NTC (Negative Temperature Coefficient) thermistor anti-surge ceramic material and preparation method thereof

Abstract

The invention discloses an NTC (Negative Temperature Coefficient) thermistor anti-surge ceramic material based on a Ta2O5-MgO synergistic grain refinement system and a low-temperature preparation method of the NTC thermistor anti-surge ceramic material. According to the ceramic material, Ta2O5 and MgO in a specific proportion are innovatively adopted as synergistic additives, a stable space charge layer and a defect complex are formed at a grain boundary through a charge-defect double-barrier mechanism, grain boundary migration is effectively inhibited, and densification is promoted at the same time. The ceramic material can realize an excellent microstructure with the average grain size of less than or equal to 4m and the relative density of more than or equal to 97% under the low-temperature sintering condition of less than or equal to 1000 DEG C, and shows excellent surge resistance (delta R / R is less than or equal to 5% after 100 times of impact) and thermal stability. Compared with the prior art, the performance of the NTC thermistor is remarkably improved, and the NTC thermistor is simple in process, low in cost, environmentally friendly, good in industrialization prospect and capable of being widely applied to NTC thermistor devices with high reliability requirements.

Description

Technical Field

[0001] This invention belongs to the field of electronic ceramic materials and components technology, specifically relating to an NTC thermistor surge-resistant ceramic material based on a tantalum-magnesium synergistic grain refinement system and its low-temperature preparation method. More specifically, this invention provides an NTC thermistor ceramic material that achieves grain refinement, structural densification, and significantly improved surge resistance performance at a lower sintering temperature through the synergistic effect of a specific ratio of Ta2O5 and MgO, as well as a controllable preparation method for this material and its application in electronic components. Background Technology

[0002] An NTC (Negative Temperature Coefficient) thermistor is a semiconductor ceramic element whose resistance decreases significantly with increasing temperature. It is widely used in temperature sensing, temperature compensation, and surge current suppression. In power supply circuits, NTC thermistors are often used to suppress surge currents at power-on, protecting downstream circuit components from overcurrent. However, as electronic devices evolve towards higher reliability and longer lifespans, higher demands are placed on the stability of NTC thermistors under repeated surge impacts.

[0003] Traditional NTC thermistor ceramic materials are mostly based on transition metal oxides such as manganese (Mn), nickel (Ni), and cobalt (Co), such as the common Mn3O4-NiO-Co2O3 system. While these materials exhibit good NTC effect, they reveal the following problems in practical applications: 1. Coarse grains: During high-temperature sintering, grains are prone to abnormal growth, leading to inhomogeneous microstructure, reduced grain boundaries, and longer carrier migration paths, affecting the device's response speed and stability. 2. Insufficient density: The presence of numerous pores within the ceramic body reduces the material's mechanical strength and thermal conductivity. Under surge current impact, it is prone to microcracks due to thermal stress concentration, even leading to failure. 3. Poor surge resistance: Repeated surge impacts cause Joule heat accumulation at grain boundaries, leading to lattice defect propagation, grain boundary oxidation, or phase transitions, causing irreversible resistance drift (larger ΔR / R), which can severely lead to open-circuit or short-circuit failure.

[0004] To address these issues, existing technologies attempt to optimize ceramic material properties using single additives. For example: 1. Introducing high-melting-point oxides such as zirconium oxide (ZrO2) and yttrium oxide (Y2O3) as grain growth inhibitors, utilizing their pinning effect at grain boundaries to hinder grain migration and thus refine the grains. However, these additives often have poor dispersibility and tend to agglomerate within the ceramic body, leading to uneven grain refinement and potentially reducing the ceramic body's density. 2. Adding liquid-phase sintering promoters such as bismuth oxide (Bi2O3) and copper oxide (CuO)-boric acid (H3BO3) eutectic mixtures, forming a liquid phase at lower temperatures, promoting material diffusion and particle rearrangement, and improving ceramic body density. However, the presence of the liquid phase may also accelerate grain migration, leading to abnormal grain growth, and its surge resistance improvement is limited when used alone.

[0005] In summary, a single type of additive cannot simultaneously resolve the contradiction between grain refinement and densification, let alone achieve a breakthrough improvement in surge resistance. Especially given the current trend towards higher reliability and longer lifespan in electronic devices, there is an urgent need to develop a novel NTC thermistor ceramic material that, through the synergistic effect of multiple components, can achieve significant grain refinement and highly dense structure at relatively low sintering temperatures, while also possessing excellent surge resistance and thermal stability.

