Alumina-based continuous fiber with oriented structure and preparation method thereof

Abstract

The invention discloses an alumina-based continuous fiber with directional structure and a preparation method thereof. The continuous alumina-based original growth fiber is transferred to a medium-temperature muffle furnace, heated to 700-900°C, kept warm for 1-20 minutes, and cooled to obtain a continuous alumina-based pre-sintered fiber; the continuous alumina-based pre-sintered fiber is transferred to a vacuum furnace, quickly heated to 1500-1650°C at a heating rate of 50-200°C / min, kept warm for 1-20 minutes, and cooled to obtain an alumina-based continuous fiber with directional structure. The grains are in the shape of long rods, the grain diameters are 200-1000nm, the aspect ratios of the grains are 5-20, and the density reaches more than 99.9%. The length direction of the grains is along the crystal axis c-axis direction, and the grains are parallel and directionally arranged in the long axis direction inside the whole fiber. The mechanical properties are excellent and the applicable temperature range is high.

Description

Technical Field

[0001] The invention belongs to high-temperature thermal structural materials and relates to the fields of composite material reinforcement and toughening and high-temperature oxidation environment, and in particular to a high-strength polycrystalline alumina-based continuous fiber with directional structure that can be wound or woven and a preparation method thereof. Background Art

[0002] Alumina-based ceramic fibers combine multiple functions such as structure and heat protection, and are important toughening and reinforcing materials for high-performance thermal structural composite materials. Domestic high-performance alumina-based ceramic long fibers are still in the laboratory research stage, and there is a significant gap in performance with similar foreign products. There has long been a huge demand gap in the domestic market.

[0003] The average tensile strength of alumina-based ceramic fibers is around 2GPa, which is not only incomparable to carbon fibers known for their high strength, but also incomparable to glass fibers and boron fibers at their respective operating temperatures (the average strengths of the latter two are both above 3GPa). The reason for this is that alumina-based ceramic fibers have a high degree of crystallinity and a grain shape that is nearly circular equiaxed crystals. Equiaxed crystal cracks propagate quickly and are not prone to segregation and other crack energy-consuming phenomena, which can easily cause fiber damage. This structural feature fundamentally limits the room for improvement in the strength and toughness of alumina-based ceramic fibers. At the same time, at 1500°C (α-Al 2 O 3 When used above the phase transition temperature, α-Al 2 O 3 Equiaxed grains can easily grow rapidly out of control, resulting in grain coarsening, loss of overall organization and loss of nanocrystalline structure, thus reducing the performance of alumina-based ceramic fibers. If the sintering temperature of alumina-based fibers can be raised to above 1500°C, a complete and stable α-Al2O3 phase transition can be obtained. 2 O 3 It can improve the room temperature mechanical properties of alumina-based fibers and improve their applicable temperature range, thus eliminating the hidden danger of grain loss in high-temperature applications.

[0004] Silicon nitride ceramic fiber grains have a typical rod-shaped interlocking structure. Rod-shaped crystals can easily deflect cracks, consume crack energy, and reduce fiber damage. At the same time, the typical rod-shaped interlocking structure can prevent the grain structure from getting out of control during high-temperature phase transitions. Therefore, rod-shaped grains with a significant aspect ratio can more effectively improve fiber performance than circular equiaxed crystals. At the same time, due to the characteristics of equiaxed grains, the grain orientation of currently available alumina-based fibers is random and disordered, and there is no technical possibility to achieve orientation.

[0005] In summary, improving the grain morphology, grain size, grain distribution uniformity and overall macroscopic orientation of the grains in the fiber of alumina-based ceramic fibers has become an effective way to improve the performance of alumina-based ceramic fibers. Summary of the invention

[0006] The purpose of the embodiments of the present invention is to provide an alumina-based continuous fiber with a directional structure and a preparation method thereof, so as to realize the structure design and high-temperature structure control of the alumina-based fiber, optimize and improve the mechanical properties of the alumina-based continuous fiber, and thereby solve the problem of poor mechanical properties of the alumina-based continuous fiber and the problem of limited applicable temperature range.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is a method for preparing alumina-based continuous fibers with oriented structure, comprising the following steps:

[0008] S1: transferring the continuous alumina-based raw fiber to a medium-temperature muffle furnace, heating it to 700-900° C., keeping it warm for 1-20 minutes, and cooling it to obtain the continuous alumina-based pre-sintered fiber;

[0009] S2: The continuous alumina-based pre-sintered fiber is transferred to a vacuum furnace, and the temperature is rapidly increased to 1500-1650° C. at a heating rate of 50-200° C. / min, and the temperature is kept for 1-20 minutes. After cooling, the alumina-based continuous fiber with oriented structure is obtained.

