Silicon carbide ceramic material based on gradient activated sintering and nanocomposite reinforcement, and preparation method and application thereof

Abstract

The application provides a kind of silicon carbide ceramic material based on gradient activation sintering and nanocomposite reinforcement and its preparation method and application, the preparation method includes: silicon carbide raw materials are mixed and ball milled to obtain sintering raw materials, the sintering raw materials are sequentially subjected to magnetic field strengthening sintering, pressure sintering and microwave sintering, SiC nanowires grow in the pressure sintering, and finally obtain silicon carbide ceramic material. The preparation method provided by the application is subjected to segmented sintering under the intensification of magnetic field, pressure and microwave respectively, the sintering powder is activated, particle arrangement and growth are promoted by using specific intensification means in different sintering stages, the densification of silicon carbide ceramic is improved, and SiC nanowires grow in the sintering process, so that the mechanical properties and thermal properties of silicon carbide ceramic material are significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of ceramic materials technology, and relates to a silicon carbide ceramic material, particularly a silicon carbide ceramic material based on gradient activation sintering and nanocomposite reinforcement, its preparation method and application. Background Technology

[0002] As a representative of third-generation advanced ceramic materials, silicon carbide ceramics exhibit outstanding high-temperature mechanical properties, ultra-high hardness, and excellent thermal shock resistance and chemical inertness due to their covalent crystal structure. They are irreplaceable in extreme environment fields such as aerospace thermal protection systems, nuclear reactor cladding materials, and semiconductor manufacturing equipment.

[0003] However, the industrial application of silicon carbide ceramics has long been constrained by the technical limitations of traditional solid-state sintering processes. First, atmospheric pressure sintering requires ultra-high temperatures above 2000℃, which not only consumes a great deal of energy but also easily leads to abnormal grain growth and structural defects. Second, based on silicon carbide micron-sized powder raw materials, the diffusion activation energy is high, making it difficult to further improve the material density. In addition, to promote material densification, sintering aids such as Al2O3-Y2O3 need to be added. These sintering aids tend to form a glassy phase at grain boundaries, which softens at high temperatures and reduces the high-temperature performance of the material.

[0004] In recent years, researchers have made a number of innovations in the preparation technology of silicon carbide ceramics.

[0005] For example, CN109592984A discloses a method for preparing liquid-phase sintered silicon carbide ceramics, using SiC powder as the raw material powder and alumina precursor and ytterbium oxide precursor as sintering aids, and preparing the silicon carbide ceramics by hot pressing sintering. This method optimizes the compounding of sintering aids, but optimizing sintering aids alone has limited effect on improving the performance of silicon carbide materials.

[0006] CN119504275A discloses a silicon carbide ceramic material and its preparation method. The method involves first preparing silicon carbide composite nanowires and modifying them with praseodymium, then sintering and annealing them using liquid polycarbosilane and modifying agents via spark plasma sintering. However, the spark plasma sintering method is limited by mold size and plasma uniformity control, and also has high equipment investment costs.

[0007] CN115594513A discloses an in-situ carbon fiber reinforced silicon carbide ceramic matrix composite material and its preparation method. This method uses silicon carbide powder, sintering aids, binders, and catalysts. Through compression molding and segmented sintering, some silicon carbide decomposes in situ to generate carbon fibers, thereby enhancing the strength of the silicon carbide ceramic material. While the flexural strength of silicon carbide ceramics is improved by using carbon fibers, other properties such as material density still need further improvement. In addition, there are methods that use nanoparticle sintering technology to reduce the sintering activation energy and improve the density of silicon carbide ceramics; however, nanoparticles have a large specific surface area and are prone to hard agglomeration.

[0008] In summary, current silicon carbide ceramic preparation processes suffer from limitations in significantly improving material properties and extremely high sintering costs, hindering their large-scale application. Therefore, developing novel preparation processes is the core direction for achieving large-scale production of high-performance silicon carbide ceramics. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a silicon carbide ceramic material based on gradient activation sintering and nanocomposite reinforcement, its preparation method and application, thereby optimizing the preparation process of silicon carbide ceramic materials, reducing the sintering temperature of the materials, and improving the performance of the materials.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides a method for preparing silicon carbide ceramic materials based on gradient activation sintering and nanocomposite reinforcement, the preparation method comprising the following steps:

[0012] Silicon carbide raw materials are mixed and ball-milled to obtain sintering raw materials. The sintering raw materials are then subjected to magnetic field strengthening sintering, pressure sintering and microwave sintering in sequence. SiC nanowires are grown in the pressure sintering process, and finally silicon carbide ceramic materials are obtained.

[0013] The preparation method provided by this invention employs a specific three-stage sintering process. In the first stage of sintering, a magnetic field is applied for strengthening. The alternating magnetic field disrupts the interparticle bonding forces in the initial sintering state, ensuring uniform dispersion of the sintered powder, preventing uneven agglomeration, and promoting powder surface activation. In the second stage of sintering, pressure is applied, driving the Si-CO gaseous material to migrate along grain boundaries. This promotes particle rearrangement and "neck" formation during the middle stage of sintering, filling pores. Simultaneously, β-SiC nanowires grow during grain formation and growth, bridging the grains and significantly improving fracture toughness. In the third stage of sintering, microwave strengthening is used for final densification. Microwaves selectively heat grain boundary regions, accelerating bulk diffusion, significantly improving densification, and lowering the sintering temperature.

