High-strength aluminum oxide ceramic and preparation method thereof

Abstract

The invention discloses high-strength aluminum oxide ceramic and a preparation method thereof. The preparation method comprises the following steps: carrying out urea weak coordination modification on alumina powder, introducing magnesium, silicon and zirconium source compounds in a specific molar ratio, pre-calcining, and sintering at 1500-1700 DEG C to generate a multi-element non-stoichiometric composite solid solution in situ at a grain boundary. The structure can effectively cure free silicon dioxide, construct a high-rigidity grain boundary framework, inhibit grain boundary viscous flow and grain growth, and remarkably improve the bending strength and fracture toughness of the ceramic.

Description

Technical Field

[0001] This invention belongs to the field of alumina ceramic technology, specifically relating to a high-strength alumina ceramic and its preparation method. Background Technology

[0002] Alumina ceramics, as typical high-performance structural ceramic materials, are widely used in mechanical seals, wear-resistant components, electronic packaging substrates, and high-temperature structural components due to their high hardness, high wear resistance, excellent chemical stability, and good high-temperature mechanical properties. With the rapid development of high-end equipment manufacturing, aerospace, and new energy industries, higher requirements are placed on the comprehensive performance of alumina ceramics under high loads, high impacts, and complex thermo-mechanical coupling environments. To improve the problems of high brittleness and low fracture toughness of traditional alumina ceramics, existing technologies typically enhance their mechanical properties by refining grains, increasing sintering density, and introducing a second phase for toughening. This has, to some extent, promoted the development of alumina ceramics from a single-phase system to a multi-phase synergistic reinforcement direction, providing an effective way to improve the initial mechanical properties of the material.

[0003] However, existing technical solutions still have significant limitations. Taking the preparation route that introduces silane coupling agents and organic binders as an example, during the debinding and high-temperature sintering process, the SiO2 generated by the decomposition of the above organic components... 4+ With Al 3+ Significant differences exist in ionic radius, valence compensation mechanism, and crystal structure matching. Its solid solubility in the Al2O3 lattice is extremely limited, making it difficult to form a stable solid solution. Correspondingly, SiO2 tends to accumulate as an amorphous glassy phase or a continuous thin film phase at grain boundaries and grain boundary triple points. For example, a Chinese patent discloses an alumina ceramic and its preparation method (Publication No.: CN106977185A). While the grain boundary glassy phase in this patent helps fill pores and increase the density of the green body in the early stages of sintering, its viscoelastic characteristics easily induce localized viscous flow or creep deformation in the grain boundary region under high-temperature service or long-term load, weakening the grain boundary's effective load transfer capability. Simultaneously, the mismatch in mechanical properties between the glassy phase and the surrounding high-modulus ceramic phase can induce stress concentration and interface debonding under thermal cycling or continuous stress conditions, making cracks more likely to preferentially grow and propagate along grain boundaries, thus affecting the material's structural consistency and long-term service reliability. Therefore, how to effectively avoid the adverse effects of grain boundary glass on high-temperature mechanical stability and durability while ensuring sintering densification and initial strength improvement remains a key technical problem that urgently needs to be solved in the field of high-strength alumina ceramics. Summary of the Invention

[0004] This application provides a method for preparing high-strength alumina ceramics, comprising the following steps: Step S1. Provide modified alumina powder and introduce zirconium source compound, magnesium source compound and silicon source compound, wherein the amount of magnesium source compound, silicon source compound and zirconium source compound introduced is controlled by the molar ratio of MgO, SiO2 and ZrO2 as 1:(0.8~1.2):(0.5~2.5); at the same time, based on the total mass of the modified alumina powder, the zirconium source compound, the magnesium source compound and the silicon source compound, the mass percentage of the modified alumina powder is 85~96wt%, and the total mass percentage of the zirconium source compound, magnesium source compound and silicon source compound is 4~15wt%. Step S2. The modified alumina powder, zirconium source compound, magnesium source compound and silicon source compound are wet-mixed to form a uniformly distributed nanoscale precursor layer on the powder surface. Step S3. The mixed powder obtained in step S2 is subjected to pre-calcination treatment to allow the zirconium source compound, magnesium source compound and silicon source compound to undergo a preliminary solid-phase reaction; Step S4. After the pre-calcined powder is shaped, it is sintered at 1500-1700℃ to cause in-situ reactions at the grain boundaries, thereby obtaining high-strength alumina ceramic.

