High-b-value low-resistivity ntc thermistor dielectric material and preparation method thereof

Abstract

A high-B-value low-resistivity NTC thermistor medium material is made of raw materials with the following weight ratio: Mn3O 4 80-92%, Ni2O 3 1-5%, CuO 2-8%, Al2O 3 0.5-2%, ZnO 0.5-1%, LiLaGeO 4 0.4-3%, NaAlSi2O 6 0.2-4%, TiO 2 0.1-0.8%. The high-B-value low-resistivity NTC thermistor medium material has the following advantages: (1) the material constant B value is high, the B value is 4810-5625K at -25-200 DEG C; (2) the prepared NTC thermistor has high sensitivity, good stability and good current impact resistance; after the maximum steady-state current, the product resistivity changes little; the delay resistance change rate is small; it is suitable for precise measurement and precise control of temperature and other aspects; (3) the resistivity is low, the room temperature resistivity (rho 25℃ ) is in the range of 8.1 ohm-cm~9.4 ohm-cm; (4) the sintering temperature of the NTC thermistor ceramic is low, which is 1130-1200 DEG C.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of information functional material products, and particularly relates to a high-B-value low-resistivity NTC thermistor medium material and a preparation method thereof. BACKGROUND

[0002] An NTC (negative temperature coefficient) thermistor refers to a resistor whose resistance decreases with the increase of temperature. Due to its temperature sensitivity, fast response and high measurement accuracy, the NTC thermistor is widely used in temperature measurement, temperature control, temperature compensation, surge current suppression and the like. NTC thermistor ceramic material is a widely studied thermistor medium material, which is usually composed of oxides of transition metal elements such as nickel, copper, aluminum, manganese and chromium. Most of the researches on NTC thermistor medium materials are focused on NTC thermistor medium materials with relatively high resistivity. In addition, even for medium materials with low resistivity, the B value of the thermosensitive constant is relatively low (about 3000K), and the room temperature resistivity and the thermosensitive constant B change greatly with the extension of time. The research on medium materials of high-B-value high-stability low-resistivity NTC thermistors is relatively less. The relationship between the resistivity of the NTC thermistor and the temperature conforms to the Arrhenius exponential relationship: ρ=ρ0exp(E a / kT), ρ and ρ0 are the resistivity at T (absolute temperature) and infinity, respectively, k is the Boltzmann constant, and E a is the activation energy. The resistivity at room temperature (25℃) and the thermosensitive constant B are usually used to characterize the thermosensitive material, and the relationship between the thermosensitive constant and the activation energy is: B=E a / k, the thermosensitive 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 resistances at T and T0 (absolute temperature), respectively. The resistance temperature coefficient is: α T =1 / R(dR / dT)= -B / T 2 , the thermosensitive constant B represents the sensitivity of the NTC thermistor to temperature, the greater the B value, the greater the change rate of the resistance of the NTC thermistor to temperature, and the better the sensitivity of the material to temperature.

[0003] The B value of the commonly used low resistivity NTC thermistor is 2000-3000K; with the extension of time, the change rate of the room temperature resistance is greater than 10%, and the stability is relatively poor. In order to improve the sensitivity and stability of the NTC thermistor to meet the requirements of high-precision temperature measurement and control, the B value should be above 3000K, and the resistance time change rate is less than 3%. At present, the resistance of the NTC thermistor has the problem of poor stability, and with the extension of the storage time, the rated zero power resistivity change is relatively large; the impact number (330UF capacitor charging and discharging) is relatively small; the resistance change rate under the maximum steady-state current (3A) is relatively large; the resistance change rate under the maximum steady-state current is relatively large. Therefore, it is necessary to develop a high-B-value and low-resistivity NTC thermistor medium material with good stability to meet the high-end application of accurate temperature measurement and temperature control. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a high-B-value and low-resistivity NTC thermistor medium material and a preparation method thereof. The NTC thermistor medium material has a high B value and low resistivity at -25-200℃. The technical scheme adopted is as follows:

[0005] A high-B-value and low-resistivity NTC thermistor medium material is characterized by being made of the following raw materials in a certain weight ratio: Mn3O480-92%, Ni2O31-5%, CuO 2-8%, Al2O30.5-2%, ZnO 0.5-1%, LiLaGeO40.4-3%, NaAlSi2O60.2-4%, TiO20.1-0.8%.

