Preparation method of alumina ceramic

Abstract

The invention relates to a preparation method of alumina ceramics, and belongs to the technical field of alumina ceramics. The method comprises the following steps: mixing high-purity alumina micro powder, water, a high-molecular dispersant and high-purity alumina nano powder to obtain slurry; wherein the purity of the high-purity alumina micro powder and the purity of the high-purity alumina nano powder are both gt; 4N; sequentially carrying out ball milling treatment and molding on the slurry to obtain an aluminum oxide green body; and sequentially drying, pre-sintering and sintering the alumina green body to obtain the alumina ceramic. The preparation of the high-purity and high-wear-resistance aluminum oxide ceramic is realized by accurately controlling the purity of the raw materials, constructing a double-peak particle system beneficial to densification, presintering at normal pressure, sintering at high pressure in a nitrogen atmosphere and the like, and a high-performance material solution is provided for related fields.

Description

Technical Field

[0001] This application relates to the field of alumina ceramics technology, and more particularly to a method for preparing alumina ceramics. Background Technology

[0002] High-purity, high-wear-resistant alumina ceramics, as an advanced functional material, have shown broad application prospects in many high-tech and industrial fields. Specifically, these materials play an indispensable role in key areas such as grinding media, artificial joints, dental restorations, semiconductor manufacturing, and aerospace.

[0003] However, the current production and preparation technologies for high-purity, high-wear-resistant alumina ceramics are mainly monopolized by foreign companies, resulting in a technological blockade. Therefore, developing high-purity, high-wear-resistant alumina ceramic preparation technologies with independent intellectual property rights is of great significance for breaking the foreign technological blockade, improving my country's materials science level, and ensuring national industrial security.

[0004] In China, although some research has been conducted on the preparation of high-wear-resistant alumina ceramics, these methods often sacrifice purity, making it difficult to simultaneously meet the requirements of high purity and high wear resistance. For example, while adding inorganic materials such as alumina, silica, yttrium oxide, and zirconium oxide to refine the grain and lower the sintering temperature improves the wear resistance of the ceramic, it cannot guarantee its purity. This compromise on purity prevents the prepared wear-resistant ceramics from being used in fields such as grinding media materials where high purity is required. Summary of the Invention

[0005] This application provides a method for preparing alumina ceramics to solve the following technical problem: how to solve the problem of difficulty in achieving both purity and wear resistance in current alumina ceramic preparation technology. This application provides a method for preparing alumina ceramics, the method comprising: High-purity alumina micro powder, water, polymeric dispersant, and high-purity alumina nano powder are mixed to obtain a slurry; wherein the purity of both the high-purity alumina micro powder and the high-purity alumina nano powder is >4N. The slurry was sequentially ball-milled and shaped to obtain alumina green blanks; The alumina green body is sequentially dried, pre-sintered, and sintered to obtain alumina ceramic.

[0006] Optionally, the particle size of the high-purity alumina nanoparticles is 10 nm to 100 nm.

[0007] Optionally, the particle size of the high-purity alumina micro powder is 0.15 μm to 0.4 μm.

[0008] Optionally, in the slurry, the mass fraction of the high-purity alumina micro powder is 70% to 79%, the mass fraction of the polymeric dispersant is 1% to 10%, and the mass fraction of the high-purity alumina nanopowder is 15% to 29%.

[0009] Optionally, the polymeric dispersant is one or more of ammonium polyacrylate, polyethylene glycol, or polyvinylpyrrolidone.

[0010] Optionally, the ball milling time is 5h to 10h, the ball-to-material ratio is (3 to 10):1, and the ball milling speed is 100rpm to 600rpm.

[0011] Optionally, the drying temperature is 50℃~100℃, and the drying time is 6h~8h.

[0012] Optionally, the pre-sintering is atmospheric pressure sintering, the pre-sintering temperature is 1000℃~1300℃, and the pre-sintering time is 1h~5h.

[0013] Optionally, the sintering is carried out under a nitrogen atmosphere, the sintering temperature is 1250℃~1500℃, the sintering pressure is 100MPa~150MPa, and the sintering time is 1h~3h.

