A high thermal conductivity graphite material with SiC nanowire-modified SiC-ZrC coating and preparation method thereof

Abstract

The present application relates to the field of preparation of high thermal conductivity graphite materials. In view of the fact that the difference in thermal expansion coefficients between the SiC-ZrC ceramic coating and the Zr-Si-O oxide protective layer formed after oxidation and the graphite substrate will affect the bonding between the coating and the graphite, thereby reducing the thermal protection effect of the coating, the present application discloses a high thermal conductivity graphite material with a SiC nanowire-modified SiC-ZrC coating, comprising a substrate, a transition inner layer and an outer coating; the substrate is high thermal conductivity graphite, the transition inner layer is a network layer composed of SiC nanowires, the outer coating is a SiC-ZrC coating, and the SiC nanowires are directly grown on the surface of the high thermal conductivity graphite substrate, the SiC-ZrC outer coating wraps the SiC nanowires and fills the pores of the network layer to obtain a dense high thermal conductivity graphite material with a SiC nanowire-modified SiC-ZrC coating. The high thermal conductivity graphite with a SiC nanowire-modified SiC-ZrC coating proposed by the present invention has ablation resistance far superior to that of single high thermal conductivity graphite and high thermal conductivity graphite without SiC nanowire-modified SiC-ZrC coating.

Description

Technical Field

[0001] The present invention relates to the field of preparation of high thermal conductivity graphite materials, and in particular to a high thermal conductivity graphite material of a SiC nanowire-modified SiC-ZrC coating and a preparation method thereof. Background Art

[0002] High thermal conductivity graphite material has low density, high strength, high modulus, and a low coefficient of thermal expansion. Its mechanical properties improve rather than decrease at high temperatures. Furthermore, its high thermal conductivity allows for rapid heat transfer within the graphite material, dispersing excess heat from heated areas to other parts, reducing temperature differences between different parts of the material and exhibiting excellent thermal shock resistance. Therefore, high thermal conductivity graphite is considered one of the most promising candidate materials for high-temperature thermal structural components in the aerospace industry. High thermal conductivity graphite, a material composed of a single carbon element, is commonly found in nature and exhibits very stable physical and chemical properties at room temperature, low temperatures, or in the absence of oxygen.

[0003] However, in an oxygen environment with a temperature of 400°C, high thermal conductivity graphite materials begin to oxidize, and as the ambient temperature rises, the oxidation phenomenon becomes more serious, and eventually the material fails, which limits the application of high thermal conductivity graphite materials in high-temperature oxygen environments.

[0004] To enhance the thermal protection of graphite, the preparation of ultra-high-temperature ceramic composite coatings on their surfaces is an effective approach. SiC-ZrC composite coatings are a typical example. The high-temperature Zr-Si-O phase formed by oxidation of SiC-ZrC has an extremely low oxygen diffusion rate, providing excellent protection for graphite. However, the difference in thermal expansion coefficients between the SiC-ZrC ceramic coating, the Zr-Si-O oxide protective layer formed after oxidation, and the graphite substrate can affect the bonding between the coating and the graphite, reducing the coating's thermal protection effectiveness.

