NTC thermistor resistant to 100 degrees celsius low temperature and preparation method thereof

Abstract

The application discloses a kind of 100 ℃ low temperature resistant NTC thermistor and preparation method thereof, it is related to thermistor technical field.The application first metal oxide mixed powder is added into dispersing agent and is pressed into NTC thermistor matrix by isostatic pressing process;Silicon carbide, silver nitrate, sodium chloride are reacted to obtain silver-loaded silicon carbide, the silver-loaded silicon carbide is reacted with silane coupling agent to obtain modified silicon carbide;Polytetrafluoroethylene and acrylic acid are reacted under irradiation to obtain modified polytetrafluoroethylene;Modified silicon carbide and modified polytetrafluoroethylene are condensed to obtain conductive aerogel;After NTC thermistor matrix outer layer is wrapped with conductive aerogel, NTC thermistor is prepared by microwave sintering process.The application uses a kind of low temperature resistant conductive aerogel to replace conductive silver paste, which can still maintain good performance stability at low temperature.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thermistor, in particular to a NTC thermistor resistant to-100 DEG C low temperature and a preparation method thereof. BACKGROUND

[0002] As a key component of temperature sensor, thermistor is widely used in many fields. NTC thermistor plays an important role in temperature measurement and temperature control due to its negative temperature coefficient characteristic, i.e. the resistance value decreases with the increase of temperature. In some special application scenarios, such as meteorological monitoring equipment in extremely cold regions, aerospace instruments in low temperature environment, and ultra-low temperature experimental equipment, stable operation under extreme low temperature conditions is required, which puts forward high requirements on the low temperature performance of NTC thermistor.

[0003] Traditional NTC thermistor is usually designed for normal temperature or slightly wide temperature range. When the temperature decreases to-100 DEG C, the existing NTC thermistor material will have problems such as unstable performance, decreased precision, and slow response speed. Some existing low temperature resistant thermistors either have complex preparation process and high cost, which limits large-scale application, or the key performance indicators such as precision and stability under low temperature still cannot meet the actual demand. Therefore, it is of important practical significance and application value to develop a NTC thermistor which is resistant to-100 DEG C low temperature, has good performance, and has relatively simple and feasible preparation process. SUMMARY

[0004] The present application relates to the technical field of thermistor, in particular to a NTC thermistor resistant to-100 DEG C low temperature and a preparation method thereof.

[0005] In order to solve the above technical problems, the present application provides the following technical scheme: the NTC thermistor resistant to-100 DEG C low temperature is prepared by adding metal oxide mixed powder into a dispersing agent, pressing into a NTC thermistor base body by isostatic pressing process, wrapping the NTC thermistor base body with conductive aerogel, and then adopting microwave sintering; the conductive aerogel is prepared by condensation reaction of modified silicon carbide and modified polytetrafluoroethylene; the modified silicon carbide is prepared by reaction of silicon carbide, silver nitrate and sodium chloride to obtain silver-loaded silicon carbide, and then reaction of the silver-loaded silicon carbide and silane coupling agent; and the modified polytetrafluoroethylene is prepared by reaction of polytetrafluoroethylene and acrylic acid under irradiation.

[0006] Further, a NTC thermistor resistant to-100 DEG C low temperature comprises the following preparation steps:

[0007] (1) Put the mixed metal oxide mixture obtained by mixing MnO2, Co3O4, NiO according to the molar percentage (48%~55%):(25%~30%):(15%~23%) into a agate bowl for the first time ball milling, mix the metal oxide mixture: zirconium oxide ball: anhydrous ethanol according to the mass ratio of 1:2~3:1, alternate wet milling clockwise and anticlockwise, the interval time is 30 min, ball mill for 4h to obtain powder, mix the powder, dispersing agent, deionized water according to the mass ratio of 1:(0.01~0.02):(1.5~2), place in a drying oven, dry at 110~120℃, 7~10Pa for 1~2h, use the planetary ball mill for the second time ball milling at 500r / min for 8h, pass through 100 mesh sieve to obtain the precursor powder;

[0008] (2) Put the precursor powder into the hydraulic machine and keep pressure for 1min, then use the isostatic press with the pressure of 300MPa to keep pressure for 4min, the pressure is 5~10kN, to obtain the ceramic green body, place the ceramic green body in the microwave sintering furnace, heat at the rate of 10℃ / min to 500℃, take out after sintering for 30min to obtain the NTC thermistor substrate;

[0009] (3) Mix and stir evenly silicon carbide, 10% nitric acid aqueous solution, silver nitrate, sodium chloride, deionized water and anhydrous ethanol according to the mass ratio of 1:(15~20):(0.1~0.2):(0.1~0.2):30:100, stir at 70~80℃, 300~500r / min for 10~12h, filter, wash the filter cake with anhydrous ethanol and deionized water for 3~5 times, place in a drying oven, dry at 60~70℃, 5~8Pa for 12~14h to obtain silver-loaded silicon carbide; mix and stir evenly the silver-loaded silicon carbide, silane coupling agent, ethanol according to the mass ratio of 1:(0.04~0.05):(20~30), reflux at 90~100℃, 300~500r / min for 3~4h, filter, wash the filter cake with anhydrous ethanol for 2~3 times, place in a drying oven, dry at 70℃, 7~10Pa for 4h to obtain modified silicon carbide;

[0010] (4) Mix polytetrafluoroethylene, acrylic acid, ferrous ammonium sulfate hexahydrate, 50% sulfuric acid aqueous solution and ethanol according to the mass ratio of 1:(0.5~0.7):(0.01~0.02):(2~2.5):(5~10) under nitrogen atmosphere, irradiate at 25~30℃ with γ-rays with the radiation dose of 10~20kGy for 10~15h, filter, wash the filter cake with deionized water for 2~3 times, place in a drying oven, dry at 60℃, 5~7Pa for 2h to obtain modified polytetrafluoroethylene;

