Electric heater ceramic skeleton and preparation method thereof

Abstract

The invention discloses a ceramic skeleton of an electric heater, which comprises porcelain plates with heating holes and porcelain columns arranged in the heating holes of the two porcelain plates in a penetrating manner, and the porcelain plates and the porcelain columns are provided with Al2O3-based high heat conduction layers, porous ZrO2-based heat insulation layers and Si3N4-based surface radiation layers which are sequentially arranged from inside to outside; each heating hole comprises a heat-resisting sleeve hole and a buffer layer arranged between the heat-resisting sleeve and the hole wall of the porcelain plate, and the inner wall of the heat-resisting sleeve hole of each heating hole is provided with a continuous zigzag structure. By combining means such as material optimization, structural design and preparation process improvement, the thermal shock resistance of the ceramic framework of the electric heater can be effectively improved, and the problems of cracking, failure and the like under the high-temperature sudden change working condition are solved; the local overheating risk can be effectively reduced, the service life is prolonged, the equipment maintenance cost is reduced, and the device is suitable for popularization and application.

Description

Technical Field

[0001] This invention belongs to the field of electric heater technology, specifically relating to an electric heater ceramic skeleton material, structure, and preparation method. Background Technology

[0002] As the core supporting component of the heating element, the ceramic frame of the electric heater must withstand multiple effects such as thermal stress, mechanical load, and oxidation corrosion in a high-temperature environment for extended periods. Traditional ceramic frames mostly use a single alumina-based material, and their manufacturing process typically employs dry pressing combined with atmospheric pressure sintering, which has the following technical drawbacks: 1. Material performance limitations: Although conventional alumina ceramics (Al2O3 content > 95%) have good insulation properties, they have poor thermal shock resistance (thermal expansion coefficient approximately 8 × 10⁻⁶). -6 / ℃), which is prone to cracking or even fracture under rapid cooling and heating conditions; high-performance ceramics such as silicon carbide (SiC) are difficult to use on a large scale due to the difficulty of sintering and high cost; single-component materials cannot meet the requirements of high strength and thermal stability. 2. Structural design defects: The heating holes mostly adopt a simple round hole design, resulting in an excessively large contact area between the heating element and the ceramic body, and significant local thermal stress concentration; the edges of the ceramic skeleton lack effective protection, making them prone to chipping and cracking under mechanical or thermal shock; the homogeneous structure cannot achieve a gradient transition of the coefficient of thermal expansion, exacerbating interlayer stress; 3. Insufficient manufacturing process: Traditional dry pressing is difficult to prepare complex irregular parts and the density distribution of the blank is uneven; conventional sintering processes (such as single-step high-temperature sintering) are prone to abnormal grain growth, which reduces the density and mechanical properties of the material; lack of precise control over sintering atmosphere and heating rate affects the performance stability of the final product.

[0003] To address the aforementioned issues, existing technologies have attempted improvements through methods such as adding zirconia for toughening and incorporating metal edging. However, these methods still suffer from limited toughening effects, poor metal-ceramic interface bonding, and high process complexity. Therefore, there is an urgent need to develop a ceramic skeleton system for electric heaters that combines excellent thermal shock resistance, high mechanical strength, and long lifespan, achieving performance breakthroughs through synergistic innovation in material formulation, structural design, and manufacturing processes. Summary of the Invention

[0004] The main objective of this invention is to address the problems and shortcomings of traditional ceramic materials, such as easy cracking and fracture, difficulty in achieving both high toughness and high temperature resistance, and easy occurrence of thermal stress concentration and structural failure (high thermal stress at the heating hole contact surface, easy delamination of the metal-ceramic interface, and weak edge protection), and to provide a ceramic skeleton for an electric heater that has both good thermal shock resistance and long service life.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A ceramic frame for an electric heater includes a ceramic disc with heating holes and ceramic pillars interspersed in the heating holes of the two ceramic discs. The ceramic discs and ceramic pillars have an Al2O3-based high thermal conductivity layer, a porous ZrO2-based heat insulation layer, and a Si3N4-based surface radiation layer arranged sequentially from the inside to the outside. The heating holes include heat-resistant sleeves and a buffer layer disposed between the heat-resistant sleeves and the wall of the ceramic disc holes. The inner wall of the heat-resistant sleeves of the heating holes has a continuous serrated structure.

