Preparation method of porous LSMO heating element

Abstract

This invention belongs to the field of heating element technology, specifically relating to a method for preparing a porous LSMO heating element. The preparation steps are as follows: a metal salt solution is prepared using a metal salt and a solvent; citric acid is added to the metal salt solution and stirred to obtain a complexed sol; a PVA solution is added to the complexed sol, and quantum dot dispersion is added or not, and stirred to obtain a mixed solution; a pore-forming agent is added to the mixed solution and ball-milled to disperse it, obtaining a precursor solution; after degassing the precursor solution, monomers, crosslinking agents, initiators, and catalysts are added, followed by injection molding, drying, degreasing, low-temperature sintering, and high-temperature sintering to obtain a porous LSMO heating element. The material of this invention is stable in a high-temperature sintering atmosphere, has good compatibility with the LSMO matrix, does not damage the integrity of the ceramic structure, and improves conductivity and thermal response speed.

Description

Technical Field

[0001] This invention belongs to the field of heating element technology, specifically relating to a method for preparing a porous LSMO heating element. Background Technology

[0002] Perovskite oxide LSMO is a colossal magnetoresistance material, widely studied in magnetic storage devices, sensors, and heating elements due to its excellent electrical, magnetic, and thermal properties near the Curie temperature. Among them, La... 0.7 Sr 0.3 MnO3 has a Curie temperature close to room temperature, a high temperature coefficient of resistance, and stable electrothermal conversion performance, and is considered a promising electrothermal material.

[0003] Traditional LSMO ceramic heating elements are mostly dense sintered bodies. However, dense ceramics suffer from problems such as high thermal inertia, slow heating response, high brittleness, and susceptibility to thermal stress cracking. Introducing a porous structure can reduce material density, increase specific surface area, and reduce thermal inertia, thereby potentially improving heating rate and thermal shock resistance. However, porosity usually introduces excessive grain boundaries and pores, increasing resistivity and leading to reduced electro-thermal conversion efficiency, making it difficult to improve heating response speed. Summary of the Invention

[0004] Based on this, the present invention provides a method for preparing a porous LSMO heating element.

[0005] The technical solution of the present invention is as follows:

[0006] The method for preparing a porous LSMO heating element includes the following steps:

[0007] Metal salt solution is prepared using metal salt and solvent; citric acid is added to the metal salt solution and stirred to obtain a complex sol; PVA solution is added to the complex sol, and quantum dot dispersion is added or not, and stirred to obtain a mixed solution; pore-forming agent is added to the mixed solution and dispersed by ball milling to obtain a precursor solution; after degassing the precursor solution, monomer, crosslinking agent, initiator, and catalyst are added, and the mixture is injection molded, dried, degreased, sintered at low temperature, and sintered at high temperature to obtain a porous LSMO heating element.

[0008] Furthermore, the monomer includes acrylamide, the crosslinking agent includes N,N'-methylenebisacrylamide, the initiator includes ammonium persulfate, the catalyst includes tetramethylethylenediamine, and the solvent includes deionized water.

[0009] Furthermore, the pore-forming agent includes one or more of the following: carbon powder, starch, and PMMA microspheres. The pore-forming agent is dried before being added.

[0010] Furthermore, the quantum dot dispersion includes one or more of MoS2 quantum dot dispersion, WS2 quantum dot dispersion, modified MoS2 quantum dot dispersion, and modified WS2 quantum dot dispersion.

[0011] Preferably, the preparation steps of the modified MoS2 quantum dot dispersion include: adding APTES to the MoS2 quantum dot dispersion, adjusting the pH, stirring, centrifuging, discarding the supernatant, redispersing, and obtaining the quantum dot dispersion.

[0012] The preparation steps of the modified WS2 quantum dot dispersion include: adding APTES to the WS2 quantum dot dispersion, adjusting the pH, stirring, centrifuging, discarding the supernatant, redispersing, and obtaining the quantum dot dispersion.

[0013] It should be noted that this invention employs a citric acid-complexed metal nitrate precursor system, and improves molding stability and solution adhesion by introducing a polyvinyl alcohol (PVA) gel network generated by in-situ polymerization with polyacrylamide (PAM). Dried PMMA microspheres are selected as a controllable pore-forming agent to provide a uniform pore structure in the gel casting system. In some embodiments, MoS2 or WS2 quantum dots are further introduced, and their dispersibility and interfacial bonding are improved through APTES modification or ultrasonic dispersion, thereby optimizing the electrical conductivity and heating response of the heating ceramic body.

[0014] Further, the drying process includes the following steps: placing the injection-molded wet blank into a forced-air drying oven and using a gradient temperature increase for drying, first drying at 20-60℃ for 10-14 hours, then increasing the temperature to 40-80℃ for 10-14 hours, and finally increasing the temperature to 60-100℃ for 4-8 hours.

[0015] Furthermore, the degreasing process includes the following steps: placing the dried blank into a high-temperature muffle furnace, raising the temperature from room temperature to 200-300℃ at a rate of 0.2-1℃ / min, and holding it at that temperature for 0.5-2 hours; raising the temperature to 200-600℃ at a rate of 0.2-1℃ / min, and holding it at that temperature for 1-3 hours; raising the temperature to 400-800℃ at a rate of 0.5-1.5℃ / min, and holding it at that temperature for 1-3 hours.

[0016] Furthermore, the low-temperature sintering process includes the following steps: after degreasing, the temperature is raised to 800-900℃ at a heating rate of 2-4℃ / min, and held for 1-3 hours.

[0017] Furthermore, the high-temperature sintering includes the following steps: after low-temperature sintering, the temperature is raised to 1000-1200℃ at a heating rate of 2-4℃ / min, and held at this temperature for 3-7 hours. After sintering, the furnace is allowed to cool naturally to room temperature to obtain a porous LSMO heating element.

[0018] Furthermore, the metal salts include lanthanum nitrate, strontium nitrate, and manganese nitrate hexahydrate; the amount of pore-forming agent added is 10%-30% of the total mass of the metal salts.

