Method for in-situ growth of whiskers on surface of fiber preform

Abstract

The invention discloses a method for in-situ growth of whiskers on the surface of a fiber preform, and belongs to the technical field of fiber surface modification. The preparation method comprises the following steps: firstly, preparing alkaline silica sol, carrying out chemical reaction on the alkaline silica sol and an aluminum source under the catalytic action of a catalyst to generate an intermediate gas-phase product, then carrying out mullite nucleation reaction and carrying out anisotropic growth to obtain mullite whiskers, and taking an aluminum silicate fiber felt as a template; the mullite whiskers grow in the radial direction of the fibers and are evenly distributed on the surfaces of the fibers, and then the long and thin needle-shaped mullite whiskers are obtained. The mullite whiskers grow on the surfaces of the fibers in situ, the mechanical property of the aluminum silicate fibers is remarkably improved through the multi-scale structural design and the interface synergistic effect, and when the material is subjected to external force, the internal whiskers are bent, stretched and shrunk under the external force, so that the internal stress at the fiber lap joint points is weakened, and the mechanical property of the aluminum silicate fibers is improved. The mechanical property of the material is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of fiber surface modification, and particularly relates to a method for in-situ growth of whiskers on the surface of a fiber preform. BACKGROUND

[0002] As one of the most common ceramic fiber products, aluminum silicate fiber has unique chemical composition and structural characteristics, and has the advantages of high temperature resistance, good thermal shock stability, small specific heat capacity, good chemical stability, good sound absorption, low thermal conductivity, etc., and is widely used in the fields of new type of thermal insulation materials for energy, metallurgy and building. However, with the progress of science and technology, the strength of aluminum silicate fiber has been unable to meet the needs of existing technology.

[0003] Mullite has the advantages of large mechanical strength, stable chemical properties, good thermal stability, strong creep resistance, and low expansion coefficient, thermal conductivity and electrical conductivity, and is widely used in the fields of metallurgy, building and military industry as a high-temperature structural ceramic material with excellent performance. Whiskers have a small cross-sectional area (<52x10 -5 cm 2 ) and a large aspect ratio (>10), and are a one-dimensional single crystal fiber material grown under artificial control conditions. The single crystal structure of whiskers does not contain defects such as dislocations, vacancies and grain boundaries, and the strength is close to the theoretical value of the complete crystal, so it is often used in the reinforcement and toughening of metal materials and ceramic materials. Mullite whiskers have the advantages of mullite and whiskers, and have excellent mechanical properties while having high temperature resistance, corrosion resistance and electrical insulation, and can be widely used in modified and reinforced materials of metal, ceramic and polymer. The existing Chinese patent CN106119966A discloses a method for in-situ growth of mullite whiskers on an aluminum-rich fiber felt. The patent grows uniform needle-like mullite whiskers on the existing aluminum-rich fiber felt. However, the above-mentioned patent needs to be freeze-dried multiple times, which has the problem of complex process.

[0004] Therefore, there is an urgent need for a method for improving the strength of aluminum silicate fiber using mullite whiskers with a simple process. SUMMARY

[0005] To solve the above technical problems, the present application provides a method for in-situ growth of whiskers on the surface of a fiber preform.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0007] The present application provides a method for in-situ growth of whiskers on the surface of a fiber preform, comprising the following steps:

[0008] (1) mixing a silicon source, ethanol and water, and then adding ammonia water to adjust the pH to alkaline, and stirring for the first time to obtain an alkaline silicon sol;

[0009] (2) mixing the alkaline silica sol obtained in step (1) with a catalyst, an aluminum source and water, and obtaining a mixed solution through ultrasonic oscillation and second stirring;

[0010] (3) immersing the aluminum silicate fiber felt into the mixed solution obtained in step (2) to perform vacuum impregnation, and then performing drying and heat treatment to obtain the aluminum silicate fiber with mullite whiskers grown in situ on the surface.

[0011] Technical principle: the alkaline silica sol is prepared first, and the alkaline silica sol and the aluminum source react to generate intermediate gas phase products under the catalysis of the catalyst, and then mullite nucleation reaction and anisotropic growth are performed to obtain mullite whiskers, and the aluminum silicate fiber felt is used as a template, so that the mullite whiskers grow along the radial direction of the fiber and are uniformly distributed on the surface of the fiber, and then the mullite whiskers in the form of'slender needles' are obtained. In the present application, the mullite whiskers are grown in situ on the surface of the fiber, and the mechanical properties of the aluminum silicate fiber are significantly improved through multi-scale structure design and interface synergistic effect. When the material is subjected to external force, the internal whiskers bend, stretch and contract under the action of external force, so as to weaken the internal stress at the fiber lap joint point and improve the mechanical properties of the material.