[0006] In the above scheme, the thickness ratio of the Al2O3-based high thermal conductivity layer (inner layer, mainly composed of Al2O3), the porous ZrO2-based heat insulation layer (middle layer, mainly composed of ZrO2), and the Si3N4-based surface radiation layer (outer layer, mainly composed of Si3N4) is (3-5):(2-3):1.

[0007] In the above scheme, the porous ZrO2-based heat insulation layer has a porosity of 50-70%, an average pore size of 10-30 μm, and a bulk density of ≤0.9 g / cm³. 3 .

[0008] In the above scheme, the amount of alumina, zirconium oxide and silicon nitride introduced into the ceramic plate and ceramic column accounts for 60-80% of the total mass of these three functional components, zirconium oxide 10-20% and silicon nitride 5-15%.

[0009] In the above scheme, sintering aids and carbon fiber reinforcements are further introduced into the Al2O3-based high thermal conductivity layer, the porous ZrO2-based thermal insulation layer, and the Si3N4-based surface radiation layer, respectively. The composite ceramic system enhances thermal shock resistance and mechanical strength, while carbon fiber enhances toughness. Alumina, as the main phase, provides insulation and high-temperature resistance; zirconium oxide improves thermal shock resistance through a phase transformation toughening mechanism; and silicon nitride enhances thermal conductivity and mechanical strength. The introduced sintering aids (SiO2-MgO-Y2O3) promote low-temperature densification and inhibit grain coarsening; the carbon fiber reinforcements (short-cut carbon fibers, preferably with a doping amount of 0.5-3%) improve brittleness and solve the problem of easy cracking in ceramics.

[0010] Furthermore, in the Al2O3-based high thermal conductivity layer, the porous ZrO2-based heat insulation layer, and the Si3N4-based surface radiation layer, the sintering aid is added at a rate of 2-5%, and the fiber reinforcement is added at a rate of 0.5-3%.

[0011] Furthermore, the ceramic disc and ceramic pillar materials of the present invention adopt a gradient structure with a high thermal conductivity layer (dense Al2O3) → thermal insulation layer (porous ZrO2) → surface radiation layer (Si3N4 coating) arranged sequentially from the inside to the outside, so as to achieve directional heat conduction and infrared radiation; improve heating efficiency and reduce surface temperature difference.

[0012] Furthermore, the surface of the Si3N4-based surface radiation layer is provided with a yttrium oxide-stabilized zirconia thermal barrier coating, with a coating thickness of 20-50 μm and a porosity of ≤2%.

[0013] Furthermore, in the Al2O3-based high thermal conductivity layer, the porous ZrO2-based thermal insulation layer, and the Si3N4-based surface radiation layer, the layers of two adjacent functional layers are interleaved using a wave-shaped structure (amplitude 0.1-0.3 mm) to achieve a gradient transition in the coefficient of thermal expansion and strengthen the interface.

[0014] In the above scheme, the sintering aid is composed of silicon dioxide, magnesium oxide and yttrium oxide in a mass ratio of (2-3):(0.9-1.1):1, wherein the silicon dioxide particle size is ≤1μm and the yttrium oxide purity is ≥99.9%.

[0015] In the above scheme, the fiber reinforcement is made of short-cut carbon fiber; its diameter is 7-15um and its length is 1-3mm.

[0016] In the above scheme, the heat-resistant sleeve hole is a heat-resistant steel sleeve hole (thickness 0.5-2mm).

[0017] Furthermore, the heat-resistant steel bushing is made of SUS310S, Incoloy800, or GH3030 high-temperature alloy.

[0018] In the above scheme, the thickness of the buffer layer is 0.1-0.3 mm; it is filled with alumina fiber reinforced silicone rubber; wherein the length of the alumina fiber is 50-200 μm and the content is 15-30 wt% of the silicone rubber matrix.

