Self-supporting silicon carbide fiber felt framework connecting material and preparation method thereof

Abstract

The invention discloses a self-supporting silicon carbide fibrofelt skeleton connecting material and a preparation method thereof, a silicon carbide fibrofelt is degummed to obtain a degummed silicon carbide fibrofelt, the degummed silicon carbide fibrofelt is firstly subjected to surface pre-oxidation treatment and then is treated with an acidic liquid medium to obtain a pretreated silicon carbide fibrofelt, and the pretreated silicon carbide fibrofelt is subjected to self-supporting treatment to obtain the self-supporting silicon carbide fibrofelt skeleton connecting material. BN is deposited on the surface of the pretreated silicon carbide fiber felt, then heat treatment is carried out to obtain a silicon carbide fiber felt containing a BN interface layer, and then a SiC interface layer is deposited to obtain the silicon carbide fiber felt. The self-supporting silicon carbide fiber felt skeleton connecting material provided by the invention has low density, good mechanical properties and oxidation resistance.

Description

Technical Field

[0001] The present invention relates to the field of fiber composite material preparation, and particularly relates to a self-supporting silicon carbide fiber felt skeleton connecting material taking a silicon carbide fiber felt as a raw material and a preparation method thereof. Background Art

[0002] High-speed consumption and environmental pollution are two main problems faced when using fossil fuels. Among the strategies to solve these problems, energy conservation is a more valuable and important issue than energy depletion. More researchers focus their research on how to use increasingly precious energy resources in an efficient and environmentally friendly manner while meeting the requirements of economic progress and daily life needs. The porous medium combustion technology is proven to be a viable option for dealing with the above problems both technically and economically. The complex pore structure of the porous solid medium helps to premix fuel and air when embedded in the combustion zone. Due to the wide-band infrared emission characteristics of the solid, the combustion medium in the high-temperature zone can preheat the premixed fuel through radiation and conduction heat transfer.

[0003] Nowadays, porous media such as ceramic foam materials and metal fibers are usually used as combustion media. The ceramic foam combined or embedded with alumina particles can obtain the best combustion performance of the burner or low-concentration coal mine gas. The main purpose of studying honeycomb ceramic foam is to reduce emissions and improve power efficiency. However, due to its inherent brittleness, there is a possibility of crack propagation in the ceramic foam during the heating and cooling stages due to thermal shock.

[0004] Silicon carbide fiber-reinforced silicon carbide-based (SiC f / SiC) composites have excellent properties such as high strength, high modulus, low density, good oxidation resistance, and good high-temperature stability, and have been widely used in the fields of aerospace, nuclear fusion, atomic energy, etc. But SiC f / SiC composites are all prepared with continuous silicon carbide fiber braids as the reinforcing phase. The cost of silicon carbide fibers is high and the braiding technology requirements are high, which is not conducive to the popularization and application of SiC f / SiC composites. While the preparation process of silicon carbide fiber felt-reinforced ceramic matrix composites is simple, the production cost is low, and the processing cycle is short. The silicon carbide fiber skeleton connecting material assembled from silicon carbide fiber felts can overcome the inherent brittle fracture characteristics of the foam ceramics, and can further reduce the material density on the premise of maintaining the excellent properties of the material such as isotropy and high strength. By optimizing the microstructure, the thermophysical properties and oxidation and ablation resistance of the material can be improved, making it have high permeability, as well as relatively low air pressure, density and thermal inertia to obtain more efficient combustion performance and expand its application in the fields of aerospace, new energy vehicles, etc. However, there is currently no relevant report on the use of silicon carbide fiber felt skeleton connecting materials. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the first object of the present invention is to provide a preparation method of a self-supporting silicon carbide fiber felt skeleton connection material with low density, high strength, oxidation resistance and simple preparation process.

[0006] The second object of the present invention is to provide a self-supporting silicon carbide fiber felt skeleton connection material prepared by the above preparation method.

[0007] In order to achieve the above object, the technical scheme adopted by the present invention is as follows:

[0008] The present invention provides a preparation method of a self-supporting fiber felt skeleton connection material. After degumming the silicon carbide fiber felt, the degummed silicon carbide fiber felt is obtained. The degummed silicon carbide fiber felt is first subjected to surface pre-oxidation treatment, and then treated with an acidic liquid medium to obtain a pretreated silicon carbide fiber felt. BN is deposited on the surface of the pretreated silicon carbide fiber felt, and then heat treatment is carried out to obtain a silicon carbide fiber felt with a BN interface layer, and then a SiC interface layer is deposited to obtain it;

[0009] The thickness of the BN interface layer is 200-500 nm; preferably 250-420 nm.

