NTC thermistor and preparation method thereof

Abstract

The invention discloses an NTC (Negative Temperature Coefficient) thermistor and a preparation method thereof, the NTC thermistor comprises a ceramic substrate and electrodes, the electrodes are attached to two ends of the ceramic substrate, the electrodes are connected with leads, a glass packaging layer is arranged on the outer side of the ceramic substrate, and the ceramic substrate and the electrodes are wrapped by the glass packaging layer; the ceramic matrix is prepared from the following raw materials in percentage by weight: 40%-60% of manganese oxide, 10%-20% of cobalt oxide, 20%-30% of nickel oxide, 3%-12% of copper oxide and 1%-5% of doped element oxide; the electrode is a silver-palladium alloy electrode, and the mass ratio of silver to palladium is 7: 3-9: 1. By accurately controlling the raw material proportion and the preparation process of the ceramic matrix, the thermistor has a relatively high response speed and can timely and accurately reflect the rapid change of the temperature. And meanwhile, the thermistor has a wider resistance-temperature characteristic range and higher stability, and is suitable for the field of high-precision temperature measurement and control. And the oxidation resistance and the stability of the improved thermistor are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of thermistor production, and particularly to an NTC thermistor and a preparation method thereof. Background Art

[0002] An NTC thermistor is an important temperature-sensitive component, whose resistance value changes significantly with the change of temperature, and is widely used in the fields of temperature measurement, temperature compensation, temperature control, and overheat protection. Traditional NTC thermistors are mainly composed of semiconductor ceramic materials made of metal oxides (such as manganese, nickel, cobalt, etc.), and their working principle is based on the increase of carrier concentration and mobility with the increase of temperature, resulting in a decrease in resistance value.

[0003] However, there are some deficiencies in the existing NTC thermistors. First, the response speed of traditional NTC thermistors is slow and cannot accurately reflect the rapid change of temperature in a timely manner. This is because in the preparation process, the raw material ratio and process control of the ceramic matrix are not precise enough, resulting in an uneven microstructure inside the material, thus affecting the migration speed of carriers. Second, the resistance-temperature characteristic range of traditional NTC thermistors is narrow, which limits their application in the fields of high-precision temperature measurement and control. In addition, the antioxidant property and stability of traditional NTC thermistors are poor, and they are prone to performance degradation in high-temperature or oxidation environments, thus shortening their service life.

[0004] In practical applications, these deficiencies bring many inconveniences to users. For example, in high-precision temperature control systems, such as medical equipment and aerospace instruments, it is necessary to quickly and accurately detect temperature changes and perform real-time feedback control. The slow response speed and narrow characteristic range of traditional NTC thermistors cannot meet the requirements of these high-precision applications. At the same time, in some harsh working environments, such as high temperature, high humidity, or strong oxidation environment, the antioxidant property and stability of traditional NTC thermistors are insufficient, resulting in a rapid decline in their performance, increasing the maintenance cost and replacement frequency of the equipment.

[0005] Therefore, developing an NTC thermistor with a faster response speed, a wider resistance-temperature characteristic range, higher stability, and a longer service life is an urgent problem to be solved in the current technical field. Summary of the Invention

[0006] The purpose of the present invention is to provide an NTC thermistor and a preparation method thereof. By precisely controlling the raw material ratio and preparation process of the ceramic matrix, the performance of the NTC thermistor is significantly improved, enabling it to better meet the requirements of the fields of high-precision temperature measurement and control.

[0007] The present invention is implemented as follows:

[0008] To achieve the above object, according to one aspect of the present invention, the present invention provides an NTC thermistor, comprising a ceramic substrate and electrodes. The electrodes are attached to both ends of the ceramic substrate, and the electrodes are connected with leads. A glass encapsulation layer is provided outside the ceramic substrate, and the glass encapsulation layer wraps the ceramic substrate and the electrodes. The ceramic substrate is made of raw materials in the following weight percentages: 40%-60% of manganese oxide, 10%-20% of cobalt oxide, 20%-30% of nickel oxide, 3%-12% of copper oxide, and 1%-5% of doped element oxide. The electrodes adopt silver-palladium alloy electrodes, and the mass ratio of silver to palladium is 7:3-9:1.

[0009] Further, the manganese oxide is one or more of MnO 2、 Mn2O3 or Mn3O4, and the cobalt oxide is CoO or Co3O4.

[0010] According to the second aspect of the present invention, a preparation method of an NTC thermistor is provided. The specific steps of the preparation method are as follows:

[0011] S100: Select raw materials of manganese oxide, cobalt oxide, nickel oxide, copper oxide and doped element oxide, and grind them respectively.

