CN117946425A - Ceramic-coated carbon fiber reinforced resin matrix composite material and preparation method thereof - Google Patents

Abstract

The invention relates to a ceramic-coated carbon fiber reinforced resin matrix composite material, which is prepared by immersing pretreated carbon fibers in silica sol (or silica sol and yttrium sol/zirconium sol) and preparing a silica, yttrium silicate or zirconium silicate-coated carbon fiber reinforcement body through vacuum impregnation, solidification and sintering; uniformly mixing thermoplastic phenolic resin, solvent glycol and curing agent hexamethylenetetramine to obtain a phenolic precursor solution; and then immersing the silicon oxide, yttrium silicate or zirconium silicate coated carbon fiber reinforcement body into a phenolic aldehyde precursor solution for vacuum impregnation, curing gel, immersing with deionized water and drying. The innovation point of the invention is mainly that a sol-gel method is adopted to prepare a high-temperature-resistant and oxidation-resistant ceramic coating on the fiber surface of the carbon fiber reinforcement, and the high-temperature-resistant and oxidation-resistant ceramic coating is combined with a phenolic precursor solution, so that the problem of surface retreating of the carbon fiber reinforcement resin-based heat-resistant composite material caused by fiber oxidation is solved, and the carbon/phenolic composite material has light-dimensional versatility.

Description

A ceramic-coated carbon fiber reinforced resin-based composite material and preparation method thereof

Technical Field

The present invention belongs to the technical field of hypersonic vehicle thermal protection, and in particular relates to a ceramic-coated carbon fiber reinforced resin-based composite material and a preparation method thereof.

Background technique

Near-space hypersonic aircraft uses new types of propulsion or gliding flight methods, and can perform long-term hypersonic flight in near-space. It is characterized by "rapid arrival, global strike, strong penetration and defense, and high precision". It can perform tasks such as long-range rapid strikes and force projection, rapid intelligence collection, and rapid response to entering and exiting space.

In order to achieve faster flight speed, hypersonic aircraft adopt lifting body or wave-bearing body shape, which has the characteristics of pointed and slender body. Since the stagnation point heat flux is inversely proportional to the 1/2 power of the head radius, the thermal protection materials of hypersonic aircraft face more severe aerodynamic heating. Efficient and reliable thermal protection technology is one of the key technologies of hypersonic aircraft. The next generation of hypersonic aircraft will fly faster, and the temperature in the stagnation area will be above 3000℃, which exceeds the temperature resistance limit of all thermal protection materials. The problem of passive thermal protection is becoming more and more prominent, so active thermal protection (heat pipe absorption or sweating cooling, etc.) has become an inevitable trend for thermal protection in the stagnation point and leading edge areas. At the same time, the temperature of a large area of the windward surface reaches about 1600℃. Although the resin-based thermal protection composite material is lightweight, the surface is prone to ablation (non-dimensional); although the high-temperature ceramic is dimensional, its density is too large; lightweight thermal protection structure is the continuous pursuit of aerospace vehicles, and the multifunctionality and functional integration of thermal protection systems are the inevitable requirements for the development of advanced aircraft. Resin-based thermal protection materials have excellent thermal insulation properties and have always been the focus of research on ablative thermal protection materials. Researchers from various countries have been working hard to achieve lightweight and efficient thermal protection effects. At the same time, after the resin-based material is ablated, it will form a volume retreat, which will affect the aerodynamic shape of the aircraft and cause undesirable thermal damage. Therefore, it is of great significance to study low-ablation lightweight resin-based thermal insulation composite materials.

Resin-based heat-resistant composite materials are made of fiber or filler reinforced resin matrix. The resin absorbs heat, pyrolyzes and forms a protective carbon layer. The pyrolysis gas diffuses outward to provide convection cooling, forming a mass ejection effect of gas products, delaying the transfer of heat into the material. The preparation process of resin-based heat-resistant materials is simple, low-cost, and has good thermal insulation effect. However, the carbonized layer of the resin-based composite material undergoes oxidation reaction with oxygen in the air, causing the shape of the aircraft to change and affecting its landing accuracy. If lightweight resin-based composite materials are used in large-area heat protection areas of hypersonic aircraft, such materials need to be improved and optimized to achieve a dimensional effect. In response to the demand for large-area thermal protection materials for the next generation of near-space hypersonic aircraft, research on the design, preparation and performance characterization of lightweight pyrolysis dimensional heat-resistant materials is carried out to overcome the contradiction between light weight and dimensionality of thermal protection materials, realize the transformation of thermal protection materials to lightweight dimensionality, and provide key technical support for the field of hypersonic thermal protection.

