NTC thermistor ceramic material, NTC thermistor and preparation method of NTC thermistor ceramic material

Abstract

The invention discloses an NTC thermistor ceramic material, an NTC thermistor and a preparation method of the NTC thermistor ceramic material, and relates to the field of ceramic materials. The ceramic material comprises the following components in percentage by mass: 48wt%-75wt% of Mn3O4; co3O4: 5 wt% to 21 wt%; ni2O3: 10 wt% to 30 wt%; ceO2: 0.5 wt% to 2 wt%; la2O3: 0.5 wt% to 2 wt%; and Bi2O3: 1 wt%-2 wt%. The thermal stability of the material is improved by doping CeO2 and La2O3 in a Mn-Co-Ni ceramic system, meanwhile, the sintering temperature of the material is reduced by doping Bi2O3, and meanwhile, the resistivity of the material can be improved and the compactness of a ceramic body can be improved in the high-temperature sintering process of Bi2O3; finally, low-temperature co-firing of the thermistor ceramic material and the inner electrode is realized, and the risks of cracking and metal volatilization of the inner electrode are reduced.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials, and in particular to an NTC thermistor ceramic material, an NTC thermistor, and a method for preparing the same. Background Technology

[0002] Negative temperature coefficient (NTC) thermistors are a type of sensor resistor whose resistance decreases as temperature increases. With the application and continuous development of microelectronic circuits and surface mount technology (SMT), lightness, thinness, and small size have become important indicators for evaluating electronic products. To achieve miniaturization of electronic devices, the miniaturization of electronic components must be considered first; therefore, small-sized 0201 series NTC thermistors represent the current development trend. 0201 is a common package size for surface mount resistors, with metric dimensions of 0.6mm × 0.3mm, suitable for products with strict space requirements such as smartphones and precision electronic equipment. The miniaturized design of 0201 allows for higher temperature resistance requirements on circuit boards; the previous 125℃ operating temperature of electronic components no longer meets customer needs, and the operating temperature of components is gradually being increased to 150℃.

[0003] The main component of NTC thermistor ceramics is metal oxides. These metal oxides exhibit a significant negative temperature coefficient effect within a specific temperature range. Commonly used metal oxides include oxides of elements such as manganese, cobalt, nickel, and iron. These are sintered at high temperatures to form a ceramic body with specific resistance-temperature characteristics. However, currently, the sintering temperature of NTC thermistor ceramic powder is above 1200 ℃, which is relatively high. Furthermore, 0201 series NTC thermistors often use Ag / Pd or Pd paste as the internal electrode material. This leads to cracking, delamination, and internal electrode volatilization during co-firing of the ceramic material and the internal electrode material. Summary of the Invention

[0004] This invention provides an NTC thermistor ceramic material, an NTC thermistor, and a method for preparing the same. By optimizing the ceramic material composition to reduce the sintering temperature, the invention solves the problems of cracking and volatilization of the internal electrode when the ceramic material is co-fired with the internal electrode, while ensuring that the NTC thermistor has a high operating temperature and appropriate resistivity.

[0005] To address the aforementioned technical problems, one objective of this invention is to provide an NTC thermistor ceramic material comprising the following mass fraction components: Mn3O4: 48wt%-75wt%; Co3O4: 5wt%-21wt%; Ni2O3: 10wt%-30wt%; CeO2: 0.5wt%-2wt%; La2O3: 0.5wt%-2wt%; Bi2O3: 1wt%-2wt%.

[0006] This application presents an NTC thermistor ceramic material whose thermal stability is improved by doping CeO2 and La2O3 into a Mn-Co-Ni system. NTC thermistor ceramics are typical spinel structures; by incorporating high-enthalpy, highly stable oxides into the spinel series, the thermal stability of the ceramic material is enhanced. Ce and La are primarily donor doped at grain boundaries, increasing the grain boundary barrier of the P-type semiconductor and significantly increasing the material's resistivity, but also raising the sintering temperature. By doping Bi2O3 as a sintering aid, the sintering temperature is lowered, reducing the risk of cracking and metal volatilization during co-firing of the thermistor ceramic material with the Ag / Pd or Pd paste of the internal electrode, thus achieving low-temperature co-firing of the NTC thermistor ceramic material with Ag / Pd or Pd paste. Meanwhile, during the high-temperature sintering process, some of Bi2O3 melts to form a glassy phase, which adheres to the grain boundary surface. On the one hand, this can increase the resistivity of the material and improve the density of the ceramic body to enhance its strength. On the other hand, the formation of the glassy phase makes the concentration of cation vacancy migration at the grain boundary similar to that inside the grain. Therefore, when the NTC thermistor is working under environmental conditions of 150℃, the cation migration is not obvious, thereby improving the thermal stability of the product.

