High-stability PTC ceramic material and preparation method thereof

Abstract

The application provides a high-stability PTC ceramic material and a preparation method thereof. The method comprises the following steps: S1: providing 100 parts by mass of barium titanate, 0.05-0.5 parts by mass of a donor element source as main phase raw materials; S2: after mixing the main phase raw materials, pre-sintering treatment is performed under an oxidizing atmosphere, so that the donor elements in the main phase raw materials are uniformly distributed, and a ceramic precursor is obtained; S3: after crushing 100 parts by mass of the ceramic precursor, 0.2-1 parts by mass of a non-metallic oxide, 0.05-0.5 parts by mass of a fluorine source and 0.03-0.3 parts by mass of an acceptor element source are mixed and pressed into a shape, and then reduction sintering treatment is performed under a reducing atmosphere, so that a ceramic material is obtained; and S4: the ceramic material is subjected to re-oxidation treatment, so that a PTC barrier is formed at the grain boundary, and a high-stability PTC ceramic material is obtained. The PTC ceramic material obtained by the above method has a low room-temperature resistance drift rate.

Description

Technical Field

[0001] This application relates to the field of ceramic materials technology, specifically to a highly stable PTC ceramic material and its preparation method. Background Technology

[0002] Positive Temperature Coefficient (PTC) ceramic materials are a class of functional materials whose resistance increases sharply with increasing temperature near the Curie temperature. They are widely used in overcurrent protection components, self-limiting heaters, temperature compensation devices, and battery protection systems. Among them, barium titanate (BaTiO3)-based semiconductor PTC ceramics are the most widely used PTC materials due to their wide range of tunable electrical properties, low cost, and relatively mature processing. Existing BaTiO3-based PTC ceramics typically achieve resistance transitions near the Curie temperature by using donor doping to form an n-type conductive structure within the grain and by using a reduction-re-oxidation process to form a barrier structure in the grain boundary region.

[0003] However, in practical applications, the long-term stability of PTC ceramic materials has become increasingly prominent. Since the PTC effect depends on the electrical difference between grains and grain boundaries, when the material is used under long-term thermal stress, electrical stress, or environmental changes, the defect distribution and oxygen vacancy concentration in the grain boundary region are prone to change. The diffusion and redistribution of oxygen in the grain boundary region are difficult to control effectively, leading to high barrier fluctuations and consequently drift in room temperature and high temperature resistance characteristics. Some existing PTC ceramics exhibit a gradual increase or decrease in room temperature resistance under high-temperature aging or prolonged energization conditions, making it difficult to guarantee the repeatability and consistency of electrical performance, thus affecting the reliability and lifespan of the device. Furthermore, multi-component doped systems may experience mutual reactions or uneven diffusion during high-temperature sintering, leading to uneven grain growth or unstable grain boundary phase distribution, further exacerbating the fluctuations in material electrical performance. Traditional processes are also highly sensitive to the control of reduction and re-oxidation steps. Improper control of atmosphere, temperature, or time may result in insufficient internal conductive structure of the grains or incomplete formation of the grain boundary barrier, making it difficult to simultaneously achieve both PTC characteristics and long-term stability.

[0004] Therefore, how to achieve long-term synergistic stability of grain conductive structure and grain boundary barrier structure while ensuring PTC transition characteristics, thereby reducing resistance drift rate and improving material consistency and reliability, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This application provides a highly stable PTC ceramic material and its preparation method, which solves the problem of high room temperature resistivity drift rate of existing PTC ceramic materials under long-term thermal or electrical stress, thereby reducing the room temperature resistivity drift rate of PTC ceramic materials and improving their long-term stability.

[0006] In a first aspect, this application provides a method for preparing highly stable PTC ceramic materials, comprising the following steps:

[0007] S1: Provide 100 parts by mass of barium titanate and 0.05~0.5 parts by mass of donor element source as main phase raw materials;

[0008] S2: The main phase raw materials are mixed and pre-sintered in an oxidizing atmosphere to make the donor elements in the main phase raw materials uniformly distributed, thus obtaining a ceramic precursor.

[0009] S3: 100 parts by mass of the ceramic precursor are pulverized and mixed with 0.2-1 parts by mass of non-metallic oxide, 0.05-0.5 parts by mass of fluorine source and 0.03-0.3 parts by mass of main element source, pressed into shape, and then subjected to reduction sintering treatment in a reducing atmosphere. The non-metallic oxide includes silicon oxide and boron oxide, and the mass ratio of silicon oxide to boron oxide is 1:0.3-0.9, so that the ceramic precursor forms n-type conductive grains. Silicon oxide, boron oxide and fluorine source melt in the grain boundary region to form a B-Si-OF glass phase layer, thus obtaining the ceramic material.

[0010] S4: The ceramic material is subjected to re-oxidation treatment to form a grain boundary barrier structure, thereby obtaining a highly stable PTC ceramic material.

[0011] According to this application, by synergistic control of pre-sintering solid solution doping, reduction sintering to form conductive grains, and the formation of grain boundary glass phase layers and the establishment of re-oxidation barriers, the conductive structure of grains and the grain boundary barrier structure can be made more stable under long-term thermal stress conditions, thereby effectively reducing the room temperature resistivity drift rate of PTC ceramic materials.

