Alumina ceramic material as well as preparation method and application thereof

Abstract

The invention discloses an aluminum oxide ceramic material as well as a preparation method and application thereof. The aluminum oxide ceramic material comprises an alpha-Al2O3 matrix phase, reinforced phase particles dispersed and distributed in the matrix phase, and a grain boundary phase formed among matrix phase grains, the average grain size of the alpha-Al2O3 matrix phase is smaller than or equal to 5 microns, the size of the reinforced phase particles is 0.3-1.5 microns, and the width of the grain boundary phase is 50-200 nm. By adjusting the components of the aluminum oxide matrix and adding the composite sintering aid and the grain boundary strengthening phase, material densification and grain refinement are achieved, and therefore high insulativity and high strength are both considered.

Description

Technical Field

[0001] This invention relates to the field of functional ceramic materials and their manufacturing technology, specifically to an alumina ceramic material, its preparation method, and its applications. Background Technology

[0002] With the technological iteration in fields such as 5G / 6G communication, high-frequency medical equipment, airborne electronic systems and high-power lasers, the performance requirements of equipment for core components are constantly being upgraded. In particular, the electrode holder, as a key carrier for current transmission and signal conduction, must simultaneously meet three core requirements: high power and high current carrying capacity, high withstand voltage insulation, and stable mechanical structure.

[0003] Early electrode holders were mostly made of metals such as copper, aluminum, and stainless steel. Their advantages were high mechanical strength and easy processing and forming. However, they had many defects in high-voltage and high-power scenarios: 1) Insufficient insulation performance. Metals are conductive. Even if the surface is coated with an insulating layer, the insulation is easily broken down due to coating wear and high-temperature aging. The withstand voltage is low and cannot meet the requirements of high-voltage applications; 2) Poor thermal stability. Metals are prone to heat generation when large currents pass through them, which leads to material creep and increased contact resistance. Long-term use can easily cause loosening, burning and other failures, affecting the reliability of equipment operation; 3) Insufficient adaptability. In precision electronic equipment, the electromagnetic shielding interference problem of metal electrode holders is prominent, and they are not compatible with the insulation packaging process in high-frequency and high-voltage scenarios.

[0004] To address the insulation limitations of metallic materials, the industry has begun using ceramics as electrode substrates, with alumina (Al2O3) ceramics becoming the mainstream choice due to their excellent insulation properties and strong chemical stability. However, traditional pure alumina ceramics have a flexural strength of only about 200 MPa, coarse grains, and high porosity, resulting in significant brittleness. During the metallization coating, welding with the metal core, and assembly processes of the electrode substrate, key structures such as bosses and blind holes are prone to cracking and chipping due to localized stress concentration, leading to a high product scrap rate. The long high-temperature sintering time required for pure alumina ceramics not only results in high energy costs but also increases the risk of abnormal grain growth due to high temperatures, further exacerbating brittleness. Some improved solutions involve adding a single sintering aid, which can reduce the sintering temperature to some extent, but the strength improvement is limited. Other solutions introduce a single reinforcing phase to increase the ceramic's hardness, but this leads to a decrease in insulation performance, failing to simultaneously meet the requirements of high insulation and high strength.

[0005] In addition, the microstructure stability of existing ceramic materials is poor. Under the high temperature environment of the metallization process, grain boundary oxidation and pore expansion are prone to occur, which leads to a decrease in the bonding force between the metal layer and the ceramic matrix and affects the service life of the electrode holder. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the purpose of this application is to provide an alumina ceramic material that achieves material densification and grain refinement by adjusting the composition of the alumina matrix and adding composite sintering aids and grain boundary strengthening phases, thereby achieving both high insulation and high strength.

[0007] To solve the above problems, the technical solution adopted in this application is as follows:

[0008] This application provides an alumina ceramic material comprising an α-Al2O3 matrix phase, reinforcing phase particles dispersed in the matrix phase, and grain boundary phases formed between the matrix phase grains; the average grain size of the α-Al2O3 matrix phase is ≤5μm, the size of the reinforcing phase particles is 0.3-1.5μm, and the width of the grain boundary phase is 50-200nm.

[0009] As a further preferred embodiment, the alumina ceramic material described in this application includes alumina as the main component, a reinforcing phase, a sintering aid, and an insulating modifier; the mass fraction of the alumina is 85wt%-95wt%, the mass fraction of the reinforcing phase is 2wt%-8wt%, the mass fraction of the sintering aid is 2wt%-5wt%, and the mass fraction of the insulating modifier is 0.5wt%-2wt%.

[0010] As a further preferred embodiment, the reinforcing phase described in this application is one or a mixture of two or more of zirconium oxide, zirconium silicate, silicon carbide, and silicon nitride; the sintering aid is a mixture of silicon dioxide and magnesium oxide; and the insulating modifier is yttrium oxide or calcium oxide.

[0011] As a further preferred embodiment, the grain boundary phase described in the embodiments of this application is a glassy phase or solid solution phase formed by SiO2 and MgO.

[0012] As a further preferred embodiment, the α-Al₂O₃ grains in the α-Al₂O₃ matrix phase described in this application are short columnar or equiaxed, with a grain aspect ratio of (1-1.5):1; the coefficient of variation of grain size distribution is ≤20%, and the dislocation density is ≤10⁻⁶. 6 cm -2 .

[0013] As a further preferred embodiment, the alumina ceramic material described in this application has a flexural strength of 300-400 MPa and a volume resistivity ≥10⁻⁶. 14 Ω·cm, porosity ≤1%

[0014] This application also provides a method for preparing alumina ceramic materials, which solves the problems of insulation breakdown and thermal creep in high-voltage scenarios of traditional metal electrode holders, and overcomes the defects of existing ceramic electrode holders, such as low bending strength, high brittleness, and easy cracking during metallization and welding, due to large grains and high porosity. At the same time, it reduces the ceramic sintering temperature to reduce energy consumption and ensures the compatibility of the material with the subsequent manufacturing processes of the electrode holder.

