Barium strontium titanate ceramic, high-resolution barium strontium titanate temperature sensing element and preparation method of high-resolution barium strontium titanate temperature sensing element

Abstract

The invention relates to barium strontium titanate ceramic, a high-resolution barium strontium titanate temperature sensing element and a preparation method of the high-resolution barium strontium titanate temperature sensing element. The chemical composition of the barium strontium titanate ceramic is (1-m-n) (BaxSryCazNpuTivO3)-m (Al2O3-SiO2-TiO2)-nMnCO3, in the formula, n is equal to 0.09% to 0.18%, and m is equal to 1.2% to 3%. In BaxSryCazNpuTivO3, x is equal to 0.6 to 0.8, y is equal to 0.15 to 0.35, z is equal to 0.01 to 0.07, u is equal to 0.001 to 0.004, v is equal to 1.005 to 1.02, and x + y + z is equal to 1. The high-resolution barium strontium titanate temperature sensing element comprises a barium strontium titanate ceramic chip and a single-sided metal electrode or a double-sided metal electrode on the surface of the barium strontium titanate ceramic chip.

Description

Technical Field

[0001] The present invention belongs to the field of sensing elements and devices, and particularly relates to a barium strontium titanate ceramic material, a high-resolution barium strontium titanate temperature sensing element and a preparation method thereof. Background Art

[0002] Space optical remote sensing components are widely used in earth observation and space exploration. They are the core key components for realizing high-resolution satellite earth monitoring and precision strikes, and have important strategic application values. Space optical remote sensing components will face a temperature environment with alternating cold and heat during on-orbit operation, which is likely to cause deformation of precision optical remote sensing components, thereby generating test errors and further affecting the monitoring accuracy. In order to achieve high-resolution monitoring of the environmental temperature of optical remote sensing components for rapid and effective adjustment to make the remote sensing components in an ideal operating temperature environment, a temperature sensor with a resolution of the order of μK must be designed to improve the satellite monitoring accuracy. According to the design requirements of the temperature sensing circuit, a high-precision thermistor needs to be equipped as the temperature sensing element. A larger resistance change can result in more resistance change values in the same temperature range, and correspondingly, only a smaller temperature change is required for the same resistance value change; in addition, a larger resistance value can suppress the self-heating effect of the thermistor during the measurement process, avoiding interference with the measured object and thus improving the measurement accuracy. Existing NTC thermistor elements for temperature measurement have a relatively low resistance temperature coefficient (-2% / °C to -6.5% / °C), and the temperature monitoring resolution that can be obtained is 10 -3 K. In order to improve the temperature monitoring resolution to above 10 -6 K and better ensure the high-quality operation of high-precision optical elements in orbit, a temperature-sensitive element with a high room temperature resistance and a resistance temperature coefficient above 10% / °C is required.

[0003] Barium strontium titanate ceramic material is a semi-conducting ferroelectric ceramic. Above the Curie temperature point, it shows a stepwise increase in resistance due to phase change, presenting a good PTC (Positive Temperature Coefficient) effect, and having characteristics such as resistance-temperature, voltage-current, and current-time, which can be applied to related electronic components such as constant temperature heating, overcurrent protection, and temperature sensors. However, the current mainstream market application of barium strontium titanate PTC materials is for constant temperature heating and switch on / off, and there are few reports on their application in temperature sensing tests. The main reason is that after the switching temperature, the resistance stepwise increase of PTC materials is non-linear, and it is difficult to achieve accurate algorithm fitting in a wide temperature range, resulting in large measurement errors. Therefore, for the application scenario of temperature testing and sensing in a wide temperature range, the universality is relatively low, which limits its application in the field of temperature sensing and monitoring. In order to try to broaden the algorithm fitting continuous interval of the resistance-temperature curve and reduce the fitting test error at the same time, it is necessary to improve the linearity of the PTC resistance-temperature curve after appropriate dimensionality reduction processing in a wide temperature range. Summary of the Invention

