Linear NTC thermistor material Al2O3-ZnO and its preparation method

Abstract

The application provides a linear NTC thermistor material Al2O3-ZnO and a preparation method thereof, and belongs to the technical field of NTC thermistor materials; the NTC thermistor material adopts ZnO as a main crystal phase, Al2O3 with a mole fraction of 5-15% is doped in the main crystal phase to change the overall electrical property of the material; experiments show that the NTC thermistor material Al2O3-ZnO has a linear resistance-temperature characteristic in the range of 100 DEG C-300 DEG C, and the linearity reaches more than 99.2%; the linear NTC thermistor material has simple components, stable electrical property, and can be applied to a relatively wide temperature range.

Description

Technical Field

[0001] This invention belongs to the field of NTC thermistor material technology, specifically relating to a linear NTC thermistor material Al2O3-ZnO and its preparation method. Background Technology

[0002] NTC thermistors are a type of sensor resistor whose resistance decreases as temperature increases. Based on the relationship between resistance and temperature, they are classified into nonlinear NTC thermistors (resistance changes exponentially with temperature) and linear NTC thermistors (resistance changes linearly with temperature). This nonlinear resistance-temperature characteristic significantly limits the application of this material, typically requiring complex electronic circuits to linearize the output signal, leading to complex circuit structures and increased costs. Linear thermistors, on the other hand, provide a clear linear display of the resistance-temperature relationship, simplifying the entire circuit. Therefore, developing NTC thermistor ceramic materials with linear resistance-temperature characteristics is of great significance for the practical application of NTC thermistors.

[0003] Among the linear NTC thermistors reported so far, Chinese invention patent application CN202311238841.1 discloses a linear NTC thermistor material LaMnO3-Al2O3. This material has LaMnO3 as the main crystal phase, and its electrical properties are adjusted by doping 10-30% Al2O3 into LaMnO3. The resulting LaMnO3-Al2O3 exhibits linear resistance-temperature characteristics in the range of 30℃ to 65℃. Chinese invention patent application CN202311236250.0 discloses a linear NTC thermistor material CdSnO3-Al2O3. This material has CdSnO3 as the main crystal phase, and its electrical properties are adjusted by doping 10-30% Al2O3 into CdSnO3. The resulting CdSnO3-Al2O3 exhibits linear resistance-temperature characteristics in the range of 25℃ to 175℃. The common characteristic of the aforementioned linear NTC thermistors is that they all use oxides containing two transition metal elements and a spinel-type crystal structure as the main crystalline phase. Because these transition metal oxides have low volatilization temperatures, the raw material components are prone to volatilization during the preparation and sintering process of these linear NTC thermistor materials. This makes it difficult to control the final product composition and the repeatability between different production batches, and also results in a low linear temperature range. Therefore, there is an urgent need to develop linear NTC thermistor materials based on novel oxides. Summary of the Invention

[0004] In view of this, the present invention provides a linear NTC thermistor material Al2O3-ZnO and its preparation method.

[0005] The technical solution adopted by this invention to solve its technical problem is as follows:

[0006] A linear NTC thermistor material Al2O3-ZnO, comprising Al2O3 and ZnO, wherein the molar fraction of Al2O3 accounts for 5% to 15% of the total molar fraction of the system.

[0007] A method for preparing the linear NTC thermistor material Al2O3-ZnO includes the following steps:

[0008] (1) Al2O3 and ZnO were mixed according to the formula and then ball-milled. The resulting product was dried, sieved and ground to obtain a powdered precursor.

[0009] (2) Add polyvinyl alcohol to the powdered precursor and press the powdered precursor by molding to make the powder particles in close contact and obtain a block precursor.

[0010] (3) The bulk precursor is sintered to obtain the linear NTC thermistor material Al2O3-ZnO.

[0011] Preferably, in step (1), ethanol is added during ball milling, the ball milling speed is 400 rpm, the ball milling time is 4 h, the drying temperature is 70℃, and the material is sieved through a 200 mesh.

[0012] Preferably, in step (2), the amount of polyvinyl alcohol added accounts for 5% of the total mass of the powdered precursor.

[0013] Preferably, in step (2), the molding pressure is 200-300 MPa and the holding time is 30-60 s.

[0014] Preferably, in step (3), during sintering, the temperature is first raised to 500°C at a heating rate of 1°C / min to achieve the purpose of removing the binder, and then cooled to room temperature with the furnace. Then, the temperature is rapidly raised to 1100~1200°C at a heating rate of 10°C / min, sintered for 6~8 hours, and then cooled to room temperature with the furnace to obtain the linear NTC thermistor material Al2O3-ZnO.

