High-thermal-conductivity reaction-sintered silicon carbide ceramic material and preparation method thereof

Abstract

The invention belongs to the technical field of ceramics, and relates to a high-thermal-conductivity reaction-sintered silicon carbide ceramic material and a preparation method thereof. According to the invention, SiC is mainly used as a raw material, resorcinol and formaldehyde are used as carbon sources, and the SiC / C porous preform which is uniform and compact in microstructure and has excellent heat-conducting property can be manufactured by combining gel casting with a reaction siliconizing process. In the process, a porous carbon network is formed after a product generated by reaction of resorcinol and formaldehyde is carbonized, SiC particles are uniformly wrapped by the network, and when siliconizing treatment is carried out, due to the existence of the porous carbon network, the finally obtained reaction sintered silicon carbide ceramic material has more uniform phase distribution, so that the performance of the silicon carbide ceramic material is improved, and the service life of the silicon carbide ceramic material is prolonged. Meanwhile, the content of residual silicon is remarkably reduced, so that the thermal conductivity of the material is effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of ceramics and relates to a high thermal conductivity reaction sintered silicon carbide ceramic material and a preparation method thereof. Background Art

[0002] Reaction-bonded silicon carbide (RBSC) ceramics are considered to be one of the ideal materials for manufacturing high-performance heat exchangers due to their unique physical and chemical properties, such as high thermal conductivity, low thermal expansion coefficient, and excellent corrosion resistance. These properties give RBSC ceramics stability and durability in extreme environments, making them have broad application prospects in aerospace, military protection, automotive industry, chemical processing, and energy conversion.

[0003] However, although the melt infiltration silicon process used in the preparation process can effectively achieve material densification, it also brings a significant problem - the presence of residual silicon phase. Due to the difference in thermal expansion coefficient between silicon and silicon carbide, the former is 3.6×10 -6 / ℃, while the latter is 4.6×10 -6 / ℃, this thermal expansion mismatch will lead to the generation of interface stress when the temperature changes. Excessive residual silicon not only increases the stress concentration points inside the material, but also may become the starting point for crack initiation and expansion, thereby reducing the overall mechanical strength and thermal conductivity of the material. In addition, oxygen impurities are inevitably mixed in the silicon carbide powder raw materials, and these impurities will further affect the thermal conductivity of the material because they can hinder the effective conduction of heat, forming the so-called "thermal resistance".

[0004] In response to these problems, researchers have been exploring ways to improve the preparation process of RBSC ceramics. An effective strategy is to repeatedly impregnate the preform with phenolic resin to reduce the porosity and thus the residual silicon content in the final product. This method reduces the infiltration space of silicon liquid during the infiltration process by filling the pores in the preform, thereby reducing the introduction of excess silicon. The results show that the thermal conductivity of RBSC ceramics treated in this way has been significantly improved. However, the uniformity of phase distribution remains a challenge, which is directly related to whether the material properties can be further optimized. In addition to controlling the content of residual silicon, reducing oxygen impurities is also an important part of improving the thermal conductivity of RBSC ceramics. This needs to start with the selection of raw materials, ensuring that the silicon carbide powder used has the lowest possible oxygen content, and taking measures to avoid the introduction or retention of oxygen during subsequent processing. At the same time, the regulation of silicon size distribution is also crucial because it affects the distribution of silicon phases in the material, thereby indirectly affecting the comprehensive performance of the material.

[0005] A Chinese patent application document (publication number: CN117550898A) discloses a method for preparing reaction-sintered silicon carbide using phenolic epoxy resin gel injection molding, and a reaction-sintered silicon carbide ceramic with uniform microstructure is prepared. However, this method cannot control the content and distribution of residual silicon.

[0006] A Chinese patent application document (publication number: CN108892524A) discloses a method for preparing a C / SiC composite material. A carbon fiber preform is repeatedly impregnated, cured, and cracked using a mixture of resorcinol, formaldehyde, and water, and then a high-strength C / SiC composite material is prepared through two-step siliconization. However, this method requires repeated impregnation-curing-cracking processes to increase the density of the preform, and a two-step siliconization process is performed to obtain a C / SiC composite material. This method has the problems of complex process and high preparation cost.

