A class of aluminum-magnesium rare earth-diketone coordination polymer precursors, rare earth magnesium aluminate fibers and their preparation methods

Abstract

This invention relates to a class of aluminum-magnesium rare earth-diketone coordination polymer precursors, rare earth magnesium aluminate fibers, and their preparation methods. The invention first involves adding an aluminum source, a magnesium source, and a rare earth source to a mixture of water and an organic solvent, introducing a β-diketone compound as a ligand source for coordination to obtain aluminum-magnesium rare earth-diketone coordination polymer precursor powder. Then, using the aluminum-magnesium rare earth-diketone coordination polymer precursor as raw material, a small amount of spinning aid is added to obtain a spinning solution. After electrospinning and heat treatment, rare earth magnesium hexaaluminate fibers are obtained. The rare earth magnesium hexaaluminate fibers obtained by this invention have a uniform and adjustable diameter, a dense structure, and plate-like surface grains. They can be used for extended periods at temperatures above 1200°C and have broad application prospects in ceramic refractory materials, aerospace thermal protection, high-temperature energy and metallurgical industries, adsorption catalysis and environmental protection, oil-water separation, and sound absorption and noise reduction.

Description

Technical Field

[0001] This invention relates to a class of aluminum-magnesium rare earth-diketone coordination polymer precursors, rare earth magnesium aluminate fibers and their preparation methods, belonging to the field of inorganic functional material synthesis technology. Background Technology

[0002] Hexaaluminates are hexagonal (space group P63 / mmc) aluminate compounds with a lamellar crystal structure obtained through heat treatment based on the alumina system. In their lamellar crystal structure, the grains are thin lamellae with a high aspect ratio and randomly arranged layers. Compared with traditional high-temperature insulation materials (such as alumina, magnesium oxide, mullite, and spinel), hexaaluminates have a lower thermal conductivity and better insulation performance. Even in high-temperature environments exceeding 1200 °C, hexaaluminates still exhibit excellent phase stability, sintering resistance, and a high specific surface area. During growth, the surface energy continuously increases, resulting in a relatively slow sintering process; the good sintering resistance also determines that the material has a low volume shrinkage rate, thereby improving the reliability and service life of hexaaluminate materials in the field of thermal protection, thus making them a highly promising next-generation high-temperature material. Furthermore, rare-earth hexaaluminates (LnMgAl) with a magnetoplumbleite-type structure... 11 O 19 Materials containing Ln (La, Ce, Pr, Nd, Sm, Eu, Gd) have been successively developed, showing potential application value and broad prospects in the protection of hot-end components of next-generation hypersonic aerospace engines. Meanwhile, due to their excellent thermal stability, thermal insulation, and optical properties, the related properties and research of rare-earth hexaaluminates in high-temperature catalysts and optics have also been widely reported.

[0003] Rare earth hexaaluminates are composite metal oxide materials. Precursors can be obtained through various preparation methods, resulting in rare earth hexaaluminates exhibiting different properties. The ease with which rare earth hexaaluminate crystal phases form during calcination is closely related to the homogeneity of the mixing of components in the precursor. Commonly used preparation methods for this series of materials include solid-state sintering, sol-gel method, co-precipitation method, and hydrothermal method. Among these, the solid-state sintering method requires higher preparation temperatures, generally exceeding 1500 °C, and places strict requirements on the sintering equipment. The sol-gel method is mainly based on the hydrolysis of precursors such as alkoxides and nitrates. The hydrolyzed mixed salt solution forms a homogeneous sol with the assistance of an organic complexing agent, and eventually transforms into a gel. Compared with the solid-state sintering method, this method is more advantageous in lowering the crystallization temperature, obtaining the pure phase of hexaaluminate at lower calcination temperatures, thereby reducing energy consumption and the need for high-temperature sintering equipment. Compared to nanopowders, one-dimensional nanofibers possess advantages such as self-support, non-agglomeration, higher specific surface area and porosity, better filtration performance, higher thermal stability, high temperature resistance, lightweight, and high strength. In summary, nanofibers exhibit unique properties superior to nanopowders in multiple aspects, giving them potential advantages in many application fields. Therefore, combining the sol-gel method with electrospinning technology to prepare rare-earth hexaaluminate fibers with nanoscale grains and low thermal conductivity is of significant research importance.

