A silicate-doped C / SiC composite material and its preparation method

Abstract

This invention belongs to the field of ceramic matrix composite technology, and discloses a silicate-doped C / SiC composite material and its preparation method. The method comprises: Step 1, pretreating carbon felt; Step 2, vacuum impregnating the pretreated carbon felt in a polycarbosilane solution, followed by drying and high-temperature pyrolysis; Step 3, performing a cycle I consisting of vacuum impregnation of modified carbon felt A in silicate sol, followed by drying and high-temperature pyrolysis; repeating cycle I several times; Step 4, combining steps 2 and 3 as a cycle II, repeating cycle II several times to obtain the silicate-doped C / SiC composite material. This invention uses silicate materials as antioxidant components. Through alternating modification cycles of the SiC matrix and silicate matrix, the prepared silicate matrix can fill pores while simultaneously encapsulating carbon fibers and the SiC matrix, thereby improving the antioxidant properties of both the carbon fibers and the SiC matrix.

Description

Technical Field

[0001] This invention relates to the field of ceramic matrix composites, and more particularly to a silicate-doped C / SiC composite material and its preparation method. Background Technology

[0002] Continuous carbon fiber reinforced silicon carbide (C / SiC) composites possess properties such as high temperature resistance, thermal shock resistance, high wear resistance, high hardness, chemical corrosion resistance, high thermal conductivity, and low coefficient of thermal expansion (1×10⁻⁶). -6 K -1 ~4×10 -6 K -1 With its superior performance, it does not require additional heat insulation measures when operating at high temperatures, and has wide applications in strategic weapons, space technology, energy technology, chemical and transportation industries.

[0003] Currently, the main method involves using polycarbosilane as a precursor, impregnating and pyrolyzing it to form SiC on the surface of carbon materials, thus creating C / SiC composites. However, this preparation method suffers from drawbacks because the SiC particles produced by polycarbosilane pyrolysis are relatively large and have high porosity, making these pores easy channels for oxygen diffusion. Furthermore, SiC itself has poor oxidation resistance. Therefore, the C / SiC composites prepared by impregnating and pyrolyzing polycarbosilane as a precursor exhibit poor oxidation resistance, limiting their further applications.

[0004] Therefore, the present invention provides a silicate-doped C / SiC composite material and its preparation method. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention provides a silicate-doped C / SiC composite material and its preparation method. This invention introduces silicate materials as antioxidant components into the C / SiC composite material matrix for doping. These materials possess excellent properties such as high thermal stability, high oxidation resistance, and low thermal conductivity, effectively improving the oxidation resistance of the C / SiC composite material. Furthermore, their coefficient of thermal expansion is similar to that of SiC, and the multiple alternating cycle process results in a tighter bond between the matrix components, further reducing the oxidation rate of the SiC matrix. Therefore, the silicate-doped C / SiC composite material prepared by this invention exhibits superior oxidation resistance compared to the pure SiC matrix C / SiC composite material.

[0006] The silicate-doped C / SiC composite material and its preparation method of the present invention are achieved through the following technical solutions:

[0007] The first objective of this invention is to provide a method for preparing silicate-doped C / SiC composite materials, comprising the following steps:

[0008] Step 1: Ultrasonic cleaning and drying of carbon felt to obtain pretreated carbon felt;

[0009] Step 2: Vacuum impregnation of the pretreated carbon felt in a polycarbosilane solution, followed by drying and high-temperature pyrolysis treatment to obtain modified carbon felt A.

[0010] Step 3 involves performing a vacuum impregnation treatment of the modified carbon felt A in silicate sol, followed by drying and high-temperature pyrolysis treatment, as a cycle treatment I; the cycle treatment I is performed several times to obtain the modified carbon felt B;

[0011] Step 4: Steps 2, 3 and 4 are combined into a cycle II, and the cycle II is repeated several times to obtain the silicate-doped C / SiC composite material.

[0012] Preferably, in step 3, the number of times the loop process I is performed is 1 to 3.

[0013] Preferably, in step 4, the number of times the loop process II is performed is 4 to 7.

[0014] Preferably, in step 2, the impregnation time of the vacuum impregnation treatment is 6 to 10 hours;

[0015] The drying process is carried out in an air atmosphere, at a temperature of 60–80°C, and for a time of 10–14 hours.

[0016] The atmosphere for the high-temperature pyrolysis treatment is argon, the treatment temperature is 1050–1150℃, the treatment time is 0.5–1h, and the heating rate is 4–8℃ / min.

[0017] Preferably, in step 3, the impregnation time of the vacuum impregnation treatment is 6 to 10 hours;

[0018] The drying process is carried out in an air atmosphere, at a temperature of 60–80°C, and for a time of 10–14 hours.