[0012] S200: Weigh the pretreated raw materials according to the above weight percentages, put them into a three-dimensional mixer for mixing to form a slurry.

[0013] S300: Dry the slurry at 80°C to 120°C, and then pre-burn it at 800°C to 1000°C for 2 to 4 hours to obtain a pre-burned powder. Add a binder to the pre-burned powder and press it into a green body with the required shape by using a mold.

[0014] S400: Put the green body into a high-temperature furnace for debinding treatment to remove the binder in the green body. After the debinding is completed, sinter it.

[0015] S500: Coat the two ends of the sintered ceramic substrate with silver-palladium alloy slurry by screen printing, and then sinter it at 700-850°C for 30-60 minutes to firmly bond the electrodes with the ceramic substrate.

[0016] S600: Connect a platinum-plated alloy wire or Dumet wire to the electrodes of the ceramic substrate by welding or crimping.

[0017] S700: Adopt a glass encapsulation process to glass-encapsulate the ceramic substrate, the electrodes and the connection position between the electrodes and the leads.

[0018] S800. Conduct an appearance inspection on the thermistor after glass encapsulation to ensure that there are no cracks and bubble defects in the encapsulation layer; and conduct performance tests on the resistance value, B value, and accuracy of the thermistor, and sort according to the test results.

[0019] Further, in the step S100, a planetary ball mill is used for grinding the raw materials, the ball-to-material ratio is 3:1 - 5:1, and the ball milling time is 12 - 24 hours to ensure the fineness and uniformity of the raw materials, and the average particle size of the raw materials reaches 0.5 - 1 μm.

[0020] Further, in the step S200, the mixing time for mixing the raw materials is 6 - 10 hours to ensure that all raw materials are fully and evenly mixed; during the mixing process, an appropriate amount of deionized water is added as a dispersion medium, and the addition amount of deionized water is 10% - 20% of the total weight of the raw materials.

[0021] Further, in the step S400, during the debinding process, the debinding temperature is 300 - 500 °C, the heating rate is 1 - 3 °C / min, and the holding time is 2 - 4 hours to remove the binder in the green body; the sintering temperature is 1200 - 1400 °C, the heating rate is 2 - 5 °C / min, and the holding time is 4 - 8 hours; during the sintering process, by precisely controlling the gas content and pressure in the furnace, the microstructure of the ceramic matrix is improved, and its electrical properties are enhanced.

[0022] Further, in the step S700, the specific steps for glass encapsulating the thermistor are as follows:

[0023] S710. Grind the glass material into powder, add an appropriate amount of binder to make a glass paste;

[0024] S720. Uniformly coat the glass paste around the ceramic matrix and the lead to form a preliminary glass encapsulation layer

[0025] S730. Place the component coated with the glass paste into a high-temperature furnace, and conduct glass melting encapsulation at 800 °C - 1000 °C, and hold for 10 - 30 minutes to completely melt the glass material and wrap the ceramic matrix, electrodes, and the connection positions between the electrodes and the leads.

[0026] S740. Cool in the furnace until the glass encapsulation layer is cured to form a sealed structure, and then transfer the thermistor with the cured glass encapsulation layer to the inside of an air-cooling device for accelerated cooling treatment.

[0027] Further, in the step S740, the air-cooling device includes a fan, a filter element, an air-cooling box, and a material tank; the filter element is installed at the air inlet end of the fan, and the air inlet end of the air-cooling box is connected to the air outlet end of the fan, and a plurality of material tanks are evenly arranged on the air-cooling box.

[0028] Further, one end of the blower is set as an air inlet, and a bayonet is arranged along the air inlet of the blower. On both sides inside the bayonet, limiting clamping rods are symmetrically arranged. At the other end of the blower, a first flange is provided, and a plurality of first flange holes are evenly arranged on the first flange; an electric connection wire is arranged on the side of the blower, and an electric connection plug is arranged at the end of the electric connection wire.

[0029] A pulling groove is arranged at the top of the filter element, and limiting clamping grooves are symmetrically arranged on both sides of the filter element. The limiting clamping grooves are clamped on the limiting clamping rods; a filter cotton is arranged in the middle of the filter element.

[0030] Further, one end of the air-cooling box facing the blower is provided with a second flange, and a plurality of second flange holes are arranged on the second flange. A wind distribution plate is arranged at one end of the air-cooling box close to the blower. A plurality of threaded holes are evenly arranged on the front surface of the air-cooling box, and an air outlet is arranged at the other end of the air-cooling box.