[0004] Currently, there are very few reports on rare earth hexaaluminate fiber precursors. The paper "Sintering-resistant hollow fibers of LaMgAl" published in the *Journal of Crystal Growth* in 2008 is one such example. 11 O 19 In the paper "Prepared by Electrospinning", researchers prepared sinter-resistant hollow LaMgAl using electrospinning technology. 11 O 19 Fibers. The preparation of this magnesium lanthanum hexaaluminate fiber uses inorganic salts as raw materials, adds a large amount of spinning aids (such as PVP), and then performs spinning. Patent document CN 117418332 A uses aluminum sol as the aluminum source, rare earth salts as the rare earth source, and polymer as the spinning aid to prepare rare earth aluminate fibers by electrospinning. The main crystalline phase of the prepared inorganic fiber consists of two crystalline phases, with a crystal formation temperature above 1200℃. The microstructure is composed of both granular and lamellar structures, exhibiting excellent high-temperature structural stability. Patent document CN 117431663 A similarly mixes aluminum sol, rare earth salts, magnesium salts, and polymers in water to obtain a sol, and then prepares magnesium-based rare earth hexaaluminate fibers by electrospinning. The main crystalline phase of the obtained fiber consists of ReMgAl 11 O 19The fiber composition is (Re = La, Ce, Pr, Nd, Eu), with a diameter ranging from 0.1 to 7.0 μm and a sheet-like microstructure. Within a temperature range of -196℃ to 1750℃, the fiber maintains stable microstructure, crystal phase, and morphology. Apart from this, there are few reports on rare-earth aluminate fibers. However, existing rare-earth hexaaluminate fibers suffer from non-dense structures and high brittleness, requiring further optimization.

[0005] In summary, the current method for preparing rare-earth magnesium aluminate nanofibers using electrospinning technology presents at least two problems: First, the precursor fibers have low solid content, resulting in low preparation efficiency; second, the obtained fibers have poor mechanical properties. This is mainly because inorganic salts themselves are not spinnable, and the precursor fibers are highly hygroscopic in air, leading to a large number of porous structures in the prepared fibers, making them brittle and severely affecting their performance.

[0006] Based on the above multi-dimensional analysis and comprehensive considerations, and combined with the urgent need and practical background of energy conservation and consumption reduction in high-temperature industries, the development of high-performance hexaaluminate-based lightweight thermal insulation and refractory materials, and the exploration of their application potential in high-temperature fields, especially ultra-high-temperature environments, are of significant practical importance. This research can lay a solid scientific and technological foundation for the large-scale application of this material in domestic high-temperature industries, and further enable the preparation of rare-earth magnesium hexaaluminate fibers with high precursor quality, high target product content, good fiber morphology, and uniform grain growth. Summary of the Invention

[0007] To address the shortcomings of existing technologies, particularly the use of inorganic salts in the preparation process, which leads to a non-dense fiber structure, high brittleness, and low solid content, this invention provides a class of aluminum-magnesium rare-earth-diketone coordination polymer precursors, rare-earth magnesium aluminate fibers, and their preparation methods.

[0008] This invention obtains a novel aluminum-magnesium rare earth-diketone coordination polymer precursor with a linear polymerization structure through trimetallic co-coordination and co-hydrolysis condensation. The obtained aluminum-magnesium rare earth-diketone coordination polymer precursor is dissolved in a solvent, a small amount of spinning aid is added, and a combination of electrospinning and heat treatment is used to successfully prepare rare earth magnesium hexaaluminate fiber with high solid content.

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

[0010] In a first aspect, the present invention provides a method for preparing a type of aluminum-magnesium rare earth-diketone coordination polymer precursor, comprising the following steps:

[0011] Aluminum, magnesium, and rare earth sources were added to a mixed solution and stirred to dissolve. A ligand source was added and stirred, and then triethylamine was added dropwise. The mixture was stirred under ice bath conditions and concentrated under reduced pressure. The resulting product was extracted with an extractant. The filtrate was concentrated under reduced pressure to obtain an aluminum-magnesium-rare earth-diketone coordination polymer precursor.

