Method for preparing sheet-shaped heating body

Abstract

The invention belongs to the technical field of heating bodies, and particularly relates to a method for preparing a sheet-shaped heating body. The preparation method comprises the following steps: stirring and dissolving lanthanum nitrate, strontium nitrate, manganese nitrate hexahydrate and a solvent to obtain a metal salt solution; preparing the metal salt solution into a precursor, wherein the precursor is a precursor solution or precursor sol; and carrying out tape casting and drying on the precursor to obtain a biscuit sheet, and carrying out glue removal treatment and sintering on the biscuit sheet to obtain the sheet-shaped heating body. According to the preparation method, a precursor system is optimized, the dispersion stability of the precursor is improved, casting, drying and sintering processes are matched, the problem of powder agglomeration is solved, the defects of green bodies are reduced, the drying shrinkage rate of green body pieces in the preparation process is reduced, the surface roughness is reduced, the stability and heat output uniformity of a heating body are improved, and the compactness is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of heating bodies, and particularly relates to a method for preparing a sheet-shaped heating body. BACKGROUND

[0002] Traditional slurries are usually used to form heating bodies by means of doctor-blade coating or tabletting in combination with a drying or sintering process. However, the heating bodies formed in this way are prone to thickness fluctuation, local stress concentration, drying cracks or incomplete film formation, and in severe cases, the stability and thermal output uniformity of the heating body are affected.

[0003] Subsequently, tape casting technology emerged. The advantage of tape casting technology is that it is very suitable for the preparation of large thin ceramic parts. However, the disadvantages of tape casting are that powder agglomeration, green body defects (cracking, uneven thickness, etc.) and low product density are prone to occur during the preparation process. SUMMARY

[0004] The purpose of the present application is to provide a method for preparing a sheet-shaped heating body.

[0005] The above-mentioned purpose of the present application is achieved by adopting the following technical solutions: The method for preparing a sheet-shaped heating body comprises the following steps: Dissolve lanthanum nitrate, strontium nitrate, manganese nitrate hexahydrate and a solvent by stirring to obtain a metal salt solution; Prepare the metal salt solution into a precursor, wherein the precursor is a precursor solution or a precursor sol; Tape cast the precursor, dry to obtain a green body sheet, perform degassing treatment on the green body sheet, and sinter to obtain a sheet-shaped heating body.

[0006] According to an aspect of the present application, the method for preparing the precursor solution comprises the following steps: Add polyvinyl butyral solution and dibutyl phthalate to the metal salt solution, stir, adjust the solid content and viscosity, and remove impurities to obtain the precursor solution.

[0007] It should be noted that the traditional method uses pre-synthesized powder as raw material. The present application uses a metal salt solution as the starting raw material to solve the problem of powder agglomeration.

[0008] According to an aspect of the present application, the method for preparing the precursor sol comprises the following steps: Heat the metal salt solution to 80-90℃, add citric acid, stir, then add ethylene glycol, continue to react, cool after the reaction is completed, and obtain the sol; Ultrasonic the solvent and hexagonal boron nitride, stir, react, and obtain a suspension; Add the suspension into the sol while stirring, disperse, and obtain a mixed sol; The low-melting glass micro powder is added to the mixed sol, stirred, the polyvinyl butyral solution is added, the dibutyl phthalate is added, the solid content and the viscosity are adjusted, impurities are removed, and vacuum defoaming is performed to obtain a precursor sol.

[0009] It should be noted that, by adopting the technical scheme, the metal salt is chelated to obtain a metal-citric acid complex, under heating conditions, the carboxyl group on the citric acid reacts with the hydroxyl group on the ethylene glycol to form a long chain of “citric acid-ethylene glycol-citric acid” polymer, and the metal complex formed before is used as a crosslinking point, and finally a three-dimensional and elastic polymer gel network is formed, which fixes the metal ions at their respective positions.