For carbon/phenolic ablation heat protection composite materials, the main way to achieve lightweight is to use phenolic aerogel as the matrix material. Phenolic aerogel is a lightweight material with a three-dimensional spatial structure formed by cross-linking and stacking of nanoparticles. Its internal pores are also nanoscale interconnected pores, which are close to the mean free path of air molecules, limiting heat conduction and heat convection, making it show extremely low thermal conductivity in the macroscopic sense. Phenolic aerogel not only has the traditional phenolic pyrolysis heat protection mechanism, but its pyrolysis product - carbon aerogel has low thermal conductivity, so it can still produce heat insulation effect after ablation. Therefore, phenolic aerogel has broad application prospects as the matrix of resin-based heat protection materials.

At present, the main method used to optimize the ablation resistance of carbon/phenolic composite materials is to add high-temperature resistant ceramics to the phenolic matrix, so that it produces high-temperature resistant oxides during the ablation process, preventing the inflow of oxygen from directly contacting the pyrolytic carbon and carbon fiber on the ablation surface, but this method will increase the density of the composite material and affect the lightweight performance of the material; the research team of Harbin Institute of Technology prepared a ceramic-resin layer with a thickness of about 3mm on the ablation surface of the carbon/phenolic material, and then impregnated phenolic aerogel, and achieved lightweight and ablation-resistant effects through the preparation of variable density composite materials. The above processes all provide measures for ablation resistance optimization, but there is still a common problem, that is, carbon/phenolic composite materials use carbon fiber as reinforcement, and carbon fiber will oxidize at 400℃ in a high-temperature oxygen environment, and the addition of ceramics cannot prevent the oxidation of carbon fiber. This method can only improve the antioxidant performance of the composite material, and cannot achieve light weight and low ablation. The reasons are as follows: For carbon/phenolic composite materials, the main heat protection method is that the resin pyrolysis absorbs a large amount of heat and the pyrolysis gas diffuses outward to produce a heat blocking effect. Therefore, the optimization method of adding ceramics as fillers and forming an ablation-resistant coating during the ablation process is limited by the heat protection mechanism. The added ceramic content cannot be too high and the formed coating cannot be too dense to prevent the overflow and diffusion of the pyrolysis gas. The dense coating will cause a large amount of pyrolysis gas to be stored inside the material during the ablation process, and the increased gas pressure will cause the coating or material to be damaged from the inside. Carbon fiber reinforcements still have problems with oxidation and low performance during the ablation process under this optimization method.

The existing patent CN101440193A discloses a carbon/phenolic heat-resistant composite material, which uses viscose-based carbon fiber as reinforcement and phenolic resin as matrix, and is obtained by impregnating viscose-based carbon fiber in phenolic resin solution to form prepreg, and then laminating or winding with cloth tape to form and solidify. The prepared carbon/phenolic heat-resistant composite material has a density of 1.38~1.50 g/ ^cm3 , a radial thermal conductivity of 0.70~0.90 W/(m∙K), and a linear ablation rate of 0.10~0.12 mm/s. It still has defects such as high density, excessive thermal conductivity and linear ablation rate, and cannot meet the existing requirements for light weight and high efficiency heat protection.

The existing patent CN110668839A discloses a low-cost, high-strength carbon fiber reinforced silicon carbide composite material and a preparation method thereof, which comprises the following steps: (1) soaking treatment: soaking a carbon fiber preform in a precursor solution composed of phenolic resin, ethylene glycol and a curing agent for a period of time and taking it out; (2) curing treatment: curing the carbon fiber preform soaked in the precursor solution to obtain a carbon fiber reinforced porous resin-based composite material; (3) carbonization treatment: carbonizing the carbon fiber reinforced porous resin-based composite material obtained in step (2) to obtain a porous carbon/carbon composite material; (4) repeating the soaking, curing and carbonization treatment processes in steps (1) to (3) for multiple times until a porous carbon/carbon composite material of a desired density is obtained; (5) siliconization treatment: melt siliconizing the carbon/carbon composite material obtained in step (4) to obtain the low-cost, high-strength carbon fiber reinforced silicon carbide composite material. Although the patent discloses soaking the fiber preform in a phenolic precursor solution, the process requires repeated soaking, curing, and carbonization steps, which is cumbersome. In addition, the density of the carbon fiber reinforced silicon carbide composite material finally prepared by this method is still maintained at 2.0-2.5g/ ^cm3 , and the three-point bending strength is 80-270MPa, resulting in the material still having a relatively high density and failing to truly meet the existing requirements for lightweight materials and high efficiency heat protection.

