A magnesium-based rare earth hexaaluminate inorganic fiber and its preparation method

Abstract

This invention relates to a magnesium-based rare earth hexaaluminate inorganic fiber and its preparation method, wherein the main crystalline phase of the magnesium-based rare earth hexaaluminate is composed of ReMgAl 11 O 19 Composed of Re = La, Ce, Pr, Nd, Eu, the fibers have a diameter of 0.1 μm to 7.0 μm and a sheet-like microstructure. They maintain stable microstructure, crystal phase, and morphology within a temperature range of -196℃ to 1750℃. The preparation method involves dissolving an aluminum sol, rare earth salts, magnesium salts, and a polymer in water to obtain a sol, followed by electrospinning or centrifugation to obtain precursor fibers. These precursor fibers are then subjected to high-temperature heat treatment to obtain magnesium-based rare earth hexaaluminate inorganic fibers. This invention utilizes inexpensive raw materials, and the prepared inorganic fibers exhibit structural stability over a wide temperature range, showing broad application prospects in structural reinforcement, thermal insulation, and separation and purification.

Description

Technical Field

[0001] This invention relates to a magnesium-based rare earth hexaaluminate inorganic fiber and its preparation method, belonging to the field of inorganic non-metallic materials. Background Technology

[0002] In recent years, with the increasing demand for thermal insulation and high-temperature filtration in fields such as energy conservation and emission reduction, high-temperature thermal protection, battery safety protection, special equipment thermal protection, and high-temperature flue gas filtration and high-temperature dust filtration, ceramic fibers and their products have broad application prospects in these fields due to their excellent high-temperature structural stability, low thermal conductivity, low density, high oxidation resistance, and high chemical stability. Among many oxide fibers, such as alumina fibers, zirconium oxide fibers, aluminosilicate fibers, and mullite fibers, the main problem in high-temperature applications remains fiber brittleness or even pulverization caused by grain growth. Therefore, improving the high-temperature stability of grains is still urgent for improving the high-temperature stability of fibers. From the perspective of microstructure, lamellar crystals have better high-temperature stability than granular grains. Obtaining micro / nanofibers composed of lamellar structures is an effective way to improve the high-temperature stability of fibers.

[0003] Magnesium-based rare earth hexaaluminate ReMgAl 11 O 19 (Re = La, Ce, Pr, Nd, Eu) not only possesses a high melting point, low thermal conductivity, and excellent oxidation and sintering resistance, but its unique crystal structure can also induce the formation of lamellar crystal structures, making it a potentially high-performance high-temperature ceramic fiber. In 2008, the article "Sintering-resistant hollow fibers of LaMgAl" was published. 11 O 19 A hollow-structured LaMgAl was prepared by electrospinning. 11 O 19Although the prepared fibers exhibit brittleness due to their numerous pores, their lamellar crystal microstructure demonstrates excellent high-temperature stability. In 2023, the invention patent "A Rare Earth Aluminate Inorganic Fiber and Its Preparation Method" disclosed a method for preparing rare earth aluminate inorganic fibers. The inorganic fibers prepared by this invention consist of two main crystalline phases, with the formation temperature exceeding 1200℃. The microstructure comprises both granular and lamellar structures, exhibiting excellent high-temperature structural stability. Other reports on rare earth aluminate fibers are limited. From the above research, it can be seen that research on magnesium-based rare earth aluminate inorganic fibers is scarce. While the lamellar structure of magnesium-based rare earth lanthanum aluminate fibers reported in the literature exhibits excellent high-temperature stability, it still suffers from high porosity, non-dense structure, and high fiber brittleness, requiring further optimization.

[0004] Therefore, in order to prepare high-performance magnesium-based rare earth hexaaluminate inorganic fibers, optimize the precursor sol, increase the solid content of magnesium-based rare earth hexaaluminate in the sol, reduce the formation temperature of the hexaaluminate crystal phase, increase the content of lamellar structure in the fiber microstructure, prepare high-temperature stable and dense magnesium-based rare earth hexaaluminate fibers, improve the service temperature of flexible oxide fibers, and promote the application of magnesium-based rare earth hexaaluminate fibers in energy conservation and emission reduction, high-temperature thermal protection, battery safety protection, special equipment thermal protection, high-temperature flue gas filtration, high-temperature dust filtration, and other fields, this invention is proposed. Summary of the Invention

