A method for improving oxidation resistance of C / SiC composite materials

Abstract

The present invention belongs to the technical field of ceramic-based composite materials and discloses a method for improving the oxidation resistance of a C / SiC composite material. The method comprises: impregnating carbon felt in a SiC precursor solution, followed by drying and pyrolysis, and repeating these steps several times to obtain a composite material A; directly subjecting the composite material A to a silica sol pore sealing treatment, or first subjecting the composite material A to a silicate sol modification treatment followed by silica sol pore sealing treatment, thereby improving the oxidation resistance of the C / SiC composite material. The present invention introduces a silicate having a thermal expansion coefficient similar to that of SiC and having high oxidation resistance and thermal stability into the C / SiC composite material to improve the composite material's oxidation resistance. Furthermore, SiO2 is introduced into the composite material matrix by silica sol impregnation and heat treatment to achieve pore sealing, thereby further reducing the composite material's porosity and improving the C / SiC composite material's oxidation resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic-based composite materials, and in particular to a method for improving the oxidation resistance of a C / SiC composite material. Background Art

[0002] Carbon fiber reinforced silicon carbide (C / SiC) ceramic matrix composites combine the high strength, high modulus, and corrosion resistance of carbon fibers with the high specific strength, high specific modulus, and high fracture toughness of carbonized ceramics. Due to their excellent mechanical properties and stable chemical properties, they are widely used in energy, automotive manufacturing, aerospace, and other fields.

[0003] However, C / SiC composites have poor oxidation resistance due to the inherent SiC nature, primarily due to the susceptibility of the SiC matrix to oxidation in high-temperature oxidizing atmospheres. Furthermore, C / SiC composites produced using the precursor impregnation and pyrolysis method have high porosity, which easily serves as oxygen diffusion channels, accelerating the oxidation process. This results in poor oxidation resistance, severely limiting their further application.

[0004] To this end, the present invention provides a method for improving the oxidation resistance of a C / SiC composite material. Summary of the Invention

[0005] To address the deficiencies in the prior art, the present invention provides a method for improving the oxidation resistance of C / SiC composites. This method improves the oxidation resistance of C / SiC composites by combining a doped silicate matrix with a SiO2 matrix. This is based on the fact that the selected zirconium silicate, yttrium silicate, and hafnium silicate closely match the thermal expansion coefficient of SiC itself, and that zirconium silicate and yttrium silicate possess high thermal stability and excellent oxidation resistance. Furthermore, given the low efficiency of preparing the silicate matrix by the sol-gel method, which can easily lead to high porosity in the final matrix, a pore sealing treatment using silica sol is performed during the final densification stage to further reduce the porosity of the composite.

[0006] A method for improving the oxidation resistance of C / SiC composite materials of the present invention is achieved by the following technical solutions:

[0007] A method for improving the oxidation resistance of a C / SiC composite material comprises the following steps:

[0008] SiC modification treatment: the carbon felt is immersed in a SiC precursor solution for vacuum impregnation treatment, and then the impregnated carbon felt is dried and subjected to high-temperature cracking treatment in sequence; this step is repeated several times to obtain composite material A;

[0009] The composite material A is directly subjected to silica sol sealing treatment, or the composite material A is first subjected to silicate sol modification treatment and then subjected to silica sol sealing treatment, so as to improve the oxidation resistance of the C / SiC composite material;

[0010] Wherein, the silicate sol modification treatment is carried out by the following steps:

[0011] The composite material A is immersed in a silicate sol for vacuum impregnation treatment, and then the composite material A after the impregnation treatment is dried and subjected to high-temperature cracking treatment in sequence; this step is repeated several times to obtain a composite material B;

[0012] The silica sol sealing treatment is carried out by the following steps:

[0013] The composite material A or the composite material B is immersed in silica sol for vacuum impregnation treatment, and then the composite material A or the composite material B after impregnation treatment is dried and heat treated in sequence; this step is repeated several times to improve the oxidation resistance of the C / SiC composite material.

[0014] Preferably, the SiC precursor solution is a xylene solution of polycarbosilane with a mass concentration of 45% to 55%.

[0015] Preferably, the mass concentration of the silica sol is 20% to 30%.

[0016] Preferably, the concentration of the silicate sol is 3 to 5 mol / L;

[0017] The silicate sol is composed of metal salt, tetraethyl silicate, anhydrous ethanol and LiF;

[0018] Wherein, the metal salt is zirconium chloride, yttrium nitrate or hafnium chloride;

[0019] In the silicate sol, the molar ratio of silicon to metal salt is 1.2:1, and the molar ratio of silicon to Li is 10:3.

[0020] Preferably, during the SiC modification treatment, the vacuum impregnation treatment lasts for 4 to 8 hours each time;

[0021] The temperature of each drying treatment is 65-75°C and the treatment time is 4-8 hours;

[0022] The reaction atmosphere of each high-temperature cracking treatment is argon, the heating rate is 3-7°C / min, the reaction temperature is 1050-1150°C, and the holding time is 0.5-1.5h.

[0023] Preferably, during the SiC modification treatment, the steps are repeated 4 to 14 times.

[0024] Preferably, during the silicate sol modification treatment, the vacuum impregnation treatment is carried out for 4 to 8 hours each time;

[0025] The temperature of each drying treatment is 65-75°C and the treatment time is 4-8 hours;

[0026] The reaction atmosphere of each high-temperature cracking treatment is argon, the heating rate is 3-7°C / min, the reaction temperature is 850-1150°C, and the holding time is 0.5-1.5h.