[0012] Specifically, in steps S1 and S2, pre-sintering treatment is performed under an oxidizing atmosphere to allow donor elements to be dissolved and doped into the barium titanate lattice. This enables the stable supply of charge carriers during the subsequent reduction sintering process and reduces the migration or redistribution of doped elements in the final sintering stage. This results in a more uniform internal composition of the formed conductive grains, which is beneficial for obtaining a stable grain conductive structure and reducing resistance drift caused by changes in the internal structure of the grains.

[0013] In step S3, sintering under a reducing atmosphere forms an n-type conductive structure within the grains. Simultaneously, since silicon oxide, boron oxide, and fluorine sources are introduced after the pre-sintering to form the ceramic precursor, they are mainly distributed at the contact interfaces between the ceramic precursor particles. During subsequent reduction sintering, the ceramic precursor particles become densified and form a grain structure, while silicon oxide, boron oxide, and fluorine sources melt at the sintering temperature to form a low-viscosity liquid phase. This liquid phase, driven by surface energy and capillary action, preferentially wets the interface regions between particles and extends along the particle contact areas, thereby preferentially enriching the grain boundary regions and forming a B-Si-OF glass phase layer. This results in the glass phase being spatially distributed mainly between grains rather than within the grains.

[0014] Furthermore, since the acceptor element source is introduced together with the non-metallic oxide and fluorine source at this stage, its diffusion path mainly proceeds along the particle contact interface during sintering. During the formation and spreading of the glass phase, the acceptor element is more likely to remain at the grain boundary and its adjacent region, and participate in the formation and regulation of the grain boundary defect structure, thus mainly playing a role in the establishment and stabilization of the grain boundary barrier structure.

[0015] This glassy phase layer, located between grains, reduces the rate of mass exchange between the grain boundary region and the external environment, thereby decreasing the oxygen diffusion rate and the rate of change in oxygen vacancy concentration in the grain boundary region, and slowing down the change in the grain boundary barrier structure over time. Specifically, by controlling the mass ratio of silicon oxide to boron oxide within the range of 1:0.3~0.9, the glassy phase simultaneously possesses good structural stability and appropriate melt flowability: silicon oxide improves the structural stability of the glassy phase, ensuring its stability under long-term thermal stress; boron oxide lowers the melting temperature of the glassy phase, allowing it to fully melt and distribute within the grain boundary region during sintering. When the boron oxide content is too low, the glassy phase is difficult to fully melt and form an effective grain boundary phase structure; when the boron oxide content is too high, the structural stability of the glassy phase decreases, making it prone to structural changes during long-term use. By controlling the ratio within the aforementioned range, the glassy phase can stably exist in the grain boundary region, thereby reducing the degree of change in the grain boundary structure over time.

[0016] In step S4, a PTC barrier structure is formed in the grain boundary region through re-oxidation treatment. Since there is a stable glass phase layer in the grain boundary region, the glass phase layer can reduce the re-diffusion rate of oxygen in the grain boundary region, making the formed grain boundary barrier structure more stable in subsequent use, thereby reducing the room temperature resistivity drift rate of the material under long-term thermal stress.

[0017] Through the synergistic effect of the above steps, the internal conductive structure and grain boundary barrier structure of the grains remain stable under long-term thermal stress conditions, thereby significantly reducing the room temperature resistivity drift rate of PTC ceramic materials and improving the long-term stability of the materials.

[0018] In some embodiments, the donor element source includes at least one of Nb2O5, Ta2O5, and Sb2O5; the acceptor element source includes at least one of MnO2 and Mn2O3.

[0019] In some of the above embodiments, pentavalent metal ions in Nb₂O₅, Ta₂O₅, and Sb₂O₅ can replace Ti in the barium titanate lattice. 4+ The location of the manganese element in MnO2 and Mn2O3 allows for the introduction of free electrons into the crystal lattice, resulting in a stable n-type conductive structure within the grain. This helps reduce grain resistance and improve the stability of the conductive structure. Simultaneously, manganese preferentially distributes in the grain boundary region during sintering and participates in the formation of the grain boundary barrier structure during re-oxidation, creating a stable high-resistivity layer structure in the grain boundary region. This enhances the stability of the grain boundary barrier structure upon which the PTC effect depends. By introducing donor and acceptor element sources, the conductive structure within the grain and the grain boundary barrier structure can be effectively regulated. Donor elements primarily stabilize the conductive structure within the grain, while acceptor elements primarily stabilize the grain boundary barrier structure, thereby reducing the degree of structural change within the grain and grain boundary regions under long-term thermal stress.

[0020] In some embodiments, the pre-sintering treatment conditions in step S2 include: pre-sintering at 1000-1200°C for 1-4 hours under an oxidizing atmosphere at a heating rate of 2-5°C / min.

[0021] In some of the above embodiments, by performing pre-sintering treatment under an oxidizing atmosphere, the donor elements can be fully dissolved into the barium titanate lattice, thereby obtaining a ceramic precursor with uniform composition. This is beneficial for the formation of a stable conductive grain structure during subsequent sintering and reduces the room temperature resistivity drift rate of the material during long-term use.