[0019] It should be noted that: 1. Lanthanum nitrate, strontium nitrate, and manganese nitrate hexahydrate, as sources of La, Sr, and Mn elements, form a stable and homogeneous metal complex sol under the complexing effect of citric acid, effectively avoiding the hydrolysis or local enrichment of metal ions, and providing a highly uniform precursor basis for subsequent solid-phase reactions. 2. In addition to stabilizing the distribution of metal ions as a complexing agent, citric acid also participates in the organic-inorganic transformation process during heat treatment, regulating crystal nucleation and grain growth behavior through slow-release decomposition, thereby helping to reduce the risk of abnormal grain growth during sintering. 3. Polyvinyl alcohol (PVA) mainly plays a role in increasing the viscosity of the precursor solution and stabilizing the suspended dispersion state in the system. At the same time, its molecular chains have a physical adsorption and coating effect on two-dimensional quantum dots, which can inhibit the aggregation of quantum dots in the solution stage and make them uniformly distributed in the metal complex network. 4. Acrylamide and N,N'-methylenebisacrylamide are polymerized in situ under the initiation system of ammonium persulfate and tetramethylethylenediamine to form a three-dimensional cross-linked polyacrylamide gel framework. This gel network not only endows the wet preform with high molding strength and structural stability, but also spatially confines the metal complex, quantum dots, and pore-forming agent, providing template support for maintaining the pore structure in the subsequent sintering stage. 5. Pre-dried PMMA microspheres serve as pore-forming agents, uniformly distributed in the gel network and controllably decomposed during the degreasing stage, thus forming a porous structure with good connectivity and uniform size distribution. This porous structure increases the specific surface area while providing more continuous and efficient channels for current transport and heat release. 6. The introduction of MoS2 or WS2 quantum dots provides the system with two-dimensional conductive units with high carrier mobility, dispersed in La... 0.7 Sr 0.3 MnO3 grains and grain boundaries can create localized fast electron transport channels at the microscopic level, thereby reducing overall resistivity and accelerating electron transport. Thermal response process. 7. When modified with APTES, APTES introduces silanol and amino functional groups on the surface of quantum dots, enabling the quantum dots to generate stronger interfacial interactions with metal oxide precursors and gel networks, enhancing the anchoring stability and interfacial coupling strength of quantum dots in the ceramic matrix, thereby further amplifying the enhancing effect of quantum dots on conductivity and heating performance.

[0020] In existing technologies, methods to improve the conductivity of porous ceramics mainly include optimizing the sintering process to enhance grain conductivity or adding conductive phases such as metals or carbon nanotubes. However, metal phases are easily oxidized at high temperatures, and carbon nanotubes may be oxidized or react adversely with the matrix in high-temperature sintering atmospheres. Furthermore, interfacial bonding and uniform dispersion with the ceramic matrix are significant problems. Therefore, how to develop a modification system that can exist stably in a high-temperature sintering atmosphere, is well compatible with the LSMO matrix, and improves conductivity and thermal response speed without compromising the integrity of the ceramic structure is the technical problem that this invention attempts to solve.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] This invention combines gel injection molding with a pore-forming agent to construct a three-dimensional porous LSMO framework with high porosity and good connectivity.

[0023] In addition, while maintaining the advantages of the porous structure, we also attempted to introduce two-dimensional transition metal chalcogenide quantum dots as a nano-conductive reinforcing phase. The quantum dots are uniformly dispersed in the LSMO precursor during the sol-gel process. During subsequent high-temperature sintering, the quantum dots partially decompose or undergo interfacial reactions with the matrix. The residual carbon / sulfur species or the heterostructures formed can effectively modify the LSMO grain boundaries, constructing an additional conductive network within the ceramic framework. This reduces the overall resistivity while maintaining high porosity, enabling rapid heating.

[0024] Specifically,

[0025] 1. This invention achieves high porosity and low resistivity by introducing a pore-forming agent (such as PMMA microspheres) and combining it with a gel casting process to successfully prepare porous LSMO materials with a porosity as high as 40%-47%. Specifically, this invention uses a gel casting process and a controllable pore-forming agent to synergistically regulate the porous framework structure. By introducing PMMA microspheres with appropriate particle size and combining them with a three-dimensional polyacrylamide gel support network, the controllable construction of a porous ceramic framework with high porosity and excellent connectivity in LSMO is achieved. This structure not only expands the specific surface area but also retains relatively complete three-dimensional pore channels during sintering, providing a low-resistivity pathway for charge migration and thermal diffusion, thus solving the problems of poor thermal conductivity and low charge conduction efficiency in traditional dense ceramics.

[0026] 2. In this invention, after doping the material with trace amounts of two-dimensional quantum dots, the resistivity of the porous LSMO material does not deteriorate due to the increase in pore size. In fact, the resistivity is lower than that of the dense material without pore-forming agent (Comparative Example 1), which is different from the traditional trend that "the more pores a material has, the higher its resistance tends to be."

[0027] 3. The high porosity of the material prepared by this invention results in low thermal inertia, and the low resistivity results in high electrothermal conversion efficiency, enabling the prepared material to have an ultra-fast electrothermal response speed. In Examples 1-5 of this invention, the time for the material to heat to 200°C is shortened to 17-21 seconds, which can meet the needs of rapid heating applications.

[0028] 4. The heating element material of this invention is based on La 0.7 Sr 0.3 A three-dimensional interconnected porous ceramic framework structure was formed from a MnO3 (LSMO) perovskite oxide system through gel casting and high-temperature sintering. Quantum dot modification was then introduced to create a nano-interface heterostructure, allowing for the modulation of electron transport pathways and thermal response behavior. Quantum dots possess a two-dimensional layered structure and strong quantum confinement effect; their surface and interfacial activity can establish quasi-continuous conductive and thermal channels between LSMO grains, enabling electron density modulation and enhanced carrier mobility, thereby improving the material's electrothermal conversion efficiency and thermal stability.