[0004] In order to solve the problem of low resolution in temperature sensing tests of existing NTC temperature sensors and achieve high-resolution temperature fluctuation monitoring in a constant temperature or relatively stable temperature application environment, the present invention utilizes the characteristic that the PTC resistance-temperature curve of barium strontium titanate ceramic has a large resistance-temperature coefficient due to the stepwise increase in resistance near the Curie temperature point, and provides a barium strontium titanate ceramic material, a high-resolution barium strontium titanate temperature sensing element and its preparation method. In the barium strontium titanate ceramic material (PTC material), an appropriate amount of glass phase material Al2O3 - SiO2 - TiO2 is introduced. The obtained high-resolution barium strontium titanate temperature sensing element has a high room temperature resistance, a large resistance-temperature coefficient, and a high linear fitting degree in the application environment temperature range after the resistance-temperature curve undergoes one-dimensional reduction (taking the logarithm of the original resistance value test data), and is suitable for achieving high-resolution response and monitoring of temperature in a relatively narrow temperature range. Further, in order to broaden the temperature monitoring range of the PTC material, the present invention changes the content of the glass phase Al2O3 - SiO2 - TiO2 (AST) in the PTC material system, increases the thickness of the grain boundary layer in the polycrystalline structure, reduces the overall ferroelectricity of the material, so that the resistance change changes from sharp to slow, improves the linearity and fitting accuracy of the material resistance-temperature curve after one-dimensional reduction treatment in a wider temperature range, reduces the temperature test error, and is conducive to appropriately broadening the temperature test range.

[0005] In the first aspect, the present invention provides a barium strontium titanate ceramic, and the chemical composition of the barium strontium titanate ceramic is (1 - m - n)(Ba x Sr y Ca z Nb u Ti v O3)-m(Al2O3 - SiO2 - TiO2)-nMnCO3, where n = 0.09% - 0.18%, m = 1.2% - 3%; in Ba x Sr y Ca z Nb u Ti v O3, x = 0.6 - 0.8, y = 0.15 - 0.35, z = 0.01 - 0.07, u = 0.001 - 0.004, v = 1.005 - 1.02, and x + y + z = 1.

[0006] In the second aspect, the present invention provides a preparation method of a barium strontium titanate ceramic, including: (1) Weigh matrix raw materials according to the stoichiometric ratio of the barium strontium titanate ceramic, perform the first ball milling for 23 - 25 hours for mixing and drying, and obtain base material powder through high-temperature synthesis; (2) Weigh the base powder and the auxiliary raw materials, conduct secondary ball milling for 23 to 25 hours for mixing and drying, and perform high-temperature pre-sintering to obtain the barium strontium titanate raw material powder and the barium strontium titanate ceramic powder. (3) Granulate, mold, degrease, and sinter the obtained barium strontium titanate ceramic powder to obtain the barium strontium titanate ceramic.

[0007] Preferably, the matrix raw materials include BaCO3, TiO2, SrCO3, CaCO3, and Nb2O5; the auxiliary raw materials include Al2O3, SiO2, TiO2, and MnCO3, where the mass ratio of Al2O3:SiO2:TiO2 is 1:(7 - 12):(4 - 9).

[0008] Preferably, the temperature of the high-temperature synthesis is 1000 - 1200 °C, and the heat preservation time is 0.5 - 2 hours; The temperature of the high-temperature pre-sintering is 900 - 1000 °C, and the heat preservation time is 0.5 - 2 hours.

[0009] Preferably, polyvinyl alcohol is selected as the binder for granulation, and the mass of the binder is 4 - 10% of the mass of the barium strontium titanate ceramic powder; The pressure of the molding is 1 - 2 T / cm 2 , and the pressure holding time is 1 - 3 min; The temperature of the degreasing is 600 - 800 °C, and the heat preservation time is 1 - 3 hours; The temperature of the sintering is 1200 °C - 1300 °C, and the heat preservation time is 10 - 60 minutes; preferably, the sintering parameters include: between room temperature and 1000 °C, the heating rate is 4 - 5 °C / min, and between 1000 °C and the sintering temperature, the heating rate is 6 - 10 °C / min.

[0010] In a third aspect, the present invention provides a high-resolution barium strontium titanate temperature sensing element, including the above-mentioned barium strontium titanate ceramic sheet and a single-sided metal electrode or a double-sided metal electrode on the surface of the barium strontium titanate ceramic sheet.

[0011] Preferably, the high-resolution barium strontium titanate temperature sensing element has a good PTC effect. After the resistance-temperature curve is dimensionally reduced once, the linear fitting determination coefficient R of the high-resolution barium strontium titanate temperature sensing element in the temperature range of 28 - 36 °C 2 ≥0.99; in the temperature range of 28 - 45 °C, the linear fitting determination coefficient R 2≥0.97. In the present invention, the barium strontium titanate temperature sensing element with high resolution has a polycrystalline structure of barium strontium titanate ceramic, including crystal grains and grain boundary layers between the crystal grains, wherein the thickness of the grain boundary layer can be adjusted by changing the content of the glass phase Al2O3 - SiO2 - TiO2 in the barium strontium titanate ceramic. Specifically, by changing the content of the glass frit in the barium strontium titanate ceramic material system, the thickness of the grain boundary layer can be increased, the phase transition can be changed from a concentrated phase transition to a diffuse phase transition, thereby increasing the length of the temperature range with a good linear fitting degree and appropriately broadening the temperature measurement application range.