[0019] The atmosphere for the high-temperature pyrolysis treatment is argon, the treatment temperature is 850–950°C, the treatment time is 0.5–1 h, and the heating rate is 4–8°C / min.

[0020] Preferably, the polycarbosilane solution is prepared by reacting polycarbosilane with xylene; and the concentration of polycarbosilane in the polycarbosilane solution is 40-60 wt.%.

[0021] The concentration of the silicate sol is 2–5 mol / L.

[0022] Preferably, the silicate sol is prepared from a metal salt, tetraethyl silicate, anhydrous ethanol, and LiF.

[0023] In the silicate sol, the molar ratio of Si to metal ions is 1.2:1, and the molar ratio of Si to Li is 10:3.

[0024] The metal salt is hafnium chloride, zirconium chloride, or yttrium nitrate.

[0025] Preferably, the silicate sol is prepared by the following steps:

[0026] According to the above ratio, the metal salt and tetraethyl silicate are uniformly dispersed in anhydrous ethanol, stirred and filtered to obtain solution A;

[0027] The LiF is uniformly dispersed in solution A to obtain solution B;

[0028] The solution B is reacted at 105–115°C for 1.5–2.5 h, and then allowed to stand at room temperature for 20–28 h to obtain the silicate sol.

[0029] Preferably, the cleaning solution used in the ultrasonic cleaning is any one of anhydrous ethanol, acetone, and distilled water;

[0030] The ultrasonic cleaning time is 4–6 minutes;

[0031] In step 1, the drying temperature is 60-80℃ and the drying time is 4-6 hours.

[0032] A second objective of this invention is to provide a silicate-doped C / SiC composite material prepared by the above-described preparation method.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] This invention is based on a matrix alternation preparation strategy. By alternately forming SiC and silicate matrices around the carbon fibers in a carbon felt, it helps to refine both the SiC and silicate matrix particles, resulting in a tighter bond between the matrix material and the carbon fibers in the carbon felt. This effectively reduces the porosity of air diffusion channels between the carbon fibers in the carbon felt and the matrix material, thereby effectively reducing the oxidation of carbon fibers and silicon carbide within the material and thus effectively improving the oxidation resistance of the C / SiC composite material. The preparation method of this invention is simple, highly feasible, and conducive to widespread application.

[0035] This invention introduces silicate materials as an antioxidant component into the matrix of C / SiC composites for matrix doping. These materials possess excellent properties such as high thermal stability, high oxidation resistance, and low thermal conductivity, effectively improving the oxidation resistance of C / SiC composites. Furthermore, their coefficient of thermal expansion is similar to that of SiC, and the multiple alternating cycle process results in a tighter bond between the matrix components, further reducing the oxidation rate of the SiC matrix. Therefore, the silicate-doped C / SiC composite prepared by this invention exhibits superior oxidation resistance compared to pure SiC matrix C / SiC composites.

[0036] This invention introduces silicate materials such as hafnium silicate, zirconium silicate, and yttrium silicate as antioxidant components into the matrix of C / SiC composite materials for matrix doping. These materials exhibit excellent properties such as high thermal stability, high oxidation resistance, and low thermal conductivity, and their coefficient of thermal expansion is similar to that of SiC (4 × 10⁻⁶). -6 K -1 ~5×10 -6 K -1 Furthermore, since the silicate particles prepared by the sol-gel method are small, the resulting silicate matrix can fill the pores and encapsulate the carbon fibers and SiC matrix, thereby improving the oxidation resistance of the carbon fibers and SiC matrix and ultimately obtaining a silicate-doped C / SiC composite material with high oxidation resistance. Attached Figure Description

[0037] Figure 1 This is a process flow diagram for preparing the silicate-doped C / SiC composite material of the present invention;

[0038] Figure 2 The image shows the microstructure of the C / SiC composite material prepared in Comparative Example 1.

[0039] Figure 3 The image shows the microstructure of the C / SiC composite material prepared in Comparative Example 2.

[0040] Figure 4 The image shows the microstructure of the C / SiC composite material prepared in Example 1.

[0041] Figure 5 This is a comparison chart showing the calculated results of the antioxidant properties test at 1000℃ for the materials prepared in Examples 1-3 and Comparative Example 1;

[0042] Figure 6 This is a comparison chart showing the calculated results of the antioxidant properties test at 1200℃ for the materials prepared in Examples 1-3 and Comparative Example 1;

[0043] Figure 7 A comparison chart showing the calculated results of antioxidant performance tests at 1000℃ and 1200℃ for the materials prepared in Example 4 and Comparative Example 1;

[0044] Figure 8 The graph shows a comparison of the calculated antioxidant properties of the materials prepared in Example 5 and Comparative Example 1 at 1000℃ and 1200℃. Detailed Implementation

[0045] The technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0046] Please see Figure 1 This invention provides a silicate-doped C / SiC composite material, and its preparation method includes the following steps:

[0047] Step 1, Pre-treat the carbon felt:

[0048] The carbon felt is ultrasonically cleaned and then dried to obtain pretreated carbon felt.

