A composite negative temperature coefficient thermistor ceramic material and its preparation method

Abstract

This invention relates to the field of thermistor materials technology, specifically to a composite negative temperature coefficient thermistor ceramic material and its preparation method. The method involves uniformly mixing acetates of nickel, cobalt, and manganese with oxalic acid, then ball-milling the mixture. The resulting powder is dried and calcined to obtain a powder. Lanthanum and strontium nitrates, manganese acetates, and citric acid are dissolved in dilute nitric acid solution, adjusting the pH to approximately 7. The solution is heated and stirred with a constant-temperature magnetic stirrer until completely dissolved. Heating further evaporates the water, resulting in a mixed powder, which is then calcined to obtain another powder. The powders prepared from both methods are then stirred and mixed uniformly, a binder is added for granulation, followed by molding, calcination, and cooling to obtain the composite negative temperature coefficient thermistor ceramic material. The negative temperature coefficient thermistor ceramic material prepared by this invention exhibits good density, high stability, high precision, excellent conductivity, and suitability for industrial production. Its room temperature resistivity is 7.56–170.34 Ω·cm, and its B value is 1614–3200 K, making it suitable for applications in low-temperature measurement and surge current suppression.

Description

Technical Field

[0001] This invention relates to the field of thermistor materials technology, specifically to a composite negative temperature coefficient thermistor ceramic material and its preparation method. Background Technology

[0002] Mn-Co-Ni-O transition metal oxides with a spinel structure possess negative temperature coefficients and are important materials for the production of various instruments and meters, widely used in sensors, controllers, infrared detectors, and voltage regulators. However, with the gradual development of society, the precision requirements for instruments and meters are becoming increasingly stringent, making it necessary to conduct systematic research on the electrical properties, stability, and consistency of these materials. To effectively suppress surge currents and protect components in electronic circuits, it is significant to prepare NTC thermistors with low resistivity, high B-value, and high stability. Generally, there are two ways to reduce the resistance of thermistor ceramics. One is to modify the functional ceramic properties through ion doping. The other method is two-phase composite materials. It is well known that the properties and functions of a single substance often cannot meet the requirements of comprehensive material performance. However, composite material technology can utilize additive and coupling effects to create new effects not present in the raw materials, or to create composite materials with performance exceeding that of the raw materials. Existing technologies include the preparation of high-temperature NTC thermistors (1-x)CaMn with different weight ratios using solid-state methods. 0.05 Zr 0.95 O 3-x The NiMn2O4 (x=0, 0.1, 0.2, 0.3) phases have a clear composition and a dense and uniform microstructure. With increasing NiMn2O4 weight ratio, ρ... 400 and ρ 700 From 4.9 × 10 6 Ω·cm and 1.4 × 10 5 The Ω·cm decreased to 1.2 × 10 4 Ω·cm and 0.8 × 10 3 Ω·cm, B 400 / 700 The K temperature decreased from 12739 K to 5923 K, and it exhibited good NTC performance over a wide temperature range (150-900 °C). Existing technologies include the preparation of (1-x)Ni via solid-state methods. 0.9 Mn 2.1 O4-xLaCr 0.6 Mn 0.4 O3 composite thermistor ceramics were found to have a similar effect to LaCr. 0.6 Mn 0.4 With increasing O3 content, the resistivity and B value of the composite ceramic gradually decrease. When x = 0.5, ρ 25 It is 17.4 Ω·cm, B25 / 85 The value is 2140 K. Existing technologies include adding LaMnO3 to Bi. 0.2 Sr 0.5 La 0.3 The composite thermistor ceramic prepared in TiO3 still exhibits a room-temperature resistivity as high as 17376.92 Ω·cm. This underscores the urgent need to develop new NTC thermistor materials with low resistance and high stability.

[0003] In view of the above-mentioned defects, the inventors of this invention have finally obtained this invention after a long period of research and practice. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of high resistivity and low stability of negative temperature coefficient thermistor ceramic materials in the prior art, and to provide a composite negative temperature coefficient thermistor ceramic material and its preparation method.

[0005] To achieve the above objectives, this invention discloses a composite negative temperature coefficient thermistor ceramic material, wherein the composite negative temperature coefficient thermistor ceramic material has a composition of (1-x)Ni. 0.6 CoMn 1.4 O4-xLa 0.5 Sr 0.5 MnO3, where x = 0.1~0.5, is derived from Ni. 0.6 CoMn 1.4 O4 and La 0.5 Sr 0.5 MnO3 was prepared by mixing according to a specific molar ratio.

[0006] The composite negative temperature coefficient thermistor ceramic material has a composition of (1-x)Ni. 0.6 CoMn 1.4 O4-xLa 0.5 Sr 0.5 MnO3, where x = 0.1, 0.2, 0.3, 0.4, 0.5, and Ni 0.6 CoMn 1.4 O4 has a spinel structure, La 0.5 Sr 0.5 MnO3 has a perovskite structure.

[0007] This invention also discloses a method for preparing the above-mentioned composite negative temperature coefficient thermistor ceramic material, comprising the following steps:

[0008] S1, after uniformly mixing the acetates of nickel, cobalt, and manganese with oxalic acid, a mixture is obtained. The mixture is then ball-milled, dried, and calcined to obtain powder A;

[0009] S2, Lanthanum and Strontium nitrates, Manganese acetates and citric acid are dissolved in dilute nitric acid solution, stirred thoroughly and then ammonia water is added. After adjusting the pH value, the solution is heated and stirred until 100 mL of solution remains after evaporation. Then the solution is transferred to an evaporating dish and heated with an electric furnace to make the solution completely evaporate and burn. After calcination, powder B is obtained.

[0010] S3, Powder A and powder B obtained in step S1 are ball-milled and mixed to obtain a mixed powder. A binder is added for granulation, molding, calcination and cooling are performed to obtain a composite negative temperature coefficient thermistor ceramic material.

[0011] In step S1, the acetates of nickel, cobalt, and manganese are proportioned in atomic percentage as follows: nickel 20%, cobalt 33.33%, and manganese 46.67%, and the oxalic acid content is 1 to 1.5 times the total molar amount of the metal atoms.

[0012] In step S1, the mixture, grinding media, and dispersant are loaded into a ball mill jar at a weight ratio of 1:(1~3):(1~3) and ball milled for 6~24 h. The dispersant is anhydrous ethanol. The calcination temperature is 650~900 ℃ and the time is 2~4 h.

[0013] In step S2, lanthanum, strontium nitrates, and manganese acetates are mixed in atomic percentages of 25% lanthanum, 25% strontium, and 50% manganese, and the citric acid content is 1 to 1.5 times the total molar amount of the metal atoms.

[0014] In step S2, the calcination temperature is 950~1100 ℃ and the time is 2~4 h.

[0015] In step S3, the adhesive is a polyvinyl alcohol solution with a concentration of 5-8 wt%, and the mass ratio of the adhesive to the mixed powder is (5-8):(95-92).

[0016] In step S3, the calcination temperature is 1200~1300 ℃ and the time is 3~12 h.

[0017] The present invention also discloses a composite negative temperature coefficient thermistor ceramic material prepared by the above preparation method.

