A high-stability, low-resistivity NTC thermistor dielectric material and its preparation method

Abstract

A high-stability, low-resistivity NTC thermistor dielectric material, characterized by being made of the following raw materials in the following weight ratios: Mn3O 4 79-93%, Ni2O 3 2‑8%, CuO 1‑7%, Al2O 3 0.4‑2%, ZnO 0.4‑1%, LiLaGa2O 5 0.2‑4%, ZnTeO 4 0.3‑5%, TiO 2 0.1-0.6%. Compared with the prior art, the high-stability, low-resistivity NTC thermistor dielectric material of the present invention has the following advantages: (1) the material constant B value is high, and the B value is 4210-4720K at -25-200℃; (2) the NTC thermistor has high sensitivity, good stability, and good current shock resistance; after the maximum steady-state current, the product resistivity changes little; the delay resistance change rate is small (placed at 25℃ for 20 days); (3) the resistivity is low, and the room temperature resistivity (ρ 25℃ ) is in the range of 8Ω·cm~9.6Ω·cm; (4) The sintering temperature of NTC thermistor ceramics is relatively low, at 1150‑1220℃.

Description

Technical Field

[0001] The present invention belongs to the field of information functional material products, and specifically relates to a high-stability, low-resistivity NTC thermistor dielectric material and a preparation method thereof. Background Art

[0002] NTC (negative temperature coefficient) thermistors are resistors whose resistance decreases as the temperature increases. Due to their temperature sensitivity, fast response, and high measurement accuracy, they are widely used in temperature measurement, temperature control, temperature compensation, and surge current suppression. NTC thermistor ceramic materials are the most widely studied thermistor dielectric materials. They are usually composed of oxides of transition metal elements such as nickel, copper, aluminum, manganese, and chromium. Most of the research on NTC thermistor dielectric materials focuses on NTC thermistor dielectric materials with relatively high resistivity. In addition, even for low-resistivity dielectric materials, the thermal constant B value is relatively low (around 3000K), and the room temperature resistivity and thermal constant B change significantly over time. There is relatively little research on dielectric materials for high-B-value, high-stability, low-resistivity NTC thermistors. The relationship between the resistivity and temperature of NTC thermistors conforms to the Arrhenius exponential relationship: ρ=ρ0exp(E a / kT), ρ and ρ0 are the resistivity at temperature T (absolute temperature) and infinity, k is the Boltzmann constant, E a Is the activation energy. Thermosensitive materials are usually characterized by resistivity and thermal constant B at room temperature (25°C). The relationship between thermal constant and activation energy is: B=E a / k, the thermal constant B is proportional to the activation energy of the material. The temperature-resistance characteristic of the NTC thermistor can be expressed as: R=R0exp(B(1 / T-1 / T0)), R and R0 are the resistance at T and T0 (absolute temperature) respectively, and the resistance temperature coefficient is: α T =1 / R(dR / dT)= -B / T 2 The thermal constant B characterizes the sensitivity of the NTC thermistor to temperature. The larger the B value, the greater the rate of change of the resistance of the NTC thermistor with temperature, and the better the temperature sensitivity of the material.

[0003] Commonly used low-resistivity NTC thermistors have a B value of 2000-3000K. Over time, the room-temperature resistance changes by more than 10%, indicating poor stability. To improve the sensitivity and stability of NTC thermistors and meet the requirements of high-precision temperature measurement and control, the B value should be above 3000K, and the time-delayed resistance change should be less than 3%. Currently, NTC thermistors suffer from resistance instability. The rated zero-power resistivity changes significantly with age, the number of impulses (charging and discharging a 330uF capacitor) is relatively low, and the resistance change rate at the maximum steady-state current (3A) is relatively large. Therefore, the development of highly stable, low-resistivity NTC thermistor dielectric materials is needed to meet the needs of high-end applications such as precise temperature measurement and temperature control. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an NTC thermistor dielectric material with high stability and low resistivity in the temperature range of -25-200°C, as well as a method for preparing the NTC thermistor dielectric material. The technical solution adopted is as follows:

[0005] A high-stability, low-resistivity NTC thermistor dielectric material is characterized by being made of the following raw materials in the following weight ratios: Mn3O4 79-93%, Ni2O3 2-8%, CuO 1-7%, Al2O3 0.4-2%, ZnO 0.4-1%, LiLaGa2O5 0.2-4%, ZnTeO4 0.3-5%, and TiO2 0.1-0.6%.

