A method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering

Abstract

This invention belongs to the field of inorganic non-metallic materials technology and discloses a method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering. Using high-entropy oxide precursor powder and silicon carbide powder as raw materials, the mixture is prepared by wet or dry ball milling. The resulting powder is molded into a compact and placed in a microwave sintering furnace for microwave sintering under vacuum or a protective atmosphere. After heat treatment, the high-entropy oxide-silicon carbide composite ceramic is synthesized. This invention innovatively introduces silicon carbide into the high-entropy oxide ceramic, which can act as a microwave heat source to achieve rapid heating of the composite ceramic at low temperatures. The activity of the high-entropy oxide promotes densification; as a hard reinforcing phase, it simultaneously improves the strength of the composite material through particle strengthening and crack deflection mechanisms. The constructed thermally conductive network combines the high wear resistance and excellent heat dissipation capacity of the high-entropy oxide. The prepared composite ceramic material possesses excellent comprehensive properties such as high hardness, high thermal conductivity, and good wear resistance.

Description

Technical Field

[0001] This invention belongs to the field of inorganic non-metallic materials technology, specifically relating to a method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering. Background Technology

[0002] High-entropy oxide ceramics, with their flexible composition design, exhibit significant advantages in wear resistance, possessing extremely high hardness and excellent wear and high-temperature resistance, representing a major breakthrough in the field of wear-resistant ceramics. However, these materials typically have low thermal conductivity, making it difficult to dissipate heat accumulated during friction. This can easily lead to material softening at high temperatures, affecting their wear resistance and service life. Silicon carbide materials, with their high thermal conductivity, can effectively improve overall heat dissipation, promoting the release of frictional heat. While maintaining the excellent wear resistance of high-entropy oxides, they avoid overheating and softening, thereby extending service life.

[0003] However, the sintering of high-entropy oxides and silicon carbide ceramics is extremely difficult, mainly due to the following: (1) The high-entropy phase is difficult to sinter or has an uneven distribution due to the uneven temperature caused by the traditional sintering method. (2) Silicon carbide has extremely strong covalent bonds, and a second phase is generally introduced to achieve sintering, but there are still problems of high sintering temperature and high energy consumption. (3) For example, in the patent document "A high-entropy oxide ceramic and its preparation method" (CN118290129A), the oxide ceramic has extremely poor impedance matching under microwave action, and heating can only be achieved by increasing the microwave input power, which results in high energy consumption and long cycle.

[0004] How to combine silicon carbide materials with high-entropy oxides to synergistically enhance the mechanical properties, wear resistance, and thermal conductivity of composite ceramic materials, thereby improving their service life, is an urgent problem to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering. It innovatively introduces silicon carbide material and employs microwave sintering. Silicon carbide exhibits excellent microwave absorption properties and low energy consumption. Furthermore, silicon carbide combines thermal conductivity and wear resistance; combining it with high-entropy oxides enhances the overall heat dissipation capacity of the material, preventing overheating and softening. The prepared high-entropy oxide-silicon carbide composite ceramics exhibit high strength, good wear resistance, and extended service life.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering, comprising the following steps:

[0007] Step 1: Preparation of sintering precursor: High-entropy oxide precursor powder and silicon carbide powder are ball-milled into a mixed powder.

[0008] Among them, high-entropy oxide precursor powder includes Five or seven oxides are added, and the amount of silicon carbide powder accounts for 20-50% of the total weight of the raw materials. When the SiC content is <20%, the impedance matching is insufficient, making it difficult to raise the temperature under microwave action. When the SiC content is >50%, the high-entropy oxide bonding phase is insufficient, affecting the densification and mechanical properties of the composite ceramic material.

[0009] Step 2, Blank Forming: After drying the mixed powder, it is molded into a blank to obtain the blank.

[0010] Step 3, Microwave Sintering: Place the green body in an alumina crucible and put it into a microwave sintering furnace for microwave sintering; the sintering temperature is 900-1350℃, the initial power is 700W, the heating is carried out at a power rate of 100W / min, the holding time is 10~30min, the microwave heating frequency is 2450MHz, and the sintering atmosphere is vacuum or argon protection.

