A clean, low-cost PTC thermistor and its preparation method

Abstract

The present invention discloses a clean, low-cost PTC thermistor and a preparation method thereof, relating to the technical field of thermistor preparation. The method comprises the following raw materials in parts by weight: 48.1-49.3 parts of BaCO3, 48.1-49.3 parts of TiO2, 0.05-0.8 parts of La2O3, 0.03-0.5 parts of CuCO3, 0.03-0.5 parts of Ag2CO3, 0.8-1.2 parts of CaCO3, and 0.5-0.8 parts of SiO2. The present invention uses BaTiO3 as a matrix and, at low cost and without the production of toxic substances, prepares a PTC thermistor having high resistance stability and durability, capable of maintaining relatively stable performance during long-term use, and having a significant positive temperature coefficient characteristic that can accurately and quickly respond to changes in ambient temperature. The present invention solves the problems of existing thermistor preparation methods, such as high cost, pollution, and poor product performance.

Description

Technical Field

[0001] The present invention relates to the technical field of thermistor preparation, and in particular to a clean, low-cost PTC thermistor and a preparation method thereof. Background Art

[0002] Since their introduction, PTC thermistor materials have been widely used. In power distribution systems, they suppress fault currents to protect power equipment; in industry, they measure and control temperature; and in automobiles, they detect and regulate the temperature of key components. However, as their application expands, there is an urgent need to develop high-performance PTC thermistor materials with a higher lift-to-drag ratio and lower room-temperature resistivity.

[0003] Existing PTC thermistors are generally manufactured using ceramic-based composite PTC materials, organic polymer-based PTC materials, or V2O3-based PTC materials. Ceramic-based composite PTC materials primarily use ceramic as their matrix material. As temperature rises, the matrix material undergoes a phase change, causing a volume change, which separates the conductive particles and increases resistance. However, these materials have a relatively low lift-to-resistance ratio and, therefore, have not been widely used. Organic polymer-based PTC materials primarily use a semicrystalline or amorphous polymer matrix. Their PTC effect is primarily due to the expansion of the matrix material as temperature rises, which causes the conductive network to break, leading to an increase in resistance. However, organic polymer-based PTC materials have the disadvantage of exhibiting a large negative temperature coefficient at high temperatures. The PTC effect of V2O3-based PTC materials is based on a metal-insulator phase transition with increasing temperature. Because the metal has a relatively low resistance and the insulator has a high resistance, the ratio of maximum resistance to minimum resistance is large, resulting in a certain lift-to-resistance ratio. However, this lift-to-resistance ratio of these materials does not meet the requirements for widespread use. In addition, the existing preparation method is expensive, produces toxic substances that pollute the environment during the preparation process, and also has problems such as slow response speed, easy drift of resistance value, and easy change of temperature characteristics. Summary of the Invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a clean and low-cost PTC thermistor and a preparation method thereof, so as to solve the problems of high cost, pollution and poor product performance of the existing thermistor preparation method.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: a clean, low-cost PTC thermistor is provided, comprising the following raw materials in parts by weight: 48.1-49.3 parts of BaCO3, 48.1-49.3 parts of TiO2, 0.05-0.8 parts of La2O3, 0.03-0.5 parts of CuCO3, 0.03-0.5 parts of Ag2CO3, 0.8-1.2 parts of CaCO3 and 0.5-0.8 parts of SiO2.

[0006] On the basis of the above technical solution, the present invention can also be improved as follows:

[0007] Furthermore, the clean low-cost PTC thermistor includes the following raw materials in parts by weight: 48.57-48.74 parts of BaCO3, 48.61-48.74 parts of TiO2, 0.23-0.77 parts of La2O3, 0.13-0.41 parts of CuCO3, 0.08-0.45 parts of Ag2CO3, 0.84-1.09 parts of CaCO3 and 0.59-0.75 parts of SiO2.

[0008] Furthermore, the clean low-cost PTC thermistor includes the following raw materials in parts by weight: 48.57 parts of BaCO3, 48.61 parts of TiO2, 0.77 parts of La2O3, 0.13 parts of CuCO3, 0.08 parts of Ag2CO3, 1.09 parts of CaCO3 and 0.75 parts of SiO2.

[0009] The present invention also provides a method for preparing a clean and low-cost PTC thermistor, comprising the following steps:

[0010] (1) BaCO3, TiO2, La2O3, CuCO3 and Ag2CO3 are mixed to obtain raw materials, and then ball milled, dried and pre-sintered to obtain a pre-sintered material;

[0011] (2) Adding SiO2 and CaCO3 to the pre-burned material obtained in step (1), ball milling and mixing until uniform, to obtain granulated material;

[0012] (3) Adding polyvinyl alcohol solution to the granulated material obtained in step (2), mixing evenly, and then granulating, tableting, debinding, sintering, spraying electrodes and heat treating, cooling to room temperature, to obtain a clean low-cost PTC thermistor.