Summary of the invention

The present invention aims to overcome the defects of the prior art. For an ablation heat-resistant composite material taking carbon/phenolic aldehyde as an example, the present invention provides a ceramic-coated carbon fiber reinforced resin-based composite material, which is obtained by preparing a ceramic sol (including silica sol, yttrium sol or zirconium sol, etc.) coating on the fiber surface of a carbon fiber reinforcement to form an anti-oxidation carbon fiber porous material, and then impregnating a phenolic aldehyde precursor solution. While achieving light weight and high efficiency heat protection, the composite material has the ability of low ablation dimension (density varies in the range of 0.474~0.54g/ ^cm3 , thermal conductivity varies in the range of 0.142~0.146 W/(m∙K); the linear ablation rate after 120s of ablation by a 1.5 MW/ ^m2 heat flow is 1.408~4.142 μm/s; the linear ablation rate after 120s of ablation by a 2.44 MW/ ^m2 heat flow is 5~8.442μm/s, and the back surface temperature is between 121.26~141.51℃).

The present invention also provides a method for preparing the ceramic-coated carbon fiber reinforced resin-based composite material.

To achieve the above object, the present invention adopts the following technical solution:

A method for preparing a ceramic-coated carbon fiber reinforced resin-based composite material, which mainly uses a ceramic-coated carbon fiber needle-punched felt as a reinforcement phase and a phenolic precursor solution as an impregnation phase, and is prepared by a process combining a vacuum impregnation method and a sol-gel method, and specifically includes the following steps (the process flow is shown in Figure 1):

1) Preparation of silicon oxide, yttrium silicate or zirconium silicate coated carbon fiber reinforcement:

The pretreated carbon fiber is immersed in silica sol, and then immersed in vacuum (using a vacuum pump to gradually maintain the environment below -0.01 kPa, the same below) at room temperature for 1-3 hours, and then dried and sintered once to obtain a silicon oxide-coated carbon fiber reinforcement;

The pretreated carbon fiber is immersed in silica sol, and then vacuum impregnated at room temperature for 1-3 hours, dried and solidified and sintered once, taken out and vacuum impregnated in yttrium sol or zirconium sol again, dried and sintered twice, so as to obtain yttrium silicate or zirconium silicate coated carbon fiber reinforcement;

During the vacuum impregnation of ceramic sol, the same sol can be repeatedly impregnated, or other types of sol can be continuously impregnated. The impregnation process is the same. After the last solidification, the preparation of the reinforcement is completed.

2) preparing a phenolic precursor solution: uniformly mixing a raw material thermoplastic phenolic resin, a solvent ethylene glycol and a curing agent hexamethylenetetramine to obtain a phenolic precursor solution;

3) Add the silicon oxide, yttrium silicate or zirconium silicate coated carbon fiber reinforcement prepared in step 1) to the phenolic precursor solution prepared in step 2), and vacuum impregnate for 0.5-1h at room temperature to allow the precursor solution to completely fill the interior of the reinforcement material, then transfer to a muffle furnace for gel curing, take out, soak in deionized water, and dry.

The surface of commercial carbon fiber generally has a resin-based coating to protect the fiber precursor from damage. It is generally smooth and has low surface energy, lacking polar functional groups, so the bonding force between carbon fiber and other materials is weak. The surface of the pretreated carbon fiber has increased roughness and active groups. Specifically, in step 1), the carbon fiber pretreatment is specifically as follows: heat treat the carbon fiber at 300-400°C in a muffle furnace for 2-4 hours, use deionized water to fully ultrasonically clean and dry the carbon fiber material, soak it in concentrated nitric acid for 2-3 hours, then wash it with deionized water until it is neutral, and dry it. Conventional technology can be used for drying in step 1), such as drying at 80°C for 12-24 hours to remove excess moisture.

Furthermore, the carbon fiber includes one or more of carbon fiber needle-punched felt, carbon fiber three-dimensional braided body, carbon felt, chopped carbon fiber and the like.

Specifically, in step 1), the primary curing sintering is specifically: heating to 250-350°C at 3-5°C/min and keeping the temperature for 1-3 hours, then heating to sintering temperature 800-1400°C at 1-2°C/min and keeping the temperature for 50-70 minutes. The secondary sintering is specifically: heating to 1200-1400°C and keeping the temperature for 50-70 minutes.

Furthermore, in step 1), the mass concentration of the silica sol is 10-30%, and the mass concentration of the yttrium sol or zirconium sol is 5-14%.