[0012] The aluminum-magnesium rare earth-diketone coordination polymer precursor prepared by this invention has excellent stability, solubility and spinnability, and can be used for electrospinning, centrifugal spinning and dry spinning to prepare rare earth magnesium hexaaluminate fibers or films thereof.

[0013] According to a preferred embodiment of the present invention, the aluminum source is selected from one or more of the following: anhydrous aluminum chloride, aluminum chloride hexahydrate, anhydrous aluminum nitrate, aluminum nitrate hexahydrate, aluminum nitrate nonahydrate, aluminum hydroxide, aluminum isopropoxide, and aluminum sec-butoxide.

[0014] According to a preferred embodiment of the present invention, the magnesium source is selected from one or more of the following: anhydrous magnesium chloride, magnesium chloride hexahydrate, anhydrous magnesium nitrate, magnesium nitrate hexahydrate, magnesium nitrate nonahydrate, magnesium acetate tetrahydrate, basic magnesium carbonate, magnesium sulfate, and magnesium sulfate heptahydrate.

[0015] According to the present invention, the rare earth source is selected from one or more of the following: lanthanum source, cerium source, praseodymium source, neodymium source, samarium source, europium source, gadolinium source, terbium source, dysprosium source, holmium source, erbium source, thulium source, ytterbium source, and lutetium source; the rare earth source is selected from one of its chloride, nitrate, acetate, and sulfate.

[0016] According to a preferred embodiment of the present invention, the ligand source is a β-diketone compound.

[0017] According to a preferred embodiment of the present invention, the β-diketone compound is selected from one or more of acetylacetone, ethyl acetoacetate, methyl acetoacetate, dimethyl malonate, diethyl malonate, and dipropyl malonate.

[0018] According to a preferred embodiment of the present invention, the molar ratio of aluminum source, magnesium source and rare earth source is 11:(0.5~1.5):(0.5~1.5).

[0019] According to a preferred embodiment of the present invention, the mixed solution is a mixture of water and an organic solvent.

[0020] According to a preferred embodiment of the present invention, the organic solvent is selected from one or a combination of two or more of the following: anhydrous methanol, anhydrous ethanol, isopropanol, n-propanol, formic acid, acetic acid, propionic acid, N,N-dimethylformamide (DMF), N-methylformamide (NMF), N,N-dimethylacetamide (DMA), and N-methylpyrrolidone (NMP).

[0021] According to a preferred embodiment of the present invention, the mass ratio of aluminum source to water and organic solvent is 1:(0~0.5):(5~20).

[0022] More preferably, the mass ratio of aluminum source to water and organic solvent is 1:(0.25~0.35):(6~10).

[0023] According to a preferred embodiment of the present invention, the stirring time in the mixed solution is 20-60 min.

[0024] According to a preferred embodiment of the present invention, the molar ratio of aluminum source to ligand source is 1:(0.8~1.2), the molar ratio of magnesium source to ligand source is 1:(0.8~1.2), and the molar ratio of rare earth source to ligand source is 1:(0.8~1.2).

[0025] According to a preferred embodiment of the present invention, the stirring time after adding the ligand source is 1 to 4 hours.

[0026] According to a preferred embodiment of the present invention, the molar ratio of aluminum source to triethylamine is 1:(2~4), the molar ratio of magnesium source to triethylamine is 1:(1~3), and the molar ratio of rare earth source to triethylamine is 1:(2~4).

[0027] According to a preferred embodiment of the present invention, the extractant is one or a combination of two or more of acetone, butanone, tetrahydrofuran, and 1,4-dioxane.

[0028] In a second aspect, the present invention provides a type of aluminum-magnesium rare earth-diketone coordination polymer precursor, which is prepared by the above method.

[0029] This invention provides a type of aluminum-magnesium rare earth-diketone coordination polymer precursor, the chemical formula of which is LnMgAl. 11 O 19 , Ln: La, Ce,Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,Yb, Lu.

[0030] In a third aspect, the present invention provides a method for preparing rare earth magnesium aluminate fibers, comprising the following steps:

[0031] The aluminum-magnesium rare earth-coordination polymer precursor prepared above was dissolved in a solvent, and a small amount of spinning aid was added to obtain a spinning solution; the spinning solution was electrospun and then heat-treated to obtain rare earth magnesium hexaaluminate fiber.

