Synthesis of yttrium-containing aluminum-silicon carbide ceramic fiber precursor and method for preparing fiber

Abstract

The application discloses a kind of synthesis of yttrium-containing aluminum SiC ceramic fiber precursor and fiber preparation method.The method uses PDMS as raw material, and liquid viscous poly-silicon-carbon-silane is obtained by cracking, PSCS is uniformly mixed with Y (AcAc) 3, Al (AcAc) 3 Heat polymerization, after cooling, by dissolving, filtering, vacuum distillation, obtained the molecular weight distribution uniform, excellent spinning performance of yttrium-containing aluminum polycarbosilane precursor, again through melt spinning, iodine infusibility, high-temperature sintering and sintering process and be prepared yttrium-containing aluminum SiC fiber.The application selects acetylacetone yttrium and acetylacetone aluminum and poly-silicon-carbon-silane to synthesize yttrium-containing aluminum polycarbosilane, after melt spinning, using iodine infusibility treatment.Al and Y can form yttrium-aluminum garnet liquid phase system as SiC structural ceramic sintering aid at high temperature, which is conducive to reducing the sintering temperature of SiC ceramic, realizes SiC ceramic densification.

Description

Technical Field

[0001] The present invention belongs to the field of ceramic fibers, and in particular relates to a method for synthesizing a yttrium-aluminum-containing SiC ceramic fiber precursor and preparing the fibers. Background Art

[0002] Continuous silicon carbide ceramic fibers have the characteristics of high strength, high modulus, high temperature resistance, oxidation resistance, and resistance to high temperature molten salts. They have broad application prospects in the fields of ceramic-based composite thermal structures. Currently, they are mainly prepared by the precursor conversion method. This method mainly includes the preparation of the precursor, melt spinning, infusibility treatment, high-temperature firing and sintering. Among them, the composition and structure of the precursor directly affect the performance of the final ceramic fiber. With the development of science and technology, higher requirements are placed on the performance of SiC ceramic fibers. At present, the main method for preparing high-performance SiC ceramic fibers is to introduce heterogeneous elements into the precursor to improve the comprehensive performance of SiC ceramic fibers. The key to the process lies in the synthesis of SiC ceramic precursors containing heterogeneous elements. At present, a variety of SiC ceramic precursors containing heterogeneous elements have been synthesized at home and abroad, and the comprehensive performance of the prepared SiC ceramic fibers containing heterogeneous elements has been significantly improved.

[0003] The introduction of high melting point compounds or heterogeneous elements (such as Ta, Hf, Nb, Ti, Mo, Cr, Zr, etc.) into SiC ceramic precursors to prepare SiC ceramic fibers containing heterogeneous elements has the following main purposes: 1) improving the performance of the precursor. After the heterogeneous elements are introduced into the precursor, they can act as crosslinking agents due to their valence diversity. Moreover, the heterogeneous elements are homogenized at the molecular level in the precursor, and their content is controllable and adjustable, which can improve the rheological properties of the precursor, facilitate the reshaping processing of the precursor, and improve the spinning performance of the precursor; 2) improving the temperature resistance of the SiC fiber. 1) Introducing heterogeneous elements into the SiC ceramic precursor, the heterogeneous elements form ultra-high temperature silicides with Si in the fiber, and form ultra-high temperature carbides or intermetallic compounds with C, thereby improving the temperature resistance of SiC ceramics; 2) Diversifying the functions of SiC fibers. After introducing heterogeneous elements into the SiC ceramic precursor, the functions of the prepared SiC ceramic fibers can be diversified, such as having excellent absorption performance and electrical properties, which have important application value in military and electronic fields; 3) Assisting sintering and densification. SiC fiber densification is one of the keys to preparing high-performance fibers by the precursor conversion method.