Specifically, in step 2), the mass fraction of the thermoplastic phenolic resin in the phenolic precursor solution is 15-40%. Further, the amount of hexamethylenetetramine added is 5-15% of the mass of the thermoplastic phenolic resin. When preparing the phenolic precursor solution, the phenolic resin can be first dissolved in ethylene glycol by mechanical stirring, and then the hexamethylenetetramine is added to the phenolic-ethylene glycol solution by stirring and adding.

Specifically, in step 3), the gel curing is carried out in two stages, specifically: keeping warm at 110-130°C for 0.5-1.5 hours, and then keeping warm at 150-170°C for 1.5-2.5 hours. After gel curing, the material is cooled to room temperature with the furnace, and the material is taken out and immersed in deionized water for solution replacement. The immersion liquid surface is at least 10 cm away from the material surface, and the solution is replaced every 4-6 hours. After 2 days, the material is taken out and dried at 80°C until the material quality does not change, and finally a ceramic-coated carbon fiber reinforced resin-based composite material is obtained.

The present invention also provides a ceramic-coated carbon fiber reinforced resin-based composite material prepared by the method.

This paper adopts a research method that combines experiments, theoretical analysis, composite material preparation and assessment. Through the cross-infiltration of composite materials, mechanics, heat transfer, aerodynamic thermodynamics and other disciplines, the existing experimental technology is combined with theory, based on experiments, and designed and prepared on the basis of thermal protection mechanism analysis. The ceramic-coated carbon fiber reinforced resin-based composite material is composed of a phenolic resin precursor solution matrix phase and a ceramic-coated carbon fiber reinforcement material. The ceramic-coated carbon fiber reinforcement plays a supporting role as a skeleton, and in the ablative service environment, it has the effect of resisting airflow scouring and maintaining the shape of the material; the phenolic precursor solution reduces thermal conductivity through a special spatial structure, and at the same time absorbs a large amount of heat and releases pyrolysis gas during the ablation process. The pyrolysis gas injected into the boundary layer will produce a thermal blocking effect to prevent heat from transferring to the inside of the material, and the pyrolysis carbon produced by pyrolysis will also radiate and dissipate heat. The present application uses low-density, low-thermal conductivity carbon fiber needle-punched felt as a raw material to prepare a ceramic-coated carbon fiber reinforced material, which solves the problem that carbon fiber is easily oxidized and loses mechanical properties in an aerobic environment, thereby achieving a dimensional effect; commercial phenolic resin is used as a raw material to prepare a phenolic precursor solution, and the characteristics of low density and low thermal conductivity of aerogel are used to achieve the purpose of light weight and high-efficiency thermal protection, and the content of the curing agent is optimized to improve the high temperature resistance of the aerogel; the carbon fiber reinforced material is impregnated in the phenolic precursor solution by a vacuum impregnation method to prepare a ceramic-coated carbon fiber reinforced resin-based composite material, and the thermal physical properties and ablation insulation mechanism of the material are studied by means of thermogravimetric analysis, thermal conductivity testing, compression mechanical testing, oxyacetylene ablation and other means, and the ablation response mechanism is explored.

Carbon fiber is commonly used as the reinforcement of resin-based composite materials. Carbon fiber has excellent high-temperature mechanical properties. However, carbon fiber is easily oxidized in an oxygen environment. It starts to oxidize at 400°C, causing the mechanical properties of the composite material to deteriorate and the surface to ablate and recede. Therefore, the present application considers improving the antioxidant properties of the reinforcement to achieve the dimensional effect of the resin-based material. The innovation of the present invention mainly lies in the use of a sol-gel method to prepare a high-temperature resistant and antioxidant ceramic coating on the fiber surface of the carbon fiber reinforcement, and combining it with a phenolic aerogel to solve the problem of surface receding of the carbon fiber reinforced heat-resistant composite material due to fiber oxidation, so that the carbon/phenolic composite material has the multifunctionality of light weight and dimensional shape.