[0022] In some embodiments, in step S3, the mass ratio of the non-metallic oxide to the fluorine source is 1:0.1~0.5.

[0023] In some of the above embodiments, by controlling the mass ratio of non-metallic oxide to fluorine source within the aforementioned range, silicon oxide, boron oxide, and fluorine source can co-melt during sintering to form a stable glassy phase structure, which is preferentially distributed in the grain boundary region. The fluorine source helps to lower the formation temperature of the glassy phase and improve its flowability during sintering, allowing the glassy phase to be more uniformly distributed in the grain boundary region and forming a stable grain boundary phase structure. This is beneficial for improving the stability of the grain boundary barrier structure and further reducing the room temperature resistivity drift of the PTC ceramic material.

[0024] In some embodiments, step S3 further includes: pulverizing 100 parts by mass of the ceramic precursor and mixing it with 0.2-1 parts by mass of non-metallic oxide, 0.05-0.5 parts by mass of fluorine source, 0.03-0.3 parts by mass of acceptor element source and 0.01-0.2 parts by mass of CeO2, pressing it into shape, and then performing reduction sintering treatment in a reducing atmosphere.

[0025] In some of the above embodiments, the inventors found that after introducing CeO2 in step S3, the room temperature resistivity drift of the obtained PTC ceramic material under long-term thermal stress was further reduced, and the resistivity stability of the material was significantly improved. The possible reason is that CeO2 is partially converted to Ce2O3 during the reduction sintering process, causing the Ce element to be converted to Ce2O3. 4+ / Ce 3+ The two phases coexist, with Ce ions exhibiting some diffusion ability during high-temperature sintering. The B-Si-OF glass phase layer formed during sintering is an amorphous structure with high structural disorder and large free volume. Compared to the ordered lattice structure inside barium titanate grains, this glass phase region provides lower lattice confinement and higher solubility for ions, making it easier for Ce ions to enter and remain stably in the glass phase region. Furthermore, the glass phase contains numerous non-bridging oxygen structures (such as Si-O...). - BO - (Structural units) and coordination unsaturated sites can interact with Ce through electrostatic or coordination interactions. 4+ / Ce 3+ This forms a stable bond, thereby reducing the migration tendency of Ce ions in this region and causing Ce to preferentially accumulate near the grain boundary glass phase layer.

[0026] Meanwhile, F released from the fluorine source during the sintering process - Ce ions can enter the glassy phase structure or distribute near grain boundaries, forming relatively stable coordination structures with cations such as Ce, thereby reducing the migration rate of oxygen ions in the grain boundary region and contributing to the stabilization of the local structural environment of the glassy phase. Based on this, Ce... 4+ / Ce 3+ The reversible valence state transition can modulate the charge state of the grain boundary region, while F - Ions stabilize the local structure of grain boundaries and inhibit oxygen ion migration, making the generation and migration of oxygen vacancies more controllable, thereby making the oxygen vacancy concentration distribution in the grain boundary region more stable.

[0027] Since Ce is mainly enriched in the grain boundary glass phase region, and is associated with F -Together with the glass phase structure, these components can synergistically regulate and stabilize the defect structure in the grain boundary region during reduction and re-oxidation, making the grain boundary barrier structure more stable under long-term thermal stress. Since the room temperature resistivity of PTC ceramic materials is mainly determined by the grain boundary barrier structure, maintaining a stable grain boundary defect structure can effectively reduce the room temperature resistivity drift rate of the material, thereby further improving the long-term stability of PTC ceramic materials.

[0028] In some embodiments, the conditions for the reduction sintering treatment in step S3 include: heating to 1250-1400°C for 1-3 hours at a heating rate of 2-5°C / min under a reducing atmosphere.

[0029] In some of the above embodiments, by performing reduction sintering under the temperature range and time conditions, the barium titanate grains can be fully densified and form a stable conductive grain structure. At the same time, it promotes the formation of a uniformly distributed glass phase layer of silicon oxide, boron oxide and fluorine source in the grain boundary region, which is beneficial to the stable formation of grain structure and grain boundary structure, thereby helping to improve the long-term electrical performance stability of PTC ceramic materials.

[0030] In some embodiments, in step S3, the fluorine source includes at least one of BaF2 and SrF2.

[0031] In some of the above embodiments, BaF2 and SrF2 can gradually release F during the sintering process. - Ions, the F - Ions can enter the B-Si-OF glass phase structure formed during sintering or be distributed in the grain boundary region, making the structure of the grain boundary glass phase more stable and helping to reduce the migration rate of oxygen ions in the grain boundary region, thus making the grain boundary barrier structure more stable under long-term thermal stress. Furthermore, Ba in BaF2 and SrF2... 2+ or Sr 2+ It exhibits good lattice matching and chemical compatibility with the barium titanate matrix, making it less likely to introduce new impurity phases. This helps maintain the stability of the grain structure and grain boundary structure, thereby further reducing the room temperature resistivity drift of PTC ceramic materials and improving the long-term stability of the materials.

[0032] In some embodiments, the conditions for the re-oxidation treatment in step S4 include: heating to 700-900°C at a heating rate of 2-5°C / min and holding at that temperature for 1-5 hours under an oxidizing atmosphere.