[0014] Optionally, the alumina ceramic satisfies at least one of the following properties: purity > 4N, wear < 1‰, and average grain size < 1μm.

[0015] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for preparing alumina ceramics. The method includes: mixing high-purity alumina micro powder, water, a polymeric dispersant, and high-purity alumina nanoparticles to obtain a slurry; wherein the purity of both the high-purity alumina micro powder and the high-purity alumina nanoparticles is >4N; sequentially ball-milling and molding the slurry to obtain alumina green bodies; and sequentially drying, pre-sintering, and sintering the alumina green bodies to obtain alumina ceramics. First, by selecting high-purity alumina micro powder and high-purity alumina nanoparticles with a purity greater than 4N as the sole ceramic phase raw materials, the high purity of the ceramics is guaranteed from the source, avoiding the drawback of sacrificing purity due to the addition of other inorganic materials in traditional methods. Second, by mixing high-purity alumina micro powder, water, a polymeric dispersant, and high-purity alumina nanoparticles to form a slurry, and precisely controlling the particle size and mass fraction of the high-purity alumina micro powder and high-purity alumina nanoparticles in the slurry, an optimized bimodal particle size distribution system is constructed. This system enables the densest particle packing during subsequent molding, laying the microstructural foundation for obtaining high-density, uniform alumina green bodies. The polymeric dispersant achieves uniform dispersion of the alumina powder, reducing porosity and cracks during molding and improving the uniformity of the alumina green bodies. Further, the alumina green bodies are sequentially dried, pre-sintered, and sintered. The drying process removes moisture in a controlled manner to obtain dried green bodies. Pre-sintering is carried out under normal pressure to achieve complete decomposition of organic matter and initial strengthening of the green body, resulting in a pre-sintered green body. Sintering is performed under a nitrogen atmosphere and at high temperature and pressure, effectively eliminating residual porosity, achieving complete densification of the pre-sintered green body, and strongly inhibiting grain growth, significantly improving the hardness, strength, and wear resistance of the alumina ceramics. Ultimately, high-performance alumina ceramics with a purity >4N, wear loss <1‰, and average grain size <1μm were obtained. High density and fine-grained structure were achieved while maintaining high purity, thus successfully improving the wear resistance of the alumina ceramics. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a cross-sectional SEM image of the alumina ceramic provided in Embodiment 1 of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0021] This application provides a method for preparing alumina ceramics, the method comprising: High-purity alumina micro powder, water, polymeric dispersant, and high-purity alumina nano powder are mixed to obtain a slurry; wherein the purity of both the high-purity alumina micro powder and the high-purity alumina nano powder is >4N. The slurry was sequentially ball-milled and shaped to obtain alumina green blanks; The alumina green body is sequentially dried, pre-sintered, and sintered to obtain alumina ceramic.

[0022] This application embodiment transforms high-purity raw materials into alumina ceramics with excellent comprehensive properties through a series of interconnected and precisely controlled steps. Specifically, the method of this application embodiment begins by mixing high-purity alumina micro powder, water, a polymeric dispersant, and high-purity alumina nanoparticles to obtain a slurry. This step is the material basis for all subsequent processes. Strictly selecting high-purity alumina micro powder and high-purity alumina nanoparticles with a purity >4N is the fundamental prerequisite for ensuring the final product's purity >4N from the source. High-purity alumina micro powder serves as the main structural framework, high-purity alumina nanoparticles serve as the filler and activating phase, and the polymeric dispersant is used to achieve stable and uniform dispersion of both in water. Through mixing, an initial slurry with controllable composition and particle distribution is formed. Next, the obtained slurry is subjected to ball milling and molding. Ball milling is a mechanical activation and homogenization process applied to the slurry. By controlling the ball milling time, ball-to-powder ratio, and rotation speed, ball milling can further break up the agglomeration of high-purity alumina nanoparticles, allowing the polymeric dispersant to fully coat the surface of all particles, thus obtaining a highly uniform and stable ball-milled slurry. Subsequently, the ball-milled slurry is shaped to obtain a predetermined shape and preliminary particle packing structure, yielding alumina green bodies. This step transforms the uniform slurry state into a solid green body with a geometric shape and a certain density. Then, the obtained alumina green bodies are sequentially dried, pre-sintered, and sintered. The drying step aims to remove moisture from the alumina green bodies under gentle, controlled conditions (specific temperature and time), obtaining a moisture-free, structurally intact dried green body, avoiding cracking due to rapid water loss. The pre-sintering step is a heat treatment of the dried green body at normal pressure and moderate temperature. The pre-sintering process thoroughly decomposes and removes organic matter such as the polymeric dispersant added to the slurry, while simultaneously improving the strength of the green body through preliminary interparticle bonding, forming a pre-sintered green body, creating conditions for withstanding final sintering without introducing impurities. The final sintering step involves densifying the pre-sintered green body under high temperature and high pressure in a nitrogen protective atmosphere. By precisely controlling the sintering temperature, pressure, and time, the sintering step drives the material to achieve complete densification in an inert environment and strongly inhibits excessive grain growth, thereby directly obtaining alumina ceramics with fine grains (average grain size <1μm) and a dense structure.