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

The ceramic-coated carbon fiber reinforced resin-based composite material of the present invention is used as a resin-based ablation material, which achieves a dimensional effect in the ablation process while achieving lightness. The density thereof is in the range of 0.474-0.54 g/cm ³ , and the thermal conductivity thereof is in the range of 0.142-0.146 W/(m∙K); the linear ablation rate is 1.408-4.142 μm/s after 120 s of ablation by a 1.5 MW/m ² heat flux; the linear ablation rate is 5-8.442 μm/s after 120 s of ablation by a 2.44 MW/m ² heat flux, and the back surface temperature is between 121.26-141.51°C. Under similar ablation test conditions, the linear ablation rate of the material is at least one order of magnitude lower than that of the carbon/phenolic material with the same density, and is equivalent to the linear ablation rate of ceramic-based thermal protection materials. Compared with the carbon/phenolic material and ceramic-based thermal protection materials with the same linear ablation rate, the density and thermal conductivity of the material studied in the present invention are both the lowest, proving that the carbon/phenolic material in the present invention has both light weight and dimensional properties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of the preparation process of a ceramic-coated carbon fiber reinforced resin-based composite material according to the present invention;

Figure 2 shows the density of YS-CF/PR with different HMTA contents;

Figure 3 shows the thermal conductivity of YS-CF/PR with different HMTA contents;

Figure 4 shows the ablation surface temperature of YS-CF/PR with different HMTA contents under 1.5 MW/m ² heat flux ablation;

Figure 5 shows the comparison of samples before and after ablation: (a) 14-YS-CFs-1300; (b) YS-CF/PR-8; (c) YS-CF/PR-10; (d) YS-CF/PR-12;

Figure 6 shows the linear ablation rate and mass ablation rate of YS-CF/PR with different HMTA contents under 1.5MW/m ² heat flux ablation;

Figure 7 shows the ablation surface temperature and back surface temperature of YS-CF/PR with different HMTA contents under 2.44 MW/m ² heat flux ablation;

Figure 8 shows the linear ablation rate and mass ablation rate of YS-CF/PR with different HMTA contents under 2.44 MW/m ² heat flux ablation.

Detailed ways

The technical solution of the present invention is further described in detail below in conjunction with the embodiments, but the protection scope of the present invention is not limited thereto.

In the following test process, the raw materials used are all common commercial products that can be directly purchased or obtained by conventional methods in the art. Room temperature refers to 25±5°C.

During the test, drying that was not mentioned in detail refers to drying at 80°C for 24 hours. Vacuum impregnation refers to using a vacuum pump to gradually maintain the environment below minus 0.01 kPa.

Example 1

1.1 Preparation of silicon oxide coated carbon fiber reinforcement (SiO ₂ -CFs)

The experiment prepared silica sols with different mass concentrations (10%, 20%, 30%), and used vacuum impregnation, drying, curing and sintering processes in sequence to prepare silicon oxide-coated carbon fiber reinforcement (SiO ₂ -CFs) using carbon fiber needle felts of different densities. The detailed experimental components and sintering parameter settings are shown in Table 1. The specific steps are as follows:

(1) Surface pretreatment of CF: Place CF in a muffle furnace, heat it at 300°C for 3 hours, then use deionized water for ultrasonic cleaning for 2 hours, dry it, soak it in concentrated nitric acid for 2 hours at room temperature, finally use deionized water to wash it until it is neutral, dry it, and set it aside;

(2) Impregnation with silica sol: The surface pretreated CF was impregnated with silica sols of different mass concentrations (10%, 20%, 30%) and placed in a vacuum drying oven for vacuum impregnation for 3 hours to make the silica sol evenly distributed inside the needle felt;

(3) Drying: Take out the impregnated CF and dry it in a forced air drying oven at 80 °C for 12 hours to remove the free water in the material;

(4) Curing and sintering: The material was placed in a vacuum sintering furnace, heated to 300°C at a rate of 5°C/min, and then kept at this temperature for 2 hours. Then, the temperature was further increased to different sintering temperatures (800°C, 1200°C, and 1300°C) at a rate of 1°C/min, and then kept at this temperature for 1 hour. Then, the material was cooled in the furnace to complete the curing process and SiO ₂ -CFs was obtained. In Table 1, the SiO ₂ -CFs samples prepared according to different experimental conditions were marked as 30SiO ₂ -CFs-800, 30SiO ₂ -CFs-1200, 30SiO ₂ -CFs-1300, 20SiO _{2 -CFs-1300, 10SiO 2 -CFs} -1200, 20SiO ₂ -CFs-1200, and 30SiO ₂ -CFs-1200.

Table 1 Experimental conditions for the preparation of SiO ₂ -CFs

After testing the results in Table 1 above, it was found that uniform and dense ceramic coatings can be prepared. After comprehensive consideration, the following silicon oxide-coated carbon fiber reinforcement material (referred to as 20SiO ₂ -CFs-1300) prepared with a carbon fiber needle felt density of 0.2 g/cm ³ , a silica sol concentration of 20%, and a sintering temperature of 1300°C was selected for subsequent tests.