[0018] Ni with spinel structure 0.6 CoMn 1.4 O4 exhibits a high activation energy due to its small polaron hopping conductivity mechanism, resulting in high resistivity and B value. Ion doping of spinel-structured materials is insufficient to reduce their resistivity below 10 Ω·cm. In contrast, perovskite-structured La... 0.5 Sr 0.5The Curie temperature of MnO3 is approximately 360 K, or about 85 °C. At room temperature, its conductivity is a double electron exchange process with a low activation energy, resulting in low room temperature resistivity and a low B-value. By adjusting the formulation, materials with low resistivity and high B-value can be obtained, improving upon the situation where a single spinel phase cannot simultaneously achieve low resistivity, high B-value, and high stability.

[0019] Compared with existing technologies, the beneficial effects of this invention are as follows: First, powders are prepared using nickel, cobalt, and manganese acetates and excess oxalic acid as raw materials via a room-temperature solid-phase coordination method. Then, powders are prepared using lanthanum and strontium nitrates, manganese acetates, and excess citric acid as raw materials via a combustion method. The powders prepared from both methods are then mixed, and a novel negative temperature coefficient (NTC) thermistor ceramic material is prepared using a ceramic preparation process. The NTC thermistor ceramic material obtained by this invention exhibits good density, high stability, high precision, excellent conductivity, and suitability for industrial production. Its room-temperature resistivity is 7.56–170.34 Ω·cm, and its B value is 1614–3200 K, making it suitable for applications in low-temperature measurement and surge current suppression. Attached Figure Description

[0020] Figure 1 The 0.9Ni obtained in Example 1 0.6 CoMn 1.4 O4-0.1La 0.5 Sr 0.5 X-ray diffraction pattern of MnO3 ceramic materials;

[0021] Figure 2 The 0.9Ni obtained in Example 1 0.6 CoMn 1.4 O4-0.1La 0.5 Sr 0.5 Scanning electron microscope image of MnO3 ceramic material;

[0022] Figure 3 The 0.8Ni obtained in Example 6 0.6 CoMn 1.4 O4-0.2La 0.5 Sr 0.5 X-ray diffraction pattern of MnO3 ceramic materials;

[0023] Figure 4 The 0.8Ni obtained in Example 6 0.6 CoMn 1.4 O4-0.2La 0.5 Sr 0.5 Scanning electron microscope image of MnO3 ceramic material;

[0024] Figure 5 The 0.7Ni obtained in Example 70.6 CoMn 1.4 O4-0.3La 0.5 Sr 0.5 X-ray diffraction pattern of MnO3 ceramic materials;

[0025] Figure 6 The 0.7Ni obtained in Example 7 0.6 CoMn 1.4 O4-0.3La 0.5 Sr 0.5 Scanning electron microscope image of MnO3 ceramic material;

[0026] Figure 7 The 0.6Ni obtained in Example 8 0.6 CoMn 1.4 O4-0.4La 0.5 Sr 0.5 X-ray diffraction pattern of MnO3 ceramic materials;

[0027] Figure 8 The 0.6Ni obtained in Example 8 0.6 CoMn 1.4 O4-0.4La 0.5 Sr 0.5 Scanning electron microscope image of MnO3 ceramic material;

[0028] Figure 9 The 0.5Ni obtained in Example 9 0.6 CoMn 1.4 O4-0.5La 0.5 Sr 0.5 X-ray diffraction pattern of MnO3 ceramic materials;

[0029] Figure 10 The 0.5Ni obtained in Example 9 0.6 CoMn 1.4 O4-0.5La 0.5 Sr 0.5 Scanning electron microscope image of MnO3 ceramic material;

[0030] Figure 11 Ni obtained in Comparative Example 1 0.6 CoMn 1.4 X-ray diffraction pattern of O4 ceramic material;

[0031] Figure 12 Ni obtained in Comparative Example 1 0.6 CoMn 1.4 Scanning electron microscope image of O4 ceramic material;

[0032] Figure 13 La obtained in Comparative Example 20.5 Sr 0.5 X-ray diffraction pattern of MnO3 ceramic materials;

[0033] Figure 14 The 0.6Ni obtained by solid-phase coordination method in Comparative Example 3 0.6 CoMn 1.4 O4-0.4La 0.5 Sr 0.5 X-ray diffraction pattern of MnO3 ceramic materials;

[0034] Figure 15 The 0.6Ni obtained by solid-phase coordination method in Comparative Example 3 0.6 CoMn 1.4 O4-0.4La 0.5 Sr 0.5 Scanning electron microscope image of MnO3 ceramic material;

[0035] Figure 16 0.6Ni obtained by combustion method in Comparative Example 4 0.6 CoMn 1.4 O4-0.4La 0.5 Sr 0.5 X-ray diffraction pattern of MnO3 ceramic materials;

[0036] Figure 17 0.6Ni obtained by combustion method in Comparative Example 4 0.6 CoMn 1.4 O4-0.4La 0.5 Sr 0.5 Scanning electron microscope image of MnO3 ceramic material. Detailed Implementation

[0037] The above-mentioned and other technical features and advantages of the present invention will be described in more detail below with reference to the embodiments.

[0038] Example 1

[0039] This embodiment provides a composite negative temperature coefficient thermistor ceramic material (1-x)Ni. 0.6 CoMn 1.4 O4-xLa 0.5 Sr 0.5 The preparation method of MnO3 (x=0.1, 1300℃, 5 h) includes the following steps:

[0040] (1) Using analytically pure nickel acetate, cobalt acetate, manganese acetate and oxalic acid as raw materials, the atomic percentages of Ni, Co and Mn were accurately weighed at 20%, 33.33% and 46.67% respectively, and the oxalic acid was weighed at 1.1 times the total molar amount of metal atoms (Ni, Co and Mn). The mixture was loaded into a ball mill jar with agate balls and anhydrous ethanol as dispersant at a weight ratio of 1:2:3 and ball milled (at a speed of 250 r / min) for 5 h. The obtained powder was dried and then calcined (calcined at 700 ℃ for 4 h) to obtain the powder.

[0041] (2) Using analytical grade nickel nitrate, strontium nitrate, manganese acetate and citric acid as raw materials, accurately weigh them according to the atomic percentages of La, Sr and Mn of 25%, 25% and 50% respectively, and weigh citric acid according to 1.2 times the total molar amount of metal atoms (La, Sr and Mn). Then dissolve them in 500 mL of dilute nitric acid solution, stir thoroughly, add ammonia water, adjust the pH value to about 7, heat and stir the solution with a constant temperature magnetic stirrer until 100 mL of solution evaporates. Then transfer the solution to an evaporating dish, use an electric furnace to heat it so that the water evaporates completely and burns. After complete combustion, transfer the powder to a muffle furnace for calcination (calcination at 1050 ℃ for 4 h) to finally obtain the powder.

[0042] (3) Weigh the powder obtained in steps (1) and (2) at a molar ratio of 90:10, and then put the mixture into a ball mill jar with the grinding media agate balls and the dispersant anhydrous ethanol at a weight ratio of 1:2:3 and ball mill (speed of 250 r / min) for 12 h. Dry the obtained powder for later use.

[0043] (4) Add binder (5 wt% polyvinyl alcohol solution) to the powder from step (3) for granulation. The mass ratio of binder to powder is 8:92. Then, mold it into a disc with a diameter of 10 mm under a pressure of 6 MPa. Calcinate the shaped blank at 1300 ℃ for 5 h and finally cool it to obtain the composite negative temperature coefficient thermistor ceramic material 0.9Ni. 0.6 CoMn 1.4 O4-0.1La 0.5 Sr 0.5 MnO3.