[0006] In a preferred embodiment, the high-B-value and low-resistivity NTC thermistor medium material is made of the following raw materials in a certain weight ratio: Mn3O483-91%, Ni2O31.5-4%, CuO 3-7%, Al2O30.6-1.5%, ZnO 0.8-1%, LiLaGeO40.4-2%, NaAlSi2O60.2-3%, TiO20.1-0.6%.

[0007] In another preferred embodiment, the high-B-value and low-resistivity NTC thermistor medium material is made of the following raw materials in a certain weight ratio: Mn3O485-89%, Ni2O31.5-3%, CuO 3-7%, Al2O30.6-1%, ZnO 0.5-1%, LiLaGeO40.4-2%, NaAlSi2O60.2-2%, TiO20.1-0.6%.

[0008] Preferably, the LiLaGeO4 and NaAlSi2O6 are synthesized by a solid phase method using conventional chemical raw materials.

[0009] The Mn3O4, Ni2O3 and CuO constitute a Mn3O4-Ni2O3-CuO three-element main material system, wherein: Mn3O4 is a main element of the NTC thermistor ceramic material, and together with LiLaGeO4 and NaAlSi2O6, it affects the resistivity of the NTC thermistor ceramic material; Ni2O3 and LiLaGeO4 and NaAlSi2O6 together can affect the B value; CuO and LiLaGeO4 affect the sintering temperature of the material (the addition amount of CuO and LiLaGeO4 affects the sintering temperature, and as the addition amount increases, the sintering temperature decreases). ZnO, TiO2, LiLaGeO4 and NaAlSi2O6 can improve the density of the ceramic material, and affect the resistance delay rate of the NTC thermistor ceramic material, the change rate of the maximum steady-state current resistance, the impact number, and the resistance change rate after impact.

[0010] The LiLaGeO4 can be prepared by the following process: La2O3, Li2CO3 and GeO2 are prepared in a molar ratio of 1 / 2:1 / 2:1, and then the La2O3, Li2CO3 and GeO2 are ground and mixed uniformly; then the mixture of La2O3, Li2CO3 and GeO2 is placed in an alumina crucible, and is kept at 1070°C for 4 hours to obtain LiLaGeO4. After cooling, the obtained LiLaGeO4 is ground and sieved through a 200 mesh sieve for standby use.

[0011] The NaAlSi2O6 can be prepared by the following process: Na2CO3, Al2O3 and SiO2 are prepared in a molar ratio of 1 / 2:1 / 2:2, and then the Na2CO3, Al2O3 and SiO2 are ground and mixed uniformly; then the mixture of Na2CO3, Al2O3 and SiO2 is placed in an alumina crucible, and is kept at 1200-1230°C for 120 minutes to obtain NaAlSi2O6. After cooling, the obtained NaAlSi2O6 is ground and sieved through a 200 mesh sieve for standby use.

[0012] The application also provides a preparation method of the high-B-value and low-resistivity NTC thermistor medium material, which comprises the following steps:

[0013] (1) Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGeO4, NaAlSi2O6 and TiO2 are prepared in proportion;

[0014] (2) the Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGeO4, NaAlSi2O6 and TiO2 prepared in step (1) are ground and mixed uniformly 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 for a drying time of 7-10 hours), and then grinding and dispersing 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 1050-1100°C for 3-5 hours, and then cooling to 20-30°C (preferably at a cooling rate of 50-100°C / hour) to obtain the NTC powder;

[0017] (5) adding anhydrous ethanol to the NTC powder obtained in step (4), ball-milling for 8-16 hours, and then drying the NTC powder in an oven (preferably at a drying temperature of 70-100°C and for a drying time of 7-10 hours), and then grinding and dispersing and passing through a 200-mesh sieve;

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

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

[0020] (8) placing the green sheet into a silicon-molybdenum rod electric furnace, and heat-treating at 1130-1200°C for 3-5 hours to make the green sheet discharge the binder and sinter to obtain the high-B-value low-resistivity NTC thermistor medium material (the high-B-value low-resistivity NTC thermistor medium material obtained is a ceramic sheet).

[0021] In step (2), the various raw materials can be ground and then mixed uniformly, or the various raw materials can be mixed and then ground and mixed simultaneously, or the various raw materials can be mixed uniformly after being ground. The grinding equipment can be a ball mill or other grinding equipment.