[0019] In the above scheme, the tooth depth of the sawtooth structure is 0.8-1.5mm, and the tooth tip angle is 60-90°; the continuous sawtooth structure is spirally distributed along the axial direction; the spiral angle is 15-30°, which can effectively reduce thermal stress concentration.

[0020] In the above scheme, the center distance between adjacent heating holes in the ceramic plate is 2.5-3.5 times the hole diameter.

[0021] The above-mentioned method for preparing a ceramic skeleton for an electric heater, wherein the ceramic disc and ceramic column are prepared by injection molding and stepwise sintering, specifically including the following steps: 1) Slurry preparation: For the formulation systems of Al2O3-based high thermal conductivity layer, porous ZrO2-based heat insulation layer and Si3N4-based surface radiation layer, slurries with a solid content of 55-65 vol% were prepared using water as solvent, and then dispersants were added to adjust the viscosity of the slurry. 2) Mold casting: A multi-cavity mold matching the gradient structure is used to cast a slurry of Al2O3-based high thermal conductivity layer, porous ZrO2-based heat insulation layer and Si3N4-based surface radiation layer to form a three-layer gradient structure. 3) Stepwise sintering: Pre-sintering: Heat to 800-1000℃ and hold for initial shaping; Final sintering: The temperature is raised to 1550-1650℃ in a reducing atmosphere and held to achieve complete densification; thus, porcelain plates and porcelain pillars are obtained.

[0022] In the above scheme, the dispersant can be ammonium polyacrylate, polyvinylpyrrolidone, or sodium polyacrylate, etc., and its amount accounts for 0.5-1.5% of the total powder mass in the total Al2O3-based high thermal conductivity layer, porous ZrO2-based heat insulation layer, or Si3N4-based surface radiation layer formulation system.

[0023] Furthermore, the slurry viscosity is controlled at 2000-5000 mPa·s.

[0024] Furthermore, the curing time for injection molding is 30-90 minutes.

[0025] Furthermore, the heating rate used in the pre-sintering stage is 2-5℃ / min; after heating to 800-1000℃, the temperature is held for 1-2 hours.

[0026] Furthermore, a yttrium oxide-stabilized zirconia thermal barrier coating is applied to the surface of the preliminarily shaped component, and the porosity is controlled to be ≤2%.

[0027] Furthermore, the heating rate used in the final sintering stage is 8-15℃ / min; after heating to 1550-1650℃, the temperature is held for 3-5 hours.

[0028] Furthermore, the reducing atmosphere is a mixture of hydrogen and nitrogen, wherein the hydrogen content is 5-10 vol.

[0029] Furthermore, the flow rate of the reducing atmosphere is 0.5-1.2 m / s. 3 / h.

[0030] Furthermore, during the final sintering stage, when the temperature is raised to 1200-1300℃ (the first time it reaches 1200-1300℃), it is pressurized at 5-10MPa for 0.5-1h, and then the temperature is raised to 1550-1650℃ for heat preservation.

[0031] Furthermore, according to the design requirements of the ceramic disc, holes matching the size of the heating holes are made, a heat-resistant sleeve (with a continuous serrated structure on the inner wall) is installed, and a buffer layer of ceramic pillars is filled between it and the wall of the ceramic disc holes to form a ceramic disc with heating holes; the ceramic pillars are inserted between the heating holes of the two ceramic discs to obtain the ceramic skeleton of the electric heater.

[0032] The principles of this invention include: Material optimization: Alumina is used as the main phase to provide insulation and high temperature resistance; zirconia improves thermal shock resistance through phase transformation toughening mechanism; silicon nitride enhances thermal conductivity and mechanical strength; and sintering aids are further combined to promote low-temperature densification and inhibit grain coarsening; carbon fiber improves strength and toughness.

[0033] Heating hole optimization: This invention effectively enhances the anti-fracture performance of ceramic materials and reduces contact thermal stress by introducing heat-resistant sleeve holes into the heating holes of the ceramic disc and setting a continuous serrated structure on the inner wall of the sleeve holes.

