A ceramic insulator and a method of manufacturing the same

Abstract

The application provides a ceramic insulator and a preparation method thereof, and belongs to the technical field of power equipment. The insulator comprises a core layer and a shell layer. The core layer comprises the following components in percentage by mass: 70-80% of alumina, 15-25% of yttrium stabilized zirconia, 2-5% of cerium oxide, and 0.5-1% of yttrium oxide. The shell layer comprises the following components in percentage by mass: 90-95% of alumina, 1-2% of magnesium oxide, 1-3% of silicon oxide, and 0.5-1% of boron oxide. The ceramic insulator of the application adopts a core-shell structure design. The alumina in the core layer provides a high mechanical strength basis, and the yttrium stabilized zirconia as a toughening phase can effectively improve the toughness of the insulator and reduce the risk of brittle fracture. The high content of alumina in the shell layer further enhances the surface hardness and wear resistance of the insulator.

Description

Technical Field

[0001] This application relates to the field of power equipment technology, and in particular to a ceramic insulator and its preparation method. Background Technology

[0002] Ceramic insulators are widely used in power equipment, electronic components, and other fields, but some problems still exist in the current technology. Traditional ceramic insulators are mostly composed of alumina as the main phase, which, although possessing high mechanical strength and insulation performance, is brittle and prone to fracture. To improve toughness, toughening phases such as zirconium oxide are often added, but this often leads to a decrease in insulation performance. In addition, the manufacturing process involves high sintering temperatures and high energy consumption, and microscopic defects are easily generated due to uneven composition or improper sintering, affecting the reliability and lifespan of the insulator.

[0003] Patent CN202110794104.4 discloses a toughened columnar porcelain insulator, comprising an insulator body and an insulating layer. The base material includes the following raw materials in parts by weight: 15-25 parts bauxite, 12-20 parts feldspar, 12-20 parts kaolin, 12-20 parts alumina, 12-20 parts Hubei clay, 5-15 parts molecular sieve, 5-15 parts boric acid, 5-12 parts talc, 5-12 parts zirconium silicate, 3-8 parts zinc oxide, and 0.5-2.5 parts water-reducing agent. The insulator of this patent has low fracture toughness, making it prone to cracking due to external impact or internal stress concentration during use, thus affecting its normal operation in complex environments such as high voltage and strong earthquakes.

[0004] Patent CN202011438746.2 discloses a low-temperature resistant high-voltage power transmission porcelain insulator and its preparation method. The porcelain insulator includes a porcelain insulator component; the porcelain insulator component comprises the following raw materials: alumina, calcined high-alumina bauxite, potassium feldspar, zirconium dioxide / kaolin composite material, fluorapatite, cerium oxide / lanthanum oxide-coated nano-boron nitride, and sintering aids; a reinforcing layer and a self-cleaning layer are sequentially disposed on the outside of the porcelain insulator component; the coating used for the reinforcing layer is made by mixing the following raw materials: nano-alumina sol, cerium oxide / SiO2-coated graphene oxide composite material, aluminum dihydrogen phosphate, nano-attapulgite, and nano-boron nitride; the coating used for the self-cleaning layer is made by mixing the following raw materials: lanthanum / cerium co-doped titanium dioxide sol, nano-alumina sol, needle-like wollastonite, and tetra-needle-like zinc oxide whiskers. The insulator of this patent has low bending strength, and during use, the insulator is prone to deformation or damage when subjected to large bending forces, failing to meet the requirements of some special application scenarios with high mechanical performance requirements. Meanwhile, its preparation process is relatively complex, requiring the separate preparation of various composite materials and coatings, which increases production costs and preparation difficulty.

[0005] Furthermore, existing manufacturing processes mostly employ uniform components and a single sintering process, making it difficult to achieve precise control over the microstructure and thus limiting further performance improvements. Therefore, there is an urgent need for a ceramic insulator solution that can balance mechanical strength, insulation performance, and manufacturing efficiency. Summary of the Invention

[0006] This application is made in view of the problem that it is difficult to balance the mechanical strength of insulators and the insulation of shoes in the prior art, and its purpose is to provide a ceramic insulator and a method for preparing the same.

[0007] Specifically, the first aspect of this application provides a ceramic insulator, which includes a core layer and a shell layer. By volume percentage, the core layer accounts for 60%-70% of the total volume of the insulator, and the shell layer accounts for 30%-40% of the total volume of the insulator.

[0008] Furthermore, the core layer comprises the following components by mass percentage: 70%-80% alumina, 15%-25% yttrium-stabilized zirconium oxide, 2%-5% cerium oxide, and 0.5%-1% yttrium oxide.