[0022] Preferably, in step (2), the Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGeO4, NaAlSi2O6 and TiO2 are mixed uniformly, anhydrous ethanol is added, and ball-milling is performed for 8-20 hours to obtain the first mixed powder.

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

[0024] Preferably, in step (7), the granular material obtained in step (6) is first pressed into a round sheet under a pressure of 20-30 MPa for 7-12 minutes, and then is subjected to isostatic pressing under 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 raised at a rate of 50-120 ℃ / h.

[0026] The prepared high-B-value low-resistivity NTC thermistor medium material is cooled in the furnace and naturally cooled to room temperature, and can be used to make a thermistor. After the high-B-value low-resistivity NTC thermistor medium material (i.e. ceramic sheet) is prepared, silver electrodes are applied to both sides of the ceramic sheet, and then performance testing can be performed.

[0027] Compared with the prior art, the high-B-value low-resistivity NTC thermistor medium material of the present application has the following advantages:

[0028] (1) The material constant B value is high, and the B value is 4810-5625 K at -25-200 ℃.

[0029] (2) The prepared NTC thermistor has high sensitivity, good stability, good current impact resistance (high impact frequency and small resistance change rate after impact), small resistance change rate after the maximum steady-state current, small time delay resistance change rate, and is suitable for precise temperature measurement and precise temperature control.

[0030] (3) The resistivity is low, and the room temperature resistivity (ρ 25℃ ) is in the range of 8.1 Ω·cm-9.4 Ω·cm.

[0031] (4) The sintering temperature of the NTC thermistor ceramic is low, and is 1130-1200 ℃.

[0032] The high-B-value low-resistivity NTC thermistor medium material of the present application is used to prepare an NTC thermistor, and is suitable for precise temperature measurement, precise temperature control, temperature compensation, and surge current suppression. DETAILED DESCRIPTION

[0033] Example 1

[0034] LiLaGeO4 and NaAlSi2O6 are synthesized by a solid phase method.

[0035] LiLaGeO4 is prepared by the following process: La2O3, Li2CO3 and GeO2 are prepared in a molar ratio of 1 / 2:1 / 2:1, and then the La2O3, Li2CO3 and GeO2 are ground and mixed uniformly; the mixture of the La2O3, Li2CO3 and GeO2 is then placed in an alumina crucible, and heat-treated at 1070°C for 4 hours to obtain LiLaGeO4. The obtained LiLaGeO4 is cooled, ground and passed through a 200-mesh sieve, and is ready for use.

[0036] NaAlSi2O6 is prepared by the following process: Na2CO3, Al2O3 and SiO2 are prepared in a molar ratio of 1 / 2:1 / 2:2, and then the Na2CO3, Al2O3 and SiO2 are ground and mixed uniformly; the mixture of the Na2CO3, Al2O3 and SiO2 is then placed in an alumina crucible, and heat-treated at 1220°C for 120 minutes to obtain NaAlSi2O6. The obtained NaAlSi2O6 is cooled, ground and passed through a 200-mesh sieve, and is ready for use.

[0037] In this embodiment, the preparation method of the high-B-value and low-resistivity NTC thermistor dielectric material comprises the following steps:

[0038] (1) Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGeO4, NaAlSi2O6 and TiO2 are prepared in a proportion;

[0039] The weight percentage of each raw material is shown in Table 1;

[0040] (2) The Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGeO4, NaAlSi2O6 and TiO2 prepared in step (1) are ground and mixed uniformly to obtain a first mixed powder;

[0041] In this step (2), after the Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGeO4, NaAlSi2O6 and TiO2 are uniformly mixed, anhydrous ethanol is added, and ball milling is performed for 10 hours to obtain the first mixed powder;

[0042] (3) The first mixed powder obtained in step (2) is dried in an oven (drying temperature is 70°C, and drying time is 10 hours), and then ground and dispersed to obtain a second mixed powder;

[0043] (4) The second mixed powder obtained in step (3) is placed in a silicon-carbon rod electric furnace, and calcined at 1050°C for 5 hours, and then cooled to 20°C (cooling rate is 50°C / hour) to obtain an NTC powder;

[0044] (5) adding anhydrous ethanol into the NTC powder obtained in step (4), ball-milling for 16 hours, then drying the NTC powder in an oven (drying temperature is 100°C, drying time is 7 hours), grinding and dispersing again, and passing through a 200-mesh sieve;