1.2 Preparation of yttrium silicate coated carbon fiber reinforced material (YS-CFs)

The preparation process of yttrium silicate coated carbon fiber reinforced material (YS-CFs) adopts the same vacuum impregnation, sol-gel and sintering curing process as SiO ₂ -CFs, and further preparation and processing are carried out on the basis of SiO ₂ -CFs; the details are as follows:

The steps of (1) pre-treating the surface of CF, (2) impregnating with silica sol, (3) drying and (4) curing and sintering are referred to the preparation process of the above-mentioned silicon oxide coated carbon fiber reinforced material (SiO ₂ -CFs) to obtain a silicon oxide coated carbon fiber reinforced material (denoted as 20SiO ₂ -CFs-1300);

(5) Impregnation with yttrium sol: Take out and immerse again in yttrium sol with different mass concentrations (5%, 10%, 14%), and place in a vacuum drying oven for vacuum impregnation for 3 hours;

(6) Secondary sintering: After being taken out and dried in a forced air drying oven at 80°C for 12 hours, the YS-CFs material was obtained by keeping the temperature at different sintering temperatures (1200°C, 1300°C and 1400°C) for 60 minutes. The detailed experimental conditions are shown in Table 2.

Table 2 Experimental conditions for preparation of YS-CFs

1.3 Preparation of phenolic precursor solution

The specific preparation process of the phenolic precursor solution is as follows: first, dissolve the thermoplastic phenolic resin (SFB PR) in the solvent ethylene glycol by mechanical stirring; then add hexamethylenetetramine (HMTA) to the phenolic-ethylene glycol solution while stirring, and mix evenly to obtain. In the phenolic precursor solution, the mass fraction of thermoplastic phenolic resin is 20%; the amount of hexamethylenetetramine added is 8%, 10%, and 12% of the mass of thermoplastic phenolic resin, respectively. According to the content of HMTA, the materials are named PR-8, PR-10, and PR-12, respectively.

Table 3 Synthesis conditions and physical properties of phenolic precursor solution

1.4 Preparation method of ceramic-coated carbon fiber reinforced resin matrix composite material

Ceramic-coated carbon fiber reinforced resin matrix composite (YS-CF/PR) was prepared by vacuum impregnation assisted sol-gel process. First, 14-YS-CFs-1300 and different phenolic precursor solutions were prepared respectively, and then 14-YS-CFs-1300 was immersed in different phenolic precursor solutions for half an hour under vacuum conditions. The negative pressure and the surface tension of the phenolic precursor solution were used to fully fill the solution into the internal pores of the YS-CFs material. Next, the material was gelled and cured (120℃ for 1 hour and 150℃ for 2 hours), and then cooled to room temperature with the furnace. Finally, the material was taken out and immersed in deionized water for solution replacement. The immersion liquid surface was at least 10cm away from the upper surface of the material. The solution was replaced every 4-6h. After 2 days, the material was taken out and dried at 80℃ until the material quality did not change. Finally, a ceramic-coated carbon fiber reinforced resin matrix composite (YS-CF/PR) was obtained. Table 4 shows the preparation condition parameters of YS-CF/PR. According to different phenolic precursor solutions, the materials were named YS-CF/PR-8, YS-CF/PR-10 and YS-CF/PR-12.

Table 4 Preparation parameters of YS-CF/PR

Example 2 Performance of ceramic coated carbon fiber reinforced resin matrix composites

Figure 2 shows the density of YS-CF/PR with different HMTA contents (8%, 10%, 12%). The density of YS-CF/PR increases from 0.474 g/cm ³ to 0.540 g/cm ^3. The phenolic precursor solution is filled into the interior of YS-CFs, so the density of YS-CF/PR increases compared with 14-YS-CFs-1300 (0.394 g/cm ³ ). At the same time, with the increase of HMTA content, the density of YS-CF/PR gradually increases.

The room temperature thermal conductivity of YS-CF/PR was characterized, and the results are shown in Figure 3. The composite material exhibits good thermal insulation performance, and the thermal conductivity varies in the range of 0.142 ~ 0.146 W/(m∙K), and its value is basically unaffected by the HMTA content. However, compared with 14-YS-CFs-1300 (0.155W/m∙K), the thermal conductivity of YS-CF/PR decreased by 5.8 ~8.39%.

