CN101319414A - A kind of manufacturing method of high temperature resistance silicon carbide fiber - Google Patents

Abstract

The invention relates to a method for manufacturing silicon carbide fibers with high temperature resistance. Using low-molecular-weight silane LPS as a raw material, it reacts with organic compounds containing densification elements to synthesize polycarbosilanes containing Al and Y, namely PACS and PYCS, and then melt-spins to obtain continuous PACS and PYCS fibers, which are infused The non-melting fibers with controllable oxygen content are obtained by treatment, and then high-temperature firing and sintering are carried out under the protection of an inert atmosphere to obtain SiC fibers with high crystallinity and high temperature resistance. The process of the invention is simple, the operation is convenient, it can be implemented by using the usual SiC fiber production equipment, and the manufacturing cost is low. The product of the invention has excellent characteristics such as high strength, high temperature resistance, and high oxidation resistance, and is suitable for industrial batch production.

Description

A kind of manufacturing method of high temperature resistance silicon carbide fiber

technical field

The invention relates to a method for manufacturing silicon carbide fibers with high temperature resistance.

Background technique

Silicon carbide (SiC) ceramic fiber has important application value in high-tech fields such as aviation, aerospace, nuclear industry, and weaponry because of its high strength, high modulus, high temperature resistance, oxidation resistance, and corrosion resistance. Industrially, the industrial production of continuous SiC fibers has been realized by using the organosilicon polymer-polycarbosilane (PCS) precursor conversion method. Its typical preparation process is as follows: polycarbosilane PCS obtained by high-temperature cracking, rearrangement and polycondensation of organosilicon polymers is used as a precursor, and continuous PCS fibers are prepared by melt spinning, and the continuous PCS fibers are placed in air for oxidation reaction. After intermolecular cross-linking to form non-melting fibers (called non-melting treatment), high-temperature firing is carried out under the protection of an inert atmosphere in a high-temperature furnace, and SiC fibers are obtained through thermal decomposition transformation and inorganicization. Taking two major foreign manufacturers-Nippon Carbon Corporation and Ube Industrial Corporation as examples, continuous SiC fiber products with different performance characteristics have been produced by this method, and they have entered the market under the trade names of "Nicalon" and "Tyranno" respectively. Sale. Compared with carbon fiber, which has been widely used, one of the performance characteristics of SiC fiber is its high temperature resistance, especially its oxidation resistance at high temperature. At present, the oxidation resistance of general-purpose SiC fiber has been greatly improved compared with carbon fiber (the use temperature of carbon fiber in air is about 400 ° C), but because its precursor PCS itself is rich in carbon, and the air oxidation non-melting method is used in the manufacturing process. After treatment, the prepared SiC fiber is a carbon-rich, oxygen-containing non-stoichiometric SiC fiber. When the temperature is higher than 1200 ° C, the impurity phase undergoes severe thermal decomposition, producing a large amount of gaseous CO, SiO and accompanied by rapid The crystal growth of the fiber produces a large number of defects and becomes a loose structure, and the strength of the fiber decreases sharply and loses its usability. Therefore, the use temperature of general-purpose SiC fiber is only 1000°C. Therefore, in recent years, the preparation of SiC fibers with high purity and near-stoichiometric ratio and high temperature resistance has become a research and development focus.

It is an effective way to improve the high temperature resistance of SiC fiber by changing the preparation method and process to reduce the content of impurity oxygen and carbon in the fiber. In the current research and industrial development, the methods used can be divided into three categories: (1) By synthesizing high molecular weight PCS, the fibrils are obtained by dry or wet spinning, and directly fired at high temperature without non-melting treatment. A low oxygen content SiC fiber is obtained. However, this method has high requirements on the control of the synthesis process, the spinning process technology is difficult and there is environmental pollution, and it is difficult to obtain fine-diameter SiC fibers; (2) electron beam or γ-ray irradiation under an inert atmosphere is used instead of air oxidation Melting treatment (such as US patents US4220600, US4283367 and US4342712). Japan Carbon Corporation (Michio Takeda, Jun-ichi Sakamoto, Yoshikazu Imai, Hiroshi Ichikawa. Thermalstability of the low-oxygen-content silicon carbide fiber, Hi-Nicalon ^TM. Comp. Sci. Technol., 1999, 59: 813-819.) Using this technology to achieve industrial production, the low-oxygen SiC fiber-trade name Hi-Nicalon (oxygen content <0.5wt%) was produced, and a near-stoichiometric SiC fiber-Hi- Nicalon S. These two fibers have high strength (2.6-2.8GPa), high modulus (270-420GPa), high density, good crystallinity and high temperature resistance; (3) in the preparation process of SiC fiber, mainly in the pioneer In the synthesis of bulk polymer PCS, the elements boron (B) and aluminum (Al) are introduced through chemical reactions, and then after melt spinning, non-melting treatment and higher temperature sintering, the decomposition reaction of the impurity phase at high temperature is used to remove impurities. Oxygen and carbon, while using the above-mentioned densification elements to promote the densification of fibers, so as to prepare SiC fibers with high temperature resistance near stoichiometric ratio. Japan's Ube Industrial Corporation (Kumagawa K., Yamaoka H., Shibuya M., Yamamura T. Fabrication and Mechanical Properties of new lmproved Si-MC-(O) Tyranno Fiber. Ceramic Engineering and Science Proceedings, 1998, 19 (3): 65-72.) Using this method, using Al-containing PCS as a precursor, Si-Al-OC fibers were prepared through melt spinning, air-infused treatment and sintering at 1300 ° C, and multi- Crystalline SiC fiber, trade name Tyranno-SA.