[0015] The preparation method includes the following steps:

[0016] Raw material mixing: Using deionized water as the medium, the raw materials of alumina ceramic material are ball-milled in a ball mill to make the particle size of the mixture reach D50≤1μm, forming a uniform slurry;

[0017] Molding: The above slurry is made into a green body with a density controlled at 2.5-3.0 g / cm³. 3 ;

[0018] Pre-sintering: The green body is pre-sintered in an air atmosphere to remove organic matter and moisture, and a green body is obtained;

[0019] Sintering: The above-mentioned green body is sintered to obtain a ceramic body.

[0020] As a further preferred embodiment, in the raw material mixing step described in this application, the ball-to-material ratio of the ball mill is 5:1, the ball diameter is a mixture of 10mm and 5mm balls, the ball milling time is 4-6 hours, the rotation speed is 200-300rpm, and the solid content of the resulting slurry is 50wt%-60wt%.

[0021] As a further preferred embodiment, in the molding step described in this application, the green body is prepared by dry pressing, with a molding pressure of 50-100MPa, a pressing speed of 3-8MPa / s, and a holding time of 30-60s.

[0022] As a further preferred embodiment, in the pre-sintering step described in this application, the sintering temperature is 800-1000℃, the sintering time is 2-3 hours, and the heating rate is 4-6℃ / min.

[0023] As a further preferred embodiment, the sintering steps described in this application adopt a segmented sintering method; the first stage: sintering at 1400-1500℃ for 1-2 hours, with a heating rate of 3-5℃ / min; the second stage: final sintering at 1550-1600℃ for 2-4 hours, with a heating rate of 1-2℃ / min and a cooling rate of 3-8℃ / min.

[0024] As a further preferred embodiment, the sintering step described in this application uses hot pressing sintering, with a sintering temperature of 1300-1400℃, a hot pressing pressure of 20MPa-50MPa, a holding time of 30-60 minutes, a heating rate of 5℃ / min-10℃ / min, a cooling rate of 5℃ / min-8℃ / min, and a sintering atmosphere of air or argon.

[0025] The alumina ceramic material described in this application is used to prepare ceramic electrode holders. It can also be used in other high-insulation, high-strength ceramic components, such as insulators or sensor bases.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. The α-Al₂O₃ matrix phase in the alumina ceramic material described in this application has refined grains, increasing the number of grain boundaries and effectively hindering dislocation slip and crack propagation. Combined with the dispersed distribution of reinforcing phase particles, it forms a dual reinforcement effect of fine-grained strengthening and dispersion strengthening. On the one hand, the fine-grained matrix increases the flexural strength of the material to 300-400 MPa; on the other hand, the reinforcing phase particles can absorb crack propagation energy through martensitic phase transformation, or delay crack extension through particle bridging and crack deflection, significantly improving the material's impact resistance and fracture toughness, and effectively reducing the risk of edge chipping and cracking of ceramic electrode holders during metallization, welding, and assembly. At the same time, the refined matrix grains and appropriately sized reinforcing phase particles can reduce the internal thermal stress gradient of the material. The 50-200 nm wide grain boundary phase has good toughness and thermal expansion matching, which can buffer the thermal stress generated by temperature changes and avoid structural failure caused by thermal shock.

[0028] 2. The alumina ceramic material α-Al2O3 matrix described in this application has excellent insulation properties. The refined grain structure, the dispersed reinforcing phase particles, and the 50-200nm continuous grain boundary phase together construct a dense and uniform insulation structure. This results in an overall porosity of ≤1% with isolated closed pores as the main component, avoiding insulation breakdown channels caused by pores. The fine grains and continuous grain boundary phases hinder charge migration, increasing the material's withstand voltage and volume resistivity. This allows it to stably meet the insulation requirements of high-voltage, high-power scenarios such as 5G base stations and high-frequency medical equipment, eliminating the risk of insulation breakdown.

[0029] 3. Furthermore, the alumina ceramic material described in this application does not have brittle phases such as Al2SiO5 generated in the grain boundary phase, and the total content of harmful impurities (Fe, Na, etc.) is ≤0.05%, with no obvious impurity segregation, thus avoiding the grain boundary becoming a weak link in insulation; at the same time, the reinforcing phase particles are tightly bonded to the matrix phase interface, and local electric field concentration will not occur due to interface defects, ensuring that the insulation performance of the material does not decay during long-term use and improving the reliability of equipment operation.

[0030] 4. The refined grain structure and uniform microstructure of the alumina ceramic material described in this application make the sintered ceramic body easy to grind and polish, and can accurately control the dimensional accuracy of the electrode holder to meet the requirements of precision assembly.

[0031] The present invention will be further described in detail below with reference to specific embodiments. Attached Figure Description

[0032] Figure 1 This is a scanning electron microscope (SEM) image of the alumina ceramic material obtained in this embodiment. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0034] The term "comprising" and other equivalent descriptive terms used in the specification and claims of this application are intended to cover a non-exclusive inclusion, which includes both the contents explicitly described in the specification and claims and steps or units that are not described in the specification and claims but are inherent in the product, method or structure.