[0010] Furthermore, in S1, the method for preparing the continuous alumina-based raw growth fiber comprises the following steps:

[0011] S11: mixing polyaluminium chloride sol and silica sol in a molar ratio of effective oxide of 3:(0.5-2) to obtain a mixed sol;

[0012] S12: adding a polyvinyl alcohol solution dropwise to the mixed sol, wherein the polyvinyl alcohol accounts for 4 to 14% of the mass of the mixed sol, and stirring to obtain a precursor sol;

[0013] S13: adding the template seed crystal to the precursor sol, wherein the mass ratio of the template seed crystal to the effective oxide in the mixed sol is (0.01-0.15):1, and stirring at a temperature of 50° C. for 2-4 hours to obtain a precursor sol having the template seed crystal;

[0014] S14: concentrating the precursor sol with the template seed crystals to a spinnable state to obtain a sol to be spun;

[0015] S15: The sol to be spun is continuously spun by dry method, dried in hot air at 30-200° C. for 5-60 seconds, and collected by winding to obtain green fibers. The green fibers are dried in an oven at 50-180° C. for 3-10 hours to obtain the continuous alumina-based primary growth fibers.

[0016] Furthermore, in S1, the temperature is increased to 700-900°C at a heating rate of 0.1-1°C / min.

[0017] Furthermore, in S11, the polyaluminium chloride used is a polyaluminium chloride solution, and the mass fraction of polyaluminium chloride in the polyaluminium chloride solution is 25-40%; the mass fraction of silicon dioxide in the silica sol is 15-30%.

[0018] Furthermore, in S12, the mass percentage of polyvinyl alcohol in the polyvinyl alcohol solution is 5-10%.

[0019] Furthermore, in S13, the template seed crystal includes a rod-shaped, needle-shaped or sheet-shaped template seed crystal; the aspect ratio of the rod-shaped or needle-shaped template seed crystal is (7-50):1; the ratio of the width to thickness of the sheet-shaped template seed crystal is (10-40):1; one dimension of the template seed crystal is less than 100nm and the maximum dimension does not exceed 5μm; the viscosity of the precursor sol with the template seed crystal is 1000-5000mPa·s.

[0020] Furthermore, in S14, the viscosity of the sol to be spun is 9000-90000 mPa·s.

[0021] Furthermore, in S15, during the continuous dry spinning, the winding speed is 40 to 80 r / min, and the air humidity is 5% to 40%.

[0022] Another technical solution adopted by the present invention is that the alumina-based continuous fibers with oriented structures are prepared by the method for preparing the alumina-based continuous fibers with oriented structures as described above.

[0023] Furthermore, the alumina-based continuous fiber with oriented structure has long rod-shaped grains, a grain diameter of 200 to 1000 nm, an aspect ratio of 5 to 20, and a density of more than 99.9%. The length direction of the grains is along the crystal axis c-axis, and the grains are oriented and arranged parallel to the long axis direction inside the entire fiber.

[0024] The beneficial effects of the present invention are as follows: the alumina-based continuous fiber obtained in the embodiment of the present invention has an oriented long rod-shaped grain structure with a significant aspect ratio, its crystal form is more stable, and is oriented in the same direction as the fiber axis, and its mechanical properties are more excellent, which solves the problem of poor mechanical properties of alumina-based continuous fibers. At the same time, the preparation method of alumina-based continuous fibers is combined with vacuum rapid sintering technology to overcome the disadvantage of traditional alumina-based fibers losing control of their organization after high-temperature sintering at above 1500°C, enhance the high-temperature organization control of alumina-based fibers, and obtain an oriented organization after sintering at above 1500°C, solving the problem of limited applicable temperature range of alumina-based continuous fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 It is a schematic diagram of the process flow for preparing alumina-based continuous fibers with oriented tissue and the principle of tissue orientation according to Example 3 of the present invention.