[0011] (5) mixing modified silicon carbide, modified polytetrafluoroethylene, dicyclohexyl carbodiimide, triethylamine and N,N-dimethylformamide according to a mass ratio of 1:(0.3-0.5):(1-1.2):(2-3):(10-20), stirring at 25-30℃ and 300-500r / min for 10-12h, filtering, taking the solid, placing in a drying box, drying at 60-70℃ and 6-10Pa for 4-6h to obtain functional silicon carbide; mixing silicon source, 0.5mol / L hydrochloric acid aqueous solution and anhydrous ethanol according to a ratio of 1:(0.05-0.08):(4-6), stirring at 40-50℃ and 300-500r / min for 1-2h, adding 0.3-0.8 times of functional silicon carbide of the silicon source, continuing to stir for 2-3h to obtain wet gel, placing in a high-pressure reaction kettle, replacing with liquid carbon dioxide for 12h to obtain conductive aerogel;

[0012] (6) evenly spreading a layer of conductive aerogel on the bottom of the groove of the mold, coating adhesive with a thickness of 0.05mm, placing NTC thermistor substrate with a thickness of 0.5-0.8mm into the mold, then sequentially spreading adhesive with a thickness of 0.05mm and conductive aerogel on the NTC thermistor substrate, placing the mold into a microwave sintering furnace, calcining, naturally cooling, taking out the mold, demolding to obtain NTC thermistor; the adhesive is polyimide glue.

[0013] Further, the dispersant in step (1) is polyether P123.

[0014] Further, the parameters of the hydraulic machine in step (2) are as follows: the mold is 10mm, and the pressure is 5-10KN.

[0015] Further, the silane coupling agent in step (3) is one or more of (3-aminopropyl)trimethoxysilane, γ-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane.

[0016] Further, the silicon carbide in step (5) is RS07.

[0017] Further, the silicon source in step (5) is tetraethyl orthosilicate.

[0018] Further, the parameters of the high-pressure reaction kettle in step (5) are as follows: the temperature is 35-40℃, and the pressure is 6-10MPa.

[0019] Further, the setting parameters of the microwave sintering furnace in step (6) are as follows: the temperature rising rate is 5℃ / min, and the temperature is respectively raised to 100℃, 200℃ and 300℃, and the temperature is respectively maintained for 30min, 50min and 1-2h in each temperature zone.

[0020] Compared with the prior art, the present application has the advantages of:

[0021] (1) The present application uses a microwave sintering process, and the temperature difference of each part of the electrode is small, so that a uniform fine-grained structure can be obtained. The small grain size makes the electron transmission speed in the material fast, and the response time at low temperature shorter.

[0022] (2) The present application uses a low-temperature-resistant conductive aerogel to replace conductive silver paste, providing more abundant conductive channels and improving the conductive properties of the thermistor. The conductive aerogel has excellent low-temperature resistance, and the molecular chain can still maintain the ability to move at extremely low temperatures, avoiding brittle fracture and water absorption, and avoiding performance degradation due to icing. The stress transfer between interfaces is good, reducing the shrinkage phenomenon of the thermistor caused by stress concentration in a low-temperature environment, and maintaining good electrical property stability at low temperatures. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0024] Example 1: (1) Put the mixed metal oxide mixture obtained by mixing MnO2, Co3O4 and NiO according to the molar percentage of 51%:26%:23% into a maragda mortar for the first time ball milling, mix the metal oxide mixture: zirconia balls: anhydrous ethanol according to the mass ratio of 1:2:1, and alternately cycle wet milling clockwise and counterclockwise, with an interval of 30 minutes, ball mill for 4 hours to obtain a powder, mix the powder, polyether P123 and deionized water according to the mass ratio of 1:0.01:1.5, and place them in a drying box at 110℃ and 7Pa for 1 hour, and then use a planetary ball mill for the second time ball milling at a speed of 500r / min for 8 hours, and then pass through a 100 mesh sieve to obtain a precursor powder;

[0025] (2) Put the precursor powder into a mold for a 10mm hydraulic machine, set the pressure to 5KN and keep it for 1 minute, and then use an isostatic press with a pressure of 300MPa to keep it for 4 minutes to obtain a ceramic embryo, and then place the ceramic embryo in a microwave sintering furnace and heat it to 500℃ at a rate of 10℃ / min, and then take it out after sintering for 30 minutes to obtain an NTC thermistor substrate;

[0026] (3) mixing and stirring evenly silicon carbide, 10% nitric acid aqueous solution, silver nitrate, sodium chloride, deionized water and anhydrous ethanol according to a mass ratio of 1:15:0.1:0.1:30:100, stirring at 300 r / min for 10 h at 70℃, filtering, washing the filter cake with anhydrous ethanol and deionized water for 3 times respectively, placing in a drying box, drying at 60℃, 5 Pa for 12 h, to obtain silver-loaded silicon carbide; mixing and stirring evenly the silver-loaded silicon carbide, γ-aminoethyl aminopropyl trimethoxysilane and ethanol according to a mass ratio of 1:0.04:20, refluxing at 300 r / min for 3 h at 90℃, filtering, washing the filter cake with anhydrous ethanol for 2 times, placing in a drying box, drying at 70℃, 7 Pa for 4 h, to obtain modified silicon carbide;

[0027] (4) mixing polytetrafluoroethylene, acrylic acid, ferrous ammonium sulfate hexahydrate, 50% sulfuric acid aqueous solution and ethanol according to a mass ratio of 1:0.5:0.01:2:5 under nitrogen atmosphere, irradiating with γ-rays with a radiation dose of 10 kGy for 10 h at 25℃, filtering, washing the filter cake with deionized water for 2 times, placing in a drying box, drying at 60℃, 5 Pa for 2 h, to obtain modified polytetrafluoroethylene; the molecular weight of the polytetrafluoroethylene is 10 6 g / mol;