[0010] The thickness of the SiC interface layer is 100-700 nm, preferably 250-700 nm.

[0011] In the preparation method of the present invention, after degumming the silicon carbide fiber felt, surface pre-oxidation treatment is first carried out to completely or partially eliminate the carbon existing on the fiber surface, and all or part of the carbon oxides containing elements Si, O and C existing on the fiber surface are converted into silicon dioxide, and then the silicon dioxide is washed and removed with an acidic liquid medium to obtain a pure silicon carbide surface, which is beneficial to the deposition of the interface. Then, the deposition thicknesses of the BN and SiC interface layers in the CVI process are regulated, which can optimize the microstructure of the self-supporting silicon carbide fiber felt skeleton connection material and improve the uniformity and mechanical strength of the material; at the same time, the composite structure of the BN and SiC interface layers can enhance the oxidation resistance and mechanical properties of the material. Through multiple experiments by the inventor, it is found that when the thickness of the BN interface prepared on the surface of the self-supporting silicon carbide fiber felt skeleton connection material is 200-500 nm and the thickness of the SiC interface is 100-700 nm, the self-supporting silicon carbide fiber felt skeleton connection material has a high porosity, good mechanical properties and good oxidation resistance. However, when the thickness of the BN interface < 200 nm, the oxidation resistance of the self-supporting silicon carbide fiber felt skeleton connection material is not good, and when the thickness of the SiC interface < 100 nm, the mechanical properties of the self-supporting silicon carbide fiber felt skeleton connection material are not good. When the thickness of the BN interface > 500 nm and the thickness of the SiC interface > 700 nm, the porosity in the self-supporting silicon carbide fiber felt skeleton connection material is too low, which will affect the permeability of the combustion medium.

[0012] Preferably, the thickness of the silicon carbide fiber felt is 0.5 to 200 mm. With the silicon carbide fiber felt having the above thickness, the performance of the finally obtained self-supporting silicon carbide fiber felt skeleton connecting material is optimal. If it is too thin, the integrity is poor, and if it is too thick, there will be a problem of poor uniformity.

[0013] Preferably, the density of the silicon carbide fiber felt is 0.03 to 0.085 g / cm 3 .

[0014] Preferably, the silicon carbide fiber felt is obtained by wet forming of chopped silicon carbide fibers. The length of the chopped silicon carbide fibers is 4 to 15 mm. By wet forming of chopped silicon carbide fibers with the above length, a silicon carbide fiber felt with high porosity, low density, and strong temperature resistance can be obtained. If the fibers are too long, the isotropy of the silicon carbide fiber felt will be reduced, and if the fibers are too short, its ability to form a self-supporting structure by skeleton lapping will be reduced.

[0015] The inventor found that it is crucial to use the silicon carbide fiber felt obtained by wet forming of chopped silicon carbide fibers as the raw material. If the silicon carbide fiber felt is prepared by the method of first forming a felt from a polycarbosilane precursor pre-oxidized fiber and then sintering, volume shrinkage and pore collapse are likely to occur, and it does not have the characteristics of low density and controllable pore structure, and cannot be used to prepare the self-supporting skeleton connecting material.

[0016] Preferably, the process of degumming the silicon carbide fiber felt is as follows: soak the silicon carbide fiber felt in acetone for 24 to 60 h, wash it with alcohol multiple times, and then dry it at 70 to 80 °C to obtain the degummed silicon carbide fiber felt.

[0017] Preferably, the process of pre-oxidation treatment is to perform heat treatment on the degummed silicon carbide fiber felt in air. The temperature of the heat treatment is 650 °C to 1000 °C, and the time of the heat treatment is 1 to 2 h.

[0018] Preferably, the acidic liquid medium is a mixed aqueous solution containing hydrofluoric acid and nitric acid.

[0019] In the mixed aqueous solution, the concentration of hydrofluoric acid ≥ 0.5 mol / L, and the concentration of nitric acid is 0.5 to 5 mol / L.

[0020] Preferably, the process of treating with the acidic liquid medium is to immerse the pre-oxidized silicon carbide fiber felt in the acidic liquid medium for 5 to 30 min, and then lift out the silicon carbide fiber felt and dry it to obtain the treated product.

[0021] After treatment with an acidic liquid medium, a pure silicon carbide fiber surface is obtained. Since the deposition of the BN / SiC composite interface is at the nanoscale on the fiber surface, it will not significantly change the original pore structure and porosity. Moreover, the synergistic oxidation of BN and SiC can form a borosilicate self-healing phase at 700 - 1200 °C in a high-temperature oxidation environment, which can effectively protect the fibers and ensure that the pores do not collapse, taking into account both the structural integrity and oxidation resistance.