[0032] According to the present invention, preferably, the solvent is one or a combination of two or more of the following: water, anhydrous methanol, anhydrous ethanol, isopropanol, n-propanol, formic acid, acetic acid, propionic acid, DMF, NMF, DMA, and NMP.

[0033] According to the present invention, preferably, the mass ratio of aluminum-magnesium rare earth-coordination polymer precursor to solvent is 1:(2~6).

[0034] According to the present invention, preferably, the spinning aid is one or a combination of two or more of polyethylene oxide (PEO), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), and polyvinyl butyral (PVB).

[0035] According to the present invention, preferably, the mass ratio of the aluminum-magnesium rare earth-coordination polymer precursor to the spinning aid is 1:(0.005~0.02).

[0036] According to the present invention, the preferred electrospinning conditions are as follows: the spinning voltage is 5~20 kV, the distance between the spinneret and the receiving device is 10~30 cm, the spinning solution propulsion speed is 0.5~5 mL / h, the ambient temperature is 10~45℃, the ambient humidity is 10~70% RH, the receiving device is a metal roller, and the roller rotation speed is 40~400 r / min.

[0037] Further preferred electrospinning conditions are: spinning voltage 8~15kV, distance between spinneret and receiving device 15~25cm, spinning solution propulsion speed 0.8~3mL / h, ambient temperature 20~40℃, and ambient humidity 30~60%RH.

[0038] According to the present invention, preferably, the heat treatment process is carried out in an air environment.

[0039] According to the present invention, preferably, the heat treatment process is as follows: heating to 400~800℃ at a rate of 0.5℃~5℃ / min, then heating to 1000~1500℃ at a rate of 0.5℃~10℃ / min, and holding at the highest temperature for 30~180min, and then cooling with the furnace.

[0040] Technical features and superior effects of the present invention:

[0041] 1. This invention employs a trimetallic co-coordination and co-hydrolysis condensation method, introducing β-diketone compounds as ligand sources for coordination. While maintaining the overall linear chain structure of the coordination polymer, the ligand source is successfully converted into an anion in its enol form to coordinate with aluminum, magnesium, and rare earth elements, thus obtaining an aluminum, magnesium, and rare earth-diketone coordination polymer precursor powder. This precursor has a high degree of linear polymerization, and the resulting aluminum, magnesium, and rare earth-complex precursor exhibits similar properties to IVB metal and rare earth element coordination polymers, possessing excellent stability, solubility, and spinnability, and also has a high solid content.

[0042] 2. The precursor obtained by this invention can be used to prepare rare earth magnesium hexaaluminate fibers with a diameter of 50nm~2μm and a continuously controllable range by electrospinning; it can also be used to prepare rare earth magnesium hexaaluminate fibers by spinning or dry spinning.

[0043] 3. The aluminum-magnesium rare earth-coordination polymer precursor prepared by this invention has stable properties, and the spinning solution prepared with it is clear and transparent.

[0044] 4. This invention can obtain high-purity stoichiometric rare earth magnesium hexaaluminate fiber, pure magnetic lead stone phase, and stable crystal phase. Attached Figure Description

[0045] Figure 1 Optical photograph of the polyacetylacetone-aluminum-magnesium-lanthanum precursor powder obtained in Example 1.

[0046] Figure 2 The image shows the TG-DSC curve of the polyacetylacetone-aluminum magnesium lanthanum precursor obtained in Example 1.

[0047] Figure 3 Photograph of the polyacetylacetone-aluminum-magnesium-lanthanum spinning solution obtained in Example 2.

[0048] Figure 4 An optical photograph of the magnesium lanthanum hexaaluminate precursor fiber obtained in Example 2.

[0049] Figure 5 The image shows the XRD pattern of the magnesium lanthanum hexaaluminate precursor fiber obtained in Example 2.

[0050] Figure 6 This is an optical photograph of the magnesium lanthanum hexaaluminate fiber obtained by heat treatment at 1200°C in Example 2.