[0028] (5) mixing the modified silicon carbide, the modified polytetrafluoroethylene, dicyclohexyl carbodiimide, triethylamine and N,N-dimethylformamide according to a mass ratio of 1:0.3:1:2:10, stirring at 300 r / min for 10 h at 25℃, filtering, taking the solid, placing in a drying box, drying at 60℃, 6 Pa for 4 h, to obtain functional silicon carbide; mixing tetraethyl orthosilicate, 0.5 mol / L hydrochloric acid aqueous solution and anhydrous ethanol according to a ratio of 1:0.05:4, stirring at 300 r / min for 1 h at 40℃, adding 0.3 times of the functional silicon carbide of the tetraethyl orthosilicate, continuing to stir for 2 h, to obtain a wet gel, placing in a high-pressure reaction kettle, temperature is 35℃, pressure is 6 MPa, replacing with liquid carbon dioxide for 12 h, to obtain a conductive aerogel;

[0029] (6) evenly spreading a layer of the conductive aerogel on the bottom of the groove of the mold, coating the adhesive with a thickness of 0.05 mm, placing the NTC thermistor substrate with a thickness of 0.5 mm into the mold, then sequentially spreading the adhesive with a thickness of 0.05 mm, the conductive aerogel with a thickness of 0.05 mm on the NTC thermistor substrate, placing the mold into a microwave sintering furnace, heating at a rate of 5℃ / min, respectively heating to 100℃, 200℃, 300℃, respectively keeping at each temperature zone for 30 min, 50 min, 1 h. naturally cooling, taking out the mold, demolding, to obtain the NTC thermistor; the adhesive is polyimide glue, model YJ-22.

[0030] Example 2; (1) Put the mixed metal oxide mixture obtained by mixing MnO2, Co3O4, NiO according to the molar percentage of 48%:30%:22% into a agate mortar for the first time ball milling, mix the metal oxide mixture: zirconium oxide ball: anhydrous ethanol according to the mass ratio of 1:2.5:1, alternate wet milling in clockwise and anticlockwise directions, the interval time of alternation is 30 min, ball mill for 4h to obtain powder, mix the powder, polyether P123, deionized water according to the mass ratio of 1:0.015:1.7, place in a drying oven, dry at 110℃, 8Pa for 2h, use a planetary ball mill for the second time ball milling at a speed of 500r / min for 8h, pass through a 100 mesh sieve to obtain a precursor powder;

[0031] (2) Put the precursor powder into a mold for a 10mm hydraulic machine, set the pressure to 8KN and keep pressure for 1min, then use an isostatic press with a pressure of 300MPa to keep pressure for 4min to obtain a ceramic embryo, place the ceramic embryo in a microwave sintering furnace, heat at a rate of 10℃ / min to 500℃, take out after sintering for 30min to obtain an NTC thermistor substrate;

[0032] (3) Mix and stir evenly silicon carbide, 10% nitric acid aqueous solution, silver nitrate, sodium chloride, deionized water and anhydrous ethanol according to the mass ratio of 1:17:0.15:0.15:30:100, stir at 75℃, 400r / min for 11h, filter, take the filter cake and wash with anhydrous ethanol and deionized water for 4 times each, place in a drying oven, dry at 70℃, 8Pa for 13h to obtain silver-loaded silicon carbide; mix and stir evenly the silver-loaded silicon carbide, γ- aminoethyl aminopropyl trimethoxysilane, ethanol according to the mass ratio of 1:0.045:25, reflux at 100℃, 400r / min for 4h, filter, take the filter cake and wash with anhydrous ethanol for 3 times, place in a drying oven, dry at 70℃, 10Pa for 4h to obtain modified silicon carbide;

[0033] (4) Under a nitrogen atmosphere, mix polytetrafluoroethylene, acrylic acid, ferrous ammonium sulfate hexahydrate, 50% sulfuric acid aqueous solution and ethanol according to the mass ratio of 1:0.6:0.015:2.3:8, irradiate with a γ-ray with a radiation dose of 15kGy for 12.5h at 25℃, filter, take the filter cake and wash with deionized water for 2 times, place in a drying oven, dry at 60℃, 5Pa for 2h to prepare modified polytetrafluoroethylene; the molecular weight of the polytetrafluoroethylene is 10 6 g / mol;

[0034] (5) modified silicon carbide, modified polytetrafluoroethylene, dicyclohexyl carbodiimide, triethylamine and N, N-dimethylformamide are mixed in a mass ratio of 1:0.4:1.1:2.5:15, stirred at 30℃ and 400r / min for 11h, and then the solid is filtered and dried in a drying box at 70℃ and 70Pa for 5h to obtain functional silicon carbide; tetraethyl orthosilicate, 0.5mol / L hydrochloric acid aqueous solution and anhydrous ethanol are mixed in a ratio of 1:0.07:5, stirred at 45℃ and 400r / min for 1h, and then 0.5 times of functional silicon carbide is added to the tetraethyl orthosilicate, and the stirring is continued for 2h to obtain a wet gel, which is placed in a high-pressure reaction kettle at a temperature of 40℃ and a pressure of 10MPa, and replaced with liquid carbon dioxide for 12h to obtain a conductive aerogel;

[0035] (6) a layer of conductive aerogel is evenly laid on the bottom of the groove of the mold, a bonding agent with a thickness of 0.05mm is coated, the NTC thermistor substrate with a thickness of 0.6mm is placed into the mold, and then the bonding agent with a thickness of 0.05mm and the conductive aerogel are sequentially laid on the NTC thermistor substrate, the mold is placed into a microwave sintering furnace, the temperature is raised to 100℃, 200℃ and 300℃ at a rate of 5℃ / min, and the temperature is maintained at each temperature zone for 30min, 50min and 2h respectively, and then the mold is naturally cooled and demolded to obtain the NTC thermistor; the bonding agent is a polyimide glue with a model number of YJ-22.