[0005] In order to alleviate the difference in thermal expansion coefficient between the ultra-high temperature ceramic coating and the substrate material, it is an effective method to prepare a SiC nanowire network layer between the coating and the substrate. Literature 1 "Wang C, Guo B, Lu P, Xu Q, Tu R, Kosinova M, et al. Fabrication of porous SiC nanostructured coatings on C / C composite by laser chemical vapor deposition for improving the thermal shock resistance. Ceramics International. 2022; 48(9): 12450-9." reports a SiC coating toughened by SiC nanowires prepared on the surface of C / C composite material by laser chemical vapor deposition. This technology shows that compared with the SiC coating without the introduction of SiC nanowires, the thermal expansion coefficient of the SiC coating modified with SiC nanowires is significantly reduced. At 1000℃, the thermal expansion coefficient of the SiC coating without the introduction of SiC nanowires is 5.80×10 -6 ℃ -1 , while the thermal expansion coefficient of the SiC coating modified with SiC nanowires is 2.69×10 -6 ℃ -1; Document 2 "Zhuang L, Fu QG, Yu X. Improved thermal shock resistance of SiCnw / PyC core-shell structure-toughened CVD-SiC coating. Journal of the European Ceramic Society. 2018; 38(7): 2808-14." reports a SiC coating modified with SiC nanowire / pyrolytic carbon core-shell structure prepared on the surface of C / C composite material using traditional chemical vapor deposition method. This technology shows that after 8 thermal cycles between 1773K and room temperature, the mass loss of the SiC nanowire-modified SiC coating is only 0.07%, while the mass loss of the pure SiC coating is 2.62%; Literature 3 "Tong M, Fu Q, Yao S, LiuT, Feng T, Hu D, et al. A novel HfSiO wire drawing phenomenon after ablation of SiCnws / HfC-SiC coating on C / C composites. Journal of Materiomics. 2020; 6(2): 263-73." reports a SiC nanowire-modified HfC-SiC composite coating prepared on the surface of C / C composite material by a two-step chemical vapor deposition method. This technology shows that after modification with SiC nanowires, the fracture toughness of the composite coating increases from 4.2±0.5MPa·m 1 / 2 Increased to 13.8±3.2MPa·m 1 / 2 . After 60 seconds of ablation under an oxyacetylene flame, the linear ablation rate and mass ablation rate of the C / C composite material of SiC nanowires / HfC-SiC coating were -0.67±0.08μm / s and -0.20±0.03mg / s, respectively. These reports show that the introduction of SiC nanowires can not only alleviate the difference in thermal expansion coefficient between the coating and the substrate, but also improve the brittleness of the ceramic coating and enhance the bonding strength between the substrate and the coating. However, at present, such technology is mainly used for thermal protection of C / C composites. Because graphite material has a higher density than C / C composites and its surface is smoother, the graphite matrix lacks active sites for the growth of SiC nanowires. It is more challenging to prepare SiC-ZrC ceramic protective coatings on its surface, and the thermal expansion coefficient difference between the coating and the graphite coating is obvious. Summary of the Invention

[0006] In view of the above, the technical problems that this application aims to solve are how to improve the brittleness of SiC-ZrC coatings, how to quickly transfer the heat on the coating surface to the high thermal conductivity graphite substrate through SiC nanowires, and how to improve the ablation resistance of the high thermal conductivity graphite material of the SiC nanowire-modified SiC-ZrC coating;

[0007] On the one hand, the present application provides a high thermal conductivity graphite material of a SiC nanowire-modified SiC-ZrC coating, comprising a substrate, a transition inner layer and an outer coating; the substrate is high thermal conductivity graphite, the transition inner layer is a network layer composed of SiC nanowires, the outer coating is a SiC-ZrC coating, and the SiC nanowires are directly grown on the surface of the high thermal conductivity graphite substrate, the SiC-ZrC outer coating wraps the SiC nanowires and fills the pores of the network layer, thereby obtaining a dense SiC nanowire-modified SiC-ZrC coating high thermal conductivity graphite material.

[0008] On the other hand, the present application provides a method for preparing the high thermal conductivity graphite material, comprising the following steps:

[0009] Step 1: Pretreatment of high thermal conductivity graphite substrate;

[0010] Step 2: uniformly growing a SiC nanowire network layer on the surface of the pretreated high thermal conductivity graphite substrate by chemical vapor deposition;

[0011] Step 3: Wrap the SiC nanowires with the SiC-ZrC outer coating by embedding, and fill the pores of the network layer.

[0012] Preferably, step 1 includes the following sub-steps:

[0013] S1. Polish the surface of the processed high thermal conductivity graphite substrate, clean it with ultrasonic cleaning, and then dry it in a 120°C oven;

[0014] S2. Place the high thermal conductivity graphite substrate in a tubular furnace, turn on the vacuum pump, evacuate the furnace until the pressure is below 200 Pa, close the air inlet and outlet of the tubular furnace and maintain the pressure for 20 minutes, check that the pressure in the tubular furnace reaches the standard, then introduce argon gas into the furnace to normal pressure, turn off the vacuum pump, control the argon flow rate to 500 mL / min, and heat the high temperature zone of the tubular furnace to 800-1000°C at a rate of 6-12°C / min;

[0015] S3. After the tubular furnace reaches the set temperature, turn on the vacuum pump and stop introducing argon. Evacuate the furnace until the pressure is below 200 Pa. After maintaining the pressure for 20 minutes, pass air. Adjust the air inlet and outlet valves to control the pressure in the furnace to be stable at 2500-7500 Pa. After keeping warm for 10-30 minutes, stop heating, stop introducing air, and re-introduce argon until the pressure in the furnace is normal pressure. Turn off the vacuum pump, cool to room temperature, and obtain the pretreated high thermal conductivity graphite substrate.

