A highly stable negative temperature coefficient thermistor material and its preparation method

Abstract

The present invention relates to a highly stable negative temperature coefficient thermistor material and a preparation method thereof. The material is prepared by a solid-phase method using La2O3, MnO2, Fe2O3, and SiO2 as raw materials, and is made through grinding, calcination, shaping, and high-temperature sintering to obtain a La-Mn-Fe-Si-O ceramic NTC thermistor with a perovskite structure. Its electrical performance parameters: resistivity ρ 25℃ = 6.13 - 65.38 Ω·cm, material constant B 25 / 50 = 340.24 - 1751.78 K, resistance change rate ∆R / R0 ≤ 0.39%. The NTC thermistor described in the present invention can be applied to temperature monitoring and control in an environment with a temperature range of -200°C to 125°C, has obvious NTC characteristics, a wide temperature measurement range, stable material performance, good anti-aging property, and is suitable for temperature detection fields such as low temperature, deep sea, aerospace, etc.

Description

Technical Field

[0001] The present invention relates to a highly stable negative temperature coefficient thermistor material and a preparation method thereof. Based on the electrical performance parameters of the material, it is applicable to temperature detection fields such as low temperature, deep sea, aerospace, etc. Background Art

[0002] A thermistor is a temperature sensor whose resistance value changes with temperature. According to different temperature coefficients, thermistors can be divided into positive temperature coefficient (Positive Temperature Coefficient; PTC) thermistors and negative temperature coefficient thermistors (Negative Temperature Coefficient; NTC). PTC thermistor materials are semiconductor materials whose resistance values increase with the increase of temperature, and NTC thermistor materials are semiconductor materials whose resistance values decrease with the increase of temperature. Thermistors have the advantages of high sensitivity, fast response, small volume, low cost, etc., and have been widely used in many fields such as temperature measurement and control, voltage stabilization, compensation, and suppression of surge current.

[0003] In practical applications of negative temperature coefficient (NTC) thermistors, the resistance value will change significantly with the increase of the use time. Long-term use is likely to cause the comprehensive performance parameters of the thermistor components to deviate seriously from the design values, which greatly limits the application of NTC thermistors. Therefore, it is necessary to evaluate the aging performance of NTC thermistors. The aging condition adopted is to place at a temperature of 125°C for more than 50h. After aging, the NTC thermistor generally shows an increase in the resistance value, and the change rate of the resistance value is generally above 5%. Summary of the Invention

[0004] The purpose of the present invention is to provide a highly stable negative temperature coefficient thermistor material and a preparation method thereof. The material is prepared by a solid-phase method using La2O3, MnO2, Fe2O3, and SiO2 as raw materials, and is made through grinding, calcination, forming, and high-temperature sintering to obtain a La-Mn-Fe-Si-O ceramic NTC thermistor with a perovskite structure; its electrical performance parameters: resistivity ρ 25℃ = 6.13 - 65.38 Ω·cm, material constant B 25 / 50 = 340.24 - 1751.78 K, resistance change rate ΔR / R0 ≤ 0.39%. The NTC thermistor material described in the present invention can be applied to temperature monitoring and control in an environment with a temperature of -200°C - 125°C, has obvious NTC characteristics, a wide temperature measurement range, stable material performance, good anti-aging property, and is applicable to temperature detection fields such as low temperature, deep sea, aerospace, etc.

[0005] A highly stable negative temperature coefficient thermistor material according to the present invention is made from La2O3, MnO2, Fe2O3 and SiO2 as raw materials through grinding, calcination, forming and high-temperature sintering to obtain a La-Mn-Fe-Si-O ceramic material with a perovskite structure. The specific operations are carried out according to the following steps:

[0006] a. Powder ratio: Weigh La2O3, MnO2 and Fe2O3 according to the molar ratio of La2O3:MnO2:Fe2O3 = 1:1 - 1.8:0.1 - 0.5 respectively, place them in an agate mortar, add SiO2, and mix and grind for 6 - 10 h to obtain a La-Mn-Fe-Si-O mixed powder. The mass ratio of the La2O3:MnO2:Fe2O3 mixture to SiO2 is 198 - 199:1 - 2;

[0007] b. Calcination: Place the La-Mn-Fe-Si-O mixed powder obtained in step a in a furnace at a temperature of 1050°C - 1200°C and calcine for 1 - 4 h to obtain a La-Mn-Fe-Si-O powder with a perovskite structure;

[0008] c. Grinding: Place the perovskite La-Mn-Fe-Si-O powder after calcination in step b in an agate mortar and grind for 2 - 6 h;

