Regenerated carbon-ceramic composite thermal protection material for recovering carbon-carbon material based on photovoltaic thermal field and preparation method of regenerated carbon-ceramic composite thermal protection material

Abstract

The invention discloses a regenerated carbon-ceramic composite thermal protection material for recovering a carbon-carbon material based on a photovoltaic thermal field and a preparation method of the regenerated carbon-ceramic composite thermal protection material. The waste C / C material is converted into the quaternary composite system thermal protection material containing regenerated short carbon fiber, cracked carbon, silicon carbide and silicon through the processes of crushing, mixing, hot press molding, carbonization, melting siliconizing and the like. The material realizes all-component recovery of the waste composite material, the cost is reduced by more than 60%, the waste utilization rate is greater than or equal to 95%, and the CO2 emission is reduced by 70%. The thermal conductivity is larger than or equal to 200 W / (m.K), the temperature resistance is larger than or equal to 1600 DEG C, excellent ablation resistance and oxidation resistance are achieved, and a green high-performance solution is provided for the photovoltaic and aerospace fields.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature composite materials, and particularly relates to a regenerated carbon-ceramic composite thermal protection material based on photovoltaic hot field recycled carbon-carbon materials and a preparation method thereof. Background Art

[0002] With the rapid development of the photovoltaic industry, a large number of photovoltaic hot field components such as single crystal furnace crucibles and heat preservation cylinders generate a large amount of carbon-carbon composite material (C / C) waste after completing their life cycles. Through investigation, it is found that more than 70% of the current research in the field of high-temperature composite materials focuses on preparing high-performance materials from brand-new raw materials, and only less than 10% involves recycling technologies, and these recycling technologies mainly target carbon-carbon composite materials in the aerospace field. The recycling of carbon-carbon composite materials in the aerospace field focuses on restoring the high-strength and high-modulus characteristics of the materials, while the recycling of photovoltaic hot field components pays more attention to the low cost, high thermal conductivity of the materials and the adaptability to the production process of the photovoltaic industry. There are significant differences in recycling requirements and technical paths between the two.

[0003] C / C composite materials have excellent high-temperature performance, but traditional treatment methods such as landfilling or incineration have many problems. On the one hand, this treatment method leads to the loss of high-value carbon fiber resources. Carbon fibers are difficult to degrade naturally, and landfilling will cause long-term idling of resources and land occupation. On the other hand, the incineration process not only releases a large amount of carbon dioxide, exacerbating the greenhouse effect, but also generates pollutants such as dust, causing a serious burden on the environment and contradicting the global carbon reduction goal.

[0004] Currently, most of the existing C / C composite material recycling technologies are limited to the extraction of single components, and it is difficult to achieve the efficient utilization of the entire life cycle of the materials. For example, the existing technology A only extracts carbon fibers through chemical dissolution, resulting in the resin matrix and other components being treated as waste; although technology B attempts to recycle as a whole, due to the lack of effective means for component reconstruction, the thermal conductivity of the obtained recycled material is only 120 W / (m·K), far lower than the actual application requirement of more than 180 W / (m·K) in the photovoltaic hot field. Moreover, these recycling technologies have complex technological processes and consume a large amount of energy during the recycling process, resulting in high recycling costs, which seriously restricts the development of circular economy in this field.

[0005] The introduction of silicon carbide (SiC) brings new ideas to solve the above problems. Research shows that SiC has multiple excellent properties in the material system. When serving at high temperatures, a dense silicon dioxide layer (SiO2) will form on the surface of SiC, which can significantly inhibit the diffusion of oxygen and provide long-term antioxidant protection for the material. As a rigid reinforcement, SiC inhibits crack propagation through the pinning effect, thereby improving the mechanical strength of the composite material. In addition, SiC has excellent interfacial compatibility with carbon fiber and pyrolytic carbon matrix, which can optimize the heat conduction path of the material and reduce the interfacial thermal resistance. In the recycled material involved in the present invention, the residual silicon (5-10%) can react with free carbon during the infiltration process to generate a new SiC phase, further filling the material pores and realizing the self-repair of material densification. By converting the retired photovoltaic thermal field material into a multi-component system of short carbon fiber - pyrolytic carbon - SiC, it can not only give a second life to the waste C / C material, but also upgrade the material performance through component reconstruction, while reducing the recycling cost, providing a green and sustainable development path for the high-temperature industry. Summary of the Invention

[0006] In view of the above technical problems, this application solves the problems of resource waste, environmental pollution, high recycling cost and low efficiency existing in the existing treatment methods of retired C / C materials in photovoltaic thermal fields. At the same time, it overcomes the technical prejudice in traditional cognition that recycled materials are difficult to achieve high performance.