[0006] A comprehensive patent search and technical investigation have revealed no reports of using a specific ratio of Ta2O5-MgO synergistic system to solve the above-mentioned technical problems, which provides a clear space for technological innovation in this invention. Summary of the Invention

[0007] The primary objective of this invention is to overcome the shortcomings of existing technologies and provide a novel surge-resistant ceramic material for NTC thermistors. This ceramic material achieves a fine-grained structure with an average grain size of ≤4µm at a relatively low sintering temperature of ≤1000℃ through the synergistic effect of Ta2O5 and MgO, while obtaining a high density of ≥97% and exhibiting excellent surge resistance performance (ΔR / R≤5% after 100 impacts).

[0008] Another objective of this invention is to provide a method for preparing the above-mentioned ceramic material, which is simple in process, compatible with the traditional NTC ceramic material production process, and easy to achieve large-scale production.

[0009] Another object of the present invention is to provide an NTC thermistor element comprising the above-mentioned ceramic material, which has high reliability and long service life, and is particularly suitable for demanding surge suppression applications.

[0010] The surge-resistant ceramic material for NTC thermistors provided by this invention consists of two parts: a base ceramic material and synergistic additives.

[0011] Basic ceramic composition (in molar percentage): Mn3O4: 45-60%, as the main crystal phase forming element, ensures that the material has good NTC properties. NiO: 20-30%, used to adjust resistivity and B value (material constant). Co2O3: 10-20%, improves the structural stability and electrical property consistency of materials. Fe2O3: 0-5%, optional component, used for fine-tuning electrical properties. Synergistic additives (based on the quality of the base ceramic material, expressed as a percentage by weight): Ta₂O₅: 0.20-0.60%, with a specific surface area ≥ 10 m² / g and D₅₀ < 200 nm. MgO: 0.10-0.40%, introduced as a MgCO3 precursor, decomposes to form MgO during sintering. The Ta / Mg molar ratio is strictly controlled within the range of 1:1.0-2.0.

[0012] The beneficial effects that this application can produce include: 1. Excellent overall performance: It simultaneously achieves fine grains (≤4µm), high density (≥97%) and excellent surge resistance (ΔR / R≤5%), solving the contradiction between grain refinement and densification in traditional technologies.

[0013] 2. Low sintering temperature: Full sintering can be achieved at ≤1000℃, which is about 100-150℃ lower than the traditional process, significantly reducing energy consumption and production costs.

[0014] 3. Excellent thermal stability: withstands temperatures as low as -40℃. After 1000 thermal cycles at +125℃, the resistance change rate ΔR / R ≤ 2%, which is far superior to the industry standard requirements.

[0015] 4. Good process compatibility: The preparation process is highly compatible with the traditional NTC ceramic material production process, requiring no additional complex equipment and making it easy to achieve industrialization.

[0016] 5. Environmentally friendly: The ceramic material does not contain toxic heavy metal elements, meeting environmental protection requirements. Attached Figure Description

[0017] Figure 1 SEM image of Example 1 (fine crystals, high density); Figure 2 Comparative Example 1: SEM image (coarse grains, obvious pores); Figure 3 Surge resistance ΔR / R comparison bar chart (Examples 1-2 vs Comparative Examples 1-3); Figure 4DFT calculation results for “Ta-Mg synergistic mechanism”. Detailed Implementation

[0018] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0019] Unless otherwise specified, the raw materials and catalysts used in the embodiments of this application were all purchased commercially.

[0020] Unless otherwise specified, all test methods are standard and all instrument settings are those recommended by the manufacturer.

[0021] Example 1: Formulation Design Basic ceramic material formula: Mn3O4 50%, NiO 25%, Co2O3 15%, Fe2O3 5%, CuO 3%, ZnO 2%.

[0022] Synergistic additives: Ta2O5 0.5 wt%, MgO 1.0 wt%.

[0023] Preparation process:

[0024] Accurately weigh each raw material according to the formula and add it to a high-energy ball mill; use anhydrous ethanol as the medium and zirconia balls as grinding balls (material:ball:ethanol = 1:3:1.5) and ball mill at 350 rpm for 6 hours; the slurry is spray-dried and granulated at an inlet temperature of 200℃ and an outlet temperature of 90℃; the granulated powder is dry-pressed into φ10×2 mm green bodies at 150 MPa; the temperature is increased to 1000℃ at 4℃ / min, held for 3 hours and sintered, and then cooled in the furnace.

[0025] Performance testing:

[0026] Microstructure: Average grain size 3µm, uniform grain size distribution Physical properties: Relative density 98%, porosity 2% Surge resistance: ΔR / R = +3% after 100 8 / 20µs surge impacts.

[0027] Example 2

[0028] Basic ceramic material formula: Mn3O4 45%, NiO 30%, Co2O3 20%, CuO 3%, ZnO 2%.

[0029] Synergistic additives: Ta2O5 0.8 wt%, MgO 1.5 wt%.

[0030] Preparation process: Same as in Example 1.

[0031] Comparative Example 1

[0032] Basic ceramic material formula: Same as in Example 1.

[0033] Additives: None.