[0012] Preferably, the room temperature resistance value of the barium strontium titanate temperature sensing element with high resolution is 8 - 50 kΩ; The resistance temperature coefficient of the barium strontium titanate temperature sensing element with high resolution in the temperature range of 29.5 - 35.5 °C is ≥10% / °C, preferably ≥20% / °C. In the present invention, the barium strontium titanate temperature sensing element with high resolution has a relatively high room temperature resistance and resistance temperature coefficient, and has good linearity in a relatively wide temperature range after one - dimensional reduction, can effectively sense and collect temperature changes at the μK level, and realizes high - resolution sensing and measurement of temperature.

[0013] Preferably, the material of the single - sided metal electrode or the double - sided metal electrode is at least one of nickel, silver, copper, titanium, aluminum, and gold.

[0014] Preferably, the total thickness h of the barium strontium titanate temperature sensing element with high resolution is ≤1 mm, and the diameter Φ is ≤6 mm. The reduction of the size of the temperature sensing element is beneficial to reducing the thermal time constant of the temperature sensing element and improving the response speed. Preferably, the thermal time constant τ of the barium strontium titanate temperature sensing element with high resolution is ≤10 s.

[0015] Fourthly, the present invention provides a preparation method of the above - mentioned barium strontium titanate temperature sensing element with high resolution, including: fabricating metal electrodes on one side or both sides of the barium strontium titanate ceramic sheet by using screen printing or a composite process of magnetron sputtering and laser ablation to obtain the barium strontium titanate temperature sensing element with high resolution.

[0016] When the barium strontium titanate temperature sensing element with high resolution of the present invention works, it is connected to a Wheatstone bridge. The change in the resistance value of the barium strontium titanate temperature sensing element is obtained through the Wheatstone bridge, and after the curve after linear fitting is compared and calibrated by a resistance - temperature conversion system, the corresponding temperature change can be accurately obtained. When the metal electrode on the surface of the barium strontium titanate ceramic sheet is a double - sided metal electrode, in the form of flanging or perforation, the wire is welded on one - side surface and then connected to the circuit.

[0017] Compared with traditional temperature sensing elements, the barium strontium titanate temperature sensing element with high resolution provided by the present invention has the following advantages: (1) Using barium strontium titanate ceramic material as the temperature-sensitive element, it has a relatively large room-temperature resistance value of 8 - 50 kΩ, and the temperature coefficient of resistance in the working temperature range is ≥ 10% / °C, which can improve the temperature resolution and can effectively sense and collect temperature changes at the μK level; (2) Using barium strontium titanate ceramic material as the temperature-sensitive element, after the material's resistance-temperature curve undergoes one-dimensional reduction, it has a good linear fitting degree. In the temperature range of 28 - 36 °C, the fitting determination coefficient R 2 ≥ 0.99, and in the temperature range of 28 - 45 °C, the linear fitting determination coefficient R 2 ≥ 0.97. The good linear fitting characteristics are conducive to accurate temperature measurement and are suitable for temperature measurement in a narrow temperature range and high-resolution monitoring of temperature fluctuations in a constant-temperature environment; (3) Using the glass phase AST to improve the width of the grain boundary layer in the polycrystalline structure of barium strontium titanate, increasing the non-ferroelectricity of the material system, enabling the material system to transform from a concentrated phase transition to a diffuse phase transition, increasing the feasibility of linear fitting after one-dimensional reduction in a wider temperature range. In the temperature range of 28 - 45 °C, the linear fitting determination coefficient R 2 ≥ 0.97, broadening the temperature monitoring range.

[0018] Beneficial effects: (1) By replacing the NTC material in the traditional temperature-sensing element with a PTC material, it has a relatively large room-temperature resistance value of 8 - 50 kΩ, and the temperature coefficient of resistance can be achieved above 10% / °C, and some are above 20% / °C or even higher. The larger resistance change can result in more resistance change values in the same temperature range. Correspondingly, only a smaller temperature change is required for the same resistance value change, improving the temperature resolution; (2) Using barium strontium titanate ceramic material as the temperature-sensitive element, its resistance-temperature change curve has a good linear fitting degree after one-dimensional reduction in a relatively narrow temperature range, breaking through the limitation that non-linear curves are difficult to fit algorithmically in wide-temperature-range test applications, and having good applicability in monitoring temperature fluctuations in a constant-temperature environment, enabling the application of barium strontium titanate PTC material in precise measurement; (3) By increasing the content of AST in the auxiliary materials, increasing the non-ferroelectricity of the material system, thereby improving the feasibility of linear fitting after one-dimensional reduction of the component in a wider temperature range, which is conducive to broadening the temperature measurement range. Description of the drawings