[0049] It should be noted that, considering the ease with which impurities can adhere to the surface and pores of carbon felt, which hinders the subsequent impregnation with polycarbosilane solution and silicate sol, thus affecting the effectiveness of subsequent modification treatments, this invention first places the carbon felt in a cleaning solution and performs ultrasonic cleaning in an ultrasonic cleaner to remove impurities from the surface and pores of the carbon felt to avoid affecting subsequent preparation and testing results, while also improving the adhesion of the substrate to the carbon felt.

[0050] In a preferred embodiment of the present invention, the cleaning solution used during ultrasonication can be any one of anhydrous ethanol, acetone and distilled water; and the ultrasonication time is 4 to 6 minutes to ensure that impurities are removed from the surface and pores of the carbon felt.

[0051] Considering that residual cleaning solution may remain in the carbon felt after ultrasonic cleaning, which could affect the impregnation effect of subsequent polycarbosilane solution and silicate sol, the present invention also performs a drying process on the carbon felt after ultrasonic cleaning.

[0052] In a preferred embodiment of the present invention, the drying temperature is 60-80°C and the drying time is 4-6 hours, so as to drain the cleaning liquid from the carbon felt and provide the necessary space for subsequent substrate alternation preparation.

[0053] Step 2, SiC matrix modification treatment:

[0054] The pretreated carbon felt was vacuum impregnated in a polycarbosilane solution, followed by drying and high-temperature pyrolysis to obtain modified carbon felt A.

[0055] It should be noted that the present invention first immerses the pretreated carbon felt in a polycarbosilane solution so that the polycarbosilane solution wets and enters the pores of the carbon felt, thereby making the polycarbosilane solution uniformly coat the carbon fibers in the carbon felt. Then, the excess solvent is removed by drying, and then high-temperature pyrolysis is performed to convert the polycarbosilane on the surface and in the pores of the carbon felt into a SiC matrix, so that the SiC matrix covers the carbon fibers, thereby obtaining a SiC matrix modified carbon felt.

[0056] In a preferred embodiment of the present invention, the pretreated carbon felt is immersed in a polycarbosilane solution under vacuum for 6 to 10 hours to ensure that the polycarbosilane solution completely wets the carbon felt and enters the pores of the carbon felt, so that the polycarbosilane solution uniformly coats the carbon fibers in the carbon felt.

[0057] In order to remove excess solvent after impregnation, in a preferred embodiment of the present invention, the drying atmosphere is air, the drying temperature is 60-80°C, and the drying time is 10-14 hours to ensure the removal of excess solvent, thereby avoiding excessive porosity in the matrix due to volatilization of the polycarbosilane solution during high-temperature pyrolysis.

[0058] To ensure the conversion of polycarbosilane on the carbon felt into the SiC matrix, in a preferred embodiment of the present invention, the atmosphere for the high-temperature pyrolysis treatment is argon, the treatment temperature is 1050–1150°C, the treatment time is 0.5–1 h, and the heating rate is 4–8°C / min.

[0059] Step 3, silicate matrix modification treatment to obtain modified carbon felt B:

[0060] The modified carbon felt A is subjected to vacuum impregnation in silicate sol, followed by drying and high-temperature pyrolysis, which constitutes a cycle I. The cycle I is repeated several times to obtain the modified carbon felt B.

[0061] This invention uses silicates as an antioxidant component. Modified carbon felt A, obtained after SiC matrix modification, is impregnated in a silicate sol, allowing the silicate sol to further encapsulate the carbon fibers within the modified carbon felt A. Excess solvent is removed through drying, followed by high-temperature pyrolysis to transform the silicate sol around the carbon fibers into a silicate matrix. This silicate matrix fills the pores in the overall material while simultaneously encapsulating the carbon fibers and the SiC matrix, thereby enhancing the bonding density between the carbon fibers and the matrix. This reduces the porosity of air diffusion channels between the carbon fibers and the matrix material, thus improving the antioxidant properties of both the carbon fibers and the SiC matrix. Furthermore, to ensure that the silicate sol uniformly encapsulates the carbon fibers in the modified carbon felt A in step 3, in a preferred embodiment, the impregnation time for the vacuum impregnation process is 6–10 hours.

[0062] To ensure the removal of excess solvent from the silicate sol coating the surface of the modified carbon felt A, in a preferred embodiment of the present invention, the drying process is carried out in an air atmosphere, at a drying temperature of 60–80°C, and for a drying time of 10–14 h, in order to avoid the silicate sol from generating excessive pores in the matrix due to volatilization during high-temperature pyrolysis.