The last two of the above three methods have been successfully applied in industrial production, and continuous SiC fiber products with high temperature resistance have been obtained. Among them, the temperature resistance of Hi-NicalonS fiber in air and inert atmosphere reaches 1400 ℃ and 1500 ℃ respectively, and the temperature resistance of Tyranno-SA fiber in air and inert atmosphere also reaches 1400 ℃ and 1800 ℃ respectively, showing that with The content of impurity oxygen and carbon in the fiber is reduced, and the temperature resistance of the continuous SiC fiber is significantly improved.

However, when the second method uses electron beam irradiation for non-melting treatment in the manufacturing process of SiC fibers, an expensive electron accelerator is required, and high-dose irradiation far higher than the usual chemical fiber irradiation is required, It also needs to consume a large amount of high-purity argon for heat dissipation and oxygen isolation, and the process is extremely complicated, which leads to a significant increase in the manufacturing cost of SiC fibers. Taking Hi-Nicalon as an example, its price is 7 to 8 times that of general-purpose Nicalon fibers. . When the third method is used to prepare SiC fibers, since the introduced Al element produces densification above 1600°C, the decomposition of impurity phases still causes great damage to the fibers at 1200-1600°C. , the strength of the fiber shows a "saddle-shaped" change that decreases rapidly at 1200-1600°C and rises above 1600°C. Therefore, if too much impurity oxygen is introduced during the fiber preparation process and the fiber strength loss is too large at the temperature range of 1200-1600 ° C, it is difficult to obtain SiC fiber products with good properties even if there is densification. Therefore, when using the third method to prepare SiC fibers with high temperature resistance, how to control the impurity oxygen content in the fibers is a problem that must be solved.

Therefore, it is very necessary to prepare SiC fibers with high temperature resistance by a method that is simple, convenient, and easy to realize industrialized mass production.

Contents of the invention

Aiming at the problems existing in the above-mentioned prior art preparation methods, the technical problem to be solved in the present invention is to provide a simple and convenient method that is easy to realize industrialized batch production and can manufacture high temperature-resistant SiC fibers according to the usual preparation process and equipment. .

Technical scheme of the present invention is as follows:

Using polycarbosilane PCS or low molecular silane LPS generated by high temperature cracking of polydialkylsilane as raw material, react with organic compounds containing densification elements to synthesize polycarbosilane containing Al and Y, hereinafter referred to as PACS and PYCS, and then Continuous PACS and PYCS fibers are prepared by melt spinning, and the fibers are placed in air and an active atmosphere for non-melting treatment to obtain non-melting fibers with controllable oxygen content, and the non-melting fibers are placed in a high-temperature furnace under the protection of an inert atmosphere. High-temperature firing and sintering to obtain SiC fibers.

Concrete preparation process is as follows:

(1) Co-dissolve the raw material PCS and organic compounds containing densification elements Al and Y in xylene, heat it while stirring under the protection of high-purity nitrogen until the xylene is distilled out, and then continue to react at 300-350°C, and finally Insulate the reaction at high temperature for 2-10 hours; or mix the raw material LPS with an organic compound containing Al and Y, heat it to 420-480°C under the protection of high-purity nitrogen for reaction, and keep it at the final temperature for 2-10 hours. The crude product is dissolved in xylene and then filtered, then heated to 300-360°C for vacuum distillation to remove the solvent and a small amount of low-molecular substances, and obtain PACS or PYCS after cooling;

(2) Put the above PACS or PYCS in the spinning cylinder of the melt spinning device, heat up to 300-400°C under the protection of high-purity nitrogen, wait until it is completely melted into a uniform melt and remove residual bubbles, that is, defoaming treatment Finally, at 250-350°C, 0.1-0.6MPa pressure, melt spinning at a speed of 300-600m/min, after bundled and drawn, continuous PCS fibers with a diameter of 8-16um are obtained;

(3) Place the above-mentioned PACS or PYCS fiber in a non-melting treatment device for air oxidation treatment, that is, heat it to 180-220 °C at a heating rate of 10-20 °C/hour in an air atmosphere, and heat preservation oxidation treatment for 2-4 Hours, then replace the air with high-purity nitrogen, heat up and introduce an active reaction atmosphere, heat from 100°C to 300-400°C at a heating rate of 10-20°C/min, and keep it at this temperature for 2-4 hours. , cooled to room temperature to make PACS or PYCS non-melting fibers;

(4) Place the above-mentioned PACS or PYCS non-melting fibers in a high-temperature furnace, and under the protection of high-purity nitrogen, heat up to 1200-1300°C at a heating rate of 100-200°C/hour, and heat preservation treatment at this temperature for 1- Amorphous SiC fibers were prepared in 2 hours;

(5) Put the above-mentioned amorphous SiC fibers in a high-temperature furnace protected by high-purity argon gas, raise the temperature to 1800°C, and heat-preserve and sinter at this temperature for 1-2 hours to obtain high-crystallinity and high-temperature fibers. Temperature resistant SiC fiber.

