subsequent ball milling. Furthermore, ultrafine silica can undergo slight solid solution with the barium titanate lattice, optimizing the temperature range stability of the PTC ceramic effect and mitigating the resistance abrupt change near the Curie temperature. In addition, it can synergistically optimize the interfacial bonding state of the ceramic system with the alumina coating layer on the lead tetroxide surface, enhancing the interfacial bonding force between the composite powder and the barium titanate matrix, reducing interfacial gaps generated during sintering, and exhibiting no side reactions during subsequent calcination and high-temperature sintering of the ceramic. It does not affect the lattice solid solution and Curie temperature control function of lead ions, forming a highly efficient synergy with the original formulation components.

[0016] Preferably, the rare earth oxide is a mixture of yttrium oxide and lanthanum oxide in a mass ratio of 5:(4-6).

[0017] By adopting the above technical solution, yttrium oxide and lanthanum oxide form a rare earth composite doping system, achieving functional synergy. This system adapts to the solid solution characteristics of barium titanate perovskite lattice, avoiding the lattice distortion or barrier inhomogeneity problems associated with single rare earth doping. After modification with silane, the dispersion is improved, allowing for uniform solid solution entry into the barium titanate lattice, optimizing the grain boundary barrier structure, effectively increasing the resistivity of PTC ceramics, and maintaining the room temperature resistivity within a suitable range. This ratio synergizes with the in-situ pre-dispersed nano-zirconia in the composite powder, effectively suppressing the abnormal growth of barium titanate grains during the high-temperature sintering stage of the ceramic, and significantly improving the electrical performance and thermal stability of the ceramic under high and low temperature cycling.

[0018] Preferably, the method for preparing the rare earth oxide includes the following steps: S1, yttrium oxide and lanthanum oxide are surface modified by a stepwise process of first grafting with KH550 and then grafting with KH560, respectively, and then dried to obtain modified yttrium oxide and modified lanthanum oxide; the amount of KH550 and KH560 used is 3.2%-4.8% of the mass of yttrium oxide or lanthanum oxide; S2, modified yttrium oxide and modified lanthanum oxide in a mass ratio of 5:(4-6) were annealed at 120-150℃ for 30 min to obtain rare earth oxides.

[0019] By adopting the above technical solution, the preparation method employs a stepwise silane modification process of first grafting KH550 and then grafting KH560, which avoids the competitive adsorption problem of simultaneous modification of dual coupling agents, making the silane grafting on the surface of yttrium oxide and lanthanum oxide more thorough and uniform, significantly improving the dispersibility of rare earth powder and the interfacial bonding ability of the system; then, the compounded modified rare earth oxides are annealed and shaped, which can not only solidify the silane modified layer to prevent the modified layer from falling off during subsequent ball milling and slurry preparation, but also allow the two modified rare earths to be fully homogenized and dispersed. The resulting composite rare earth dopant can be uniformly dissolved in the barium titanate lattice, ultimately ensuring the simultaneous improvement of the PTC ceramic's resistance ratio, room temperature resistivity stability, and high and low temperature cycling thermal stability.

[0020] Preferably, in step S2, modified yttrium oxide, modified lanthanum oxide, and hexamethyldisilazane in a mass ratio of 5:(4-6):(0.1-0.3) are annealed at 120-150°C for 30 min to obtain rare earth oxides.

[0021] By adopting the above technical solution, hexamethyldisilazane undergoes a deamination condensation reaction with the silane hydroxyl groups and rare earth hydroxyl groups remaining on the surface of modified yttrium oxide and modified lanthanum oxide during annealing, forming a stable Si-OY and Si-O-La covalent bond structure. This not only further solidifies the stepwise grafted silane modified layer, preventing the modified layer from falling off during subsequent ball milling and slurry preparation, but also achieves homogeneous dispersion of the two modified rare earths through chemical bonding. This component can be completely decomposed and volatilized during high-temperature sintering, leaving no solid phase impurities and not interfering with the ceramic crystal phase and doping system. The resulting composite rare earth oxide has improved dispersibility and interface compatibility, and can be more uniformly dissolved into the barium titanate lattice. It also works synergistically with nano-zirconia to enhance the grain boundary control effect, further optimizing the drag ratio and high and low temperature cycling stability of PTC ceramics.

[0022] Preferably, the alumina is prepared by adding 2-4 parts by weight of alumina with a particle size ≤1μm and 0.09-0.12 parts by weight of trisodium citrate to 30-36 parts by weight of deionized water, stirring at 55-65℃ for 1 hour, drying, sieving, and mixing with 6-8 parts by weight of alumina with a particle size of 3-5μm to obtain the alumina.

[0023] By adopting the above technical solution, the alumina prepared by this method is an ultrafine and coarse particle size gradient powder. First, the ultrafine alumina is modified with trisodium citrate, which not only improves its aqueous phase dispersibility and prevents agglomeration, but also allows it to synergistically disperse with rare earth ions and nano-zirconia in the system, optimizing the overall powder distribution. The gradient particle size can efficiently fill the gaps between barium titanate and composite powder particles, increasing the packing density. The modified ultrafine alumina also synergistically strengthens the interfacial bonding and buffers the sintering internal stress with the ultrafine silica and the alumina coating layer on the surface of lead tetroxide in the composite powder, significantly improving the density and mechanical strength of the ceramic. Moreover, there is no residue after calcination of trisodium citrate, which does not affect the suppression of lead vapor and the control of Curie temperature. At the same time, it improves the interfacial bonding ability between alumina and organic forming aids, improves the formability of ceramic blanks, and reduces cracking.