[0005] To address the problems of existing technologies, such as low spinnability of magnesium-based rare earth hexaaluminate inorganic fiber precursor sol, low solid content, high main crystal phase formation temperature, high fiber porosity, and insufficient lamellar structure in the microstructure, and to further improve the high-temperature stability of the oxide fiber microstructure, this invention provides a novel method for preparing magnesium-based rare earth hexaaluminate inorganic fibers. This provides a new method and approach for the development of novel ceramic fibers and the engineering application of magnesium-based rare earth hexaaluminate inorganic fibers. Invention Overview

[0007] The main crystalline phase of the magnesium-based rare earth hexaaluminate inorganic fiber has the molecular formula ReMgAl. 11 O 19 (Re=La,Ce,Pr,Nd,Eu), the main crystalline phase content in the fiber is not less than 90%, and the main crystalline phase exists mainly in a lamellar structure in the microstructure. The fiber diameter is 0.1μm~7.0μm. The fiber maintains its flexibility and appearance integrity in the temperature range from low temperature -196℃ to high temperature 1600℃, and maintains the stability of the fiber microstructure, crystal phase and morphology in the temperature range from low temperature -196℃ to high temperature 1750℃.

[0008] The invention utilizes aluminum sources with certain spinnability, such as aluminum chloride, aluminum hydroxychloride, and aluminum carboxylate, as precursors to significantly improve the spinnability of the sol. Using commercially available rare earth metal salts and magnesium salts as the rare earth and magnesium sources, respectively, significantly reduces the preparation cost of the sol. Then, using water as a solvent and a polymer as a spinning aid, precursor fibers are prepared by electrospinning or centrifugal spinning, followed by high-temperature heat treatment to obtain the main crystalline phase with the molecular formula ReMgAl. 11 O 19 Magnesium-based rare earth hexaaluminate inorganic fibers (Re=La,Ce,Pr,Nd,Eu) have a microstructure that is mainly sheet-like.

[0009] Compared with existing methods for preparing magnesium-based rare earth hexaaluminate inorganic fibers, the main crystalline phase is the same as that of existing methods, namely ReMgAl. 11 O 19 (Re = La, Ce, Pr, Nd, Eu). The technical advantages of this invention are that the raw materials are economical, inexpensive, and readily available; the sol solids content is high; the spinnability is good; the fiber microstructure has interwoven lamellar structures, a dense structure, and low porosity; and the fiber maintains flexibility and intact appearance within a temperature range from -196℃ to 1600℃. Furthermore, the fiber microstructure, crystal phase, and morphology remain stable within a temperature range from -196℃ to 1750℃, demonstrating broad application prospects under wide temperature range conditions, including both high and low temperatures.

[0010] Compared with existing methods for preparing rare earth aluminate inorganic fibers, the addition of a magnesium source promotes the formation of a single hexagonal ReMgAl crystal phase as the main crystalline phase of magnesium-based rare earth hexaaluminate inorganic fibers. 11 O 19 (Re=La,Ce,Pr,Nd,Eu), the initial formation temperature of the main crystal phase is 1150℃, the microstructure of the fiber is mainly composed of lamellar structure, and the microstructure has better high temperature stability.

[0011] In addition, the electrospinning and centrifugal spinning technologies provided by this invention can not only obtain magnesium-based rare earth hexaaluminate inorganic fiber cotton, but also, through collection devices, rolling devices and needle punching devices adapted to the technology, obtain magnesium-based rare earth hexaaluminate inorganic fiber membranes, fiber paper, fiber felt, fiber blankets and needle-punched blankets with high-temperature structural stability and good flexibility. Invention Details

[0013] The technical solution of the present invention is as follows:

[0014] According to the present invention, a method for preparing magnesium-based rare earth hexaaluminate inorganic fibers includes the following steps:

[0015] (a) Preparation of magnesium-based rare earth hexaaluminate precursor sol

[0016] Aluminum source, rare earth source, and magnesium source were added to water in a molar ratio of Al:Re:Mg = 11:(0.5-2.5):(0.5-2.5) to dissolve and obtain a magnesium-based rare earth hexaaluminate solution with a mass fraction of 8-40%. Under heating and stirring conditions at 20-90°C, a polymer with a mass fraction of 0.2-15% was added to the magnesium-based rare earth hexaaluminate solution and dissolved completely to obtain a magnesium-based rare earth hexaaluminate precursor sol.

