Silicon carbide ceramic material and preparation method thereof

Abstract

The invention discloses a silicon carbide ceramic material and a preparation method thereof, and relates to the field of ceramic technology. When preparing the silicon carbide ceramic material, the invention first mixes apricot shell carbon with nano silicon dioxide and sodium salt and calcines them in a nitrogen atmosphere to obtain modified silicon carbide composite nanowires; the modified silicon carbide composite nanowires and praseodymium powder are modified by a molten salt method to obtain praseodymium-modified silicon carbide composite nanowires; liquid polycarbosilane, praseodymium-modified silicon carbide composite nanowires, modification aids, silicon carbide particles, and sintering aids are mixed and solidified by wet ball milling to obtain composite sintering powder; the composite sintering powder is sintered by a discharge plasma sintering method, and then annealed in an argon atmosphere to obtain a silicon carbide ceramic material. The silicon carbide ceramic material prepared by the invention has the advantages of high thermal conductivity, electromagnetic shielding, high strength, and high density.

Description

Technical Field

[0001] The invention relates to the technical field of ceramics, in particular to a silicon carbide ceramic material and a preparation method thereof. Background Art

[0002] Since the 21st century, with the rapid development of global science and technology, breakthroughs have been made in high-tech fields such as aerospace, electronic communications, deep-sea exploration, and nuclear energy industry, among which the contribution of high-performance materials is indelible. Silicon carbide ceramics and their composite materials play an important role in aerospace, armor, nuclear energy, and semiconductors due to their low density, high melting point, high thermal conductivity, low thermal expansion coefficient, excellent high-temperature mechanical properties, and excellent corrosion resistance, oxidation resistance, and radiation resistance. However, when silicon carbide ceramics and their composite materials are used in aerospace and nuclear energy, high-density structural parts are usually required. On the other hand, due to the strong covalent bond structural characteristics of silicon carbide, its surface self-diffusion coefficient is extremely low. Therefore, the preparation of high-density silicon carbide ceramics often requires a high temperature of 2100~2500℃. Such a high sintering densification temperature brings huge challenges to the industrial application of silicon carbide ceramics and their composite materials.

[0003] With the rapid changes in microelectronics technology and the update and iteration of advanced electronic equipment, the frontier market has increasingly stringent performance requirements for electronic components and functional materials. Since its development, the size of electronic components has continued to be compressed, and miniaturization and high integration have become the general trend. This irreversible trend has also put forward more stringent application standards for the thermal conductivity, bending strength, resistivity and other properties of electronic materials.

[0004] Among many electronic device materials, silicon carbide has emerged with its excellent comprehensive performance. Although silicon carbide materials have been limited to the field of refractory materials in the past few decades, with the deeper exploration and research of this type of material, its outstanding performance in thermal, mechanical, electrical and optical properties has successfully attracted the attention of more researchers and has become a new type of popular electronic material. Electronic packaging technology is an important part of the manufacturing process of electronic devices. Using this packaging technology, various electronic components can be integrated and isolated from the outside world, thereby playing a good protective role, such as corrosion resistance, resistance to external force damage and electromagnetic interference. At the same time, the packaging material can also serve as a heat dissipation channel to quickly conduct the heat generated by the electronic components out of the device, thereby preventing the adverse effects of local heat accumulation on the life of the electronic components. Therefore, for high-quality and excellent electronic packaging materials, they usually need to have the following important characteristics: excellent thermal conductivity, mechanical properties, insulation, electromagnetic shielding performance, excellent thermal stability and chemical stability. Summary of the invention

[0005] The object of the present invention is to provide a silicon carbide ceramic material and a preparation method thereof to solve the problems existing in the prior art.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A silicon carbide ceramic material, wherein the silicon carbide ceramic material is obtained by sintering a composite sintered powder by spark plasma sintering and then annealing in an argon atmosphere;

[0008] The composite sintering powder is prepared by mixing and solidifying liquid polycarbosilane, praseodymium-modified silicon carbide composite nanowires, a modification aid, silicon carbide particles, and a sintering aid by wet ball milling.

[0009] The praseodymium-modified silicon carbide composite nanowires are prepared by modifying the modified silicon carbide composite nanowires and praseodymium powder by a molten salt method;

[0010] The modified silicon carbide composite nanowire is prepared by mixing apricot shell carbon with nano silicon dioxide and sodium salt and calcining the mixture under a nitrogen atmosphere.

[0011] As an optimization, the liquid polycarbosilane model is KH-AHPCS-1, purchased from Jinjinle Chemical Co., Ltd.

[0012] As an optimization, the modification aid is divinylbenzene.