[0036] Example 3; (1) the metal oxide mixture obtained by mixing MnO2, Co3O4 and NiO in a molar percentage of 53%:25%:22% is placed into a agate mortar for first ball milling, and the metal oxide mixture: zirconia balls: anhydrous ethanol are mixed in a mass ratio of 1:3:1, and then wet milling is alternately performed in clockwise and counterclockwise directions with an interval of 30min, and the ball milling is performed for 4h to obtain a powder, and then the powder, polyether P123 and deionized water are mixed in a mass ratio of 1:0.02:2, and then placed in a drying box and dried at 120℃ and 10Pa for 2h, and then the planetary ball mill is used for second ball milling at a speed of 500r / min for 8h, and then the powder is sieved through a 100 mesh sieve to obtain a precursor powder;

[0037] (2) the precursor powder is placed into a mold of a hydraulic machine with a pressure of 10KN for 1min, and then an isostatic pressing instrument with a pressure of 300MPa is used for pressure maintaining for 4min to obtain a ceramic embryo, and then the ceramic embryo is placed into a microwave sintering furnace and heated to 500℃ at a rate of 10℃ / min, and then taken out after sintering for 30min to obtain an NTC thermistor substrate;

[0038] (3) mixing and stirring evenly silicon carbide, 10% nitric acid aqueous solution, silver nitrate, sodium chloride, deionized water and anhydrous ethanol according to a mass ratio of 1:20:0.2:0.2:30:100, stirring at 80℃ and 500r / min for 12h, filtering, washing the filter cake with anhydrous ethanol and deionized water for 5 times respectively, placing in a drying box, drying at 70℃ and 8Pa for 14h, to obtain silver-loaded silicon carbide; mixing and stirring evenly the silver-loaded silicon carbide, γ-aminoethyl aminopropyl trimethoxysilane and ethanol according to a mass ratio of 1:0.05:30, refluxing at 100℃ and 500r / min for 4h, filtering, washing the filter cake with anhydrous ethanol for 3 times, placing in a drying box, drying at 70℃ and 10Pa for 4h, to obtain modified silicon carbide;

[0039] (4) mixing polytetrafluoroethylene, acrylic acid, ferrous ammonium sulfate hexahydrate, 50% sulfuric acid aqueous solution and ethanol according to a mass ratio of 1:0.7:0.02:2.5:10 under nitrogen atmosphere, irradiating with γ-rays with a radiation dose of 20kGy for 15h at 30℃, filtering, washing the filter cake with deionized water for 3 times, placing in a drying box, drying at 60℃ and 7Pa for 2h, to obtain modified polytetrafluoroethylene; the molecular weight of the polytetrafluoroethylene is 10 6 g / mol;

[0040] (5) mixing the modified silicon carbide, the modified polytetrafluoroethylene, dicyclohexyl carbodiimide, triethylamine and N,N-dimethylformamide according to a mass ratio of 1:0.5:1.2:3:20, stirring at 30℃ and 500r / min for 12h, filtering, placing the solid in a drying box, drying at 70℃ and 10Pa for 6h, to obtain functional silicon carbide; mixing tetraethyl orthosilicate, 0.5mol / L hydrochloric acid aqueous solution and anhydrous ethanol according to a ratio of 1:0.08:6, stirring at 50℃ and 500r / min for 2h, adding 0.6 times of the functional silicon carbide of the tetraethyl orthosilicate, continuing to stir for 3h, to obtain a wet gel, placing in a high-pressure reaction kettle, temperature 40℃, pressure 10MPa, replacing with liquid carbon dioxide for 12h, to obtain a conductive aerogel;

[0041] (6) evenly spreading a layer of the conductive aerogel on the bottom of the groove of the mold, coating the adhesive with a thickness of 0.05mm, placing the NTC thermistor substrate with a thickness of 0.8mm into the mold, then evenly spreading the adhesive with a thickness of 0.05mm, the conductive aerogel with a thickness of 0.05mm on the NTC thermistor substrate in turn, placing the mold into a microwave sintering furnace, heating at a rate of 5℃ / min, respectively heating to 100℃, 200℃ and 300℃, respectively keeping at each temperature zone for 30min, 50min and 2h. naturally cooling, taking out the mold, demolding, to obtain the NTC thermistor; the adhesive is polyimide glue, model YJ-22.

[0042] Example 4; (1) put the mixed metal oxide mixture obtained by mixing MnO2, Co3O4, NiO according to the molar percentage of 55%:26%:19% into a agate mortar for the first time ball milling, mix the metal oxide mixture: zirconium oxide ball: anhydrous ethanol according to the mass ratio of 1:2:1, alternate wet milling in clockwise and anticlockwise, the alternate interval time is 30 min, ball mill for 4 h to obtain the powder, mix the powder, polyether P123, deionized water according to the mass ratio of 1:0.01:1.5, place in a drying oven, dry at 110℃, 7Pa for 1h, use the planetary ball mill for the second time ball milling at 500r / min for 8h, pass through 100 mesh sieve to obtain the precursor powder;

[0043] (2) put the precursor powder into the mold for 10mm hydraulic machine, set the pressure to 5KN for 1min, then use the isostatic press instrument with the pressure of 300MPa for 4min to obtain the ceramic embryo, place the ceramic embryo in the microwave sintering furnace, heat to 500℃ at the rate of 10℃ / min, take out after sintering for 30min to obtain the NTC thermistor substrate;

[0044] (3) mix and stir evenly silicon carbide, 10% nitric acid aqueous solution, silver nitrate, sodium chloride, deionized water and anhydrous ethanol according to the mass ratio of 1:15:0.1:0.1:30:100, stir at 70℃, 300r / min for 10h, filter, take the filter cake and wash with anhydrous ethanol and deionized water for 3 times each, place in a drying oven, dry at 60℃, 5Pa for 12h to obtain silver-loaded silicon carbide; mix and stir evenly the silver-loaded silicon carbide, γ- aminoethyl aminopropyl trimethoxysilane, ethanol according to the mass ratio of 1:0.04:20, reflux at 90℃, 300r / min for 3h, filter, take the filter cake and wash with anhydrous ethanol for 2 times, place in a drying oven, dry at 70℃, 7Pa for 4h to obtain modified silicon carbide;