[0044] The prepared composite negative temperature coefficient thermistor ceramic material was subjected to electrical performance testing. The testing method was as follows: the surface of the composite negative temperature coefficient thermistor ceramic material was first polished with diamond abrasive as the polishing medium. Then, a uniform layer of silver paste was coated on both surfaces. After drying, the silver was fired in a resistance furnace at 750 ℃ ​​and held for 15 min. After silvering, the ceramic sample was polished on the sides and then subjected to electrical performance testing.

[0045] Resistance Measurement: Silver electrode leads were soldered onto the silver-coated ceramic sample. The resistance was measured using an Agilent 34401A digital multimeter at 25 °C and 85 °C in methyl silicone oil. 25 and R 85 Calculate the resistivity according to the formula:

[0046]

[0047] In the formula: ρ is the resistivity of the sample, Ω·cm; R is the resistance of the sample, Ω; S is the area of ​​the sample, cm². 2 L represents the thickness of the sample, in cm.

[0048] B-value calculation:

[0049]

[0050] In the formula, R1 and R2 are the resistance values ​​of the sample at temperatures of 25 ℃ and 85 ℃, respectively.

[0051] Figure 1 , Figure 2 The images show its X-ray diffraction pattern and scanning electron microscope (SEM) image, respectively. The X-ray diffraction pattern reveals that the ceramic is composed of cubic spinel and tetragonal perovskite phases. The SEM image shows nanoscale La... 0.5 Sr 0.5 MnO3 particles are distributed in Ni 0.6 CoMn 1.4 At the O4 grain boundaries. The sample has good density, and no obvious pores were observed.

[0052] The electrical parameters of the composite negative temperature coefficient thermistor ceramic material prepared in this embodiment were measured as follows: room temperature resistivity of 170.34±1% Ω·cm and B value of 3200±2% K.

[0053] After aging the composite negative temperature coefficient thermistor ceramic material in an oven at 150 ℃ for 500 h, its aging value was measured to be 1.63±0.2%.

[0054] Example 2

[0055] This embodiment provides a composite negative temperature coefficient thermistor ceramic material (1-x)Ni. 0.6 CoMn 1.4 O4-xLa 0.5 Sr 0.5 The preparation method of MnO3 (x=0.1, 1200℃, 12 h) includes the following steps:

[0056] (1) Using analytically pure nickel acetate, cobalt acetate, manganese acetate and oxalic acid as raw materials, the atomic percentages of Ni, Co and Mn were accurately weighed at 20%, 33.33% and 46.67% respectively, and the oxalic acid was weighed at 1.1 times the total molar amount of metal atoms (Ni, Co and Mn). The mixture was loaded into a ball mill jar with agate balls and anhydrous ethanol as dispersant at a weight ratio of 1:2:3 and ball milled (at a speed of 250 r / min) for 5 h. The obtained powder was dried and then calcined (calcined at 700 ℃ for 4 h) to obtain the powder.

[0057] (2) Using analytical grade nickel nitrate, strontium nitrate, manganese acetate and citric acid as raw materials, accurately weigh them according to the atomic percentages of La, Sr and Mn of 25%, 25% and 50% respectively, and weigh citric acid according to 1.2 times the total molar amount of metal atoms (La, Sr and Mn). Then dissolve them in 500 mL of dilute nitric acid solution, stir thoroughly, add ammonia water, adjust the pH value to about 7, heat and stir the solution with a constant temperature magnetic stirrer until 100 mL of solution evaporates. Then transfer the solution to an evaporating dish, use an electric furnace to heat it so that the water evaporates completely and burns. After complete combustion, transfer the powder to a muffle furnace for calcination (calcination at 1050 ℃ for 4 h) to finally obtain the powder.

[0058] (3) Weigh the powder obtained in steps (1) and (2) at a molar ratio of 90:10, and then put the mixture into a ball mill jar with the grinding media agate balls and the dispersant anhydrous ethanol at a weight ratio of 1:2:3 and ball mill (speed of 250 r / min) for 12 h. Dry the obtained powder for later use.

[0059] (4) Add binder (5 wt% polyvinyl alcohol solution) to the powder in step (3) for granulation. The mass ratio of binder to powder is 8:92. Then, mold it into a disc with a diameter of 10 mm under a pressure of 6 MPa. Calcine the shaped blank at 1200 ℃ for 12 h and finally cool it to obtain the composite negative temperature coefficient thermistor ceramic material.

[0060] The electrical parameters of the composite negative temperature coefficient thermistor ceramic material prepared in this embodiment were measured as follows: room temperature resistivity of 138.04±1% Ω·cm and B value of 3153±2% K.

[0061] After aging the composite negative temperature coefficient thermistor ceramic material in an oven at 150 ℃ for 500 h, its aging value was measured to be 3.85±0.2%.

[0062] Example 3

[0063] This embodiment provides a composite negative temperature coefficient thermistor ceramic material (1-x)Ni. 0.6 CoMn 1.4 O4-xLa0.5 Sr 0.5 The preparation method of MnO3 (x=0.1, 1200℃, 3 h) includes the following steps:

[0064] (1) Using analytically pure nickel acetate, cobalt acetate, manganese acetate and oxalic acid as raw materials, the atomic percentages of Ni, Co and Mn were accurately weighed at 20%, 33.33% and 46.67% respectively, and the oxalic acid was weighed at 1.1 times the total molar amount of metal atoms (Ni, Co and Mn). The mixture was loaded into a ball mill jar with agate balls and anhydrous ethanol as dispersant at a weight ratio of 1:2:3 and ball milled (at a speed of 250 r / min) for 5 h. The obtained powder was dried and then calcined (calcined at 700 ℃ for 4 h) to obtain the powder.

[0065] (2) Using analytical grade nickel nitrate, strontium nitrate, manganese acetate and citric acid as raw materials, accurately weigh them according to the atomic percentages of La, Sr and Mn of 25%, 25% and 50% respectively, and weigh citric acid according to 1.2 times the total molar amount of metal atoms (La, Sr and Mn). Then dissolve them in 500 mL of dilute nitric acid solution, stir thoroughly, add ammonia water, adjust the pH value to about 7, heat and stir the solution with a constant temperature magnetic stirrer until 100 mL of solution evaporates. Then transfer the solution to an evaporating dish, use an electric furnace to heat it so that the water evaporates completely and burns. After complete combustion, transfer the powder to a muffle furnace for calcination (calcination at 1050 ℃ for 4 h) to finally obtain the powder.

[0066] (3) Weigh the powder obtained in steps (1) and (2) at a molar ratio of 90:10, and then put the mixture into a ball mill jar with the grinding media agate balls and the dispersant anhydrous ethanol at a weight ratio of 1:2:3 and ball mill (speed of 250 r / min) for 12 h. Dry the obtained powder for later use.

[0067] (4) Add binder (5 wt% polyvinyl alcohol solution) to the powder in step (3) for granulation. The mass ratio of binder to powder is 8:92. Then, mold it into a disc with a diameter of 10 mm under a pressure of 6 MPa. Calcine the shaped blank at 1200 ℃ for 3 h and finally cool it to obtain the composite negative temperature coefficient thermistor ceramic material.