[0005] It should be noted that, with the help of the highly active interface constructed on the surface of modified alumina powder, the zirconium, magnesium, and silicon source compounds do not simply exist as sintering aids or independent second phases. Instead, they participate in grain boundary reactions during pre-calcination and high-temperature sintering through confined diffusion and heterovalent synergistic substitution, generating in situ a phase dominated by α-Al₂O₃ lattice and containing Mg. 2+ With Zr 4+ Cooperative replacement of part of Al 3+ Site, Si 4+ This process involves embedding a multi-component, non-stoichiometric composite solid solution into the grain boundary structure using unconventional coordination methods. Simultaneously, it avoids the formation of MgAl2O4 spinel phase, ZrO2 stable phase, or continuous aluminosilicate glass phase by individual components within the system. The formation of this phase is highly dependent on specific MgO / SiO2 / ZrO2 molar ratios, nanoscale precursor layer structures, and interface activation conditions. This effectively absorbs and solidifies free SiO2, constructing a high-rigidity, high-stability grain boundary framework. It significantly suppresses grain boundary viscosity flow and abnormal grain growth, achieving a synergistic improvement in strength and high-temperature structural stability that is difficult to anticipate in existing technologies.

[0006] As a preferred technical solution for the preparation method of high-strength alumina ceramics, the pre-calcination treatment in step S3 is carried out at 700-1000℃ for 1-4 hours.

[0007] It should be noted that within this temperature range, the zirconium source compound, magnesium source compound, and silicon source compound first undergo dehydration, decomposition, and activation reactions, forming highly dispersed reactive oxides or short-range ordered intermediate structures on the surface of the modified alumina powder, thus enabling Mg... 2+ Zr 4+ With Si 4+ Without inducing liquid phase formation, the process involves preliminary heterovalent substitution and coordination reconstruction of the alumina surface through confined solid-phase diffusion. This process not only consumes and fixes SiO2, which readily forms a low-melting-point glassy phase, but also constructs a stable solid solution precursor framework at grain boundaries, thus avoiding localized transient liquid phase or component segregation during the initial high-temperature sintering stage. By controlling the holding time to 1–4 hours, the above solid-phase reaction can be ensured to proceed fully without causing abnormal grain growth or premature precipitation of independent spinel or zirconia phases. This lays a stable and controllable microstructural foundation for the continuous growth and high densification of in-situ solid solutions at grain boundaries during the subsequent sintering stage at 1500–1700℃.

[0008] In a preferred embodiment of a method for preparing high-strength alumina ceramics, the zirconium source compound is selected from one or more of zirconium oxide, zirconium oxychloride, zirconium nitrate, ammonium zirconium carbonate, and zirconium acetate.

[0009] It should be noted that using zirconium oxide, zirconium oxychloride, zirconium nitrate, ammonium zirconium carbonate, or zirconium acetate as the zirconium source compound can release Zr in a controlled manner at different temperature stages. 4+ It achieves nanoscale uniform distribution, thereby promoting the participation of zirconium elements in grain boundary synergistic solid solution and structural strengthening, significantly improving the strength and high-temperature structural stability of alumina ceramics.

[0010] In a preferred embodiment of a method for preparing high-strength alumina ceramics, the magnesium source compound is selected from one or more of magnesium oxide, magnesium carbonate, and magnesium hydroxide.

[0011] It should be noted that using magnesium oxide, magnesium carbonate, or magnesium hydroxide as the magnesium source compound can gradually release Mg during the sintering process. 2+ It achieves uniform diffusion, thereby effectively inhibiting abnormal growth of alumina grains and promoting the formation of grain boundary solid solution structure, significantly improving the mechanical properties and structural stability of ceramics.

[0012] In a preferred embodiment of a method for preparing high-strength alumina ceramics, the silicon source compound is selected from one or more of silicon dioxide, silica sol, and silicates.

[0013] It should be noted that using silica, silica sol, or silicates as silicon source compounds enables silicon components to participate in solid-phase reactions in a highly dispersed state at grain boundaries, avoiding the formation of a continuous glass phase and promoting its embedding into the grain boundary solid solution structure, thereby significantly improving the grain boundary strength and high-temperature stability of alumina ceramics.

[0014] As a preferred technical solution for the preparation of high-strength alumina ceramics, the method for preparing the modified alumina powder includes: dispersing raw alumina powder in a urea aqueous solution, adjusting the pH value of the system to 9.0-10.5 under closed conditions, and maintaining it at 50-70℃ for 1-3 hours to allow the amide groups in the urea molecules to undergo weak coordination with the aluminum atoms on the surface of the alumina powder; subsequently cooling the reaction system and changing the ionic environment by washing with water to terminate the coordination effect, performing solid-liquid separation on the obtained powder, and gently drying it at 80-110℃ to obtain modified alumina powder with improved interfacial chemical reactivity.

[0015] It should be noted that under weakly alkaline conditions (pH 9.0–10.5) and a medium-temperature environment (50–70℃), the aluminum atoms on the surface of alumina powder act as Lewis acidic sites. The surface hydroxyl groups partially dissociate and expose highly reactive coordination vacancies, which promotes the directional weak coordination adsorption of electron-rich amide groups in urea molecules, thereby forming a transient molecular-level activation layer on the particle surface. This activation layer effectively inhibits powder agglomeration and increases the surface chemical potential by reducing surface energy and weakening the strong interactions between particles. Subsequently, the coordination effect is terminated by changing the ionic environment through water washing, so that the bulk urea molecules are removed but the surface structure remains in a highly active state. After gentle drying, modified alumina powder with more reaction sites and higher interfacial reaction driving force is obtained, which provides favorable conditions for the anchoring of subsequent sintering aids and solid-phase reactions.

