A method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers

Abstract

A method for simultaneously preparing silicon carbide fibers and silicon nitride nanofibers includes the following steps: pyrolyzing PDMS under an inert atmosphere to obtain LPS; mixing LPS with ferrocene under an inert atmosphere and heating to react, obtaining PFCS after the reaction is complete; melt spinning under an inert atmosphere to obtain PFCS protofibers; performing an air-insoluble treatment to obtain PFCS pre-oxidized fibers; performing electron beam irradiation crosslinking treatment under an inert atmosphere to obtain PFCS crosslinked fibers; placing the PFCS crosslinked fibers in a graphite paper tube and pyrolyzing them under a nitrogen atmosphere to obtain the final product. This invention uses polyferrocarbosilane as a precursor and, through melt spinning, low-oxygen air-insoluble treatment, electron beam irradiation crosslinking, and high-temperature inorganic treatment in a nitrogen environment, successfully prepares SiC fibers and simultaneously prepares Si3N4 nanofibers; compared to separate preparation methods, this method is simpler and more efficient.

Description

Technical Field

[0001] This invention relates to the field of special ceramic fibers and nanofibers, specifically to a method for preparing silicon carbide fibers and silicon nitride nanofibers. Background Technology

[0002] Silicon carbide (SiC) fiber has excellent properties such as high temperature resistance, corrosion resistance, and oxidation resistance, and has broad application prospects in high-tech fields such as aviation, aerospace, national defense, and nuclear industry.

[0003] The main methods for manufacturing silicon carbide fibers include chemical vapor deposition (CVD) and precursor conversion. Precursor conversion involves using organic polymers as precursors, leveraging their solubility and fusibility to form the polymer, followed by cross-linking and high-temperature thermal decomposition to transform the organic material into an inorganic ceramic material. CVD is a process that deposits the target product onto a substrate surface through spatial gas-phase chemical reactions (thermal decomposition, hydrogen reduction, etc.). Therefore, fibers or thin films can be fabricated depending on the substrate shape. Specific applications include the preparation of diamond films, microcycloid carbon fibers, and SiC fibers.

[0004] Silicon nitride (Si3N4) fiber is an important high-performance ceramic fiber. It has excellent properties similar to SiC fiber, such as mechanical properties, creep resistance, wave transmission, and high temperature resistance. It has been widely used in aviation, aerospace, nuclear energy, automotive and other fields.

[0005] Both silicon carbide fibers and silicon nitride fibers have excellent properties and broad application prospects, and their simple and efficient preparation methods are of great value. Summary of the Invention

[0006] The technical problem to be solved by the present invention is how to provide a method for the simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers.

[0007] The technical solution adopted by this invention to solve its technical problem is as follows: A method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers, comprising the following steps:

[0008] (1) PDMS was pyrolyzed under an inert atmosphere and condensed to obtain the pyrolysis product LPS;

[0009] (2) The LPS and ferrocene are mixed evenly under an inert atmosphere and heated to react. After the reaction is completed, PFCS is obtained.

[0010] (3) The PFCS is melt-spun under an inert atmosphere to obtain PFCS fibrils;

[0011] (4) The PFCS fibrils are subjected to non-melting treatment in air to obtain PFCS pre-oxidized fibers; the PFCS pre-oxidized fibers are subjected to electron beam irradiation crosslinking treatment in an inert atmosphere to obtain PFCS crosslinked fibers.

[0012] (5) The PFCS cross-linked fibers are placed in a graphite paper tube and pyrolyzed under a nitrogen atmosphere. After the reaction is completed, silicon carbide fibers and silicon nitride nanofibers can be obtained.

[0013] PDMS represents polydimethylsilane, LPS represents liquid low molecular weight polysilane, and PFCS represents polyferric carbide silane.

[0014] This invention successfully prepared SiC fibers and simultaneously prepared Si3N4 nanofibers; compared with the separate preparation methods, the method of this invention is simpler and more efficient.

[0015] In step (1), the polymer PDMS will undergo thermal decomposition reaction after reaching a certain temperature, and the molecular chains will break. Under normal pressure, the low (small) molecular weight molecules formed by the breakage will become gaseous at a certain temperature. The gaseous molecules are collected by condensing in a condenser to obtain liquid product (LPS).

[0016] The graphite paper tube in step (5) enables the attachment of active gases and catalysts, and facilitates the growth and preparation of nanofibers. SiC fibers are prepared in situ through the inorganic transformation of PFCS cross-linked fibers. Si3N4 nanofibers are grown on the surface of graphite paper through a chemical vapor phase reaction using the atmosphere released during the inorganicization process of PFCS cross-linked fibers. The atmosphere generated during the inorganicization process of PFCS cross-linked fibers is carried away from the SiC fibers by external protective nitrogen gas, attaches to the graphite tube, and achieves reactive growth.