[0031] A handle is arranged at one end of the material tank facing the outside, and an adapter plate is arranged at one end of the material tank facing the inside of the air-cooling box. The adapter plate is in threaded connection with the threaded holes. A storage cylinder is arranged at one end of the adapter plate inserted into the air-cooling box. The surface of the storage cylinder is provided with hollow holes, and one end of the storage cylinder far away from the adapter plate is open, and a cover is arranged at the open end of the storage cylinder. A threaded connection plate is arranged at the end of the cover, and the threaded connection plate is in threaded connection with the storage cylinder.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1. By precisely controlling the raw material ratio and preparation process of the ceramic matrix, the thermistor of the present invention has a faster response speed and can timely and accurately reflect the rapid change of temperature. At the same time, the thermistor has a wider range of resistance-temperature characteristics and higher stability, and is suitable for the field of high-precision temperature measurement and control. The improved thermistor has improved oxidation resistance and stability, indirectly improving the service life of the thermistor.

[0034] 2. The preparation method of the present invention adopts a silver-palladium alloy electrode and an optimized sintering process, which improves the oxidation resistance and stability of the thermistor and reduces the resistance drift.

[0035] 3. The present invention adopts a glass encapsulation method to encapsulate the surface of the thermistor. The glass encapsulation provides excellent sealing performance and can effectively prevent the internal structure from being eroded by the external environment (such as humidity, corrosive gas). At the same time, it makes the thermistor suitable for working in a high-temperature environment.

[0036] 4. By installing a filter element at the air inlet end of the blower, the air pumped by the blower can be filtered, avoiding the adhesion of air dust on the glass encapsulation layer and ensuring the sufficient cleanliness of the surface of the produced thermistor. Description of the Drawings

[0037] Figure 1 It is a schematic structural diagram of the thermistor lamination of the present invention;

[0038] Figure 2 It is a schematic structural diagram of the air-cooling device of the present invention;

[0039] Figure 3 It is a schematic structural diagram of the fan of the present invention;

[0040] Figure 4 It is a schematic structural diagram of the filter element of the present invention;

[0041] Figure 5 It is a schematic structural diagram of the air-cooling box of the present invention;

[0042] Figure 6 It is a schematic structural diagram of the material tank of the present invention;

[0043] Figure 7 It is a flow chart of the preparation method of the present invention.

[0044] In the figure: 1, ceramic substrate; 2, electrode; 3, lead wire; 4, glass encapsulation layer; 5, fan; 51, air inlet; 52, power connection wire; 53, power connection plug; 54, bayonet; 55, limit clamping rod; 56, first flange; 57, first flange hole; 6, filter element; 61, draw groove; 62, limit card slot; 63, filter cotton; 7, air-cooling box; 71, air outlet; 72, threaded hole; 73, air distribution plate; 74, second flange; 75, second flange hole; 8, material tank; 81, handle; 82, adapter plate; 83, storage cylinder; 84, cover; 85, threaded connection plate. Detailed implementation manners

[0045] In the present invention, unless otherwise clearly defined and limited, terms such as "installation", "connection", "connection", "fixation" and other terms should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0046] The following will be further described in conjunction with the accompanying drawings and specific embodiments:

[0047] Embodiment 1

[0048] As Figure 1As shown, an NTC thermistor includes a ceramic substrate 1 and electrodes 2. The electrodes 2 are attached to both ends of the ceramic substrate 1. The electrodes 2 are connected to leads 3. A glass encapsulation layer 4 is provided outside the ceramic substrate 1, and the glass encapsulation layer 4 wraps the ceramic substrate 1 and the electrodes 2. The glass encapsulation layer 4 can effectively prevent the internal structure from being eroded by the external environment (such as humidity and corrosive gases). The glass material has high heat resistance and is suitable for working in high-temperature environments. The glass encapsulation layer 4 can withstand a certain amount of mechanical shock and vibration. The glass encapsulation structure makes the resistance value and temperature characteristics of the thermistor more stable. The ceramic substrate 1 is made of raw materials with the following weight percentages: 40%-60% of manganese oxide, 10%-20% of cobalt oxide, 20%-30% of nickel oxide, 3%-12% of copper oxide, and 1%-5% of doped element oxide. The manganese oxide is one or more of MnO 2、 Mn2O3 or Mn3O4, and the cobalt oxide is CoO or Co3O4. When selecting these oxide raw materials, high-purity oxides with a purity ≥99.9% should be selected. By adjusting the proportions of these metal oxides, the B value (material constant) and resistance-temperature characteristics of the thermistor can be precisely controlled. According to the empirical formula:

[0049]