[0033] In some of the above embodiments, by performing re-oxidation treatment within the range of 700~900℃, oxygen preferentially diffuses to the grain boundary region and interacts with defects near the grain boundary, thereby forming a stable barrier structure between the grains. This maintains the conductivity within the grains while creating a high-resistivity region at the grain boundaries, which is beneficial for establishing a stable PTC grain boundary barrier structure. Simultaneously, by controlling the heating rate and holding time, the re-oxidation process is made relatively uniform, avoiding excessive differences in local oxidation levels. This helps improve the consistency of the grain boundary barrier structure, making the room temperature resistivity of the material more stable and further reducing the resistance drift rate during long-term use.

[0034] In some embodiments, step S4 further includes an annealing treatment after the re-oxidation treatment, wherein the annealing treatment conditions include holding at 600~800℃ for 1~3 hours.

[0035] In some of the above embodiments, annealing after re-oxidation allows for further structural relaxation of the grain boundary region at a lower temperature, making the grain boundary barrier structure formed during re-oxidation more stable and reducing the degree of disorder in grain boundary defects. Simultaneously, this annealing process helps release localized stresses generated during sintering and re-oxidation, further stabilizing the interface structure between the grain boundary glass phase layer and the barium titanate grains, thereby improving the stability of the grain boundary barrier structure and helping to reduce the room temperature resistivity drift of the material under long-term thermal stress conditions.

[0036] Secondly, this application provides a highly stable PTC ceramic material, prepared according to the method described in any embodiment of the first aspect.

[0037] According to this application, during the preparation of barium titanate-based PTC ceramics, donor elements are fully dissolved and doped during the pre-sintering stage, and non-metallic oxides and fluorine sources form a B-Si-OF glass phase layer in the grain boundary region during reduction sintering. Acceptor elements are introduced to regulate the grain boundary structure, and a stable grain boundary barrier structure is formed through re-oxidation treatment. This results in PTC ceramic materials possessing both a stable grain conductivity structure and a stable grain boundary barrier structure. Under long-term thermal stress, oxygen diffusion and defect structure changes in the grain boundary region are effectively suppressed, thereby reducing the degree of change in the grain boundary barrier structure over time. This significantly reduces the room temperature resistivity drift of the material, thus improving the long-term resistivity stability and reliability of the PTC ceramic material.

[0038] Compared with the prior art, the beneficial effects of this application are at least as follows:

[0039] By controlling the steps of pre-sintering solid solution doping, subsequent introduction of silicon oxide and boron oxide to form a grain boundary B-Si-OF glass phase layer, and re-oxidation to establish a grain boundary barrier structure, the grain conductive structure and grain boundary barrier structure remain more stable under long-term thermal stress conditions, thereby effectively reducing the room temperature resistivity drift rate of PTC ceramic materials. At the same time, the introduction of CeO2 further helps to stabilize the defect state and oxygen vacancy distribution in the grain boundary region, making the grain boundary barrier structure more stable, thereby further improving the long-term stability and reliability of PTC ceramic materials. Detailed Implementation

[0040] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0041] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0042] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0043] In this specification, unless otherwise specified, "parts" refers to "parts by weight".

[0044] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0045] Example 1

[0046] A method for preparing a highly stable PTC ceramic material

[0047] S1: Weigh 100 parts by mass of barium titanate (BaTiO3) powder with an average particle size of 0.6 μm as the matrix material, and add 0.20 parts by mass of niobium pentoxide (Nb2O5) as the donor element source. Add the above powder to a zirconia ball mill jar, and add anhydrous ethanol at a mass ratio of 1.5 times the total powder mass as the dispersion medium. Add zirconia balls (ball-to-powder mass ratio of 3:1), and ball mill at 300 rpm for 12 hours to ensure uniform mixing of all components. After ball milling, dry the slurry at 80℃ for 12 hours to obtain a uniformly mixed main phase raw material powder.

[0048] S2: The main phase raw material powder was placed in an alumina crucible and pre-sintered in air. The temperature was increased to 1100℃ at a heating rate of 3℃ / min and held for 2 hours to allow the donor elements to dissolve into the barium titanate lattice. After pre-sintering, the powder was cooled to room temperature in the furnace. The sintered block was then removed and pulverized. Subsequently, anhydrous ethanol was added and ball-milled for 6 hours to obtain an average particle size of approximately 0.8μm. After drying, ceramic precursor powder was obtained.

[0049] S3: Weigh 100 parts by mass of the ceramic precursor powder obtained in step S2, and add: 0.50 parts by mass of silicon dioxide; 0.30 parts by mass of boron oxide; 0.20 parts by mass of barium fluoride; 0.05 parts by mass of cerium dioxide; and 0.10 parts by mass of manganese dioxide (MnO2) as acceptor element sources; wherein the mass ratio of silicon dioxide to boron oxide is 1:0.6; and the mass ratio of non-metallic oxide to fluorine source is 1:0.25. Add the above powder to a ball mill jar, add anhydrous ethanol as a dispersion medium, and ball mill at 300 rpm for 10 h to ensure uniform mixing of all components. After ball milling, dry the powder and add 3 parts by mass of 10 wt% polyvinyl alcohol aqueous solution with a number average molecular weight of 30,000 as a binder for granulation. Press the granulated powder into circular blanks with a diameter of approximately 12 mm and a thickness of approximately 1.5 mm under a pressure of 50 MPa.