[0063] To ensure that the silicate sol can form a silicate matrix around the carbon fibers in the modified carbon felt A after drying, in a preferred embodiment of the present invention, the atmosphere of the high-temperature pyrolysis treatment is argon, the treatment temperature is 850-950°C, the treatment time is 0.5-1h, and the heating rate is 4-8°C / min.

[0064] It should be noted that, in order to ensure that the silicate matrix is ​​fully wrapped around the carbon fibers in the modified carbon felt A and fully bonded with the SiC matrix around the carbon fibers in the modified carbon felt A, in a preferred embodiment of the present invention, the cyclic treatment I is performed 1 to 3 times to ensure that the silicate matrix and SiC matrix are tightly bonded to the carbon fibers in the formed modified carbon felt B.

[0065] Step 4: Steps 2 and 3 are treated as a cycle II, and the cycle II is performed several times to improve the oxidation resistance of the C / SiC composite material and obtain the silicate-doped C / SiC composite material.

[0066] It should be noted that step 2 is the SiC matrix modification treatment of the carbon felt, and step 3 is the silicate matrix modification treatment of the carbon felt. This invention first modifies the carbon felt with SiC matrix to form a SiC matrix around the carbon fibers. Then, the modified carbon felt A, which has a SiC matrix around the carbon fibers, undergoes silicate matrix modification treatment to further form a silicate matrix around the carbon fibers. This effectively reduces the porosity of air diffusion channels between the carbon fibers and the matrix material, thereby effectively reducing the oxidation of carbon fibers and silicon carbide within the material. This improves the density of the C / SiC composite material while simultaneously enhancing its high thermal stability, high oxidation resistance, and low thermal conductivity by introducing a silicate matrix as an antioxidant component, thus further improving the oxidation resistance of the prepared C / SiC composite material.

[0067] This invention employs an alternating process of SiC matrix modification and silicate matrix modification to form a multilayer modified matrix structure with alternating SiC and silicate matrices on the surface of the carbon felt. Steps 2 and 3 are treated as a cycle II, which is repeated several times. This process helps to refine the SiC matrix particles and silicate matrix particles, resulting in a tighter bond between the matrix material and the carbon fibers in the carbon felt. This significantly reduces the porosity of the air diffusion channels between the carbon felt and the matrix material, thereby greatly reducing the oxidation of carbon fibers and silicon carbide within the material. This further reduces the oxidation rate of the SiC matrix, thus significantly improving the oxidation resistance of the prepared C / SiC composite material.

[0068] The present invention takes into account that when the number of cycles II is less than 4, it is impossible to effectively improve the porosity between the carbon felt material and the SiC matrix particles, resulting in poor oxidation resistance of the prepared material; while when the number of repeated cycles is more than 7, the densification effect will not be significantly improved, and too many cycles will only prolong the preparation cycle. Therefore, in a preferred embodiment of the present invention, the number of cycles is 4 to 7.

[0069] It should be noted that the polycarbosilane solution used in this invention is prepared by mixing polycarbosilane and xylene; and the concentration of polycarbosilane in the polycarbosilane solution is 40-60 wt.%.

[0070] The silicate sol used in this invention has a concentration of 2–5 mol / L. The silicate sol is prepared from a metal salt, tetraethyl silicate, anhydrous ethanol, and LiF; wherein, in the silicate sol, the molar ratio of Si to metal ions is 1.2:1, and the molar ratio of Si to Li is 10:3; the metal salt is hafnium chloride, zirconium chloride, or yttrium nitrate.

[0071] The silicate sol is prepared by the following steps:

[0072] According to the above ratio, the metal salt and tetraethyl silicate are uniformly dispersed in anhydrous ethanol, stirred and filtered to obtain solution A;

[0073] The LiF is uniformly dispersed in solution A to obtain solution B;

[0074] The solution B is reacted at 105–115°C for 1.5–2.5 h, and then allowed to stand at room temperature for 20–28 h to obtain the silicate sol.

[0075] Example 1

[0076] This embodiment provides a method for preparing a silicate-doped C / SiC composite material, including the following steps:

[0077] Step 1: Pre-treat the carbon felt:

[0078] The carbon felt was cut into 10mm×10mm pieces. Anhydrous ethanol was used as the cleaning solution. The carbon felt was immersed in the cleaning solution and ultrasonically cleaned for 5 minutes in an ultrasonic cleaner. Then it was placed in an oven at 70℃ and dried for 5 hours to obtain the pretreated carbon felt.

[0079] Step 2, SiC matrix modification treatment:

[0080] The pretreated carbon felt obtained in step one was immersed in a 50 wt.% polycarbosilane solution and vacuum impregnated for 8 hours. The carbon felt was then removed and dried in an oven at 70°C for 12 hours. Subsequently, it was placed in a tube furnace filled with argon atmosphere and pyrolyzed at a pyrolysis temperature of 1100°C for 1 hour to obtain modified carbon felt A.

