Preparation method of polycarboxylic acid aluminum precursor and alumina fiber

Abstract

The invention relates to a preparation method of an aluminum polycarboxylate precursor and an aluminum oxide fiber, the aluminum polycarboxylate precursor is stable and has good spinnability, and the aluminum oxide fiber keeps complete fiber morphology and stable crystal phase at 1200 DEG C. The preparation method comprises the following steps: by taking aluminum chloride salt as an aluminum source and potassium carboxylate as an organic ligand of aluminum ions, removing chloride ions by utilizing a potassium salt precipitation method to obtain a polycarboxylic acid aluminum precursor; and taking a high-molecular polymer as a spinning aid, obtaining an alumina precursor fiber by virtue of an electrostatic spinning technology or a centrifugal thread throwing technology, and carrying out heat treatment to obtain the alumina fiber. The method has the advantages of simple synthesis process, good sol stability and spinnability, low cost, no environmental pollution in heat treatment and the like. The prepared alumina fiber is stable in crystalline phase and microstructure, complete in fiber form under the high-temperature condition and capable of being applied to the fields of high-temperature heat insulation, catalyst carriers and the like.

Description

Technical Field

[0001] The invention relates to a preparation method of a polycarboxylate aluminum precursor and an aluminum oxide fiber, and belongs to the field of inorganic non-metallic materials. Background Art

[0002] Alumina fiber is an inorganic ceramic material with excellent properties such as resistance to high-temperature oxidation, high-temperature creep, chemical corrosion, and mechanical vibration. It is widely used in aerospace, high-temperature insulation, and catalyst carriers. The high specific strength, low thermal conductivity, and thermal insulation of alumina fibers are unmatched by other fiber materials. At present, the main methods for preparing alumina fibers are melt spinning, impregnation, slurry, and sol-gel. Compared with traditional preparation methods, the sol-gel method has the advantages of low processing temperature, high fiber purity, good uniformity, simple preparation process, diversified fiber design, and controllable performance. The preparation of alumina fibers by the sol-gel method requires three steps: 1) Using aluminum alkoxide or inorganic salt as a raw material and mixing it with a suitable spinning aid, a sol with uniform properties is obtained by hydrolysis or alcoholysis reaction; 2) Precursor gel fibers are obtained by centrifugal spinning, dry spinning, electrospinning, etc.; 3) A reasonable heat treatment system is set to obtain polycrystalline alumina fibers. In order to obtain high-quality alumina fibers, the above three steps need to be strictly controlled.

[0003] In recent years, a lot of research has been conducted on the preparation of alumina ceramic fibers, but there are still problems with the fibers being brittle and easy to break. Combining the three steps of the sol-gel method, the spinnability of the precursor sol and the solid content of alumina in the precursor fiber are the key factors in obtaining high-strength and high-toughness alumina fibers. Patent CN111235693B provides a method for preparing spun alumina fibers, wherein the mass ratio of Al2O3 in the polyaluminium chloride sol to SiO2 in the silica sol is (70-100): (0-30), and a spinning aid with a solid content of Al2O3 of 12-18wt% is added to the spinning solution. In addition, one or more crystal phase sintering aids and an emulsified paraffin solution are introduced to solve the problem of easy breakage and surface smoothness of the alumina fiber. Patent CN114685149B provides a functionalized alumina ceramic fiber and a preparation method thereof. In the preparation of the precursor solution, one or more of a grain nucleating agent, a grain inhibitor, and a sintering aid are added to optimize the performance of the alumina fiber. Compared with the sol preparation of patent CN111235693B, the amount of other substances added is reduced, but it still affects the preparation of the high-purity alumina fiber precursor sol. Patent CN115924946A provides a preparation method of an alumina fiber precursor sol, a sol, and an alumina fiber. Since the aluminum source and the oxide source react together, the amount of water added is reduced, the concentration of the reactants is increased, and the solid content of the prepared alumina fiber precursor sol can reach 15-30%. In the process of preparing the alumina fiber precursor sol, it is necessary to divide the aluminum source and pre-treat the oxide source in multiple portions and perform multiple complete reactions, and the second phase oxide source must be pre-treated with acid or alkali. Patent CN117658185A provides an alumina nanofiber and a preparation method thereof, wherein firstly, aluminum-lithium binary alloys (metal aluminum and lithium raw materials with purity greater than 99.9%) with different raw material ratios are smelted, and then the alloys are dealloyed in an inert atmosphere to obtain an alkoxide aluminum nanofiber precursor.