[0010] The hexagonal boron nitride in the suspension exists in a monodisperse or few-layer state, avoiding agglomeration in the later stage, the hexagonal boron nitride is added to the sol, which can improve the thermal conductivity of the finished product and avoid local overheating of the heating body. It can also inhibit excessive shrinkage and deformation during sintering of the green sheet.

[0011] The low-melting glass micro powder is added before the polyvinyl butyral solution is added, that is, the low-melting glass micro powder is added after the gel network is formed and before the organic reagent is added, so that: the low-melting glass micro powder can be partially wrapped or adsorbed by the gel network, achieving initial uniform distribution, avoiding competitive adsorption or entanglement with the polymer chains of polyvinyl butyral, and affecting the subsequent casting performance.

[0012] In some embodiments, the solid content is 35-45 wt%, and the viscosity at room temperature is 500-1500 mPa·s.

[0013] In some embodiments, the solvent is obtained by mixing ethanol, ethylene glycol methyl ether, glacial acetic acid and deionized water.

[0014] In some embodiments, the precursor is cast into a shape, including the following steps: The height of the doctor blade of the casting machine is set to 250-300 μm, the precursor is poured into the hopper of the casting machine, the casting machine is started, and the base band moves at a speed of 2-3 cm / min, while the flow rate of the hopper is controlled to make the precursor uniformly coated on the base band to form a continuous wet film. During the casting process, the environmental temperature is maintained at 23-27℃, and the relative humidity is 40%-50%.

[0015] In some embodiments, the drying includes the following steps: The wet film after casting is dried together with the base band, dried at 35-45℃ for 2-3h, then heated to 55-65℃, dried for 4-6h, and finally heated to 75-85℃, dried for 1-2h. After drying is completed, the dried wet film is peeled off from the base band to obtain a green sheet.

[0016] It should be noted that the drying process adopts the gradient heating mode: 35-45℃ to preliminarily dry the wet film surface; 55-65℃ to further remove the solvent; and 75-85℃ to completely dry the wet film.

[0017] In some embodiments, the green sheet degassing treatment comprises the following steps: The green sheet is placed in the furnace, and the temperature is raised from room temperature to 550-650℃ at a rate of 1-2℃ / min, and the degassing process is completed after holding for 2-3h.

[0018] In some embodiments, the sintering comprises the following steps: After the degassing is completed, the temperature is continuously raised at a rate of 3-5℃ / min in the atmosphere, and the sheet-shaped heating body is obtained after holding for 4-6h and cooling after the reaction.

[0019] It should be noted that, during the sintering holding, the green sheet undergoes a solid phase reaction to form a dense crystal structure.

[0020] According to an aspect of the present application, when the precursor is a precursor solution, the sintering atmosphere is air, and the temperature is raised to 1200-1250℃.

[0021] According to an aspect of the present application, when the precursor is a precursor sol, the sintering atmosphere is nitrogen, and the temperature is raised to 1075-1125℃.

[0022] It should be noted that, when the precursor is a precursor sol, the addition of low-melting glass powder can improve the densification degree of sintering in cooperation with hexagonal boron nitride. The chemical inertness of hexagonal boron nitride makes the interface energy between it and the LSMO matrix high, which is theoretically not conducive to sintering, but the present application adds low-melting glass powder. The molten glass phase can preferentially wet the surface of hexagonal boron nitride and fill the interface between hexagonal boron nitride and LSMO, which on the one hand solves the interface bonding problem, and on the other hand promotes material transport through the liquid phase sintering mechanism, achieving high densification of the material at a lower sintering temperature. Moreover, sintering in a low-temperature nitrogen atmosphere can also form more oxygen vacancies, which is conducive to the improvement of electrical conductivity and thermal conductivity.

[0023] Compared with the prior art, the present application has the following advantages: 1. Different from the prior art which uses La 0.7 Sr 0.3 MnO3 pre-synthesized powder as raw material, the present application directly dissolves metal salt in solvent to prepare a metal salt solution, which is used as a starting raw material, solving the problem of easy agglomeration of powder.

