A continuous YAG nanofiber and its preparation method

Abstract

The present invention relates to a method for preparing continuous YAG nanofibers, which comprises mixing an inorganic yttrium salt, citric acid monohydrate and an ethanol-water mixture, and then heating and stirring at 30-100 °C for 1-10 h to obtain a yttrium-containing complex solution; mixing an inorganic aluminum salt, an organic aluminum salt, oxalic acid and water, and then heating and stirring at 30-100 °C for 2-8 h to obtain an aluminum sol; mixing the obtained yttrium-containing complex solution and the obtained aluminum sol in proportion, and then heating and stirring at 50-90 °C for 0.5-3 h to obtain a Y-Al sol; adding polyethylene oxide into the obtained Y-Al sol, and stirring for 1-3 h to obtain a precursor spinning solution; and then obtaining the fibers through electrospinning and high-temperature heat treatment. The fibers solve the problems existing in the existing YAG fibers, such as poor flexibility, many broken ends, low purity, long preparation process time, high cost, and low fiber aspect ratio.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber preparation, and particularly relates to a continuous YAG nanofiber and a preparation method thereof. Background Art

[0002] YAG ceramics, namely yttrium aluminum garnet, has a molecular formula of Y 3 Al 5 O 12 and a melting point of 1942 °C. YAG ceramics have the advantages of high temperature resistance, thermal shock resistance, high temperature creep resistance, good physical / chemical stability, high high-temperature strength, excellent structural stability, etc., and have broad application prospects in high-temperature structural materials. Although YAG ceramics have many good properties and have been widely applied, due to their inevitable ceramic characteristics such as brittleness and poor strength, their wider application in high-temperature fields is restricted.

[0003] Preparing ceramic fibers with a high aspect ratio is one of the important methods to improve the strength of ceramic materials. From the perspective of the microstructure of ceramic fibers, reducing the diameter of ceramic fibers to the nanometer level is expected to significantly improve the performance of ceramic fibers and further expand the functionality of ceramic fibers. Currently, the main methods for preparing ceramic fibers include melt spinning, centrifugal spinning, dry spinning, and electrospinning, etc. Melt spinning for fiber preparation has a high cost and high requirements for equipment. The fibers obtained by the centrifugal spinning method are relatively short. The dry spinning method can obtain continuous fibers, but the preparation method is difficult and the cost is extremely high. In addition, the diameters of the fibers prepared by the above methods are all in the micron level and it is difficult to further refine them. Electrospinning has simple equipment, strong operability, low cost, and a wide application range, and is a method that can directly and continuously prepare nanofibers.

[0004] CN201510436025.0 (CN105002601A) discloses a preparation method of polycrystalline Al 2 O 3- Y 3 Al 5 O 12 composite micron fibers or pure YAG micron fibers. It heats and refluxes an anhydrous aluminum chloride solution and aluminum micropowder to obtain a polyaluminum chloride mother liquor A; then adds yttrium nitrate, yttrium acetate, and the spinning aid glacial acetic acid to obtain a precursor solution B, which is concentrated under reduced pressure to obtain a precursor sol, and then obtained through centrifugal spinning, drying, and heat treatment. Its average diameter is 6 - 7 microns, and it has advantages such as high temperature resistance and good creep resistance, but there are defects such as a low aspect ratio of the fibers, short fiber length, cumbersome process, high cost, etc.

[0005] However, the existing YAG nanofibers have disadvantages such as poor flexibility, many fiber breakages, low purity, complex preparation process, and long preparation cycle. For example, the YAG-Al 2 O 3 nanofibers prepared in Journal of European ceramic society 40(2020)2463-2469 obtained continuous YAG-Al 2 O 3 nanofibers with a certain flexibility by increasing the content of Al 2 O 3 The prepared YAG-Al 2 O 3 nanofibers exhibited good flexibility and tensile strength; however, in this preparation method, the content of the second-phase substance Al 2 O 3 was too high (the introduced Al 2 O 3 reached 30%), resulting in low YAG purity of the product.

[0006] Journal of alloys and compounds 879 (2021) 159978 prepared YAG nanofiber membranes with good flexibility. The fiber membranes were lightweight and heat-resistant. However, this method requires the prior synthesis of spinnable acetylacetone polymer powder, has high requirements for the preparation process, a long preparation cycle, and high preparation costs.