[0012] Further, in step (1), the silicon source is selected from tetraethyl orthosilicate and / or sodium silicate.

[0013] Further, in step (1), the ammonia water is added to adjust the pH to 8-9.

[0014] Further, in step (1), the concentration of the alkaline silica sol is 0.10-0.25 mol / L.

[0015] Further, in step (2), the catalyst is selected from one or more of borax, ammonium molybdate, aluminum fluoride, hydrofluoric acid and ammonium fluoride; and / or,

[0016] The aluminum source is selected from aluminum nitrate and / or aluminum chloride.

[0017] Further, in step (2), the concentration of the catalyst in the mixed solution is 0.10-0.25 mol / L, and the concentration of the aluminum source is 0.30-0.75 mol / L.

[0018] Further, in step (2), the ultrasonic oscillation time is 15-25 min; and / or,

[0019] The second stirring temperature is 45-55℃, and the second stirring time is 4-7h.

[0020] Further, in step (3), the vacuum impregnation time is 15-25 min, and the vacuum impregnation frequency is 2-5 times.

[0021] Further, in step (3), the temperature of drying is 65-90 DEG C, and the time of drying is 10-12h; and / or,

[0022] The temperature of heat treatment is 850-1200 DEG C, and the time of heat treatment is 2-5h.

[0023] The application also provides the aluminum silicate fiber with the surface in-situ grown mullite whiskers obtained by the method.

[0024] Compared with the prior art, the application has the following advantages and technical effects:

[0025] The method for growing whiskers on the surface of the fiber preform in-situ provided by the application realizes the significant improvement of the mechanical properties of the aluminum silicate fiber through the multi-scale structure design and the interface synergistic effect. BRIEF DESCRIPTION OF DRAWINGS

[0026] The accompanying drawings, which form a part of the present application, are intended to provide further understanding of the present application, and are used to interpret the specific embodiments of the present application and their descriptions, and do not constitute improper limitations to the present application. In the drawings:

[0027] Figure 1 The SEM image of the aluminum silicate fiber with the surface in-situ grown mullite whiskers prepared for Example 1;

[0028] Figure 2 The compression stress-strain curves of the aluminum silicate fiber and the aluminum silicate fiber with the surface in-situ grown mullite whiskers prepared for Examples 1-3; wherein 1 is Example 1, 2 is Example 2, and 3 is Example 3. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0030] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0031] The embodiment of the present application provides a method for growing whiskers in situ on the surface of a fiber preform, comprising the following steps:

[0032] (1) mixing a silicon source, ethanol and water, and then adding ammonia water to adjust the pH to alkaline, and then performing first stirring to obtain an alkaline silicon sol;

[0033] (2) mixing the alkaline silicon sol obtained in step (1) with a catalyst, an aluminum source and water, and then performing ultrasonic oscillation and second stirring to obtain a mixed solution;

[0034] (3) immersing an aluminum silicate fiber felt into the mixed solution obtained in step (2) to perform vacuum impregnation, and then performing drying and heat treatment to obtain an aluminum silicate fiber with mullite whiskers grown in situ on the surface.

[0035] In the preferred embodiment, in step (1), the silicon source is selected from tetraethyl orthosilicate and / or sodium silicate. The silicon source in the present application is used to provide the silicon element necessary for growing mullite whiskers.

[0036] In the preferred embodiment, in step (1), the ethanol is anhydrous ethanol; and the water is deionized water.

[0037] In the preferred embodiment, in step (1), the ammonia water is added to adjust the pH to 8-9.

[0038] In the preferred embodiment, in step (1), the concentration of the alkaline silicon sol is 0.10-0.25 mol / L, and is further preferably 0.10-0.20 mol / L.

[0039] In the preferred embodiment, in step (2), the catalyst is selected from one or more of borax, ammonium molybdate, aluminum fluoride, hydrofluoric acid and ammonium fluoride, and is further preferably one or more of borax, aluminum fluoride and ammonium fluoride. The catalyst in the present application reacts with the silicon source and the aluminum source to generate an intermediate gas phase product.

[0040] In the preferred embodiment, in step (2), the aluminum source is selected from aluminum nitrate and / or aluminum chloride. The aluminum source in the present application is used to provide the aluminum element necessary for growing mullite whiskers.

