High-al content si-al-c-o ceramic precursor, its synthesis method and application

Abstract

The application discloses a Si-Al-C-O ceramic precursor with high aluminum content and a synthesis method and application thereof, and the Si-Al-C-O ceramic precursor has a softening point of 120-250 DEG C, a number average molecular weight of 2500-4000, and an aluminum content of 1-20 wt%. The preparation method comprises the following steps: firstly, dissolving polysiloxane resin and an aluminum source in a solvent; and then, transferring the reaction solution into a high-pressure reaction kettle to perform a high-temperature and high-pressure synthesis reaction. Under the high-temperature and high-pressure conditions, the solvent reaches a supercritical state, the molecules of the reactants are uniformly mixed, and the polysiloxane resin molecules and the aluminum source molecules fully react. The reaction solution is subjected to distillation treatment to remove the solvent and small molecular substances, and the ceramic precursor is obtained. The raw materials used in the preparation method are all commercial reagents, and the raw materials are widely sourced. The synthesis route of the precursor is simple, and the cost is low.

Description

Technical Field

[0001] This invention relates to the field of ceramic precursor technology, and in particular to a high-alumina-content Si-Al-CO ceramic precursor, its synthesis method, and its application. Background Technology

[0002] Silicon carbide fibers possess excellent properties such as low density, high strength, high temperature resistance, and oxidation resistance, making them promising for applications in aerospace and nuclear energy equipment. Compared to first- and second-generation silicon carbide fibers, third-generation aluminum-containing silicon carbide (SiC(Al)) fibers exhibit superior high-temperature resistance and creep resistance, attracting widespread attention from researchers both domestically and internationally in recent years. Synthesizing precursors with high aluminum content is crucial for preparing high-performance SiC(Al) fibers.

[0003] Currently, there are two main methods for synthesizing SiC(Al) fiber precursors: one method involves reacting an organosilicon polymer (such as polydimethylsilane) with an aluminum source (such as aluminum acetylacetonate) under normal pressure to synthesize SiC(Al) fiber precursors (Zhao Dafang, Research on Continuous Technology of SA-type Silicon Carbide Fibers [D]. Changsha: National University of Defense Technology, 2008; Polymer. 2011, 52(17): 3811-3818; 200910111053.X). Although this method is simple, the reaction temperature is high (>420℃), which easily causes the aluminum source to volatilize, resulting in a low aluminum content (1-2 wt%) in the obtained precursor. Furthermore, the high reaction temperature leads to excessive reaction between the organosilicon polymer and the aluminum source, forming an over-branched three-dimensional network structure, which is detrimental to the spinning and forming of SiC(Al) fibers. Another method is to react organosilicon polymers with Si-C bonds as the main chain (such as polycarbosilane) with aluminum sources (such as aluminum acetylacetonate) under high pressure to synthesize SiC(Al) fiber precursors. Although using organosilicon polymers with Si-C bonds as the main chain and high-pressure reaction conditions can reduce the reaction temperature to some extent (300-350℃) and overcome the problem of aluminum acetylacetonate volatilization (Yuan Qin, Basic Research on the Preparation Process of Third-Generation Continuous SiC Fibers [D]. Changsha: National University of Defense Technology, 2016), the low reaction temperature of this method results in insufficient reaction between the organosilicon polymer and the aluminum source, and the poor solubility of aluminum acetylacetonate in the solvent leads to a low aluminum content (0.3-0.7 wt%) in the obtained SiC(Al) fiber precursors. In addition, the high cost of polycarbosilane also leads to a high cost of the obtained precursors.

[0004] Therefore, given the problems of low aluminum content and high cost of SiC(Al) precursors in existing technologies, the key issue is how to design and prepare SiC(Al) ceramic precursors with high aluminum content and uniform molecular structure. Summary of the Invention

[0005] This invention provides a high-alumina-content Si-Al-CO ceramic precursor, its synthesis method, and its application, which overcomes the shortcomings of existing SiC(Al) precursors, such as low aluminum content and high cost.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The present invention provides a high-alumina-content Si-Al-CO ceramic precursor, wherein the high-alumina-content Si-Al-CO ceramic precursor has a softening point of 120-250℃, a number-average molecular weight of 2500-4000, and an aluminum content of 1-20wt%.