[0009] d. Forming: Use a mold with a diameter of 10 mm to form the powder after grinding in step c to obtain a green body material, then vacuum package it, and perform cold isostatic pressing at a pressure of 280 MPa - 350 MPa for 140 s - 180 s to obtain a formed block;

[0010] e. Sintering: Place the formed block in step d in a furnace at a temperature of 1300°C - 1450°C and sinter for 4 - 10 h, then cool to room temperature to obtain a ceramic block material;

[0011] f. Electrode preparation: Coat both sides of the ceramic block material obtained in step e with platinum paste, and sinter at a temperature of 800°C - 1000°C for 20 - 40 min to obtain a highly stable NTC thermistor material.

[0012] A preparation method of a highly stable negative temperature coefficient thermistor material is carried out according to the following steps:

[0013] a. Powder ratio: Weigh La2O3, MnO2 and Fe2O3 according to the molar ratio of La2O3:MnO2:Fe2O3 = 1:1 - 1.8:0.1 - 0.5 respectively, place them in an agate mortar, add SiO2, and mix and grind for 6 - 10 h to obtain a La-Mn-Fe-Si-O mixed powder, where the mass ratio of the La2O3:MnO2:Fe2O3 mixture to SiO2 is 198 - 199:1 - 2;

[0014] b. Calcination: The La-Mn-Fe-Si-O mixed powder obtained in step a is calcined at a temperature of 1050 °C - 1200 °C for 1 - 4 h to obtain La-Mn-Fe-Si-O powder with a perovskite structure;

[0015] c. Grinding: The perovskite La-Mn-Fe-Si-O powder after calcination in step b is placed in an agate mortar and ground for 2 - 6 h;

[0016] d. Molding: The powder after grinding in step c is molded with a mold having a diameter of 10 mm. The obtained green body material is vacuum-packaged and cold isostatically pressed at a pressure of 280 MPa - 350 MPa for 140 s - 180 s to form a molded block;

[0017] e. Sintering: The molded block in step d is placed in a temperature range of 1300 °C - 1450 °C and sintered for 4 - 10 h, and then cooled to room temperature to obtain a ceramic block material;

[0018] f. Electrode preparation: Platinum paste is coated on both the front and back sides of the ceramic block material obtained in step e, and sintered at a temperature of 800 °C - 1000 °C for 20 - 40 min to obtain a highly stable NTC thermistor material.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. Wide temperature test range: -200 °C - 125 °C;

[0021] 2. Small resistance change rate: ΔR / R0 ≤ 0.39%;

[0022] 3. Small resistivity change range: ρ 25℃ = 6.13 - 65.38 Ω·cm;

[0023] 4. Adjustable B value: B 25 / 50 = 340.24 - 1751.78 K. Specific embodiments

[0024] The present invention will be further described in detail below in conjunction with embodiments, but is not limited to the given embodiments.

[0025] Embodiment 1

[0026] a. Powder ratio: Weigh La2O3:MnO2:Fe2O3 according to a molar ratio of 1:1.8:0.1 respectively, place them in an agate mortar, add SiO2 according to a mass ratio of 199:1 of the La2O3:MnO2:Fe2O3 mixture, and mix and grind for 10 h to obtain La-Mn-Fe-Si-O mixed powder;

[0027] b. Calcination: The La-Mn-Fe-Si-O mixed powder obtained in step a is calcined at 1150 °C for 2 h to obtain La-Mn-Fe-Si-O powder with a perovskite structure;

[0028] c. Grinding: The perovskite La-Mn-Fe-Si-O powder after calcination in step b is placed in an agate mortar and ground for 6 h;

[0029] d. Molding: The powder after grinding in step c is molded with a mold of 10 mm in diameter to obtain a green body material, which is then vacuum-packaged and cold isostatically pressed at 300 MPa for 180 s to obtain a molded block;

[0030] e. Sintering: The molded block in step d is sintered at 1400 °C for 6 h and cooled to room temperature to obtain a ceramic block material;

[0031] f. Electrode preparation: Platinum paste is coated on both sides of the ceramic block material obtained in step e and sintered at 900 °C for 30 min; The high-stability NTC thermistor material after electrode preparation is subjected to electrical property tests;

[0032] The resistances at 25 °C and 50 °C are measured respectively, and the B value is calculated according to formula (1). The test samples are aged: kept at 125 °C for 500 hours. The resistances at 25 °C and 50 °C after aging are measured respectively, and the B value after aging is calculated according to formula (1);

[0033] B 25 / 50 = 3853.89 × ln(R 25 / R 50 ) (1)

[0034] The test performance is shown in Table 1:

[0035] Table 1

[0036]

[0037] As can be seen from the results in Table 1, the B values of the three samples of the LaMn 0.9 Fe 0.1 O3-SiO2 thermosensitive ceramic material are maintained at about 1147.07 K, the resistivity is about 9.93 Ω·cm, and after aging at 125 °C for 500 h, the change rate of resistivity is less than 0.39%.