[0009] Furthermore, the shell layer comprises the following components by mass percentage: 90%-95% aluminum oxide, 1%-2% magnesium oxide, 1%-3% silicon oxide, and 0.5%-1% boron oxide.

[0010] Furthermore, the shell also contains 0.5%-1% calcium oxide.

[0011] A second aspect provides a method for preparing a ceramic insulator, the method comprising the following steps:

[0012] S1: Prepare core ceramic slurry and shell ceramic slurry separately;

[0013] S2: Using a co-injection molding process, the core layer slurry and the shell layer slurry are simultaneously injected into the mold to form a green body with a core-shell structure;

[0014] S3: Perform segmented degreasing on the green body;

[0015] S4: Perform staged controllable sintering on the degreased green body to obtain the ceramic insulator matrix.

[0016] Further, in the co-injection molding process described in step S2, the injection pressure of the core layer slurry is 20-30 MPa, the injection pressure of the shell layer slurry is 15-25 MPa, and / or

[0017] The mold temperature is 40-60℃.

[0018] Furthermore, the segmented degreasing process described in step S3 is carried out under nitrogen protection at a nitrogen flow rate of 5 L / min, including:

[0019] First stage: Heat to 200-220℃ at a rate of 0.5-1℃ / min, and hold for 4-5 hours;

[0020] Second stage: Heat to 400-420℃ at a rate of 1-2℃ / min, and hold for 6-7 hours;

[0021] The third stage: heat up to 600-620℃ at a rate of 0.8-1.5℃ / min, hold for 4-5 hours, and then cool to room temperature.

[0022] Furthermore, the staged controllable sintering described in step S4 includes:

[0023] S41: In the first stage, the green blank is heated from room temperature to 1150-1250℃ at a rate of 2-4℃ / min and held for 1-3 hours to achieve core layer pre-sintering;

[0024] S42: In the second stage, the temperature is increased to 1420-1480℃ at a rate of 4-6℃ / min and held for 1.5-2.5h to achieve core densification;

[0025] S43: In the third stage, the temperature is rapidly increased to 1530-1570℃ at a rate of 6-10℃ / min, and microwave-assisted sintering is used. The temperature is held for 0.5-1.5h to achieve full sintering of the shell layer.

[0026] S44: The fourth stage involves slowly cooling to 1150-1250℃ at a rate of 0.5-1℃ / min and holding at that temperature for 2-4 hours to promote the formation of a gradient structure at the core-shell interface.

[0027] S45: The fifth stage involves cooling to room temperature at a rate of 1-3℃ / min to complete sintering.

[0028] Furthermore, in step S43, the microwave-assisted sintering has a microwave frequency of 2.45-2.52 GHz and a power of 5-10 kW. The microwave power is periodically fluctuated during the heat preservation period, with the fluctuation range being ±5% to ±15% of the set power.

[0029] Furthermore, following step S4, a post-processing step S5 is included: surface polishing of the sintered ceramic insulator substrate, followed by coating with an insulating glaze layer and secondary sintering, wherein the thickness of the insulating glaze layer is 10-20 μm, and / or

[0030] The secondary sintering temperature is 700-800℃, and the holding time is 0.5-1.5h.

[0031] The present invention has the following beneficial effects:

[0032] (1) The ceramic insulator of the present invention adopts a core-shell structure design. The alumina in the core layer provides a high mechanical strength foundation, and the yttrium-stabilized zirconia, as a toughening phase, can effectively improve the toughness of the insulator and reduce the risk of brittle fracture. The high alumina content in the shell layer further enhances the surface hardness and wear resistance of the insulator. Tests have shown that the fracture toughness and bending strength of the insulator of the present invention are significantly improved compared with traditional insulators, and it can better adapt to complex operating environments, such as high voltage and strong earthquake scenarios.

[0033] (2) The cerium oxide and yttrium oxide in the core layer help stabilize the crystal structure and improve insulation performance. The magnesium oxide, silicon oxide, boron oxide and calcium oxide in the shell layer work together to form a dense insulating layer, effectively preventing current leakage. Compared with the traditional method of adding zirconium oxide toughening phase, which leads to a decrease in insulation performance, the present invention improves toughness while maintaining stable or even improved insulation performance, which can meet the strict requirements of power equipment for insulation performance.

