Ntc thermosensitive ceramic material and preparation method thereof

Abstract

The application provides an NTC thermosensitive ceramic material, which has a chemical composition of xFeMnSiO4-(2-x)CoNi y Mn 2.0‑y O4, 0.5≤x≤1.5, 0.1≤y≤0.8. The thermosensitive ceramic material has a thermosensitive constant B value in a range of 5000-8100 K, a resistivity of 1.0-5.8*10 7 Ω*cm at 25 DEG C, and a resistance change rate and a B value change rate controlled within 0.5% after long-time aging and temperature impact.

Description

Technical Field

[0001] This application relates to the field of thermistor ceramic materials, and in particular to an NTC thermistor ceramic material and its preparation method. Background Technology

[0002] Thermistor ceramics are ceramic materials that are sensitive to temperature changes. For example, thermistors are sensitive to temperature and exhibit different resistance values ​​at different temperatures. PTC thermistors have a higher resistance value at higher temperatures, while NTC thermistors have a lower resistance value at higher temperatures.

[0003] The resistivity of an NTC thermistor follows the Arrhenius exponential relationship with temperature: ρ = ρ0exp(Ea / kT), where ρ and ρ0 are the resistivity at temperature T (absolute temperature) and infinity, respectively, k is the Boltzmann constant, and Ea is the activation energy. Thermistor materials are typically characterized by their resistivity at room temperature (25℃) and the thermistor constant B. The thermistor constant is proportional to the activation energy as B = Ea / k. The temperature-resistance characteristic of an NTC thermistor can be expressed as: R = R0exp(B(1 / T - 1 / T0)), where R and R0 are the resistances at T and T0 (absolute temperatures), respectively. The temperature coefficient of resistance is: αT = 1 / R(dR / dT) = -B / T². The thermistor constant B characterizes the temperature sensitivity of the NTC thermistor; a larger B value indicates a greater rate of change in resistance with respect to temperature, and thus better temperature sensitivity.

[0004] Currently, NTC thermistor devices are mainly developed along the lines of high B-value and low resistance, and low B-value and high resistance, with relatively little research on high resistance and high B-value. Existing thermistor materials generally exhibit severe aging in the high-temperature range (200℃~600℃), failing to meet the requirements for use in high-temperature environments. Even if some materials are relatively stable in the high-temperature range, their resistivity is usually low, and they have drawbacks such as inconsistent thermal sensitivity coefficients, unstable thermistor constants, and large resistivity aging coefficients.

[0005] Furthermore, the application of spinel-type NTC thermistors is typically limited to temperatures below 200°C. This is because, above 200°C, tetrahedral and octahedral oxygen ions in spinel-type materials undergo ion exchange, leading to structural relaxation. This manifests as significant time-dependent resistivity drift above 200°C, causing instability in the material's electrical properties and affecting the thermistor's lifespan and operating temperature range. This drawback makes it difficult for existing NTC materials to be practically applied in high-temperature environments (200°C–600°C).

[0006] Chinese patent CN112420296B discloses a high-stability, voltage-resistant NTC ceramic thermistor, comprising component A and component B in a mass ratio of 1:0.1 to 0.4, wherein component A is a composite metal oxide M X O Y M includes Mn, Cr, Cu, and RE. Its thermistor constant B is around 7000K, but the application of this material at high temperatures of 200℃ to 600℃ is still limited.

[0007] Therefore, there is still a need for high-temperature thermistors with controllable thermistor constant B, good operational stability, and greater accuracy at service temperatures ranging from 200℃ to 600℃. Summary of the Invention

[0008] In view of this, the main objective of this application is to provide an NTC thermistor ceramic material with controllable thermistor constant B value, stable material parameters, and longer service life.

[0009] Therefore, on the one hand, this application provides an NTC thermistor ceramic material, wherein the chemical composition of the ceramic material is xFeMnSiO4-(2-x)CoNi y Mn 2.0-y O4, 0.5≤x≤1.5, 0.1≤y≤0.8.

[0010] On the other hand, this application also provides a method for preparing the above-mentioned NTC thermistor ceramic material, comprising the following steps:

[0011] (a) The raw materials MnO2, Fe2O3 and Si2O3 are subjected to a first grinding process to obtain a first grinding powder, and the first grinding powder is subjected to a first calcination to obtain the compound FeMnSiO4;

[0012] (b) The raw materials MnO2, Co2O3 and Ni2O3 are subjected to a second grinding process to obtain a second ground powder. The second ground powder is then subjected to a second calcination to obtain the compound CoNi. y Mn 2.0-y O4, where 0.1 ≤ y ≤ 0.8;

[0013] (c) The above FeMnSiO4 and CoNi y Mn 2.0-y O4 is mixed in a molar ratio of x:(2-x) and subjected to a third grinding process to obtain a third ground powder. The third ground powder is then granulated to obtain ceramic powder, wherein 0.5≤x≤1.5.

