A complex phase alumina fiber and a method for making the same

Abstract

The application discloses a kind of complex phase alumina fibers and preparation method thereof, belong to ceramic fiber technical field, the preparation method is composed of the following steps: spinning, drying, heat treatment;The spinning, alumina spinning sol is carried out dry spinning, and alumina gel fiber is obtained;The crystal phase of the complex phase alumina fiber is one of the composite crystal phase of mullite and gamma-alumina or the composite crystal phase of mullite and alpha-alumina;The preparation method of the application improves ceramic yield, solves the problem of high mullite phase transition temperature of gel fiber, and the complex phase alumina fiber prepared has good mechanical properties and temperature resistance.

Description

Technical Field

[0001] This invention relates to the field of ceramic fiber technology, specifically to a multiphase alumina fiber and its preparation method. Background Technology

[0002] Multiphase alumina fiber is a polycrystalline ceramic fiber with alumina and mullite as its main components. Mullite is a binary solid solution compound composed of alumina and silicon dioxide, possessing many excellent physical properties, such as high fracture toughness, high temperature resistance, oxidation resistance, thermal shock resistance, creep resistance, low thermal conductivity, strong electrical insulation, and low dielectric constant. It also exhibits high chemical stability, showing good resistance to corrosion in alkaline and carbonic solvents. Multiphase alumina fiber combines the advantages of alumina fiber and mullite fiber, exhibiting high strength and low thermal conductivity, and demonstrating excellent high-temperature oxidation resistance. In practical applications, multiphase alumina fibers can be used in a variety of fields, such as: for heat insulation of high-temperature industrial kilns, which can effectively extend the kiln's life and improve production efficiency; for the production of other polycrystalline mullite insulation materials, such as as a raw material for boards, paper, vacuum-formed parts, etc.; for the preparation of reinforced metal matrix composites, such as high-load mechanical parts, high-temperature and high-speed rotating parts, and high-functional components with lightweight requirements, specifically automobile connecting rods, drive rods, brake pads, and helicopter transmission devices; for the preparation of reinforced resin matrix composites and ceramic matrix composites, such as high-performance radar radomes; and for coating materials, which can increase the material's thermal shock resistance, oxidation resistance, and high-temperature corrosion resistance.

[0003] Chinese patent CN114773070B discloses a method for preparing continuous alumina fibers using aluminum carboxylate sol as a precursor. Aluminum hydroxide dispersion is used as the aluminum source, and small molecule carboxylic acid is added to obtain aluminum carboxylate sol. Then, silica sol and spinning aids are added, and alumina fibers are prepared by dry spinning and sintering. However, the mullite phase transformation temperature is high.

[0004] Chinese patent CN114162844B discloses a precursor composite sol for alumina / mullite biphase fibers and its preparation method. The method uses aluminum powder and organic acids as raw materials to prepare aluminum carboxylate sol, then adds silica sol to prepare mullite spinning sol. Alumina / mullite biphase fibers are obtained through dry spinning and sintering. However, aluminum powder is used in the preparation process; aluminum powder is a potentially explosive chemical.

[0005] Chinese patent CN113860862A discloses a low-cost method for preparing mullite fibers. It involves using aluminum hydroxide and small-molecule carboxylic acids as raw materials to prepare aluminum carboxylate sol, then adding a silicon source to obtain a spinning sol. This sol is then dry-spun and sintered to obtain mullite fibers. However, the spinning sol has a low solid content, and the fibers experience significant weight loss during sintering. The volatilization of large amounts of organic matter causes surface and internal pores and defects in the fibers, reducing their mechanical properties. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a multiphase alumina fiber and its preparation method, which improves ceramic yield, solves the problem of high mullite phase transformation temperature in gel fibers, and results in multiphase alumina fibers with good mechanical properties and temperature resistance.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing multiphase alumina fibers comprises the following steps: spinning, drying, and heat treatment;

[0009] The spinning process involves dry spinning of alumina spinning sol to obtain alumina gel fibers.

[0010] In the aforementioned spinning process, the sol temperature during dry spinning is 30-50℃, the tunnel temperature is 60-100℃, and the spinning speed is 100-500m / min.

[0011] The drying process involves drying the alumina gel fibers to obtain dried alumina gel fibers.

[0012] During the drying process, the drying temperature is 50-80℃ and the drying time is 1-3 hours.