[0024] Secondly, this application provides a method for preparing ceramic materials for PTC thermistors, employing the following technical solution: A method for preparing a ceramic material for a PTC thermistor includes the following steps: According to the weight proportions, barium titanate, silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder, rare earth oxides and alumina are mixed to obtain a mixture; the mixture is ball-milled with deionized water at a mass ratio of 1:1 at 250-300 r / min for 4-6 h to obtain an inorganic slurry; ammonium polyacrylate and polyvinyl alcohol are added to the inorganic slurry in sequence and mixed evenly to obtain a ceramic slurry; The ceramic slurry is dried, pulverized and sieved to obtain ceramic granulation powder; the ceramic granulation powder is held under pressure of 80-120MPa for 30-60s to obtain PTC ceramic green body; The ceramic green body is heated to 200℃ at a rate of 2℃ / min and held for 30min, then heated to 500-550℃ at a rate of 1℃ / min and held for 2h, and then cooled to room temperature to obtain the ceramic green body. The ceramic blank was sintered in sections in an air atmosphere: the temperature was increased to 1100℃ at a rate of 3℃ / min and held for 1 hour, then increased to 1280-1350℃ at a rate of 2℃ / min and held for 2-3 hours, and then cooled to room temperature to obtain the ceramic material for PTC thermistors.

[0025] By adopting the above technical solution, the preparation method is simple, and through the synergistic effect between the components, the prepared ceramic material for PTC thermistors has thermal stability and mechanical properties.

[0026] In summary, this application has the following beneficial effects: 1. This application adds silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder to ceramic materials. The alumina directionally coats lead tetroxide, effectively suppressing the volatilization of lead vapor during high-temperature sintering and improving the environmental friendliness of the ceramic materials. At the same time, lead tetroxide and silicon boride are combined in-situ, and the silane modification improves the interfacial bonding ability between the composite powder and the barium titanate matrix, reducing the internal stress of ceramic sintering and improving the mechanical properties of the ceramic materials. 2. The alumina obtained by first modifying ultrafine alumina with trisodium citrate and then compounding it with coarse-grained alumina can synergistically enhance the interfacial bonding and improve the density and mechanical strength of ceramics. 3. The rare earth oxides in this application improve the uniformity and dispersion of rare earth grafting through stepwise silane modification, and further solidify the modified layer by annealing with hexamethyldisilazane to achieve homogeneous dispersion of rare earth without residue, so that rare earth can be uniformly dissolved in barium titanate lattice, ultimately synergistically improving the resistance ratio, resistivity stability and high and low temperature cycling thermal stability of PTC ceramics. Detailed Implementation

[0027] The present application will be further described in detail below with reference to preparation examples, embodiments and comparative examples. Unless otherwise specified, all raw materials involved in the present application can be obtained commercially.

[0028] Preparation Example Preparation Examples 1-7: Silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder Preparation Example 1 This preparation example discloses a method for preparing silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder, including the following steps: (1) Add 10 kg of lead tetroxide and 10 kg of silicon hexaboride to 150 kg of deionized water and ultrasonically disperse them for 15 min at 300 W to obtain a suspension; add the suspension to 30 L of 15 wt% hydrogen peroxide and stir at 200 r / min for 20 min to obtain a reaction solution; (2) Add 1.2 kg of aluminum nitrate to the above reaction solution in three portions, with a 1 min interval between each portion. Stir the reaction at 200 r / min for 10 min. Then adjust the pH of the system to 8.2 with 25 wt% ammonia solution. Place the system in a constant temperature water bath at 60 °C and stir at 200 r / min for 2 h to obtain the coating. (3) A 10wt% ethanol solution containing 1.5kg γ-aminopropyltriethoxysilane was added dropwise to the coating material at a rate of 1 drop / s. After the addition was complete, the temperature was raised to 65℃ at a rate of 5℃ / min and stirred at a rate of 200r / min for 2h. After the reaction was completed, the product was vacuum filtered at -0.08MPa, washed three times with deionized water, washed once with anhydrous ethanol, and dried in a 90℃ oven for 2h. The dried product was placed in a muffle furnace and heated to 400℃ at a rate of 2℃ / min for 2h. After cooling to room temperature, it was passed through a 200-mesh sieve to obtain silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder.

[0029] Preparation Example 2 This preparation example is basically the same as Preparation Example 1, except that (1) 10 kg of lead tetroxide and 10 kg of silicon hexaboride are added to 150 kg of deionized water and ultrasonically dispersed at 300 W power for 15 min to obtain a suspension; the suspension is added to 30 L of 15 wt% hydrogen peroxide and stirred at 200 r / min for 20 min, and then 0.1 kg of trisodium citrate is added and stirred at 200 r / min for 10 min to obtain a reaction solution.

[0030] Preparation Example 3 This preparation example is basically the same as Preparation Example 1, except that (2) 0.08 kg of nano-zirconia was added to the reaction solution and ultrasonically dispersed for 10 min at 300 W power. Then, 1.2 kg of aluminum nitrate was added to the above reaction solution in 3 portions, with an interval of 1 min each time. The reaction was stirred at 200 r / min for 10 min. After that, the pH of the system was adjusted to 8.2 with 25 wt% ammonia solution and then placed in a constant temperature water bath at 60 °C and stirred at 200 r / min for 2 h to obtain the coating.

[0031] Preparation Example 4 This preparation example is basically the same as Preparation Example 1, except that (3) a 10wt% ethanol solution containing 1.5kg of γ-aminopropyltriethoxysilane is added to the coating material at a rate of 1 drop / s. After the addition is complete, the temperature is raised to 65℃ at a rate of 5℃ / min and stirred at a rate of 200r / min for 2h. After the reaction is completed, 0.15kg of ultrafine silica (particle size ≤100nm) is added and stirred at a rate of 200r / min for 30min. Then, after vacuum filtration at -0.08MPa, the product is washed 3 times with deionized water and then washed once with anhydrous ethanol. It is then dried in a 90℃ oven for 2h. The dried product is placed in a muffle furnace and heated to 400℃ at a rate of 2℃ / min. It is calcined for 2h and cooled to room temperature before being passed through a 200-mesh sieve to obtain silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder.