[0016] In a preferred embodiment of a method for preparing high-strength alumina ceramics, the mass concentration of urea in the urea aqueous solution is 4–8 wt%.

[0017] It should be noted that precisely controlling the urea concentration at 4–8 wt% helps to form a monolayer or oligolayer coordination structure with optimal coverage on the surface of alumina particles. This provides sufficient active sites to efficiently anchor additives such as magnesium, silicon, and zirconium, while effectively avoiding sintering porosity defects caused by the accumulation of organic matter due to excessive concentration.

[0018] In a preferred method for preparing high-strength alumina ceramics, the holding time for sintering in step S4 is 4–6 h.

[0019] It should be noted that strictly controlling the sintering holding time to 4-6 hours can ensure that the alumina matrix is ​​fully densified and promote the in-situ reaction at the grain boundaries to form a stable rigid interlocking structure. At the same time, it effectively avoids abnormal grain coarsening caused by prolonged high-temperature holding, thereby ensuring the uniformity of the ceramic material's microstructure and the optimal balance of mechanical properties.

[0020] The high-strength alumina ceramic prepared by this invention achieves heterovalent synergistic substitution and confined solid-phase diffusion of magnesium, silicon, and zirconium components at grain boundaries by constructing a nanoscale precursor layer on the surface of modified alumina. This in-situ reaction generates a multi-component non-stoichiometric composite solid solution that effectively engulfs and solidifies free silica, which is prone to high-temperature weakening, constructing a high-rigidity and high-stability grain boundary framework. This fundamentally solves the problems of stress concentration, grain boundary viscosity, and high-temperature creep caused by the glassy phase at grain boundaries in traditional processes. This technology, while ensuring complete material densification, significantly inhibits abnormal grain growth, resulting in a flexural strength of 510–555 MPa and a fracture toughness of 4.6–5.2 MPa·m. 1 / 2 This achieves a synergistic improvement in strength, toughness, and high-temperature structural stability, greatly enhancing the material's service reliability in complex thermo-mechanical coupling environments. Attached Figure Description

[0021] Figure 1 Here is an electron microscope image of the alumina ceramic prepared in Example 1; Figure 2 The XRD pattern of the alumina ceramic prepared in Example 1; Figure 3 Infrared spectrum of the modified alumina powder prepared in Example 1. Detailed Implementation

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0023] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0024] Secondly, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single embodiment or an embodiment selectively excluded from other embodiments.

[0025] Example 1

[0026] This application provides a method for preparing high-strength alumina ceramics, comprising the following: Step 1: Take 100g of raw alumina powder and disperse it in a 4wt% urea aqueous solution, with the total volume of the aqueous solution being twice the mass of the powder, forming a uniform suspension. Under sealed conditions, adjust the pH of the system to 9.0 using ammonia. Subsequently, heat the system to 50℃ and maintain for 1 hour to allow the amide groups in the urea molecules to weakly coordinate with the aluminum atoms on the surface of the alumina powder. After the reaction, cool the system to room temperature and wash it three times with water, each time using twice the initial solution volume, to alter the ionic environment and terminate the coordination reaction. Then, use a centrifuge for solid-liquid separation, and place the resulting wet powder in a vacuum drying oven at 80℃ for 8 hours until the moisture content is below 1wt%, obtaining modified alumina powder with improved interfacial chemical reactivity.

[0027] Step 2: Provide 85g of the modified alumina powder described above, and introduce zirconium oxide, magnesium oxide, and silicon dioxide. The amount introduced is controlled by the molar ratio of MgO, SiO2, and ZrO2 at 1:0.8:0.5. Specific calculations: Assuming 0.1mol of MgO corresponds to 4.03g of magnesium oxide, then 0.08mol of SiO2 corresponds to 4.806g of silicon dioxide, and 0.05mol of ZrO2 corresponds to 6.161g of zirconium oxide. The total mass is 100g, of which modified alumina accounts for 85wt%, and zirconium oxide, magnesium oxide, and silicon dioxide together account for 15wt%.

[0028] Step 3: Place 85g of modified alumina powder, 6.161g of zirconium oxide, 4.03g of magnesium oxide, and 4.806g of silica in a ball mill jar. Add deionized water as a dispersion medium, with the water volume being 1.5 times the total mass of the powder. Add polyvinyl alcohol as a dispersant, with the amount added being 0.5wt% of the total mass of the powder. Perform wet mixing in a planetary ball mill at 300 rpm for 4 hours to form a uniformly distributed nanoscale precursor layer of zirconium oxide, magnesium oxide, and silica on the surface of the modified alumina powder. After mixing, perform vacuum filtration to remove excess water, obtaining a wet-mixed powder.