[0019] Figure 1 It is the resistance-temperature curve diagram of Examples 1 - 3 and Comparative Examples 1 - 3; Figure 2 It is the schematic diagram of the principle of the present invention, where 1 is the crystal grain, 2 is the grain boundary, and 3 is Al2O3 - SiO2 - TiO2 (AST) in the auxiliary materials; Figure 3Schematic diagram of the electrode design of the high-resolution barium strontium titanate temperature sensing element of the present invention, where (a) is a single-sided electrode design, (b) is a double-sided electrode through-hole design, and (c) is a double-sided electrode side flanging design. Here, 1 is the electrode, 2 is the solder joint, 3 is the wire, and 4 is the ceramic body; Figure 4 Schematic diagram of the connection of the high-resolution barium strontium titanate temperature sensing element of the present invention to a Wheatstone bridge, where R S is the temperature sensing element, R1 and R2 are fixed resistors, R x is a variable sliding resistor, E is the power supply, K is the switch, and G is the voltmeter. Detailed implementation manners

[0020] To further illustrate the invention content, features and actual effects of the present invention, the present invention will be described in detail below in conjunction with embodiments. It should be noted that the modified methods designed by the present invention are not limited to these specific implementation manners. Without departing from the spirit and connotation of the design of the present invention, equivalent replacements and modifications made by those skilled in the art on the basis of reading the content of the present invention are also within the scope of protection required by the present invention.

[0021] First, the present invention provides a barium strontium titanate ceramic (or PTC ceramic), and the chemical composition of the barium strontium titanate ceramic is (1 - m - n)(Ba x Sr y Ca z Nb u Ti v O3)-m(Al2O3 - SiO2 - TiO2)-nMnCO3, where n = 0.09% - 0.18%, m = 1.2% - 3%; Ba x Sr y Ca z Nb u Ti vIn O3, x = 0.6 - 0.8, y = 0.15 - 0.35, z = 0.01 - 0.07, u = 0.001 - 0.004, v = 1.005 - 1.02, and x + y + z = 1. In the present invention, by changing the content of the glass frit (Al2O3 - SiO2 - TiO2) in the barium strontium titanate ceramic material system, the phase transition is changed from a concentrated phase transition to a diffuse phase transition, which can increase the thickness of the grain boundary layer, thereby increasing the length of the temperature range with a good linear fitting degree and appropriately broadening the temperature measurement application range. This is because the glass phase Al2O3 - SiO2 - TiO2 is enriched at the grain boundaries and is in a liquid phase at high temperatures, which can act as a sintering aid, facilitating the diffusion of oxygen vacancies in the material and causing grain boundary oxidation. The grain boundary barrier is increased to a certain extent, thereby enhancing the PTC effect; an excessive amount of the liquid phase is prone to agglomeration, resulting in abnormal grain growth and hindering the semiconduction of the material; on the other hand, the liquid phase at the grain boundaries separates the grains, reducing the consistency of the phase transition steps of each grain to a certain extent. When m < 1.2%, the glass phase at the grain boundaries is less enriched, the grain boundary layer is thinner, the phase transition is concentrated, the resistance - temperature curve of the material has a large mutation, and the linearity is poor; when m > 3%, too much glass phase is enriched at the grain boundaries, the grain boundary layer is thicker, the phase transition is diffuse, and too much glass frit at the grain boundaries is not conducive to the semiconduction of the material, resulting in an extremely high resistance value. The role of MnCO3 in the barium strontium titanate ceramic material is to act as an acceptor, form surface acceptor states, generate barriers at the grain boundaries in the polycrystalline material system, and ensure and enhance the PTC effect of the material.

[0022] In the present invention, the preparation method of the barium strontium titanate ceramic includes: First, weigh the matrix raw materials according to the stoichiometric ratio of the barium strontium titanate ceramic, perform the first ball - milling and mixing and drying, and obtain the base powder through high - temperature synthesis; then, weigh the base powder and the auxiliary raw materials, perform the second ball - milling and mixing and drying, and obtain the barium strontium titanate raw material powder through high - temperature pre - sintering to obtain the barium strontium titanate ceramic powder; finally, granulate, mold, degrease, and sinter the obtained barium strontium titanate ceramic powder to obtain a single - layer barium strontium titanate ceramic. Alternatively, when preparing the barium strontium titanate ceramic using a multi - layer process, the barium strontium titanate ceramic powder is tape - cast, drilled, cut, printed, laminated, isostatically pressed, degreased, and sintered to obtain a multi - layer barium strontium titanate ceramic.