[0032] Preparation Example 5 This preparation example is basically the same as Preparation Example 4, except that (3) a 10wt% ethanol solution containing 1.5kg of silane coupling agent (a mixture of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 1:1) is added dropwise to the coating material at a rate of 1 drop / s. After the addition is complete, the temperature is raised to 65℃ at a rate of 5℃ / min, and the mixture is stirred at a constant temperature of 200r / min for 2h. After the reaction is completed, 0.15kg of ultrafine silane coupling agent is added. Silica (particle size ≤ 100 nm) was stirred at 200 r / min for 30 min. After vacuum filtration at -0.08 MPa, it was washed three times with deionized water and once with anhydrous ethanol. It was then dried in a 90℃ oven for 2 h. The dried product was placed in a muffle furnace and heated to 400℃ at a rate of 2℃ / min. It was calcined for 2 h and cooled to room temperature before being passed through a 200-mesh sieve to obtain silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder.

[0033] Preparation Example 6 This preparation example discloses a method for preparing silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder, including the following steps: (1) Add 10 kg of lead tetroxide and 8 kg of silicon hexaboride to 140 kg of deionized water and ultrasonically disperse at 300 W for 15 min to obtain a suspension; add the suspension to 28 L of 15 wt% hydrogen peroxide and stir at 200 r / min for 20 min, then add 0.08 kg of trisodium citrate and stir at 200 r / min for 10 min to obtain a reaction solution; (2) Add 0.05 kg of nano-zirconia to the reaction solution and ultrasonically disperse it for 10 min at 300 W power. Then add 1 kg of aluminum nitrate to the above reaction solution in 3 portions, with an interval of 1 min each time. Stir the reaction at 200 r / min for 8 min. Then adjust the pH of the system to 8 with 25 wt% ammonia solution and place it in a constant temperature water bath at 55 ℃. Stir at 200 r / min for 2 h to obtain the coating. (3) A 10wt% ethanol solution containing 1kg of silane coupling agent (a mixture of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 1:0.8) was added dropwise to the coating material at a rate of 1 drop / s. After the addition was complete, the temperature was raised to 60℃ at a rate of 5℃ / min and stirred at a constant temperature of 200r / min for 2h. After the reaction was completed, 0.1kg of ultrafine silica (particle size ≤100nm) was added. Continue stirring at 200 r / min for 30 min; then vacuum filter at -0.08 MPa, wash three times with deionized water, then wash once with anhydrous ethanol, and dry in a 90℃ oven for 2 h; the dried product is placed in a muffle furnace, heated to 380℃ at a rate of 2℃ / min, calcined for 2 h, cooled to room temperature, and passed through a 200 mesh sieve to obtain silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder.

[0034] Preparation Example 7 This preparation example discloses a method for preparing silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder, including the following steps: (1) Add 10 kg of lead tetroxide and 12 kg of silicon hexaboride to 160 kg of deionized water and ultrasonically disperse at 300 W for 15 min to obtain a suspension; add the suspension to 32 L of 15 wt% hydrogen peroxide and stir at 200 r / min for 20 min, then add 0.12 kg of trisodium citrate and stir at 200 r / min for 10 min to obtain a reaction solution; (2) Add 0.1 kg of nano-zirconia to the reaction solution and ultrasonically disperse it for 10 min at 300 W power. Then add 1.4 kg of aluminum nitrate to the above reaction solution in 3 portions, with an interval of 1 min each time. Stir the reaction at 200 r / min for 12 min. Then adjust the pH of the system to 8.5 with 25 wt% ammonia solution and place it in a constant temperature water bath at 65 ℃. Stir at 200 r / min for 2 h to obtain the coating. (3) A 10wt% ethanol solution containing 2kg of silane coupling agent (a mixture of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 1:1.2) was added dropwise to the coating material at a rate of 1 drop / s. After the addition was complete, the temperature was raised to 70℃ at a rate of 5℃ / min and stirred at a constant temperature of 200r / min for 2h. After the reaction was completed, 0.2kg of ultrafine silica (particle size ≤100nm) was added. Continue stirring at 200 r / min for 30 min; then vacuum filter at -0.08 MPa, wash three times with deionized water, then wash once with anhydrous ethanol, and dry in a 90℃ oven for 2 h; the dried product is placed in a muffle furnace, heated to 420℃ at a rate of 2℃ / min, calcined for 2 h, cooled to room temperature, and passed through a 200 mesh sieve to obtain silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder.

[0035] Preparation Examples 8-12: Rare Earth Oxides Preparation Example 8 This preparation example discloses a method for preparing rare earth oxides, which involves mixing 5 kg of yttrium oxide and 5 kg of lanthanum oxide at 200 r / min for 30 min to obtain rare earth oxides.

[0036] Preparation Example 9 This preparation example discloses a method for preparing rare earth oxides, including the following steps: S1. Add 5 kg of yttrium oxide to 50 L of deionized water and sonicate at 300 W for 10 min to obtain a suspension. Adjust the pH of the system to 8.2 by adding 2.5 wt% ammonia dropwise, sonicate at 300 W for 15 min, and then vacuum filter. Place the filter cake in a vacuum dryer at 80 °C for 4 h to obtain pretreated yttrium oxide. Add 5 kg of lanthanum oxide to 50 L of deionized water and sonicate at 300 W for 10 min to obtain a suspension. Adjust the pH of the system to 8.2 by adding 2.5 wt% ammonia dropwise, sonicate at 300 W for 15 min, and then vacuum filter. Place the filter cake in a vacuum dryer at 80 °C for 4 h to obtain pretreated lanthanum oxide. Add the pretreated yttrium oxide to 50 L of anhydrous ethanol and sonicate at 300 W. The modified yttrium oxide was obtained by ultrasonic dispersion for 15 min, followed by the addition of a 0.2 kg 10 wt% KH550 ethanol solution and stirring at 60 °C for 30 min. Then, a 0.2 kg 10 wt% KH560 ethanol solution was added, and stirring was continued at 60 °C for another 30 min. After filtration, the yttrium oxide was vacuum dried at 80 °C for 4 h. The pretreated lanthanum oxide was then added to 50 L of anhydrous ethanol and ultrasonically dispersed at 300 W for 15 min. The 0.2 kg 10 wt% KH550 ethanol solution was added, and stirring was continued at 60 °C for 30 min. Then, a 0.2 kg 10 wt% KH560 ethanol solution was added, and stirring was continued at 60 °C for another 30 min. After filtration, the lanthanum oxide was vacuum dried at 80 °C for 4 h. S2, the modified yttrium oxide and modified lanthanum oxide were stirred and mixed at 200 r / min for 30 min to obtain a mixture; the mixture was placed in a muffle furnace and annealed at 135 °C for 30 min, and then cooled to room temperature with the furnace to obtain rare earth oxides.