[0013] As an optimization, the average particle size of the silicon carbide particles is 0.58 μm, and they are purchased from Shandong Huamei New Materials Co., Ltd.

[0014] As an optimization, the sintering aid is a mixture of yttrium oxide, aluminum nitride, and cerium oxide in a mass ratio of 2:1:2.

[0015] As an optimization, the average particle size of the yttrium oxide and the cerium oxide is 0.5 μm, and the average particle size of the aluminum nitride is 1.5 μm.

[0016] As an optimization, the average particle size of the praseodymium powder is 7.4 μm and the purity is 99.9%.

[0017] As an optimization, the apricot shell carbon particle size is 40-70 mesh and is purchased from Chifeng Jinqiao Activated Carbon Factory.

[0018] As an optimization, the nano-silica model is AEROSIL 200, purchased from Evonik Specialty Chemicals (Shanghai) Co., Ltd.

[0019] As an optimization, the sodium salt is a mixture of sodium fluoride and sodium chloride.

[0020] A method for preparing a silicon carbide ceramic material comprises the following preparation steps:

[0021] (1) According to the weight ratio, 5-8 parts of apricot shell carbon, 2-3 parts of nano-silicon dioxide, 0.2-0.3 parts of sodium fluoride and 0.14-0.2 parts of sodium chloride were mixed evenly, ground at room temperature for 50-60 minutes, pre-calcined at 200-210°C for 4-5 hours in an air atmosphere, heated to 1400-1500°C at a heating rate of 5°C / min in a nitrogen atmosphere, calcined for 3-4 hours, and then naturally cooled to room temperature. In an air atmosphere, the mixture was kept at 700°C for 2 hours to remove carbon, naturally cooled to room temperature, and ground for 40-50 minutes to obtain modified silicon carbide composite nanowires;

[0022] (2) By weight, 5-6 parts of praseodymium powder, 2-3 parts of modified silicon carbide composite nanowires, 6-7 parts of sodium chloride, and 8-9 parts of potassium chloride were mixed evenly, ground for 30-40 min, heated to 500°C at a heating rate of 8°C / min in an argon atmosphere and kept warm for 30-40 min, then heated to 850°C at a heating rate of 5°C / min and kept warm for 5 h, cooled naturally to room temperature, ultrasonically cleaned with pure water for 30-40 min, filtered, washed with pure water for 3-4 times, vacuum dried at 50-60°C for 8-10 h, ground, and sieved through a 200-mesh sieve to obtain praseodymium-modified silicon carbide composite nanowires;

[0023] (3) By weight, 8-10 parts of liquid polycarbosilane, 5-6 parts of praseodymium-modified silicon carbide composite nanowires, 1.6-2 parts of divinylbenzene, 30-40 parts of silicon carbide particles, and 2-3 parts of sintering aids were mixed evenly, added into a ball mill, and silicon carbide grinding balls were used as the medium, with a ball-to-material ratio of 5:1, ground at 300-350 rpm for 20-24 h, dried at 70-80 ° C for 8-10 h, and passed through a 200-mesh sieve after grinding to obtain a composite sintering powder;

[0024] (4) The composite sintering powder is pre-pressed in a graphite mold, an external pressure of 150 MPa is applied, the pressure is maintained for 2 minutes, and the powder is placed in a spark plasma furnace for sintering according to the sintering system. The sintering pressure is 30-40 MPa to obtain silicon carbide ceramic material.

[0025] As an optimization, the sintering system of step (4) is as follows: in an argon atmosphere, the temperature is increased to 800-900°C at a heating rate of 100°C / min and kept at a temperature for 3-4 min; the temperature is increased to 1200-1300°C at a heating rate of 100°C / min and kept at a temperature for 7-8 min; the temperature is further increased to 1600°C at a heating rate of 100°C / min; the temperature is further increased to 1850-1900°C at a heating rate of 40°C / min and kept at a temperature for 10-15 min; the temperature is decreased to 1200°C at a cooling rate of 50°C / min; then the temperature is naturally cooled to room temperature; after demolding, the temperature is kept at 600°C for 2 h in an air atmosphere for decarburization; and annealing is performed at 1300-1400°C for 1 h in an argon atmosphere.

[0026] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0027] When preparing silicon carbide ceramic material, the present invention comprises the following steps: firstly, apricot shell carbon is mixed with nano silicon dioxide and sodium salt, and the mixture is calcined in a nitrogen atmosphere to obtain modified silicon carbide composite nanowires; the modified silicon carbide composite nanowires and praseodymium powder are modified by a molten salt method to obtain praseodymium-modified silicon carbide composite nanowires; liquid polycarbosilane, praseodymium-modified silicon carbide composite nanowires, a modification aid, silicon carbide particles and a sintering aid are mixed and solidified by wet ball milling to obtain composite sintering powder; the composite sintering powder is sintered by a discharge plasma sintering method, and then annealed in an argon atmosphere to obtain the silicon carbide ceramic material.

