Hollow carbon / mullite composite fiber and preparation method thereof

Abstract

The invention discloses a hollow carbon / mullite composite fiber and a preparation method thereof. The method comprises the following steps: washing and drying natural hollow fibers, sintering in an argon atmosphere to obtain hollow carbon fibers, putting the hollow carbon fibers into an impregnation liquid composed of aluminum nitrate nonahydrate, tetraethoxysilane and absolute ethyl alcohol, fully impregnating, leaching out excess solution, and drying to obtain the hollow carbon fibers. Finally, the hollow carbon / mullite composite fiber is obtained through high-temperature sintering. The process is simple and convenient, the effect is stable, and the prepared fiber is high in hollowness and good in toughness and has better fracture toughness compared with single mullite fiber.

Description

Technical Field

[0001] The invention belongs to the field of thermal insulation ceramic fibers and relates to a hollow carbon / mullite composite fiber and a preparation method thereof. Background Art

[0002] Mullite (3Al2O3·2SiO2) is the only stable binary compound in the Al2O3-SiO2 system and a type of oxide ceramic. Due to its oxidized structure, mullite cannot further oxidize during heating, resulting in excellent high-temperature resistance. Mullite fiber is a polycrystalline material with mullite as the primary crystalline phase. It has low thermal conductivity and excellent high-temperature stability and thermal shock resistance, making it widely used in high-temperature insulating refractory materials.

[0003] The traditional methods for producing mullite fiber are mainly as follows: (1) Melting method: After melting mullite powder, it is formed into fibers by spinning or blowing. The melting method for preparing mullite fiber is simple, but due to the high production temperature, the product is easily formed into a glassy state, which is not conducive to the performance of the fiber. (2) Sol-gel method: Aluminum source (aluminum nitrate, aluminum chloride or aluminum isopropoxide) and silicon source (ethyl orthosilicate) are dissolved in the liquid phase, hydrolyzed and condensed to form a stable transparent sol, and the sol is aged to form a gel with a three-dimensional network structure. Finally, mullite fiber can be obtained by spinning technology. The mullite fiber prepared by the sol-gel method has high purity and low synthesis temperature, but the production process is complex, the cycle is long, the raw materials are expensive, and there are micropores in the gel, which leads to defects in the fiber. The traditional method for preparing mullite fiber is complex and the cost is high. At the same time, the mullite fibers prepared by the traditional method are all solid fibers, which is not conducive to further improvement of thermal insulation performance.

[0004] The main existing method for preparing hollow mullite fibers is the template impregnation method, which involves using a natural hollow fiber template, impregnating and drying it, and then sintering it in an air atmosphere to produce the hollow mullite fibers. While this method is simple and efficient, it suffers from poor mechanical properties and is prone to breakage and fracture.

[0005] The current method for preparing carbon / mullite composite materials mainly involves uniformly mixing aluminum oxide powder, silicon oxide powder and carbon fiber, and then using a hot pressing sintering method under argon protection to obtain a block carbon / mullite composite material. The carbon / mullite composite material prepared by this method has a low carbon content, and the carbon fiber inside cannot be retained at high temperatures. In addition, the carbon / mullite composite material prepared by this method mainly exists in the form of blocks, which greatly reduces its application scenarios. Summary of the Invention

[0006] The present invention aims to provide a hollow carbon / mullite composite fiber and a preparation method thereof. The present invention utilizes hollow carbon fibers to prepare hollow carbon / mullite composite fibers with low density, high hollowness, good thermal insulation performance and excellent mechanical properties.