[0014] Preferably, the silicon carbide raw material includes: silicon carbide powder and sintering additives, wherein the sintering additives include at least one of sintering aids, binders, dispersants, solvents, dispersants, release agents, or defoamers.

[0015] Preferably, the sintering aid includes carbon powder and / or boron carbide.

[0016] Preferably, the mass ratio of the toner to boron carbide is (1-10):1, for example, it can be 1:1, 3:1, 5:1, 8:1 or 10:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] Preferably, the adhesive comprises polyvinyl alcohol and / or polyacrylic acid.

[0018] Preferably, the mass ratio of polyvinyl alcohol to polyacrylic acid is (0.1-2):1, for example, it can be 0.1:1, 0.5:1, 1:1, 1.5:1 or 2:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] Preferably, the dispersing agent includes at least one of polyethylene glycol, ammonia, or glycerol.

[0020] Preferably, the solvent includes deionized water.

[0021] Preferably, the silicon carbide raw material comprises, by weight, 100 parts silicon carbide powder, 100-120 parts deionized water, 2-5 parts carbon powder, 0.6-1.5 parts boron carbide, 0.8-2 parts polyvinyl alcohol, 0.8-2 parts polyethylene glycol, 0.5-2 parts ammonia, 0.5-4 parts glycerol, 0.5-1.5 parts dispersant, 1-5 parts polyacrylic acid, 0.5-1.5 parts release agent, and 0.3-1 part defoamer.

[0022] The silicon carbide raw material contains 100-120 parts by mass of deionized water, for example, 100 parts, 105 parts, 110 parts, 115 parts or 120 parts, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] In the silicon carbide raw material, the mass fraction of carbon powder is 2-5 parts, for example, it can be 2 parts, 3 parts, 4 parts or 5 parts, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] In the silicon carbide raw material, the mass fraction of boron carbide is 0.6-1.5 parts, for example, it can be 0.6 parts, 0.8 parts, 1.0 parts, 1.2 parts, 1.4 parts or 1.5 parts, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] In the silicon carbide raw material, the mass fraction of polyvinyl alcohol is 0.8-2 parts, for example, it can be 0.8 parts, 1.0 parts, 1.2 parts, 1.5 parts, 1.8 parts or 2 parts, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] In the silicon carbide raw material, the mass fraction of polyethylene glycol is 0.8-2 parts, for example, it can be 0.8 parts, 1.0 parts, 1.2 parts, 1.5 parts, 1.8 parts or 2 parts, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] In the silicon carbide raw material, the mass fraction of ammonia water is 0.5-2 parts, for example, it can be 0.5 parts, 0.8 parts, 1.0 parts, 1.2 parts, 1.5 parts, 1.8 parts or 2 parts, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] In the silicon carbide raw material, the mass fraction of glycerol is 0.5-4 parts, for example, it can be 0.5 parts, 1 part, 2 parts, 3 parts or 4 parts, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] The mass fraction of the dispersant in the silicon carbide raw material is 0.5-1.5 parts, for example, it can be 0.5 parts, 0.8 parts, 1.0 parts, 1.2 parts or 1.5 parts, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] The mass fraction of polyacrylic acid in the silicon carbide raw material is 1-5 parts, for example, it can be 1 part, 2 parts, 3 parts, 4 parts or 5 parts, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] The release agent in the silicon carbide raw material is 0.5-1.5 parts by mass, for example, 0.5 parts, 0.8 parts, 1.0 parts, 1.2 parts or 1.5 parts, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] The defoamer in the silicon carbide raw material is 0.3-1 parts by mass, for example, 0.3 parts, 0.5 parts, 0.8 parts or 1 part, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the dispersant comprises polyethyleneimine.

[0034] Preferably, the release agent comprises sodium tripolyphosphate.

[0035] Preferably, the defoamer comprises emulsified silicone oil.

[0036] Preferably, the rotational speed of the ball mill is 20-70 rpm, for example, it can be 20 rpm, 30 rpm, 35 rpm, 40 rpm, 50 rpm, 60 rpm or 70 rpm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0037] Preferably, the ball milling time is 12-48 hours, for example, 12 hours, 18 hours, 24 hours, 30 hours, 36 hours, 42 hours or 48 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the sintering temperature of the magnetic field-strengthened sintering is 800-1200℃, for example, it can be 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃ or 1200℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0039] Preferably, the holding time for magnetic field-strengthened sintering is 30-60 min, for example, it can be 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] Preferably, the magnetic field-enhanced sintering method includes applying a pulsed electromagnetic field during the sintering process.