[0013] The heat treatment involves heating the dried alumina gel fibers to 650-750°C at a heating rate of 3-5°C / min and holding for 50-70 min; then heating them to 1100-1300°C at a heating rate of 5-8°C / min and holding for 60-120 min to obtain multiphase alumina fibers.

[0014] The crystal phase of the multiphase alumina fiber is one of a composite crystal phase of mullite and γ-alumina or a composite crystal phase of mullite and α-alumina.

[0015] When the crystal phase of the multiphase alumina fiber is a composite crystal phase of mullite and γ-alumina, the preparation method of the alumina spinning sol in the spinning process is as follows: add the No. 1 single-phase mullite sol precursor to the No. 2 alumina sol and stir at room temperature for 30-40 min; then concentrate under vacuum for 1-1.5 h to obtain the alumina spinning sol.

[0016] When the crystal phase of the multiphase alumina fiber is a composite crystal phase of mullite and γ-alumina, in the preparation of the alumina spinning sol in the spinning process, the mass ratio of No. 1 single-phase mullite sol precursor to No. 2 alumina sol is 2-3:1.

[0017] The vacuum concentration temperature is 40-60℃ and the vacuum degree is 0-0.03MPa;

[0018] The preparation method of the No. 1 single-phase mullite sol precursor consists of the following steps: preparing single-phase mullite sol stock solution and activating it by heating.

[0019] To prepare the single-phase mullite sol stock solution, aluminum nitrate is dissolved in water and stirred at room temperature until dissolved; then aluminum isopropoxide is added and stirred at room temperature for 5-30 min; then tetraethyl orthosilicate is added and stirred at room temperature for 1-3 h; then the temperature is raised to 50-80℃ and stirred for 3-5 h to obtain the single-phase mullite sol stock solution.

[0020] In the preparation of the single-phase mullite sol stock solution, the molar ratio of aluminum isopropoxide to aluminum nitrate is 2.5-3.5:1;

[0021] The molar ratio of aluminum to silicon is 2.8-3.2:1;

[0022] The molar ratio of aluminum nitrate to water is 1:30-50;

[0023] The heating activation involves heating the single-phase mullite sol stock solution to 70-90°C at a heating rate of 5-8°C / min and holding it for 5-8 hours, which is the solvent removal process; then heating it to 100-120°C at a heating rate of 3-5°C / min and holding it for 3-5 hours to obtain the No. 1 single-phase mullite sol precursor.

[0024] The preparation method of the No. 2 aluminum sol consists of the following steps: preparing aluminum carboxylate stock solution and activating it;

[0025] To prepare the aluminum carboxylate stock solution, deionized water is heated to 70-90℃, aluminum hydroxide is added, and the mixture is stirred for 15-30 min. Then, monocarboxylic acid and dicarboxylic acid are added, and the mixture is stirred for 15-30 min. The temperature is increased to boiling at a rate of 15-25℃ / min, and the mixture is kept under reflux for 5-10 h. After cooling, the mixture is filtered, and the filtrate is collected to obtain the aluminum carboxylate stock solution.

[0026] In the preparation of the aluminum carboxylate stock solution, the monocarboxylic acid is one of formic acid, acetic acid, and propionic acid;

[0027] The dicarboxylic acid is one of oxalic acid, malonic acid, and succinic acid;

[0028] The molar ratio of aluminum hydroxide, monocarboxylic acid, and dicarboxylic acid is 1:0.5-1:2.5-3.5;

[0029] The molar ratio of aluminum hydroxide to deionized water is 1:20-40;

[0030] The activation process in the preparation of aluminum sol No. 2 involves heating the aluminum carboxylate stock solution to 80-100℃ at a heating rate of 5-8℃ / min and holding it for 5-8 hours; then heating it to 100-150℃ at a heating rate of 3-5℃ / min and holding it for 3-5 hours to obtain aluminum sol precursor No. 1; dispersing 1 part by weight of aluminum sol precursor No. 1 in 1.5-2.5 parts by weight of water to obtain aluminum sol No. 1; then heating aluminum sol No. 1 to 150-250℃ at a heating rate of 3-5℃ / min and holding it for 3-5 hours to obtain aluminum sol precursor No. 2; and then dispersing 1 part by weight of aluminum sol precursor No. 2 in 1.5-2.5 parts by weight of water to obtain aluminum sol No. 2.