[0022] In a preferred embodiment, the process of depositing BN on the surface of the pretreated silicon carbide fiber felt is as follows: The pretreated silicon carbide fiber felt is suspended in the isothermal zone of a deposition furnace, and BN is deposited by chemical vapor deposition. During the chemical vapor deposition process, the flow rate of boron trichloride (BCl 3 ) is controlled to be 1 - 3 L / min, the flow rate of ammonia (NH 3 ) is 3 - 7 L / min, the flow rate of hydrogen (H 2 ) is 3 - 4.8 L / min, and the flow rate of argon (Ar) is 3 - 6 L / min. The pressure inside the deposition furnace is controlled to be 0.5 - 4 kPa, the deposition temperature is 650 °C - 950 °C, and the deposition time is 30 - 90 min.

[0023] In a preferred embodiment, the heat treatment is carried out in a vacuum environment. The heat treatment temperature is 1000 - 1300 °C, preferably 1000 - 1200 °C, and the heat treatment time is 1 - 2 h.

[0024] In the present invention, by controlling the heat treatment temperature within the above range, BN coexisting in amorphous and crystalline states is obtained. The inventor found that the material properties are optimal at this time. If the temperature is too low, it is all amorphous and prone to hydrolysis and oxidation. If the temperature is too high, the performance of the silicon carbide fiber felt itself will be reduced. First, through chemical vapor deposition and then heat treatment, the BN interface layer prepared by the two-step method has good lubricity and oxidation resistance, and can protect the fibers from damage during the subsequent preparation process.

[0025] In a preferred embodiment, during the process of depositing the SiC interface layer, the flow rate of trichloromethylsilane (CH 3 SiCl 3 ) is controlled to be 1 - 2 L / min, the flow rate of hydrogen (H 2 ) is 2 - 4 L / min, and the flow rate of argon (Ar) is 1.5 - 2.5 L / min; the pressure inside the furnace is 0.5 - 4 kPa, the deposition temperature is 1000 - 1100 °C, and the deposition time is 1 - 2 h.

[0026] The present invention also provides a self-supporting silicon carbide fiber skeleton connecting material prepared by the above preparation method.

[0027] In a preferred embodiment, the self-supporting silicon carbide fiber framework connecting material is composed of a silicon carbide fiber felt, a BN interface layer and a SiC interface layer that successively wrap the silicon carbide fiber felt.

[0028] In a preferred embodiment, the density of the self-supporting silicon carbide fiber framework connecting material is 0.15 - 0.5 g / cm 3 The self-supporting framework connecting material prepared by the present invention has the following advantages:

[0029] (1) The self-supporting silicon carbide fiber framework connecting material prepared by the present invention is isotropic, has high mechanical strength, does not delaminate, and can be widely applied in the fields of aviation, aerospace, chemical engineering, etc.

[0030] (2) For the preparation method of the self-supporting silicon carbide fiber framework connecting material provided by the present invention, the silicon carbide fiber felt obtained by wet forming of chopped silicon carbide fibers is used. The silicon carbide fiber felt has the characteristics of low density and high porosity. The prepared silicon carbide fiber felt is first deposited with a BN interface by a chemical vapor infiltration (CVI) process using a two-step method, which can protect the fibers from damage and achieve a toughening effect during the subsequent preparation process. Then, a SiC interface is deposited, which can improve the strength and oxidation resistance of the silicon carbide fiber felt on the premise of ensuring the porosity of the silicon carbide fiber felt. The present invention only needs to adjust the thickness of the BN and SiC interfaces to optimize the microstructure of the material, thereby improving the mechanical properties, porosity, microstructure, thermophysical properties, oxidation resistance and ablation resistance of the material.

[0031] (3) The self-supporting silicon carbide fiber felt framework connecting material provided by the present invention has low density, good mechanical properties and oxidation resistance. The density of the prepared silicon carbide fiber felt framework connecting material is 0.15 - 0.5 g / cm 3 When it is in this range, the compressive strength in the x / y and z directions is 0.50 - 6.0 MPa and 0.20 - 2.40 MPa respectively, meeting the requirements of the fields of aviation, aerospace and new energy vehicles for lightweight and high-strength materials.

[0032] (4) The self-supporting silicon carbide fiber felt framework connecting material prepared by the present invention has pure components and no impurity elements.

[0033] (5) The self-supporting silicon carbide fiber framework connecting material prepared by the present invention has excellent mechanical properties, uniform microstructure and few defects, and can be used as a candidate for lightweight and high-strength framework materials. Description of the Drawings

[0034] Figure 1 is the process flow chart of the preparation of the self-supporting silicon carbide fiber framework connecting material involved in the present invention.