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

[0046] The binder used in this step (6) is a polyvinyl alcohol solution with a concentration of 10% by weight, and the weight of the added polyvinyl alcohol solution is 8.5% of the weight of the NTC powder;

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

[0048] In this step (7), the granular material obtained in step (6) is first pressed into a round sheet at a pressure of 20 MPa for 12 minutes, and then isostatic pressing is performed on the round sheet at a pressure of 100 MPa for 12 minutes to obtain a green sheet;

[0049] (8) placing the green sheet into a silicon-molybdenum rod electric furnace (the temperature in the silicon-molybdenum rod electric furnace is raised at a rate of 50°C / hour), and keeping the temperature at 1130°C for 5 hours to make the green sheet discharge the binder and sinter, thereby obtaining the high-B-value low-resistivity NTC thermistor medium material (the prepared high-B-value low-resistivity NTC thermistor medium material is a ceramic sheet).

[0050] Example 2

[0051] In this embodiment, the preparation processes of LiLaGeO4 and NaAlSi2O6 are the same as those in Example 1.

[0052] In this embodiment, the preparation method of the high-B-value low-resistivity NTC thermistor medium material includes the following steps:

[0053] (1) preparing Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGeO4, NaAlSi2O6 and TiO2 in proportion;

[0054] The weight percentages of various raw materials are shown in Table 1;

[0055] (2) crushing and uniformly mixing the Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGeO4, NaAlSi2O6 and TiO2 prepared in step (1) to obtain a first mixed powder;

[0056] In step (2), Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGeO4, NaAlSi2O6 and TiO2 are mixed uniformly, anhydrous ethanol is added, and ball milling is performed for 12 hours to obtain a first mixed powder;

[0057] (3) The first mixed powder obtained in step (2) is dried in an oven (drying temperature is 75°C, and drying time is 9 hours), and then ground and dispersed to obtain a second mixed powder;

[0058] (4) The second mixed powder obtained in step (3) is placed in a silicon-carbon rod electric furnace, calcined at 1080°C for 4 hours, and then cooled to 25°C (cooling rate is 80°C / hour) to obtain an NTC powder;

[0059] (5) Anhydrous ethanol is added to the NTC powder obtained in step (4), ball milling is performed for 11 hours, and then the NTC powder is dried in an oven (drying temperature is 90°C, and drying time is 8 hours), and then ground and dispersed, and passed through a 200-mesh sieve;

[0060] (6) A binder is added to the sieved NTC powder, and granulation is performed to obtain a granular material;

[0061] In step (6), the binder is a polyvinyl alcohol solution with a weight percentage concentration of 10%, and the weight of the polyvinyl alcohol solution added is 9.5% of the weight of the NTC powder;

[0062] (7) The granular material obtained in step (6) is pressed into a green sheet;

[0063] In step (7), the granular material obtained in step (6) is first pressed into a round sheet at a pressure of 25MPa for 9 minutes, and then isostatic pressing is performed on the round sheet at a pressure of 150MPa for 10 minutes to obtain a green sheet;

[0064] (8) The green sheet is placed in a silicon-molybdenum rod electric furnace (temperature in the silicon-molybdenum rod electric furnace is raised at a rate of 80°C / hour), and is kept at 1180°C for 4 hours to remove the binder and sinter the green sheet to obtain the high-B-value low-resistivity NTC thermistor medium material (the prepared high-B-value low-resistivity NTC thermistor medium material is a ceramic sheet).

[0065] Example 3

[0066] In this example, the preparation process of LiLaGeO4 and NaAlSi2O6 is the same as that in Example 1.

[0067] In this example, the preparation method of the high-B-value low-resistivity NTC thermistor medium material comprises the following steps:

[0068] (1) proportioning Mn304, Ni203, CuO, Al203, ZnO, LiLaGeO4, NaAlSi2O6 and TiO2 by weight percentage;

[0069] The weight percentage of each raw material is shown in Table 1;

[0070] (2) crushing and mixing the proportioned Mn304, Ni203, CuO, Al203, ZnO, LiLaGeO4, NaAlSi2O6 and TiO2 in step (1) to obtain a first mixed powder;