[0023] In some embodiments, the particle size of the high-purity alumina nanoparticles is 10 nm to 100 nm.

[0024] In the preparation method of alumina ceramics, limiting the particle size of high-purity alumina nanoparticles to 10nm–100nm is to synergistically optimize the microstructure of alumina ceramics by introducing nanoscale starting materials, thereby significantly improving wear resistance while ensuring high purity. Specifically, high-purity alumina nanoparticles possess extremely high surface and sintering activity due to their nanoscale size (10nm–100nm). During the ball milling process of the slurry, high-purity alumina nanoparticles can effectively fill the gaps between high-purity alumina microparticles. In the subsequent pre-sintering and sintering processes, as a highly active component, high-purity alumina nanoparticles preferentially diffuse, transfer mass, and grow grains at the contact points and grain boundaries of high-purity alumina microparticles, thereby promoting the densification process of the alumina green body.

[0025] In some embodiments, the particle size of the high-purity alumina micro powder is 0.15 μm to 0.4 μm.

[0026] In the preparation method of alumina ceramics, limiting the particle size of high-purity alumina micro powder to 0.15 μm to 0.4 μm is to optimize the particle size distribution and sintering behavior of the slurry, thereby improving wear resistance while ensuring the purity of the alumina ceramic. Specifically, controlling the particle size of high-purity alumina micro powder within the range of 0.15 μm to 0.4 μm ensures that the high-purity alumina micro powder possesses a suitable specific surface area and sintering activity. During slurry preparation, high-purity alumina micro powder serves as the main particle and is mixed with high-purity alumina nanoparticles with a particle size of 10 nm to 100 nm. The high-purity alumina nanoparticles effectively fill the voids between the high-purity alumina micro powder particles, forming a dense particle packing structure. This particle size distribution helps reduce the viscosity of the slurry during ball milling, improving its uniformity and stability, thus obtaining a ball-milled slurry with good flowability. The good flowability of the ball-milled slurry ensures that alumina green body with uniform density and few defects is obtained in the forming step.

[0027] In some embodiments, the slurry contains 70% to 79% by mass of the high-purity alumina micro powder, 1% to 10% by mass of the polymeric dispersant, and 15% to 29% by mass of the high-purity alumina nanoparticles.

[0028] Setting the mass fraction of high-purity alumina micropowder to 70%–79% is to establish a continuous main particle skeleton in the slurry. The particle size of high-purity alumina micropowder (0.15μm–0.4μm) is relatively large, and its mass fraction dominates the solid loading and initial bulk density of the slurry. If the mass fraction of high-purity alumina micropowder is below 70%, the slurry's solid content is insufficient, resulting in low density and large shrinkage of the alumina green body obtained during subsequent molding, which is detrimental to obtaining high-density ceramics. If the mass fraction of high-purity alumina micropowder is above 79%, it will excessively compress the necessary space for the high-purity alumina nanopowder and polymeric dispersant, leading to excessively high slurry viscosity, poor fluidity, and inability to mix and mold uniformly.