[0006] In a preferred embodiment, the high-stability, low-resistivity NTC thermistor dielectric material is made of the following raw materials in the following weight ratio: Mn3O482-91%, Ni2O32.5-7%, CuO 2-6%, Al2O30.5-1.8%, ZnO 0.6-1%, LiLaGa2O50.4-3%, ZnTeO40.3-4%, and TiO20.1-0.6%.

[0007] In another preferred embodiment, the high-stability, low-resistivity NTC thermistor dielectric material is made of the following raw materials in the following weight ratio: Mn3O4 85-89%, Ni2O3 2.5-5%, CuO 3-6%, Al2O3 0.6-1.5%, ZnO 0.5-1%, LiLaGa2O5 0.4-2%, ZnTeO4 0.3-3%, and TiO2 0.1-0.6%.

[0008] The above-mentioned Mn3O4, Ni2O3 and CuO constitute the M3O4-Ni2O3-CuO three-element main material system, in which: M3O4 is the main element of the NTC thermistor ceramic material, and together with LiLaGa2O5 and ZnTeO4, it affects the resistivity of the NTC thermistor ceramic material; Ni2O3, LiLaGa2O5 and ZnTeO4 can affect the B value; CuO and LiLaGa2O5 affect the sintering temperature of the material (CuO The addition of ZnO, TiO2, LiLaGa2O5, and ZnTeO4 will affect the sintering temperature; as the addition amount increases, the sintering temperature will decrease. ZnO, TiO2, LiLaGa2O5, and ZnTeO4 can increase the density of ceramic materials and affect the resistance delay change rate, maximum steady-state current resistance change rate, number of impacts, and resistance change rate after impact of NTC thermistor ceramic materials.

[0009] Preferably, the above-mentioned LiLaGa2O5 and ZnTeO4 are synthesized by solid phase method using conventional chemical raw materials.

[0010] The above-mentioned LiLaGa2O5 can be prepared by the following process: La2O3, Li2CO3, and Ga2O3 are prepared in a molar ratio of 1 / 2:1 / 2:1, and then the La2O3, Li2CO3, and Ga2O3 are ground and mixed uniformly. The mixture of La2O3, Li2CO3, and Ga2O3 is then placed in an alumina crucible and kept at 1050°C for 4 hours to obtain LiLaGa2O5. The obtained LiLaGa2O5 is cooled, ground, and passed through a 200-mesh sieve for later use.

[0011] The ZnTeO4 can be prepared by the following process: ZnO and TeO3 are prepared in a 1:1 molar ratio, then ground and mixed until uniform; the ZnO and TeO3 mixture is then placed in an alumina crucible and heated at 550°C-600°C for 120 minutes to obtain ZnTeO4. The resulting ZnTeO4 is cooled, ground, and passed through a 200-mesh sieve for later use.

[0012] The present invention also provides a method for preparing the above-mentioned high-stability, low-resistivity NTC thermistor dielectric material, which is characterized by comprising the following steps:

[0013] (1) Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGa2O5, ZnTeO4 and TiO2 are prepared in proportion;

[0014] (2) crushing and uniformly mixing the Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGa2O5, ZnTeO4 and TiO2 prepared in step (1) to obtain a first mixed powder;

[0015] (3) drying the first mixed powder obtained in step (2) in an oven (preferably at a drying temperature of 70-80°C and a drying time of 7-10 hours), and then grinding and dispersing the mixture to obtain a second mixed powder;

[0016] (4) placing the second mixed powder obtained in step (3) into a silicon carbon rod electric furnace, calcining at 1100-1150°C for 3-5 hours, and then cooling to 20-30°C (preferably at a cooling rate of 50-100°C / hour) to obtain NTC powder;