[0007] To achieve the above object, the technical solution adopted in this application is: a regenerated carbon-ceramic composite thermal protection material based on recycled carbon-carbon materials in photovoltaic thermal fields, which is composed of the following quaternary composite system by mass percentage:

[0008] Recycled short carbon fiber: 30%, the length of the recycled short carbon fiber is 50-300 μm, and the diameter is 5-10 μm; when the length of the recycled short carbon fiber is less than 50 μm, it is impossible to effectively form a three-dimensional framework reinforcement structure, and the mechanical properties of the material will decrease by more than 20%; when the length is greater than 300 μm, agglomeration is likely to occur during the mixing and forming processes, resulting in uneven material properties. By selecting this length and diameter range in the present invention, it can fully cooperate with other components. Compared with simply using recycled carbon fiber in the prior art, this application can improve the thermal shock resistance of the material by 35% through precise control of the fiber size.

[0009] Pyrolytic carbon: 45%, the graphitization degree of the pyrolytic carbon ≥ 80%, and the specific surface area is 10-50m 2 / g; The pyrolytic carbon is the high-temperature pyrolysis product of the resin matrix of waste carbon fiber composites. Its high graphitization degree and porous structure formation process are remarkable. During the high-temperature pyrolysis process, by controlling the heating rate and pyrolysis time, the resin matrix is orderly transformed into pyrolytic carbon with a structure. This structure can not only reduce the material density by 15% as a filler, but also form chemical bonds with the fibers through surface active sites, and the interfacial bonding strength is increased by 40% compared with ordinary carbon fillers in the prior art.

[0010] Silicon carbide: 20%, and the average particle size of the silicon carbide is 0.5 - 5 μm; The silicon carbide within this particle size range can be evenly dispersed in the material and fully play a synergistic role with other components. Different from using silicon carbide with a single particle size in the prior art, in this application, by optimizing the particle size distribution, the high-temperature strength of the material is increased by 25%.

[0011] Silicon: 5%, and the purity of the silicon ≥ 99.9%, and the particle size is 1 - 10 μm. Silicon undergoes an in-situ reaction with pyrolytic carbon during sintering to generate nano-SiC whiskers to fill pores and consume free carbon simultaneously. When the purity of silicon is lower than 99.9%, impurities will affect the progress of the in-situ reaction, resulting in an 8% increase in the porosity of the material and a significant decline in performance; The present invention strictly controls the purity and particle size of silicon to achieve precise regulation of material densification.

[0012] To better implement the present invention, further, the recycled short carbon fibers serve as a three-dimensional framework reinforcement.

[0013] To better implement the present invention, further, the pyrolytic carbon is the high-temperature pyrolysis product of the resin matrix of waste carbon fiber composites, and has a high graphitization degree and a porous structure.

[0014] To better implement the present invention, further, silicon undergoes an in-situ reaction with pyrolytic carbon during sintering to generate nano-SiC whiskers to fill pores and consume free carbon simultaneously.

[0015] A preparation method of the aforementioned recycled carbon-ceramic composite thermal protection material, comprising the following steps:

[0016] Crushing: Mechanically crush the recycled photovoltaic thermal field retired C / C material into powder with a particle size ≤ 200 μm. The powder composition includes 25 - 35 wt% of short carbon fibers, 35 - 50 wt% of pyrolytic carbon, 15 - 25 wt% of SiC, and 5 - 10 wt% of silicon; When the crushing particle size is greater than 200 μm, the subsequent mixing uniformity decreases, resulting in an increased range of material property fluctuations; When the sieving rate is lower than 95%, the coarse particles will affect the forming quality and final performance of the material. The present invention strictly controls the crushing particle size and sieving rate to lay a foundation for the subsequent process.

[0017] Mixing: Add 2 - 5 wt% phenolic resin as a binder and ball mill for 2 - 4 hours to ensure uniform components. When the binder addition is less than 2 wt%, it is difficult to form the material; when it exceeds 5 wt%, it will increase the impurity content of the material and reduce the material performance. By optimizing the ball milling time and speed, the present application achieves sufficient and uniform mixing of each component, increasing the material performance consistency by 30%.

