Alumina fiber precursor and preparation method therefor, and alumina fiber

Abstract

The present application relates to an alumina fiber precursor and a preparation method therefor, and an alumina fiber. The raw material of the alumina fiber precursor comprises a precursor spinning solution, and the raw material components of the precursor spinning solution comprise: a nano-aluminum sol and a surfactant, wherein the weight of the surfactant is 0.1%-6.0% of the weight of alumina in the nano-aluminum sol.

Description

Alumina fiber precursor and its preparation method, alumina fiber

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese patent application No. 202411563040.7, filed on November 5, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of alumina fiber technology, and in particular to an alumina fiber precursor and its preparation method, and alumina fiber. Background Technology

[0004] Alumina fiber is a high-performance polycrystalline inorganic fiber with advantages such as high mechanical strength, low thermal conductivity, and electrical insulation. It maintains high strength and modulus, especially in high-temperature oxidizing environments, making it a promising ultra-lightweight high-temperature structural material for such applications. The sol-gel method is an important industrial method for preparing alumina fibers. This method uses inorganic aluminum salts or organic aluminum alkoxides as precursors, which undergo hydrolysis / alcoholization to obtain a homogeneous sol. The sol is then aged and concentrated to form a spinnable precursor spinning solution. The precursor spinning solution is processed using spinning technology to obtain alumina fiber precursors. Finally, these precursors are treated with different sintering processes to obtain polycrystalline alumina fibers. The quality and performance of the alumina fiber precursors directly affect the uniformity of the alumina fiber's microstructure and the stability of its application performance.

[0005] However, research on the properties of alumina fiber precursors is still lacking. Furthermore, the uniformity of the microstructure of alumina fiber precursors is difficult to control, resulting in relatively low fiber strength and a high breakage rate during the spinning process. Summary of the Invention

[0006] By utilizing one or more embodiments of the present disclosure, an alumina fiber precursor and its preparation method, as well as an alumina fiber, solves the problem of how to improve the uniformity of the microstructure of the alumina fiber precursor.

[0007] In a first aspect, this disclosure provides an alumina fiber precursor, the raw material of which includes a precursor spinning solution, the raw material components of which include nano-alumina sol and a surfactant; wherein the weight of the surfactant is 0.1% to 6.0% of the weight of alumina in the nano-alumina sol.

[0008] In a second aspect, this disclosure provides a method for preparing alumina fiber precursor as described in any one of the first aspects, comprising: obtaining alumina nano-sol; mixing the alumina nano-sol with the surfactant to obtain a mixture; aging and concentrating the mixture sequentially to obtain a precursor spinning solution; and spinning the precursor spinning solution to obtain alumina fiber precursor.

[0009] Thirdly, this disclosure provides a method for preparing alumina fiber precursor according to any one of the first aspects, comprising: obtaining nano-alumina sol; mixing the nano-alumina sol, a composite grain control agent, and a surfactant to obtain a mixture; aging and concentrating the mixture sequentially to obtain a precursor spinning solution; and spinning the precursor spinning solution to obtain alumina fiber precursor.

[0010] Fourthly, this disclosure provides an alumina fiber, wherein the raw material of the alumina fiber includes the alumina fiber precursor described in any one of the first aspects. Attached Figure Description

[0011] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0012] To more clearly illustrate the technical solutions in the embodiments or related technologies of this disclosure, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 shows a schematic flowchart of a method for preparing alumina fiber precursor according to some embodiments of the present disclosure.

[0014] Figure 2 shows the particle size distribution of the nano-aluminum sol according to Example 1 of this disclosure.

[0015] Figure 3 shows a TEM image of an aged mixture of nano-aluminum sol, composite grain control agent, and surfactant provided in Example 1 of this disclosure.

[0016] Figure 4 shows a SEM image of the alumina fiber precursor provided according to Example 1 of this disclosure.

[0017] Figure 5 shows the stretch curve of the alumina fiber precursor provided according to Example 1 of this disclosure.

[0018] Figure 6 shows a SEM image of alumina fibers provided according to Example 1 of this disclosure.

[0019] Figure 7 shows the tensile curve of the alumina fiber provided according to Example 1 of this disclosure. Embodiments of the present invention

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0021] Various embodiments of this disclosure may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this disclosure; therefore, it should be considered that the range description has specifically disclosed all possible subranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0022] In this document, terms including "comprising" and the like mean "including but not limited to". "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A alone, A and B simultaneously, or B alone; where A and B can be singular or plural. "At least one" means one or more, and "more than one" means two or more. "At least one", "at least one of the following", or similar expressions refer to any combination of these items, including any combination of single or plural items; for example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0023] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this disclosure are available on the market or can be prepared by existing methods.

[0024] Alumina precursor sols can be classified into organic, inorganic, and organic-inorganic mixed systems. Due to the complex formation process of alumina precursor sols, the composition and structure of alumina grains (i.e., hydrated alumina grains) within them vary significantly. During the concentration process of the alumina precursor sol, the alumina grains aggregate to form secondary particles or larger aggregates. The inhomogeneity of the aggregate structure leads to poor spinnability of the alumina precursor sol, necessitating the use of large amounts of spinning auxiliaries to improve spinning quality. Although this can improve the surface quality of alumina fiber precursors, the internal structure is difficult to control, resulting in relatively low strength and a high breakage rate during spinning. Therefore, the poor uniformity of the alumina fiber structure and low strength are pressing problems to be solved in the field of alumina fibers. To date, research on the properties of alumina fiber precursors is still lacking. The performance of alumina fiber precursors is not only related to the spinnability of alumina precursor sols, but also to the uniformity and cross-linking degree of aggregates in the alumina precursor sols. Simply using the spinning length and surface quality of alumina fiber precursors to measure their performance is incomplete. Preparing alumina fiber precursors with uniform structure and excellent mechanical properties has become the key to the preparation of high-performance alumina fibers.