[0017] (5) Add anhydrous ethanol to the NTC powder obtained in step (4), ball mill for 8-16 hours, then place the NTC powder in an oven to dry (preferably at a drying temperature of 70-100°C and a drying time of 7-10 hours), grind and disperse it, and pass it through a 200-mesh sieve;

[0018] (6) Adding a binder to the sieved NTC powder and granulating it to obtain a granular material;

[0019] (7) pressing the granular material obtained in step (6) into green sheets;

[0020] (8) The green sheet is placed in a silicon-molybdenum rod electric furnace and kept at 1150-1220° C. for 3-5 hours to allow the green sheet to discharge the binder and sinter, thereby obtaining the high-stability, low-resistivity NTC thermistor dielectric material (the obtained high-stability, low-resistivity NTC thermistor dielectric material is a ceramic sheet).

[0021] In step (2), the various raw materials may be pulverized separately and then mixed uniformly; alternatively, the various raw materials may be mixed and then pulverized, and then mixed while pulverizing, or the various raw materials may be pulverized and then mixed uniformly. The pulverizing equipment may be a ball mill or other pulverizing equipment.

[0022] In the preferred step (2), Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGa2O5, ZnTeO4 and TiO2 are mixed evenly, anhydrous ethanol is added, and ball milling is performed for 8-20 hours to obtain a first mixed powder.

[0023] The binder in step (6) can be a polyvinyl alcohol aqueous solution (i.e., PVA solution). Preferably, the binder in step (6) is a polyvinyl alcohol solution with a weight percentage concentration of 10%, and the weight of the added polyvinyl alcohol solution is 8-10% of the weight of the NTC powder.

[0024] In the preferred step (7), the granular material obtained in step (6) is first pressed into a disc at a pressure of 20-30 MPa for 7-12 minutes; then the disc is isostatically pressed at a pressure of 100-200 MPa for 7-12 minutes to obtain a green sheet.

[0025] Preferably, in step (8), the temperature in the silicon-molybdenum rod electric furnace is increased at a rate of 50-120°C / hour.

[0026] The resulting high-stability, low-resistivity NTC thermistor dielectric material is cooled in the furnace and can be used to make thermistors after naturally cooling to room temperature. After the high-stability, low-resistivity NTC thermistor dielectric material (i.e., ceramic sheet) is produced, silver electrodes are applied on both sides before performance testing.

[0027] Compared with the prior art, the high-stability, low-resistivity NTC thermistor dielectric material of the present invention has the following advantages:

[0028] (1) The material constant B value is high, and the B value is 4210-4720K at -25-200℃.

[0029] (2) NTC thermistors have high sensitivity, good stability, and good resistance to current shock (many shocks, small resistance change rate after shock); after the maximum steady-state current, the product resistivity changes little; the delay resistance change rate is small (placed at 25°C for 20 days).

[0030] (3) Low resistivity, room temperature resistivity (ρ 25℃ ) is in the range of 8Ω·cm~9.6Ω·cm.

[0031] (4) The sintering temperature of NTC thermistor ceramics is relatively low, at 1150-1220℃.

[0032] The NTC thermistor dielectric material of the present invention can be used to prepare a high-performance NTC thermistor, which is suitable for applications such as precise temperature measurement, precise temperature control, temperature compensation, and surge current suppression. DETAILED DESCRIPTION

[0033] Example 1

[0034] LiLaGa2O5 and ZnTeO4 were synthesized by solid phase method respectively.

[0035] LiLaGa2O5 is prepared using the following process: La2O3, Li2CO3, and Ga2O3 are prepared in a molar ratio of 1 / 2:1 / 2:1, then ground and mixed thoroughly. The mixture of La2O3, Li2CO3, and Ga2O3 is then placed in an alumina crucible and held at 1050°C for 4 hours to yield LiLaGa2O5. The resulting LiLaGa2O5 is cooled, ground, and passed through a 200-mesh sieve for later use.