[0068] The electrical parameters of the composite negative temperature coefficient thermistor ceramic material prepared in this embodiment were measured as follows: room temperature resistivity of 144.32±1% Ω·cm and B value of 3137±2% K.

[0069] The composite negative temperature coefficient thermistor ceramic material was aged in an oven at 150 ℃ for 500 h, and its aging value was measured to be 2.88±0.3%.

[0070] Example 4

[0071] This embodiment provides a composite negative temperature coefficient thermistor ceramic material (1-x)Ni. 0.6 CoMn 1.4 O4-xLa 0.5 Sr 0.5 The preparation method of MnO3 (x=0.1, 1250℃, 3 h) includes the following steps:

[0072] 1) Using analytically pure nickel acetate, cobalt acetate, manganese acetate, and oxalic acid as raw materials, the atomic percentages of Ni, Co, and Mn were accurately weighed at 20%, 33.33%, and 46.67%, respectively, and the oxalic acid was weighed at 1.1 times the total molar amount of metal atoms (Ni, Co, and Mn). The mixture was then loaded into a ball mill jar with agate balls as grinding media and anhydrous ethanol as dispersant at a weight ratio of 1:2:3 and ball-milled (at a speed of 250 r / min) for 5 h. The resulting powder was dried and then calcined (calcined at 700 ℃ for 4 h) to obtain the powder.

[0073] (2) Using analytical grade nickel nitrate, strontium nitrate, manganese acetate and citric acid as raw materials, accurately weigh them according to the atomic percentages of La, Sr and Mn of 25%, 25% and 50% respectively, and weigh citric acid according to 1.2 times the total molar amount of metal atoms (La, Sr and Mn). Then dissolve them in 500 mL of dilute nitric acid solution, stir thoroughly, add ammonia water, adjust the pH value to about 7, heat and stir the solution with a constant temperature magnetic stirrer until 100 mL of solution evaporates. Then transfer the solution to an evaporating dish, use an electric furnace to heat it so that the water evaporates completely and burns. After complete combustion, transfer the powder to a muffle furnace for calcination (calcination at 1050 ℃ for 4 h) to finally obtain the powder.

[0074] (3) Weigh the powder obtained in steps (1) and (2) at a molar ratio of 90:10, and then put the mixture into a ball mill jar with the grinding media agate balls and the dispersant anhydrous ethanol at a weight ratio of 1:2:3 and ball mill (speed of 250 r / min) for 12 h. Dry the obtained powder for later use.

[0075] (4) Add binder (5 wt% polyvinyl alcohol solution) to the powder in step (3) for granulation. The mass ratio of binder to powder is 8:92. Then, press it into a disc with a diameter of 10 mm under a pressure of 6 MPa. Calcine the shaped blank at 1250 ℃ for 3 h and finally cool it to obtain the composite negative temperature coefficient thermistor ceramic material.

[0076] The electrical parameters of the composite negative temperature coefficient thermistor ceramic material prepared in this embodiment were measured as follows: room temperature resistivity of 140.51±1% Ω·cm and B value of 3157±2% K.

[0077] After aging the composite negative temperature coefficient thermistor ceramic material in an oven at 150 ℃ for 500 h, its aging value was measured to be 2.04±0.2%.

[0078] Example 5

[0079] This embodiment provides a composite negative temperature coefficient thermistor ceramic material (1-x)Ni. 0.6 CoMn 1.4 O4-xLa 0.5 Sr 0.5 The preparation method of MnO3 (x=0.1, 1300℃, 3 h) includes the following steps:

[0080] (1) Using analytically pure nickel acetate, cobalt acetate, manganese acetate and oxalic acid as raw materials, the atomic percentages of Ni, Co and Mn were accurately weighed at 20%, 33.33% and 46.67% respectively, and the oxalic acid was weighed at 1.1 times the total molar amount of metal atoms (Ni, Co and Mn). The mixture was loaded into a ball mill jar with agate balls and anhydrous ethanol as dispersant at a weight ratio of 1:2:3 and ball milled (at a speed of 250 r / min) for 5 h. The obtained powder was dried and then calcined (calcined at 700 ℃ for 4 h) to obtain the powder.

[0081] (2) Using analytical grade nickel nitrate, strontium nitrate, manganese acetate and citric acid as raw materials, accurately weigh them according to the atomic percentages of La, Sr and Mn of 25%, 25% and 50% respectively, and weigh citric acid according to 1.2 times the total molar amount of metal atoms (La, Sr and Mn). Then dissolve them in 500 mL of dilute nitric acid solution, stir thoroughly, add ammonia water, adjust the pH value to about 7, heat and stir the solution with a constant temperature magnetic stirrer until 100 mL of solution evaporates. Then transfer the solution to an evaporating dish, use an electric furnace to heat it so that the water evaporates completely and burns. After complete combustion, transfer the powder to a muffle furnace for calcination (calcination at 1050 ℃ for 4 h) to finally obtain the powder.

[0082] (3) Weigh the powder obtained in steps (1) and (2) at a molar ratio of 90:10, and then put the mixture into a ball mill jar with the grinding media agate balls and the dispersant anhydrous ethanol at a weight ratio of 1:2:3 and ball mill (speed of 250 r / min) for 12 h. Dry the obtained powder for later use.

[0083] (4) Add binder (5 wt% polyvinyl alcohol solution) to the powder in step (3) for granulation. The mass ratio of binder to powder is 8:92. Then, press it into a disc with a diameter of 10 mm under a pressure of 6 MPa. Calcine the shaped blank at 1300 ℃ for 3 h and finally cool it to obtain the composite negative temperature coefficient thermistor ceramic material.

[0084] The electrical parameters of the composite negative temperature coefficient thermistor ceramic material prepared in this embodiment were measured as follows: room temperature resistivity of 142.68±1% Ω·cm and B value of 3197±2% K.

[0085] After aging the composite negative temperature coefficient thermistor ceramic material in an oven at 150 ℃ for 500 h, its aging value was measured to be 1.36±0.2%.

[0086] Examples 1-5 are examples of optimized sintering process parameters with x = 0.1 composition. Comparing the performance of the composite negative temperature coefficient thermistor ceramic materials obtained in Examples 1-5, it can be seen that the ceramic has the lowest resistivity when sintered at 1200℃, but the ceramic density is relatively low, resulting in a higher aging value. The ceramic prepared by holding at 1300℃ for 5 hours has higher density and a lower aging value, which are suitable sintering process parameters.

[0087] Example 6

[0088] This embodiment provides a composite negative temperature coefficient thermistor ceramic material (1-x)Ni. 0.6 CoMn 1.4 O4-xLa 0.5 Sr 0.5 The preparation method of MnO3 (x=0.2, 1300℃, 5 h) includes the following steps:

[0089] (1) Using analytically pure nickel acetate, cobalt acetate, manganese acetate and oxalic acid as raw materials, the atomic percentages of Ni, Co and Mn were accurately weighed at 20%, 33.33% and 46.67% respectively, and the oxalic acid was weighed at 1.1 times the total molar amount of metal atoms (Ni, Co and Mn). The mixture was loaded into a ball mill jar with agate balls and anhydrous ethanol as dispersant at a weight ratio of 1:2:3 and ball milled (at a speed of 250 r / min) for 5 h. The obtained powder was dried and then calcined (calcined at 700 ℃ for 4 h) to obtain the powder.