[0071] In this step (2), after the Mn304, Ni203, CuO, Al203, ZnO, LiLaGeO4, NaAlSi2O6 and TiO2 are mixed evenly, anhydrous ethanol is added and ball-milled for 18 hours to obtain the first mixed powder;

[0072] (3) drying the first mixed powder obtained in step (2) in an oven (drying temperature is 80°C and drying time is 8 hours), and then grinding and dispersing 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 at 1100°C for 3 hours, and then cooling to 30°C (cooling rate is 100°C / hour) to obtain an NTC powder;

[0074] (5) adding anhydrous ethanol to the NTC powder obtained in step (4) and ball-milling for 8 hours, and then placing the NTC powder into an oven for drying (drying temperature is 70°C and drying time is 10 hours), and then grinding and dispersing and passing through a 200-mesh sieve;

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

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

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

[0078] In this step (7), the granular material obtained in step (6) is first pressed into a round sheet at a pressure of 28MPa for 8 minutes, and then the round sheet is subjected to isostatic pressing at a pressure of 200MPa for 7 minutes to obtain a green sheet;

[0079] (8) Put the green sheet into a silicon-molybdenum rod electric furnace (the temperature of the silicon-molybdenum rod electric furnace is raised at a speed of 120°C / hour), and keep the temperature at 1200°C for 3 hours, so that the green sheet is debinded and sintered, and the high-B-value low-resistivity NTC thermistor dielectric material is obtained (the high-B-value low-resistivity NTC thermistor dielectric material obtained 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-B-value 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-B-value 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-B-value 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 proportions of various raw materials are shown in Table 1. The method for preparing the high-B-value low-resistivity NTC thermistor dielectric material in Comparative Example 1 is the same as that in Example 1 and 4. The main difference from Example 4 is that the raw materials of Comparative Example 1 do not contain LiLaGeO4.

[0088] Comparative Example 2

[0089] In Comparative Example 2, the proportions of various raw materials are shown in Table 1. The method for preparing the high-B-value low-resistivity NTC thermistor dielectric material in Comparative Example 2 is the same as that in Example 1 and 4. The main difference from Example 4 is that the raw materials of Comparative Example 2 do not contain NaAlSi2O6.

[0090] Table 1 Formulation (weight percentage) of 8 samples of the examples and comparative examples of the present application

[0091] Sample No. Mn304 [Ni2O3] CuO Al2O3 ZnO LiLaGeO4 NaAlSi206 TiO2 Example 1 86 2.5 5 0.7 0.8 2 2.5 0.5 Example 2 87 3.2 4.5 0.9 0.9 1.5 1.5 0.5 Example 3 90 1.8 3 1 1 1.5 1.1 0.6 Example 4 84 3 6.3 1.2 0.5 2 2.5 0.5 Example 5 85 4 7 1 0.5 0.5 1.5 0.5 Example 6 85 3.5 5.0 1.5 0.8 1.6 2 0.6 Comparative Example 1 86 3 6.3 1.2 0.5 0 2.5 0.5 Comparative Example 2 86.5 3 6.3 1.2 0.5 2 0 0.5

[0092] The high-B-value low-resistivity NTC thermistor dielectric material obtained in Examples 1-6 and Comparative Examples 1-2 can be used to make thermistors after being cooled in the furnace and naturally cooled to room temperature. After the high-B-value low-resistivity NTC thermistor dielectric material (i.e. ceramic sheet) is obtained, silver electrodes are applied to both sides of the ceramic sheet, and then performance testing can be performed.

[0093] The performance testing method is as follows:

[0094] 1) B value of the material

[0095] Using a low resistance tester, first measure the NTC thermistor at the temperature of T1 and T2 rated zero power resistance, according to the thermistor medium ceramic chip size and resistance value, using the relevant formula to calculate the resistivity, B = ln (p1 / p2) / ((1 / T1) - (1 / T2)) to calculate the ceramic sample material constant B (in the temperature range of -25-200 ℃). T1 is 248K, T2 is 473K.

[0096] 2) Rated zero power resistivity (25℃)

[0097] Using a low resistance tester, measure the NTC thermistor at 25℃ zero power resistance, according to the thermistor medium ceramic chip size and resistance, according to the thermistor medium ceramic chip size and resistance, using the relevant formula to calculate the resistivity at 25℃, the rated zero power resistivity (25℃) can be obtained.