[0018] Hot press forming: In a vacuum hot press furnace, cure at a pressure of 30 - 60 MPa and a temperature of 180 - 220 °C for 1 - 2 hours to obtain a preform. When the pressure is less than 30 MPa, the density of the preform is insufficient and the strength is low; when the pressure is higher than 60 MPa, it may cause damage to the internal structure of the material. When the temperature is lower than 180 °C, the resin cures incompletely; when it is higher than 220 °C, the resin will decompose, affecting the material performance. The hot press pressure determined in the present invention is 50 MPa. Under this condition, the comprehensive performance of the preform is the best, and the strength is increased by 25% compared with other pressure settings.

[0019] Carbonization: Heat up to 900 °C at a rate of 5 °C / min in a nitrogen atmosphere and hold for 2 hours to pyrolyze the resin to form a porous carbon skeleton;

[0020] Molten silicon infiltration: At 1420 - 1600 °C under argon protection, molten silicon infiltrates into the pores and reacts with free carbon to form SiC. The reaction time is 2 - 4 hours, and finally the porosity of the material is ≤ 3%. When the silicon infiltration temperature is lower than 1420 °C, the fluidity of silicon is insufficient and it cannot fully infiltrate into the pores; when it is higher than 1600 °C, it will cause excessive reaction of the material and performance degradation. The silicon infiltration temperature determined in the present application is 1550 °C. At this temperature, the reaction rate is maximized, and the thermal conductivity of the material is increased by 20% compared with other temperature settings.

[0021] To better implement the present invention, further, in the crushing step, the crushing particle size is ≤ 200 μm and the sieving rate is ≥ 95%.

[0022] To better implement the present invention, further, in the hot press forming step, the hot press pressure is 50 MPa.

[0023] To better implement the present invention, further, in the molten silicon infiltration step, the silicon infiltration temperature is 1550 °C.

[0024] The regenerated carbon-ceramic composite thermal protection material can be applied to the fields of photovoltaic thermal field components or aerospace high-temperature resistant composite materials.

[0025] The technical solution provided by the present invention has the following beneficial effects compared with the prior art:

[0026] 1. The present invention directly utilizes short carbon fibers and in-situ generated silicon carbide in photovoltaic thermal field recycling materials, avoiding the high energy consumption process of separately synthesizing SiC and the procurement of new fibers, thereby reducing the raw material cost by 60%.

[0027] 2. In the preparation method of the present invention, the waste utilization rate is ≥95%. Compared with the traditional process, the CO2 emissions are reduced by 70%, effectively reducing the impact on the environment.

[0028] 3. The thermal conductivity of the regenerated material prepared by the present invention is ≥200 W / (m·K), and the temperature resistance is ≥1600 °C. It has excellent multi-level structure ablation resistance and antioxidant synergistic performance (residual silicon preferentially generates a SiO2 glass layer in a high-temperature oxidation environment (see Reaction Formula 1), covering the surface of SiC to prevent oxygen diffusion: SiC + 3O2 → SiO2 + CO2↑ (1)). In a simulated photovoltaic thermal field at a high temperature of 1500 °C, it continuously works for 100 hours, and the mass loss of the material is only 3%, while the mass loss of existing similar materials exceeds 15%; in the high-temperature oxidation environment test commonly used in the aerospace field, the antioxidant time of the material of the present invention is more than twice that of the existing materials. It can meet the application requirements in fields such as photovoltaic thermal fields and aerospace ablation-resistant components.

[0029] 4. Compared with the prior art, the existing carbon-carbon composite material recycling technology is limited to single-component extraction or simple mixing recycling. In this application, through the construction of a quaternary composite system, full-component recycling is achieved. In terms of the introduction and application of silicon carbide, the prior art does not consider using the in-situ reaction of residual silicon and other components in retired materials to achieve material densification and performance improvement. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following-described drawings are only some embodiments of the present application. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0031] Figure 1 It is a flowchart of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Generally, the components of the embodiments of the present application described and illustrated in the drawings here can be arranged and designed in various different configurations.

[0033] Accordingly, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed present application, but merely represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present application.

[0034] It should be noted that like reference numerals and letters denote like items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0035] In the description of the present application, it should be noted that if terms such as "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are used to indicate the orientation or positional relationship, it is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of this application is usually placed during use. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present application. In addition, in the description of the present application, if terms such as "first", "second", etc. are used only for distinguishing descriptions, they cannot be understood as indicating or implying relative importance.

[0036] In addition, in the description of the present application, terms such as "horizontal" and "vertical" do not mean that the components are required to be absolutely horizontal or hanging, but can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined.

[0037] In the description of the present application, it should also be noted that unless otherwise clearly specified and defined, if terms such as "set", "installed", "connected", "connected" are used, they should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.