[0025] Therefore, in a first aspect, according to some embodiments of the present disclosure, an alumina fiber precursor is provided, wherein the raw material of the alumina fiber precursor includes a precursor spinning solution, and the raw material components of the precursor spinning solution include nano-alumina sol and a surfactant; wherein the weight of the surfactant is 0.1% to 6.0% of the weight of alumina in the nano-alumina sol.

[0026] In some embodiments of this disclosure, the nano-aluminum sol is a colloidal solution in which positively charged hydrated alumina grains are uniformly dispersed in water. The nano-aluminum sol possesses nanoscale size, a large specific surface area, good stability, and good dispersibility, which can impart high dispersibility and high activity to the precursor spinning solution, improving the stability of the spinning process and the performance of the alumina fiber precursor. Surfactants, with their unique molecular structure characteristics (such as linear configuration) and adsorption mechanisms, can precisely control the aggregation behavior of alumina grains (i.e., hydrated alumina grains) in the nano-aluminum sol. Specifically, surfactants adsorb onto the surface of alumina grains through a bridging mechanism, forming chain-like connections, while their long-chain structure extends outwards, constructing a steric hindrance layer. This steric hindrance effect effectively hinders the close contact of alumina grains, preventing disordered and compact agglomeration between alumina grains, thereby improving the dispersibility and stability of the nano-aluminum sol. Furthermore, surfactants, through anisotropic adsorption mechanisms (such as the synergistic effect of electrostatic shielding and steric hindrance), induce the orderly aggregation of alumina grains along specific directions, forming one-dimensional chain aggregates, thereby improving the stretch flow properties and spinnability of the precursor spinning solution. The weight of the surfactant can be 0.1% to 6.0% of the weight of alumina in the nano-alumina sol. Within this range, the surfactant, on the one hand, inhibits the disordered and compact aggregation of alumina grains through electrostatic steric hindrance, ensuring high dispersibility and stability of the system; on the other hand, the hydrophilic-hydrophobic segments of the surfactant generate anisotropic adsorption on the grain surface, causing the alumina grains to connect orderly along one-dimensional directions, forming longer and less entangled chain aggregates. This controllable aggregation state significantly improves the stretch flow properties of the spinning solution, thereby obtaining a highly dispersed, highly uniform, and highly stable precursor spinning solution, ultimately improving the uniformity of the microstructure of the alumina fiber precursor. If the weight of the surfactant exceeds 6.0% of the weight of alumina in the nano-alumina sol, it may form a large number of pores in the subsequent alumina fibers, making it difficult to densify the alumina fibers. If the weight of the surfactant is less than 0.1% of the weight of alumina in the nano-alumina sol, it may be difficult to improve the uniformity of the microstructure of the alumina fiber precursor. For example, the weight of the surfactant can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, 6.0% of the weight of alumina in the nano-alumina sol.

[0027] In some embodiments, the surfactant may include at least one of the following: polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyethylene glycol (PEG), polyethylene oxide (PEO), and polyacrylic acid (PAA).

[0028] In some embodiments of this disclosure, the surfactant may be one or more of polyvinylpyrrolidone, polyvinyl alcohol, carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene glycol, polyethylene oxide, and polyacrylic acid.

[0029] In some embodiments, the raw material components of the precursor spinning solution also include a composite grain control agent.

[0030] In some embodiments of this disclosure, the raw material components of the precursor spinning solution also include a composite grain control agent. The grain control agent can control the nucleation and growth of alumina grains, maintaining a stable microstructure and preventing abnormal grain growth that could affect the density and mechanical properties of the alumina fibers. Compared to a single grain control agent, the composite grain control agent can simultaneously regulate both the size of the alumina grains and the density of the alumina fibers.

[0031] In some embodiments, the composite grain control agent includes at least two of the following: SiO2, CaO, MgO, Fe2O3, Y2O3, ZrO2, and Al2O3.

[0032] In some embodiments of this disclosure, the composite grain control agent can be a combination of two or more of SiO2, CaO, MgO, Fe2O3, Y2O3, ZrO2, and Al2O3. These grain control agents can act as nucleation agents for alumina grains, increasing the nucleation rate and refining the microstructure of alumina fibers. The grain control agent can form a eutectic system with alumina, which is beneficial for the densification of alumina fibers. Simultaneously, the grain control agent can react with alumina to form new microstructures, inhibiting abnormal growth of alumina grains and improving the stability of the alumina fiber microstructure. Furthermore, since the composite grain control agent is an oxide, it can optimize the subsequent sintering process of the alumina fiber precursor, improving the purity and uniformity of the microstructure of the alumina fibers, avoiding side reactions, and thus reducing impurities in the fibers. The physical state of the grain control agent can be nanoparticles or colloidal aqueous dispersions.

[0033] In some embodiments, the weight of the composite grain control agent is 0.1% to 18% of the weight of alumina in the nano-alumina sol.