[0027] Preferably, during the silicate sol modification treatment, the steps are repeated 4 to 10 times.

[0028] Preferably, during the silica sol sealing treatment, the time of each silica sol vacuum impregnation treatment is 4 to 8 hours;

[0029] The temperature of each drying treatment is 95-105°C and the treatment time is 3-6 hours;

[0030] The reaction atmosphere of each heat treatment is argon, the heating rate is 3-7°C / min, the reaction temperature is 1150-1250°C, and the holding time is 0.5-1.5h.

[0031] Preferably, during the silica sol sealing treatment, the steps are repeated 4 to 5 times.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The present invention adopts a method of precursor liquid impregnation, drying, cracking or heat treatment cycle to carry out the densification process of the composite material matrix. The required equipment is simple and easy to obtain, and the process flow is highly feasible.

[0034] The present invention introduces silicate, which has a thermal expansion coefficient similar to that of SiC and has high oxidation resistance and thermal stability, into the C / SiC composite material, thereby improving the oxidation resistance of the composite material. SiO2 is introduced into the composite material matrix by means of silica sol impregnation and heat treatment to achieve pore sealing, thereby further reducing the porosity of the composite material, thereby improving the oxidation resistance of the prepared C / SiC composite material, so that the oxidation resistance of the C / SiC composite material prepared by the present invention is better than that of a C / SiC composite material with a pure SiC matrix. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a process flow chart of the method for improving the oxidation resistance of C / SiC composite materials according to the present invention. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present invention will be described clearly and completely below.

[0037] See also Figure 1 The present invention provides a method for improving the oxidation resistance of a C / SiC composite material, comprising the following steps:

[0038] Step 1, SiC modification treatment:

[0039] The carbon felt is immersed in a SiC precursor solution for vacuum impregnation treatment, and then the impregnated carbon felt is dried and subjected to high-temperature cracking treatment in sequence; this step is repeated several times to achieve SiC modification of the carbon felt, thereby obtaining a carbon felt with SiC loaded on its surface, namely, composite material A.

[0040] It should be noted that the present invention uses carbon felt as the carbon matrix and a xylene solution of polycarbosilane with a mass concentration of 45% to 55% as the SiC precursor solution. The carbon felt is immersed in the SiC precursor solution and vacuum impregnation is performed to allow the polycarbosilane in the SiC precursor solution to enter the pores of the carbon felt. This allows the polycarbosilane in the SiC precursor solution to be converted into silicon carbide on the carbon felt during the subsequent high-temperature cracking process, thereby achieving a preliminary modification of the carbon felt. In order to prevent the xylene solution from volatilizing during the high-temperature cracking process and generating excessive pores in the matrix, the present invention removes the impregnated carbon felt and then performs a drying process before the high-temperature cracking process. The drying process removes the solvent, thereby preventing the solvent from volatilizing during the high-temperature cracking process and generating excessive pores in the matrix.

[0041] The present invention preferably repeats the impregnation, drying, and pyrolysis steps 4 to 14 times to allow more polycarbosilane to enter the pores of the carbon felt through gradual impregnation, producing a sufficient amount of SiC matrix after pyrolysis to fill the pores of the carbon felt and reduce the porosity. Each vacuum impregnation treatment lasts 4 to 8 hours to allow the precursor to completely infiltrate the carbon felt, helping to evenly disperse the polycarbosilane in the precursor throughout the carbon felt, and further facilitating the formation of evenly distributed SiC within the carbon felt through subsequent pyrolysis. To ensure that the solvent can be removed through drying, each drying treatment is performed at a temperature of 65 to 75°C for 4 to 8 hours. To ensure that the polycarbosilane impregnated in the carbon felt is pyrolyzed to form SiC, the reaction atmosphere for each pyrolysis treatment in the present invention is argon, the heating rate is 3 to 7°C / min, the reaction temperature is 1050 to 1150°C, and the holding time is 0.5 to 1.5 hours.

[0042] Step 2: directly performing silica sol sealing treatment on the composite material A, or first performing silicate sol modification treatment on the composite material A and then performing silica sol sealing treatment, so as to improve the oxidation resistance of the C / SiC composite material.

[0043] Wherein, the silicate sol modification treatment is carried out by the following steps:

[0044] The composite material A is immersed in a silicate sol for vacuum impregnation treatment, and then the composite material A after the impregnation treatment is dried and subjected to high-temperature cracking treatment in sequence; this step is repeated several times to obtain a composite material B.

[0045] It should be noted that the concentration of the silicate sol used in the present invention is 3 to 5 mol / L. The silicate sol is composed of a metal salt, tetraethyl silicate, anhydrous ethanol and LiF, and in the silicate sol, the molar ratio of silicon to metal salt is 1.2:1, and the molar ratio of silicon to Li is 10:3. The metal salt preferably used in the present invention is zirconium chloride, yttrium nitrate or hafnium chloride. The silicate sol used in the present invention is prepared by the following steps: dissolving the metal salt in anhydrous ethanol and stirring thoroughly to obtain solution A. LiF and tetraethyl silicate are mixed thoroughly to obtain solution B. Solution B is added dropwise to solution A via a peristaltic pump. After completion, the mixed solution is heated to 110°C in an oil bath for reaction for 2 hours. After completion, it is allowed to stand at room temperature for one day and then filtered to obtain a silicate precursor sol.