[0016] Preferably, step 2 includes the following sub-steps:

[0017] S4, suspending the pretreated high thermal conductivity graphite substrate above the graphite crucible, evenly spreading a mixed powder of SiO2 powder and Si powder on the bottom of the graphite crucible, and covering the graphite crucible with a lid;

[0018] S5. Place the graphite crucible in a high-temperature heat treatment furnace, turn on the vacuum pump, pump the pressure in the furnace to below 500 Pa, close the air inlet and outlet of the high-temperature heat treatment furnace and maintain the pressure for 20 minutes. After checking that the pressure in the furnace reaches the standard, introduce argon gas into the furnace to normal pressure, and increase the temperature of the high-temperature zone of the high-temperature heat treatment furnace to 1300-1500°C at a heating rate of 4-6°C / min, and keep it warm for 0.5-2 hours. Control the argon flow rate to 500 mL / min.

[0019] S6. After the heat preservation is completed, the power is turned off and the furnace is naturally cooled to room temperature to obtain a high thermal conductivity graphite substrate with a uniformly grown SiC nanowire network layer.

[0020] Preferably, step 3 includes the following sub-steps:

[0021] S7, placing the high thermal conductivity graphite substrate with SiC nanowires grown on the surface in a graphite crucible with the mixed powder evenly spread on the bottom, and then filling the graphite crucible with the mixed powder of Si powder, C powder and ZrC powder and compacting it;

[0022] S8. Place the graphite crucible in a high-temperature sintering furnace, turn on the vacuum pump, reduce the pressure in the furnace to below 500 Pa, close the air inlet and outlet of the high-temperature heat treatment furnace and maintain the pressure for 20 minutes. After checking that the pressure in the furnace reaches the standard, introduce argon gas into the furnace to normal pressure, increase the temperature of the high-temperature zone of the high-temperature sintering furnace to 1800-2000°C at a heating rate of 4-6°C / min, and maintain the temperature for 0.5-2 hours. Control the argon flow rate to 500 mL / min.

[0023] S9. After the heat preservation is completed, the power is turned off and the furnace is naturally cooled to room temperature to obtain high thermal conductivity graphite with SiC nanowire modified SiC-ZrC coating.

[0024] Preferably, the mixed powder of SiO2 powder and Si powder is obtained by grinding and mixing SiO2 powder and Si powder in a mass fraction ratio of 1:1.

[0025] Preferably, the mixed powder of Si powder, C powder and ZrC powder is obtained by grinding and uniformly mixing Si powder, C powder and ZrC powder in a mass fraction ratio of 6:2:2.

[0026] Preferably, the sandpaper used for polishing the S1 surface is 80 mesh, 300 mesh, 600 mesh, 1000 mesh, 1500 mesh and 2000 mesh, respectively.

[0027] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0028] The present invention proposes a high thermal conductivity graphite material with a SiC nanowire-modified SiC-ZrC coating and a preparation method. By utilizing the directional air flow during negative pressure pre-oxidation, the surface roughness of the high thermal conductivity graphite is uniformly controlled, providing sufficient active sites for the growth of SiC nanowires and precisely controlling their uniform growth.

[0029] By utilizing the characteristics of SiC thermal expansion coefficient being close to that of graphite materials and the one-dimensional linear characteristics of SiC nanowires, the difference in thermal expansion coefficient between the SiC-ZrC coating and the high thermal conductivity graphite substrate is alleviated, the bonding strength between the coating and the substrate is strengthened, and the brittleness of the SiC-ZrC coating is improved;

[0030] By utilizing the high thermal conductivity of SiC nanowires and the thermal conductivity advantages of the high thermal conductivity graphite substrate, the heat on the ablation surface is quickly transferred from the SiC-ZrC outer coating through the SiC nanowire network to other parts of the high thermal conductivity graphite substrate, thereby reducing the temperature of the ablation surface during the material ablation process, balancing the overall heat distribution of the material, and thereby improving the ablation resistance of the high thermal conductivity graphite material of the SiC nanowire-modified SiC-ZrC coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be considered as limiting the scope. A person of ordinary skill in the art can also derive other relevant drawings based on these drawings without inventive effort.