[0007] Based on this, the present application was developed. Summary of the Invention

[0008] The object of the present invention is to overcome the defects of the prior art and provide a continuous YAG nanofiber, which is prepared by the citric acid complexation and sol-gel method. This fiber solves the problems of poor flexibility, many breakages, low purity, long preparation time-consuming, high cost, and low fiber aspect ratio of the existing YAG fibers.

[0009] The present invention also provides a preparation method for the above-mentioned continuous YAG nanofiber.

[0010] To achieve the above object, the present invention adopts the following technical solutions:

[0011] A preparation method for a continuous YAG nanofiber, which comprises the following steps:

[0012] 1) Mix an inorganic yttrium salt, citric acid monohydrate, and an ethanol-water mixture, and then heat and stir at 30 - 100 °C for 1 - 10 h to obtain a yttrium-containing complex solution;

[0013] 2) Mix the inorganic aluminum salt, organic aluminum salt, oxalic acid and water, and then heat and stir at 30 - 100 °C for 2 - 8 h to obtain aluminum sol;

[0014] 3) Mix the yttrium-containing complex solution obtained in step 1) and the aluminum sol obtained in step 2) in a ratio (according to nY:nAl = 3:5, molar ratio), and then heat and stir at 50 - 90 °C for 0.5 - 3 h to obtain Y-Al sol;

[0015] 4) Add polyethylene oxide (PEO) to the Y-Al sol obtained in step 3), and stir for 1 - 3 h to obtain a precursor spinning solution;

[0016] 5) Electrospin the precursor spinning solution obtained in step 4) to obtain continuous YAG precursor fibers;

[0017] 6) Perform high-temperature heat treatment on the continuous YAG precursor fibers obtained in step 5) in an air environment to obtain continuous YAG nanofibers. The diameter of the fibers is 200 - 900 nm, the fibers are continuous in microstructure, there are few broken ends, the structure is dense, the surface is smooth, and the purity is high.

[0018] Specifically, in step 1), the molar ratio of the inorganic yttrium salt to citric acid monohydrate can be 1:1.5 - 2. The inorganic yttrium salt includes, but is not limited to, one or more of yttrium nitrate, yttrium chloride, yttrium acetate, etc. Further, in step 1), the mass fraction of the inorganic yttrium salt in the yttrium-containing complex solution is 15 - 30 wt%. The ethanol-water mixture can be a mixture of ethanol and water in any ratio, and preferably, the mass ratio of the two is 1:1 - 3.

[0019] Specifically, in step 2), the molar ratio of the inorganic aluminum salt, organic aluminum salt, oxalic acid to water is 1:2 - 2.5:0.03 - 0.04:1.5 - 60. The inorganic aluminum salt includes, but is not limited to, one or two of aluminum chloride, aluminum nitrate, etc.; the organic aluminum salt can be an aluminum alkoxide, including, but is not limited to, one or two of aluminum isopropoxide, aluminum sec-butoxide, etc.

[0020] Specifically, in step 4), the molecular weight of polyethylene oxide is 30 - 100W, and the addition amount is 0.01 - 10 wt% of the weight of the Y-Al sol.

[0021] Specifically, in step 5), the electrospinning voltage is 18 - 25 kV, the curing distance is 15 - 25 cm, and the feeding speed is 0.5 - 3 mL / h. Further, in step 6), the high-temperature heat treatment temperature is 800 - 1300 °C, and the time is 1 - 6 h. More preferably, the temperature is raised to the high-temperature heat treatment temperature at a heating rate of 1 - 10 °C / min.

[0022] The present invention also provides continuous YAG nanofibers prepared by the above preparation method.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1) The continuous YAG nanofibers prepared by the present invention have good flexibility, with a diameter of 200 - 900 nm; the fibers are continuous in microstructure, with few broken ends, a dense structure, a smooth surface, and high purity.

[0025] 2) The present invention uses the citric acid complexation and sol-gel method to prepare a precursor spinning solution, and obtains continuous YAG nanofibers through electrospinning technology. Citric acid has multiple functions. As a ligand, it complexes with inorganic yttrium salts and then crosslinks with colloidal particles in the aluminum sol to form a stable crosslinked network structure, thereby improving the spinnability of the precursor spinning solution; it can also act as an inhibitor to delay the hydrolysis of aluminum salts and obtain a Y-Al sol with good stability. The fibers prepared by this method overcome the defect of easy introduction of other impurity components in the existing preparation process, improve the purity of the product, and ensure the quality of the product; at the same time, this method is simple to operate and has low requirements for labor and equipment.