[0029] 5. Quantum dots possess narrow band gaps and high electron mobility, forming interfacial polarization layers at LSMO grain boundaries. This allows for the regulation of carrier concentration and spatial distribution, suppressing inelastic scattering of thermally excited electrons and improving thermoelectric conversion efficiency. Quantum dots distributed between grain boundaries and pore walls construct electron-phonon coupled microchannels through bridging effects, enhancing local thermal conductivity across both low and high temperature ranges. Especially after surface modification using APTES, quantum dots and LSMO precursors can form stable interfaces through Si–O–Mn or Si–O–La / Sr bonds, improving their anti-migration ability and distribution uniformity during sintering. This enhances the anchoring effect of quantum dots in the grain boundary region, improving the long-term thermal stability of the material.

[0030] 6. The porous La described in this invention 0.7 Sr 0.3 MnO3 heating materials, due to their high thermal responsiveness, low resistivity, structural tunability, and interface stability, can be applied in scenarios such as integrated micro heat sources, localized heating units, and on-chip thermal control modules in next-generation high-performance chip systems. For example, modern high-performance chips (such as CPUs, GPUs, AI-specific chips, and 3D stacked SoCs) are increasingly incorporating micro-integrated heat sources to assist in localized high-temperature processes such as solder ball remelting, wafer bonding, and MEMS packaging. Traditional electrothermal films or dense ceramic heating elements suffer from slow response, high thermal inertia, and difficulties in miniaturization. The porous La2O3 heating element provided by this invention... 0.7 Sr 0.3 MnO3 materials have the advantages of rapid heating, low thermal inertia, and adjustable size. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0032] Unless otherwise specified, the equipment and materials used in the embodiments can be readily obtained from commercial companies.

[0033] It should be noted that the raw materials used are:

[0034] Lanthanum nitrate: purity ≥ 99.0%.

[0035] Strontium nitrate: purity ≥ 99.0%.

[0036] Manganese nitrate hexahydrate: purity ≥ 98.0%.

[0037] Solvent: Ethylene glycol methyl ether, analytical grade, purity ≥99.5%.

[0038] Ethanol: Purity ≥ 99.7%.

[0039] Acrylamide: chemically pure.

[0040] N,N'-Methylenebisacrylamide: chemically pure.

[0041] Pore-forming agent: Select carbon powder, starch or polymethyl methacrylate (PMMA) microspheres with appropriate particle size as pore-forming agent. Determine the amount of pore-forming agent to be added according to the required pore structure and porosity. Generally, it is 10%-30% of the total mass of metal salt. The pore-forming agent needs to be dried before use.

[0042] MoS2 quantum dot dispersion: 95% purity, 5mg / mL concentration, ethanol as solvent, available from Xi'an Qiyue Biotechnology Co., Ltd.

[0043] 3-Aminopropyltriethoxysilane: APTES.

[0044] WS2 quantum dot dispersion: monolayer, purity 95%, concentration 5mg / mL, solvent is ethanol, available from Xi'an Qiyue Biotechnology Co., Ltd.

[0045] Citric acid: Anhydrous citric acid, analytical grade (AR).

[0046] PVA: Polyvinyl alcohol, degree of polymerization around 1700, degree of alcoholysis 88%, PVA17-88 can be selected.

[0047] Example 1

[0048] Porous LSMO (La) was prepared using the aforementioned raw materials. 0.7 Sr 0.3The specific steps for preparing the MnO3 heating element are as follows:

[0049] According to La 0.7 Sr 0.3 To determine the stoichiometric ratio of MnO3, weigh 7.001g of lanthanum nitrate. The remaining strontium nitrate and manganese nitrate hexahydrate should be weighed in a mass ratio of 0.7:0.3:1 to ensure that the molar ratio of La, Sr, and Mn is 0.7:0.3:1. Then, pour the lanthanum nitrate, strontium nitrate, and manganese nitrate hexahydrate into a beaker, add 40mL of deionized water, place the beaker on a magnetic stirrer, and stir at 300r / min until the metal nitrates are completely dissolved to form a uniform and transparent metal salt solution.

[0050] Weigh 13.31g of citric acid and add it to the metal salt solution. Stir continuously for 2 hours in a 60℃ water bath to form a stable complex sol.

[0051] Weigh 1.5g of PVA powder into 50mL of deionized water, heat in an 85℃ water bath while stirring to dissolve, and obtain a PVA solution.

[0052] The PVA solution was slowly added to the complexed sol and stirred until homogeneous to obtain a mixed solution.

[0053] PMMA microspheres were selected as pore-forming agents. The PMMA microspheres had a particle size D50 of 5.0 μm. They were dried in an oven at 80℃ for 4 hours. Then, 3g of the dried pore-forming agent was slowly added to the above mixed solution and dispersed by ball milling using a planetary ball mill with zirconia grinding balls. The ball milling speed was 300 r / min and the ball milling time was 4 hours to obtain a uniform and stable precursor solution.

[0054] The prepared precursor solution was ultrasonically defoamed for 10 minutes at a power of 100W to obtain a pretreated precursor solution.

[0055] Gel injection molding: Add 11.04g acrylamide and 0.88g N,N'-methylenebisacrylamide to the pretreated precursor solution. Dissolve 0.88g ammonium persulfate in 5mL of deionized water and add it to the solution. Stir well. Then immediately add 20μL tetramethylethylenediamine and stir well. Pour the solution into the mold. The solution gels and solidifies under the action of the initiator and catalyst. Then demold.

[0056] Drying: Place the shaped wet blank into a forced-air drying oven and dry it using a gradient temperature increase. First, dry at 40℃ for 12 hours, then increase the temperature to 60℃ for 12 hours, and finally increase the temperature to 80℃ for 6 hours to ensure that the blank is completely dry.

[0057] Degreasing: The dried green body is placed in a high-temperature muffle furnace and heated from room temperature to 250°C at a rate of 0.5°C / min and held for 1 hour; then heated to 400°C at a rate of 0.5°C / min and held for 2 hours; then heated to 600°C at a rate of 1°C / min and held for 2 hours, so that the organic matter and pore-forming agent in the green body can be fully decomposed and volatilized.