[0029] Step 4: Place the wet mixed powder obtained in Step 3 in a muffle furnace and heat it to 700℃ at a heating rate of 5℃ / min. Perform pre-calcination treatment at 700℃ for 1 hour to allow zirconium oxide, magnesium oxide, and silicon dioxide to undergo a preliminary solid-phase reaction. After pre-calcination, allow it to cool naturally to room temperature to obtain pre-calcined powder.

[0030] Step 5: Add 2 wt% polyvinyl alcohol solution as a binder to the pre-calcined powder. After mixing evenly, form a green body by dry pressing at 200 MPa. Then, place the green body in a high-temperature sintering furnace and heat to 1500℃ at a heating rate of 10℃ / min. Sinter at 1500℃ for 6 hours to allow in-situ reactions at the grain boundaries. After sintering, allow it to cool naturally to room temperature to obtain high-strength alumina ceramic.

[0031] Example 2

[0032] This application provides a method for preparing high-strength alumina ceramics, comprising the following: Step 1: Take 100g of raw alumina powder and disperse it in an 8wt% urea aqueous solution, with the total volume of the aqueous solution being three times the mass of the powder, forming a uniform suspension. Under sealed conditions, adjust the pH of the system to 10.5 using sodium hydroxide solution. Subsequently, heat the system to 70℃ and maintain it for 3 hours to allow the amide groups in the urea molecules to weakly coordinate with the aluminum atoms on the surface of the alumina powder. After the reaction is complete, cool the system to room temperature and wash it three times with water, each time using twice the initial solution volume, to alter the ionic environment and terminate the coordination reaction. Then, use a filter for solid-liquid separation, and place the resulting wet powder in a vacuum drying oven at 110℃ for gentle drying for 6 hours until the moisture content is below 1wt%, obtaining modified alumina powder with improved interfacial chemical reactivity.

[0033] Step 2: Provide 96g of the modified alumina powder described above, and introduce zirconium nitrate, magnesium carbonate, and silica sol. The amount introduced is controlled by the molar ratio of MgO, SiO2, and ZrO2 at 1:1.2:2.5. Specific calculations: Assume 0.004mol of MgO, corresponding to 0.337g of magnesium carbonate (Mg carbonate MW = 84.31g / mol), then 0.0048mol of SiO2, corresponding to 0.288g of SiO2, 0.961g of silica sol (SiO2 content in silica sol is 30wt%), and 0.01mol of ZrO2, corresponding to 2.702g of zirconium nitrate (Zr(NO3)4 MW = 339.24g / mol, ZrO2 MW = 123.22g / mol, mass conversion factor 339.24 / 123.22 ≈ 2.753). The total mass of introduced compounds (2.702g zirconium nitrate + 0.337g magnesium carbonate + 0.961g silica sol) = 4g, with a total mass of 100g. Among them, modified alumina accounted for 96wt%, and the combined proportion of zirconium source compound, magnesium source compound and silicon source compound was 4wt%.

[0034] Step 3: Place 96g of modified alumina powder, 2.702g of zirconium nitrate, 0.337g of magnesium carbonate, and 0.961g of silica sol in a ball mill jar. Add deionized water as a dispersion medium, with the water volume being 1.5 times the total mass of the powder. Add polyvinyl alcohol as a dispersant, with the amount added being 0.5wt% of the total mass of the powder. Perform wet mixing in a planetary ball mill at 300 rpm for 6 hours to form a uniformly distributed nanoscale precursor layer of zirconium nitrate, magnesium carbonate, and silica sol on the surface of the modified alumina powder. After mixing, perform vacuum filtration to remove excess water, obtaining a wet-mixed powder.

[0035] Step 4: Place the wet mixed powder obtained in Step 3 in a muffle furnace and heat it to 1000℃ at a heating rate of 5℃ / min. Perform pre-calcination treatment at 1000℃ for 4 hours to allow zirconium nitrate, magnesium carbonate, and silica sol to undergo a preliminary solid-phase reaction. After pre-calcination, allow it to cool naturally to room temperature to obtain pre-calcined powder.

[0036] Step 5: Add 2 wt% polyvinyl alcohol solution as a binder to the pre-calcined powder. After mixing evenly, form a green body by dry pressing at 200 MPa. Then, place the green body in a high-temperature sintering furnace and heat to 1700℃ at a heating rate of 10℃ / min. Sinter at 1700℃ for 4 hours to allow in-situ reactions at the grain boundaries. After sintering, allow it to cool naturally to room temperature to obtain high-strength alumina ceramic.