[0017] (b) Preparation of magnesium-based rare earth hexaaluminate precursor fibers

[0018] Magnesium-based rare earth hexaaluminate precursor sol obtained in step (a) is used to prepare magnesium-based rare earth hexaaluminate precursor fibers by electrospinning; or the magnesium-based rare earth hexaaluminate precursor sol obtained in step (a) is concentrated under reduced pressure at a temperature of 45 to 90°C to obtain a precursor sol with a viscosity of 5 to 35 Pa·s, and then magnesium-based rare earth hexaaluminate precursor fibers are obtained by centrifugal spinning.

[0019] (c) Preparation of magnesium-based rare earth hexaaluminate fibers

[0020] The magnesium-based rare earth hexaaluminate precursor fiber obtained in step (b) is heated to 450–600°C at a heating rate of 0.5–10°C / min under atmospheric conditions and held for 0–4 h; then heated to 1100–1300°C at a heating rate of 2–10°C / min and held for 1–4 h to obtain magnesium-based rare earth hexaaluminate inorganic fiber.

[0021] According to a preferred embodiment of the present invention, the molar ratio of aluminum source, rare earth source, and magnesium source in step (a) is Al:Re:Mg = 11:(0.5~1.5):(0.5~1.5).

[0022] According to a preferred embodiment of the present invention, the spinning aid described in step (a) is one or a combination of polyvinylpyrrolidone, polyethylene oxide, and polyvinyl alcohol;

[0023] According to a preferred embodiment of the present invention, the mass fraction of the spinning aid in step (a) is 0.8% to 7.5%.

[0024] According to a preferred embodiment of the present invention, the process conditions for the electrospinning method in step (b) are as follows: sol injection rate of 0.6-2.0 mL / h, spinning voltage of 12-30 kV, fiber receiving distance of 15-30 cm, spinning ambient temperature of 20-45 °C, and spinning ambient humidity of 20-55%.

[0025] According to a preferred embodiment of the present invention, the process conditions for the centrifugal spinning method in step (b) are as follows: the spinning environment temperature is 35-85℃, the spinning environment humidity is 25-45%, the centrifuge speed is 18000-24000 r / min, the spinning hole linear velocity is 25-45 m / s, and the spinning hole diameter is 0.20-0.65 mm.

[0026] According to a preferred embodiment of the present invention, the atmosphere described in step (c) is an air atmosphere.

[0027] According to a preferred embodiment of the present invention, the heat treatment process in step (c) is as follows: heating to 400-600°C at a heating rate of 2-5°C / min, and then heating to 1150-1250°C at a heating rate of 4-10°C / min.

[0028] The superior effects of this invention are as follows:

[0029] 1. The aluminum sol, rare earth source and magnesium source used in this invention are widely available, the solvent is water, the cost is low, and the requirements for the spinning environment are low. It has the characteristics of low cost in the preparation of magnesium-based rare earth hexaaluminate inorganic fibers.

[0030] 2. The preparation technology used in this invention belongs to the sol-gel technology. Multiple metal sources can be uniformly mixed at the atomic scale, and the heat treatment temperature is as low as 1150℃ when the main crystalline phase is formed. Compared with the powder preparation technology, the heat treatment temperature is low, which can significantly reduce energy consumption and save production costs.

[0031] 3. The magnesium-based rare earth hexaaluminate inorganic fiber phase prepared in this invention consists of a hexagonal ReMgAl crystal system. 11 O 19 The fiber is composed of (Re = La, Ce, Pr, Nd, Eu) and has a sheet-like microstructure, exhibiting excellent high-temperature crystal phase stability and microstructure stability.

[0032] 4. The magnesium-based rare earth hexaaluminate inorganic fiber prepared by this invention can maintain fiber flexibility and appearance integrity in a temperature range from low temperature -196℃ to high temperature 1600℃, and maintain fiber microstructure stability, crystal phase stability and morphology integrity in a temperature range from low temperature -196℃ to high temperature 1750℃, providing a good structural basis for the application of the fiber in a wide temperature range and extreme environmental conditions.