[0023] In an alternative embodiment, the matrix raw materials include BaCO3, TiO2, SrCO3, CaCO3, Nb2O5; the auxiliary raw materials include Al2O3, SiO2, TiO2, MnCO3, where the mass ratio of Al2O3:SiO2:TiO2 is 1:(7 - 12):(4 - 9).

[0024] In an alternative embodiment, the rotation speed of the first ball - milling is 150 - 250 r / min (such as 200 r / min), and the ball - milling time is 23 - 25 hours.

[0025] In an alternative embodiment, the temperature for the high-temperature synthesis is 1000 - 1200 °C, and the heat preservation time is 0.5 - 2 hours. The temperature for the high-temperature pre-sintering is 900 - 1000 °C, and the heat preservation time is 0.5 - 2 hours.

[0026] In an alternative embodiment, the rotation speed for the second ball milling is 150 - 250 r / min (such as 200 r / min), and the ball milling time is 23 - 25 hours.

[0027] In an alternative embodiment, polyvinyl alcohol is selected as the binder for granulation, and the mass of the binder is 4 - 10% (such as 6%) of the mass of the barium strontium titanate ceramic powder. The pressure for die pressing is 1 - 2 T / cm 2 , and the pressure holding time is 1 - 3 min. The temperature for debinding is 600 - 800 °C, and the heat preservation time is 1 - 3 hours. The temperature for sintering is 1200 °C - 1300 °C, and the heat preservation time is 10 - 60 minutes; preferably, the sintering parameters include: between room temperature and 1000 °C, the heating rate is 4 - 5 °C / min, between 1000 °C and the sintering temperature, the heating rate is 6 - 10 °C / min, heat preservation for 10 - 60 minutes, and then natural cooling in the furnace.

[0028] In an alternative embodiment, the pressure for lamination is 3 - 5 MPa, the temperature for lamination is 60 - 80 °C, and the time for lamination is 30 - 50 s. The pressure for isostatic pressing is 2 - 3 T / cm 2 , and the pressure holding time is 3 - 8 minutes.

[0029] The high-resolution barium strontium titanate temperature sensing element provided by the present invention is prepared from the above-mentioned barium strontium titanate ceramic. The high-resolution barium strontium titanate temperature sensing element includes the above-mentioned barium strontium titanate ceramic sheet and a single-sided metal electrode or a double-sided metal electrode on the surface of the barium strontium titanate ceramic sheet. When the high-resolution barium strontium titanate temperature sensing element works, wires are welded from the surface of the metal electrode and led out from one side, and then connected to a Wheatstone bridge. After being powered on, the resistance value of the element is obtained by monitoring a tiny current. The curve after linear fitting is compared and calibrated by a resistance-temperature conversion system to obtain the corresponding temperature value. It should be noted that whether the metal electrode is designed as a single-sided metal electrode or a double-sided metal electrode, it must be led out from one side to ensure that one side of the sensing element can be better mounted. When the metal electrode is designed as double-sided, the electrode on the other side can be extended to the same side through perforation or flanging (as Figure 3 shown).

[0030] In the present invention, the barium strontium titanate ceramic element has a PTC effect. As the temperature increases, the resistance increases significantly in a relatively narrow temperature range, and it has a large temperature coefficient of resistance. Therefore, small temperature changes can be obtained by monitoring the resistance. The preparation of the barium strontium titanate ceramic element needs to meet the room temperature resistance value of 8 - 50 kΩ to meet the design of the Wheatstone bridge temperature control circuit; the temperature coefficient of resistance in the range of 28.5 - 35.5 °C ≥ 10% / °C to ensure the resolution of the test temperature. The larger the temperature coefficient of resistance, the corresponding improvement in the test resolution. At the same time, to ensure the accuracy and timeliness of the barium strontium titanate ceramic element in sensing temperature, the thermal time constant τ of the element should ≤ 10 s and be minimized as much as possible. The thickness of the element should ≤ 1 mm and be as thin as possible under the condition of meeting the mechanical strength.

[0031] In addition, the barium strontium titanate in the high-resolution barium strontium titanate temperature sensing element of the present invention has a polycrystalline structure. By improving the polycrystalline structure of the PTC material and adjusting the thickness of the grain boundary layer between the grains, the ferroelectric phase transition of barium strontium titanate tends to be diffused, reducing the overall ferroelectricity of the material system and the concentration of resistance changes. Thus, the linear fitting degree of the resistance-temperature curve after dimension reduction in a wider temperature range is adjusted, and the application range of the element for temperature monitoring is appropriately broadened.

[0032] The following exemplarily describes the preparation method of the high-resolution barium strontium titanate temperature sensing element provided by the present invention.