[0027] Figure 2 This is the SEM image of the alumina-based continuous fiber prepared in Comparative Example 3.

[0028] Figure 3 This is a SEM image of the surface of the alumina-based continuous fiber with oriented structure obtained in Example 3 of the present invention.

[0029] Figure 4 This is a SEM image of the cross section of the alumina-based continuous fiber with oriented structure obtained in Example 3 of the present invention. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments 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 creative work are within the scope of protection of the present invention.

[0031] A method for preparing an alumina-based continuous fiber with a directional structure comprises the following steps:

[0032] S1: transferring the continuous alumina-based raw fiber to a medium-temperature muffle furnace for pre-sintering, heating from room temperature to 700-900°C at a heating rate of 0.1-1°C / min, keeping the temperature for 1-20 minutes, and then cooling with the furnace to obtain a continuous alumina-based pre-sintered fiber;

[0033] S2: The continuous alumina-based pre-sintered fiber is transferred to a vacuum furnace, and the temperature is rapidly increased to 1500-1650°C at a heating rate of 50-200°C / min, and the temperature is kept for 1-20 minutes, and then the furnace is cooled to obtain an alumina-based continuous fiber with a directional structure.

[0034] In S1, the method for preparing the continuous alumina-based primary growth fiber comprises the following steps:

[0035] S11: Polyaluminium chloride (PAC) sol and silica sol are mixed according to the effective oxide Al 2 O 3 :SiO 2 The molar ratio of the raw materials is 3:(0.5-2), and during the mixing process, one raw material is diluted by distilled water to one half and then continuously stirred magnetically at room temperature at a stirring speed of 1000-3000r / min; the other raw material is added dropwise at a speed of 1-2 drops per second, and is added dropwise in 3-5 times, with an interval of 10 minutes between each addition, to obtain a mixed sol;

[0036] S12: adding polyvinyl alcohol (PVA) solution as a spinning aid to the mixed sol at a rate of 1 to 3 drops per second, wherein the polyvinyl alcohol accounts for 4 to 14% of the mass of the mixed sol, and stirring at room temperature for 3 hours to obtain a precursor sol;

[0037] S13: adding the template seed crystal to the precursor sol, wherein the template seed crystal and the effective oxide (Al 2 O 3 and SiO 2 ) with a mass ratio of (0.01-0.15):1, and magnetically stirring for 2-4 hours at a temperature of 50° C. to obtain a precursor sol with template seed crystals;

[0038] S14: concentrating the precursor sol with the template seed crystals to a spinnable state, to obtain a sol to be spun with a viscosity ranging from 9000 to 90000 mPa·s;

[0039] S15: The sol to be spun is continuously spun by dry method, dried in hot air at 30-200° C. for 5-60 seconds, and collected by winding to obtain green fibers. The collected green fibers are dried in an oven at a temperature of 50-180° C. for 3-10 hours to obtain continuous alumina-based primary growth fibers.

[0040] The polyaluminium chloride used in S11 is a polyaluminium chloride solution, in which the mass fraction of polyaluminium chloride is 25-40%; the mass fraction of silicon dioxide in the silica sol is 15-30%, and the obtained mixed sol must be transparent and uniform, and no precipitation or discoloration occurs after being placed for 24 hours.

[0041] The mass percentage of polyvinyl alcohol in the polyvinyl alcohol solution used in S12 is 5% to 10%. The obtained precursor solution is uniform and transparent, has a viscosity below 100 mPa·s, and no precipitation or discoloration occurs after being placed for 24 hours.