[0041] Preferably, the frequency of the pulsed electromagnetic field is 10-50kHz, for example, it can be 10kHz, 15kHz, 20kHz, 25kHz, 30kHz, 35kHz, 40kHz, 45kHz or 50kHz, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] Preferably, the power of the pulsed electromagnetic field is 5-10kW, for example, it can be 5kW, 6kW, 7kW, 8kW, 9kW or 10kW, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] Preferably, the pressure sintering temperature is 1400-1600℃, for example, it can be 1400℃, 1425℃, 1450℃, 1475℃, 1500℃, 1525℃, 1550℃, 1575℃ or 1600℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0044] Preferably, the pressure sintering method includes three-stage pressure sintering, which is divided into a first pressure sintering, a second pressure sintering, and a third pressure sintering.

[0045] Preferably, the pressure of the first pressure sintering is 4-6 MPa, for example, it can be 4 MPa, 4.5 MPa, 5 MPa, 5.5 MPa or 6 MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] Preferably, the holding time for the first pressure sintering is 8-12 min, for example, it can be 8 min, 9 min, 10 min, 11 min or 12 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] Preferably, the pressure of the second pressure sintering is 18-22 MPa, for example, it can be 18 MPa, 19 MPa, 20 MPa, 21 MPa or 22 MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] Preferably, the holding time for the second pressure sintering is 8-12 minutes, for example, it can be 8 minutes, 9 minutes, 10 minutes, 11 minutes or 12 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] Preferably, the pressure of the third pressure sintering is 48-52 MPa, for example, it can be 48 MPa, 49 MPa, 50 MPa, 51 MPa or 52 MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0050] Preferably, the holding time for the third pressure sintering is 8-12 minutes, for example, it can be 8 minutes, 9 minutes, 10 minutes, 11 minutes or 12 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0051] Preferably, the method for growing SiC nanowires includes: introducing a silicon carbide source for vapor deposition.

[0052] Preferably, the silicon carbide source includes methyltrichlorosilane.

[0053] Preferably, the flow rate of the silicon carbide source is 45-55 mL / min, for example, it can be 45 mL / min, 48 mL / min, 50 mL / min, 52 mL / min or 55 mL / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0054] Preferably, the diameter of the SiC nanowire is 50-100 nm, for example, it can be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0055] Preferably, the microwave sintering temperature is 1600-1700℃, for example, it can be 1600℃, 1620℃, 1640℃, 1650℃, 1660℃, 1680℃ or 1700℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0056] Preferably, the holding time for microwave sintering is 30-60 min, for example, it can be 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0057] Preferably, the microwave frequency of the microwave sintering is 2.4-2.5 GHz, for example, it can be 2.4 GHz, 2.42 GHz, 2.45 GHz, 2.48 GHz or 2.5 GHz, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0058] Preferably, the microwave power of the microwave sintering is 3-5kW, for example, it can be 3kW, 3.5kW, 4kW, 4.5kW or 5kW, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0059] Preferably, after microwave sintering, the preparation method further includes a cooling treatment.

[0060] Preferably, a mixture of argon and hydrogen is introduced during the cooling process.

[0061] Preferably, the volume ratio of argon to hydrogen is (0.1-10):1, for example, it can be 0.1:1, 1:1, 3:1, 5:1, 8:1 or 10:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0062] In this invention, argon and hydrogen are introduced during the cooling stage. By controlling the gas atmosphere, material oxidation is suppressed, surface atomic migration is promoted, and microcrack healing is facilitated, with a healing rate of over 85%.

[0063] As a preferred embodiment of the preparation method provided by the present invention, the preparation method includes the following steps:

[0064] (1) The silicon carbide raw materials are mixed and ball-milled, wherein the composition of the silicon carbide raw materials, by mass parts, includes: 100 parts silicon carbide powder, 100-120 parts deionized water, 2-5 parts carbon powder, 0.6-1.5 parts boron carbide, 0.8-2 parts polyvinyl alcohol, 0.8-2 parts polyethylene glycol, 0.5-2 parts ammonia water, 0.5-4 parts glycerol, 0.5-1.5 parts dispersant, 1-5 parts polyacrylic acid, 0.5-1.5 parts release agent, and 0.3-1 part defoamer. The ball milling speed is 20-70 rpm, and the ball milling time is 12-48 h to obtain sintered raw materials.

[0065] (2) The sintering raw material is subjected to magnetic field strengthening sintering. The magnetic field strengthening sintering method includes applying a pulsed electromagnetic field during the sintering process. The frequency of the pulsed electromagnetic field is 10-50kHz, the power of the pulsed electromagnetic field is 5-10kW, the sintering temperature of the magnetic field strengthening sintering is 800-1200℃, and the holding time of the magnetic field strengthening sintering is 30-60min, to obtain the first sintered green body.

[0066] (3) The first sintered green body is subjected to three-stage pressure sintering. The temperature of the three-stage pressure sintering is 1400-1600℃. The three-stage pressure sintering process includes: first, increasing the pressure to 4-6MPa and holding for 8-12min, then increasing the pressure to 18-22MPa and holding for 8-12min, and finally increasing the pressure to 48-52MPa and holding for 8-12min. During the three-stage pressure sintering process, methyltrichlorosilane with a flow rate of 45-55mL / min is introduced to decompose and grow SiC nanowires with a diameter of 50-100nm to obtain the second sintered green body.