[0029] Setting the mass fraction of high-purity alumina nanoparticles to 15%–29% is key to achieving bimodal gradation optimization and nano-reinforcement effects. The function of high-purity alumina nanoparticles (particle size 10nm–100nm) is to fill the voids between high-purity alumina microparticles and to act as a highly active sintering phase. If the mass fraction of high-purity alumina nanoparticles is below 15%, the filling and activation effects are not significant, making it difficult to sufficiently refine the final grain size. If the mass fraction of high-purity alumina nanoparticles is above 29%, dispersion may be difficult due to increased nanoparticle agglomeration, and slurry viscosity management will become challenging.

[0030] The mass fraction of the polymeric dispersant is set at 1% to 10% based on the requirement that the dispersant fully coats and stabilizes the surface of all alumina particles. If the mass fraction of the polymeric dispersant is less than 1%, it may not be able to effectively disperse high-purity alumina nanopowder and stabilize high-purity alumina micropowder, leading to flocculation or sedimentation of the slurry. If the mass fraction of the polymeric dispersant is greater than 10%, it may introduce too much organic matter, which not only increases costs but also increases the risk of cracking or porosity in the green body due to excessive gas generation during the subsequent pre-sintering step.

[0031] In some embodiments, the polymeric dispersant is one or more of ammonium polyacrylate, polyethylene glycol, or polyvinylpyrrolidone.

[0032] The selection of one or more polymeric dispersants—ammonium polyacrylate, polyethylene glycol, or polyvinylpyrrolidone—is designed to effectively disperse and stabilize solid particles in the slurry, thereby ensuring the uniformity of the alumina ceramic microstructure and ultimately achieving a balance between high purity and high wear resistance. Specifically, in the process of mixing high-purity alumina micropowder, water, the polymeric dispersant, and high-purity alumina nanopowder to obtain the slurry, the core role of the polymeric dispersant is adsorption onto the surface of the high-purity alumina micropowder and nanopowder particles. The selected ammonium polyacrylate, polyethylene glycol, or polyvinylpyrrolidone all contain functional groups on their molecular chains that can adsorb onto the alumina surface, and prevent particle aggregation through steric hindrance or electrostatic repulsion. This effect is particularly important for high-purity alumina nanoparticles with particle sizes of only 10nm to 100nm. It can effectively inhibit the spontaneous agglomeration of high-purity alumina nanoparticles due to their high specific surface area and surface energy, ensuring that the high-purity alumina nanoparticles can be uniformly dispersed and filled in the skeleton formed by the high-purity alumina microparticles.

[0033] In some embodiments, the ball milling time is 5h to 10h, the ball-to-material ratio is (3 to 10):1, and the ball milling speed is 100rpm to 600rpm.

[0034] In the preparation method of alumina ceramics, limiting the ball milling time, ball-to-material ratio and rotation speed is to ensure that the slurry is fully mixed, dispersed and activated. This is a key process step to obtain alumina green bodies with high uniformity and high density, and ultimately achieve high purity and high wear resistance of alumina ceramics.

[0035] Specifically, ball milling is a mechanical treatment process performed on the slurry obtained after mixing. A ball milling time of 5 to 10 hours ensures that the high-purity alumina micro-powder and high-purity alumina nano-powder in the slurry undergo sufficient mechanical grinding and mixing. This 5-10 hour milling time ensures that the polymeric dispersant can fully act on the surface of all particles, promoting further homogenization of the high-purity alumina micro-powder and achieving thorough dispersion of the high-purity alumina nano-powder in the system, thereby eliminating agglomerates. If the time is less than 5 hours, dispersion and mixing may be insufficient; if the time exceeds 10 hours, the wear of the grinding media (balls) may be accelerated, increasing the risk of introducing impurities, which is detrimental to maintaining the final alumina ceramic purity requirement of >4N, or may cause unnecessary phase transitions in the high-purity alumina nano-powder.

[0036] The ball-to-material ratio in ball milling is defined as the ratio of the total mass of the grinding media (balls) to the total mass of the slurry. A ball-to-material ratio of 3:1 to 10:1 directly affects the collision frequency and intensity of the grinding media on the particles in the slurry during ball milling. If the ball-to-material ratio is lower than 3:1, the grinding energy is insufficient, resulting in low particle refinement and mixing efficiency.