[0090] (2) Using analytical grade nickel nitrate, strontium nitrate, manganese acetate and citric acid as raw materials, accurately weigh them according to the atomic percentages of La, Sr and Mn of 25%, 25% and 50% respectively, and weigh citric acid according to 1.2 times the total molar amount of metal atoms (La, Sr and M8n). Then dissolve them in 500 mL of dilute nitric acid solution, stir thoroughly, add ammonia water, adjust the pH value to about 7, heat and stir the solution with a constant temperature magnetic stirrer until 100 mL of solution evaporates. Then transfer the solution to an evaporating dish, heat it with an electric furnace to make the water evaporate completely and burn it. After the combustion is complete, transfer the powder to a muffle furnace for calcination (calcination at 1050 ℃ for 4 h) to finally obtain the powder.

[0091] (3) Weigh the powder obtained in steps (1) and (2) according to a molar ratio of 80:20. Then, put the mixture, agate balls and anhydrous ethanol as the dispersant into a ball mill jar at a weight ratio of 1:2:3 and ball mill (250 r / min) for 12 h. Dry the obtained powder for later use.

[0092] (4) Add binder (5 wt% polyvinyl alcohol solution) to the powder from step (3) for granulation. The mass ratio of binder to powder is 8:92. Then, mold it into a disc with a diameter of 10 mm under a pressure of 6 MPa. Calcinate the shaped blank at 1300 ℃ for 5 h and finally cool it to obtain the composite negative temperature coefficient thermistor ceramic material 0.8Ni. 0.6 CoMn 1.4 O4-0.2La 0.5 Sr 0.5 MnO3.

[0093] Figure 3 , Figure 4 The images shown are its X-ray diffraction pattern and scanning electron microscope image. The X-ray diffraction pattern reveals that the ceramic is composed of cubic spinel and tetragonal perovskite phases. (Compared to 0.9Ni...) 0.6 CoMn 1.4 O4-0.1La 0.5 Sr 0.5 Compared to the X-ray diffraction pattern of MnO3, due to La 0.5 Sr 0.5 With increasing MnO3 content, the diffraction peaks of the tetragonal perovskite phase were significantly enhanced. Scanning electron microscopy images showed nanoscale La... 0.5 Sr 0.5 The number of MnO3 particles increased significantly, and they were distributed in Ni. 0.6 CoMn 1.4 At the O4 grain boundary. This further confirms the presence of La. 0.5 Sr 0.5 Increase in MnO3 content.

[0094] The electrical parameters of the composite negative temperature coefficient thermistor ceramic material prepared in this embodiment were measured as follows: room temperature resistivity of 108.02±1% Ω·cm and B value of 2868±2% K.

[0095] After aging the composite negative temperature coefficient thermistor ceramic material in an oven at 150 ℃ for 500 h, its aging value was measured to be 1.64±0.1%.

[0096] Example 7

[0097] This embodiment provides a composite negative temperature coefficient thermistor ceramic material (1-x)Ni. 0.6 CoMn 1.4 O4-xLa0.5 Sr 0.5 The preparation method of MnO3 (x=0.3, 1300℃, 5 h) includes the following steps:

[0098] (1) Using analytically pure nickel acetate, cobalt acetate, manganese acetate and oxalic acid as raw materials, the atomic percentages of Ni, Co and Mn were accurately weighed at 20%, 33.33% and 46.67% respectively, and the oxalic acid was weighed at 1.1 times the total molar amount of metal atoms (Ni, Co and Mn). The mixture was loaded into a ball mill jar with agate balls and anhydrous ethanol as dispersant at a weight ratio of 1:2:3 and ball milled (at a speed of 250 r / min) for 5 h. The obtained powder was dried and then calcined (calcined at 700 ℃ for 4 h) to obtain the powder.

[0099] (2) Using analytical grade nickel nitrate, strontium nitrate, manganese acetate and citric acid as raw materials, accurately weigh them according to the atomic percentages of La, Sr and Mn of 25%, 25% and 50% respectively, and weigh citric acid according to 1.2 times the total molar amount of metal atoms (La, Sr and Mn). Then dissolve them in 500 mL of dilute nitric acid solution, stir thoroughly, add ammonia water, adjust the pH value to about 7, heat and stir the solution with a constant temperature magnetic stirrer until 100 mL of solution evaporates. Then transfer the solution to an evaporating dish, use an electric furnace to heat it so that the water evaporates completely and burns. After complete combustion, transfer the powder to a muffle furnace for calcination (calcination at 1050 ℃ for 4 h) to finally obtain the powder.

[0100] (3) Weigh the powder obtained in steps (1) and (2) according to a molar ratio of 70:30. Then, put the mixture, agate balls and anhydrous ethanol as the dispersant into a ball mill jar at a weight ratio of 1:2:3 and ball mill (250 r / min) for 12 h. Dry the obtained powder for later use.

[0101] (4) Add binder (5 wt% polyvinyl alcohol solution) to the powder from step (3) for granulation. The mass ratio of binder to powder is 8:92. Then, mold it into a disc with a diameter of 10 mm under a pressure of 6 MPa. Calcinate the shaped blank at 1300 ℃ for 5 h and finally cool it to obtain the composite negative temperature coefficient thermistor ceramic material 0.7Ni. 0.6 CoMn 1.4 O4-0.3La 0.5 Sr 0.5 MnO3.

[0102] Figure 5 , Figure 6 The images shown are its X-ray diffraction pattern and scanning electron microscope image. The X-ray diffraction pattern reveals that the ceramic is composed of cubic spinel and tetragonal perovskite phases. 0.5 Sr 0.5The strongest peak of the MnO3 phase is higher than that of Ni. 0.6 CoMn 1.4 The strongest peak in the O4 phase. Scanning electron microscopy images show nanoscale La. 0.5 Sr 0.5 MnO3 particles are distributed in Ni 0.6 CoMn 1.4 At the O4 grain boundaries, a connected network gradually forms. Due to La... 0.5 Sr 0.5 The increase in MnO3 content inhibited Ni 0.6 CoMn 1.4 Growth of O4 grains.

[0103] The electrical parameters of the composite negative temperature coefficient thermistor ceramic material prepared in this embodiment were measured as follows: room temperature resistivity of 20.26±1% Ω·cm and B value of 2026±2% K.

[0104] The composite negative temperature coefficient thermistor ceramic material was aged in an oven at 150 ℃ for 500 h, and its aging value was measured to be 4.23±0.1%.

[0105] Example 8

[0106] This embodiment provides a composite negative temperature coefficient thermistor ceramic material (1-x)Ni. 0.6 CoMn 1.4 O4-xLa 0.5 Sr 0.5 The preparation method of MnO3 (x=0.4, 1300℃, 5 h) includes the following steps:

[0107] (1) Using analytically pure nickel acetate, cobalt acetate, manganese acetate and oxalic acid as raw materials, the atomic percentages of Ni, Co and Mn were accurately weighed at 20%, 33.33% and 46.67% respectively, and the oxalic acid was weighed at 1.1 times the total molar amount of metal atoms (Ni, Co and Mn). The mixture was loaded into a ball mill jar with agate balls and anhydrous ethanol as dispersant at a weight ratio of 1:2:3 and ball milled (at a speed of 250 r / min) for 5 h. The obtained powder was dried and then calcined (calcined at 700 ℃ for 4 h) to obtain the powder.