[0034] In some embodiments of this disclosure, the weight of the composite grain control agent can be 0.1% to 18% of the weight of alumina in the nano-alumina sol, so as to fully control the nucleation and growth of alumina grains, thereby obtaining alumina fibers with a fine, dense, and uniform microstructure. If the weight of the composite grain control agent is higher than 18% of the weight of alumina in the nano-alumina sol, it may be difficult to obtain dense alumina fibers through subsequent sintering of the alumina fiber precursor; if the weight of the composite grain control agent is lower than 0.1% of the weight of alumina in the nano-alumina sol, it may be difficult to control the nucleation and growth of alumina grains. For example, the weight of the composite grain control agent can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18% of the weight of alumina in the nano-alumina sol.

[0035] In some embodiments, the alumina fiber precursor meets the following specifications: fineness of 1.5 dtex to 7.2 dtex and strength of 0.1 cN / dtex to 4.0 cN / dtex.

[0036] In some embodiments of this disclosure, the alumina fiber precursor has a relatively uniform structure and very high strength, which solves the problems of poor uniformity and high breakage rate of alumina fiber precursor.

[0037] Secondly, this disclosure provides a method for preparing alumina fiber precursor according to any one of the first aspects, comprising:

[0038] Nano-aluminum sol was obtained;

[0039] The nano-aluminum sol and the surfactant are mixed to obtain a mixture.

[0040] The mixture was sequentially aged and concentrated to obtain a precursor spinning solution; and...

[0041] The precursor spinning solution is spun to obtain alumina fiber precursor.

[0042] Thirdly, this disclosure provides a method for preparing alumina fiber precursor according to any one of the first aspects. Figure 1 shows a schematic flowchart of a method for preparing alumina fiber precursor according to some embodiments of this disclosure; referring to Figure 1, the method for preparing alumina fiber precursor includes:

[0043] S1. Obtain nano-aluminum sol.

[0044] S2. Mix the nano-aluminum sol, composite grain control agent and surfactant to obtain a mixture.

[0045] S3. The mixture is subjected to aging and concentration sequentially to obtain the precursor spinning solution. And,

[0046] S4. Spin the precursor spinning solution to obtain alumina fiber precursor.

[0047] In some embodiments, obtaining nano-aluminum sol includes: performing a solvothermal sol reaction between hydrated alumina and a complex carboxylic acid to obtain nano-aluminum sol.

[0048] In some embodiments, the temperature of the solvothermal sol-gel reaction is 60°C to 200°C, and the pH value is 1.0 to 4.0.

[0049] In some embodiments, the carboxyl group in the complex carboxylic acid has a weight fraction of 60% to 90%.

[0050] In some embodiments, the complex carboxylic acid includes at least two of the following: formic acid, acetic acid, lactic acid, tartaric acid, and citric acid.

[0051] In some embodiments of this disclosure, hydrated alumina is an alumina compound containing water of crystallization, whose general chemical formula can be represented as (Al2O3·nH2O, 0.5≤n≤6). This hydrated alumina can be one or more combinations of boehmite, diatomite, and aluminum hydroxide. As one embodiment of step S1, it may include: preparing a slurry from readily soluble hydrated alumina (Al2O3·nH2O, 0.5≤n≤6); adding a complex carboxylic acid solution to the slurry to adjust its pH; performing a solvothermal sol reaction at a temperature of 60°C to 200°C; filtering and centrifuging the product of the solvothermal sol reaction to obtain nano-aluminum sol; the solid phase weight of this slurry can be 5% to 30% (based on Al2O3).

[0052] The composite carboxylic acid in the solution provides an acidic environment during the solvothermal gelation reaction. Furthermore, the composite carboxylic acid can react with hydrated alumina to form nano-alumina sol. During the precursor spinning solution preparation stage, on the one hand, the active sites of alumina grains (i.e., hydrated alumina grains) coordinate with carboxylic acid molecules, which is beneficial for the formation of chain-like structures in the alumina grains, thereby improving the spinnability of the precursor spinning solution. On the other hand, the Al-OH groups on the surface of the alumina grains undergo a condensation reaction with the -COOH groups of the carboxylic acid molecules, forming a strongly cross-linked Al-OC structure. This chemical connection is beneficial for improving the strength of the alumina fiber precursor. Since different carboxylic acids have different chemical structures and properties, their interaction with hydrated alumina may also differ. Therefore, by using composite carboxylic acids, their synergistic effect can be utilized to improve the gelation effect on hydrated alumina. The carboxyl group in the carboxylic acid structure ionizes into hydrogen ions in the solvent. These hydrogen ions undergo proton exchange with the Al-OH groups on the surface of hydrated alumina, while the carboxylate group (-COOH) is formed.- It forms Al-OC coordination bonds with surface aluminum atoms to generate surface Al-COO. - Coordination structure. The surface Al-COO - The formation of coordination structures on the surface of alumina grains imbues them with an electrical charge, resulting in electrostatic repulsion and preventing grain aggregation. This allows the alumina grains to exist stably in the solvent, forming nano-alumina sols. Both carboxyl groups and hydroxyl groups on the surface of hydrated alumina can form hydrogen bonds, increasing the contact opportunities between hydrated alumina and different carboxylic acid molecules, promoting acid-base reactions and ligand exchange reactions, thereby facilitating the formation of nano-alumina sols.

[0053] The process parameters for the solvothermal sol-gel reaction described above include: a temperature of 60℃ to 200℃ and a pH value of 1.0 to 4.0. Under these parameters, hydrated alumina and the complex carboxylic acid can react fully to form stable nano-aluminum sol. For example, the temperature can be 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, etc.; and the pH value can be 1.0, 2.0, 3.0, 4.0, etc. Furthermore, the reaction time can be 2 hours to 24 hours.