[0045] (4) mix polytetrafluoroethylene, acrylic acid, ferrous ammonium sulfate hexahydrate, 50% sulfuric acid aqueous solution and ethanol according to the mass ratio of 1:0.5:0.01:2:5 under nitrogen atmosphere, irradiate with γ-rays with the radiation dose of 10kGy for 10h at 25℃, filter, take the filter cake and wash with deionized water for 2 times, place in a drying oven, dry at 60℃, 5Pa for 2h to obtain modified polytetrafluoroethylene; the molecular weight of the polytetrafluoroethylene is 10 6 g / mol;

[0046] (5) modified silicon carbide, modified polytetrafluoroethylene, dicyclohexyl carbodiimide, triethylamine and N, N-dimethylformamide are mixed in a mass ratio of 1:0.3:1:2:10, stirred at 25°C and 300 r / min for 10 hours, and then filtered to obtain a solid, which is placed in a drying box and dried at 60°C and 6 Pa for 4 hours to obtain functional silicon carbide; tetraethyl orthosilicate, 0.5 mol / L hydrochloric acid aqueous solution and anhydrous ethanol are mixed in a ratio of 1:0.05:4, stirred at 40°C and 300 r / min for 1 hour, and then 0.8 times the functional silicon carbide of tetraethyl orthosilicate is added and stirred for 2 hours to obtain a wet gel, which is placed in a high-pressure reaction kettle at a temperature of 35°C and a pressure of 6 MPa, and replaced with liquid carbon dioxide for 12 hours to obtain a conductive aerogel;

[0047] (6) A layer of conductive aerogel is evenly laid on the bottom of the groove of the mold, a bonding agent with a thickness of 0.05 mm is coated, the NTC thermistor base body with a thickness of 0.5 mm is placed into the mold, and then the bonding agent with a thickness of 0.05 mm and the conductive aerogel are sequentially laid on the NTC thermistor base body. The mold is placed in a microwave sintering furnace and calcined at a heating rate of 5°C / min, and then heated to 100°C, 200°C and 300°C, respectively, and kept at each temperature zone for 30 min, 50 min and 1 h, respectively. The mold is taken out after natural cooling, demolded, and an NTC thermistor is obtained; the bonding agent is a polyimide glue with a model number of YJ-22.

[0048] Example 5: (1) The metal oxide mixture obtained by mixing MnO2, Co3O4 and NiO in a molar percentage of 50%:29%:21% is placed in a agate mortar for the first time ball milling, and the metal oxide mixture: zirconia balls: anhydrous ethanol are mixed in a mass ratio of 1:2.5:1, and then wet milling is alternately performed in clockwise and counterclockwise directions with an interval of 30 min, and the ball milling is performed for 4 h to obtain a powder, and then the powder, polyether P123 and deionized water are mixed in a mass ratio of 1:0.015:1.7, and then placed in a drying box and dried at 110°C and 8 Pa for 2 h, and then secondly ball milled by a planetary ball mill at a speed of 500 r / min for 8 h, and then sieved through a 100-mesh sieve to obtain a precursor powder;

[0049] (2) The precursor powder is placed into a mold of a 10 mm hydraulic machine, and then set to a pressure of 8 KN and kept for 1 min, and then kept by an isostatic press with a pressure of 300 MPa for 4 min to obtain a ceramic embryo, and then the ceramic embryo is placed in a microwave sintering furnace and heated to 500°C at a rate of 10°C / min, and then taken out after sintering for 30 min to obtain an NTC thermistor base body;

[0050] (3) mixing silicon carbide, 10% nitric acid aqueous solution, silver nitrate, sodium chloride, deionized water and anhydrous ethanol according to a mass ratio of 1:17:0.15:0.15:30:100, stirring uniformly at 75℃ and 400r / min for 11h, filtering, washing the filter cake with anhydrous ethanol and deionized water for 4 times respectively, placing in a drying box, drying at 70℃ and 8Pa for 13h, to obtain silver-loaded silicon carbide; mixing the silver-loaded silicon carbide, γ-aminoethyl aminopropyl trimethoxysilane and ethanol according to a mass ratio of 1:0.045:25, stirring uniformly at 100℃ and 400r / min for 4h, filtering, washing the filter cake with anhydrous ethanol for 3 times, placing in a drying box, drying at 70℃ and 10Pa for 4h, to obtain modified silicon carbide;

[0051] (4) mixing polytetrafluoroethylene, acrylic acid, ferrous ammonium sulfate hexahydrate, 50% sulfuric acid aqueous solution and ethanol according to a mass ratio of 1:0.6:0.015:2.3:8 under nitrogen atmosphere, irradiating with γ-rays with a radiation dose of 15kGy for 10-15h at 25℃, filtering, washing the filter cake with deionized water for 2 times, placing in a drying box, drying at 60℃ and 5Pa for 2h, to obtain modified polytetrafluoroethylene; the molecular weight of the polytetrafluoroethylene is 10 6 g / mol;

[0052] (5) mixing the modified silicon carbide, the modified polytetrafluoroethylene, dicyclohexyl carbodiimide, triethylamine and N,N-dimethylformamide according to a mass ratio of 1:0.4:1.1:2.5:15, stirring at 30℃ and 400r / min for 10-12h, filtering, taking the solid, placing in a drying box, drying at 70℃ and 70Pa for 5h, to obtain functional silicon carbide; mixing tetraethyl orthosilicate, 0.5mol / L hydrochloric acid aqueous solution and anhydrous ethanol according to a ratio of 1:0.07:5, stirring at 45℃ and 400r / min for 1h, adding 0.5 times of the functional silicon carbide of the tetraethyl orthosilicate, continuing to stir for 2h, to obtain a wet gel, placing in a high-pressure reaction kettle, temperature 40℃, pressure 10MPa, replacing with liquid carbon dioxide for 12h, to obtain a conductive aerogel;

[0053] (6) evenly spreading a layer of the conductive aerogel on the bottom of the groove of the mold, coating the adhesive with a thickness of 0.05mm, placing the NTC thermistor substrate with a thickness of 0.6mm into the mold, then sequentially spreading the adhesive with a thickness of 0.05mm, the conductive aerogel on the NTC thermistor substrate, placing the mold into a microwave sintering furnace, heating at a rate of 5℃ / min, respectively heating to 100℃, 200℃, 300℃, respectively keeping at each temperature zone for 30min, 50min, 2h, naturally cooling, taking out the mold, demolding, to obtain the NTC thermistor; the adhesive is polyimide glue, model YJ-22.