[0014] (d) Pressing the ceramic powder to obtain a ceramic blank; and

[0015] (e) The ceramic blank is sintered to obtain the NTC thermistor ceramic material.

[0016] In some embodiments, the first grinding process, the second grinding process, and the third grinding process are respectively performed by ball milling in a pure water medium.

[0017] In some embodiments, the first grinding process takes 8 to 12 hours; the second grinding process takes 8 to 14 hours; and the third grinding process takes 22 to 26 hours.

[0018] In some embodiments, the first calcination temperature is 1050℃~1200℃, and the first calcination time is 4h~12h.

[0019] In some embodiments, the second calcination temperature is 1150℃~1280℃, and the second calcination time is 3h~5h.

[0020] In some embodiments, the granulation process includes the following steps: adding a binder to the third ground powder to granulate and obtain ceramic powder.

[0021] In some embodiments, the adhesive is a polyvinyl alcohol aqueous solution with a mass concentration of 6% to 10%, and the amount of the adhesive used is 1 wt% to 2 wt% relative to the weight of the third grinding powder.

[0022] In some embodiments, the sintering process is carried out in an air atmosphere.

[0023] In some embodiments, the sintering temperature is 1250℃~1350℃ and the time is 5h~12h.

[0024] This application provides a controllable NTC thermistor ceramic material with the general chemical formula xFeMnSiO4-(2-x)CoNi y Mn 2.0-y O4, where 0.5≤x≤1.5, 0.1≤y≤0.8; the thermistor constant B of this controllable thermistor ceramic material ranges from 5000 to 8100 K, and the resistivity at 25℃ is 1.0 to 5.8 × 10⁻⁶. 7 After prolonged aging and temperature shock, the resistance change rate and B-value change rate are controlled within 0.5% (Ω·cm). Furthermore, the preparation method provided in this application allows for control of the FeMnSiO4 crystal phase and CoNi phase during the preparation process. y Mn 2.0-y The content ratio of O4 crystal phase and CoNi y Mn 2.0-yThe thermistor constant B and resistivity of the obtained thermistor material are adjusted by modifying the Ni and Mn content ratio in the O4 crystal phase to meet the actual temperature measurement requirements in high-temperature environments (200℃~600℃). Furthermore, the preparation method of this application is convenient to sinter and uses an air atmosphere, making it suitable for large-scale industrialization. Detailed Implementation

[0025] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0026] Throughout this specification, unless otherwise specified, the terminology used herein should be understood as having the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. In the event of any conflict, this specification shall prevail.

[0027] It should be noted that, in the embodiments of this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a method or apparatus that includes a list of elements includes not only the elements expressly stated, but also other elements not expressly listed, or elements inherent to implementing the method or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other related elements in the method or apparatus that includes that element.

[0028] It should be noted that the terms "first," "second," and "third" used in the embodiments of this application are merely to distinguish similar objects and do not represent a specific ordering of objects. It is understood that "first," "second," and "third" can be interchanged in a specific order or sequence where permitted. It should be understood that the objects distinguished by "first," "second," and "third" can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in an order other than those described herein.

[0029] In view of the existing technology's need for thermistor materials with high B value, high resistance, and stable performance in the high temperature range (200℃~600℃), this application aims to provide a controllable NTC thermistor ceramic material and its preparation method.

[0030] In a first aspect, this application provides a controllable NTC thermistor ceramic material, wherein the chemical composition of the ceramic material is xFeMnSiO4-(2-x)CoNi y Mn 2.0-yO4, 0.5≤x≤1.5, 0.1≤y≤0.8. Where CoNi y Mn 2.0-y In the O4 crystal phase, the Ni to Mn content ratio is y:(2.0-y), 0.1≤y≤0.8. As the value of y increases, both the thermistor constant B and resistivity of the obtained controllable NTC thermistor ceramic material increase. Furthermore, the FeMnSiO4 crystal phase and CoNi... y Mn 2.0-y The O4 crystal phase content ratio is x:(2-x), where 0.5≤x≤1.5. As the value of x decreases, the thermistor constant B of the obtained controllable NTC thermistor ceramic material can be further increased, but the resistivity decreases. The thermistor constant B of this controllable thermistor ceramic material ranges from 5000 to 8100 K, and the resistivity at 25℃ is 1.0 to 5.8 × 10⁻⁶. 7 Ω·cm, after long-term aging and temperature shock, the rate of change of resistance and the rate of change of B value are controlled within 0.5%.