[0007] In some embodiments, the NTC thermistor ceramic material further includes 0.5wt%-1wt% TiO2 by mass.

[0008] The NTC thermistor ceramic material of this application improves the thermal stability of NTC thermistor ceramic by simultaneously doping CeO2, La2O3 and TiO2. Moreover, Ce and La are mainly doped in the grain boundary as donors, which improves the grain boundary barrier of P-type semiconductor and improves the high-temperature operation stability of NTC thermistor.

[0009] In some embodiments, the mass ratio of CeO2 to La2O3 is (0.5-1.5):(0.5-1.5).

[0010] In some embodiments, the following components by mass fraction are included: Mn3O4: 60wt%-70wt%; Co3O4: 18wt%-21wt%; Ni2O3: 10wt%-15wt%; CeO2: 0.5wt%-1.5wt%; La2O3: 0.5wt%-1.5wt%; Bi2O3: 1wt%-1.5wt%; TiO2: 0.5wt%-1wt%.

[0011] To address the aforementioned technical problems, a second objective of this invention is to provide a method for preparing NTC thermistor ceramic materials, comprising the following steps: S1. Accurately weigh all components of the NTC thermistor ceramic material except Bi2O3, then ball mill and mix them, dry and sieve them, and pre-fire them at 880-920 ℃ for 1-5 h. After sieving, the calcined material of the main formula is obtained. S2. Bi2O3 is added to the calcined material of the main formula, and after ball milling, drying and sieving, NTC thermistor ceramic material is obtained.

[0012] In some embodiments, in S1, the ball milling mixing medium is water and zirconium balls in a mass ratio of 1:(1-2), and the mass ratio of the mixture to the medium during ball milling is 1:(2-4).

[0013] In some embodiments, in S1, the ball milling speed is 200-500 rpm and the ball milling time is 4-8 h.

[0014] In some embodiments, the drying temperature in S1 and S2 is 120-160 °C.

[0015] In some implementations, the mesh size of the sieve used for sieving is 30-60 mesh in S1 and S2.

[0016] In some embodiments, in S2, the ball milling medium is water and zirconium balls in a mass ratio of 1:(2-3), and the mass ratio of the mixture to the medium during ball milling is 1:(4-5).

[0017] In some embodiments, in S2, the powder is ball-milled until the particle size is below 0.8 μm.

[0018] To address the aforementioned technical problems, a third objective of this invention is to provide an NTC thermistor, comprising a diaphragm, wherein the diaphragm comprises the NTC thermistor ceramic material.

[0019] In some embodiments, the NTC thermistor further includes an internal electrode comprising a silver-palladium alloy comprising 29%-31% palladium and 69%-71% silver by mass.

[0020] In some embodiments, the diaphragm comprises an NTC thermistor ceramic material, a resin binder, a plasticizer, and a dispersant in a mass ratio of (50-60):(2-8):(1-4):(0.2-0.5).

[0021] To address the aforementioned technical problems, the fourth objective of this invention is to provide a method for fabricating an NTC thermistor, comprising the following steps: (1) A slurry is prepared by mixing 50wt%-60wt% of the NTC thermistor ceramic material, 2wt%-8wt% of the resin binder, 30wt%-45wt% of the solvent, 1wt%-4wt% of the plasticizer, and 0.2wt%-0.5wt% of the dispersant, and the slurry is then cast into a film by dry casting. (2) The inner electrode is printed in a multilayer design of the diaphragm, stacked into a block, isostatically pressed, cut and glued, and then sintered at a temperature of 1080-1160 ℃. Then, the diaphragm is chamfered, sealed, sintered and electroplated to obtain an NTC thermistor.