[0035] Figure 2 is the microstructure diagram of the self-supporting silicon carbide fiber felt framework connecting material involved in the present invention.

[0036] Figure 3 It is a scanning electron microscope photograph of the BN / SiC composite interface of the self-supporting silicon carbide felt fiber skeleton connection material prepared in Invention Example 1.

[0037] Figure 4 It is a scanning electron microscope photograph of the BN / SiC composite interface of the self-supporting silicon carbide fiber felt skeleton connection material prepared in Invention Example 2.

[0038] Figure 5 It is a scanning electron microscope photograph of the BN / SiC composite interface of the self-supporting silicon carbide fiber felt skeleton connection material prepared in Invention Example 3.

[0039] Figure 6 It is a scanning electron microscope photograph of the BN / SiC composite interface of the self-supporting silicon carbide fiber felt skeleton connection material prepared in Invention Example 4.

[0040] Figure 7 It is an SEM image of the chopped silicon carbide fiber skeleton connection material prepared in Comparative Example 1.

[0041] Figure 8 It is an SEM image of the chopped silicon carbide fiber skeleton connection material prepared in Comparative Example 2.

[0042] Figure 9 It is an SEM image of the chopped silicon carbide fiber skeleton connection material prepared in Comparative Example 3.

[0043] Figure 10 It is an SEM image of the chopped silicon carbide fiber skeleton connection material prepared in Comparative Example 4.

[0044] Figure 11 It is an SEM image of the chopped silicon carbide fiber skeleton connection material prepared in Comparative Example 5.

[0045] Figure 12 It is an SEM image of the chopped silicon carbide fiber skeleton connection material prepared in Comparative Example 6.

[0046] Figure 13 It is an SEM image of the chopped silicon carbide fiber skeleton connection material prepared in Comparative Example 7. Detailed implementation manners

[0047] The silicon carbide fiber felts used in the present invention are all prepared by a wet forming method using short silicon carbide fiber felts of different lengths.

[0048] Example 1:

[0049] A preparation method of a self-supporting silicon carbide fiber felt skeleton connection material, as Figure 1 shown, includes the following steps:

[0050] Step 1. Pretreatment of silicon carbide fiber felt: The silicon carbide fiber felt made of silicon carbide with a length of 4 mm is first immersed in acetone for 24 h, then washed repeatedly with alcohol, and then dried at 70 °C to remove the glue layer;

[0051] Step 2. Pretreatment of the surface of silicon carbide fibers: The silicon carbide fiber felt is heat-treated in air and kept at 650 °C for 1 h.

[0052] Step 3. Pretreatment of the surface of silicon carbide fibers: After pre-oxidation treatment, the silicon carbide fiber felt is immersed in a mixed solution of hydrofluoric acid and nitric acid, where the concentration of hydrofluoric acid is 0.5 mol / L and the concentration of nitric acid is 0.5 mol / L, and treated for 5 min.

[0053] Step 4. Preparation of boron nitride (BN) interface: The treated silicon carbide fiber felt is suspended in the isothermal zone of the deposition furnace, and a BN interface is prepared in the silicon carbide fiber felt by the CVI method; the precursor boron trichloride BCl 3 has a flow rate of 1 L / min, ammonia gas NH 3 has a flow rate of 3 L / min, hydrogen gas H 2 has a flow rate of 3.5 L / min, argon gas Ar has a flow rate of 3 L / min, the furnace pressure is 0.5 kPa, the deposition temperature is 650 °C, the deposition time is 30 min, and then the silicon carbide fiber felt is heat-treated in a vacuum environment at 1200 °C for 1 h to obtain a SiC fiber felt with a BN interface, and the heat treatment time is 1 h, and the obtained BN interface layer

[0054] Step 5. Preparation of silicon carbide (SiC) interface: The SiC fiber felt with a BN interface is suspended in the isothermal zone of the deposition furnace, and a BN / SiC composite interface is prepared in the fiber preform by the CVI method to obtain a SiC fiber felt with a BN / SiC composite interface; the precursor is trichloromethylsilane CH 3 SiCl 3 、hydrogen gas H 2 and argon gas Ar; the flow rates of the respective gases are: CH 3 SiCl 3 is 1 L / min, H 2 is 2 L / min, Ar is 1.5 L / min; the furnace pressure is 0.5 kPa, the deposition temperature is 1100 °C, the deposition time is 1 h, and the obtained SiC interface layer.

[0055] Figure 2 is a schematic diagram of the microstructure of the self-supporting silicon carbide fiber felt skeleton connecting material.