[0054] The weight fraction of carboxyl groups in the composite carboxylic acid can be 60%–90%. The surface of hydrated alumina is rich in Al–OH hydroxyl groups, and the efficiency of the solvothermal sol reaction mainly depends on the ionization constant of the carboxyl groups in the carboxylic acid and their acid-base / coordination reactivity with the surface Al–OH groups. Therefore, maintaining an appropriate carboxyl group ratio in the carboxylic acid plays a crucial role in forming stable nano-aluminum sol and subsequent spinnability. For example, the weight fraction of carboxyl groups in this composite carboxylic acid can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc. This composite carboxylic acid can be a combination of two or more of formic acid, acetic acid, lactic acid, tartaric acid, and citric acid.

[0055] In some embodiments of this disclosure, the grain control agent and the alumina grains in the nano-alumina sol can fully contact each other to form a uniformly dispersed sol system. The surfactant adsorbs on the surface of the alumina grains and the grain control agent to form a physical barrier, while adjusting their surface charge, increasing the electrostatic repulsion between the alumina grains, preventing contact and aggregation between the alumina grains, thereby improving the dispersion characteristics of the grain control agent and the alumina grains, and thus improving the spinnability of the precursor spinning solution.

[0056] In some implementations, the aging temperature is 30°C to 80°C.

[0057] In some embodiments of this disclosure, the aging temperature can be from 30°C to 80°C. Aging allows the alumina grains of the nano-alumina sol to fully interact with the surfactant, causing the alumina grains to aggregate and interconnect to form a linear structure. Aging also facilitates the subsequent concentration process by controlling the aggregation mode of the alumina grains, inducing the alumina grain aggregates to form longer chain-like structures, and avoiding abnormal or excessive agglomeration of the alumina grains, thereby obtaining uniform alumina grain aggregates. Therefore, after aging and concentration, a spinnable precursor spinning solution is obtained. For example, the aging temperature can be 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 70°C, 75°C, 80°C, etc. Furthermore, the aging time can be from 10 hours to 48 hours.

[0058] In some embodiments of this disclosure, the spinning process parameters may include: the length of the spinning tunnel is 1m to 10m; the environmental parameters of the spinning tunnel are as follows: wind speed is 0.1m / s to 1m / s, temperature is 20℃ to 150℃, and humidity is 20% to 70%. The precursor spinning solution enters the spinning tunnel through the micropores of the spinneret, and undergoes drying and stretching deformation in the spinning tunnel to obtain alumina fiber precursor. Under the action of the above spinning process parameters, the spinning environment can be optimized, the solvent evaporation rate can be controlled, and the spinning process can be made more stable and continuous, thereby obtaining uniform alumina fiber precursor.

[0059] The method for preparing alumina fiber precursor uses the aforementioned alumina fiber precursor as raw material. The specific raw materials for the alumina fiber precursor can be found in the above embodiments. Since this method for preparing alumina fiber precursor possesses all the technical features of some of the above embodiments, it therefore has at least all the beneficial effects brought about by the above embodiments, and will not be elaborated further here.

[0060] Thirdly, this disclosure provides an alumina fiber, the raw material of which includes the alumina fiber precursor described in any one of the first aspects.

[0061] In some embodiments of this disclosure, alumina fibers are prepared from the aforementioned alumina fiber precursor. The fineness of the alumina fibers (monofibers) is 3.1 dtex to 5.0 dtex, and the strength is 5 cN / dtex to 12 cN / dtex.

[0062] The alumina fiber is prepared using the aforementioned alumina fiber precursor, and therefore the raw material for this alumina fiber precursor can refer to the above embodiments. Since this alumina fiber possesses all the technical features of some of the above embodiments, it therefore has at least all the beneficial effects brought about by some of the above embodiments, which will not be elaborated further here.

[0063] The present disclosure is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the disclosure. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If no corresponding national standard exists, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0064] Example 1

[0065] An alumina fiber precursor, the raw material of which includes a precursor spinning solution, the raw material components of which include: nano-alumina sol, surfactant and composite grain control agent; wherein the weight of the surfactant is 1.4% of the weight of alumina in the nano-alumina sol; the surfactant includes PVP and PEO.

[0066] The weight of the composite grain control agent is 1.6% of the weight of alumina in the nano-aluminum sol; the composite grain control agent includes silica sol, CaO and MgO, and the solid phase weight of silica sol is 30%.

[0067] The preparation method of the above-mentioned alumina fiber precursor includes the following steps.

[0068] (1) Preparation of nano-aluminum sol

[0069] 500g of boehmite (Al2O3 content 62%) was mixed with deionized water to prepare a slurry, the solid phase weight of which was 15% (based on Al2O3). A complex carboxylic acid, comprising 50g formic acid, 54g acetic acid, and 10g citric acid, was added to the slurry to maintain the pH at 2.1. A solvothermal sol-gel reaction was then carried out at 80℃ for 4 hours. The sol obtained from the solvothermal sol-gel reaction was then filtered to remove undissolved large particles. The filtrate was then centrifuged to further remove undissolved impurities, resulting in a uniformly dispersed nano-aluminum sol.

[0070] (2) Preparation of precursor spinning solution

[0071] A composite grain control agent was added to the nano-aluminum sol obtained in step (1). The composite grain control agent included 8g of silica sol with a solid weight of 30%, 1.6g of CaO and 0.8g of MgO. After stirring and mixing evenly, a surfactant was added to it. The surfactant included 3.1g of PVP and 1.2g of PEO. After mixing, the mixture was aged at 45°C for 24h. Then the aged mixture was concentrated to obtain a spinnable precursor spinning solution.