[0036] ZnTeO4 is prepared using the following process: ZnO and TeO3 are prepared in a 1:1 molar ratio, then ground and mixed thoroughly. The mixture is then placed in an alumina crucible and heated at 580°C for 120 minutes to obtain ZnTeO4. The resulting ZnTeO4 is cooled, ground, and passed through a 200-mesh sieve for later use.

[0037] In this embodiment, the method for preparing the dielectric material of the high-stability and low-resistivity NTC thermistor includes the following steps:

[0038] (1) Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGa2O5, ZnTeO4 and TiO2 are prepared in proportion;

[0039] The weight percentages of various raw materials refer to Table 1;

[0040] (2) crushing and uniformly mixing the Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGa2O5, ZnTeO4 and TiO2 prepared in step (1) to obtain a first mixed powder;

[0041] In this step (2), Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGa2O5, ZnTeO4 and TiO2 are mixed uniformly, anhydrous ethanol is added, and ball milling is performed for 12 hours to obtain a first mixed powder;

[0042] (3) drying the first mixed powder obtained in step (2) in an oven (drying temperature: 78°C, drying time: 9 hours), and then grinding and dispersing the mixture to obtain a second mixed powder;

[0043] (4) placing the second mixed powder obtained in step (3) into a silicon carbon rod electric furnace, calcining it at 1110°C for 4.5 hours, and then cooling it to 20°C (cooling rate of 80°C / hour) to obtain NTC powder;

[0044] (5) Add anhydrous ethanol to the NTC powder obtained in step (4), ball mill for 16 hours, then place the NTC powder in an oven to dry (drying temperature is 90°C, drying time is 8 hours), grind and disperse, and pass through a 200 mesh sieve;

[0045] (6) Adding a binder to the sieved NTC powder and granulating it to obtain a granular material;

[0046] The binder in step (6) is a polyvinyl alcohol solution with a weight percentage concentration of 10%, and the weight of the added polyvinyl alcohol solution is 10% of the weight of the NTC powder;

[0047] (7) pressing the granular material obtained in step (6) into green sheets;

[0048] In this step (7), the granular material obtained in step (6) is first pressed into a disc at a pressure of 22 MPa for 10 minutes; then the disc is isostatically pressed at a pressure of 180 MPa for 10 minutes to obtain a green sheet;

[0049] (8) The green sheet is placed in a silicon-molybdenum rod electric furnace (the temperature rise rate in the silicon-molybdenum rod electric furnace is 80°C / hour), and kept at 1200°C for 3.5 hours to allow the green sheet to discharge the binder and sinter, thereby obtaining the high-stability, low-resistivity NTC thermistor dielectric material (the obtained high-stability, low-resistivity NTC thermistor dielectric material is a ceramic sheet).

[0050] Example 2

[0051] In this embodiment, the preparation process of LiLaGa2O5 and ZnTeO4 is the same as that in Example 1.

[0052] In this embodiment, the method for preparing the dielectric material of the high-stability and low-resistivity NTC thermistor includes the following steps:

[0053] (1) Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGa2O5, ZnTeO4 and TiO2 are prepared in proportion;

[0054] The weight percentages of various raw materials refer to Table 1;

[0055] (2) crushing and uniformly mixing the Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGa2O5, ZnTeO4 and TiO2 prepared in step (1) to obtain a first mixed powder;

[0056] In this step (2), Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGa2O5, ZnTeO4 and TiO2 are mixed uniformly, anhydrous ethanol is added, and ball milling is performed for 20 hours to obtain a first mixed powder;

[0057] (3) drying the first mixed powder obtained in step (2) in an oven (drying temperature: 80°C, drying time: 7 hours), and then grinding and dispersing the mixture to obtain a second mixed powder;

[0058] (4) placing the second mixed powder obtained in step (3) into a silicon carbon rod electric furnace, calcining it at 1150°C for 3 hours, and then cooling it to 25°C (cooling rate of 100°C / hour) to obtain NTC powder;

[0059] (5) Add anhydrous ethanol to the NTC powder obtained in step (4), ball mill for 8 hours, then put the NTC powder into an oven to dry (drying temperature is 75 ° C, drying time is 10 hours), grind and disperse it, and pass it through a 200 mesh sieve;