[0037] Example 3

[0038] This application provides a method for preparing high-strength alumina ceramics, comprising the following: Step 1: Take 100g of raw alumina powder and disperse it in a 6wt% urea aqueous solution, with the total volume of the aqueous solution being 2.5 times the mass of the powder, to form a uniform suspension. Under sealed conditions, adjust the pH of the system to 9.8 using ammonia. Subsequently, heat the system to 60℃ and maintain it for 2 hours to allow the amide groups in the urea molecules to weakly coordinate with the aluminum atoms on the surface of the alumina powder. After the reaction, cool the system to room temperature and wash it three times with water, each time using twice the initial solution volume, to alter the ionic environment and terminate the coordination reaction. Then, use a centrifuge to separate the solid and liquid phases, and place the resulting wet powder in a vacuum drying oven at 95℃ for 7 hours until the moisture content is below 1wt%, obtaining modified alumina powder with improved interfacial chemical reactivity.

[0039] Step 2: Provide 92g of the above-mentioned modified alumina powder, and introduce zirconium oxychloride, magnesium hydroxide, and sodium silicate. The amount introduced is controlled by the molar ratio of MgO, SiO2, and ZrO2 being 1:1:1.5. Specific calculations: Assume 0.02 mol of MgO corresponds to 1.166 g of magnesium hydroxide (Mg hydroxide MW = 58.32 g / mol). Then, 0.02 mol of SiO2 corresponds to 1.202 g of SiO2 and 2.441 g of sodium silicate (sodium silicate Na2SiO3 MW = 122.06 g / mol, providing SiO2 MW = 60.08 g / mol, mass conversion factor 122.06 / 60.08 ≈ 2.032). 0.03 mol of ZrO2 corresponds to 3.393 g of zirconium oxychloride (zirconium oxychloride ZrOCl2·8H2O MW = 322.25 g / mol, providing ZrO2 MW = 123.22 g / mol, mass conversion factor 322.25 / 123.22 ≈ 2.615). The total mass of introduced compounds (3.393g zirconium oxychloride + 1.166g magnesium hydroxide + 2.441g sodium silicate) = 8g, with a total mass of 100g. Modified alumina accounted for 92wt%, and the zirconium source compound, magnesium source compound and silicon source compound accounted for a total of 8wt%.

[0040] Step 3: Place the above-mentioned 92g modified alumina powder, 3.393g zirconium oxychloride, 1.166g magnesium hydroxide, and 2.441g sodium silicate in a ball mill jar. Add deionized water as a dispersion medium, with the water volume being 1.5 times the total mass of the powder. Add polyvinyl alcohol as a dispersant, with the amount added being 0.5wt% of the total mass of the powder. Perform wet mixing in a planetary ball mill at 300 rpm for 5 hours to form a uniformly distributed nanoscale precursor layer of zirconium oxychloride, magnesium hydroxide, and sodium silicate on the surface of the modified alumina powder. After mixing, perform vacuum filtration to remove excess water, obtaining a wet-mixed powder.

[0041] Step 4: Place the wet mixed powder obtained in Step 3 in a muffle furnace and heat it to 850°C at a heating rate of 5°C / min. Perform a pre-calcination treatment at 850°C for 2.5 hours to allow zirconium oxychloride, magnesium hydroxide, and sodium silicate to undergo a preliminary solid-phase reaction. After pre-calcination, allow it to cool naturally to room temperature to obtain the pre-calcined powder.

[0042] Step 5: Add 2 wt% polyvinyl alcohol solution as a binder to the pre-calcined powder. After mixing evenly, form a green body by dry pressing at 200 MPa. Then, place the green body in a high-temperature sintering furnace and heat to 1600℃ at a heating rate of 10℃ / min. Sinter at 1600℃ for 5 hours to allow in-situ reactions at the grain boundaries. After sintering, allow it to cool naturally to room temperature to obtain high-strength alumina ceramic.

[0043] Example 4 This application provides a method for preparing high-strength alumina ceramics, comprising the following:

[0044] Step 1: Take 100g of raw alumina powder and disperse it in a 5wt% urea aqueous solution, with the total volume of the aqueous solution being twice the mass of the powder, forming a uniform suspension. Under sealed conditions, adjust the pH of the system to 9.5 using sodium hydroxide solution. Subsequently, heat the system to 55℃ and maintain it for 1.5h, allowing the amide groups in the urea molecules to weakly coordinate with the aluminum atoms on the surface of the alumina powder. After the reaction, cool the system to room temperature and wash it three times with water, each time using twice the initial solution volume, to alter the ionic environment and terminate the coordination reaction. Then, use a filter for solid-liquid separation, and place the resulting wet powder in a vacuum drying oven at 90℃ for gentle drying for 8h until the moisture content is below 1wt%, obtaining modified alumina powder with improved interfacial chemical reactivity.