[0072] (3) Preparation of alumina fiber precursor

[0073] The precursor spinning solution obtained in step (2) is spun on a dry spinning equipment with a spinning tunnel length of 4m and tunnel environmental parameters of wind speed 0.3m / s, temperature 85℃, and humidity 55%. The alumina fiber precursor is obtained by bundling and collecting the fibers at a speed of 150m / min.

[0074] The obtained alumina fiber precursor has a fineness of 2.65 dtex and a strength of 3.22 cN / dtex.

[0075] The alumina fiber precursor obtained above is continuously sintered to obtain alumina fiber with a fineness of 3.91 dtex and a strength of 9.90 cN / dtex.

[0076] For example, Figure 2 shows the particle size distribution of the nano-aluminum sol provided according to Example 1 of this disclosure. Referring to Figure 2, the particle size distribution of the nano-aluminum sol exhibits a unimodal shape, with a relatively concentrated and uniform particle size distribution, and an average particle size of 11.7 nm. Figure 3 shows a transmission electron microscope (TEM) image of the mixture of nano-aluminum sol, composite grain control agent, and surfactant provided according to Example 1 of this disclosure after aging. Referring to Figure 3, after aging, the alumina grains in the mixture aggregate to form aggregates of approximately 60 nm to 90 nm. These aggregates interconnect to form a linear structure, which has a positive effect on improving the spinnability of the spinning solution and the uniformity of the alumina fiber precursor. Figure 4 shows a scanning electron microscope (SEM) image of the alumina fiber precursor provided according to Example 1 of this disclosure. Referring to Figure 4, the size of the alumina fiber precursor is approximately 15 μm, with a smooth surface free of cracks. Figure 5 shows the tensile curve of the alumina fiber precursor provided according to Example 1 of this disclosure. Please refer to Figure 5; the breaking strength of the alumina fiber precursor is as high as 8.53 cN. Figure 6 shows a SEM image of the alumina fiber provided according to Example 1 of this disclosure. Please refer to Figure 6; the size of the alumina fiber is approximately 11 μm. Figure 7 shows the tensile curve of the alumina fiber provided in Example 1 of this disclosure. Please refer to Figure 7; the breaking strength of the alumina fiber is 38.70 cN.

[0077] Example 2

[0078] An alumina fiber precursor, the raw material of which includes a precursor spinning solution, the raw material components of which include: nano-alumina sol, surfactant and composite grain control agent; wherein, the weight of the surfactant is 0.8% of the weight of alumina in the nano-alumina sol; the surfactant includes PVP and PVA.

[0079] The weight of the composite grain control agent is 1.1% of the weight of alumina in the nano-aluminum sol; the composite grain control agent includes silica sol and Fe2O3, with the solid phase weight of silica sol being 30%.

[0080] The preparation method of the above-mentioned alumina fiber precursor includes the following steps.

[0081] (1) Preparation of nano-aluminum sol

[0082] 500g of boehmite (Al2O3 content 80%) was mixed with deionized water to prepare a slurry, the solid weight of which was 17% (based on Al2O3). A complex carboxylic acid, comprising 46g formic acid, 50g acetic acid, and 5g tartaric acid, was added to the slurry to maintain the pH at 1.7. The slurry was then subjected to a solvothermal sol reaction at 110℃ for 8 hours. The sol obtained from the solvothermal sol reaction was then filtered to remove undissolved large particles. The filtrate was then centrifuged to further remove undissolved impurities, resulting in a uniformly dispersed nano-aluminum sol.

[0083] (2) Preparation of precursor spinning solution

[0084] A composite grain control agent was added to the nano-aluminum sol obtained in step (1). The composite grain control agent included 8g of silica sol with a solid weight of 30% and 1.8g of Fe2O3. After stirring and mixing evenly, a surfactant was added to it. The surfactant included 2.6g of PVP and 0.4g of PVA. After mixing, the mixture was aged at 60°C for 20h. Then, the aged mixture was concentrated to obtain a spinnable precursor spinning solution.

[0085] (3) Preparation of alumina fiber precursor

[0086] The precursor spinning solution obtained in step (2) is spun on a dry spinning equipment with a spinning tunnel length of 3m and tunnel environmental parameters of wind speed 0.3m / s, temperature 90℃, and humidity 45%. The alumina fiber precursor is obtained by bundling and collecting the fibers at a speed of 100m / min.

[0087] The obtained alumina fiber precursor has a fineness of 3.47 dtex and a strength of 2.18 cN / dtex.

[0088] The alumina fiber precursor obtained above is continuously sintered to obtain alumina fiber with a fineness of 4.09 dtex and a strength of 8.55 cN / dtex.

[0089] Example 3

[0090] An alumina fiber precursor, the raw material of which includes a precursor spinning solution, the raw material components of which include: nano-alumina sol, surfactant and composite grain control agent; wherein, the weight of the surfactant is 2.5% of the weight of alumina in the nano-alumina sol; the surfactant includes CMC and PAA.

[0091] The weight of the composite grain control agent is 1.4% of the weight of alumina in the nano-aluminum sol; the composite grain control agent includes silica sol, CaO and MgO, and the solid phase weight of silica sol is 30%.

[0092] The preparation method of the above-mentioned alumina fiber precursor includes the following steps.