[0022] This application presents an NTC thermistor made from NTC thermistor ceramic material, which is then co-fired at low temperature with the internal electrode. The ceramic material is doped with CeO2 and La2O3 to improve its high-temperature stability, resulting in a low resistance change rate after long-term operation at 150 °C. Simultaneously, Ce and La, as donor dopant, enhance the grain boundary barrier of the P-type semiconductor, increasing the resistivity to 1900-2450 Ω·cm. 25 / 50 The value is between 3300-3450 K; by using Bi2O3 in the ceramic material to lower the sintering temperature of the ceramic, it is possible to co-fire with the Ag / Pd paste or Pd paste of the internal electrode at a lower temperature of 1080-1160 ℃, which reduces the risk of cracking, delamination and volatilization of the internal electrode in the product.

[0023] In some embodiments, in step (1), the resin adhesive is at least one of PVB resin and acrylic resin.

[0024] In some embodiments, in step (1), the plasticizer is dioctyl phthalate.

[0025] In some embodiments, in step (1), the solvent comprises propyl acetate and ethanol in a mass ratio of (25-35):(5-10).

[0026] In some implementations, in step (2), the glue discharge temperature is 450-490 ℃ and the time is 5-10 h.

[0027] In some implementations, the sintering time in step (2) is 4-8 h.

[0028] Compared with the prior art, the present invention has the following beneficial effects: 1. In this application, the NTC thermistor ceramic in the Mn-Co-Ni system ceramic material belongs to a typical spinel structure. By doping with high enthalpy and stable oxides such as CeO2, La2O3, and TiO2, the temperature stability of the material can be improved, resulting in a low resistance change rate of the NTC thermistor after long-term operation at 150 ℃. Furthermore, Ce and La, as donor dopant, increase the grain boundary barrier of the P-type semiconductor, ensuring that the resistivity of the material is within the range of 1900 Ω·cm-2450 Ω·cm. 25 / 50 The value is in the range of 3300-3450 K.

[0029] 2. In this application, the NTC thermistor ceramic material is doped with Bi2O3 as a sintering aid to reduce its sintering temperature, thereby reducing the risk of cracking and volatilization of the internal electrode metal when the thermistor ceramic material is co-fired with the Ag / Pd paste or Pd paste of the internal electrode, and realizing low-temperature co-firing of the NTC thermistor ceramic material with the Ag / Pd paste or Pd paste.

[0030] 3. During the high-temperature sintering process, the Bi2O3 doped in the NTC thermistor ceramic material of this application can partially melt to form a glass phase, which adheres to the grain boundary surface. This not only optimizes the resistivity of the material and improves the density of the ceramic body to enhance its strength, but also makes the concentration of cation vacancy migration at the grain boundary similar to that inside the grain due to the formation of the glass phase. Therefore, the cation migration under high-temperature conditions is not obvious, thereby improving the thermal stability of the product. Attached Figure Description

[0031] Figure 1 : This is a SEM image of the cross-section of an NTC thermistor in Application Example 6 of this invention; Figure 2 : This is a SEM image of the cross-section of an NTC thermistor in Comparative Application Example 7 of the present invention. Detailed Implementation

[0032] 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 embodiments of the present invention, and not all embodiments. 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.

[0033] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0034] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0035] As used in this article: In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0036] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0037] In the description of this invention, it should be understood that the terms "upper", "lower", "left", "right", "top", "bottom", etc., indicating orientation or positional relationship are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0038] To further illustrate the present invention, the following detailed description is provided in conjunction with embodiments, but these should not be construed as limiting the scope of protection of the present invention. Unless otherwise specified, the raw materials used in the following embodiments and comparative examples are all commercially available, and the same raw materials were used in parallel experiments.

[0039] Example 1 An NTC thermistor ceramic material, as shown in Table 1, comprises the following components by mass fraction: 55.6 wt% Mn3O4, 18 wt% Co3O4, 23.6 wt% Ni2O3, 0.8 wt% CeO2, 0.5 wt% La2O3, 0.5 wt% TiO2 and 1 wt% sintering aid, wherein the sintering aid is Bi2O3.