[0035] This application provides an alumina ceramic material comprising an α-Al₂O₃ matrix phase, reinforcing phase particles dispersed in the matrix phase, and grain boundary phases formed between the matrix phase grains. α-Al₂O₃ is the core load-bearing phase of the ceramic material. The average grain size of the α-Al₂O₃ matrix phase is controlled to ≤5μm, significantly increasing the grain boundary density and raising the flexural strength to over 300MPa, thus solving the problem of insufficient strength in traditional ceramics at the matrix level. The ≤5μm fine grain size distribution is more uniform, reducing stress concentration points within the material. Simultaneously, the fine grain structure allows for stress distribution during forming, sintering, and subsequent processing of the ceramic body. The more uniform grain size avoids edge chipping and cracking caused by excessive local stress, thus improving product processing yield. α-Al2O3 itself has excellent insulation properties. The fine-grained structure can reduce intracrystalline defects, and the improved uniformity of grain size can avoid the electric field concentration effect formed by large and small grains, reducing the risk of insulation breakdown. At the same time, the fine-grained matrix is ​​more likely to combine with the reinforcing phase and grain boundaries to form a dense structure, reducing weak points in insulation such as pores. In addition, the thermal expansion coefficient of fine grains is more uniformly distributed, and the internal thermal stress gradient of the material is smaller when the temperature changes. It is not easy to generate microcracks due to differences in thermal expansion and contraction, so that the ceramic material can be adapted to temperature fluctuation scenarios during electrode holder processing and use. In this embodiment, the reinforcing phase particles are mechanically strengthening phases with a size of 0.3-1.5 μm. The hardness and elastic modulus of the reinforcing phase particles are higher than those of the α-Al₂O₃ matrix. Through dispersed distribution (no agglomeration, uniformly dispersed within the grains or grain boundaries), they can form micro-support points in the matrix, hindering dislocation slip and grain deformation. This, combined with grain refinement, creates a dual strengthening effect, further increasing the flexural strength of the material to 350-400 MPa. The reinforcing phase is selected from zirconium oxide, zirconium silicate, silicon carbide, silicon nitride, etc. When the reinforcing phase is ZrO₂, ZrO₂ particles in the 0.3-1.5 μm size range exhibit better mechanical properties under stress. During cooling, a martensitic phase transformation from tetragonal to monoclinic phase can occur, resulting in a volume expansion of approximately 3%-5%. This expansion absorbs energy for crack propagation and creates a compressive stress field at the crack tip, hindering further crack extension. When the reinforcing phase is ZrSiO4, SiC, or Si3N4, the 0.3-1.5μm particle size can delay crack instability and propagation through particle bridging and crack deflection, significantly improving the material's fracture toughness and impact resistance. The reinforcing phase particles themselves are insulating materials, and their dispersed distribution forms conductive channels. Combined with a fine-grained matrix, this ensures that the overall insulation performance of the material remains unaffected, achieving a synergy between toughness and strength.The grain boundary phase described in this application embodiment is the link connecting the α-Al2O3 matrix phase and the reinforcing phase particles, and is formed by sintering aids during the sintering process. In this application embodiment, the width of the grain boundary phase is 50-200 nm. The grain boundary phase exists in liquid phase form during sintering. The width of 50-200 nm ensures that the liquid phase fully fills the gaps between the matrix grains and the reinforcing phase particles, reducing porosity and achieving material densification. At the same time, the presence of the liquid phase can lower the sintering temperature, reduce energy consumption, and form a stable structure without excessively long holding time, thus improving production efficiency. The grain boundary phase can interact with the α-Al2O3 matrix and the reinforcing phase. The phase particles form chemical bonds or physical wetting, and the width of 50-200 nm ensures that the interface is free of cracks and impurity enrichment layers, avoiding particle detachment or crack propagation along the interface due to weak interface bonding, and further enhancing the overall mechanical properties of the material. In addition, the continuous grain boundary phase can hinder charge migration, and the total content of harmful impurities in the grain boundary phase is ≤0.05%, with no impurity segregation, preventing the grain boundary from becoming a weak link in insulation. The thermal expansion coefficient of the grain boundary phase is between that of the matrix and the reinforcing phase, and the width of 50-200 nm can buffer the thermal stress generated by temperature changes, which can further reduce interface peeling or crack formation caused by thermal shock.

[0036] The alumina ceramic material described in this application includes alumina as the main component, a reinforcing phase, a sintering aid, and an insulating modifier. The mass fraction of alumina is 85wt%-95wt%, the mass fraction of the reinforcing phase is 2wt%-8wt%, the mass fraction of the sintering aid is 2wt%-5wt%, and the mass fraction of the insulating modifier is 0.5wt%-2wt%. In this application, the mass fraction of alumina as the main component is the core variable determining the comprehensive performance of the ceramic material, directly affecting the material's insulation performance, mechanical properties, and thermal stability. The alumina matrix is ​​the mechanical load-bearing skeleton; if the amount is too low, the skeleton will become loose, and the reinforcing phase particles will lack effective support, failing to exert a dispersion strengthening effect. If the amount of alumina is too low, not only will the increased proportion of the reinforcing phase lead to agglomeration and the formation of internal defects, but the increased proportion of the sintering aid will also result in excessively wide grain boundaries, thus causing the material's bending strength and toughness to fail to meet application requirements. In addition, the glassy grain boundaries formed by excessive sintering aid are prone to softening at high temperatures, leading to material structural deformation. In terms of insulation, an alumina content of 85wt%-95wt% ensures the continuity and integrity of the alumina matrix, forming an uninterrupted insulation network. The 3wt%-8wt% reinforcing phase exists in a dispersed distribution, without disrupting the insulation network. The 2wt%-5wt% sintering aid purifies grain boundary impurities, and together with the continuous matrix, ensures that the withstand voltage and volume resistivity meet application requirements. Regarding mechanical properties and toughness, optimizing the proportions of the alumina matrix, reinforcing phase, and sintering aid achieves a balance between strength and toughness. The alumina matrix forms a stable load-bearing skeleton, reinforced by fine grains. The reinforcing phase, through phase transformation toughening, crack deflection, or dispersion strengthening, creates a dual reinforcing effect, improving flexural strength. The sintering aid forms an appropriate amount of liquid phase to promote densification, avoid interface defects, and further enhance mechanical stability. In terms of thermal stability, the high proportion of alumina ensures that the material is resistant to high temperatures and has strong chemical inertness; an appropriate amount of sintering aids reduces the sintering temperature and energy consumption, and can also prevent high-temperature softening caused by excessive grain boundary phase; the appropriate amount of reinforcing phase has good matching with the thermal expansion coefficient of the matrix, excellent thermal shock resistance, and can cope with temperature fluctuation scenarios.