[0024] The precursor defect is reduced, the stability is improved, after the flow casting, the green body drying shrinkage is also reduced, the surface roughness is reduced, so that the green body internal stress is reduced, not easy to crack, warping. Because the precursor uniformity is good, the sintering activity is high, the final obtained heating body is more dense, the defect is less, the internal efficient electron conduction path is formed, the surface resistance is reduced.

[0025] 2, when the precursor is a precursor solution, the metal salt solution is mixed with the organic carrier to form a molecular level and uniform precursor, and then through flow casting and sintering, the dense heating body is realized by in-situ reaction synthesis. This method is more uniform than directly using pre-synthesized powder (such as comparative example 1), which proves that flow casting does not necessarily use powder slurry, and using molecular level precursor solution is also feasible, and the effect is better.

[0026] 3, when the precursor is a precursor sol, the two-dimensional sheet-shaped hexagonal boron nitride tends to be oriented and arranged parallel to the flow casting base band direction under the action of shear force and interfacial energy in the flow casting process, thereby causing the in-plane orientation. The hexagonal boron nitride is limited at the grain boundary of the LSMO crystal grain. However, the hexagonal boron nitride will not directly contact with the LSMO, because the molten low-melting glass phase will wet the surface of the hexagonal boron nitride, and then wrap the hexagonal boron nitride. At the same time, this layer of glass phase will also combine with the surrounding LSMO crystal grains. In this way, a three-phase interface structure of LSMO crystal grain, glass phase and hexagonal boron nitride is formed. The glass phase becomes a "bridge" between the hexagonal boron nitride and the LSMO matrix, solving the problem of poor bonding caused by chemical incompatibility.

[0027] In addition, because the hexagonal boron nitride is distributed at the grain boundary, it will pin the grain boundary, prevent the grain boundary migration, and inhibit the abnormal growth of the LSMO crystal grain at high temperature. Therefore, a finer and more uniform LSMO crystal grain structure can be obtained. The fine crystal structure can reduce the resistance of the material. DETAILED DESCRIPTION

[0028] In order to facilitate the understanding of the present application, the present application will be described more fully below, and the preferred embodiments of the present application will be given. However, the present application can be realized in many different forms, and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0030] The equipment and materials used in the examples can be easily obtained from commercial companies if not specifically stated.

[0031] The raw materials, equipment, etc. involved in the present application are as follows: (I) Raw materials Lanthanum nitrate: purity ≥ 99.0% Strontium nitrate: purity ≥ 99.0% Manganese nitrate hexahydrate: purity ≥ 98.0% Ethylene glycol methyl ether: purity ≥ 99.5% Polyvinyl butyral: PVB, degree of polymerization about 1500 Dibutyl phthalate: DBP, purity ≥ 99.0% Ethanol: purity ≥ 99.7% Glacial acetic acid: purity ≥ 99.5% Hexagonal boron nitride: D50 < 1 μm, purity ≥ 99.0% Low-melting glass micro powder: low-melting glass powder, melting temperature 500°C, D50 < 2 μm La 0.7 Sr 0.3 MnO3 pre-synthesized powder: purity ≥ 99.5%, D50 < 1 μm, specific surface area (BET) 5 m 2 / g.

[0032] (II) Equipment preparation Cast machine: clean the base band, doctor blade and other components of the cast machine with ethanol and deionized water in turn, then wipe dry with clean dust-free cloth to ensure that there is no impurity residue on the surface of the equipment. Install the cleaned base band on the cast machine and adjust the tension of the base band to make it flat and the tension moderate. Adjust the distance between the cast machine doctor blade and the base band according to the thickness requirement of the sheet-shaped heating body to be prepared.

[0033] (III) Reagent preparation Prepare the solvent by mixing ethanol, ethylene glycol methyl ether, glacial acetic acid and deionized water, and the volume ratio of ethanol, ethylene glycol methyl ether, glacial acetic acid and deionized water is 7:3:1:0.2.