[0007] The Chinese patent application document (publication number: CN114956852A) discloses silicon carbide ceramics with extremely low residual silicon obtained by multi-step reaction sintering and its preparation method, using phenolic resin, ethylene glycol, silicon carbide powder, petroleum coke powder, carbon microsphere powder, polyethylene glycol, and benzenesulfonyl chloride as raw materials, and preparing low residual silicon silicon carbide ceramics through curing, carbonization, and siliconization. However, the sulfonyl chloride added by this method has acute toxicity and ethylene glycol promotes its volatilization, which is easy to cause environmental pollution and personnel harm; on the other hand, this method obtains extremely low residual silicon content while also leaving residual carbon impurities in the silicon carbide ceramic, which is more unfavorable to the mechanical, thermal conductivity, and antioxidant properties of the ceramic.

[0008] The Chinese patent application document (publication number: CN10577130A) discloses a gel injection molding preparation method for reaction sintered boron carbide ceramic composite materials, using resorcinol, formaldehyde, water, sodium carbonate and boron carbide as raw materials to obtain a high-strength composite material. However, this method requires the addition of water to dilute the slurry in order to adjust the uniformity of the material, and it is easy to cause the preform to shrink and crack; the added water is also easy to introduce oxygen impurities, affecting the material performance. Summary of the invention

[0009] The purpose of the present invention is to address the above-mentioned problems existing in the prior art and propose a high thermal conductivity reaction sintered silicon carbide ceramic material. A SiC / C porous preform is prepared by a gel injection molding process using a low-toxic resorcinol-formaldehyde gel system, and a high thermal conductivity reaction sintered silicon carbide ceramic material is obtained by a melt infiltration method.

[0010] The purpose of the present invention can be achieved by the following technical solutions:

[0011] A high thermal conductivity reaction sintered silicon carbide ceramic material contains 65-75 vol% alpha-SiC, 10-20 vol% beta-SiC and 5-20 vol% Si.

[0012] The silicon carbide ceramic material of the present invention uses 65-75 vol% α-SiC as a high-temperature phase to provide the main structural support and give the material excellent mechanical strength and high temperature resistance. β-SiC is a low-temperature phase formed by the reaction of a carbon source with molten silicon to fill the α-SiC stacking gaps. β-SiC helps to reduce the residual silicon content in the ceramic, improve the density and interface flatness of the material, and thus improve the overall thermal conductivity. Si as a continuous phase further fills the remaining pores and tightly binds the α-SiC and β-SiC particles together. However, excessive residual silicon will increase the interface stress due to its different thermal expansion coefficient from silicon carbide, thereby affecting the thermal conductivity of the material. In the present invention, the density and thermal expansion behavior of the material can be effectively balanced by precisely controlling the proportion of Si, ensuring that the material maintains good dimensional stability within the operating temperature range, thereby improving the thermal conductivity.

[0013] In the above-mentioned high thermal conductivity reaction sintered silicon carbide ceramic material, the density of the silicon carbide ceramic material is 3.0-3.2 g / cm 3 , the open porosity is 0.15-0.35%, the residual Si content is 5-20 vol%, and the thermal conductivity is 143-220 W / (m·k).

[0014] The present invention also provides a method for preparing the above-mentioned high thermal conductivity reaction sintered silicon carbide ceramic material, the method comprising the following steps:

[0015] S1, adding SiC powder to resorcinol formaldehyde solution to obtain a mixed solution, and then ball milling to obtain a slurry;

[0016] S2, after vacuum degassing, pour the slurry into a mold and seal it, and obtain a solidified body after gelation and normal pressure drying;

[0017] S3, carbonizing the solidified body to obtain a preform;

[0018] S4. Spread silicon particles on the preform and perform high-temperature infiltration in a vacuum, and finally obtain a high-strength and tough reaction-sintered boron carbide ceramic composite material by cooling.

[0019] In the above-mentioned method for preparing a high thermal conductivity reaction-sintered silicon carbide ceramic material, the resorcinol formaldehyde solution is prepared by mixing a catalyst, resorcinol and formaldehyde, wherein the molar ratio of resorcinol, formaldehyde and catalyst is 1:(1-3):(0.001-0.01).

[0020] Preferably, the catalyst is one of an alkali metal or alkaline earth metal carbonate, and an alkali metal or alkaline earth metal bicarbonate.

[0021] Preferably, the catalyst is sodium carbonate.

[0022] The present invention can more easily achieve precise control of the pore size of the preform by controlling the amount of catalyst added. However, if the amount added is too high, the reaction rate of resorcinol and formaldehyde gel is too fast, and the preform is prone to cracking during the drying process; if the amount added is too low, the preform will take a long time to form and internal stratification defects will occur.