[0004] It can be seen from the above preparation methods of alumina fibers that the current methods have the problems that the spinnability of the precursor sol and the solid content of the precursor fiber cannot be satisfied at the same time, and the purity of the alumina fibers is not high. Therefore, improving the spinnability of the sol and the solid content of the fiber, simplifying the heat treatment process, reducing the preparation cost and environmental pollution to obtain high-strength, high-toughness, high-purity alumina fibers, and providing technical support for the preparation and industrial application of alumina fibers.

[0005] Therefore, in order to optimize the alumina precursor sol, prepare high-purity alumina fibers, and promote the industrial application of alumina fibers, the present invention is specially proposed. Summary of the invention

[0006] In view of the shortcomings of the prior art such as sol spinnability, solid content, heat treatment preparation process, and low purity of alumina, the present invention provides a method for preparing a polycarboxylate aluminum precursor and alumina fiber, providing a new approach for the industrial application of the preparation of alumina fiber. SUMMARY OF THE INVENTION

[0008] The invention utilizes the coordination effect of aluminum ions and carboxylic acid groups, prepares polycarboxylate aluminum precursors by potassium salt precipitation method, prepares aluminum oxide precursor fibers by electrostatic spinning method or centrifugal spinning method, obtains aluminum oxide fibers by heat treating the precursor fibers, and the aluminum oxide content of the aluminum oxide fibers is not less than 99.5%. The main crystal phase of the precursor heat treated to 800-1000°C is γ phase, and the main crystal phase of the precursor heat treated to 1200°C and above is α phase. Compared with the existing aluminum oxide precursor sol preparation method, this method has a simple preparation process, a low content of contaminating ions in the precursor, and the prepared aluminum oxide fibers still maintain a good fiber morphology at a high temperature of 1200°C. DETAILED DESCRIPTION OF THE INVENTION

[0010] The technical solution of the present invention is as follows:

[0011] According to the present invention, a method for preparing a polycarboxylate aluminum precursor and alumina fiber comprises the following steps:

[0012] (1) Preparation of polycarboxylate aluminum precursor

[0013] (a) weighing the aluminum source and dissolving it in anhydrous ethanol in a mass ratio of the aluminum source to anhydrous ethanol of 1:(1-60) to obtain an aluminum chloride ethanol solution;

[0014] (b) according to the mass ratio of KR1 to anhydrous ethanol being 1:(10-30), weighing potassium carboxylate salt and dissolving it in anhydrous ethanol to obtain a potassium carboxylate ethanol solution;

[0015] (c) slowly dropping the potassium carboxylate ethanol solution obtained in step (b) into the aluminum chloride ethanol solution obtained in step (a) at a molar ratio of KR1 to Al ion of (0-3):1, while stirring, to obtain an organic ligand aluminum ethanol mixed solution; after the dropwise addition is completed, continuing to stir sufficiently, filtering the precipitate, and obtaining a polycarboxylate aluminum precursor solution;

[0016] (d) pouring the aluminum carboxylate precursor solution obtained in step (c) into a flask, placing it on a rotary evaporator set at a temperature of 35 to 50° C. and evaporating it to dryness by reduced pressure distillation to obtain a polycarboxylate aluminum precursor.

[0017] (2) Preparation of alumina precursor fibers

[0018] Preparation of aluminum oxide precursor fibers by electrospinning: according to the mass ratio of aluminum polycarboxylate precursor to solvent being 1:(1.5-5), a certain mass of aluminum polycarboxylate precursor obtained in step (1) is weighed and slowly added into a certain mass of solvent, and continuously stirred until dissolved, and then a spinning aid of the mass of aluminum polycarboxylate precursor (0.5%-10%) is added, and stirring is continued until dissolved to obtain a precursor sol, and aluminum oxide precursor fibers are obtained by electrospinning technology;

[0019] Preparation of alumina precursor fibers by centrifugal spinning method: according to the mass ratio of polycarboxylate aluminum precursor to solvent being 1:(2-50), a certain mass of the polycarboxylate aluminum precursor obtained in step (1) is weighed and slowly added into a certain mass of solvent, and continuously stirred until dissolved, and then a spinnable precursor sol with a viscosity of 1-30 Pa·s is obtained by vacuum distillation, and alumina precursor fibers are obtained by centrifugal spinning technology.

[0020] (3) Preparation of alumina fibers

[0021] The alumina precursor fibers obtained in step (2) are heat-treated to a certain temperature under atmospheric conditions to obtain alumina inorganic fibers.