[0067] (4) The second sintered green body is subjected to microwave sintering. The microwave frequency of the microwave sintering is 2.4-2.5 GHz, the microwave power of the microwave sintering is 3-5 kW, the microwave sintering temperature is 1600-1700℃, the microwave sintering holding time is 30-60 min, and the cooling process after sintering is carried out in a mixed atmosphere of argon and hydrogen with a volume ratio of argon to hydrogen of (0.1-10):1. After cooling, silicon carbide ceramic material is obtained.

[0068] In a second aspect, the present invention provides a silicon carbide ceramic material, which is prepared by the preparation method described in the first aspect.

[0069] The silicon carbide ceramic material provided by this invention has uniform microcrystalline grain size, ranging from 1 to 2 μm, with β-SiC nanowires distributed in a network structure. The material exhibits high density, a porosity ≤1.3%, and excellent mechanical and thermal properties, with a flexural strength ≥576 MPa and a fracture toughness ≥5.9 MPa·m. 1 / 2Thermal conductivity ≥150W / m·K, coefficient of thermal expansion ≤4×10 -6 / K.

[0070] Thirdly, the present invention provides an application of the silicon carbide ceramic material described in the second aspect, wherein the silicon carbide ceramic material is applied to at least one of spacecraft thermal protection devices, nuclear reactor cladding materials, or semiconductor devices.

[0071] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0072] (1) The preparation method provided by the present invention performs segmented sintering under magnetic field, pressure and microwave strengthening respectively. By adopting specific strengthening means at different sintering stages, the powder is dispersed and the surface is activated by electromagnetic field, the material in the structure is driven to migrate by pressure to fill the pores, and the grain boundary is selectively heated by microwave, thereby significantly improving the homogenization and densification effect of silicon carbide ceramic materials and significantly reducing the sintering temperature.

[0073] (2) During the pressure sintering process, SiC nanowires are promoted to grow by pressure, and the grains are bridged by the nanowires, which significantly improves the fracture toughness of silicon carbide ceramic materials.

[0074] (3) The obtained silicon carbide ceramic material has excellent mechanical and thermal properties, with a bending strength ≥576MPa and a fracture toughness ≥5.9MPa·m. 1 / 2 Thermal conductivity ≥150W / m·K, coefficient of thermal expansion ≤4×10 -6 / K. Detailed Implementation

[0075] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0076] To clearly illustrate the technical solution of the present invention, in a specific embodiment, the dispersant is polyethyleneimine, a commercially available product with CAS number 9002-98-6, Mn of 10000, and PDI ≤ 1.3; the release agent is sodium tripolyphosphate, CAS number 7758-29-4, a commercially available product; and the defoamer is emulsified silicone oil, a commercially available product.

[0077] Example 1

[0078] This embodiment provides a method for preparing silicon carbide ceramic materials based on gradient activation sintering and nanocomposite reinforcement. The preparation method includes the following steps:

[0079] (1) The silicon carbide raw materials are mixed and ball-milled. The composition of the silicon carbide raw materials, by mass, includes: 100 parts silicon carbide powder, 110 parts deionized water, 3 parts carbon powder, 1 part boron carbide, 1 part polyvinyl alcohol, 1 part polyethylene glycol, 1 part ammonia water, 2 parts glycerol, 1 part dispersant, 3 parts polyacrylic acid, 1 part release agent, and 0.6 parts defoamer. The ball milling speed is 50 rpm and the ball milling time is 30 h to obtain sintered raw materials.

[0080] (2) An electromagnetic generator is used to generate a pulsed electromagnetic field, and the sintering raw material is subjected to magnetic field strengthening sintering under the pulsed electromagnetic field. The power of the pulsed electromagnetic field is 8kW, the frequency of the pulsed electromagnetic field is 30kHz, the temperature of the magnetic field strengthening sintering is 1000℃, and the holding time is 45min, to obtain the first sintered green body.

[0081] (3) The first sintered green body is subjected to pressure sintering at a temperature of 1500℃. The pressure is increased by a high-pressure gas pump to 5MPa, 20MPa and 50MPa in sequence. The holding time of each pressure is 10min. During the pressure sintering process, CH3SiCl3 gas with a flow rate of 50mL / min is introduced. During the sintering process, CH3SiCl3 gas decomposes and grows into SiC nanowires. After the pressure sintering is completed, the second sintered green body is obtained.

[0082] (4) The second sintered green body is microwave sintered in a microwave sintering furnace. The microwave frequency of the microwave sintering is 2.45 GHz, the microwave power is 4 kW, the microwave sintering temperature is 1650 °C, the holding time is 45 min, and the cooling process after microwave sintering is carried out in a mixed atmosphere of argon and hydrogen (the volume ratio of argon to hydrogen is 1:1). Finally, silicon carbide ceramic material is obtained.