[0093] (1) Preparation of nano-aluminum sol

[0094] 500g of aluminum hydroxide (Al2O3 content 65%) was mixed with deionized water to prepare a slurry. The solid weight of the slurry was 12% (based on Al2O3). A complex carboxylic acid was added to the slurry. The carboxyl group weight fraction of the complex carboxylic acid was 85.3%. The complex carboxylic acid included 50g of formic acid, 30g of acetic acid and 9g of lactic acid. The pH of the slurry was controlled at 2.4 by adding the complex carboxylic acid. The solvothermal sol reaction was carried out at 145℃ for 6 hours. The sol obtained by the solvothermal sol reaction was then filtered to remove undissolved large particulate impurities. The filtrate was then centrifuged to further remove undissolved impurities, resulting in a uniformly dispersed nano-aluminum sol.

[0095] (2) Preparation of precursor spinning solution

[0096] A composite grain control agent was added to the nano-aluminum sol obtained in step (1). The composite grain control agent included 6g of silica sol with a solid weight of 30%, 1.5g of CaO and 1.0g of MgO. After stirring and mixing evenly, a surfactant was added to it. The surfactant included 6.8g of CMC and 1.2g of PAA. After mixing, the mixture was aged at 50°C for 30h. Then the aged mixture was concentrated to obtain a spinnable precursor spinning solution.

[0097] (3) Preparation of alumina fiber precursor

[0098] Same as Example 1.

[0099] The obtained alumina fiber precursor has a fineness of 3.08 dtex and a strength of 2.64 cN / dtex.

[0100] The alumina fiber precursor obtained above is continuously sintered to obtain alumina fiber with a fineness of 4.16 dtex and a strength of 8.19 cN / dtex.

[0101] Example 4

[0102] An alumina fiber precursor, the composition of which is the same as in Example 1.

[0103] A method for preparing alumina fiber precursor includes the following steps.

[0104] (1) Preparation of nano-aluminum sol

[0105] 500g of boehmite (Al2O3 content 62%) was mixed with deionized water to prepare a slurry. The solid weight of the slurry was 15% (based on Al2O3). A complex carboxylic acid was added to the slurry. The carboxyl group weight fraction of the complex carboxylic acid was 75.5%. The complex carboxylic acid included 23g of formic acid, 50g of propionic acid and 9g of lactic acid. The pH of the slurry was controlled at 1.5 by adding the complex carboxylic acid. The solvothermal sol reaction was carried out at 105℃ for 7h. The sol obtained by the solvothermal sol reaction was then filtered to remove undissolved large particles of impurities. The filtrate was then centrifuged to further remove undissolved impurities, resulting in a uniformly dispersed nano-aluminum sol.

[0106] (2) Preparation of precursor spinning solution

[0107] Same as Example 1.

[0108] (3) Preparation of alumina fiber precursor

[0109] Same as Example 1.

[0110] The obtained alumina fiber precursor has a fineness of 2.93 dtex and a strength of 2.68 cN / dtex.

[0111] The alumina fiber precursor obtained above is continuously sintered to obtain alumina fiber with a fineness of 4.05 dtex and a strength of 9.12 cN / dtex.

[0112] Example 5

[0113] An alumina fiber precursor, the raw material of which includes a precursor spinning solution, the raw material components of which include: nano-alumina sol, surfactant and composite grain control agent; wherein the weight of the surfactant is 1.7% of the weight of alumina in the nano-alumina sol; the surfactant includes PVP and HEC.

[0114] The weight of the composite grain control agent is 8.6% of the weight of alumina in the nano-aluminum sol; the composite grain control agent includes silica sol, Fe2O3 and MgO, and the solid phase weight of silica sol is 30%.

[0115] The preparation method of the above-mentioned alumina fiber precursor includes the following steps.

[0116] (1) Preparation of nano-aluminum sol

[0117] Same as Example 1.

[0118] (2) Preparation of precursor spinning solution

[0119] A composite grain control agent was added to the nano-aluminum sol obtained in step (1). The composite grain control agent included 80g of silica sol with a solid weight of 30%, 1.79g of Fe2O3 and 0.8g of MgO. After stirring and mixing evenly, a surfactant was added to it. The surfactant included 3.6g of PVP and 1.4g of HEC. After mixing, the mixture was aged at 50°C for 18h. Then the aged mixture was concentrated to obtain a spinnable precursor spinning solution.

[0120] (3) Preparation of alumina fiber precursor

[0121] The precursor spinning solution obtained in step (2) is spun on a dry spinning equipment with a spinning tunnel length of 5m, and the tunnel environmental parameters are: wind speed 0.5m / s, temperature 95℃, humidity 65%. The alumina fiber precursor is obtained by bundling and collecting the fibers at a speed of 120m / min.

[0122] The obtained alumina fiber precursor has a fineness of 3.02 dtex and a strength of 2.47 cN / dtex.

[0123] The alumina fiber precursor obtained above is continuously sintered to obtain alumina fiber with a fineness of 4.17 dtex and a strength of 8.23 ​​cN / dtex.

[0124] Example 6

[0125] An alumina fiber precursor, the raw material of which includes a precursor spinning solution, the raw material components of which include: nano-alumina sol, surfactant and composite grain control agent; wherein the weight of the surfactant is 2.0% of the weight of alumina in the nano-alumina sol; the surfactant includes PVP and PEO.

[0126] The weight of the composite grain control agent is 12.3% of the weight of alumina in the nano-aluminum sol; the composite grain control agent includes zirconium sol, Y2O3 and MgO, and the solid phase weight of zirconium sol is 20%.

[0127] The preparation method of the above-mentioned alumina fiber precursor includes the following steps.