[0022] According to the preferred embodiment of the present invention, the preparation environment described in step (1) is carried out under ice bath conditions;

[0023] Preferably, according to the present invention, the mass ratio of the aluminum source to anhydrous ethanol in step (a) is 1:10-30;

[0024] According to the preferred embodiment of the present invention, the potassium carboxylate salt in step (b) preferably has a mass ratio of potassium carboxylate salt to anhydrous ethanol of 1:(10-25);

[0025] Preferably, according to the present invention, the molar ratio of the potassium carboxylate salt to the Al ion in step (c) is (1.0-3.5):1;

[0026] Preferably according to the present invention, the solvent in step (2) is anhydrous ethanol, anhydrous methanol, N,N-dimethylformamide, water or a combination thereof.

[0027] Preferably according to the present invention, the spinning aid in step (2) is one or a combination of polyvinyl pyrrolidone, polyethylene oxide, polyvinyl alcohol, polyvinyl butyral.

[0028] Preferably according to the present invention, the spinning aid described in step (2) is a polycarboxylate aluminum precursor with a mass fraction of: 1% to 5%. Preferably according to the present invention, the process conditions of the electrospinning method described in step (2) are: stainless steel needle model: 18 to 24G (inner diameter: 0.31 to 0.92mm), sol injection rate of 0.5 to 2mL / h, spinning voltage of 10 to 20kV, fiber receiving distance of 10 to 25cm, spinning environment temperature of 23 to 35°C, and spinning environment humidity of 20 to 55%.

[0029] Preferably, according to the present invention, the process conditions of the centrifugal spinning method described in step (2) are: the spinning environment temperature is 25-45°C, the spinning environment humidity is 25-60%, the centrifuge speed is 12000-25000r / min, and the spinning aperture is 0.20-0.45mm.

[0030] According to a preferred embodiment of the present invention, the atmosphere in step (3) is an air atmosphere.

[0031] Preferably, according to the present invention, the heat treatment system described in step (3) is: heating to 400-600°C at a heating rate of 0.5-3°C / min, and keeping warm for 60-120min; then heating to 800-1000°C at a heating rate of 3-5°C / min; then heating to 1500°C at a heating rate of 5-10°C / min, and keeping warm for 1-3h.

[0032] The excellent effects of the present invention are as follows:

[0033] 1. The present invention has simple process and low cost, and can realize the preparation of highly stable, high-viscosity and environmentally friendly aluminum oxide precursor sol.

[0034] 2. The alumina precursor fiber prepared by the present invention does not generate environmentally polluting gases during the heat treatment process. The prepared alumina can maintain the integrity of the fiber morphology at 1200°C. The alumina content in the alumina fiber is not less than 99.5%. The main crystal phase of the precursor heat-treated to 1200°C and above is α phase, which has good high-temperature crystal phase stability and fiber structure stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a photograph of the alumina precursor fiber obtained in Example 1 after heat treatment to 800°C.

[0036] Figure 2 This is the XRD spectrum of the alumina precursor fiber obtained in Example 2 after heat treatment to 1200°C.

[0037] Figure 3 This is a SEM photograph of the cross-section of the alumina precursor fiber obtained in Example 3 after heat treatment to 1200°C. DETAILED DESCRIPTION

[0038] The present invention will be further described below by way of embodiments in conjunction with the accompanying drawings, but is not limited thereto.

[0039] Embodiment 1:

[0040] A method for preparing alumina fiber comprises the following steps:

[0041] (a) According to the mass ratio of aluminum chloride to anhydrous ethanol being 1:25, 10.000 g of aluminum chloride was dissolved in 250.120 g of anhydrous ethanol to obtain an aluminum chloride ethanol solution; according to the molar ratio of potassium acetate to aluminum chloride being 2.8:1, 20.608 g of potassium acetate was dissolved in 309.126 g of anhydrous ethanol, and after dissolution, the mixture was slowly added dropwise to the aluminum chloride ethanol solution, and after the addition was completed, the mixture was stirred for 2 h and then filtered to precipitate, and the clear and transparent solution was placed on a rotary evaporator and evaporated to dryness at 38° C. to obtain a polyaluminum acetate precursor.

[0042] (b) 2.000 g of polyaluminum acetate precursor was dissolved in 10.000 g of anhydrous ethanol, and 0.03 g of polyethylene oxide (relative molecular weight 1,000,000) was added after dissolution. After dissolution, alumina precursor fibers were obtained by electrospinning. The electrospinning process conditions were: stainless steel jet needle model 22G, the distance from the receiving device roller was 20 cm, the injection rate was 1 mL / h, the spinning voltage was 15 kV, the spinning environment temperature was 25-30°C, and the spinning environment humidity was 45% to 55%.