[0011] Step 4: Cool the furnace to room temperature to obtain high-entropy oxide-silicon carbide composite ceramic material.

[0012] High-entropy oxide-silicon carbide composite ceramics have a hardness ≥18 GPa and a thermal conductivity ≥25 W / (m·K); wear rate .

[0013] The The five oxides were mixed in a molar ratio of 1:1:2:1~2:1~2.

[0014] The The seven oxides were mixed and prepared in a molar ratio of 1 to 5:1:1:1:1:1:1.

[0015] in, The purity is 99.99%, and the particle size is 50-80nm.

[0016] in, The purity is 99.5%, and the particle size is 50-80nm.

[0017] The NiO has a purity of 99.6% and a particle size of 30-50 nm.

[0018] in, The purity is 99.8%, and the particle size is 5-10 nm.

[0019] The CuO has a purity of 99.9% and a particle size of 50 nm.

[0020] in, The purity is 99.9% and the particle size is 80nm.

[0021] in, The purity is 99.9%, and the particle size is 80-100nm.

[0022] The particle size of the SiC powder is 500nm-10μm.

[0023] In step one, dry or wet ball milling is used. The ball milling parameters are a ball-to-material ratio of 2:1 to 10:1, a rotation speed of 200 to 500 rpm, and a time of 6 to 24 hours. The medium for wet ball milling is anhydrous ethanol, acetone, or isopropanol, and the weight ratio of the ball milling medium to the raw material is 0.5 to 1.5:1.

[0024] In step two, the ball-milled mixed powder is dried at a temperature of 80°C for 12 hours.

[0025] In step two, the precursor mixed powder is molded into a preform by placing the mixed powder in a cylindrical compression mold and holding it under pressure of 20-80 MPa for 40-60 seconds; the preform is then obtained through molding. Molding the precursor mixed powder into a preform makes the mixed powder more tightly bound, prevents the gas generated during microwave heating from escaping, generates microwave plasma that promotes temperature rise, and intensifies the synthesis reaction.

[0026] When the sintering atmosphere in step three is a vacuum atmosphere, the vacuum level is... When the sintering atmosphere is an argon protective atmosphere, the purity of the high-purity argon gas is ≥99.99%.

[0027] The high-entropy oxide-silicon carbide composite ceramic prepared by this invention can be applied to high-temperature wear-resistant and thermal management structural components, expanding the application scenarios of high-entropy ceramics.

[0028] This invention uses raw materials comprising at least five oxides, which react in situ at high temperatures to generate a high-entropy phase, thus synthesizing the product. When five or more metallic elements coexist in approximately equal proportions within the same crystal lattice, the configurational entropy of the entire system becomes extremely high. This high degree of disorder plays a stabilizing role thermodynamically, causing the material to tend to form a single, stable solid solution phase at high temperatures, rather than separating into multiple simple oxides. The high-entropy oxide matrix itself has a stable phase structure at sintering and operating temperatures and is not easily decomposed; its core lies in "high-entropy stabilization." Silicon carbide, a material with extremely strong covalent bonds, relies on the generated high-entropy phase to bind (bond) silicon carbide. By carefully selecting element combinations, the chemical properties of the high-entropy oxide can be adjusted, making it less prone to violent chemical reactions (such as the formation of excessive low-melting-point silicates) when in contact with SiC at high temperatures. Instead, physical bonding and limited interdiffusion of elements are the main mechanisms, avoiding the formation of a harmful brittle reaction layer. The resulting high-entropy oxide-silicon carbide composite ceramic combines the unique mechanical properties of high-entropy oxide ceramics with the high thermal conductivity of silicon carbide ceramics.

