Linear ntc thermistor material la mn o3-al2o3 and method of making

Abstract

The application relates to a linear NTC thermistor material LaMnO3-Al2O3 and a preparation method thereof, and belongs to the technical field of NTC thermistor materials. The linear NTC thermistor material LaMnO3-Al2O3 is composed of a Mn-based perovskite LaMnO3 and Al2O3, and the mole fraction of the Al2O3 accounts for 10-30% of the total mole fraction of the system. The material is prepared by ball milling, drying, sieving, pressing and sintering of the Mn-based perovskite LaMnO3 and the Al2O3. The NTC thermistor material LaMnO3-Al2O3 has a linear resistance-temperature characteristic in the range of 30 DEG C-65 DEG C, and the linearity reaches more than 99.6%. The linear NTC thermistor material can make the working circuit more simple and the whole system operation more simple and reliable.

Description

Technical Field

[0001] This invention belongs to the field of NTC thermistor material technology, specifically relating to a linear NTC thermistor material LaMnO3-Al2O3 and its preparation method. Background Technology

[0002] A thermistor, as a sensor resistor, is characterized by its resistance changing with temperature. Therefore, it is also considered a variable resistor. Resistive elements are indispensable in daily life.

[0003] 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.

[0004] Among the reported linear NTC thermistors, Chinese invention patent application CN202211264709.3 discloses a linear negative temperature coefficient thermistor material and its preparation method. This material uses graphene oxide and transition metal oxide powder as base materials and urea, melamine, dicyandiamide, thiourea, boric acid, and sodium borohydride as dopants. It is synthesized by hydrothermal method. This material has good linearity and can be used in the range of 20-80℃, but it requires more raw materials and has a higher manufacturing cost. Chinese invention patent application CN202210637174.3 discloses a linear wide temperature range high temperature thermistor material and its preparation method. This material is prepared by weighing calcium carbonate, aluminum oxide, and manganese dioxide according to the stoichiometric ratio of xAl2O3-(1-x)CaMnO3 (0.2≤x≤0.4), mixing and grinding, pre-firing, molding, sintering, and coating electrodes. This material has linear temperature resistance characteristics only in a wide temperature range of 250℃-950℃. The above research results provide a feasible solution for the development of linear NTC thermistors. However, the addition of different transition metal elements, sintering temperature, and holding time all affect the resistance-temperature characteristics of NTC thermistors. Therefore, to enrich the selection of linear NTC thermistor materials, expand the scope of material research and development, and synthesize novel linear NTC thermistor materials with potential application value, this has become a hot topic for researchers. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a linear NTC thermistor material LaMnO3-Al2O3 and its preparation method.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows:

[0007] A linear NTC thermistor material, LaMnO3-Al2O3, comprises Mn-based perovskite LaMnO3 and Al2O3, wherein the molar fraction of Al2O3 accounts for 10% to 30% of the total molar fraction of the system.

[0008] Preferably, the Mn-based perovskite LaMnO3 is synthesized from MnO2 and La2O3 by a high-temperature solid-state reaction, wherein the molar ratio of MnO2 to La2O3 is 2:1.

[0009] A method for preparing the linear NTC thermistor material LaMnO3-Al2O3 includes the following steps:

[0010] (1) MnO2 and La2O3 powders were mixed according to the formula and then ball-milled. The resulting product was dried, sieved, ground and then pre-calcined at high temperature to obtain Mn-based perovskite LaMnO3.

[0011] (2) Mix Mn-based perovskite LaMnO3 and Al2O3 powders according to the formula and then ball mill them. The resulting product is dried, sieved and ground to obtain a powdered precursor.

[0012] (3) Add polyvinyl alcohol to the powdered precursor and press the powdered precursor by molding to obtain a block precursor.

[0013] (4) The bulk precursor is sintered to obtain the linear NTC thermistor material LaMnO3-Al2O3.