[0041] In the preferred embodiment, in step (2), the concentration of the catalyst in the mixed solution is 0.10-0.25 mol / L, and is further preferably 0.10-0.20 mol / L; and the concentration of the aluminum source in the mixed solution is 0.30-0.75 mol / L, and is further preferably 0.40-0.65 mol / L. Controlling the concentrations of the catalyst and the aluminum source in the mixed solution within the above ranges is advantageous for obtaining mullite whiskers in the form of "slender needles".

[0042] In the preferred embodiment, in step (2), the water is deionized water.

[0043] In the preferred embodiment, in step (2), the time of ultrasonic oscillation is 15-25 min. The present application makes the catalyst and the silicon source and the aluminum source fully react to generate intermediate gas phase products through ultrasonic oscillation.

[0044] In the preferred embodiment, in step (2), the temperature of the second stirring is 45-55℃, and further preferably 45-50℃; the time of the second stirring is 4-7h, and further preferably 4-6h.

[0045] In the preferred embodiment, in step (3), the time of vacuum impregnation is 15-25 min, and the number of vacuum impregnation is 2-5 times. The present application makes the mixed solution fully and uniformly impregnate into the aluminum silicate fiber felt, so as to realize the uniform growth of the mullite whiskers on the fiber surface.

[0046] In the preferred embodiment, in step (3), the temperature of drying is 65-90℃, and further preferably 65-80℃; the time of drying is 10-12h, and further preferably 10-11h.

[0047] In the preferred embodiment, in step (3), the temperature of heat treatment is 850-1200℃, and further preferably 850-1100℃; the time of heat treatment is 2-5h, and further preferably 2-4h. The mullite nucleation reaction and anisotropic growth occur in the heat treatment process, and the mullite whiskers are obtained; the temperature and time of heat treatment are controlled in the above range, which is beneficial to obtain the mullite whiskers in the form of "slim needle" and uniformly distributed on the fiber surface.

[0048] The present application also provides an aluminum silicate fiber with mullite whiskers grown in situ on the surface obtained by the method.

[0049] Unless otherwise specified, the raw materials in the embodiments of the present application are obtained by commercial purchase.

[0050] Embodiment 1

[0051] A method for growing whiskers in situ on the surface of a fiber preform, and the specific steps are as follows:

[0052] (1) Mix sodium silicate, anhydrous ethanol and deionized water, add ammonia water dropwise and stir until the pH reaches 8, and continue to stir for 10h to obtain an alkaline silicon sol with a concentration of 0.10 mol / L.

[0053] (2) The basic silicon sol obtained in step (1) is mixed with a catalyst, aluminum nitrate, and deionized water, ultrasonic oscillation is performed for 15 min, stirring is performed at 45°C for 4 h, and a mixed solution is obtained; wherein the catalyst is ammonium fluoride and aluminum fluoride (the mass ratio of ammonium fluoride to aluminum fluoride is 1:1), the concentration of the catalyst in the mixed solution is 0.25 mol / L, and the concentration of aluminum nitrate is 0.30 mol / L.

[0054] (3) The aluminum silicate fiber felt is immersed in the mixed solution obtained in step (2), vacuum impregnation is performed for 15 min, and the operation is repeated for 3 times; then the aluminum silicate fiber felt is placed in a drying box and dried at 90°C for 10 h, and dried aluminum silicate fiber felt is obtained.

[0055] (4) The dried aluminum silicate fiber felt obtained in step (3) is placed in a high-temperature sintering furnace and heat treated at 850°C for 2 h, and aluminum silicate fiber with mullite whiskers grown in situ on the surface is obtained.

[0056] Example 2

[0057] A method for growing whiskers in situ on the surface of a fiber preform, which is different from example 1 in that step (2) is as follows: the basic silicon sol obtained in step (1) is mixed with borax, an aluminum source, and deionized water, ultrasonic oscillation is performed for 25 min, stirring is performed at 55°C for 7 h, and a mixed solution is obtained; wherein the aluminum source is aluminum nitrate and aluminum chloride (the mass ratio of aluminum nitrate to aluminum chloride is 1:1), the concentration of borax in the mixed solution is 0.25 mol / L, and the concentration of the aluminum source is 0.45 mol / L; steps (1) and (3) are the same as in example 1.

[0058] Example 3

[0059] A method for growing whiskers in situ on the surface of a fiber preform, and the specific steps are as follows:

[0060] (1) Ethyl orthosilicate, anhydrous ethanol, and deionized water are mixed, ammonia water is added dropwise, and stirring is performed until the pH reaches 9, and stirring is continued for 12 h, and a basic silicon sol with a concentration of 0.25 mol / L is obtained.