[0083] Example 2

[0084] This embodiment provides a method for preparing silicon carbide ceramic materials based on gradient activation sintering and nanocomposite reinforcement. The preparation method includes the following steps:

[0085] (1) The silicon carbide raw materials are mixed and ball-milled. The composition of the silicon carbide raw materials, by mass, includes: 100 parts silicon carbide powder, 110 parts deionized water, 3 parts carbon powder, 1 part boron carbide, 1 part polyvinyl alcohol, 1 part polyethylene glycol, 1 part ammonia water, 2 parts glycerol, 1 part dispersant, 3 parts polyacrylic acid, 1 part release agent, and 0.6 parts defoamer. The ball milling speed is 20 rpm and the ball milling time is 48 h to obtain the sintering raw material.

[0086] (2) An electromagnetic generator is used to generate a pulsed electromagnetic field, and the sintering raw material is subjected to magnetic field strengthening sintering under the pulsed electromagnetic field. The power of the pulsed electromagnetic field is 10kW, the frequency of the pulsed electromagnetic field is 10kHz, the temperature of the magnetic field strengthening sintering is 1200℃, and the holding time is 30min, to obtain the first sintered green body.

[0087] (3) The first sintered green body is subjected to pressure sintering at a temperature of 1600℃. The pressure is increased by a high-pressure gas pump to 4MPa, 18MPa and 48MPa in sequence. The holding time of each pressure is 12min. During the pressure sintering process, CH3SiCl3 gas with a flow rate of 55mL / min is introduced. During the sintering process, CH3SiCl3 gas decomposes and grows into SiC nanowires. After the pressure sintering is completed, the second sintered green body is obtained.

[0088] (4) The second sintered green body is microwave sintered in a microwave sintering furnace. The microwave frequency of the microwave sintering is 2.5 GHz, the microwave power is 3 kW, the microwave sintering temperature is 1600 ℃, the holding time is 60 min, and the cooling process after microwave sintering is carried out in a mixed atmosphere of argon and hydrogen (the volume ratio of argon to hydrogen is 1:1). Finally, silicon carbide ceramic material is obtained.

[0089] Example 3

[0090] This embodiment provides a method for preparing silicon carbide ceramic materials based on gradient activation sintering and nanocomposite reinforcement. The preparation method includes the following steps:

[0091] (1) The silicon carbide raw materials are mixed and ball-milled. The composition of the silicon carbide raw materials, by mass, includes: 100 parts silicon carbide powder, 110 parts deionized water, 3 parts carbon powder, 1 part boron carbide, 1 part polyvinyl alcohol, 1 part polyethylene glycol, 1 part ammonia water, 2 parts glycerol, 1 part dispersant, 3 parts polyacrylic acid, 1 part release agent, and 0.6 parts defoamer. The ball milling speed is 70 rpm and the ball milling time is 12 h to obtain sintered raw materials.

[0092] (2) An electromagnetic generator is used to generate a pulsed electromagnetic field, and the sintering raw material is subjected to magnetic field strengthening sintering under the pulsed electromagnetic field. The power of the pulsed electromagnetic field is 5kW, the frequency of the pulsed electromagnetic field is 50kHz, the temperature of the magnetic field strengthening sintering is 800℃, and the holding time is 60min, to obtain the first sintered green body.

[0093] (3) The first sintered green body is subjected to pressure sintering at a temperature of 1400℃. The pressure is increased by a high-pressure gas pump to 6MPa, 22MPa and 52MPa in sequence. The holding time of each pressure is 8min. During the pressure sintering process, CH3SiCl3 gas with a flow rate of 45mL / min is introduced. During the sintering process, CH3SiCl3 gas decomposes and grows into SiC nanowires. After the pressure sintering is completed, the second sintered green body is obtained.

[0094] (4) The second sintered green body is microwave sintered in a microwave sintering furnace. The microwave frequency of the microwave sintering is 2.4 GHz, the microwave power is 5 kW, the microwave sintering temperature is 1700 ℃, the holding time is 30 min, and the cooling process after microwave sintering is carried out in a mixed atmosphere of argon and hydrogen (the volume ratio of argon to hydrogen is 1:1). Finally, silicon carbide ceramic material is obtained.

[0095] Example 4

[0096] This embodiment provides a method for preparing silicon carbide ceramic materials based on gradient activation sintering and nanocomposite reinforcement. Compared with Example 1, the pressure of pressure sintering in step (3) is kept constant at 50 MPa and the holding time is 30 min. The rest are the same as in Example 1.

[0097] Example 5

[0098] This embodiment provides a method for preparing silicon carbide ceramic materials based on gradient activation sintering and nanocomposite reinforcement. Compared with Example 1, the cooling process in step (4) does not introduce a mixture of argon and hydrogen, that is, the cooling process is carried out in an air atmosphere. The rest is the same as in Example 1.