[0040] The above-mentioned method for preparing an NTC thermistor ceramic material includes the following steps: S1. Accurately weigh all components of the NTC thermistor ceramic material except for the sintering aid, and then ball mill them together. The ball milling media are deionized water and zirconia balls. The mass ratio of the mixed powder, zirconia balls and deionized water is 1:2:1. The ball milling time is 6 h and the ball milling speed is 320 rpm. Pour the ball-milled material into a stainless steel pan and dry it in an oven at 150 ℃. Then sieve it through a 40-mesh sieve and pre-fire it in a box furnace at 900 ℃ for 2.5 h. After pre-firing, sieve it through a 40-mesh sieve to obtain the calcined material of the main formula. S2. Add the sintering aid to the sintered material of the main formula, and mix it with the mixed powder, zirconium balls and pure water in a mass ratio of 1:3:1.2. Ball mill for 8 hours to ensure uniform ball milling, and ball mill the powder particles to a particle size of less than 0.8μm. After drying and sieving, NTC thermistor ceramic material is obtained.

[0041] Example 2 An NTC thermistor ceramic material, which differs from Example 1, comprises the following components by mass fraction: 48wt% Mn3O4, 16wt% Co3O4, 30wt% Ni2O3, 2wt% CeO2, 1.5wt% La2O3, 1wt% TiO2 and 1.5wt% sintering aid, wherein the sintering aid is Bi2O3.

[0042] Example 3 An NTC thermistor ceramic material, which differs from Example 1 in that it comprises the following components by mass fraction: 75wt% Mn3O4, 5wt% Co3O4, 14wt% Ni2O3, 1.5wt% CeO2, 2wt% La2O3, 1wt% TiO2 and 1.5wt% sintering aid, wherein the sintering aid is Bi2O3.

[0043] Example 4 An NTC thermistor ceramic material, which differs from Example 1, comprises the following components by mass fraction: 69.8 wt% Mn3O4, 14.7 wt% Co3O4, 10 wt% Ni2O3, 1 wt% CeO2, 2 wt% La2O3, 1 wt% TiO2 and 1.5 wt% sintering aid, wherein the sintering aid is Bi2O3.

[0044] Example 5 An NTC thermistor ceramic material, which differs from Example 1, comprises the following components by mass fraction: 63.5 wt% Mn3O4, 20.2 wt% Co3O4, 12.3 wt% Ni2O3, 1 wt% CeO2, 1 wt% La2O3, 1 wt% TiO2 and 1 wt% sintering aid, wherein the sintering aid is Bi2O3.

[0045] Example 6 An NTC thermistor ceramic material, which differs from Example 1, comprises the following components by mass fraction: 63.5 wt% Mn3O4, 20.2 wt% Co3O4, 12.3 wt% Ni2O3, 0.5 wt% CeO2, 1.5 wt% La2O3, 1 wt% TiO2 and 1 wt% sintering aid, wherein the sintering aid is Bi2O3.

[0046] Example 7 An NTC thermistor ceramic material, which differs from Example 1, comprises the following components by mass fraction: 63.5 wt% Mn3O4, 20.2 wt% Co3O4, 12.3 wt% Ni2O3, 1.5 wt% CeO2, 0.5 wt% La2O3, 1 wt% TiO2 and 1 wt% sintering aid, wherein the sintering aid is Bi2O3.

[0047] Example 8 An NTC thermistor ceramic material, which differs from Example 1, comprises the following components by mass fraction: 64.5 wt% Mn3O4, 20.2 wt% Co3O4, 12.3 wt% Ni2O3, 1 wt% CeO2, 1 wt% La2O3 and 1 wt% sintering aid, wherein the sintering aid is Bi2O3.

[0048] Comparative Example 1 An NTC thermistor ceramic material, which differs from Example 1, comprises the following components by mass fraction: 63.5 wt% Mn3O4, 20.2 wt% Co3O4, 12.3 wt% Ni2O3, 2 wt% La2O3, 1 wt% TiO2 and 1 wt% sintering aid, wherein the sintering aid is Bi2O3.