[0046] The present invention further immerses the carbon felt with SiC loaded on its surface obtained after step 1, i.e., composite material A, in a silicate sol. The immersion treatment allows the precursor in the silicate sol to infiltrate composite material A, thereby producing a silicate matrix. The impregnated composite material A is then removed and dried to remove the solvent, thereby preventing excessive pores from forming in the matrix due to volatilization of the solvent during pyrolysis. The dried composite material A is then subjected to pyrolysis treatment, whereby the silicate sol is cracked into a silicate matrix, which fills the pores of the matrix, thereby producing composite material B.

[0047] The present invention preferably repeats the impregnation, drying, and pyrolysis steps 0 to 10 times to allow more silicate sol to enter the pores of the carbon felt. After pyrolysis, more silicate matrix is ​​produced, filling the pores of the carbon felt and thus reducing porosity. Each vacuum impregnation treatment lasts 4 to 8 hours to allow the silicate sol to fully penetrate the pores of the carbon felt of Composite Material A. To ensure that the solvent components in the silicate sol are removed and to prevent excessive pores in the matrix from volatilization during the pyrolysis process, each drying treatment is performed at a temperature of 95 to 105°C and a treatment time of 3 to 6 hours. To ensure that the silicate sol impregnated in Composite Material A is pyrolyzed into a silicate matrix during the pyrolysis process to fill the matrix pores, each pyrolysis treatment is performed in an argon atmosphere, with a heating rate of 3 to 7°C / min, a reaction temperature of 850 to 1150°C, and a holding time of 0.5 to 1.5 hours.

[0048] The silica sol sealing treatment is carried out by the following steps:

[0049] The composite material A or the composite material B is immersed in silica sol for vacuum impregnation treatment, and then the composite material A or the composite material B after impregnation treatment is dried and heat treated in sequence; this step is repeated several times to improve the oxidation resistance of the C / SiC composite material.

[0050] The present invention further immerses the composite material A or composite material B prepared above in silica sol. Vacuum impregnation is performed by immersing the composite material A or composite material B in the silica sol, allowing the SiO2 in the silica sol to fill the pores in the composite material A or composite material B. The impregnated composite material A or composite material B is then removed and dried to remove the solvent from the silica sol, thereby preventing excessive pores from forming in the matrix due to volatilization of the solvent during high-temperature cracking. The dried material is then heat-treated to reduce recrystallization of the SiO2. The silica sol used in the present invention has a mass concentration of 20% to 30%.

[0051] The present invention preferably repeats the steps of impregnation, drying and heat treatment 4 to 5 times to improve the sealing effect and thereby reduce the porosity of the composite material. The time of each vacuum impregnation treatment is 4 to 8 hours to achieve the purpose of complete infiltration of the composite material by the silica sol. In order to reduce or avoid the interference of the solvent components in the silica sol, the temperature of each drying treatment of the material after impregnation with the silica sol is 95 to 105°C, and the treatment time is 3 to 6 hours. In order to ensure that the recrystallization of SiO2 is reduced and affect the subsequent oxidation experiment, the reaction atmosphere of each high-temperature cracking treatment is argon, the heating rate is 3 to 7°C / min, the reaction temperature is 1150 to 1250°C, and the holding time is 0.5 to 1.5 hours.

[0052] Example 1

[0053] This embodiment provides a method for improving the oxidation resistance of a C / SiC composite material, comprising the following steps:

[0054] Step 1: Pre-treat carbon felt:

[0055] The carbon felt was cut into small pieces of 10 mm × 10 mm, cleaned with ethanol, and dried for later use.

[0056] Step 2: SiC modification to prepare composite material A:

[0057] 1) Immersing the dried carbon felt obtained in step 1 above in a 50% by mass polycarbosilane-xylene mixed solution, vacuum impregnating for 6 hours, removing the impregnated carbon felt and drying it in a 70°C drying oven for 6 hours, then placing it in a tubular furnace and performing high-temperature pyrolysis at a pyrolysis temperature of 1100°C for 1 hour, with argon gas introduced throughout the pyrolysis process;

[0058] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0059] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0060] Steps 1), 2), and 3) constitute one cycle, and the sample is subjected to 5 cycles of impregnation and cracking to obtain composite material A.

[0061] Step 3: Modification of silicate sol to prepare composite material B:

[0062] 1) The dried composite material A obtained above was placed in a 3 mol / L zirconium silicate sol and vacuum impregnated for 6 h. The impregnated composite material A was then placed in a drying oven at 70°C and dried for 6 h. The composite material A was then placed in a tubular furnace and subjected to high-temperature pyrolysis at a pyrolysis temperature of 1100°C for 1 h. Argon was introduced throughout the pyrolysis process.

[0063] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0064] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0065] Steps 1), 2), and 3) constitute one cycle, and the sample is subjected to 9 cycles of impregnation and cracking, that is, step 3 is repeated 9 times to obtain composite material B, which is directly used as the C / SiC composite material.

[0066] Step 4: Silica sol sealing treatment:

[0067] 1) The dried composite material B obtained above was placed in a silica sol with a mass concentration of 25% and vacuum impregnated for 6 hours. The impregnated composite material B was then placed in a drying oven at 100°C for 5 hours and then placed in a tubular furnace for high-temperature pyrolysis at a pyrolysis temperature of 1200°C for 1 hour, with argon gas introduced throughout the high-temperature pyrolysis process;

[0068] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0069] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0070] Steps 1), 2), and 3) constitute one cycle, and the sample is subjected to four cycles of impregnation and cracking, that is, step 4 is repeated four times to obtain a matrix-modified C / SiC composite material sealed with silica sol.