[0028] Firstly, in a nitrogen atmosphere, apricot shell carbon is used as the carbon source, nano-silicon dioxide is used as the silicon source, and sodium fluoride and sodium chloride are used as dopants for high-temperature calcination to form modified silicon carbide composite nanowires. The silicon carbide nanowires prepared with apricot shell carbon as the carbon source have good dielectric and microwave absorption properties. The incorporation of mixed sodium salts of sodium fluoride and sodium chloride enhances the microwave absorption performance and absorption bandwidth, improves the micromorphology of the nanowires, and increases the specific surface area. During the heat treatment in a nitrogen atmosphere, silicon nitride grains are incorporated into the silicon carbide grains, forming a 3D network structure with rich mesopores and a large specific surface area. This structure effectively expands the attenuation path of electromagnetic waves. The synergy of silicon carbide and silicon nitride improves the dielectric loss and effectively improves the electromagnetic wave absorption performance. Subsequently, the rare earth metal praseodymium is used to modify the modified silicon carbide composite nanowires by the molten salt method to obtain praseodymium-modified silicon carbide composite nanowires. Under the condition of molten salt, praseodymium and silicon carbide crystals form a Pr3Si2C2 composite phase coated on the surface of the modified silicon carbide composite nanowires. The composite phase can undergo a eutectic liquid phase transition with silicon carbide at 1150°C, which promotes the dispersion and compatibility of the praseodymium-modified silicon carbide composite nanowires during the sintering process, so that the nanowires can be toughened while reducing the negative impact on bending strength, thereby improving the mechanical strength of silicon carbide ceramic materials.

[0029] Secondly, liquid polycarbosilane, praseodymium-modified silicon carbide composite nanowires, modification aids, silicon carbide particles, and sintering aids are mixed and solidified by wet ball milling to form a composite sintering powder, wherein the liquid polycarbosilane is used as a binder and dispersant, and divinylbenzene is added to modify it, which reduces the viscosity of the liquid polycarbosilane and promotes the high-temperature cracking of the polycarbosilane to generate silicon carbide ceramics. The modification of divinylbenzene optimizes the crystal phase structure of the silicon carbide ceramics formed by the cracking of the polycarbosilane, improves the thermal conductivity and the electromagnetic shielding effectiveness, and the polycarbosilane as a binder also forms a silicon carbide ceramic phase during the high-temperature cracking, thereby avoiding the introduction of impurities that lead to a decrease in strength, and the divinylbenzene modification The polycarbosilane after conditioning has good wettability and can effectively coat the surface of other raw materials during ball milling. Yttrium oxide, cerium oxide and aluminum nitride are selected as sintering aids. Yttrium oxide and cerium oxide are used as rare earth additives to effectively improve the grain size of silicon carbide ceramics during sintering. By introducing an insulating second phase at the silicon carbide grain boundary and the triangular grain boundary, the rare earth elements have a low solid solubility in the silicon carbide lattice due to their large radius, which reduces the damage of the second phase and lattice oxygen to thermal conductivity. While improving the mechanical strength, the thermal conductivity and resistivity are improved. In order to further improve the flexural strength, aluminum nitride is introduced as a sintering aid. Aluminum nitride and silicon carbide can form 2H ss The solid solution phase strengthens the silicon carbide grain boundaries and improves the flexural strength. By controlling the amount of aluminum nitride added, the flexural strength is improved while avoiding the reduction of thermal conductivity.

[0030] Finally, the composite sintering powder is sintered by spark plasma sintering, and then annealed in an argon atmosphere to obtain silicon carbide ceramic material. Spark plasma sintering is a new sintering process that can complete the sintering of ceramic materials at a lower temperature and in a shorter time, and can quickly complete the sintering and densification process of silicon carbide powder in a shorter time, thereby improving the quality and efficiency of sintering. At the same time, spark plasma sintering has a shorter sintering time, thereby retaining fine and uniform grains, thereby improving the density and mechanical strength of the prepared silicon carbide ceramic material. After sintering, low-temperature annealing in an argon atmosphere can weaken the anisotropy caused by sintering, making the internal performance of the product more uniform, and further improving thermal conductivity and mechanical strength. DETAILED DESCRIPTION

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0032] Embodiment 1:

[0033] A method for preparing a silicon carbide ceramic material, the method for preparing a silicon carbide ceramic material comprising the following preparation steps:

[0034] (1) By weight, 5 parts of apricot shell carbon, 2 parts of nano-silicon dioxide, 0.2 parts of sodium fluoride, and 0.14 parts of sodium chloride were mixed evenly, ground at room temperature for 50 minutes, pre-calcined at 200°C for 5 hours in an air atmosphere, heated to 1400°C at a heating rate of 5°C / min in a nitrogen atmosphere, and calcined for 4 hours, and then naturally cooled to room temperature. In an air atmosphere, the mixture was kept at 700°C for 2 hours for decarbonization, naturally cooled to room temperature, and ground for 40 minutes to obtain modified silicon carbide composite nanowires;

[0035] (2) By weight, 5 parts of praseodymium powder, 2 parts of modified silicon carbide composite nanowires, 6 parts of sodium chloride, and 8 parts of potassium chloride were mixed evenly, ground for 30 minutes, heated to 500°C at a heating rate of 8°C / min in an argon atmosphere and kept warm for 30 minutes, then heated to 850°C at a heating rate of 5°C / min and kept warm for 5 hours, cooled naturally to room temperature, ultrasonically cleaned with pure water for 30 minutes, filtered, washed with pure water three times, vacuum dried at 50°C for 10 hours, ground, and sieved through a 200-mesh sieve to obtain praseodymium-modified silicon carbide composite nanowires;

[0036] (3) By weight, 8 parts of liquid polycarbosilane, 5 parts of praseodymium-modified silicon carbide composite nanowires, 1.6 parts of divinylbenzene, 30 parts of silicon carbide particles, and 2 parts of sintering aid were mixed evenly, added into a ball mill, and silicon carbide grinding balls were used as the medium. The ball-to-material ratio was 5:1, and the mixture was ground at 300 rpm for 24 h, dried at 70 ° C for 10 h, and passed through a 200-mesh sieve after grinding to obtain a composite sintering powder;

[0037] (4) The composite sintering powder was pre-pressed in a graphite mold, an external pressure of 150 MPa was applied, the pressure was maintained for 2 min, and then the powder was placed in a discharge plasma furnace for sintering. The sintering pressure was 30 MPa. The sintering process was as follows: in an argon atmosphere, the temperature was first increased to 800 °C at a heating rate of 100 °C / min and kept for 4 min, then increased to 1200 °C at a heating rate of 100 °C / min and kept for 8 min, then increased to 1600 °C at a heating rate of 100 °C / min, then increased to 1850 °C at a heating rate of 40 °C / min and kept for 15 min, then decreased to 1200 °C at a cooling rate of 50 °C / min, and then naturally cooled to room temperature. After demolding, the powder was kept at 600 °C for 2 h in an air atmosphere for decarbonization, and then annealed at 1400 °C for 1 h in an argon atmosphere to obtain silicon carbide ceramic material.

[0038] Embodiment 2:

[0039] A method for preparing a silicon carbide ceramic material, the method for preparing a silicon carbide ceramic material comprising the following preparation steps:

[0040] (1) According to the weight percentage, 6 parts of apricot shell carbon, 2.5 parts of nano-silicon dioxide, 0.25 parts of sodium fluoride and 0.17 parts of sodium chloride were mixed evenly, ground at room temperature for 55 minutes, pre-calcined at 205°C for 4.5 hours in an air atmosphere, heated to 1450°C at a heating rate of 5°C / min in a nitrogen atmosphere and calcined for 3.5 hours, and then naturally cooled to room temperature. In an air atmosphere, the mixture was kept at 700°C for 2 hours for decarbonization, naturally cooled to room temperature, and ground for 45 minutes to obtain modified silicon carbide composite nanowires;

[0041] (2) By weight, 5.5 parts of praseodymium powder, 2.5 parts of modified silicon carbide composite nanowires, 6.5 parts of sodium chloride, and 8.5 parts of potassium chloride were mixed evenly, ground for 35 minutes, heated to 500°C at a heating rate of 8°C / min under an argon atmosphere and kept warm for 35 minutes, then heated to 850°C at a heating rate of 5°C / min and kept warm for 5 hours, cooled naturally to room temperature, ultrasonically cleaned with pure water for 35 minutes, filtered, washed with pure water for 4 times, vacuum dried at 55°C for 9 hours, ground, and sieved through a 200-mesh sieve to obtain praseodymium-modified silicon carbide composite nanowires;

