High curie point low voltage small resistance ceramic PTC element, preparation method and application

Abstract

This invention discloses a high Curie point, low voltage, and low resistance ceramic PTC element, its preparation method, and its application, relating to the field of ceramic PTC technology. The invention uses a solid solution system composed of barium titanate and lead titanate as the main components, controlling the molar ratio of barium to lead within the range of 0.63-0.70:0.30-0.37. This allows the Curie point of the material to be stably distributed in the high-temperature range of 240℃ to 280℃. By optimizing the doping system, a high temperature coefficient of resistance and a high step-up resistance ratio are maintained while achieving low room temperature resistance. The invention employs separate pre-firing methods, allowing barium titanate and lead titanate to be synthesized and semiconducted separately under their respective optimal temperature conditions, ensuring precise control of the Curie point. This avoids localized inhomogeneities caused by difficulties in solid solution during final mixing, achieving controllable and repeatable product performance, suitable for large-scale production. This invention successfully solves the problems of high Curie point, low voltage, and low resistance PTC element preparation difficulty and unstable performance in existing technologies, and has good prospects for industrial application.

Description

Technical Field

[0001] This invention relates to the field of ceramic PTC technology, and in particular to a high Curie point, low voltage, and low resistance ceramic PTC element, its preparation method, and its application. Background Technology

[0002] PTC (Positive Temperature Coefficient) thermistor ceramics are semiconducting ferroelectric ceramic materials whose resistivity increases abruptly with increasing temperature near the Curie temperature. This characteristic makes them widely used in overcurrent protection, isothermal heating, and temperature sensing. The temperature control characteristics of PTC ceramics can be adjusted by modifying factors such as material composition, doping system, and microstructure, providing the possibility for optimizing the performance of PTC materials in different application scenarios.

[0003] Currently, PTC ceramic products in the industry are mostly concentrated in high-resistance, high-voltage, and high-power applications, such as air conditioning auxiliary heating and automotive preheaters. These products typically have high room temperature resistance (tens to hundreds of ohms) and high rated voltage (tens to hundreds of volts), exhibiting a significant PTC effect, and their manufacturing processes are relatively mature. However, with the development of emerging fields such as consumer electronics, new energy vehicle thermal management systems, smart homes, and portable medical devices, the market demand for PTC elements with low-voltage (e.g., 12V, 24V) power supply, low resistance (1-10Ω), and high Curie point (above 240℃) is increasing. These elements can achieve rapid heating at lower voltages while meeting energy-saving and miniaturization design requirements.

[0004] However, the resistance change rate of low-voltage, low-resistivity ceramic PTC elements at high temperatures is not as significant as that of high-resistivity elements. They generally suffer from problems such as low temperature coefficient of resistance, small resistance-to-weight ratio, unstable Curie point temperature, poor voltage withstand strength, and poor aging performance. Therefore, their manufacturing process places extremely high demands on the composition, formulation, uniformity of materials, and control of production processes. Furthermore, the performance of low-resistivity PTC elements is extremely sensitive to material composition, doping ratio, raw material uniformity, and production process control; any slight fluctuation in composition, sintering process differences, or inhomogeneities can significantly affect the electrical performance of the final product. Therefore, how to achieve a high Curie point while simultaneously obtaining low room temperature resistance and maintaining excellent PTC effects (high temperature coefficient of resistance, high resistance-to-weight ratio) through the selection of appropriate material composition and doping technology, semiconductorization and phase transition control, and sintering process optimization has become a pressing technical problem to be solved in this field. Summary of the Invention

[0005] The technical problem to be solved by the present invention is how to obtain a high Curie point, low room temperature resistance and maintain excellent PTC effect by selecting appropriate material composition and doping technology, controlling semiconductorization and phase transformation, and optimizing sintering process, so as to obtain a high Curie point, low voltage and low resistance ceramic PTC element.

[0006] To address the above problems, the present invention proposes the following technical solution: In a first aspect, the present invention provides a high Curie point, low voltage, and low resistance ceramic PTC element, wherein the material of the ceramic PTC element includes a main component, a semiconductor agent, a dopant, and a sintering aid; The main components include barium titanate and lead titanate, and the molar ratio of barium titanate to lead titanate is 0.63-0.70 : 0.30-0.37; Based on a total molar amount of 1.00 mol of the main component, the semiconductor agent contains at least 0.0010 - 0.0014 mol of niobium pentoxide; The dopant contains at least 0.0003-0.0005 mol of manganese dioxide and 0.0003-0.0005 mol of antimony trioxide; The sintering aid contains at least 0.005-0.015 mol of silicon monoxide; The ceramic PTC element has a Curie point of 240-280℃ and a room temperature resistance of 1-10Ω.

[0007] Furthermore, the semiconductor agent also contains 0-0.0006 mol of an auxiliary semiconductor agent, wherein the auxiliary semiconductor agent is selected from at least one of lanthanum oxide, neodymium oxide, samarium oxide, praseodymium oxide, gadolinium oxide, and tantalum pentoxide.

[0008] Furthermore, the dopant also contains 0 0.00015 mol of chromium trioxide.

[0009] Furthermore, the sintering aid also includes 0-0.0285 mol of auxiliary sintering aid, wherein the auxiliary sintering aid is selected from at least one of aluminum oxide, boron nitride, silicon nitride, calcium oxide, and cerium dioxide.

[0010] Furthermore, the material also contains 0 0.08 mol% zinc oxide.

[0011] In a second aspect, the present invention provides a method for preparing the high Curie point, low voltage, low resistance ceramic PTC element, comprising the following steps: (1) Preparation of the first pre-calcined powder: According to the ratio, the barium source, titanium source and semiconductor agent are mixed, ball-milled, dried and pre-calcined to obtain the first pre-calcined powder with barium titanate as the matrix; (2) Preparation of the second pre-calcined powder: According to the ratio, the lead source, titanium source and semiconductor agent are mixed, ball-milled, dried and pre-calcined to obtain the second pre-calcined powder with lead titanate as the matrix; (3) Preparation of mixed powder: The first pre-calcined powder, the second pre-calcined powder, dopant and sintering aid are mixed, and the mixture is ball-milled and granulated to obtain mixed powder; (4) The mixed powder is shaped, sintered, ground into wafers and electrodes to obtain a ceramic PTC element.