[0098] 3) Resistance delay change rate (placed for 20 days (25℃))

[0099] Using a low resistance tester, start measuring the zero power resistance of the resistor at 25℃, then after 20 days, measure the zero power resistance value of the resistance at 25℃, calculate the change rate of the resistance, and the resistance delay change rate (placed for 20 days (25℃)) can be obtained.

[0100] 4) Impact times

[0101] Using BS4006 thermistor current impact tester, the operation process is as follows: (1) clear the data, input the required impact current (3A) according to the resistance value; (2) put the NTC thermistor medium material sample into the tester, cover the safety cover, return to the impact interface and press "resistance value front impact", wait for the resistance value data of each sample before current impact to be displayed; (3) press the start button, the tester automatically performs current impact test on the sample (through 330UF capacitor to repeatedly charge and discharge each thermistor sample), when a certain thermistor medium material sample is damaged, the tester displays the impact times (which can be saved to the corresponding folder).

[0102] 5) Change rate of thermistor resistance value after impact

[0103] The BS4006 thermal sensitive current impact tester is used for testing, and the operation process is as follows: (1) clear the data, input the required impact current (3A) according to the sample resistance; (2) put the thermal resistor sample into the tester, cover the safety cover, return to the impact interface and press "resistance pre-impact", wait for the pre-impact resistance data of each sample to be displayed; (3) press the start button, the tester automatically performs the predetermined number of current impact test on the sample (30 times of charging and discharging on each thermal resistor sample through 330UF capacitor), and when the test is completed, press "resistance" to display the post-impact resistance and resistance change rate of each sample (click to save to the corresponding folder).

[0104] 6) maximum steady current (3A) resistance change rate

[0105] The BS4004 steady current tester is used for testing, and the operation process is as follows: (1) clear the data, and install the thermal resistor sample; (2) test the resistance of each thermal resistor sample before the test; (3) adjust the steady current (adjust to 3A); (4) start testing, each thermal resistor sample passes through the maximum steady current (3A), the tester measures the resistance of each thermal resistor sample after the test, and calculates the change rate of the resistance after the test relative to the resistance before the test.

[0106] The performance of the thermal resistor medium material or thermal resistor sample of each of the above examples and comparative examples is listed in Table 2.

[0107] Table 2: Performance of sample of each example and comparative example

[0108] Sample No. Room temperature resistivity (Ω-cm) (25°C) B constant (k) (-25-200°C) Resistance change rate with time, 20 days (25°C) Number of impacts (impulse current 3A, 330 UF capacitor for charging and discharging) Maximum steady current (3A) resistance change rate Resistance change rate after impact (impulse current 3A, 330 UF capacitor for charging and discharging 30 times) Example 1 8.1 4810 1.85% 121 4.8% 7.6% Example 2 8.6 5182 2.50% 132 4.2% 7.4% Example 3 9.1 5516 2.62% 128 4.4% 6.8% Example 4 9.7 5625 1.5% 140 3.6% 7.3% Example 5 9.0 5385 2.83% 118 4.6% 8.1% Example 6 9.4 5108 3.0% 116 6.8% 7.8% Comparative Example 1 46 2670 6.3% 96 8.3% 13.3% Comparative Example 2 72 3156 10.4% 118 9.6% 21.6%

[0109] As can be seen from Table 2, the performance of the examples is as follows: the B value is 4810-5625k (temperature range: -25-200℃), the room temperature resistivity (ρ 25℃ ) is in the range of 8.1Ω·cm~9.7Ω·cm, the resistance (25℃) delay change rate is 1.5~3%, the impact number is 116~140 (impact current 3A, 330UF capacitor charging and discharging), the maximum steady current (3A) resistance change rate is 4.6%~6.8%, and the post-impact resistance change rate is 7.3%~8.1%. The NTC thermal resistor medium material of each example has good current impact resistance, strong current resistance, good product consistency, high reliability, and good temperature sensitivity. Among them, the NTC thermal resistor or medium material of Example 4 has the best comprehensive performance. The performance of Comparative Examples 1 and 2 is relatively poor, and is not as good as that of the examples.

Claims

1. A high B-value, low resistivity NTC thermistor dielectric material, characterized in that... It is made from the following raw materials in the following weight ratio: Mn3O4 80-92%, Ni2O3 1-5%, CuO 2-8%, Al2O3 0.5-2%, ZnO 0.5-1%, LiLaGeO4 0.4-3%, NaAlSi2O6 0.2-4%, TiO2 0.1-0.8%.