[0013] Furthermore, in step (1), zirconium balls and ethanol are used for ball milling; wherein the mass ratio of the raw material, the zirconium balls and the ethanol is 1:1:(1-1.5).

[0014] Furthermore, the diameter of the zirconium ball is 3-10 mm.

[0015] Furthermore, in step (1), the mixture is ball milled at 250-350 RPM for 9-12 hours.

[0016] Furthermore, in step (1), the product is dried at 80-95° C. for 2-3 hours.

[0017] Furthermore, in step (1), the pre-sintering process is as follows: first, the temperature is raised from room temperature to 450-550°C, maintained for 0.8-1.2h, then the temperature is raised to 850-950°C, maintained for 0.8-1.2h, then the temperature is raised to 1100-1200°C, maintained for 2.8-3.2h, then the temperature is lowered to 800-900°C, maintained for 0.8-1.2h, and finally the temperature is lowered to 500-600°C, maintained for 0.8-1.2h, and then the temperature is automatically lowered to room temperature.

[0018] Furthermore, the time for heating from room temperature to 450-550°C is 0.8-1.2h, the time for heating to 850-950°C is 0.8-1.2h, the time for heating to 1100-1200°C is 1-2.5h, the time for cooling to 800-900°C is 1-2.5h, and the time for cooling to 500-600°C is 0.8-1.2h.

[0019] Furthermore, the time for heating from room temperature to 450-550°C is 1 hour, the time for heating to 850-950°C is 1 hour, the time for heating to 1100-1200°C is 2 hours, the time for cooling to 800-900°C is 2 hours, and the time for cooling to 500-600°C is 1 hour.

[0020] Furthermore, in step (1), the pre-sintering process is as follows: first, the temperature is raised from room temperature to 500°C, maintained for 1 hour, then raised to 900°C, maintained for 1 hour, then raised to 1200°C, maintained for 3 hours, then cooled to 850°C, maintained for 1 hour, and finally cooled to 550°C, maintained for 1 hour, and then automatically cooled to room temperature.

[0021] Furthermore, in step (2), the mixture is ball milled at 250-350 RPM for 3-4 hours.

[0022] Furthermore, in step (3), the polyvinyl alcohol solution is prepared by the following method: polyvinyl alcohol and deionized water are uniformly mixed at a mass ratio of (5-10): (90-95) at 85-95°C.

[0023] Furthermore, in step (3), wet granulation is performed at 350-450 RPM and 70-100°C.

[0024] Furthermore, in step (3), wet granulation is adopted, the main shaft speed of the granulator is 350-450RPM, and the wall temperature of the granulator barrel is 70-100°C.

[0025] Furthermore, in step (3), the green tablet has a diameter of 10-15 mm and a thickness of 1-2.5 mm.

[0026] Furthermore, in step (3), the pressure is maintained at 15-25 MPa for 5-10 minutes to complete the tableting process.

[0027] Furthermore, in step (3), the process of debinding is as follows: firstly, the temperature is raised from room temperature to 400-500°C, maintained for 1-2 hours, and then automatically cooled to room temperature.

[0028] Furthermore, the time for heating to 400-500°C is 6-8h.

[0029] Furthermore, in step (3), the sintering process is as follows: first, the temperature is raised from room temperature to 500-600°C, maintained for 1.8-2.2 hours, then the temperature is raised to 900-1000°C, maintained for 1.8-2.2 hours, then the temperature is raised to 1200-1400°C, maintained for 6-8 hours, then the temperature is lowered to 900-1000°C, maintained for 0.8-1.2 hours, and finally the temperature is lowered to 550-650°C, maintained for 1.8-2.2 hours, and then the temperature is automatically lowered to room temperature.

[0030] Furthermore, the time for heating from room temperature to 500-600°C is 0.8-1.2h, the time for heating to 900-1000°C is 0.8-1.2h, the time for heating to 1200-1400°C is 2-3h, the time for cooling to 900-1000°C is 2-3h, and the time for cooling to 550-650°C is 0.8-1.2h.

[0031] Furthermore, the time for heating from room temperature to 500-600°C is 1 hour, the time for heating to 900-1000°C is 1 hour, the time for heating to 1200-1400°C is 2.5 hours, the time for cooling to 900-1000°C is 2.5 hours, and the time for cooling to 550-650°C is 1 hour.

[0032] Furthermore, in step (3), the sintering process is as follows: first, the temperature is raised from room temperature to 550°C, maintained for 2 h, then raised to 950°C, maintained for 2 h, then raised to 1300°C, maintained for 7 h, then cooled to 950°C, maintained for 1 h, and finally cooled to 600°C, maintained for 2 h, and then automatically cooled to room temperature.

