A SiC fiber based on polycarbosilane raw material and its production process

Abstract

The present invention discloses a SiC fiber based on a polycarbosilane raw material and a production process thereof, belonging to the technical field of silicon carbide fibers. The SiC fiber comprises 80 to 95 parts of linear polycarbosilane and 5 to 20 parts of hyperbranched polycarbosilane, wherein the hyperbranched polycarbosilane is obtained by polymerizing AB3-type monomers. The present invention provides a SiC fiber based on a polycarbosilane raw material and a production process thereof. The SiC fiber is prepared by preparing a hyperbranched polycarbosilane obtained by polymerizing AB3-type monomers, and mixing the hyperbranched polycarbosilane with a linear polycarbosilane. The hyperbranched polycarbosilane can be used as a partial solvent and crosslinking agent for the linear polycarbosilane, thereby avoiding the step of oxidative curing, reducing the oxygen content and carbon enrichment of the SiC, and improving the strength and heat resistance of the SiC.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon carbide fibers, and in particular relates to a SiC fiber based on polycarbosilane raw materials and a production process thereof. Background Art

[0002] Silicon carbide (SiC) ceramics are an extremely important specialty ceramic among high-temperature structural ceramics. SiC ceramics, also known as corundum, are covalently bonded inorganic compounds composed of equal amounts of silicon and carbon (in practice, SiC ceramics are carbon-rich or oxygen-rich) forming a regular tetrahedral crystal structure similar to diamond. This unique structure endows SiC ceramics with excellent properties, including high-temperature stability, oxidation resistance, and high hardness. They have broad application prospects in aerospace, military, nuclear power engineering, automotive, mechanical and chemical engineering, energy, and electronic information technology, making them an irreplaceable high-temperature structural ceramic material. However, ceramics are primarily composed of ionic and covalent bonds, making dislocations difficult to glide and undergo elastic and plastic deformation, often leading to brittle fracture. Therefore, strengthening and toughening ceramics are often achieved through the addition of secondary phases such as particles, whiskers, and fibers. When ceramic materials are subjected to stress, the toughness of these materials can be significantly improved through whisker or fiber pullout, bridging, and crack deflection. Ceramic-matrix composites reinforced with continuous ceramic fibers have shown the most significant toughening effect.

[0003] There are four main methods for preparing continuous SiC fibers: chemical vapor deposition, chemical vapor reaction, high-temperature sintering of ultrafine powders, and precursor conversion. The precursor conversion method uses an organic precursor, polycarbosilane, as a raw material, which undergoes melt spinning, crosslinking, and pyrolysis to transform the organic compound into a ceramic material, producing SiC fibers. The precursor conversion method offers low production costs, readily available organic polymer precursors, and the ability to tailor its composition to the desired fiber's intended use. This facilitates large-scale industrial production and is the primary method for the industrial production of fine-diameter continuous SiC fibers. Currently, it is the only successful route for preparing SiC fibers for use in hot-end components of aircraft engines. However, polycarbosilane is solid at room temperature, and a large amount of good solvents such as xylene, tetrahydrofuran, and n-hexane are required during the impregnation process; and carbon enrichment will occur, affecting the temperature resistance. In addition, the molecular weight of polycarbosilane is quite low, and the spinning ability is poor. When over-stretched, the fiber is easy to break, and it is difficult to obtain continuous small-diameter fibers. Therefore, some studies have added polyethylene silane as a plasticizer to polycarbosilane to improve its spinning ability. However, polyethylene silane has poor compatibility with polycarbosilane, and phase separation is easy to occur during the solvent removal process. In addition, a freeze-drying step is required to remove the solvent, and the process is relatively complicated. Summary of the Invention

[0004] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a SiC fiber based on a polycarbosilane raw material and a production process thereof. A hyperbranched polycarbosilane obtained by polymerizing an AB3-type monomer is prepared and mixed with a linear polycarbosilane to prepare the SiC fiber. The hyperbranched polycarbosilane can serve as a partial solvent and cross-linking agent for the linear polycarbosilane, thereby avoiding the oxidative curing step, reducing the oxygen content and carbon enrichment of the SiC, and improving the strength and heat resistance of the SiC.