[0042] The template seed crystals used in S13 include rod-shaped, needle-shaped or sheet-shaped template seed crystals, wherein the aspect ratio of the rod-shaped or needle-shaped template seed crystals is (7-50):1; the ratio of the width to the thickness of the sheet-shaped template seed crystals is (10-40):1; one dimension of the template seed crystals is less than 100nm, and the maximum dimension does not exceed 5μm; the template seed crystals used in this step are preferably sheet-shaped alumina or mullite whiskers. The template seed crystals used are used as oriented templates and initial nucleation areas. During the heat treatment process, the alumina fiber matrix is ​​induced to use the template seed crystals as the crystal nuclei, and homoepitaxial growth is carried out according to the Oswald ripening mode, i.e., the large swallowing the small, to obtain large, long rod-shaped oriented nano-scale grains.

[0043] In S13, the viscosity of the precursor sol with the template seed crystals is in the range of 1000 to 5000 mPa·s. The viscosity increases during stirring, which can prevent the template seed crystals from settling and improve the uniformity of the template seed crystals in the precursor sol.

[0044] In S15, during continuous dry spinning, the winding speed is 40-80 r / min, the air humidity is 5-40%, and the continuous alumina-based primary growth fiber can be continuously spun for 50-300 meters. During the spinning and stretching process, the template seed crystals are oriented along the fiber axis under the action of the axial tension exerted on the gel fiber, thereby achieving oriented arrangement of the template seed crystals.

[0045] The purpose of S1 pre-burning is to expel useless components (debinding) such as structural water and organic spinning aids in the continuous alumina-based native growth fibers to ensure the densification of the fibers during the high-temperature phase change stage. The pre-burning process has a low temperature and no phase change. It is only a debinding process and the organization is still amorphous.

[0046] S2 uses vacuum rapid sintering to shorten the action time of the surface diffusion coarsening mechanism of alumina-based ceramic fibers at low temperature, provide a strong driving force for grain boundary diffusion densification at high temperature, and combine vacuum conditions to promote rapid densification of ceramic fibers and reduce excess grain growth, thereby achieving the effect of increasing the sintering temperature of alumina-based ceramic fibers, refining grains and increasing density. This method not only provides a new idea for solving the problem of uncontrolled performance collapse of alumina-based fiber high-temperature organizational structure, but also has great benefits for improving the high-temperature stability of fibers due to the stabilization of the crystal form.

[0047] The embodiment of the present invention redesigns the oriented alumina-based continuous fiber structure by matching and screening the size of the template seed crystal, combined with the control of pre-sintering and vacuum rapid sintering technology. Through vacuum rapid sintering, it is possible to maintain fine nanocrystals when the sintering temperature is increased and the phase change is complete, overcoming the difficulty of the existing alumina fiber that the grains grow rapidly at 1500 degrees and cause the structure to be out of control, and obtaining oriented structure fibers that are still controllable after high-temperature sintering above 1500 degrees. During the vacuum rapid sintering process, alumina and mullite phase changes occur simultaneously, and the final phases of mullite and corundum are obtained. The grains are in the shape of long rods. The long rod-shaped grains are oriented and arranged parallel to the long axis direction of the entire fiber. The long rod-shaped grains are affected by the crystal structure of the template seed crystal, and the length direction is along the crystal axis c-axis direction (AlO 6 The octahedrons grow in chains along the c-axis direction (with a faster growth rate), resulting in a crystal structure with fewer defects, closer to a single crystal, and various performance indicators that are closer to theoretical values. The grain diameter is 200-1000nm, the aspect ratio of the grain is 5-20, and the density reaches more than 99.9%, effectively improving the operating temperature and mechanical properties of alumina-based continuous fibers.

[0048] Example 1

[0049] A method for preparing an alumina-based continuous fiber with a directional structure comprises the following steps:

[0050] S1: The continuous alumina-based raw fiber is transferred to a medium-temperature muffle furnace for pre-sintering. The temperature is raised from room temperature to 700°C at a heating rate of 0.1°C / min, and the temperature is kept at this temperature for 20 minutes. The continuous alumina-based pre-sintered fiber is then cooled with the furnace to obtain the continuous alumina-based pre-sintered fiber.

[0051] S2: The continuous alumina-based pre-sintered fibers were transferred to a vacuum furnace, rapidly heated to 1500°C at a heating rate of 50°C / min, kept at that temperature for 20 minutes, and then cooled with the furnace to obtain alumina-based continuous fibers with oriented structure.