[0042] (3) By weight, 9 parts of liquid polycarbosilane, 5.5 parts of praseodymium-modified silicon carbide composite nanowires, 1.8 parts of divinylbenzene, 35 parts of silicon carbide particles, and 2.5 parts of sintering aid were mixed evenly, added into a ball mill, and silicon carbide grinding balls were used as the medium. The ball-to-material ratio was 5:1, and the mixture was ground at 300 rpm for 22 h, dried at 75 °C for 9 h, and passed through a 200-mesh sieve after grinding to obtain a composite sintering powder;

[0043] (4) The composite sintering powder was pre-pressed in a graphite mold, an external pressure of 150 MPa was applied, the pressure was maintained for 2 min, and then the powder was placed in a spark plasma furnace for sintering. The sintering pressure was 30 MPa. The sintering system was as follows: in an argon atmosphere, the temperature was first increased to 850 °C at a heating rate of 100 °C / min and kept for 3.5 min, then increased to 1250 °C at a heating rate of 100 °C / min and kept for 7.5 min, then increased to 1600 °C at a heating rate of 100 °C / min, then increased to 1875 °C at a heating rate of 40 °C / min and kept for 12 min, then decreased to 1200 °C at a cooling rate of 50 °C / min, and then naturally cooled to room temperature. After demolding, the powder was kept at 600 °C for 2 h in an air atmosphere for decarbonization, and annealed at 1350 °C for 1 h in an argon atmosphere to obtain silicon carbide ceramic material.

[0044] Embodiment 3:

[0045] A method for preparing a silicon carbide ceramic material, the method for preparing a silicon carbide ceramic material comprising the following preparation steps:

[0046] (1) By weight, 8 parts of apricot shell carbon, 3 parts of nano-silicon dioxide, 0.3 parts of sodium fluoride, and 0.2 parts of sodium chloride were mixed evenly, ground at room temperature for 60 minutes, pre-calcined at 210°C for 4 hours in an air atmosphere, heated to 1500°C at a heating rate of 5°C / min in a nitrogen atmosphere, and calcined for 3 hours. The mixture was then naturally cooled to room temperature, kept at 700°C for 2 hours in an air atmosphere for decarbonization, naturally cooled to room temperature, and ground for 50 minutes to obtain modified silicon carbide composite nanowires.

[0047] (2) By weight, 6 parts of praseodymium powder, 3 parts of modified silicon carbide composite nanowires, 7 parts of sodium chloride, and 9 parts of potassium chloride were mixed evenly, ground for 40 minutes, heated to 500°C at a heating rate of 8°C / min in an argon atmosphere and kept warm for 40 minutes, then heated to 850°C at a heating rate of 5°C / min and kept warm for 5 hours, cooled naturally to room temperature, ultrasonically cleaned with pure water for 40 minutes, filtered, washed with pure water for 4 times, vacuum dried at 60°C for 8 hours, ground, and sieved through a 200-mesh sieve to obtain praseodymium-modified silicon carbide composite nanowires;

[0048] (3) By weight, 10 parts of liquid polycarbosilane, 6 parts of praseodymium-modified silicon carbide composite nanowires, 2 parts of divinylbenzene, 40 parts of silicon carbide particles, and 3 parts of sintering aids were mixed evenly, added into a ball mill, and silicon carbide grinding balls were used as the medium. The ball-to-material ratio was 5:1, and the mixture was ground at 350 rpm for 20 h. The mixture was dried at 80 °C for 10 h. After grinding, the mixture was sieved through a 200-mesh sieve to obtain a composite sintering powder.

[0049] (4) The composite sintering powder was pre-pressed in a graphite mold, an external pressure of 150 MPa was applied, the pressure was maintained for 2 min, and then the powder was placed in a discharge plasma furnace for sintering. The sintering pressure was 30 MPa. The sintering system was as follows: in an argon atmosphere, the temperature was first increased to 900 °C at a heating rate of 100 °C / min and kept for 3 min, then increased to 1300 °C at a heating rate of 100 °C / min and kept for 7 min, then increased to 1600 °C at a heating rate of 100 °C / min, then increased to 1900 °C at a heating rate of 40 °C / min, kept for 10 min, then decreased to 1200 °C at a cooling rate of 50 °C / min, and then naturally cooled to room temperature. After demolding, the powder was kept at 600 °C for 2 h in an air atmosphere for decarbonization, and annealed at 1300 °C for 1 h in an argon atmosphere to obtain silicon carbide ceramic material.