[0014] Preferably, in steps (1) and (2), ethanol is added during ball milling, the ball milling speed is 200 rpm, the ball milling time is 6 h, the drying temperature is 70 °C, and the material is sieved through a 200 mesh screen.

[0015] Preferably, in step (1), the pre-firing temperature is 1200℃, the pre-firing time is 6h, and the heating rate is 5℃ / min.

[0016] Preferably, in step (3), the amount of polyvinyl alcohol added accounts for 5% of the total mass of the precursor.

[0017] Preferably, in step (3), the molding pressure is 200-300 MPa and the holding time is 30-60 s.

[0018] Preferably, in step (4), 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 1280-1350°C at a heating rate of 10°C / min, and sintered for 6-8 hours. The temperature is then cooled to room temperature with the furnace to obtain the linear NTC thermistor material LaMnO3-Al2O3.

[0019] As can be seen from the above technical solution, the present invention provides a linear NTC thermistor material LaMnO3-Al2O3 and its preparation method. Compared with the prior art, its beneficial effects are as follows: The NTC thermistor material of the present invention uses Mn-based perovskite LaMnO3 as the main crystal phase, and does not contain 10% to 30% Al2O3 to change the overall electrical properties of the material. This material is prepared by ball milling, drying, sieving, pressing, and sintering Mn-based perovskite LaMnO3 and Al2O3. Experiments show that the NTC thermistor material LaMnO3-Al2O3 has linear resistance-temperature characteristics in the range of 30℃ to 65℃, with a linearity of over 99.6%. It is a linear NTC thermistor material, which can simplify the working circuit and make the whole system operation simpler and more reliable during use. Attached Figure Description

[0020] Figure 1 This is a temperature resistance characteristic curve of the thermistor material LaMnO3-Al2O3 prepared in Example 1 of the present invention. Detailed Implementation

[0021] 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.

[0022] The present invention provides a linear NTC thermistor material LaMnO3-Al2O3, comprising Mn-based perovskite LaMnO3 and Al2O3, wherein the molar fraction of Al2O3 accounts for 10% to 30% of the total molar fraction of the system.

[0023] Specifically, the Mn-based perovskite LaMnO3 is synthesized from MnO2 and La2O3 through a high-temperature solid-state reaction, and the molar ratio of MnO2 to La2O3 is 2:1.

[0024] The NTC thermistor material of this invention uses Mn-based perovskite LaMnO3 as the main crystalline phase. In the Mn-based perovskite structure, Al doping is less prone to valence changes compared to Mn, and it occupies the B sites in the perovskite, thus leading to the formation of more Mn at the B sites. 3+ / Mn 4+Ion pairs provide the preconditions for electron hopping and conduction, enhancing conductivity. Furthermore, due to the significant difference in resistivity and B-value between Al₂O₃ and the main crystalline phase LaMnO₃, the overall electrical properties of the material can be altered. This invention, by doping LaMnO₃ with 10%–30% molar fraction of Al₂O₃, produces an NTC thermistor material, LaMnO₃-Al₂O₃, which exhibits good linearity between 30℃ and 65℃, making it a linear NTC thermistor material. This linear NTC thermistor material allows for a simpler operating circuit and makes the entire system simpler and more reliable to operate.

[0025] The present invention also provides a method for preparing the linear NTC thermistor material LaMnO3-Al2O3, comprising the following steps:

[0026] (1) MnO2 and La2O3 powders were mixed according to the formula and then ball-milled. The resulting product was dried, sieved, ground and then pre-calcined at high temperature to obtain Mn-based perovskite LaMnO3.

[0027] (2) Mix Mn-based perovskite LaMnO3 and Al2O3 powders according to the formula and then ball mill them. The resulting product is dried, sieved and ground to obtain a powdered precursor.

[0028] (3) Add polyvinyl alcohol to the powdered precursor and press the powdered precursor by molding to obtain a block precursor.