[0004] The heterogeneous elements introduced into SiC ceramic fibers can effectively heal defects such as pores and cracks generated during the high-temperature sintering process of SiC ceramic fibers, thereby increasing the densification degree of SiC ceramic fibers and improving the performance of SiC ceramic fibers. For example, the introduction of iron in the literature "Transactions of Nonferrous Metals Society of China, 2007, 17(5): 987-991," the introduction of cobalt in the patent (application number: CN201310374328.5), the introduction of nickel in the literature "Ceramics International, 2022, 48(14): 20495-20505," and the introduction of titanium in the patent (application number: CN201611054103.1) can give silicon carbide ceramic fibers superior microwave absorption properties. The introduction of aluminum in the patent (application number: CN200510031778.X), zirconium in the patent (application number: CN201711449898.0), and boron in the patent (application number: CN202011383826.2) can give it higher temperature resistance. For example, in China, Cao Feng et al. used aluminum acetylacetonate (AlAcAc)3) and polysilicon carbosilane (PSCS) and, after several hours of heat preservation reaction under nitrogen atmosphere, obtained a pale yellow resinous aluminum-containing SiC ceramic precursor - polyaluminocarbosilane (PACS), in which the mass fraction of Al is generally around 0.4%, Mn is about 1500-2000, and Mn is about 1000-2000. w The melting point is about 1800~2300℃ and the softening point is about 200℃. The research found that there is Kumada rearrangement phenomenon in the reaction. The main reaction is Si-H and Al(AcAc)3 to form Si-O-Al bond, while a small amount of Si-Al-Si bond is formed. SiC(Al) ceramic fiber is made from PACS. The chemical composition of SiC(Al) ceramic fiber is Si 1.15 O 0.026 Al 0.013 Its main structure is β-SiC with an average grain size of 95nm. Auger electron spectroscopy analysis shows that the Si, C, O, and Al elements are evenly distributed within the ceramic fiber, and it has good heat resistance. After being treated in argon at 1800°C for 1 hour, the strength retention rate of SiC(Al) ceramic fiber is 71%. However, the silicon carbide ceramic fibers obtained by polyaluminocarbosilane have problems such as abnormal grain growth and poor grain uniformity, which affect the mechanical properties of the obtained polycrystalline silicon carbide ceramic fibers.

[0005] The preparation of SiC ceramic fibers described in the above literature generally involves reacting polycarbosilane with an organic reagent to synthesize polycarbosilane containing heterogeneous elements. The prepared polymer easily forms a cross-linked network polymer, resulting in the inability to spin. Summary of the Invention

[0006] In order to solve the problems existing in the background technology, the purpose of the present invention is to provide a method for synthesizing a yttrium-aluminum-containing SiC ceramic fiber precursor and preparing the fiber.

[0007] Compared with polycarbosilane, the present invention uses polysilicon carbosilane (PSCS) to polymerize with aluminum acetylacetonate and yttrium acetylacetonate to generate yttrium aluminum-containing polycarbosilane, and the polymer has good melt spinning performance. Compared with air infusibility, air infusibility requires high temperature and higher requirements for precursors, and is mainly carried out at 200-300°C. Iodine infusibility treatment is short in time and low in temperature, which can reduce the cross-linking reaction temperature to 80°C and accelerate the reaction rate. Yttrium aluminum-doped precursors are conducive to the preparation of sintered, densified, and high-temperature resistant silicon carbide ceramic fibers.

[0008] Al and Y, as sintering aids for SiC structural ceramics, can form a yttrium aluminum garnet (YAG) liquid phase system at high temperatures, which helps lower the sintering temperature of SiC ceramics and achieve densification of SiC ceramics. If the fiber can form a YAG phase at high temperatures, it is beneficial to the densification of SiC fibers. The present invention uses polysilicacarbosilane (PSCS) to react with yttrium acetylacetonate and aluminum acetylacetonate to prepare yttrium aluminum polycarbosilane (PYACS). Through melt spinning, iodine infusibility, high-temperature firing, sintering and other processes, yttrium aluminum SiC ceramic fibers are produced. Iodine infusibility was used to achieve fiber crosslinking, and amorphous Si-CO-(Y / Al) fibers were obtained by pyrolysis at 1000°C with a ceramic yield of 73.96%. With increasing sintering temperature, SiC fibers prepared by sintering at 1900°C showed a higher degree of crystallinity, larger grain size, smaller fiber diameter, and a denser structure, indicating that the high-temperature doping of Al and Y played a role in sintering densification. Polycrystalline silicon carbide ceramic fibers with excellent temperature resistance can be obtained from a conventional spinnable polycarbosilane precursor through spinning, air infusibility treatment, high-temperature firing, and sintering. However, air infusibility requires high temperatures and high precursor requirements, primarily at 200-300°C, because PCS begins to react with oxygen above 150°C. Iodine infusibility treatment, due to its short duration and low temperature, can reduce the reaction temperature of PCS and oxygen to 80°C, accelerating the reaction rate and producing SiC fibers with a low softening point. This method has promising applications in low-temperature crosslinking (80-150°C).