[0012] Furthermore, in step (1), the pre-firing temperature is 1140°C. 1150℃ for 2 hours; in step (2), the pre-firing temperature is 950℃. 980℃, for 2 hours.

[0013] Furthermore, in step (4), the sintering adopts a segmented sintering process, including a discharge stage and a sintering stage; The combustion phase includes: raising the temperature from room temperature to 600℃ and holding it at that temperature for 0.5-1.5 hours, then continuing to raise the temperature to 850℃. Hold at 900℃ for 0.5-1.5 hours; the sintering stage includes: heating to 1150℃ and holding for 0-30 minutes, then heating to 1230℃. 1280℃ heat preservation for 30 60 minutes, then cool to 1100℃ and hold for 0 minutes. Leave for 30 minutes, then cool to room temperature.

[0014] Furthermore, during the combustion phase, the heating rate from room temperature to 600°C is 200°C / h, and the temperature is maintained at 600°C for 1 hour; from 600°C to 850°C... The heating rate to 900℃ is 200℃ / h, and the holding time is 1 hour; during the sintering stage, the heating rate to 1150℃ is 360℃ / h, and the holding time is 0 hours. 30 minutes; from 1150℃ to 1230℃ The heating rate to 1280℃ is 600℃ / h. 800℃ / h, heat preservation for 30 60 minutes; from 1230℃ After cooling from 1280℃ to 1100℃, maintain the temperature for 0 seconds. 30 minutes; the cooling rate from 1100℃ to room temperature is 250-350℃ / h.

[0015] Thirdly, the present invention provides an electronic device including the aforementioned ceramic PTC element.

[0016] The present invention also provides the application of the ceramic PTC element in a low-pressure heating device.

[0017] Compared with the prior art, the technical effects achieved by the present invention include: The high Curie point, low voltage, low resistance ceramic PTC element provided by this invention uses a solid solution system composed of barium titanate and lead titanate as the main component, and controls the molar ratio of barium to lead at 0.63. 0.70:0.30 Within the range of 0.37, the Curie point of the material can be stably distributed in the high-temperature range of 240℃ to 280℃, meeting the needs of high-temperature self-regulating heating elements in fields such as thermal management of new energy vehicles, smart homes, and portable medical devices. This invention defines the doping system as follows: at least niobium pentoxide is included in the semiconductor agent, at least manganese dioxide and antimony trioxide are included in the dopant, and at least silicon monoxide is included in the sintering aid. Niobium pentoxide, as a semiconductor element in high Curie temperature materials, has a good effect on suppressing lead volatilization, and as a donor impurity, it replaces titanium sites, providing free electrons to achieve semiconductorization of the ceramic body; manganese dioxide, as an acceptor impurity, is enriched at grain boundaries, forming a barrier layer and significantly enhancing the PTC effect; antimony trioxide assists in semiconductorization and improves grain boundary properties, better suppressing grain growth; silicon monoxide, as a sintering aid, results in lower room temperature resistivity. The above components work together to achieve low room temperature resistance (1-10Ω) while maintaining a high temperature coefficient of resistance and a high step-up resistance ratio. This solves the problems of low temperature coefficient of resistance, small step-up resistance ratio, unstable Curie point, and poor withstand voltage performance that are common in low-resistance PTC elements in the prior art. It achieves a stable unity of high Curie point, low resistance, and high PTC effect.

[0018] The preparation method provided by this invention employs separate pre-calcination, allowing barium titanate and lead titanate to be synthesized and semiconductorized separately under their respective optimal temperature conditions. This avoids the volatilization loss of lead at high temperatures and ensures precise control of the Curie point. Simultaneously, the semiconductor agent is uniformly dissolved in its respective matrix lattice during the pre-calcination stage, avoiding localized inhomogeneities caused by difficulties in solid solution during final mixing. This invention solves the problems of existing low-resistivity PTC elements being extremely sensitive to compositional fluctuations and sintering process differences, and having difficulty in stable performance control. It achieves controllable and repeatable product performance, making it suitable for mass production.

[0019] The ceramic PTC element provided by this invention has the characteristics of high Curie point, low room temperature resistance, and significant PTC effect. It can achieve rapid heating and precise temperature control under low voltage power supply conditions such as 12V and 24V, while maintaining excellent voltage resistance and aging stability. It meets the urgent needs of emerging fields such as new energy vehicle thermal management systems, smart home devices, and portable medical devices for high-performance, miniaturized, and energy-saving heating elements, and has good market application prospects and industrialization value. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic flowchart of a method for preparing a high Curie point, low voltage, low resistance ceramic PTC element according to an embodiment of the present invention; Figure 2 The resistance of the ceramic PTC element with a Curie point of 240°C in Embodiment 1 of the present invention Temperature characteristic curve; Figure 3 The resistance of the ceramic PTC element with a Curie point of 260°C in Embodiment 2 of the present invention Temperature characteristic curve; Figure 4 The resistance of the ceramic PTC element with a Curie point of 280°C in Embodiment 3 of the present invention Temperature characteristic curve. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0024] It should also be understood that the process parameters of each step in this invention can be adapted and adjusted by those skilled in the art based on actual production equipment, batch size and conventional process experience, without deviating from the technical concept of this invention, as long as the expected technical effect of each step can be achieved. This invention does not impose strict limitations.

[0025] This invention provides a high Curie point, low voltage, and low resistance ceramic PTC element. The material of the ceramic PTC element includes a main component, a semiconductor agent, a dopant, and a sintering aid.