The raw material polycarbosilane PCS is an organosilicon polymer whose main chain is composed of Si-C bonds, and its molecular structural unit is:

Wherein the alkyl groups R ¹ and R ² =H, -CH ₂ -, -CH-, Me, Et, Pt, Bt, Ph and other organic groups, they may be the same or different. A specific example is polycarbosilane obtained by pyrolysis, rearrangement and polycondensation of polydimethylsilane at high temperature.

The low-molecular-weight silane LPS as a raw material is a silane oligomer mixture whose main chain is composed of Si-Si bonds and a small amount of Si-C bonds, and its structure is linear or cyclic. LPS is polydialkylsilane (the following formula, wherein R ¹ , R ² =H, Me, Et, Pt, Bt,

Ph, etc.) is a mixture of oligomer compounds formed by pyrolysis, which is a transparent liquid at room temperature, with a boiling point of 60-300°C and a molecular weight of 100-600.

The densification element is aluminum (Al) or yttrium (Y), and the compound containing the densification element is a compound containing Al and Y such as aluminum acetylacetonate Al(acac) ₃ , yttrium acetylacetonate Y(acac) ₃ and Corresponding alkoxy compounds such as Al(OR) ₃ , Y(OR) ₃ where R=Me, Et, Pt, Bt, Ph, etc.

In the synthesis of PACS or PYCS, when PCS is used as raw material, the molecular weight of PCS, that is, the number average molecular weight Mn, is 800-2000, and the mass ratio of the compound containing Al, Y, and B is 1:0.05-1:0.15 , the synthesis temperature is 200-350 ° C, and when the molecular weight of PCS is high, the synthesis temperature is lower; when more densification elements need to be introduced, that is, when the mass ratio of the compound containing Al and Y is high, it is better to PCS with lower molecular weight is used as raw material; when LPS is used as raw material, the mass ratio of LPS to the compound containing Al and Y is 1:0.05-1:0.15, the synthesis temperature is 400-500°C, and the synthesis temperature is too low, LPS If the structural rearrangement and polycondensation are insufficient, the synthesis temperature is too high, and the cross-linking reaction caused by excessive polycondensation will easily occur and affect the rheology of the product. The more suitable synthesis temperature is 420-460°C.

In the synthesis of the PACS or PYCS, densification elements such as Al and Y may also be mixed and introduced. For example, when PCS is used as raw material, the mass ratio of PCS to the compound containing Al and Y is 1:0.05-1:0.15, and the mass ratio between the compound containing Al and Y is 3:1-1:3 , and other synthesis conditions remain unchanged. When LPS is used as raw material, it is also the same ratio.

The active reaction atmosphere used in the non-melting treatment of the PACS or PYCS fiber is a low-boiling, volatile oxygen-free olefin, alkyne organic compound with a specific structure, such as ethylene, propylene, butene, pentene, etc. Alkenes such as alkenes, cyclohexene, and butadiene, and alkynes such as acetylene, propyne, butyne, pentyne, and hexyne.

The non-melting treatment of the PACS or PYCS fiber in the air and active atmosphere can also be carried out by mixing air and active atmosphere, and treating it at a certain temperature in the mixed atmosphere, but the more suitable method is to carry out air oxidation first treatment, and then replace the air with high-purity nitrogen and then pass it into an active reaction atmosphere for treatment, which is conducive to the control of the oxygen content in the non-melting fiber. By controlling the treatment temperature and time, the oxygen content in the non-melting fiber is controlled at 2-12wt%. If the oxygen content in the fiber is too high, the impurity phase will decompose violently during the high-temperature sintering process, the fiber will be seriously damaged, and it is difficult to obtain good performance. ; If the oxygen content in the fiber is too low, the decomposition of impurity phases cannot be used to remove impurity oxygen and carbon, and it is difficult to obtain SiC fibers with high purity and near stoichiometric ratio. A more suitable oxygen content control range is 3-8wt%.

In the existing literature research, non-oxidative non-melting treatment of PCS fibers can be realized in a common non-melting treatment furnace by using a non-oxygen active atmosphere to treat PCS fibers (Mao Xianhe, Song Yongcai, Li Wei by polycarbonate Silicon carbide fiber with low oxygen content prepared by chemical vapor phase crosslinking of silane fiber. Journal of Silicate Society, 2006, 34(1): 16-20; Mao Xianhe, Song Yongcai, Li Wei, etc. Polycarbosilane fiber in cyclohexene atmosphere Insoluble Processing Research Journal of Materials Research, 2007, 21(2): 177-182). The present invention uses air + active atmosphere to carry out non-melting treatment on PCS fibers, thereby regulating the oxygen content in the fibers, and combines this technology with the technology of introducing densification elements (Al, Y) into PCS to prepare SiC fibers through chemical reactions together to prepare the high temperature resistant SiC fiber.