[0050] Comparative Example 1:

[0051] The preparation method of the silicon carbide ceramic material of Comparative Example 1 is different from that of Example 2 in step (1). Step (1) is modified as follows: 6 parts of apricot shell carbon and 2.5 parts of nano-silicon dioxide are mixed uniformly by mass, ground for 55 minutes at room temperature, pre-calcined at 205°C for 4.5 hours in an air atmosphere, heated to 1450°C at a heating rate of 5°C / min in a nitrogen atmosphere, calcined for 3.5 hours, and then naturally cooled to room temperature. In an air atmosphere, the carbon is removed at 700°C for 2 hours, naturally cooled to room temperature, and ground for 45 minutes to obtain modified silicon carbide composite nanowires. The remaining steps are the same as those of Example 2.

[0052] Comparative Example 2:

[0053] The preparation method of the silicon carbide ceramic material of Comparative Example 2 is different from that of Example 2 in step (1). Step (1) is modified as follows: 6 parts of apricot shell carbon, 2.5 parts of nano-silicon dioxide, 0.25 parts of sodium fluoride, and 0.17 parts of sodium chloride are mixed uniformly by mass, ground for 55 minutes at room temperature, pre-calcined at 205°C for 4.5 hours in an air atmosphere, heated to 1450°C at a heating rate of 5°C / min in an argon atmosphere, calcined for 3.5 hours, and then naturally cooled to room temperature. In an air atmosphere, the carbon is removed at 700°C for 2 hours, naturally cooled to room temperature, and ground for 45 minutes to obtain modified silicon carbide composite nanowires. The remaining steps are the same as those of Example 2.

[0054] Comparative Example 3:

[0055] The preparation method of silicon carbide ceramic material in Comparative Example 3 is different from that in Example 2 in that step (2) is not performed, and step (3) is modified as follows: 9 parts of liquid polycarbosilane, 5.5 parts of modified silicon carbide composite nanowires, 1.8 parts of divinylbenzene, 35 parts of silicon carbide particles, and 2.5 parts of sintering aids are mixed uniformly by mass, added to a ball mill, and silicon carbide grinding balls are used as the medium, with a ball-to-material ratio of 5:1, ground at 300 rpm for 22 hours, dried at 75° C. for 9 hours, and passed through a 200-mesh sieve after grinding to obtain a composite sintered powder. The remaining steps are the same as in Example 2.

[0056] Comparative Example 4:

[0057] The preparation method of silicon carbide ceramic material in Comparative Example 4 is different from that in Example 2 in that steps (1) and (2) are not performed, and step (3) is modified as follows: 9 parts of liquid polycarbosilane, 1.8 parts of divinylbenzene, 35 parts of silicon carbide particles, and 2.5 parts of sintering aid are mixed uniformly by mass, added to a ball mill, and silicon carbide grinding balls are used as the medium, with a ball-to-material ratio of 5:1, ground at 300 rpm for 22 hours, dried at 75° C. for 9 hours, and passed through a 200-mesh sieve after grinding to obtain a composite sintered powder. The remaining steps are the same as in Example 2.

[0058] Comparative Example 5:

[0059] The preparation method of the silicon carbide ceramic material of Comparative Example 5 is different from that of Example 2 in step (3). Step (3) is modified as follows: 9 parts of liquid polycarbosilane, 5.5 parts of praseodymium-modified silicon carbide composite nanowires, 35 parts of silicon carbide particles, and 2.5 parts of sintering aids are mixed uniformly by mass, added to a ball mill, and silicon carbide grinding balls are used as the medium, with a ball-to-material ratio of 5:1, ground at 300 rpm for 22 hours, dried at 75° C. for 9 hours, and passed through a 200-mesh sieve after grinding to obtain a composite sintered powder. The remaining steps are the same as those of Example 2.

[0060] Comparative Example 6:

[0061] The preparation method of the silicon carbide ceramic material of Comparative Example 6 is different from that of Example 2 in step (3). Step (3) is modified as follows: 9 parts of liquid polycarbosilane, 5.5 parts of praseodymium-modified silicon carbide composite nanowires, 1.8 parts of divinylbenzene, 35 parts of silicon carbide particles, and 1 part of yttrium oxide are mixed uniformly by mass, added to a ball mill, and silicon carbide grinding balls are used as the medium, with a ball-to-material ratio of 5:1, ground at 300 rpm for 22 hours, dried at 75°C for 9 hours, and passed through a 200-mesh sieve after grinding to obtain a composite sintered powder. The remaining steps are the same as those of Example 2.