[0099] Comparative Example 1

[0100] This comparative example provides a method for preparing a silicon carbide ceramic material, the method comprising the following steps:

[0101] Silicon carbide raw materials are mixed and ball-milled, wherein the composition of the silicon carbide raw materials and the ball-milling process are the same as in Example 1, to obtain sintering raw materials. The sintering raw materials are sintered in a sintering furnace at a sintering temperature of 2050°C for 2 hours to obtain silicon carbide ceramic materials.

[0102] Comparative Example 2

[0103] This comparative example provides a method for preparing a silicon carbide ceramic material, the method comprising the following steps:

[0104] (1) The silicon carbide raw materials are mixed and ball-milled, wherein the composition of the silicon carbide raw materials and the ball-milling process are the same as in Example 1, to obtain sintering raw materials;

[0105] (2) The sintering raw material is sintered. During the sintering process, a pulsed electromagnetic field, pressure and microwave are applied simultaneously. CH3SiCl3 gas with a flow rate of 50 mL / min is introduced during the sintering process. CH3SiCl3 gas decomposes and grows into SiC nanowires during the sintering process. The sintering temperature is 1650℃ and the sintering time is 2h. The power of the pulsed electromagnetic field is 8kW and the frequency is 30kHz. The pressure is applied sequentially to 5MPa, 20MPa and 50MPa. The holding time of each pressure is 40min. The frequency of the microwave is 2.45GHz and the power is 4kW. The cooling process after sintering is carried out in a mixed atmosphere of argon and hydrogen (the volume ratio of argon to hydrogen is 1:1). Finally, silicon carbide ceramic material is obtained.

[0106] Comparative Example 3

[0107] This comparative example provides a method for preparing silicon carbide ceramic material. Compared with Example 1, no pulsed electromagnetic field is applied in step (2), no pressure is applied in step (3), and no microwave is applied in step (4). The rest are the same as in Example 1.

[0108] Comparative Example 4

[0109] This comparative example provides a method for preparing silicon carbide ceramic material. Compared with Example 1, no pulsed electromagnetic field is applied in step (2), and the rest is the same as in Example 1.

[0110] Comparative Example 5

[0111] This comparative example provides a method for preparing silicon carbide ceramic material. Compared with Example 1, no pressure is applied in step (3), and the rest is the same as in Example 1.

[0112] Comparative Example 6

[0113] This comparative example provides a method for preparing silicon carbide ceramic materials. Compared with Example 1, in step (3), CH3SiCl3 gas is not introduced to grow SiC nanowires, and the rest is the same as in Example 1.

[0114] Comparative Example 7

[0115] This comparative example provides a method for preparing a silicon carbide ceramic material, the method comprising the following steps:

[0116] (1) The silicon carbide raw materials are mixed and ball-milled, wherein the silicon carbide raw materials and ball milling parameters are the same as in Example 1, to obtain sintering raw materials;

[0117] (2) The sintering raw material is subjected to pressure sintering at a temperature of 1000℃. The pressure is increased by a high-pressure air pump to 5MPa, 20MPa and 50MPa in sequence. The holding time of each pressure is 10min to obtain the first sintered green body.

[0118] (3) The first sintered green body is microwave sintered in a microwave sintering furnace. The microwave frequency of the microwave sintering is 2.45 GHz, the microwave power is 4 kW, the microwave sintering temperature is 1500 ℃, the holding time is 45 min, and CH3SiCl3 gas with a flow rate of 50 mL / min is introduced during the microwave sintering process. CH3SiCl3 gas decomposes and grows into SiC nanowires during the sintering process. After the sintering is completed, the second sintered green body is obtained.

[0119] (4) An electromagnetic generator is used to generate a pulsed electromagnetic field, and the second sintered blank is subjected to magnetic field strengthening sintering under the pulsed electromagnetic field. The power of the pulsed electromagnetic field is 8kW, the frequency of the pulsed electromagnetic field is 30kHz, the temperature of the magnetic field strengthening sintering is 1650℃, the holding time is 45min, and the cooling process after sintering is carried out in a mixed atmosphere of argon and hydrogen (the volume ratio of argon to hydrogen is 1:1), and finally silicon carbide ceramic material is obtained.

[0120] Performance testing

[0121] The silicon carbide ceramic materials provided in the examples and comparative examples were tested for density, mechanical properties and thermal properties, and the results are listed in Table 1.

[0122] The bulk density was determined using the Archimedes displacement method, the flexural strength was determined using the three-point bending method, the fracture toughness was determined using the single-sided notched beam (SENB) method, and the thermal conductivity at 25℃ was determined using the laser scintillation method.

[0123] Table 1

[0124]

[0125]

[0126] As can be seen from Table 1:

[0127] (1) The preparation method provided by this invention employs a gradient activation sintering approach, combined with specific strengthening techniques and a three-stage sintering process. This effectively reduces the sintering temperature of the ceramic material, lowers the process difficulty and cost, and effectively improves and strengthens the microstructure of the material. Furthermore, nanowires are grown within the material to enhance its strength. The resulting ceramic material exhibits high density, reaching a bulk density of 3.16 g / cm³. 3It has a porosity of less than 1.3% and excellent mechanical properties, with a flexural strength of over 576 MPa, especially exceeding 650 MPa, and a fracture toughness of 5.9 MPa·m. 1 / 2 The above is true; at the same time, it possesses excellent thermal properties, with a thermal conductivity exceeding 150 W / m·K and a coefficient of thermal expansion exceeding 3.7 × 10⁻⁶. -6 / K or above.