[0015] As can be seen from the above technical solution, this invention provides a linear NTC thermistor material Al2O3-ZnO and its preparation method. Compared with the prior art, its advantages are: the NTC thermistor material of this invention uses ZnO as the main crystal phase. ZnO raw material is inexpensive and readily available, has high chemical stability and high temperature resistance, and the resistivity and chromatic alumina (B) value of ZnO differ significantly from those of Al2O3. By doping ZnO with 5%~15% molar fraction of Al2O3, the overall electrical properties of the material are changed. Experiments show that the NTC thermistor material Al2O3-ZnO exhibits linear resistance-temperature characteristics in the temperature range of 100℃~300℃, with a linearity exceeding 99.2%, making it a novel linear NTC thermistor material. The linear NTC thermistor material provided by this invention has a simple composition, stable electrical properties, and is suitable for a wide temperature range. Attached Figure Description

[0016] Figure 1 This is a temperature resistance characteristic curve of the thermistor material Al2O3-ZnO prepared in Example 2.

[0017] Figure 2 This is a temperature resistance characteristic curve of the thermistor material Al2O3-ZnO prepared in the comparative example. Detailed Implementation

[0018] The technical solutions and effects of the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0019] The present invention provides a linear NTC thermistor material Al2O3-ZnO, which comprises Al2O3 and ZnO, wherein the molar fraction of Al2O3 accounts for 5% to 15% of the total molar fraction of the system.

[0020] The NTC thermistor material of this invention uses ZnO as the main crystalline phase. ZnO is inexpensive and readily available, possesses high chemical stability and high-temperature resistance, and its resistivity and chromatic alumina (B) differ significantly from those of Al2O3. The overall electrical properties of the material are modified by doping ZnO with 5%–15% Al2O3. Experiments show that the Al2O3-ZnO NTC thermistor material exhibits linear resistance-temperature characteristics within the temperature range of 100℃–300℃, with a linearity exceeding 99.2%, making it a novel linear NTC thermistor material. The linear NTC thermistor material provided by this invention has a simple composition, stable electrical properties, and is suitable for a wide temperature range.

[0021] The present invention also provides a method for preparing the linear NTC thermistor material Al2O3-ZnO, comprising the following steps:

[0022] (1) Al2O3 and ZnO were mixed according to the formula and then ball-milled. The resulting product was dried, sieved and ground to obtain a powdered precursor.

[0023] (2) Add polyvinyl alcohol to the powdered precursor and press the powdered precursor by molding to make the powder particles in close contact and obtain a block precursor.

[0024] (3) The bulk precursor is sintered to obtain the linear NTC thermistor material Al2O3-ZnO.

[0025] Furthermore, in step (1), ethanol is added during ball milling, the ball milling speed is 400 rpm, the ball milling time is 4 hours, the drying temperature is 70℃, and the material is sieved through a 200-mesh sieve.

[0026] Furthermore, in step (2), the amount of polyvinyl alcohol added accounts for 5% of the total mass of the powdered precursor.

[0027] Furthermore, in step (2), the molding pressure is 200-300 MPa and the holding time is 30-60 s.

[0028] Furthermore, in step (3), during sintering, the temperature is first raised to 500°C at a heating rate of 1°C / min to remove the binder, then cooled to room temperature in the furnace, and then rapidly raised to 1100~1200°C at a heating rate of 10°C / min for sintering for 6~8 hours, and then cooled to room temperature in the furnace to obtain the linear NTC thermistor material Al2O3-ZnO. During sintering, the bulk precursor material is first sintered at a low temperature to remove the PVA from the pressing process, so as not to affect the subsequent sintering process. Then, high-temperature short-time sintering is used to create conditions for volume diffusion, thereby densifying the powder.

[0029] The following are specific preparation examples and comparative examples: Example 1

[0030] (1) Weigh a total of 30g of metal oxide powder, including 3.67g of Al2O3 and 26.33g of ZnO; put the weighed metal oxide powder into a ball mill jar, add 120g of grinding beads and 100mL of ethanol, and mill the ball mill jar at 400rpm for 4h in a planetary ball mill. Place the obtained product in a 70℃ oven to dry, and sieve it through a 200-mesh nylon sieve to obtain a powdered precursor.

[0031] (2) Weigh 5% of the total mass of the precursor PVA solution and add it to the powdered precursor. Press the powdered precursor by molding to densify the powder. The pressure is 200 MPa and the pressure is held for 30 s to obtain a sheet-like precursor with a diameter of 12 mm.

[0032] (3) The block precursor was placed in an air furnace for high-temperature sintering. During sintering, the temperature was first raised to 500°C at a rate of 1°C / min to remove the binder, and then cooled to room temperature with the furnace. Then, the temperature was rapidly raised to 1100°C at a rate of 10°C / min and sintered for 8 hours. After cooling to room temperature with the furnace, the linear NTC thermistor material Al2O3-ZnO was obtained and named AZ-1. The doping ratio of Al2O3 in Example 1 was 0.05. Example 2

[0033] (1) Weigh a total of 30g of metal oxide powder, including 7.34g of Al2O3 and 22.66g of ZnO. Put the weighed metal oxide powder into a ball mill jar, add 120g of grinding beads and 100mL of ethanol, and mill the ball mill jar at 400rpm for 4h in a planetary ball mill. Place the obtained product in a 70℃ oven to dry, and sieve it through a 200-mesh nylon sieve to obtain a powdered precursor.