[0062] Comparative Example 7:

[0063] The preparation method of the silicon carbide ceramic material of Comparative Example 7 is different from that of Example 2 in that step (4) is different. Step (4) is modified as follows: pre-press the composite sintering powder in a graphite mold, apply an external pressure of 150 MPa, hold the pressure for 2 min, and place it in a discharge plasma furnace for sintering. The sintering pressure is 30 MPa. The sintering system is as follows: in an argon atmosphere, first heat to 850°C at a heating rate of 100°C / min and hold for 3.5 min, heat to 1250°C at a heating rate of 100°C / min and hold for 7.5 min, continue to heat to 1600°C at a heating rate of 100°C / min, continue to heat to 1875°C at a heating rate of 40°C / min, hold for 12 min, cool to 1200°C at a cooling rate of 50°C / min, and then naturally cool to room temperature. After demolding, heat to 600°C for 2 h in an air atmosphere to remove carbon, and obtain a silicon carbide ceramic material. The remaining steps are the same as in Example 2.

[0064] Test Example 1:

[0065] Mechanical properties test: Test the flexural strength, fracture toughness and density of the prepared ceramic materials to evaluate their mechanical strength properties. The specific test methods are as follows:

[0066] Bending strength: According to the GB / T6569-86 ceramic bending strength test method, the sample size is prepared to be 38mm long, 3mm wide, and 4mm thick. The four edges of the sample are ground into an arc shape with a chamfer of 3mm. The sample strip is placed on the platform of the universal testing machine. During the loading process, the loading rate is 0.5mm / min, the span L is 30mm, and the indenter is slowly pressed down until the sample breaks. The applied load value is recorded, and the width and height of the fracture are measured with a vernier caliper, and the calculated results are substituted into the calculation formula to obtain the bending strength. The average value of 5 measured values ​​is selected for each group of samples for recording.

[0067] Fracture toughness: The fracture toughness of silicon carbide ceramic materials is tested by indentation method. The polished ceramic piece is pressed with a digital micro-Vickers hardness tester at P = 4.9N and maintained for 15s to cause cracks on the ceramic surface. The total length of the crack is measured, 2c, and calculated according to the following formula: K IC =0.016×(E÷H v ) 0.5 ×P÷(c) 1.5 , E is the elastic modulus, H v Vickers hardness, unit is MPa·m 1 / 2 Each group of samples was tested 5 times and the average value was recorded.

[0068] Density: After demoulding, grinding, polishing and rinsing, the silicon carbide ceramic material is placed in an environment of 80°C and dried for 10 hours before weighing to obtain its mass m in the air. a Then soak the sample in boiling water for 2 hours, and then use a thin copper wire to hang the sample in pure water at room temperature and weigh it to obtain the apparent water-carrying mass m1 of the sample. Finally, take out the saturated sample and quickly wipe it dry with a wet clean towel, and quickly measure its mass m2. The actual measured density ρ and density D of the sample are: ρ=m a ÷(m2-m1)×ρ w , D = ρ ÷ ρ th ×100%;ρ w is the density of pure water 1.0g / cm3, ρ th Represents the theoretical density of ceramic materials, calculated according to the mixing rule.

[0069] The results are shown in Table 1.

[0070] Table 1

[0071] ;

[0072] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 7 in Table 1, it can be found that the silicon carbide ceramic material prepared by the present invention has higher bending strength, fracture toughness and density.

[0073] By comparing the data in the table, it is shown that the sodium salt doping of the composite nanowires, the composite of the silicon nitride crystal phase and the praseodymium modification of the surface have effectively improved the flexural strength and fracture toughness of the ceramic materials. The praseodymium-modified silicon carbide composite nanowires are the main contributor to the improvement of fracture toughness. The sintering modification of liquid polycarbosilane by divinylbenzene has improved the ceramic yield and density of liquid polycarbosilane, and contributed to the improvement of flexural strength and fracture toughness. In terms of sintering aids, the addition of aluminum nitride and cerium oxide has greatly improved the density, and also effectively improved the flexural strength and fracture toughness. The annealing operation under argon has optimized various properties.

[0074] Test Example 2:

[0075] Thermal conductivity test: The prepared silicon carbide ceramic material was first processed into φ10 mm×1 mm, and then its surface was polished to a roughness of 0.5 μm, and its thermal conductivity at room temperature was measured using a laser thermal conductivity meter.

[0076] The results are shown in Table 2.

[0077] Table 2

[0078] ;

[0079] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 7 in Table 2, it can be found that the silicon carbide ceramic material prepared in the present invention has good thermal conductivity performance.

[0080] By comparing the data in the table, it is shown that the various modifications of silicon carbide nanowires and the addition of praseodymium-modified silicon carbide composite nanowires have effectively improved the thermal conductivity of the material. The modification and addition of divinylbenzene, the compound introduction of sintering aids and the optimization of the annealing process have improved the microscopic crystal structure of the material and improved the thermal conductivity of the prepared silicon carbide ceramic material.