[0033] Furthermore, in step (3), heat treatment is performed at 400-600° C. for 30-60 min.

[0034] The present invention has the following beneficial effects:

[0035] 1. The present invention uses BaTiO3 as a matrix and realizes semiconductorization through processes such as doping modification or atmosphere sintering. Under the conditions of low cost and no generation of toxic substances, a PTC thermistor with high resistance stability and durability is prepared. The PTC thermistor can maintain relatively stable performance during long-term use, has a significant positive temperature coefficient characteristic, and can accurately and quickly respond to changes in ambient temperature.

[0036] 2. Due to its improved sensitivity and enhanced stability, the PTC thermistor of the present invention can be used in a wider range of applications requiring high temperature sensitivity and precision. Furthermore, the clean, low-cost PTC thermistor of the present invention can be applied in a variety of fields. In power distribution systems, positive temperature coefficient thermistors can be used to suppress fault currents to protect power equipment; in industry, positive temperature coefficient thermistors can be used to measure and control temperature; and in automobiles, thermistor materials can detect and regulate the temperature of key parts. Therefore, the high-performance, lead-free barium titanate-based PTC thermistor material with low room-temperature resistivity and high lift-to-resistance ratio prepared by the method provided by the present invention is of great significance for its application.

[0037] 3. Conventional thermistors are made of expensive materials and have high production costs. In addition, harmful substances such as Pb are produced during the production process. The present invention uses Ba instead of Pb and adds a trace amount of doping agent to improve PTC performance to reduce costs. This method produces no harmful substances during the processing process, and a thermistor with excellent PTC performance can be obtained.

[0038] 4. During long-term use, the performance of conventional thermistors may change, such as resistance drift and temperature characteristic changes. These changes may affect their accuracy and reliability. The present invention improves this problem by adding La, Cu and Ag. La2O3 and CuCO3 can form a stable solid solution with BaTiO3, so that the thermistor can maintain its stable performance in harsh environments such as high temperature and high humidity, thereby extending its service life. The silver ions in Ag2CO3 will participate in the crystal phase structure of the PTC thermistor, which helps to improve the stability and reliability of the PTC thermistor. The incorporation of Ag will increase the material distortion energy, thereby increasing the energy required for the material to transform from the ferroelectric phase to the paraelectric phase, resulting in an increase in the Curie temperature.

[0039] 5. Conventional thermistors do not respond quickly enough to changes in ambient temperature. This may result in the PTC thermistor failing to function in a timely manner when rapid protection is required. The present invention changes the material's band structure by adding La2O3, thereby improving carrier mobility and making the PTC thermistor respond faster to temperature changes. The easily variable valence Cu increases the barrier height of the grain boundary, causing the grain boundary resistance to increase sharply, thereby improving the material's lift-to-resistance ratio. The introduction of silver ions affects the conductive properties of the PTC thermistor, optimizing the resistance-temperature characteristics of the PTC thermistor and making the PTC thermistor more sensitive to temperature changes.

[0040] 6. It should be noted that the amount of trace dopant added also needs to be strictly controlled. Excessive trace dopant may cause changes in material properties and even affect the normal operation of the PTC thermistor. Therefore, during the preparation process, it is necessary to determine the appropriate amount of trace dopant added based on the specific formula and process conditions. The reason is that when donor doping is performed, in order to meet the charge balance, there are generally two methods: electron compensation and cation vacancy compensation. When the donor concentration is low, electron compensation dominates. Therefore, at this time, the free electron concentration in the material increases, which increases its conductivity and reduces the room temperature resistivity. When the donor concentration is too high, cation compensation dominates and cannot provide too many free electrons, which reduces the conductivity of the material and increases the resistivity.

[0041] 7. The present invention improves sintering efficiency by adding SiO2 as a sintering aid, which helps the densification and grain growth of barium titanate ceramic materials, enhances the stability of the thermistor, and has higher accuracy and stability in temperature measurement and control; by adding CaCO3 as a grain refiner, the excessive growth of barium titanate grains is suppressed, the number of grain boundaries per unit thickness is increased, and the resistance performance is improved; by adding La2O3, CuCO3 and Ag2CO3 as trace dopants, La2O3 and CuCO3 can form a stable solid solution with BaTiO3, so that the thermistor can still maintain its performance stability in harsh environments such as high temperature and high humidity, and extend its service life. In addition, La2O3 can change the material The band structure of the material is improved, the carrier mobility is increased, and the PTC thermistor responds faster to temperature changes. The easily variable valence Cu increases the barrier height of the grain boundary, which sharply increases the grain boundary resistance, thereby increasing the material lift-resistance ratio. The silver ions in Ag2CO3 will participate in the crystal phase structure of the PTC thermistor, which helps to improve the stability and reliability of the PTC thermistor. The silver ions will also affect the conductive properties of the PTC thermistor, optimize the resistance-temperature characteristics of the PTC thermistor, and make the PTC thermistor more sensitive to temperature changes. The incorporation of Ag will increase the material distortion energy, thereby increasing the energy required for the material to transform from the ferroelectric phase to the paraelectric phase, resulting in an increase in the Curie temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of the production of a PTC thermistor;