The invention synthesizes PACS or PYCS, uses it as a precursor, and after melt spinning to obtain raw silk, adopts air + active atmosphere without melting to control the oxygen content, and then prepares SiC fiber with high temperature resistance through high temperature firing and sintering. Compared with the prior art, it has the following positive effects:

1. The present invention adopts the air + active atmosphere non-melting treatment method to carry out the non-melting treatment of PACS or PYCS fibers, which can effectively control the oxygen content in the non-melting fibers. Compared with the existing air oxidation non-melting method, the fiber can be significantly reduced. Oxygen content; Compared with the existing electron beam irradiation non-melting method, it has the characteristics of simple process, convenient operation and low manufacturing cost;

2. The method for preparing SiC fibers with high temperature resistance according to the present invention utilizes the purification effect of impurity phase decomposition at high temperature, and compared with the electron beam irradiation method, no additional decarburization process is required;

3. Compared with the existing method of using densification elements to prepare SiC fibers with high temperature resistance, the present invention can stably produce high-performance fiber products due to lower and controllable oxygen content;

4. Compared with the existing preparation methods, the present invention does not need to add expensive equipment, the process is relatively simple, and can be implemented by using the usual SiC fiber production equipment, so it is more suitable for batch industrial production.

Description of drawings

Fig. 1 is a flow chart of the process for preparing SiC fibers with high temperature resistance in the present invention;

Fig. 2 is a comparison diagram of the change in tensile strength of amorphous SiC fibers with different oxygen contents obtained in Example 4, Example 5 and Example 6 during high-temperature sintering;

Fig. 3 is a comparison diagram of the change in tensile strength of the amorphous SiC fibers prepared in Example 4, Example 7 and Comparative Example 1 during high-temperature sintering;

Fig. 4 is the temperature resistance comparative figure of the SiC fiber that embodiment 4, embodiment 7 and comparative example 1, comparative example 2 make;

Fig. 5 is the comparative figure of oxidation resistance of the SiC fiber that embodiment 4, embodiment 7 and comparative example 1, comparative example 2 make;

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments. The present invention is not limited to the following examples.

Fig. 1 is the process flow of the present invention for preparing SiC fibers with near-stoichiometric ratio and high temperature resistance.

The present invention prepares near-stoichiometric SiC fibers through five process steps, that is, using polycarbosilane PCS or low-molecular silane LPS generated by high-temperature cracking of polydialkylsilane as a raw material, and reacting with an organic compound containing densification elements to synthesize PACS or PYCS, and then melt-spun to obtain continuous PACS or PYCS fibers, the fibers are placed in air and an active atmosphere for non-melting treatment to obtain PACS or PYCS non-melting fibers with controllable oxygen content, and the non-melting fibers are placed at high temperature High-temperature firing and sintering are carried out under the protection of an inert atmosphere in the furnace to obtain SiC fibers with high temperature resistance.

Reference example 1.

Take 1000g of polydimethylsilane and place it in a reaction kettle, and after passing through high-purity nitrogen to replace the air, slowly heat to 460°C, and keep warm at this temperature for 4 hours for pyrolysis polymerization. The crude product was dissolved in xylene and then filtered. The filtrate was distilled at about 200°C to remove the solvent and then distilled to 350°C under reduced pressure. After cooling, about 520g of light yellow resinous polycarbosilane PCS was obtained. The number average molecular weight Mn was 1840, and the softening point was 210-225°C.

Example 1.

Take 1,000 g of polydimethylsilane and place it in a reaction kettle. After replacing the air with high-purity nitrogen, it is slowly heated to 420° C., and thermally decomposed and polymerized at this temperature for 5 hours. The crude product was dissolved in xylene and filtered. The filtrate was distilled at about 200°C to remove the solvent. After cooling, about 550 g of light yellow resinous polycarbosilane PCS was obtained. The number average molecular weight Mn was 990 and the softening point was 110-117°C. Co-dissolve PCS and aluminum acetylacetonate Al(acac) ₃ in xylene at a mass ratio of 1:0.08, heat to 350°C for reaction while stirring under the protection of high-purity nitrogen, and keep the reaction at 350°C for 4 hours, distill to remove small The light yellow product PACS was obtained after the molecule, its Mn was 1704, and the softening point was 205-218°C.

Example 2.

Take 1000g of polydimethylsilane and put it in a distillation reaction kettle. After replacing the air with high-purity nitrogen, heat it slowly to 400°C, and pyrolyze it at this temperature for 4 hours, and collect the decomposition products by condensation while pyrolysis. It is a mixture of low molecular silanes (referred to as LPS), and the pyrolysis reaction yield is 74%. LPS is a transparent liquid at room temperature, with a boiling point of 60-300°C and a number-average molecular weight of 100-600. After dissolving and mixing LPS and aluminum acetylacetonate Al(acac) ₃ at a mass ratio of 1:0.10, heat the reaction under the protection of high-purity nitrogen and gradually raise the temperature to 450°C, and keep the reaction at 450°C for 4 hours. The crude product was dissolved in xylene and then filtered, heated to distill off the solvent, and then distilled under reduced pressure at 320°C to remove a small amount of low-molecular substances. After cooling, the product PACS was obtained, with an Mn of 1680 and a softening point of 196-209°C.

Example 3.

Take 1000g of polydimethylsilane and place it in a reaction kettle, and after replacing the air with high-purity nitrogen gas, slowly heat to 420°C, and keep warm at this temperature for 10 hours for pyrolysis polymerization. The crude product was dissolved, filtered and distilled at about 200°C to obtain about 520 g of PCS with a number average molecular weight Mn of 1224 and a softening point of 135-144°C. Co-dissolve PCS and aluminum acetylacetonate Y (acac) ₃ in xylene at a mass ratio of 1:0.08, heat to 320°C while stirring under the protection of high-purity nitrogen to react, and keep the reaction at 320°C for 4 hours, distill to remove small The reddish-brown product PYCS is obtained after the molecule, its Mn is 1639, and its softening point is 195-205°C.