[0045] Step 2: Provide 88g of the modified alumina powder described above, and introduce ammonium zirconium carbonate, magnesium oxide, and silicon dioxide. The amount introduced is controlled by the molar ratio of MgO, SiO2, and ZrO2 at 1:0.9:1. Specific calculations: Assume 0.04mol of MgO, corresponding to 1.612g of magnesium oxide (MgO MW = 40.3g / mol); 0.036mol of SiO2, corresponding to 2.163g of silicon dioxide (Silicon dioxide MW = 60.08g / mol); and 0.04mol of ZrO2, corresponding to 8.225g of ammonium zirconium carbonate (Ammonium zirconium carbonate (NH4)2Zr(CO3)2 MW = 371.33g / mol, ZrO2 provided MW = 123.22g / mol, mass conversion factor 371.33 / 123.22≈3.013). The total mass of introduced compounds (8.225g of ammonium zirconium carbonate + 1.612g of magnesium oxide + 2.163g of silicon dioxide) = 12g, with a total mass of 100g. The modified alumina accounted for 88wt%, and the zirconium source compound, magnesium source compound and silicon source compound accounted for a total of 12wt%.

[0046] Step 3: Place 88g of modified alumina powder, 8.225g of ammonium zirconium carbonate, 1.612g of magnesium oxide, and 2.163g of silica in a ball mill jar. Add deionized water as a dispersion medium, with the water volume being 1.5 times the total mass of the powder. Add polyvinyl alcohol as a dispersant, with the amount added being 0.5wt% of the total mass of the powder. Perform wet mixing in a planetary ball mill at 300 rpm for 4.5 hours to form a uniformly distributed nanoscale precursor layer of ammonium zirconium carbonate, magnesium oxide, and silica on the surface of the modified alumina powder. After mixing, vacuum filter to remove excess water to obtain the wet-mixed powder.

[0047] Step 4: Place the wet mixed powder obtained in Step 3 into a muffle furnace and heat it to 800℃ at a heating rate of 5℃ / min. Perform pre-calcination treatment at 800℃ for 2 hours to allow ammonium zirconium carbonate, magnesium oxide, and silicon dioxide to undergo a preliminary solid-phase reaction. After pre-calcination, allow it to cool naturally to room temperature to obtain pre-calcined powder.

[0048] Step 5: Add 2 wt% polyvinyl alcohol solution as a binder to the pre-calcined powder. After mixing evenly, form a green body by dry pressing at 200 MPa. Then, place the green body in a high-temperature sintering furnace and heat to 1550℃ at a heating rate of 10℃ / min. Sinter at 1550℃ for 4.5 hours to allow in-situ reactions at the grain boundaries. After sintering, allow it to cool naturally to room temperature to obtain high-strength alumina ceramic.

[0049] Compare with Example 1

[0050] The difference between this comparative example and Example 1 is that it does not use modified alumina powder, but uses original alumina powder.

[0051] Compare with Example 2

[0052] The difference between this comparative example and Example 1 is that the pre-calcination treatment step is omitted, and the forming and sintering are carried out directly.

[0053] Compare with Example 3

[0054] The difference between this comparative example and Example 1 is that an equal mass of MgO was used instead of zirconium oxide.

[0055] Compare with Example 4

[0056] The difference between this comparative example and Example 1 is that an equal mass of zirconium oxide was used instead of MgO.

[0057] Performance testing methods

[0058] 1. Bending strength: The sintered alumina ceramic specimens were tested using the three-point bending method or the four-point bending method. The specimens were processed into standard long strips (e.g., 3mm×4mm×36mm). They were loaded using an electronic universal testing machine at room temperature with a loading rate controlled between 0.5 and 1mm / min. The bending strength was calculated by recording the maximum load at which the specimen broke and combining it with the specimen dimensions.

[0059] 2. Fracture toughness: The fracture toughness of ceramic materials is tested by indentation method. Indentation method is to form a crack by applying a Vickers indenter to the polished surface, measuring the crack length and calculating the fracture toughness in combination with the indentation load.

[0060] 3. Bulk density and relative density: The bulk density of the sintered body was determined by Archimedes' water displacement method. Deionized water was used as the immersion solution. The dry weight, suspended weight and saturated weight of the sample were measured respectively, and the bulk density was calculated. The relative density was calculated in combination with the theoretical density.

[0061] 4. Microhardness: A Vickers hardness tester is used to apply a load to the polished surface of the sample, hold it for a certain period of time, and then unload it. The microhardness value is calculated by measuring the length of the diagonal of the indentation.

[0062] Table 1 shows the mechanical property test results of the alumina ceramics obtained in Examples 1 to 4 and Comparative Examples 1 to 4.