[0049] Comparative Example 2 An NTC thermistor ceramic material, which differs from Example 1 in that it comprises the following components by mass fraction: 64.5 wt% Mn3O4, 20.2 wt% Co3O4, 12.3 wt% Ni2O3, 1 wt% CeO2, 1 wt% La2O3 and 1 wt% TiO2.

[0050] Comparative Example 3 An NTC thermistor ceramic material, which differs from Example 1, comprises the following components by mass fraction: 64.5 wt% Mn3O4, 20.2 wt% Co3O4, 12.3 wt% Ni2O3, 1 wt% CeO2, 1 wt% TiO2 and 1 wt% sintering aid, wherein the sintering aid is Bi2O3.

[0051] Comparative Example 4 An NTC thermistor ceramic material, which differs from Example 1 in that it comprises the following components by mass fraction: 75wt% Mn3O4, 5wt% Co3O4, 14wt% Ni2O3, 1.5wt% CeO2, 2wt% La2O3, 1wt% TiO2 and 1.5wt% sintering aid, wherein the sintering aid is B2O3.

[0052] Comparative Example 5 An NTC thermistor ceramic material, which differs from Example 1, comprises the following components by mass fraction: 63.5 wt% Mn3O4, 20.2 wt% Co3O4, 12.3 wt% Ni2O3, 2 wt% ZnO, 1 wt% TiO2 and 1 wt% sintering aid, wherein the sintering aid is Bi2O3.

[0053] Comparative Example 6 An NTC thermistor ceramic material differs from Example 1 in that it comprises the following components by mass fraction: 45.3 wt% Mn3O4, 38.4 wt% Co3O4, 12.3 wt% Ni2O3, 1 wt% CeO2, 1 wt% La2O3, 1 wt% TiO2 and 1 wt% sintering aid, wherein the sintering aid is Bi2O3.

[0054] Comparative Example 7 An NTC thermistor ceramic material, which differs from Example 1 in that it comprises the following components by mass fraction: 33.5wt% Mn3O4, 35.2wt% Co3O4, 27.3wt% Ni2O3, 1wt% CeO2, 1wt% La2O3, 1wt% TiO2 and 1wt% sintering aid, wherein the sintering aid is Bi2O3.

[0055] Table 1 - Components and mass fractions of NTC thermistor ceramic materials in the embodiments and comparative examples of this application Application Example 1-10 and Comparative Application Example 1-11 A method for fabricating an NTC thermistor includes the following steps: (1) A slurry was prepared by mixing 54.2 wt% NTC thermistor ceramic material, 5 wt% PVB resin, 30.4 wt% n-propyl acetate solvent, 2.5 wt% dioctyl phthalate (DOP) plasticizer, 0.3 wt% AKM0351 dispersant and 7.6 wt% anhydrous ethanol. The NTC thermistor ceramic material was prepared in the examples and comparative examples, as shown in Table 2. The slurry was then cast into a film by dry casting. (2) The inner electrode is printed in a multilayer design according to the 0201 specification. The inner electrode is made of 30%Ag70Pd (70%Pd+30%Ag) alloy material, stacked into a block, and the block is pressed into a dense layer by equal water static pressure. It is then cut into NTC blanks, kept at 460 ℃ for 8 h for debinding, and kept at 1130-1190 ℃ for 5 h for sintering. The specific sintering temperature is shown in Table 2 below. Then, the NTC thermistor is obtained by chamfering, sealing, sintering, and electroplating.

[0056] Performance testing 1. The cross-sections of the NTC thermistors prepared in Application Example 4 and Comparative Application Example 7 were observed using a scanning electron microscope (SEM). The SEM images are shown below. Figure 1-2 As shown. By observing the microstructure of the NTC thermistor cross-section, it can be found that the NTC thermistor material prepared in Example 3 of this application is more dense after sintering, and there are fewer pores and voids in the resistor cross-section. In contrast, the NTC thermistor cross-section prepared in Comparative Example 3 has a lower density after sintering, and there are a large number of voids in the resistor cross-section.