The ablation resistance of YS-CF/PR prepared with different curing agents. The ablation resistance of YS-CF/PR was evaluated by oxyacetylene flame simulation with a heat flux of 1.5 MW/m ² and compared with 14-YS-CFs-1300. The ablation time was 120 s. The surface temperature of the material during the ablation process is shown in Figure 4. At the beginning of ablation, the surface temperature of the material rose rapidly, reaching 1600℃ within 15 s, and then slowly rose and gradually remained stable until the end of the test, indicating that a dynamic balance of heat transfer-pyrolysis-radiation was established on the surface of the ablated material. 14-YS-CFs-1300 had the highest ablation surface temperature of 1817.74℃, the ablation surface temperature of YS-CF/PR-8 was the lowest, at 1696.24℃, and the ablation surface temperatures of YS-CF/PR-10 and YS-CF-12 were close, at about 1759℃. The surface temperature of YS-CF/PR is lower than that of 14-YS-CFs-1300 because the phenolic matrix forms a large amount of pyrolytic gas and produces pyrolytic carbon during the ablation process. The pyrolytic gas hinders the heat transfer inside the material. The pyrolytic carbon has a high emissivity and dissipates heat through the re-radiation mechanism, reducing the proportion of heat flow used to heat the material surface.

The sample morphology before and after ablation is shown in Figure 5. During the ablation process, the material can maintain a good appearance without obvious surface ablation retreat. The linear ablation rate and mass ablation rate of the material are calculated based on the material thickness and mass changes before and after ablation, and the results are shown in Figure 6. After 120 s of ablation at 1.5 MW/ ^m2 , the linear ablation rates of 14-YS-CFs-1300, YS-CF/PR-8, YS-CF/PR-10 and YS-CF/PR-12 are 4.525, 4.142, 3.858 and 1.408 μm/s, respectively; 14-YS-CFs-1300 has the smallest mass ablation rate compared to YS-CF/PR. The mass loss of YS-CFs mainly comes from the oxidation of carbon fiber. The ablation surface temperature above 1800℃ destroys the yttrium silicate coating on the surface of the carbon fiber. The mass loss of YS-CF/PR is mainly due to two reasons. First, the reason is the same as that of 14-YS-CFs-1300. Carbon fiber oxidation occurs on the surface of the material, which accounts for about 25% of the total mass loss. The main reason is that the resin is pyrolyzed. The pyrolysis gas overflow caused by the pyrolysis of the resin and the oxidation of pyrolytic carbon on the surface of the material account for a large proportion of the total mass loss. With the increase of HMTA content, the mass loss rate gradually decreases under the same ablation condition. The TG results show that HMTA can increase the residual carbon rate of the phenolic precursor solution and form a more solid pyrolytic carbon layer on the ablation surface, thereby improving the ablation resistance of the composite material. By comparing the linear ablation rate of YS-CF/PR, it can be found that all three materials show good ablation resistance. As a reinforcement of the composite material, 14-YS-CFs-1300 shows a good ablation dimension effect during the ablation process. After 120 s of ablation, the linear ablation rate of the material is only 4.525 μm/s. Based on 14-YS-CFs-1300 and combined with the resin pyrolysis heat protection mechanism, YS-CF/PR achieved the effect of ablating the dimensional shape. The performance of YS-CF/PR-12 was the most outstanding, with a mass ablation rate and a linear ablation rate of 9.083 mg/s and 1.408 μm/s respectively.

The heat flux density was increased to 2.44 MW/m ² , and YS-CF/PR-8, YS-CF/PR-10 and YS-CF/PR-12 were subjected to 120s ablation test, and the thermal response results of low heat flux and medium heat flux were compared. The ablation surface temperature and back surface temperature of ablation under 2.44 MW/m ² heat flux are shown in Figure 7. As in the case of low heat flux, the surface temperature of the material rises rapidly in the first 15 s of the ablation process and then stabilizes. The ablation surface temperature of the material in Figure 7 increases with the increase of HMTA content, and has a higher surface temperature than that of 1.5 MW/m ² ablation. All three materials are higher than 1800℃. The thermal response process of the back surface temperature is slow, and the material heating rate is slow. After 120 s ablation, the back surface temperature of YS-CF/PR-8, YS-CF/PR-10 and YS-CF/PR-12 is not significantly different, ranging from 121.26 to 141.51℃. The factors that affect the backside temperature are: (1) ablation surface temperature; (2) material thermal conductivity; (3) heat blocking effect during ablation; and (4) thickness of thermal insulation layer. Comparing the YS-CF/PR prepared at three HMTA concentrations, the ablation surface temperature and the residual carbon rate of the phenolic precursor solution (representing the ablation resistance of the resin matrix) gradually increase with the increase of HMTA content, while the thermal conductivity is similar and the thickness of the thermal insulation layer is the same. The combined effect of these factors makes the temperature difference on the backside of the material not obvious.