[0029] Because this powder is prone to breakage during the pressing process, polyvinyl alcohol (PVA) is added as a thickener during the pressing process to increase the adhesion of the powder, so that a complete block precursor can be obtained after pressing.

[0030] (4) The bulk precursor is sintered to obtain the linear NTC thermistor material LaMnO3-Al2O3.

[0031] Furthermore, in steps (1) and (2), ethanol is added during ball milling, the ball milling speed is 200 rpm, the ball milling time is 6 hours, the drying temperature is 70°C, and the material is sieved through a 200-mesh sieve.

[0032] Furthermore, in step (1), the pre-firing temperature is 1200℃, the pre-firing time is 6h, and the heating rate is 5℃ / min.

[0033] Furthermore, in step (3), the amount of polyvinyl alcohol added accounts for 5% of the total mass of the precursor.

[0034] Furthermore, in step (3), the molding pressure is 200-300 MPa and the holding time is 30-60 s.

[0035] Furthermore, in step (4), 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 1280-1350°C at a heating rate of 10°C / min. Sintering is carried out for 6-8 hours, and then cooled to room temperature in the furnace to obtain the linear NTC thermistor material LaMnO3-Al2O3. 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.

[0036] The following are specific preparation examples:

[0037] Example 1

[0038] (1) Weigh a total of 40g of metal oxide powder, including 13.918g of MnO2 and 26.082g of La2O3. 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 200rpm for 6h in a planetary ball mill. Place the obtained product in a 70℃ oven to dry, and sieve it through a 200-mesh nylon sieve. Grind the larger particles with a mortar and pestle, sieve it again, and put it into a crucible. Place it in a muffle furnace for pre-calcination. Heat the temperature to 1200℃ at 5℃ / min, hold for 6h, and then cool it with the furnace to obtain Mn-based perovskite LaMnO3.

[0039] (2) Add Mn-based perovskite LaMnO3 back into the ball mill jar, add 9.6789g of Al2O3, 100g of ball milling beads and 100mL of ethanol, and mill in a planetary ball mill at 200rpm for 6h. Place the product in a 70℃ oven to dry, and sieve it through a 200-mesh nylon sieve. Grind the larger particles in a mortar and pestle and sieve again to obtain a powdered precursor.

[0040] (3) Add polyvinyl alcohol to the powdered precursor. The amount of polyvinyl alcohol added accounts for 5% of the total mass of the precursor. The powdered precursor is pressed by molding to make the powder dense. The pressure is 200 MPa and the pressure is held for 30s to obtain a block precursor with a diameter of 12 mm.

[0041] (4) The block precursor is placed in an air furnace for high-temperature sintering. During sintering, the temperature is first raised to 500°C at a heating rate of 1°C / min in the air furnace to achieve the purpose of debinding. Then, it is cooled to room temperature with the furnace and then rapidly heated to 1280°C at a heating rate of 10°C / min. Sintering is carried out for 8 hours and then cooled to room temperature with the furnace to obtain the linear NTC thermistor material LaMnO3-Al2O3.

[0042] Example 2

[0043] (1) Weigh a total of 40g of metal oxide powder, including 13.918g of MnO2 and 26.082g of La2O3. 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 200rpm for 6h in a planetary ball mill. Place the obtained product in a 70℃ oven to dry, and sieve it through a 200-mesh nylon sieve. Grind the larger particles with a mortar and pestle, sieve it again, and put it into a crucible. Place it in a muffle furnace for pre-calcination. Heat the temperature to 1200℃ at 5℃ / min, hold for 6h, and then cool it with the furnace to obtain Mn-based perovskite LaMnO3.

[0044] (2) Add Mn-based perovskite LaMnO3 back into the ball mill jar, add 16.5924g of Al2O3, 100g of ball milling beads and 100mL of ethanol, and ball mill in a planetary ball mill at 200rpm for 6h. Place the product in a 70℃ oven to dry, and sieve it through a 200-mesh nylon sieve. Grind the larger particles in a mortar and pestle and sieve them again to obtain a powdered precursor.