[0005] The technical solutions for achieving the purpose of the present invention are as follows:

[0006] A SiC fiber based on a polycarbosilane raw material comprises, by weight, 80 to 95 parts of linear polycarbosilane and 5 to 20 parts of hyperbranched polycarbosilane, wherein the hyperbranched polycarbosilane is obtained by polymerizing an AB3 type monomer, and the structural formula of the AB3 type monomer is shown in Formula 1 or Formula 2:

[0007] Formula 1, Formula 2.

[0008] The preparation method of the AB3 type monomer is as follows: under anhydrous and oxygen-free conditions, 4-bromochlorobenzene or m-chlorobromobenzene, magnesium, and tetrahydrofuran are mixed in a container, the temperature is raised to 50-80° C. with stirring, trivinylchlorosilane is added dropwise and reacted for 8-16 hours, then the reaction temperature is raised to 100-110° C., dimethylmonochlorosilane is added dropwise, the stirring reaction is continued for 8-16 hours, water is added to quench the reaction, the organic solution layer is collected by ether extraction, the organic solution layer is washed, dried, and then filtered, and the filtrate is concentrated under reduced pressure to prepare the AB3 type monomer.

[0009] Preferably, the molar ratio of the 4-bromochlorobenzene or m-chlorobromobenzene, trivinylchlorosilane and dimethylmonochlorosilane is (0.95-1.05): (0.95-1.05): (0.95-1.05).

[0010] Preferably, the molar amount of magnesium added is 2.0 to 2.5 times the molar amount of 4-bromochlorobenzene or m-chlorobromobenzene added.

[0011] Preferably, the preparation method of the hyperbranched polycarbosilane is: dissolving the monomer in toluene, then adding a Custer catalyst, stirring and reacting at room temperature for 12 to 24 hours, purifying and drying to obtain the hyperbranched polycarbosilane.

[0012] The present invention also protects a production process of SiC fiber based on polycarbosilane raw material, comprising the following steps:

[0013] S1. Dissolving linear polycarbosilane and hyperbranched polycarbosilane in hexane to obtain a clear solution, and then drying under vacuum at 60° C. to obtain a precursor mixture;

[0014] S2. The mixture is spun by a melt spinning machine at a spinning temperature of 205~285°C to obtain a precursor fiber;

[0015] S3. Cut the precursor fiber into short fibers, heat it to 150-180°C at 5-10°C / h under nitrogen protection, and crosslink and cure it for 1-2 hours to obtain cured fibers;

[0016] S4. The cured fiber is heated to 1000-1400°C at a rate of 2-10°C / min under a hydrogen atmosphere and kept at this temperature for 5-90 minutes to obtain silicon carbide fiber.

[0017] In a specific embodiment, the precursor fiber can also be cured using an electron beam; the steps include:

[0018] S1. Dissolving linear polycarbosilane and hyperbranched polycarbosilane in hexane in an amount of 300 to 500 wt % of the linear polycarbosilane to obtain a clear solution, followed by vacuum drying at 60° C. to obtain a precursor mixture;

[0019] S2. The mixture is spun by a melt spinning machine at a spinning temperature of 205~235°C to obtain a precursor fiber;

[0020] S3. The precursor fiber is cross-linked and cured by electron beam irradiation at a dose of 10 to 20 MGy for 3 to 5 seconds under an inert gas atmosphere to obtain a cured fiber;

[0021] S4. The cured fiber is heated to 1000-1400° C. at a rate of 2-10° C. / min under a hydrogen atmosphere and kept at this temperature for 5-90 minutes to obtain silicon carbide fiber.