[0043] Figure 2 This is a schematic diagram of the pre-sintering process of Example 1;

[0044] Figure 3 This is a schematic diagram of the debinding process of Example 1;

[0045] Figure 4 This is a schematic diagram of the sintering process of Example 1;

[0046] Figure 5 The XRD patterns of the PTC thermistors of Examples 1, 3, 4-5 and Comparative Examples 1-4 are shown;

[0047] Figure 6 Graph showing the temperature-resistance characteristics of the PTC thermistors prepared in Examples 1-3;

[0048] Figure 7 4-5 is a temperature-resistance characteristic diagram of the PTC thermistor prepared in Example 4-5. DETAILED DESCRIPTION

[0049] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not intended to limit the scope of the invention. In the embodiments, if specific conditions are not specified, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0050] Example 1:

[0051] A clean, low-cost PTC thermistor comprises the following raw materials in parts by weight: 48.57 parts of BaCO3, 48.61 parts of TiO2, 0.77 parts of La2O3, 0.13 parts of CuCO3, 0.08 parts of Ag2CO3, 1.09 parts of CaCO3, and 0.75 parts of SiO2.

[0052] A clean and low-cost PTC thermistor, the preparation method of which comprises the following steps: (See the preparation diagram for details) Figure 1 )

[0053] (1) BaCO3, TiO2, La2O3, CuCO3 and Ag2CO3 were mixed to obtain raw materials, and then ball-milled with zirconium balls and ethanol at 350 RPM for 12 h. The mass ratio of raw materials, zirconium balls and ethanol was 1:1:1.5, and the diameter of zirconium balls was 3 mm. The raw materials were then dried in a drying oven at 90 °C for 2.5 h and pre-sintered in a muffle furnace. The pre-sintering process was as follows (see Figure 2): first, heating from room temperature to 500°C for 1 hour, maintaining for 1 hour, then heating to 900°C for 1 hour, maintaining for 1 hour, then heating to 1200°C for 2 hours, maintaining for 3 hours, then cooling to 850°C for 2 hours, maintaining for 1 hour, finally cooling to 550°C for 1 hour, maintaining for 1 hour, and then automatically cooling to room temperature to obtain a pre-sintered material;

[0054] (2) SiO2 and CaCO3 were added to the pre-calcined material obtained in step (1), and the mixture was ball-milled at 320 RPM for 3.5 h to mix the mixture evenly. The diameter of the zirconium balls was 4 mm, and granulated material was obtained.

[0055] (3) Add polyvinyl alcohol solution (prepared by mixing polyvinyl alcohol and deionized water at a mass ratio of 10:95 at a temperature of 95°C) to the granulated material obtained in step (2), mix them evenly, and then adopt wet granulation. The main shaft speed of the granulator is 400RPM and the wall temperature of the granulator is 95°C. The green sheet diameter of the tablet is 10mm and the thickness is 1.5mm. The molding pressure is 25MPa and the pressure is maintained for 8min to obtain a sheet material. Place it in a muffle furnace for debinding. The debinding process is as follows (see Figure 3 ): First, the temperature is raised to 500℃ at room temperature for 7 hours, maintained for 2 hours, and then automatically cooled to room temperature; then sintered. The sintering process is as follows (see Figure 4 ): first, the temperature was raised to 550°C from room temperature for 1 hour and maintained for 2 hours, then the temperature was raised to 950°C for 1 hour and maintained for 2 hours, then the temperature was raised to 1300°C for 2.5 hours and maintained for 8 hours, then the temperature was lowered to 950°C for 2.5 hours and maintained for 1 hour, and finally the temperature was lowered to 600°C for 1 hour and maintained for 2 hours, and then the temperature was automatically lowered to room temperature to obtain a sintered material; after the electrodes were sprayed on both sides of the sintered material, heat treated at 500°C for 45 minutes, and cooled to room temperature to obtain a clean and low-cost PTC thermistor (sample A).

[0056] Example 2:

[0057] A clean, low-cost PTC thermistor comprises the following raw materials in parts by weight: 48.68 parts of BaCO3, 48.62 parts of TiO2, 0.23 parts of La2O3, 0.38 parts of CuCO3, 0.43 parts of Ag2CO3, 0.99 parts of CaCO3, and 0.67 parts of SiO2.

[0058] A clean, low-cost PTC thermistor, the preparation method of which comprises the following steps:

[0059] Similar to Example 1, a clean and low-cost PTC thermistor (Sample B) was prepared.