[0034] (3) The staged controllable sintering process in the preparation method allows for precise sintering based on the different characteristics of the core and shell layers, reducing the overall sintering temperature and energy consumption. Simultaneously, the application of microwave-assisted sintering technology further improves sintering efficiency and shortens sintering time. Furthermore, this invention precisely controls the ratio and distribution of the core and shell layers through co-injection molding, and the staged degreasing treatment and staged controllable sintering process avoid component inhomogeneity and microscopic defects, achieving precise control of the microstructure. The gradient structure formed at the core-shell interface enhances the bonding force between the core and shell layers, improving the reliability and lifespan of the insulator. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0036] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0037] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0038] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0039] An embodiment of the first aspect of this application provides a ceramic insulator, the insulator comprising a core layer and a shell layer, wherein the core layer accounts for 60%-70% of the total volume of the insulator and the shell layer accounts for 30%-40% of the total volume of the insulator by volume percentage.

[0040] In this embodiment, the ceramic insulator adopts a core-shell structure design. Alumina in the core layer provides a high mechanical strength foundation, while yttrium-stabilized zirconia, as a toughening phase, effectively improves the insulator's toughness and reduces the risk of brittle fracture. The high alumina content in the shell layer further enhances the insulator's surface hardness and wear resistance, enabling it to better adapt to complex operating environments, such as high-voltage and strong-vibration scenarios.

[0041] In this embodiment, the core layer comprises the following components by mass percentage: 70%-80% alumina, 15%-25% yttrium-stabilized zirconium oxide, 2%-5% cerium oxide, and 0.5%-1% yttrium oxide.

[0042] The alumina has a purity of ≥99.9% and a D50 of 0.5μm. The mass percentage of alumina is any value or combination of 70%, 73%, 75%, 78%, and 80%. When the amount of alumina is higher than 80%, the toughness of the insulator will decrease and the brittleness will increase; when it is lower than 70% by mass, it cannot provide a sufficient mechanical strength basis.

[0043] The Y2O3 content in the yttrium-stabilized zirconium oxide is 3 mol%, and the D50 is 0.3 μm. The mass percentage of yttrium-stabilized zirconium oxide can be any value or combination of 15%, 18%, 20%, 23%, and 25%. When the mass percentage of yttrium-stabilized zirconium oxide is less than 15%, the improvement effect on the insulator toughness is not obvious; when it is higher than 25%, it may affect other properties of the core layer.

[0044] Cerium oxide has a purity of ≥99.5% and a D50 of 0.8μm. The mass percentage of cerium oxide is any value or combination of 2%, 3%, 4%, and 5%. Cerium oxide helps stabilize the crystal structure and improve insulation performance, and its dosage within this range can play a better role.

[0045] Yttrium oxide has a purity of ≥99.9% and a D50 of 0.5μm. The mass percentage of yttrium oxide is any value or combination of 0.5%, 0.6%, 0.8%, and 1%. Yttrium oxide also helps to stabilize the crystal structure and improve insulation performance. A reasonable amount can ensure the stability of the core layer performance.

[0046] In this embodiment, the shell layer comprises the following components by mass percentage: 90%-95% aluminum oxide, 1%-2% magnesium oxide, 1%-3% silicon oxide, 0.5%-1% boron oxide, and the shell layer also contains 0.5%-1% calcium oxide.

[0047] The alumina content is any value or combination of 90%, 92%, 93%, and 95% by mass. The high alumina content further enhances the surface hardness and wear resistance of the insulator.

[0048] Magnesium oxide is present in any value or combination of 1%, 1.2%, 1.5%, and 2% by mass. Magnesium oxide can work synergistically with other components to help form a dense insulating layer.

[0049] The mass percentage of silicon oxide is any value or combination of 1%, 2%, 3%, etc. Silicon oxide has a certain influence on insulation performance and structural stability in the shell.

[0050] Boron oxide, with a mass percentage of 0.5%, 0.6%, 0.8%, or 1% or any combination thereof, can promote the sintering process and optimize the performance of the shell.

[0051] The mass percentage of calcium oxide is any value or combination of 0.5%, 0.6%, 0.8%, 1%, and calcium oxide can further improve the insulation performance and stability of the shell.

[0052] In the ceramic insulator of this invention, the core layer provides a good foundation for the insulator's mechanical strength and toughness through the synergistic effect of components such as alumina, yttrium-stabilized zirconium oxide, cerium oxide, and yttrium oxide. Alumina, as one of the main components, not only helps to improve the overall hardness of the core layer but also works with other components to enhance the stability of the core layer structure. Yttrium-stabilized zirconium oxide undergoes a phase transition under external force, absorbing energy and effectively preventing crack propagation, thus greatly improving the insulator's fracture resistance. The synergistic effect of cerium oxide and yttrium-stabilized zirconium oxide further optimizes the phase transition toughening effect, enabling the core layer to maintain good mechanical properties even under complex working conditions. Yttrium oxide plays a regulatory role in the microstructure of the core layer, promoting uniform grain growth and improving the density and strength of the core layer.