[0033] The obtained barium strontium titanate ceramic is machined mechanically to obtain a barium strontium titanate element for temperature sensing with a specified diameter and thickness, and a weldable single-sided metal electrode or double-sided metal electrode is made on the surface of the machined barium strontium titanate ceramic element.

[0034] In an alternative embodiment, the material of the single-sided metal electrode or double-sided metal electrode is at least one of nickel, silver, copper, titanium, aluminum, and gold. The methods for making the metal electrode include: screen printing, magnetron sputtering, evaporation plating, or laser ablation.

[0035] A wire is welded to the surface of the electrode of the barium strontium titanate temperature sensing element and led out from one side. The sensing element is connected to a Wheatstone bridge. After power-on, when the ambient temperature changes, the resistance value of the element is obtained in real time by testing the tiny current of the bridge; through the resistance-temperature conversion processing system, the resistance-temperature curve after fitting of the element is systematically compared, and the corresponding temperature value can be obtained.

[0036] According to the specific requirements of the application scenario, a peripheral insulation package design is carried out for the barium strontium titanate temperature sensing element.

[0037] Based on the application of traditional NTC sensors for temperature measurement, the present invention innovatively proposes to use PTC materials for temperature measurement applications. Based on the characteristics of PTC materials, the barium strontium titanate ceramic element has higher room temperature resistance and resistance temperature coefficient than NTC materials, and has higher temperature resolution, which is particularly suitable for narrow temperature range temperature measurement and high-resolution monitoring of temperature fluctuations in constant temperature environments. At the same time, the present invention adjusts the enrichment content of the glass phase Al2O3-SiO2-TiO2 at the grain boundary and the thickness of the grain boundary layer to achieve a linear fitting determination coefficient R of the resistance-temperature curve after a one-time dimensionality reduction in a wider temperature range. 2 ≥0.97.

[0038] The following further examples are given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are also only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values ​​​​exemplified below.

[0039] Example 1

[0040] The method for preparing the high-resolution barium strontium titanate temperature sensor element provided in this embodiment 1 comprises the following steps: (1) According to the Curie temperature of barium strontium titanate ceramics (PTC ceramics) of 30°C 0.65 Sr 0.32 Nb 0.0015 Ca 0.03 Ti 1.0 1O3 stoichiometric ratio of base material raw materials BaCO3, TiO2, Nb2O5, SrCO3, CaCO3 are weighed, the weighed raw materials are put into a ball mill, anhydrous ethanol is added, wherein the raw material: ball: anhydrous ethanol is 1:3:2, after mixing for 24 hours by planetary ball mill (speed 200r / min), it is placed in an 80℃ oven for drying, sieved through a 40-mesh sieve, placed in a high-temperature electric furnace and kept at 1150℃ for 2 hours to synthesize base material powder; (2) Weighing and mixing the synthesized base powder and auxiliary raw materials Al2O3, SiO2, TiO2, and MnCO3 according to the mass percentage of base powder: Al2O3: SiO2: TiO2: MnCO3 = 98.71: 0.08: 0.72: 0.4: 0.09, and the raw material: ball: anhydrous ethanol is 1: 3: 2. After mixing for 24 hours by planetary ball milling (speed 200 r / min), it is placed in an oven at 80°C and pre-calcined at 900°C for 2 hours to obtain barium strontium titanate ceramic powder (PTC ceramic powder); (3) Add 6 wt.% of PVA to the obtained PTC ceramic powder for granulation, sieve it through a 40-mesh sieve, and place it on a tablet press for dry pressing (select a pressure of 1.5 T / cm 2 , with a pressure holding time of 1 min) to preform a green body with a diameter of 11 mm and a thickness of 5 mm. Then, perform cold isostatic pressing on an isostatic press (select a pressure of 2.5 T / cm 2 , with a pressure holding time of 5 min) to obtain a PTC ceramic green body; (4) Place the PTC ceramic green body in a high-temperature furnace and heat it at a rate of 2 °C / min to 700 °C for 2 hours for debinding; then first heat it at a rate of 4 °C / min to 1000 °C, and then heat it at a rate of 7 °C / min to 1280 °C for 15 minutes for sintering, and then cool it naturally to obtain barium strontium titanate ceramic; (5) Machine the semi-conducted PTC ceramic obtained above into a ceramic sheet with a diameter of 6 mm and a thickness of 1 mm; screen-print a layer of ohmic silver paste with a designed pattern on the surface of the PTC ceramic wafer, dry it at 80 °C, and then put it into a furnace and heat it at a rate of 2 °C / min to 500 °C for 20 minutes to burn the metal electrode. Then, print three layers of surface silver paste on the basis of this electrode, dry it again at 80 °C, and then put it into a furnace and heat it at a rate of 2 °C / min to 500 °C for 20 minutes to burn the metal electrode; (6) Place the PTC ceramic wafer with the printed electrode above in a resistance-temperature curve testing instrument to test the basic parameters of the relevant materials; (7) After welding the wire to the above PTC ceramic wafer, connect it to a Wheatstone bridge (as Figure 4 shown), turn on the power supply, adjust through the opposite arms of the bridge to obtain the small current value in the circuit and the resistance value of the temperature sensing element under the balance of the bridge, and perform a systematic comparison on the resistance-temperature curve after fitting the element through a resistance-temperature conversion processing system to obtain the temperature value.