[0034] Example 1 Prepare the metal salt solution, the specific steps are as follows: According to the chemical formula La 0.7 Sr 0.3The stoichiometric ratio of MnO3 was used to weigh the metal nitrate by an electronic balance, so that the amount-of-substance ratio of La, Sr, and Mn was 0.7:0.3:1. Specifically, 3.031 g of lanthanum nitrate, 0.635 g of strontium nitrate, and 2.870 g of manganese nitrate hexahydrate were weighed into a beaker, and 13 mL of solvent was added. The magnetic stirrer was stirred at a speed of 300-400 r / min until the metal nitrate was completely dissolved, forming a uniform metal salt solution.

[0035] Example 2 The precursor solution was prepared according to the following specific steps: 0.419 g of polyvinyl butyral was first dissolved in 5 mL of a mixture of ethanol and glacial acetic acid to obtain a polyvinyl butyral solution. The volume ratio of ethanol to glacial acetic acid was 7:1.

[0036] The polyvinyl butyral solution was added to the metal salt solution of Example 1, 0.209 g of dibutyl phthalate was added, and stirred for 10-15 min. The solvent was added to adjust the solid content to 40 wt%, the target viscosity at room temperature was 500-1500 mPa·s, and the centrifugal speed was 4000-5000 r / min for 10-15 min. The supernatant was taken, ultrasonic was performed for 30-45 min, and the impurity-removed precursor solution was obtained.

[0037] Example 3 The precursor sol was prepared according to the following specific steps: The metal salt solution of Example 1 was heated to 80-90℃, 17.29 g of citric acid was added, and stirred for 30-60 min. Then 5.59 g of ethylene glycol was added at 80-90℃, and the reaction was continued for 30-60 min. After the reaction was completed, the solution was naturally cooled to room temperature to obtain the sol.

[0038] In another beaker, 4 mL of solvent was added, and 0.034 g of hexagonal boron nitride was added. Ultrasonic was performed for 10-15 min, and the solution was stirred at room temperature for 30 min and then heated to 40-50℃. The solution was kept at a constant temperature for 60-90 min to obtain the suspension.

[0039] The suspension was added to the sol while stirring, and ultrasonic was performed for 15-30 min to obtain the mixed sol.

[0040] 0.419 g of polyvinyl butyral was first dissolved in 5 mL of a mixture of ethanol and glacial acetic acid to obtain a polyvinyl butyral solution. The volume ratio of ethanol to glacial acetic acid was 7:1.

[0041] To the mixed sol, 0.016 g of low-melting glass micro powder was added, stirred for 10 min, a polyvinyl butyral solution was added, 0.209 g of dibutyl phthalate was added, stirred for 10-15 min, solvent was supplemented, the solid content was adjusted to 40 wt%, the target viscosity at room temperature was 500-1500 mPa·s, centrifugation was performed at 4000-5000 r / min for 10-15 min, filtration was performed, and vacuum degassing was performed for 10-20 min to obtain a doped precursor sol.

[0042] Example 4 The green sheet was prepared according to the following specific steps: The doctor blade height of the casting machine was set to 200 μm, the doped precursor sol of Example 2 was slowly poured into the hopper of the casting machine, the casting machine was started, the base strip was moved at a speed of 2-3 cm / min, and the flow rate of the hopper was controlled to uniformly coat the doped precursor sol on the base strip to form a continuous wet film. During the casting process, the environmental temperature was maintained at 23-27℃, and the relative humidity was 40%-50%.

[0043] The wet film after casting was placed in a blast drying oven together with the base strip for drying. The drying process adopted a gradient heating mode: first, drying at 40℃ for 2-3 h to preliminarily dry the surface of the wet film; then, heating to 60℃ for 4-6 h to further remove the solvent; finally, heating to 80℃ for 1-2 h to completely dry the green sheet. After drying, the green sheet was carefully peeled off from the base strip to obtain the green sheet.

[0044] Example 5 The green sheet was prepared according to the following specific steps: The doctor blade height of the casting machine was set to 200 μm, the doped precursor sol of Example 3 was slowly poured into the hopper of the casting machine, the casting machine was started, the base strip was moved at a speed of 2-3 cm / min, and the flow rate of the hopper was controlled to uniformly coat the doped precursor sol on the base strip to form a continuous wet film. During the casting process, the environmental temperature was maintained at 23-27℃, and the relative humidity was 40%-50%.