[0071] Example 2

[0072] This embodiment provides a method for improving the oxidation resistance of a C / SiC composite material, comprising the following steps:

[0073] Step 1: Pre-treat carbon felt:

[0074] The carbon felt was cut into small pieces of 10 mm × 10 mm, cleaned with ethanol, and dried for later use.

[0075] Step 2: SiC modification to prepare composite material A:

[0076] 1) Immersing the dried carbon felt obtained in step 1 above in a 50% by mass polycarbosilane-xylene mixed solution, vacuum impregnating for 6 hours, removing the impregnated carbon felt and drying it in a 70°C drying oven for 6 hours, then placing it in a tubular furnace and performing high-temperature pyrolysis at a pyrolysis temperature of 1100°C for 1 hour, with argon gas introduced throughout the pyrolysis process;

[0077] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0078] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0079] Steps 1), 2), and 3) constitute one cycle, and the sample is subjected to 4 cycles of immersion and cracking, that is, step 2 is repeated 4 times to obtain composite material A.

[0080] Step 3: Modification of silicate sol to prepare composite material B:

[0081] 1) The dried composite material A obtained above was placed in a 3 mol / L hafnium silicate sol and vacuum impregnated for 6 h. The impregnated composite material A was then dried in a 70°C drying oven for 6 h. The composite material A was then placed in a tubular furnace and subjected to high-temperature pyrolysis at 900°C for 1 h, with argon gas being introduced throughout the pyrolysis process.

[0082] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0083] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0084] Steps 1), 2), and 3) constitute one cycle. The sample is subjected to 10 cycles of impregnation and cracking, i.e., step 3 is repeated 10 times to obtain composite material B, which is directly used as the C / SiC composite material.

[0085] Step 4: Silica sol sealing treatment:

[0086] 1) The dried composite material B obtained above was placed in a silica sol with a mass concentration of 25% and vacuum impregnated for 6 hours. The impregnated composite material B was then placed in a drying oven at 100°C for 5 hours and then placed in a tubular furnace for high-temperature pyrolysis at a pyrolysis temperature of 1200°C for 1 hour, with argon gas introduced throughout the high-temperature pyrolysis process;

[0087] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0088] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0089] Steps 1), 2), and 3) constitute one cycle, and the sample is subjected to 5 cycles of impregnation and cracking, that is, step 4 is repeated 5 times to obtain a matrix-modified C / SiC composite material sealed with silica sol.

[0090] Example 3

[0091] This embodiment provides a C / SiC composite material with improved oxidation resistance, and the method is as follows:

[0092] Step 1: Pre-treat carbon felt:

[0093] The carbon felt was cut into small pieces of 10 mm × 10 mm, cleaned with ethanol, and dried for later use.

[0094] Step 2: SiC modification to prepare composite material A:

[0095] 1) Immersing the dried carbon felt obtained in step 1 above in a 50% by mass polycarbosilane-xylene mixed solution, vacuum impregnating for 6 hours, removing the impregnated carbon felt and drying it in a 70°C drying oven for 6 hours, then placing it in a tubular furnace and performing high-temperature pyrolysis at a pyrolysis temperature of 1100°C for 1 hour, with argon gas introduced throughout the pyrolysis process;

[0096] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0097] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0098] Steps 1), 2), and 3) constitute one cycle, and the sample is subjected to 8 cycles of immersion and cracking, that is, step 2 is repeated 8 times to obtain composite material A.

[0099] Step 3: Preparation of composite material B:

[0100] 1) The dried composite material A obtained above was placed in a 5 mol / L yttrium silicate sol and vacuum impregnated for 6 h. The impregnated composite material A was then dried in a 70°C drying oven for 6 h. The composite material A was then placed in a tubular furnace and subjected to high-temperature pyrolysis at a pyrolysis temperature of 900°C for 1 h. Argon was introduced throughout the pyrolysis process.

[0101] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0102] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0103] Steps 1), 2), and 3) constitute one cycle. The sample is subjected to 6 cycles of impregnation and cracking, i.e., step 3 is repeated 6 times to obtain composite material B, which is directly used as the C / SiC composite material.

[0104] Step 4: Silica sol sealing treatment:

[0105] 1) The dried composite material B obtained above was placed in a silica sol with a mass concentration of 25% and vacuum impregnated for 6 hours. The impregnated composite material B was then placed in a drying oven at 100°C for 5 hours and then placed in a tubular furnace for high-temperature pyrolysis at a pyrolysis temperature of 1200°C for 1 hour, with argon gas introduced throughout the high-temperature pyrolysis process;

[0106] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0107] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0108] Steps 1), 2), and 3) constitute one cycle, and the sample is subjected to 5 cycles of impregnation and cracking, that is, step 4 is repeated 5 times to obtain a matrix-modified C / SiC composite material sealed with silica sol.

[0109] Example 4

[0110] This embodiment provides a C / SiC composite material with improved oxidation resistance, and the method is as follows:

[0111] Step 1: Pre-treat carbon felt:

[0112] The carbon felt was cut into small pieces of 10 mm × 10 mm, cleaned with ethanol, and dried for later use.