[0052] The method for preparing the continuous alumina-based primary growth fiber comprises the following steps:

[0053] S11: Polyaluminium chloride sol and silica sol are mixed according to the effective oxide Al2 O 3 :SiO 2 The molar ratio of the polyaluminium chloride sol is 3:0.5, and during the mixing process, the polyaluminium chloride sol is diluted by distilled water to one half, and then continuously magnetically stirred at room temperature, and the stirring speed is 1000r / min; the silica sol is added dropwise at a speed of 1 drop per second, and the addition is divided into 3 drops, and each drop is added with an interval of 10min to obtain a mixed sol; the polyaluminium chloride used is a polyaluminium chloride solution, and the mass fraction of the polyaluminium chloride in the polyaluminium chloride solution is 25%, and the mass fraction of silicon dioxide in the silica sol used is 15%, and the obtained mixed sol is transparent and uniform, and no precipitation and discoloration occur after being placed for 24 hours;

[0054] S12: adding polyvinyl alcohol (PVA) solution as a spinning aid to the mixed sol at a rate of 1 drop per second, the polyvinyl alcohol accounting for 4% of the mass of the mixed sol, stirring at room temperature for 3 hours to obtain a precursor sol; the polyvinyl alcohol used is 2088 type, the mass percentage of polyvinyl alcohol in the polyvinyl alcohol solution is 5%, the obtained precursor solution is uniform and transparent, has a viscosity of less than 100 mPa·s, and no precipitation or discoloration occurs after being placed for 24 hours;

[0055] S13: adding the template seed crystal to the precursor sol, wherein the template seed crystal and the effective oxide (Al 2 O 3 and SiO 2 ) with a mass ratio of 0.01:1, and magnetic stirring for 2 hours at a temperature of 50°C to obtain a precursor sol with a template seed crystal; the template seed crystal used is flaky aluminum oxide, the ratio of the diameter to the thickness of the flaky aluminum oxide is 10:1, and the average thickness of the flaky aluminum oxide is 80nm; the viscosity of the precursor sol with the template seed crystal is 1000mPa·s;

[0056] S14: concentrating the precursor sol with the template seed crystals to be spinnable, to obtain a sol to be spun with a viscosity of 9000 mPa·s;

[0057] S15: The sol to be spun is continuously spun by dry method, dried in hot air at 30°C for 60s, and collected by winding to obtain green fibers. The green fibers are dried in an oven at 50°C for 10h to obtain continuous alumina-based primary growth fibers. During continuous dry spinning, the winding speed is 40r / min, the air humidity is 5%, and the continuous alumina-based primary growth fibers can be continuously spun for 100 meters.

[0058] Example 2

[0059] A method for preparing an alumina-based continuous fiber with a directional structure comprises the following steps:

[0060] S1: The continuous alumina-based raw fiber is transferred to a medium-temperature muffle furnace for pre-sintering. The temperature is raised from room temperature to 900°C at a heating rate of 1°C / min, and the temperature is kept for 1 minute. The continuous alumina-based pre-sintered fiber is then cooled with the furnace to obtain the continuous alumina-based pre-sintered fiber.

[0061] S2: The continuous alumina-based pre-sintered fibers were transferred to a vacuum furnace, rapidly heated to 1650°C at a heating rate of 200°C / min, kept at that temperature for 1 minute, and then cooled with the furnace to obtain alumina-based continuous fibers with oriented structure.

[0062] The method for preparing the continuous alumina-based primary growth fiber comprises the following steps:

[0063] S11: Polyaluminium chloride sol and silica sol are mixed according to the effective oxide Al 2 O 3 :SiO 2 The molar ratio of the polyaluminium chloride sol is 3:2. During the mixing process, the polyaluminium chloride sol is diluted by distilled water to one half and then continuously stirred magnetically at room temperature at a stirring speed of 3000r / min. The silica sol is added dropwise at a speed of 2 drops per second, and the addition is divided into 4 drops, with an interval of 10 minutes between each addition, to obtain a mixed sol. The polyaluminium chloride used is a polyaluminium chloride solution, the mass fraction of the polyaluminium chloride in the polyaluminium chloride solution is 40%, and the mass fraction of silicon dioxide in the silica sol used is 30%. The obtained mixed sol is transparent and uniform, and no precipitation or discoloration occurs after being placed for 24 hours.