[0050] where T1 and T2 are two different temperature points (unit: K), and R1 and R2 are the resistance values corresponding to the respective temperatures. By changing the raw material ratio, the B value can be precisely adjusted within the range of 2500K - 4500K to meet the requirements of different application scenarios. For example, increasing the content of MnO2 usually reduces the B value because the change in the valence state of manganese ions (Mn 3+ / Mn 4+ ) enhances electron hopping conduction. Increasing the content of NiO usually increases the B value because the change in the valence state of nickel ions (Ni 2+ / Ni 3+ ) introduces additional energy levels and increases the activation energy of electron hopping. Increasing the content of Co2O3 usually increases the B value because the change in the valence state of cobalt ions (Co 2 + / Co 3+ ) increases lattice defects and hinders electron conduction. Increasing the content of CuO usually reduces the B value because the change in the valence state of copper ions (Cu + / Cu 2+ ) enhances electron hopping conduction. Increasing the content of Fe2O3 usually increases the B value because the change in the valence state of iron ions (Fe 2+ / Fe 3+ ) increases lattice defects. Increasing the content of Al2O3 usually significantly increases the B value because aluminum ions (Al 3+)It does not participate in conduction but will introduce additional lattice defects. By adjusting the raw material ratio of the NTC thermistor, its B value can be significantly changed. Increasing the content of MnO2 and CuO usually reduces the B value, while increasing the content of NiO, Co2O3, and Al2O3 increases the B value. The electrode 2 uses a silver-palladium alloy electrode 2, and the mass ratio of silver to palladium is 7:3 - 9:1. This alloy electrode 2 has good electrical conductivity, oxidation resistance, and bonding force with the ceramic substrate 1, can effectively reduce the contact resistance, and improve the stability of the thermistor.

[0051] Example 2

[0052] As Figure 7 shown, a preparation method of an NTC thermistor, and the specific steps of this preparation method are as follows:

[0053] S100. Select raw materials of manganese oxide, cobalt oxide, nickel oxide, copper oxide, and doped element oxide, and grind them separately. When grinding the raw materials, a planetary ball mill is used, the ball-to-material ratio is 3:1 - 5:1, and the ball milling time is 12 - 24 hours to ensure the fineness and uniformity of the raw materials, and the average particle size of the raw materials reaches 0.5 - 1 μm. During the ball milling process, according to the rotational speed n (r / min) of the ball mill, the ball milling time t (h), and the particle size change ΔD (μm) of the raw materials, the ball milling effect can be evaluated by formula (2):

[0054]

[0055] Among them, k is a constant related to the characteristics of the ball mill and raw materials, and its value range is 0.05 - 0.1. Through this formula, the ball milling parameters can be reasonably adjusted to obtain appropriate raw material particle sizes. The particle size of the NTC hot film resistor raw materials affects various aspects. For example, raw materials (such as MnO2, NiO, Co2O3, etc.) need to be uniformly mixed to ensure that the sintered ceramic matrix has a consistent chemical composition and microstructure. The smaller the particle size, the larger the contact area between raw material particles, and the better the mixing uniformity. Smaller particle sizes have a higher specific surface area and surface energy, which can promote diffusion and reaction during sintering. The smaller the particle size, the lower the sintering temperature can be, and at the same time, the density and uniformity of the sintered body are improved. Raw materials with a uniform particle size distribution contribute to the formation of a uniform grain structure and conductive channels, thereby improving the electrical properties of the NTC thermistor. Uneven particle size may lead to defects such as pores and cracks in the sintered ceramic matrix, affecting the mechanical strength and electrical properties of the product. Moreover, when the particle size is small, the contact area between particles increases, the conductive channels are more continuous, and the resistance value decreases. When the particle size is large, the contact area between particles decreases, the conductive channels are discontinuous, and the resistance value increases. Also, when the raw material particle size is small, the number of grain boundaries increases, the activation energy of electron hopping conduction increases, and the B value increases. It can be seen that the particle size of the raw materials has a great influence on the performance of the NTC thermistor. Therefore, the particle size of the raw materials must be controlled during the raw material grinding process. Usually, the particle size of the ball-milled raw materials is required to be in the range of 0.5 - 1 μm. The particle size distribution should be as narrow as possible to ensure that the sintered ceramic matrix has a uniform microstructure.

[0056] S200. Weigh the pretreated raw materials according to the above weight percentages and put them into a three-dimensional mixer for mixing to form a slurry. When mixing the raw materials, the mixing time is 6 - 10 hours to ensure that all raw materials are fully and uniformly mixed. During the mixing process, an appropriate amount of deionized water is added as a dispersion medium, and the addition amount of deionized water is 10% - 20% of the total weight of the raw materials.