[0037] Setting the ball milling speed to 100 rpm to 600 rpm is to control the intensity of impact and shear forces during the grinding process. If the speed is too low (below 100 rpm), the kinetic energy of the grinding media will be insufficient, resulting in poor mixing and dispersion. If the speed is too high (above 600 rpm), it may cause excessive rise in slurry temperature, slurry splashing, or unexpected excessive breakage of particles, affecting the stability of the slurry and its subsequent molding performance.

[0038] By synergistically controlling the time, ball-to-material ratio, and rotation speed parameters described above, ball milling can efficiently transform the slurry into a highly uniform, stable, and well-modified ball-milled slurry. This ball-milled slurry exhibits excellent rheological properties in subsequent forming steps and can be molded into alumina green blanks with uniform structure and minimal defects.

[0039] In some embodiments, the drying temperature is 50°C to 100°C, and the drying time is 6 hours to 8 hours.

[0040] The drying temperature is controlled within the range of 50℃ to 100℃ to provide adequate heat energy for the evaporation of moisture inside the alumina green blank. This range, significantly higher than room temperature, effectively accelerates the diffusion and evaporation rate of water molecules. Simultaneously, the upper limit of 100℃ helps prevent excessively rapid vaporization of moisture, which could lead to excessively high vapor pressure inside the alumina green blank, thus preventing defects such as cracking or deformation. The temperature range of 50℃ to 100℃ also matches the stability of the polymeric dispersant contained in the alumina green blank, ensuring that during the moisture removal stage, the polymeric dispersant does not undergo drastic thermal decomposition but rather gradually concentrates and solidifies between the alumina particles, acting as a temporary binder and maintaining the strength of the alumina green blank.

[0041] Setting the drying time to 6 to 8 hours ensures that the internal moisture of the alumina green billet is fully and evenly removed. A drying time of less than 6 hours may only remove free water from the surface of the green billet, while a significant amount of bound water or capillary water remains inside. Directly pre-sintering such incompletely dried green billets will cause cracking or microstructural damage due to the rapid evaporation of residual moisture at high temperatures. A drying time exceeding 8 hours yields little benefit and may even reduce production efficiency. The 6-8 hour drying time window, combined with a drying temperature of 50℃-100℃, ensures that the alumina green billet undergoes gradual moisture removal from the surface inwards, resulting in a dried green billet with extremely low moisture content, improved overall strength, and no internal damage.

[0042] In some embodiments, the pre-sintering is atmospheric pressure sintering, the pre-sintering temperature is 1000℃~1300℃, and the pre-sintering time is 1h~5h.

[0043] Pre-sintering employs atmospheric pressure sintering, meaning it is carried out under ambient atmospheric pressure without the need for additional mechanical pressure. Atmospheric pressure sintering simplifies equipment requirements and operational procedures. Under atmospheric pressure, heat is transferred to the alumina green blank through convection and radiation in the air or a specific static atmosphere, ensuring uniform heating. The atmospheric pressure environment allows trace amounts of residual moisture inside the alumina green blank, as well as gaseous products generated during the thermal decomposition of the polymeric dispersants contained in the alumina green blank, to escape smoothly, avoiding internal defects caused by gas stagnation due to pressure limitations. Within the pre-sintering temperature range of 1000℃ to 1300℃, the following changes mainly occur: First, any residual organic matter (polymeric dispersants) and moisture in the alumina green blank are completely decomposed and removed. Second, atomic diffusion on the surface of alumina particles (high-purity alumina micro powder and high-purity alumina nano powder) becomes active, and the particle contact points (necks) gradually grow through mass transport, initially forming a strong sintering neck connection between particles. This process significantly improves the mechanical strength of the alumina green billet, enabling it to be safely transported and subjected to subsequent sintering operations. It also forms an open and interconnected preliminary sintered body network structure. The upper temperature limit of 1300℃ is designed to prevent premature over-densification or abnormal grain growth in the alumina green billet, thus preserving sufficient pore channels to facilitate the final discharge of any trace amounts of gaseous products that may remain in subsequent sintering steps.