[0050] The pressed green body was placed in an air atmosphere for debinding treatment, and the temperature was raised to 500℃ at 2℃ / min and held for 1h to completely decompose and remove polyvinyl alcohol. Then the green body was placed in a reducing atmosphere (volume fraction 5% H2 / N2), and the temperature was raised to 1350℃ at 3℃ / min and held for 2h for reduction sintering. Then it was cooled to room temperature in the furnace to obtain ceramic material.

[0051] S4: The obtained ceramic material is placed in an air atmosphere for re-oxidation treatment, heated to 800℃ at 3℃ / min and held for 3h, and then cooled to room temperature with the furnace.

[0052] After re-oxidation, the ceramic material is placed in an air atmosphere and annealed at 700℃ for 2 hours, and then cooled to room temperature to obtain a highly stable PTC ceramic material.

[0053] Example 2

[0054] A method for preparing a highly stable PTC ceramic material:

[0055] It is largely the same as Example 1, except that S3 is different, specifically:

[0056] S3: Weigh 100 parts by mass of the ceramic precursor powder obtained in step S2, and add: 0.50 parts by mass of silicon dioxide; 0.30 parts by mass of boron oxide; 0.05 parts by mass of barium fluoride; 0.05 parts by mass of cerium dioxide; and 0.10 parts by mass of manganese dioxide (MnO2) as acceptor element sources; wherein the mass ratio of silicon dioxide to boron oxide is 1:0.6; and the mass ratio of non-metallic oxide to fluorine source is 1:0.0625. Add the above powder to a ball mill jar, add anhydrous ethanol as a dispersion medium, and ball mill at 300 rpm for 10 h to ensure uniform mixing of all components. After ball milling, dry the powder and add 3 parts by mass of 10 wt% polyvinyl alcohol aqueous solution with a number average molecular weight of 30,000 as a binder for granulation. Press the granulated powder into circular blanks with a diameter of approximately 12 mm and a thickness of approximately 1.5 mm under a pressure of 50 MPa.

[0057] The pressed green body was placed in an air atmosphere for debinding treatment, and the temperature was raised to 500℃ at 2℃ / min and held for 1h to completely decompose and remove polyvinyl alcohol. Then the green body was placed in a reducing atmosphere (volume fraction 5% H2 / N2), and the temperature was raised to 1350℃ at 3℃ / min and held for 2h for reduction sintering. Then it was cooled to room temperature in the furnace to obtain ceramic material.

[0058] Example 3

[0059] A method for preparing a highly stable PTC ceramic material:

[0060] It is largely the same as Example 1, except that S3 is different, specifically:

[0061] S3: Weigh 100 parts by mass of the ceramic precursor powder obtained in step S2, and add: 0.50 parts by mass of silicon dioxide; 0.30 parts by mass of boron oxide; 0.50 parts by mass of barium fluoride; 0.05 parts by mass of cerium dioxide; and 0.10 parts by mass of manganese dioxide (MnO2) as acceptor element sources; wherein the mass ratio of silicon dioxide to boron oxide is 1:0.6; and the mass ratio of non-metallic oxide to fluorine source is 1:0.625. Add the above powder to a ball mill jar, add anhydrous ethanol as a dispersion medium, and ball mill at 300 rpm for 10 h to ensure uniform mixing of all components. After ball milling, dry the powder and add 3 parts by mass of 10 wt% polyvinyl alcohol aqueous solution with a number average molecular weight of 30,000 as a binder for granulation. Press the granulated powder into circular blanks with a diameter of approximately 12 mm and a thickness of approximately 1.5 mm under a pressure of 50 MPa.

[0062] The pressed green body was placed in an air atmosphere for debinding treatment, and the temperature was raised to 500℃ at 2℃ / min and held for 1h to completely decompose and remove polyvinyl alcohol. Then the green body was placed in a reducing atmosphere (volume fraction 5% H2 / N2), and the temperature was raised to 1350℃ at 3℃ / min and held for 2h for reduction sintering. Then it was cooled to room temperature in the furnace to obtain ceramic material.

[0063] Example 4

[0064] A method for preparing a highly stable PTC ceramic material:

[0065] It is largely the same as Example 1, except that S3 is different, specifically:

[0066] S3: Weigh 100 parts by mass of the ceramic precursor powder obtained in step S2, and add: 0.50 parts by mass of silicon dioxide; 0.30 parts by mass of boron oxide; 0.20 parts by mass of barium fluoride; and 0.10 parts by mass of manganese dioxide (MnO2) as acceptor element sources; wherein the mass ratio of silicon dioxide to boron oxide is 1:0.6; and the mass ratio of non-metallic oxide to fluorine source is 1:0.25. Add the above powder to a ball mill jar, add anhydrous ethanol as a dispersion medium, and ball mill at 300 rpm for 10 h to ensure uniform mixing of all components. After ball milling, dry the powder and add 3 parts by mass of a 10 wt% polyvinyl alcohol aqueous solution with a number average molecular weight of 30,000 as a binder for granulation. Press the granulated powder into circular blanks with a diameter of approximately 12 mm and a thickness of approximately 1.5 mm under a pressure of 50 MPa.