[0045] The wet film after casting was placed in a blast drying oven together with the base strip for drying. The drying process adopted a gradient heating mode: first, drying at 40℃ for 2-3 h to preliminarily dry the surface of the wet film; then, heating to 60℃ for 4-6 h to further remove the solvent; finally, heating to 80℃ for 1-2 h to completely dry the green sheet. After drying, the green sheet was carefully peeled off from the base strip to obtain the green sheet.

[0046] Example 6 The sheet-shaped heating body was prepared according to the following specific steps: Glue removal treatment: Put the green sheet of Example 4 into a high-temperature muffle furnace, and raise the temperature from room temperature to 600℃ at a rate of 1-2℃ / min, and keep the temperature at 600℃ for 2-3h, so that the organic matter in the green sheet is fully decomposed and volatilized, and the glue removal process is completed. High-temperature sintering: After the glue removal is completed, continue to raise the temperature to 1200℃ at a rate of 3-5℃ / min in an air atmosphere, keep the temperature at 1200℃ for 4-6h, and then naturally cool to room temperature to obtain a sheet-shaped heating body.

[0047] Example 7 Prepare a sheet-shaped heating body, and the specific steps are as follows: Glue removal treatment: Put the green sheet of Example 5 into a high-temperature muffle furnace, and raise the temperature from room temperature to 600℃ at a rate of 1-2℃ / min, and keep the temperature at 600℃ for 2-3h, so that the organic matter in the green sheet is fully decomposed and volatilized, and the glue removal process is completed. High-temperature sintering: After the glue removal is completed, continue to raise the temperature to 1125℃ at a rate of 3-5℃ / min in a nitrogen atmosphere, keep the temperature at 1125℃ for 3-5h, and then naturally cool to room temperature to obtain a sheet-shaped heating body.

[0048] Comparative Example 1 In a beaker, add 13mL of solvent, add 0.419g of polyvinyl butyral and 0.209g of dibutyl phthalate, and stir with a magnetic stirrer at a speed of 300-400r / min until the mixture is completely dissolved to form an organic carrier solution.

[0049] In the organic carrier solution, add 4.5g of La 0.7 Sr 0.3 MnO3pre-synthesized powder, mechanically stir for 2-4h to obtain a slurry, adjust the solid content to 40wt%, the target viscosity at room temperature is 500-1500mPa·s, centrifuge at 4000-5000r / min for 10-15min to remove impurities, and obtain a doped precursor slurry.

[0050] Set the height of the doctor blade of the casting machine to 200μm, slowly pour the doped precursor slurry into the hopper of the casting machine, start the casting machine, and move the base belt at a constant speed of 2-3cm / min, while controlling the flow rate of the hopper, so that the doped precursor slurry is uniformly coated on the base belt to form a continuous wet film. During the casting process, the ambient temperature is kept at 23-27℃, and the relative humidity is kept at 40%-50%.

[0051] The wet film after casting is dried together with the base tape in a blast drying oven. The drying process adopts a gradient heating mode: first, drying at 40℃ for 2-3h; then heating to 60℃, drying for 4-6h; finally, heating to 80℃, drying for 1-2h. After drying, the green sheet is carefully peeled off from the base tape to obtain the green sheet.

[0052] Glue removal treatment: the green sheet is placed in a high-temperature muffle furnace, and the temperature is raised from room temperature to 600℃ at a rate of 1-2℃ / min, and the glue removal process is completed at 600℃ for 2-3h. High-temperature sintering: after the glue removal is completed, the temperature is continuously raised to 1200℃ at a rate of 3-5℃ / min in an air atmosphere, and the temperature is kept at 1200℃ for 4-6h, and then naturally cooled to room temperature to obtain a sheet-shaped heating body.

[0053] The metal salt solution is prepared in Example 1.

