Method for preparing high-entropy oxide-silicon carbide composite ceramic through microwave sintering

Abstract

The invention belongs to the technical field of inorganic non-metallic materials, and discloses a method for preparing high-entropy oxide-silicon carbide composite ceramic through microwave sintering, high-entropy oxide precursor powder and silicon carbide powder are used as raw materials, wet ball milling or dry ball milling is adopted, the obtained mixed powder is molded into a blank, the blank is put into a microwave sintering furnace, and the high-entropy oxide-silicon carbide composite ceramic is prepared through microwave sintering. And carrying out microwave sintering in a vacuum or protective atmosphere, and carrying out heat preservation treatment to synthesize the high-entropy oxide-silicon carbide composite ceramic. Silicon carbide is innovatively introduced into the high-entropy oxide ceramic and can serve as a microwave absorbing heat source, low-temperature rapid heating of the composite ceramic is achieved, and densification is promoted through the activity of the high-entropy oxide; as a hard reinforcing phase, through particle strengthening and crack deflection mechanisms, the strength of the composite material is improved at the same time; the constructed heat-conducting network combines high wear resistance and excellent heat dissipation capability of the high-entropy oxide, and the prepared composite ceramic material has excellent comprehensive properties such as high hardness, high heat conductivity, good wear resistance and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of inorganic non-metallic materials, and particularly relates to a method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering. BACKGROUND

[0002] High-entropy oxide ceramics have significant advantages in wear resistance due to their flexible composition, high hardness, excellent wear resistance and high-temperature resistance, and have become an important breakthrough in the field of wear-resistant ceramics. However, such materials usually have low thermal conductivity, and the heat generated during friction is not easily dissipated, which can cause the material to soften at high temperatures, thereby affecting its wear resistance and service life. Silicon carbide materials have high thermal conductivity, which can effectively improve the overall heat dissipation capacity and promote the release of friction heat, thereby maintaining the excellent wear resistance of high-entropy oxides and avoiding overheating and softening, thereby prolonging the service life.

[0003] However, sintering of high-entropy oxides and silicon carbide ceramics is extremely difficult, mainly reflected in the following aspects: (1) High-entropy phases are difficult to sinter or have uneven distribution due to uneven temperature during traditional sintering. (2) Silicon carbide has strong covalent bonds, and sintering can only be achieved by introducing a second phase, but there are still problems of high sintering temperature and high energy consumption. (3) As disclosed in the patent document "High-entropy oxide ceramic and its preparation method" (CN118290129A), the impedance matching of oxide ceramics under the action of microwaves is poor, and only by increasing the microwave input power can heating be achieved, which is high in energy consumption and long in cycle.

[0004] Therefore, it is an urgent problem to be solved how to combine silicon carbide materials with high-entropy oxides to synergistically enhance the mechanical properties, wear resistance and thermal conductivity of the composite ceramic material, and improve its service life. SUMMARY

[0005] In order to solve the above technical problems, the application provides a method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering, which innovatively introduces silicon carbide materials and uses microwave sintering. The silicon carbide has excellent wave absorption performance and low energy consumption. The silicon carbide material has both thermal conductivity and wear resistance, and when it is combined with high-entropy oxides, the overall heat dissipation capacity of the material can be improved to avoid overheating and softening. The high-entropy oxide-silicon carbide composite ceramics prepared have high strength, good wear resistance and long service life.

[0006] In order to achieve the above purpose, the technical scheme adopted by the application is as follows: a method for preparing high-entropy oxide-silicon carbide composite ceramics by microwave sintering, comprising the following steps:

[0007] Step 1, preparing a sintering precursor: using high-entropy oxide precursor powder and silicon carbide powder as raw materials to ball mill into a mixed powder;

[0008] Among them, high-entropy oxide precursor powder includes Five or seven oxides are used in the process, with silicon carbide powder accounting 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 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 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 green body 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 of microwave sintering for preparing high-entropy oxide-silicon carbide composite ceramics, characterized in that, The method comprises the following steps: Step one, preparing sintering precursor: using high-entropy oxide precursor powder and silicon carbide powder as raw materials, ball milling to obtain mixed powder; Among them, high-entropy oxide precursor powder includes Five or seven oxides are used, and the amount of silicon carbide powder added accounts for 20-50% of the total weight of the raw materials; Step two, preparing green body: after drying treatment, the mixed powder is molded to obtain green body; Step three, microwave sintering: the green body is placed in an alumina crucible and put into a microwave sintering furnace for microwave sintering; the sintering temperature is 900-1350℃, the initial power is 700W, the power is increased at a 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 four, cooling to room temperature in the furnace to obtain high-entropy oxide-silicon carbide composite ceramic material; The hardness of the high-entropy oxide-silicon carbide composite ceramic is greater than or equal to 18GPa, and the thermal conductivity is greater than or equal to 25W / (m·K).

2. The method of claim 1, wherein the method is characterized by: In step one The five oxides are mixed in a molar ratio of 1:1:2:1-2:1-2.

3. The method of claim 1, wherein the method is characterized by: In step one The seven oxides were mixed in a molar ratio of 1-5:1:1:1:1:1:

1.

4. The method of claim 1, wherein the method is a microwave sintering method for preparing high-entropy oxide-silicon carbide composite ceramics. 99.99% purity, 50-80 nm particle size; 99.5% purity, 50-80 nm particle size; NiO 99.6% purity, 30-50 nm particle size; 99.8% purity, 5-10 nm particle size.

5. The method of claim 1, wherein the method is characterized by: CuO purity of 99.9%, particle size of 50nm; purity of 99.9%, particle size of 80nm; purity of 99.9%, particle size of 80-100nm; SiC powder particle size of 500nm-10μm.

6. The method of claim 1, wherein the method is a microwave sintering method for preparing high-entropy oxide-silicon carbide composite ceramics. In step one, dry or wet ball milling is used, the ball milling parameters are as follows: ball-to-material ratio 2:1-10:1, rotation speed 200-500rpm, and time 6-24h; the wet ball milling medium is anhydrous ethanol, acetone or isopropyl alcohol, and the weight ratio of the ball milling medium to the raw material is 0.5-1.5:

1.

7. The method of claim 1, wherein the method is a microwave sintering method for preparing high-entropy oxide-silicon carbide composite ceramics. In step two, the mixed powder after ball milling is dried, the drying temperature is 80℃, and the drying time is 12h.

8. The method of claim 1, wherein the method is a microwave sintering method for preparing high-entropy oxide-silicon carbide composite ceramics. In step two, the mixed powder is molded to prepare green body, that is, the mixed powder is placed in a cylindrical tablet mold, and the pressure is maintained at 20-80MPa for 40-60s; the green body is prepared by molding.

9. The method of claim 1, wherein the method is a microwave sintering method for preparing high-entropy oxide-silicon carbide composite ceramics. The vacuum degree when the sintering atmosphere in step three is a vacuum atmosphere The high-purity argon purity ≥ 99.99% when the sintering atmosphere is an argon protective atmosphere.

Images