[0044] Setting a pre-sintering time of 1 to 5 hours ensures that heat can fully penetrate into the core of the alumina green billet, allowing the entire cross-section of the alumina green billet to undergo a consistent heat treatment process. This pre-sintering time allows for the smooth decomposition of organic components and the release of gases, and also provides the necessary kinetic conditions for the full growth of the sintered neck. A time shorter than 1 hour may result in residual organic matter or insufficient strength; a time longer than 5 hours may reduce production efficiency and is not conducive to further improvement of the final performance.

[0045] In some embodiments, the sintering is carried out under a nitrogen atmosphere, the sintering temperature is 1250℃~1500℃, the sintering pressure is 100MPa~150MPa, and the sintering time is 1h~3h.

[0046] Sintering is the final densification treatment performed on the pre-sintered green body obtained after pre-sintering. Sintering is confined to a nitrogen atmosphere to create an inert heat treatment environment. The nitrogen atmosphere effectively isolates oxygen, preventing trace amounts of metallic impurities or carbon residues from the pre-sintering stage from being oxidized at high temperatures or undergoing unnecessary chemical reactions with alumina, thereby avoiding the formation of a second phase or porosity at the alumina ceramic grain boundaries.

[0047] Setting the sintering temperature to 1250℃~1500℃ represents a precise balance between achieving sufficient densification and suppressing excessive grain growth. The lower limit of 1250℃ ensures that, with the assistance of a high pressure of 100MPa~150MPa, the alumina particles have sufficient diffusion driving force, eliminating the remaining micropores in the pre-sintered green body through mechanisms such as plastic flow and diffusion creep, achieving complete densification close to the theoretical density. The upper limit of 1500℃ is strictly limited to prevent excessive thermal activation from causing rapid grain coarsening.

[0048] The sintering pressure of 100MPa to 150MPa is much higher than that of atmospheric pressure sintering. The high pressure acting on the pre-sintered green body significantly increases the contact stress and diffusion driving force between particles, reducing the activation energy required for densification and making it possible to achieve complete sintering at temperatures of 1250℃ to 1500℃. Furthermore, the high pressure effectively suppresses surface diffusion (a material migration mechanism that leads to grain growth but not densification), thus strongly inhibiting grain boundary migration and grain growth while promoting pore shrinkage. Pressures below 100MPa are insufficient to achieve complete densification at the set temperature and time, and may not effectively suppress grain growth; pressures above 150MPa place excessive demands on equipment and may introduce unnecessary technical complexity and cost.

[0049] Sintering time refers to the duration of heat and pressure holding after reaching the specified sintering temperature and pressure. A minimum sintering time of 1 hour ensures sufficient time for material migration to complete the final densification stage under the set temperature and pressure, ensuring that porosity is completely eliminated. A maximum sintering time of 3 hours avoids the risk of abnormal local grain growth that may be caused by excessive heat holding under high pressure and high temperature conditions, which is beneficial for stabilizing the average grain size of alumina ceramics within the range of <1μm.

[0050] In some embodiments, the alumina ceramic satisfies at least one of the following properties: purity > 4N, wear < 1‰, and average grain size < 1μm.

[0051] The preparation method of alumina ceramics in this application aims to obtain alumina ceramics that combine high purity, high wear resistance, and fine grain structure.

[0052] The alumina ceramic's purity (>4N) stems from the strict control over impurity introduction throughout the entire preparation chain. The high-purity alumina micro-powder and nano-powder used at the starting point both have a purity >4N, ensuring the intrinsic high purity of the material system from the source. During slurry preparation, the added polymeric dispersant is an organic compound that can be completely decomposed and volatilized during subsequent heat treatment. In the pre-sintering step, the pre-sintering temperature and time are set sufficiently to completely decompose and remove these polymeric dispersants. During the sintering step, a nitrogen atmosphere is used for protection, effectively preventing possible oxidation or harmful reactions at high temperatures. No metal ion sintering aids or other impurities that would remain in the final product are introduced in any of the critical steps. Therefore, starting with high-purity raw materials and undergoing a purification process, the purity of the final alumina ceramic is strictly maintained at a level >4N.