[0009] The technical solutions adopted in the present invention are as follows:

[0010] 1. A Yttrium-aluminum-containing SiC ceramic fiber

[0011] The yttrium-aluminum SiC ceramic fiber precursor is prepared by melt spinning, iodine infusibility, pyrolysis and sintering to obtain the yttrium-aluminum SiC ceramic fiber; the yttrium-aluminum SiC ceramic fiber precursor is obtained by polymerizing polysilicon carbosilane, aluminum acetylacetonate and yttrium acetylacetonate, and then dissolving, filtering and distilling under reduced pressure.

[0012] 2. Synthesis of a Yttrium-Aluminum-Containing SiC Ceramic Fiber Precursor and Preparation Method of Yttrium-Aluminum-Containing SiC Ceramic Fiber

[0013] The following steps are involved:

[0014] Step 1) Synthesis of yttrium-aluminum-containing SiC ceramic fiber precursor: polysilicon carbosilane, organometallic aluminum reagent and organometallic yttrium reagent are placed in a three-necked flask according to a certain ratio;

[0015] The principle of the reaction between PSCS and Al(AcAc)3 and Y(AcAc)3 in spinnable yttrium aluminum polycarbosilane is as follows: Si-H reacts with an organometallic reagent to introduce the metal element into the precursor molecular structure. The reaction diagram is as follows:

[0016]

[0017] Step 2) heating the mixture to a target temperature at a certain heating rate under nitrogen protection and maintaining the temperature for a certain time to react, and cooling the mixture to room temperature after the reaction to obtain a primary product of yttrium aluminum polycarbosilane;

[0018] Step 3) dissolving the primary product yttrium aluminum polycarbosilane obtained in step 2) in an organic solvent, filtering to remove over-crosslinked products and impurities, and performing vacuum distillation to obtain the final spinnable yttrium aluminum polycarbosilane;

[0019] Step 4) adding the spinnable yttrium aluminum polycarbosilane obtained in step 3) to a spinning drum, heating to a high temperature under the protection of high-purity nitrogen, standing to degas, then lowering to the spinning temperature, pressurizing with high-purity nitrogen, melt-spinning into filaments through a single-hole spinning plate, and winding onto a receiving drum to obtain yttrium aluminum polycarbosilane PYACS fibrils;

[0020] Step 5) Iodine infusibility: The yttrium aluminum-containing polycarbosilane (PYACS) fibrils prepared in step 4) and iodine are placed in a glass container at a predetermined mass, and the temperature is slowly increased to obtain yttrium aluminum-containing polycarbosilane (PYACS) cross-linked fibers. Excessive heating may result in insufficient infusibility of the fibers, and the fibers may be partially melted and stranded during high-temperature sintering, resulting in stiffness, brittleness, and reduced strength.

[0021] Step 6) placing the yttrium aluminum polycarbosilane (PYACS) cross-linked filaments in a TL1200-12001 resistance tube furnace for high-temperature pyrolysis to obtain Si-CO-(Y / Al) fibers;

[0022] Step 7) The pyrolyzed Si-CO-(Y / Al) fiber is placed in a crucible, placed in a ZT-40-21Y high-temperature vacuum hot pressing sintering furnace, and sintered at high temperature to finally obtain the desired yttrium-aluminum-containing SiC ceramic fiber.

[0023] In the step 1):

[0024] Polysilicone carbosilane is liquid polysilicone carbosilane PSCS;

[0025] The organometallic aluminum reagent is aluminum acetylacetonate Al(AcAc)3;

[0026] The organometallic yttrium reagent is yttrium acetylacetonate Y(AcAc)3;

[0027] Aluminum acetylacetonate and yttrium acetylacetonate are uniformly mixed with polysilicon carbosilane, wherein the mass fraction of the added aluminum acetylacetonate is 1% to 3%, and the mass fraction of the added yttrium acetylacetonate is 1% to 3%.

[0028] In the step 2):

[0029] The heating rate is 5-10℃ / min;

[0030] The target temperature is 400°C and the holding time is 9 to 13 hours.