[0054] The metal salt solution is prepared into a precursor, and the precursor has two forms: a precursor solution (Example 2) and a precursor sol (Example 3).

[0055] The precursor is then cast and dried (Examples 4 and 5) and sintered (Examples 6 and 7) to obtain a sheet-shaped heating body.

[0056] In Comparative Example 1, commercially available La 0.7 Sr 0.3 MnO3 powder is directly used as a raw material to prepare a sheet-shaped heating body.

[0057] The precursors prepared in Examples 2 and 3 and Comparative Example 1 are detected, and the results are as follows: The room temperature viscosity of Example 2 is 980mPa·s, the pH value is 5.8, and the Zeta potential is -27.4mV; The room temperature viscosity of Example 3 is 1130mPa·s, the pH value is 6.1, and the Zeta potential is -33.2mV.

[0058] The room temperature viscosity of the precursor slurry in Comparative Example 1 is 1400mPa·s, the pH value is 6.3, and the Zeta potential is -10mV.

[0059] The green sheets prepared in Examples 4 and 5 and Comparative Example 1 are sampled, the thickness of the sample is controlled to be 100μm, the side length is 20mm, and the sample is detected, and the results are as follows: The drying shrinkage of Example 4 is 8.6%, and the surface roughness Ra is 1.8μm; The drying shrinkage of Example 5 is 7.2%, and the surface roughness Ra is 1.3μm; The drying shrinkage of the green sheet in Comparative Example 1 was 12.2%, and the surface roughness Ra was 3.5 μm.

[0060] The sheet-shaped heat generating bodies prepared in Example 6 and Example 7 and Comparative Example 1 were tested, and the results were as follows: The surface resistance of the sheet-shaped heat generating body in Example 6 was 72.4 Ω·sq -1 , and the thermal conductivity was 2.4 W / m·K. The surface resistance of the sheet-shaped heat generating body in Example 7 was 61.7 Ω·sq -1 , and the thermal conductivity was 3.1 W / m·K. The surface resistance of the sheet-shaped heat generating body in Comparative Example 1 was 108.5 Ω·sq -1 , and the thermal conductivity was 1.6 W / m·K.

[0061] Analysis: Regarding the precursor: (1) Zeta potential: the absolute value of the Zeta potential of Example 2 and Example 3 was higher than that of Comparative Example 1, indicating that the precursor of Example 2 and Example 3 was not easy to agglomerate and had better dispersion stability. Compared with Example 2 and Example 3, the colloid of Example 3 showed better stability. (2) Viscosity at room temperature: the viscosity of Comparative Example 1 was higher than that of Example 2 and Example 3. The precursor slurry of Comparative Example 1 may have uneven particle dispersion and agglomerates, resulting in increased viscosity and subsequent poor casting uniformity.

[0062] Regarding the green sheet: compared with Comparative Example 1, the shrinkage of Example 4 and Example 5 was lower, and the surface was smoother, indicating that the precursor dispersion of Example 4 and Example 5 was better, which could reduce particle agglomeration and stress concentration during the preparation of the green sheet.

[0063] Regarding the sheet-shaped heat generating body: compared with Comparative Example 1, the resistance of Example 6 and Example 7 was lower, indicating that the precursor in Example 6 and Example 7 was more uniform, had better crystallinity, and the structure of the sheet-shaped heat generating body was more compact. The powder of Comparative Example 1 agglomerated and sintered not densely enough, resulting in high resistance and low thermal conductivity of the finished product.

[0064] Example 2, Example 4, and Example 6: The metal salt was directly dissolved in the solvent and mixed with the organic carrier to form a molecular-level mixed solution. During the subsequent drying and sintering process, the metal salt decomposed and reacted to form the target product. This method was more uniform than directly using pre-synthesized powder (Comparative Example 1), proving that tape casting does not necessarily have to use powder slurry, and using a molecular-level precursor solution is also feasible and has better results.