[0007] The technical solutions for achieving the purpose of the present invention are as follows:

[0008] The preparation method of hollow carbon / mullite composite fiber comprises the following steps:

[0009] (1) Preparation of hollow carbon fibers:

[0010] The hollow fiber is washed and dried, placed in a tube furnace, sintered at 700-900°C in an argon atmosphere, and kept warm for 1-3 hours. After sintering, it is cooled to room temperature to obtain a hollow carbon fiber;

[0011] (2) Preparation of impregnation solution:

[0012] Aluminum nitrate nonahydrate and ethyl orthosilicate were mixed according to n(Al 3+ ):n(Si 4+ )=3:1 is dissolved in anhydrous ethanol to obtain an impregnation solution, wherein the concentration of aluminum nitrate nonahydrate is 10-30wt%;

[0013] (3) Preparation of precursor fibers:

[0014] The hollow carbon fibers are immersed in the impregnation liquid, taken out after the impregnation is complete, drained, and dried to obtain precursor fibers;

[0015] (4) Preparation of hollow carbon / mullite composite fibers:

[0016] The precursor fiber is placed in a tubular furnace, sintered at 900-1300° C. in an argon atmosphere, kept warm for 2-4 hours, and cooled along with the furnace to obtain a hollow carbon fiber mullite composite material.

[0017] Preferably, in step (1), the hollow fiber is radish, reed or kapok fiber.

[0018] Preferably, in step (1), the washing times are 3 to 5 times, the drying temperature is 40 to 80° C., the drying time is 10 to 20 h, and the heating rate during the sintering process is 2 to 5° C. / min.

[0019] Preferably, in step (1), the washing times are 3 times, the drying temperature is 50°C, the drying time is 12 hours, the sintering temperature is 800°C, the holding time is 1 hour, and the heating rate during the sintering process is 3°C / min.

[0020] Preferably, in step (2), the concentration of aluminum nitrate nonahydrate in the impregnation solution is 15 wt %.

[0021] Preferably, in step (3), the impregnation time of the hollow carbon fiber is 1 hour, the drying temperature is 70° C., and the drying time is 12 hours.

[0022] Preferably, in step (4), the sintering temperature is 1000° C., the heating rate during the sintering process is 5° C. / min, and the holding time is 3 h.

[0023] The present invention provides hollow carbon / mullite composite fibers prepared by the above preparation method.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] The hollow carbon / mullite composite fiber prepared by the present invention inherits the hollow structure of hollow carbon fiber, and hollow carbon fiber also retains the hollow structure of natural fiber. Compared with pure mullite fiber, it has unique hollow structure, lower thermal conductivity, better heat preservation effect, and simultaneously has the reinforcing effect of carbon fiber, so that fiber has higher bending strength, tensile strength and fracture toughness. In addition, compared with other carbon / mullite composite materials, in the hollow carbon / mullite composite fiber prepared by the present invention, mullite is tightly wrapped around carbon fiber, so that it is not oxidized, and exists in a fibrous form, and can be subsequently processed into fiber cloth, fiber mat, fiberboard etc., with a wide range of application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 These are morphological images of the natural hollow fiber Radix Astragali in Example 1, wherein a: macroscopic image; b: high-magnification SEM image; c: low-magnification SEM image.

[0027] Figure 2 This is a microscopic morphology of the hollow carbon fiber obtained in Example 2.

[0028] Figure 3 This is a physical picture of the hollow carbon fiber obtained in Example 2.

[0029] Figure 4 3 is a fiber morphology diagram of the hollow carbon / mullite composite fiber obtained in Example 3.

[0030] Figure 5 This is a photo of the hollow carbon / mullite composite fiber obtained in Example 3.

[0031] Figure 6 3 is the XRD pattern of the hollow carbon / mullite composite fiber obtained in Example 3. DETAILED DESCRIPTION

[0032] The present invention will be described in detail below with reference to specific embodiments and accompanying drawings.

[0033] Example 1

[0034] The natural hollow fiber radish is initially processed as follows:

[0035] Peel the radish fruit, remove the seeds, and obtain the radish fiber.

[0036] Figure 1 Figures (a) and (b) show the morphology of radish fibers. A macroscopic image shows radish fibers, while b shows a high-magnification SEM image and c shows a low-magnification SEM image. The images show that radish fibers appear curly, long, and fluffy under macroscopic observation, while smooth and flat, with a hollow structure, under microscopic observation.