[0081] Step 3, Silicate matrix modification treatment:

[0082] The modified carbon felt A prepared in step two above was impregnated in 2 mol / L HfSiO4 sol and vacuum impregnated for 8 h. The carbon felt was then removed and dried in an oven at 70 °C for 12 h. After that, it was placed in a tube furnace filled with argon atmosphere and pyrolyzed at a pyrolysis temperature of 900 °C for 1 h to obtain modified carbon felt B.

[0083] Step four: Steps two and three are treated as a cycle and this cycle is performed seven times to improve the oxidation resistance of the C / SiC composite material and obtain silicate-doped C / SiC composite material.

[0084] Example 2

[0085] This embodiment provides a method for preparing a silicate-doped C / SiC composite material, including the following steps:

[0086] Step 1: Pre-treat the carbon felt:

[0087] The carbon felt was cut into 10mm×10mm pieces. Anhydrous ethanol was used as the cleaning solution. The carbon felt was immersed in the cleaning solution and ultrasonically cleaned for 5 minutes in an ultrasonic cleaner. Then it was placed in an oven at 70℃ and dried for 5 hours to obtain the pretreated carbon felt.

[0088] Step 2, SiC matrix modification treatment:

[0089] The pretreated carbon felt obtained in step one was immersed in a 50 wt.% polycarbosilane solution and vacuum impregnated for 8 hours. The carbon felt was then removed and dried in an oven at 70°C for 12 hours. Subsequently, it was placed in a tube furnace filled with argon atmosphere and pyrolyzed at a pyrolysis temperature of 1100°C for 1 hour to obtain modified carbon felt A.

[0090] Step 3, Silicate matrix modification treatment:

[0091] The modified carbon felt A prepared in step two above was impregnated in 2 mol / L HfSiO4 sol and vacuum impregnated for 8 h. The carbon felt was then removed and dried in an oven at 70 °C for 12 h. After that, it was placed in a tube furnace filled with argon atmosphere and pyrolyzed at a pyrolysis temperature of 900 °C for 1 h to obtain modified carbon felt B.

[0092] Step four, repeat step three once more, that is, perform step three a total of 2 times.

[0093] Step 5: Steps 2, 3, and 4 are treated as a cycle and this cycle is repeated 5 times to improve the oxidation resistance of the C / SiC composite material and obtain silicate-doped C / SiC composite material.

[0094] Example 3

[0095] This embodiment provides a method for preparing a silicate-doped C / SiC composite material, including the following steps:

[0096] Step 1: Pre-treat the carbon felt:

[0097] The carbon felt was cut into 10mm×10mm pieces. Anhydrous ethanol was used as the cleaning solution. The carbon felt was immersed in the cleaning solution and ultrasonically cleaned for 5 minutes in an ultrasonic cleaner. Then it was placed in an oven at 70℃ and dried for 5 hours to obtain the pretreated carbon felt.

[0098] Step 2, SiC matrix modification treatment:

[0099] The pretreated carbon felt obtained in step one was immersed in a 50 wt.% polycarbosilane solution and vacuum impregnated for 8 hours. The carbon felt was then removed and dried in an oven at 70°C for 12 hours. Subsequently, it was placed in a tube furnace filled with argon atmosphere and pyrolyzed at a pyrolysis temperature of 1100°C for 1 hour to obtain modified carbon felt A.

[0100] Step 3, Silicate matrix modification treatment:

[0101] The modified carbon felt A prepared in step two above was impregnated in 2 mol / L HfSiO4 sol and vacuum impregnated for 8 h. The carbon felt was then removed and dried in an oven at 70 °C for 12 h. After that, it was placed in a tube furnace filled with argon atmosphere and pyrolyzed at a pyrolysis temperature of 900 °C for 1 h to obtain modified carbon felt B.

[0102] Step four, repeat step three twice more, for a total of three steps.

[0103] Step 5: Steps 2, 3, and 4 are treated as a cycle and this cycle is performed 4 times to improve the oxidation resistance of the C / SiC composite material and obtain silicate-doped C / SiC composite material.

[0104] Example 4

[0105] This embodiment provides a method for preparing a silicate-doped C / SiC composite material, and the only difference between this embodiment and Embodiment 1 is:

[0106] In this embodiment, the silicate sol used is Zr(SiO4) sol.

[0107] Example 5

[0108] This embodiment provides a method for preparing a silicate-doped C / SiC composite material, and the only difference between this embodiment and Embodiment 3 is that:

[0109] In this embodiment, the silicate sol used is Y2(Si2O7) sol.