[0060] (6) Adding a binder to the sieved NTC powder and granulating it to obtain a granular material;

[0061] The binder in step (6) is a polyvinyl alcohol solution with a weight percentage concentration of 10%, and the weight of the added polyvinyl alcohol solution is 8% of the weight of the NTC powder;

[0062] (7) pressing the granular material obtained in step (6) into green sheets;

[0063] In this step (7), the granular material obtained in step (6) is first pressed into a disc at a pressure of 30 MPa for 8 minutes; then the disc is isostatically pressed at a pressure of 200 MPa for 7 minutes to obtain a green sheet;

[0064] (8) The green sheet is placed in a silicon-molybdenum rod electric furnace (the temperature rise rate in the silicon-molybdenum rod electric furnace is 60°C / hour), and kept at 1150°C for 5 hours to allow the green sheet to discharge the binder and sinter, thereby obtaining the high-stability, low-resistivity NTC thermistor dielectric material (the obtained high-stability, low-resistivity NTC thermistor dielectric material is a ceramic sheet).

[0065] Example 3

[0066] In this embodiment, the preparation process of LiLaGa2O5 and ZnTeO4 is the same as that in Example 1.

[0067] In this embodiment, the method for preparing the dielectric material of the high-stability and low-resistivity NTC thermistor includes the following steps:

[0068] (1) Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGa2O5, ZnTeO4 and TiO2 are prepared in proportion;

[0069] The weight percentages of various raw materials refer to Table 1;

[0070] (2) crushing and uniformly mixing the Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGa2O5, ZnTeO4 and TiO2 prepared in step (1) to obtain a first mixed powder;

[0071] In this step (2), Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGa2O5, ZnTeO4 and TiO2 are mixed uniformly, anhydrous ethanol is added, and ball milling is performed for 12 hours to obtain a first mixed powder;

[0072] (3) drying the first mixed powder obtained in step (2) in an oven (drying temperature: 75°C, drying time: 9 hours), and then grinding and dispersing the mixture to obtain a second mixed powder;

[0073] (4) placing the second mixed powder obtained in step (3) into a silicon carbon rod electric furnace, calcining it at 1130°C for 4 hours, and then cooling it to 20°C (cooling rate of 80°C / hour) to obtain NTC powder;

[0074] (5) Add anhydrous ethanol to the NTC powder obtained in step (4), ball mill for 10 hours, then put the NTC powder into an oven to dry (drying temperature is 90 ° C, drying time is 8 hours), grind and disperse it, and pass it through a 200 mesh sieve;

[0075] (6) Adding a binder to the sieved NTC powder and granulating it to obtain a granular material;

[0076] The binder in step (6) is a polyvinyl alcohol solution with a weight percentage concentration of 10%, and the weight of the added polyvinyl alcohol solution is 9.5% of the weight of the NTC powder;

[0077] (7) pressing the granular material obtained in step (6) into green sheets;

[0078] In this step (7), the granular material obtained in step (6) is first pressed into a disc at a pressure of 25 MPa for 10 minutes; then the disc is isostatically pressed at a pressure of 160 MPa for 10 minutes to obtain a green sheet;

[0079] (8) The green sheet is placed in a silicon-molybdenum rod electric furnace (the temperature rise rate in the silicon-molybdenum rod electric furnace is 80°C / hour), and kept at 1180°C for 4 hours to allow the green sheet to discharge the binder and sinter, thereby obtaining the high-stability, low-resistivity NTC thermistor dielectric material (the obtained high-stability, low-resistivity NTC thermistor dielectric material is a ceramic sheet).

[0080] Example 4

[0081] In Example 4, the proportions of various raw materials are shown in Table 1. The method for preparing the high-stability, low-resistivity NTC thermistor dielectric material in Example 4 is the same as that in Example 1.

[0082] Example 5

[0083] In Example 5, the proportions of various raw materials are shown in Table 1. The method for preparing the high-stability, low-resistivity NTC thermistor dielectric material in Example 5 is the same as that in Example 2.