[0022] In another specific embodiment, ultraviolet light may be used to cure the precursor fiber, comprising the following steps:

[0023] S1. Dissolving linear polycarbosilane and hyperbranched polycarbosilane in hexane to obtain a clear solution, and then drying under vacuum at 60° C. to obtain a precursor mixture;

[0024] S2. The mixture is spun by a melt spinning machine at a spinning temperature of 205~235°C to obtain a precursor fiber;

[0025] S3. The precursor fiber is cross-linked and cured by ultraviolet irradiation for 10 to 30 minutes under an inert gas atmosphere to obtain a cured fiber;

[0026] S4. The cured fiber is heated to 1000-1400°C at a rate of 2-10°C / min under a hydrogen atmosphere and kept at this temperature for 5-90 minutes to obtain silicon carbide fiber.

[0027] The present invention also protects the use of SiC fibers based on polycarbosilane raw materials in SiC ceramic-based materials.

[0028] Beneficial effects

[0029] The present invention has the following beneficial effects:

[0030] (1) Hyperbranched polycarbosilane was prepared using an AB3 type monomer. Compared with the dual monomer system, the AB3 type monomer can generate a hyperbranched structure through one-step self-condensation, without the need to precisely control the dual monomer ratio, without small molecular monomer residue, and reducing the purification steps. In addition, the molecular weight distribution is narrower, the degree of branching is higher, a compact spherical structure is formed, molecular chain entanglement is reduced, and low viscosity, high fluidity and high solubility are imparted.

[0031] (2) Hyperbranched polycarbosilane contains vinyl groups, and the cross-linking reaction is mainly a hydrosilylation reaction, which reduces the cross-linking temperature. At the same time, the hydrosilylation reaction does not produce small molecular gases. The introduction of vinyl groups can also cross-link with the residual Si-H in linear polycarbosilane, increase the cross-linking density, avoid rearrangement and escape of small molecules during high temperature and weight loss, and improve the ceramic yield.

[0032] (3) There is no need for oxidative cross-linking, and hydrogen is used to react excess carbon during the sintering stage. The oxygen content of the silicon carbide fiber product is low, the Si / C of the ceramic is more reasonable, and the product exhibits better high temperature resistance and oxidation resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the synthesis route and structure of AB3 type monomer 1 and hyperbranched polycarbosilane of the present invention;

[0034] Figure 2 This is the H NMR spectrum of the AB3 type monomer 1 of the present invention;

[0035] Figure 3 This is the infrared spectrum of the hyperbranched polycarbosilane 1 of the present invention. DETAILED DESCRIPTION

[0036] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0037] In the examples, the experimental methods used are conventional methods unless otherwise specified, and the materials, reagents, etc. used are all commercially available unless otherwise specified.

[0038] The raw materials and equipment used in the embodiments and comparative examples are described below:

[0039] Trivinylchlorosilane: CAS: 1871-21-2, purity 95%, purchased from Beijing Bailingwei Technology Co., Ltd.;

[0040] Dimethylmonochlorosilane: CAS: 1066-35-9, purity 98%, purchased from Sigma-Aldrich;

[0041] 4-Bromochlorobenzene: CAS: 106-39-8, purity 99%, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.;

[0042] m-Chlorobromobenzene: CAS: 108-37-2, purity 99%, purchased from Sigma-Aldrich;

[0043] Custer catalyst: CAS: 81032-58-8, purity 3000 ppm, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.;

[0044] Hexane: n-Hexane was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0045] Linear polycarbosilane: CAS: 62306-27-8, molecular weight 1400, purchased from Henan Weitixi Chemical Technology Co., Ltd., with the following structural formula:

[0046]

[0047] AB3 type monomer 1: The preparation method is as follows:

[0048] Weigh 10g of dry and anhydrous magnesium chips and place them in a three-necked flask. Pass an inert gas and continue to purge. Add 20ml of tetrahydrofuran and purge with inert gas for 30min. Add 0.2mol of 4-bromochlorobenzene and reflux under 65°C. Stir at a rate of 200rpm. Add 0.2mol of trivinylchlorosilane dropwise and react for 16h. Raise the reaction temperature to 100°C and add 0.2mol of dimethylchlorosilane dropwise. Continue stirring and reacting for 16 hours. Add 150ml of distilled water to quench the reaction. Add 60ml of ether and extract three times. Collect the organic solution layer and wash it again with 100ml of distilled water and 100ml of saturated NaCl solution. Dry it over anhydrous sodium sulfate and filter it. The filtrate is concentrated under reduced pressure to obtain an AB3 type monomer with a yield of 80%. Keep it at 0°C for use. The reaction route is as follows: Figure 1 As shown, the test was performed using an Avance 500 Bruker nuclear magnetic resonance spectrometer, with CDCl3 as the solvent. 1 H-NMR spectrum Figure 2 shown.

[0049] AB3 type monomer 2: The preparation method is similar to AB3 type monomer 1, except that 4-bromochlorobenzene is replaced with m-chlorobromobenzene, with a yield of 76%;

[0050] Hyperbranched polycarbosilane 1: Weigh 0.2 mol of monomer 1 and 100 ml of toluene in a flask, slowly add dropwise a toluene solution of Custer's catalyst, stir at room temperature for 24 h, add 100 ml of chloroform and 10 g of activated carbon, stir or shake vigorously, let stand for 6 hours, collect the organic phase by filtration, and concentrate under reduced pressure. The residue is added to 500 ml of methanol to form a white precipitate, which is collected by filtration and dried in vacuo at 60°C for 12 hours to obtain hyperbranched polycarbosilane precursor 1.

[0051] The test was performed using a Nicolet 5700 infrared spectrometer produced by Thermo Electron Corporation, with a wavenumber range of 500–4000 cm -1 , pressed with KBr, infrared spectrum as Figure 3 As shown. Among them, 3069cm -1 and 1625cm -1 The antisymmetric stretching vibration peak corresponding to C=C is 2873~2952cm -1 The characteristic peak corresponding to CH2 is 2124 cm -1 、928cm -1 The characteristic peak corresponding to Si-H is 1248 cm -1 The symmetrical deformation vibration of Si-CH3 is at 1023cm -1 The corresponding position is the deformation vibration of CH in Si-CH2-Si, 746 cm -1 corresponds to the stretching vibration of Si-C.

[0052] Hyperbranched polycarbosilane 2: The preparation method is similar to that of hyperbranched polycarbosilane 1, except that monomer 1 is replaced by monomer 2.

[0053] Example 1

[0054] A SiC fiber based on polycarbosilane raw material, comprising 80 parts of linear polycarbosilane and 20 parts of hyperbranched polycarbosilane, is prepared as follows:

[0055] S1. The linear polycarbosilane and the hyperbranched polycarbosilane 1 were dissolved in hexane, wherein the amount of hexane added was 300 wt % of the mass of the linear polycarbosilane to obtain a clear light yellow solution, which was dried in vacuo at 60 ° C to obtain a white powdery precursor mixture;

[0056] S2. The white powder obtained in step S1 was charged into a storage tank of a melt spinning machine, which was then heated to the melt spinning temperature under the protection of high-purity nitrogen. The polymer melt was extruded through a single-hole spinneret with an orifice diameter of 0.3 mm, a spinning temperature of 220°C, and a winding speed of 400 m / min to obtain a precursor fiber;

[0057] S3. Under nitrogen protection, the precursor fiber was heated to 170°C in a tube furnace at a heating rate of 10°C / h and kept at this temperature for 1 h to obtain a cured fiber;

[0058] S4. The cured fiber was heated to 1250°C in high-purity hydrogen at a heating rate of 5°C / min and kept at this temperature for 5 min to obtain a glossy black SiC fiber.