[0056] Figure 3It is a scanning electron microscope image of the BN / SiC composite interface, which is the skeleton connection material of the self-supporting silicon carbide fiber felt prepared in this example. In the figure, D1 is the BN interface layer with a thickness of 402.40 nm, and D2 is the SiC interface layer with a thickness of 298.51 nm.

[0057] The prepared silicon carbide fiber felt skeleton connection material has a density of 0.25 g / cm 3 , and the compressive strengths of the self-supporting silicon carbide fiber felt skeleton connection material in the x / y and z directions are 0.50 - 2.5 MPa and 0.20 - 1.50 MPa respectively, with a weight loss rate of 5%.

[0058] Example 2:

[0059] A preparation method of a self-supporting silicon carbide fiber skeleton connection material includes the following steps:

[0060] Step 1, pretreatment of the silicon carbide fiber preform: Place the silicon carbide fiber felt made of silicon carbide with a length of 8 mm in acetone and soak it for 60 h, then wash it with alcohol multiple times, and then dry it at 80 °C to remove the glue layer;

[0061] Step 2, surface pretreatment of the silicon carbide fiber: Heat-treat the silicon carbide fiber felt in air and keep it at different temperatures of 850 °C for 1 h.

[0062] Step 3, surface pretreatment of the silicon carbide fiber: After pre-oxidation treatment, the silicon carbide fiber felt is treated with a mixed solution of hydrofluoric acid and nitric acid, where the concentration of hydrofluoric acid is 0.5 mol / L and the concentration of nitric acid is 0.5 mol / L for 15 min.

[0063] Step 4, preparation of the boron nitride (BN) interface: Hang the treated silicon carbide fiber felt in the isothermal zone of the deposition furnace, and use the CVI method to prepare the BN interface in the silicon carbide fiber felt; the parameters are: the flow rate of the precursor boron trichloride BCl 3 is 1 L / min, the flow rate of ammonia gas NH 3 is 4 L / min, the flow rate of hydrogen gas H 2 is 4.8 L / min, the flow rate of argon gas Ar is 3 L / min, the furnace pressure is 1.0 kPa, the deposition temperature is 850 °C, the deposition time is 45 min, and then heat-treat the silicon carbide fiber felt in a vacuum environment at 1000 °C for 1 h to obtain the SiC fiber felt with a BN interface, and the heat-treatment time is 1 h to obtain the BN interface layer;

[0064] Step 5, preparation of the silicon carbide (SiC) interface: Hang the SiC fiber felt with a BN interface in the isothermal zone of the deposition furnace, and use the CVI method to prepare the BN / SiC composite interface in the fiber preform to obtain the SiC fiber felt with a BN / SiC composite interface; the precursor is trichloromethylsilane CH 3SiCl 3 , hydrogen gas H 2 and argon gas Ar; the flow rate of each gas is as follows: CH 3 SiCl 3 is 1 L / min, H 2 is 2 L / min, Ar is 2.0 L / min; the pressure in the furnace is 0.5 kPa, the deposition temperature is 1100 °C, and the deposition time is 1.5 h; the obtained SiC interface layer.

[0065] Figure 4 is the scanning electron micrograph of the self-supporting silicon carbide fiber skeleton connecting material BN / SiC composite interface prepared in Example 2 of the invention. D1 is the BN / SiC composite interface with a thickness of 809.05 nm, D2 is the BN interface layer with a thickness of 281.13 nm, and D3 is the SiC interface layer with a thickness of 490.65 nm.

[0066] The prepared silicon carbide fiber felt skeleton connecting material has a density of 0.32 g / cm 3 , and the compressive strengths of the self-supporting silicon carbide fiber felt skeleton connecting material in the x / y and z directions are 1.3 - 3.50 MPa and 0.4 - 1.8 MPa respectively, with a weight loss rate of 6%.

[0067] Example 3:

[0068] A preparation method of a self-supporting silicon carbide fiber skeleton connecting material, comprising the following steps:

[0069] Step 1, pretreatment of the silicon carbide fiber preform: Place the silicon carbide fiber felt made of silicon carbide with a length of 12 mm in acetone and soak for 48 h, then wash it with alcohol multiple times, and then dry it at 75 °C to remove the glue layer;

[0070] Step 2, surface pretreatment of the silicon carbide fiber: Heat-treat the silicon carbide fiber felt in air and store it at different temperatures of 900 °C for 1 h.

[0071] Step 3, surface pretreatment of the silicon carbide fiber: After pre-oxidation treatment, the silicon carbide fiber felt is treated with a mixed solution of hydrofluoric acid and nitric acid, where the concentration of hydrofluoric acid is 1.0 mol / L and the concentration of nitric acid is 0.5 mol / L for 30 min.