[0026] 3) The continuous YAG nanofibers prepared by the present invention are continuous, have few broken ends, high purity, and a dense structure, have good flexibility, and have broad application prospects in the fields of high-temperature heat insulation and structural toughening, etc.

[0027] 4) The method for preparing continuous YAG nanofibers of the present invention has the characteristics of simple process, low cost, high purity, and good operability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 SEM image of the continuous YAG nanofibers prepared in Example 1;

[0029] Figure 2 XRD diffraction pattern of the continuous YAG nanofibers prepared in Example 1;

[0030] Figure 3 Bending diagram of the continuous YAG nanofibers prepared in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] In the following examples, the raw materials used are all ordinary commercially available products that can be directly purchased or can be prepared by conventional methods in the art. Room temperature refers to 25 ± 5°C.

[0033] Example 1

[0034] A method for preparing continuous YAG nanofibers includes the following steps:

[0035] (1) Mix 5 g (0.013 mol) of yttrium nitrate hexahydrate, 5.48 g (0.026 mol) of citric acid monohydrate, 10 g of water, and 10 g of ethanol, heat and stir to dissolve at 70°C for 2 h, and obtain a clear and transparent yttrium-containing complex solution;

[0036] (2) Mix 7.24 g (0.03 mol) of aluminum chloride hexahydrate, 15.3 g (0.075 mol) of aluminum isopropoxide, 0.1 g (0.001 mol) of oxalic acid, and 32.4 g (1.8 mol) of water, heat and stir at 90°C for 6 h, and obtain a homogeneous and transparent aluminum sol;

[0037] (3) Mix 30.48 g of the yttrium-containing complex solution obtained in step (1) and 11.46 g of the aluminum sol obtained in step (2) (nY:nAl = 3:5, molar ratio), heat and stir at 70°C for 0.5 h, and obtain a transparent Y-Al sol;

[0038] (4) Add 0.4 g of PEO with a molecular weight of 60W to the Y-Al sol obtained in step (3), stir for 3 h to obtain a precursor spinning solution;

[0039] (5) Electrospinning is carried out on the precursor spinning solution obtained in step (4) in an environment with a temperature of 25°C and a humidity of 10% to prepare continuous YAG precursor fibers. The electrospinning voltage is 25 kV, the curing distance is 18 cm, and the feeding speed is 1.5 mL / h;

[0040] (6) Perform high-temperature heat treatment on the continuous YAG precursor fibers obtained in step (5) in an air environment. The heat treatment regime is: heat from room temperature to 1000°C at a heating rate of 1°C / min and hold for 1 h, and then cool to room temperature with the furnace, thus obtaining.

[0041] Perform SEM testing on the continuous YAG nanofibers obtained in Example 1, and the results are as Figure 1 shown. It can be Figure 1 seen that the fibers are continuous and have few broken ends, and their diameters are in the range of 400 - 700 nm.

[0042] Perform XRD testing on the continuous YAG nanofibers obtained in Example 1, and the results are as Figure 2 shown. It can be Figure 2 seen that the XRD diffraction peaks of the fibers all belong to Y3 Al 5 O 12 (PDF#33-0040), indicating that there are almost no impurities in the fibers and they have extremely high purity.

[0043] The flexibility test was carried out on the continuous YAG nanofibers obtained in Example 1, and the results are as Figure 3 shown. It can be Figure 3 seen that the fibers have good flexibility and can be bent 180 degrees without breakage.