[0058] Low-temperature sintering: After degreasing, the temperature is raised to 850℃ at a heating rate of 3℃ / min and held for 2 hours to promote the initial densification of the green body.

[0059] High-temperature sintering: Continue to raise the temperature to 1150℃ at a heating rate of 3℃ / min, and hold at this temperature for 5 hours to allow La to sinter. 0.7 Sr 0.3 MnO3 undergoes a complete solid-state reaction, forming a stable crystal structure. After sintering, it is naturally cooled to room temperature in the furnace to obtain porous La. 0.7 Sr 0.3 MnO3 heating element.

[0060] Example 2

[0061] The specific steps for preparing the porous LSMO heating element using the aforementioned raw materials are as follows:

[0062] According to La 0.7 Sr 0.3 To determine the stoichiometric ratio of MnO3, weigh 7.001g of lanthanum nitrate. The remaining strontium nitrate and manganese nitrate hexahydrate should be weighed in a mass ratio of 0.7:0.3:1 to ensure that the molar ratio of La, Sr, and Mn is 0.7:0.3:1. Then, pour the lanthanum nitrate, strontium nitrate, and manganese nitrate hexahydrate into a beaker, add 40mL of deionized water, place the beaker on a magnetic stirrer, and stir at 300r / min until the metal nitrates are completely dissolved to form a uniform and transparent metal salt solution.

[0063] Weigh 13.31g of citric acid and add it to the metal salt solution. Stir continuously for 2 hours in a 60℃ water bath to form a stable complex sol.

[0064] Take 2 mL of MoS2 quantum dot dispersion, add 0.1 mL of APTES, adjust the pH to 5-6 with dilute acetic acid, stir magnetically at room temperature for 12 hours, then centrifuge at 8000 rpm for 5 minutes, discard the supernatant, redisperse with deionized water, and finally bring the volume to 2 mL to obtain the quantum dot dispersion.

[0065] Weigh 1.5g of PVA powder into 50mL of deionized water, heat in an 85℃ water bath while stirring to dissolve, and obtain a PVA solution.

[0066] The PVA solution was slowly added to the complexed sol and stirred until homogeneous. Then, the quantum dot dispersion was added dropwise while stirring at low speed to obtain a mixed solution.

[0067] PMMA microspheres were selected as pore-forming agents. The PMMA microspheres had a particle size D50 of 5.0 μm. They were dried in an oven at 80℃ for 4 hours. Then, 3g of the dried pore-forming agent was slowly added to the above mixed solution and dispersed by ball milling using a planetary ball mill with zirconia grinding balls. The ball milling speed was 300 r / min and the ball milling time was 4 hours to obtain a uniform and stable precursor solution.

[0068] The prepared precursor solution was ultrasonically defoamed for 10 minutes at a power of 100W to obtain a pretreated precursor solution.

[0069] Gel injection molding: Add 11.04g acrylamide and 0.88g N,N'-methylenebisacrylamide to the pretreated precursor solution. Dissolve 0.88g ammonium persulfate in 5mL of deionized water and add it to the solution. Stir well. Then immediately add 20μL tetramethylethylenediamine and stir well. Pour the solution into the mold. The solution gels and solidifies under the action of the initiator and catalyst. Then demold.

[0070] Drying: Place the shaped wet blank into a forced-air drying oven and dry it using a gradient temperature increase. First, dry at 40℃ for 12 hours, then increase the temperature to 60℃ for 12 hours, and finally increase the temperature to 80℃ for 6 hours to ensure that the blank is completely dry.

[0071] Degreasing: The dried green body is placed in a high-temperature muffle furnace and heated from room temperature to 250°C at a rate of 0.5°C / min and held for 1 hour; then heated to 400°C at a rate of 0.5°C / min and held for 2 hours; then heated to 600°C at a rate of 1°C / min and held for 2 hours, so that the organic matter and pore-forming agent in the green body can be fully decomposed and volatilized.

[0072] Low-temperature sintering: After degreasing, the temperature is raised to 850℃ at a heating rate of 3℃ / min and held for 2 hours to promote the initial densification of the green body.

[0073] High-temperature sintering: Continue to raise the temperature to 1150℃ at a heating rate of 3℃ / min, and hold at this temperature for 5 hours to allow La to sinter. 0.7 Sr 0.3 MnO3 undergoes a complete solid-state reaction, forming a stable crystal structure. After sintering, it is naturally cooled to room temperature in the furnace to obtain porous La. 0.7 Sr 0.3 MnO3 heating element.

[0074] Example 3

[0075] The specific steps for preparing the porous LSMO heating element using the aforementioned raw materials are as follows:

[0076] According to La 0.7 Sr 0.3 To determine the stoichiometric ratio of MnO3, weigh 7.001g of lanthanum nitrate. The remaining strontium nitrate and manganese nitrate hexahydrate should be weighed in a mass ratio of 0.7:0.3:1 to ensure that the molar ratio of La, Sr, and Mn is 0.7:0.3:1. Then, pour the lanthanum nitrate, strontium nitrate, and manganese nitrate hexahydrate into a beaker, add 40mL of deionized water, place the beaker on a magnetic stirrer, and stir at 300r / min until the metal nitrates are completely dissolved to form a uniform and transparent metal salt solution.

[0077] Weigh 13.31g of citric acid and add it to the metal salt solution. Stir continuously for 2 hours in a 60℃ water bath to form a stable complex sol.

[0078] Take 2 mL of MoS2 quantum dot dispersion and perform ultrasonic dispersion treatment in an ice-water bath with the parameters of 100 W power and 30 minutes to depolymerize the aggregates. Then centrifuge at 8000 rpm for 5 minutes, discard the supernatant, redisperse with deionized water, and finally adjust the volume to 2 mL to obtain the quantum dot dispersion.

[0079] Weigh 1.5g of PVA powder into 50mL of deionized water, heat in an 85℃ water bath while stirring to dissolve, and obtain a PVA solution.

[0080] The PVA solution was slowly added to the complexed sol and stirred until homogeneous. Then, the quantum dot dispersion was added dropwise while stirring at low speed to obtain a mixed solution.