[0037] When SiO2 is used as a single additive, it readily reacts with Al2O3 to form the brittle Al2SiO5 (mullite) phase. In some embodiments, preferably, the sintering aid used is a mixture of silicon dioxide and magnesium oxide. The addition of MgO can suppress the formation of mullite. The two can form a low-melting-point eutectic system, which will preferentially melt to form a uniform liquid phase within the sintering temperature range. The liquid phase fills the voids between the α-Al2O3 matrix particles and the reinforcing phase, reducing the diffusion resistance between particles, and pulls the solid particles closer together through capillary attraction, promoting the bonding and densification between particles. After cooling, the liquid phase transforms into a glassy phase or a solid solution grain boundary phase, connecting the matrix and the reinforcing phase to form a stable microstructure. In this embodiment, the use of mixed sintering aids can fully fill the internal voids of the material, reducing the porosity of the ceramic material from 2%-3% in traditional pure Al2O3 ceramics to ≤1%. Furthermore, the pores are predominantly isolated and closed, preventing crack initiation and propagation at the pores, directly improving flexural strength, avoiding local electric field concentration, and ensuring withstand voltage and volume resistivity. The liquid phase formed by SiO2 and MgO can inhibit abnormal growth of α-Al2O3 grains, ensuring a stable average grain size of ≤5μm in the matrix. The liquid phase, by wetting the matrix and the surface of the reinforcing phase, promotes interfacial chemical bonding or physical wetting, preventing the formation of cracks and impurity enrichment layers at the interface, reducing the risk of particle shedding and crack propagation along the interface. The liquid phase also has fluidity, dissolving and uniformly dispersing conductive impurities such as Fe and Na, further improving insulation reliability. The glassy / solid solution grain boundary phase formed by SiO2 and MgO has a certain toughness, buffering stress impacts and avoiding the brittle fracture problem of traditional ceramic grain boundaries, improving the material's impact resistance and fracture toughness, and adapting to the mechanical stress in electrode holder processing (grinding, welding). The glassy phase / solid solution formed by SiO2 and MgO is itself an insulating material, forming a continuous insulating network with the Al2O3 matrix without conductive channels. The mass ratio of SiO2 to MgO affects the densification, mechanical properties, insulation properties, and process compatibility of ceramic materials to varying degrees. When MgO is excessive, the liquid phase has poor fluidity, weak interfacial bonding, high grain boundary brittleness, and increased porosity, leading to a significant stress concentration effect and insufficient flexural strength. It also causes discontinuity in the grain boundary phase, forming localized weak points in insulation. Although MgO itself is insulating, these defects cause fluctuations in withstand voltage, making it prone to breakdown under high voltage conditions. Excessive MgO also increases the melting point of the liquid phase, necessitating a higher sintering temperature, and high temperatures can easily lead to abnormal phase transformations in the reinforcing phase. If SiO2 is excessive, the formation of the brittle mullite phase reduces the flexural strength and impact resistance of the ceramic material. Excessive SiO2 also results in an excessively high proportion of the glassy phase, making it prone to absorbing environmental moisture. Grain boundary defects in the mullite phase can cause electric field concentration, ultimately leading to a decrease in withstand voltage.In the embodiments of this application, the mass ratio of SiO2 to MgO is controlled at (1-1.5):1, which can simultaneously meet the three major requirements of forming a low-melting-point liquid phase, suppressing the formation of brittle phase, and optimizing the flowability and stability of grain boundary phase, thereby maximizing the core role of the mixed sintering aid; by precisely balancing the liquid phase characteristics and grain boundary phase structure, densification, low energy consumption, mechanical and insulating properties are achieved.

[0038] In some embodiments of this application, the insulating modifier used is yttrium oxide (Y₂O₃) or calcium oxide (CaO). Y₂O₃ can form stable composite oxides with conductive impurities such as Fe, Na, and K, preventing impurities from segregating at grain boundaries and forming conductive channels, thus eliminating weak points in the insulation at the source and stabilizing the volume resistivity of the ceramic material. When the reinforcing phase is yttrium-stabilized zirconium oxide, Y₂O₃ can react with the Y₂O₂ in ZrO₂. 3+ A synergistic stabilizing effect is formed, avoiding interfacial lattice defects during the ZrO2 phase transformation, ensuring the continuity of insulation between the reinforcing phase and the matrix interface, and preventing local electric field concentration caused by interfacial defects. Y2O3 can adsorb on the surface of Al2O3 grains, hindering grain diffusion and fusion, and further refining the average grain size of the matrix. Y2O3 can inhibit the growth of brittle phases during sintering, preventing crack propagation along brittle phases. Y2O3 can also form a slight solid solution with Al2O3 and ZrO2, improving the interfacial bonding force among the matrix, reinforcing phase, and grain boundary phase, reducing interfacial cracks and voids, and effectively reducing the risk of edge chipping of ceramic electrode holders during welding and assembly. In addition, Y2O3 has a high melting point and does not decompose or volatilize during the sintering of the ceramic green body, and the grain boundary phase structure remains stable, avoiding performance degradation due to modifier failure. As an insulating modifier, CaO can form a lower viscosity composite liquid phase with SiO2-MgO sintering aids, resulting in better fluidity. This allows it to fully fill the tiny gaps between the matrix and the reinforcing phase, reducing porosity and improving densification efficiency, while also reducing sintering holding time. CaO and SiO2-MgO can form a low dielectric loss glass phase, avoiding insulation heating caused by poor dielectric properties of the grain boundary phase. This is particularly suitable for high-frequency and high-voltage applications, reducing energy loss. Furthermore, CaO can react with free SiO2 in the grain boundary phase to form CaSiO3, reducing the hygroscopicity of the grain boundary phase and preventing fluctuations in withstand voltage due to changes in environmental humidity, ensuring stable operation of the material in humid conditions.