[0108] (2) Using analytical grade nickel nitrate, strontium nitrate, manganese acetate and citric acid as raw materials, accurately weigh them according to the atomic percentages of La, Sr and Mn of 25%, 25% and 50% respectively, and weigh citric acid according to 1.2 times the total molar amount of metal atoms (La, Sr and Mn). Then dissolve them in 500 mL of dilute nitric acid solution, stir thoroughly, add ammonia water, adjust the pH value to about 7, heat and stir the solution with a constant temperature magnetic stirrer until 100 mL of solution evaporates. Then transfer the solution to an evaporating dish, use an electric furnace to heat it so that the water evaporates completely and burns. After complete combustion, transfer the powder to a muffle furnace for calcination (calcination at 1050 ℃ for 4 h) to finally obtain the powder.

[0109] (3) Weigh the powder obtained in steps (1) and (2) according to a molar ratio of 60:40. Then, put the mixture into a ball mill jar with the grinding media agate balls and the dispersant anhydrous ethanol at a weight ratio of 1:2:3 and ball mill (speed of 250 r / min) for 12 h. Dry the obtained powder for later use.

[0110] (4) Add binder (5 wt% polyvinyl alcohol solution) to the powder from step (3) for granulation. The mass ratio of binder to powder is 8:92. Then, mold it into a disc with a diameter of 10 mm under a pressure of 6 MPa. Calcinate the shaped blank at 1300 ℃ for 5 h and finally cool it to obtain the composite negative temperature coefficient thermistor ceramic material 0.6Ni. 0.6 CoMn 1.4 O4-0.4La 0.5 Sr 0.5 MnO3.

[0111] Figure 7 , Figure 8 The images shown are its X-ray diffraction pattern and scanning electron microscope image. The X-ray diffraction pattern reveals that the ceramic is composed of cubic spinel and tetragonal perovskite phases. Ni 0.6 CoMn 1.4 The diffraction peak intensity of the O4 phase is significantly reduced. Scanning electron microscopy images show that La 0.5 Sr 0.5 MnO3 particles are distributed in Ni 0.6 CoMn 1.4 At the O4 grain boundaries, a connected network is formed. Ni 0.6 CoMn 1.4 The number of O4 grains is significantly reduced.

[0112] The electrical parameters of the composite negative temperature coefficient thermistor ceramic material prepared in this embodiment were measured as follows: room temperature resistivity of 7.560±1% Ω·cm and B value of 1614±1% K.

[0113] After aging the composite negative temperature coefficient thermistor ceramic material in an oven at 150 ℃ for 500 h, its aging value was measured to be 3.07±0.2%.

[0114] Example 9

[0115] This embodiment provides a composite negative temperature coefficient thermistor ceramic material (1-x)Ni. 0.6 CoMn 1.4 O4-xLa 0.5 Sr 0.5 The preparation method of MnO3 (x = 0.5, 1300℃, 5 h) includes the following steps:

[0116] (1) Using analytically pure nickel acetate, cobalt acetate, manganese acetate and oxalic acid as raw materials, the atomic percentages of Ni, Co and Mn were accurately weighed at 20%, 33.33% and 46.67% respectively, and the oxalic acid was weighed at 1.1 times the total molar amount of metal atoms (Ni, Co and Mn). The mixture was loaded into a ball mill jar with agate balls and anhydrous ethanol as dispersant at a weight ratio of 1:2:3 and ball milled (at a speed of 250 r / min) for 5 h. The obtained powder was dried and then calcined (calcined at 700 ℃ for 4 h) to obtain the powder.

[0117] (2) Using analytical grade nickel nitrate, strontium nitrate, manganese acetate and citric acid as raw materials, accurately weigh them according to the atomic percentages of La, Sr and Mn of 25%, 25% and 50% respectively, and weigh citric acid according to 1.2 times the total molar amount of metal atoms (La, Sr and Mn). Then dissolve them in 500 mL of dilute nitric acid solution, stir thoroughly, add ammonia water, adjust the pH value to about 7, heat and stir the solution with a constant temperature magnetic stirrer until 100 mL of solution evaporates. Then transfer the solution to an evaporating dish, use an electric furnace to heat it so that the water evaporates completely and burns. After complete combustion, transfer the powder to a muffle furnace for calcination (calcination at 1050 ℃ for 4 h) to finally obtain the powder.

[0118] (3) Weigh the powder obtained in steps (1) and (2) according to a molar ratio of 50:50. Then, put the mixture, agate balls for grinding media, and anhydrous ethanol for dispersant into a ball mill jar at a weight ratio of 1:2:3 and ball mill (speed of 250 r / min) for 12 h. Dry the obtained powder for later use.

[0119] (4) Add binder (5 wt% polyvinyl alcohol solution) to the powder from step (3) for granulation. The mass ratio of binder to powder is 8:92. Then, mold it into a disc with a diameter of 10 mm under a pressure of 6 MPa. Calcinate the shaped blank at 1300 ℃ for 5 h and finally cool it to obtain the composite negative temperature coefficient thermistor ceramic material 0.5Ni. 0.6 CoMn 1.4O4-0.5La 0.5 Sr 0.5 MnO3.

[0120] Figure 9 , Figure 10 The images shown are its X-ray diffraction pattern and scanning electron microscope (SEM) image. The X-ray diffraction pattern reveals that the ceramic consists of a cubic spinel phase and a tetragonal perovskite phase. The SEM image shows La... 0.5 Sr 0.5 MnO3 particles form a connected network.

[0121] The electrical parameters of the composite negative temperature coefficient thermistor ceramic material prepared in this embodiment were measured as follows: room temperature resistivity of 12.39±1% Ω·cm and B value of 1686±1% K.

[0122] The composite negative temperature coefficient thermistor ceramic material was aged in an oven at 150 ℃ for 500 h, and its aging value was measured to be 2.19±0.2%.

[0123] Examples 1 and 6-9 illustrate the effect of x variation under determined process parameters. Comparing the performance of the composite negative temperature coefficient thermistor ceramic materials obtained in Examples 1 and 6-9, it can be seen that as La... 0.5 Sr 0.5 With increasing MnO3 content, the resistivity and B value of the composite ceramic initially decrease and then increase. 0.6Ni 0.6 CoMn 1.4 O4-0.4La 0.5 Sr 0.5 MnO3 has the lowest resistivity.

[0124] Comparative Example 1

[0125] This embodiment provides a composite negative temperature coefficient thermistor ceramic material (1-x)Ni. 0.6 CoMn 1.4 O4-xLa 0.5 Sr 0.5 The preparation method of MnO3 (x=0, 1300℃, 5 h) includes the following steps:

[0126] (1) Using analytically pure nickel acetate, cobalt acetate, manganese acetate and oxalic acid as raw materials, the atomic percentages of Ni, Co and Mn were accurately weighed at 20%, 33.33% and 46.67% respectively, and the oxalic acid was weighed at 1.1 times the total molar amount of metal atoms (Ni, Co and Mn). The mixture was loaded into a ball mill jar with agate balls and anhydrous ethanol as dispersant at a weight ratio of 1:2:3 and ball milled (at a speed of 250 r / min) for 5 h. The obtained powder was dried and then calcined (calcined at 700 ℃ for 4 h) to obtain the powder.