[0044] Example 2

[0045] A method for preparing continuous YAG nanofibers, comprising the following steps:

[0046] (1) Mix 5 g (0.013 mol) of yttrium nitrate hexahydrate, 5.48 g (0.026 mol) of citric acid monohydrate, 10 g of water and 10 g of ethanol, and heat and stir to dissolve at 50 °C for 5 h to obtain a clear and transparent yttrium-containing complex solution;

[0047] (2) Mix 7.24 g (0.03 mol) of aluminum chloride hexahydrate, 15.3 g (0.075 mol) of aluminum isopropoxide, 0.1 g (0.001 mol) of oxalic acid and 32.4 g (1.8 mol) of water, and heat and stir at 90 °C for 6 h to obtain a homogeneous and transparent aluminum sol;

[0048] (3) Mix 30.48 g of the yttrium-containing complex solution obtained in step (1) and 11.46 g of the aluminum sol obtained in step (2) (nY:nAl = 3:5, molar ratio), heat and stir at 70 °C for 0.5 h to obtain a transparent Y-Al sol;

[0049] (4) Add 0.2 g of PEO with a molecular weight of 60W to the Y-Al sol obtained in step (3), and stir for 3 h to obtain a precursor spinning solution;

[0050] (5) Electrospinning is carried out on the precursor spinning solution obtained in step (4) in an environment with a temperature of 25 °C and a humidity of 10% to prepare continuous YAG precursor fibers. The electrospinning voltage is 25 kV, the curing distance is 18 cm, and the feeding speed is 1.5 mL / h;

[0051] (6) The continuous YAG precursor fibers obtained in step (5) are subjected to high-temperature heat treatment in an air environment. The heat treatment regime is: heating from room temperature to 1000 °C at a heating rate of 1 °C / min and holding for 1 h, and then cooling to room temperature with the furnace, thus obtaining.

[0052] Example 3

[0053] A method for preparing continuous YAG nanofibers, comprising the following steps:

[0054] (1) Mix 5 g (0.013 mol) of yttrium nitrate hexahydrate, 5.48 g (0.026 mol) of citric acid monohydrate, 10 g of water and 10 g of ethanol, and heat and stir to dissolve for 2 h at 70 °C to obtain a clear and transparent yttrium-containing complex solution;

[0055] (2) Mix 7.24 g (0.03 mol) of aluminum chloride hexahydrate, 15.3 g (0.075 mol) of aluminum isopropoxide, 0.1 g (0.001 mol) of oxalic acid and 32.4 g (1.8 mol) of water, and heat and stir for 8 h at 90 °C to obtain a homogeneous and transparent aluminum sol;

[0056] (3) Mix 30.48 g of the yttrium-containing complex solution obtained in step (1) and 11.46 g of the aluminum sol obtained in step (2) (nY:nAl = 3:5, molar ratio), and heat and stir for 0.5 h at 70 °C to obtain a transparent Y-Al sol;

[0057] (4) Add 0.8 g of PEO with a molecular weight of 60W to the Y-Al sol obtained in step (3), and stir for 3 h to obtain a precursor spinning solution;

[0058] (5) Electrospinning is carried out on the precursor spinning solution obtained in step (4) in an environment with a temperature of 25 °C and a humidity of 10% to prepare continuous YAG precursor fibers. The electrospinning voltage is 25 kV, the curing distance is 18 cm, and the feeding speed is 1.5 mL / h;

[0059] (6) The continuous YAG precursor fibers obtained in step (5) are subjected to high-temperature heat treatment in an air environment. The heat treatment regime is: heating from room temperature to 1000 °C at a heating rate of 1 °C / min and holding for 1 h, and then cooling to room temperature with the furnace, thus obtaining.

[0060] Example 4

[0061] A method for preparing continuous YAG nanofibers, comprising the following steps:

[0062] (1) Mix 5 g (0.013 mol) of yttrium nitrate hexahydrate, 5.48 g (0.026 mol) of citric acid monohydrate, 5 g of water and 15 g of ethanol, and heat and stir to dissolve for 2 h at 70 °C to obtain a clear and transparent yttrium-containing complex solution;

[0063] (2) Mix 7.24 g (0.03 mol) of aluminum chloride hexahydrate, 15.3 g (0.075 mol) of aluminum isopropoxide, 0.1 g (0.001 mol) of oxalic acid and 32.4 g (1.8 mol) of water, and heat and stir for 6 h at 90 °C to obtain a homogeneous and transparent aluminum sol;

[0064] (3) Mix the 30.48 g of yttrium complex solution obtained in step (1) with the 11.46 g of aluminum sol obtained in step (2) (nY:nAl = 3:5, molar ratio), heat and stir at 70 °C for 0.5 h to obtain a transparent Y-Al sol;

[0065] (4) Add 0.4 g of PEO with a molecular weight of 60W to the Y-Al sol obtained in step (3), and stir for 3 h to obtain a precursor spinning solution;

[0066] (5) Electrospinning is carried out on the precursor spinning solution obtained in step (4) in an environment with a temperature of 25 °C and a humidity of 10% to prepare continuous YAG precursor fibers. The electrospinning voltage is 25 kV, the curing distance is 18 cm, and the feeding speed is 1.5 mL / h;

[0067] (6) The continuous YAG precursor fibers obtained in step (5) are subjected to high-temperature heat treatment in an air environment. The heat treatment regime is: heat from room temperature to 1000 °C at a heating rate of 5 °C / min and hold for 3 h, and then cool to room temperature with the furnace, thus obtaining.