[0032] Figure 1 : Flow chart of the method of the present invention;

[0033] Figure 2 : Structural design diagram of the high thermal conductivity graphite material of SiC nanowire modified SiC-ZrC coating of the present invention;

[0034] Figure 3 : SEM image of the surface of the high thermal conductivity graphite of the present invention;

[0035] Figure 4 : SEM image of the surface of the high thermal conductivity graphite after pre-oxidation of the present invention;

[0036] Figure 5: Surface SEM image of SiC nanowires grown on pre-oxidized high thermal conductivity graphite of the present invention;

[0037] Figure 6 : Cross-sectional SEM image of SiC nanowires grown on pre-oxidized high thermal conductivity graphite of the present invention;

[0038] Figure 7 : SEM image of the surface of the high thermal conductivity graphite material of the SiC nanowire-modified SiC-ZrC coating in Example 1 of the present invention;

[0039] Figure 8 : Cross-sectional SEM image of the high thermal conductivity graphite material of SiC nanowire-modified SiC-ZrC coating in Example 1 of the present invention;

[0040] Figure 9 : Macroscopic photograph of the high thermal conductivity graphite material of the SiC nanowire-modified SiC-ZrC coating in Example 1 of the present invention after ablation for 120 seconds;

[0041] Figure 10 : Macroscopic photograph of the high thermal conductivity graphite material of the SiC nanowire-modified SiC-ZrC coating in Example 1 of the present invention after ablation for 240 seconds;

[0042] Figure 11 : SEM image of the ablation center of the high thermal conductivity graphite material of the SiC nanowire-modified SiC-ZrC coating in Example 1 of the present invention after ablation for 120 seconds;

[0043] Figure 12 : SEM image of the ablation center of the high thermal conductivity graphite material of the SiC nanowire-modified SiC-ZrC coating in Example 1 of the present invention after ablation for 240s. DETAILED DESCRIPTION

[0044] In order to make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present invention and are not intended to limit the present invention. That is, the embodiments described herein are only some embodiments of the present invention, not all embodiments. Generally, the components of the embodiments of the present invention described and illustrated in the drawings herein may be arranged and designed in various different configurations.

[0045] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but is merely intended to represent selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0046] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element.

[0047] Example 1:

[0048] 1) Pre-treating the high thermal conductivity graphite substrate;

[0049] S1: polishing the high thermal conductivity graphite substrate using 80 mesh, 300 mesh, 600 mesh, 1000 mesh, 1500 mesh and 2000 mesh sandpaper in sequence, ultrasonically cleaning the polished high thermal conductivity graphite substrate, and drying it in a 120°C oven after cleaning;

[0050] S2: Place the high thermal conductivity graphite substrate dried in S1 into a tubular furnace, turn on the vacuum pump, evacuate the furnace until the pressure is below 200 Pa, close the air inlet and outlet of the tubular furnace and maintain the pressure for 20 minutes. After checking that the pressure in the tubular furnace reaches the standard, introduce argon gas into the furnace to normal pressure, turn off the vacuum pump, control the argon flow rate to 500 mL / min, and raise the temperature of the high temperature zone of the tubular furnace to 900°C at a rate of 6°C / min;

[0051] S3: After the tubular furnace reaches 900°C set in S2, the vacuum pump is turned on and the introduction of argon is stopped. The furnace is evacuated until the pressure is below 200 Pa. After maintaining the pressure for 20 minutes, air is passed through. The inlet and outlet valves are adjusted to control the pressure in the furnace to be stable at 5000 Pa. After maintaining the temperature for 20 minutes, heating is stopped, the introduction of air is stopped, and argon is reintroduced until the pressure in the furnace is at normal pressure. The vacuum pump is turned off, and the furnace is cooled to room temperature to obtain a pretreated high thermal conductivity graphite substrate.