[0031] Secondly, this application also provides a method for preparing controllable NTC thermistor ceramic materials, comprising the following steps:

[0032] (a) The raw materials MnO2, Fe2O3 and Si2O3 are subjected to a first grinding process to obtain a first grinding powder, and the first grinding powder is subjected to a first calcination to obtain the compound FeMnSiO4;

[0033] (b) The raw materials MnO2, Co2O3 and Ni2O3 are subjected to a second grinding process to obtain a second ground powder. The second ground powder is then subjected to a second calcination to obtain the compound CoNi. y Mn 2.0-y O4, where 0.1 ≤ y ≤ 0.8;

[0034] (c) The above FeMnSiO4 and CoNi y Mn 2.0-y O4 is mixed in a molar ratio of x:(2-x) and subjected to a third grinding process to obtain a third ground powder. The third ground powder is then granulated to obtain ceramic powder, wherein 0.5≤x≤1.5.

[0035] (d) Pressing the ceramic powder to obtain a ceramic blank; and

[0036] (e) The ceramic blank is sintered to obtain the NTC thermistor ceramic material.

[0037] In step (a), the raw materials MnO2, Fe2O3, and Si2O3 undergo a first grinding process to obtain a first ground powder, which is then subjected to a first calcination to obtain the compound FeMnSiO4. In some embodiments, the mass percentages of each raw material are 37.5 wt% to 38.5 wt%, 34.5 wt% to 35.5 wt% of Fe2O3, and 26.0 wt% to 27.0 wt% of Si2O3, respectively. In a preferred embodiment, the mass percentages of each raw material are 38.32 wt% of MnO2, 35.19 wt% of Fe2O3, and 26.49 wt% of Si2O3, and they are mixed and subjected to a first grinding process to obtain the first ground powder.

[0038] In some embodiments, the first grinding process may be ball milling in a pure water medium. In some embodiments, the first grinding process takes 8 to 12 hours, for example, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, or any range between these; preferably, the first grinding time is 10 hours. In some embodiments, the first grinding process further includes sieving the powder obtained after grinding, using a sieve with a mesh size of, for example, 80 to 120 mesh, 90 to 110 mesh, preferably 100 mesh; the powder obtained after sieving is the first ground powder. In some embodiments, the average particle size D50 of the first ground powder is 1.1 μm to 1.3 μm.

[0039] The first ground powder is calcined to obtain the compound FeMnSiO4. In some embodiments, the first calcination can be carried out in, for example, a high-temperature muffle furnace, a box furnace, or an atmosphere sintering furnace; this application does not specifically limit this method. In some embodiments, the first calcination temperature is 1050℃~1200℃, for example, 1100℃~1200℃, for example, 1100℃~1150℃, preferably 1100℃. In some embodiments, the first calcination time is 4h~12h, for example, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, or any range between two of these, preferably 12h.

[0040] In step (b), the raw materials MnO2, Co2O3 and Ni2O3 are subjected to a second grinding process to obtain a second ground powder, and the second ground powder is subjected to a second calcination to obtain the compound CoNi. y Mn 2.0-yO4, where 0.1 ≤ y ≤ 0.8. In some embodiments, the mass percentages of each raw material are 41.0 wt% to 61.5 wt%, Co2O3 32.3 wt% to 32.8 wt%, and Ni2O3 6.0 wt% to 26.5 wt%, respectively, and they are mixed and subjected to a second grinding process to obtain a second ground powder. For example, the following raw materials in mass percentages are taken: 61.14 wt% MnO2, 32.40 wt% Co2O3, and 6.46 wt% Ni2O3, mixed, subjected to a second grinding process to obtain a second ground powder, which, after a second calcination, yields the compound CoNi. 0.2 Mn 1.8 O4.