[0037] Preparation Example 10 This preparation example is basically the same as Preparation Example 9, except that in S2, the above-mentioned modified yttrium oxide, modified lanthanum oxide and 0.2 kg hexamethyldisilazane are stirred and mixed at 200 r / min for 30 min to obtain a mixture; the mixture is placed in a muffle furnace and annealed at 135 °C for 30 min, and then cooled to room temperature with the furnace to obtain rare earth oxides.

[0038] Preparation Example 11 This preparation example discloses a method for preparing rare earth oxides, including the following steps: S1. Add 5 kg of yttrium oxide to 50 L of deionized water and sonicate at 300 W for 10 min to obtain a suspension. Add 2.5 wt% ammonia to adjust the pH to 8, sonicate at 300 W for 15 min, and then vacuum filter. Dry the filter cake at 80 °C for 4 h to obtain pretreated yttrium oxide. Add 4 kg of lanthanum oxide to 40 L of deionized water and sonicate at 300 W for 10 min to obtain a suspension. Add 2.5 wt% ammonia to adjust the pH to 8, sonicate at 300 W for 15 min, and then vacuum filter. Dry the filter cake at 80 °C for 4 h to obtain pretreated lanthanum oxide. Add the pretreated yttrium oxide to 50 L of anhydrous ethanol and sonicate at 300 W. After dispersing for 15 minutes, first add a solution containing 0.2 kg of 10 wt% KH550 ethanol and stir at 60°C for 30 minutes; then add a solution containing 0.2 kg of 10 wt% KH560 ethanol and continue stirring at 60°C for 30 minutes; after filtration, dry under vacuum at 80°C for 4 hours to obtain modified yttrium oxide; add pretreated lanthanum oxide to 40 L of anhydrous ethanol and ultrasonically disperse at 300 W for 15 minutes, first add a solution containing 0.16 kg of 10 wt% KH550 ethanol and stir at 60°C for 30 minutes; then add a solution containing 0.16 kg of 10 wt% KH560 ethanol and continue stirring at 60°C for 30 minutes; after filtration, dry under vacuum at 80°C for 4 hours to obtain modified lanthanum oxide; S2, the modified yttrium oxide, modified lanthanum oxide and 0.1 kg hexamethyldisilazane were stirred and mixed at 200 r / min for 30 min to obtain a mixture; the mixture was placed in a muffle furnace and annealed at 120 °C for 30 min, and then cooled to room temperature with the furnace to obtain rare earth oxides.

[0039] Preparation Example 12 This preparation example discloses a method for preparing rare earth oxides, including the following steps: S1. Add 5 kg of yttrium oxide to 50 L of deionized water and sonicate at 300 W for 10 min to obtain a suspension. Adjust the pH to 8.5 by adding 2.5 wt% ammonia dropwise, sonicate at 300 W for 15 min, and then vacuum filter. Dry the filter cake at 80 °C for 4 h to obtain pretreated yttrium oxide. Add 6 kg of lanthanum oxide to 60 L of deionized water and sonicate at 300 W for 10 min to obtain a suspension. Adjust the pH to 8.5 by adding 2.5 wt% ammonia dropwise, sonicate at 300 W for 15 min, and then vacuum filter. Dry the filter cake at 80 °C for 4 h to obtain pretreated lanthanum oxide. Add the pretreated yttrium oxide to 50 L of anhydrous ethanol and sonicate at 300 W. The modified yttrium oxide was obtained by ultrasonic dispersion for 15 min, followed by the addition of a 0.2 kg 10 wt% KH550 ethanol solution and stirring at 60 °C for 30 min. Then, a 0.2 kg 10 wt% KH560 ethanol solution was added, and stirring was continued at 60 °C for another 30 min. After filtration, the yttrium oxide was vacuum dried at 80 °C for 4 h. The pretreated lanthanum oxide was then added to 60 L of anhydrous ethanol and ultrasonically dispersed at 300 W for 15 min. Next, a 0.24 kg 10 wt% KH550 ethanol solution was added, and stirring was continued at 60 °C for 30 min. Then, a 0.24 kg 10 wt% KH560 ethanol solution was added, and stirring was continued at 60 °C for another 30 min. After filtration, the lanthanum oxide was vacuum dried at 80 °C for 4 h. S2, the modified yttrium oxide, modified lanthanum oxide and 0.3 kg hexamethyldisilazane were stirred and mixed at 200 r / min for 30 min to obtain a mixture; the mixture was placed in a muffle furnace and annealed at 150 °C for 30 min, and then cooled to room temperature with the furnace to obtain rare earth oxides.

[0040] Preparation Examples 13-15 Preparation Example 13 This preparation example discloses a method for preparing alumina, specifically as follows: 2 kg of ultrafine alumina with a particle size ≤ 1 μm and 0.09 kg of trisodium citrate are added to 30 kg of deionized water and stirred at 200 r / min for 5 min; then placed in a constant temperature water bath at 55℃ and stirred at 200 r / min for 1 h; after stirring, it is vacuum dried at 80℃ for 2 h and passed through a 200-mesh sieve to obtain modified ultrafine alumina; the modified ultrafine alumina is then mixed with 6 kg of coarse alumina particles with a particle size of 3 μm at 200 r / min for 30 min to obtain alumina.

[0041] Preparation Example 14 This preparation example discloses a method for preparing alumina, specifically as follows: 3 kg of ultrafine alumina with a particle size ≤ 1 μm and 0.1 kg of trisodium citrate are added to 33 kg of deionized water and stirred at 200 r / min for 5 min; then placed in a constant temperature water bath at 60℃ and stirred at 200 r / min for 1 h; after stirring, it is vacuum dried at 80℃ for 2 h and passed through a 200 mesh sieve to obtain modified ultrafine alumina; the modified ultrafine alumina is then mixed with 7 kg of coarse alumina particles with a particle size of 4 μm at 200 r / min for 30 min to obtain alumina.