[0029] This invention utilizes the microwave absorption properties of SiC to achieve low-temperature, rapid, and uniform microwave sintering of high-entropy oxides. SiC plays a special role in microwave sintering; its excellent microwave absorption properties allow it to efficiently convert microwave energy into heat, forming an internal heat source mechanism. Most oxides, however, exhibit weak microwave absorption. After uniform mixing of high-entropy oxides and silicon carbide powders, the silicon carbide within the raw materials absorbs microwaves, and under microwave influence, this absorption couples with the microwaves to generate heat, which serves as a heat source. The uniformly distributed SiC particles in the mixed powder rapidly heat up in the microwave field, becoming numerous micro-heat sources that directly heat the surrounding high-entropy oxide powder from the inside, achieving low-temperature, uniform sintering. In contrast, traditional hot-pressing heating methods involve heat conduction from the outside in, requiring external heating for both silicon carbide and oxide powders. Compared to traditional heating methods, microwave heating significantly reduces the overall energy consumption and temperature required for sintering and achieves uniform heating of the material, eliminating the temperature gradient and uneven sintering issues caused by traditional external heating methods. This facilitates the formation of a high-entropy phase with uniform diffusion of multiple elements.

[0030] The combination of high-entropy oxides and SiC can mutually promote and synergistically densify, resulting in superior performance. This solves the problem of the difficulty in sintering pure SiC due to its extremely strong covalent bonds. After synergistic sintering, the composite material forms a two-phase microstructure. SiC particles, as the reinforcing phase, are uniformly embedded in the high-entropy oxide matrix, forming a nanoscale interdiffusion layer. This structure exhibits the strengthening effect of particle-reinforced composite materials. The hard SiC particles directly bear external loads, resisting plastic deformation and wear; the high-entropy oxide matrix plays a role in bonding and transferring loads, while its own solid solution strengthening and grain refinement also enhance the hardness of the composite material.

[0031] Through the synergistic integration of advantages, the mechanical properties of high-entropy oxide-SiC composite ceramic materials are synergistically enhanced, exhibiting strengthening and toughening effects. This is attributed to the dispersion strengthening of hard SiC particles, the solid solution strengthening of the high-entropy oxide matrix, and the fine grain size. When cracks propagate within the material, they encounter SiC particles. Unable to easily penetrate the harder SiC, the cracks are deflected, bypassing the particles or propagating along the interface. This process significantly prolongs the crack propagation path, consuming more energy and thus improving the material's fracture toughness. Furthermore, due to the difference in thermal expansion coefficients between the two materials, moderate residual stress is generated near the interface after cooling, which also helps to hinder crack propagation.

[0032] This invention combines high-entropy oxides with SiC, achieving both high wear resistance and high thermal conductivity. Oxide ceramics are inherently poor conductors of heat, exhibiting extremely high thermal resistance. During service, particularly during wear, they generate significant heat. The unavoidable release of this heat can lead to localized overheating, causing softening and affecting their usability. In contrast, silicon carbide possesses extremely high thermal conductivity. When present in sufficient quantity and uniformly distributed within the matrix, it can interconnect to form a rapidly conducting network or pathway. This is analogous to embedding metal wires in thermal insulation materials, creating heat conduction pathways. Adding silicon carbide to oxide ceramics allows for rapid conduction of localized high temperatures, preventing softening due to excessive heat and extending the lifespan of the composite ceramic.

[0033] Furthermore, during friction and wear, a large amount of heat is generated at the contact surface. Traditional high-entropy oxides, due to their poor thermal conductivity, experience heat accumulation leading to surface softening and accelerated wear. However, in this composite material, the generated frictional heat can be rapidly dissipated from the surface to the interior and overall structure of the material through the thermally conductive network constructed by SiC, preventing a sharp increase in local temperature. This composite material also possesses an adaptive wear-resistant surface. During friction, the surface material undergoes slight oxidation and plastic flow, forming an extremely thin, dense, and tough enamel layer. This in-situ formed protective layer further reduces the wear rate. Thus, the surface material's hardness and wear resistance are maintained, significantly extending its service life.