[0023] In the above-mentioned method for preparing a high thermal conductivity reaction-sintered silicon carbide ceramic material, SiC powder is graded according to a mass ratio, with an average particle size of 20-50 μm: an average particle size of 5-10 μm: an average particle size of 0.3-1 μm = (5-7): 1: (2-4).

[0024] The present invention can optimize the arrangement of particles at a microscopic level by grading SiC powder. Large particles provide the main structural support as a skeleton, while medium particles and small particles are filled between large particles, reducing porosity and increasing packing density. This multi-level particle structure can maximize the use of space, ensure close contact between particles, and thus form a denser preform. Higher packing density means fewer voids, which not only improves the mechanical strength of the material, but also reduces the penetration space of silicon liquid during the infiltration process, effectively reducing the content of residual silicon; due to the large difference in thermal expansion coefficients between silicon and silicon carbide, excessive residual silicon will generate interfacial stress when the temperature changes, reducing the overall performance of the material. Through particle grading, especially increasing the proportion of fine particles, the voids between large particles can be more effectively filled, reducing the penetration space of silicon liquid. This not only reduces the total amount of residual silicon, but also makes the remaining silicon phase more evenly distributed, reduces the possibility of local stress concentration, and thus improves the comprehensive performance of the material.

[0025] Preferably, the SiC powder content in the slurry of step S1 is 40-75wt%.

[0026] The present invention needs to control the SiC powder content in the slurry. Too much silicon carbide powder in the slurry will cause the slurry to be too viscous and unable to be poured into the mold, and the bubbles in the slurry are difficult to remove, thereby forming closed-cell defects in the preform; too little silicon carbide powder in the slurry will cause the preform to shrink too much during the drying and carbonization process, and easily cause delamination and cracking defects in the preform.

[0027] In the above-mentioned method for preparing a high thermal conductivity reaction-sintered silicon carbide ceramic material, the gelation temperature in step S2 is 50-90° C., and the insulation time is 6-24 hours; the drying temperature is 110-150° C., and the time is 6-24 hours.

[0028] In the above-mentioned method for preparing a high thermal conductivity reaction-sintered silicon carbide ceramic material, the carbonization treatment temperature in step S3 is 1100-1600° C., the carbonization holding time is 2-4 hours, and the heating rate is 1-5° C. / min.

[0029] Preferably, the carbonization atmosphere is a vacuum, nitrogen or argon flowing atmosphere.

[0030] More preferably, the gas flow rate of the carbonization atmosphere flowing atmosphere is 0.5 to 1.5 mL / min.

[0031] In the above-mentioned method for preparing a high thermal conductivity reaction sintered silicon carbide ceramic material, the preform in step S3 has a nanoporous structure, the pore size is unimodal, the pore size range is 5 to 200 nm, and the carbon content is 10 to 20 wt%, and the volume density is 1.5 to 2.0 g / cm 3 , the open porosity is 20-30%.

[0032] The present invention utilizes the polymerization reaction of resorcinol and formaldehyde to introduce a porous carbon source into the preform. The introduction of the carbon source can enhance the ability to eliminate SiO2 on the surface of the α-SiC raw material, reduce the residual oxygen impurities at the SiC grain boundaries in the reaction-sintered silicon carbide material, reduce the interface thermal resistance, and further improve the thermal conductivity of the material.

[0033] In the above-mentioned method for preparing a high thermal conductivity reaction-sintered silicon carbide ceramic material, the particle size of the silicon powder is 1 to 5 mm, and the actual amount of silicon particles added is ≥ 1.5 times the theoretical amount.

[0034] The present invention requires strict control of the silicon powder particle size, because silicon powder with too small a size has a high specific surface area and is easily oxidized, and oxygen impurities are easily introduced into the ceramic during the infiltration process to reduce thermal conductivity; silicon powder with too large a size requires more time to melt.

[0035] In the above-mentioned method for preparing a high thermal conductivity reaction-sintered silicon carbide ceramic material, the high-temperature infiltration reaction is heated to 1650-1850° C. at a rate of 1-10° C. / min, and the holding time is 0.5-6 hours.

[0036] Preferably, in step S4, the size of residual Si in the reaction-sintered silicon carbide ceramic material is less than 1 μm.