[0017] Preferably, in step (1), the pyrolysis time is 1-20h.

[0018] The above-mentioned technical solution achieves good preparation results.

[0019] More preferably, in step (1), the pyrolysis time is 1-10h.

[0020] The above-mentioned technical solution achieves good preparation results.

[0021] Preferably, in step (1), the pyrolysis temperature is 350-500℃.

[0022] The above-mentioned technical solution achieves good preparation results.

[0023] More preferably, in step (1), the pyrolysis temperature is 380-480°C.

[0024] The above-mentioned technical solution achieves good preparation results.

[0025] Preferably, in step (1), the heating rate is 1~50℃ / min.

[0026] The above-mentioned technical solution achieves good preparation results.

[0027] More preferably, in step (1), the heating rate is 1~20℃ / min.

[0028] The above-mentioned technical solution achieves good preparation results.

[0029] Preferably, in step (2), the mass ratio of LPS to ferrocene is 100:0.1-100:5.

[0030] The above-mentioned technical solution achieves good preparation results.

[0031] More preferably, in step (2), the mass ratio of LPS to ferrocene is 100:0.5-100:3.

[0032] The above-mentioned technical solution achieves good preparation results.

[0033] Preferably, in step (2), the reaction temperature is 400-600℃.

[0034] The above-mentioned technical solution has a good reaction effect.

[0035] More preferably, in step (2), the reaction temperature is 420-550℃.

[0036] The above-mentioned technical solution has a good reaction effect.

[0037] Preferably, in step (2), the heating rate is 1~30℃ / min.

[0038] The above-mentioned technical solution has a good reaction effect.

[0039] Preferably, in step (2), the reaction time is 1-5 hours.

[0040] The above-mentioned technical solution has a good reaction effect.

[0041] More preferably, in step (2), the reaction time is 1-3 hours.

[0042] The above-mentioned technical solution has a good reaction effect.

[0043] Preferably, in step (2), the stirring rate during the reaction is 1-60 r / min.

[0044] The above-mentioned technical solution has a good reaction effect.

[0045] More preferably, in step (2), the stirring rate during the reaction is 10-50 r / min.

[0046] The above-mentioned technical solution has a good reaction effect.

[0047] Preferably, in step (3), the diameter of the PFCS fibrils is 8-50 μm.

[0048] The above-mentioned technical solution achieves good preparation results.

[0049] More preferably, in step (3), the diameter of the PFCS fibrils is 10-35 μm.

[0050] The above-mentioned technical solution achieves good preparation results.

[0051] Preferably, in step (4), the temperature of the non-melting treatment is 150-210℃.

[0052] The above-mentioned technical solution achieves good processing results.

[0053] More preferably, in step (4), the temperature of the non-melting treatment is 170-190°C.

[0054] The above-mentioned technical solution achieves good processing results.

[0055] Preferably, in step (4), the non-melting treatment time is 0.5-5h.

[0056] The above-mentioned technical solution achieves good processing results.

[0057] More preferably, in step (4), the non-melting treatment time is 1-4 hours.

[0058] The above-mentioned technical solution achieves good processing results.

[0059] Preferably, in step (4), the irradiation dose of the electron beam irradiation crosslinking treatment is 10-70 kGy.

[0060] The above-mentioned technical solution achieves good processing results.

[0061] More preferably, in step (4), the irradiation dose of the electron beam irradiation crosslinking treatment is 15-50 kGy.

[0062] The above-mentioned technical solution achieves good processing results.

[0063] Preferably, in step (5), the pyrolysis temperature is 1400-1750℃.

[0064] The above-mentioned technical solution achieves good preparation results.

[0065] More preferably, in step (5), the pyrolysis temperature is 1450-1600℃.

[0066] The above-mentioned technical solution achieves good preparation results.

[0067] Preferably, in step (5), the heating rate is 0.1-50℃ / min.

[0068] The above-mentioned technical solution achieves good preparation results.

[0069] More preferably, in step (5), the heating rate is 0.5-15℃ / min.

[0070] The above-mentioned technical solution achieves good preparation results.

[0071] Preferably, in step (5), the pyrolysis time is 1-5 hours.

[0072] The above-mentioned technical solution achieves good preparation results.

[0073] More preferably, in step (5), the pyrolysis time is 1.5-4h.