[0034] The beneficial effects of this invention are as follows: This invention innovatively introduces silicon carbide into high-entropy oxide ceramics, improving the thermal conductivity of the composite material without affecting wear resistance, thus avoiding softening problems caused by localized overheating during wear. Furthermore, the introduction of silicon carbide can serve as a microwave heat source, enabling rapid low-temperature heating of the composite ceramic. Compared to traditional heating methods, this achieves uniform heating throughout the material, avoiding the difficulty or uneven firing of the high-entropy phase due to temperature differences. This invention achieves high-entropy oxide-silicon carbide composite ceramics through a one-step microwave sintering method, possessing both the unique mechanical properties of high-entropy oxide ceramics and the high thermal conductivity of silicon carbide ceramics. The prepared composite ceramic material exhibits excellent comprehensive properties such as high hardness, high strength, and good wear resistance. Attached Figure Description

[0035] Figure 1 The XRD pattern of the high-entropy oxide-SiC composite ceramic prepared in Example 1 of this invention;

[0036] Figure 2 The image shows the microstructure of the high-entropy oxide-SiC composite ceramic prepared in Example 1 of this invention.

[0037] Figure 3 The heating curve of the high-entropy oxide-SiC composite ceramic prepared in Example 1 of this invention is shown.

[0038] Figure 4 The image shows the microstructure of the high-entropy oxide-SiC composite ceramic prepared in Example 2 of this invention.

[0039] Figure 5 The image shows the microstructure of the high-entropy oxide-SiC composite ceramic prepared in Example 3 of this invention. Detailed Implementation

[0040] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0041] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; and the reagents and materials used are commercially available unless otherwise specified.

[0042] Example 1

[0043] A method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering includes the following steps:

[0044] Step 1: Preparation of sintering precursors: Using high-entropy oxide precursor powder and silicon carbide powder as raw materials, the high-entropy oxide precursor powder includes... Seven oxides were mixed in a molar ratio of 5:1:1:1:1:1:1, with silicon carbide powder accounting for 50% of the total weight of the raw materials. Wet ball milling was performed using isopropanol as the medium, with an isopropanol to raw material weight ratio of 0.5:1. The ball milling parameters were a ball-to-material ratio of 2:1, a rotation speed of 200 rpm, and a time of 12 hours to obtain the mixed powder.

[0045] Step 2, Preform Preparation: The ball-milled mixed powder is dried at 80℃ for 12 hours; the dried mixed powder is then placed in a cylindrical tableting mold and molded at a pressure of 30MPa for 60 seconds to obtain the preform.

[0046] Step 3: Microwave Sintering: Place the green body in an alumina crucible and put it into a microwave sintering furnace for microwave sintering; the initial power is 700W, and the temperature is raised to 1350℃ at a power rate of 100W / min, with a holding time of 20min. The microwave heating frequency is 2450MHz, and the vacuum degree during sintering is... .

[0047] Step 4: Cool the furnace to room temperature to obtain high-entropy oxide-silicon carbide composite ceramic material.

[0048] Example 2

[0049] A method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering includes the following steps:

[0050] Step 1: Preparation of sintering precursors: Using high-entropy oxide precursor powder and silicon carbide powder as raw materials, the high-entropy oxide precursor powder includes... Five oxides were mixed in a molar ratio of 1:1:2:1:2, with silicon carbide powder accounting for 30% of the total weight of the raw materials. Wet ball milling was performed using anhydrous ethanol as the medium. The weight ratio of anhydrous ethanol to raw materials was 1.5:1. The ball milling parameters were a ball-to-material ratio of 5:1, a rotation speed of 350 rpm, and a time of 6 hours to obtain the mixed powder.

[0051] Step 2, Preform Preparation: The ball-milled mixed powder is dried at 80℃ for 12 hours; the dried mixed powder is then placed in a cylindrical tableting mold and molded at a pressure of 20MPa for 50 seconds to obtain the preform.