[0059] Example 2

[0060] Compared with Example 1, the difference is that hyperbranched polycarbosilane 1 is replaced by hyperbranched polycarbosilane 2;

[0061] Example 3

[0062] Compared with Example 1, the difference is that 95 parts of linear polycarbosilane and 5 parts of hyperbranched polycarbosilane are included, and the amount of hexane added is 500wt% of the linear polycarbosilane;

[0063] Example 4

[0064] Compared with Example 1, the difference is that the thermal crosslinking in step S3 is replaced by electron beam irradiation crosslinking; the dosage is 15 MGy, and the curing time is 5 s;

[0065] Example 5

[0066] Compared with Example 1, the difference is that the thermal crosslinking in step S3 is replaced by ultraviolet radiation crosslinking; the wavelength is 365nm, and the irradiation time is 30min;

[0067] Comparative Example 1

[0068] Compared with Example 1, the difference is that 70 parts of linear polycarbosilane and 30 parts of hyperbranched polycarbosilane are included, and the amount of hexane added is 200wt% of the linear polycarbosilane;

[0069] Comparative Example 2

[0070] Compared with Example 1, the difference is that no hyperbranched polycarbosilane is added, the amount of hexane added is 1000 wt % of the linear polycarbosilane, and the spinning temperature is 285° C.

[0071] The following are the test methods for the performance parameters involved in the present invention:

[0072] (1) Molecular weight M w: The molecular weight and molecular weight distribution of hyperbranched polycarbosilane were analyzed using gel permeation chromatography (GPC) (Agilent 1100 system, Agilent).

[0073] (2) Softening point: The softening point of the precursor mixture was tested using a capillary method using a melting point apparatus (MP30, Mettler Toledo). The test method followed the standard GB / T 21781 “Test method for melting point and melting range of chemicals—Capillary method”. The sample was ground into a fine powder and filtered through a 400-mesh filter. The capillary filling height was 3 mm, and the heating rate was 1°C / min.

[0074] (3) Ceramic yield: The ceramic yield of the precursor mixture was determined using a thermogravimetric analyzer (TGA2, Mettler Toledo). 5 mg of the sample was ground in a mortar with a mesh size between 60 and 80. The entire test system was evacuated with a vacuum pump to replace the inert gas. The sample was heated from 30 to 900 °C at a heating rate of 10 °C.

[0075] (4) Average diameter: The cross-sectional diameter of SiC fibers was measured at 50 locations using a scanning electron microscope (XL30, Philips-FEI).

[0076] (5) Tensile strength: The tensile strength of a single SiC fiber was measured using a tensile testing machine (YG(B)003A, Wenzhou Darong Textile Instrument Co., Ltd.). The gauge length was 25 mm, and the crosshead speed was 1 mm / min. The average value was calculated for 20 fibers tested.

[0077] (6) Heat resistance: The SiC fiber was heat treated at 1200°C, 1300°C and 1500°C for 30 min, respectively. The tensile strength after heat treatment was tested and compared with the tensile strength before the test, and the tensile strength retention rate was calculated.

[0078] Table 1 Molecular weight test of hyperbranched polycarbosilane

[0079]

[0080] Table 2 Performance test of examples and comparative examples

[0081]

[0082] As can be seen from the results of the Examples and Comparative Examples, the addition of hyperbranched polycarbosilane to blend with linear polycarbosilane reduces the softening point of the polycarbosilane, allowing it to be spun at lower melt-spinning temperatures. This prevents degradation reactions such as chain breakage or excessive crosslinking in the polycarbosilane at high temperatures, helping to maintain a stable molecular structure and avoid a sudden drop in molecular weight or the formation of impurities. Furthermore, due to the presence of liquid hyperbranched polycarbosilane, only a small amount of solvent is required to dissolve the solid polycarbosilane. Furthermore, the hyperbranched polycarbosilane introduces a large number of vinyl groups, acting as both a partial solvent and a crosslinking agent, reducing the introduction of oxygen into the system. The use of hydrogen to react with excess carbon during the sintering stage results in a more reasonable Si / C ratio in the ceramic, improving its density and significantly increasing the ceramic yield and tensile strength, as well as its heat resistance.