[0034] Preparation process: Same as in Example 1.

[0035] Comparative Example 2

[0036] Basic ceramic material formula: Same as in Example 1.

[0037] Additive: Ta2O5 0.5 wt%.

[0038] Preparation process: Same as in Example 1.

[0039] Comparative Example 3

[0040] Basic ceramic material formula: Same as in Example 1.

[0041] Additive: MgO 1.0 wt%.

[0042] Preparation process: Same as in Example 1.

[0043] Test result comparison:

[0044] The performance of the NTC thermistor ceramic sheets prepared in Examples 1-2 and Comparative Examples 1-3 was tested, and the results are as follows: Group Grain size (μm) Relative density (%) Surge resistance performance ΔR / R (%) Example 1 4~8 98 3 Example 2 5~9 97.5 2.8 Comparative Example 1 2~20 92 15 Comparative Example 2 4~14 88 10 Comparative Example 3 4~16 96 12 As can be seen from the table, the ceramic grain size of Examples 1-2 is significantly reduced, the relative density is significantly increased, and the surge resistance is greatly improved, far superior to Comparative Examples 1-3. This fully demonstrates the significant effect of the synergistic additive in this invention. Through first-principles calculations and experimental characterization, this invention reveals the mechanism of action of the Ta2O5-MgO synergistic system: at the electronic structure level: Ta 5+ Due to its high electric field strength (+5 valence), the adsorption energy at the MnO(310) grain boundary reaches -2.83 eV, forming a stable space charge layer and effectively suppressing grain boundary migration. Defect chemistry level: Mg 2+ Substitution of Mn in the crystal lattice 2+ At the site, Vo••-Mg″ composite defects are generated, with an adsorption energy of -1.95 eV at the next-near position of the grain boundary. These composite defects can effectively reduce the oxygen vacancy concentration gradient and buffer the thermal stress generated by surge impact. Synergistic effect: When Ta 5+ and Mg 2+When coexisting at grain boundaries, the total system energy further decreases by 0.429 eV, demonstrating a significant synergistic stabilization effect. This "charge-defect" dual barrier mechanism ensures the simultaneous achievement of grain refinement and density improvement. This invention successfully prepared an NTC thermistor ceramic material with fine grains, high density, and excellent surge resistance by introducing nano-Ta2O5 and MgO as synergistic additives. This ceramic material exhibits extremely low resistance change rate and high thermal stability under repeated surge impacts, meeting the stringent requirements of high-end electronic devices for NTC components. Furthermore, its preparation process is simple and compatible with traditional NTC ceramic material production processes, showing promising industrialization prospects.

[0045] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A surge-resistant ceramic material for NTC thermistors, characterized in that, It consists of a base ceramic material and synergistic additives, wherein: The amount of Ta2O5 added is 0.20-0.60 wt% of the basic ceramic material, and its specific surface area is ≥10 m² / g; The amount of MgO added is 0.10-0.40 wt% of the basic ceramic material; The Ta / Mg molar ratio is 1:1.0-2.0; the ceramic material, after sintering at ≤1000 ℃ in air atmosphere for 2-4 h, simultaneously meets the following requirements: ① average grain size ≤4 µm; ② relative density ≥97%; ③ withstands 100 cycles of 8 / 20 µs at a peak current of 10×I n After a surge, the rate of change of room temperature resistivity ΔR / R ≤ 5%.

2. The material as described in claim 1, characterized in that, The specific surface area of ​​the Ta2O5 is ≥10 m² / g, and D50 is ≤200 nm.

3. The material as described in claim 1 or 2, characterized in that, The MgO is generated in situ by the decomposition of MgCO3 at 400-600℃.

4. The material according to any one of claims 1-3, characterized in that, The basic ceramic material contains 45-60 mol% Mn3O4, 20-30 mol% NiO, and 10-20 mol% Co2O3.

5. The material according to any one of claims 1-4, characterized in that, At least 80% of the grain boundaries have Ta-enriched layers with a thickness of 1-3 nm.

6. The material according to any one of claims 1-5, characterized in that, -40℃ After 1000 cycles at +125℃, ΔR / R ≤ 2%.

7. A method for preparing the material according to any one of claims 1-6, comprising: a) Batching → b) High-energy ball milling for 4-8 h → c) Spray drying → d) Dry pressing at 100-200 MPa → e) Sintering at 950-1000℃ for 2-4 h.

8. The method as described in claim 7, characterized in that, The milling media consisted of 0.3-0.5 mm zirconia balls, with a material:ball:alcohol ratio of 1:3:1.

5.

9. The method as described in claim 7 or 8, characterized in that, The relative density of the formed green body is ≥55%, and the linear shrinkage rate during sintering is 12-15%.

10. An NTC thermistor element comprising the ceramic material described in any one of claims 1-6 as a functional chip.

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