[0043] (c) The alumina precursor fiber obtained in step (b) was heated to 600°C at a heating rate of 1°C / min under air conditions and kept at this temperature for 60 min; then heated to 800°C at a heating rate of 3°C / min and kept at this temperature for 3 h, and a photo of the alumina fiber heat-treated to 800°C was obtained, as shown in FIG. Figure 1 shown.

[0044] Embodiment 2:

[0045] As described in Example 1, the difference is that the aluminum chloride in step (a) is replaced with aluminum chloride hexahydrate and aluminum trichloride, and the obtained alumina precursor fiber is heated to 600°C at a heating rate of 1°C / min under air conditions and kept warm for 60 minutes; then heated to 1000°C at a heating rate of 3°C / min; then heated to 1200°C at a heating rate of 5°C / min, and kept warm for 3 hours, and the XRD spectrum of the alumina fiber heat-treated to 1200°C is obtained as shown Figure 2 As shown, the main crystal phase is α phase.

[0046] Embodiment 3:

[0047] As described in Example 1, the difference is that the molar ratio of potassium acetate to aluminum chloride used in step (a) is changed from 2.8:1 to 3:1. According to the mass ratio of aluminum chloride to anhydrous ethanol of 1:25, 10.000g of aluminum chloride is dissolved in 250.120g of anhydrous ethanol to obtain an aluminum chloride ethanol solution; according to the molar ratio of potassium acetate to aluminum chloride of 3:1, 22.080g of potassium acetate is dissolved in 350.205g of anhydrous ethanol, and after dissolution, it is slowly added dropwise to the aluminum chloride ethanol solution, and after the addition is completed, the precipitation is filtered after stirring for 2 hours, and the clear and transparent solution is placed on a rotary evaporator and evaporated to dryness at 40°C to obtain a polyaluminum acetate precursor.

[0048] Embodiment 4:

[0049] As described in Example 1, the difference is that the solvent used in step (b) is 75% ethanol solution. The SEM photo of the cross section of the aluminum oxide precursor fiber obtained by electrospinning and heat-treated to 1200°C is as follows: Figure 3 shown.

[0050] Embodiment 5:

[0051] As described in Example 1, the difference is that the polyethylene oxide in step (b) is replaced by polyvinyl pyrrolidone. 2.000g of polyaluminum acetate precursor is dissolved in 10.000g of anhydrous ethanol, and 0.09g of polyvinyl pyrrolidone (relative molecular weight 1,300,000) is added after dissolution. After dissolution, aluminum oxide precursor fiber is obtained by electrospinning. The electrospinning process conditions are: stainless steel injection needle model 22G, the distance from the receiving device roller is 20cm, the injection rate is 1.5mL / h, the spinning voltage is 18kV, the spinning environment temperature is 25-35℃, and the spinning environment humidity is 45% to 55%.

[0052] Embodiment 6:

[0053] As described in Example 1, the difference is that the electrostatic spinning method in step (b) is replaced by a centrifugal spinning method to obtain an alumina precursor fiber. According to the mass ratio of the polycarboxylate aluminum precursor to the solvent of 1:20, 1.000g of the obtained polycarboxylate aluminum precursor is weighed and slowly added to 20.000g of anhydrous ethanol, and continuously stirred until dissolved. A spinnable precursor sol with a viscosity of 20Pa·s is obtained by a vacuum distillation method, and an alumina precursor fiber is obtained by a centrifugal spinning technology. The process conditions of centrifugal spinning are: the spinning environment temperature is 25°C, the spinning environment humidity is 30-45%, the spinning aperture is 0.25mm, and the centrifuge speed is 18000r / min.