[0034] Improved sintering process: This invention adopts a stepwise sintering process. First, the temperature is slowly raised to 800-1000℃ and held for a period of time for preliminary shaping. Then, the temperature is rapidly raised to 1550-1650℃ under a reducing atmosphere for densification sintering. Pressure sintering is carried out when the temperature is raised to 1200-1300℃, which can effectively promote grain boundary diffusion, inhibit porosity formation, and assist particle rearrangement, significantly improving the density, mechanical properties and microstructure uniformity of the material.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention achieves the following significant advantages through synergistic innovation in materials, structure, and process: 1) Significantly enhanced thermal shock resistance, effectively preventing cracking failure under rapid temperature changes; 2) Mechanical strength and toughness are improved simultaneously, taking into account both high load-bearing capacity and impact resistance; 3) The thermal stress distribution is uniform, reducing the risk of local overheating and extending the component life; the edge anti-fracture ability is enhanced, improving the overall structural reliability; 4) High-precision molding of complex structures ensures consistency in mass production; the overall service life is extended several times, reducing equipment maintenance costs. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of the ceramic frame of the electric heater according to one embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of the electric heater ceramic frame with heating holes according to an embodiment of the present invention; Figure 3 This is a cross-sectional view of the ceramic material of the electric heater according to an embodiment of the present invention; In the figure: 1-ceramic disc, 2-ceramic pillar, 1-1-high thermal conductivity layer, 1-2-insulation layer, 1-3-surface radiation layer, 1-4-yttrium oxide stabilized zirconia thermal barrier coating, 1-5-serrated heating hole, 1-6-heat resistant steel sleeve hole, 1-7-buffer layer between the inner wall of the sleeve hole and the wall of the ceramic disc hole. Detailed Implementation

[0037] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

[0038] like Figure 1 , Figure 2 , Figure 3 As shown, the present invention provides a ceramic skeleton structure for an electric heater, which includes a ceramic disc 1 with heating holes and ceramic pillars 2 interspersed in the heating holes of the two ceramic discs. The ceramic disc 1 and the ceramic pillars 2 have an Al2O3-based high thermal conductivity layer 1-1, a porous ZrO2-based heat insulation layer 1-2 and a Si3N4-based surface radiation layer 1-3 arranged sequentially from the inside to the outside. The surface of the Si3N4-based surface radiation layer 1-3 is further coated with a yttrium oxide-stabilized zirconia thermal barrier coating 1-4. The heating holes include heat-resistant steel sleeve holes 1-6 and a buffer layer 1-7 disposed between the heat-resistant steel sleeve 1-6 and the wall of the ceramic disc hole. The inner wall of the heat-resistant sleeve hole of the heating hole has a continuous serrated structure.

[0039] In the following examples, the sintering aid used is composed of silicon dioxide, magnesium oxide, and yttrium oxide in a mass ratio of (2-3):1:1; wherein the silicon dioxide particle size is ≤1μm and the yttrium oxide purity is ≥99.9%.

[0040] The fiber reinforcement used is short-cut carbon fiber with a diameter of 7-15μm and a length of 1-3mm.

[0041] In the alumina fiber reinforced silicone rubber used, the average length of the alumina fiber is 150 μm and the content is 20 wt% of the silicone rubber matrix.