[0038] Example 2

[0039] a. Powder ratio: Weigh La2O3, MnO2, and Fe2O3 according to the molar ratio La2O3:MnO2:Fe2O3 = 1:1.4:0.3 respectively, place them in an agate mortar, add SiO2 according to the mass ratio of the La2O3:MnO2:Fe2O3 mixture to be 198:2, and mix and grind for 8 h to obtain a La-Mn-Fe-Si-O mixed powder;

[0040] b. Calcination: Place the La-Mn-Fe-Si-O mixed powder obtained in step a in a furnace and calcine it at 1100 °C for 3 h to obtain a La-Mn-Fe-Si-O powder with a perovskite structure;

[0041] c. Grinding: Place the perovskite La-Mn-Fe-Si-O powder after calcination in step b in an agate mortar and grind it for 4 h;

[0042] d. Molding: Mold the powder after grinding in step c with a mold with a diameter of 10 mm to obtain a green body material, then vacuum package it and perform cold isostatic pressing at a pressure of 320 MPa for 145 s to form a block;

[0043] e. Sintering: Place the formed block in step d in a furnace and sinter it at 1350 °C for 8 h, then cool it to room temperature to obtain a ceramic block material;

[0044] f. Electrode preparation: Coat both sides of the ceramic block material obtained in step e with platinum paste and sinter it at 1000 °C for 20 min; Test the electrical properties of the highly stable NTC thermistor material after electrode preparation;

[0045] Measure the resistance at 25 °C and 50 °C respectively, calculate the B value according to formula (1), and perform aging treatment on the test samples: Keep them at 125 °C for 500 h, measure the resistance at 25 °C and 50 °C after aging respectively, and calculate the B value after aging according to formula (1);

[0046] B 25 / 50 = 3853.89 × ln(R 25 / R 50 ) (1)

[0047] The test performance is shown in Table 2:

[0048] Table 2

[0049]

[0050] As can be seen from the results in Table 2, the B values of the three samples of the LaMn 0.7 Fe 0.3 O3-SiO2 thermosensitive ceramic material are maintained at about 1249.08 K, the resistivity is about 14.47 Ω·cm, and after aging at 125 °C for 500 h, the change rate of the resistivity is less than 0.36%.

[0051] Example 3

[0052] a. Powder ratio: Weigh La2O3, MnO2, and Fe2O3 according to the molar ratio La2O3:MnO2:Fe2O3 = 1:1:0.5 respectively, place them in an agate mortar, add SiO2 according to the mass ratio of the La2O3:MnO2:Fe2O3 mixture to be 199:1, and mix and grind for 6 h to obtain a La-Mn-Fe-Si-O mixed powder;

[0053] b. Calcination: Calcinate the La-Mn-Fe-Si-O mixed powder obtained in step a at a temperature of 1050 °C for 4 h to obtain a La-Mn-Fe-Si-O powder with a perovskite structure;

[0054] c. Grinding: Grind the perovskite La-Mn-Fe-Si-O powder after calcination in step b in an agate mortar for 2 h;

[0055] d. Molding: Mold the powder after grinding in step c with a mold of diameter 10 mm to obtain a green body material, and then vacuum package it and perform cold isostatic pressing at a pressure of 280 MPa for 160 s to form a block;

[0056] e. Sintering: Sinter the block formed in step d at a temperature of 1450 °C for 4 h, and cool it to room temperature to obtain a ceramic block material;

[0057] f. Electrode preparation: Coat both sides of the ceramic block material obtained in step e with platinum paste and sinter at a temperature of 800 °C for 40 min; Test the electrical properties of the highly stable NTC thermistor material after electrode preparation.