[0053] The wear resistance of alumina ceramics (<1‰) and average grain size (<1μm) are closely related and both stem from the successful control of the ceramic microstructure. An average grain size of <1μm is the structural basis for achieving high wear resistance. This fine grain structure relies on the cumulative effect of multiple processes: First, in the slurry formulation, high-purity alumina nanopowder and high-purity alumina micropowder form an optimized particle size distribution, providing the material prerequisite for a fine-grained structure. Second, ball milling ensures sufficient dispersion and uniform mixing of the nanopowder, laying the foundation for structural uniformity. Then, the drying and pre-sintering processes, while avoiding defects in the green body, achieve the clean removal of organic matter and preliminary strengthening of the green body, preparing a defect-free and highly active pre-sintered green body for final sintering. Finally, the sintering step is carried out under a nitrogen atmosphere, using a relatively low sintering temperature (1250℃~1500℃), a relatively high sintering pressure (100MPa~150MPa), and a relatively short sintering time (1h~3h). The high-pressure environment greatly promotes densification while strongly inhibiting grain boundary migration and grain growth; the lower temperature and shorter time further limit grain coarsening. This allows the pre-sintered green body to achieve complete densification while precisely controlling the grain size at the submicron scale (<1μm). This fully dense and fine-grained microstructure effectively hinders crack initiation and propagation, thus directly endowing alumina ceramics with excellent wear resistance, exhibiting wear of <1‰.

[0054] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0055] Example 1 High-purity alumina micropowder with a purity >4N (99.99%) and an average particle size D50 of 0.2μm, polyacrylic acid, and high-purity alumina nanopowder with a purity >4N and an α-type crystal size between 10nm and 50nm were added to a mixing tank along with high-purity water and manually stirred to initially mix, resulting in a slurry. The slurry contained 79% high-purity alumina micropowder, 6% dispersant, and 15% high-purity alumina nanopowder. The slurry was ball-milled for 5 hours at a ball-to-powder ratio of 3:1 at 300 rpm. The milled slurry was then poured into a mold and air-cooled to form a wear-resistant ceramic green body. The demolded ceramic green body was then cooled to 50°C. o Drying at C for 8 hours for further curing, followed by 1200... o Pre-fired ceramic (C) for 4 hours yields a pre-fired ceramic with a certain strength, which is then transferred to a hot isostatic pressing furnace for secondary sintering at 1400°C. oC, sintering pressure 120 MPa, sintering time 2 h. The density of the prepared alumina ceramic was measured to be 3.91 g / cm³. 3 The wear rate is 0.8‰, and the average grain size is <1μm.

[0056] Example 2 High-purity alumina micropowder with a purity >4N (99.99%) and an average particle size D50 of 0.15μm, polyethylene glycol, and high-purity alumina nanopowder with a purity >4N and an α-type grain size between 60nm and 80nm were added to a mixing tank along with high-purity water and manually stirred to initially mix, resulting in a slurry. The slurry contained 70% high-purity alumina micropowder, 10% dispersant, and 20% high-purity alumina nanopowder. The slurry was ball-milled for 10 hours at a ball-to-powder ratio of 6:1 at 300 rpm. The ball-milled slurry was then poured into a mold and air-cooled to form a wear-resistant ceramic green body. The demolded ceramic green body was then cooled to 80°C. o Drying at C for 7 hours for further curing, followed by 1000... o Pre-fired ceramic (C) for 5 hours yields a pre-fired ceramic with a certain strength. It is then transferred to a hot isostatic pressing furnace for secondary sintering at 1250°C. o C, sintering pressure 150 MPa, sintering time 3 h. The density of the prepared alumina ceramic was tested to be 3.93 g / cm³. 3 Wear rate 0.6‰, average grain size <1μm.

[0057] Example 3 High-purity alumina micropowder with a purity >4N (99.99%) and an average particle size D50 of 0.4μm, polyvinylpyrrolidone, and high-purity alumina nanopowder with a purity >4N and an α-type grain size between 70nm and 100nm were added to a mixing tank along with high-purity water and manually stirred to initially mix, resulting in a slurry. The slurry contained 70% high-purity alumina micropowder, 1% dispersant, and 29% high-purity alumina nanopowder. The slurry was ball-milled for 7 hours at a ball-to-powder ratio of 10:1 at 100 rpm. The ball-milled slurry was then poured into a mold and air-cooled to form a wear-resistant ceramic green body. The demolded ceramic green body was then air-cooled at 100 rpm. o Drying at C for 6 hours, then at 1300 o Pre-firing at temperature C for 1 hour yields pre-fired ceramics with a certain strength. These ceramics are then transferred to a hot isostatic pressing furnace for secondary sintering at 1500°C. o C, sintering pressure 100 MPa, sintering time 1 h, the density of the prepared alumina ceramic was measured to be 3.89 g / cm³. 3 Wear rate 1‰, average grain size <1μm.