[0053] Furthermore, the dense insulating layer design of the shell provides a solid guarantee for the electrical performance of the insulator. High-purity Al2O3 itself has excellent insulating properties, reducing the formation of leakage paths. This dense insulating layer can effectively prevent current leakage, improve the insulation resistance of the insulator, and ensure the safe operation of the power system. In summary, the ceramic insulator of this invention, through the careful design and composition optimization of the core layer, shell layer, and core-shell interface, achieves a perfect combination of mechanical and electrical properties, providing the power industry with a high-performance and reliable insulating material.

[0054] A second aspect of the present invention provides a method for preparing a ceramic insulator, comprising the following steps:

[0055] S1: Prepare core ceramic slurry and shell ceramic slurry separately;

[0056] S2: Using a co-injection molding process, the core layer slurry and the shell layer slurry are simultaneously injected into the mold to form a green body with a core-shell structure;

[0057] S3: Perform segmented degreasing on the green body;

[0058] S4: Perform staged controllable sintering on the degreased green body to obtain the ceramic insulator matrix.

[0059] In step S1, the core layer slurry is prepared by mixing the components of the core layer in proportion, adding anhydrous ethanol containing 0.5% sodium polyacrylate dispersant, ball milling for 48 hours, using zirconia milling balls, with a ball-to-material ratio of 3:1, a rotation speed of 200 rpm, and controlling the slurry viscosity at 3000±200 mPa·s (25℃) and pH=9.5±0.2.

[0060] Shell slurry preparation: Mix the shell components, add deionized water containing 0.3% sodium tripolyphosphate dispersant, ball mill for 36 hours, use alumina grinding balls, ball-to-material ratio 2.5:1, rotation speed 180 rpm, slurry viscosity controlled at 2500±150 mPa·s (25℃), pH=8.5±0.2.

[0061] In this embodiment, a dual-cavity injection mold is used in step S2. In the co-injection molding process, the injection pressure of the core layer slurry is 20-30 MPa, the temperature is 40-50°C, and the holding time is 120 s; the injection pressure of the shell layer slurry is 15-25 MPa, the mold temperature is 50-60°C, and the holding time is 90 s. This step ensures that the core and shell layers are uniformly and tightly bonded together, forming a stable core-shell structure green body. Precise control of the injection parameters of the core and shell layer slurries is crucial during co-injection molding. The higher injection pressure and suitable temperature of the core layer slurry help it to fully fill the mold, providing a solid core foundation for the insulator. The relatively lower injection pressure and slightly higher mold temperature of the shell layer slurry facilitate its uniform coating on the core layer surface, forming a good outer layer structure.

[0062] In this embodiment, the segmented degreasing process in step S3 is carried out under nitrogen protection, with a nitrogen flow rate of 5 L / min, including:

[0063] First stage: Heat to 200-220℃ at a rate of 0.5-1℃ / min, and hold for 4-5 hours;

[0064] Second stage: Heat to 400-420℃ at a rate of 1-2℃ / min, and hold for 6-7 hours;

[0065] The third stage: heat up to 600-620℃ at a rate of 0.8-1.5℃ / min, hold for 4-5 hours, and then cool to room temperature.

[0066] The purpose of this segmented degreasing process is to gradually remove organic additives from the green body, avoiding defects such as bubbles and cracks caused by excessively rapid decomposition of organic matter due to rapid heating. In the first stage, a lower heating rate and appropriate holding time allow some low-boiling-point organic matter in the green body to slowly volatilize, reducing its impact on the green body structure. As the temperature rises, the second stage begins, where the heating rate is appropriately accelerated to further remove medium-boiling-point organic matter. In the third stage, a higher temperature and a readjusted heating rate ensure that the remaining high-boiling-point organic matter is completely decomposed and removed. The entire segmented degreasing process is carried out under nitrogen protection to prevent oxidation of the green body at high temperatures, ensuring its quality and performance. This segmented degreasing method allows the green body to maintain structural integrity and stability during the degreasing process, laying a good foundation for subsequent sintering steps.

[0067] In this embodiment, the staged controllable sintering described in step S4 includes:

[0068] S41: In the first stage, the green blank is heated from room temperature to 1150-1250℃ at a rate of 2-4℃ / min and held for 1-3 hours to achieve core layer pre-sintering;

[0069] S42: In the second stage, the temperature is increased to 1420-1480℃ at a rate of 4-6℃ / min and held for 1.5-2.5h to achieve core densification;

[0070] S43: In the third stage, the temperature is rapidly increased to 1530-1570℃ at a rate of 6-10℃ / min, and microwave-assisted sintering is used. The temperature is held for 0.5-1.5h to achieve full sintering of the shell layer.