[0051] Figure 7 This is a SEM image of the magnesium lanthanum hexaaluminate fiber obtained in Example 2. Detailed Implementation

[0052] The present invention will be further described below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. It should also be noted that those skilled in the art can make various improvements and modifications without departing from the precursors of the present invention, and these improvements and modifications should also be within the scope of protection of the present invention.

[0053] All raw materials used in the examples are commercially available products.

[0054] Example 1

[0055] The preparation method of the aluminum-magnesium-lanthanum coordination polymer precursor includes the following steps:

[0056] (1) Mix 26.66 g of anhydrous aluminum chloride, 1.43 g of anhydrous magnesium chloride, 5.30 g of lanthanum chloride hexahydrate, 7.5 g of water and 200 g of anhydrous methanol. After the mixture is completely dissolved, add 20 g of acetylacetone to the solution and stir for 1 h. Then add 60 g of triethylamine dropwise and stir in an ice bath for 10 h to obtain a clear mixed solution of polyacetylacetone aluminum magnesium lanthanum precursor / triethylamine hydrochloride.

[0057] (2) Transfer the mixed solution obtained in step (1) into a round bottom flask, concentrate it under reduced pressure at 38°C to dry powder, then add 200 g of acetone, dissolve it completely, seal it and place it in a refrigerator to stand for 24 h.

[0058] (3) The solution from step (2) that has been allowed to stand and separate into layers is filtered to remove insoluble triethylamine hydrochloride, yielding a polyacetylacetonate aluminum magnesium lanthanum precursor solution. This solution is then transferred to another round-bottom flask and concentrated under reduced pressure at 32 °C to obtain polyacetylacetonate aluminum magnesium lanthanum precursor powder. An optical photograph of the obtained polyacetylacetonate aluminum magnesium lanthanum precursor powder is shown below. Figure 1 .

[0059] The TG-DSC curve of the obtained polyacetylacetone-aluminum magnesium lanthanum precursor is shown in Figure 1. Figure 2 ,Depend on Figure 2 It can be seen that the precursor mainly undergoes solvent and partial coordinating water volatilization in the range of room temperature to about 200 °C; a significant weight loss process occurs in the range of 200~500 °C, corresponding to the decomposition of organic ligands (acetylacetone groups); above 500 °C, the weight loss tends to level off, indicating that the organic components are basically completely decomposed and gradually form an inorganic framework structure. Combined with the DSC curve, a significant exothermic peak appears near about 1100~1200 °C, corresponding to the formation of the lanthanum magnesium hexaaluminate crystal phase.

[0060] Example 2

[0061] A method for preparing magnesium lanthanum hexaaluminate fiber, comprising the following steps:

[0062] (1) Weigh 5 g of the polyacetylacetone-aluminum magnesium lanthanum precursor prepared in Example 1, 10 g of anhydrous methanol, and 0.05 g of PEO into a beaker, stir and mix at 45 °C, and after complete dissolution, obtain a clear and transparent spinning solution. Figure 3 );

[0063] (2) The spinning solution obtained in step (1) is transferred to a syringe and the precursor fiber is obtained by electrospinning. The spinning voltage is 10 kV, the receiving distance is 20 cm, the stainless steel needle is 23#, the syringe advance speed is 1.3 mL / h, the ambient humidity is 40%, and the spinning is carried out at 25℃ to obtain magnesium lanthanum hexaaluminate precursor fiber.

[0064] Optical photographs of the obtained lanthanum magnesium hexaaluminate precursor fibers are shown below. Figure 4 XRD patterns of magnesium lanthanum hexaaluminate precursor fibers are shown in [reference needed]. Figure 5 Infrared spectroscopy results show that the magnesium lanthanum hexaaluminate precursor fiber structure contains both acetylacetone anion and hydroxyl groups, indicating that the β-diketone ligand successfully participated in the coordination reaction.

[0065] (3) The magnesium lanthanum hexaaluminate precursor fiber prepared in step (2) is heated to 600℃ at 1℃ / min in a muffle furnace, and then heated to 1200℃ at 10℃ / min and held for 1 h. The fiber is then cooled in the furnace to obtain magnesium lanthanum hexaaluminate fiber.

[0066] The final optical photograph of the obtained magnesium lanthanum hexaaluminate fiber is shown below. Figure 6 SEM images of lanthanum hexaaluminate magnesium fiber are shown below. Figure 7 It can be clearly seen that the present invention successfully prepared magnesium lanthanum hexaaluminate fiber, and the fiber surface has plate-like grains.