[0110] Comparative Example 1

[0111] This comparative example provides a method for improving the oxidation resistance of C / SiC composite materials, including the following steps:

[0112] Step 1: Pre-treat the carbon felt:

[0113] The carbon felt was cut into 10mm×10mm pieces. Anhydrous ethanol was used as the cleaning solution. The carbon felt was immersed in the cleaning solution and ultrasonically cleaned for 5 minutes in an ultrasonic cleaner. Then it was placed in an oven at 70℃ and dried for 5 hours to obtain the pretreated carbon felt.

[0114] Step 2, SiC matrix modification:

[0115] The pretreated carbon felt obtained in step one was immersed in a 50 wt.% polycarbosilane solution and vacuum impregnated for 8 hours. The carbon felt was then removed and dried in an oven at 70°C for 12 hours. Subsequently, it was placed in a tube furnace filled with argon atmosphere and pyrolyzed at a pyrolysis temperature of 1100°C for 1 hour to obtain modified carbon felt A.

[0116] Step two was repeated 13 times to obtain the C / SiC composite material.

[0117] Comparative Example 2

[0118] This embodiment provides a method for preparing a silicate-doped C / SiC composite material, including the following steps:

[0119] Step 1: Pre-treat the carbon felt:

[0120] The carbon felt was cut into 10mm×10mm pieces. Anhydrous ethanol was used as the cleaning solution. The carbon felt was immersed in the cleaning solution and ultrasonically cleaned for 5 minutes in an ultrasonic cleaner. Then it was placed in an oven at 70℃ and dried for 5 hours to obtain the pretreated carbon felt.

[0121] Step 2, SiC matrix modification treatment:

[0122] The pretreated carbon felt obtained in step one was immersed in a 50 wt.% polycarbosilane solution and vacuum impregnated for 8 hours. The carbon felt was then removed and dried in an oven at 70°C for 12 hours. Subsequently, it was placed in a tube furnace filled with argon atmosphere and pyrolyzed at a pyrolysis temperature of 1100°C for 1 hour.

[0123] Step 3: Repeat the SiC matrix modification treatment in Step 2 seven times to obtain modified carbon felt A.

[0124] Step 4, Silicate matrix modification treatment:

[0125] The modified carbon felt A obtained in step three above was impregnated in 2 mol / L HfSiO4 sol and vacuum impregnated for 8 h. The carbon felt was then removed and dried in an oven at 70 °C for 12 h. After that, it was placed in a tube furnace filled with argon atmosphere and pyrolyzed at a pyrolysis temperature of 900 °C for 1 h.

[0126] Step 5: Repeat the silicate matrix modification treatment in Step 4 seven times to improve the oxidation resistance of the C / SiC composite material and obtain silicate-doped C / SiC composite material.

[0127] Experimental Section

[0128] (I) Microscopic morphology testing

[0129] This invention uses the silicate-doped C / SiC composite materials prepared in Comparative Examples 1, 2, and 1 as examples to conduct microstructure tests, and the test results are as follows: Figure 2 , Figure 3 and Figure 4 As shown, where, Figure 2 The image shows the microstructure of the C / SiC composite material prepared in Comparative Example 1. Figure 3 The image shows the microstructure of the silicate-doped C / SiC composite material prepared in Comparative Example 2. Figure 4 The image shows the microstructure of the silicate-doped C / SiC composite material prepared in Example 1.

[0130] Comparative Example 1 directly obtained the complete silicon carbide matrix by multiple impregnation-drying-pyrolysis processes using a polycarbosilane precursor, but from... Figure 2It can be seen that the silicon carbide matrix particles in Comparative Example 1 are larger in size. Therefore, air diffusion channels must be formed between the larger particles at high temperatures, resulting in more oxidation of the internal carbon fibers and silicon carbide matrix, i.e., a higher weight loss rate.

[0131] Comparative Example 2 first obtained a portion of silicon carbide matrix by repeatedly impregnating, drying, and pyrolyzing a polycarbosilane precursor, and then obtained a portion of silicate matrix by repeatedly impregnating, drying, and pyrolyzing a silicate sol. The morphology of the matrix still retains the morphology of the larger matrix particles, such as... Figure 3 As shown, Comparative Example 2 still creates air diffusion channels at high temperatures in the gaps between larger particles in the matrix, leading to more oxidation of the carbon fiber and silicon carbide matrix, i.e., a higher weight loss rate.