[0041] Through research, the inventors discovered that by adjusting the compound CoNi y Mn 2.0-y The content of Ni and Mn in O4 can be adjusted to obtain a final NTC thermistor ceramic material with a controllable thermistor constant B value. For example, increasing the content of the compound CoNi can help. y Mn 2.0-y By reducing the Ni content in O4 and correspondingly decreasing the Mn content, the thermistor constant B and resistivity of the resulting NTC thermistor ceramic material are both improved. Those skilled in the art can refer to the detailed embodiments described below to select the NTC thermistor material with the desired thermistor constant B and the corresponding preparation method.

[0042] In some embodiments, the second grinding process may be ball milling in a pure water medium. In some embodiments, the second grinding process takes 8 to 14 hours, for example, 8, 9, 10, 11, 12, 13, or 14 hours, or any range thereof. Preferably, the second grinding time is 10 to 12 hours, and more preferably, it is 12 hours. In some embodiments, the second grinding process further includes sieving the powder obtained after grinding, using a sieve with a mesh size of, for example, 80 to 120 mesh, 90 to 110 mesh, and preferably 100 mesh; the powder obtained after sieving is the second-ground powder. In some embodiments, the average particle size D50 of the second-ground powder is 1.1 μm to 1.5 μm.

[0043] The second ground powder was subjected to a second calcination to obtain the compound CoNi. y Mn 2.0-yO4 (0.1≤y≤0.8). In some embodiments, the second calcination can be carried out in, for example, a high-temperature muffle furnace, a box-type calcination furnace, or an atmosphere sintering furnace; this application does not specifically limit this. In some embodiments, the second calcination temperature is 1150℃~1280℃, preferably, for example, 1150℃~1250℃, preferably, for example, 1250℃. In some embodiments, the second calcination time is 3h~5h, for example, it can be 3h, 4h, 5h or any range between them, preferably, for example, 5h.

[0044] In step (c), the above FeMnSiO4 and CoNi are... y Mn 2.0-y O4 is mixed at a molar ratio of x:(2-x) and subjected to a third grinding process to obtain a third ground powder. The third ground powder is then granulated to obtain ceramic powder, wherein 0.5 ≤ x ≤ 1.5. In some embodiments, the third grinding process may be ball milling in a pure water medium. In some embodiments, the third grinding process takes place for 22h to 26h, for example, 22h, 23h, 24h, 25h, 26h, or any range thereof. It is understood that those skilled in the art can adjust the third grinding process time according to actual needs to obtain the third powder with the desired particle size. In some embodiments, the third grinding process further includes sieving the powder obtained after grinding, using a sieve of, for example, 80-120 mesh, 90-110 mesh, preferably 100 mesh; the powder obtained after sieving is the third ground powder. In some embodiments, the average particle size D50 of the third ground powder is 0.7μm to 0.9μm.

[0045] Through research, the inventors discovered that by adjusting FeMnSiO4 and CoNi y Mn 2.0-y The molar ratio of the two compounds, x:(2-x), can be adjusted to modify the thermistor constant B and resistivity of the final NTC ceramic material. For example, the adjustment of the compound CoNi as described above... y Mn 2.0-y Based on the Ni and Mn element content in O4, reducing the value of x, i.e., reducing the molar content of the compound FeMnSiO4, increases the thermistor constant B of the final NTC thermistor material, but decreases the resistivity. Alternatively, increasing the value of x, i.e., increasing the molar content of the compound FeMnSiO4, decreases the thermistor constant B of the final NTC thermistor material, but increases the resistivity. Those skilled in the art can refer to the detailed embodiments below to select the NTC thermistor material with the desired thermistor constant B value and the corresponding preparation method. The chemical composition of the ceramic material obtained according to the preparation method provided in this application is xFeMnSiO4-(2-x)CoNi.y Mn 2.0-y O4, 0.5≤x≤1.5, 0.1≤y≤0.8, its thermistor constant B ranges from 5000 to 8100 K, and its resistivity at 25℃ is 1.0 to 5.8 × 10⁻⁶. 7 Ω·cm, after long-term aging and temperature shock, the rate of change of resistance and the rate of change of B value are controlled within 0.5%.

[0046] In step (c), after the third grinding process, the method further includes granulating the third ground powder. In some embodiments, the granulation process includes adding a binder to the third ground powder for granulation. The binder is used to increase the bonding strength between the powders, and may be, for example, vinyl acetate, polyvinyl alcohol, acrylic acid, etc. In a preferred embodiment, the binder may be a 6% to 10% (w / w) aqueous solution of polyvinyl alcohol, more preferably an 8% (w / w) aqueous solution of polyvinyl alcohol. In some embodiments, the amount of binder used is 1 wt% to 2 wt% relative to the weight of the third ground powder, preferably 1.5 wt% relative to the weight of the third ground powder. In some embodiments, the granulation process further includes drying the third ground powder mixed with the binder, then pulverizing and sieving it to obtain ceramic powder with good flowability, wherein the sieve may be 180 mesh to 220 mesh, preferably 200 mesh.