[0057] S300. Dry the slurry at 80°C - 120°C, and then pre-sinter it at 800°C - 1000°C for 2 - 4 hours to obtain a pre-sintered powder. Add a binder to the pre-sintered powder and use a mold to press it into a green body of the required shape.

[0058] S400. Put the green body into a high-temperature furnace for debinding treatment to remove the binder in the green body. After the debinding is completed, sintering is carried out. During the debinding treatment, the debinding temperature is 300 - 500°C, the heating rate is 1 - 3°C / min, and the holding time is 2 - 4 hours to remove the binder in the green body. The sintering temperature is 1200 - 1400°C, the heating rate is 2 - 5°C / min, and the holding time is 4 - 8 hours. During the sintering process, by precisely controlling the gas content and pressure in the furnace, the microstructure of the ceramic matrix 1 is improved, and its electrical properties are enhanced. According to the equation:

[0059]

[0060] Calculate and control the reaction rate constant of the ceramic matrix. Among them, K is the reaction rate constant, A is the pre-exponential factor, E a is the activation energy, R is the gas constant, and T is the absolute temperature. By adjusting the sintering temperature and time, the diffusion rate of ions and the crystal growth process in the ceramic matrix 1 can be controlled, thereby optimizing its performance. The reaction rate constant directly affects the grain growth rate. By calculating the reaction rate constant, the grain size can be controlled, thereby adjusting the B value and electrical properties of the NTC thermistor; the calculation of the reaction rate constant helps to optimize the raw material ratio and sintering process, ensuring the consistency and reliability of the product; by calculating the reaction rate constant, the lowest sintering temperature and time can be determined, thereby reducing energy consumption and production costs.

[0061] The influence of the reaction rate constant on the NTC thermistor includes the following aspects:

[0062] (1) Sintering density

[0063] High reaction rate constant:

[0064] The raw materials react rapidly during sintering, and the density of the ceramic matrix is relatively high. There are fewer pores and defects in the sintered body, and the mechanical strength is relatively high.

[0065] Low reaction rate constant:

[0066] The raw materials react slowly, and the density of the ceramic matrix is relatively low. There may be pores and defects in the sintered body, affecting the mechanical strength and electrical properties.

[0067] (2) Grain size

[0068] High reaction rate constant:

[0069] The grains grow faster, which may lead to larger grain sizes. The number of grain boundaries decreases, the activation energy for electron hopping conduction decreases, and the B value decreases.

[0070] Low reaction rate constant:

[0071] The grains grow slower, and the grain size is smaller. The number of grain boundaries increases, the activation energy for electron hopping conduction increases, and the B value increases.

[0072] (3) Electrical properties

[0073] High reaction rate constant:

[0074] The conductive channels in the ceramic matrix are more continuous, and the resistance value is relatively low. The temperature characteristics may be unstable, and the response speed of the thermistor is relatively fast.

[0075] Low reaction rate constant:

[0076] The conductive channels of the ceramic matrix are discontinuous, and the resistance value is relatively high. The temperature characteristics are more stable, and the response speed of the thermistor is slower.

[0077] (4) Consistency and reliability

[0078] High reaction rate constant:

[0079] The sintering process is relatively fast, which may lead to non-uniform microstructure and affect the consistency and reliability of the product.

[0080] Low reaction rate constant:

[0081] The sintering process is slower, the microstructure is more uniform, and the consistency and reliability of the product are higher. In actual production, the optimization of the reaction rate constant usually needs to consider the following factors:

[0082] Raw material ratio: Adjust the reaction rate constant by adjusting the types and proportions of raw materials.

[0083] Sintering temperature and time: Determine the optimal sintering temperature and time according to the reaction rate constant.

[0084] Cooling rate: Control the cooling rate to avoid non-uniform microstructure caused by too fast reaction rate.

[0085] S500. Coat the two ends of the sintered ceramic matrix 1 with silver-palladium alloy paste by screen printing, and then sinter at 700 - 850 °C for 30 - 60 minutes to firmly bond the electrode 2 to the ceramic matrix 1.

[0086] S600. Connect the platinum-plated alloy wire or Dumet wire to the electrode 2 of the ceramic matrix 1 by welding or crimping.

[0087] S700. Adopt the process of glass encapsulation to encapsulate the ceramic matrix 1, the electrode 2, and the connection position between the electrode 2 and the lead 3 with glass. The specific steps for glass encapsulation of the thermistor are as follows:

[0088] S710. Grind the glass material into powder, add an appropriate amount of binder to make glass paste.