[0054] Example 6; (1) Put the mixed metal oxide mixture obtained by mixing MnO2, Co3O4, NiO in a molar percentage of 52%:28%:20% into a agate mortar for the first time ball milling, mix the metal oxide mixture: zirconium oxide ball: anhydrous ethanol according to the mass ratio of 1:3:1, alternate wet milling in clockwise and anticlockwise directions, the interval time of alternation is 30 min, ball mill for 4 h to obtain powder, mix the powder, polyether P123, deionized water according to the mass ratio of 1:0.02:2, place in a drying oven, dry at 120℃, 10Pa for 2h, use a planetary ball mill for the second time ball milling at a speed of 500r / min for 8h, pass through a 100 mesh sieve to obtain a precursor powder;

[0055] (2) Put the precursor powder into a mold for a 10mm hydraulic machine, set the pressure to 10KN and keep it for 1min, then use an isostatic press with a pressure of 300MPa to keep it for 4min to obtain a ceramic embryo, place the ceramic embryo in a microwave sintering furnace, heat at a rate of 10℃ / min to 500℃, take it out after sintering for 30min to obtain an NTC thermistor substrate;

[0056] (3) Mix and stir evenly silicon carbide, 10% nitric acid aqueous solution, silver nitrate, sodium chloride, deionized water and anhydrous ethanol according to the mass ratio of 1:20:0.2:0.2:30:100, stir at 80℃, 500r / min for 12h, filter, take the filter cake and wash it with anhydrous ethanol and deionized water for 5 times each, place it in a drying oven, dry at 70℃, 8Pa for 14h to obtain silver-loaded silicon carbide; mix and stir evenly the silver-loaded silicon carbide, γ-aminoethyl aminopropyl trimethoxysilane, ethanol according to the mass ratio of 1:0.05:30, reflux stir at 100℃, 500r / min for 4h, filter, take the filter cake and wash it with anhydrous ethanol for 3 times, place it in a drying oven, dry at 70℃, 10Pa for 4h to obtain modified silicon carbide;

[0057] (4) Under a nitrogen atmosphere, mix polytetrafluoroethylene, acrylic acid, ferrous ammonium sulfate hexahydrate, 50% sulfuric acid aqueous solution and ethanol according to the mass ratio of 1:0.7:0.02:2.5:10, irradiate with a γ-ray with a radiation dose of 20kGy for 15h at 30℃, filter, take the filter cake and wash it with deionized water for 3 times, place it in a drying oven, dry at 60℃, 7Pa for 2h to obtain modified polytetrafluoroethylene; the molecular weight of the polytetrafluoroethylene is 10 6 g / mol;

[0058] (5) modified silicon carbide, modified polytetrafluoroethylene, dicyclohexyl carbodiimide, triethylamine and N, N-dimethylformamide are mixed in a mass ratio of 1:0.5:1.2:3:20, stirred at 30°C and 500 r / min for 12 hours, and then filtered to obtain a solid which is placed in a drying box and dried at 70°C and 10 Pa for 6 hours to obtain functional silicon carbide; tetraethyl orthosilicate, 0.5 mol / L hydrochloric acid aqueous solution and anhydrous ethanol are mixed in a ratio of 1:0.08:6, stirred at 50°C and 500 r / min for 2 hours, and then 0.3 times of functional silicon carbide of tetraethyl orthosilicate is added and stirred for 3 hours to obtain a wet gel which is placed in a high-pressure reaction kettle at a temperature of 40°C and a pressure of 10 MPa, and replaced with liquid carbon dioxide for 12 hours to obtain a conductive aerogel;

[0059] (6) a layer of conductive aerogel is evenly laid on the bottom of the groove of the mold, a binder with a thickness of 0.05 mm is coated, an NTC thermistor base with a thickness of 0.8 mm is placed in the mold, and then the binder and the conductive aerogel with a thickness of 0.05 mm are sequentially laid on the NTC thermistor base, the mold is placed in a microwave sintering furnace, the temperature is raised to 100°C, 200°C and 300°C at a rate of 5°C / min, and the temperature is maintained at each temperature zone for 30 min, 50 min and 2 h respectively. The mold is taken out after natural cooling, demolding is performed, and an NTC thermistor is obtained; the binder is a polyimide glue with a model number of YJ-22.

[0060] Comparative Example 1; the difference between Comparative Example 1 and Example 2 is only that the microwave sintering process is not used, and step (2) is changed to: the precursor powder is placed in a 10 mm hydraulic machine, the pressure is set to 8 KN and pressure is maintained for 1 min, and then an isostatic press with a pressure of 300 MPa is used to maintain pressure for 4 min to obtain a ceramic embryo, the ceramic embryo is placed in a calcining furnace, the temperature is raised to 750°C at a rate of 10°C / min, and the sintering is performed for 2 h before the ceramic embryo is taken out to obtain an NTC thermistor base; step (6) is changed to: a layer of conductive aerogel is evenly laid on the bottom of the groove of the mold, a binder with a thickness of 0.05 mm is coated, an NTC thermistor base with a thickness of 0.6 mm is placed in the mold, and then the binder and the conductive aerogel with a thickness of 0.05 mm are sequentially laid on the NTC thermistor base, the mold is placed in a calcining furnace, the temperature is raised to 200°C at a rate of 10°C / min, the temperature is maintained at 200°C for 1 h, the temperature is raised from 200°C to 320°C, and the temperature is maintained at 320°C for 2 h, the mold is taken out after natural cooling, demolding is performed, and an NTC thermistor is obtained; the remaining steps are the same as those of Example 2.