[0047] In step (d), the ceramic powder obtained in step (c) is pressed to obtain a ceramic green body. The pressing includes: pressing the ceramic powder obtained in step (c) into a disc under a pressure of 20-30 MPa for 5-8 minutes; then performing isostatic pressing on the disc under a pressure of 100-200 MPa for 10-20 minutes, for example, 12-20 minutes, or for example, 15-20 minutes, to obtain the ceramic green body. In some embodiments, the ceramic powder is pressed into a disc under a pressure of 30 MPa for 5 minutes; then the disc is subjected to isostatic pressing under a pressure of 200 MPa for 20 minutes to obtain the ceramic green body.

[0048] In step (e), the ceramic preform is sintered to obtain a controllable NTC thermistor ceramic material. Sintering can be performed, for example, in a high-temperature muffle furnace, a box furnace, or an atmosphere sintering furnace. In one embodiment, sintering is performed in an air atmosphere. In some embodiments, the sintering temperature is 1250°C to 1350°C, preferably, for example, 1300°C to 1350°C, and more preferably, for example, 1350°C. In some embodiments, the sintering time is 5 hours to 12 hours, for example, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, or any range between these, preferably, for example, 5 hours.

[0049] Unless otherwise specified in this document, there is no strict order in which these steps are performed, and they may be performed in any other order.

[0050] This application provides a controllable NTC thermistor ceramic material prepared by the above method. The general chemical formula of this controllable NTC thermistor ceramic material is xFeMnSiO4-(2-x)CoNi. y Mn 2.0-y O4, where 0.5≤x≤1.5, 0.1≤y≤0.8; the thermistor constant B of this controllable thermistor ceramic material ranges from 5000 to 8100 K, and the resistivity at 25℃ is 1.0 to 5.8 × 10⁻⁶. 7 After prolonged aging and temperature shock, the resistance change rate and B-value change rate are controlled within 0.5% (Ω·cm). Furthermore, the preparation method provided in this application allows for control of the FeMnSiO4 crystal phase and CoNi phase during the preparation process. y Mn 2.0-y The content ratio of O4 crystal phase and CoNi y Mn 2.0-y The thermistor constant B and resistivity of the obtained thermistor material are adjusted by modifying the Ni and Mn content ratio in the O4 crystal phase to meet the actual temperature measurement requirements in high-temperature environments (200℃~600℃). Furthermore, the preparation method of this application is convenient to sinter and uses an air atmosphere, making it suitable for large-scale industrialization.

[0051] The present application will now be described in further detail with reference to specific embodiments.

[0052] Example

[0053] Example 1

[0054] MnO2, Fe2O3, and Si2O3 were weighed out at weight percentages of 38.32%, 35.19%, and 26.49%, respectively, and mixed. Pure water was added as the ball milling medium, and the mixture was milled in a planetary ball mill for 10 hours. After milling, the mixture was dried and passed through a 100-mesh sieve. The mixture was then calcined in a high-temperature muffle furnace at 1100°C for 6 hours to obtain the compound FeMnSiO4.

[0055] MnO2, Co2O3, and Ni2O3 were weighed out at weight percentages of 61.14%, 32.40%, and 6.46%, respectively, and mixed. Pure water was added as the ball milling medium, and the mixture was milled in a planetary ball mill for 12 hours. After milling, the mixture was dried and passed through a 100-mesh sieve, and then calcined in a muffle furnace at 1200℃ for 3 hours to obtain the compound CoNi. 0.2 Mn 1.8 O4.

[0056] The above compounds FeMnSiO4 and CoNi 0.2Mn 1.8 O4 was mixed at a molar ratio of 1:1 to obtain a mixed powder. After ball milling in pure water for 22 hours, the powder was dried and passed through a 100-mesh sieve. An 8% polyvinyl alcohol aqueous solution powder was added as a binder (accounting for 1.5 wt% of the total powder mass) for granulation. After drying, the powder was ground and crushed and passed through a 200-mesh sieve to obtain ceramic powder.

[0057] The ceramic powder was first pressed into a disc under a pressure of 30 MPa for 5 minutes; then it was subjected to isostatic pressing at a pressure of 200 MPa for 10 minutes to obtain a ceramic blank.