[0057] 2. Density: The NTC thermistor ceramic materials prepared in the examples and comparative examples were sintered at the temperatures shown in Table 2 for 5 hours, and their density was tested. The test results are shown in Table 2 below, including the following steps: (1) Dry the chip at 105°C for 2 hours and then cool it to room temperature; (2) Weighing (W) air Weigh the sample in air using a precision balance (accuracy must be 0.1 mg). (3) Immersion weighing (W) liquid ): Place the sample in a special basket and immerse it in distilled water to suspend it, remove air bubbles, weigh its mass in the liquid, and calculate the density according to the following formula: ; In the formula, ρ liquid This refers to the density of a liquid, such as distilled water ≈ 1 g / cm³. 3 .

[0058] 3. Resistivity: The resistance of the NTC thermistors prepared in the application examples and comparative application examples was measured under constant temperature oil bath conditions of 25 ℃ ± 0.01 ℃, and the resistivity was calculated according to the following formula: Resistivity = R 25 ×S / L; where R is the value of S / L. 25 The resistance of the resistor was measured in Ω under constant temperature oil bath conditions of 25 ℃±0.01 ℃; S is the effective area of ​​the component design in cm; L is the effective thickness of the component design in cm. The resistivity requirement is within the range of 1900Ω.cm-2450Ω.cm. The resistivity test results are shown in Table 2 below.

[0059] 4. B value: Calculated using the thermistor values ​​tested at 25℃ and 50℃, according to the following formula: B = [2.303 × (273.15 + 50) × (273.15 + 25) / (50 - 25)] × lg(R) 25 / R 50 In the formula, R 25 The resistance value of the resistor was measured under constant temperature oil bath conditions of 25 ℃ ± 0.01 ℃, and the unit is Ω; R 50 The resistance value of the resistor was measured under constant temperature oil bath conditions of 50 ℃±0.01 ℃, and the unit is Ω; B 25 / 50 The required value is within the range of 3300-3450 K. The test results are shown in Table 2 below.

[0060] Among them, the resistance value R of the NTC thermistor 25 R 50 The testing method includes the following steps: (1) Secure the product with appropriate copper clamps. (2) Place it in a constant temperature bath at 25℃±0.01℃ or 50℃±0.01℃ for 10 minutes, and then measure it with a resistance tester that meets the accuracy requirements.

[0061] 5. High-temperature aging △R 25 / R 25 The initial R of the thermistors in the application example and the comparative application example was measured under constant temperature oil bath conditions of 25 ℃±0.01 ℃. 25 The resistance value was determined, and the component was then placed in a constant temperature chamber at 150 °C for 1000 h for aging. After the test, the component was placed in a normal temperature and humidity environment for 24 h before visual inspection and measurement of the resistor R. 25 The resistance value R is calculated using the following formula. 25 Rate of change: ΔR 25 / R 25 = (X2-X1) / X1×100%; where X1 is the R measured before aging. 25Resistance value, in Ω; X2 is the R measured after aging. 25 Resistance values ​​are measured in Ω; the test results are shown in Table 2 below.

[0062] Table 2 - Sintering Temperature and Performance Test Results of NTC Thermistors in Various Application Examples As shown in Table 2, the NTC thermistor ceramic materials of Examples 1-5 of this application are doped with Bi2O3 to reduce the sintering temperature, allowing them to be co-fired with the internal electrode at a lower temperature of 1080-1160 °C, achieving a material density of 5 g / cm³. 3 The above measures lower the required sintering temperature, thereby reducing the risk of delamination and cracking between the magnet and the internal electrode, and also reducing the amount of metal volatilization from the internal electrode. Furthermore, the added Bi₂O₃ can improve the density of the ceramic material after sintering and optimize the resistivity of the resistor. Simultaneously, the NTC thermistor ceramic material is also doped with CeO₂, La₂O₃, and TiO₂ to improve the material's temperature stability. Ce and La are mainly doped as donors at the grain boundaries, increasing the grain boundary barrier of the P-type semiconductor and thus increasing the resistivity of the resistor. This ensures that the resistivity and B-value of the NTC thermistors prepared in Examples 1-7 meet the requirements of this application. Moreover, as the sintering temperature within this range increases, the resistivity and B-value increase synchronously, and the ΔR value decreases after high-temperature aging. 25 / R 25 Its rate of change is low, allowing it to adapt to higher operating temperatures.