[0042] Example 1 A ceramic frame for an electric heater, using, for example Figure 1 , Figure 2 , Figure 3 The structure shown is prepared by the following steps: 1) Both the ceramic plate and the ceramic pillar adopt a multi-layered composite structure, including: a. High thermal conductivity layer: Dense Al2O3-based high thermal conductivity layer; b. Thermal insulation layer: Porous ZrO2-based thermal insulation layer; c. Surface radiation layer: Si3N4-based surface radiation coating; In the multilayer composite structure, the amounts of alumina, zirconium oxide, and silicon nitride introduced are 70%, 20%, and 10% of the total mass of these three functional components, respectively. Furthermore, sintering aids and carbon fiber reinforcements are further introduced into the Al2O3-based high thermal conductivity layer, the porous ZrO2-based thermal insulation layer, and the Si3N4-based surface radiation layer, respectively; wherein, the amount of sintering aids in each functional layer is 3%; and the amount of fiber reinforcement is 2%. The material gradient distribution achieves the "internal conduction and external isolation" function, solving the problem of local overheating, improving heating efficiency, and reducing surface temperature difference; For the above formulation systems of Al2O3-based high thermal conductivity layer, porous ZrO2-based heat insulation layer and Si3N4-based surface radiation layer, slurries with a solid content of 60 vol% were prepared using water as solvent, and then ammonium polyacrylate (accounting for 1% of the total mass of powder) was added as a dispersant to adjust the viscosity of the slurry to 3500 mPa·s. 2) Mold casting: Using a multi-cavity mold that matches the gradient structure, pour a slurry of Al2O3-based high thermal conductivity layer, porous ZrO2-based heat insulation layer and Si3N4-based surface radiation layer, and cure for 60 minutes to form a three-layer gradient structure. 3) Stepwise sintering: Pre-sintering: First, heat to 900℃ at a rate of 4℃ / min and hold for 1.5h to achieve preliminary shaping; A yttrium-stabilized zirconia thermal barrier coating with an average thickness of 30 μm and a porosity of ≤2% was applied to the surface of the above-mentioned shaped component. Final sintering: The components coated with the thermal barrier coating are sintered in a reducing atmosphere (H2 + N2 mixed atmosphere, H2 concentration of 8 vol%; gas flow rate of 1.0 m). 3 / In h), the temperature is increased at a rate of 8℃ / min to reach 1200-1300℃ for the first time, and then pressurized at this temperature and 7.5MPa for 1h; finally, the temperature is increased to 1600℃ at the same rate and held for 4h to achieve complete densification, resulting in ceramic disc and ceramic column components. 4) Assemble and reinforce the structure: a. The obtained ceramic disk hole wall is covered with a heat-resistant steel sleeve (1mm thick, SUS310S / Incoloy800), and a 0.2mm thick buffer layer is set between the inner wall of the sleeve and the ceramic disk hole wall, and filled with alumina fiber reinforced silicone rubber. b. The inner wall of the heat-resistant steel sleeve hole is provided with a continuous sawtooth structure, with a tooth depth of 1.2 mm, a tooth tip angle of 75°, and the distance between adjacent teeth is 1.5 times the tooth depth; the sawtooth heating holes are spirally distributed in the axial direction, with a spiral angle of 25°, and the center distance between adjacent heating holes is 3 times the hole diameter; c. Insert the ceramic column between the heating holes of the two ceramic discs to obtain the ceramic skeleton of the electric heater; wherein the thickness ratio of the Al2O3-based high thermal conductivity layer, the porous ZrO2-based heat insulation layer and the Si3N4-based surface radiation layer is 4:2.5:1.

[0043] The ceramic frame of the electric heater obtained in this embodiment is applied to the electric radiant heating tube of the heat treatment furnace in a steel plant. The furnace temperature is 950℃. It has good mechanical strength and toughness and a service life of more than 12 months.