[0113] Step 2: SiC modification to prepare composite material A:

[0114] 1) Immersing the dried carbon felt obtained in step 1 above in a 50% by mass polycarbosilane-xylene mixed solution, vacuum impregnating for 6 hours, removing the impregnated carbon felt and drying it in a 70°C drying oven for 6 hours, then placing it in a tubular furnace and performing high-temperature pyrolysis at a pyrolysis temperature of 1100°C for 1 hour, with argon gas introduced throughout the pyrolysis process;

[0115] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0116] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0117] Steps 1), 2), and 3) constitute one cycle, and the sample is subjected to 10 cycles of immersion and cracking, that is, step 2 is repeated 10 times to obtain composite material A.

[0118] Step 3: Modification of silicate sol to prepare composite material B:

[0119] 1) The dried composite material A obtained above was placed in a 5 mol / L yttrium silicate sol and vacuum impregnated for 6 h. The impregnated composite material A was then dried in a 70°C drying oven for 6 h. The composite material A was then placed in a tubular furnace and subjected to high-temperature pyrolysis at a pyrolysis temperature of 900°C for 1 h. Argon was introduced throughout the pyrolysis process.

[0120] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0121] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0122] Steps 1), 2), and 3) constitute one cycle. The sample is subjected to four cycles of impregnation and cracking, i.e., step 3 is repeated four times to obtain composite material B, which is directly used as the C / SiC composite material.

[0123] Step 4: Silica sol sealing treatment:

[0124] 1) The dried composite material B obtained above was placed in a silica sol with a mass concentration of 25% and vacuum impregnated for 6 hours. The impregnated composite material B was then placed in a drying oven at 100°C for 5 hours and then placed in a tubular furnace for high-temperature pyrolysis at a pyrolysis temperature of 1200°C for 1 hour, with argon gas introduced throughout the high-temperature pyrolysis process;

[0125] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0126] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0127] Steps 1), 2), and 3) constitute one cycle, and the sample is subjected to 5 cycles of impregnation and cracking, that is, step 4 is repeated 5 times to obtain a matrix-modified C / SiC composite material sealed with silica sol.

[0128] Example 5

[0129] This embodiment provides a silica sol-sealed C / SiC composite material, and its preparation method is as follows:

[0130] Step 1: Pre-treat carbon felt:

[0131] The carbon felt was cut into small pieces of 10 mm × 10 mm, cleaned with ethanol, and dried for later use.

[0132] Step 2: Preparation of composite material A:

[0133] 1) Immersing the dried carbon felt obtained in step 1 above in a 50% by mass polycarbosilane-xylene mixed solution, vacuum impregnating for 6 hours, removing the impregnated carbon felt and drying it in a 70°C drying oven for 6 hours, then placing it in a tubular furnace and performing high-temperature pyrolysis at a pyrolysis temperature of 1100°C for 1 hour, with argon gas introduced throughout the pyrolysis process;

[0134] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0135] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0136] Steps 1), 2), and 3) constitute one cycle, and the sample is subjected to 14 cycles of impregnation and cracking, that is, step 2 is repeated 14 times to obtain a C / SiC composite material with a pure PCS matrix.

[0137] Step 3: Silica sol sealing treatment:

[0138] 1) The dried composite material A obtained above was placed in a silica sol with a mass concentration of 25% and vacuum impregnated for 6 hours. The impregnated composite material A was then placed in a drying oven at 100°C for 5 hours and then placed in a tube furnace for high-temperature pyrolysis at a pyrolysis temperature of 1200°C for 1 hour, with argon gas being introduced throughout the high-temperature pyrolysis process;

[0139] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0140] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0141] Steps 1), 2), and 3) constitute one cycle, and the sample is subjected to 5 cycles of impregnation and cracking to obtain a C / SiC composite material with a pure PCS matrix sealed with SiO2.

[0142] Comparative Example 1

[0143] This comparative example provides a C / SiC composite material, and the method thereof is as follows:

[0144] Step 1: Pre-treat carbon felt:

[0145] The carbon felt was cut into small pieces of 10 mm × 10 mm, cleaned with ethanol, and dried for later use.

[0146] Step 2: Preparation of composite material A:

[0147] 1) Immersing the dried carbon felt obtained in step 1 above in a 50% by mass polycarbosilane-xylene mixed solution, vacuum impregnating for 6 hours, removing the impregnated carbon felt and drying it in a 70°C drying oven for 6 hours, then placing it in a tubular furnace and performing high-temperature pyrolysis at a pyrolysis temperature of 1100°C for 1 hour, with argon gas introduced throughout the pyrolysis process;

[0148] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0149] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0150] Steps 1), 2), and 3) constitute one cycle, and the sample is subjected to 14 cycles of impregnation and cracking to obtain a C / SiC composite material with a pure PCS matrix.

[0151] Comparative Example 2

[0152] This comparative example provides a matrix-modified C / SiC composite material, and the method is as follows:

[0153] Step 1: Pre-treat carbon felt:

[0154] The carbon felt was cut into small pieces of 10 mm × 10 mm, cleaned with ethanol, and dried for later use.

[0155] Step 2: Preparation of composite material A:

[0156] 1) Immersing the dried carbon felt obtained in step 1 above in a 50% by mass polycarbosilane-xylene mixed solution, vacuum impregnating for 6 hours, removing the impregnated carbon felt and drying it in a 70°C drying oven for 6 hours, then placing it in a tubular furnace and performing high-temperature pyrolysis at a pyrolysis temperature of 1100°C for 1 hour, with argon gas introduced throughout the pyrolysis process;

[0157] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0158] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0159] Steps 1), 2), and 3) constitute one cycle, and the sample is subjected to 5 cycles of immersion and cracking, that is, step 2 is repeated 5 times to obtain composite material A.