[0089] S720. Uniformly coat the glass paste around the ceramic matrix 1 and the lead 3 to form a preliminary glass encapsulation layer 4

[0090] S730. Put the component coated with glass paste into a high-temperature furnace, perform glass melting encapsulation at 800 °C - 1000 °C, and keep warm for 10 - 30 minutes to completely melt the glass material and wrap the ceramic matrix 1, the electrode 2, and the connection position between the electrode 2 and the lead 3.

[0091] S740. Cool it in the furnace until the glass encapsulation layer 4 is cured to form a sealed structure, and then transfer the thermistor with the cured glass encapsulation layer 4 into the air-cooling device for accelerated cooling treatment.

[0092] S800. Conduct an appearance inspection on the glass-encapsulated thermistor to ensure that there are no cracks and bubble defects in the encapsulation layer. And conduct performance tests on the resistance value, B value, and accuracy of the thermistor, and sort them according to the test results.

[0093] Embodiment 3

[0094] As Figure 2 shown, this embodiment provides the structure of the air-cooling device in Embodiment 2. The air-cooling device includes a fan 5, a filter element 6, an air-cooling box 7, and a material tank 8. The filter element 6 is installed at the air inlet end of the fan 5, and the air inlet end of the air-cooling box 7 is connected to the air outlet end of the fan 5. A plurality of material tanks 8 are evenly arranged on the air-cooling box 7. This structure facilitates filtering the air pumped by the fan 5 through the filter element 6, so that the air pumped by the fan 5 is purified. The purified air enters the interior of the air-cooling box 7, and the thermistors to be cooled are installed inside the material tanks 8. The air flow blowing onto the material tanks 8 will take away the heat of the thermistors inside, thus facilitating and effectively quickly cooling the thermistors.

[0095] As Figure 3 shown, one end of the fan 5 is set as an air inlet 51, which is convenient for the fan 5 to suck and intake air. A bayonet 54 is arranged along the air inlet 51 of the fan 5, and limiting clamping rods 55 are symmetrically arranged on both sides inside the bayonet 54. The bayonet 54 and the limiting clamping rods 55 are convenient for installing the filter element 6, facilitating the flexible disassembly, assembly, and cleaning of the filter element 6. A first flange 56 is arranged at the other end of the fan 5, and a plurality of first flange holes 57 are evenly arranged on the first flange 56. The first flange 56 and the first flange holes 57 are convenient for connecting the fan 5 to the air-cooling box 7 through bolts. A power connection wire 52 is arranged on the side of the fan 5, and a power connection plug 53 is arranged at the end of the power connection wire 52. The power connection wire 52 and the power connection plug 53 are convenient for powering on the fan 5, facilitating the operation and use of the fan 5

[0096] As Figure 4 shown, a pulling groove 61 is arranged at the top of the filter element 6, which is convenient for the disassembly and assembly of the filter element 6 and facilitates its use. Limiting card slots 62 are symmetrically arranged on both sides of the filter element 6, and the limiting card slots 62 are clamped on the limiting clamping rods 55. This structure ensures that the filter element 6 is stable inside the bayonet 54. A filter cotton 63 is arranged in the middle of the filter element 6, and the filter cotton 63 is convenient for filtering the air passing through the filter element 6, thus facilitating the purification of dust in the air.

[0097] As Figure 5As shown, the end of the air-cooling box 7 facing the fan 5 is provided with a second flange 74, and the second flange 74 is provided with a plurality of second flange holes 75. The second flange 74 and the second flange holes 75 are convenient for the air-cooling box 7 to be fixed to the fan 5 by bolts. An air-distributing plate 73 is provided at one end of the air-cooling box 7 close to the fan 5. The air-distributing plate 73 is convenient for evenly distributing the wind blown out by the fan 5, so as to facilitate cooling and evenly blowing on the thermistor. The front of the air-cooling box 7 is evenly provided with a plurality of threaded holes 72. The threaded holes 72 are convenient for installing the material tank 8, and are convenient for disassembly and use of the material tank 8. The other end of the air-cooling box 7 is set as an air outlet 71, and the air outlet 71 is convenient for discharging the airflow for cooling the thermistor.