[0039] In this application, grain morphology and aspect ratio are key factors determining stress transmission and crack propagation paths under stress. The α-Al₂O₃ grains in the α-Al₂O₃ matrix phase described in this application are short columnar or equiaxed, with an aspect ratio of (1-1.5):1. The equiaxed or short columnar grains have no obvious orientation, allowing stress to be evenly distributed among the grains and grain boundaries under stress, avoiding stress concentration caused by the orientation of long columnar grains. Combined with the compact shape of the (1-1.5):1 aspect ratio, the grains are more tightly interlocked, effectively improving flexural strength. The coefficient of variation of grain size distribution in the ceramic material described in this application is ≤20%, and the dislocation density is ≤10⁻⁶. 6 cm -2 The grain size is uniform (concentrated at 3-5 μm), with no abnormally large grains, and the stress is evenly distributed across all grains and grain boundaries. The uniform grain size ensures uniform grain boundary distribution, and impurities are dispersed at each grain boundary without local enrichment. The uniform grain size also ensures consistent particle diffusion rate during sintering, with no large grains hindering densification. Pores are easily filled by the liquid phase, and the ceramic body surface is smooth after sintering. The machining allowance is uniform during grinding and polishing, and the dimensional accuracy of the electrode holder (e.g., blind hole perpendicularity, roughness, etc.) can be precisely controlled.

[0040] The alumina ceramic material described in this application has a flexural strength of 300-400 MPa and a volume resistivity ≥10⁻⁶. 14 Ω·cm, porosity ≤1%

[0041] This application also provides a method for preparing alumina ceramic materials, which solves the problems of insulation breakdown and thermal creep in high-voltage scenarios of traditional metal electrode holders, and overcomes the defects of existing ceramic electrode holders, such as low bending strength, high brittleness, and easy cracking during metallization and welding, due to large grains and high porosity. At the same time, it reduces the ceramic sintering temperature to reduce energy consumption and ensures the compatibility of the material with the subsequent manufacturing processes of the electrode holder.

[0042] The preparation method includes the following steps:

[0043] Raw material mixing: Using deionized water as the medium, the alumina ceramic material raw materials are ball-milled in a ball mill. The ball-to-material ratio of the ball mill is set to 5:1. This ball-to-material ratio provides sufficient grinding impact force, ensuring that the balls have sufficient impact, compression, and shearing force on the raw material particles during the grinding process, quickly breaking up the raw material agglomerates and achieving particle size refinement. A mixture of 10mm and 5mm balls is used to achieve coarse crushing and fine grinding in one step. The ball milling time is controlled at 4-6 hours and the rotation speed is 200-300 rpm. Through the coordination of time and rotation speed, the particle size of the mixture reaches D50≤1μm, forming a uniform slurry. The finer the raw material particle size, the larger the specific surface area, and the higher the sintering activity. During sintering, the particle diffusion rate is faster, making it easier to form a dense structure and reducing the porosity to ≤1%. Fine particle size is also a prerequisite for α-Al₂O₃ matrix grains to be ≤5μm after sintering. The finer the raw material particle size, the finer and more uniform the grains after sintering, thus improving flexural strength. Simultaneously, fine-grained raw material particles are easier to disperse uniformly, allowing the reinforcing phase and sintering aids to be evenly coated on the surface of alumina particles, avoiding local enrichment or absence, ensuring continuous grain boundary phase and diffuse distribution of the reinforcing phase after sintering, achieving synergistic insulation and mechanical properties. The slurry obtained in this application embodiment has a solid content of 50wt%-60wt%, exhibits uniform flow, no stratification, and moderate thixotropy, making it suitable for dry pressing and slurry casting.

[0044] Forming: The above slurry is made into a green body. The density of the green body is one of the key factors determining whether a dense ceramic body can be formed during subsequent sintering. If the density is too low, the particles are loosely packed, with many interconnected internal pores, resulting in extremely low green body strength. It is easily damaged during transportation, and uneven shrinkage, deformation, and cracking are likely to occur during pre-sintering. During sintering, it is necessary to compensate for the excessive pores, which can easily lead to insufficient densification. The final ceramic has a high porosity, and the pores form insulation breakdown channels and stress concentration sources, resulting in insufficient compressive and flexural strength. If the density is too high, the green body is over-compacted, generating a large amount of internal stress. During subsequent sintering and heating, the internal stress is released with the expansion of the particles, which can easily cause the green body to crack and warp, significantly increasing the scrap rate. During sintering, the release of internal stress triggers microcracks. Even if densification is achieved, cracks will remain, leading to a decrease in the fracture toughness of the ceramic, easy chipping during processing, and poor thermal shock resistance. In this step, the green body density is controlled at 2.5-3.0 g / cm³. 3 The green body exhibits dense particle packing with no obvious loose pores, delamination, or cracks, resulting in moderate strength after molding. During sintering, the diffusion distance between particles is short, leading to tight bonding. Subsequent pre-sintering and sintering achieves sufficient densification. In some embodiments, dry pressing is used to prepare the green body, with a pressing pressure of 50-100 MPa, a pressing speed of 3-8 MPa / s, and a holding time of 30-60 s. In this embodiment, the pressing pressure of 50-100 MPa can overcome the agglomeration and repulsion forces between slurry particles, resulting in dense particle packing, stable green body density, and controllable green body density between 2.5-3.0 g / cm³.3 Within a certain range, insufficient pressure should be avoided to prevent the sintered ceramic from becoming porous and loose; excessive pressure should also be avoided to prevent over-compaction of the green body, plastic deformation between particles, and a sharp increase in internal stress. During subsequent sintering and heating, the release of this internal stress can lead to cracking and warping of the green body. The pressing speed determines the pressure transmission efficiency and the effect of gas expulsion from the green body. A pressing speed of 3-8 MPa / s allows sufficient time for air to escape from the mold gaps, preventing air bubbles and shrinkage cavities, resulting in a dense and uniform green body without localized porosity. Pressure is quickly and evenly transmitted to all parts of the green body, resulting in high compaction efficiency and timely air expulsion. Holding pressure releases the internal stress generated by the instantaneous pressure, ensuring stable green body density and preventing springback deformation after demolding. A holding time of 30-60 seconds allows for sufficient rearrangement of particles within the green body, eliminating localized stress generated during pressing, and ensuring even pressure transmission to complex areas such as blind holes and bosses, ensuring consistent density throughout the green body. After holding pressure and demolding, the green body exhibits no springback deformation and stable dimensions. In other embodiments, a slurry injection method can also be used to form the green body.