[0128] (1) Preparation of nano-aluminum sol

[0129] Same as Example 2

[0130] (2) Preparation of precursor spinning solution

[0131] A composite grain control agent was added to the nano-aluminum sol obtained in step (1). The composite grain control agent included 200g of zirconium sol with a solid weight of 20%, 5.0g of Y2O3 and 4.2g of MgO. After stirring and mixing evenly, a surfactant was added to it. The surfactant included 6.7g of PVP and 1.2g of PEO. After mixing, the mixture was aged at 55℃ for 30h. Then the aged mixture was concentrated to obtain a spinnable precursor spinning solution.

[0132] (3) Preparation of alumina fiber precursor

[0133] The precursor spinning solution obtained in step (2) is spun on a dry spinning equipment with a spinning tunnel length of 3m and tunnel environmental parameters of wind speed 0.25m / s, temperature 80℃, and humidity 45%. The alumina fiber precursor is obtained by bundling and collecting the fibers at a speed of 120m / min.

[0134] The obtained alumina fiber precursor has a fineness of 4.41 dtex and a strength of 1.57 cN / dtex.

[0135] The alumina fiber precursor obtained above is continuously sintered to obtain alumina fiber with a fineness of 4.65 dtex and a strength of 6.73 cN / dtex.

[0136] Example 7

[0137] An alumina fiber precursor, the raw material of which includes a precursor spinning solution, the raw material components of which include: nano-alumina sol, surfactant and composite grain control agent; wherein the weight of the surfactant is 2.2% of the weight of alumina in the nano-alumina sol; the surfactant includes HEC and PAA.

[0138] The weight of the composite grain control agent is 3.2% of the weight of alumina in the nano-aluminum sol; the composite grain control agent includes silica sol, Y2O3 and MgO, with the solid phase weight of silica sol being 30%.

[0139] The preparation method of the above-mentioned alumina fiber precursor includes the following steps.

[0140] (1) Preparation of nano-aluminum sol

[0141] 500g of aluminum hydroxide (Al2O3 content 65%) was mixed with deionized water to prepare a slurry. The solid phase weight of the slurry was 12% (based on Al2O3). A complex carboxylic acid was added to the slurry. The carboxyl group weight fraction of the complex carboxylic acid was 74.5%. The complex carboxylic acid included 30g of formic acid, 50g of propionic acid, and 5g of citric acid. The pH of the slurry was controlled at 1.9 by adding the complex carboxylic acid. The solvothermal sol reaction was carried out at 130℃ for 8 hours. The sol obtained from the solvothermal sol reaction was then filtered to remove undissolved large particles. The filtrate was then centrifuged to further remove undissolved impurities, resulting in a uniformly dispersed nano-aluminum sol.

[0142] (2) Preparation of precursor spinning solution

[0143] A composite grain control agent was added to the nano-aluminum sol obtained in step (1). The composite grain control agent included 6g of silica sol with a solid weight of 30%, 6.4g of Y2O3 and 2.1g of MgO. After stirring and mixing evenly, a surfactant was added to it. The surfactant included 5.4g of HEC and 1.5g of PAA. After mixing, the mixture was aged at 55℃ for 24h. Then the aged mixture was concentrated to obtain a spinnable precursor spinning solution.

[0144] (3) Preparation of alumina fiber precursor

[0145] The precursor spinning solution obtained in step (2) is spun on a dry spinning equipment with a spinning tunnel length of 5m and tunnel environmental parameters of wind speed 0.45m / s, temperature 75℃, and humidity 50%. The alumina fiber precursor is obtained by bundling and collecting the fibers at a speed of 100m / min.

[0146] The obtained alumina fiber precursor has a fineness of 4.32 dtex and a strength of 1.72 cN / dtex.

[0147] The alumina fiber precursor obtained above was continuously sintered to obtain alumina fiber with a fineness of 4.41 dtex and a strength of 6.59 cN / dtex.

[0148] Comparative Example 1

[0149] Based on the content disclosed in Example 1, the difference between Comparative Example 1 and Example 1 is that there is no surfactant in the precursor spinning solution.

[0150] Results: Since no surfactant was added to the precursor spinning solution, the aggregation behavior of alumina grains changed significantly. The aggregates gradually changed from a linear structure to a three-dimensional network structure. The precursor spinning solution became a thixotropic fluid, that is, its fluidity changed significantly with time and shear force, and thus it lost its spinnability.

[0151] Comparative Example 2

[0152] Based on the content disclosed in Example 1, Comparative Example 2 differs from Example 1 in that the weight of the surfactant is 0.07% of the weight of alumina in the nano-aluminum sol.

[0153] Results: Due to the low amount of surfactant added to the precursor spinning solution, although the precursor spinning solution has a certain degree of spinnability, the spinning process cannot be continuous, the breakage rate is still high, and the strength of the obtained alumina fiber precursor is low.

[0154] Comparative Example 3

[0155] Based on the content disclosed in Example 1, Comparative Example 3 differs from Example 1 in that the weight of the surfactant is 7.0% of the weight of alumina in the nano-alumina sol.

[0156] Results: Alumina precursor sol can achieve continuous spinning. The fineness of the obtained alumina fiber precursor is 2.44 dtex and the strength is 1.87 cN / dtex. However, after sintering, a large number of pores appear in the fiber and the fiber strength is low.

[0157] Comparative Example 4

[0158] Based on the content disclosed in Example 1, the difference between Comparative Example 4 and Example 1 is that the precursor spinning solution contains a single grain control agent.