[0061] (2) The basic silicon sol obtained in step (1) is mixed with borax, aluminum chloride, and deionized water, ultrasonic oscillation is performed for 20 min, stirring is performed at 50°C for 5 h, and a mixed solution is obtained; wherein the concentration of borax in the mixed solution is 0.20 mol / L, and the concentration of aluminum chloride is 0.55 mol / L.

[0062] Steps (3)-(5) are the same as in example 1.

[0063] Figure 1 The SEM image of the aluminum silicate fiber with mullite whiskers grown in situ on the surface prepared in example 1. From the SEM image, it can be seen that the mullite whiskers are evenly distributed on the surface of the aluminum silicate fiber. Figure 1It can be seen that the embodiment 1 realizes the in-situ growth of mullite whiskers on the surface of the aluminum silicate fiber, and the mullite whiskers are in the shape of'slim needle' and uniformly distributed on the surface of the fiber.

[0064] Figure 2 The compressive stress-strain curves of the aluminum silicate fiber and the aluminum silicate fiber with the mullite whiskers in-situ grown on the surface prepared in the embodiments 1-3; wherein 1 is the embodiment 1, 2 is the embodiment 2, and 3 is the embodiment 3. Figure 2 It can be seen that, compared with the untreated aluminum silicate fiber, the compressive strength of the aluminum silicate fiber with the mullite whiskers in-situ grown on the surface by the method of the present application is higher, and the mechanical properties are obviously improved.

[0065] The above merely describes the preferred embodiments of the present application, but the protection scope of the present application is not limited to this. Any changes or replacements within the technical scope disclosed by the present application can be easily thought by those skilled in the art, and should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for in-situ growth of whiskers on the surface of a fiber preform, characterized in that: The following steps are involved: (1) mixing a silicon source, ethanol and water, adding ammonia water to adjust the pH to alkaline, and stirring for the first time to obtain an alkaline silica sol; (2) mixing the alkaline silica sol obtained in step (1) with a catalyst, an aluminum source and water, and subjecting the mixture to ultrasonic oscillation and a second stirring to obtain a mixed solution; (3) Immersing the aluminum silicate fiber felt in the mixed solution obtained in step (2) for vacuum impregnation, and then drying and heat treating to obtain aluminum silicate fibers with mullite whiskers in situ grown on the surface.

2. The method for in-situ growth of whiskers on the surface of a fiber preform according to claim 1, characterized in that: In step (1), the silicon source is selected from ethyl orthosilicate and / or sodium silicate.

3. The method for in-situ whisker growth on the surface of a fiber preform according to claim 1, characterized in that: In step (1), ammonia water is added to adjust the pH to 8-9.

4. The method for in-situ growth of whiskers on the surface of a fiber preform according to claim 1, characterized in that: In step (1), the concentration of the alkaline silica sol is 0.10 to 0.25 mol / L.

5. The method for in-situ growth of whiskers on the surface of a fiber preform according to claim 1, characterized in that: In step (2), the catalyst is selected from one or more of borax, ammonium molybdate, aluminum fluoride, hydrofluoric acid and ammonium fluoride; and / or, The aluminum source is selected from aluminum nitrate and / or aluminum chloride.

6. The method for in-situ growth of whiskers on the surface of a fiber preform according to claim 1, characterized in that: In step (2), the concentration of the catalyst in the mixed solution is 0.10-0.25 mol / L, and the concentration of the aluminum source is 0.30-0.75 mol / L.

7. The method for in-situ whisker growth on the surface of a fiber preform according to claim 1, characterized in that: In step (2), the ultrasonic oscillation time is 15 to 25 minutes; and / or, The temperature of the second stirring is 45-55° C., and the time of the second stirring is 4-7 hours.

8. The method for in-situ whisker growth on the surface of a fiber preform according to claim 1, characterized in that: In step (3), the vacuum impregnation time is 15 to 25 minutes, and the number of vacuum impregnations is 2 to 5 times.

9. The method for in-situ whisker growth on the surface of a fiber preform according to claim 1, characterized in that: In step (3), the drying temperature is 65 to 90° C. and the drying time is 10 to 12 hours; and / or, The heat treatment temperature is 850-1200° C., and the heat treatment time is 2-5 hours.

10. Aluminum silicate fiber with in-situ growth of mullite whiskers on the surface obtained by the method according to any one of claims 1 to 9.

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