[0128] (2) Compared to Example 1, in Example 4, the pressure was kept constant during pressure sintering, and the gradient gas pressure was lacking. The mechanical strength of the silicon carbide material decreased slightly, its thermal conductivity decreased, and its porosity increased significantly. The enhancement of the gradient gas pressure facilitated particle rearrangement during sintering, thereby improving the material's microstructure, increasing its mechanical strength, and driving Si-CO gaseous substances to migrate along grain boundaries, filling pores, effectively reducing material porosity and increasing density. In Example 5, the cooling process was completed using an air atmosphere, resulting in a decrease in the material's mechanical strength. The use of an argon-hydrogen mixture during cooling helped repair microcracks on the ceramic material surface, thereby improving the material's strength.

[0129] (3) In Comparative Example 1, the traditional one-stage sintering method was used, and the performance and density of the ceramic material could not meet the requirements for high quality. In Comparative Example 3, only three-stage sintering was used, lacking strengthening methods, and the corresponding temperature could not be reached to achieve the sintering temperature, so the material could not be densified and silicon carbide ceramic material could not be obtained. Combining the results of Comparative Examples 2 and 7, in Comparative Example 2, multiple strengthening methods were applied simultaneously during the one-stage sintering process, and in Comparative Example 7, pressure sintering, microwave sintering, and magnetic field-strengthened sintering were used in sequence. Despite the use of multiple strengthening methods, the performance of the material was not significantly improved. It can be seen that strengthening methods need to be combined with specific sintering processes to achieve significant enhancement of material performance. Compared with Example 1, Comparative Examples 4-6 show that in Comparative Example 4, no pulsed electromagnetic field was applied, which easily led to uneven agglomeration during sintering and lacked powder activation effect, affecting the sintering effect and causing a significant decline in the performance of the material in all aspects. In Comparative Example 5, no pressure sintering was performed, which resulted in the lack of the migration-promoting effect of pressure and poor growth of nanowires without pressure, leading to the failure of the material performance to meet the standards. In Comparative Example 6, the material performance also deteriorated significantly under the condition of lacking composite reinforcement of nanowires.

[0130] In summary, the preparation method provided by this invention significantly improves the homogenization and densification of silicon carbide ceramic materials through gradient activation sintering and nanowire composite reinforcement, and significantly reduces the sintering temperature required. The resulting silicon carbide ceramic materials have excellent mechanical and thermal properties.

[0131] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. 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 silicon carbide ceramic materials based on gradient activation sintering and nanocomposite reinforcement, characterized in that, The preparation method includes the following steps: Silicon carbide raw materials are mixed and ball-milled to obtain sintering raw materials. The sintering raw materials are then subjected to magnetic field strengthening sintering, pressure sintering, and microwave sintering in sequence. The pressure sintering method includes three-stage pressure sintering, which is divided into a first pressure sintering, a second pressure sintering, and a third pressure sintering. The pressure of the first pressure sintering is 4-6 MPa, the pressure of the second pressure sintering is 18-22 MPa, and the pressure of the third pressure sintering is 48-52 MPa. SiC nanowires are grown during the pressure sintering, and finally, silicon carbide ceramic materials are obtained.

2. The preparation method according to claim 1, characterized in that, The silicon carbide raw material includes: silicon carbide powder and sintering additives, wherein the sintering additives include at least one of sintering aids, binders, dispersants, solvents, dispersants, release agents, or defoamers.

3. The preparation method according to claim 2, characterized in that, The sintering aids include carbon powder and / or boron carbide.

4. The preparation method according to claim 3, characterized in that, The mass ratio of the carbon powder to boron carbide is (1-10):

1.

5. The preparation method according to claim 2, characterized in that, The adhesive includes polyvinyl alcohol and / or polyacrylic acid.

6. The preparation method according to claim 5, characterized in that, The mass ratio of polyvinyl alcohol to polyacrylic acid is (0.1-2):

1.

7. The preparation method according to claim 2, characterized in that, The dispersing agent includes at least one of polyethylene glycol, ammonia, or glycerol.

8. The preparation method according to claim 2, characterized in that, The solvent includes deionized water.

9. The preparation method according to claim 2, characterized in that, The silicon carbide raw material comprises, by weight, 100 parts silicon carbide powder, 100-120 parts deionized water, 2-5 parts carbon powder, 0.6-1.5 parts boron carbide, 0.8-2 parts polyvinyl alcohol, 1-5 parts polyacrylic acid, 0.8-2 parts polyethylene glycol, 0.5-2 parts ammonia, 0.5-4 parts glycerol, 0.5-1.5 parts dispersant, 0.5-1.5 parts release agent, and 0.3-1 part defoamer.