[0067] Example 3

[0068] The preparation method of the aluminum-magnesium-lanthanum-coordination polymer precursor described in Example 1 differs from that in:

[0069] In step (1), 3.05 g of magnesium chloride hexahydrate was used to replace 1.43 g of anhydrous magnesium chloride, and the rest was carried out as in Example 1.

[0070] The preparation of magnesium lanthanum hexaaluminate fibers was carried out according to Example 2.

[0071] Example 4

[0072] The preparation method of the aluminum-magnesium-lanthanum-coordination polymer precursor described in Example 1 differs from that in:

[0073] In step (1), 61.88 g of aluminum chloride hexahydrate replaced 26.66 g of anhydrous aluminum chloride, and the rest was carried out as in Example 1.

[0074] The preparation of magnesium lanthanum hexaaluminate fibers was carried out according to Example 2.

[0075] Example 5

[0076] The preparation method of the aluminum-magnesium-lanthanum-coordination polymer precursor described in Example 1 differs from that in:

[0077] In step (1), anhydrous methanol is replaced with an equal mass of anhydrous ethanol.

[0078] The preparation of magnesium lanthanum hexaaluminate fibers was carried out according to Example 2.

[0079] Example 6

[0080] The preparation method of the aluminum-magnesium-lanthanum-coordination polymer precursor described in Example 1 differs from that in:

[0081] In step (1), anhydrous methanol is replaced with an equal mass of isopropanol.

[0082] The preparation of magnesium lanthanum hexaaluminate fibers was carried out according to Example 2.

[0083] Example 7

[0084] The preparation method of the aluminum-magnesium-lanthanum-coordination polymer precursor described in Example 1 differs from that in:

[0085] In step (1), the ligand source acetylacetone was replaced with 26 g of ethyl acetoacetate to obtain polyethyl acetoacetate aluminum magnesium lanthanum.

[0086] The preparation of magnesium lanthanum hexaaluminate fibers was carried out according to Example 2.

[0087] Example 8

[0088] The preparation method of the aluminum-magnesium-lanthanum-coordination polymer precursor described in Example 1 differs from that in:

[0089] In step (2), the extractant acetone is replaced with an equal mass of tetrahydrofuran.

[0090] The preparation of magnesium lanthanum hexaaluminate fibers was carried out according to Example 2.

[0091] Example 9

[0092] The preparation method of the aluminum-magnesium-lanthanum-coordination polymer precursor described in Example 1 differs from that in:

[0093] In step (2), the extractant acetone is replaced with an equal mass of butanone.

[0094] The preparation of magnesium lanthanum hexaaluminate fibers was carried out according to Example 2.

[0095] Example 10

[0096] The preparation of the aluminum-magnesium-lanthanum-coordination polymer precursor was carried out according to Example 1.

[0097] The preparation of magnesium lanthanum hexaaluminate fiber is the same as described in Example 2, except that:

[0098] In step (1), 0.05 g of spinning aid PEO is replaced with 0.025 g of PEO.

[0099] Example 11

[0100] A method for preparing magnesium gadolinium hexaaluminate fiber, comprising the following steps:

[0101] (1) Mix 26.66 g of anhydrous aluminum chloride, 1.43 g of anhydrous magnesium chloride, 5.58 g of gadolinium chloride hexahydrate, 7.5 g of water and 200 g of anhydrous methanol. After the mixture is completely dissolved, add 20 g of acetylacetone to the solution and stir for 1 h. Then add 60 g of triethylamine dropwise and stir in an ice bath for 10 h to obtain a clear mixed solution of polyacetylacetone aluminum magnesium gadolinium precursor / triethylamine hydrochloride.

[0102] (2) Transfer the mixed solution obtained in step (1) into a round bottom flask, concentrate it under reduced pressure at 38 °C to dry powder, then add 40 g of acetone, dissolve it completely, seal it and place it in a refrigerator to stand for 24 h.