Example 4.

The PACS synthesized in Example 1 was placed in a melt-spinning device, heated under the protection of high-purity nitrogen and subjected to defoaming treatment, and then melt-spun at a speed of 500 m/min at 290 ° C and a pressure of 0.4 MPa to produce A continuous PACS fiber was obtained with an average fiber diameter of 12.5um. Put the PACS fiber in a non-melting furnace, heat it to 140°C in the air for 1 hour, then heat it from 140°C to 180°C at a heating rate of 10°C/hour, and heat-preserve and oxidize it for 2 hours. After the temperature in the furnace drops to about 100°C, replace the air in the furnace with a high-purity inert atmosphere, and use high-purity nitrogen as a carrier gas to blow cyclohexene into the system at a flow rate of 10ml/min/g. Continue to heat up to 350° C. at a rate of heating up per hour, and heat-preserve for 2 hours. Put this non-melting fiber in a high-temperature furnace, under the protection of high-purity nitrogen, heat-treat it at a heating rate of 150 °C/hour to 1200 °C, and keep it for 2 hours to prepare SiC fiber, and X-ray diffraction (XRD) to detect its structure It is basically amorphous, with an average fiber diameter of 10.8um, a tensile strength of 3.1GPa, a Young's modulus of 205GPa, and a fiber oxygen content of 5.43%. Put the fiber in a high-temperature furnace, raise the temperature to 1800°C under the protection of high-purity argon, and keep it at this temperature for 1 hour to prepare SiC fiber. XRD detection shows that its main structure is β-SiC, and there is also a small amount of α-SiC. SiC, the grain size of β-SiC is 20.4nm, indicating that it is a SiC fiber with high crystallinity, the O content in the fiber composition is 0.84wt%, the Al content is 1.08wt%, the average fiber diameter is 10.2um, and the tensile strength is 2.5 GPa, Young's modulus is 390Gpa.

Example 5.

Put the PACS fiber prepared by melt spinning in Example 4 in a non-melting furnace, heat it to 140°C in the air for 1 hour, and then heat it from 140°C to 200°C at a heating rate of 10°C/hour, and keep it oxidized Process for 4 hours. After the temperature in the furnace dropped to about 130° C., the non-melting treatment was carried out in a cyclohexene atmosphere under the same conditions as in Example 4. Put this non-melting fiber in a high-temperature furnace, and under the protection of high-purity nitrogen, heat-treat it at a heating rate of 150°C/hour to 1200°C, and after holding it for 2 hours, an amorphous SiC fiber is obtained, with an average diameter of 10.5 um, the tensile strength is 2.8GPa, the Young's modulus is 205GPa, and the fiber oxygen content is 9.59%. Put the fiber in a high-temperature furnace, and raise the temperature to 1800°C under the protection of high-purity argon gas. After heat preservation treatment at this temperature for 1 hour, a SiC fiber with high crystallinity is obtained. The O content in the fiber composition is 1.86wt%, Al The content is 1.02wt%, the average diameter is 10.0um, the tensile strength is 1.1GPa, and the Young's modulus is 350Gpa.

Example 6.

Put the PACS fiber prepared by melt spinning in Example 4 in a non-melting furnace, heat it to 140°C in the air for 1 hour, and then heat it from 140°C to 220°C at a heating rate of 10°C/hour, and keep it oxidized Process for 2 hours. After the temperature in the furnace dropped to about 130° C., the non-melting treatment was carried out in a cyclohexene atmosphere under the same conditions as in Example 4. Put this non-melting fiber in a high-temperature furnace, and under the protection of high-purity nitrogen, heat-treat it at a heating rate of 150 °C/hour to 1200 °C, and after holding it for 2 hours, an amorphous SiC fiber is obtained, with an average diameter of 10.6 um, the tensile strength is 2.6GPa, the Young's modulus is 180GPa, and the fiber oxygen content is 13.18%. Put the fiber in a high-temperature furnace, raise the temperature to 1800°C under the protection of high-purity argon, and heat-preserve at this temperature for 1 hour to obtain a high-crystallinity SiC fiber. The O content in the fiber composition is 2.24wt%, and the Al content It is 1.06wt%, but the fiber is extremely fragile, and the tensile strength and modulus cannot be measured.

Example 7.

The PYCS synthesized in Example 3 was placed in a melt spinning device, heated under the protection of high-purity nitrogen and subjected to defoaming treatment, and then melt-spun at a speed of 500 m/min at 280 ° C and a pressure of 0.4 MPa to produce A continuous PACS fiber was obtained with an average fiber diameter of 11.6um. Put the PACS fiber in a non-melting furnace, heat it to 140°C in the air for 1 hour, then heat it from 140°C to 190°C at a heating rate of 10°C/hour, and heat-preserve and oxidize it for 4 hours. After the temperature in the furnace dropped to about 130° C., the non-melting treatment was carried out in a cyclohexene atmosphere under the same conditions as in Example 4. Put this non-melting fiber in a high-temperature furnace, under the protection of high-purity nitrogen, heat-treat it at a heating rate of 150 °C/hour to 1200 °C, and keep it for 2 hours to prepare an amorphous SiC fiber with an average diameter of 10.2 um, the tensile strength is 2.8GPa, the Young's modulus is 198GPa, and the fiber oxygen content is 5.92%. Put the fiber in a high-temperature furnace, raise the temperature to 1800°C under the protection of high-purity argon, and heat it at this temperature for 1 hour to prepare a SiC fiber with high crystallinity. The β-SiC grain size is 18.6 by XRD. nm, the O content in the fiber composition is 0.86wt%, the Y content is 1.04wt%, the average fiber diameter is 9.5um, the tensile strength is 2.3GPa, and the Young's modulus is 380Gpa.