[0034] (2) Weigh 5% of the total mass of the precursor PVA solution and add it to the powdered precursor. Press the powdered precursor by molding to densify the powder. The pressure is 200 MPa and the pressure is held for 30 s to obtain a sheet-like precursor with a diameter of 12 mm.

[0035] (3) During sintering, the temperature is first raised to 500℃ at a heating rate of 1℃ / min to achieve the purpose of debinding. Then, it is cooled to room temperature with the furnace, and then rapidly heated to 1100℃ at a heating rate of 10℃ / min. Sintering is carried out for 8 hours, and then cooled to room temperature with the furnace to obtain the linear NTC thermistor material Al2O3-ZnO, named AZ-2. The doping ratio of Al2O3 in Example 2 is 0.1.

[0036] Comparative Example

[0037] (1) Weigh a total of 30g of metal oxide powder, including 7.155g of Al2O3 and 22.845g of ZnO. Put the weighed metal oxide powder into a ball mill jar, add 120g of grinding beads and 100mL of ethanol, and mill in a planetary ball mill at 400rpm for 4h. Place the product in a 70℃ oven to dry, and sieve it through a 200-mesh nylon sieve to obtain a powdered precursor.

[0038] (2) PVA solution is added to powdered precursor, and the powdered precursor is pressed by molding to densify the powder. The pressure is 200 MPa and the pressure is held for 30 s to obtain a sheet-like precursor with a diameter of 12 mm.

[0039] (3) During sintering, the temperature was first raised to 500℃ at a heating rate of 1℃ / min to achieve the purpose of debinding. Then, it was cooled to room temperature with the furnace, and then rapidly heated to 1100℃ at a heating rate of 10℃ / min. Sintering was carried out for 8 hours, and then cooled to room temperature with the furnace to obtain the linear NTC thermistor material Al2O3-ZnO, named AZ-3. The doping ratio of Al2O3 in the comparative example was 0.2.

[0040] Five NTC thermistor material samples were prepared using the preparation methods of Example 2 and the comparative example. The Rt curves of each NTC thermistor material were obtained through testing. The Rt curve is one of the important parameters describing the electrical performance of thermistor materials. Silver paste was applied to both sides of the sample to form electrodes; the resistance-temperature relationship was measured using a four-probe measurement system.

[0041] Figure 1 The figure shows the resistance-temperature curve of the NTC thermistor prepared in Example 2. In the figure, the black solid line is the actual resistance-temperature curve, and the red solid line is an auxiliary linear curve used as a reference. The results show that the mixed material composed of 10% Al2O3 doped in ZnO has linear resistance-temperature characteristics in the range of 135℃ to 260℃, with a linearity of over 99.2%, indicating that the Al2O3-ZnO prepared in this invention is a linear NTC thermistor material. Figure 2 The figure shows the resistance-temperature curves of the NTC thermistors prepared in a comparative manner. The results indicate that when 20% Al₂O₃ is doped into ZnO, the resulting material does not exhibit linearity in the temperature range of 80℃ to 240℃. These results demonstrate that the amount of Al₂O₃ is crucial for controlling the overall electrical properties of the material.

[0042] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that implementing all or part of the above-described embodiments and making equivalent changes in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A method for preparing a linear NTC thermistor material Al2O3-ZnO, characterized in that: Includes the following steps: (1) Al2O3 and ZnO were mixed according to the formula and then ball-milled. The resulting product was dried, sieved and ground to obtain a powdered precursor. (2) Add polyvinyl alcohol to the powdered precursor and press the powdered precursor by molding to make the powder particles in close contact and obtain a block precursor. (3) The bulk precursor is sintered to obtain the linear NTC thermistor material Al2O3-ZnO. Its components consist of Al2O3 and ZnO, wherein the molar fraction of Al2O3 accounts for 5% to 15% of the total molar fraction of the system; In step (3), during sintering, the temperature is first raised to 500°C at a heating rate of 1°C / min to achieve the purpose of removing the binder. Then, the temperature is cooled to room temperature with the furnace, and then rapidly raised to 1100~1200°C at a heating rate of 10°C / min. Sintering is carried out for 6~8 hours and then cooled to room temperature with the furnace to obtain the linear NTC thermistor material Al2O3-ZnO. The NTC thermistor material Al2O3-ZnO exhibits linear resistance-temperature characteristics in the temperature range of 100℃ to 300℃, with a linearity of over 99.2%.

2. The preparation method of the linear NTC thermistor material Al2O3-ZnO as described in claim 1, characterized in that: The process includes the following steps: In step (1), ethanol is added during ball milling, the ball milling speed is 400 rpm, the ball milling time is 4 h, the drying temperature is 70℃, and the material is sieved through a 200 mesh screen.

3. The preparation method of the linear NTC thermistor material Al2O3-ZnO as described in claim 1, characterized in that: In step (2), the amount of polyvinyl alcohol added accounts for 5% of the total mass of the powdered precursor.

4. The preparation method of the linear NTC thermistor material Al2O3-ZnO as described in claim 1, characterized in that: In step (2), the molding method uses a molding pressure of 200-300 MPa and a holding time of 30-60 s.

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