[0063] Compared to Example 5, the NTC thermistor ceramic material of Comparative Example 2 did not contain Bi2O3. Therefore, a sintering temperature above 1190 °C was required for the resistor to achieve relatively high thermal stability and density. The density of the NTC thermistor ceramic material of Comparative Example 2 decreased significantly at a sintering temperature of 1130-1160 °C. Furthermore, as shown in Comparative Application Examples 4-6, the NTC prepared by sintering at 1130-1190 °C exhibited a higher rate of resistance change and poorer thermal stability after high-temperature aging.

[0064] Compared to Example 3, the NTC thermistor ceramic material of Comparative Example 4 uses B2O3 as a sintering aid instead of Bi2O3 doping. However, B2O3 reacts with the silver and palladium of the internal electrode during high-temperature sintering, generating metal oxides or borides that cause the ceramic body to expand. As shown in Comparative Application Example 8, the NTC prepared by sintering at 1130 °C has delamination between the internal electrode and the ceramic body, and the product is unqualified.

[0065] Compared to Example 5, under the same sintering temperature of 1130 °C, the CeO2 doped in the NTC thermistor ceramic material of Comparative Example 1 was replaced by an equal amount of La2O3, and the single La... 3+ Doping leads to an excessively high potential barrier, causing the resistivity of comparative application examples 1-3 to gradually increase with decreasing sintering temperature and exceed the range required by this application, and the potential barrier uniformity is poor. This is because Ce deficiency weakens the sintering-aiding synergistic effect of Bi2O3, thus requiring a higher temperature to achieve a better sintering effect; the density after sintering at 1130℃ is <5 g / cm³. 3 The lack of Ce-La synergy weakens the spinel structure's resistance to cation migration, resulting in a lower high-temperature aging ΔR compared to Application Examples 1-3. 25 / R 25 It ranges from 2.45% to 10.57%.

[0066] Compared to Example 5, Comparative Example 3 did not contain La2O3 doping and only Ce was present. 3+ / Ce 4+ The doping cannot form a sufficiently high barrier. The absence of La leads to an imbalance in the concentration of cation vacancy migration at the grain boundaries. Even if Bi2O3 forms a glass phase, it cannot suppress ion migration at high temperatures. The absence of La increases the risk of spinel lattice distortion. Long-term high temperature can easily lead to the appearance of micro-defects inside, which in turn leads to the excessively low resistivity of the NTC prepared in Comparative Application Example 7.

[0067] Compared to Example 5, in Comparative Example 5, the CeO2 and La2O3 doped with CeO2 and La2O3 were replaced by ZnO in equal amounts. 2+ Unable to be like Ce 3+ / La 3+ When such doping occurs as a donor at the grain boundary, it will penetrate into the spinel lattice to form impurity ions, leading to lattice distortion. Lattice distortion hinders carrier migration. In comparison, the resistivity of the NTC prepared in Example 9 increased to 2850 Ω·cm, which is too high. Furthermore, due to the change in lattice energy level, the B value is 3550 k. The structural distortion results in poor long-term stability.

[0068] Compared to Example 5, the NTC thermistor ceramic materials in Comparative Examples 6-7 have different proportions of Mn3O4, Co3O4, and Ni2O3. Since the negative temperature coefficient effect of NTC thermistor ceramics depends on Mn-Co-Ni spinel structures such as MnCo2O4 and MnNi2O4 solid solutions, this structure requires Mn... 4+ / Mn 3+ Co 3+ / Co 2+ Ni 3+ / Ni 2+In the crystal lattice, the Mn3O4 content of Example 5, at 63.5%, provides sufficient Mn ions to ensure the filling of the "octahedral interstitial spaces" in the spinel. However, in Comparative Examples 6-7, the Mn content is far below the lower limit of 48%, and the Co content exceeds the upper limit of 21%, resulting in an excessive number of "Mn vacancies" and "Co impurities" in the crystal lattice. This prevents the formation of a continuous spinel solid solution and instead generates a Co3O4 impurity phase (when Co is in excess), thus destroying the structural integrity.