[0044] Example 2 A ceramic frame for an electric heater, using, for example Figure 1 , Figure 2 , Figure 3 The structure shown is prepared by the following steps: 1) Both the ceramic plate and the ceramic pillar adopt the same multi-layer composite structure as described in Example 1. In the multilayer composite structure, the amount of alumina, zirconium oxide, and silicon nitride introduced in the design accounts for 75% of the total mass of these three functional components, zirconium oxide 10%, and silicon nitride 15%, respectively. Furthermore, sintering aids and carbon fiber reinforcements are further introduced into the Al2O3-based high thermal conductivity layer, the porous ZrO2-based thermal insulation layer, and the Si3N4-based surface radiation layer, respectively; wherein, the amount of sintering aids in each functional layer is 1%; and the amount of fiber reinforcement is 1.5%. The material gradient distribution achieves the "internal conduction and external isolation" function, solving the problem of local overheating, improving heating efficiency, and reducing surface temperature difference; For the formulation systems of Al2O3-based high thermal conductivity layer, porous ZrO2-based heat insulation layer and Si3N4-based surface radiation layer, slurries with a solid content of 65 vol% were prepared using water as solvent, and then polyvinylpyrrolidone (accounting for 1.5% of the total mass of powder) was added as a dispersant to adjust the viscosity of the slurry to 5000 mPa·s. 2) Mold casting: Using a multi-cavity mold that matches the gradient structure, pour a slurry of Al2O3-based high thermal conductivity layer, porous ZrO2-based heat insulation layer and Si3N4-based surface radiation layer, and cure for 60 minutes to form a three-layer gradient structure. 3) Stepwise sintering: Pre-sintering: First, heat to 1000℃ at a rate of 2℃ / min, hold for 2 hours, and preliminarily shape. A yttrium-stabilized zirconia thermal barrier coating with a thickness of approximately 30 μm and a porosity of ≤2% is applied to the surface of the aforementioned shaped component. Final sintering: The components coated with the thermal barrier coating are sintered in a reducing atmosphere (H2 + N2 mixed atmosphere, H2 concentration of 8 vol%; gas flow rate of 1.2 m). 3 / In h), the temperature is increased at a rate of 8℃ / min to reach 1200-1300℃ for the first time, and then pressurized at this temperature and 10MPa for 1h; finally, the temperature is increased to 1650℃ at the same rate and held for 5h to achieve complete densification, resulting in ceramic disc and ceramic column components. 4) Assemble and reinforce the structure: a. The obtained ceramic disk hole wall is covered with a heat-resistant steel sleeve (1.5mm thick, SUS310S / Incoloy800), and a 0.2mm thick buffer layer is set between the inner wall of the sleeve and the ceramic disk hole wall, and filled with alumina fiber reinforced silicone rubber. b. The inner wall of the heat-resistant steel sleeve hole is provided with a continuous sawtooth structure, with a tooth depth of 1.5mm, a tooth tip angle of 80°, and the distance between adjacent teeth is 1.5 times the tooth depth; the sawtooth heating holes are spirally distributed in the axial direction, with a spiral angle of 30°, and the center distance between adjacent heating holes is 3.5 times the hole diameter; c. Insert the ceramic column between the heating holes of the two ceramic discs to obtain the ceramic skeleton of the electric heater; wherein the thickness ratio of the Al2O3-based high thermal conductivity layer, the porous ZrO2-based heat insulation layer and the Si3N4-based surface radiation layer is (3-5):(2-3):1.

[0045] The ceramic frame of the electric heater obtained in this embodiment is applied to the electric radiant heating tube of the heat treatment furnace in a steel plant. The furnace temperature is 950℃. It has good mechanical strength and toughness and a service life of more than 15 months.

[0046] Comparative Example 1 Commercially available pure alumina ceramic skeletons are used in electric radiant heating tubes for heat treatment furnaces in steel plants, with a furnace temperature of 950℃ and a service life of 6 months.

[0047] Comparative Example 2 A ceramic skeleton for an electric heater is prepared in a manner similar to that of Example 1, except that the component is not subjected to a pressure densification heat treatment during the final sintering process.

[0048] The resulting ceramic frame for the electric heater is used in the electric radiant heating tube of the heat treatment furnace in a steel plant, with a furnace temperature of 950℃ and a service life of 9 months.

[0049] Comparative Example 3 A ceramic frame for an electric heater is prepared using a method largely the same as in Example 1, except that the final sintering process specifically includes: Final sintering: The component coated with a thermal barrier coating is sintered in a reducing atmosphere (a mixture of H2 and N2, with an H2 concentration of 8 vol% and a gas flow rate of 1.0 m / s²). 3 / In h), the temperature is increased to 1600℃ at a rate of 3℃ / min and held at 6MPa for 4h to achieve complete densification, resulting in ceramic disc and ceramic column components.

[0050] The resulting ceramic frame for the electric heater was applied to the electric radiant heating tube of the heat treatment furnace in a steel plant, with a furnace temperature of 950℃ and a service life of less than 10 months.