[0045] Pre-sintering: The green body is pre-sintered in an air atmosphere. The purpose of pre-sintering is to gently remove moisture and organic matter from the green body, improve the strength of the green body, and eliminate residual defects from the early forming process, laying a solid foundation for densification and performance stability in subsequent staged high-temperature sintering. Temperature is the core control indicator for pre-sintering. In this step, the sintering temperature is set at 800-1000℃, which allows the free water and bound water in the green body to completely evaporate, avoiding the internal stress caused by moisture vaporization during subsequent high-temperature sintering, which could lead to cracking and warping of the green body. At the same time, it can prevent the green body particles from becoming dense during sintering, maintaining a certain porosity and reserving space for particle diffusion and liquid phase filling during subsequent high-temperature sintering. Controlling the sintering time ensures uniform impurity removal in all parts of the green body. In this step, the sintering time is set at 2-3 hours, which not only ensures that heat is conducted to the interior of the green body, allowing deep moisture and organic matter to fully evaporate and oxidize, but also allows impurities to evaporate slowly, avoiding blistering and deformation of the green body caused by concentrated evaporation in a short period of time, resulting in a more complete green body structure. The heating rate determines the pace of heat conduction and impurity volatilization within the billet, which is crucial to preventing cracking and deformation. The heating rate should be controlled at 4-6℃ / min. Low-speed heating allows heat to be slowly conducted from the surface of the billet to the interior, keeping the temperature difference between the inside and outside within 50℃. Moisture and organic matter gradually volatilize and oxidize, preventing bubbling caused by localized violent vaporization. This also avoids excessive thermal stress caused by large temperature differences between the inside and outside, which can lead to cracking and warping of the billet.

[0046] Sintering: The above-mentioned green body is sintered to obtain a ceramic body. In some embodiments, the sintering step adopts a segmented sintering method; two-stage heating and gradient cooling, through gradual densification, avoids defects caused by one-time high temperature; the first stage is preheating densification, sintering at 1400-1500℃ for 1-2 hours. The temperature of 1400-1500℃ is lower than the rapid growth temperature of α-Al2O3 grains, only promoting grain germination growth, without abnormally large grains. 1400℃ is the critical temperature for the formation of liquid phase of SiO2-MgO mixed additive. The liquid phase begins to wet the Al2O3 matrix and reinforcing phase particles, initially filling the pores of the green body, and the density of the green body is improved after sintering; holding at 1-2 hours allows sufficient heat to be conducted to the interior of the green body, the liquid phase uniformly wets and fills the pores, and the density of each area of ​​the green body is consistent, avoiding surface density and internal looseness; at the same time, it allows the reinforcing phase particles to initially disperse, without local agglomeration. The first stage involves a heating rate of 3-5℃ / min, keeping the temperature difference between the inside and outside of the billet below 80℃ to prevent significant thermal stress and avoid cracking and warping caused by excessively rapid heating. Simultaneously, it allows the liquid phase to form slowly, preventing bubbles caused by rapid expansion. The second stage of sintering involves final sintering at 1550-1600℃ for 2-4 hours. This temperature range represents the optimal fluidity of the SiO2-MgO liquid phase, ensuring sufficient liquid flow to thoroughly fill residual pores in the billet and achieve complete densification. This promotes the uniform growth of α-Al2O3 grains to 3-5μm without abnormal growth. Simultaneously, it allows the grain boundary phase to form with an optimal width of 50-200nm, connecting the matrix and reinforcing phase. Sufficient sintering time allows for full diffusion of the liquid phase, ensuring all pores are filled and densification is thorough. The grain boundary phase is evenly distributed without local enrichment / deficiency, while the insulating modifier fully purifies the grain boundaries, eliminating the segregation of conductive impurities. The second stage heating rate is 1-2℃ / min, which can control the temperature difference between the inside and outside of the green body within 30℃, ensuring absolutely uniform heating and avoiding coarse grains caused by local overheating. Simultaneously, it allows the liquid phase to flow slowly, preventing bubble formation and resulting in more uniform grain boundary phase formation. In this step, after the second stage of sintering, the ceramic body is cooled at a rate of 3-8℃ / min. The purpose of this cooling is to control the ZrO2 phase transformation, lock the grain boundary phase structure, and prevent thermal stress cracking. In other embodiments, hot pressing sintering is used, combining pressure-assisted sintering with low-temperature sintering. The sintering temperature is 1300-1400℃, and the hot pressing pressure is 20MPa-50MPa. This can inhibit grain growth. With pressure assistance, the sintering aid can form a liquid phase at 1300℃, achieving densification without the need for high temperatures, thus avoiding oxidation of the reinforcing phase caused by high temperatures. The holding time is 30-60 minutes, the heating rate is 5℃ / min-10℃ / min, the cooling rate is 5℃ / min-8℃ / min, and the sintering atmosphere is air or argon.