[0074] The above-mentioned technical solution achieves good preparation results.

[0075] Preferably, in each step, the inert atmosphere is nitrogen.

[0076] An inert atmosphere primarily serves a protective function; besides nitrogen, other protective atmospheres are also feasible. An inert atmosphere can be obtained by first creating a vacuum and then introducing an inert gas.

[0077] More preferably, in each step, the inert atmosphere is a nitrogen atmosphere with a purity of ≥99.999%.

[0078] More preferably, in step (5), the nitrogen atmosphere is a nitrogen atmosphere with a purity of ≥99.999%.

[0079] Principle of this invention:

[0080] This invention combines precursor conversion and chemical vapor deposition to introduce small amounts of Fe and O elements into the molecular structure of PCS fibers. The PFCS cross-linked fibers are then subjected to high-temperature sintering. While successfully preparing SiC fibers, Si3N4 nanofibers are prepared through the chemical reaction of overflowing SiO and N2 under Fe catalysis, thus achieving efficient and simultaneous preparation of SiC fibers and Si3N4 nanofibers.

[0081] Beneficial effects of this invention:

[0082] This invention uses polyferric carbon silane as a precursor and, through melt spinning, low-oxygen air non-melting, electron beam irradiation crosslinking, and high-temperature inorganic treatment in a nitrogen environment, successfully prepares SiC fibers while simultaneously preparing Si3N4 nanofibers. Compared with preparing the two fibers separately, the method of this invention is simpler and more efficient. Attached Figure Description

[0083] Figure 1 This is a general optical photograph of the final product of Embodiment 1 of the present invention, in which black represents SiC fibers and white represents Si3N4 nanofibers.

[0084] Figure 2 These are SEM images of the silicon nitride nanofibers obtained in Example 1 of this invention at two magnifications; Figure 2 (a) is a low magnification. Figure 2 (b) is a high magnification.

[0085] Figure 3 This is the XRD pattern of the silicon nitride nanofibers obtained in Example 1 of this invention. Detailed Implementation

[0086] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0087] The raw materials used in the embodiments of the present invention are all obtained through conventional commercial channels. Example 1

[0088] The method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers in this embodiment includes the following steps:

[0089] (1) Place 100g of PDMS (polydimethylsilane) in a pyrolysis vessel, evacuate and replace with high-purity nitrogen, raise the system temperature to 380℃ at a heating rate of 1℃ / min and keep it at that temperature for 1h, condense and obtain the pyrolysis product LPS (liquid low molecular weight polysilane).

[0090] (2) Place 75g LPS and 0.375g ferrocene (weight percentage 100:0.5) in a synthesis reactor, evacuate and replace with high-purity nitrogen, and then raise the system temperature to 420℃ at a stirring rate of 10r / min and react for 1h. Then lower the system temperature to room temperature to obtain PFCS (polyferric carbon silane).

[0091] (3) Place 25g of PFCS in a melt spinning machine and melt spin under the protection of high-purity nitrogen to obtain PFCS fibrils with a fiber diameter of 12.3μm;

[0092] (4) 25g of PFCS raw fiber was treated in air at 170℃ to obtain PFCS pre-oxidized fiber for 1h; under the protection of high-purity nitrogen, the PFCS pre-oxidized fiber was subjected to electron beam irradiation crosslinking treatment to obtain PFCS crosslinked fiber, with an irradiation dose of 15kGy.

[0093] (5) Place 20g of PFCS cross-linked fiber in a graphite paper tube and place it together in a high-temperature pyrolysis furnace. After evacuation, high-purity nitrogen gas is introduced. Then the system is heated to 1450℃ at a heating rate of 0.5℃ / min and kept at that temperature for 1.5h. Finally, the system is naturally cooled to room temperature to obtain silicon carbide fiber and silicon nitride nanofiber.

[0094] Figure 1 This is a standard optical photograph of the final product obtained simultaneously in this embodiment, where black represents SiC fibers and white represents Si3N4 nanofibers.

[0095] Figure 2 Here is a SEM image of the silicon nitride nanofibers obtained in this embodiment; Figure 2 (a) and Figure 2 (b) has a different magnification. From Figure 2 As can be seen, the diameter distribution of the nanofibers is 65-170 nm.

[0096] Figure 3 The XRD analysis results of the silicon nitride nanofibers obtained in this embodiment show that the nanofibers possess... α -Si3N4 structure.

[0097] Tests showed that the silicon carbide fiber has a diameter of 9.5 μm.