[0033] 5. The magnesium-based rare earth hexaaluminate inorganic fibers prepared by this invention have excellent high-temperature crystal phase stability and microstructure stability, making them promising for applications in structural reinforcement, thermal insulation, separation and purification. Attached Figure Description

[0034] Figure 1This is the XRD pattern of the magnesium lanthanum hexaaluminate inorganic fiber obtained in Example 1 after heat treatment to 1200°C.

[0035] Figure 2 This is a SEM image of the magnesium lanthanum hexaaluminate inorganic fibers obtained in Example 1 after heat treatment to 1200°C.

[0036] Figure 3 This is a SEM image of the magnesium lanthanum hexaaluminate inorganic fibers obtained in Example 1 after heat treatment to 1500°C.

[0037] Figure 4 This is a SEM image of the magnesium lanthanum hexaaluminate inorganic fibers obtained in Example 2 after heat treatment to 1300°C. Detailed Implementation

[0038] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0039] All raw materials used in the examples were commercially available.

[0040] Example 1:

[0041] A magnesium lanthanum hexaaluminate (LaMgAl) 11 O 19 The method for preparing inorganic fibers includes the following steps:

[0042] (a) 8.00 g of water was added to 50.00 g of 24 wt% aluminum hydroxychloride sol to dissolve and obtain aluminum sol. Lanthanum acetate and magnesium acetate were added to the aluminum sol in a molar ratio of Al:La:Mg = 11:1:1. Then 0.58 g of polyethylene oxide was added and stirred to dissolve to obtain magnesium lanthanum hexaaluminate precursor sol.

[0043] (b) Magnesium lanthanum hexaaluminate precursor fibers were prepared by electrospinning. The electrospinning process conditions were: injection rate of 0.6 mL / h, voltage of 16 kV, spinning distance of 18 cm, ambient humidity of 30% to 40%, and ambient temperature of 25 °C.

[0044] (c) The magnesium-based rare earth lanthanum hexaaluminate precursor fiber membrane obtained in step (b) was heated to 600℃ in air at a heating rate of 1℃ / min, and then to 1200℃ at a heating rate of 2℃ / min, and held at this temperature for 2 hours to obtain magnesium lanthanum hexaaluminate inorganic fibers. The XRD pattern of the prepared magnesium lanthanum hexaaluminate inorganic fibers is shown below. Figure 1 As shown, the SEM image is as follows: Figure 2 As shown.

[0045] To further illustrate the structural stability of lanthanum magnesium hexaaluminate inorganic fibers, SEM images of the lanthanum magnesium hexaaluminate micro / nano inorganic fibers prepared by the above method after heat treatment to 1500℃ are shown below. Figure 3 As shown.

[0046] Example 2:

[0047] A magnesium lanthanum hexaaluminate (LaMgAl) 11 O 19 Preparation method of inorganic fibers

[0048] As described in Example 1, except that the aluminum hydroxide sol in step (a) was replaced with aluminum acetate sol. SEM images of the prepared magnesium lanthanum hexaaluminate inorganic fibers after reheating to 1300°C are shown below. Figure 4 As shown.

[0049] Example 3:

[0050] A magnesium cerium lanthanum hexaaluminate (La 0.5 Ce 0.5 MgAl 11 O 19 Preparation method of inorganic fibers

[0051] As described in Example 1, except that in step (a), lanthanum acetate is replaced with cerium acetate and lanthanum acetate, and the molar ratio Al:La:Mg = 11:1:1 is replaced with Al:La:Ce:Mg = 11:0.5:0.5:1.

[0052] Example 4:

[0053] A magnesium cerium hexaaluminate (CeMgAl) 11 O 19 The method for preparing inorganic fibers is as described in Example 1, except that lanthanum acetate in step (a) is replaced by cerium nitrate.

[0054] Example 5:

[0055] A multi-component magnesium hexaaluminate lanthanum cerium praseodymium neodymium europium (La 0.25 Ce 0.25 Pr 0.25 Nd 0.25 Eu 0.25 MgAl 11 O 19 Preparation method of inorganic fibers

[0056] As described in Example 1, except that lanthanum acetate in step (a) is replaced with cerium acetate, lanthanum acetate, praseodymium nitrate, neodymium nitrate, and europium nitrate, and the molar ratio Al:La:Mg = 11:1:1 is replaced with Al:La:Ce:Pr:Nd:Eu:Mg = 11:0.25:0.25:0.25:0.25:0.25:1.