[0042] Preparation Example 15 This preparation example discloses a method for preparing alumina, specifically as follows: 4 kg of ultrafine alumina with a particle size ≤ 1 μm and 0.12 kg of trisodium citrate are added to 36 kg of deionized water and stirred at 200 r / min for 5 min; then placed in a constant temperature water bath at 65℃ and stirred at 200 r / min for 1 h; after stirring, it is vacuum dried at 80℃ for 2 h and passed through a 200-mesh sieve to obtain modified ultrafine alumina; the modified ultrafine alumina is then mixed with 8 kg of coarse alumina particles with a particle size of 5 μm at 200 r / min for 30 min to obtain alumina.

[0043] Example 1 This embodiment discloses a method for preparing ceramic materials for PTC thermistors, including the following steps: 60 kg of barium titanate, 28 kg of silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder, 0.4 kg of rare earth oxides, and 9 kg of alumina were mixed at 200 r / min for 30 min to obtain a mixture. The mixture was then added to 97.4 kg of deionized water in a zirconia ball mill (ball milling ratio of 1:2.5) and ball milled at 250 r / min for 4 h to obtain an inorganic slurry. 1 kg of ammonium polyacrylate was added to the inorganic slurry and stirred at 200 r / min for 15 min. Then, 4 kg of polyvinyl alcohol was added and stirred for another 15 min to obtain a ceramic slurry. The silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder was obtained in Preparation Example 1, the rare earth oxides were obtained in Preparation Example 8, and the alumina was obtained in Preparation Example 13. The ceramic slurry was dried to constant weight in a vacuum oven at 80℃, then pulverized and passed through an 80-mesh standard sieve to obtain ceramic granulated powder. The ceramic granulated powder was filled into a molding die and pressed under 80MPa pressure for 30s to obtain a ceramic green body. The ceramic green body was placed in a drying oven and heated to 200℃ at a rate of 2℃ / min and held for 30min. Then it was heated to 500℃ at a rate of 1℃ / min and held for 2h. Finally, it was allowed to cool naturally to room temperature to obtain a ceramic body. The ceramic blank is placed in a sintering furnace and heated to 1100℃ at a rate of 3℃ / min under air atmosphere, and held for 1 hour; then heated to 1280℃ at a rate of 2℃ / min and held for 2 hours; after sintering, it is naturally cooled to room temperature with the furnace to obtain the ceramic material for PTC thermistors.

[0044] Example 2 The difference between this embodiment and Example 1 is that the silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder is the same as that obtained in Preparation Example 2.

[0045] Example 3 The difference between this embodiment and Example 1 is that the silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder is the one obtained in Preparation Example 3.

[0046] Example 4 This embodiment is basically the same as Example 1, except that the silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder is the one obtained in Preparation Example 4.

[0047] Example 5 This embodiment is basically the same as Example 1, except that the silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder is the one obtained in Preparation Example 5.

[0048] Example 6 This embodiment is basically the same as Example 1, except that the rare earth oxide is the one obtained in Preparation Example 9.

[0049] Example 7 This embodiment is basically the same as Example 1, except that the rare earth oxide is the one obtained in Preparation Example 10.

[0050] Example 8 This embodiment discloses a method for preparing ceramic materials for PTC thermistors, including the following steps: 64 kg of barium titanate, 30 kg of silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder, 0.5 kg of rare earth oxides, and 10 kg of alumina were mixed at 200 r / min for 30 min to obtain a mixture. The mixture was then added to 104.5 kg of deionized water in a zirconia ball mill (ball milling ratio of 1:2.5) and ball milled at 250 r / min for 4 h to obtain an inorganic slurry. 1.5 kg of ammonium polyacrylate was added to the inorganic slurry and stirred at 200 r / min for 15 min. Then, 5 kg of polyvinyl alcohol was added and stirred for another 15 min to obtain a ceramic slurry. The silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder was obtained in Preparation Example 6, the rare earth oxides were obtained in Preparation Example 11, and the alumina was obtained in Preparation Example 14. The ceramic slurry was dried to constant weight in a vacuum oven at 80℃, then pulverized and passed through an 80-mesh standard sieve to obtain ceramic granulated powder. The ceramic granulated powder was filled into a molding die and pressed under 100MPa pressure for 45s to obtain a ceramic green body. The ceramic green body was placed in a drying oven and heated to 200℃ at a rate of 2℃ / min and held for 30min. Then it was heated to 525℃ at a rate of 1℃ / min and held for 2h. Finally, it was allowed to cool naturally to room temperature to obtain a ceramic body. The ceramic blank was placed in a sintering furnace and heated to 1100℃ at a rate of 3℃ / min under air atmosphere, and held for 1 hour; then heated to 1315℃ at a rate of 2℃ / min and held for 2.5 hours; after sintering, it was naturally cooled to room temperature with the furnace to obtain the ceramic material for PTC thermistors.

[0051] Example 9 This embodiment discloses a method for preparing ceramic materials for PTC thermistors, including the following steps: 68 kg of barium titanate, 32 kg of silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder, 0.6 kg of rare earth oxides, and 11 kg of alumina were mixed at 200 r / min for 30 min to obtain a mixture. The mixture was then added to 111.6 kg of deionized water in a zirconia ball mill (ball milling ratio of 1:2.5) and ball milled at 250 r / min for 4 h to obtain an inorganic slurry. 2 kg of ammonium polyacrylate was added to the inorganic slurry and stirred at 200 r / min for 15 min. Then, 6 kg of polyvinyl alcohol was added and stirred for another 15 min to obtain a ceramic slurry. The silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder was obtained in Preparation Example 7, the rare earth oxides were obtained in Preparation Example 12, and the alumina was obtained in Preparation Example 15. The ceramic slurry was dried to constant weight in a vacuum oven at 80℃, then pulverized and passed through an 80-mesh standard sieve to obtain ceramic granulated powder. The ceramic granulated powder was filled into a molding die and pressed under 120MPa pressure for 60s to obtain a ceramic green body. The ceramic green body was placed in a drying oven and heated to 200℃ at a rate of 2℃ / min and held for 30min. Then it was heated to 550℃ at a rate of 1℃ / min and held for 2h. Finally, it was allowed to cool naturally to room temperature to obtain a ceramic body. The ceramic blank is placed in a sintering furnace and heated to 1100℃ at a rate of 3℃ / min under air atmosphere, and held for 1 hour; then heated to 1350℃ at a rate of 2℃ / min and held for 3 hours; after sintering, it is naturally cooled to room temperature with the furnace to obtain the ceramic material for PTC thermistors.