[0063]

[0064] In conjunction with Example 1 and Figure 1 It can be seen that the high-strength alumina ceramic prepared by this invention has excellent density and uniform grain size distribution. The grains in the figure are mostly regular polyhedral in shape, and the grain boundaries are extremely tightly bonded, with no obvious micropores or abnormal grain coarsening observed. This confirms that the high-strength alumina ceramic prepared by Mg... 2+ Zr 4+ With Si 4+ The multi-component non-stoichiometric composite solid solution formed by heterovalent synergistic substitution effectively inhibits grain growth and promotes sintering densification. The extremely clear grain boundaries, devoid of obvious second-phase agglomeration (such as coarse ZrO2 particles) or continuous aluminosilicate glass phase films, strongly corroborate that the components have, as expected, constructed a high-rigidity grain boundary framework in situ at the grain boundaries and solidified free SiO2. This microscopically rigid interlocking structure significantly enhances the effective load transfer capacity of the grain boundaries and suppresses high-temperature viscous flow, forming the microstructural basis for the synergistic improvement in flexural strength and fracture toughness in the embodiments.

[0065] In conjunction with Example 1 and Figure 3 It can be seen that at 610 cm -1 With 820 cm -1A distinct broad peak exists at 1662 cm⁻¹, characterizing the Al-O lattice vibrations of the alumina matrix, indicating that the main structure remains stable; simultaneously, at 1662 cm⁻¹... -1 With 1615 cm -1 Characteristic absorption peaks of amide I (C=O stretching) and amide II (NH bending) appeared nearby, and the C=O peak showed a certain red shift compared to free urea, with a binding peak at 3225 cm⁻¹. -1 With 3345 cm -1 The N–H stretching vibration at this location proves that the amide group in the urea molecule undergoes weak coordination with the surface Al-Lewis acidic site; furthermore, at 3460 cm⁻¹... -1 The broad and strong absorption bands at the point correspond to surface hydroxyl groups and adsorbed water, indicating that the surface hydroxyl groups partially dissociate and form active sites under weakly alkaline conditions. Overall, this spectrum provides molecular-level evidence that a transient activated layer characterized by weak urea coordination was successfully constructed on the alumina surface under pH 9.0–10.5 and 50–70 °C conditions. This process effectively modulates the surface energy and interparticle forces, retaining highly active coordination vacancies even after subsequent water washing to remove urea. This significantly improves the surface reactivity and interfacial driving force of the powder, providing favorable conditions for the uniform anchoring of sintering aids and in-situ reactions at grain boundaries.

[0066] In conjunction with Example 1 and Figure 2 It can be seen that, while maintaining the α-Al₂O₃ main phase, the characteristic diffraction peaks of the red curve of the high-strength alumina ceramic prepared by this invention have undergone a slight overall shift towards a lower angle (left side) due to lattice distortion (the black dashed line represents the standard peak position, which is clearly visible in the contrast). This confirms the presence of a larger radius Mg 2+ With Zr 4+ Ions have been embedded into the alumina lattice through heterovalent co-substitution, forming a multi-element non-stoichiometric composite solid solution. The spectrum completely lacks impurity peaks from MgAl₂O₄ spinel, monoclinic / tetragonal ZrO₂, and other silicate crystals, and the background is stable with no diffuse peaks representing the glassy state. This fully demonstrates that the additive components have undergone in-situ reaction at the grain boundaries according to the designed MgO / SiO₂ / ZrO₂ molar ratio (1:0.8:0.5), successfully solidifying and transforming the easily weakened free SiO₂ into a high-rigidity grain boundary framework. This unique microscopic solid solution structure effectively solves the stress concentration and high-temperature creep problems caused by the grain boundary glass phase in traditional alumina ceramics, explaining the flexural strength (520±15 MPa) and fracture toughness (4.8±0.2 MPa·m) of Example 1 from the perspective of microscopic phase evolution. 1 / 2 The fundamental reason for the significant improvement.

[0067] As can be seen from Examples 1 to 4 and Table 1, the high-strength alumina ceramic prepared by this invention exhibits excellent comprehensive mechanical properties, with its flexural strength remaining stable between 510 and 555 MPa and its fracture toughness reaching 4.6 to 5.2 MPa·m. 1 / 2 The bulk density is 3.91 g / cm³. -3 The microhardness is in the range of 18.3 to 18.9 HV, which indicates that by precisely controlling the molar ratio of MgO / SiO2 / ZrO2 and using modified powder processing, ceramic materials with uniform microstructure and extremely high density can be obtained.

[0068] Combining Example 1, Comparative Example 1, and Table 1, it can be seen that Comparative Example 1, which uses the original powder, has a higher flexural strength (430 MPa) and fracture toughness (3.6 MPa·m). 1 / 2 The results were significantly lower than those in Example 1. This is because the modification process improved the surface activity of the powder through the weak coordination between urea molecules and aluminum atoms, which provided a stronger driving force for the uniform anchoring of subsequent additives and in-situ reaction at grain boundaries. In contrast, the original powder was prone to agglomeration and had low interfacial reaction activity, making it difficult to construct an ideal grain boundary solid solution structure.