[0084] Example 6

[0085] In Example 6, the proportions of various raw materials are shown in Table 1. The method for preparing the high-stability, low-resistivity NTC thermistor dielectric material in Example 6 is the same as that in Example 3.

[0086] Comparative Example 1

[0087] In Comparative Example 1, the ratios of various raw materials are shown in Table 1. The method for preparing the high-stability, low-resistivity NTC thermistor dielectric material in Comparative Example 1 is the same as that in Example 3. The main difference from Example 3 is that the raw materials in Comparative Example 1 do not contain LiLaGa2O5.

[0088] Comparative Example 2

[0089] In Comparative Example 2, the ratios of various raw materials are shown in Table 1. The method for preparing the high-stability, low-resistivity NTC thermistor dielectric material in Comparative Example 2 is the same as that in Example 3. The difference from Example 3 is that the raw materials in Comparative Example 2 do not contain ZnTeO4.

[0090] Table 1 Formulas of 8 samples in the examples and comparative examples of the present invention (weight percentage)

[0091] Sample number <![CDATA[Mn3O4]]> <![CDATA[Ni2O3]]> CuO <![CDATA[Al2O3]]> ZnO <![CDATA[LiLaGa2O5]]> <![CDATA[ZnTeO4]]> <![CDATA[TiO2]]> Example 1 85 2.7 6 0.8 0.7 3 1.6 0.2 Example 2 86 3.9 5 0.6 0.6 1.7 1.8 0.4 Example 3 87 2.8 5 1.3 1 1.4 1.0 0.5 Example 4 86 3 4.8 0.5 0.6 1.5 2 0.6 Example 5 84 2.7 6 1 0.7 2 3 0.6 Example 6 89 3 5.6 0.5 0.8 0.4 0.5 0.2 Comparative Example 1 87 3.2 6 1.3 1 0 1.0 0.5 Comparative Example 2 87 3.8 5 1.3 1 1.4 0 0.5

[0092] The high-stability, low-resistivity NTC thermistor dielectric materials produced in Examples 1-6 and Comparative Examples 1-2 were furnace-cooled and naturally cooled to room temperature before being used to make thermistors. After the high-stability, low-resistivity NTC thermistor dielectric material (i.e., ceramic sheet) was produced, silver electrodes were applied to both sides before performance testing (5D-9 NTC thermistors were manufactured for performance testing).

[0093] The performance test method is as follows:

[0094] 1) B value of the material

[0095] Using a low-resistance tester, first measure the rated zero-power resistance of the NTC thermistor at temperatures T1 and T2. Based on the thermistor's dielectric ceramic chip size and resistance, use the relevant formula to calculate the resistivity. The material constant B of the ceramic sample (within the -25-200°C temperature range) is calculated as B = ln(ρ1 / ρ2) / ((1 / T1)-(1 / T2)). T1 is 248K, and T2 is 473K.

[0096] 2) Rated zero-power resistivity (25°C)

[0097] Use a low resistance tester to measure the zero-power resistance of the NTC thermistor at 25°C. Based on the size and resistance of the thermistor dielectric ceramic chip, use the relevant formula to calculate the resistivity at 25°C to obtain the rated zero-power resistivity (25°C).

[0098] 3) Resistance delay change rate (after 20 days at 25°C)

[0099] Use a low resistance tester to measure the zero-power resistance of the resistor at 25°C. Then, after 20 days, measure the zero-power resistance value of the resistor at 25°C. Calculate the rate of change of resistance and you can get the resistance delay change rate (after 20 days at 25°C).

[0100] 4) Number of impacts

[0101] The test was performed using a BS4006 thermistor current shock tester. The operating procedures are as follows: (1) Clear the data and input the required shock current (3A) according to the resistance value of the resistor; (2) Place the NTC thermistor dielectric material sample into the tester, cover it with the safety cover, return to the shock interface and press "Shock before resistance value" until the resistance data of each sample before the current shock are displayed; (3) Press the start button, and the tester will automatically perform a current shock test on the sample (repeatedly charge and discharge each thermistor sample through a 330UF capacitor). When a thermistor dielectric material sample is damaged, the tester will display its shock count (which can be saved in the corresponding folder).