[0058] The ceramic blank was placed in a high-temperature muffle furnace and heated to 1300°C in an air atmosphere, and held for 6 hours to obtain high-temperature NTC thermistor ceramic.

[0059] Example 2

[0060] MnO2, Fe2O3, and Si2O3 were weighed out at weight percentages of 38.32%, 35.19%, and 26.49%, respectively, and mixed. Pure water was added as the ball milling medium, and the mixture was milled for 10 hours using a planetary ball mill. After milling, the mixture was dried and passed through a 100-mesh sieve, and then calcined in a muffle furnace at 1100℃ for 6 hours to obtain the compound FeMnSiO4.

[0061] MnO2, Co2O3, and Ni2O3 were weighed out at weight percentages of 54.53%, 32.51%, and 12.96%, respectively, and mixed. Pure water was added as the ball milling medium, and the mixture was milled for 12 hours using a planetary ball mill. After milling, the mixture was dried and passed through a 100-mesh sieve, and then calcined in a muffle furnace at 1200℃ for 4 hours to obtain the compound CoNi. 0.4 Mn 1.6 O4

[0062] The above compounds FeMnSiO4 and CoNi 0.4 Mn 1.6 O4 was mixed at a molar ratio of 1:1 to obtain a mixed powder. After ball milling in pure water for 22 hours, the powder was dried and passed through a 100-mesh sieve. An 8% polyvinyl alcohol aqueous solution was added as a binder (accounting for 1.5 wt% of the total powder mass) for granulation. After drying, the powder was ground and crushed and passed through a 200-mesh sieve to obtain ceramic powder.

[0063] The ceramic powder was first pressed into a disc under a pressure of 30 MPa for 5 minutes; then it was subjected to isostatic pressing at a pressure of 200 MPa for 10 minutes to obtain a ceramic blank.

[0064] The ceramic blank was placed in a high-temperature muffle furnace and heated to 1300°C in an air atmosphere, and held for 6 hours to obtain high-temperature NTC thermistor ceramic.

[0065] Example 3

[0066] MnO2, Fe2O3, and Si2O3 were weighed out at weight percentages of 38.32%, 35.19%, and 26.49%, respectively, and mixed. Pure water was added as the ball milling medium, and the mixture was milled for 10 hours using a planetary ball mill. After milling, the mixture was dried and passed through a 100-mesh sieve, and then calcined in a muffle furnace at 1100℃ for 6 hours to obtain the compound FeMnSiO4.

[0067] MnO2, Co2O3, and Ni2O3 were weighed out at weight percentages of 47.87%, 32.62%, and 19.51%, respectively, and mixed. Pure water was added as the ball milling medium, and the mixture was milled in a planetary ball mill for 12 hours. After milling, the mixture was dried and passed through a 100-mesh sieve, and then calcined in a muffle furnace at 1200℃ for 5 hours to obtain the compound CoNi. 0.6 Mn 1.4 O4

[0068] The above compounds FeMnSiO4 and CoNi 0.6 Mn 1.4 O4 was mixed at a molar ratio of 1:1 to obtain a mixed powder. After ball milling in pure water for 22 hours, the powder was dried and passed through a 100-mesh sieve. An 8% polyvinyl alcohol aqueous solution was added as a binder (accounting for 1.5 wt% of the total powder mass) for granulation. After drying, the powder was ground and crushed and passed through a 200-mesh sieve to obtain ceramic powder.

[0069] The ceramic powder was first pressed into a disc under a pressure of 30 MPa for 5 minutes; then it was subjected to isostatic pressing at a pressure of 200 MPa for 10 minutes to obtain a ceramic blank.

[0070] The ceramic blank was placed in a high-temperature muffle furnace and heated to 1300°C in an air atmosphere, and held for 6 hours to obtain high-temperature NTC thermistor ceramic.

[0071] Example 4

[0072] MnO2, Fe2O3, and Si2O3 were weighed out at weight percentages of 38.32%, 35.19%, and 26.49%, respectively, and mixed. Pure water was added as the ball milling medium, and the mixture was milled for 10 hours using a planetary ball mill. After milling, the mixture was dried and passed through a 100-mesh sieve, and then calcined in a muffle furnace at 1100℃ for 6 hours to obtain the compound FeMnSiO4.