[0061] Comparative Example 2; Comparative Example 2 differs from Example 2 in that step (3) is changed to: mixing silicon carbide, γ-aminoethyl aminopropyl trimethoxysilane, and ethanol in a mass ratio of 1:0.045:25, stirring uniformly at 100°C and 400 r / min for 4h, filtering, washing the filter cake with anhydrous ethanol for 3 times, and placing in a drying box for drying at 70°C and 10 Pa for 4h to obtain modified silicon carbide; the remaining steps are the same as those in Example 2.

[0062] Comparative Example 3; Comparative Example 3 differs from Example 2 in that there is no step (4), and step (5) is changed to: mixing modified silicon carbide, polytetrafluoroethylene, and N,N-dimethylformamide in a mass ratio of 1:2.5:15, stirring at 30°C and 400 r / min for 10h, filtering to obtain a solid, and placing in a drying box for drying at 70°C and 70 Pa for 5h to obtain functional silicon carbide; mixing tetraethyl orthosilicate, 0.5 mol / L hydrochloric acid aqueous solution, and anhydrous ethanol in a ratio of 1:0.07:5, stirring at 45°C and 400 r / min for 1h, adding functional silicon carbide 0.5 times of tetraethyl orthosilicate, and continuing to stir for 2h to obtain a wet gel, which is placed in a high-pressure reaction kettle at a temperature of 40°C and a pressure of 10 MPa, and is replaced with liquid carbon dioxide for 12h to prepare a conductive aerogel; the remaining steps are the same as those in Example 2.

[0063] Comparative Example 4; Comparative Example 4 differs from Example 1 in that there is no polytetrafluoroethylene, and thus Comparative Example 4 has no step (4), and step (5) is changed to: mixing modified silicon carbide, dicyclohexyl carbodiimide, triethylamine, and N,N-dimethylformamide in a mass ratio of 1:1:2:10, stirring at 25°C and 300 r / min for 10h, filtering to obtain a solid, and placing in a drying box for drying at 60°C and 6 Pa for 4h to obtain functional silicon carbide; mixing tetraethyl orthosilicate, 0.5 mol / L hydrochloric acid aqueous solution, and anhydrous ethanol in a ratio of 1:0.05:4, stirring at 40°C and 300 r / min for 1h, adding functional silicon carbide 0.3 times of tetraethyl orthosilicate, and continuing to stir for 2h to obtain a wet gel, which is placed in a high-pressure reaction kettle at a temperature of 35°C and a pressure of 6 MPa, and is replaced with liquid carbon dioxide for 12h to prepare a conductive aerogel.

[0064] Effect Example

[0065] Aging Performance Test

[0066] Test method: NTC thermistors were prepared according to the method in the examples and comparative examples, the sintered wafer was taken out from the microwave sintering furnace, the resistivity of the wafer was detected, the normal temperature resistance at 25℃ and the low temperature resistance at -100℃ were measured respectively in a liquid helium refrigeration constant temperature tank, the B value was calculated from the two resistance values, the B value was the resistance drift rate, the resistance values of the NTC thermistors in the examples and comparative examples were tested after aging treatment at -100℃ for 1500h, the resistance drift rate before and after aging treatment was calculated according to the standard resistance at 25℃ before aging treatment, the resistance drift rate = the resistance value of the sample after aging treatment - the standard resistance / the standard resistance x 100%. The results are shown in Table 1.

[0067] Table 1

[0068]

[0069] The experimental data of Comparative Example 1 and Example 2 reflect the necessity of the microwave sintering process of the present application; heat is transferred from the external heat source to the sample surface through thermal radiation and convection, and then into the sample interior through thermal conduction; this results in high surface temperature and low internal temperature; in order to ensure that the interior reaches a sufficient sintering temperature, the overall temperature, especially the surface temperature, must be increased to 750℃, the microwave effect, microwave energy directly penetrates the material and is absorbed by the whole material, converting into molecular kinetic energy, significantly reducing the temperature gradient between the sample interior and surface; the interior and exterior are heated to the target temperature almost simultaneously, avoiding the problem of overheating of the surface, so Comparative Example 1 needs to increase the corresponding temperature to achieve the same effect as Example 1; the experimental data of Comparative Example 2 and Example 2 verify the indispensability of silver-loaded modified silicon carbide (rather than ordinary silicon carbide) for low-temperature conductive pathways; the experimental data of Comparative Example 3 and Example 2 prove the role of dicyclohexyl carbodiimide (DCC) and triethylamine in the crosslinking reaction, indicating that the lack of crosslinking agent will significantly reduce the durability of the material; the experimental data of Comparative Example 4 and Example 2 verify the necessity of polytetrafluoroethylene (PTFE) modification for aerogel structure.

[0070] From the data results of Examples 1-6 and Comparative Examples 1-4 and Table 1, it can be seen that the NTC thermistors prepared by the present application have small resistivity and B value, small resistance value drift rate, and excellent low temperature stability within 1.0% after aging treatment; in contrast, Comparative Examples 1-4 do not use the preparation process, and their performance test results are significantly lower than Examples 1-6.