[0072] Step 4, preparation of the boron nitride (BN) interface: Hang the treated silicon carbide fiber felt in the isothermal zone of the deposition furnace, and use the CVI method to prepare the BN interface in the silicon carbide fiber felt; the parameters are: the flow rate of the precursor boron trichloride BCl 3 is 1 L / min, the flow rate of ammonia gas NH 3 is 3.5 L / min, and the flow rate of hydrogen gas H 2The flow rate is 4.8 L / min, the flow rate of argon Ar is 3 L / min, the pressure in the furnace is 2 kPa, the deposition temperature is 850 °C, the deposition time is 30 min, and then the silicon carbide fiber felt is heat-treated in a vacuum environment at 1200 °C for 1 h to obtain a SiC fiber felt with a BN interface, and the BN interface layer is obtained;

[0073] Step 5, preparing a silicon carbide (SiC) interface: On the basis of the BN interface layer, deposit a rigid silicon carbide (SiC) interface layer. The SiC interface layer has excellent high-temperature resistance and high-strength properties. Suspend the SiC fiber felt with a BN interface in the isothermal zone of the deposition furnace, and use the CVI method to prepare a BN / SiC composite interface in the fiber preform to obtain a SiC fiber felt with a BN / SiC composite interface; The precursor is trichloromethylsilane CH 3 SiCl 3 , hydrogen H 2 and argon Ar; The flow rates of the respective gases are: CH 3 SiCl 3 is 1 L / min, H 2 is 2 L / min, and Ar is 2.5 L / min; The pressure in the furnace is 2 kPa, the deposition temperature is 1100 °C, and the deposition time is 1 h; The obtained SiC interface layer.

[0074] Figure 5 is the scanning electron micrograph of the BN / SiC composite interface of the self-supporting silicon carbide fiber skeleton connecting material prepared in Example 3 of the invention. In the figure, D1 is the BN interface layer with a thickness of 431.09 nm, and D2 is the SiC interface layer with a thickness of 677.57 nm.

[0075] The prepared silicon carbide fiber felt skeleton connecting material has a density of 0.45 g / cm 3 , and the tensile strengths of the self-supporting silicon carbide fiber felt skeleton connecting material in the x / y and z directions are 3.0 - 5.5 MPa and 1.0 - 2.2 MPa respectively.

[0076] Example 4:

[0077] A preparation method of a self-supporting silicon carbide fiber skeleton connecting material, comprising the following steps:

[0078] Step 1, pretreatment of the silicon carbide fiber preform: Place the silicon carbide fiber felt made of silicon carbide with a length of 15 mm in acetone and soak it for 50 h, then wash it repeatedly with alcohol, and then dry it at 80 °C to remove the glue layer;

[0079] Step 2, surface pretreatment of the silicon carbide fiber: Heat-treat the silicon carbide fiber felt in air and store it at different temperatures of 1000 °C for 1 h.

[0080] Step 3. Surface pretreatment of silicon carbide fibers: After pre-oxidation treatment, the silicon carbide fiber felt is treated with a mixed solution of hydrofluoric acid and nitric acid, where the concentration of hydrofluoric acid is 1.0 mol / L and the concentration of nitric acid is 2 mol / L, for 30 min.

[0081] Step 4. Preparation of boron nitride (BN) interface: The treated silicon carbide fiber felt is suspended in the isothermal zone of the deposition furnace, and a BN interface is prepared in the silicon carbide fiber felt by the CVI method; the parameters are as follows: the flow rate of the precursor boron trichloride BCl 3 is 1 L / min, the flow rate of ammonia gas NH 3 is 4 L / min, the flow rate of hydrogen gas H 2 is 4.8 L / min, the flow rate of argon gas Ar is 5 L / min, the pressure in the furnace is 4 kPa, the deposition temperature is 950 °C, the deposition time is 30 min, and then the silicon carbide fiber felt is heat-treated in a vacuum environment at 1100 °C for 2 h to obtain a SiC fiber felt with a BN interface layer;

[0082] Step 5. Preparation of silicon carbide (SiC) interface: On the basis of the BN interface layer, a rigid silicon carbide (SiC) interface layer is further deposited. The SiC interface layer has excellent high-temperature resistance and high-strength properties. The SiC fiber felt with a BN interface is suspended in the isothermal zone of the deposition furnace, and a BN / SiC composite interface is prepared in the fiber preform by the CVI method to obtain a SiC fiber felt with a BN / SiC composite interface; the precursors are trichloromethylsilane CH 3 SiCl 3 hydrogen gas H 2 and argon gas Ar; the flow rates of the respective gases are as follows: CH 3 SiCl 3 is 1 L / min, H 2 is 2 L / min, and Ar is 2.5 L / min; the pressure in the furnace is 4 kPa, the deposition temperature is 1000 °C, and the deposition time is 1 h to obtain the SiC interface layer.