[0045] (3) Add polyvinyl alcohol to the powdered precursor. The amount of polyvinyl alcohol added accounts for 5% of the total mass of the precursor. The powdered precursor is pressed by molding to make the powder dense. The pressure is 200 MPa and the pressure is held for 30s to obtain a block precursor with a diameter of 12 mm.

[0046] (4) The block precursor is placed in an air furnace for high-temperature sintering. During sintering, the temperature is first raised to 500°C at a heating rate of 1°C / min in the air furnace to achieve the purpose of debinding. Then, it is cooled to room temperature with the furnace and then rapidly heated to 1280°C at a heating rate of 10°C / min. Sintering is carried out for 8 hours and then cooled to room temperature with the furnace to obtain the linear NTC thermistor material LaMnO3-Al2O3.

[0047] Silver paste was applied to both sides of the sample prepared in the example to form electrodes; the resistance-temperature relationship of the electrodes was measured using a four-probe measurement system. Figure 1 This is a temperature resistance curve of the NTC thermistor prepared in Example 1 of this invention. In the figure, the black solid line is the actual temperature resistance curve, and the red solid line is an auxiliary linear curve used as a reference. The results show that the mixed material composed of LaMnO3 and Al2O3 with a molar fraction of 10% to 30% exhibits linear temperature resistance characteristics in the range of 30℃ to 65℃, with a linearity of over 99.6%. This indicates that the LaMnO3-Al2O3 prepared by this invention is a linear NTC thermistor material.

[0048] 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 linear NTC thermistor material LaMnO3-Al2O3, characterized in that: Its components include Mn-based perovskite LaMnO3 and Al2O3, with the molar fraction of Al2O3 accounting for 10%~30% of the total molar fraction of the system. This linear NTC thermistor material LaMnO3-Al2O3 exhibits linear resistance-temperature characteristics in the range of 30℃~65℃. The Mn-based perovskite LaMnO3 is synthesized from MnO2 and La2O3 through a high-temperature solid-state reaction, with a molar ratio of MnO2 to La2O3 of 2:

1. The preparation method of the linear NTC thermistor material LaMnO3-Al2O3 is as follows: (1) MnO2 and La2O3 powders were mixed according to the formula and then ball-milled. The resulting product was dried, sieved, ground and then pre-calcined at high temperature to obtain Mn-based perovskite LaMnO3. The pre-calcination temperature was 1200℃, the pre-calcination time was 6h and the heating rate was 5℃ / min. (2) Mix Mn-based perovskite LaMnO3 and Al2O3 powders according to the formula and then ball mill them. The resulting product is dried, sieved and ground to obtain a powdered precursor. (3) Add polyvinyl alcohol to the powdered precursor and press the powdered precursor by molding to obtain a block precursor; (4) The block precursor is sintered to obtain the linear NTC thermistor material LaMnO3-Al2O3. The linear NTC thermistor material LaMnO3-Al2O3 has linear resistance-temperature characteristics in the range of 30℃~65℃. 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 1280~1350℃ at a heating rate of 10℃ / min. Sintering is carried out for 6~8h and then cooled to room temperature with the furnace to obtain the linear NTC thermistor material LaMnO3-Al2O3.

2. The linear NTC thermistor material LaMnO3-Al2O3 as described in claim 1, characterized in that: In steps (1) and (2), ethanol is added during ball milling, the ball milling speed is 200 rpm, the ball milling time is 6 h, the drying temperature is 70 ℃, and the material is sieved through a 200 mesh screen.

3. The linear NTC thermistor material LaMnO3-Al2O3 as described in claim 1, characterized in that: In step (3), the amount of polyvinyl alcohol added accounts for 5% of the total mass of the precursor.

4. The linear NTC thermistor material LaMnO3-Al2O3 as described in claim 1, characterized in that: In step (3), the molding method uses a molding pressure of 200-300 MPa and a holding time of 30-60 s.

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