[0052] Step 3, Microwave Sintering: Place the blank in an alumina crucible and put it into a microwave sintering furnace for microwave sintering; the initial power is 700W, and the temperature is raised to 1100℃ according to the power regime of 100W / min, the holding time is 30min, and the microwave heating frequency is 2450MHz; the sintering atmosphere is an argon protective atmosphere with a purity of ≥99.99%.

[0053] Step 4: Cool the furnace to room temperature to obtain high-entropy oxide-silicon carbide composite ceramic material.

[0054] Example 3

[0055] A method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering includes the following steps:

[0056] Step 1: Preparation of sintering precursors: Using high-entropy oxide precursor powder and silicon carbide powder as raw materials, the high-entropy oxide precursor powder includes... Seven oxides were mixed in a molar ratio of 1:1:1:1:1:1:1, with silicon carbide powder accounting for 20% of the total weight of the raw materials. Dry ball milling was used with ball-to-material ratio of 10:1, rotation speed of 500 rpm, and time of 12 hours to obtain the mixed powder.

[0057] Step 2, Preform Preparation: The ball-milled mixed powder is dried at 80℃ for 12 hours; the dried mixed powder is then placed in a cylindrical tableting mold and molded at a pressure of 80MPa for 40 seconds to obtain the preform.

[0058] Step 3, Microwave Sintering: Place the blank in an alumina crucible and put it into a microwave sintering furnace for microwave sintering; the initial power is 700W, the temperature is raised to 900℃ according to the power regime of 100W / min, the holding time is 30min, the microwave heating frequency is 2450MHz, and the sintering atmosphere is an argon protective atmosphere with a purity of ≥99.99%.

[0059] Step 4: Cool the furnace to room temperature to obtain high-entropy oxide-silicon carbide composite ceramic material.

[0060] Example 4

[0061] A method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering includes the following steps:

[0062] Step 1: Preparation of sintering precursors: Using high-entropy oxide precursor powder and silicon carbide powder as raw materials, the high-entropy oxide precursor powder includes... Five oxides were mixed in a molar ratio of 1:1:2:2:1, with silicon carbide powder accounting for 35% of the total weight of the raw materials. Wet ball milling was performed using propanol as the medium. The weight ratio of propanol to raw materials was 1:1. The ball milling parameters were a ball-to-material ratio of 7:1, a rotation speed of 300 rpm, and a time of 10 h to obtain the mixed powder.

[0063] Step 2, Preform Preparation: The ball-milled mixed powder is dried at 80℃ for 12 hours; the dried mixed powder is then placed in a cylindrical tableting mold and molded at a pressure of 50MPa for 40 seconds to obtain the preform.

[0064] Step 3, Microwave Sintering: Place the blank in an alumina crucible and put it into a microwave sintering furnace for microwave sintering; the initial power is 700W, and the temperature is raised to 1200℃ according to the power regime of 100W / min, the holding time is 25min, and the microwave heating frequency is 2450MHz; the sintering atmosphere is an argon protective atmosphere with a purity of ≥99.99%.

[0065] Step 4: Cool the furnace to room temperature to obtain high-entropy oxide-silicon carbide composite ceramic material.

[0066] Example 5

[0067] A method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering includes the following steps:

[0068] Step 1: Preparation of sintering precursors: Using high-entropy oxide precursor powder and silicon carbide powder as raw materials, the high-entropy oxide precursor powder includes... Seven oxides were mixed in a molar ratio of 3:1:1:1:1:1:1, with silicon carbide powder accounting for 40% of the total weight of the raw materials. Wet ball milling was performed using anhydrous ethanol as the medium, with an anhydrous ethanol to raw material weight ratio of 1.5:1. The ball milling parameters were a ball-to-material ratio of 8:1, a rotation speed of 350 rpm, and a time of 12 hours to obtain the mixed powder.

[0069] Step 2, Preform Preparation: The ball-milled mixed powder is dried at 80℃ for 12 hours; the dried mixed powder is then placed in a cylindrical tableting mold and molded at a pressure of 60MPa for 50 seconds to obtain the preform.