[0071] S44: The fourth stage involves slowly cooling to 1150-1250℃ at a rate of 0.5-1℃ / min and holding at that temperature for 2-4 hours to promote the formation of a gradient structure at the core-shell interface.

[0072] S45: The fifth stage involves cooling to 800-820℃ at a rate of 1-3℃ / min, holding at 800-820℃ for 1 hour, and then cooling to room temperature with the furnace to complete sintering.

[0073] This step, through precise control of the heating rate, holding time, and temperature range at different stages, fully utilizes the characteristics of each component in the core and shell layers to achieve optimal sintering results. In the first stage, a lower heating rate and a specific temperature range are used for pre-sintering of the core layer, allowing the components in the core layer to initially crystallize and react, preparing for the subsequent densification process and preventing uneven core layer structure caused by excessively rapid heating. The heating rate and temperature in the second stage further promote a tighter bond between the core layer particles, achieving core layer densification and improving the mechanical strength and stability of the core layer.

[0074] The third stage, rapid heating and microwave-assisted sintering, enables the shell to reach a fully sintered state in a short time. Microwave-assisted sintering not only improves sintering efficiency but also allows the components in the shell to fuse better, forming a dense insulating layer and enhancing the electrical performance of the insulator. Simultaneously, rapid heating reduces grain growth time, resulting in finer grains in the shell and further improving its hardness and wear resistance.

[0075] The fourth stage involves slow cooling and heat preservation, providing favorable conditions for the formation of a gradient structure at the core-shell interface. During this process, atoms between the core and shell layers can diffuse and migrate sufficiently, forming a gradient structure with gradually changing composition and properties. This enhances the bonding force between the core and shell layers, improving the overall reliability and lifespan of the insulator.

[0076] The fifth stage, cooling, allows the sintered insulator to gradually return to room temperature, preventing defects such as cracks caused by thermal stress due to sudden temperature drops and ensuring the stability of the insulator's quality and performance. Through this staged, controllable sintering process, the ceramic insulator of this invention achieves an optimal balance between mechanical and electrical properties, meeting the power industry's demand for high-performance insulation materials.

[0077] In this embodiment, the microwave-assisted sintering described in step S43 uses a microwave frequency of 2.45-2.52 GHz and a power of 5-10 kW. The microwave power is periodically fluctuated during the heat preservation period, with a fluctuation range of ±5% to ±15% of the set power. This step, by precisely controlling the microwave frequency, power, and periodic power fluctuations, can better promote the full integration of the components in the shell layer. A suitable microwave frequency allows the shell material to absorb microwave energy more effectively, accelerating the sintering reaction. The periodically fluctuating power control can simulate different energy environments, promoting the formation of a more uniform and dense microstructure in the shell layer during sintering. When the microwave power is at a higher fluctuation value, it provides sufficient energy for the sintering of the shell layer, accelerating atomic diffusion and migration, and promoting grain growth and bonding. When the power is at a lower fluctuation value, it allows the shell layer time for structural adjustment and optimization, preventing excessive grain growth that could lead to a porous structure. This power fluctuation control method helps form fine and uniform grains, further enhancing the hardness, wear resistance, and insulation properties of the shell layer. Meanwhile, periodic power variations can also alleviate the internal stress generated during sintering to some extent, reduce the possibility of cracks and defects in the shell, and thus improve the overall quality and reliability of ceramic insulators.

[0078] In this embodiment, after step S4, a post-processing step S5 is further included: the surface of the sintered ceramic insulator substrate is polished using diamond polishing paste with a particle size ranging from W40 to W0.5; then an insulating glaze layer is coated and a secondary sintering is performed. The insulating glaze layer, in parts by mass, comprises the following raw materials: SiO2 55%, Al2O3 15%, B2O3 10%, CaO 8%, MgO 7%, K2O 5%; the thickness of the insulating glaze layer is 10-20 μm, the secondary sintering temperature is 700-800℃, and the holding time is 0.5-1.5 h.

[0079] Example

[0080] The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight. Unless otherwise stated, all reagents used in the examples are available commercially or synthesized using conventional methods and are ready for use without further processing. Unless otherwise stated, all instruments used in the examples are available commercially.

[0081] Example 1

[0082] A ceramic insulator includes a core layer and a shell layer, wherein the volume ratio of the core layer to the shell layer is 60:40.