Comparative example 1.

The PCS synthesized in Reference Example 1 was placed in a melt-spinning device, heated under the protection of high-purity nitrogen and subjected to defoaming treatment, and then melt-spun at a speed of 500 m/min at 300 ° C and a pressure of 0.3 MPa to produce A continuous PCS fiber was obtained with an average fiber diameter of 14.3um. The PCS fiber was placed in a non-melting furnace, and the same conditions as in Example 4 were used to carry out the non-melting treatment in the atmosphere of air and cyclohexene. After the non-melting treatment, the Si-H bond reaction degree of the PCS fiber was 42%. Put this non-melting fiber in a high-temperature furnace, under the protection of high-purity nitrogen, heat-treat it at a heating rate of 150 °C/hour to 1300 °C, and keep it for 2 hours to prepare SiC fibers. XRD detects the existence of β-SiC crystallites in the fibers , the grain size is 2.6nm. The average fiber diameter is 12.6um, the tensile strength is 2.8GPa, the Young's modulus is 210GPa, and the fiber oxygen content is 5.6%. Put the fiber in a high-temperature furnace, raise the temperature to 1800°C under the protection of high-purity argon, and keep it at this temperature for 1 hour to prepare SiC fibers. The diameter is 11.8um, and the tensile strength and modulus cannot be measured.

Comparative example 2.

Put the PCS fiber prepared in Comparative Example 1 in a non-melting furnace, heat it to 140°C in the air for 1 hour, then heat it from 140°C to 210°C at a heating rate of 8°C/hour, and heat-preserve and oxidize it for 6 hours. The degree of Si-H bond reaction of the post-PCS fibers was 75%. Put the non-melting fiber in a high-temperature furnace, under the protection of high-purity nitrogen, heat-treat it at a heating rate of 150°C/hour to 1300°C, and keep it for 2 hours to prepare SiC fiber. The XRD detection structure is β-SiC crystallite, and the grain size is 2.1nm. The fiber diameter is 12.5um, the tensile strength is 2.5GPa, the Young's modulus is 180GPa, and the fiber oxygen content is 13.4%.

Below the above embodiment and comparative example are combined and comparatively analyzed, further illustrate the characteristics of the present invention.

From Example 4, Example 5 and Example 6, it can be seen that the same polycarbosilane PACS containing Al synthesized by Example 1 is used as a raw material, and after continuous PACS fibers are obtained through melt spinning, the PACS fibers The PACS infusible fibers with controllable oxygen content were obtained by placing them in air and active atmosphere for infusibility treatment. The infusible fibers were fired at a high temperature at 1200°C under the protection of an inert atmosphere to obtain three types of amorphous fibers with different oxygen contents. SiC fibers. Through the control of non-melting treatment conditions, the oxygen contents of these three fibers were 6.93%, 9.59%, and 13.18%, respectively. It can be seen that reducing the oxygen content helps to obtain high-strength amorphous SiC fibers. But more importantly, when this amorphous SiC fiber is sintered at a high temperature of 1800 °C to make a highly crystalline SiC fiber, the fiber with different oxygen content exhibits different final properties. Among them, as in Example 4, SiC fibers with low oxygen content have higher mechanical properties after high-temperature sintering, but when the oxygen content in the fibers is high, as in Example 6, SiC fibers with high temperature resistance cannot be produced. In order to illustrate this point more clearly, during the high temperature sintering process of the amorphous fiber, the change of the fiber tensile strength at different temperatures is measured, and the results are shown in accompanying drawing 2, from the comparison of the change curves of the three kinds of fiber tensile strength shown in the figure It can be clearly seen that the tensile strength of the three fibers increases slightly when fired at high temperature up to 1400°C, but decreases rapidly with the increase of sintering temperature at 1400-1600°C, which has been shown by many studies. It is due to the rapid decomposition of impurity phase SiCxOy in the fiber at this stage, which causes damage to the fiber. This detrimental reaction can be suppressed by reducing the impurity phase content in the fiber, which can be achieved by reducing the oxygen content introduced during the fiber infusion process. As can be seen from the figure, after the oxygen content in the fiber is reduced by the method of non-melting treatment in the air and active atmosphere adopted by the present invention, the reduction in the strength of the fiber at 1400-1600 ° C is suppressed, and more importantly, at Under such conditions, the densification elements can produce effective densification. As shown in Figure 2, when the fiber also contains Al, when the oxygen content in the fiber is high (such as Example 5 and Example 6), due to the excessive loss of fiber strength at 1200-1600 ° C, the densification effect It cannot be played, or the densification effect cannot offset the destructive effect caused by the decomposition of the impurity phase SiCxOy, and it is difficult to obtain SiC fibers with good performance. However, when the oxygen content in the fiber is controlled to a low state (such as Example 4), the densification effect produces a significant strength recovery after treatment at 1800 ° C, and high crystallinity SiC fibers with good mechanical properties can be produced.