[0067] The pressed green body was placed in an air atmosphere for debinding treatment, and the temperature was raised to 500℃ at 2℃ / min and held for 1h to completely decompose and remove polyvinyl alcohol. Then the green body was placed in a reducing atmosphere (volume fraction 5% H2 / N2), and the temperature was raised to 1350℃ at 3℃ / min and held for 2h for reduction sintering. Then it was cooled to room temperature in the furnace to obtain ceramic material.

[0068] Comparative Example 1

[0069] A method for preparing a highly stable PTC ceramic material:

[0070] It is largely the same as Example 1, except that S3 is different, specifically:

[0071] S3: Weigh 100 parts by mass of the ceramic precursor powder obtained in step S2, and add 0.10 parts by mass of manganese dioxide (MnO2) as the acceptor element source; add the above ceramic precursor powder into a ball mill jar, add anhydrous ethanol as the dispersion medium, and ball mill at 300 rpm for 10 h. After ball milling, dry the powder, and add 3 parts by mass of 10 wt% polyvinyl alcohol aqueous solution with a number average molecular weight of 30,000 as a binder for granulation. Press the granulated powder into a disc-shaped green body with a diameter of about 12 mm and a thickness of about 1.5 mm under a pressure of 50 MPa.

[0072] The pressed green body was placed in an air atmosphere for debinding treatment, and the temperature was raised to 500℃ at 2℃ / min and held for 1h to completely decompose and remove polyvinyl alcohol. Then the green body was placed in a reducing atmosphere (volume fraction 5% H2 / N2), and the temperature was raised to 1350℃ at 3℃ / min and held for 2h for reduction sintering. Then it was cooled to room temperature in the furnace to obtain ceramic material.

[0073] Comparative Example 2

[0074] A method for preparing a highly stable PTC ceramic material:

[0075] It is largely the same as Example 1, except that S3 is different, specifically:

[0076] S3: Weigh 100 parts by mass of the ceramic precursor powder obtained in step S2, and add: 0.50 parts by mass of silicon dioxide; 0.30 parts by mass of boron oxide; 0.05 parts by mass of cerium dioxide; and 0.10 parts by mass of manganese dioxide (MnO2) as acceptor element sources; wherein the mass ratio of silicon dioxide to boron oxide is 1:0.6; add the above powder to a ball mill jar, add anhydrous ethanol as a dispersion medium, and ball mill at 300 rpm for 10 h to ensure uniform mixing of all components. After ball milling, dry the powder and add 3 parts by mass of 10 wt% polyvinyl alcohol aqueous solution with a number average molecular weight of 30,000 as a binder for granulation. Press the granulated powder into circular blanks with a diameter of approximately 12 mm and a thickness of approximately 1.5 mm under a pressure of 50 MPa.

[0077] The pressed green body was placed in an air atmosphere for debinding treatment, and the temperature was raised to 500℃ at 2℃ / min and held for 1h to completely decompose and remove polyvinyl alcohol. Then the green body was placed in a reducing atmosphere (volume fraction 5% H2 / N2), and the temperature was raised to 1350℃ at 3℃ / min and held for 2h for reduction sintering. Then it was cooled to room temperature in the furnace to obtain ceramic material.

[0078] Comparative Example 3

[0079] A method for preparing a highly stable PTC ceramic material:

[0080] It is largely the same as Example 1, except that S3 is different, specifically:

[0081] S3: Weigh 100 parts by mass of the ceramic precursor powder obtained in step S2, and add: 0.625 parts by mass of silicon dioxide; 0.375 parts by mass of boron oxide; and 0.10 parts by mass of manganese dioxide (MnO2) as acceptor element sources; wherein the mass ratio of silicon dioxide to boron oxide is 1:0.6; add the above powder to a ball mill jar, add anhydrous ethanol as a dispersion medium, and ball mill at 300 rpm for 10 h to ensure uniform mixing of all components. After ball milling, dry the powder and add 3 parts by mass of 10 wt% polyvinyl alcohol aqueous solution with a number average molecular weight of 30,000 as a binder for granulation. Press the granulated powder into circular blanks with a diameter of approximately 12 mm and a thickness of approximately 1.5 mm under a pressure of 50 MPa.

[0082] The pressed green body was placed in an air atmosphere for debinding treatment, and the temperature was raised to 500℃ at 2℃ / min and held for 1h to completely decompose and remove polyvinyl alcohol. Then the green body was placed in a reducing atmosphere (volume fraction 5% H2 / N2), and the temperature was raised to 1350℃ at 3℃ / min and held for 2h for reduction sintering. Then it was cooled to room temperature in the furnace to obtain ceramic material.