[0031] The organic solvent in step 3) is one of tetrahydrofuran, benzene, toluene, xylene, n-hexane, and cyclohexane.

[0032] The reduced pressure distillation temperature in step 3) is 40°C to 90°C.

[0033] In the iodine infusibility process of step 5), the infusibility temperature is 80° C.-150° C., and the holding time is 3 hours.

[0034] In the step 5), the mass ratio of PYACS fibrils to iodine is 3:5.

[0035] During the infusibility process, iodine reacts with the active groups of the original fibers, causing them to crosslink and solidify. If the iodine content is too low, the fibers will partially crosslink and solidify; if the iodine content is too high, the fiber oxygen content will increase, affecting fiber performance. Taking all factors into consideration, the mass ratio of original fibers to iodine is 3:5.

[0036] The high temperature pyrolysis process of step 6) is specifically as follows:

[0037] The heating rate from 20°C to 400°C is 2.5°C / min, the heating rate from 400°C to 800°C is 1.7°C / min, and the heating rate from 800°C to 1000°C is 2.5°C / min.

[0038] The high temperature sintering process of step 7) is specifically as follows:

[0039] The heating rate from 1000°C to 1400°C is 2.5°C / min, the heating rate from 1400°C to 1600°C is 2.5°C / min, and the heating rate from 1600°C to 1900°C is 7.5°C / min.

[0040] After sintering at 1900℃, the SiC crystallinity of Si-CO-(Y / Al) fibers was higher, the β-SiC grain size increased, the structure gradually became denser, and the fiber diameter became smaller. The doping of Al and Y at high temperature played a role in sintering densification.

[0041] The heat treatment heating rate significantly influences the fiber's microstructure and mechanical properties. A slower heating rate slows grain growth, hindering its development. Rapidly sintered fibers exhibit a rough, uneven surface, with defects such as nodules, cracks, and grooves. Reducing the sintering rate not only reduces microcracks on the fiber surface and within it, but also improves its mechanical properties. The fiber surface is very smooth and dense, with a small number of small protrusions. Reducing the sintering rate can improve tensile strength. This is primarily because reducing or eliminating microcracks on the fiber surface and within it increases fiber density and makes the fiber's composition and structure more complete.

[0042] Taking into account the influence of firing rate on fiber properties and production efficiency, the heating rate from 20℃ to 400℃ is 2.5℃ / min, the heating rate from 400℃ to 800℃ is 1.7℃ / min, the heating rate from 800℃ to 1000℃ is 2.5℃ / min, the heating rate from 1000℃ to 1400℃ is 2.5℃ / min, the heating rate from 1400℃ to 1600℃ is 2.5℃ / min, and the heating rate from 1600℃ to 1900℃ is 7.5℃ / min, which is more reasonable.

[0043] The present invention synthesizes yttrium-aluminum polycarbosilane (PCS) by combining yttrium acetylacetonate and aluminum acetylacetonate with polysilicon carbosilane. After melt spinning, the resulting material is treated with iodine to render it infusible. Al and Y, acting as sintering aids for SiC structural ceramics, form a liquid phase system of yttrium aluminum garnet (YAG) at high temperatures, which helps lower the sintering temperature of SiC ceramics and achieve densification.

[0044] The beneficial effects of the present invention are:

[0045] (1) The present invention uses liquid low molecular weight polysilicon carbosilane to react with aluminum acetylacetonate and yttrium acetylacetonate to synthesize yttrium aluminum polycarbosilane. Compared with the use of larger molecular weight polycarbosilane reported in the literature, the reaction of polysilicon carbosilane (PSCS) with aluminum acetylacetonate and yttrium acetylacetonate to synthesize yttrium aluminum polycarbosilane is not easy to crosslink and solidify during the polymerization process, and the polymer has good melt spinning performance;

[0046] (2) The iodine infusibility treatment has a short time and low temperature, which can reduce the reaction temperature of PCS and oxygen to 80°C to accelerate the reaction rate to prepare SiC fibers with low softening points, and can achieve lower temperature crosslinking (80-150°C);