[0007] More importantly, this invention provides a method for synthesizing the above-mentioned high-alumina-content Si-Al-CO ceramic precursor, comprising the following steps:

[0008] S1: Weigh out the polysiloxane resin and the first solvent, mix and stir to dissolve, and obtain a polysiloxane resin solution;

[0009] S2: Weigh the aluminum source and the second solvent, mix and stir to dissolve, and obtain an aluminum source solution;

[0010] S3: After mixing and stirring the polysiloxane resin solution and aluminum source solution evenly, add them to a high-pressure reactor and carry out a high-temperature and high-pressure reaction under an inactive atmosphere to obtain a precursor solution;

[0011] S4: The precursor solution is distilled under an inactive atmosphere to obtain a high-alumina Si-Al-CO ceramic precursor.

[0012] Furthermore, in S1 above, the number average molecular weight of the polysiloxane resin is 2000-3500, and the softening point is 50-150℃.

[0013] Furthermore, in S1 above, the first solvent is one or more of xylene, toluene, benzene, N'N dimethylformamide, ethanol, tetrahydrofuran, and n-hexane; the mass ratio of polysiloxane resin to the first solvent is (1-5):(1-10).

[0014] Furthermore, in S2 above, the second solvent is one or more of toluene, benzene, methanol, ethanol and acetone; the aluminum source is one or more of aluminum acetylacetonate, methylaluminoxane, dimethylaluminum chloride and aluminum triformate; the mass ratio of the aluminum source to the second solvent is (0.1-5):(1-10).

[0015] Furthermore, in S3 above, the mass ratio of the polysiloxane resin to the aluminum source is 10:3 to 10:1.

[0016] Furthermore, in the above S3, the high-pressure synthesis reaction conditions include: reaction temperature: 250~400℃; heating rate: 1~50℃ / min; reaction time: 0.1~50h; reaction pressure: 1~7MPa.

[0017] Furthermore, in S3 and S4 above, the inactive atmosphere is one or more of nitrogen, argon and helium.

[0018] Furthermore, in S4 above, the distillation reaction conditions include: when the distillation temperature is between room temperature and 250°C, the heating rate is 1–50°C / min; when the distillation temperature is between 250°C and 400°C, the heating rate is 1–20°C / min; and the distillation time is 0.1–50 h.

[0019] This invention also provides the application of the above-mentioned high-alumina content Si-Al-CO ceramic precursor in the preparation of high-temperature resistant aluminum-containing SiC ceramic fibers and aluminum-containing SiC ceramics.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. The Si-Al-CO ceramic precursor provided by this invention has a high aluminum content (1-20 wt%), a moderate softening point (120-250℃) and a moderate molecular weight (number average molecular weight of 2500-4000), which is conducive to melt spinning and can be used to prepare high-performance SiC(Al) fibers.

[0022] 2. In the preparation method of the high-alumina content Si-Al-CO ceramic precursor provided by this invention, polysiloxane resin and aluminum source are first dissolved in solvents respectively; then, the two solutions are placed in an autoclave for high-pressure synthesis reaction. Temperature and pressure are controlled to reach the supercritical values ​​of the solvent. At this point, the solution in the reactor reaches a supercritical fluid state, with no clear distinction between liquid and gas. The reaction system is homogeneous, with a density comparable to a liquid and a viscosity comparable to a gas, exhibiting good mass and heat transfer efficiency. Under these conditions, polysiloxane resin molecules and aluminum source molecules are uniformly mixed, allowing for a full and uniform reaction when the reaction conditions are met, which is beneficial for fully utilizing the raw materials and synthesizing a product with a uniform molecular structure. The reaction solution is further distilled to remove the solvent and small molecules, yielding the final precursor. The raw materials used in the preparation method provided by this invention are readily available, widely sourced, and the synthesis route is simple and low-cost.