[0098] like Figure 6 As shown, a handle 81 is provided at one end of the material tank 8 facing the outside, and the handle 81 is convenient for holding the material tank 8, and is convenient for disassembly and use of the material tank 8. An adapter plate 82 is provided at one end of the material tank 8 facing the inside of the air-cooled box 7, and the adapter plate 82 is threadedly connected to the threaded hole 72, so that the material tank 8 is conveniently connected to the air-cooled box 7. A storage barrel 83 is provided at one end of the adapter plate 82 inserted into the air-cooled box 7, and the storage barrel 83 is convenient for storing glass-encapsulated thermistors that need to be cooled. The surface of the storage barrel 83 is hollowed out, and this structure is convenient for cooling wind to pass through the storage barrel 83, thereby taking away the heat on the thermistor. The storage barrel 83 is open at one end away from the adapter plate 82, and a cover 84 is provided at the open end of the storage barrel 83, and a threaded connecting plate 85 is provided at the end of the cover 84, and the threaded connecting plate 85 is threadedly connected to the storage barrel 83. This structure is convenient for blocking the open end of the storage barrel, so that the thermistor is stable inside the opening of the material tank 8.

[0099] Working principle: When in use, the glass-encapsulated thermistor with solidified surface is taken out from the furnace, and the thermistor is loaded into the storage barrel 83, and the opening of the storage barrel 83 is sealed with the cover 84. Then, multiple material tanks 8 are sequentially installed in the air-cooled box 7, and then the fan 5 is started, and the fan 5 drives the external airflow to blow into the air-cooled box. When the airflow passes through the thermistor, it will take away the heat of the glass encapsulation layer 4 on the surface of the thermistor, thereby achieving the purpose of cooling the thermistor.

[0100] In summary, compared with the prior art, by precisely controlling the raw material ratio and preparation process of the ceramic matrix 1, the thermistor of the present application has a faster response speed and can promptly and accurately reflect the rapid change of temperature. At the same time, the thermistor has a wider range of resistance-temperature characteristics and higher stability, and is suitable for the field of high-precision temperature measurement and control. Moreover, the oxidation resistance and stability of the improved thermistor are enhanced, indirectly prolonging the service life of the thermistor. The surface of the thermistor is encapsulated by means of glass encapsulation, which provides excellent sealing performance and can effectively prevent the internal structure from being eroded by the external environment (such as humidity, corrosive gas). At the same time, it enables the thermistor to work in a high-temperature environment. By installing a filter element 6 at the air inlet end of the fan 5, the air drawn by the fan 5 can be filtered to avoid dust in the air sticking to the glass encapsulation layer 4, ensuring that the surface of the produced thermistor is sufficiently clean.

[0101] The above is only the preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An NTC thermistor, comprising a ceramic substrate (1) and electrodes (2), characterized in that, The electrode (2) is attached to both ends of the ceramic substrate (1). The electrode (2) is connected with a lead wire (3). A glass encapsulation layer (4) is provided outside the ceramic substrate (1), and the glass encapsulation layer (4) wraps the ceramic substrate (1) and the electrode (2). The ceramic substrate (1) is made of raw materials with the following weight percentages: 40%-60% of manganese oxide, 10%-20% of cobalt oxide, 20%-30% of nickel oxide, 3%-12% of copper oxide, and 1%-5% of doped element oxide. The electrode (2) is a silver-palladium alloy electrode (2), and the mass ratio of silver to palladium is 7:3 - 9:

1.

2. The NTC thermistor according to claim 1, characterized in that, The manganese oxide is one or more of MnO 2、 Mn2O3 or Mn3O4, and the cobalt oxide is CoO or Co3O4.

3. A method for preparing an NTC thermistor, which is used to prepare the NTC thermistor according to any one of claims 1-2, characterized in that, The specific steps of the preparation method are as follows: S100. Select raw materials of manganese oxide, cobalt oxide, nickel oxide, copper oxide, and doped element oxide, and grind them separately. S200. Weigh the pretreated raw materials according to the above weight percentages, put them into a three-dimensional mixer for mixing to form a slurry. S300. Dry the slurry at 80°C - 120°C, and then pre-burn it at 800°C - 1000°C for 2 - 4 hours to obtain a pre-burned powder. Add a binder to the pre-burned powder and press it into a green body of the required shape using a mold. S400. Put the green body into a high-temperature furnace for debinding treatment to remove the binder in the green body. After the debinding is completed, perform sintering. S500. Coat the silver-palladium alloy slurry on both ends of the sintered ceramic substrate (1) by screen printing, and then sinter it at 700 - 850°C for 30 - 60 minutes to firmly bond the electrode (2) to the ceramic substrate (1). S600. Connect a platinum-plated alloy wire or Dumet wire to the electrode (2) of the ceramic substrate (1) by welding or crimping. S700. Adopt a glass encapsulation process to encapsulate the ceramic substrate (1), the electrode (2), and the connection position between the electrode (2) and the lead wire (3) with glass. S800. Conduct an appearance inspection on the glass-encapsulated thermistor to ensure that there are no crack and bubble defects in the encapsulation layer. Perform performance tests on the resistance value, B value, and accuracy of the thermistor, and sort them according to the test results.