[0103] (3) Filter the solution that has been allowed to stand and separate in step (2) to remove insoluble triethylamine hydrochloride and obtain polyacetylacetone aluminum magnesium gadolinium precursor solution. Transfer it to another round bottom flask and dry it under reduced pressure at 32 °C to obtain polyacetylacetone aluminum magnesium gadolinium precursor powder.

[0104] (4) Weigh 4 g of the precursor obtained in step (3), 8 g of anhydrous methanol and 0.04 g of PEO into a beaker, stir and mix at 38 °C, and after complete dissolution, a clear and transparent spinning solution is obtained.

[0105] (5) Transfer the spinning solution obtained in step (4) into a syringe. The spinning solution is electrospun to obtain precursor fibers. The spinning voltage is 10 kV, the receiving distance is 20 cm, the stainless steel needle is 23#, the syringe advance speed is 1.3 mL / h, the ambient humidity is 30%, and spinning is carried out at room temperature.

[0106] (6) The precursor fiber prepared in (5) was heated to 600 ℃ at 1 ℃ / min in a muffle furnace, and then heated to 1200 ℃ at 10 ℃ / min and held for 1 h. The fiber was then cooled in the furnace to obtain gadolinium hexaaluminate fiber.

[0107] Comparative Example 1:

[0108] The preparation method of the aluminum-magnesium-lanthanum-coordination polymer precursor described in Example 1 differs from that in:

[0109] In step (1), replacing 20 g of acetylacetone with 10 g of acetylacetone resulted in a white suspension, indicating poor precursor stability. This suggests that a low ligand content leads to precursor hydrolysis and the formation of metal hydroxide precipitates.

[0110] Comparative Example 2:

[0111] The preparation method of the aluminum-magnesium-lanthanum-coordination polymer precursor described in Example 1 differs from that in:

[0112] In step (1), 20 g of acetylacetone was replaced with 30 g of acetylacetone. The excess acetylacetone resulted in poor fiber morphology. This indicates that the high ligand content caused the organic matter to decompose at high temperatures, producing a large number of pores.

[0113] Comparative Example 3:

[0114] The preparation method of the aluminum-magnesium-lanthanum-coordination polymer precursor described in Example 1 differs from that in:

[0115] In step (1), 60g of triethylamine was added directly with stirring instead of dropwise. This process produced a large amount of precipitate. After adding an appropriate amount of methanol, the precipitate dissolved, indicating that triethylamine salts had precipitated. Similarly, 100g of the dechlorinating agent triethylamine was added directly with stirring. This process also produced a large amount of precipitate because excessive triethylamine caused the solution to become alkaline, resulting in insoluble hydroxides.

[0116] Comparative Example 4:

[0117] The preparation method of magnesium lanthanum hexaaluminate fiber is the same as that described in Example 2, except that:

[0118] In step (2), the ambient humidity is 50% and the temperature is 30℃. Compared with Example 2, excessive humidity can easily lead to water solubility or hydrolysis during electrospinning, resulting in caking after drying.

[0119] Comparative Example 5:

[0120] The preparation method of magnesium lanthanum hexaaluminate fiber is the same as that described in Example 2, except that:

[0121] In step (2), the magnesium lanthanum hexaaluminate fibers were heated to 1200℃ at a heating rate of 5℃ / min and held for 1 h, then cooled in the furnace. The resulting fiber lamellar crystals were too large. During the heat treatment process, the slow heating rate led to excessive growth of the crystals, resulting in reduced strength and toughness.

Claims

1. A method for preparing a type of aluminum-magnesium rare earth-diketone coordination polymer precursor, comprising the following steps: Aluminum, magnesium, and rare earth sources were added to a mixed solution and stirred to dissolve. A ligand source was added and stirred, and then triethylamine was added dropwise. The mixture was stirred under ice bath conditions and concentrated under reduced pressure. The resulting product was extracted with an extractant. The filtrate was concentrated under reduced pressure to obtain an aluminum-magnesium-rare earth-diketone coordination polymer precursor.