The ablation rate change trend of YS-CF/PR-8, YS-CF/PR-10 and YS-CF/PR-12 after 2.44 MW/m ² heat flux ablation is the same as that of 1.5 MW/m ² (as shown in Figure 8). After 120s of 2.44 MW/m ² heat flux ablation, the linear ablation rates of YS-CF/PR-8, YS-CF/PR-10 and YS-CF/PR-12 are 8.442, 5.25 and 5μm/s, respectively. For the same material, high heat flux ablation increases both the linear ablation rate and the mass ablation rate of the material. Taking YS-CF/PR-8 as an example, the mass ablation rate increased by 25% and the linear ablation rate increased by 1.03 times. Comprehensively comparing the anti-ablation-thermal insulation properties of YS-CF/PR under two heat flux conditions, YS-CF/PR-12 performs best.

Claims (10)

1. The preparation method of the ceramic-coated carbon fiber reinforced resin matrix composite material is characterized by comprising the following steps of:

1) Preparing a silicon oxide, yttrium silicate or zirconium silicate coated carbon fiber reinforcement:

immersing the pretreated carbon fiber into silica sol, then immersing for 1-3 hours at room temperature in vacuum, drying, and curing and sintering once to obtain the silica-coated carbon fiber reinforcement;

Immersing the pretreated carbon fiber into silica sol, then vacuum-immersing for 1-3h at room temperature, drying, curing and sintering for the first time, taking out, vacuum-immersing in yttrium sol or zirconium sol again, drying, and sintering for the second time to obtain yttrium silicate or zirconium silicate coated carbon fiber reinforcement;

2) Preparing a phenolic aldehyde precursor solution: uniformly mixing raw materials of thermoplastic phenolic resin, solvent glycol and curing agent hexamethylenetetramine to obtain a phenolic precursor solution;

3) Adding the silica, yttrium silicate or zirconium silicate coated carbon fiber reinforcement prepared in the step 1) into the phenolic precursor solution prepared in the step 2), vacuum impregnating for 0.5-1h at room temperature, then performing gel curing, taking out, soaking with deionized water, and drying.

2. The method for preparing the ceramic-coated carbon fiber reinforced resin matrix composite according to claim 1, wherein in the step 1), the carbon fiber pretreatment is specifically: and (3) carrying out heat treatment on the carbon fiber for 2-4 hours at 300-400 ℃, carrying out ultrasonic cleaning and drying by using deionized water, then acidizing in concentrated nitric acid for 2-3 hours, washing by using deionized water to be neutral, and drying to obtain the carbon fiber.

3. The method of preparing a ceramic coated carbon fiber reinforced resin matrix composite according to claim 2, wherein the carbon fibers comprise one or more of carbon fiber needled felt, carbon fiber three-dimensional braid, carbon felt, chopped carbon fiber.

4. The method for preparing the ceramic-coated carbon fiber reinforced resin matrix composite according to claim 1, wherein in the step 1), the primary curing and sintering is specifically as follows: heating to 250-350 deg.C, maintaining for 1-3 hr, heating to 800-1400 deg.C, and maintaining for 50-70min.

5. The method for preparing the ceramic-coated carbon fiber reinforced resin matrix composite according to claim 1, wherein in the step 1), the secondary sintering is specifically: heating to 1200-1400 deg.C and maintaining for 50-70min.

6. The method for preparing a ceramic-coated carbon fiber reinforced resin matrix composite according to claim 1, wherein in the step 1), the mass concentration of the silica sol is 10-30%, and the mass concentration of the yttrium sol or zirconium sol is 5-14%.

7. The method for preparing the ceramic-coated carbon fiber reinforced resin matrix composite material according to claim 1, wherein in the step 2), the mass fraction of the thermoplastic phenolic resin in the phenolic precursor solution is 15-40%.

8. The method for preparing the ceramic-coated carbon fiber reinforced resin matrix composite according to claim 7, wherein in the step 2), the addition amount of hexamethylenetetramine is 5-15% of the mass of the thermoplastic phenolic resin.

9. The method for preparing the ceramic-coated carbon fiber reinforced resin matrix composite according to claim 1, wherein in the step 3), the gel curing is specifically: preserving heat at 110-130 ℃ for 0.5-1.5 hours, and preserving heat at 150-170 ℃ for 1.5-2.5 hours.

10. The ceramic-coated carbon fiber reinforced resin matrix composite prepared by the method of any one of claims 1 to 9.