[0047] (3) SiC ceramic fibers doped with Al and Y sintering aids can form a yttrium aluminum garnet (YAG) liquid phase system at high temperature, which is beneficial to reduce the sintering temperature of SiC ceramics and greatly improve the fiber density. The yttrium aluminum-containing fibers prepared by the method have high strength after infusibility, high-temperature firing and sintering. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 The chemical reaction formula of the spinnable yttrium-aluminum-containing polycarbosilane prepared by the method of the present invention is:

[0049] Figure 2 These are images of spinnable yttrium-containing aluminum polycarbosilane with different aluminum yttrium contents prepared by the method of the present invention; wherein, a is a digital image of the spinnable yttrium-containing aluminum polycarbosilane of Example 1; b is a digital image of the spinnable yttrium-containing aluminum polycarbosilane of Example 2; c is a digital image of the spinnable yttrium-containing aluminum polycarbosilane of Example 3; d is a digital image of the spinnable yttrium-containing aluminum polycarbosilane of Example 4; and e is a digital image of the spinnable yttrium-containing aluminum polycarbosilane of Example 5.

[0050] Figure 3 is a gel liquid chromatogram of the precursor of Example 3;

[0051] Figure 4 This is an optical image of the PYACS fibrils of Example 5;

[0052] Figure 5 The molecular weight, molecular weight distribution and spinning performance of PYACS with different aluminum yttrium contents;

[0053] Figure 6 SEM images of PYACS fibrils with different aluminum yttrium contents;

[0054] Figure 7 These are optical images of PYACS fibrils in Example 3 and Example 5 that were subjected to infusibility and rapid sintering;

[0055] Figure 8 SEM images of Si-CO-(Y / Al) fibers sintered in air according to different embodiments;

[0056] Figure 9 SEM images of Si-CO-(Y / Al) fibers sintered under argon conditions according to different embodiments.

[0057] Figure 10This is the SEM image of the Si-CO-(Y / Al) fiber sintered at the first heating rate in Example 6. DETAILED DESCRIPTION

[0058] The present invention is described in detail below with reference to specific implementation cases. The following implementation cases will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form.

[0059] The implementation process of the embodiment of the present invention is as follows:

[0060] Example 1

[0061] Weigh 10.000g of polycarbosilane, 0.1g of aluminum acetylacetonate and 0.2g of yttrium acetylacetonate in a three-necked flask. Under nitrogen protection, heat the flask to 400℃ at a heating rate of 5-10℃ / min for 9h. After the reaction, cool to room temperature to obtain the initial product of yttrium aluminum polycarbosilane. Dissolve the initial product of yttrium aluminum polycarbosilane in n-hexane, filter to remove the cross-linked product and impurities, and obtain the final spinnable yttrium aluminum polycarbosilane by vacuum distillation. Figure 2 As shown in a, PYACS cross-linked fibers were obtained by melt spinning and iodine infusibility treatment. PYACS fibers were pyrolyzed at high temperature to obtain Si-CO-(Y / Al) fibers. The obtained Si-CO-(Y / Al) fibers were subjected to high temperature treatment under air and argon conditions, respectively. SEM images were shown as follows: Figure 8 a and Figure 9 As shown in a.

[0062] Example 2

[0063] Weigh 10.000g of polycarbosilane, 0.2g of aluminum acetylacetonate and 0.2g of yttrium acetylacetonate in a three-necked flask. Under nitrogen protection, heat the flask to 400℃ at a heating rate of 5-10℃ / min for 9h. After the reaction, cool to room temperature to obtain the initial product of yttrium aluminum polycarbosilane. Dissolve the initial product of yttrium aluminum polycarbosilane in n-hexane, filter to remove the cross-linked product and impurities, and distill under reduced pressure to obtain the final spinnable yttrium aluminum polycarbosilane. Figure 2 As shown in b, PYACS cross-linked fibers were obtained by melt spinning and iodine infusibility treatment. PYACS fibers were pyrolyzed at high temperature to obtain Si-CO-(Y / Al) fibers. The obtained Si-CO-(Y / Al) fibers were subjected to high temperature treatment under air and argon conditions, respectively. SEM images were shown. Figure 8 b and Figure 9 As shown in b.