[0058] Measure the resistance at 25 °C and 50 °C respectively, and calculate the B value according to formula (1). Perform aging treatment on the test sample: Keep it at 125 °C for 500 hours. Measure the resistance at 25 °C and 50 °C respectively after aging, and calculate the B value after aging according to formula (1);

[0059] B 25 / 50 = 3853.89×ln(R 25 / R 50 )(1)

[0060] The measured performance is shown in Table 3:

[0061] Table 3

[0062]

[0063] As can be seen from the results in Table 3, LaMn 0.5 Fe 0.5The B values of three samples of the O3-SiO2 thermosensitive ceramic material are maintained at about 1751.78 K, the resistivity is about 65.38 Ω·cm, and after aging at 125 °C for 500 h, the change rate of the resistivity is less than 0.29%.

[0064] Any of the highly stable NTC thermosensitive resistor materials prepared by the present invention has a perovskite structure. The microscopic morphologies of all ceramic sheets show good densification, good porcelain forming, consistency and reproducibility, a wide temperature test range, stable material properties, and good anti-aging performance.

[0065] The above are only specific application examples of the present invention and do not constitute any limitation to the protection scope of the present invention. Any technical solutions formed by equivalent transformation or equivalent substitution fall within the scope of the protection of the rights of the present invention.

Claims

1. A highly stable negative temperature coefficient thermistor material, characterized in that This material is made from La2O3, MnO2, Fe2O3, and SiO2 as raw materials through grinding, calcination, shaping, and high-temperature sintering to obtain a La-Mn-Fe-Si-O ceramic material with a perovskite structure. The specific operations are carried out according to the following steps: a. Powder ratio: Weigh La2O3, MnO2, and Fe2O3 according to the molar ratio La2O3:MnO2:Fe2O3 = 1:1 - 1.8:0.1 - 0.5 respectively, place them in an agate mortar, add SiO2, and mix and grind for 6 - 10 h to obtain a La-Mn-Fe-Si-O mixed powder; the mass ratio of the La2O3:MnO2:Fe2O3 mixture to SiO2 is 198 - 199:1 - 2. b. Calcination: Place the La-Mn-Fe-Si-O mixed powder obtained in step a in a furnace and calcine at a temperature of 1050°C - 1200°C for 1 - 4 h to obtain a La-Mn-Fe-Si-O powder with a perovskite structure. c. Grinding: Place the perovskite La-Mn-Fe-Si-O powder after calcination in step b in an agate mortar and grind for 2 - 6 h. d. Shaping: Use a mold with a diameter of 10 mm to shape the powder after grinding in step c to obtain a green body material, then vacuum package it, and perform cold isostatic pressing at a pressure of 280 MPa - 350 MPa for 140 s - 180 s to obtain a shaped block. e. Sintering: Place the shaped block obtained in step d in a furnace and sinter at a temperature of 1300°C - 1450°C for 4 - 10 h, and then cool to room temperature to obtain a ceramic block material. f. Electrode preparation: Coat both sides of the ceramic block material obtained in step e with platinum paste, and sinter at a temperature of 800°C - 1000°C for 20 - 40 min to obtain a highly stable NTC thermistor material.

2. A preparation method of a high-stability negative temperature coefficient thermistor material, characterized in that Carry out according to the following steps: a. Powder ratio: Weigh La2O3, MnO2, and Fe2O3 according to the molar ratio La2O3:MnO2:Fe2O3 = 1:1 - 1.8:0.1 - 0.5 respectively, place them in an agate mortar, add SiO2, and mix and grind for 6 - 10 h to obtain a La-Mn-Fe-Si-O mixed powder, where the mass ratio of the La2O3:MnO2:Fe2O3 mixture to SiO2 is 198 - 199:1 - 2. b. Calcination: Place the La-Mn-Fe-Si-O mixed powder obtained in step a in a furnace and calcine at a temperature of 1050°C - 1200°C for 1 - 4 h to obtain a La-Mn-Fe-Si-O powder with a perovskite structure. c. Grinding: Place the perovskite La-Mn-Fe-Si-O powder after calcination in step b in an agate mortar and grind for 2 - 6 h. d. Shaping: Use a mold with a diameter of 10 mm to shape the powder after grinding in step c to obtain a green body material, vacuum package it, and perform cold isostatic pressing at a pressure of 280 MPa - 350 MPa for 140 s - 180 s to obtain a shaped block. e. Sintering: Place the shaped block obtained in step d in a furnace and sinter at a temperature of 1300°C - 1450°C for 4 - 10 h, and then cool to room temperature to obtain a ceramic block material. f. Electrode preparation: Coat both the front and back sides of the ceramic bulk material obtained in step e with platinum paste, and sinter at a temperature of 800°C - 1000°C for 20 - 40 minutes to obtain a highly stable NTC thermistor material.

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