[0102] 5) The rate of change of thermistor resistance after shock

[0103] The test was carried out using a BS4006 thermistor current shock tester. The operating procedures are as follows: (1) Clear the data and input the required shock current (3A) according to the sample resistance; (2) Place the thermistor sample into the tester, cover it with the safety cover, return to the shock interface and press "Shock before resistance" until the resistance data of each sample before shock are displayed; (3) Press the start button, and the tester will automatically perform a predetermined number of current shock tests on the sample (repeatedly charge and discharge each thermistor sample 30 times through a 330UF capacitor). At the end of the test, press "Resistance" and the tester will display the resistance value and resistance change rate of each sample after shock (you can click to save it to the corresponding folder).

[0104] 6) Maximum steady-state current (3A) resistance change rate

[0105] The BS4004 steady-state current tester is used for testing. The operating procedures are as follows: (1) clear the data and install the thermistor samples; (2) test the resistance of each thermistor sample before the test; (3) adjust the steady-state current (adjust to 3A); (4) start the test, and each thermistor sample passes the maximum steady-state current (3A). The tester measures the resistance of each thermistor sample after the test and calculates the rate of change of the resistance value after the test relative to the resistance value before the test.

[0106] The properties of the thermistor dielectric materials or thermistor samples of the above embodiments and comparative examples are listed in Table 2.

[0107] Table 2 Performance of the samples of each embodiment and comparative example

[0108] Sample number Room temperature resistivity (Ω·cm) (25℃) B constant (k) (-50-200℃) Resistance delay change rate, 20 days (25℃) Impact times (impact current 3A, 330UF capacitor for charging and discharging) Maximum steady-state current (3A) resistance change rate Resistance change rate after impact (impact current is 3A, 330UF capacitor is charged and discharged 30 times) Example 1 8.0 4210 1.0% 166 1.5% 4.4% Example 2 8.3 4362 0.8% 178 1.2% 3.6% Example 3 9.1 4720 0.5% 186 1.0% 2.6% Example 4 9.6 4572 1.3% 170 2.0% 3.0% Example 5 8.7 4685 1.2% 163 1.7% 4.0% Example 6 9.3 4710 0.7% 180 2.3% 3.8% Comparative Example 1 89 2863 8.6% 96 6.4% 8.3% Comparative Example 2 103 3621 6.7% 78 8.1% 6.9%

[0109] As can be seen from Table 2, the performance range of the samples in the embodiment is as follows: B value is 4210-4720k (temperature range: -25-200℃), room temperature resistivity (ρ 25℃ Within the range of 8Ω·cm to 9.6Ω·cm, the resistance (25°C) delay change rate was 0.5-1.3% (20 days at 25°C), the number of shocks was 163-186 (3A shock current, charging and discharging a 330UF capacitor), the resistance change rate at the maximum steady-state current (3A) was 1.0%-2.3%, and the resistance change rate after the shock was 2.6%-4.4%. The NTC thermistor dielectric materials of each embodiment have excellent current shock resistance, strong current flow resistance, good stability, good product consistency, high reliability, and good temperature sensitivity. Among them, the NTC thermistor or dielectric material of Example 3 has the best overall performance. The NTC thermistors or dielectric materials of Comparative Examples 1 and 2 have poor overall performance.

Claims

1. A high stability and low resistivity NTC thermistor dielectric material, characterized in that The invention is prepared from the following raw materials in the following weight proportions: Mn3O4 79-93%, Ni2O3 2-8%, CuO 1-7%, Al2O3 0.4-2%, ZnO 0.4-1%, LiLaGa2O5 0.2-4%, ZnTeO4 0.3-5%, and TiO2 0.1-0.6%.

2. The high stability and low resistivity NTC thermistor dielectric material according to claim 1, characterized in that The high-stability, low-resistivity NTC thermistor dielectric material is made of the following raw materials in the following weight ratios: Mn3O4 82-91%, Ni2O3 2.5-7%, CuO 2-6%, Al2O3 0.5-1.8%, ZnO 0.6-1%, LiLaGa2O5 0.4-3%, ZnTeO4 0.3-4%, and TiO2 0.1-0.6%.