[0037] When the residual Si size is less than 1μm, compressive stress rather than tensile stress is formed at the interface between the residual Si and the silicon carbide matrix. This compressive stress has a positive effect on the transmission of phonons (quantum carriers of thermal energy) at the interface. On a microscopic scale, compressive stress helps to reduce the scattering effect at the interface, allowing phonons to pass through the interface more smoothly, thereby improving the efficiency of heat conduction. In contrast, large-sized or irregular-shaped residual Si will produce tensile stress at the interface, which increases interface scattering, hinders the effective transmission of phonons, and thus reduces thermal conductivity. Therefore, by controlling the size of residual Si to below the micron level, the thermal conductivity of reaction-sintered silicon carbide ceramic materials can be significantly improved.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. The present invention mainly uses SiC as raw material, and uses resorcinol and formaldehyde as carbon sources. Through gel injection molding combined with reactive siliconization process, a SiC / C porous preform with uniform and dense microstructure and excellent thermal conductivity can be manufactured. In this process, the product generated by the reaction of resorcinol and formaldehyde forms a porous carbon network after carbonization, which uniformly wraps the SiC particles. When siliconization treatment is performed, due to the presence of the porous carbon network, the final reaction-sintered silicon carbide ceramic material has a more uniform phase distribution, and the residual silicon content is significantly reduced, thereby effectively improving the thermal conductivity of the material;

[0040] 2. The present invention can control the change of the pore size in the SiC / C porous preform by adjusting the raw material ratio, thereby affecting the content and size of residual silicon, providing flexibility for optimizing material properties. In addition, the introduction of a porous carbon network with strong adsorption capacity enhances the deoxidation capacity of the preform, which helps to improve the quality of the final product.

[0041] 3. The present invention optimizes the microstructure of reaction-sintered silicon carbide ceramics by means of gel injection molding method, and successfully prepares a new type of material with high thermal conductivity. This high thermal conductivity reaction-sintered silicon carbide ceramic material is of great significance to the development of space optical components, heat exchange systems, semiconductor industry and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The present invention is a process flow chart for preparing high thermal conductivity reaction sintered silicon carbide ceramic material.

[0043] Figure 2 : is the pore size distribution curve of the SiC / C preform prepared in Example 1 of the present invention.

[0044] Figure 3 : is the pore size distribution curve of the SiC / C preform prepared in Comparative Example 1 of the present invention.

[0045] Figure 4 This is a SEM image of the SiC / C preform prepared in Example 1 of the present invention.

[0046] Figure 5 This is a SEM image of the SiC / C preform prepared in Comparative Example 1 of the present invention.

[0047] Figure 6 This is a SEM image of the porous carbon portion in the SiC / C preform prepared in Example 1 of the present invention.

[0048] Figure 7 This is a SEM image of the porous carbon portion in the SiC / C preform prepared in Comparative Example 1 of the present invention.

[0049] Figure 8 This is a SEM image of the reaction-sintered silicon carbide ceramic prepared in Example 1 of the present invention.

[0050] Fig. 9 This is a SEM image of the reaction-sintered silicon carbide ceramic prepared in Comparative Example 1 of the present invention.

[0051] Fig.10 TEM image of the reaction-sintered silicon carbide ceramic prepared in Example 1 of the present invention.

[0052] Fig.11 TEM image of the reaction-sintered silicon carbide ceramic prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0053] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments. The following embodiments further illustrate the content of the present invention, but should not be construed as limiting the present invention. Without departing from the essence of the invention, modifications and substitutions made to the inventive methods, steps or conditions all belong to the scope of the present invention.

[0054] The raw materials used in the embodiment are as follows:

[0055] α-SiC powder, Qinhuangdao Yinuo New Material Technology Co., Ltd.

[0056] The average particle size range of silicon powder raw materials is 1 to 3 mm.

[0057] Resorcinol (C6H6O2), analytical grade, Sinopharm Chemical Reagent Co., Ltd.

[0058] Formaldehyde (CH2O), analytical grade, Sinopharm Chemical Reagent Co., Ltd.

[0059] Anhydrous sodium carbonate (Na2CO3), analytical grade, Sinopharm Chemical Reagent Co., Ltd.

[0060] Deionized water, P ≥ 18 MΩ / cm.

[0061] The equipment used for melt infiltration in the embodiment of the present invention is a graphite vacuum sintering furnace.

[0062] The thermal conductivity test method in the embodiment of the present invention is the laser thermal conductivity method, and the test is performed using the LFA 467 laser thermal conductivity instrument produced by the German NETZSCH company.

[0063] The test method for the open porosity and the volume density in the embodiment of the present invention adopts the Archimedean drainage method.

[0064] The pore size distribution in the embodiments of the present invention is tested using an Auto Pore IV 9500 mercury porosimeter.

[0065] The reaction-sintered silicon carbide ceramic material prepared in the embodiment of the present invention is composed of α-SiC, β-SiC and Si.