[0037] Example 2

[0038] The natural hollow fiber radish is carbonized as follows:

[0039] (1) Wash the radish fiber three times with deionized water to remove impurities in the fiber, and then dry the washed radish fiber in a drying oven at 50°C for 12 hours to obtain clean and dry radish fiber;

[0040] (2) The clean and dry radish fiber was placed in a tubular furnace and heated to 800°C at a heating rate of 3°C / min under an argon atmosphere. After keeping the temperature for 1 hour, the fiber was cooled in the furnace to obtain hollow carbon fibers.

[0041] from Figure 2 It can be seen that the carbon fiber retains the hollow structure of the radish fiber very well.

[0042] Example 3

[0043] The hollow carbon fiber mullite composite material is prepared as follows:

[0044] (1) 2.8339 g of aluminum nitrate nonahydrate and 0.5246 g of ethyl orthosilicate were dissolved in 10 ml of ethanol to prepare an impregnation solution having an aluminum nitrate nonahydrate concentration of 15 wt %.

[0045] (2) Immerse 1.5 g of hollow carbon fibers in the impregnation solution, immerse for 1 h, drain the excess solution, and dry in a drying oven at 70 °C for 12 h to obtain precursor fibers;

[0046] (3) The precursor fiber was placed in a tubular furnace and sintered to 1000°C in an argon atmosphere at a heating rate of 5°C / min. After being kept warm for 3 hours, the fiber was cooled in the furnace to obtain a hollow carbon / mullite composite fiber.

[0047] from Figure 4 It can be seen that the hollow carbon / mullite composite fiber prepared in Example 3 well inherits the hollow structure of the hollow carbon fiber.

[0048] from Figure 6It can be seen that the hollow carbon / mullite composite fiber prepared in Example 3 successfully synthesized the mullite crystal phase on the basis of retaining the carbon element.

Claims

1. A method for preparing hollow carbon / mullite composite fibers, characterized in that: The steps include: (1) Preparation of hollow carbon fibers: The hollow fiber was washed and dried, then placed in a tube furnace and sintered at 700-900 °C in an argon atmosphere for 1-3 h. After sintering, it was cooled to room temperature to obtain hollow carbon fibers. (2) Preparation of impregnation solution: Aluminum nitrate nonahydrate and ethyl orthosilicate were mixed according to n(Al 3+ ):n(Si 4+ )=3:1 is dissolved in anhydrous ethanol to obtain an impregnation solution, wherein the concentration of aluminum nitrate nonahydrate is 10~30 wt%; (3) Preparation of precursor fibers: The hollow carbon fibers are immersed in the impregnation liquid, taken out after the impregnation is complete, drained, and dried to obtain precursor fibers; (4) Preparation of hollow carbon / mullite composite fibers: The precursor fiber is placed in a tubular furnace, sintered at 900-1300° C. in an argon atmosphere, kept warm for 2-4 hours, and cooled along with the furnace to obtain a hollow carbon fiber mullite composite material.

2. The preparation method according to claim 1, characterized in that In step (1), the hollow fiber is radish, reed or kapok fiber.

3. The preparation method according to claim 1, wherein In step (1), the washing times are 3 to 5 times, the drying temperature is 40 to 80°C, the drying time is 10 to 20 h, and the heating rate during the sintering process is 2 to 5°C / min.

4. The preparation method according to claim 1, wherein In step (1), the washing times are 3 times, the drying temperature is 50 °C, the drying time is 12 h, the sintering temperature is 800 °C, the holding time is 1 h, and the heating rate during the sintering process is 3 °C / min.

5. The preparation method according to claim 1, characterized in that In step (2), the concentration of aluminum nitrate nonahydrate in the impregnation solution is 15 wt %.

6. The preparation method according to claim 1, wherein In step (3), the impregnation time of the hollow carbon fiber is 1 h, the drying temperature is 70 °C, and the drying time is 12 h.

7. The preparation method according to claim 1, characterized in that In step (4), the sintering temperature is 1000°C, the heating rate during the sintering process is 5°C / min, and the holding time is 3h.

8. The hollow carbon / mullite composite fiber prepared according to the preparation method according to any one of claims 1 to 7.

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