[0069] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. An NTC thermistor ceramic material, characterized in that, It includes the following components by mass fraction: Mn3O4: 48wt%-75wt%; Co3O4: 5wt%-21wt%; Ni2O3: 10wt%-30wt%; CeO2: 0.5wt%-2wt%; La2O3: 0.5wt%-2wt%; Bi2O3: 1wt%-2wt%.

2. The NTC thermistor ceramic material as described in claim 1, characterized in that, The NTC thermistor ceramic material also includes TiO2 with a mass fraction of 0.5wt%-1wt%.

3. The NTC thermistor ceramic material as described in claim 1, characterized in that, The mass ratio of CeO2 to La2O3 is (0.5-1.5):(0.5-1.5).

4. The NTC thermistor ceramic material as described in claim 1, characterized in that, It includes the following components by mass fraction: Mn3O4: 60wt%-70wt%; Co3O4: 18wt%-21wt%; Ni2O3: 10wt%-15wt%; CeO2: 0.5wt%-1.5wt%; La2O3: 0.5wt%-1.5wt%; Bi2O3: 1wt%-1.5wt%; TiO2: 0.5wt%-1wt%.

5. A method for preparing the NTC thermistor ceramic material as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Accurately weigh all components of the NTC thermistor ceramic material except Bi2O3, then ball mill and mix them, dry and sieve them, and pre-fire them at 880-920℃ for 1-5 hours. After sieving, the calcined material of the main formula is obtained. S2. Bi2O3 is added to the calcined material of the main formula, and after ball milling, drying and sieving, NTC thermistor ceramic material is obtained.

6. The method for preparing the NTC thermistor ceramic material as described in claim 5, characterized in that, In S1, the ball milling mixing medium is water and zirconium balls in a mass ratio of 1:(1-2), and the mass ratio of the mixture to the medium during ball milling is 1:(2-4). And / or, in S1, the ball milling speed is 200-500 rpm and the ball milling time is 4-8 h; And / or, in S1 and S2, the drying temperature is 120-160 ℃; And / or, in S1 and S2, the mesh size of the sieve used for sieving is 30-60 mesh; And / or, in S2, the ball milling media is water and zirconium balls in a mass ratio of 1:(2-3), and the mass ratio of the mixture to the media during ball milling is 1:(4-5). And / or, in S2, ball milling is performed until the particle size of the powder is below 0.8 μm.

7. An NTC thermistor, employing the NTC thermistor ceramic material as described in any one of claims 1-5, characterized in that, Includes a diaphragm, the diaphragm comprising the NTC thermistor ceramic material.

8. The NTC thermistor as described in claim 7, characterized in that, The NTC thermistor also includes an internal electrode, which comprises a silver-palladium alloy, wherein the silver-palladium alloy comprises 29%-31% palladium and 69%-71% silver by mass. And / or, the diaphragm comprises NTC thermistor ceramic material, resin binder, plasticizer and dispersant in a mass ratio of (50-60):(2-8):(1-4):(0.2-0.5).

9. A method for fabricating an NTC thermistor as described in claim 7 or 8, characterized in that, Includes the following steps: (1) A slurry is prepared by mixing 50wt%-60wt% of the NTC thermistor ceramic material, 2wt%-8wt% of the resin binder, 30wt%-45wt% of the solvent, 1wt%-4wt% of the plasticizer, and 0.2wt%-0.5wt% of the dispersant, and the slurry is then cast into a film by dry casting. (2) The inner electrode is printed in a multilayer design of the diaphragm, stacked into a block, isostatically pressed, cut and de-adhesive removed, and then sintered at a temperature of 1080-1160 ℃. Then, the diaphragm is chamfered, sealed, sintered and electroplated to obtain an NTC thermistor.

10. The method for preparing an NTC thermistor as described in claim 9, characterized in that, In step (1), the resin adhesive is at least one of PVB resin and acrylic resin; And / or, in step (1), the plasticizer is dioctyl phthalate; And / or, in step (1), the solvent comprises propyl acetate and ethanol in a mass ratio of (25-35):(5-10); And / or, in step (2), the glue discharge temperature is 450-490 ℃ and the time is 5-10 h; And / or, in step (2), the sintering time is 4-8 h.

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