[0026] In a specific embodiment of the present invention, the main components of the ceramic PTC element include barium titanate and lead titanate. Barium titanate is the basic material for the PTC effect, and its Curie point is approximately 120°C. The present invention, by introducing a suitable proportion of lead titanate to form a solid solution, can effectively raise the Curie point of the PTC element to the required high-temperature range. To achieve the target Curie point of 240°C to 280°C, the molar ratio of barium titanate to lead titanate should be controlled within the range of 0.63:0.37 to 0.70:0.30 (the sum of the two is 1). For example, when the molar ratio of barium titanate to lead titanate is 0.70:0.30, the Curie point is approximately 240°C; when the molar ratio is 0.67:0.33, the Curie point is approximately 260°C; and when the molar ratio is 0.63:0.37, the Curie point is approximately 280°C. If the proportion of barium titanate is too high, exceeding 0.70, the Curie point will be lower than 240℃, making it difficult to meet the requirements of high-temperature applications. If the proportion of lead titanate is too high, exceeding 0.37, the Curie point can be further increased, but the increased lead content will lead to greater sintering difficulty, semiconductorization difficulties, and difficulty in reducing room temperature resistance to the target range. At the same time, lead volatilization will be aggravated, and the product performance stability will decrease.

[0027] It should be noted that the selection of semiconductor agents must follow the crystal chemistry principle of donor doping: one type selects those related to Ba... 2+ Similar ionic radius and higher valence than Ba 2+ The element replaces Ba 2+ La acts as a donor impurity. 3+ 、Sm 3+ Another type of selection involves atoms with ionic radii similar to those of titanium and valences higher than those of Ti. 4+ The element replaces Ti 4+ The person acts as a benefactor, such as Nb 5+ Ta 5+ Therefore, in a specific embodiment of the present invention, the semiconductor agent at least comprises niobium pentoxide (Nb₂O₅), Nb 5+ Mainly replaces Ti 4 + Bits, each Nb 5+ Replace a Ti 4+Each time a free electron is released, the ceramic body becomes semiconductive. Based on the total molar amount of the main components, the amount of niobium pentoxide added is 0.0010 mol to 0.0014 mol. In actual preparation, the amount of niobium pentoxide added can be 0.0010 mol, 0.0011 mol, 0.0012 mol, 0.0013 mol, or 0.0014 mol. If the amount of niobium pentoxide added is less than 0.0010 mol, the semiconductivity is insufficient, the room temperature resistance is too high, and it is difficult to achieve the low resistance target of 1Ω to 10Ω; if the amount added is greater than 0.0014 mol, too many donor impurities may be introduced, causing increased resistance and more lead volatilization, affecting the PTC effect.

[0028] To further optimize the semiconductor effect, the semiconductor agent of the present invention also includes an auxiliary semiconductor agent, wherein the auxiliary semiconductor agent is selected from at least one of lanthanum oxide (La₂O₃), neodymium oxide (Nd₂O₃), samarium oxide (Sm₂O₃), praseodymium oxide (Pr₂O₃), gadolinium oxide (Gd₂O₃), and tantalum pentoxide (Ta₂O₅). Among them, La… 3+ 、Nd 3+ 、Sm 3+ Pr 3+ Gd 3+ Trivalent rare earth ions mainly replace Ba 2+ Each substitution at position Nb also releases a free electron, similar to Nb 5+ The formation of dual-site donor doping significantly increases carrier concentration, further reducing room temperature resistance; while Ta 5+ With Nb 5+ Both being pentavalent elements with similar ionic radii, they compete for Ti. 4+ This allows for the formation of a more uniform solid solution, preventing donor element segregation and increasing the effective donor concentration. The synergistic effect of these two factors not only ensures more complete semiconductorization but also optimizes the grain boundary barrier distribution, improving the temperature coefficient of resistance and the rise-up resistance ratio. Based on the total molar amount of the main component, the amount of niobium pentoxide added is 0.0010 mol to 0.0014 mol; the amount of auxiliary semiconductor agent added is 0 to 0.0006 mol, for example, 0, 0.0001 mol, 0.0002 mol, 0.0003 mol, 0.0004 mol, 0.0005 mol, or 0.0006 mol. When the amount of auxiliary semiconductor agent added is in the range of 0.0001 mol to 0.0006 mol, a better semiconductorization effect than single doping can be obtained; if the amount added exceeds 0.0006 mol, the excessively high total donor amount may weaken the PTC effect, leading to negative effects such as decreased breakdown voltage.

[0029] In a specific embodiment of the present invention, the dopant comprises manganese dioxide and antimony trioxide. Manganese dioxide, as an acceptor impurity, accumulates at grain boundaries during sintering, forming acceptor state energy levels and generating grain boundary barriers, making it a key component for the generation and enhancement of the PTC effect. Antimony trioxide assists in semiconductorization, improves grain boundary properties, and can also form a liquid phase with a lower melting point with the introduced AST, better suppressing grain growth. Based on the total molar amount of the main components, the amount of manganese dioxide added is 0.0003 mol to 0.0005 mol, and the amount of antimony trioxide added is 0.0003 mol to 0.0005 mol. In actual preparation, the amount of manganese dioxide added can be 0.0003 mol, 0.0004 mol, or 0.0005 mol; the amount of antimony trioxide added can be 0.0003 mol, 0.0004 mol, or 0.0005 mol. If the amount of manganese dioxide or antimony trioxide added is less than 0.0003 mol, the PTC effect will be insufficient, the resistance ratio will be low, and the temperature coefficient of resistance will decrease. If the amount added is greater than 0.0005 mol, it may be overdoped, resulting in a significant increase in room temperature resistance, making it difficult to achieve the low resistance target, or even destroying the semiconducting state.

[0030] In a specific embodiment of the present invention, the dopant may further include an auxiliary dopant, wherein the auxiliary dopant is chromium trioxide. The introduction of chromium trioxide helps stabilize the phase transition temperature and resistivity abrupt change characteristics of PTC ceramics, ensuring that the material exhibits reliable positive temperature coefficient behavior within a specific temperature range, which is particularly suitable for applications requiring high temperature stability. Based on the total molar amount of the main component, the amount of chromium trioxide added is 0 to 0.00015 mol. In actual preparation, 0.00005 mol, 0.0001 mol, or 0.00015 mol of chromium trioxide may be added, or none may be added. If the amount of chromium trioxide added exceeds 0.00015 mol, it may lead to an increase in resistivity and a weakening of the PTC effect.