[0047] The alumina ceramic material described in this application is used to prepare ceramic electrode holders. It can also be used in other high-insulation, high-strength ceramic components, such as insulators or sensor bases.

[0048] Example 1

[0049] An alumina ceramic material is provided, wherein the raw materials for preparing the alumina ceramic material include 90wt% α-Al2O3 (matrix, purity 99.8%); 5wt% ZrO3 as reinforcing phase; 3.5wt% SiO2+MgO ​​as sintering aid (mass ratio 2:1.5); and 1.5wt% Y2O3 as insulating modifier; the total proportion is 100%.

[0050] The preparation method of this alumina ceramic material is as follows;

[0051] Ball milling: using deionized water as the medium, a ball-to-material ratio of 5:1, a mixture of 10mm and 5mm balls, a milling time of 5 hours, a rotation speed of 250 rpm, and controlling the slurry D... 50 It has a particle size of 0.8 μm and a solid content of 55 wt%.

[0052] Molding: Dry pressing, molding pressure 80MPa, pressing speed 5MPa / s, holding time 45s, green density 2.8g / cm³ 3 ;

[0053] Pre-sintering: air atmosphere, heating rate 5℃ / min, holding at 850℃ for 2.5h to remove moisture and organic matter, and obtain a dense green body;

[0054] Sintering: Segmented sintering, the first stage is held at 1450℃ for 1.5h with a heating rate of 4℃ / min; the second stage is held at 1580℃ for 3h with a heating rate of 1.5℃ / min; the cooling rate is 5℃ / min.

[0055] Figure 1 The image shows a scanning electron microscope (SEM) image of the alumina ceramic material obtained in this embodiment. The α-Al2O3 matrix grains are mainly short columnar and equiaxed, with an aspect ratio of approximately 1 to 1.5:1. The grain size is concentrated in the range of 3 to 5 μm, and the grains are evenly distributed without any obvious abnormally large grains, indicating that the grain growth is effectively controlled. At the same time, the microstructure of the material is extremely dense, with only a few isolated closed pores. In addition, the grain boundaries between grains are continuous and uniform in width, with no obvious agglomeration of brittle phases (such as mullite) or reinforcing phases.

[0056] Example 2

[0057] An alumina ceramic material is provided, wherein the raw materials for preparing the alumina ceramic material include 85 wt% α-Al2O3 (matrix, purity 99.8%); 4 wt% ZrSiO4 + 4 wt% SiC (mixed reinforcement, total 7 wt%); 5 wt% SiO2 + MgO sintering aid (mass ratio 1:1); and 2 wt% CaO insulating modifier; the total proportion is 100%.

[0058] The preparation method of this alumina ceramic material is as follows;

[0059] Ball milling: using deionized water as the medium, a ball-to-material ratio of 5:1, mixed balls with diameters of 10mm + 5mm, milling time of 4.5 hours, rotation speed of 230 rpm, and controlling the slurry D... 50 It has a particle size of 0.9 μm and a solid content of 52 wt%.

[0060] Molding: Slip casting, with a blind-hole electrode holder structure in the mold cavity, gradient drying (room temperature → 60℃ → 120℃), green density 2.6 g / cm³ 3 ;

[0061] Pre-sintering: air atmosphere, heating rate 4.5℃ / min, holding at 900℃ for 2h to remove moisture and organic matter and obtain a dense green body;

[0062] Sintering: Segmented sintering, the first stage is held at 1480℃ for 1 hour with a heating rate of 3.5℃ / min; the second stage is held at 1560℃ for 3.5 hours with a heating rate of 1.2℃ / min; the cooling rate is 4℃ / min.

[0063] Example 3

[0064] An alumina ceramic material is provided, wherein the raw materials for preparing the alumina ceramic material include 95 wt% α-Al2O3 (matrix, purity 99.8%); 2 wt% Si3N4 reinforcing phase; wt% SiO2+MgO2 sintering aid (mass ratio 3:2); 1 wt% CaO insulating modifier; total proportion 100%.

[0065] The preparation method of this alumina ceramic material is as follows;

[0066] Ball milling: using deionized water as the medium, ball-to-material ratio of 5:1, ball diameter of 10mm + 5mm mixed balls, ball milling time of 6h, rotation speed of 280rpm, controlling slurry D50 = 0.7μm, solid content of 58wt%;

[0067] Molding: Dry pressing, molding pressure 90MPa, pressing speed 6MPa / s, holding time 50s, green density 2.9g / cm³ 3 ;

[0068] Pre-sintering: air atmosphere, heating rate 5℃ / min, holding at 950℃ for 2h to remove moisture and organic matter and obtain a dense green body;

[0069] Sintering: Hot pressing sintering, argon atmosphere (to prevent Si3N4 oxidation), heating rate 8℃ / min, holding at 1380℃ for 45min, hot pressing pressure 35MPa; cooling rate 6℃ / min.

[0070] Comparative Example 1

[0071] An alumina ceramic material is provided. The raw materials for preparing the alumina ceramic material are the same as those in Example 1, wherein the insulating modifier Y2O3 is 3wt%; the preparation method steps and parameters are also the same as those in the example.

[0072] Comparative Example 2

[0073] An alumina ceramic material is provided. The raw materials and amounts used to prepare the alumina ceramic material are the same as in Example 1, except that the sintering aid is replaced with 3.5 wt% SiO2 (without MgO). All other steps and parameters are the same as in Example 1.

[0074] Comparative Example 3

[0075] An alumina ceramic material is provided. The raw materials and amounts used to prepare the alumina ceramic material are the same as in Example 1. In the preparation method, the sintering temperature in the second stage is 1650℃, and other steps and parameters are the same as in Example 1.