[0127] (2) The powder obtained in step (1) is mixed with the grinding media agate balls and the dispersant anhydrous ethanol in a weight ratio of 1:2:3 and then ball-milled in a ball mill (rotation speed of 250 r / min) for 12 h. The resulting powder is then dried for later use.

[0128] (3) Add binder (5 wt% polyvinyl alcohol solution) to the powder from step (2) for granulation. The mass ratio of binder to powder is 8:92. Then, mold it into a disc with a diameter of 10 mm under a pressure of 6 MPa. Calcinate the shaped blank at 1300 ℃ for 5 h and finally cool it to obtain the negative temperature coefficient thermistor ceramic material Ni. 0.6 CoMn 1.4 O4.

[0129] Figure 11 , Figure 12 The images shown are its X-ray diffraction pattern and scanning electron microscope (SEM) image. The X-ray diffraction pattern reveals that the ceramic consists of cubic spinel and tetragonal spinel phases. This is due to the decomposition of the cubic spinel phase caused by high temperature. The SEM image shows that the ceramic is highly toxic, containing Ni. 0.6 CoMn 1.4 O4 particles are relatively large.

[0130] The electrical parameters of the negative temperature coefficient thermistor ceramic material prepared in this comparative example were measured as follows: room temperature resistivity of 390.45±1% Ω·cm and B value of 3386±2% K.

[0131] After aging the negative temperature coefficient thermistor ceramic material in an oven at 150 ℃ for 500 h, its aging value was measured to be 0.94±0.3%.

[0132] Comparative Example 2

[0133] This embodiment provides a composite negative temperature coefficient thermistor ceramic material (1-x)Ni. 0.6 CoMn 1.4 O4-xLa 0.5 Sr 0.5 The preparation method of MnO3 (x=1, 1300℃, 5 h) includes the following steps:

[0134] (1) Using analytical grade nickel nitrate, strontium nitrate, manganese acetate and citric acid as raw materials, accurately weigh them according to the atomic percentages of La, Sr and Mn of 25%, 25% and 50% respectively, and weigh citric acid according to 1.2 times the total molar amount of metal atoms (La, Sr and Mn). Then dissolve them in 500 mL of dilute nitric acid solution, stir thoroughly, add ammonia water, adjust the pH value to about 7, heat and stir the solution with a constant temperature magnetic stirrer until 100 mL of solution evaporates. Then transfer the solution to an evaporating dish, heat it with an electric furnace to make the water evaporate completely and burn it. After the combustion is complete, transfer the powder to a muffle furnace for calcination (calcination at 1050 ℃ for 4 h) to finally obtain the powder.

[0135] (2) The powder obtained in step (1) is mixed with the grinding media agate balls and the dispersant anhydrous ethanol in a weight ratio of 1:2:3 and then ball-milled in a ball mill (rotation speed of 250 r / min) for 12 h. The resulting powder is then dried for later use.

[0136] (3) Add binder (5 wt% polyvinyl alcohol solution) to the powder from step (2) for granulation. The mass ratio of binder to powder is 8:92. Then, mold it into a disc with a diameter of 10 mm under a pressure of 6 MPa. Calcinate the shaped blank at 1300 ℃ for 5 h and finally cool it to obtain the composite negative temperature coefficient thermistor ceramic material La. 0.5 Sr 0.5 MnO3.

[0137] Figure 13 The X-ray diffraction pattern shows that the ceramic consists of a single-phase tetragonal perovskite phase. The sample has high crystallinity, and no obvious impurity phases were observed.

[0138] The electrical parameters of the negative temperature coefficient thermistor ceramic material prepared in this comparative example were measured as follows: room temperature resistivity of 0.22±10% Ω·cm and B value of 557±5% K.

[0139] After aging the composite negative temperature coefficient thermistor ceramic material in an oven at 150 ℃ for 500 h, its aging value was measured to be 8.84±1%.

[0140] Comparative Example 3

[0141] Preparation of 0.6 Ni by solid-phase coordination method 0.6 CoMn 1.4 O4-0.4 La 0.5 Sr 0.5 MnO3:

[0142] (1) Using analytically pure nickel acetate, cobalt acetate, manganese acetate, strontium acetate, lanthanum acetate and oxalic acid as raw materials, the atomic percentages of Ni, Co, Mn, La and Sr were accurately weighed as 13.8%, 23.1%, 47.7%, 7.7% and 7.7% respectively. Oxalic acid was weighed as 1.1 times the total molar amount of metal atoms (Ni, Co, Mn, La and Sr). The mixture was loaded into a ball mill jar with agate balls and anhydrous ethanol as dispersant at a weight ratio of 1:2:3 and ball milled (at a speed of 250 r / min) for 5 h. The obtained powder was dried and then calcined (calcined at 700 ℃ for 4 h) to obtain powder.

[0143] (2) The powder obtained in step (1) is mixed with the grinding media agate balls and the dispersant anhydrous ethanol in a weight ratio of 1:2:3 and then ball-milled in a ball mill (rotation speed of 250 r / min) for 12 h. The resulting powder is then dried for later use.

[0144] (3) Add binder (5 wt% polyvinyl alcohol solution) to the powder in step (2) for granulation. The mass ratio of binder to powder is 8:92. Then, mold it into a disc with a diameter of 10 mm under a pressure of 6 MPa. Calcine the shaped blank at 1300 ℃ for 5 h and finally cool it to obtain the composite negative temperature coefficient thermistor ceramic material.

[0145] Figure 14 , Figure 15 The images show its X-ray diffraction pattern and scanning electron microscope (SEM) image. The X-ray diffraction pattern reveals that the ceramic consists of cubic spinel and tetragonal perovskite phases. The SEM results show that the sample contains nanoscale La... 0.5 Sr 0.5 MnO3 grains and micron-sized Ni 0.6 CoMn 1.4 The sample is composed of O4 grains. In addition, a small number of pores can be observed in the sample.

[0146] The electrical parameters of the composite negative temperature coefficient thermistor ceramic material prepared in this comparative example were measured as follows: room temperature resistivity of 23.13±1% Ω·cm and B value of 2073±2% K.

[0147] The composite negative temperature coefficient thermistor ceramic material was aged in an oven at 150 ℃ for 500 h, and its aging value was measured to be 5.81±0.3%.

[0148] Comparative Example 4

[0149] 0.6 Ni was prepared by combustion method. 0.6 CoMn 1.4 O4-0.4 La 0.5 Sr 0.5 MnO3:

[0150] (1) Using analytical grade nickel nitrate, cobalt nitrate, manganese acetate, strontium nitrate, lanthanum nitrate and citric acid as raw materials, the atomic percentages of Ni, Co, Mn, La and Sr were accurately weighed as 13.8%, 23.1%, 47.7%, 7.7% and 7.7% respectively. Citric acid was weighed as 1.2 times the total molar amount of metal atoms (Ni, Co, Mn, La and Sr). The solutions were then dissolved in 500 mL of dilute nitric acid solution. After thorough stirring, ammonia water was added to adjust the pH to about 7. The solution was heated and stirred with a constant temperature magnetic stirrer until 100 mL of solution evaporated. The solution was then transferred to an evaporating dish and heated with an electric furnace to completely evaporate the water and burn it. After complete combustion, the powder was transferred to a muffle furnace for calcination (calcined at 1050 °C for 4 h) to finally obtain the powder.

