Mullite reinforced zirconium oxide inorganic fiber and preparation method thereof

Abstract

The invention relates to a micro-nano mullite reinforced zirconium oxide inorganic fiber, the phase of the micro-nano mullite reinforced zirconium oxide inorganic fiber is composed of two phases of tetragonal zirconium oxide and mullite, the fiber diameter is 0.1-1.5 [mu] m, and crystal phase stability, microstructure stability and fiber flexibility are maintained at the temperature from room temperature to high temperature of 1400 DEG C. The preparation method comprises the following steps: taking acidic aluminum sol, silica sol, zirconium sol and yttrium salt as metal sources, taking a high-molecular polymer as a spinning auxiliary agent, obtaining micro-nano mullite reinforced zirconium oxide precursor fibers through an electrostatic spinning technology, and carrying out heat treatment on the precursor fibers to obtain the mullite reinforced zirconium oxide inorganic fibers. The invention has the advantages of wide raw material source, cheap raw materials, stable system, good spinnability, high solid content, simple preparation process and the like. The prepared inorganic fiber has good high-temperature stability and flexibility in a wide temperature range from room temperature to high temperature of 1400 DEG C, and has application prospects in the fields of aerospace vehicle flexible heat insulation felts, high-temperature crystal growing furnaces and other high-temperature flexible heat insulation and heat preservation.

Description

Technical Field

[0001] The present invention relates to an oxide inorganic fiber and a preparation method thereof, belonging to the field of inorganic non-metallic materials. Background Art

[0002] Zirconia fiber has the characteristics of high melting point, low thermal conductivity, oxidation resistance, acid and alkali erosion resistance, and oxide erosion resistance. It is an excellent multifunctional structural material and has broad application prospects in the fields of high-temperature heat insulation, low-temperature heat preservation, water environment purification, high-temperature gas-solid separation, catalyst carriers, etc. In addition, the one-dimensional fiber structure of zirconia fiber endows it with new advantages such as light weight, small volume density, lower thermal conductivity, and excellent thermal shock stability, making zirconia fiber show more excellent application advantages in high-temperature flexible adiabatic heat preservation fields such as flexible heat insulation felts for aerospace vehicles and high-temperature crystal growth furnaces.

[0003] In recent years, with the progress of electrospinning technology, electrospray spinning technology, and centrifugal electrospinning technology, the preparation of zirconia micro-nano fibers has developed rapidly. The micro-nanoization of zirconia fiber can not only improve the flexibility of zirconia fiber but also further reduce the thermal conductivity of fiber products, improve the high-temperature adiabatic performance of fibers and their products, and further expand the application of zirconia fiber in the high-temperature flexible field. Therefore, it is of great significance to break through and realize the industrial production of micro-nano zirconia fiber. Invention patents CN106929927A and CN106929947A respectively realized the preparation of sub-micron zirconia crystal fibers through zirconium acetylacetonate and zirconium oxyacetate sols to reduce the diameter of zirconia fiber and improve the high-temperature heat insulation performance and mechanical properties of the fiber. This invention patent provides a sub-micron zirconia crystal fiber that can be used for a long time under ultra-high temperature conditions of 1800 °C and above; in 2021, the article "An efficient strategy for reinforcing flexible ceramic membranes" was published, and the flexible composite fiber prepared by compounding zirconia and silica can be used at a temperature of up to 1000 °C; in 2022, the article "Highly flexible ceramic nanofibrous membranes for superior thermal insulation and fire retardancy" prepared sub-micron yttrium-stabilized zirconia fibers by electrospinning method, and the zirconia fibers maintained good flexibility at a temperature as high as 1200 °C. Zirconia micro-nano fibers can maintain the integrity of fiber morphology and crystal phase stability at temperatures above 1200 °C, but the growth and significant growth of grains in zirconia fibers lead to an increase in fiber brittleness, making it difficult to ensure that the fibers maintain good flexibility above 1200 °C, thus limiting the application of sub-micron zirconia fibers in the high-temperature flexible field.