[0064] Example 3

[0065] Weigh 10.000g of polycarbosilane, 0.3g of aluminum acetylacetonate and 0.2g of yttrium acetylacetonate in a three-necked flask. Under nitrogen protection, heat the mixture to 400℃ at a heating rate of 5-10℃ / min and polymerize for 10h. After the reaction, cool the mixture to room temperature to obtain the initial product of yttrium aluminum-containing polycarbosilane. Dissolve the initial product of yttrium aluminum-containing polycarbosilane in n-hexane, filter to remove the cross-linked product and impurities, and distill under reduced pressure to obtain the final spinnable yttrium aluminum-containing polycarbosilane. Figure 2 As shown in Figure c, the gel liquid chromatogram containing yttrium aluminum polycarbosilane was measured using a gel permeation chromatograph, as shown in Figure 5. Figure 3 Then, PYACS cross-linked fibers were obtained through melt spinning and iodine infusibility treatment. PYACS fibers were subjected to high-temperature pyrolysis to obtain Si-CO-(Y / Al) fibers. The obtained Si-CO-(Y / Al) fibers were subjected to high-temperature treatment under air and argon conditions, as shown in FIG. Figure 7 As shown in (a), SEM Figure 8 c and Figure 9 As shown in c.

[0066] Example 4

[0067] Weigh 10.000g of polycarbosilane, 0.2g of aluminum acetylacetonate and 0.3g of yttrium acetylacetonate in a three-necked flask. Under nitrogen protection, heat the flask to 400℃ at a heating rate of 5-10℃ / min and polymerize for 12h. After the reaction, cool to room temperature to obtain the initial product of yttrium aluminum polycarbosilane. Dissolve the initial product of yttrium aluminum polycarbosilane in n-hexane, filter to remove the cross-linked product and impurities, and obtain the final spinnable yttrium aluminum polycarbosilane by vacuum distillation. Figure 2 d, PYACS cross-linked fibers were obtained by melt spinning and iodine infusibility treatment. PYACS fibers were pyrolyzed at high temperature to obtain Si-CO-(Y / Al) fibers. The obtained Si-CO-(Y / Al) fibers were subjected to high temperature treatment under air and argon conditions, respectively. SEM images were shown as follows: Figure 8 d and Figure 9 As shown in d.

[0068] Example 5

[0069] Weigh 10.000g of polycarbosilane, 0.3g of aluminum acetylacetonate and 0.3g of yttrium acetylacetonate in a three-necked flask. Under nitrogen protection, heat the mixture to 400℃ at a heating rate of 5-10℃ / min and polymerize for 13h. After the reaction, cool the mixture to room temperature to obtain the initial product of yttrium aluminum-containing polycarbosilane. Dissolve the initial product of yttrium aluminum-containing polycarbosilane in n-hexane, filter to remove over-crosslinked products and impurities, and obtain the final spinnable yttrium aluminum-containing polycarbosilane by vacuum distillation. Figure 2Then, PYACS cross-linked fibers were obtained through melt spinning and iodine infusibility treatment. PYACS fibers were subjected to high-temperature pyrolysis to obtain Si-CO-(Y / Al) fibers. The obtained Si-CO-(Y / Al) fibers were subjected to high-temperature treatment under air and argon conditions, as shown in FIG. Figure 7 As shown in (b), SEM Figure 8 d and Figure 9 d. The optical image of the original fiber obtained after spinning the precursor is shown in Figure 4 shown.

[0070] Example 6

[0071] The PYACS cross-linked fibers in Example 3 were subjected to high-temperature cracking to obtain Si-CO-(Y / Al) fibers. The obtained Si-CO-(Y / Al) fibers were divided into two parts and subjected to high-temperature treatment under argon conditions at different heating rates: 1) the heating rate from 20°C to 100°C was 4°C / min, the heating rate from 100°C to 1300°C was 15°C / min, the heating rate from 1300°C to 1600°C was 2.5°C / min, and the heating rate from 1600°C to 1900°C was 7.5°C / min. The SEM images of the finally obtained fibers are as follows: Figure 10 2) the heating rate from 20°C to 400°C is 2.5°C / min, the heating rate from 400°C to 800°C is 1.7°C / min, the heating rate from 800°C to 1000°C is 2.5°C / min, the heating rate from 1000°C to 1400°C is 2.5°C / min, the heating rate from 1400°C to 1600°C is 2.5°C / min, and the heating rate from 1600°C to 1900°C is 7.5°C / min. The SEM of the finally obtained fiber is as shown Figure 9 Comparing the two heating rates, the fibers sintered at the first heating rate exhibit a loose porous structure, are not dense, and have almost no mechanical properties. Therefore, considering the impact of the firing rate on fiber properties and production efficiency, the heating rates from 20°C to 400°C are 2.5°C / min, from 400°C to 800°C is 1.7°C / min, from 800°C to 1000°C is 2.5°C / min, from 1000°C to 1400°C is 2.5°C / min, from 1400°C to 1600°C is 2.5°C / min, and from 1600°C to 1900°C is 7.5°C / min, which is more reasonable.