[0066] Compared with the preform before sintering, the size change of the sintered body obtained after sintering in the embodiment of the present invention is less than 1%.

[0067] Embodiment 1:

[0068] according to Figure 1 The process flow chart shown is for preparing ceramic materials.

[0069] S1. Resorcinol, formaldehyde and anhydrous sodium carbonate were mixed evenly in a molar ratio of 1:2:0.01, and stirred until completely dissolved, and SiC mixed powders in a mass ratio of 50 μm:5 μm:0.5 μm=6:1:3 were added, and ball milled for 12 hours to form SiC ceramic slurry; wherein the SiC powder content in the SiC ceramic slurry was 63wt%;

[0070] S2, after vacuum degassing, the SiC ceramic slurry is sealed by injection molding, and placed in a 75°C forced air drying oven for gelation for 12 hours; then demolded and transferred to a 130°C forced air drying oven for normal pressure drying for 18 hours to obtain a gel solidified body;

[0071] S3, carbonizing the gel solidified body at high temperature in a flowing N2 environment to obtain a SiC / C preform, wherein the carbonization heating rate is 2°C / min, the carbonization temperature is 1000°C, and the carbonization holding time is 3h; the carbon content in the SiC / C preform is 15wt%, and the volume density is 1.94g / cm 3 , the open porosity is 23.2%, and the most probable pore size of the preform is 9 nm;

[0072] S4. Place the SiC / C preform into a graphite crucible, spread silicon powder with an average particle size of 1 mm on the top of the preform (the amount of silicon powder is 1.5 times the theoretical silicon mass required), and perform high-temperature infiltration to obtain a sintered body; wherein, the high-temperature infiltration heating rate is 5°C / min, the infiltration temperature is 1850°C, and the insulation time is 6h.

[0073] S5. After the sintered body is cooled in the furnace, it is taken out and the excess silicon on the surface is removed to obtain a reaction-sintered silicon carbide ceramic material.

[0074] Embodiment 2:

[0075] S1. Resorcinol, formaldehyde and anhydrous sodium carbonate were mixed evenly in a molar ratio of 1:2:0.01, and stirred until completely dissolved, and SiC mixed powder in a mass ratio of 20 μm:5 μm:0.5 μm=6:1:3 was added, and ball milled for 12 hours to form SiC ceramic slurry; wherein the SiC powder content in the SiC ceramic slurry was 63wt%;

[0076] S2, after vacuum degassing, the SiC ceramic slurry is injection molded and sealed, and placed in a 70°C forced air drying oven for gelation for 12 hours; then demolded and transferred to a 120°C forced air drying oven for normal pressure drying for 12 hours to obtain a gel solidified body;

[0077] S3, the gel solidified body is carbonized at high temperature in a flowing N2 environment with a gas flow rate of 1.0 mL / min to obtain a SiC / C preform, wherein the carbonization heating rate is 2°C / min, the carbonization temperature is 1000°C, and the carbonization holding time is 3 h; the carbon content in the SiC / C preform is 15 wt%, and the volume density is 1.94 g / cm 3 , the open porosity is 20.3%, and the most probable pore size of the preform is 9 nm;

[0078] S4. Place the SiC / C preform into a graphite crucible, spread silicon powder with an average particle size of 1 mm on the top of the preform (the amount of silicon powder is 1.5 times the theoretical silicon mass required), and perform high-temperature infiltration to obtain a sintered body; wherein, the high-temperature infiltration heating rate is 5°C / min, the infiltration temperature is 1750°C, and the insulation time is 2h.

[0079] S5. After the sintered body is cooled in the furnace, it is taken out and the excess silicon on the surface is removed to obtain a reaction-sintered silicon carbide ceramic material.

[0080] Embodiment 3:

[0081] S1. Resorcinol, formaldehyde and anhydrous sodium carbonate were mixed evenly in a molar ratio of 1:2:0.02, and stirred until completely dissolved, and SiC mixed powders in a mass ratio of 30 μm:5 μm:0.5 μm=6:1:3 were added, and ball milled for 12 hours to form SiC ceramic slurry; wherein the SiC powder content in the SiC ceramic slurry was 63wt%;

[0082] S2, after vacuum degassing, the SiC ceramic slurry is sealed by injection molding, and placed in an 80°C forced air drying oven for gelation for 12 hours; then demolded and transferred to a 120°C forced air drying oven for normal pressure drying for 12 hours to obtain a gel solidified body;