[0069] Combining Example 1, Comparative Example 2, and Table 1, it can be seen that the mechanical properties of Comparative Example 2, which omitted the pre-calcination step, decreased the most drastically (flexural strength was only 405 MPa). This is because pre-calcination allows the zirconium, magnesium, and silicon components to undergo a preliminary solid-state reaction and solidify free SiO2 before high-temperature sintering. If sintering is performed directly, local transient liquid phases or component segregation are easily generated in the early stage, leading to abnormal grain growth or the formation of a continuous glassy phase with weakened grain boundaries.

[0070] Combining Example 1, Comparative Example 3, Comparative Example 4, and Table 1, it can be seen that the flexural strength (520±15MPa) and fracture toughness (4.8±0.2 MPa·m) of Example 1 are... 1 / 2 It was significantly superior to Control Example 3, which used an equal mass of MgO instead of zirconium oxide (450±13 MPa, 3.9±0.2 MPa·m). 1 / 2 ) and a control example 4 (440±12 MPa, 3.7±0.1 MPa·m) where zirconium oxide was used instead of MgO. 1 / 2 By precisely controlling the molar ratio of MgO / SiO2 / ZrO2 to 1:(0.8~1.2):(0.5~2.5), a larger radius MgO can be produced. 2+ With Zr 4+ During high-temperature sintering, ions undergo confined diffusion to collaboratively replace Al in the α-Al₂O₃ lattice. 3+The site is thus formed in situ, resulting in a multi-component non-stoichiometric composite solid solution. This solid solution engulfs and solidifies free SiO2, constructing a highly rigid locked grain boundary framework, which microscopically inhibits grain boundary viscosity flow and abnormal grain growth. In contrast, Control Example 3, lacking the structural strengthening effect of a zirconium source, cannot form such a highly stable grain boundary framework; while Control Example 4, lacking a magnesium source, loses the key driving force for inhibiting grain coarsening and promoting densification. Both examples disrupt the chemical potential balance and coordination reconstruction conditions between the components, leading to a greater enrichment of brittle glassy phases at the grain boundaries, resulting in a significant decline in mechanical properties.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-strength alumina ceramic, characterized in that, Includes the following steps: Step S1. Provide modified alumina powder and introduce zirconium source compound, magnesium source compound and silicon source compound, wherein the amount of magnesium source compound, silicon source compound and zirconium source compound introduced is controlled by the molar ratio of MgO, SiO2 and ZrO2 as 1:(0.8~1.2):(0.5~2.5); at the same time, based on the total mass of the modified alumina powder, the zirconium source compound, the magnesium source compound and the silicon source compound, the mass percentage of the modified alumina powder is 85~96wt%, and the total mass percentage of the zirconium source compound, magnesium source compound and silicon source compound is 4~15wt%. Step S2. The modified alumina powder, zirconium source compound, magnesium source compound and silicon source compound are wet-mixed to form a uniformly distributed nanoscale precursor layer on the powder surface. Step S3. The mixed powder obtained in step S2 is subjected to pre-calcination treatment to allow the zirconium source compound, magnesium source compound and silicon source compound to undergo a preliminary solid-phase reaction; Step S4. After the pre-calcined powder is shaped, it is sintered at 1500-1700℃ to cause in-situ reactions at the grain boundaries, thereby obtaining high-strength alumina ceramic.

2. The preparation method according to claim 1, characterized in that, The pre-calcination treatment in step S3 is carried out at 700–1000℃ for 1–4 hours.

3. The preparation method according to claim 1, characterized in that, The zirconium source compound is selected from one or more of zirconium oxide, zirconium oxychloride, zirconium nitrate, ammonium zirconium carbonate, and zirconium acetate.

4. The preparation method according to claim 1, characterized in that, The magnesium source compound is selected from one or more of magnesium oxide, magnesium carbonate, and magnesium hydroxide.

5. The preparation method according to claim 1, characterized in that, The silicon source compound is selected from one or more of silicon dioxide, silica sol, and silicates.

6. The preparation method according to claim 1, characterized in that, The method for preparing the modified alumina powder includes: dispersing raw alumina powder in a urea aqueous solution, adjusting the pH of the system to 9.0–10.5 under closed conditions, and maintaining it at 50–70°C for 1–3 hours to allow the amide groups in the urea molecules to undergo weak coordination with the aluminum atoms on the surface of the alumina powder; subsequently cooling the reaction system and changing the ionic environment by washing with water to terminate the coordination effect, performing solid-liquid separation on the obtained powder, and gently drying it at 80–110°C to obtain modified alumina powder with improved interfacial chemical reactivity.

7. The preparation method according to claim 6, characterized in that, The mass concentration of urea in the urea aqueous solution is 4-8 wt%.

8. The preparation method according to claim 1, characterized in that, The holding time for sintering in step S4 is 4 to 6 hours.

9. A high-strength alumina ceramic is prepared based on the preparation method described in claim 1.

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