[0004] Therefore, on the basis of ensuring the good spinnability of zirconia precursor sol, the high-temperature heat insulation performance and high-temperature stability of zirconia fibers, in order to further improve the flexibility of micro-nano zirconia fibers, starting from the perspective of the second phase, by introducing mullite with a high melting point, a complex crystal structure, and a low grain growth rate, the growth of zirconia grains is hindered, the high-temperature flexibility of zirconia fibers is improved, the use temperature limit of maintaining high-temperature flexibility of sub-micron zirconia fibers at 1200 °C is broken through, and the industrial application of flexible micro-nano zirconia fibers is promoted. The present invention is specifically proposed. Summary of the Invention

[0005] Aiming at the problems of unstable microstructure and insufficient high-temperature flexibility caused by rapid grain growth of micron-sized zirconia fibers at high temperatures of 1200 °C and above in the prior art, the present invention provides a method for strengthening micro-nano zirconia fibers by introducing mullite. The addition of a small amount of mullite can hinder the grain growth of zirconia under high-temperature conditions, and further improve the microstructure stability and high-temperature flexibility of micro-nano zirconia fibers. In particular, the zirconia-based fibers prepared by the present invention break through the use temperature limit of 1200 °C for micro-nano zirconia fibers with good flexibility, and can maintain good crystal phase stability, microstructure stability and high-temperature flexibility at 1400 °C, providing a new way for the engineering application of flexible zirconia fibers. Overview of the Invention

[0007] In the present invention, the second-phase mullite is added to zirconia fibers. By using the second phase to hinder the growth of zirconia grains, the high-temperature microstructure stability and flexibility of zirconia fibers are improved. Compared with the existing micro-nano zirconia fibers and their preparation technologies, firstly, theoretically, mullite has a high melting point, good crystal phase stability, a complex crystal structure, and a slow grain growth rate within the temperature range of use of micro-nano zirconia fibers, and does not react with zirconia. The addition of a small amount of mullite can further hinder the grain growth of zirconia on the premise of ensuring the basic properties of zirconia fibers, thereby improving the high-temperature microstructure stability and high-temperature flexibility of zirconia fibers; secondly, in terms of fiber preparation process technology, the present invention uses the sol-gel method combined with electrospinning to prepare mullite-reinforced micro-nano zirconia fibers. The raw materials of zirconia sol, alumina sol, and silica sol used in the invention are widely available in the market, the system is stable, the spinnability is good, the solid content is high, the raw materials are cheap, and the electrospinning technology has a simple preparation process. It can also be combined with centrifugal spinning and blow spinning technologies, providing a good raw material and process technology basis for the industrialization of the present invention; finally, the mullite-reinforced zirconia fibers prepared by the present invention can not only maintain good crystal phase stability of tetragonal zirconia phase and mullite phase and fiber morphology stability at 1400 °C, but also have small grain sizes, good microstructure stability and flexibility, breaking through the 1200 °C use temperature limit of micro-nano flexible zirconia fibers, providing an idea for the engineering application of flexible zirconia fibers in high-temperature fields. Detailed description of the invention

[0009] The technical solution of the present invention is as follows:

[0010] According to the present invention, a method for preparing micro-nano mullite-reinforced zirconia inorganic fibers includes the following steps:

[0011] (1) Using commercially available acidic silica sol and alumina sol, and mixing the silica sol and alumina sol according to a molar ratio of Si:Al = 1:3 - 4 to obtain a mullite precursor sol;

[0012] (2) Mixing the mullite precursor sol obtained in step (1) with zirconia sol according to a molar ratio of Zr:Al = 1:0.2 - 2 to obtain a mullite-reinforced zirconia composite sol;

[0013] (3) Adding an organic polymer solution with a mass fraction of 0.5 - 10% to the mullite and zirconia composite sol obtained in step (2), stirring and dissolving to obtain a mullite-reinforced zirconia precursor sol;

[0014] (4) Using electrospinning technology on the mullite-reinforced zirconia precursor sol obtained in step (3) to obtain mullite-reinforced zirconia precursor fibers;

[0015] (5) The mullite-reinforced zirconia precursor fibers obtained in step (4) are obtained by heat treatment to obtain the ultrafine inorganic fibers.

[0016] Preferably according to the present invention, in step (1), the molar ratio of Si:Al = 1:2.8 - 3.2, and the acidic silica sol and acidic alumina sol have a pH value of: pH = 3 - 4;

[0017] Preferably according to the present invention, in step (2), the molar ratio of Zr:Al = 1:0.2 - 0.6, and the zirconia sol is one of formic acid zirconia sol and acetic acid zirconia sol or a mixed sol thereof;

[0018] Preferably according to the present invention, in step (3), the organic polymer solution is one of polyethylene oxide and polyvinyl alcohol or a mixed solution thereof, wherein the mass fraction of polyethylene oxide is 0.5 - 2%, and the mass fraction of polyvinyl alcohol is 6 - 8%.