[0083] The core layer comprises the following components by mass percentage: 76% aluminum oxide, 20% yttrium-stabilized zirconium oxide, 3% cerium oxide, and 1% yttrium oxide;

[0084] The shell comprises the following components by mass percentage: 94.5% aluminum oxide, 1.5% magnesium oxide, 2.5% silicon oxide, 0.8% boron oxide, and 0.7% calcium oxide.

[0085] The method for preparing the ceramic insulator includes the following steps:

[0086] S1: Prepare core ceramic slurry and shell ceramic slurry separately;

[0087] S2: Using a co-injection molding process, the core layer slurry and the shell layer slurry are simultaneously injected into the mold, wherein the injection pressure of the core layer slurry is 25MPa, the temperature is 45℃, and the holding time is 120s; the injection pressure of the shell layer slurry is 20MPa, the mold temperature is 50℃, and the holding time is 90s, forming a green body with a core-shell structure.

[0088] S3: Perform segmented degreasing on the green body; the segmented degreasing is carried out under nitrogen protection at a nitrogen flow rate of 5 L / min, including:

[0089] First stage: Heat to 200℃ at a rate of 0.5℃ / min and hold for 4 hours;

[0090] Second stage: Heat to 400℃ at a rate of 1℃ / min and hold for 6 hours;

[0091] Third stage: Heat to 600℃ at a rate of 1℃ / min, hold for 4 hours, and then cool to room temperature.

[0092] S4: The degreased green body is subjected to staged controllable sintering, wherein the staged controllable sintering includes:

[0093] S41: In the first stage, the green blank is heated from room temperature to 1200℃ at a rate of 3℃ / min and held for 2 hours to achieve core layer pre-sintering;

[0094] S42: In the second stage, the temperature is increased to 1450℃ at a rate of 5℃ / min and held for 2 hours to achieve core densification.

[0095] S43: In the third stage, the temperature is rapidly increased to 1550℃ at a rate of 8℃ / min, and microwave-assisted sintering is used. The microwave frequency is 2.45GHz and the power is 8kW. The microwave power is periodically fluctuated during the holding period, with the fluctuation range being ±5% to ±15% of the set power. The holding time is 1 hour to achieve full sintering of the shell layer.

[0096] S44: In the fourth stage, the temperature is slowly cooled to 1200℃ at a rate of 0.5℃ / min and held for 3 hours to promote the formation of the core-shell interface gradient structure.

[0097] S45: In the fifth stage, the temperature is cooled to 800°C at a rate of 2°C / min, held at 800°C for 1 hour, and then cooled to room temperature with the furnace to complete the sintering; the ceramic insulator matrix is ​​obtained.

[0098] Example 2

[0099] A ceramic insulator includes a core layer and a shell layer, wherein the core layer comprises the following components by mass percentage: 78% alumina, 18% yttrium-stabilized zirconium oxide, 2.5% cerium oxide, and 1.5% yttrium oxide;

[0100] The shell comprises the following components by mass percentage: 94% aluminum oxide, 2% magnesium oxide, 2.5% silicon oxide, 0.9% boron oxide, and 0.6% calcium oxide.

[0101] The preparation method is the same as in Example 1.

[0102] Example 3

[0103] A ceramic insulator includes a core layer and a shell layer, wherein the core layer comprises the following components by mass percentage: 74% alumina, 22% yttrium-stabilized zirconium oxide, 3.2% cerium oxide, and 0.8% yttrium oxide;

[0104] The shell comprises the following components by mass percentage: 93.2% aluminum oxide, 1.8% magnesium oxide, 3% silicon oxide, 1% boron oxide, and 1% calcium oxide.

[0105] The preparation method is the same as in Example 1.

[0106] Example 4

[0107] A ceramic insulator includes a core layer and a shell layer, wherein the volume ratio of the core layer to the shell layer is 70:30.

[0108] The components and preparation method are the same as in Example 1.

[0109] Example 5

[0110] This embodiment is basically the same as Embodiment 1, except that 0.3% MnO2 is added as a sintering aid based on the shell formulation, and the alumina content is 94.2%.

[0111] Comparative Example 1

[0112] Insulators were prepared using the conventional composition of Al2O3 92%, ZrO 25%, MgO 1%, and SiO 22%.

[0113] Comparative Example 2

[0114] This comparative example is basically the same as the example, except that the preparation process involves first forming a core layer green body and then wrapping it with a shell layer slurry, and the sintering process involves directly heating to 1550°C and holding for 3 hours.

[0115] Comparative Example 3

[0116] This comparative example is basically the same as the example, except that the core layer does not contain cerium oxide and the mass percentage of aluminum oxide is 79%.