[0083] It can be seen from Examples 1, 4, and 5 that the SiC fibers obtained by thermal crosslinking, electron beam irradiation crosslinking, and UV irradiation crosslinking and curing have good mechanical properties and heat resistance, and electron beam irradiation is more advantageous due to its time period and high performance.

[0084] Comparative Examples 1 and 2 show that when an excessive amount of hyperbranched polycarbosilane is added, the softening point is too low, resulting in a low melt viscosity and a thin melt, making fiber formation difficult and prone to breakage. Without hyperbranched polycarbosilane, the resulting fibers are larger in diameter and brittle, making them difficult to weave.

[0085] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A production process for SiC fiber based on polycarbosilane raw material, characterized in that: The following steps are involved: S1. Dissolving linear polycarbosilane and hyperbranched polycarbosilane in hexane to obtain a clear solution, and then drying under vacuum at 60° C. to obtain a precursor mixture; S2. The mixture is spun by a melt spinning machine at a spinning temperature of 205~235°C to obtain a precursor fiber; S3. The precursor fiber is cross-linked and cured by heating to 150~180°C at 5~10°C / h under an inert gas atmosphere and holding for 1~2h to obtain a cured fiber; or, the precursor fiber is cross-linked and cured by electron beam irradiation at a dose of 10~20MGy for 3~5s under an inert gas atmosphere to obtain a cured fiber; S4. The cured fiber was heated to 1000-1400°C at 2-10°C / min under a hydrogen atmosphere and kept at this temperature for 5-90 min to obtain silicon carbide fiber; The polycarbosilane raw material is composed of 80-95 parts of linear polycarbosilane and 5-20 parts of hyperbranched polycarbosilane in parts by weight. The hyperbranched polycarbosilane is obtained by polymerizing AB3 type monomers. The structural formula of the AB3 type monomers is shown in Formula 1 or Formula 2: Formula 1, Formula 2 The preparation method of the AB3 type monomer is as follows: under anhydrous and oxygen-free conditions, 4-bromochlorobenzene or m-chlorobromobenzene, magnesium, and tetrahydrofuran are mixed in a container, the temperature is raised to 50-80° C. with stirring, trivinylchlorosilane is added dropwise and reacted for 8-16 hours, then the reaction temperature is raised to 100-110° C., dimethylmonochlorosilane is added dropwise, the stirring reaction is continued for 8-16 hours, water is added to quench the reaction, the organic solution layer is collected by ether extraction, the organic solution layer is washed, dried, and then filtered, and the filtrate is concentrated under reduced pressure to prepare the AB3 type monomer.

2. The production process of SiC fiber based on polycarbosilane raw material according to claim 1, characterized in that: The molar ratio of the 4-bromochlorobenzene or m-chlorobromobenzene, trivinylchlorosilane and dimethylmonochlorosilane is (0.95-1.05): (0.95-1.05): (0.95-1.05).

3. The production process of SiC fiber based on polycarbosilane raw material according to claim 1, characterized in that: The molar amount of the added magnesium is 2.0 to 2.5 times the molar amount of the added 4-bromochlorobenzene or m-chlorobromobenzene.

4. The production process of SiC fiber based on polycarbosilane raw material according to claim 1, characterized in that: The preparation method of the hyperbranched polycarbosilane comprises: dissolving a monomer in toluene, then adding a Custer catalyst, stirring and reacting at room temperature for 12 to 24 hours, purifying, and drying to obtain the hyperbranched polycarbosilane.

5. Use of SiC fiber produced by the production process of SiC fiber based on polycarbosilane raw material according to any one of claims 1 to 4 in SiC ceramic-based materials.

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