[0160] Step 3: Preparation of composite material B:

[0161] 1) The dried composite material A obtained above was placed in a 3 mol / L zirconium silicate sol and vacuum impregnated for 6 h. The impregnated composite material A was then placed in a drying oven at 70°C and dried for 6 h. The composite material A was then placed in a tubular furnace and subjected to high-temperature pyrolysis at a pyrolysis temperature of 1100°C for 1 h. Argon was introduced throughout the pyrolysis process.

[0162] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0163] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0164] Steps 1), 2), and 3) constitute one cycle, and the sample is subjected to 9 cycles of impregnation and cracking, that is, step 3 is repeated 9 times to obtain composite material B, which is directly used as the C / SiC composite material.

[0165] Comparative Example 3

[0166] This comparative example provides a matrix-modified C / SiC composite material, and the method is as follows:

[0167] Step 1: Pre-treat carbon felt:

[0168] The carbon felt was cut into small pieces of 10 mm × 10 mm, cleaned with ethanol, and dried for later use.

[0169] Step 2: Preparation of composite material A:

[0170] 1) Immersing the dried carbon felt obtained in step 1 above in a 50% by mass polycarbosilane-xylene mixed solution, vacuum impregnating for 6 hours, removing the impregnated carbon felt and drying it in a 70°C drying oven for 6 hours, then placing it in a tubular furnace and performing high-temperature pyrolysis at a pyrolysis temperature of 1100°C for 1 hour, with argon gas introduced throughout the pyrolysis process;

[0171] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0172] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0173] Steps 1), 2), and 3) constitute one cycle, and the sample is subjected to 8 cycles of immersion and cracking, that is, step 2 is repeated 8 times to obtain composite material A.

[0174] Step 3: Preparation of composite material B:

[0175] 1) The dried composite material A obtained above was placed in a 5 mol / L yttrium silicate sol and vacuum impregnated for 6 h. The impregnated composite material A was then dried in a 70°C drying oven for 6 h. The composite material A was then placed in a tubular furnace and subjected to high-temperature pyrolysis at a pyrolysis temperature of 900°C for 1 h. Argon was introduced throughout the pyrolysis process.

[0176] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0177] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0178] Steps 1), 2), and 3) constitute one cycle, and the sample is subjected to 6 cycles of impregnation and cracking, i.e., step 3 is repeated 6 times to obtain composite material B, which is directly used as the C / SiC composite material.

[0179] Comparative Example 4

[0180] This comparative example provides a matrix-modified C / SiC composite material, and the method is as follows:

[0181] Step 1: Pre-treat carbon felt:

[0182] The carbon felt was cut into small pieces of 10 mm × 10 mm, cleaned with ethanol, and dried for later use.

[0183] Step 2: Preparation of composite material A:

[0184] 1) Immersing the dried carbon felt obtained in step 1 above in a 50% by mass polycarbosilane-xylene mixed solution, vacuum impregnating for 6 hours, removing the impregnated carbon felt and drying it in a 70°C drying oven for 6 hours, then placing it in a tubular furnace and performing high-temperature pyrolysis at a pyrolysis temperature of 1100°C for 1 hour, with argon gas introduced throughout the pyrolysis process;

[0185] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0186] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0187] Steps 1), 2), and 3) constitute one cycle, and the sample is subjected to 4 cycles of immersion and cracking, that is, step 2 is repeated 4 times to obtain composite material A.

[0188] Step 3: Preparation of composite material B:

[0189] 1) The dried composite material A obtained above was placed in a 3 mol / L hafnium silicate sol and vacuum impregnated for 6 h. The impregnated composite material A was then dried in a 70°C drying oven for 6 h. The composite material A was then placed in a tubular furnace and subjected to high-temperature pyrolysis at 900°C for 1 h, with argon gas being introduced throughout the pyrolysis process.

[0190] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0191] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0192] Steps 1), 2), and 3) constitute one cycle. The sample is subjected to 10 cycles of impregnation and cracking, i.e., step 3 is repeated 10 times to obtain composite material B, which is directly used as the C / SiC composite material.

[0193] Comparative Example 5

[0194] This comparative example provides a matrix-modified C / SiC composite material, and the method is as follows:

[0195] Step 1: Pre-treat carbon felt:

[0196] The carbon felt was cut into small pieces of 10 mm × 10 mm, cleaned with ethanol, and dried for later use.

[0197] Step 2: Preparation of composite material A:

[0198] 1) Immersing the dried carbon felt obtained in step 1 above in a 50% by mass polycarbosilane-xylene mixed solution, vacuum impregnating for 6 hours, removing the impregnated carbon felt and drying it in a 70°C drying oven for 6 hours, then placing it in a tubular furnace and performing high-temperature pyrolysis at a pyrolysis temperature of 1100°C for 1 hour, with argon gas introduced throughout the pyrolysis process;

[0199] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0200] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0201] Steps 1), 2), and 3) constitute one cycle, and the sample is subjected to 10 cycles of immersion and cracking, that is, step 2 is repeated 10 times to obtain composite material A.

[0202] Step 3: Preparation of composite material B:

[0203] 1) The dried composite material A obtained above was placed in a 5 mol / L yttrium silicate sol and vacuum impregnated for 6 h. The impregnated composite material A was then dried in a 70°C drying oven for 6 h. The composite material A was then placed in a tubular furnace and subjected to high-temperature pyrolysis at a pyrolysis temperature of 900°C for 1 h. Argon was introduced throughout the pyrolysis process.