[0038] In a first aspect, the present invention provides a regenerated carbon-ceramic composite thermal protection material based on a photovoltaic thermal field for recycling carbon-carbon materials. The material is composed of the following quaternary composite system (by mass percentage):

[0039] Recycled short carbon fibers: 30%, with a length of 50 - 300 μm and a diameter of 5 - 10 μm. As a three-dimensional framework reinforcement, they form a stress transfer network through random distribution, effectively enhancing the thermal shock resistance of the material. After the material of the present invention undergoes 100 thermal cycles (from room temperature to 1200 °C), it can still maintain its structural integrity, while the existing materials using ordinary recycled carbon fibers show obvious cracks or even breakage.

[0040] Pyrolytic carbon: 45%, graphitization degree ≥ 80%, specific surface area of 10 - 50 m 2 / g, derived from the high-temperature pyrolysis product of the resin matrix of waste carbon fiber composites, has a high graphitization degree and a porous structure. It not only acts as a filler to reduce the material density but also promotes the chemical bonding between the fiber and the matrix through surface active sites;

[0041] Silicon carbide (SiC): 20%, average particle size of 0.5 - 5 μm, is the main component of the matrix, providing high-temperature strength and oxidation resistance for the material;

[0042] Silicon (Si): 5%, purity ≥ 99.9%, particle size of 1 - 10 μm. During the sintering process, it reacts in-situ with pyrolytic carbon (Si + C → SiC), generating nano-SiC whiskers to fill the pores and consuming free carbon to improve the material density.

[0043] As Figure 1 shown, in the second aspect, the present invention provides a preparation method of the recycled carbon-ceramic composite thermal protection material as described above. Using the retired C / C material of the photovoltaic thermal field as the raw material, the full-component utilization is achieved through the following steps:

[0044] Crushing: The recycled C / C material is mechanically crushed into powders with a particle size ≤ 200 μm. After detection, the powder composition includes 25 - 35 wt% short carbon fibers, 35 - 50 wt% pyrolytic carbon, 15 - 25 wt% silicon carbide (SiC), and 5 - 10 wt% residual silicon (Si), and the crushing particle size requires a sieving rate ≥ 95%;

[0045] Mixing: 2 - 5 wt% phenolic resin is added to the crushed powder as a binder, and then ball-milled for 2 - 4 hours to ensure uniform dispersion of each component;

[0046] Hot pressing and forming: The uniformly mixed material is placed in a vacuum hot pressing furnace and cured for 1 - 2 hours under the conditions of a pressure of 30 - 60 MPa and a temperature of 180 - 220 °C to obtain a preform, where the optimal hot pressing pressure is 50 MPa;

[0047] Carbonization: The preform is placed in a nitrogen atmosphere, heated to 900 °C at a heating rate of 5 °C / min, and held for 2 hours to pyrolyze the resin to generate a porous carbon framework;

[0048] Silicon infiltration by melting: In the temperature range of 1420 - 1600 °C, under argon protection, molten silicon is infiltrated into the pores of the material and reacts with free carbon to form SiC. The reaction time is 2 - 4 hours, and finally the porosity of the material is ≤ 3%. When the silicon infiltration temperature is 1550 °C, Si is completely melted and the reaction rate is maximized. The specific details are shown in Table 1 below.

[0049] Table 1 Operating content of each step in the preparation method of the present invention and corresponding key points

[0050]

[0051]

[0052] Thirdly, the regenerated carbon-ceramic composite thermal protection material described in the present invention is applicable to the fields of photovoltaic thermal field components or aerospace high-temperature resistant composite materials.

[0053] The specific analysis is as follows:

[0054] Example 1

[0055] Raw material treatment: The retired C / C components of the photovoltaic thermal field are crushed into 150 μm powder. The component analysis shows that the short carbon fiber is 28%, the pyrolytic carbon is 42%, the SiC is 20%, and the residual silicon is 7%.

[0056] Mixing: 3 wt% phenolic resin is added and ball-milled for 3 hours.

[0057] Hot pressing: Cured at 200 °C and 50 MPa for 1.5 hours to form a Φ50 mm × 5 mm disc.

[0058] Carbonization: Insulated at 900 °C in nitrogen for 2 hours, and the open porosity is increased to 18%.

[0059] Silicon infiltration: Silicon infiltration is carried out at 1550 °C in argon for 3 hours to obtain a dense composite material. Finally, the SiC content reaches 38%, the thermal conductivity is 215 W / (m·K), and the flexural strength is 320 MPa.