[0151] (2) The powder obtained in step (1) is mixed with the grinding media agate balls and the dispersant anhydrous ethanol in a weight ratio of 1:2:3 and then ball-milled in a ball mill (rotation speed of 250 r / min) for 12 h. The resulting powder is then dried for later use.

[0152] (3) Add binder (5 wt% polyvinyl alcohol solution) to the powder in step (2) for granulation. The mass ratio of binder to powder is 8:92. Then, mold it into a disc with a diameter of 10 mm under a pressure of 6 MPa. Calcine the shaped blank at 1300 ℃ for 5 h and finally cool it to obtain the composite negative temperature coefficient thermistor ceramic material.

[0153] Figure 16 , Figure 17 The images show its X-ray diffraction pattern and scanning electron microscope (SEM) image. The X-ray diffraction pattern reveals that the ceramic consists of cubic spinel and tetragonal perovskite phases. The SEM results show that the sample contains nanoscale La... 0.5 Sr 0.5 MnO3 grains and micron-sized Ni 0.6 CoMn 1.4 The sample is composed of O4 grains and has good density.

[0154] The electrical parameters of the composite negative temperature coefficient thermistor ceramic material prepared in this comparative example were measured as follows: room temperature resistivity of 15.65±1% Ω·cm and B value of 1857±2% K.

[0155] The composite negative temperature coefficient thermistor ceramic material was aged in an oven at 150 ℃ for 500 h, and its aging value was measured to be 2.66±0.2%.

[0156] Comparative Examples 1-4 show 0.6Ni prepared using single-phase materials and different processes, respectively. 0.6 CoMn 1.4 O4-0.4La 0.5 Sr0.5 Examples of MnO3. Results showed that Ni... 0.6 CoMn 1.4 The resistivity of O4 ceramics is much greater than that of composite ceramics, and La 0.5 Sr 0.5 The resistivity of MnO3 ceramics is much lower than that of composite ceramics, and its B value is only 557 K. 0.6NiO3 was synthesized via solid-state coordination and combustion methods. 0.6 CoMn 1.4 O4-0.4La 0.5 Sr 0.5 The resistivity of the MnO3 composite ceramics is higher than that of the 0.6Ni obtained by the preparation method used in this patent. 0.6 CoMn 1.4 O4-0.4La 0.5 Sr 0.5 MnO3 composite ceramic resistivity.

[0157] In general, neither single-phase materials nor composite materials prepared by different processes can achieve the combination of simple processing and superior performance. This patent employs a two-step synthesis method to synthesize spinel-structured Ni. 0.6 CoMn 1.4 O4 and La in perovskite structure 0.5 Sr 0.5 MnO3 powder is then mechanically mixed, which can effectively avoid the diffusion of transition metal elements during the powder synthesis stage, ensuring that the two phases give full play to their respective advantages, thereby achieving the purpose of preparing low-resistance, high-B-value, and high-stability composite NTC thermistor ceramics.

[0158] The above description is merely a preferred embodiment of the present invention and is illustrative rather than restrictive. Those skilled in the art will understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, all of which will fall within the protection scope of the present invention.

Claims

1. A composite negative temperature coefficient thermistor ceramic material, characterized in that, The composite negative temperature coefficient thermistor ceramic material has a composition of (1-x)Ni. 0.6 CoMn 1.4 O4-xLa 0.5 Sr 0.5 MnO3, where x = 0.1~0.5, is derived from Ni. 0.6 CoMn 1.4 O4 and La 0.5 Sr 0.5 MnO3 was prepared by mixing according to a specific molar ratio.

2. The composite negative temperature coefficient thermistor ceramic material as described in claim 1, characterized in that, The composite negative temperature coefficient thermistor ceramic material has a composition of (1-x)Ni. 0.6 CoMn 1.4 O4-xLa 0.5 Sr 0.5 MnO3, where x = 0.1, 0.2, 0.3, 0.4, 0.5, and Ni 0.6 CoMn 1.4 O4 has a spinel structure, La 0.5 Sr 0.5 MnO3 has a perovskite structure.

3. A method for preparing a composite negative temperature coefficient thermistor ceramic material as described in claim 1 or 2, characterized in that, Includes the following steps: S1, after uniformly mixing the acetates of nickel, cobalt, and manganese with oxalic acid, a mixture is obtained. The mixture is then ball-milled, dried, and calcined to obtain powder A; S2, Lanthanum and Strontium nitrates, Manganese acetates and citric acid are dissolved in dilute nitric acid solution, stirred thoroughly and then ammonia water is added. After adjusting the pH value, the solution is heated and stirred until 100 mL of solution remains after evaporation. Then the solution is transferred to an evaporating dish and heated with an electric furnace to make the solution completely evaporate and burn. After calcination, powder B is obtained. S3, Powder A and powder B obtained in step S1 are ball-milled and mixed to obtain a mixed powder. A binder is added for granulation, molding, calcination and cooling are performed to obtain a composite negative temperature coefficient thermistor ceramic material.

4. The preparation method of a composite negative temperature coefficient thermistor ceramic material as described in claim 1, characterized in that, In step S1, the acetates of nickel, cobalt, and manganese are proportioned in atomic percentage as follows: nickel 20%, cobalt 33.33%, and manganese 46.67%, and the oxalic acid content is 1 to 1.5 times the total molar amount of the metal atoms.

5. The method for preparing a composite negative temperature coefficient thermistor ceramic material as described in claim 1, characterized in that, In step S1, the mixture, grinding media, and dispersant are loaded into a ball mill jar at a weight ratio of 1:(1~3):(1~3) and ball milled for 6~24 h. The dispersant is anhydrous ethanol. The calcination temperature is 650~900 ℃ and the time is 2~4 h.

6. The method for preparing a composite negative temperature coefficient thermistor ceramic material as described in claim 1, characterized in that, In step S2, lanthanum, strontium nitrates, and manganese acetates are mixed in atomic percentages of 25% lanthanum, 25% strontium, and 50% manganese, and the citric acid content is 1 to 1.5 times the total molar amount of the metal atoms.

7. The method for preparing a composite negative temperature coefficient thermistor ceramic material as described in claim 1, characterized in that, In step S2, the calcination temperature is 950~1100 ℃ and the time is 2~4 h.

8. The method for preparing a composite negative temperature coefficient thermistor ceramic material as described in claim 1, characterized in that, In step S3, the molar ratio of powder A to powder B is (9~6):(1~4), and the ball milling time is 6~24 h.

9. The method for preparing a composite negative temperature coefficient thermistor ceramic material as described in claim 1, characterized in that, In step S3, the adhesive is a polyvinyl alcohol solution with a concentration of 5-8 wt%, and the mass ratio of the adhesive to the mixed powder is (5-8):(95-92).

10. The method for preparing a composite negative temperature coefficient thermistor ceramic material as described in claim 1, characterized in that, In step S3, the calcination temperature is 1200~1300 ℃ and the time is 3~12 h.

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