[0052] 2) Preparation of SiC nanowire network layer:

[0053] S4: The pretreated high thermal conductivity graphite is suspended above the graphite crucible, and the bottom of the graphite crucible is evenly spread with a mixture of SiO2 powder and Si powder with a mass fraction of 1:1, and the graphite crucible is covered with a lid to seal it;

[0054] S5: Place the graphite crucible in a high-temperature heat treatment furnace, turn on the vacuum pump, pump the pressure in the furnace to below 500 Pa, close the air inlet and outlet of the high-temperature heat treatment furnace and maintain the pressure for 20 minutes. After checking that the pressure in the furnace reaches the standard, introduce argon gas into the furnace to normal pressure, and increase the temperature of the high-temperature zone of the high-temperature heat treatment furnace to 1400°C at a heating rate of 4°C / min. Maintain the temperature for 1 hour, and control the argon flow rate to 500 mL / min.

[0055] S6: After the heat preservation is completed, the power is turned off and the furnace is naturally cooled to room temperature to obtain a high thermal conductivity graphite with a uniformly grown SiC nanowire network layer;

[0056] 3) Preparation of SiC-ZrC outer coating:

[0057] S7: placing the high thermal conductivity graphite with SiC nanowires grown on the surface in a graphite crucible with a mixed powder of Si, C and ZrC in a mass fraction of 6:2:2 evenly spread on the bottom, and then filling the graphite crucible with the mixed powder and compacting it;

[0058] S8: Place the graphite crucible in a high-temperature sintering furnace, turn on the vacuum pump, reduce the pressure in the furnace to below 500 Pa, close the air inlet and outlet of the high-temperature heat treatment furnace and maintain the pressure for 20 minutes. After checking that the pressure in the furnace reaches the standard, introduce argon gas into the furnace to normal pressure, and increase the temperature of the high-temperature zone of the high-temperature sintering furnace to 1900°C at a heating rate of 6°C / min. Maintain the temperature for 1 hour, and control the argon flow rate to 500 mL / min.

[0059] S9: After the insulation is completed, the power is turned off and the furnace is naturally cooled to room temperature to obtain high thermal conductivity graphite with SiC nanowire modified SiC-ZrC coating.

[0060] Example 2:

[0061] 1) Pretreatment of high thermal conductivity graphite substrate

[0062] S1: Use 80 mesh, 300 mesh, 600 mesh, 1000 mesh, 1500 mesh and 2000 mesh sandpaper to polish the high thermal conductivity graphite substrate, ultrasonically clean it and then dry it in a 120℃ oven;

[0063] S2: Place the high thermal conductivity graphite substrate dried in S1 into a tubular furnace, turn on the vacuum pump, evacuate the furnace until the pressure is below 200 Pa, close the air inlet and outlet of the tubular furnace and maintain the pressure for 20 minutes. After checking that the pressure in the tubular furnace reaches the standard, introduce argon gas into the furnace to normal pressure, turn off the vacuum pump, control the argon flow rate to 500 mL / min, and raise the temperature of the high temperature zone of the tubular furnace to 800°C at a rate of 9°C / min;

[0064] S3: After the tubular furnace reaches 800°C set in S2, turn on the vacuum pump and stop introducing argon. Evacuate the furnace until the pressure is below 200 Pa. After maintaining the pressure for 20 minutes, pass air. Adjust the air inlet and outlet valves to control the pressure in the furnace to be stable at 7500 Pa. After maintaining the temperature for 30 minutes, stop heating, stop introducing air, and re-introduce argon until the pressure in the furnace is at normal pressure. Turn off the vacuum pump, cool to room temperature, and obtain a pretreated high thermal conductivity graphite substrate.

[0065] 2) Preparation of SiC nanowire network layer:

[0066] S4: The pretreated high thermal conductivity graphite is suspended above the graphite crucible, and the bottom of the graphite crucible is evenly spread with a mixture of SiO2 powder and Si powder with a mass fraction of 1:1, and the graphite crucible is covered with a lid to seal it;

[0067] S5: Place the graphite crucible in a high-temperature heat treatment furnace, turn on the vacuum pump, pump the pressure in the furnace to below 500 Pa, close the air inlet and outlet of the high-temperature heat treatment furnace and maintain the pressure for 20 minutes. After checking that the pressure in the furnace reaches the standard, introduce argon gas into the furnace to normal pressure, and increase the temperature of the high-temperature zone of the high-temperature heat treatment furnace to 1500°C at a heating rate of 5°C / min. Maintain the temperature for 0.5 hours, and control the argon flow rate to 500 mL / min.