[0073] MnO2, Co2O3, and Ni2O3 were weighed out at weight percentages of 41.17%, 32.73%, and 26.10%, respectively, and mixed. Pure water was added as the ball milling medium, and the mixture was milled in a planetary ball mill for 12 hours. After milling, the mixture was dried and passed through a 100-mesh sieve, and then calcined in a muffle furnace at 1250°C for 5 hours to obtain the compound CoNi. 0.8 Mn1.2 O4

[0074] The above compounds FeMnSiO4 and CoNi 0.8 Mn 1.2 O4 was mixed at a molar ratio of 1:1 to obtain a mixed powder. After ball milling in pure water for 22 hours, the powder was dried and passed through a 100-mesh sieve. An 8% polyvinyl alcohol aqueous solution was added as a binder (accounting for 1.5 wt% of the total powder mass) for granulation. After drying, the powder was ground and crushed and passed through a 200-mesh sieve to obtain ceramic powder.

[0075] The ceramic powder was first pressed into a disc under a pressure of 30 MPa for 5 minutes; then it was subjected to isostatic pressing at a pressure of 200 MPa for 20 minutes to obtain a ceramic blank.

[0076] The ceramic blank was placed in a high-temperature muffle furnace and heated to 1250°C in an air atmosphere, and held for 6 hours to obtain high-temperature NTC thermistor ceramic.

[0077] Example 5

[0078] MnO2, Fe2O3, and Si2O3 were weighed out at weight percentages of 38.32%, 35.19%, and 26.49%, respectively, and mixed. Pure water was added as the ball milling medium, and the mixture was milled for 10 hours using a planetary ball mill. After milling, the mixture was dried and passed through a 100-mesh sieve, and then calcined in a muffle furnace at 1100℃ for 6 hours to obtain the compound FeMnSiO4.

[0079] MnO2, Co2O3, and Ni2O3 were weighed out at weight percentages of 41.17%, 32.73%, and 26.10%, respectively, and mixed. Pure water was added as the ball milling medium, and the mixture was milled in a planetary ball mill for 12 hours. After milling, the mixture was dried and passed through a 100-mesh sieve, and then calcined in a muffle furnace at 1250°C for 5 hours to obtain the compound CoNi. 0.8 Mn 1.2 O4

[0080] The above compounds FeMnSiO4 and CoNi 0.8 Mn 1.2 O4 was mixed at a molar ratio of 0.5:1.5 to obtain a mixed powder. After ball milling in pure water for 22 hours, the powder was dried and passed through a 100-mesh sieve. An 8% polyvinyl alcohol aqueous solution was added as a binder (accounting for 1.5 wt% of the total powder mass) for granulation. After drying, the powder was ground and crushed and passed through a 200-mesh sieve to obtain ceramic powder.

[0081] The ceramic powder was first pressed into a disc under a pressure of 30 MPa for 5 minutes; then it was subjected to isostatic pressing at a pressure of 200 MPa for 20 minutes to obtain a ceramic blank.

[0082] The ceramic blank was placed in a high-temperature muffle furnace and heated to 1350°C in an air atmosphere, and held for 5 hours to obtain high-temperature NTC thermistor ceramic.

[0083] Example 6

[0084] MnO2, Fe2O3, and Si2O3 were weighed out at weight percentages of 38.32%, 35.19%, and 26.49%, respectively, and mixed. Pure water was added as the ball milling medium, and the mixture was milled for 10 hours using a planetary ball mill. After milling, the mixture was dried and passed through a 100-mesh sieve, and then calcined in a muffle furnace at 1100℃ for 6 hours to obtain the compound FeMnSiO4.

[0085] MnO2, Co2O3, and Ni2O3 were weighed out at weight percentages of 41.17%, 32.73%, and 26.10%, respectively, and mixed. Pure water was added as the ball milling medium, and the mixture was milled in a planetary ball mill for 12 hours. After milling, the mixture was dried and passed through a 100-mesh sieve, and then calcined in a muffle furnace at 1250°C for 5 hours to obtain the compound CoNi. 0.8 Mn 1.2 O4

[0086] The above compounds FeMnSiO4 and CoNi 0.8 Mn 1.2 O4 was mixed at a molar ratio of 1.5:0.5 to obtain a mixed powder. After ball milling in pure water for 22 hours, the powder was dried and passed through a 100-mesh sieve. An 8% polyvinyl alcohol aqueous solution was added as a binder (accounting for 1.5 wt% of the total powder mass) for granulation. After drying, the powder was ground and crushed and passed through a 200-mesh sieve to obtain ceramic powder.