[0023] 3. The method of this invention is simple and low in cost, so the high aluminum content Si-Al-CO ceramic precursor obtained has a good application prospect in the preparation of high performance SiC(Al) ceramic fibers and ceramics. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0025] Figure 1 An optical photograph of the Si-Al-CO precursor obtained in Example 1 of this invention;

[0026] Figure 2 This is the X-ray electron spectrum of the Si-Al-CO precursor obtained in Example 1 of the present invention.

[0027] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0030] Unless otherwise specified, all medicines / reagents used are commercially available.

[0031] Example 1

[0032] The steps for preparing the Si-Al-CO ceramic precursor in this embodiment are as follows:

[0033] (1) Add 3 kg of polysiloxane resin (number average molecular weight 2200, softening point 70℃) to a mixed solvent of 1.5 kg xylene and 1.5 kg N'N dimethylformamide, and stir at room temperature for 12 h to obtain a polysiloxane resin solution.

[0034] (2) Add 300g of aluminum acetylacetonate to a mixed solvent of 3Kg xylene and toluene, and stir at room temperature for 6h to obtain an aluminum acetylacetonate solution; wherein the volume ratio of xylene and toluene is 1:2.

[0035] (3) High-pressure synthesis reaction: Place the two solutions mentioned above in a high-pressure reactor and evacuate them three times to purge with nitrogen. Set the initial reaction pressure to 3 MPa and close the inlet and outlet valves. The reaction proceeds at 10℃·min -1 The heating rate was set to 300℃, and the temperature was maintained for 4 hours. After the reaction was completed, the mixture was allowed to cool naturally.

[0036] (4) Distillation: The precursor solution synthesized under high pressure was transferred into a distillation vessel, and the vessel was evacuated three times to purge with nitrogen. Distillation was then carried out under a nitrogen atmosphere. The distillation temperature was 10℃·min. -1 Heat to 200℃ and hold for 1 hour. Then, increase the temperature by 5℃·min. -1 The temperature was raised to 350℃ and held for 2 hours. After cooling, the distillation product was removed to obtain the Si-Al-CO precursor.

[0037] The optical photograph of the Si-Al-CO precursor obtained in this embodiment is as follows: Figure 1 As shown, the X-ray electron spectroscopy analysis results of the precursor are as follows: Figure 2 As shown in the figure, the precursor mainly contains four elements: Si, Al, C, and O, with mass fractions of 28.8 wt%, 6.3 wt%, 47.4 wt%, and 17.5 wt%, respectively. The Si-Al-CO precursor obtained in this embodiment has a number-average molecular weight of 2803 and a softening point of 183 °C.

[0038] Example 2

[0039] The steps for preparing the Si-Al-CO ceramic precursor in this embodiment are as follows:

[0040] (1) Add 3 kg of polysiloxane resin (number average molecular weight 2700, softening point 91℃) to a mixed solvent of 3 kg of xylene and toluene, and stir at room temperature for 12 h to obtain a polysiloxane resin solution; wherein the volume ratio of xylene and toluene is 2:1.

[0041] (2) Add 900g of aluminum acetylacetonate to 3kg of benzene and stir at room temperature for 6h to obtain an aluminum acetylacetonate solution;

[0042] (3) High-pressure synthesis reaction: Place the two solutions mentioned above in a high-pressure reactor and purge with nitrogen three times. Set the initial reaction pressure to 1 MPa and close the inlet and outlet valves. The reaction proceeds at 10℃·min. -1 The heating rate was set to 350℃, and the temperature was maintained for 4 hours. After the reaction was complete, the mixture was allowed to cool naturally.

[0043] (4) Distillation: The precursor solution synthesized under high pressure was transferred into a distillation vessel, and the vessel was evacuated three times to purge with nitrogen. Distillation was then carried out under a nitrogen atmosphere. The distillation temperature was 10℃·min. -1 Heat to 210℃ and hold for 1 hour. Then, increase the temperature by 5℃·min.-1 The temperature was raised to 400℃ and held for 2 hours. After cooling, the distillation product was removed to obtain the Si-Al-CO precursor.