[0052] Comparative Example 1 This comparative example is basically the same as Example 1, except that 28 kg of silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder was replaced with 14 kg of lead tetroxide and 14 kg of modified silicon boride. The modified silicon boride was prepared by dispersing 10 kg of silicon boride in 150 L of ethanol, sonicating for 45 min, drying and then dispersing in 150 L of deionized water, adding 120 L of 15 wt% hydrogen peroxide, reacting in a water bath at 75 °C and 400 r / min for 4 h, centrifuging, washing and drying the product to obtain modified silicon boride.

[0053] Performance testing 1. High-Temperature Lead Volatilization: During the sintering process of ceramic materials for PTC thermistors prepared in various embodiments and comparative examples, a DN80 316L stainless steel high-temperature resistant sealing flange (with fluororubber gaskets installed on the end face, and leak-proof after soap solution testing) was used at the tail gas outlet of the sintering furnace to achieve in-situ sealing connection with the lead vapor capture device. The flange outlet was connected to a porous glass plate absorption bottle containing 50mL of 2% (v / v) pure nitric acid absorption solution via a PTFE pipe wrapped with glass wool insulation. A rotor flow meter and pressure regulating valve were used to stably control the sampling flow rate at 0.3L / min from the sintering furnace. Volatile lead components in the exhaust gas were captured from the start of heating until the furnace cooled to room temperature. During the capture process, the absorption bottle was gently shaken every 2 hours to enhance gas-liquid contact. After sintering, an additional 30 minutes of sampling was conducted to capture residual lead vapor in the furnace. After fixing the lead vapor with nitric acid absorbent, the absorbent was transferred to a 50 mL volumetric flask and washed with deionized water to make up to volume. The lead content in the solution was quantitatively determined by ICP-MS (three parallel determinations were performed and the average value was taken). Finally, the high-temperature lead volatilization per unit mass of sintered ceramic was calculated based on the measured total mass of lead and the actual mass of the sintered ceramic. The test results are recorded in Table 1.

[0054] 2. The ceramic materials prepared for PTC thermistors in each embodiment and comparative example were used to prepare standard strip specimens of 3mm×4mm×45mm according to GB / T6569-2006. The bending strength was tested, and the test results are recorded in Table 1.

[0055] 3. The ceramic materials for PTC thermistors prepared in Examples 1-9 and Comparative Example 1 were ground to a size of 24mm × 15mm × 2.42mm, chamfered, cleaned with anhydrous ethanol for 5 minutes, dried at 80℃ for 30 minutes, and then coated with 10μm thick aluminum electrodes on both sides. The samples were then aged at 100℃ for 1 hour to obtain the final samples, and the following tests were performed: The room temperature resistance of the sample was tested using a multimeter in a constant temperature environment of 25℃. The temperature corresponding to the steepest rise in resistivity of the sample was the Curie temperature, and the resistance at this point was the Curie point resistance. The resistance rise index = lg(Curie point resistance / room temperature resistance) was used to reflect the resistance rise ratio. The test results are recorded in Table 2. The breakdown voltage was tested using a BYD-GN-02 withstand voltage tester, and the test results are recorded in Table 2. High and low temperature cycling resistivity change rate: After the sample is cycled 100 times from -40℃ to 125℃, the room temperature resistance is tested and the change rate is calculated. The test results are recorded in Table 2.

[0056] Table 1 Performance test data of Examples 1-9 and Comparative Example 1 Table 2 Performance test data of Examples 1-9 and Comparative Example 1 Combining Example 1 and Comparative Example 1 with reference to Tables 1 and 2, it can be seen that the formulation scheme of Example 1, which uses basic silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder, significantly suppresses lead volatilization compared to Comparative Example 1, which directly physical blends the lead source with modified silicon boride without coating. This results in a significantly higher effective lead doping ratio and thus a higher Curie temperature. Simultaneously, the suppression effect on lead volatilization is significantly improved during the high-temperature sintering stage, effectively enhancing the flexural strength of the ceramic material. Furthermore, the silane modification and in-situ composite design optimizes the titanate... The interfacial bonding ability between the barium matrix and the filler reduces interfacial defects and doping segregation, making the grain boundary barrier structure more regular. The rise resistance ratio of the PTC ceramic core is significantly enhanced, and the breakdown voltage performance related to electrical insulation is also improved. The optimization of the dispersion and bonding state between components also improves the resistivity stability of the material after high and low temperature cycling. In contrast, Comparative Example 1 lacks lead source coating protection, resulting in prominent high-temperature lead volatilization problems. Furthermore, the poor interfacial bonding and poor doping uniformity caused by physical blending directly lead to poor mechanical properties, PTC electrical properties, and resistivity stability under high and low temperature cycling.

[0057] Combining Examples 1 and 2 and referring to Tables 1 and 2, it can be seen that in Example 2, trisodium citrate was introduced into the preparation process of the silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder based on Example 1. Compared with Example 1, the addition of this dispersant effectively improved the dispersion uniformity of lead tetroxide and silicon boride in the aqueous system, avoided the problem of powder agglomeration, and made the directional coating of alumina on lead tetroxide more dense and complete, further enhancing the inhibition effect on high-temperature lead volatilization. At the same time, trisodium citrate also improved the dispersion of rare earth dopants in subsequent ceramic preparation, reduced doping segregation, made the interface between barium titanate matrix and composite powder more compact, and reduced internal defects in ceramics. This not only further improved the bending strength of the material, but also optimized the grain boundary barrier structure, resulting in better resistance ratio performance, improved breakdown voltage, and a slight improvement in resistivity stability under high and low temperature cycling.