[0081] PMMA microspheres were selected as pore-forming agents. The PMMA microspheres had a particle size D50 of 5.0 μm. They were dried in an oven at 80℃ for 4 hours. Then, 3g of the dried pore-forming agent was slowly added to the above mixed solution and dispersed by ball milling using a planetary ball mill with zirconia grinding balls. The ball milling speed was 300 r / min and the ball milling time was 4 hours to obtain a uniform and stable precursor solution.

[0082] The prepared precursor solution was ultrasonically defoamed for 10 minutes at a power of 100W to obtain a pretreated precursor solution.

[0083] Gel injection molding: Add 11.04g acrylamide and 0.88g N,N'-methylenebisacrylamide to the pretreated precursor solution. Dissolve 0.88g ammonium persulfate in 5mL of deionized water and add it to the solution. Stir well. Then immediately add 20μL tetramethylethylenediamine and stir well. Pour the solution into the mold. The solution gels and solidifies under the action of the initiator and catalyst. Then demold.

[0084] Drying: Place the shaped wet blank into a forced-air drying oven and dry it using a gradient temperature increase. First, dry at 40℃ for 12 hours, then increase the temperature to 60℃ for 12 hours, and finally increase the temperature to 80℃ for 6 hours to ensure that the blank is completely dry.

[0085] Degreasing: The dried green body is placed in a high-temperature muffle furnace and heated from room temperature to 250°C at a rate of 0.5°C / min and held for 1 hour; then heated to 400°C at a rate of 0.5°C / min and held for 2 hours; then heated to 600°C at a rate of 1°C / min and held for 2 hours, so that the organic matter and pore-forming agent in the green body can be fully decomposed and volatilized.

[0086] Low-temperature sintering: After degreasing, the temperature is raised to 850℃ at a heating rate of 3℃ / min and held for 2 hours to promote the initial densification of the green body.

[0087] High-temperature sintering: Continue to raise the temperature to 1150℃ at a heating rate of 3℃ / min, and hold at this temperature for 5 hours to allow La to sinter. 0.7 Sr 0.3 MnO3 undergoes a complete solid-state reaction, forming a stable crystal structure. After sintering, it is naturally cooled to room temperature in the furnace to obtain porous La. 0.7 Sr 0.3 MnO3 heating element.

[0088] Example 4

[0089] The specific steps for preparing the porous LSMO heating element using the aforementioned raw materials are as follows:

[0090] According to La 0.7 Sr 0.3 To determine the stoichiometric ratio of MnO3, weigh 7.001g of lanthanum nitrate. The remaining strontium nitrate and manganese nitrate hexahydrate should be weighed in a mass ratio of 0.7:0.3:1 to ensure that the molar ratio of La, Sr, and Mn is 0.7:0.3:1. Then, pour the lanthanum nitrate, strontium nitrate, and manganese nitrate hexahydrate into a beaker, add 40mL of deionized water, place the beaker on a magnetic stirrer, and stir at 300r / min until the metal nitrates are completely dissolved to form a uniform and transparent metal salt solution.

[0091] Weigh 13.31g of citric acid and add it to the metal salt solution. Stir continuously for 2 hours in a 60℃ water bath to form a stable complex sol.

[0092] Take 2 mL of WS2 quantum dot dispersion, add 0.1 mL of APTES, adjust the pH to 5-6 with dilute acetic acid, stir magnetically at room temperature for 12 hours, then centrifuge at 8000 rpm for 5 minutes, discard the supernatant, redisperse with deionized water, and finally bring the volume to 2 mL to obtain the quantum dot dispersion.

[0093] Weigh 1.5g of PVA powder into 50mL of deionized water, heat in an 85℃ water bath while stirring to dissolve, and obtain a PVA solution.

[0094] The PVA solution was slowly added to the complexed sol and stirred until homogeneous. Then, the quantum dot dispersion was added dropwise while stirring at low speed to obtain a mixed solution.

[0095] PMMA microspheres were selected as pore-forming agents. The PMMA microspheres had a particle size D50 of 5.0 μm. They were dried in an oven at 80℃ for 4 hours. Then, 3g of the dried pore-forming agent was slowly added to the above mixed solution and dispersed by ball milling using a planetary ball mill with zirconia grinding balls. The ball milling speed was 300 r / min and the ball milling time was 4 hours to obtain a uniform and stable precursor solution.

[0096] The prepared precursor solution was ultrasonically defoamed for 10 minutes at a power of 100W to obtain a pretreated precursor solution.

[0097] Gel injection molding: Add 11.04g acrylamide and 0.88g N,N'-methylenebisacrylamide to the pretreated precursor solution. Dissolve 0.88g ammonium persulfate in 5mL of deionized water and add it to the solution. Stir well. Then immediately add 20μL tetramethylethylenediamine and stir well. Pour the solution into the mold. The solution gels and solidifies under the action of the initiator and catalyst. Then demold.

[0098] Drying: Place the shaped wet blank into a forced-air drying oven and dry it using a gradient temperature increase. First, dry at 40℃ for 12 hours, then increase the temperature to 60℃ for 12 hours, and finally increase the temperature to 80℃ for 6 hours to ensure that the blank is completely dry.

[0099] Degreasing: The dried green body is placed in a high-temperature muffle furnace and heated from room temperature to 250°C at a rate of 0.5°C / min and held for 1 hour; then heated to 400°C at a rate of 0.5°C / min and held for 2 hours; then heated to 600°C at a rate of 1°C / min and held for 2 hours, so that the organic matter and pore-forming agent in the green body can be fully decomposed and volatilized.

[0100] Low-temperature sintering: After degreasing, the temperature is raised to 850℃ at a heating rate of 3℃ / min and held for 2 hours to promote the initial densification of the green body.

[0101] High-temperature sintering: Continue to raise the temperature to 1150℃ at a heating rate of 3℃ / min, and hold at this temperature for 5 hours to allow La to sinter. 0.7 Sr 0.3 MnO3 undergoes a complete solid-state reaction, forming a stable crystal structure. After sintering, it is naturally cooled to room temperature in the furnace to obtain porous La. 0.7 Sr 0.3 MnO3 heating element.