[0041] Example 2

[0042] In this Example 2, the preparation process of the high-resolution barium strontium titanate temperature sensing element refers to Example 1, with the only difference being that in step (2), the base powder: Al2O3: SiO2: TiO2: MnCO3 = 97.45: 0.16: 1.44: 0.8: 0.15.

[0043] Example 3

[0044] In this Example 3, the preparation process of the high-resolution barium strontium titanate temperature sensing element refers to Example 1, with the only difference being that in step (2), the base powder: Al2O3: SiO2: TiO2: MnCO3 = 96.82: 0.2: 1.8: 1: 0.18.

[0045] Comparative Example 1

[0046] The preparation process of the barium strontium titanate temperature sensing element in Comparative Example 1 was referred to that of Example 1, with the only difference being that in step (2), the base powder: Al2O3: SiO2: TiO2: MnCO3 = 99.36: 0.04: 0.36: 0.2: 0.04.

[0047] Comparative Example 2

[0048] The preparation process of the barium strontium titanate temperature sensing element in Comparative Example 2 was referred to that of Example 1, with the only difference being that in step (2), the base powder: Al2O3: SiO2: TiO2: MnCO3 = 96.2: 0.24: 2.16: 1.2: 0.2.

[0049] Comparative Example 3

[0050] The preparation process of the barium strontium titanate temperature sensing element in Comparative Example 3 was referred to that of Example 1, with the only difference being that in step (2), the base powder: Al2O3: SiO2: TiO2: MnCO3 = 99.96: 0: 0: 0: 0.04.

[0051] Table 1 shows the material formulas and mass percentages of each component of the samples of Examples 1 - 3 and Comparative Examples 1 - 3.

[0052] Table 1:

[0053] Figure 1 For the resistance - temperature curves of Examples 1 - 3 and Comparative Examples 1 - 3, linear fitting was performed on the resistance - temperature curves of Examples 1 - 3 and Comparative Examples 1 - 3, and the fitting parameters are shown in Table 2. Table 2 is the table of linear fitting parameters of the resistance - temperature curves of the samples of Examples 1 - 3 and Comparative Examples 1 - 3 (y is LgR, x is Temperature).

[0054] Table 2:

[0055] Table 3 shows the room - temperature resistance values and temperature - coefficient of resistance at different temperatures of the samples of Examples 1 - 3 and Comparative Examples 1 - 3.

[0056] Table 3:

[0057] As can be seen from Table 1-3, when the mass percentage m of AST in the auxiliary material is 1.2% - 3% (Examples 1-3), the barium strontium titanate temperature sensing element simultaneously has a relatively high room temperature resistance value and a good linear fitting degree. In Examples 1-3, the temperature coefficient of resistance at each temperature point in the temperature range of 29.5 - 35.5 °C is greater than 10% / °C. In particular, Example 1 satisfies that the temperature coefficient of resistance at each temperature point is greater than 20% / °C, which can better meet the temperature sensing test application of the element; although Comparative Example 1 also has a relatively high temperature coefficient of resistance, the fitting determination coefficient R 2 is relatively low in the temperature range of 28 - 36 °C, which will cause large temperature test errors and decreased accuracy, and the low room temperature resistance value is not conducive to circuit test applications. The room temperature resistance of the sample in Comparative Example 2 is too high, and the temperature coefficient of resistance at each temperature point in the temperature range of 29.5 - 35.5 °C is less than 6% / °C, which cannot meet the temperature test accuracy requirements. The room temperature resistance of the sample in Comparative Example 3 is relatively low, and the fitting determination coefficient R 2 is only 0.69335, which cannot be used for temperature testing; and the temperature coefficient of resistance at each temperature point in the temperature range of 29.5 - 31.5 °C is less than 10% / °C, which cannot meet the temperature test accuracy requirements.

[0058] Figure 2 is a schematic diagram of the principle of the present invention. As can be seen from the figure, as the amount of AST glass frit increases, the grain boundary layer thickens, separating the grains from each other, reducing the consistency of the phase change steps of each grain. When the material reaches the Curie temperature point, the phase changes of each grain are out of sync, showing a phenomenon of phase change one by one within a certain time, so the phase change is dispersed, and the linear fitting degree of the resistance-temperature curve of the polycrystalline system material is improved.