[0065] Example 3, Example 5, Example 7: Fine and uniform LSMO grains are firmly combined together through an extremely thin glass phase grain boundary layer. At the same time, hexagonal boron nitride is inlaid at the grain boundary intersection, and its surface is wetted and wrapped by a layer of glass phase, thereby forming a high-efficiency heat conduction network with the LSMO grains.

[0066] By comparing between examples, it can be further known that: Example 3, Example 5, Example 7: Compared with Example 2, Example 4, Example 6, the performance is further improved, the precursor sol makes the site material uniformity higher, the solid phase reaction path is shortened, the grain boundary defect is reduced, and thus a higher densification degree is realized at a lower temperature.

[0067] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or make equivalent replacements to some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a sheet heating element, characterized in that: The steps include: Lanthanum nitrate, strontium nitrate, manganese nitrate hexahydrate and a solvent are stirred and dissolved to obtain a metal salt solution; preparing a metal salt solution into a precursor, wherein the precursor is a precursor solution or a precursor sol; The precursor is tape-casted and dried to obtain a green sheet, which is then subjected to a binder removal process and sintered to obtain a sheet-like heating element.

2. The method for preparing a sheet heating element according to claim 1, wherein: The preparation method of the precursor solution comprises the following steps: Adding polyvinyl butyral solution to the metal salt solution, adding dibutyl phthalate, stirring, adjusting the solid content and viscosity, and removing impurities to obtain a precursor solution.

3. The method for preparing a sheet heating element according to claim 1, wherein: The preparation method of the precursor sol comprises the following steps: The metal salt solution is heated to 80-90°C, citric acid is added, stirred, and then ethylene glycol is added and the reaction is continued. After the reaction is completed, the solution is cooled to obtain a sol; The solvent and hexagonal boron nitride are ultrasonically treated, stirred, and reacted to obtain a suspension; adding the suspension to the sol while stirring and dispersing to obtain a mixed sol; Add low-melting glass powder to the mixed sol, stir, add polyvinyl butyral solution, add dibutyl phthalate, stir, adjust solid content and viscosity, remove impurities, and vacuum degas to obtain a precursor sol.

4. The method for preparing a sheet heating element according to claim 1, wherein: The solvent is obtained by mixing ethanol, ethylene glycol methyl ether, glacial acetic acid and deionized water.

5. The method for preparing a sheet heating element according to claim 1, wherein: The precursor is tape-casted and includes the following steps: Set the scraper height of the casting machine to 250-300μm, pour the precursor into the hopper of the casting machine, start the casting machine, move the base belt at a constant speed of 2-3cm / min, and control the flow rate of the hopper at the same time so that the precursor is evenly coated on the base belt to form a continuous wet film. During the casting process, maintain the ambient temperature at 23-27℃ and the relative humidity at 40%-50%.

6. The method for preparing a sheet heating element according to claim 5, wherein: Drying includes the following steps: The wet film after tape casting is dried together with the base tape, dried at 35-45℃ for 2-3h, then heated to 55-65℃ and dried for 4-6h; finally heated to 75-85℃ and dried for 1-2h. After drying, the dried wet film is peeled off from the base tape to obtain a green sheet.

7. The method for preparing a sheet heating element according to claim 1, wherein: The debinding process for the green sheet includes the following steps: Place the green sheet in a furnace, heat it from room temperature to 550-650°C at a heating rate of 1-2°C / min, and keep it warm for 2-3 hours to complete the debinding process.

8. The method for preparing a sheet heating element according to claim 1, wherein: Sintering includes the following steps: After the debinding is completed, the temperature is continued to be raised at a rate of 3-5°C / min in the atmosphere, and the reaction is kept at this temperature for 4-6 hours. After the reaction, the reaction is cooled to obtain a sheet-like heating element.

9. The method for preparing a sheet heating element according to claim 8, wherein: When the precursor is a precursor solution, the sintering atmosphere is air and the temperature is raised to 1200-1250°C.

10. The method for preparing a sheet heating element according to claim 8, wherein: When the precursor is a precursor sol, the sintering atmosphere is nitrogen and the temperature is raised to 1075-1125°C.