[0057] Example 6:

[0058] A magnesium lanthanum hexaaluminate (LaMgAl) 11 O 19 Preparation method of inorganic fibers

[0059] As described in Example 1, except that magnesium acetate in step (a) is replaced with magnesium nitrate.

Claims

1. A magnesium-based rare earth hexaaluminate inorganic fiber, characterized in that, The main crystalline phase of the magnesium-based rare earth hexaaluminate has the molecular formula ReMgAl. 11 O 19 Re = one or a combination of La, Ce, Pr, Nd, Eu, the main crystalline phase content in the fiber is not less than 90%, the fiber microstructure is mainly composed of lamellar structure, and the fiber diameter is 0.1μm~7.0μm; The magnesium-based rare earth hexaaluminate fiber is prepared through the following steps: (a) Preparation of magnesium-based rare earth hexaaluminate precursor sol Aluminum source, rare earth source, and magnesium source were added to water in a molar ratio of Al:Re:Mg = 11:(0.5~2.5):(0.5~2.5) to obtain a magnesium-based rare earth hexaaluminate solution with a mass fraction of 8~40%. Under heating and stirring conditions at 20~90℃, a polymer with a mass fraction of 0.2~15% was added to the magnesium-based rare earth hexaaluminate solution and dissolved completely to obtain a magnesium-based rare earth hexaaluminate precursor sol. (b) Preparation of magnesium-based rare earth hexaaluminate precursor fibers Magnesium-based rare earth hexaaluminate precursor sol obtained in step (a) is used to prepare magnesium-based rare earth hexaaluminate precursor fibers by electrospinning; or the magnesium-based rare earth hexaaluminate precursor sol obtained in step (a) is concentrated under reduced pressure at a temperature of 45 to 90°C to obtain a precursor sol with a viscosity of 5 to 35 Pa•s, and then magnesium-based rare earth hexaaluminate precursor fibers are obtained by centrifugal spinning. (c) Preparation of magnesium-based rare earth hexaaluminate fibers The magnesium-based rare earth hexaaluminate precursor fiber obtained in step (b) is heated to 450-600℃ at a heating rate of 0.5-10℃ / min under atmospheric conditions and held for 0-4h; then heated to 1100-1300℃ at a heating rate of 2-10℃ / min and held for 1-4h to obtain magnesium-based rare earth hexaaluminate inorganic fiber.

2. The magnesium-based rare earth hexaaluminate inorganic fiber as described in claim 1, characterized in that, The aluminum source mentioned in step (a) is one or a combination of aluminum chloride, aluminum hydroxychloride, and aluminum carboxylate.

3. The magnesium-based rare earth hexaaluminate inorganic fiber as described in claim 1, characterized in that, The rare earth source in step (a) is one or a combination of rare earth chloride, rare earth acetate, rare earth nitrate, and rare earth sulfate.

4. The magnesium-based rare earth hexaaluminate inorganic fiber as described in claim 1, characterized in that, The magnesium source in step (a) is one or a combination of magnesium chloride, magnesium nitrate, magnesium acetate, magnesium sulfate, magnesium formate, and magnesium propionate.

5. The magnesium-based rare earth hexaaluminate inorganic fiber as described in claim 1, characterized in that, The polymer mentioned in step (a) is one or a combination of polyvinylpyrrolidone, polyethylene oxide, polymethyl methacrylate, polyethylene glycol, and polyvinyl alcohol.

6. The magnesium-based rare earth hexaaluminate inorganic fiber as described in claim 1, characterized in that, The electrospinning process conditions described in step (b) are: spinning distance of 6 to 50 cm, spinning voltage of 6 to 45 kV, sol propulsion rate of 0.25 to 5.0 mL / h, ambient temperature of 20 to 105 °C, and ambient humidity of 10 to 65%.

7. The magnesium-based rare earth hexaaluminate inorganic fiber as described in claim 1, characterized in that, The process conditions for the centrifugal spinning method described in step (b) are as follows: the spinning environment temperature is 15-105℃, the spinning environment humidity is 10-65%, the centrifuge speed is 12000-32000 r / min, the spinning hole linear velocity is 20-60 m / s, and the spinning hole diameter is 0.15-0.95 mm.

8. The magnesium-based rare earth hexaaluminate inorganic fiber as described in claim 1, characterized in that, The atmosphere described in step (c) is air or water vapor.

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