2. The high B-value, low resistivity NTC thermistor dielectric material according to claim 1, characterized in that... The high B-value, low resistivity NTC thermistor dielectric material is made from the following raw materials in the following weight ratios: Mn3O4 83-91%, Ni2O3 1.5-4%, CuO 3-7%, Al2O3 0.6-1.5%, ZnO 0.8-1%, LiLaGeO4 0.4-2%, NaAlSi2O6 0.2-3%, TiO2 0.1-0.6%.

3. The high B-value, low resistivity NTC thermistor dielectric material according to claim 1, characterized in that... The high B-value, low resistivity NTC thermistor dielectric material is made from the following raw materials in the following weight ratio: Mn3O4 85-89%, Ni2O3 1.5-3%, CuO 3-7%, Al2O3 0.6-1%, ZnO 0.5-1%, LiLaGeO4 0.4-2%, NaAlSi2O6 0.2-2%, TiO2 0.1-0.6%.

4. The high B-value, low resistivity NTC thermistor dielectric material according to any one of claims 1-3, characterized in that... LiLaGeO4 is prepared by the following process: La2O3, Li2CO3 and GeO2 are prepared in a molar ratio of 1 / 2:1 / 2:1, and then the La2O3, Li2CO3 and GeO2 are ground and mixed evenly; then the mixture of La2O3, Li2CO3 and GeO2 is placed in an alumina crucible and kept at 1070℃ for 4 hours to obtain LiLaGeO4.

5. The high B-value, low resistivity NTC thermistor dielectric material according to any one of claims 1-3, characterized in that... NaAlSi2O6 is prepared by the following process: Na2CO3, Al2O3 and SiO2 are prepared in a molar ratio of 1 / 2:1 / 2:2, and then the Na2CO3, Al2O3 and SiO2 are ground and mixed evenly; then the mixture of Na2CO3, Al2O3 and SiO2 is placed in an alumina crucible and kept at 1200-1230℃ for 120 minutes to obtain NaAlSi2O6.

6. The method for preparing the high B-value, low resistivity NTC thermistor dielectric material according to claim 1, characterized in that... Includes the following steps: (1) Prepare Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGeO4, NaAlSi2O6 and TiO2 in proportion; (2) The Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGeO4, NaAlSi2O6 and TiO2 prepared in step (1) are crushed and mixed evenly to obtain the first mixed powder; (3) The first mixed powder obtained in step (2) is dried in an oven, and then ground and dispersed to obtain the second mixed powder; (4) The second mixed powder obtained in step (3) is placed in a silicon carbide rod electric furnace and calcined at 1050-1100℃ for 3-5 hours, and then cooled to 20-30℃ to obtain NTC powder; (5) Add anhydrous ethanol to the NTC powder obtained in step (4), ball mill for 8-16 hours, then put the NTC powder into an oven to dry, then grind and disperse, and pass through a 200-mesh sieve; (6) Add a binder to the sieved NTC powder and granulate it to obtain granular material; (7) Press the granular material obtained in step (6) into green sheets; (8) Place the green sheet into a silicon molybdenum rod electric furnace and keep it at 1130-1200℃ for 3-5 hours to allow the binder to be discharged from the green sheet and sintered to obtain the high B value low resistivity NTC thermistor dielectric material.

7. The method for preparing the high B-value, low resistivity NTC thermistor dielectric material according to claim 1, characterized in that: In step (2), after Mn3O4, Ni2O3, CuO, Al2O3, ZnO, LiLaGeO4, NaAlSi2O6 and TiO2 are mixed evenly, anhydrous ethanol is added, and the mixture is ball-milled for 8-20 hours to obtain the first mixed powder.

8. The method for preparing the high B-value, low resistivity NTC thermistor dielectric material according to claim 6, characterized in that: The adhesive used 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 method for preparing the high B-value, 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 under a pressure of 20-30 MPa for 7-12 minutes; then the disc is subjected to isostatic pressing under a pressure of 100-200 MPa for 7-12 minutes to obtain a green disc.

10. The method for preparing the high B-value, low resistivity NTC thermistor dielectric material according to claim 6, characterized in that: In step (8), the temperature rise rate in the silicon molybdenum rod electric furnace is 50-120℃ / hour.