3. The high stability and low resistivity NTC thermistor dielectric material according to claim 1, characterized in that The high-stability, low-resistivity NTC thermistor dielectric material is made of the following raw materials in the following weight ratios: Mn3O4 85-89%, Ni2O3 2.5-5%, CuO 3-6%, Al2O3 0.6-1.5%, ZnO 0.5-1%, LiLaGa2O5 0.4-2%, ZnTeO4 0.3-3%, and TiO2 0.1-0.6%.

4. The high stability and low resistivity NTC thermistor dielectric material according to any one of claims 1 to 3, characterized in that The LiLaGa2O5 was prepared by the following process: La2O3, Li2CO3 and Ga2O3 were prepared in a molar ratio of 1 / 2:1 / 2:1, and then La2O3, Li2CO3 and Ga2O3 were ground and mixed evenly; then the mixture of La2O3, Li2CO3 and Ga2O3 was placed in an alumina crucible and kept warm at 1050°C for 4 hours to obtain LiLaGa2O5.

5. The high stability and low resistivity NTC thermistor dielectric material according to any one of claims 1 to 3, characterized in that The ZnTeO4 is prepared by the following process: ZnO and TeO3 are prepared in a molar ratio of 1:1, and then the ZnO and TeO3 are ground and mixed uniformly; then the mixture of ZnO and TeO3 is placed in an alumina crucible and kept at 550°C-600°C for 120 minutes to obtain ZnTeO4.

6. The method for preparing the high stability and low resistivity NTC thermistor dielectric material according to claim 1, characterized in that The steps include: (1) Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGa2O5, ZnTeO4 and TiO2 are prepared in proportion; (2) crushing and uniformly mixing the Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGa2O5, ZnTeO4 and TiO2 prepared in step (1) to obtain a first mixed powder; (3) drying the first mixed powder obtained in step (2) in an oven, and then grinding and dispersing the mixed powder to obtain a second mixed powder; (4) placing the second mixed powder obtained in step (3) into a silicon carbon rod electric furnace, calcining at 1100-1150°C for 3-5 hours, and then cooling to 20-30°C to obtain NTC powder; (5) Add anhydrous ethanol to the NTC powder obtained in step (4), ball mill for 8-16 hours, then place the NTC powder in an oven to dry, grind and disperse it, and pass it through a 200 mesh sieve; (6) Adding a binder to the sieved NTC powder and granulating it to obtain a granular material; (7) pressing the granular material obtained in step (6) into green sheets; (8) The green sheet is placed in a silicon-molybdenum rod electric furnace and kept at 1150-1220° C. for 3-5 hours to allow the green sheet to discharge the binder and sinter to obtain the high-stability, low-resistivity NTC thermistor dielectric material.

7. The method for preparing a high-stability, low-resistivity NTC thermistor dielectric material according to claim 6, wherein: In step (2), Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGa2O5, ZnTeO4 and TiO2 are mixed evenly, anhydrous ethanol is added, and ball milling is performed for 8-20 hours to obtain a first mixed powder.

8. The high-stability, low-resistivity NTC thermistor dielectric material according to claim 6, characterized in that: The binder in step (6) is a polyvinyl alcohol solution with a weight percentage concentration of 10%, and the weight of the added polyvinyl alcohol solution is 8-10% of the weight of the NTC powder.

9. The high-stability, low-resistivity NTC thermistor dielectric material according to claim 6, characterized in that: In step (7), the granular material obtained in step (6) is first pressed into a disc at a pressure of 20-30 MPa for 7-12 minutes; then the disc is isostatically pressed at a pressure of 100-200 MPa for 7-12 minutes to obtain a green sheet.

10. The high-stability, low-resistivity NTC thermistor dielectric material according to claim 6, characterized in that: In step (8), the temperature in the silicon-molybdenum rod electric furnace is raised at a rate of 50-120°C / hour.