[0204] 2) calculating the porosity of the pyrolysis product sample obtained in step 1) using the Archimedean drainage method;

[0205] 3) After the porosity test, the sample was placed in a drying oven at 70°C and dried for 6 hours;

[0206] Steps 1), 2), and 3) constitute one cycle. The sample is subjected to four cycles of impregnation and cracking, i.e., step 3 is repeated four times to obtain composite material B, which is directly used as the C / SiC composite material.

[0207] It should be noted that the porosity of the samples in the above embodiments and comparative examples of the present invention was calculated according to the following method:

[0208] The mass of the sample after pyrolysis was weighed on an analytical balance and recorded as m1;

[0209] The sample was placed in kerosene and vacuum immersed for 6 h, after which the sample was taken out and the residual kerosene on the surface of the sample was wiped off, and the wet weight of the sample was weighed using an analytical balance and recorded as m3;

[0210] Tie the sample with a thin wire and suspend it in a beaker filled with kerosene (the sample does not touch the bottom or wall of the beaker). Use an analytical balance to measure the floating weight of the sample, which is recorded as m2.

[0211] Experimental part

[0212] (1) Porosity

[0213] The present invention tests the porosity of the material samples prepared in Examples 1-5 and Comparative Examples 1-5, respectively, and the test results are shown in Table 1.

[0214] Table 1 Porosity test results

[0215]

[0216] By comparing the test results of Example 1 with Comparative Example 2, the test results of Comparative Example 2 with Comparative Example 4, the test results of Comparative Example 3 with Comparative Example 3, and the test results of Example 4 with Comparative Example 5, the porosity of the material after silica sol sealing treatment is greatly reduced.

[0217] By comparing the test results of Example 5 with that of Example 1, the test results of Example 5 with that of Example 3, the test results of Comparative Example 2 with that of Comparative Example 1, and the test results of Comparative Example 4 with that of Comparative Example 1, it can be seen that compared with the C / SiC composite material with a pure PCS matrix, the porosity of the material is increased to a certain extent after doping with the ZrSiO4 component, the Y2Si2O7 component, and the HfSiO4 component.

[0218] By comparing the test results of Example 1 with those of Comparative Example 1, the test results of Comparative Example 3 with those of Comparative Example 1, and the test results of Comparative Example 4 with those of Comparative Example 1, the porosity of the material can be further reduced by performing silica sol sealing treatment on the matrix-modified C / SiC composite material.

[0219] (2) Antioxidant performance test

[0220] Table 2 Maximum weight loss rates of Comparative Examples 1-5 and Examples 1-5

[0221]

[0222] The present invention tests the antioxidant properties of the material samples prepared in Examples 1-5 and Comparative Examples 1-5, respectively, and summarizes the maximum weight loss rates in the test results of Examples 1-5 and Comparative Examples 1-5 as shown in Table 2.

[0223] The test method for antioxidant performance is: static constant temperature oxidation test. The specific test steps are as follows:

[0224] First, weigh the sample mass and record it as m1. Put the sample into the muffle furnace and set the heating rate to 3≤RHF≤5℃ / min. The total oxidation time is 50h. In the first 10h of the oxidation process, set the holding time to 2h as a time node. In the next 40h, set the holding time to 10h as a time node. Take out the sample at each time node and weigh it as m2. After the oxidation is completed, follow the Calculate the ω oxidation weight loss rate.

[0225] The composite material of Example 1 exhibited a maximum oxidation weight loss of 5.93% after 4 hours of oxidation at 1000°C, and a maximum oxidation weight loss of 3.68% after 6 hours of oxidation at 1200°C. The composite material of Comparative Example 2 exhibited a maximum oxidation weight loss of 5.41% after 2 hours of oxidation at 1000°C, and a maximum oxidation weight loss of 4.91% after 4 hours of oxidation at 1200°C. As shown in Tables 1 and 2, silica sol sealing treatment significantly reduced the porosity of the zirconium silicate matrix-modified C / SiC composite material, significantly prolonged the time to maximum oxidation weight loss, and enhanced its antioxidant effect.

[0226] The composite material of Example 2 exhibited a maximum oxidation weight loss of 5.02% after 2 hours of oxidation at 1000°C, and a maximum oxidation weight loss of 3.62% after 2 hours of oxidation at 1200°C. The composite material of Comparative Example 4 exhibited a maximum oxidation weight loss of 5.26% after 2 hours of oxidation at 1000°C, and a maximum oxidation weight loss of 4.78% after 2 hours of oxidation at 1200°C. As shown in Tables 1 and 2, silica sol sealing treatment on the C / SiC composite material modified with a hafnium silicate matrix significantly reduced the material's porosity and maximum oxidation weight loss, thereby enhancing its antioxidant properties.

[0227] The composite material of Example 3 exhibited a maximum oxidation weight loss of 5.2% after 4 hours of oxidation at 1000°C, and a maximum oxidation weight loss of 4.58% after 2 hours of oxidation at 1200°C. The composite material of Comparative Example 3 exhibited a maximum oxidation weight loss of 5.44% after 4 hours of oxidation at 1000°C, and a maximum oxidation weight loss of 4.46% after 2 hours of oxidation at 1200°C. As shown in Tables 1 and 2, the silica sol sealing treatment on the yttrium silicate matrix-modified C / SiC composite material significantly reduced the material's porosity and maximum oxidation weight loss, thereby enhancing its antioxidant effect.