[0051] The embodiments of the present invention have been described above. These descriptions are exemplary and not intended to limit the implementation of the invention. Any changes or modifications made to individual components based on the principles of the present invention should not be excluded from the scope of protection of the present invention.

Claims

1. A ceramic frame for an electric heater, characterized in that, It includes a ceramic disc with heating holes and ceramic pillars interspersed in the heating holes of the two ceramic discs. The ceramic disc and ceramic pillars have an Al2O3-based high thermal conductivity layer, a porous ZrO2-based heat insulation layer and a Si3N4-based surface radiation layer arranged sequentially from the inside to the outside. The heating holes include heat-resistant sleeve holes and a buffer layer disposed between the heat-resistant sleeve and the wall of the ceramic disc hole. The inner wall of the heat-resistant sleeve hole of the heating hole has a continuous serrated structure.

2. The ceramic frame for the electric heater according to claim 1, characterized in that, The thickness ratio of the Al2O3-based high thermal conductivity layer, the porous ZrO2-based heat insulation layer, and the Si3N4-based surface radiation layer is (3-5):(2-3):

1.

3. The ceramic frame for the electric heater according to claim 1, characterized in that, The porous ZrO2-based thermal insulation layer has a porosity of 50-70%, an average pore size of 10-30 μm, and a bulk density of ≤0.9 g / cm³. 3 .

4. The ceramic frame for the electric heater according to claim 1, characterized in that, In the ceramic disc and ceramic column, the amount of alumina, zirconium oxide and silicon nitride introduced by design accounts for 60-80%, 10-20% and 5-15% of the total mass of these three functional components, respectively.

5. The ceramic frame for the electric heater according to claim 1, characterized in that, Sintering aids and fiber reinforcements are introduced into the Al2O3-based high thermal conductivity layer, the porous ZrO2-based thermal insulation layer, and the Si3N4-based surface radiation layer, respectively. The dosage of sintering aids is 2-5%, and the dosage of fiber reinforcements is 0.5-3%.

6. The ceramic frame for the electric heater according to claim 1, characterized in that, In the Al2O3-based high thermal conductivity layer, the porous ZrO2-based thermal insulation layer, and the Si3N4-based surface radiation layer, adjacent functional layers are interleaved in a wavy pattern.

7. The ceramic frame for the electric heater according to claim 1, characterized in that, The tooth depth of the serrated structure is 0.8-1.5mm, and the tooth tip angle is 60-90°; the continuous serrated structure is spirally distributed along the axial direction; the spiral angle is 15-30°.

8. The method for preparing the ceramic skeleton of the electric heater according to any one of claims 1 to 7, characterized in that, The porcelain plates and pillars are produced using a casting and step-by-step sintering process, specifically including the following steps: 1) Slurry preparation: For the formulation systems of Al2O3-based high thermal conductivity layer, porous ZrO2-based heat insulation layer and Si3N4-based surface radiation layer, slurries with a solid content of 55-65 vol% were prepared using water as solvent, and then dispersants were added to adjust the viscosity of the slurry. 2) Mold casting: A multi-cavity mold matching the gradient structure is used to cast a slurry of Al2O3-based high thermal conductivity layer, porous ZrO2-based heat insulation layer and Si3N4-based surface radiation layer to form a three-layer gradient structure. 3) Stepwise sintering: Pre-sintering: Heat to 800-1000℃ and hold for initial shaping; Final sintering: The temperature is raised to 1550-1650℃ in a reducing atmosphere and held to achieve complete densification; thus, porcelain plates and porcelain pillars are obtained.

9. The preparation method according to claim 8, characterized in that, The heating rate used in the pre-sintering stage is 2-5℃ / min; after heating to 800-1000℃, the temperature is held for 1-2 hours.

10. The preparation method according to claim 8, characterized in that, The heating rate used in the final sintering stage is 8-15℃ / min; after heating to 1550-1650℃, the temperature is held for 3-5 hours; a pressurization step is added during the heating process.

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