[0058] Combining Examples 1 and 3 and referring to Tables 1 and 2, it can be seen that Example 3 introduced nano-zirconia in the preparation process of the silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder based on Example 1. Compared with Example 1, nano-zirconia is uniformly dispersed in the system and does not interfere with the directional coating of lead tetroxide by alumina. It can also be pre-dispersed by in-situ adhering to the surface of the composite powder. It not only synergistically optimizes the grain boundary barrier structure of barium titanate lattice with rare earth dopants, effectively suppressing the abnormal growth of barium titanate grains, but also complements the alumina coating layer on the surface of lead tetroxide and the alumina reinforcing agent in the formula, optimizing the matching of the thermal expansion coefficient of the ceramic system, buffering the internal stress during sintering, and reducing the generation of microcracks inside the ceramic. This not only further enhances the suppression effect of high-temperature lead volatilization, but also significantly improves the bending strength of the ceramic material. The optimization of the grain boundary barrier also improves the resistance ratio, and the breakdown voltage and resistivity stability under high and low temperature cycling are also improved.

[0059] Combining Examples 1 and 4 and referring to Tables 1 and 2, it can be seen that in Example 4, during the preparation of the silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder based on Example 1, ultrafine silica was introduced after the silane modification reaction. Compared to Example 1, the addition of this component did not interfere with the core processes of directional coating of alumina and silane modification of silicon boride in the early stage. It can also achieve pre-dispersion by relying on physical adsorption to adhere in-situ to the surface of the modified composite powder, avoiding the problem of component agglomeration in subsequent ceramic preparation. At the same time, the ultrafine silica forms a composite inorganic reinforcing system with the alumina in the formula, which efficiently fills the tiny gaps between powder particles and improves the powder's performance. The bulk density can also form weak bonds with the silane-modified layer on the surface of silicon borate, enhancing the structural stability of the composite powder and preventing the modified layer from falling off during subsequent ball milling. It can also undergo mild solid solution with the barium titanate lattice to optimize the temperature range stability of the PTC effect, and synergistically optimize the interfacial bonding state of the ceramic system with the alumina coating layer on the surface of lead tetroxide, reducing the interfacial gaps generated during sintering. This not only further enhances the suppression effect of high-temperature lead volatilization, but also significantly enhances the density and flexural strength of the ceramic material. The optimization of the grain boundary barrier and interfacial bonding state also significantly improves the resistance ratio and breakdown voltage, and the resistivity stability under high and low temperature cycling is also improved simultaneously.

[0060] Combining Examples 4 and 5 and referring to Tables 1 and 2, it can be seen that Example 5, based on Example 4, replaces the single silane coupling agent with a bissilane coupling agent composed of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 1:1. Compared with Example 4, the functional groups of the two silane coupling agents form a synergistic complementary effect. Among them, aminosilane improves the dispersibility and spreading of the coupling agent, while epoxysilane accelerates the grafting reaction and increases the grafting density, forming a siloxane transition layer. After calcination, the organic segments decompose, and the siloxane groups condense to form a Si-O-Si inorganic network, which fills the pores of the alumina coating layer, enhances the lead vapor suppression effect, and provides inorganic bonding sites, optimizing the interfacial bonding between the composite powder and the matrix and the overall ceramic performance.

[0061] Combining Examples 1 and 6 and referring to Tables 1 and 2, it can be seen that Example 6, based on Example 1, employs a stepwise silane modification process of grafting rare earth oxides with KH550 first and KH560 later, followed by annealing. Compared to the conventional mixed rare earth oxides used in Example 1, this modification method avoids the competitive adsorption problem of simultaneous modification with dual coupling agents, allowing for more thorough and uniform silane grafting on the surfaces of yttrium oxide and lanthanum oxide. This improves the dispersibility of the rare earth powder and its interfacial bonding ability with the ceramic system. The subsequent annealing and shaping also solidifies the silane modification of the rare earth powder. The layer prevents the modified layer from falling off and allows for better homogenization and dispersion of the two modified rare earth elements. This enables rare earth ions to dissolve more uniformly into the barium titanate lattice, precisely optimizing the grain boundary barrier structure. The improved uniformity of rare earth dispersion further optimizes the overall dispersion state of the ceramic system, strengthening the suppression effect of high-temperature lead volatilization and increasing the flexural strength of the ceramic material. The optimization of the grain boundary barrier also significantly improves the rise-resistance ratio effect of the PTC core, simultaneously enhancing the breakdown voltage performance. The resistivity stability under high and low temperature cycling is also optimized due to the improved uniformity of rare earth doping.

[0062] Combining Examples 6 and 7 and referring to Tables 1 and 2, it can be seen that Example 7, based on the stepwise silane modification and annealing of rare earth oxides using KH550 grafting followed by KH560 grafting in Example 6, adds hexamethyldisilazane to the annealing process of rare earth oxides. Compared to Example 6, hexamethyldisilazane undergoes a deamination condensation reaction with the residual hydroxyl groups on the surfaces of modified yttrium oxide and modified lanthanum oxide during annealing, forming a stable covalent bond structure. This not only further solidifies the silane-modified layer on the surface of the rare earth powder, completely avoiding the problem of the modified layer falling off during subsequent ball milling, sintering, and other processes, but also achieves chemical bonding. The two modified rare earth elements achieve better homogeneous dispersion, significantly improving the solid solution uniformity of rare earth ions in the barium titanate lattice. This results in a stronger synergistic grain boundary regulation effect with components such as nano-zirconia in the ceramic system. At the same time, it further optimizes the overall interface bonding state and component dispersion of the ceramic. As a result, Example 7 is superior to Example 6 in suppressing high-temperature lead volatilization. The flexural strength of the ceramic material is further improved, and the regulation effect of the grain boundary barrier structure is more significant, resulting in a better resistance ratio and improved breakdown voltage. The resistivity stability under high and low temperature cycling is also optimized due to the further improvement in the uniformity of rare earth doping.