[0068] S6: After the heat preservation is completed, the power is turned off and the furnace is naturally cooled to room temperature to obtain a high thermal conductivity graphite with a uniformly grown SiC nanowire network layer;

[0069] 3) Preparation of SiC-ZrC outer coating:

[0070] S7: placing the high thermal conductivity graphite with SiC nanowires grown on the surface in a graphite crucible with a mixed powder of Si, C and ZrC in a mass fraction of 6:2:2 evenly spread on the bottom, and then filling the graphite crucible with the mixed powder and compacting it;

[0071] S8: Place the graphite crucible in a high-temperature sintering furnace, turn on the vacuum pump, pump the pressure in the furnace to below 500 Pa, close the air inlet and outlet of the high-temperature heat treatment furnace and maintain the pressure for 20 minutes. After checking that the pressure in the furnace reaches the standard, introduce argon gas into the furnace to normal pressure, and increase the temperature of the high-temperature zone of the high-temperature sintering furnace to 1800°C at a heating rate of 5°C / min. Maintain the temperature for 2 hours, and control the argon flow rate to 500 mL / min.

[0072] S9: After the insulation is completed, the power is turned off and the furnace is naturally cooled to room temperature to obtain high thermal conductivity graphite with SiC nanowire modified SiC-ZrC coating.

[0073] Example 3:

[0074] 1) Pretreatment of high thermal conductivity graphite substrate

[0075] S1: Use 80 mesh, 300 mesh, 600 mesh, 1000 mesh, 1500 mesh and 2000 mesh sandpaper to polish the high thermal conductivity graphite substrate, ultrasonically clean it and then dry it in a 120℃ oven;

[0076] S2: Place the high thermal conductivity graphite substrate dried in S1 into a tubular furnace, turn on the vacuum pump, evacuate the furnace until the pressure is below 200 Pa, close the air inlet and outlet of the tubular furnace and maintain the pressure for 20 minutes. After checking that the pressure in the tubular furnace reaches the standard, introduce argon gas into the furnace to normal pressure, turn off the vacuum pump, control the argon flow rate to 500 mL / min, and heat the high temperature zone of the tubular furnace to 1000°C at a rate of 12°C / min;

[0077] S3: After the tubular furnace reaches 1000°C set in S2, turn on the vacuum pump and stop introducing argon gas. Evacuate the furnace until the pressure is below 200 Pa. After maintaining the pressure for 20 minutes, pass air. Adjust the air inlet and outlet valves to control the pressure in the furnace to be stable at 2500 Pa. After maintaining the temperature for 10 minutes, stop heating, stop introducing air, and re-introduce argon gas until the pressure in the furnace is at normal pressure. Turn off the vacuum pump, and cool to room temperature to obtain a pretreated high thermal conductivity graphite substrate.

[0078] 2) Preparation of SiC nanowire network layer:

[0079] S4: The pretreated high thermal conductivity graphite is suspended above the graphite crucible, and the bottom of the graphite crucible is evenly spread with a mixture of SiO2 powder and Si powder with a mass fraction of 1:1, and the graphite crucible is covered with a lid to seal it;

[0080] S5: Place the graphite crucible in a high-temperature heat treatment furnace, turn on the vacuum pump, pump the pressure in the furnace to below 500 Pa, close the air inlet and outlet of the high-temperature heat treatment furnace and maintain the pressure for 20 minutes. After checking that the pressure in the furnace reaches the standard, introduce argon gas into the furnace to normal pressure, and increase the temperature of the high-temperature zone of the high-temperature heat treatment furnace to 1300°C at a heating rate of 6°C / min. Maintain the temperature for 2 hours, and control the argon flow rate to 500 mL / min.

[0081] S6: After the heat preservation is completed, the power is turned off and the furnace is naturally cooled to room temperature to obtain a high thermal conductivity graphite with a uniformly grown SiC nanowire network layer;

[0082] 3) Preparation of SiC-ZrC outer coating:

[0083] S7: placing the high thermal conductivity graphite with SiC nanowires grown on the surface in a graphite crucible with a mixed powder of Si, C and ZrC in a mass fraction of 6:2:2 evenly spread on the bottom, and then filling the graphite crucible with the mixed powder and compacting it;

[0084] S8: Place the graphite crucible in a high-temperature sintering furnace, turn on the vacuum pump, reduce the pressure in the furnace to below 500 Pa, close the air inlet and outlet of the high-temperature heat treatment furnace and maintain the pressure for 20 minutes. After checking that the pressure in the furnace reaches the standard, introduce argon gas into the furnace to normal pressure, and increase the temperature of the high-temperature zone of the high-temperature sintering furnace to 2000°C at a heating rate of 4°C / min. Maintain the temperature for 0.5 hours, and control the argon flow rate to 500 mL / min.