[0117] Comparative Example 4

[0118] This comparative example is basically the same as the embodiment, except that microwave assistance is removed in step S43, and the heat preservation time at 1550°C is extended to 3 hours.

[0119] Comparative Example 5

[0120] This comparative example is basically the same as the example, except that the shell contains only 96.5% aluminum oxide and 3.5% magnesium oxide.

[0121] Experimental Case

[0122] The performance of insulators in Examples 1-5 and Comparative Examples 1-5 was tested, including the bending strength (σ). nThe following tests were conducted according to GB / T 4741 "Test Method for Bending Strength of Ceramic Materials": Three-point bending method with a span of 30 mm and a loading rate of 0.5 mm / min. Fracture toughness (Kɪᴄ): Tested according to GB / T 23806-2025 "Test Method for Fracture Toughness of Fine Ceramics", using the single-sided notched beam method. Volume resistivity (ρᵥ): Tested according to GB / T 31838.2-2019 "Test Method for Dielectric and Resistance Characteristics of Solid Insulating Materials". Thermal shock resistance (ΔT): According to GB / T 11416-2013 "Determination of Thermal Shock Resistance of Daily-Use Ceramic Ware", the sample was held in a muffle furnace for 20 min and then rapidly immersed in room temperature water for quenching; the highest temperature difference at which cracking occurred was observed. The test results are shown in Table 1.

[0123]

[0124] As shown in Table 1, the flexural strength of Examples 1-5 is significantly higher than that of Comparative Example 1. The flexural strength of Example 3 reaches 438 MPa, far exceeding the 285 MPa of Comparative Example 1. This indicates that the core-shell structure and staged controlled sintering methods used in this invention can significantly improve the flexural performance of ceramic insulators, making them less prone to fracture under external forces. Regarding fracture toughness, the values ​​of the examples are also generally superior to those of the comparative examples. For example, the fracture toughness of Example 3 is 7.0 MPa·m. 1 / 2 Comparative Example 1, however, only reached 4.0 MPa·m. 1 / 2 This demonstrates that the ceramic insulator prepared by this invention has better resistance to crack propagation and can maintain better integrity under impact or stress concentration. Regarding volume resistivity, each embodiment and comparative example has a certain value, but there are also differences between the embodiments. For example, the volume resistivity of Example 2 is 5.1 × 10⁻⁶. 15 The volume resistivity is relatively high at Ω·cm, indicating good insulation performance. Comparative Example 5 has a volume resistivity of 5.5 × 10⁻⁶ Ω·cm. 13 The Ω·cm value is significantly lower than that of the examples, demonstrating that a proper combination of shell components is crucial for improving the insulation performance of insulators. Regarding thermal shock resistance, the examples also show significantly better performance than the comparative examples. Example 3 achieved a thermal shock resistance of 330°C, while Comparative Example 1 only reached 180°C. This means that the ceramic insulator of the present invention is less prone to cracking and other defects in environments with rapid temperature changes, exhibiting better thermal stability and reliability.

[0125] Example 1: The synergistic effect of CeO2 and YSZ in the core layer achieved excellent phase transformation toughening; MgO in the shell layer acted as a grain boundary pinning agent, inhibiting grain growth; the B2O3-SiO2-CaO system formed an appropriate amount of glass phase at the end of sintering, effectively sealing grain boundary pores, thus obtaining high insulation. The bulk heating characteristics of microwaves promoted rapid densification of the shell layer and interdiffusion of interfacial elements. Example 2: The slightly higher Al2O3 content further improved the insulation performance of the shell layer. The increased Y2O3 content in the core layer strengthened the stabilizing effect on ZrO2; although the toughness decreased slightly, the dimensional stability was better. Example 3: The higher YSZ content and more sufficient interfacial diffusion time resulted in the best toughening effect and interfacial bonding strength, thus the toughness and thermal shock resistance were the most outstanding. Example 4: The increased shell volume ratio slightly improved the overall insulation, but the toughening effect of the core layer was relatively weakened, leading to a slight decrease in toughness. In Example 5, the addition of trace amounts of MnO2 further reduced the sintering temperature of the shell and promoted densification, but had a slight impact on the insulation performance.