[0072] The experimental conditions of each embodiment are compared. Figure 5As shown in the figure, it can be seen that too low a foreign element content will not contribute to sintering densification, while too high a foreign element content will destroy grain boundaries and form impurity phases that are detrimental to the fiber's mechanical properties and high-temperature stability. The optimal spinning conditions for yttrium aluminum polycarbosilane are 3% aluminum acetylacetonate and 2% yttrium acetylacetonate by mass. The present invention uses liquid polysilicon carbosilane to react with an organoaluminum reagent and an organoyttrium reagent to synthesize yttrium aluminum polycarbosilane. The resulting fiber has the advantages of high temperature resistance and high strength. Al and Y, as sintering aids for SiC structural ceramics, can form a yttrium aluminum garnet (YAG) liquid phase system at high temperatures, which helps reduce the sintering temperature of SiC ceramics. The resulting yttrium aluminum-containing fiber exhibits high strength after infusibility, high-temperature firing, and sintering. The iodine infusibility treatment has a short time and low temperature, which can reduce the reaction temperature of PCS and oxygen to 80°C to accelerate the reaction rate to prepare SiC fibers with low softening points. It has good application prospects in the field of low-temperature crosslinking (80-150°C).

[0073] Polycarbosilane (PCS) has a high molecular weight. Traditional methods using PCS to prepare ceramic fibers containing heterogeneous elements can easily lead to polymer crosslinking during polymerization, making spinning difficult. To address this issue, the present invention uses liquid PSCS with a lower molecular weight to synthesize it with Y(AcAc)3 and Al(AcAc)3 to obtain an aluminum- and yttrium-containing PYACS precursor with uniform molecular weight distribution and excellent spinning performance. Compared with air infusibility treatment, the present invention uses iodine infusibility treatment, which shortens the time and lowers the temperature, reducing the crosslinking reaction temperature to 80°C and accelerating the reaction rate. To address the problem that the amorphous SiCxOy phase can lead to a loose fiber structure and a sharp decline in mechanical properties, the present invention introduces heterogeneous elements aluminum and yttrium. After sintering at 1900°C, the SiC fibers become more crystallized, the grain size increases, and the fiber diameter further decreases. The high-temperature doping of Al and Y contributes to the sintering densification.

Claims

1. A yttrium-aluminum-containing SiC ceramic fiber, characterized in that: The precursor of yttrium aluminum SiC ceramic fiber is melt-spun to obtain yttrium aluminum polycarbosilane PYACS fibril, which is then subjected to iodine infusibility, pyrolysis and sintering processes to obtain yttrium aluminum SiC ceramic fiber. The iodine infusibility step comprises: placing yttrium aluminum polycarbosilane (PYACS) fibrils and iodine in a certain mass in a glass container, and heating the container to obtain yttrium aluminum polycarbosilane (PYACS) cross-linked fibers; In the iodine infusibility process, the infusibility temperature is 80°C-150°C, the holding time is 3 hours, and the mass ratio of PYACS fibrils to iodine is 3:

5. The yttrium-aluminum-containing SiC ceramic fiber precursor is obtained by polymerizing polysilicon carbosilane, aluminum acetylacetonate and yttrium acetylacetonate, and then dissolving, filtering and distilling under reduced pressure.