[0044] The Si-Al-CO precursor obtained in this embodiment has an aluminum content of 11.2 wt%, a number-average molecular weight of 3243, and a softening point of 204 °C.

[0045] Example 3

[0046] The steps for preparing the Si-Al-CO ceramic precursor in this embodiment are as follows:

[0047] (1) Add 3 kg of polysiloxane resin (number average molecular weight 2800, softening point 106℃) to a mixed solvent of 3 kg of xylene and ethanol, and stir at room temperature for 12 h to obtain a polysiloxane resin solution; wherein the volume ratio of xylene and ethanol is 2:1.

[0048] (2) Add 600g of aluminum acetylacetonate to a mixed solution of 3Kg toluene and benzene, and stir at room temperature for 6h to obtain an aluminum acetylacetonate solution; wherein the volume ratio of xylene and benzene is 2:1.

[0049] (3) High-pressure synthesis reaction: Place the two solutions mentioned above in a high-pressure reactor and purge with nitrogen three times. Set the initial reaction pressure to 5 MPa and close the inlet and outlet valves. The reaction proceeds at 10℃·min -1 The temperature was increased to 400℃ and held for 4 hours. After the reaction was complete, the mixture was allowed to cool naturally.

[0050] (4) Distillation: The precursor solution synthesized under high pressure was transferred into a distillation vessel, and the vessel was evacuated three times to purge with nitrogen. Distillation was then carried out under a nitrogen atmosphere. The distillation temperature was 10℃·min. -1 Heat to 240℃ and hold for 1 hour. Then, increase the temperature by 5℃·min. -1 The temperature was raised to 400℃ and held for 2 hours. After cooling, the distillation product was removed to obtain the Si-Al-CO precursor.

[0051] The Si-Al-CO precursor obtained in this embodiment has an aluminum content of 9.9 wt%, a number-average molecular weight of 3600, and a softening point of 230℃.

[0052] Example 4

[0053] The steps for preparing the Si-Al-CO ceramic precursor in this embodiment are as follows:

[0054] (1) Add 3 kg of polysiloxane resin (number average molecular weight 2800, softening point 106℃) to a mixed solvent of 3 kg of xylene and ethanol, and stir at room temperature for 12 h to obtain a polysiloxane resin solution; wherein the volume ratio of xylene and ethanol is 2:1.

[0055] (2) Add 600g of aluminum acetylacetonate to a mixed solution of 3Kg toluene and benzene, and stir at room temperature for 6h to obtain an aluminum acetylacetonate solution; wherein the volume ratio of xylene and benzene is 2:1.

[0056] (3) High-pressure synthesis reaction: Place the two solutions mentioned above in a high-pressure reactor and purge with nitrogen three times. Set the initial reaction pressure to 5 MPa and close the inlet and outlet valves. The reaction proceeds at 10℃·min -1 The heating rate was set to 300℃, and the temperature was maintained for 4 hours. After the reaction was completed, the mixture was allowed to cool naturally.

[0057] (4) Distillation: The precursor solution synthesized under high pressure was transferred into a distillation vessel, and the vessel was evacuated three times to purge with nitrogen. Distillation was then carried out under a nitrogen atmosphere. The distillation temperature was 10℃·min. -1 Heat to 180℃ and hold for 1 hour. Then, increase the temperature by 5℃·min. -1 The temperature was raised to 300℃ and held for 2 hours. After cooling, the distillation product was removed to obtain the Si-Al-CO precursor.

[0058] The Si-Al-CO precursor obtained in this embodiment has an aluminum content of 9.1 wt%, a number-average molecular weight of 3060, and a softening point of 213℃.

[0059] Example 5

[0060] The steps for preparing the Si-Al-CO ceramic precursor in this embodiment are as follows:

[0061] (1) Add 3 kg of polysiloxane resin (number average molecular weight 2800, softening point 106℃) to a mixed solvent of 3 kg of xylene and ethanol, and stir at room temperature for 12 h to obtain a polysiloxane resin solution; wherein the volume ratio of xylene and ethanol is 2:1.