[0058] Comparative Example 1 The content is basically the same as that disclosed in Example 1, except that: High-purity alumina micropowder with a purity >4N (99.99%) and an average particle size D50 of 0.5 μm was selected. The resulting alumina ceramic had a density of 3.7 g / cm³. 3 Wear rate 30‰, average grain size >1μm.

[0059] Comparative Example 2 The content is basically the same as that disclosed in Example 1, except that: The slurry contained 82% high-purity alumina micro powder and 8% dispersant; it also contained 10% high-purity alumina nanoparticles. The prepared alumina ceramic had a density of 3.8 g / cm³. 3 Wear rate 5‰, average grain size >1μm.

[0060] Appendix Figure 1 Detailed explanation: Figure 1 This is a cross-sectional SEM image of the alumina ceramic provided in Embodiment 1 of this application; by Figure 1 It can be seen that the alumina wear-resistant ceramic prepared in Example 1 has high density, low porosity, average grain size <1μm, high grain uniformity, and no abnormally large particles in the original crystals. The alumina wear-resistant ceramic in this state will exhibit excellent mechanical properties, high bending strength and low wear, with wear <1‰.

[0061] Furthermore, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages: Achieving both high purity and high wear resistance: The embodiments of the present invention successfully prepared alumina ceramics that meet both high purity (purity > 4N) and high wear resistance (wear loss < 1‰).

[0062] Broad application prospects: The high-purity, high-wear-resistant alumina ceramics prepared in the embodiments of this invention can be used to produce high-purity alumina wear-resistant beads of 4N and above, bearing balls, chromatographic adsorbents, aerospace materials and other fields, and have broad market application prospects.

[0063] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A method for preparing alumina ceramics, characterized in that, The method includes: High-purity alumina micro powder, water, polymeric dispersant, and high-purity alumina nano powder are mixed to obtain a slurry; wherein the purity of both the high-purity alumina micro powder and the high-purity alumina nano powder is >4N. The slurry was sequentially ball-milled and shaped to obtain alumina green blanks; The alumina green body is sequentially dried, pre-sintered, and sintered to obtain alumina ceramic.

2. The method according to claim 1, characterized in that, The particle size of the high-purity alumina nanoparticles is 10nm to 100nm.

3. The method according to claim 1, characterized in that, The particle size of the high-purity alumina micro powder is 0.15μm to 0.4μm.

4. The method according to claim 1, characterized in that, In the slurry, the mass fraction of the high-purity alumina micro powder is 70% to 79%, the mass fraction of the polymeric dispersant is 1% to 10%, and the mass fraction of the high-purity alumina nano powder is 15% to 29%.

5. The method according to claim 1, characterized in that, The polymeric dispersant is one or more of ammonium polyacrylate, polyethylene glycol, or polyvinylpyrrolidone.

6. The method according to claim 1, characterized in that, The ball milling time is 5h to 10h, the ball-to-material ratio is (3 to 10): 1, and the ball milling speed is 100rpm to 600rpm.

7. The method according to claim 1, characterized in that, The drying temperature is 50℃~100℃, and the drying time is 6h~8h.

8. The method according to claim 1, characterized in that, The pre-sintering is atmospheric pressure sintering, the pre-sintering temperature is 1000℃~1300℃, and the pre-sintering time is 1h~5h.

9. The method according to claim 1, characterized in that, The sintering is carried out under a nitrogen atmosphere, the sintering temperature is 1250℃~1500℃, the sintering pressure is 100MPa~150MPa, and the sintering time is 1h~3h.

10. The method according to claim 1, characterized in that, The alumina ceramic satisfies at least one of the following properties: purity > 4N, wear < 1‰, and average grain size < 1μm.

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