[0060] Example 3:

[0061] A clean, low-cost PTC thermistor comprises the following raw materials in parts by weight: 48.74 parts of BaCO3, 48.74 parts of TiO2, 0.23 parts of La2O3, 0.41 parts of CuCO3, 0.45 parts of Ag2CO3, 0.84 parts of CaCO3, and 0.59 parts of SiO2.

[0062] A clean, low-cost PTC thermistor, the preparation method of which comprises the following steps:

[0063] (1) BaCO3, TiO2, La2O3, CuCO3 and Ag2CO3 were mixed to obtain raw materials, and then ball-milled with zirconium balls and ethanol at 320 RPM for 10 h, wherein the mass ratio of raw materials, zirconium balls and ethanol was 1:1:1.3, and the diameter of zirconium balls was 5 mm. The raw materials were then dried in a drying oven at 85°C for 2 h, and finally pre-sintered in a muffle furnace. The pre-sintering process was as follows: first, the temperature was raised to 500°C from room temperature for 1 h, maintained for 1 h, then the temperature was raised to 900°C for 1 h, maintained for 1 h, then the temperature was raised to 1150°C for 1 h, maintained for 2.5 h, then the temperature was lowered to 850°C for 1 h, maintained for 1 h, and finally the temperature was lowered to 550°C for 1 h, maintained for 1 h, and then automatically cooled to room temperature to obtain pre-sintered materials;

[0064] (2) SiO2 and CaCO3 were added to the pre-sintered material obtained in step (1), and the mixture was evenly mixed by ball milling at 300 RPM for 2.5 h. The diameter of the zirconium balls was 4 mm, and granules were obtained.

[0065] (3) Add polyvinyl alcohol solution (prepared by mixing polyvinyl alcohol and deionized water at a mass ratio of 6:95 at a temperature of 90°C) to the granulated material obtained in step (2), mix them evenly, and then adopt wet granulation. The main shaft speed of the granulator is 350RPM and the wall temperature of the granulator is 90°C. The diameter of the green tablet is 10mm and the thickness is 1.5mm. The molding pressure is 15MPa and the pressure is maintained for 5min to obtain a sheet material. The sheet material is placed in a muffle furnace for debinding. The debinding process is as follows: first, the temperature is raised from room temperature to 450°C for 6.5h and maintained for 1.5h. Then it automatically cools down to room temperature; followed by sintering, the sintering process is: first, the temperature is raised to 550℃ from room temperature for 1 hour, maintained for 2 hours, then the temperature is raised to 950℃ for 1 hour, maintained for 2 hours, then the temperature is raised to 1200℃ for 2 hours, maintained for 7 hours, then the temperature is lowered to 950℃ for 2 hours, maintained for 1 hour, and finally the temperature is lowered to 600℃ for 1 hour, maintained for 2 hours, and then automatically cooled to room temperature to obtain a sintered material; after the electrodes are sprayed on both sides of the sintered material, heat treatment is carried out at 400℃ for 30 minutes, and cooling is carried out to room temperature to obtain a clean and low-cost PTC thermistor (sample C).

[0066] Example 4:

[0067] A clean, low-cost PTC thermistor comprises the following raw materials in parts by weight: 48.1 parts of BaCO3, 48.1 parts of TiO2, 0.05 parts of La2O3, 0.03 parts of CuCO3, 0.03 parts of Ag2CO3, 0.8 parts of CaCO3 and 0.5 parts of SiO2.

[0068] A clean, low-cost PTC thermistor, the preparation method of which comprises the following steps:

[0069] (1) BaCO3, TiO2, La2O3, CuCO3 and Ag2CO3 were mixed to obtain raw materials, and then ball-milled with zirconium balls and ethanol at 250 RPM for 12 h, wherein the mass ratio of raw materials, zirconium balls and ethanol was 1:1:1, and the diameter of zirconium balls was 3 mm. The raw materials were then dried in a drying oven at 80 °C for 3 h, and finally pre-sintered in a muffle furnace. The pre-sintering process was as follows: first, the temperature was raised to 450 °C from room temperature for 0.8 h and maintained for 1.2 h, then the temperature was raised to 850 °C for 0.8 h and maintained for 1.2 h, then the temperature was raised to 1100 °C for 1 h and maintained for 3.2 h, then the temperature was lowered to 800 °C for 1 h and maintained for 1.2 h, and finally the temperature was lowered to 500 °C for 0.8 h and maintained for 1.2 h, and then the temperature was automatically lowered to room temperature to obtain pre-sintered materials;

[0070] (2) SiO2 and CaCO3 were added to the pre-sintered material obtained in step (1), and the mixture was ball-milled at 250 RPM for 4 h to obtain a uniform mixture. The diameter of the zirconium balls was 4 mm, and a granulated material was obtained.