[0085] S9: After the insulation is completed, the power is turned off and the furnace is naturally cooled to room temperature to obtain high thermal conductivity graphite with SiC nanowire modified SiC-ZrC coating.

[0086] The working principle of this application is that through the negative pressure pre-oxidation treatment technology, a uniform airflow with directional flow can be provided. The pre-oxidation process can be regulated to achieve precise control of the surface roughness of the high thermal conductivity graphite substrate, such as Figure 3 As shown, the SiC-ZrC coating forms a mechanical bite with the high thermal conductivity graphite substrate, thereby improving the coating bonding strength; the SiC-ZrC coating and the high thermal conductivity graphite substrate form a gradient distribution at the bonding interface, thereby alleviating the difference in thermal expansion coefficient; and providing more active sites, such as Figure 4 The SEM image of SiC nanowires grown on the surface of a pre-oxidized high thermal conductivity graphite substrate is shown. The SiC nanowires overlap each other to form a network structure. The structural characteristics of the SiC nanowire network layer can alleviate the difference in thermal expansion coefficient between the SiC-ZrC coating and the high thermal conductivity graphite substrate, strengthen the bonding strength between the coating and the substrate, and improve the brittleness of the SiC-ZrC coating. The high thermal conductivity of the SiC nanowires and the thermal conductivity advantage of the high thermal conductivity graphite substrate are utilized to quickly transfer the heat of the ablation surface from the SiC-ZrC outer coating to other parts of the high thermal conductivity graphite substrate through the SiC nanowire network, thereby reducing the temperature of the ablation surface during the material ablation process and balancing the overall heat distribution of the material, thereby improving the ablation resistance of the high thermal conductivity graphite material of the SiC nanowire-modified SiC-ZrC coating.

[0087] Figure 5 The surface and cross-sectional SEM images of the high thermal conductivity graphite substrate material of the SiC nanowire-modified SiC-ZrC coating in Example 1 show that the outer coating completely wraps around the SiC nanowires, the coating is dense and crack-free, and the coating is well bonded to the high thermal conductivity graphite substrate.

[0088] Figure 6 These are macroscopic photographs of the high thermal conductivity graphite substrate material of the SiC nanowire-modified SiC-ZrC coating in Example 1 after ablation for 120s and 240s. Figure 7 This is the SEM image of its ablation center. The material as a whole shows excellent ablation resistance.

[0089] The comparison of the ablation of single high thermal conductivity graphite and high thermal conductivity graphite substrate without SiC nanowire modified SiC-ZrC coating and high thermal conductivity graphite substrate with SiC nanowire modified SiC-ZrC coating prepared in Examples 1, 2 and 3 of the present invention under 2300°C plasma flame is shown in the following table:

[0090]

[0091] The high thermal conductivity graphite substrate with SiC nanowire-modified SiC-ZrC coating proposed in the present invention has ablation resistance far superior to that of single high thermal conductivity graphite and high thermal conductivity graphite substrate without SiC nanowire-modified SiC-ZrC coating.

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements 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 high thermal conductivity graphite material with SiC nanowire-modified SiC-ZrC coating, characterized in that: Here are the steps: Step 1: Pretreatment of high thermal conductivity graphite substrate; Step 2: uniformly growing a SiC nanowire network layer on the surface of the pretreated high thermal conductivity graphite substrate by chemical vapor deposition; Step 3: Encapsulating the SiC nanowires with a SiC-ZrC outer coating to fill the pores of the network layer; Step 1 includes the following sub-steps: S1. Polish the surface of the processed high thermal conductivity graphite substrate, clean it with ultrasonic cleaning, and then dry it in a 120°C oven; S2. Place the high thermal conductivity graphite substrate in a tube furnace, turn on the vacuum pump, and evacuate the furnace until the pressure is below 200 Pa. Close the air inlet and outlet of the tube furnace and maintain the pressure for 20 minutes. After checking that the pressure in the tube furnace reaches the standard, introduce argon gas into the furnace to normal pressure. Turn off the vacuum pump, control the argon flow rate to 500 mL / min, and heat the high temperature zone of the tube furnace to 800-1000°C at a rate of 6-12°C / min. S3. After the tubular furnace reaches the set temperature, turn on the vacuum pump and stop introducing argon. Evacuate the furnace until the pressure is below 200 Pa. After maintaining the pressure for 20 minutes, pass air. Adjust the air inlet and outlet valves to control the pressure in the furnace to be stable at 2500~7500 Pa. After keeping warm for 10~30 minutes, stop heating, stop introducing air, and re-introduce argon until the pressure in the furnace is at normal pressure. Turn off the vacuum pump, and cool to room temperature to obtain the pretreated high thermal conductivity graphite substrate.