4. The preparation method of an NTC thermistor according to claim 3, wherein, In the step S100, when grinding the raw materials, a planetary ball mill is used, the ball-to-material ratio is 3:1 - 5:1, and the ball milling time is 12 - 24 hours to ensure the fineness and uniformity of the raw materials, and the average particle size of the raw materials reaches 0.5 - 1 μm.

5. The preparation method of an NTC thermistor according to claim 3, characterized in that, In the step S200, when mixing the raw materials, the mixing time is 6 - 10 hours to ensure that all raw materials are fully and evenly mixed. During the mixing process, an appropriate amount of deionized water is added as a dispersion medium, and the addition amount of deionized water is 10% - 20% of the total weight of the raw materials.

6. The preparation method of an NTC thermistor according to claim 3, characterized in that, In the step S400, during the debinding treatment, the debinding temperature is 300 - 500°C, the heating rate is 1 - 3°C / min, and the holding time is 2 - 4 hours to remove the binder in the green body. The sintering temperature is 1200 - 1400°C, the heating rate is 2 - 5°C / min, and the holding time is 4 - 8 hours. During the sintering process, by precisely controlling the gas content and pressure in the furnace, the microstructure of the ceramic matrix (1) is improved, and its electrical properties are enhanced.

7. The preparation method of an NTC thermistor according to claim 3, characterized in that, In the step S700, the specific steps for glass encapsulating the thermistor are as follows: S710. Grind the glass material into powder, add an appropriate amount of binder, and make a glass paste. S720. Uniformly coat the glass paste around the ceramic matrix (1) and the lead (3) to form a preliminary glass encapsulation layer (4). S730. Place the component coated with the glass paste into a high-temperature furnace, perform glass melting encapsulation at 800°C - 1000°C, and keep it warm for 10 - 30 minutes to completely melt the glass material and wrap the ceramic matrix (1), the electrode (2), and the connection position between the electrode (2) and the lead (3). S740. Cool in the furnace until the glass encapsulation layer (4) solidifies to form a sealed structure, and then transfer the thermistor with the solidified glass encapsulation layer (4) into the air-cooling device for accelerated cooling treatment.

8. The preparation method of an NTC thermistor according to claim 7, characterized in that, In the step S740, the air-cooling device includes a fan (5), a filter element (6), an air-cooling box (7), and a material tank (8); the filter element (6) is installed at the air inlet end of the fan (5), and the air inlet end of the air-cooling box (7) is connected to the air outlet end of the fan (5), and a plurality of material tanks (8) are evenly arranged on the air-cooling box (7).

9. The preparation method of an NTC thermistor according to claim 8, characterized in that, One end of the fan (5) is set as an air inlet (51), a bayonet (54) is arranged along the air inlet (51) of the fan (5), two symmetrically arranged limiting clamping rods (55) are provided on both sides inside the bayonet (54), a first flange plate (56) is arranged at the other end of the fan (5), and a plurality of first flange holes (57) are evenly arranged on the first flange plate (56); a power connection wire (52) is arranged on the side of the fan (5), and a power connection plug (53) is arranged at the end of the power connection wire (52). A pulling groove (61) is arranged at the top of the filter element (6), two symmetrically arranged limiting card slots (62) are provided on both sides of the filter element (6), and the limiting card slots (62) are clamped on the limiting clamping rods (55); a filter cotton (63) is arranged in the middle of the filter element (6).

10. The preparation method of an NTC thermistor according to claim 8, characterized in that, One end of the air-cooling box (7) facing the fan (5) is provided with a second flange plate (74), a plurality of second flange holes (75) are provided on the second flange plate (74), an air distribution plate (73) is arranged at the end of the air-cooling box (7) close to the fan (5), a plurality of threaded holes (72) are evenly arranged on the front of the air-cooling box (7), and the other end of the air-cooling box (7) is set as an air outlet (71). One end of the material tank (8) facing the outside is provided with a handle (81), and one end of the material tank (8) facing the inside of the air-cooling box (7) is provided with an adapter plate (82). The adapter plate (82) is threadedly connected to the threaded hole (72). One end of the adapter plate (82) inserted into the air-cooling box (7) is provided with a storage cylinder (83). The surface of the storage cylinder (83) is provided with hollow holes, and one end of the storage cylinder (83) away from the adapter plate (82) is provided with an opening. A cover (84) is provided at the opening end of the storage cylinder (83). A threaded connection plate (85) is provided at the end of the cover (84). The threaded connection plate (85) is threadedly connected to the storage cylinder (83).

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