[0031] In specific embodiments of the present invention, the sintering aid may further include an auxiliary sintering aid, wherein the auxiliary sintering aid is selected from one or more of aluminum oxide, boron nitride, silicon nitride, calcium oxide, and cerium dioxide. Aluminum oxide can form an appropriate amount of liquid-phase AST with silicon and titanium at high temperature, adsorbing harmful impurities and improving the density of the ceramic body; boron nitride and silicon nitride can lower the sintering temperature and reduce room temperature resistance, thereby improving the withstand voltage strength; calcium oxide can prevent grain growth and secondary recrystallization, obtaining a finer and more uniform microstructure, and can obtain PTC ceramics with low resistance, low voltage sensitivity, and high thermal shock resistance; cerium dioxide can effectively reduce the resistivity of the material and improve the PTC effect of the material. Based on the total molar amount of the main components, the total amount of auxiliary sintering aids added is 0 to 0.0285 mol, for example, 0, 0.005 mol, 0.010 mol, 0.015 mol, 0.020 mol, 0.025 mol, or 0.0285 mol, where the amount of each component added can be adjusted independently as needed. In actual preparation, various combinations can be used, such as adding 0.013 mol of aluminum oxide, 0.008 mol of boron nitride, and 0.005 mol of calcium oxide; or adding 0.015 mol of aluminum oxide, 0.005 mol of boron nitride, and 0.0002 mol of cerium dioxide; or adding 0.0175 mol of aluminum oxide, 0.003 mol of silicon nitride, and 0.0003 mol of zinc oxide; or not adding auxiliary sintering aids. If the total amount of auxiliary sintering agent added exceeds 0.0285 mol, too much liquid phase may be introduced, which may easily lead to the formation of giant crystals and abnormal grain growth.

[0032] In a specific embodiment of the present invention, the material of the ceramic PTC element may further include trace raw materials, wherein the trace raw materials are selected from zinc oxide. The introduction of zinc oxide can reduce the requirements for the purity of raw materials, adjust the resistivity of the material, and make the material easier to obtain low-resistivity characteristics. Based on the total molar amount of the main components, expressed as a molar percentage, the amount of zinc oxide added is 0 to 0.08 mol%. In actual preparation, the amount of zinc oxide added may be 0.01 mol%, 0.02 mol%, 0.03 mol%, 0.04 mol%, 0.05 mol%, 0.06 mol%, 0.07 mol%, or 0.08 mol%, or not added at all. If the amount of zinc oxide added exceeds 0.08 mol%, it may lead to an increase in the resistivity of the material.

[0033] Under the combined effect of the above components, the high Curie point, low voltage, and low resistance ceramic PTC element provided by the present invention achieves low room temperature resistance (1-10Ω) while maintaining a Curie point of 240-280℃, thus maintaining a high temperature coefficient of resistance and a high step-up resistance ratio.

[0034] See Figure 1 The present invention also provides a method for preparing the above-mentioned high Curie point, low voltage, low resistance ceramic PTC element, comprising the following steps: (1) Preparation of the first pre-calcined powder: According to the ratio, the barium source, titanium source and semiconductor agent are mixed, ball-milled, dried and pre-calcined to obtain the first pre-calcined powder with barium titanate as the matrix.

[0035] In a specific embodiment of the present invention, barium carbonate is used as the barium source in step (1), and titanium dioxide is used as the titanium source, preferably rutile titanium dioxide, which helps to prepare PTC ceramics with low room temperature resistance and high temperature coefficient of resistance. During ball milling, barium carbonate, semiconducting agent, and titanium dioxide are added to the ball mill jar in the following order: barium carbonate, semiconducting agent, and titanium dioxide. A dispersant is also added; the dispersant can be CE-64 or DA-40, with an addition amount of 0.1wt% to 0.3wt%. The ratio of material, balls, and water is 1:1.5:1.2, and wet ball milling is performed for 24 hours. After ball milling, the material is filtered, dried, pulverized, sieved, and then placed in a crucible for pre-firing. The pre-calcination process employs a segmented heating regime: the temperature is raised from room temperature to 850°C at a rate of 200°C / h, and held at 850°C for 1 hour. During this stage, barium carbonate reacts with titanium dioxide to form barium titanate and removes carbon dioxide. Then, the temperature is raised from 850°C to 1140°C to 1150°C at a rate of 250°C / h, and held for 2 hours to complete the synthesis reaction. Through these steps, the semiconductor agent dissolves in the barium titanate lattice during the synthesis process, forming a uniformly semiconductorized barium titanate powder.

[0036] (2) Preparation of the second pre-calcined powder: According to the ratio, the lead source, titanium source and semiconductor agent are mixed, ball-milled, dried and pre-calcined to obtain the second pre-calcined powder with lead titanate as the matrix.

[0037] In a specific embodiment of the present invention, the lead source in step (2) is lead tetroxide, the titanium source is titanium dioxide, and the semiconductor agent is the same as that of the first pre-calcined powder. During ball milling, lead tetroxide, semiconductor agent, and titanium dioxide are added to the ball mill jar in the order of addition. Dispersant CE-64 or DA-40 is added at a rate of 0.1 wt% to 0.3 wt%, and the ratio of material, balls, and water is 1:1.5:1.0. Wet ball milling is performed for 24 hours. After ball milling, the powder is filtered, dried, pulverized, and sieved, and then placed in a sagger for pre-calcination. Pre-calcination is performed by directly heating to the synthesis temperature, from room temperature to 950℃-980℃ at a rate of 200℃ / h, and holding for 2 hours. This synthesis temperature is lower than the synthesis temperature of the first pre-calcined powder, which can effectively suppress the volatilization of lead and at the same time allow the semiconductor agent to be fully dissolved in the lead titanate lattice.