[0228] The composite material of Example 4 exhibited a maximum oxidation weight loss of 5.42% after 4 hours of oxidation at 1000°C; the maximum oxidation weight loss of 4.92% after 4 hours of oxidation at 1200°C; the maximum oxidation weight loss of 5.5% after 2 hours of oxidation at 1000°C; and the maximum oxidation weight loss of 5.15% after 2 hours of oxidation at 1200°C. As shown in Tables 1 and 2, the silica sol sealing treatment on the yttrium silicate matrix-modified C / SiC composite material significantly reduced the material's porosity, prolonged the maximum weight loss time, decreased the maximum oxidation weight loss rate, and enhanced the antioxidant effect.

[0229] The composite material of Example 5 exhibited maximum oxidation weight loss of 6.82% after 4 hours of oxidation at 1000°C, and 6.9% after 4 hours of oxidation at 1200°C. The composite material of Example 1 exhibited maximum oxidation weight loss of 5.93% after 4 hours of oxidation at 1000°C, and 3.68% after 6 hours of oxidation at 1200°C. As shown in Tables 1 and 2, silica sol sealing treatment significantly reduced the porosity of the yttrium silicate-modified C / SiC composite material, prolonged the maximum weight loss time, decreased the maximum oxidation weight loss rate, and enhanced its antioxidant effect.

[0230] By comparing the maximum oxidation weight loss test results of Example 5 with those of Example 1, the maximum oxidation weight loss test results of Comparative Example 2 with those of Comparative Example 1, the maximum oxidation weight loss test results of Comparative Example 3 with those of Comparative Example 1, the maximum oxidation weight loss test results of Comparative Example 4 with Comparative Example 1, and the maximum oxidation weight loss test results of Comparative Example 5 with Comparative Example 1, it can be seen from the data in Table 2 that, compared with the C / SiC composite material with a pure PCS matrix, the maximum oxidation weight loss of the C / SiC composite material after silicate matrix modification is reduced.

[0231] Based on the above, it can be seen that the present invention performs the densification process of the composite material matrix by adopting a precursor liquid impregnation, drying, cracking or heat treatment cycle, and performs each step in sequence. Through the organic synergistic effect between the components, the porosity of the prepared C / SiC composite material is finally reduced, and its antioxidant performance is improved.

[0232] Obviously, the above embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

Claims

1. A method for improving the oxidation resistance of C / SiC composite materials, characterized in that: The following steps are involved: SiC modification treatment: the carbon felt is immersed in SiC precursor solution for vacuum impregnation treatment, and then the impregnated carbon felt is dried and pyrolyzed in sequence; Repeat this step several times to obtain composite material A; The composite material A is first subjected to silicate sol modification treatment and then to silica sol sealing treatment to improve the oxidation resistance of the C / SiC composite material; Wherein, the silicate sol modification treatment is carried out by the following steps: The composite material A is immersed in a silicate sol for vacuum impregnation treatment, and then the composite material A after the impregnation treatment is dried and subjected to high-temperature cracking treatment in sequence; this step is repeated several times to obtain a composite material B; The silica sol sealing treatment is carried out by the following steps: The composite material B is immersed in silica sol for vacuum impregnation treatment, and then the composite material B after impregnation treatment is dried and heat-treated in sequence; this step is repeated several times to improve the oxidation resistance of the C / SiC composite material; The concentration of the silicate sol is 3-5 mol / L; The silicate sol is composed of metal salt, tetraethyl silicate, anhydrous ethanol and LiF; Wherein, the metal salt is zirconium chloride, yttrium nitrate or hafnium chloride; In the silicate sol, the molar ratio of silicon to metal salt is 1.2:1, and the molar ratio of silicon to Li is 10:

3.

2. The method according to claim 1, wherein The SiC precursor solution is a xylene solution of polycarbosilane with a mass concentration of 45% to 55%.

3. The method according to claim 1, wherein The mass concentration of the silica sol is 20% to 30%.

4. The method according to claim 1, wherein During the SiC modification treatment, the vacuum impregnation treatment time is 4 to 8 hours each time; The temperature of each drying treatment is 65~75℃ and the treatment time is 4~8h; The reaction atmosphere of each high-temperature cracking treatment is argon, the heating rate is 3~7℃ / min, the reaction temperature is 1050~1150℃, and the holding time is 0.5~1.5h.

5. The method according to claim 1, wherein During the SiC modification process, the steps were repeated 4 to 14 times.

6. The method according to claim 1, wherein During the silicate sol modification treatment, the vacuum impregnation treatment time is 4 to 8 hours each time; The temperature of each drying treatment is 65~75℃ and the treatment time is 4~8h; The reaction atmosphere of each high-temperature cracking treatment is argon, the heating rate is 3~7°C / min, the reaction temperature is 850~1150°C, and the holding time is 0.5~1.5h.

7. The method according to claim 1, wherein During the silicate sol modification treatment, the steps are repeated 4 to 10 times.

8. The method according to claim 1, wherein During the silica sol sealing treatment, the vacuum impregnation treatment time is 4 to 8 hours each time; The temperature of each drying treatment is 95~105℃ and the treatment time is 3~6h; The reaction atmosphere of each heat treatment is argon, the heating rate is 3~7℃ / min, the reaction temperature is 1150~1250℃, and the holding time is 0.5~1.5h.

9. The method according to claim 1, wherein During the silica sol sealing treatment, the steps are repeated 4 to 5 times.

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