[0102] Example 5

[0103] The specific steps for preparing the porous LSMO heating element using the aforementioned raw materials are as follows:

[0104] According to La 0.7 Sr 0.3 To determine the stoichiometric ratio of MnO3, weigh 7.001g of lanthanum nitrate. The remaining strontium nitrate and manganese nitrate hexahydrate should be weighed in a mass ratio of 0.7:0.3:1 to ensure that the molar ratio of La, Sr, and Mn is 0.7:0.3:1. Then, pour the lanthanum nitrate, strontium nitrate, and manganese nitrate hexahydrate into a beaker, add 40mL of deionized water, place the beaker on a magnetic stirrer, and stir at 300r / min until the metal nitrates are completely dissolved to form a uniform and transparent metal salt solution.

[0105] Weigh 13.31g of citric acid and add it to the metal salt solution. Stir continuously for 2 hours in a 60℃ water bath to form a stable complex sol.

[0106] Take 2 mL of WS2 quantum dot dispersion and perform ultrasonic dispersion treatment in an ice-water bath with the parameters of 100 W power and 30 minutes to depolymerize the aggregates. Then centrifuge at 8000 rpm for 5 minutes, discard the supernatant, redisperse with deionized water, and finally adjust the volume to 2 mL to obtain the quantum dot dispersion.

[0107] Weigh 1.5g of PVA powder into 50mL of deionized water, heat in an 85℃ water bath while stirring to dissolve, and obtain a PVA solution.

[0108] The PVA solution was slowly added to the complexed sol and stirred until homogeneous. Then, the quantum dot dispersion was added dropwise while stirring at low speed to obtain a mixed solution.

[0109] PMMA microspheres were selected as pore-forming agents. The PMMA microspheres had a particle size D50 of 5.0 μm. They were dried in an oven at 80℃ for 4 hours. Then, 3g of the dried pore-forming agent was slowly added to the above mixed solution and dispersed by ball milling using a planetary ball mill with zirconia grinding balls. The ball milling speed was 300 r / min and the ball milling time was 4 hours to obtain a uniform and stable precursor solution.

[0110] The prepared precursor solution was ultrasonically defoamed for 10 minutes at a power of 100W to obtain a pretreated precursor solution.

[0111] Gel injection molding: Add 11.04g acrylamide and 0.88g N,N'-methylenebisacrylamide to the pretreated precursor solution. Dissolve 0.88g ammonium persulfate in 5mL of deionized water and add it to the solution. Stir well. Then immediately add 20μL tetramethylethylenediamine and stir well. Pour the solution into the mold. The solution gels and solidifies under the action of the initiator and catalyst. Then demold.

[0112] Drying: Place the shaped wet blank into a forced-air drying oven and dry it using a gradient temperature increase. First, dry at 40℃ for 12 hours, then increase the temperature to 60℃ for 12 hours, and finally increase the temperature to 80℃ for 6 hours to ensure that the blank is completely dry.

[0113] Degreasing: The dried green body is placed in a high-temperature muffle furnace and heated from room temperature to 250°C at a rate of 0.5°C / min and held for 1 hour; then heated to 400°C at a rate of 0.5°C / min and held for 2 hours; then heated to 600°C at a rate of 1°C / min and held for 2 hours, so that the organic matter and pore-forming agent in the green body can be fully decomposed and volatilized.

[0114] Low-temperature sintering: After degreasing, the temperature is raised to 850℃ at a heating rate of 3℃ / min and held for 2 hours to promote the initial densification of the green body.

[0115] High-temperature sintering: Continue to raise the temperature to 1150℃ at a heating rate of 3℃ / min, and hold at this temperature for 5 hours to allow La to sinter. 0.7 Sr 0.3 MnO3 undergoes a complete solid-state reaction, forming a stable crystal structure. After sintering, it is naturally cooled to room temperature in the furnace to obtain porous La. 0.7 Sr 0.3 MnO3 heating element.

[0116] Comparative Example 1

[0117] The specific steps for preparing the porous LSMO heating element using the aforementioned raw materials are as follows:

[0118] According to La 0.7 Sr 0.3 To determine the stoichiometric ratio of MnO3, weigh 7.001g of lanthanum nitrate. The remaining strontium nitrate and manganese nitrate hexahydrate should be weighed in a mass ratio of 0.7:0.3:1 to ensure that the molar ratio of La, Sr, and Mn is 0.7:0.3:1. Then, pour the lanthanum nitrate, strontium nitrate, and manganese nitrate hexahydrate into a beaker, add 40mL of deionized water, place the beaker on a magnetic stirrer, and stir at 300r / min until the metal nitrates are completely dissolved to form a uniform and transparent metal salt solution.

[0119] Weigh 13.31g of citric acid and add it to the metal salt solution. Stir continuously for 2 hours in a 60℃ water bath to form a stable complex sol.

[0120] Weigh 1.5g of PVA powder into 50mL of deionized water, heat in an 85℃ water bath while stirring to dissolve, and obtain a PVA solution.

[0121] The PVA solution was slowly added to the complexed sol and stirred until homogeneous to obtain the precursor solution.

[0122] The prepared precursor solution was ultrasonically defoamed for 10 minutes at a power of 100W to obtain a pretreated precursor solution.

[0123] Gel injection molding: Add 11.04g acrylamide and 0.88g N,N'-methylenebisacrylamide to the pretreated precursor solution. Dissolve 0.88g ammonium persulfate in 5mL of deionized water and add it to the solution. Stir well. Then immediately add 20μL tetramethylethylenediamine and stir well. Pour the solution into the mold. The solution gels and solidifies under the action of the initiator and catalyst. Then demold.

[0124] Drying: Place the shaped wet blank into a forced-air drying oven and dry it using a gradient temperature increase. First, dry at 40℃ for 12 hours, then increase the temperature to 60℃ for 12 hours, and finally increase the temperature to 80℃ for 6 hours to ensure that the blank is completely dry.