2. A method for synthesizing a yttrium-aluminum-containing SiC ceramic fiber precursor and preparing a yttrium-aluminum-containing SiC ceramic fiber, characterized in that: The following steps are involved: Step 1) Synthesis of yttrium-aluminum-containing SiC ceramic fiber precursor: polysilicon carbosilane, organometallic aluminum reagent and organometallic yttrium reagent are placed in a three-necked flask according to a certain ratio; Step 2) heating the mixture to a target temperature at a certain heating rate under nitrogen protection and maintaining the temperature for a certain time to carry out the reaction, and cooling the mixture to room temperature after the reaction is completed to obtain a primary product of yttrium aluminum polycarbosilane; Step 3) dissolving the initial product yttrium aluminum polycarbosilane obtained in step 2) in an organic solvent, filtering to remove over-crosslinked products and impurities, and performing vacuum distillation to obtain the final spinnable yttrium aluminum polycarbosilane; Step 4) adding the spinnable yttrium aluminum polycarbosilane obtained in step 3) to a spinning cylinder, heating under the protection of high-purity nitrogen, standing to degas, then cooling to the spinning temperature, pressurizing with high-purity nitrogen, melt-spinning through a single-hole spinning plate into filaments, and winding onto a receiving cylinder to obtain yttrium aluminum polycarbosilane PYACS fibrils; Step 5) Iodine insolubility: The yttrium aluminum-containing polycarbosilane (PYACS) fibrils prepared in step 4) and iodine of a certain mass are placed in a glass container, and the temperature is raised to obtain yttrium aluminum-containing polycarbosilane (PYACS) cross-linked fibers; Step 6) placing the yttrium aluminum-containing polycarbosilane (PYACS) cross-linked filaments in a resistance tube furnace for high-temperature pyrolysis to obtain Si-CO-(Y / Al) fibers; Step 7) The pyrolyzed Si-CO-(Y / Al) fiber is placed in a crucible, placed in a high-temperature vacuum hot-pressing sintering furnace, and sintered at high temperature to obtain the desired yttrium-aluminum-containing SiC ceramic fiber; In the iodine infusibility process of step 5), the infusibility temperature is 80° C.-150° C., the holding time is 3 h, and the mass ratio of PYACS fibrils to iodine is 3:

5.

3. The method for synthesizing a yttrium-aluminum-containing SiC ceramic fiber precursor and preparing a yttrium-aluminum-containing SiC ceramic fiber according to claim 2, characterized in that: In the step 1): Polysilicone carbosilane is liquid polysilicone carbosilane PSCS; The organometallic aluminum reagent is aluminum acetylacetonate Al(AcAc)3; The organometallic yttrium reagent is yttrium acetylacetonate Y(AcAc)3; Aluminum acetylacetonate and yttrium acetylacetonate are uniformly mixed with polysilicon carbosilane, wherein the mass fraction of the added aluminum acetylacetonate is 1% to 3%, and the mass fraction of the added yttrium acetylacetonate is 1% to 3%.

4. The method for synthesizing a yttrium-aluminum-containing SiC ceramic fiber precursor and preparing a yttrium-aluminum-containing SiC ceramic fiber according to claim 2, characterized in that: In the step 2): The heating rate is 5~10℃ / min; The target temperature is 400°C and the holding time is 9 to 13 hours.

5. The method for synthesizing a yttrium-aluminum-containing SiC ceramic fiber precursor and preparing a yttrium-aluminum-containing SiC ceramic fiber according to claim 2, characterized in that: The organic solvent in step 3) is one of tetrahydrofuran, benzene, toluene, xylene, n-hexane, and cyclohexane.

6. The method for synthesizing a yttrium-aluminum-containing SiC ceramic fiber precursor and preparing a yttrium-aluminum-containing SiC ceramic fiber according to claim 2, characterized in that: The reduced pressure distillation temperature in step 3) is 40°C to 90°C.

7. The method for synthesizing a yttrium-aluminum-containing SiC ceramic fiber precursor and preparing a yttrium-aluminum-containing SiC ceramic fiber according to claim 2, characterized in that: The high temperature pyrolysis process of step 6) is specifically as follows: The heating rate from 20°C to 400°C is 2.5°C / min, the heating rate from 400°C to 800°C is 1.7°C / min, and the heating rate from 800°C to 1000°C is 2.5°C / min.

8. The method for synthesizing a yttrium-aluminum-containing SiC ceramic fiber precursor and preparing a yttrium-aluminum-containing SiC ceramic fiber according to claim 2, characterized in that: The high temperature sintering process of step 7) is specifically as follows: The heating rate from 1000°C to 1400°C is 2.5°C / min, the heating rate from 1400°C to 1600°C is 2.5°C / min, and the heating rate from 1600°C to 1900°C is 7.5°C / min.

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