[0071] (3) Add polyvinyl alcohol solution (prepared by mixing polyvinyl alcohol and deionized water at a mass ratio of 5:90 at a temperature of 85°C) to the granulated material obtained in step (2), mix them evenly, and then adopt wet granulation. The main shaft speed of the granulator is 350RPM and the wall temperature of the granulator is 70°C. The diameter of the green tablet is 10mm and the thickness is 2.5mm. The molding pressure is 15MPa and the pressure is maintained for 10min to obtain a sheet material. The sheet material is placed in a muffle furnace for debinding. The debinding process is as follows: first, the temperature is raised to 400°C at room temperature for 6h, maintained for 2h, and then automatically cooled to room temperature. ; Then sintering, the sintering process is: first, heating from room temperature to 500℃ for 0.8h, maintaining for 2.2h, then heating to 900℃ for 0.8h, maintaining for 2.2h, then heating to 1200℃ for 2h, maintaining for 8h, then cooling to 900℃ for 2h, maintaining for 1.2h, and finally cooling to 550℃ for 0.8h, maintaining for 2.2h, and then automatically cooling to room temperature to obtain a sintered material; after the electrodes are sprayed on both sides of the sintered material, heat treatment is carried out at 400℃ for 60min, and cooled to room temperature to obtain a clean and low-cost PTC thermistor (sample D).

[0072] Example 5:

[0073] A clean, low-cost PTC thermistor comprises the following raw materials in parts by weight: 49.3 parts of BaCO3, 49.3 parts of TiO2, 0.8 parts of La2O3, 0.5 parts of CuCO3, 0.5 parts of Ag2CO3, 1.2 parts of CaCO3 and 0.8 parts of SiO2.

[0074] A clean, low-cost PTC thermistor, the preparation method of which comprises the following steps:

[0075] (1) BaCO3, TiO2, La2O3, CuCO3 and Ag2CO3 were mixed to obtain raw materials, and then ball-milled with zirconium balls and ethanol at 350 RPM for 9 hours, wherein the mass ratio of raw materials, zirconium balls and ethanol was 1:1:1.5, and the diameter of zirconium balls was 10 mm. The raw materials were then dried in a drying oven at 95°C for 2 hours, and finally pre-sintered in a muffle furnace. The pre-sintering process was as follows: first, the temperature was raised to 550°C from room temperature for 1.2 hours and maintained for 0.8 hours, then the temperature was raised to 950°C for 1.2 hours and maintained for 0.8 hours, then the temperature was raised to 1200°C for 2.5 hours and maintained for 2.8 hours, then the temperature was lowered to 900°C for 2.5 hours and maintained for 0.8 hours, and finally the temperature was lowered to 600°C for 1.2 hours and maintained for 0.8 hours, and then the temperature was automatically lowered to room temperature to obtain pre-sintered materials;

[0076] (2) SiO2 and CaCO3 were added to the pre-sintered material obtained in step (1), and the mixture was ball-milled at 350 RPM for 3 h to mix the mixture evenly. The diameter of the zirconium balls was 4 mm, and granulated material was obtained.

[0077] (3) Add polyvinyl alcohol solution (prepared by mixing polyvinyl alcohol and deionized water at a mass ratio of 10:95 at a temperature of 95°C) to the granulated material obtained in step (2), mix them evenly, and then adopt wet granulation. The spindle speed of the granulator is 450RPM and the wall temperature of the granulator is 100°C. The green tablet has a diameter of 15mm and a thickness of 1mm. The molding pressure is 25MPa and the pressure is maintained for 5min to obtain a sheet material. The sheet material is placed in a muffle furnace for debinding. The debinding process is as follows: first, the temperature is raised to 500°C from room temperature for 8h, maintained for 1h, and then automatically cooled to room temperature. Then sintering was carried out, and the sintering process was as follows: first, the temperature was raised to 600°C from room temperature for 1.2 hours and maintained for 1.8 hours, then the temperature was raised to 1000°C for 1.2 hours and maintained for 1.8 hours, then the temperature was raised to 1400°C for 3 hours and maintained for 6 hours, then the temperature was lowered to 1000°C for 3 hours and maintained for 0.8 hours, and finally the temperature was lowered to 650°C for 1.2 hours and maintained for 1.8 hours, and then the temperature was automatically lowered to room temperature to obtain a sintered material; after the electrodes were sprayed on both sides of the sintered material, heat treatment was carried out at 600°C for 30 minutes, and cooling was carried out to room temperature to obtain a clean and low-cost PTC thermistor (sample E).

[0078] Comparative Example 1:

[0079] A PTC thermistor comprises the following raw materials in parts by weight: 48.57 parts of BaCO3, 48.61 parts of TiO2, 0.77 parts of La2O3, 0.13 parts of CuCO3, 0.08 parts of Ag2CO3, 1.09 parts of CaCO3 and 0.75 parts of SiO2.