[0083] S3, the gel solidified body is carbonized at high temperature in a flowing N2 environment with a gas flow rate of 1.0 mL / min to obtain a SiC / C preform, wherein the carbonization heating rate is 2°C / min, the carbonization temperature is 900°C, and the carbonization holding time is 3 h; the carbon content in the SiC / C preform is 15 wt%, and the volume density is 1.87 g / cm 3 , the open porosity is 26.6%, and the most probable pore size of the preform is 43nm;

[0084] S4. Place the SiC / C preform into a graphite crucible, spread silicon powder with an average particle size of 1 mm on the top of the preform (the amount of silicon powder is 1.5 times the theoretical silicon mass required), and perform high-temperature infiltration to obtain a sintered body; wherein, the high-temperature infiltration heating rate is 5°C / min, the infiltration temperature is 1650°C, and the insulation time is 2h.

[0085] S5. After the sintered body is cooled in the furnace, it is taken out and the excess silicon on the surface is removed to obtain a reaction-sintered silicon carbide ceramic material.

[0086] Comparative Example 1:

[0087] S1. Mix SiC mixed powder with a mass ratio of 20 μm: 5 μm: 0.5 μm = 6: 1: 3 and carbon black with an average particle size of 20 nm, add deionized water and polyvinyl alcohol, and ball mill for 12 hours to prepare SiC / C ceramic slurry, wherein the content of the mixed powder is 30wt%, and the content of polyvinyl alcohol is 0.6wt%.

[0088] S2. Pour the SiC / C ceramic slurry into a rotary evaporator for drying, grind it into powder, pass it through a 100-mesh sieve, and then use a dry pressing process to prepare a SiC / C green body.

[0089] S3, the SiC / C blank is carbonized at high temperature in a flowing N2 environment to obtain a SiC / C preform. The carbonization heating rate is 2°C / min, the carbonization temperature is 900°C, the carbonization holding time is 3h, the carbon content in the preform is 15wt%, and the volume density is 1.81g / cm 3, the open porosity is 33.3%.

[0090] S4. Place the SiC / C preform into a graphite crucible, spread silicon powder with an average particle size of 1 mm on the top of the preform (the amount of silicon powder is 1.5 times the theoretical silicon mass required), and perform high-temperature infiltration to obtain a sintered body; wherein the high-temperature infiltration heating rate is 5°C / min, the infiltration temperature is 1650°C, and the insulation time is 2h.

[0091] S5. After the sintered body is cooled in the furnace, it is taken out and the excess silicon on the surface is removed to obtain a reaction-sintered silicon carbide ceramic material.

[0092] The preform prepared by the comparative example method has a higher open porosity and an uneven pore size distribution. The phases in the obtained reaction-sintered silicon carbide ceramic material are unevenly distributed, with a lot of residual silicon and more oxygen impurities at the silicon carbide interface, which reduces its thermal conductivity.

[0093] Comparative Example 2:

[0094] The only difference from Example 1 is that the slurry in step S2 is not poured into a mold for molding, but poured into a rotary evaporator for drying, ground into powder, passed through a 100-mesh sieve, and then pressed into a green blank by a dry pressing process, and then a SiC / C preform is obtained by step (3), wherein the carbon content in the preform is 15wt% and the volume density is 1.83g / cm 3 , the open porosity is 31.4%.

[0095] Although the comparative example uses the same carbon source, it does not have the effect of gel polycondensation, and the prepared preform has a higher open porosity, resulting in a large amount of free silicon in the obtained reaction-sintered silicon carbide ceramic material, which reduces its thermal conductivity.

[0096] Comparative Example 3:

[0097] The only difference from Example 1 is that in step S1, resorcinol: formaldehyde: anhydrous sodium carbonate: deionized water are mixed uniformly in a molar ratio of 1:2:0.002:12.7, and stirred until completely dissolved, and SiC mixed powder in a mass ratio of 30 μm:5 μm:0.5 μm=6:1:3 is added.

[0098] The ceramic material prepared in Comparative Example 3 significantly slows down the rate of "polymerization-induced phase separation" between the resorcinol formaldehyde resin phase and the water phase by adding water, so that the pore size and porosity of the preform after molding are significantly increased. Large pore size and high porosity not only reduce the density of the preform, but also increase the silicon liquid penetration space in the subsequent silicon infiltration process, which not only means that more silicon is introduced into the material, but also these silicon phases will form larger "silicon island" areas, resulting in a significant increase in the size and content of residual silicon. Larger-sized residual silicon will form irregular structures inside the material. These structures produce tensile stress rather than compressive stress at the interface, increase the interface scattering effect, hinder the effective transmission of phonons, and thus reduce the thermal conductivity of the material. In addition, too much residual silicon will also reduce the overall mechanical strength of the material and increase the risk of crack initiation and expansion.