[0098] The average tensile strength of the silicon carbide fiber bundle was tested and the result was 3.38 GPa. The specific test data are listed in Table 1. Example 2

[0099] The method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers in this embodiment includes the following steps:

[0100] (1) Place 100g of PDMS (polydimethylsilane) in a pyrolysis vessel, evacuate and replace with high-purity nitrogen, raise the system temperature to 480℃ at a heating rate of 20℃ / min and keep it at that temperature for 10h, condense and obtain the pyrolysis product LPS (liquid low molecular weight polysilane).

[0101] (2) Place 75g LPS and 2.25g ferrocene (weight percentage 100:3) in a synthesis reactor, evacuate and replace with high-purity nitrogen, and then raise the system temperature to 550℃ at a stirring rate of 10℃ / min for 3h. Then lower the system temperature to room temperature to obtain PFCS (polyferric carbon silane).

[0102] (3) 27g of PFCS was placed in a melt spinning machine and melt-spun under the protection of high-purity nitrogen to obtain PFCS fibrils with a fiber diameter of 33.8μm;

[0103] (4) 23g of PFCS raw fiber was treated in air at 190℃ to obtain PFCS pre-oxidized fiber for 4h; under the protection of high-purity nitrogen, the PFCS pre-oxidized fiber was subjected to electron beam irradiation crosslinking treatment to obtain PFCS crosslinked fiber, with an irradiation dose of 50kGy.

[0104] (5) Place 23g of PFCS crosslinked fiber in a graphite paper tube and place it together in a high-temperature pyrolysis furnace. After evacuation, high-purity nitrogen gas is introduced. Then the system is heated to 1600℃ at a heating rate of 15℃ / min and kept at that temperature for 4h. Finally, the system is naturally cooled to room temperature to obtain silicon carbide fiber and silicon nitride nanofiber.

[0105] In the above preparation process, the purity of the high-purity nitrogen gas used is ≥99.999%.

[0106] In this embodiment, silicon carbide fibers and silicon nitride nanofibers were prepared simultaneously. XRD analysis revealed that the silicon nitride nanofibers possessed... α -Si3N4 structure.

[0107] Tests showed that the silicon carbide fiber has a diameter of 26.1 μm.

[0108] The average tensile strength of the silicon carbide fiber bundle was tested and the result was 3.32 GPa. The specific test data are listed in Table 1. Example 3

[0109] The method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers in this embodiment includes the following steps:

[0110] (1) Place 100g of PDMS (polydimethylsilane) in a pyrolysis vessel, evacuate and replace with high-purity nitrogen, raise the system temperature to 420℃ at a heating rate of 15℃ / min and keep it at that temperature for 3h, condense and obtain the pyrolysis product LPS (liquid low molecular weight polysilane).

[0111] (2) Place 75g LPS and 0.75g ferrocene (weight percentage 100:1) in a synthesis reactor, evacuate and replace with high-purity nitrogen, and then raise the system temperature to 480℃ at a stirring rate of 15℃ / min for 2h. Then lower the system temperature to room temperature to obtain PFCS (polyferric carbon silane).

[0112] (3) Place 25g of PFCS in a melt spinning machine and melt spin under the protection of high-purity nitrogen to obtain PFCS fibrils with a fiber diameter of 15.5μm;

[0113] (4) 25g of PFCS raw fiber was treated in air at 180℃ without melting to obtain PFCS pre-oxidized fiber. The treatment time was 2h. Under the protection of high-purity nitrogen, the PFCS pre-oxidized fiber was subjected to electron beam irradiation crosslinking treatment to obtain PFCS crosslinked fiber. The irradiation dose was 30kGy.

[0114] (5) Place 20g of PFCS cross-linked fiber in a graphite paper tube and place it together in a high-temperature pyrolysis furnace. After evacuation, high-purity nitrogen gas is introduced. Then the system is heated to 1500℃ at a heating rate of 8℃ / min and kept at that temperature for 2h. Finally, the system is naturally cooled to room temperature to obtain silicon carbide fiber and silicon nitride nanofiber.

[0115] In the above preparation process, the purity of the high-purity nitrogen gas used is ≥99.999%.

[0116] In this embodiment, silicon carbide fibers and silicon nitride nanofibers were prepared simultaneously. XRD analysis revealed that the silicon nitride nanofibers possessed... α -Si3N4 structure.

[0117] Tests showed that the silicon carbide fiber has a diameter of 12 μm.

[0118] The average tensile strength of the silicon carbide fiber bundle was tested and the result was 3.35 GPa. The specific test data are listed in Table 1.