2. The method for preparing the high thermal conductivity graphite material according to claim 1, wherein: Step 2 includes the following sub-steps: S4, suspending the pretreated high thermal conductivity graphite substrate above the graphite crucible, evenly spreading a mixed powder of SiO2 powder and Si powder on the bottom of the graphite crucible, and covering the graphite crucible with a lid; S5. Place the graphite crucible in a high-temperature heat treatment furnace, turn on the vacuum pump, reduce the pressure in the furnace to below 500 Pa, close the air inlet and outlet of the high-temperature heat treatment furnace and maintain the pressure for 20 minutes. After checking that the pressure in the furnace reaches the standard, introduce argon gas into the furnace to normal pressure, and increase the temperature of the high-temperature zone of the high-temperature heat treatment furnace to 1300-1500°C at a heating rate of 4-6°C / min. Maintain the temperature for 0.5-2 hours, and control the argon flow rate to 500 mL / min. S6. After the heat preservation is completed, the power is turned off and the furnace is naturally cooled to room temperature to obtain a high thermal conductivity graphite substrate with a uniformly grown SiC nanowire network layer.

3. The method for preparing the high thermal conductivity graphite material according to claim 1, wherein: Step 3 includes the following sub-steps: S7, placing the high thermal conductivity graphite substrate with SiC nanowires grown on the surface in a graphite crucible with the mixed powder evenly spread on the bottom, and then filling the graphite crucible with the mixed powder of Si powder, C powder and ZrC powder and compacting it; S8. Place the graphite crucible in a high-temperature sintering furnace, turn on the vacuum pump, and reduce the pressure in the furnace to below 500 Pa. Close the air inlet and outlet of the high-temperature heat treatment furnace and maintain the pressure for 20 minutes. After checking that the pressure in the furnace reaches the standard, introduce argon gas into the furnace to normal pressure. Raise the temperature of the high-temperature zone of the high-temperature sintering furnace to 1800-2000°C at a heating rate of 4-6°C / min, and maintain the temperature for 0.5-2 hours. Control the argon gas flow rate at 500 mL / min. S9. After the heat preservation is completed, the power is turned off and the furnace is naturally cooled to room temperature to obtain high thermal conductivity graphite with SiC nanowire modified SiC-ZrC coating.

4. The method for preparing the high thermal conductivity graphite material according to claim 2, wherein: The mixed powder of SiO2 powder and Si powder is obtained by grinding and mixing SiO2 powder and Si powder in a mass fraction ratio of 1:

1.

5. The method for preparing the high thermal conductivity graphite material according to claim 3, wherein: The mixed powder of Si powder, C powder and ZrC powder is obtained by grinding and uniformly mixing Si powder, C powder and ZrC powder in a mass fraction ratio of 6:2:

2.

6. The method for preparing the high thermal conductivity graphite material according to claim 1, wherein: The sandpaper used for polishing the S1 surface is 80 mesh, 300 mesh, 600 mesh, 1000 mesh, 1500 mesh and 2000 mesh, respectively.

7. A high thermal conductivity graphite material with SiC nanowire-modified SiC-ZrC coating prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The method comprises a substrate, a transition inner layer and an outer coating; the substrate is high thermal conductivity graphite, the transition inner layer is a network layer composed of SiC nanowires, the outer coating is a SiC-ZrC coating, and the SiC nanowires are directly grown on the surface of the high thermal conductivity graphite substrate, the SiC-ZrC outer coating wraps the SiC nanowires and fills the pores of the network layer, thereby obtaining a dense SiC nanowire-modified SiC-ZrC coating high thermal conductivity graphite material.

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