[0068] The continuous YAG nanofibers obtained in Examples 2 to 4 are subjected to SEM and XRD tests. The results show that the fibers are continuous with few broken ends, the diameter is in the range of 300 - 750 nm, and there are no impurities in the fibers, with high purity. The flexibility test results show that the fibers have good flexibility and can be bent 180 degrees without breaking.

[0069] Comparative Example 1

[0070] The difference between this comparative example and Example 1 is that citric acid is not added.

[0071] The fibers prepared in this comparative example have a large difference in diameter and many fiber broken ends. The fibers are easily broken after bending and have no flexibility.

[0072] The above are only the preferred embodiments of the present invention. It should be noted that: for those of ordinary skill in the art, without departing from the premise of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing continuous YAG nanofibers, characterized in that: The steps include: 1) Mixing an inorganic yttrium salt, citric acid monohydrate and an ethanol-water mixture, and then heating and stirring at 30-100° C. for 1-10 hours to obtain a yttrium-containing complex solution; the ethanol-water mixture is a mixture of ethanol and water in a mass ratio of 1:1-3; 2) Mixing inorganic aluminum salt, organic aluminum salt, oxalic acid and water, and then heating and stirring at 30-100°C for 2-8 hours to obtain aluminum sol; 3) mixing the yttrium-containing complex solution obtained in step 1) and the aluminum sol obtained in step 2) in proportion, and then heating and stirring at 50-90° C. for 0.5-3 h to obtain Y-Al sol; 4) adding polyethylene oxide to the Y-Al sol obtained in step 3), stirring for 1-3 hours to obtain a precursor spinning solution; the amount of polyethylene oxide added is 0.01-1.91wt% of the weight of the Y-Al sol; 5) electrospinning the precursor spinning solution obtained in step 4) to obtain continuous YAG precursor fibers; 6) The continuous YAG precursor fiber obtained in step 5) is subjected to high temperature heat treatment in an air environment to obtain continuous YAG nanofibers.

2. The method for preparing continuous YAG nanofibers according to claim 1, characterized in that: In step 1), the molar ratio of the inorganic yttrium salt to citric acid monohydrate is 1:1.5-2; the inorganic yttrium salt includes one or more of yttrium nitrate, yttrium chloride, and yttrium acetate.

3. The method for preparing continuous YAG nanofibers according to claim 1, characterized in that: In step 1), the mass fraction of the inorganic yttrium salt in the yttrium-containing complex solution is 15-30 wt%.

4. The method for preparing continuous YAG nanofibers according to claim 1, characterized in that: In step 2), the molar ratio of the inorganic aluminum salt, the organic aluminum salt, the oxalic acid and the water is 1:2-2.5:0.03-0.04:1.5-60.

5. The method for preparing continuous YAG nanofibers according to claim 4, characterized in that: The inorganic aluminum salt includes one or both of aluminum chloride and aluminum nitrate; the organic aluminum salt includes one or both of aluminum isopropoxide and aluminum sec-butoxide.

6. The method for preparing continuous YAG nanofibers according to claim 1, characterized in that: In step 4), the molecular weight of polyethylene oxide is 30-100W.

7. The method for preparing continuous YAG nanofibers according to claim 1, characterized in that: In step 5), the electrospinning voltage is 18-25 kV, the curing distance is 15-25 cm, and the propulsion speed is 0.5-3 mL / h.

8. The method for preparing continuous YAG nanofibers according to claim 1, characterized in that: In step 6), the high temperature heat treatment temperature is 800-1300°C and the time is 1-6h.

9. The method for preparing continuous YAG nanofibers according to claim 8, characterized in that: The heating rate is 1-10℃ / min.

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