[0038] (3) Preparation of mixed powder: The first pre-burned powder, the second pre-burned powder, dopant and sintering aid are mixed, and the mixture is ball-milled and granulated to obtain mixed powder.

[0039] In a specific embodiment of the present invention, the first pre-calcined powder, the second pre-calcined powder, and the dopant and sintering aid are mixed, and then ball-milled and granulated to obtain a mixed powder. During ball milling, the first pre-calcined powder, dopant, sintering aid, trace raw materials, and the second pre-calcined powder are added to the ball mill jar in the following order: CE-64 or DA-40 is added at a rate of 0.1 wt% to 0.3 wt%, and the ratio of material, balls, and water is 1:1.5:1.0. Ball milling is performed for 22 hours. Subsequently, a lubricant and a binder are added. The lubricant is glycerol, added at a rate of 0.05 wt% to 0.15 wt%, and the binder is polyvinyl alcohol (PVABP-05 or PVA217). The concentration of the polyvinyl alcohol solution is 8% to 10%, and the amount added is 8 wt% to 15 wt%. After ball milling for another 2 hours, spray granulation is performed to obtain a granulated powder with good flowability.

[0040] (4) The mixed powder is shaped, sintered, ground into wafers and electrodes to obtain a ceramic PTC element.

[0041] In a specific embodiment of the present invention, the spray-granulated powder is first formed into a green blank by dry pressing, for example, a blank sheet with dimensions of 24mm × 15mm × 2.85mm. The formed blank sheet is then fired using a segmented sintering process of first sintering and then firing.

[0042] The exhaust firing stage is used to evaporate moisture, remove organic matter, and increase the strength of the green body. Specifically, the temperature is raised from room temperature to 600℃ at a rate of 200℃ / h, and held at 600℃ for 0.5-1.5h to allow moisture and some organic matter in the green body to evaporate. Then, the temperature is raised from 600℃ to 850℃-900℃ and held for 0.5-1.5h at a rate of 200℃ / h to fully decompose and remove organic matter such as binders, while simultaneously increasing the mechanical strength of the green body and preventing cracking during subsequent sintering. For example, the exhaust firing temperature can be selected as 850℃, 870℃, or 900℃. If the exhaust firing temperature is below 850℃, organic matter will not be completely removed, and porosity is likely to occur during sintering; if it is above 900℃, pre-sintering of the green body surface may occur, affecting subsequent densification.

[0043] The sintering stage includes three steps: supplementary synthesis, high-temperature firing, and full oxidation.

[0044] Supplementary synthesis stage: The temperature is raised to 1150℃ at a rate of 360℃ / h, and held at 1150℃ for 0 to 30 minutes to further dissolve the first and second pre-calcined powders, forming a uniform BaTiO3-PbTiO3 solid solution. For example, the holding time can be 0 minutes, 15 minutes, or 30 minutes. If the holding time is too short, the solid solution will be insufficient; if it is too long, it may cause grain coarsening.

[0045] It should be noted that in this embodiment of the invention, based on the scenario where the sintering and firing processes in industrial production are carried out in separate kilns, the supplementary synthesis stage of the above-mentioned sintering stage initially involves raising the temperature from room temperature to 1150°C. However, those skilled in the art will know that when continuous sintering is carried out in the same kiln (suitable for small-batch laboratory use) or when the sintered blanks are directly fed into the sintering kiln via a rotary line, the starting temperature of the sintering stage can be the final temperature of the sintering process (e.g., 850°C-900°C). Both of the above process paths are conventional choices in the art, and those skilled in the art can flexibly adjust them according to the production equipment configuration and process requirements. Their technical effects are substantially equivalent and do not depart from the technical concept of the present invention.

[0046] High-temperature firing stage: The temperature is rapidly increased from 1150℃ to the maximum firing temperature of 1230℃ to 1280℃ at a rate of 600℃ / h to 800℃ / h. This maximum firing temperature is then held for 30 to 60 minutes to achieve densification of the ceramic body. For example, the maximum firing temperature can be selected as 1230℃, 1240℃, 1250℃, 1260℃, or 1280℃, and the holding time can be selected as 30 minutes, 40 minutes, 45 minutes, 50 minutes, or 60 minutes. If the firing temperature is below 1230℃, the ceramic body will not be sufficiently densified; if it is above 1280℃, excessive grain growth will occur, increasing the electrical resistance.

[0047] Sufficient oxidation stage: The temperature is lowered from the highest firing temperature to 1100℃ using a rapid cooling method, and held at 1100℃ for 0 to 30 minutes to ensure sufficient oxidation of the grain boundaries and the formation of an ideal grain boundary barrier structure. Finally, the temperature is rapidly cooled from 1100℃ to room temperature at a rate of 250-350℃ / h. For example, holding time of 0 minutes, 15 minutes, or 30 minutes can be selected. If the holding time is too short, the grain boundary oxidation will be insufficient, resulting in a weak PTC effect; if it is too long, it may cause excessive oxidation of the grain surface, leading to increased electrical resistance. Cooling rates can be 250℃ / h, 300℃ / h, or 350℃ / h.

[0048] In a specific embodiment of the present invention, after sintering, the ceramic sheet is ground to the target thickness, for example, to 24mm×15mm×2.1mm. After chamfering, cleaning and drying, aluminum electrodes are sprayed on both sides to obtain the finished ceramic PTC element.

[0049] Understandably, the semiconductor agent in the first and second pre-calcined powders of this invention adopts the same composition and addition amount standard, that is, under the molar amount of their respective titanates (barium titanate or lead titanate), the addition amount of niobium pentoxide is 0.0010 mol to 0.0014 mol, and the addition amount of auxiliary semiconductor agent is 0 to 0.0006 mol, which is independent of the specific value of the Curie point. This design eliminates the need to re-optimize the semiconductor agent dosage when adjusting the Ba / Pb ratio to change the Curie point, simplifying process adjustment and ensuring the stability and repeatability of the semiconductor effect.