[0070] Step 3: Microwave Sintering: Place the green body in an alumina crucible and put it into a microwave sintering furnace for microwave sintering; the initial power is 700W, and the temperature is raised to 1250℃ at a power rate of 100W / min, with a holding time of 10min. The microwave heating frequency is 2450MHz, and the vacuum degree during sintering is... .

[0071] Step 4: Cool the furnace to room temperature to obtain high-entropy oxide-silicon carbide composite ceramic material.

[0072] The composite ceramic materials prepared in Examples 1-5 were subjected to performance tests, and the test results are shown in the table below:

[0073]

[0074] The above embodiments are merely examples illustrating the explanation, specific implementation, and effects of the present invention, and are not intended to limit the invention. Based on this disclosure, some modifications or improvements without contributing any inventive step can be made, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of this disclosure fall within the scope of protection claimed in this disclosure.

Claims

1. A method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering, characterized in that, Includes the following steps: Step 1: Preparation of sintering precursor: High-entropy oxide precursor powder and silicon carbide powder are ball-milled into a mixed powder. The high-entropy oxide precursor powder is prepared by mixing five oxides, Al2O3, Y2O3, ZrO2, CeO2, and TiO2, in a molar ratio of 1:1:2:1 to 2:1 to 2, or by mixing seven oxides, Al2O3, NiO, Y2O3, ZrO2, CeO2, TiO2, and CuO, in a molar ratio of 1 to 5:1:1:1:1:1:

1. The amount of silicon carbide powder added accounts for 20-50% of the total weight of the raw materials. Step 2, Blank Forming: After drying the mixed powder, it is molded into a blank to obtain the blank. Step 3, Microwave Sintering: Place the green body in an alumina crucible and put it into a microwave sintering furnace for microwave sintering; the sintering temperature is 900-1350℃, the initial power is 700W, the heating is carried out at a power rate of 100W / min, the holding time is 10-30min, the microwave heating frequency is 2450MHz, and the sintering atmosphere is vacuum or argon protection. Step 4: Cool the furnace to room temperature to obtain a high-entropy oxide-silicon carbide composite ceramic material; The hardness of high-entropy oxide-silicon carbide composite ceramics is ≥18GPa and the thermal conductivity is ≥25W / (m·K).

2. The method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering according to claim 1, characterized in that: Al2O3 has a purity of 99.99% and a particle size of 50-80 nm; ZrO2 has a purity of 99.5% and a particle size of 50-80 nm; NiO has a purity of 99.6% and a particle size of 30-50 nm; TiO2 has a purity of 99.8% and a particle size of 5-10 nm.

3. The method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering according to claim 1, characterized in that: CuO has a purity of 99.9% and a particle size of 50nm; Y2O3 has a purity of 99.9% and a particle size of 80nm; CeO2 has a purity of 99.9% and a particle size of 80-100nm; and SiC powder has a particle size of 500nm-10μm.

4. The method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering according to claim 1, characterized in that: In step one, dry or wet ball milling is used. The ball milling parameters are a ball-to-material ratio of 2:1 to 10:1, a rotation speed of 200 to 500 rpm, and a time of 6 to 24 hours. The wet ball milling media are anhydrous ethanol, acetone, or isopropanol, and the weight ratio of the ball milling media to the raw material is 0.5 to 1.5:

1.

5. The method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering according to claim 1, characterized in that: In step two, the ball-milled mixed powder is dried at a temperature of 80°C for 12 hours.

6. The method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering according to claim 1, characterized in that: In step two, the precursor mixed powder is molded into a preform by placing the mixed powder in a cylindrical tableting mold and holding it under pressure of 20-80MPa for 40-60s; the preform is obtained by molding.

7. The method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering according to claim 1, characterized in that: When the sintering atmosphere in step three is a vacuum atmosphere, the vacuum degree is ≤10. -2 Pa; when the sintering atmosphere is an argon protective atmosphere, the purity of the high-purity argon gas is ≥99.99%.

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