[0125] Degreasing: The dried green body is placed in a high-temperature muffle furnace and heated from room temperature to 250°C at a rate of 0.5°C / min and held for 1 hour; then heated to 400°C at a rate of 0.5°C / min and held for 2 hours; then heated to 600°C at a rate of 1°C / min and held for 2 hours, so that the organic matter and pore-forming agent in the green body can be fully decomposed and volatilized.

[0126] Low-temperature sintering: After degreasing, the temperature is raised to 850℃ at a heating rate of 3℃ / min and held for 2 hours to promote the initial densification of the green body.

[0127] High-temperature sintering: Continue to raise the temperature to 1150℃ at a heating rate of 3℃ / min, and hold at this temperature for 5 hours to allow La to sinter. 0.7 Sr 0.3 MnO3 undergoes a complete solid-state reaction, forming a stable crystal structure. After sintering, it is naturally cooled to room temperature in the furnace to obtain La. 0.7 Sr 0.3 MnO3 heating element.

[0128] Comparative Example 2

[0129] The specific steps for preparing the porous LSMO heating element using the aforementioned raw materials are as follows:

[0130] According to La 0.7 Sr 0.3 To determine the stoichiometric ratio of MnO3, weigh 7.001g of lanthanum nitrate. The remaining strontium nitrate and manganese nitrate hexahydrate should be weighed in a mass ratio of 0.7:0.3:1 to ensure that the molar ratio of La, Sr, and Mn is 0.7:0.3:1. Then, pour the lanthanum nitrate, strontium nitrate, and manganese nitrate hexahydrate into a beaker, add 40mL of deionized water, place the beaker on a magnetic stirrer, and stir at 300r / min until the metal nitrates are completely dissolved to form a uniform and transparent metal salt solution.

[0131] Weigh 13.31g of citric acid and add it to the metal salt solution. Stir continuously for 2 hours in a 60℃ water bath to form a stable complex sol.

[0132] Weigh 1.5g of PVA powder into 50mL of deionized water, heat in an 85℃ water bath while stirring to dissolve, and obtain a PVA solution.

[0133] The PVA solution was slowly added to the complexed sol and stirred until homogeneous to obtain a mixed solution.

[0134] PMMA microspheres were selected as the pore-forming agent. The particle size D50 of the PMMA microspheres was 5.0 μm. Without drying, 3g of the pore-forming agent was slowly added to the above mixed solution and dispersed by ball milling using a planetary ball mill with zirconia grinding balls. The ball milling speed was 300 r / min and the ball milling time was 4 hours to obtain a uniform and stable precursor solution.

[0135] The prepared precursor solution was ultrasonically defoamed for 10 minutes at a power of 100W to obtain a pretreated precursor solution.

[0136] Gel injection molding: Add 11.04g acrylamide and 0.88g N,N'-methylenebisacrylamide to the pretreated precursor solution. Dissolve 0.88g ammonium persulfate in 5mL of deionized water and add it to the solution. Stir well. Then immediately add 20μL tetramethylethylenediamine and stir well. Pour the solution into the mold. The solution gels and solidifies under the action of the initiator and catalyst. Then demold.

[0137] Drying: Place the shaped wet blank into a forced-air drying oven and dry it using a gradient temperature increase. First, dry at 40℃ for 12 hours, then increase the temperature to 60℃ for 12 hours, and finally increase the temperature to 80℃ for 6 hours to ensure that the blank is completely dry.

[0138] Degreasing: The dried green body is placed in a high-temperature muffle furnace and heated from room temperature to 250°C at a rate of 0.5°C / min and held for 1 hour; then heated to 400°C at a rate of 0.5°C / min and held for 2 hours; then heated to 600°C at a rate of 1°C / min and held for 2 hours, so that the organic matter and pore-forming agent in the green body can be fully decomposed and volatilized.

[0139] Low-temperature sintering: After degreasing, the temperature is raised to 850℃ at a heating rate of 3℃ / min and held for 2 hours to promote the initial densification of the green body.

[0140] High-temperature sintering: Continue to raise the temperature to 1150℃ at a heating rate of 3℃ / min, and hold at this temperature for 5 hours to allow La to sinter. 0.7 Sr 0.3 MnO3 undergoes a complete solid-state reaction, forming a stable crystal structure. After sintering, it is naturally cooled to room temperature in the furnace to obtain porous La. 0.7 Sr 0.3 MnO3 heating element.

[0141] The heating elements prepared in Examples 1-5 and Comparative Examples 1-2 were tested, and the results are as follows:

[0142] Example 1: Porosity 42.1%, resistivity 1.2 × 10⁻⁶ -2 Ω·cm, the time to heat to 200℃ is 21s.

[0143] Example 2: Porosity 45.6%, resistivity 9.1 × 10⁻⁶ -3 Ω·cm, the time to heat to 200℃ is 18s.

[0144] Example 3: Porosity 43.9%, resistivity 9.6 × 10⁻⁶ -3 Ω·cm, the time to heat to 200℃ is 19s.

[0145] Example 4: Porosity 47.2%, resistivity 8.4 × 10⁻⁶ -3 Ω·cm, the time to heat to 200℃ is 17s.

[0146] Example 5: Porosity 46.3%, resistivity 8.7 × 10⁻⁶ -3 Ω·cm, the time to heat to 200℃ is 17s.

[0147] Comparative Example 1: Porosity 25.4%, resistivity 3.2 × 10⁻⁶ -2 The temperature was measured in Ω·cm, and the time to heat to 200℃ was 39s.

[0148] Comparative Example 2: Porosity 31.5%, resistivity 2.6 × 10⁻⁶ -2Ω·cm, the time to heat to 200℃ is 34s.

[0149] in,

[0150] The porosity was tested using the Archimedes method. All heating element samples were polished into cylindrical shapes with dimensions of φ10mm × 2mm.

[0151] The resistivity was measured using the four-probe method.