[0050] It should be noted that in the preparation steps of this invention, the ball milling time, the ratio of ball to water, the order of feeding, the drying method and temperature, the heating rate, holding time, and atmospheric conditions during the pre-firing process can all be adjusted according to the equipment type and process requirements. The goal is to achieve thorough mixing of raw materials, fine powder, and complete solid-phase reaction. The amounts of dispersant, lubricant, and binder can also be adjusted according to process requirements, aiming to prepare granulated powder with good flowability and uniform particle size distribution. Dry pressing can be used for molding, and the molding pressure of a single-mold press can be selected within the range of 6MPa to 15MPa depending on the size of the blank. In the sintering process, the heating rate, holding time, and cooling rate during the discharge and sintering stages can all be optimized according to the furnace type, furnace loading, and target microstructure, as long as the ceramic body is sufficiently densified, an ideal grain boundary barrier structure is formed, and the target electrical properties are obtained.

[0051] The present invention will be illustrated by specific embodiments below.

[0052] Example 1 This embodiment prepares a ceramic PTC element with a Curie point of 240°C.

[0053] Preparation of the first pre-calcined powder: Barium carbonate, titanium dioxide, and a semiconductor agent are mixed according to the chemical formula Ba... 1.00 Ti 1.01The molar ratio of O3 + 0.0012Nb2O5 + 0.0003Gd2O3 was calculated and weighed, resulting in 1.00 mol barium carbonate, 1.01 mol titanium dioxide, 0.0012 mol niobium pentoxide, and 0.0003 mol gadolinium oxide. The barium carbonate, niobium pentoxide, gadolinium oxide, and titanium dioxide were added to the ball mill jar in the following order: 0.3 wt% dispersant CE-64. The ratio of material, balls, and water was 1:1.5:1.2. Wet ball milling was performed for 24 hours. After milling, the material was filtered, dried, pulverized, sieved, and then pre-fired in a crucible. The pre-calcination process employs a segmented heating regime: the temperature is raised from room temperature to 850°C at a rate of 200°C / h, and held at 850°C for 1 hour; then the temperature is raised from 850°C to 1150°C at a rate of 250°C / h, and held for 2 hours to obtain the first pre-calcined powder.

[0054] Preparation of the second pre-calcined powder: Lead tetroxide, titanium dioxide, and a semiconductor agent are prepared according to the chemical formula Pb. 1.003 Ti 1.00 The molar ratio of O3 + 0.0012Nb2O5 + 0.0003Gd2O3 was calculated and weighed, resulting in 1.003 mol lead tetroxide, 1.00 mol titanium dioxide, 0.0012 mol niobium pentoxide, and 0.0003 mol gadolinium oxide. Lead tetroxide, niobium pentoxide, gadolinium oxide, and titanium dioxide were added to a ball mill jar in the following order: 0.3 wt% dispersant CE-64. The ratio of material, balls, and water was 1:1.5:1.0. Wet ball milling was performed for 24 hours. After milling, the powder was filtered, dried, pulverized, and sieved. It was then placed in a crucible for pre-calcination, with the temperature raised from room temperature to 950°C at a rate of 200°C / h and held for 2 hours to obtain the second pre-calcined powder.

[0055] Preparation of mixed powders and sintering of finished products: Based on the barium and lead ratio corresponding to the Curie point of 240℃, according to the chemical formula Ba 0.70 Pb 0.30 Ti 1.01O3 calculation: Weigh out the first and second pre-calcined powders, where the molar amount of barium titanate is 0.70 mol and the molar amount of lead titanate is 0.30 mol. Then weigh out the dopant and sintering aid according to the following proportions: manganese dioxide 0.04 mol%, antimony trioxide 0.04 mol%, chromium trioxide 0.01 mol%, silicon monoxide 1.5 mol%, aluminum trioxide 1.3 mol%, boron nitride 0.8 mol%, and calcium oxide 0.5 mol%. Add the first pre-calcined powder, manganese dioxide, antimony trioxide, chromium trioxide, silicon monoxide, aluminum trioxide, boron nitride, calcium oxide, and the second pre-calcined powder into the ball mill jar in the following order: dispersant CE-64, 0.3 wt%. The ratio of material, balls, and water is 1:1.5:1.0. Wet ball mill for 22 hours. Subsequently, glycerol lubricant was added at a rate of 0.15 wt%, and polyvinyl alcohol (PVABP-05) binder was added at a concentration of 10% at a rate of 10 wt%. After ball milling for another 2 hours, the mixture was spray-granulated.

[0056] The above-mentioned spray-granulated material was dry-pressed to form blanks with dimensions of 24mm × 15mm × 2.85mm. The blanks were then placed in crucibles and fired in a furnace using a process of first venting and then sintering. Venting stage: The temperature was raised from room temperature to 600℃ at a rate of 200℃ / h and held at 600℃ for 1 hour; then the temperature was raised from 600℃ to 850℃ at a rate of 200℃ / h and held at 850℃ for 1 hour. Sintering stage: The temperature is raised to 1150℃ at a rate of 360℃ / h and held at 1150℃ for 30 minutes; then rapidly raised from 1150℃ to 1260℃ at a rate of 800℃ / h and held at 1260℃ for 50 minutes; then cooled from 1260℃ to 1100℃ and held at 1100℃ for 15 minutes; finally cooled from 1100℃ to room temperature at a rate of 300℃ / h. The ceramic wafers are ground to 24mm×15mm×2.1mm, chamfered, cleaned, and dried. Aluminum electrodes are then sprayed onto both sides to obtain the finished ceramic PTC element.

[0057] Example 2 This embodiment prepares a ceramic PTC element with a Curie point of 260℃. The preparation process in this embodiment is basically the same as that in Example 1, except that the ratio of the mixed powders and the sintering temperature are adjusted.