[0081] Test Example 3:

[0082] Electromagnetic shielding performance test: The shielding performance of the prepared silicon carbide ceramic material was tested using a vector network analyzer. The room temperature shielding performance of the Ku band (12.4 to 18 GHz) samples was tested. The sample size is 15.8 mm × 7.9 mm × 2.8 mm. During the test, the sample was placed vertically in the center of the test cavity, and then the instrument was installed and calibrated for S parameter testing at room temperature. Shielding effectiveness can be calculated using S parameters. The average value within the band was recorded, and each group of samples was tested 5 times, and the average value was recorded.

[0083] The results are shown in Table 3.

[0084] Table 3

[0085] ;

[0086] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 7 in Table 3, it can be found that the silicon carbide ceramic material prepared by the present invention has good electromagnetic shielding performance.

[0087] By comparing the data in the table, it is shown that the sodium salt doping modification of silicon carbide nanowires and the composite modification of silicon nitride crystal phase improve the dielectric loss by improving the micromorphology of nanowires, increasing the specific surface area, and expanding the attenuation path of electromagnetic waves, thereby effectively improving the electromagnetic shielding performance of the prepared silicon carbide ceramic material.

[0088] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a silicon carbide ceramic material, characterized in that: The method comprises the following preparation steps: (1) According to the weight ratio, 5-8 parts of apricot shell carbon, 2-3 parts of nano-silicon dioxide, 0.2-0.3 parts of sodium fluoride and 0.14-0.2 parts of sodium chloride were mixed evenly, ground at room temperature for 50-60 minutes, pre-calcined at 200-210°C for 4-5 hours in an air atmosphere, heated to 1400-1500°C at a heating rate of 5°C / min in a nitrogen atmosphere, calcined for 3-4 hours, and then naturally cooled to room temperature. In an air atmosphere, the mixture was kept at 700°C for 2 hours to remove carbon, naturally cooled to room temperature, and ground for 40-50 minutes to obtain modified silicon carbide composite nanowires; (2) By weight, 5-6 parts of praseodymium powder, 2-3 parts of modified silicon carbide composite nanowires, 6-7 parts of sodium chloride, and 8-9 parts of potassium chloride were mixed evenly, ground for 30-40 min, heated to 500°C at a heating rate of 8°C / min in an argon atmosphere and kept warm for 30-40 min, then heated to 850°C at a heating rate of 5°C / min and kept warm for 5 h, cooled naturally to room temperature, ultrasonically cleaned with pure water for 30-40 min, filtered, washed with pure water for 3-4 times, vacuum dried at 50-60°C for 8-10 h, ground, and sieved through a 200-mesh sieve to obtain praseodymium-modified silicon carbide composite nanowires; (3) By weight, 8-10 parts of liquid polycarbosilane, 5-6 parts of praseodymium-modified silicon carbide composite nanowires, 1.6-2 parts of divinylbenzene, 30-40 parts of silicon carbide particles, and 2-3 parts of sintering aids were mixed evenly, added into a ball mill, and silicon carbide grinding balls were used as the medium, with a ball-to-material ratio of 5:1, ground at 300-350 rpm for 20-24 h, dried at 70-80 ° C for 8-10 h, and passed through a 200-mesh sieve after grinding to obtain a composite sintering powder; (4) Pre-pressing the composite sintering powder in a graphite mold, applying an external pressure of 150 MPa, maintaining the pressure for 2 minutes, placing it in a spark plasma furnace and sintering it according to the sintering system, with a sintering pressure of 30-40 MPa, to obtain silicon carbide ceramic material; The sintering aid in step (3) is a mixture of yttrium oxide, aluminum nitride and cerium oxide in a mass ratio of 2:1:2; The sintering system of step (4) is as follows: in an argon atmosphere, the temperature is increased to 800-900°C at a heating rate of 100°C / min and kept for 3-4 minutes, the temperature is increased to 1200-1300°C at a heating rate of 100°C / min and kept for 7-8 minutes, the temperature is further increased to 1600°C at a heating rate of 100°C / min, the temperature is further increased to 1850-1900°C at a heating rate of 40°C / min, kept for 10-15 minutes, the temperature is decreased to 1200°C at a cooling rate of 50°C / min, and then naturally cooled to room temperature. After demolding, the material is decarbonized at 600°C for 2 hours in an air atmosphere, and annealed at 1300-1400°C for 1 hour in an argon atmosphere.

2. The method for preparing a silicon carbide ceramic material according to claim 1, characterized in that: The average particle size of the silicon carbide particles was 0.58 μm.

3. A silicon carbide ceramic material prepared according to the method for preparing a silicon carbide ceramic material according to any one of claims 1 to 2.