[0063] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A ceramic material for PTC thermistors, characterized in that, The raw materials include the following parts by weight: 60-68 parts barium titanate, 28-32 parts silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder, 0.4-0.6 parts rare earth oxides, 9-11 parts alumina, 1-2 parts ammonium polyacrylate, and 4-6 parts polyvinyl alcohol. The preparation method of the silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder includes the following steps: (1) Add 10 parts by weight of lead tetroxide and 8-12 parts by weight of silicon boride to 140-160 parts by weight of deionized water and disperse by ultrasonication to obtain a suspension; add the suspension to 29-34 parts by weight of 15wt% hydrogen peroxide and stir at 200-300r / min at room temperature for 15-25min to obtain a reaction solution. (2) Add 1-1.4 parts by weight of aluminum nitrate to the reaction solution, stir for 8-12 min, adjust the pH to 8-8.5 with ammonia water, stir at a water bath temperature of 55-65℃ for 2 h to obtain the coating; (3) Dissolve 1-2 parts by weight of silane coupling agent in ethanol to form a solution, drop it into the coating, heat to 60-70℃, stir and react for 2h; after the reaction is completed, filter, wash and dry, calcine at 380-420℃ for 2h, cool and sieve to obtain the silane modified alumina coated lead tetroxide-silicon boride in-situ composite powder; The silane coupling agent is one or both of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane.

2. The ceramic material for PTC thermistors according to claim 1, characterized in that, Step (1): Add 10 parts by weight of lead tetroxide and 8-12 parts by weight of silicon boride to 140-160 parts by weight of deionized water and disperse by ultrasonication to obtain a suspension; add the suspension to 29-34 parts by weight of 15wt% hydrogen peroxide and stir at 200-300r / min at room temperature for 15-25min to activate it; then add 0.08-0.12 parts by weight of trisodium citrate and stir to obtain a reaction solution.

3. The ceramic material for PTC thermistors according to claim 1, characterized in that, Step (2): Add 0.05-0.1 parts by weight of nano-zirconia to the reaction solution, disperse it by ultrasonication, then add 1-1.4 parts by weight of aluminum nitrate, stir the reaction for 8-12 minutes, adjust the pH to 8-8.5, stir at a water bath temperature of 55-65℃ for 2 hours to obtain the coating.

4. The ceramic material for PTC thermistors according to claim 1, characterized in that, In step (3), the silane coupling agent is a mixture of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 1:(0.8-1.2).

5. The ceramic material for PTC thermistors according to claim 4, characterized in that, Step (3): Dissolve 1-2 parts by weight of silane coupling agent in ethanol to form a solution, drop it into the coating material, heat to 60-70℃, and stir for 2 hours; after the reaction is completed, add 0.1-0.2 parts by weight of ultrafine silica, stir and disperse, filter, wash, dry, calcine at 380-420℃ for 2 hours, cool and sieve to obtain the silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder; the silane coupling agent is a mixture of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 1:

1.

6. The ceramic material for PTC thermistors according to claim 1, characterized in that, The rare earth oxide is a mixture of yttrium oxide and lanthanum oxide in a mass ratio of 5:(4-6).

7. The ceramic material for PTC thermistors according to claim 1, characterized in that, The method for preparing the rare earth oxide includes the following steps: S1, yttrium oxide and lanthanum oxide are surface modified by a stepwise process of first grafting with KH550 and then grafting with KH560, respectively, and then dried to obtain modified yttrium oxide and modified lanthanum oxide; the amount of KH550 and KH560 used is 3.2%-4.8% of the mass of yttrium oxide or lanthanum oxide; S2, modified yttrium oxide and modified lanthanum oxide in a mass ratio of 5:(4-6) were annealed at 120-150℃ for 30 min to obtain rare earth oxides.

8. The ceramic material for PTC thermistors according to claim 7, characterized in that, S2, modified yttrium oxide, modified lanthanum oxide and hexamethyldisilazane in a mass ratio of 5:(4-6):(0.1-0.3) were annealed at 120-150℃ for 30 min to obtain rare earth oxides.

9. The ceramic material for PTC thermistors according to claim 1, characterized in that, The alumina is prepared by adding 2-4 parts by weight of alumina with a particle size ≤1μm and 0.09-0.12 parts by weight of trisodium citrate to 30-36 parts by weight of deionized water, stirring at 55-65℃ for 1 hour, drying, sieving, and mixing with 6-8 parts by weight of alumina with a particle size of 3-5μm to obtain the alumina.

10. The method for preparing the ceramic material for PTC thermistors according to any one of claims 1-9, characterized in that, Includes the following steps: According to the weight proportions, barium titanate, silane-modified alumina-coated lead tetroxide-silicon boride in-situ composite powder, rare earth oxides and alumina are mixed to obtain a mixture; the mixture is ball-milled with deionized water at a mass ratio of 1:1 at 250-300 r / min for 4-6 h to obtain an inorganic slurry; ammonium polyacrylate and polyvinyl alcohol are added to the inorganic slurry in sequence and mixed evenly to obtain a ceramic slurry; The ceramic slurry is dried, pulverized and sieved to obtain ceramic granulation powder; the ceramic granulation powder is held under pressure of 80-120MPa for 30-60s to obtain PTC ceramic green body; The ceramic green body is heated to 200℃ at a rate of 2℃ / min and held for 30min, then heated to 500-550℃ at a rate of 1℃ / min and held for 2h, and then cooled to room temperature to obtain the ceramic green body. The ceramic blank was sintered in sections in an air atmosphere: the temperature was increased to 1100℃ at a rate of 3℃ / min and held for 1 hour, then increased to 1280-1350℃ at a rate of 2℃ / min and held for 2-3 hours, and then cooled to room temperature to obtain the ceramic material for PTC thermistors.

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