[0019] Preferably according to the present invention, in step (4), the process conditions of the electrospinning method are: the sol injection rate is 0.8 - 1.5 mL / h, the spinning voltage is 16 - 25 kV, the fiber receiving distance is 15 - 30 cm, the spinning environment temperature is 20 - 45 °C, and the spinning environment humidity is 20 - 50%.

[0020] Preferably according to the present invention, in step (5), the heat treatment system is: heating at a heating rate of 2 - 4 °C / min to 500 - 600 °C, holding for 60 - 120 min; then heating at a heating rate of 2 - 5 °C / min to 800 - 1500 °C, holding for 1 - 2 h.

[0021] The excellent effects of the present invention are as follows:

[0022] 1. The raw materials used in the present invention are widely sourced in the market, the system is stable, the spinnability is good, the solid content is high, the raw materials are inexpensive, and the preparation process of the electrospinning technology is simple. In addition to the electrospinning technology, centrifugal spinning and blow spinning technologies can also be combined, providing a good raw material and process technology basis for the industrialization of the present invention.

[0023] 2. The micro-nano mullite-reinforced zirconia inorganic fibers prepared by the present invention can not only maintain good crystal phase stability and fiber morphology stability of the tetragonal zirconia phase and mullite phase at a high temperature of 1400 °C, but also have small grain sizes, good microstructural stability and flexibility. Description of the Drawings

[0024] Figure 1 It is a digital photo after the micro-nano mullite-reinforced zirconia fiber membrane obtained in Example 1 is heat-treated to 1400 °C and held for 2 h and then bent 180 degrees.

[0025] Figure 2 XRD pattern of the micro-nano mullite reinforced zirconia fiber obtained in Example 1 after heat treatment at 1400 °C for 2 h

[0026] Figure 3 SEM image of the micro-nano mullite reinforced zirconia fiber obtained in Example 1 after heat treatment at 1400 °C for 2 h Detailed implementation manners

[0027] The present invention will be further described below by way of examples in conjunction with the accompanying drawings, but not limited thereto.

[0028] The raw materials used in the examples are all commercially available raw materials.

[0029] Example 1:

[0030] A preparation method of micro-nano mullite reinforced zirconia inorganic fiber, comprising the following steps:

[0031] (1) According to the molar ratio Al:Si = 3:1, hydroxyaluminum chloride sol with an alumina content of 17.3% was dissolved in tetraethyl orthosilicate silica sol with a silica content of 12.0% to obtain a mullite precursor sol;

[0032] (2) According to the molar ratio Zr:Al = 4:3, zirconium acetate sol with a zirconia content of 20.9% was added to the mullite precursor sol, and yttrium nitrate was used as the yttrium source, and yttrium nitrate with a molar ratio Zr:Y = 97:6 was added, and stirred and dissolved to obtain a mullite reinforced zirconia composite sol;

[0033] (3) 6% by mass of polyvinyl alcohol was added to the mullite reinforced zirconia composite sol, and then 1% by mass of polyethylene oxide was added, and stirred and dissolved to obtain a mullite reinforced zirconia precursor sol;

[0034] (4) The mullite reinforced zirconia precursor sol obtained in step (3) was prepared into a mullite reinforced zirconia precursor by electrospinning. The electrospinning process conditions were: voltage 16 kV, spinning distance 16 cm, injection rate 1.0 mL / h, ambient temperature 25 - 35 °C, and ambient humidity 30% - 40%.

[0035] (5) The mullite reinforced zirconia precursor fiber obtained in step (4) was heated to 600 °C at a heating rate of 2 °C / min in air, and then heated to 1200 °C at a heating rate of 4 °C / min, and held for 2 h to obtain a mullite reinforced zirconia fiber.

[0036] To further illustrate the high-temperature flexibility of the prepared mullite-reinforced zirconia fibers, the mullite-reinforced zirconia fibers were heat-treated to 1400 °C and held for 2 h. The photograph of the obtained mullite-reinforced zirconia fiber membrane after being bent 180° is as Figure 1 shown.