[0083] Comparative Example 4

[0084] A method for preparing a highly stable PTC ceramic material:

[0085] It is largely the same as Example 1, except that S3 is different, specifically:

[0086] S3: Weigh 100 parts by mass of the ceramic precursor powder obtained in step S2, and add: 0.80 parts by mass of silicon dioxide; 0.20 parts by mass of barium fluoride; 0.05 parts by mass of cerium dioxide; and 0.10 parts by mass of manganese dioxide (MnO2) as acceptor element sources; wherein the mass ratio of non-metallic oxide to fluorine source is 1:0.25; add the above powder to a ball mill jar, add anhydrous ethanol as a dispersion medium, and ball mill at 300 rpm for 10 h to ensure uniform mixing of all components. After ball milling, dry the powder and add 3 parts by mass of 10 wt% polyvinyl alcohol aqueous solution with a number average molecular weight of 30,000 as a binder for granulation. Press the granulated powder into circular blanks with a diameter of approximately 12 mm and a thickness of approximately 1.5 mm under a pressure of 50 MPa.

[0087] The pressed green body was placed in an air atmosphere for debinding treatment, and the temperature was raised to 500℃ at 2℃ / min and held for 1h to completely decompose and remove polyvinyl alcohol. Then the green body was placed in a reducing atmosphere (volume fraction 5% H2 / N2), and the temperature was raised to 1350℃ at 3℃ / min and held for 2h for reduction sintering. Then it was cooled to room temperature in the furnace to obtain ceramic material.

[0088] Comparative Example 5

[0089] A method for preparing a highly stable PTC ceramic material:

[0090] It is largely the same as Example 1, except that S3 is different, specifically:

[0091] S3: Weigh 100 parts by mass of the ceramic precursor powder obtained in step S2, and add: 0.80 parts by mass of boron oxide; 0.20 parts by mass of barium fluoride; 0.05 parts by mass of cerium dioxide; and 0.10 parts by mass of manganese dioxide (MnO2) as acceptor element sources; wherein the mass ratio of non-metallic oxide to fluorine source is 1:0.25; add the above powder to a ball mill jar, add anhydrous ethanol as a dispersion medium, and ball mill at 300 rpm for 10 h to ensure uniform mixing of all components. After ball milling, dry the powder and add 3 parts by mass of 10 wt% polyvinyl alcohol aqueous solution with a number average molecular weight of 30,000 as a binder for granulation. Press the granulated powder into circular blanks with a diameter of approximately 12 mm and a thickness of approximately 1.5 mm under a pressure of 50 MPa.

[0092] The pressed green body was placed in an air atmosphere for debinding treatment, and the temperature was raised to 500℃ at 2℃ / min and held for 1h to completely decompose and remove polyvinyl alcohol. Then the green body was placed in a reducing atmosphere (volume fraction 5% H2 / N2), and the temperature was raised to 1350℃ at 3℃ / min and held for 2h for reduction sintering. Then it was cooled to room temperature in the furnace to obtain ceramic material.

[0093] Test section

[0094] The ceramic sheets of the above embodiments and comparative examples were coated with silver paste electrodes on both sides and sintered at 750°C for 10 min to form electrodes.

[0095] Measuring room temperature resistance (R25) a After aging at 150℃ for 100 hours, the room temperature resistance (R25) was measured again. b According to the formula for calculating room temperature resistivity drift: ΔR25 = (R25) b -R25 a ) / R25 a ×100%; ΔR25 was calculated, and the results are shown in Table 1.

[0096] Table 1

[0097]

[0098] According to Table 1, the embodiments exhibit lower room temperature resistivity drift ΔR25 compared to Comparative Examples 1-5, indicating that the preparation method provided in this application can effectively improve the resistivity stability of PTC ceramic materials under long-term thermal stress conditions, thereby significantly reducing the room temperature resistivity drift and improving the long-term stability of the material. The possible reasons are as follows: In Comparative Example 1, no silicon oxide, boron oxide, or fluorine source was introduced to form a grain boundary glass phase layer. During reduction sintering and re-oxidation, the grain boundary region lacked a stable barrier structure, and oxygen vacancies easily diffused and redistributed, causing significant changes in the grain boundary barrier structure during aging, resulting in a significant increase in the room temperature resistivity drift. In Comparative Example 2, no fluorine source was introduced. Although a Si-BO glass phase was formed, the glass phase had a weak binding ability on oxygen vacancies, allowing oxygen vacancies to migrate or redistribute in the grain boundary region, resulting in insufficient stability of the grain boundary barrier structure and thus a higher resistivity drift. In Comparative Example 3, although silicon oxide and boron oxide were introduced to form a glass phase, no further fluorine source or cerium dioxide was introduced. Grain boundary glasses have a weak inhibitory effect on oxygen ion migration and a weak ability to regulate changes in oxygen vacancy concentration, making the grain boundary defect structure more prone to change under long-term thermal stress, thus leading to an increase in room temperature resistivity drift. In Comparative Example 4, boron oxide was not introduced, and the glass phase had a high melting temperature, making it difficult to fully melt and uniformly distribute in the grain boundary region during sintering. This resulted in poor continuity of the formed grain boundary phase and limited barrier effect on oxygen diffusion, leading to a high resistivity drift. In Comparative Example 5, silicon oxide was not introduced. Although the glass phase could melt to form a grain boundary phase, its structural stability was poor. Under long-term thermal stress, structural relaxation or rearrangement was prone to occur, causing changes in the distribution of oxygen vacancies at the grain boundaries, thus leading to an increase in resistivity drift.