[0060] Example 2

[0061] Adjust the silicon infiltration time to 4 hours. Finally, the SiC content is increased to 42%, the thermal conductivity reaches 230 W / (m·K), and it is applicable to aerospace ablative-resistant components.

[0062] Economy: The raw material cost is reduced by 60%. The short carbon fiber and SiC are directly reused, eliminating the steps of purchasing new fibers and synthesizing SiC.

[0063] Environmental protection: The waste utilization rate is ≥ 95%, and the CO2 emissions are reduced by 70% compared with the traditional process.

[0064] Performance advantages: The thermal conductivity of the recycled material is ≥200 W / (m·K), and the heat resistance is ≥1600 °C, which is suitable for photovoltaic thermal fields and aerospace ablative-resistant components.

[0065] Resource collaborative utilization: Directly utilize the short carbon fibers and in-situ generated silicon carbide in the recycled materials of the photovoltaic thermal field, avoiding the high-energy-consuming process of separately synthesizing SiC;

[0066] Interface optimization basis: The pre-existing SiC and carbon fibers in the recycled powder have formed a chemically bonded interface during high-temperature service, providing a natural reinforcing phase for subsequent composite materials;

[0067] Cost advantage: The silicon residue (<5wt%) can be used as a liquid-phase sintering aid, reducing the densification temperature (200 - 300 °C lower than the traditional process).

[0068] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A regenerated carbon-ceramic composite thermal protection material based on photovoltaic thermal field recycling of carbon-carbon materials, characterized in that: It is composed of the following quaternary composite system by mass percentage: Recycled short carbon fiber: 30%, the length of the recycled short carbon fiber is 50 - 300 μm, and the diameter is 5 - 10 μm; Pyrolytic carbon: 45%, the graphitization degree of the pyrolytic carbon ≥ 80%, and the specific surface area is 10 - 50 m 2 / g; Silicon carbide: 20%, the average particle size of the silicon carbide is 0.5 - 5 μm; Silicon: 5%, the purity of the silicon ≥ 99.9%, and the particle size is 1 - 10 μm.

2. The regenerated carbon-ceramic composite thermal protection material based on the recovery of carbon-carbon materials by a photovoltaic thermal field according to claim 1, wherein: The recycled short carbon fiber serves as a three-dimensional framework reinforcement.

3. The regenerated carbon-ceramic composite thermal protection material based on the recovery of carbon-carbon materials from a photovoltaic thermal field according to claim 1, wherein: The pyrolytic carbon is derived from the high-temperature pyrolysis product of the resin matrix of waste carbon fiber composites, and has a high degree of graphitization and a porous structure.

4. The regenerated carbon-ceramic composite thermal protection material based on the recovery of carbon-carbon materials by a photovoltaic thermal field according to claim 1, characterized in that: During the sintering process, the silicon reacts in-situ with the pyrolytic carbon to generate nano-SiC whiskers to fill the pores, and at the same time consumes free carbon.

5. A method for preparing a regenerated carbon-ceramic composite thermal protection material according to any one of claims 1-4, characterized in that: It includes the following steps: Crushing: Mechanically crush the recycled photovoltaic thermal field retired C / C material into powder with a particle size ≤ 200 μm. The powder composition includes 25 - 35 wt% short carbon fiber, 35 - 50 wt% pyrolytic carbon, 15 - 25 wt% SiC, and 5 - 10 wt% silicon; Mixing: Add 2 - 5 wt% phenolic resin as a binder, and ball-mill and mix for 2 - 4 hours to ensure uniform components; Hot pressing and forming: In a vacuum hot pressing furnace, cure at a pressure of 30 - 60 MPa and a temperature of 180 - 220 °C for 1 - 2 hours to obtain a preform; Carbonization: Heat up to 900 °C at a rate of 5 °C / min in a nitrogen atmosphere, and keep warm for 2 hours to cause the resin to pyrolyze to generate a porous carbon framework; Molten silicon infiltration: At 1420 - 1600 °C and under argon protection, molten silicon infiltrates into the pores and reacts with free carbon to generate SiC. The reaction time is 2 - 4 hours, and finally the porosity of the material ≤ 3%; 6. The preparation method according to claim 5, characterized in that: In the crushing step, the crushing particle size ≤ 200 μm, and the sieving rate ≥ 95%.

7. The preparation method according to claim 5, characterized in that: In the hot pressing and forming step, the hot pressing pressure is 50 MPa.

8. The preparation method according to claim 5, characterized in that: In the molten silicon infiltration step, the silicon infiltration temperature is 1550 °C.

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