[0119] Table 1. Test Table for Strength of Silicon Carbide Fiber Bundles

[0120] Test number Example 1: Fiber bundle strength (GPa) Example 2: Fiber bundle strength (GPa) Example 3: Fiber bundle strength (GPa) Sample 1 3.32 3.19 3.30 Sample 2 3.21 3.16 3.51 Sample 3 3.52 3.32 3.42 Sample 4 3.42 3.41 3.39 Sample 5 3.30 3.18 3.17 Sample 6 3.47 3.26 3.28 Sample 7 3.61 3.36 3.34 Sample 8 3.25 3.37 3.36 Sample 9 3.36 3.47 3.47 Sample 10 3.30 3.51 3.24 average value: 3.38 3.32 3.35

Claims

1. A method for the simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers, characterized in that, Includes the following steps: (1) PDMS is pyrolyzed and condensed under an inert atmosphere to obtain pyrolysis product LPS; the inert atmosphere is nitrogen. (2) The LPS and ferrocene are mixed evenly under an inert atmosphere and heated to react. After the reaction is completed, PFCS is obtained. (3) The PFCS is melt-spun under an inert atmosphere to obtain PFCS fibrils; the inert atmosphere is nitrogen. (4) The PFCS fibrils are subjected to non-melting treatment in air to obtain PFCS pre-oxidized fibers; the PFCS pre-oxidized fibers are subjected to electron beam irradiation crosslinking treatment in an inert atmosphere to obtain PFCS crosslinked fibers. The inert atmosphere is nitrogen; The temperature for the non-melting treatment is 150-210℃; the time for the non-melting treatment is 0.5-5 hours. (5) The PFCS cross-linked fibers are placed in a graphite paper tube and pyrolyzed under a nitrogen atmosphere. After the reaction is completed, silicon carbide fibers and silicon nitride nanofibers can be obtained. PDMS represents polydimethylsilane, LPS represents liquid low molecular weight polysilane, and PFCS represents polyferric carbide silane.

2. The method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers according to claim 1, characterized in that, In step (1), the pyrolysis time is 1-20h; the pyrolysis temperature is 350-500℃; and the heating rate is 1~50℃ / min.

3. The method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers according to claim 1 or 2, characterized in that, In step (2), the mass ratio of LPS to ferrocene is 100:0.1-100:

5.

4. The method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers according to claim 1 or 2, characterized in that, In step (2), the reaction temperature is 400-600℃; the heating rate is 1-30℃ / min; the reaction time is 1-5h; and the stirring rate during the reaction is 1-60r / min.

5. The method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers according to claim 3, characterized in that, In step (2), the reaction temperature is 400-600℃; the heating rate is 1-30℃ / min; the reaction time is 1-5h; and the stirring rate during the reaction is 1-60r / min.

6. The method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers according to claim 1 or 2, characterized in that, In step (3), the diameter of the PFCS fibrils is 8-50 μm.

7. The method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers according to claim 1 or 2, characterized in that, In step (4), the irradiation dose of the electron beam irradiation crosslinking treatment is 10-70 kGy.

8. The method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers according to claim 3, characterized in that, In step (4), the irradiation dose of the electron beam irradiation crosslinking treatment is 10-70 kGy.

9. The method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers according to claim 4, characterized in that, In step (4), the irradiation dose of the electron beam irradiation crosslinking treatment is 10-70 kGy.

10. The method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers according to claim 6, characterized in that, In step (4), the irradiation dose of the electron beam irradiation crosslinking treatment is 10-70 kGy.

11. The method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers according to claim 7, characterized in that, In step (4), the irradiation dose of the electron beam irradiation crosslinking treatment is 10-70 kGy.

12. The method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers according to claim 1 or 2, characterized in that, In step (5), the pyrolysis temperature is 1400-1750℃; the heating rate is 0.1-50℃ / min; and the pyrolysis time is 1-5h.

13. The method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers according to claim 3, characterized in that, In step (5), the pyrolysis temperature is 1400-1750℃; the heating rate is 0.1-50℃ / min; and the pyrolysis time is 1-5h.

14. The method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers according to claim 4, characterized in that, In step (5), the pyrolysis temperature is 1400-1750℃; the heating rate is 0.1-50℃ / min; and the pyrolysis time is 1-5h.

15. The method for simultaneous preparation of silicon carbide fibers and silicon nitride nanofibers according to claim 7, characterized in that, In step (5), the pyrolysis temperature is 1400-1750℃; the heating rate is 0.1-50℃ / min; and the pyrolysis time is 1-5h.

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