Claims

1. A barium strontium titanate ceramic, characterized in that, The chemical composition of the barium strontium titanate ceramic is (1 - m - n)(Ba x Sr y Ca z Nb u Ti v O3)-m(Al2O3 - SiO2 - TiO2)-nMnCO3, where n = 0.09% - 0.18% and m = 1.2% - 3%; in Ba x Sr y Ca z Nb u Ti v O3, x = 0.6 - 0.8, y = 0.15 - 0.35, z = 0.01 - 0.07, u = 0.001 - 0.004, v = 1.005 - 1.02, and x + y + z = 1.

2. A method for preparing barium strontium titanate ceramic as described in claim 1, characterized in that, Comprising: (1) Weigh the matrix raw materials according to the stoichiometric ratio of barium strontium titanate ceramics, conduct the first ball milling for 23 - 25 hours for mixing and drying, and obtain the base material powder through high-temperature synthesis. (2) Weigh the base material powder and the auxiliary raw materials, conduct the second ball milling for 23 - 25 hours for mixing and drying, and obtain the barium strontium titanate raw material powder and the barium strontium titanate ceramic powder through high-temperature pre-sintering. (3) Granulate, mold press, degrease, and sinter the obtained barium strontium titanate ceramic powder to obtain barium strontium titanate ceramics.

3. The preparation method according to claim 2, wherein The matrix raw materials include BaCO3, TiO2, SrCO3, CaCO3, Nb2O5; the auxiliary raw materials include Al2O3, SiO2, TiO2, MnCO3, where the mass ratio of Al2O3:SiO2:TiO2 is 1:(7 - 12):(4 - 9).

4. The preparation method according to claim 2 or 3, characterized in that, The temperature of the high-temperature synthesis is 1000 - 1200 °C, and the heat preservation time is 0.5 - 2 hours. The temperature of the high-temperature pre-sintering is 900 - 1000 °C, and the heat preservation time is 0.5 - 2 hours.

5. The preparation method according to any one of claims 2-4, characterized in that, For granulation, polyvinyl alcohol is selected as the binder, and the mass of the binder is 4 - 10% of the mass of the barium strontium titanate ceramic powder. The pressure of the molding is 1 to 2 T / cm 2 , and the pressure holding time is 1 to 3 minutes; The temperature of degreasing is 600 - 800 °C, and the heat preservation time is 1 - 3 hours. The temperature of sintering is 1200 °C - 1300 °C, and the heat preservation time is 10 - 60 minutes; preferably, the sintering parameters include: between room temperature and 1000 °C, the heating rate is 4 - 5 °C / min, and between 1000 °C and the sintering temperature, the heating rate is 6 - 10 °C / min.

6. A high-resolution barium strontium titanate temperature sensing element, characterized in that, Comprising the barium strontium titanate ceramic sheet as described in claim 1 and a single-sided metal electrode or a double-sided metal electrode on the surface of the barium strontium titanate ceramic sheet.

7. The high-resolution barium strontium titanate temperature sensing element according to claim 6, characterized in that, The material of the single-sided metal electrode or the double-sided metal electrode is at least one of nickel, silver, copper, titanium, aluminum, and gold.

8. The high-resolution barium strontium titanate temperature sensing element according to claim 6 or 7, characterized in that, After the resistance-temperature curve of the high-resolution barium strontium titanate temperature sensing element is dimensionally reduced once, the coefficient of determination R of linear fitting in the temperature range of 28 to 36 °C 2 ≥ 0.99; the coefficient of determination R of linear fitting in the temperature range of 28 to 45 °C 2 ≥ 0.97; The room temperature resistance value of the high-resolution barium strontium titanate temperature sensing element is 8 - 50 kΩ. The resistance temperature coefficient of the high-resolution barium strontium titanate temperature sensing element in the temperature range of 29.5 - 35.5 °C is ≥10% / °C, preferably ≥20% / °C.

9. The high-resolution barium strontium titanate temperature sensing element according to any one of claims 6-8, characterized in that, The total thickness h of the high-resolution barium strontium titanate temperature sensing element is ≤1 mm, and the diameter Φ is ≤6 mm.

10. A method for preparing a high-resolution barium strontium titanate temperature sensing element according to any one of claims 6-9, characterized in that, Comprising: Fabricate a metal electrode on one side or both sides of the barium strontium titanate ceramic sheet by using screen printing or a composite process of magnetron sputtering and laser ablation to obtain a high-resolution barium strontium titanate temperature sensing element.

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