[0058] The preparation methods, raw material types, and semiconductor agent dosages of the first and second pre-calcined powders are the same as in the first embodiment. Specifically, the first pre-calcined powder uses 1.00 mol of barium carbonate, 1.01 mol of titanium dioxide, 0.0012 mol of niobium pentoxide, and 0.0003 mol of gadolinium oxide; the second pre-calcined powder uses 1.003 mol of lead tetroxide, 1.00 mol of titanium dioxide, 0.0012 mol of niobium pentoxide, and 0.0003 mol of gadolinium oxide.

[0059] Preparation of mixed powder: Based on the barium to lead ratio corresponding to the Curie point of 260℃, according to the chemical formula Ba 0.67 Pb 0.33 Ti 1.01 O3 calculations were performed, and the first and second pre-calcined powders were weighed out, with barium titanate having a molar amount of 0.67 mol and lead titanate having a molar amount of 0.33 mol. Dopant and sintering aids were then weighed out according to the following proportions: manganese dioxide 0.04 mol%, antimony trioxide 0.035 mol%, silicon monoxide 1.5 mol%, aluminum oxide 1.5 mol%, boron nitride 0.5 mol%, and cerium dioxide 0.02 mol%. The first pre-calcined powder, manganese dioxide, antimony trioxide, silicon monoxide, aluminum oxide, boron nitride, cerium dioxide, and the second pre-calcined powder were added to a ball mill jar in the following order: dispersant CE-64 (0.3 wt%). The ratio of material, balls, and water was 1:1.5:1.0. Wet ball milling was performed for 22 hours, followed by the addition of lubricant glycerol and binder polyvinyl alcohol, and ball milling continued for another 2 hours before spray granulation. The dimensions of the formed blanks were the same as in Example 1.

[0060] The sintering process is basically the same as in Example 1, except that the maximum firing temperature is 1250℃ and the holding time is 45 minutes. The firing stage and other sintering parameters are the same as in Example 1. After the ceramic wafers are ground, chamfered, cleaned and dried, aluminum electrodes are sprayed on both sides to obtain the finished ceramic PTC element.

[0061] Example 3 This embodiment prepares a ceramic PTC element with a Curie point of 280℃. The preparation process in this embodiment is basically the same as that in Example 1, except that the ratio of the mixed powders and the sintering temperature are adjusted.

[0062] The preparation methods, raw material types, and semiconductor agent dosages of the first and second pre-calcined powders are the same as in the first embodiment. Specifically, the first pre-calcined powder uses 1.00 mol of barium carbonate, 1.01 mol of titanium dioxide, 0.0012 mol of niobium pentoxide, and 0.0003 mol of gadolinium oxide; the second pre-calcined powder uses 1.003 mol of lead tetroxide, 1.00 mol of titanium dioxide, 0.0012 mol of niobium pentoxide, and 0.0003 mol of gadolinium oxide.

[0063] Preparation of mixed powder: Based on the barium to lead ratio corresponding to the Curie point of 280℃, according to the chemical formula Ba 0.63 Pb 0.37 Ti 1.01 O3 calculations were performed, and the first and second pre-calcined powders were weighed out, with barium titanate having a molar content of 0.63 mol and lead titanate having a molar content of 0.37 mol. Dopant, sintering aid, and trace raw materials were then weighed out according to the following proportions: manganese dioxide 0.035 mol%, antimony trioxide 0.035 mol%, silicon monoxide 1.5 mol%, aluminum oxide 1.75 mol%, silicon nitride 0.3 mol%, and zinc oxide 0.03 mol%. The first pre-calcined powder, manganese dioxide, antimony trioxide, silicon monoxide, aluminum oxide, silicon nitride, zinc oxide, and the second pre-calcined powder were added to a ball mill jar in the following order: dispersant CE-64 (0.3 wt%). The ratio of material, balls, and water was 1:1.5:1.0. Wet ball milling was performed for 22 hours, followed by the addition of lubricant glycerol and binder polyvinyl alcohol, and ball milling continued for another 2 hours before spray granulation. The dimensions of the formed blanks were the same as in Example 1.

[0064] The sintering process is basically the same as in Example 1, except that the maximum firing temperature is 1240℃ and the holding time is 40 minutes. The firing stage and other sintering parameters are the same as in Example 1. After grinding, chamfering, cleaning and drying, aluminum electrodes are sprayed on both sides of the ceramic sheet to obtain the finished ceramic PTC element.

[0065] Performance Tests and Results To verify the technical effectiveness of the ceramic PTC element prepared by this invention, key electrical performance tests were conducted on the finished products prepared in the above three embodiments. The tests were performed under standard environmental conditions. Room temperature resistance was measured using a digital multimeter, and the resistance-temperature characteristic curve was measured using a muffle furnace-type RT curve analyzer. The Curie point was taken as the temperature corresponding to twice the minimum resistance. The resistance temperature coefficient (α coefficient) was calculated based on the rate of resistance change in each temperature range after the Curie point abrupt change. The resistance increase ratio (β) was taken as the ratio of the maximum resistance value to the minimum resistance value. Surface temperature was measured under standard conditions and in a windless environment after stabilization with a 12V DC voltage.

[0066] After testing, the resistance of the three embodiments described above was... The temperature characteristic curves are as follows: Figure 2 , Figure 3 , Figure 4 As shown in Table 1, the key performance parameters are summarized in the table.

[0067] Table 1 Key performance parameters of ceramic PTC elements prepared in each embodiment

[0068] Note: R 25 (Room temperature resistance): Resistance value at 25℃; Rmin (minimum resistance): Resistance value corresponding to the lowest point of the RT curve; Tc (Curie temperature): Temperature value corresponding to 2 times Rmin; β (resistance ratio): = Rmax / Rmin, characterizing the strength of the PTC effect; α (temperature coefficient of resistance): Slope of the curve between Tc and Tp; Ts (self-regulating temperature, i.e., surface temperature): Stable surface temperature when operating under rated voltage (12VDC) under standard conditions and no wind.