[0132] Example 1 employs an alternating matrix preparation strategy to prepare the C / SiC composite material. During the preparation process, the silicate matrix particles generated by silicate sol impregnation-drying-pyrolysis are small in size and numerous in number. These small and numerous silicate matrix particles readily become nucleation sites for silicon carbide generated during the subsequent polycarbosilane precursor impregnation-drying-pyrolysis process. Therefore, the number and size of silicon carbide particles generated by polycarbosilane precursor impregnation-drying-pyrolysis are also inevitably large. Consequently, the silicate-doped C / SiC composite material prepared by the matrix alternating strategy of this invention has a more compact microstructure, such as... Figure 4 As shown in the middle position. It should be noted that the "more dense" mentioned in this invention can be understood as the matrix portion that is aggregated or wrapped around the carbon fibers being more dense. This dense matrix is ​​caused by a matrix morphology with a large number of small particles, and its air diffusion channels are inevitably relatively blocked, resulting in less oxidation of the internal carbon fibers and silicon carbide, thus resulting in less weight loss.

[0133] In summary, this invention, based on an alternating matrix preparation strategy, helps to refine the SiC matrix particles and silicate matrix particles on the carbon felt surface by alternately forming SiC matrix and silicate matrix on the carbon felt surface. This results in a tighter bond between the matrix material near or around the carbon felt and the carbon fibers of the carbon felt, thereby greatly reducing the porosity of the air diffusion channels between the carbon felt and the matrix material. Consequently, it significantly reduces the oxidation of carbon fibers and silicon carbide inside the material, and thus greatly improves the oxidation resistance of the C / SiC composite material.

[0134] (II) Antioxidant performance test

[0135] The antioxidant properties of the samples prepared in Examples 1-3 and Comparative Example 1 were tested. The specific test steps are as follows:

[0136] First, weigh the sample using an analytical balance and record the mass as m1. Place the sample in a muffle furnace, set the heating rate to 5℃ / min, and hold it at the specified temperature for a certain duration: 2h, 4h, 6h, 8h, 10h, 20h, 30h, 40h, and 50h. After oxidation, remove the sample and weigh it, recording the weight as m2. Then proceed according to... Calculate the oxidation weight loss rate ω of the sample.

[0137] 1) Antioxidant performance test at 1000℃

[0138] The antioxidant properties of the C / SiC composite materials prepared in Examples 1-3 and Comparative Example 1 were tested at 1000℃. The test results are as follows: Figure 5 As shown.

[0139] Depend on Figure 5 It can be seen that the maximum weight loss of the silicate-doped C / SiC composite materials prepared in Examples 1-3 of this invention all occurred after 2 hours of oxidation. The maximum oxidation weight loss rate increased by 3.94%, 4.02%, and 3.81% respectively with the increase of the number of HfSiO4 sol impregnation-drying-pyrolysis treatments. Furthermore, after reaching the maximum oxidation weight loss rate, there was only a slight increase in weight with increasing holding time. This phenomenon indicates that before reaching the maximum oxidation weight loss rate, the carbon fibers were oxidized and volatilized, leading to rapid weight loss of the material, followed by slight oxidation of SiC to generate SiO2. In contrast, the maximum weight loss rate of the C / SiC composite material prepared in Comparative Example 1 occurred after 4 hours of oxidation, at 5.67%.

[0140] Based on the above, it can be seen that the maximum weight loss rate of the silicate-doped C / SiC composite materials prepared in Examples 1-3 decreased in the antioxidant performance test at 1000℃, and the antioxidant performance of the materials was improved.

[0141] 2) Antioxidant performance test at 1200℃

[0142] The present invention also tested the oxidation resistance at 1200℃ of the silicate-doped C / SiC composite materials prepared in Examples 1-3 and the C / SiC composite material prepared in Comparative Example 1. The test calculation results are as follows: Figure 6 As shown.

[0143] Depend on Figure 6It can be seen that the maximum oxidation weight loss rate of the silicate-doped C / SiC composite materials prepared in Examples 1-3 of this invention shows a decreasing trend with the increase of the number of cycles of treatment I, reaching 4.09%, 4.09%, and 3.55%, respectively. Furthermore, after reaching the maximum oxidation weight loss rate, there is only a slight increase in weight with increasing holding time. This phenomenon indicates that before reaching the maximum oxidation weight loss rate, the carbon fibers are oxidized and volatilized, leading to rapid weight loss of the material, followed by slight oxidation of SiC to generate SiO2. The maximum weight loss rate of the C / SiC composite material prepared in Comparative Example 1 is 5.66%.

[0144] Based on the above, it can be seen that the maximum weight loss rate of the silicate-doped C / SiC composite materials prepared in Examples 1-3 decreased in the antioxidant performance test at 1200℃, and the antioxidant performance of the materials was improved.

[0145] 3) Antioxidant performance test in Example 4

[0146] The oxidation resistance of the silicate-doped C / SiC composite materials prepared in Comparative Example 1 and Example 4 was tested at 1000℃ and 1200℃. The test results are as follows: Figure 7 As shown.