[0099] Comparative Example 4:

[0100] The only difference from Example 1 is that the actual amount of silicon particles added in step S4 is 0.5 times the theoretical amount.

[0101] Comparative Example 5:

[0102] The only difference from Example 1 is that the particle size of the silicon powder in step S4 is 1 μm.

[0103] Comparative Example 6:

[0104] The only difference from Example 1 is that the SiC powder content in the SiC ceramic slurry in step S1 is 35wt%.

[0105] Comparative Example 7:

[0106] The only difference from Example 1 is that the SiC powder content in the SiC ceramic slurry in step S1 is 80 wt %.

[0107] Comparative Example 8:

[0108] The only difference from Example 1 is that the SiC mixed powder in step S1 is replaced by B4C.

[0109] Table 1: Performance test results of ceramic materials prepared in Examples 1-3 and Comparative Examples 1-7

[0110]

[0111]

[0112] Figure 2 This is the pore size distribution curve of the SiC / C preform prepared in Example 1 of the present invention. As can be seen from the figure, the pore size of the preform is unimodal, the pore size distribution is uniform, and the most probable pore size is 9 nm.

[0113] Figure 3 This is the pore size distribution curve of the SiC / C preform prepared in Comparative Example 1 of the present invention. As can be seen from the figure, the pore size of the preform is multi-modal distribution, the pore size distribution is disordered, and the main pores are interstitial pores formed by the accumulation of carbon black and silicon carbide particles.

[0114] Figure 4 This is a SEM image of the SiC / C preform prepared in Example 1 of the present invention. As can be seen from the figure, the preform has a high density, wherein the silicon carbide particles are uniformly wrapped by the porous carbon skeleton.

[0115] Figure 5 This is a SEM image of the SiC / C preform prepared in Comparative Example 1 of the present invention. As can be seen from the figure, the density of the preform is low, the distribution uniformity of silicon carbide and carbon black is poor, and some carbon black is agglomerated.

[0116] Figure 6 This is a SEM image of the porous carbon part in the SiC / C preform prepared in Example 1 of the present invention. As can be seen from the figure, the porous carbon has a three-dimensional interconnected porous skeleton structure, and its pore size is relatively orderly, uniform and small.

[0117] Figure 7 This is a SEM image of the porous carbon part of the SiC / C preform prepared in Comparative Example 1 of the present invention. As can be seen from the figure, the carbon black particles are about 20 nm in size and are stacked to form irregular pores.

[0118] Figure 8 This is a SEM image of the reaction-sintered silicon carbide ceramic prepared in Example 1 of the present invention. As can be seen from the figure, the various phases in the ceramic are evenly distributed, and the small-sized silicon carbide is evenly distributed in the gaps where the large-sized silicon carbide is accumulated, forming a tightly packed structure; the residual silicon accounts for a low proportion, and the size distribution is fine.

[0119] Fig. 9 This is a SEM image of the reaction-sintered silicon carbide ceramic prepared in comparative example 1 of the present invention. As can be seen from the figure, the distribution uniformity of the various phases in the ceramic is poor, silicon carbides of different particle sizes are stacked disorderly, and residual silicon in some areas presents a "silicon island" phenomenon.

[0120] Fig.10 This is a TEM image of the reaction-sintered silicon carbide ceramic prepared in Example 1 of the present invention. As can be seen from the figure, the light gray area is silicon carbide, the dark gray area is residual silicon, the black spots at some silicon carbide grain boundaries are oxygen-enriched areas, and the oxygen impurity enrichment phenomenon is not obvious.

[0121] Fig.11 This is a TEM image of the reaction-sintered silicon carbide ceramic prepared in Comparative Example 1 of the present invention. As can be seen from the figure, there are many black spots at the silicon carbide grain boundaries, and oxygen impurities are more enriched, which seriously affects the propagation efficiency of phonons at this location and reduces thermal conductivity.