[0152] The heating response test involves taking a heating element sample (φ10mm×2mm) and applying silver paste to both electrodes; applying a constant voltage; contacting the center point with a thermocouple; and recording the heating time from 0 to 200℃, i.e., recording the time required to reach 200℃ as the response time index.

[0153] analyze:

[0154] Compared to Comparative Example 1, Example 1 incorporated a pore-forming agent. After adding PMMA, the porosity increased from 25.4% to 42.1%. Although the porous structure may introduce more grain boundary scattering, the resistivity increased from 3.2 × 10⁻⁶. -2 Ω·cm decreased to 1.2×10 -2 Ω·cm. The porous structure optimizes the conductivity pathway of LSMO by altering sintering kinetics, grain growth, or stress state. The heating time was reduced from 39 s to 21 s, demonstrating the positive impact of the porous structure on rapid electrothermal conversion energy.

[0155] Compared to Examples 1, Examples 2-5 were doped with quantum dots, and the resistivity of Examples 2-5 was lower than that of Example 1. The heating time was also correspondingly shorter, which proves that the introduction of trace amounts of two-dimensional material quantum dots can effectively improve the conductivity and heating response speed of LSMO ceramics.

[0156] Compared to Examples 2 and 3, and Examples 4 and 5, Examples 2 and 4 both incorporated APTES for modification. Example 2 exhibited lower resistivity and faster heating than Example 3. Example 4 showed lower resistivity than Example 5, with a similar heating rate. This demonstrates that in the present invention, APTES surface treatment helps quantum dots achieve superior technical performance.

[0157] Compared to Example 2, Example 4 used different quantum dots. The resistivity of Example 4 was lower than that of Example 2, and the heating time of Example 4 was shorter than that of Example 2. This indicates that after modification with APTES, WS2 quantum dots exhibited superior electrical conductivity and thermal properties compared to MoS2 quantum dots.

[0158] Compared to Example 5, Example 3 used different quantum dots, and the resistivity of Example 5 was lower than that of Example 3. Both examples had the same heating time. Without surface modification, the doping effect of WS2 quantum dots was slightly better than that of MoS2 quantum dots, although the heating rates were essentially the same.

[0159] Compared to Example 1, Comparative Example 2 did not have the pore-forming agent dried, and its porosity was lower than that of Example 1, demonstrating that moisture affects pore formation. The resistivity and heating time of Comparative Example 2 were also worse than those of Example 1, proving the effectiveness of the pore-forming agent drying process.

[0160] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0161] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

[0162] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a porous LSMO heating element, characterized in that, Includes the following steps: Metal salt solutions are prepared using metal salts and solvents; citric acid is added to the metal salt solutions and stirred to obtain complexed sols; PVA solutions are added to the complexed sols, and quantum dot dispersions are added or not, and stirred to obtain mixed solutions; The pore-forming agent was added to the mixed solution and dispersed by ball milling to obtain the precursor solution; After degassing the precursor solution, monomers, crosslinking agents, initiators, and catalysts are added, followed by injection molding, drying, degreasing, low-temperature sintering, and high-temperature sintering to obtain a porous LSMO heating element. Wherein, LSMO is La 0.7 Sr 0.3 MnO3; The pore-forming agent should be dried before being added. Low-temperature sintering includes the following steps: after degreasing, the temperature is raised to 800-900℃ at a heating rate of 2-4℃ / min, and held for 1-3 hours; The high-temperature sintering process includes the following steps: after low-temperature sintering, the temperature is raised to 1000-1200℃ at a rate of 2-4℃ / min, and held at this temperature for 3-7 hours. After sintering, the furnace is allowed to cool naturally to room temperature to obtain a porous LSMO heating element.

2. The method for preparing the porous LSMO heating element according to claim 1, characterized in that, The monomers include acrylamide, the crosslinking agent includes N,N'-methylenebisacrylamide, the initiator includes ammonium persulfate, the catalyst includes tetramethylethylenediamine, and the solvent includes deionized water.

3. The method for preparing the porous LSMO heating element according to claim 1, characterized in that, Pore-forming agents include one or more of the following: toner, starch, and PMMA microspheres.

4. The method for preparing the porous LSMO heating element according to claim 1, characterized in that, Quantum dot dispersions include one or more of MoS2 quantum dot dispersions, WS2 quantum dot dispersions, modified MoS2 quantum dot dispersions, and modified WS2 quantum dot dispersions.

5. The method for preparing the porous LSMO heating element according to claim 4, characterized in that, The preparation steps of the modified MoS2 quantum dot dispersion include: adding APTES to the MoS2 quantum dot dispersion, adjusting the pH, stirring, centrifuging, discarding the supernatant, redispersing, and obtaining the quantum dot dispersion. The preparation steps of the modified WS2 quantum dot dispersion include: adding APTES to the WS2 quantum dot dispersion, adjusting the pH, stirring, centrifuging, discarding the supernatant, redispersing, and obtaining the quantum dot dispersion.

6. The method for preparing the porous LSMO heating element according to claim 1, characterized in that, The drying process includes the following steps: placing the injection-molded wet blank into a forced-air drying oven and using a gradient temperature increase for drying. First, dry at 20-60℃ for 10-14 hours, then increase the temperature to 40-80℃ for 10-14 hours, and finally increase the temperature to 60-100℃ for 4-8 hours.

7. The method for preparing the porous LSMO heating element according to claim 1, characterized in that, The degreasing process includes the following steps: placing the dried blank into a high-temperature muffle furnace, raising the temperature from room temperature to 200-300℃ at a rate of 0.2-1℃ / min, and holding it at that temperature for 0.5-2 hours; raising the temperature to 200-600℃ at a rate of 0.2-1℃ / min, and holding it at that temperature for 1-3 hours; raising the temperature to 400-800℃ at a rate of 0.5-1.5℃ / min, and holding it at that temperature for 1-3 hours.

8. The method for preparing the porous LSMO heating element according to claim 1, characterized in that, The metal salts include lanthanum nitrate, strontium nitrate, and manganese nitrate hexahydrate; the amount of pore-forming agent added is 10%-30% of the total mass of the metal salts.