[0099] As shown in Examples 1-3, the ratio of non-metallic oxide to fluorine source has a significant impact on the room-temperature resistivity drift of PTC ceramic materials: In Example 2, the ratio of non-metallic oxide to fluorine source was 1:0.0625, with a relatively small amount of fluorine source, and the resulting ΔR25 (9.23%) was higher than that in Example 1 (4.55%), indicating that appropriately increasing the fluorine source ratio is beneficial for further reducing resistivity drift; In Example 3, the ratio of non-metallic oxide to fluorine source was 1:0.625, with a relatively large amount of fluorine source, and the resulting ΔR25 (13.28%) was further increased, indicating that more fluorine source is not necessarily better. The possible reason is that an appropriate amount of fluorine... - Fluorine sources can enhance the stability of the glassy phase network and reduce the oxygen ion migration rate, thus more effectively stabilizing the grain boundary barrier. However, when the fluorine source is insufficient, this stabilizing effect is inadequate; conversely, excessive fluorine sources may alter the viscosity / wetting behavior of the glassy phase or cause fluctuations in the composition of the grain boundary phase, leading to a decrease in the stability of the grain boundary barrier. Therefore, controlling the ratio of non-metallic oxides to fluorine sources within an appropriate range is beneficial for forming a stable grain boundary glassy phase layer and reducing ΔR25.

[0100] As shown in Examples 1 and 4, under the same conditions of silicon oxide, boron oxide, and fluorine source ratios, the further introduction of CeO2 can further reduce the room temperature resistivity drift: the ΔR25 of Example 1 (containing CeO2) is 4.55%, lower than that of Example 4 (without CeO2) (7.52%). This may be because CeO2 can form CeO2 during the reduction sintering process. 4+ / Ce 3+ This coexisting system, and more inclined to be distributed near the grain boundary glass phase, plays a buffering and regulating role in the changes of oxygen vacancy concentration in the grain boundary region through reversible valence state transitions, while also interacting with F... - The synergistic effect of inhibiting oxygen vacancy migration makes the grain boundary defect structure more stable under long-term thermal stress, thereby further reducing the room temperature resistivity drift rate of the material.

[0101] In addition, following the methods specified in GB / T 41606-2022 "Barium Titanate-based High Dielectric Strength and Low Resistivity Thermistor Ceramics", the resistance-temperature (RT) curve of the sample in Example 1 was tested and plotted; the maximum resistance Rmax was determined from the curve, and the resistance-temperature ratio (Rmax / R25) was calculated. a The value is 1.9 × 10 3 This indicates that the material obtained in this application has both a low room temperature resistivity drift rate and typical PTC characteristics.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing highly stable PTC ceramic materials, characterized in that, Includes the following steps: S1: Provide 100 parts by mass of barium titanate and 0.05~0.5 parts by mass of donor element source as main phase raw materials; S2: The main phase raw materials are mixed and pre-sintered in an oxidizing atmosphere to make the donor elements in the main phase raw materials uniformly distributed, thus obtaining a ceramic precursor. S3: 100 parts by mass of the ceramic precursor are pulverized and mixed with 0.2-1 parts by mass of non-metallic oxide, 0.05-0.5 parts by mass of fluorine source, 0.03-0.3 parts by mass of acceptor element source and 0.01-0.2 parts by mass of CeO2, pressed into shape, and then subjected to reduction sintering treatment in a reducing atmosphere. The mass ratio of the non-metallic oxide to the fluorine source is 1:0.1-0.

5. The non-metallic oxide includes silicon oxide and boron oxide, and the mass ratio of silicon oxide to boron oxide is 1:0.3-0.

9. This causes the ceramic precursor to form n-type conductive grains. Silicon oxide, boron oxide and fluorine source melt in the grain boundary region to form a B-Si-OF glass phase layer, thus obtaining the ceramic material. S4: The ceramic material is subjected to re-oxidation treatment to form a grain boundary barrier structure, thereby obtaining a highly stable PTC ceramic material.

2. The method according to claim 1, characterized in that, The donor element source includes at least one of Nb2O5, Ta2O5, and Sb2O5; the acceptor element source includes at least one of MnO2 and Mn2O3.

3. The method according to claim 1, characterized in that, In step S2, the pre-sintering conditions include: pre-sintering at 1000-1200°C for 1-4 hours under an oxidizing atmosphere at a heating rate of 2-5°C / min.

4. The method according to claim 1, characterized in that, In step S3, the conditions for the reduction sintering treatment include: heating to 1250-1400℃ and sintering for 1-3 hours at a heating rate of 2-5℃ / min under a reducing atmosphere.

5. The method according to claim 1, characterized in that, In step S3, the fluorine source includes at least one of BaF2 and SrF2.

6. The method according to claim 1, characterized in that, In step S4, the conditions for the re-oxidation treatment include: heating to 700-900°C at a heating rate of 2-5°C / min and holding at that temperature for 1-5 hours under an oxidizing atmosphere.

7. The method according to any one of claims 1 to 6, characterized in that, In step S4, the re-oxidation treatment is followed by an annealing treatment, wherein the annealing treatment is performed at 600~800℃ for 1~3 hours.

8. A highly stable PTC ceramic material, characterized in that, Prepared according to the method according to any one of claims 1 to 7.

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