[0122] In summary, the present invention mainly uses SiC as a raw material, and uses resorcinol and formaldehyde as carbon sources, and can produce a SiC / C porous preform with uniform and dense microstructure and excellent thermal conductivity through gel injection molding combined with a reactive siliconization process. In this process, the product generated by the reaction of resorcinol and formaldehyde forms a porous carbon network after carbonization, and this network uniformly wraps the SiC particles. When siliconizing treatment is performed, due to the presence of the porous carbon network, the reaction sintered silicon carbide ceramic material finally obtained has a more uniform phase distribution, and the content of residual silicon is significantly reduced, thereby effectively improving the thermal conductivity of the material.

[0123] The parts of the embodiments herein that are not exhaustive of the midpoint values ​​of the technical scope claimed for protection by the present invention and the new technical solutions formed by equivalent replacement of single or multiple technical features in the technical solutions of the embodiments are also within the scope claimed for protection by the present invention; at the same time, in all the listed or unlisted embodiments of the scheme of the present invention, each parameter in the same embodiment merely represents an example of its technical solution (i.e., a feasible solution), and there is no strict coordination and limitation relationship between the parameters, wherein the parameters can be replaced with each other without violating the axioms and the claims of the present invention, unless otherwise stated.

[0124] The technical means disclosed in the scheme of the present invention are not limited to the technical means disclosed in the above technical means, but also include technical schemes composed of any combination of the above technical features. The above is a specific implementation of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also regarded as the protection scope of the present invention.

[0125] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A high thermal conductivity reaction sintered silicon carbide ceramic material, characterized in that: The silicon carbide ceramic material contains 65-75 vol% α-SiC, 10-20 vol% β-SiC and 5-20 vol% Si.

2. A high thermal conductivity reaction sintered silicon carbide ceramic material according to claim 1, characterized in that: The density of the silicon carbide ceramic material is 3.0-3.2 g / cm 3 , the open porosity is 0.15-0.35%, the residual Si content is 5-20 vol%, and the thermal conductivity is 143-220 W / (m·k).

3. A method for preparing the high thermal conductivity reaction sintered silicon carbide ceramic material as claimed in claim 1, characterized in that: The method comprises the following steps: S1, adding SiC powder to resorcinol formaldehyde solution to obtain a mixed solution, and then ball milling to obtain a slurry; S2, after vacuum degassing, pour the slurry into a mold and seal it, and obtain a solidified body after gelation and normal pressure drying; S3, carbonizing the solidified body to obtain a preform; S4. Spread silicon particles on the preform and perform high-temperature infiltration in a vacuum, and finally obtain a high-strength and tough reaction-sintered boron carbide ceramic composite material by cooling.

4. The method for preparing a high thermal conductivity reaction-sintered silicon carbide ceramic material according to claim 3, characterized in that: The resorcinol formaldehyde solution is prepared by mixing a catalyst, resorcinol and formaldehyde, wherein the molar ratio of the resorcinol, the formaldehyde and the catalyst is 1:(1-3):(0.001-0.01).

5. The method for preparing a high thermal conductivity reaction-sintered silicon carbide ceramic material according to claim 3, characterized in that: The SiC powder is graded according to the mass ratio, with an average particle size of 20 to 50 μm: an average particle size of 5 to 10 μm: an average particle size of 0.3 to 1 μm = (5 to 7): 1: (2 to 4).

6. The method for preparing a high thermal conductivity reaction-sintered silicon carbide ceramic material according to claim 3, characterized in that: The gelation temperature of step S2 is 50-90° C., the insulation time is 6-24 hours, and the drying temperature is 110-150° C., and the drying time is 6-24 hours.

7. The method for preparing a high thermal conductivity reaction-sintered silicon carbide ceramic material according to claim 3, characterized in that: In step S3, the carbonization treatment temperature is 1100-1600° C., the carbonization holding time is 2-4 hours, and the heating rate is 1-5° C. / min.

8. The method for preparing a high thermal conductivity reaction-sintered silicon carbide ceramic material according to claim 3, characterized in that: Step S3: The preform has a nanoporous structure, the pore size is unimodal, the pore size range is 5-200nm, the carbon content is 10-20wt%, and the volume density is 1.5-2.0g / cm 3 , the open porosity is 20-30%.

9. The method for preparing a high thermal conductivity reaction-sintered silicon carbide ceramic material according to claim 3, characterized in that: The particle size of silicon powder is 1 to 5 mm. In order to allow the infiltration reaction to proceed fully, the actual amount of silicon particles added is ≥ 1.5 times the theoretical amount.

10. The method for preparing a high thermal conductivity reaction-sintered silicon carbide ceramic material according to claim 3, characterized in that: The high temperature infiltration reaction is heated to 1650-1850°C at a rate of 1-10°C / min, and the holding time is 0.5-6h.

Images