[0037] Example 2:

[0038] As described in Example 1, the difference is that the molar ratio Zr:Al = 4:3 in step (2) is replaced with the molar ratio Zr:Al = 3:2. To further illustrate the high-temperature crystal phase stability and microstructural stability of the obtained mullite-reinforced zirconia fibers, the XRD pattern of the obtained mullite-reinforced zirconia fibers after being heat-treated to 1400 °C and held for 2 h is as Figure 2 shown, and the SEM image of the fibers heat-treated to 1400 °C and held for 2 h is as Figure 3 shown.

[0039] Example 3:

[0040] As described in Example 1, the difference is that the aluminum hydroxychloride sol in step (1) is replaced with an aluminum carboxylate sol.

[0041] Example 4:

[0042] As described in Example 1, the difference is that the tetraethyl orthosilicate silica sol in step (1) is replaced with a silica sol prepared from an ion-exchanged sodium silicate solution.

[0043] Example 5:

[0044] As described in Example 1, the difference is that the zirconium acetate sol in step (2) is replaced with a zirconium formate sol.

[0045] Example 6:

[0046] As described in Example 1, the difference is that the polyethylene oxide in step (3) is replaced with polyvinylpyrrolidone.

Claims

1. A micro-nano mullite reinforced zirconia inorganic fiber, characterized in that: The inorganic fiber is composed of tetragonal zirconia and mullite, with a fiber diameter of 0.1 μm to 1.5 μm, and maintains crystal phase stability, microstructure stability and fiber flexibility from room temperature to high temperature of 1400°C; The mullite reinforced zirconia inorganic fiber is prepared by the following steps: (1) mixing silica sol and aluminum sol according to a molar ratio of Si:Al=1:3-4 to obtain a mullite precursor sol; (2) mixing the mullite precursor sol obtained in step (1) with the zirconia sol according to a molar ratio of Zr:Al=1:0.2-2 to obtain a mullite-reinforced zirconia composite sol; (3) adding an organic polymer solution to the mullite and zirconia composite sol obtained in step (2), stirring and dissolving, and obtaining a mullite-reinforced zirconia precursor sol; (4) using the mullite-reinforced zirconia precursor sol obtained in step (3) to obtain mullite-reinforced zirconia precursor fibers; (5) The mullite-reinforced zirconia precursor fiber obtained in step (4) is subjected to heat treatment to obtain the ultrafine inorganic fiber.

2. The mullite reinforced zirconia inorganic fiber according to claim 1, characterized in that The silica sol described in step (1) is an acidic silica sol with a pH value of 2 to 5, and the aluminum sol described in step (1) is one or a combination of acidic carboxylate aluminum sol and hydroxyl chloride aluminum sol with a pH value of 2 to 5.

3. The mullite reinforced zirconia inorganic fiber according to claim 1, characterized in that The zirconium oxide sol described in step (2) is one of zirconium formate sol, zirconium acetate sol, zirconium propionate sol, zirconium acetylacetonate sol, zirconium oxychloride sol or a combination thereof, and the crystal phase stabilizer in the zirconium oxide sol is one of yttrium nitrate, yttrium chloride, yttrium acetate or a combination thereof, and the molar ratio Zr:Y is 100:5~15.

4. The mullite reinforced zirconia inorganic fiber according to claim 1, characterized in that The organic high molecular polymer described in step (3) is one of polyvinyl pyrrolidone, polyethylene oxide, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral or a combination thereof, and the mass fraction of the high molecular polymer in the solution is 0.5 to 10%.

5. The mullite reinforced zirconia inorganic fiber according to claim 1, characterized in that The process conditions of the electrospinning method described in step (4) are: sol injection rate of 0.3-4.0 mL / h, spinning voltage of 8-100 kV, fiber receiving distance of 10-80 cm, spinning environment temperature of 5-75°C, and spinning environment humidity of 10-60%.

6. The mullite reinforced zirconia inorganic fiber according to claim 1, characterized in that The heat treatment process system described in step (5) is: heating to 300-600°C at a heating rate of 0.5-5°C / min, and keeping warm for 20-120min; then heating to 800-1500°C at a heating rate of 2-10°C / min, and keeping warm for 0.5-5h, and the atmosphere condition is air.

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