[0064] S12: adding polyvinyl alcohol (PVA) solution as a spinning aid to the mixed sol at a rate of 3 drops per second, the polyvinyl alcohol accounting for 14% of the mass of the mixed sol, stirring at room temperature for 3 hours to obtain a precursor sol; the polyvinyl alcohol used is 2488 type, the mass percentage of polyvinyl alcohol in the polyvinyl alcohol solution is 7%, the obtained precursor solution is uniform and transparent, has a viscosity of less than 100 mPa·s, and no precipitation and discoloration occur after being placed for 24 hours;

[0065] S13: adding the template seed crystal to the precursor sol, wherein the template seed crystal and the effective oxide (Al 2 O 3 and SiO 2 ) with a mass ratio of 0.15:1, and magnetic stirring for 4 hours at a temperature of 50°C to obtain a precursor sol with a template seed crystal; the template seed crystal used is flaky aluminum oxide, the ratio of the width to the thickness of the flaky aluminum oxide is 40:1, and the average thickness of the flaky aluminum oxide is 50nm; the viscosity of the precursor sol with the template seed crystal is 3000mPa·s;

[0066] S14: concentrating the precursor sol with the template seed crystals to be spinnable, to obtain a sol to be spun with a viscosity of 90000 mPa·s;

[0067] S15: The sol to be spun is continuously spun by dry method, dried in hot air at 200°C for 5s, and collected by winding to obtain green fibers. The green fibers are dried in an oven at 180°C for 3h to obtain continuous alumina-based primary growth fibers. During continuous dry spinning, the winding speed is 80r / min, the air humidity is 40%, and the continuous alumina-based primary growth fibers can be continuously spun for 50 meters.

[0068] Example 3

[0069] A method for preparing an alumina-based continuous fiber with a directional structure comprises the following steps:

[0070] S1: The continuous alumina-based raw fiber is transferred to a medium-temperature muffle furnace for pre-sintering. The temperature is raised from room temperature to 800°C at a heating rate of 0.5°C / min, and the temperature is kept for 10 minutes. The continuous alumina-based pre-sintered fiber is then cooled with the furnace to obtain the continuous alumina-based pre-sintered fiber.

[0071] S2: The continuous alumina-based pre-sintered fibers were transferred to a vacuum furnace, rapidly heated to 1600°C at a heating rate of 150°C / min, kept at this temperature for 5 minutes, and then cooled with the furnace to obtain alumina-based continuous fibers with oriented structure.

[0072] The method for preparing the continuous alumina-based primary growth fiber comprises the following steps:

[0073] S11: Polyaluminium chloride sol and silica sol are mixed according to the effective oxide Al 2 O 3 :SiO 2 The molar ratio of the polyaluminium chloride sol is 3:1. During the mixing process, the polyaluminium chloride sol is diluted by distilled water to one half and then continuously stirred by magnetic stirring at room temperature at a stirring speed of 2500r / min. The silica sol is added dropwise at a speed of 1 drop per second, and the addition is divided into 5 drops, with an interval of 10 minutes between each addition, to obtain a mixed sol. The polyaluminium chloride used is a polyaluminium chloride solution, the mass fraction of the polyaluminium chloride in the polyaluminium chloride solution is 30%, and the mass fraction of silicon dioxide in the silica sol used is 25%. The obtained mixed sol is transparent and uniform, and no precipitation or discoloration occurs after being placed for 24 hours.