[0159] Results: The fineness of the obtained alumina fiber precursor was 2.81 dtex and the strength was 2.63 cN / dtex. However, after sintering, abnormally large alumina structures appeared in the fiber, resulting in low fiber strength.

[0160] Comparative Example 5

[0161] Based on the content disclosed in Example 1, Comparative Example 5 differs from Example 1 in that: the pseudoboehmite and the composite carboxylic acid did not undergo a solvothermal solvation reaction, but were refluxed at a temperature of 80°C.

[0162] Results: Since the aluminum sol did not react under high temperature and high pressure, the alumina grains in the sol showed a multi-peak distribution, and there were large differences in the size, shape and structure of the alumina grains; the spinnability of the precursor spinning solution was poor, the breakage rate of the alumina fiber precursor was high, the fineness of the obtained alumina fiber precursor was 6.7 dtex, and the fiber strength was low.

[0163] Compared with related technologies, the technical solutions provided in this disclosure have the following advantages:

[0164] On the one hand, surfactants can adsorb onto the surface of alumina grains in nano-alumina sol, thereby forming a steric hindrance layer on the surface of alumina grains. At the same time, they regulate the surface charge of alumina grains, enhance the electrostatic repulsion between alumina grains, and thus prevent disordered and compact agglomeration between alumina grains, thereby improving the dispersibility and stability of nano-alumina sol. On the other hand, surfactants can induce alumina grains in nano-alumina sol to aggregate and form chain structures through a bridging mechanism, avoiding the formation of three-dimensional network structures, thereby improving the spinnability of the precursor spinning solution. Furthermore, when the weight of surfactant is 0.1% to 6.0% of the weight of alumina in nano-alumina sol, a precursor spinning solution with high dispersibility, high uniformity, and high stability can be obtained, thereby improving the uniformity of the microstructure of alumina fiber precursors.

[0165] One or more technical solutions in the embodiments of this disclosure have at least the following technical effects or advantages:

[0166] Surfactants can regulate the charge density on the surface of alumina grains in nano-alumina sol, thereby controlling the degree of alumina grain aggregation, avoiding the formation of a three-dimensional network structure, and improving the uniformity of the sol.

[0167] The complex carboxylic acid undergoes acid-base reaction and coordination exchange reaction with hydrated alumina, promoting the formation of Al-COO-coordination structure on the surface, thereby obtaining stable nano-aluminum sol;

[0168] By leveraging the interaction between surfactants and alumina grains in nano-alumina sol, the polymerization process of alumina grains was effectively controlled. Simultaneously, a composite grain control agent could be introduced, thereby enabling the precursor spinning solution to exhibit better spinning stability and continuity. The resulting alumina fiber precursor had no obvious defects on its surface, a very uniform microstructure, and its strength was significantly improved.

[0169] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. An alumina fiber precursor, wherein the raw material for the alumina fiber precursor comprises a precursor spinning solution, and the raw material components of the precursor spinning solution include nano-aluminum sol and a surfactant; wherein, The surfactant is present in an amount of 0.1% to 6.0% of the weight of alumina in the nano-alumina sol.

2. The alumina fiber precursor according to claim 1, wherein, The surfactant includes at least one of the following: polyvinylpyrrolidone, polyvinyl alcohol, carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene glycol, polyethylene oxide, and polyacrylic acid.

3. The alumina fiber precursor according to claim 1, wherein, The precursor spinning solution also includes a composite grain control agent as a raw material component.

4. The alumina fiber precursor according to claim 3, wherein, The composite grain control agent includes at least two of the following: SiO2, CaO, MgO, Fe2O3, Y2O3, ZrO2, and Al2O3.

5. The alumina fiber precursor according to claim 3 or 4, wherein, The weight of the composite grain control agent is 0.1% to 18% of the weight of alumina in the nano-alumina sol.

6. The alumina fiber precursor according to claim 1, wherein, The alumina fiber precursor meets the following specifications: fineness of 1.5 dtex to 7.2 dtex and strength of 0.1 cN / dtex to 4.0 cN / dtex.

7. A method for preparing alumina fiber precursor according to any one of claims 1 to 6, comprising: Nano-aluminum sol was obtained; The nano-aluminum sol and the surfactant are mixed to obtain a mixture. The mixture is subjected to aging and concentration in sequence to obtain a precursor spinning solution; as well as, The precursor spinning solution is spun to obtain alumina fiber precursor.

8. A method for preparing alumina fiber precursor according to any one of claims 1 to 6, comprising: Nano-aluminum sol was obtained; The nano-aluminum sol, composite grain control agent, and surfactant are mixed to obtain a mixture. The mixture is subjected to aging and concentration in sequence to obtain a precursor spinning solution; as well as The precursor spinning solution is spun to obtain alumina fiber precursor.

9. The method according to claim 7, wherein, The obtained nano-aluminum sol includes: Hydrated alumina was reacted with a complex carboxylic acid via a solvothermal sol reaction to obtain nano-aluminum sol; wherein... The process parameters for the solvothermal sol-gel reaction include: a temperature of 60℃~200℃, a pH value of 1.0~4.0; and / or, The carboxyl group in the complex carboxylic acid has a weight fraction of 60% to 90%; and / or, The complex carboxylic acid includes at least two of the following: formic acid, acetic acid, lactic acid, tartaric acid, and citric acid.

10. The method according to claim 7, wherein, The aging temperature is 30℃~80℃.

11. An alumina fiber, wherein the raw material of the alumina fiber comprises the alumina fiber precursor as described in any one of claims 1 to 6.

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