[0080] A PTC thermistor, the preparation method of which comprises the following steps:

[0081] The pre-sintering in step (1) is not included, and the rest is the same as in Example 1.

[0082] Comparative Example 2:

[0083] A PTC thermistor comprises the following raw materials in parts by weight: 48.74 parts of BaCO3, 48.74 parts of TiO2, 0.23 parts of La2O3, 0.41 parts of CuCO3, 0.45 parts of Ag2CO3, 0.84 parts of CaCO3 and 0.59 parts of SiO2.

[0084] A PTC thermistor, the preparation method of which comprises the following steps:

[0085] The pre-sintering in step (1) is not included, and the rest is the same as in Example 3.

[0086] Comparative Example 3:

[0087] A PTC thermistor comprises the following raw materials in parts by weight: 48.1 parts of BaCO3, 48.1 parts of TiO2, 0.05 parts of La2O3, 0.03 parts of CuCO3, 0.03 parts of Ag2CO3, 0.8 parts of CaCO3 and 0.5 parts of SiO2.

[0088] A PTC thermistor, the preparation method of which comprises the following steps:

[0089] The pre-sintering in step (1) is not included, and the rest is the same as in Example 4.

[0090] Comparative Example 4:

[0091] A PTC thermistor comprises the following raw materials in parts by weight: 49.3 parts of BaCO3, 49.3 parts of TiO2, 0.8 parts of La2O3, 0.5 parts of CuCO3, 0.5 parts of Ag2CO3, 1.2 parts of CaCO3 and 0.8 parts of SiO2.

[0092] A PTC thermistor, the preparation method of which comprises the following steps:

[0093] The pre-sintering in step (1) is not included, and the rest is the same as in Example 5.

[0094] Test example

[0095] 1. The clean, low-cost PTC thermistors prepared in Examples 1-5 were subjected to parameter testing. Dynamic temperature resistance parameter tests were performed according to the technical data in the national standard GB / T 7153-2002, "Directly Heated Step-Type Positive Temperature Coefficient Thermistors Part 1." The results are shown in Tables 1 and 2.

[0096] Table 1 Comparison of dynamic resistance parameters of Examples 1-3

[0097]

[0098] As shown in Table 1, when comparing sample A of Example 1 with sample B of Example 2, when more La2O3 is added, the nominal operating temperature (T NF ) and switch temperature (T b ), making the PTC thermistor more sensitive to temperature changes. When more La2O3 is added, the heating constant resistance (R P ), improve PTC performance.

[0099] Table 2 Comparison of dynamic resistance parameters of Examples 4-5

[0100]

[0101] As can be seen from Table 2, sample D of Example 4 and sample E of Example 5 still have strong PTC performance when the doping amounts of La2O3, CuCO3 and Ag2CO3 are too small, too large or at the boundary value during preparation, and the resistance value is maintained at the MΩ level over a wide temperature range and a large rise-to-resistance ratio. When the ion doping amount is too small, the doped La2O3, CuCO3 and Ag2CO3 can completely replace Ba ions and Ti ions, and the phenomenon of sample D in Example 4 will appear. However, if the ion doping amount is less than the critical value, the material will show that pure phase barium titanate does not have the performance of a positive temperature coefficient. Therefore, there is a lower limit value of the ion doping amount during preparation; when the ion doping amount is too large, the valence change of the doped ions will lead to an increase in the barrier height at the grain boundary, so as to increase its maximum resistivity and enhance the PTC performance, and the phenomenon of sample E in Example 5 will appear. However, there is a limit to the increase in the grain boundary barrier height. If the ion doping amount is greater than the critical value, when the maximum resistivity of the material reaches a certain value, it will no longer increase significantly with the increase in the doping amount or remain near a certain value. At this time, the introduction of doped ions will only increase the room temperature resistivity of the material. Therefore, there is an upper limit value of the ion doping amount during preparation.

[0102] 2. The clean low-cost PTC thermistors prepared in Examples 1, 3 and 4-5 and the PTC thermistors prepared in Comparative Examples 1-4 were subjected to XRD tests. The results are shown in FIG. Figure 5 .

[0103] Depend on Figure 5 It can be seen that the purpose of pre-firing in the examples is to reduce the shrinkage rate of the ceramic samples during final firing and to promote crystal transformation. The XRD diffraction patterns of the products of Examples 1, 3 and 4-5 and Comparative Examples 1-4 are basically consistent when compared, that is, the pre-firing process will not affect the basic materials of the samples while ensuring the quality of the ceramic sheets.

[0104] 3. The clean low-cost PTC thermistors prepared in Examples 1-5 were tested for their temperature-resistance characteristics. Figure 6 and Figure 7 .