Claims

1. A method for preparing a polycarboxylate aluminum precursor and alumina fiber, characterized in that: The chemical formula of the polycarboxylate aluminum is Al(OH) x (R1COO) y (R2COOH) z ·nH2O(R1, R2=H, CH3, C2H5-, C3H7-, C3H5O-), wherein 0<x<4, 0≤y≤2, 0≤z≤2; the alumina content of the alumina fiber is not less than 99.5%, the main crystal phase of the precursor heat-treated to 800-1000°C is γ phase, and the main crystal phase of the precursor heat-treated to 1200°C and above is α phase. The aluminum carboxylate precursor and the aluminum oxide fiber are prepared by the following steps: (1) Preparation of polycarboxylate aluminum precursor (a) dissolving the aluminum source in anhydrous ethanol to obtain an aluminum chloride ethanol solution according to a mass ratio of the aluminum source to anhydrous ethanol of 1:(1-60); (b) dissolving potassium carboxylate salt in anhydrous ethanol in a mass ratio of KR1 to anhydrous ethanol of 1:(10-30) to obtain a potassium carboxylate ethanol solution; (c) slowly dropping the potassium carboxylate ethanol solution obtained in step (b) into the aluminum chloride ethanol solution obtained in step (a) at a molar ratio of KR1 to Al ion of (0-5):1, while stirring, to obtain an organic ligand aluminum ethanol mixed solution; after the dropwise addition is completed, continuing to stir sufficiently, filtering the precipitate, and obtaining a polycarboxylate aluminum precursor solution; (d) pouring the polycarboxylate aluminum precursor solution obtained in step (c) into a flask, placing it on a rotary evaporator set at a temperature of 35 to 50° C. and evaporating it to dryness by reduced pressure distillation to obtain an aluminum carboxylate precursor. (2) Preparation of alumina precursor fibers Preparation of aluminum oxide precursor fibers by electrospinning: according to the mass ratio of aluminum polycarboxylate precursor to solvent being 1:(1.5-5), a certain mass of aluminum polycarboxylate precursor obtained in step (1) is weighed and slowly added into a certain mass of solvent, and continuously stirred until dissolved, and then a spinning aid of the mass of aluminum polycarboxylate precursor (0.5%-10%) is added, and stirring is continued until dissolved to obtain a precursor sol, and aluminum oxide precursor fibers are obtained by electrospinning technology; Preparation of alumina precursor fibers by centrifugal spinning method: according to the mass ratio of polycarboxylate aluminum precursor to solvent being 1:(2-50), a certain mass of the polycarboxylate aluminum precursor obtained in step (1) is weighed and slowly added into a certain mass of solvent, and continuously stirred until dissolved, and then a spinnable precursor sol with a viscosity of 1-30 Pa·s is obtained by vacuum distillation, and alumina precursor fibers are obtained by centrifugal spinning technology. (3) Preparation of alumina fibers The alumina precursor fibers obtained in step (2) are heat-treated to a certain temperature under atmospheric conditions to obtain alumina inorganic fibers.

2. The alumina fiber according to claim 1, characterized in that , the aluminum source described in step (a) is aluminum chloride hexahydrate, aluminum chloride or a combination thereof.

3. The alumina fiber according to claim 1, characterized in that The potassium carboxylate salt described in step (b) includes potassium acetate, potassium monoethyl malonate, potassium sorbate, monopotassium acetylenedicarboxylate, potassium tetraethyl ester, potassium stearate, potassium isooctanoate or a combination thereof.

4. The alumina fiber according to claim 1, characterized in that The solvent described in step (2) is one of water, anhydrous methanol, anhydrous ethanol, N,N-dimethylformamide, N,N-dimethylacetamide, dichloromethane or a combination thereof.

5. The alumina fiber according to claim 1, characterized in that The spinning aid described in step (2) is one of polyvinyl pyrrolidone, polyethylene oxide, polyvinyl alcohol, polyacrylonitrile, polyvinylidene fluoride, alcohol-soluble polyamide, polyvinyl butyral or a combination thereof.

6. The alumina fiber according to claim 1, characterized in that The process conditions of the electrospinning method described in step (2) are: stainless steel needle model: 16~26G (inner diameter: 0.25~1.25mm), injection rate is 0.2~4mL / h, spinning voltage is 5~35kV, fiber receiving distance is 5~40cm, spinning environment temperature is 5~65℃, and spinning environment humidity is 10~85%.

7. The alumina fiber according to claim 1, characterized in that The process conditions of the centrifugal spinning method described in step (2) are: the spinning environment temperature is 5-60°C, the spinning environment humidity is 10-80%, the centrifuge speed is 10000-55000r / min, and the spinning aperture is 0.10-0.80mm.

8. The alumina fiber according to claim 1, characterized in that The atmosphere described in step (3) is one of air, nitrogen, water vapor, rare gas, hydrogen, ammonia or a combination thereof.

9. The alumina fiber according to claim 1, characterized in that The heat treatment process system described in step (3) is as follows: heat treatment to 400-600°C at a heating rate of 0.5-5°C / min, and heat preservation for 30-120min; then heat treatment to 800-1000°C at a heating rate of 2-10°C / min; then heat treatment to 1500°C at a heating rate of 5-15°C / min, and heat preservation for 1-5h.

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