2. The preparation method according to claim 1, characterized in that, The aluminum source is selected from one or more of the following: anhydrous aluminum chloride, aluminum chloride hexahydrate, anhydrous aluminum nitrate, aluminum nitrate hexahydrate, aluminum nitrate nonahydrate, aluminum hydroxide, aluminum isopropoxide, and aluminum sec-butoxide. The magnesium source is selected from one or more of the following: anhydrous magnesium chloride, magnesium chloride hexahydrate, anhydrous magnesium nitrate, magnesium nitrate hexahydrate, magnesium nitrate nonahydrate, magnesium acetate tetrahydrate, basic magnesium carbonate, magnesium sulfate, and magnesium sulfate heptahydrate. The rare earth source is selected from one or more of the following: lanthanum source, cerium source, praseodymium source, neodymium source, samarium source, europium source, gadolinium source, terbium source, dysprosium source, holmium source, erbium source, thulium source, ytterbium source, and lutetium source; the rare earth source is one of its chloride, nitrate, acetate, and sulfate.

3. The preparation method according to claim 1, characterized in that, The ligand source is a β-diketone compound, which is selected from one or more of acetylacetone, ethyl acetoacetate, methyl acetoacetate, dimethyl malonate, diethyl malonate, and dipropyl malonate.

4. The preparation method according to claim 1, characterized in that, The molar ratio of aluminum source, magnesium source and rare earth source is 11:(0.5~1.5):(0.5~1.5). The mixed solution is a mixture of water and organic solvent. The organic solvent is selected from one or more of the following: anhydrous methanol, anhydrous ethanol, isopropanol, n-propanol, formic acid, acetic acid, propionic acid, N,N-dimethylformamide (DMF), N-methylformamide (NMF), N,N-dimethylacetamide (DMA), and N-methylpyrrolidone (NMP). The mass ratio of aluminum source to water and organic solvent is 1:(0~0.5):(5~20). The stirring time in the mixed solution is 20~60 min.

5. The preparation method according to claim 1, characterized in that, The molar ratio of aluminum source to ligand source is 1:(0.8~1.2), the molar ratio of magnesium source to ligand source is 1:(0.8~1.2), the molar ratio of rare earth source to ligand source is 1:(0.8~1.2), and the stirring time after adding the ligand source is 1~4h. The molar ratio of aluminum source to triethylamine is 1:(2~4), the molar ratio of magnesium source to triethylamine is 1:(1~3), and the molar ratio of rare earth source to triethylamine is 1:(2~4). The extractant is one or a combination of two or more of acetone, butanone, tetrahydrofuran, and 1,4-dioxane.

6. A type of aluminum-magnesium rare earth-diketone coordination polymer precursor, prepared by the method described in any one of claims 1-5.

7. A method for preparing rare earth magnesium aluminate fibers, comprising the following steps: The aluminum-magnesium rare earth coordination polymer precursor of claim 6 is dissolved in a solvent, and a small amount of spinning aid is added to obtain a spinning solution; the spinning solution is electrospun and then heat-treated to obtain rare earth magnesium hexaaluminate fiber.

8. The method for preparing rare earth magnesium aluminate fiber according to claim 7, characterized in that, The solvent is one or more of the following: water, anhydrous methanol, anhydrous ethanol, isopropanol, n-propanol, formic acid, acetic acid, propionic acid, DMF, NMF, DMA, and NMP. The mass ratio of the aluminum-magnesium rare earth coordination polymer precursor to the solvent is 1:(2~6).

9. The method for preparing rare earth magnesium aluminate fiber according to claim 7, characterized in that, The spinning aid is one or more of polyethylene oxide (PEO), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), and polyvinyl butyral (PVB), and the mass ratio of aluminum-magnesium rare earth-coordination polymer precursor to spinning aid is 1:(0.005~0.02).

10. The method for preparing rare earth magnesium aluminate fiber according to claim 7, characterized in that, The electrospinning conditions are as follows: spinning voltage is 5~20 kV, distance between spinneret and receiving device is 10~30 cm, spinning solution propulsion speed is 0.5~5 mL / h, ambient temperature is 10~45℃, ambient humidity is 10~70% RH, receiving device is metal drum, drum speed is 40~400 r / min; The heat treatment process is carried out in an air environment. The heat treatment process is as follows: the temperature is increased to 400~800℃ at a rate of 0.5℃~5℃ / min, then increased to 1000~1500℃ at a rate of 0.5℃~10℃ / min, and held at the highest temperature for 10~480min, and then cooled in the furnace.

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