[0083] Figure 6 is the scanning electron microscope image of the self-supporting silicon carbide fiber skeleton connecting material BN / SiC composite interface prepared in Example 4 of the invention. In the figure, D1 is the BN interface layer with a thickness of 363.02 nm, and D2 is the SiC interface layer with a thickness of 472.85 nm.

[0084] The prepared silicon carbide fiber felt skeleton connecting material has a density of 0.39 g / cm 3 , and the tensile strengths of the self-supporting silicon carbide fiber felt skeleton connecting material in the x / y and z directions are 2.8 - 5.20 MPa and 1.3 - 1.9 MPa, respectively.

[0085] Comparative Example 1:

[0086] The preparation method is the same as that of Example 1, except that in step 1, the 4mm chopped carbon fiber felt is used to replace the silicon carbide fiber felt. Figure 7 This is the SEM photograph of the chopped carbon fiber skeleton connecting material prepared in this comparative example. Its interface layer is affected, which affects the finishing performance of the material. The prepared carbon fiber skeleton connecting material has a density of 0.15 - 0.23 g / cm 3 , and the tensile strengths in the x / y and z directions are 0.15 - 1.17 MPa and 0.4 - 0.52 MPa respectively. It is significantly worse than Example 1.

[0087] Comparative Example 2:

[0088] The preparation method is the same as that of Example 2, except that the thickness range of the deposited BN is between 50 - 100 nm, and the thickness of the deposited SiC is between 150 - 200 nm. Figure 8 This is the SEM photograph of the chopped silicon carbide fiber skeleton connecting material prepared in this comparative example. D3 is the BN / SiC composite interface layer with a thickness of 281.87 nm, D2 is the BN interface layer with a thickness of 68.05 nm, and D1 is the SiC interface layer with a thickness of 196.02 nm. The prepared silicon carbide fiber skeleton connecting material has a density of 0.22 g / cm 3 , and the tensile strengths in the x / y and z directions are 0.8 - 1.5 MPa and 0.3 - 1.3 MPa respectively.

[0089] Comparative Example 3:

[0090] The preparation method is the same as that of Example 1, except that only the BN interface layer is deposited and the SiC interface is not deposited. Figure 9 This is the SEM photograph of the chopped silicon carbide fiber skeleton connecting material prepared in this comparative example. D1 is the BN interface layer with a thickness of 695.43 nm; the prepared silicon carbide fiber skeleton connecting material has a density of 0.12 g / cm 3 , and the tensile strengths in the x / y and z directions are 0.2 - 0.9 MPa and 0.3 - 0.48 MPa respectively.

[0091] Comparative Example 4:

[0092] The preparation method is the same as that of Example 1, except that only the SiC interface layer is deposited and the BN interface is not deposited. Figure 10 This is the SEM photograph of the chopped silicon carbide fiber skeleton connecting material prepared in this comparative example. D1 and D2 are the SiC interface layers. The thickness near the inner side of the fiber bundle is 461.56 nm, and the thickness on the outer side of the fiber bundle is 779.69 nm; the prepared silicon carbide fiber skeleton connecting material has a density of 0.56 g / cm 3, the tensile strength in the x / y and z directions is 2.8 - 6.0 MPa and 1.2 - 2.5 MPa respectively, and the weight loss rate is 11%.

[0093] Comparative Example 5:

[0094] The preparation method is the same as that of Example 2, the difference is only that only the SiC interface layer is deposited, and the BN interface is not deposited. Figure 11 This is the SEM image of the short-cut silicon carbide fiber skeleton connecting material prepared in this comparative example. D1 and D2 are SiC interface layers with a thickness of 1555.67 nm; the prepared silicon carbide fiber skeleton connecting material has a density of 0.8 g / cm 3 , the tensile strength in the x / y and z directions is 3.0 - 8.5 MPa and 1.9 - 2.3 MPa respectively, and the weight loss rate is 12%

[0095] Comparative Example 6:

[0096] The preparation method is the same as that of Example 2, the difference is only that only the BN interface layer is deposited, and the SiC interface is not deposited. Figure 12 This is the SEM image of the short-cut silicon carbide fiber skeleton connecting material prepared in this comparative example. D1 is the BN interface layer with a thickness of 2009.79 nm, and the prepared silicon carbide fiber skeleton connecting material has a density of 0.32 g / cm 3 , the tensile strength in the x / y and z directions is 0.24 - 0.8 MPa and 0.15 - 0.5 MPa respectively.