[0071] The application uses a low-temperature-resistant conductive aerogel to replace conductive silver paste, and silver-loaded silicon carbide is prepared by reacting silicon carbide, silver nitrate and sodium chloride, so that more conductive paths are provided for improving the performance of the silver-loaded silicon carbide, and the conductive performance of the thermistor is improved; the modified silicon carbide is prepared by mixing and reacting the silver-loaded silicon carbide and the silane coupling agent; the siloxyl group at one end of the silane coupling agent can react with the Si-OH on the surface of the silver-loaded silicon carbide after oxidation to form a hydrogen bond, and the -NH2 group at the other end condenses with the carboxyl group of the modified polytetrafluoroethylene to make the modified polytetrafluoroethylene and the modified silicon carbide highly cross-linked; such chemical cross-linking is conducive to stress transfer at the interface, reduces shrinkage of the thermistor due to stress concentration at low temperatures, and improves the electrical performance stability of the thermistor at low temperatures. Polytetrafluoroethylene has excellent low-temperature performance, and its molecular chain can still maintain the ability to move at extremely low temperatures, avoiding brittle fracture, and does not absorb moisture, avoiding performance degradation due to icing.

[0072] It will be obvious to a person skilled in the art that the application is not limited to the details of the above-described exemplary embodiments, but that the application can be implemented in other concrete forms without departing from the spirit or essential characteristics of the application. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, and the scope of the application is defined by the appended claims rather than the above description, and it is intended to encompass all changes falling within the meaning and scope of the equivalent elements of the claims. Any mark in the claims should not be considered as limiting the claims involved.

Claims

1. A NTC thermistor resistant to low temperature of 100°C, characterized in that, The preparation steps include: (1) Put the mixed metal oxide mixture obtained by mixing MnO2, Co3O4 and NiO according to the molar percentage (48%-55%):(25%-30%):(15%-23%) into an agate mortar for the first time ball milling, mix the metal oxide mixture: zirconia balls: anhydrous ethanol according to the mass ratio of 1:2-3:1, alternate wet milling clockwise and anticlockwise, the interval time is 30 min, ball mill for 4 h to obtain powder, mix the powder, dispersing agent and deionized water according to the mass ratio of 1:(0.01-0.02):(1.5-2), second time ball milling for 8 h, the rotation speed is 500 r / min, pass through a 100 mesh screen to obtain a precursor powder; (2) Put the precursor powder into a hydraulic machine and keep pressure for 1 min, then use an isostatic press with a pressure of 300 MPa to keep pressure for 4 min, the pressure is 5-10 kN, obtain a ceramic green body, place the ceramic green body in a microwave sintering furnace, heat at a rate of 10 ℃ / min to 500 ℃, take out after sintering for 30 min, obtain an NTC thermistor substrate; (3) Mix and stir uniformly silicon carbide, 10% mass fraction nitric acid aqueous solution, silver nitrate, sodium chloride, deionized water and anhydrous ethanol according to the mass ratio of 1:(15-20):(0.1-0.2):(0.1-0.2):30:100, stir at 70-80 ℃, 300-500 r / min for 10-12 h, filter, wash the filter cake with anhydrous ethanol and deionized water for 3-5 times, place in a drying box, dry at 60-70 ℃, 5-8 Pa for 12-14 h, obtain silver-loaded silicon carbide; mix and stir uniformly the silver-loaded silicon carbide, silane coupling agent and ethanol according to the mass ratio of 1:(0.04-0.05):(20-30), reflux at 90-100 ℃, 300-500 r / min for 3-4 h, filter, wash the filter cake with anhydrous ethanol for 2-3 times, place in a drying box, dry at 70 ℃, 7-10 Pa for 4 h, obtain modified silicon carbide; The polytetrafluoroethylene, acrylic acid, ferrous ammonium sulfate hexahydrate, 50% mass fraction sulfuric acid aqueous solution and ethanol are mixed in a mass ratio of 1:(0.5-0.7):(0.01-0.02):(2-2.5):(5-10) under a nitrogen atmosphere, and irradiated with gamma rays with a radiation dose of 10-20 kGy for 10-15 h at 25-30°C, filtered, and the filter cake is washed with deionized water for 2-3 times, and placed in a drying oven at 60°C, 5-7 Pa, and dried for 2 h to obtain modified polytetrafluoroethylene; the modified silicon carbide, modified polytetrafluoroethylene, dicyclohexyl carbodiimide, triethylamine and N,N-dimethylformamide are mixed in a mass ratio of 1:(0.3-0.5):(1-1.2):(2-3):(10-20), stirred at 25-30°C and 300-500 r / min for 10-12 h, and the solid is obtained after filtration, and placed in a drying oven at 60-70°C, 6-10 Pa, and dried for 4-6 h to obtain functional silicon carbide; the functional silicon carbide and a silicon source as the main raw material are used to prepare a wet gel, and an electrically conductive aerogel is prepared by liquid carbon dioxide. (4) A layer of conductive aerogel is evenly laid on the bottom of the groove of the mold, a bonding agent with a thickness of 0.05 mm is coated, an NTC thermistor substrate with a thickness of 0.5-0.8 mm is placed in the mold, and then a bonding agent with a thickness of 0.05 mm and conductive aerogel are laid on the NTC thermistor substrate in turn, the mold is placed in a microwave sintering furnace for calcination, naturally cooled, the mold is taken out, demolded, and an NTC thermistor is obtained; the bonding agent is a polyimide glue.

2. The NTC thermistor resistant to -100°C low temperature according to claim 1, characterized in that, The dispersant in step (1) is polyether P123.

3. The NTC thermistor resistant to -100°C low temperature according to claim 1, characterized in that, The parameters of the hydraulic machine in step (2) are as follows: the mold is 10 mm, and the pressure is 5-10 KN.

4. The NTC thermistor resistant to -100°C low temperature according to claim 1, characterized in that, The setting parameters of the microwave sintering furnace in step (4) are as follows: the heating rate is 5°C / min, and the temperature is respectively raised to 100°C, 200°C and 300°C, and the temperature is respectively maintained for 30 min, 50 min and 1-2 h.

5. The NTC thermistor resistant to -100°C low temperature according to claim 1, characterized in that, The silicon carbide in step (3) is RS07.

6. The NTC thermistor resistant to -100°C low temperature according to claim 1, characterized in that, The silicon source in step (3) is tetraethyl orthosilicate.

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