[0105] Depend on Figure 6 It can be seen that when comparing sample A of Example 1 and sample B of Example 2, when more Ag2CO3 and CuCO3 are added, the room temperature resistivity is reduced, the addition of Ag2CO3 also leads to an increase in the Curie temperature, and when more La2O3 is added, the response speed of the PTC thermistor to temperature changes is accelerated;

[0106] Comparing Sample B of Example 2 with Sample C of Example 3, when the difference in the preparation raw materials is small, the electrical properties of the samples prepared by different process compositions are quite different. From the perspective of the temperature resistance characteristics, the temperature resistance characteristic curves of Sample B of Example 2 and Sample C of Example 3 are basically the same at medium and low temperatures, but at high temperatures, the higher the temperature, the greater the difference in resistivity between Sample B of Example 2 and Sample C of Example 3.

[0107] Depend on Figure 7 It can be seen that when the doping amounts of La2O3, CuCO3 and Ag2CO3 in sample D of Example 4 and sample E of Example 5 are too small, too large or at the boundary value during preparation, they still have strong PTC performance, and the resistance value is maintained at the MΩ level over a wide temperature range and a large rise-to-resistance ratio.

[0108] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A clean, low-cost PTC thermistor, characterized in that: The invention comprises the following raw materials in parts by weight: 48.1-49.3 parts of BaCO3, 48.1-49.3 parts of TiO2, 0.05-0.8 parts of La2O3, 0.03-0.5 parts of CuCO3, 0.03-0.5 parts of Ag2CO3, 0.8-1.2 parts of CaCO3 and 0.5-0.8 parts of SiO2; The method for preparing the clean and low-cost PTC thermistor comprises the following steps: (1) BaCO3, TiO2, La2O3, CuCO3 and Ag2CO3 are mixed to obtain raw materials, and then ball milled, dried and pre-sintered to obtain a pre-sintered material; (2) Adding SiO2 and CaCO3 to the pre-burned material obtained in step (1), ball milling and mixing until uniform, to obtain granulated material; (3) adding polyvinyl alcohol solution to the granulated material obtained in step (2), mixing them evenly, and then granulating, tableting, debinding, sintering, spraying electrodes and heat treating them, and cooling them to room temperature to obtain a clean and low-cost PTC thermistor; In step (1), the pre-sintering process is: first, the temperature is raised from room temperature to 450-550°C, maintained for 0.8-1.2h, then the temperature is raised to 850-950°C, maintained for 0.8-1.2h, then the temperature is raised to 1100-1200°C, maintained for 2.8-3.2h, then the temperature is lowered to 800-900°C, maintained for 0.8-1.2h, and finally the temperature is lowered to 500-600°C, maintained for 0.8-1.2h, and then the temperature is automatically lowered to room temperature.

2. The clean, low-cost PTC thermistor according to claim 1, characterized in that: The invention comprises the following raw materials in parts by weight: 48.57-48.74 parts of BaCO3, 48.61-48.74 parts of TiO2, 0.23-0.77 parts of La2O3, 0.13-0.41 parts of CuCO3, 0.08-0.45 parts of Ag2CO3, 0.84-1.09 parts of CaCO3 and 0.59-0.75 parts of SiO2.

3. The clean, low-cost PTC thermistor according to claim 1, characterized in that: In step (1), zirconium balls and ethanol are used for ball milling; wherein the mass ratio of the raw material, the zirconium balls and the ethanol is 1:1:(1-1.5).

4. The clean, low-cost PTC thermistor according to claim 1, characterized in that: In step (1), the product is dried at 80-95°C for 2-3 hours.

5. The clean, low-cost PTC thermistor according to claim 1, characterized in that: In step (3), the polyvinyl alcohol solution is prepared by the following method: polyvinyl alcohol and deionized water are uniformly mixed at a mass ratio of (5-10): (90-95) at 85-95°C.

6. The clean, low-cost PTC thermistor according to claim 1, characterized in that: In step (3), the process of debinding is as follows: first, the temperature is raised from room temperature to 400-500°C, maintained for 1-2 hours, and then automatically cooled to room temperature.

7. The clean, low-cost PTC thermistor according to claim 1, characterized in that: In step (3), the sintering process is as follows: first, the temperature is raised from room temperature to 500-600°C, maintained for 1.8-2.2 hours, then the temperature is raised to 900-1000°C, maintained for 1.8-2.2 hours, then the temperature is raised to 1200-1400°C, maintained for 6-8 hours, then the temperature is lowered to 900-1000°C, maintained for 0.8-1.2 hours, and finally the temperature is lowered to 550-650°C, maintained for 1.8-2.2 hours, and then the temperature is automatically lowered to room temperature.

8. The clean, low-cost PTC thermistor according to claim 1, characterized in that: In step (3), heat treatment is performed at 400-600°C for 30-60 minutes.

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