[0076] Performance testing

[0077] The properties of the alumina ceramic materials obtained in Examples 1-3 and Comparative Examples 1-3 were tested. The tested performance indicators included: porosity (tested according to GB / T 25995-2010 "Test Methods for Density and Apparent Porosity of Fine Ceramics"); α-Al2O3 grain size (tested according to GB / T 6524-2017 "Corrosion of Metals and Alloys - Removal of Corrosion Products from Corrosion Specimens" (Metallographic Sample Preparation Basics) + General Methods for Grain Statistical Analysis in the Ceramic Industry); flexural strength (tested according to GB / T 6569-2006 "Test Methods for Flexural Strength of Fine Ceramics"); compressive strength (tested according to GB / T 1408.1-2016 "Electrical Strength Test Methods for Insulating Materials - Part 1: Tests at Power Frequency"); volume resistivity (tested according to GB / T 1410-2006 "Test Methods for Volume Resistivity and Surface Resistivity of Solid Insulating Materials"); and thermal shock resistance (tested according to GB / T 1410-2006). 16536-2008, "Test Method for Thermal Shock of Fine Ceramics" (Water Quenching Method). Test results are shown in Table 1.

[0078] Table 1: Performance Test Results

[0079] Performance indicators Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Porosity (%) 0.6 0.8 0.3 2.3 1.9 0.5 <![CDATA[α-Al2O3 grain size (μm)]]> 4.2 3.8 2.9 7.8 6.3 9.3 Flexural strength (MPa) 365 352 402 245 262 252 Withstand voltage (kV / mm) 34 32 38 22 25 31 Volume resistivity (Ω·cm) <![CDATA[2.8×10 14 ]]> <![CDATA[1.9×10 14 ]]> <![CDATA[5.6×10 15 ]]> <![CDATA[3.2×10 12 ]]> <![CDATA[7.2×10 13 ]]> <![CDATA[1.9×10 14 <!-- 9 -->]]> Thermal shock resistance (retention rate after 5 cycles) 88％ 86％ 92％ 62％ 68％ 58％

[0080] The above embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of protection of this application. Any non-substantial changes and substitutions made by those skilled in the art based on this application shall fall within the scope of protection claimed by this application.

Claims

1. An alumina ceramic material, characterized in that, It includes an α-Al2O3 matrix phase, reinforcing phase particles dispersed in the matrix phase, and grain boundary phases formed between the matrix phase grains; the average grain size of the α-Al2O3 matrix phase is ≤5μm, the size of the reinforcing phase particles is 0.3-1.5μm, and the width of the grain boundary phase is 50-200nm.

2. The alumina ceramic material according to claim 1, characterized in that, It includes alumina as the main material, a reinforcing phase, a sintering aid, and an insulating modifier; the alumina has a mass fraction of 85wt%-95wt%, the reinforcing phase has a mass fraction of 2wt%-8wt%, the sintering aid has a mass fraction of 2wt%-5wt%, and the insulating modifier has a mass fraction of 0.5wt%-2wt%.

3. The alumina ceramic material according to claim 2, characterized in that, The reinforcing phase is one or a mixture of two or more of zirconium oxide, zirconium silicate, silicon carbide, and silicon nitride; the sintering aid is a mixture of silicon dioxide and magnesium oxide; and the insulating modifier is yttrium oxide or calcium oxide.

4. The alumina ceramic material according to claim 1, characterized in that, The grain boundary phase is a glassy phase or solid solution phase formed by SiO2 and MgO.

5. The alumina ceramic material according to any one of claims 1-4, characterized in that, The α-Al₂O₃ grains in the α-Al₂O₃ matrix phase are short columnar or equiaxed, with a grain aspect ratio of (1-1.5):1; the coefficient of variation of grain size distribution is ≤20%, and the dislocation density is ≤10⁻⁶. 6 cm -2 .

6. A method for preparing an alumina ceramic material as described in any one of claims 1-5, characterized in that, Includes the following steps: Raw material mixing: Using deionized water as the medium, the raw materials of alumina ceramic material are ball-milled in a ball mill to make the particle size of the mixture reach D50≤1μm, forming a uniform slurry; Molding: The above slurry is made into a green body with a density controlled at 2.5-3.0 g / cm³. 3 ; Pre-sintering: The green body is pre-sintered in an air atmosphere to remove organic matter and moisture, and a green body is obtained; Sintering: The above-mentioned green body is sintered to obtain a ceramic body.

7. The preparation method according to claim 6, characterized in that, In the raw material mixing step, the ball-to-material ratio of the ball mill is 5:1, the ball diameter is a mixture of 10mm and 5mm balls, the ball milling time is 4-6 hours, the rotation speed is 200-300rpm, and the solid content of the resulting slurry is 50wt%-60wt%.

8. The preparation method according to claim 6, characterized in that, In the forming step, the green body is prepared by dry pressing, with a forming pressure of 50-100MPa, a pressing speed of 3-8MPa / s, and a holding time of 30-60s.

9. The preparation method according to claim 6, characterized in that, In the pre-sintering step, the sintering temperature is 800-1000℃, the sintering time is 2-3 hours, and the heating rate is 4-6℃ / min.

10. The preparation method according to claim 6, characterized in that, The sintering process employs a segmented sintering method; the first stage involves sintering at 1400-1500℃ for 1-2 hours with a heating rate of 3-5℃ / min; the second stage involves final sintering at 1550-1600℃ for 2-4 hours with a heating rate of 1-2℃ / min and a cooling rate of 3-8℃ / min.

11. The preparation method according to claim 6, characterized in that, In the sintering step, hot pressing sintering is adopted, the sintering temperature is 1300-1400℃, the hot pressing pressure is 20MPa-50MPa, the holding time is 30-60 minutes, the heating rate is 5℃ / min-10℃ / min, the cooling rate is 5℃ / min-8℃ / min, and the sintering atmosphere is air or argon.

12. The use of an alumina ceramic material as described in any one of claims 1-5 in the preparation of a ceramic electrode holder.

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