[0074] S12: adding polyvinyl alcohol (PVA) solution as a spinning aid to the mixed sol at a rate of 2 drops per second, the polyvinyl alcohol accounting for 10% of the mass of the mixed sol, stirring at room temperature for 3 hours to obtain a precursor sol; the polyvinyl alcohol used is 2088 type, the mass percentage of polyvinyl alcohol in the polyvinyl alcohol solution is 10%, the obtained precursor solution is uniform and transparent, has a viscosity of less than 100 mPa·s, and no precipitation or discoloration occurs after being placed for 24 hours;

[0075] S13: adding the template seed crystal to the precursor sol, wherein the template seed crystal and the effective oxide (Al 2 O 3 and SiO 2 ) with a mass ratio of 0.05:1, and magnetic stirring for 3 hours at a temperature of 50°C to obtain a precursor sol with a template seed crystal; the template seed crystal used is a mullite whisker with an aspect ratio of 20:1 and an average diameter of 20nm, and the viscosity of the precursor sol with the template seed crystal is 5000mPa·s;

[0076] S14: concentrating the precursor sol with the template seed crystals to be spinnable, to obtain a sol to be spun with a viscosity of 60000 mPa·s;

[0077] S15: The sol to be spun is continuously spun by dry method, dried in hot air at 120°C for 30s, and collected by winding to obtain green fibers. The green fibers are dried in an oven at 80°C for 6h to obtain continuous alumina-based primary growth fibers. During continuous dry spinning, the winding speed is 60r / min, the air humidity is 15%, and the continuous alumina-based primary growth fibers can be continuously spun for 300 meters.

[0078] The process of preparing alumina-based continuous fibers with directional structure in this embodiment is as follows: Figure 1 As shown, according to the template grain growth technology, mullite whiskers are used as template seed crystals, the mullite whiskers are added to the precursor sol, and then they are concentrated together to a spinnable state, and then the axial tension in the dry spinning process is used to orient the whiskers with a significant aspect ratio inside the gel fiber green body (coaxially oriented with the fiber); then in the high-temperature sintering process, the oriented whiskers act as seed crystals and undergo homoepitaxial growth, thereby guiding the overall orientation of the fiber structure.

[0079] Examples 4 to 9 and Comparative Examples 1 to 6 are the same as Example 3 except that the heating rate, sintering temperature, holding time in S2 and the heating template seed crystal in S13 are shown in Table 1. See Table 1 for details.

[0080] Table 1 Changes in heating rate, sintering temperature, holding time, template seed crystal in Examples 4 to 9 and Comparative Examples 1 to 6

[0081]

[0082] The microscopic morphology of the alumina-based continuous fibers with oriented structures obtained in Example 3 and the alumina-based continuous fibers obtained in Comparative Example 3 are as follows: Figures 2 to 4 shown. Figure 2 The alumina-based continuous fiber obtained in Comparative Example 3 is a common equiaxed crystal structure. Figure 3It shows that the aluminum oxide-based continuous fiber with oriented structure obtained in Example 3 is a rod-shaped structure with a significant aspect ratio, and the rod-shaped structure is basically arranged in the same axial direction as the fiber. Figure 4 It shows that the alumina-based continuous fibers with oriented structure prepared in Example 3 have high density.

[0083] The mechanical properties of the alumina-based continuous fibers with oriented structures prepared in the embodiment of the present invention were tested, and the test results are shown in Table 2.

[0084] Table 2 Mechanical properties test results of alumina-based continuous fibers with oriented structures prepared in the embodiments of the present invention

[0085] project Single filament tensile strength (GPa) Operating temperature(℃) Organizational form Example 1 1.86 1500-1800 Strips with certain orientation Example 2 1.91 1500-1800 Strips with certain orientation Example 3 2.38 1500-2000 Directed Strip Example 4 2.12 1500-2000 Directed Strip Example 5 2.23 1500-2000 Directed Strip Example 6 2.00 1500-1800 Strips with certain orientation Example 7 1.90 1500-2000 Directed Strip Example 8 2.06 1500-2000 Directed Strip Example 9 1.86 1500-2000 Directed Strip Comparative Example 1 1.63 <1200 Isometric Comparative Example 2 1.71 <1200 Isometric Comparative Example 3 1.80 <1500 Messy strips Comparative Example 4 1.44 <1200 Messy, extremely coarse strips and equiaxed crystals Comparative Example 5 1.55 <1500 Messy strips Comparative Example 6 1.60 <1500 Messy strips

[0086] It can be seen from Table 1 that the method for preparing alumina-based continuous fibers with oriented structures according to the embodiment of the present invention can prepare oriented equiaxed structures, which can be used at higher temperatures, and the prepared alumina-based continuous fibers with oriented structures have good mechanical properties. Only adding whiskers, not sintering according to the sintering method, or not adding whiskers, can not obtain oriented strip structures.