10. The preparation method according to claim 1, characterized in that, The ball mill rotates at a speed of 20-70 rpm.

11. The preparation method according to claim 1, characterized in that, The ball milling time is 12-48 hours.

12. The preparation method according to claim 1, characterized in that, The sintering temperature for magnetic field-strengthened sintering is 800-1200℃.

13. The preparation method according to claim 1, characterized in that, The holding time for magnetic field-strengthened sintering is 30-60 minutes.

14. The preparation method according to claim 1, characterized in that, The magnetic field-enhanced sintering method includes applying a pulsed electromagnetic field during the sintering process.

15. The preparation method according to claim 14, characterized in that, The frequency of the pulsed electromagnetic field is 10-50 kHz.

16. The preparation method according to claim 14, characterized in that, The power of the pulsed electromagnetic field is 5-10kW.

17. The preparation method according to claim 1, characterized in that, The pressure sintering temperature is 1400-1600℃.

18. The preparation method according to claim 1, characterized in that, The holding time for the first pressure sintering is 8-12 minutes.

19. The preparation method according to claim 1, characterized in that, The holding time for the second pressure sintering is 8-12 minutes.

20. The preparation method according to claim 1, characterized in that, The holding time for the third pressure sintering is 8-12 minutes.

21. The preparation method according to claim 1, characterized in that, The method for growing SiC nanowires includes: introducing a silicon carbide source for vapor deposition.

22. The preparation method according to claim 21, characterized in that, The silicon-carbon source includes methyltrichlorosilane.

23. The preparation method according to claim 21, characterized in that, The flow rate of the silicon carbide source is 45-55 mL / min.

24. The preparation method according to claim 1, characterized in that, The diameter of the SiC nanowires is 50-100 nm.

25. The preparation method according to claim 1, characterized in that, The microwave sintering temperature is 1600-1700℃.

26. The preparation method according to claim 1, characterized in that, The microwave sintering holding time is 30-60 minutes.

27. The preparation method according to claim 1, characterized in that, The microwave frequency for microwave sintering is 2.4-2.5 GHz.

28. The preparation method according to claim 1, characterized in that, The microwave power of the microwave sintering is 3-5kW.

29. The preparation method according to claim 1, characterized in that, After microwave sintering, the preparation method further includes: cooling treatment.

30. The preparation method according to claim 29, characterized in that, The cooling process involves introducing a mixture of argon and hydrogen.

31. The preparation method according to claim 30, characterized in that, The volume ratio of argon to hydrogen is (0.1-10):

1.

32. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) The silicon carbide raw materials are mixed and ball-milled, wherein the composition of the silicon carbide raw materials, by mass parts, includes: 100 parts silicon carbide powder, 100-120 parts deionized water, 2-5 parts carbon powder, 0.6-1.5 parts boron carbide, 0.8-2 parts polyvinyl alcohol, 0.8-2 parts polyethylene glycol, 0.5-2 parts ammonia water, 0.5-4 parts glycerol, 0.5-1.5 parts dispersant, 1-5 parts polyacrylic acid, 0.5-1.5 parts release agent, and 0.3-1 parts defoamer. The ball milling speed is 20-70 rpm, and the ball milling time is 12-48 h to obtain sintered raw materials. (2) The sintering raw material is subjected to magnetic field strengthening sintering. The magnetic field strengthening sintering method includes applying a pulsed electromagnetic field during the sintering process. The frequency of the pulsed electromagnetic field is 10-50kHz, the power of the pulsed electromagnetic field is 5-10kW, the sintering temperature of the magnetic field strengthening sintering is 800-1200℃, and the holding time of the magnetic field strengthening sintering is 30-60min, to obtain the first sintered green body. (3) The first sintered green body is subjected to three-stage pressure sintering. The temperature of the three-stage pressure sintering is 1400-1600℃. The three-stage pressure sintering process includes: first, increasing the pressure to 4-6MPa and holding for 8-12min, then increasing the pressure to 18-22MPa and holding for 8-12min, and finally increasing the pressure to 48-52MPa and holding for 8-12min. During the three-stage pressure sintering process, methyltrichlorosilane with a flow rate of 45-55mL / min is introduced to decompose and grow SiC nanowires with a diameter of 50-100nm to obtain the second sintered green body. (4) The second sintered blank is subjected to microwave sintering. The microwave frequency of the microwave sintering is 2.4-2.5 GHz, the microwave power of the microwave sintering is 3-5 kW, the microwave sintering temperature is 1600-1700℃, the microwave sintering holding time is 30-60 min, and the cooling process after sintering is carried out in a mixed atmosphere of argon and hydrogen with a volume ratio of argon to hydrogen of (0.1-10):

1. After cooling, silicon carbide ceramic material is obtained.

33. A silicon carbide ceramic material, characterized in that, The silicon carbide ceramic material is prepared by the preparation method according to any one of claims 1-32.

34. An application of the silicon carbide ceramic material as described in claim 33, characterized in that, The silicon carbide ceramic material is used in at least one of spacecraft thermal protection devices, nuclear reactor cladding materials, or semiconductor devices.

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