[0147] Depend on Figure 7 It can be seen that the silicate-doped C / SiC composite material prepared in Example 4 of the present invention has better oxidation resistance at 1000℃ and 1200℃ than that of Comparative Example 1. In the oxidation resistance test at 1000℃, the maximum oxidation weight loss rate of the silicate-doped C / SiC composite material prepared in Example 4 of the present invention is 5.48%; and in the oxidation resistance test at 1200℃, the maximum oxidation weight loss rate is 4.88%.

[0148] Based on the above, the maximum weight loss of the silicate-doped C / SiC composite material prepared by the present invention decreased in the oxidation performance tests at 1000℃ and 1200℃, indicating that the oxidation performance of the material was improved.

[0149] 4) Antioxidant performance test of Example 5

[0150] The present invention also tested the oxidation resistance of the silicate-doped C / SiC composite materials prepared in Comparative Example 1 and Example 5 at 1000℃ and 1200℃, and the test calculation results are as follows: Figure 8 As shown.

[0151] Depend on Figure 8It can be seen that the silicate-doped C / SiC composite material prepared in Example 5 of the present invention has better oxidation resistance at 1000℃ and 1200℃ than that of Comparative Example 1. In the oxidation resistance test at 1000℃, the maximum oxidation weight loss rate of the silicate-doped C / SiC composite material prepared in Example 5 of the present invention is 2.74%; and in the oxidation resistance test at 1200℃, the maximum oxidation weight loss rate is 1.49%.

[0152] Based on the above, the maximum weight loss of the silicate-doped C / SiC composite material prepared by the present invention is significantly reduced in the oxidation performance tests at 1000℃ and 1200℃, and the oxidation performance of the material is significantly improved.

[0153] Obviously, the above embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for the production of a silicate-doped C / SiC composite material, characterized in that, The method comprises the following steps: Step 1, after ultrasonic cleaning, the carbon felt is dried to obtain a pretreated carbon felt; Step 2, the pretreated carbon felt is vacuum-impregnated in a polycarbosilane solution, and then sequentially subjected to drying treatment and high-temperature pyrolysis treatment to obtain a modified carbon felt A; Step 3, the modified carbon felt A is vacuum-impregnated in a silicate sol, and then sequentially subjected to drying treatment and high-temperature pyrolysis treatment as a cycle I; The cycle I is performed for several times to obtain a modified carbon felt B; the number of times of performing the cycle I is 1-3; the silicate sol is prepared from a metal salt, tetraethyl orthosilicate, anhydrous ethanol and LiF; in the silicate sol, the molar ratio of Si to metal element ions is 1.2:1, and the molar ratio of Si to Li is 10:3; wherein the metal salt is hafnium chloride, zirconium chloride or yttrium nitrate; Step 4, steps 2 and 3 are taken as a cycle II, and the cycle II is performed for several times to obtain the silicate-doped C / SiC composite material; the number of times of performing the cycle II is 4-7.

2. The production method according to claim 1, wherein In step 2, the vacuum-impregnation treatment has an impregnation time of 6-10 h; The drying treatment is performed in an air atmosphere at a drying temperature of 60-80 DEG C for 10-14 h; The high-temperature pyrolysis treatment is performed in an argon atmosphere at a treatment temperature of 1050-1150 DEG C for 0.5-1 h, and the heating rate is 4-8 DEG C / min.

3. The production method according to claim 1, wherein In step 3, the vacuum-impregnation treatment has an impregnation time of 6-10 h; The drying treatment is performed in an air atmosphere at a drying temperature of 60-80 DEG C for 10-14 h; The high-temperature pyrolysis treatment is performed in an argon atmosphere at a treatment temperature of 850-950 DEG C for 0.5-1 h, and the heating rate is 4-8 DEG C / min.

4. The production method according to claim 1, wherein The polycarbosilane solution is prepared from polycarbosilane and xylene; and the concentration of polycarbosilane in the polycarbosilane solution is 40-60 wt.%; The concentration of the silicate sol is 2-5 mol / L.

5. The production method according to claim 1, wherein The silicate sol is prepared by the following steps: According to the proportion, the metal salt and tetraethyl orthosilicate are uniformly dispersed in anhydrous ethanol, stirred and filtered to obtain a solution A; The LiF is uniformly dispersed in the solution A to obtain a solution B; The solution B is reacted at 105-115 DEG C for 1.5-2.5 h, and is left to stand at room temperature for 20-28 h to obtain the silicate sol.

6. The production method according to claim 1, wherein In the ultrasonic cleaning, any one of anhydrous ethanol, acetone and distilled water is used as the cleaning liquid, and the ultrasonic cleaning time is 4-6 min; In step 1, the drying temperature is 60-80 DEG C, and the drying time is 4-6 h.

7. A silicate-doped C / SiC composite material prepared by the preparation method of any one of claims 1-6.

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