[0097] Comparative Example 7:

[0098] Other conditions are the same as those in Example 1, the difference is that no pre-oxidation treatment is carried out. It can be seen that the deposited interface morphology is relatively rough and not smooth. See Figure 13 , D1 is the BN interface layer with a thickness of 239.39 nm, and D2 is the SiC interface layer with a thickness of 346.37 nm.

Claims

1. A method for preparing a self-supporting fiber felt skeleton connecting material, characterized in that: After degumming the silicon carbide fiber felt, a degummed silicon carbide fiber felt is obtained, the degummed silicon carbide fiber felt is first subjected to surface pre-oxidation treatment, and then treated with an acidic liquid medium to obtain a pretreated silicon carbide fiber felt, BN is deposited on the surface of the pretreated silicon carbide fiber felt, and then heat-treated to obtain a silicon carbide fiber felt containing a BN interface layer, and then a SiC interface layer is deposited; The thickness of the BN interface layer is 200-500 nm; The thickness of the SiC interface layer is 100-700 nm.

2. The method for preparing a self-supporting fiber felt skeleton connection material according to claim 1, characterized in that: The thickness of the silicon carbide fiber felt is 0.5 to 200 mm; The density of the silicon carbide fiber felt is 0.05-0.085 g / cm 3 .

3. A method for preparing a self-supporting fiber felt skeleton connection material according to claim 1 or 2, characterized in that: The silicon carbide fiber felt is prepared by wet felting short-cut silicon carbide fibers, and the length of the short-cut silicon carbide fibers is 4 to 15 mm.

4. A method for preparing a self-supporting fiber felt skeleton connection material according to claim 1 or 2, characterized in that: The process of degumming the silicon carbide fiber felt is as follows: soak the silicon carbide fiber felt in acetone for 24 to 60 hours, wash it with alcohol for several times, and then dry it at 70 to 80°C.

5. A method for preparing a self-supporting fiber felt skeleton connection material according to claim 1 or 2, characterized in that: The pre-oxidation treatment process is to heat-treat the degummed silicon carbide fiber felt in air at a temperature of 650° C. to 1000° C. for a time of 1 to 2 hours.

6. A method for preparing a self-supporting fiber felt skeleton connection material according to claim 1 or 2, characterized in that: The acidic liquid medium is a mixed aqueous solution containing hydrofluoric acid and nitric acid; In the mixed aqueous solution, the concentration of hydrofluoric acid is ≥0.5 mol / L, and the concentration of nitric acid is 0.5-5 mol / L; The process of the acidic liquid medium treatment is to immerse the pre-oxidized silicon carbide fiber felt in the acidic liquid medium for 5 to 30 minutes, and then pull out the silicon carbide fiber felt and dry it.

7. A method for preparing a self-supporting fiber felt skeleton connection material according to claim 1 or 2, characterized in that: The process of depositing BN on the surface of the pretreated silicon carbide fiber felt is as follows: the pretreated silicon carbide fiber felt is suspended in the isothermal zone of the deposition furnace, and BN is deposited by chemical vapor deposition. During the chemical vapor deposition process, the flow rate of BCl3 is controlled to be 1-3 L / min, the flow rate of NH3 is 3-7 L / min, the flow rate of H2 is 3-4.8 L / min, and the flow rate of Ar is 3-6 L / min. The pressure in the deposition furnace is controlled to be 0.5-4 kPa, the deposition temperature is 650°C-950°C, and the deposition time is 30-90 min. The heat treatment is carried out in a vacuum environment, the heat treatment temperature is 1000-1300° C., and the heat treatment time is 1-2 hours.

8. A method for preparing a self-supporting fiber felt skeleton connection material according to claim 1 or 2, characterized in that: During the process of depositing the SiC interface layer, the flow rate of CH3SiCl3 is controlled to be 1-2 L / min, the flow rate of H2 is 2-4 L / min, and the flow rate of Ar is 1.5-2.5 L / min; the pressure in the furnace is 0.5-4 kPa, the deposition temperature is 1000-1100°C, and the deposition time is 1-2 h.

9. A self-supporting silicon carbide fiber skeleton connecting material prepared by the preparation method according to any one of claims 1 to 8.

10. A self-supporting fiber felt skeleton connection material according to claim 9, characterized in that: The self-supporting silicon carbide fiber skeleton connection material is composed of a silicon carbide fiber felt, a BN interface layer and a SiC interface layer that sequentially wrap the silicon carbide fiber felt; The density of the self-supporting silicon carbide fiber skeleton connecting material is 0.15-0.5 g / cm 3 .

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