[0062] (2) Add 600g of aluminum acetylacetonate to a mixed solution of 3Kg toluene and benzene, and stir at room temperature for 6h to obtain an aluminum acetylacetonate solution; wherein the volume ratio of xylene and benzene is 2:1.

[0063] (3) High-pressure synthesis reaction: Place the two solutions mentioned above in a high-pressure reactor and purge with nitrogen three times. Set the initial reaction pressure to 5 MPa and close the inlet and outlet valves. The reaction proceeds at 10℃·min -1 The heating rate was set to 300℃, and the temperature was maintained for 10 hours. After the reaction was completed, the mixture was allowed to cool naturally.

[0064] (4) Distillation: The precursor solution synthesized under high pressure was transferred into a distillation vessel, and the vessel was evacuated three times to purge with nitrogen. Distillation was then carried out under a nitrogen atmosphere. The distillation temperature was 10℃·min. -1Heat to 180℃ and hold for 1 hour. Then, increase the temperature by 5℃·min. -1 The temperature was raised to 300℃ and held for 10 hours. After cooling, the distillation product was removed to obtain the Si-Al-CO precursor.

[0065] The Si-Al-CO precursor obtained in this embodiment has an aluminum content of 9.3 wt%, a number-average molecular weight of 3250, and a softening point of 221℃.

[0066] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A high aluminum content Si-Al-C-O ceramic precursor, characterized in that, The high-aluminum-content Si-Al-C-O ceramic precursor has a softening point of 120-250 DEG C, a number average molecular weight of 2500-4000, and an aluminum content of 1-20 wt%; The synthesis method of the high-aluminum-content Si-Al-C-O ceramic precursor, The method comprises the following steps: S1: weighing polysiloxane resin and a first solvent, mixing, stirring and dissolving to obtain a polysiloxane resin solution; the polysiloxane resin has a number average molecular weight of 2000-3500 and a softening point of 50-150 DEG C; the first solvent is one or more of dimethylbenzene, toluene, benzene, N'N dimethylformamide, ethanol, tetrahydrofuran and n-hexane; the mass ratio of the polysiloxane resin to the first solvent is (1-5):(1-10); S2: weighing an aluminum source and a second solvent, mixing, stirring and dissolving to obtain an aluminum source solution; the second solvent is one or more of toluene, benzene, methanol, ethanol and acetone; the aluminum source is one or more of acetylacetone aluminum, methylaluminoxane, dimethylaluminum chloride and aluminum trifluoride; the mass ratio of the aluminum source to the second solvent is (0.1-5):(1-10); S3: after the polysiloxane resin solution and the aluminum source solution are uniformly mixed and stirred, they are added into a high-pressure reaction kettle, and high-temperature and high-pressure reaction is carried out under an inactive atmosphere; the reaction temperature is 250-400 DEG C, and the reaction pressure is 1-7 MPa; the mass ratio of the polysiloxane resin to the aluminum source is 10:3-10:1; S4: the precursor solution is distilled under an inactive atmosphere to obtain a high-aluminum-content Si-Al-C-O ceramic precursor.

2. A high aluminum content Si-Al-C-O ceramic precursor according to claim 1, characterized in that, In S3, the high-temperature and high-pressure reaction conditions include: a heating rate of 1-50 DEG C / min; and a reaction time of 0.1-50 h.

3. The high alumina content Si-Al-C-O ceramic precursor of claim 1, wherein, In S3 and S4, the inactive atmosphere is one or more of nitrogen, argon and helium.

4. The high alumina content Si-Al-C-O ceramic precursor of claim 1, wherein, In S4, the distillation reaction conditions include: when the distillation temperature is at room temperature to 250 DEG C, the heating rate is 1-50 DEG C / min; when the distillation temperature is at 250-400 DEG C, the heating rate is 1-20 DEG C / min; and the distillation time is 0.1-50 h.

5. Use of a high alumina content Si-Al-C-O ceramic precursor according to claim 1, characterized in that, The method is applied to the preparation of high-temperature-resistant aluminum-containing SiC ceramic fibers and aluminum-containing SiC ceramics.

Images