[0087] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0088] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A method for preparing alumina-based continuous fibers with directional structure, characterized in that: The following steps are involved: S1: transferring the continuous alumina-based raw fiber to a medium-temperature muffle furnace, heating it to 700-900° C., keeping it warm for 1-20 minutes, and cooling it to obtain the continuous alumina-based pre-sintered fiber; S2: transferring the continuous alumina-based pre-sintered fiber to a vacuum furnace, rapidly heating the temperature to 1500-1650°C at a heating rate of 50-200°C / min, keeping the temperature for 1-20 minutes, and obtaining the alumina-based continuous fiber with oriented structure after cooling; In S1, the method for preparing the continuous alumina-based primary growth fiber comprises the following steps: S11: mixing polyaluminium chloride sol and silica sol in a molar ratio of effective oxide of 3:(0.5-2) to obtain a mixed sol; S12: adding polyvinyl alcohol solution dropwise to the mixed sol, wherein the polyvinyl alcohol accounts for 14% of the mass of the mixed sol, and stirring to obtain a precursor sol; S13: adding the template seed crystal to the precursor sol, wherein the mass ratio of the template seed crystal to the effective oxide in the mixed sol is (0.01-0.15):1, and stirring at a temperature of 50° C. for 2-4 hours to obtain a precursor sol having the template seed crystal; S14: concentrating the precursor sol with the template seed crystals to a spinnable state to obtain a sol to be spun; S15: the sol to be spun is continuously spun by dry method, dried in hot air at 200° C. for 5 to 60 seconds, and collected by winding to obtain green fibers, and the green fibers are dried in an oven at a temperature of 180° C. for 3 to 10 hours to obtain the continuous alumina-based primary growth fibers; In S1, the temperature was raised to 900°C at a heating rate of 0.1°C / min; In S11, the polyaluminium chloride used is a polyaluminium chloride solution, and the mass fraction of the polyaluminium chloride in the polyaluminium chloride solution is 25-40%; the mass fraction of silicon dioxide in the silica sol is 15%.

2. The method for preparing alumina-based continuous fibers with directional structure according to claim 1, characterized in that: In S12, the mass percentage of polyvinyl alcohol in the polyvinyl alcohol solution is 5-10%.

3. The method for preparing alumina-based continuous fibers with directional structure according to claim 1, characterized in that: In S13, the template seed crystal includes a rod-shaped, needle-shaped or sheet-shaped template seed crystal; the aspect ratio of the rod-shaped or needle-shaped template seed crystal is (7-50):1; the ratio of the width to thickness of the sheet-shaped template seed crystal is (10-40):1; one dimension of the template seed crystal is less than 100nm and the maximum dimension does not exceed 5μm; the viscosity of the precursor sol with the template seed crystal is 1000-5000mPa·s.

4. The method for preparing alumina-based continuous fibers with oriented structure according to claim 1, characterized in that: In S14, the viscosity of the sol to be spun is 9000-90000 mPa·s.

5. The method for preparing alumina-based continuous fibers with oriented structure according to claim 1, characterized in that: In S15, during the continuous dry spinning, the winding speed is 40 to 80 r / min, and the air humidity is 5% to 40%.

6. Alumina-based continuous fibers with directional structure, characterized in that: The fiber is prepared by the method for preparing alumina-based continuous fibers with directional structure as described in any one of claims 1 to 5.

7. The alumina-based continuous fiber with directional structure according to claim 6, characterized in that: The grains are long rod-shaped, with a grain diameter of 200 to 1000 nm and an aspect ratio of 5 to 20, reaching a density of more than 99.9%. The length direction of the grains is along the crystal axis c-axis, and the grains are oriented parallel to the long axis direction inside the entire fiber.

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