From the comparison of Example 4, Example 7 and Comparative Example 1, it can be seen that although the method of air + active atmosphere non-melting treatment is also adopted, the amorphous or microcrystalline with low oxygen content is obtained by firing at 1200-1300 ° C. SiC fiber, and exhibited excellent mechanical properties, but Al was introduced into the fiber of Example 4, Y was introduced into the fiber of Example 7, and no densification element was introduced in Comparative Example 1, so sintering at 1800 ° C Finally, the first two fibers have good mechanical properties, while the comparative example 1 failed to obtain high crystallinity SiC fibers. This shows that the introduction of densification elements is very necessary, and high temperature resistant SiC fibers cannot be obtained simply by reducing the oxygen content in the fibers. Figure 3 shows the changes in the tensile strength of these three fibers at different temperatures during the high-temperature sintering process, which clearly shows that the fibers of Comparative Example 1 have no densification during the sintering process.

With four kinds of SiC fibers that embodiment 4, embodiment 7 and comparative example 1, comparative example 2 make, measure its temperature resistance under the same condition (detect its tensile strength after different temperature treatment in high-purity argon gas atmosphere) Strength change) as accompanying drawing 4, measure its oxidation resistance (detect the change of its tensile strength after being treated at different temperatures in the air atmosphere) as accompanying drawing 5. It can be clearly seen that the SiC fibers with high crystallinity produced by Example 4 and Example 7 are different from the microcrystalline SiC fibers (Comparative Example 2) produced by the usual method and the same air + active atmosphere. The microcrystalline SiC fiber with low oxygen content fired at 1300°C after melting treatment (Comparative Example 1) still has a high retention rate of tensile strength at 1800°C, and the latter two fibers are at 1000°C and 1300°C respectively In the air atmosphere, the tensile strength of the first two fibers can basically be maintained to 1500 ° C, while the latter two fibers can basically only be maintained to 1000 ° C and 1200 ° C. Obviously, the highly crystalline SiC fiber prepared by the method of the present invention has more excellent high temperature resistance and oxidation resistance.

It can be seen from the above results that it is difficult to obtain SiC fibers with high temperature resistance simply by reducing the oxygen content in the fibers, and it is not possible to obtain high temperature resistant SiC fibers simply by introducing densification elements without controlling the oxygen content in the fibers. Only by combining the two technologies can we effectively produce SiC fibers with high temperature resistance. Therefore, adopt the present invention to introduce densification elements (Al, Y) in PCS by chemical reaction to obtain PACS and PYCS, after melt spinning, carry out controllable oxygen content non-melting to PACS and PYCS fiber with air + active atmosphere The technical method of high-temperature firing and sintering is an effective method for preparing the high temperature-resistant SiC fiber.

In summary, the present invention can be used to produce highly crystalline SiC fibers, which have high strength (2.0-2.5GPa), high modulus (350-400GPa), high temperature resistance (up to 1800°C) and Oxidation resistance (up to 1500°C). Compared with the existing technology of preparing SiC fibers with low oxygen content by electron beam irradiation without melting, the technology of the present invention has the advantages of simple process, convenient operation, no need to add expensive equipment, and can be implemented by using the usual SiC fiber production equipment , The characteristics of low manufacturing cost are more suitable for industrial batch preparation. The SiC fiber prepared by the present invention is most suitable for preparing high-performance composite materials due to its excellent properties such as high strength, high temperature resistance, and high oxidation resistance. There are important application prospects in other fields.

Claims (9)

1. A method for manufacturing silicon carbide fibers with high temperature resistance, characterized in that: polycarbosilane PCS or low-molecular silane LPS generated by high-temperature cracking of polydialkylsilane is used as raw material, and organic compounds containing densification elements Synthesize polycarbosilanes containing Al and Y, namely PACS and PYCS, and then produce continuous PACS and PYCS fibers through melt spinning, and place the fibers in air and active atmosphere for non-melting treatment to obtain non-melting with controllable oxygen content. SiC fiber is obtained by placing the non-melting fiber in a high-temperature furnace under the protection of an inert atmosphere for high-temperature firing and sintering. 2. A method for manufacturing high temperature-resistant silicon carbide fibers according to claim 1, characterized in that the specific preparation process is as follows: (1) Co-dissolve the raw material PCS and organic compounds containing densification elements Al and Y in xylene, heat it while stirring under the protection of high-purity nitrogen until the xylene is distilled out, and then continue to react at 300-350°C, and finally Insulate the reaction at high temperature for 2-10 hours; or mix the raw material LPS with an organic compound containing Al and Y, heat it to 420-480°C under the protection of high-purity nitrogen for reaction, and keep it at the final temperature for 2-10 hours. The crude product is dissolved in xylene and then filtered, then heated to 300-360°C for vacuum distillation to remove the solvent and a small amount of low-molecular substances, and obtain PACS or PYCS after cooling; (2) Put the above PACS or PYCS in the spinning cylinder of the melt spinning device, heat up to 300-400°C under the protection of high-purity nitrogen, wait until it is completely melted into a uniform melt and remove residual bubbles, that is, defoaming treatment Finally, at 250-350°C, 0.1-0.6MPa pressure, melt spinning at a speed of 300-600m/min, after bundled and drawn, continuous PCS fibers with a diameter of 8-16um are obtained; (3) Place the above-mentioned PACS or PYCS fiber in a non-melting treatment device for air oxidation treatment, that is, heat it to 180-220 °C at a heating rate of 10-20 °C/hour in an air atmosphere, and heat preservation oxidation treatment for 2-4 Hours, then replace the air with high-purity nitrogen, heat up and introduce an active reaction atmosphere, heat from 100°C to 300-400°C at a heating rate of 10-20°C/min, and keep it at this temperature for 2-4 hours. , cooled to room temperature to make PACS or PYCS non-melting fibers; (4) Place the above-mentioned PACS or PYCS non-melting fibers in a high-temperature furnace, and under the protection of high-purity nitrogen, heat up to 1200-1300°C at a heating rate of 100-200°C/hour, and heat preservation treatment at this temperature for 1- Amorphous SiC fibers were prepared in 2 hours; (5) Put the above-mentioned amorphous SiC fibers in a high-temperature furnace protected by high-purity argon gas, raise the temperature to 1800°C, and heat-preserve and sinter at this temperature for 1-2 hours to obtain high-crystallinity and high-temperature fibers. Temperature resistant SiC fiber. 3. A method for manufacturing high temperature-resistant silicon carbide fibers according to claim 1 or 2, characterized in that the raw material polycarbosilane PCS is an organosilicon polymer whose main chain is composed of Si-C bonds. The molecular structural unit is:

Among them, the alkyl R ¹ , R ² =H, -CH ₂ -, -CH-, Me, Et, Pt, Bt, Ph and other organic groups, they can be the same or different, specific examples include polydimethyl Polycarbosilane obtained by pyrolysis, rearrangement and polycondensation of silane at high temperature. 4. A method for manufacturing high temperature-resistant silicon carbide fibers according to claim 1, characterized in that the low-molecular silane LPS as the raw material is a low-molecular-weight silane with Si-Si bonds and a small amount of Si-C bonds forming the main chain. Mixture of polymers, its structure is linear or cyclic, LPS is polydialkylsilane, a mixture of oligomeric compounds formed by pyrolysis, where R ¹ , R ² = H, Me, Et, Pt, Bt, Ph

The mixture is a transparent liquid at room temperature, with a boiling point of 60-300°C and a molecular weight of 100-600. 5. A method for manufacturing high temperature-resistant silicon carbide fibers according to claim 1 or 2, characterized in that the densification element is aluminum (Al) or yttrium (Y), and the densification element-containing The compound is a compound containing Al and Y, including aluminum acetylacetonate Al(acac) ₃ , yttrium acetylacetonate Y(acac) ₃ and corresponding alkoxy compounds such as Al(OR) ₃ , Y(OR) ₃ , wherein R= Me, Et, Pt, Bt, Ph. 6. A method for manufacturing high temperature-resistant silicon carbide fibers according to claim 1 or 2, characterized in that in the synthesis of PACS or PYCS, when PCS is used as raw material, the molecular weight of PCS is the number average molecular weight Mn is 800-2000, the mass ratio of the compound containing Al, Y, and B is 1:0.05-1:0.15, the synthesis temperature is 200-350°C, and when the molecular weight of PCS is higher, the synthesis temperature is lower. ; When it is necessary to introduce more densification elements, that is, when the quality ratio of the compound containing Al and Y is high, PCS with a lower molecular weight should be used as a raw material; when LPS is used as a raw material, LPS and the compound containing Al and Y The mass ratio of LPS is 1:0.05-1:0.15, and the synthesis temperature is 400-500°C. If the synthesis temperature is too low, the structural rearrangement and polycondensation of LPS will be insufficient. If the synthesis temperature is too high, the cross-linking reaction caused by excessive polycondensation will easily occur. Affecting the rheology of the product, the more suitable synthesis temperature is 420-460°C. 7. A method for manufacturing high temperature resistant silicon carbide fibers according to claim 1 or 2, characterized in that in the synthesis of the PACS or PYCS, densification elements such as Al and Y can also be mixed and introduced to When PCS is used as a raw material, the mass ratio of PCS to the compound containing Al and Y is 1:0.05-1:0.15, wherein the mass ratio between the compound containing Al and Y is 3:1-1:3, and other The synthesis conditions are unchanged, and the same ratio is also used when LPS is used as a raw material. 8. A method for manufacturing high temperature-resistant silicon carbide fibers according to claim 1 or 2, characterized in that the active reaction atmosphere used in the non-melting treatment of the PACS or PYCS fibers has a specific structure Low-boiling, volatile oxygen-free organic compounds of alkenes and alkynes, including alkenes: ethylene, propylene, butene, pentene, cyclohexene, butadiene and alkynes: acetylene, propyne, butyne, Pentyne, Hexyne. 9. A method for manufacturing high temperature-resistant silicon carbide fibers according to claim 1 or 2, characterized in that the non-melting treatment of the PACS or PYCS fibers in air and active atmosphere adopts the method of mixing air and active atmosphere Mixing and adding, processing at a certain temperature in a mixed atmosphere, or first performing air oxidation treatment, and then replacing the air with high-purity nitrogen gas and then introducing an active reaction atmosphere for treatment, by controlling the treatment temperature and time, the non-melting fiber The oxygen content is controlled at 2-12wt%, and the more suitable oxygen content control range is 3-8wt%.

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