[0087] The ceramic powder was first pressed into a disc under a pressure of 30 MPa for 5 minutes; then it was subjected to isostatic pressing at a pressure of 200 MPa for 20 minutes to obtain a ceramic blank.

[0088] The ceramic blank was placed in a high-temperature muffle furnace and heated to 1250°C in an air atmosphere, and held for 12 hours to obtain high-temperature NTC thermistor ceramic.

[0089] Example 7

[0090] Test methods

[0091] Thermistor constant B value: measured according to the method specified in national standard GB / T6663.1-4.6;

[0092] Resistivity at 25℃: The zero-power resistance value at 25℃ was measured according to the method specified in national standard GB / T6663.1-4.5.

[0093] Aging test: Tested according to the method specified in national standard GB / T6663.1-4.24;

[0094] Temperature shock test: Tested according to the method specified in national standard GB / T6663.1-4.21.

[0095] Example 7

[0096] The test results are shown in Table 1.

[0097] Table 1

[0098]

[0099] The above results show that the NTC thermistor ceramic materials provided in Examples 1-6 of this invention have a thermistor constant B value ranging from 5000 to 8100 K, and a resistivity of 1.0 to 5.8 × 10⁻⁶ at 25°C. 7 After prolonged aging and temperature shock, the resistance change rate and the B-value change rate are controlled within 0.5% (Ω·cm). The B-value and resistivity of the thermistor ceramic material in this application can be determined based on FeMnSiO4 and CoNi... y Mn 2.0-y The molar ratio of O4 and CoNi y Mn 2.0-y By adjusting the Ni and Mn content ratio in O4, the thermistor ceramic material of this application can obtain a larger B value and resistivity compared with the prior art. Moreover, the resistivity and B value of the material change little after aging, and the working stability is good. It is suitable for accurate measurement in the temperature range of 200℃~600℃ and can be used to prepare high-performance NTC thermistor sensors.

[0100] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. An NTC thermistor ceramic material, characterized in that, The chemical composition of the ceramic material is xFeMnSiO4-(2-x)CoNi y Mn 2.0-y O4, 0.5≤x≤1.5, 0.1≤y≤0.8, the thermistor constant B of the NTC thermistor ceramic material is 5000K-8100 K, and the preparation method of the NTC thermistor ceramic material includes the following steps: (a) The raw materials MnO2, Fe2O3 and Si2O3 are subjected to a first grinding process to obtain a first grinding powder, and the first grinding powder is subjected to a first calcination to obtain the compound FeMnSiO4, wherein the first calcination temperature is 1050℃~1200℃ and the first calcination time is 4h~12h; (b) The raw materials MnO2, Co2O3 and Ni2O3 are subjected to a second grinding process to obtain a second ground powder, and the second ground powder is subjected to a second calcination to obtain the compound CoNi. y Mn 2.0-y O4, where 0.1≤y≤0.8, the second calcination temperature is 1150℃~1280℃, and the second calcination time is 3h~5h; (c) The above FeMnSiO4 and CoNi y Mn 2.0-y O4 is mixed in a molar ratio of x:(2-x) and subjected to a third grinding process to obtain a third ground powder. The third ground powder is then granulated to obtain ceramic powder, wherein 0.5≤x≤1.

5. (d) Pressing the ceramic powder to obtain a ceramic blank; and (e) The ceramic blank is sintered to obtain the NTC thermistor ceramic material, wherein the thermistor constant B of the NTC thermistor ceramic material is 5000 K-8100 K, wherein the sintering temperature is 1250℃~1350℃ and the time is 5h~12h.

2. The NTC thermistor ceramic material according to claim 1, wherein, The first grinding process, the second grinding process, and the third grinding process are respectively ball milling performed in a pure water medium.

3. The NTC thermistor ceramic material according to claim 1 or 2, wherein the first grinding treatment time is 8h~12h; the second grinding treatment time is 8h~14h; and the third grinding treatment time is 22h~26h.

4. The NTC thermistor ceramic material according to claim 1, wherein, The granulation process includes the following steps: adding a binder to the third grinding powder and granulating to obtain ceramic powder.

5. The NTC thermistor ceramic material according to claim 4, wherein, The adhesive is a polyvinyl alcohol aqueous solution with a mass concentration of 6% to 10%, and the amount of the adhesive used is 1 wt% to 2 wt% relative to the mass of the third grinding powder.

6. The NTC thermistor ceramic material according to claim 1, wherein, The sintering process is carried out in an air atmosphere.

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