[0126] In Comparative Example 1, the introduction of ZrO2 into the homogeneous structure introduced charge carriers while toughening, resulting in a significant reduction in resistivity. Single high-temperature sintering led to coarse grains and poor strength and thermal shock resistance. In Comparative Example 2, due to obvious cracks at the core-shell interface, the product yield was less than 60%. Test performance data showed extremely large dispersion, and all samples fractured at the interface during thermal shock testing (ΔT=200℃). Due to the difference in thermal expansion coefficients between the core and shell layers, huge thermal stress was generated at the interface during rapid sintering, and the lack of compositional gradient buffering led to interface bonding failure. In Comparative Example 3, the absence of CeO2 prevented the full realization of the phase transformation toughening effect of YSZ, resulting in significantly lower fracture toughness than in the embodiments of this invention. Comparative Example 4 lacked selective bulk heating via microwaves, resulting in insufficient shell densification and inadequate interface diffusion, leading to a decrease in overall strength, toughness, and thermal shock resistance. Extended holding time resulted in grain growth. Comparative Example 5 lacks glass phase filling of grain boundaries formed by B2O3, SiO2, etc., and has open pores inside the shell, which leads to a sharp deterioration in insulation performance and a decrease in thermal shock resistance due to pore stress concentration.

[0127] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A ceramic insulator, characterized in that, The insulator comprises a core layer and a shell layer. By volume percentage, the core layer accounts for 60%-70% of the total volume of the insulator, and the shell layer accounts for 30%-40% of the total volume of the insulator. The core layer comprises the following components by mass percentage: 70%-80% alumina, 15%-25% yttrium-stabilized zirconium oxide, 2%-5% cerium oxide, and 0.5%-1% yttrium oxide; The shell comprises the following components by mass percentage: 90%-95% aluminum oxide, 1%-2% magnesium oxide, 1%-3% silicon oxide, 0.5%-1% boron oxide, and 0.5%-1% calcium oxide.

2. A method for preparing a ceramic insulator, characterized in that, The method for preparing the ceramic insulator according to claim 1 includes the following steps: S1: Prepare core ceramic slurry and shell ceramic slurry separately; S2: Using a co-injection molding process, the core layer slurry and the shell layer slurry are simultaneously injected into the mold to form a green body with a core-shell structure; S3: Perform segmented degreasing on the green body; S4: Perform staged controllable sintering on the degreased green body to obtain the ceramic insulator matrix.

3. The method for preparing a ceramic insulator according to claim 2, characterized in that, In step S2, the injection pressure of the core slurry in the co-injection molding process is 20-30 MPa, and the injection pressure of the shell slurry is 15-25 MPa, and / or The mold temperature is 40-60℃.

4. The method for preparing a ceramic insulator according to claim 2, characterized in that, The segmented degreasing process described in step S3 is carried out under nitrogen protection at a nitrogen flow rate of 5 L / min, and includes: First stage: Heat to 200-220℃ at a rate of 0.5-1℃ / min, and hold for 4-5 hours; Second stage: Heat to 400-420℃ at a rate of 1-2℃ / min, and hold for 6-7 hours; The third stage: heat up to 600-620℃ at a rate of 0.8-1.5℃ / min, hold for 4-5 hours, and then cool to room temperature.

5. The method for preparing a ceramic insulator according to claim 2, characterized in that, Step S4, the staged controllable sintering, includes: S41: In the first stage, the green blank is heated from room temperature to 1150-1250℃ at a rate of 2-4℃ / min and held for 1-3 hours to achieve core layer pre-sintering; S42: In the second stage, the temperature is increased to 1420-1480℃ at a rate of 4-6℃ / min and held for 1.5-2.5h to achieve core densification; S43: In the third stage, the temperature is rapidly increased to 1530-1570℃ at a rate of 6-10℃ / min, and microwave-assisted sintering is used. The temperature is held for 0.5-1.5h to achieve full sintering of the shell layer. S44: The fourth stage involves slowly cooling to 1150-1250℃ at a rate of 0.5-1℃ / min and holding at that temperature for 2-4 hours to promote the formation of a gradient structure at the core-shell interface. S45: The fifth stage involves cooling to room temperature at a rate of 1-3℃ / min to complete sintering.

6. The method for preparing a ceramic insulator according to claim 5, characterized in that, The microwave-assisted sintering described in step S43 has a microwave frequency of 2.45-2.52 GHz and a power of 5-10 kW. The microwave power is periodically fluctuated during the heat preservation period, with the fluctuation range being ±5% to ±15% of the set power.

7. The method for preparing a ceramic insulator according to claim 2, characterized in that, Following step S4, a post-processing step S5 is included: surface polishing of the sintered ceramic insulator substrate, followed by coating with an insulating glaze layer and secondary sintering, wherein the thickness of the insulating glaze layer is 10-20 μm, and / or The secondary sintering temperature is 700-800℃, and the holding time is 0.5-1.5h.

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