[0069] From the perspective of room temperature resistance, the room temperature resistances of the three embodiments are 7.9Ω, 6.7Ω and 7.3Ω, respectively, all of which are stable within the target range of 1Ω to 10Ω. This indicates that the present invention has successfully achieved the goal of low room temperature resistance by synergistic donor doping of niobium pentoxide and auxiliary semiconductor agents, combined with grain boundary regulation of manganese dioxide, antimony trioxide and other substances.

[0070] From the perspective of the PTC effect, the temperature coefficient of resistance (α coefficient) of the three embodiments reaches 23.63% / ℃, 23.70% / ℃, and 19.23% / ℃, respectively, in the range of Tc+15℃ to Tc+25℃, and the resistance ratio (Rmax / Rmin) reaches 8.093×10³, 5.031×10³, and 1.918×10³, respectively, all significantly higher than conventional low-resistance PTC elements. This indicates that the present invention optimizes the grain boundary structure by using silicon monoxide as a sintering aid, and combines it with the segmented sintering process for precise control of grain growth and grain boundary oxidation, achieving low resistance while maintaining excellent PTC effect.

[0071] In terms of Curie point stability, the measured Curie points of the three embodiments were 242.3℃, 262.3℃ and 281.1℃, respectively. The deviations from the design values ​​of 240℃, 260℃ and 280℃ were all within 2℃. This indicates that the present invention effectively avoids the volatilization loss of lead at high temperatures by synthesizing the first pre-calcined powder and the second pre-calcined powder separately and then mixing them in a precise molar ratio, thus achieving precise control and stable consistency of the Curie point.

[0072] In terms of surface temperature stability, the surface temperatures of the three embodiments remained stable within the ranges of 260℃±5℃, 280℃±5℃, and 300℃±5℃ under a 12V DC voltage, respectively. The fluctuations were small and the temperature control was precise, which fully met the performance requirements of self-temperature control elements for low-pressure heating applications such as thermal management systems for new energy vehicles, smart homes, and portable medical devices.

[0073] In summary, the ceramic PTC element prepared by this invention achieves low room temperature resistance (1Ω) within the Curie point range of 240°C to 280°C. With its excellent comprehensive performance of 10Ω, high temperature coefficient of resistance (≥19% / ℃), high step-up resistance ratio (≥10³), precise controllable Curie point, and stable surface temperature, it successfully solves the technical problems of difficult preparation and unstable performance of high Curie point, low voltage and low resistance PTC elements in the existing technology, and has good prospects for industrial application.

[0074] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0075] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Since these modifications and variations fall within the scope of the claims and their equivalents, this invention also intends to include these modifications and variations.

[0076] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A high Curie point, low voltage, small resistance ceramic PTC element, characterized by, The ceramic PTC element is made of a main component, a semiconductor agent, a dopant, and a sintering aid. The main components include barium titanate and lead titanate, and the molar ratio of barium titanate to lead titanate is 0.63-0.70: 0.30-0.37; Based on a total molar amount of 1.00 mol of the main component, the semiconductor agent contains at least 0.0010 - 0.0014 mol of niobium pentoxide; The dopant contains at least 0.0003-0.0005 mol of manganese dioxide and 0.0003-0.0005 mol of antimony trioxide; The sintering aid contains at least 0.005-0.015 mol of silicon monoxide; The ceramic PTC element has a Curie point of 240-280℃ and a room temperature resistance of 1-10Ω.

2. The ceramic PTC element according to claim 1, characterized in that, The semiconductor agent further comprises 0-0.0006 mol of an auxiliary semiconductor agent, wherein the auxiliary semiconductor agent is selected from at least one of lanthanum oxide, neodymium oxide, samarium oxide, praseodymium oxide, gadolinium oxide, and tantalum pentoxide.

3. The ceramic PTC element according to claim 1, characterized in that, The dopant further comprises 0 0.00015 mol of chromium trioxide.

4. The ceramic PTC element according to claim 1, characterized by The sintering aid further includes 0-0.0285 mol of auxiliary sintering aid, which is selected from at least one of aluminum oxide, boron nitride, silicon nitride, calcium oxide, and cerium dioxide.

5. The ceramic PTC element according to claim 1, characterized in that, The material further comprises 0 0.08 mol% of zinc oxide.

6. A method for preparing claim 1 The method for using a high Curie point, low voltage, low resistance ceramic PTC element as described in any one of the following 5 methods is characterized in that... Includes the following steps: (1) Preparation of the first pre-calcined powder: According to the ratio, the barium source, titanium source and semiconductor agent are mixed, ball-milled, dried and pre-calcined to obtain the first pre-calcined powder with barium titanate as the matrix; (2) Preparation of the second pre-calcined powder: According to the ratio, the lead source, titanium source and semiconductor agent are mixed, ball-milled, dried and pre-calcined to obtain the second pre-calcined powder with lead titanate as the matrix; (3) Preparation of mixed powder: The first pre-calcined powder, the second pre-calcined powder, dopant and sintering aid are mixed, and the mixture is ball-milled and granulated to obtain mixed powder; (4) The mixed powder is shaped, sintered, ground into wafers and electrodes to obtain a ceramic PTC element.

7. The method according to claim 6, characterized in that, In step (1), the pre-firing temperature is 1140℃. 1150℃ for 2 hours; in step (2), the pre-firing temperature is 950℃. 980℃, for 2 hours.

8. The method according to claim 6, characterized in that, In step (4), the sintering adopts a segmented sintering process, including a degassing stage and a sintering stage; The combustion phase includes: raising the temperature from room temperature to 600℃ and holding it at that temperature for 0.5-1.5 hours, then continuing to raise the temperature to 850℃. Hold at 900℃ for 0.5-1.5 hours; the sintering stage includes: heating to 1150℃ and holding for 0-30 minutes, then heating to 1230℃. 1280℃ heat preservation for 30 60 minutes, then cool to 1100℃ and hold for 0 minutes. Leave for 30 minutes, then cool to room temperature.

9. An electronic device, comprising: Including claim 1 The ceramic PTC element as described in any one of the 5.

10. The application of the ceramic PTC element according to any one of claims 1-5 in a low-pressure heating device.

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