[0031] When the crystal phase of the multiphase alumina fiber is a composite crystal phase of mullite and α-alumina, the preparation method of the alumina spinning sol in the spinning process is as follows: mix No. 1 activated silica sol and No. 1 aluminum sol, react at 40-60℃ for 3-5 hours, add spinning aids, stir at room temperature for 30-60 minutes, and then concentrate under vacuum for 1 hour to obtain alumina spinning sol.

[0032] When the crystal phase of the multiphase alumina fiber is a composite crystal phase of mullite and α-alumina, in the preparation of the alumina spinning sol in the spinning process, the mass ratio of No. 1 activated silica sol to No. 1 aluminum sol is 1:2.3-3.5.

[0033] The spinning aid is one of polyethylene glycol, polyvinyl alcohol, and polyethylene oxide;

[0034] The mass fraction of the spinning aid is 1-3%;

[0035] The vacuum concentration temperature is 40-60℃ and the vacuum degree is 0-0.03MPa;

[0036] The preparation method of the No. 1 activated silica sol is as follows: add a small molecule carboxylic acid to the silica sol to adjust the pH to 3-4, stir at 30-50℃ for 30-60 min to obtain the No. 1 activated silica sol;

[0037] In the preparation of the No. 1 activated silica sol, the silica sol contains 30-40% silica by mass.

[0038] The small molecule carboxylic acid is one of formic acid, acetic acid, and propionic acid;

[0039] The preparation method of the No. 1 aluminum sol consists of the following steps: preparing aluminum carboxylate stock solution and activating it;

[0040] The method for preparing the aluminum carboxylate stock solution in the preparation of aluminum sol No. 1 is the same as the method for preparing the aluminum carboxylate stock solution in the preparation of aluminum sol No. 2.

[0041] In the preparation of aluminum sol No. 1, the activation process involves heating the aluminum carboxylate stock solution to 80-100℃ at a heating rate of 5-8℃ / min and holding it for 5-8 hours; then heating it to 100-150℃ at a heating rate of 3-5℃ / min and holding it for 3-5 hours to obtain the aluminum sol No. 1 precursor; and dispersing 1 part by weight of the aluminum sol No. 1 precursor into 1.5-2.5 parts by weight of water to obtain aluminum sol No. 1.

[0042] A multiphase alumina fiber obtained by the aforementioned preparation method.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] (1) This invention uses chlorine-free, safe and environmentally friendly raw materials to prepare multiphase alumina fibers. It uses high solid content spinning sol, which improves the ceramic yield and solves the problem of high mullite phase transformation temperature of gel fibers. It also adjusts the composition and pH of the sol by segmented temperature control, resulting in multiphase alumina fibers with good temperature resistance.

[0045] (2) By adjusting the heat treatment temperature, this invention can obtain multiphase alumina fibers with mullite and γ-alumina crystal phases, and multiphase alumina fibers with mullite and α-alumina crystal phases, respectively. The ceramic conversion rate of the obtained multiphase alumina fibers with mullite and γ-alumina crystal phases is 45-47%, and the ceramic fiber density at 1100℃ is 3.1 g / cm³. 3 The tensile strength of the bundled fibers is 1.8-1.9 GPa, and after heat treatment at 1100℃ in air for 5 hours, the fiber strength is retained at 80-85%. The ceramic conversion rate of the obtained multiphase alumina fibers with mullite and α-alumina crystal phases is 47-48%, and the ceramic fiber density at 1300℃ is 3.2-3.3 g / cm³. 3 The tensile strength of the bundled fibers is 2.2-2.3 GPa, and after heat treatment at 1200℃ in air for 5 hours, the fiber strength is retained at 80-85%. Attached Figure Description Figure 1 The image shows the XRD pattern of the multiphase alumina fiber obtained in Example 4. Detailed Implementation

[0046] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0047] Example 1

[0048] A method for preparing multiphase alumina fibers, specifically comprising:

[0049] 1. Preparation of aluminum sol

[0050] Aluminum sol was prepared using aluminum hydroxide, monocarboxylic acid, and dicarboxylic acid as raw materials; specifically:

[0051] (1) Preparation of aluminum carboxylate stock solution: Take deionized water and heat it to 70°C, add aluminum hydroxide, stir for 15 min, add formic acid and malonic acid, stir for 15 min, heat to boiling at a heating rate of 15°C / min, keep warm and reflux for 5 h, cool, filter, take the filtrate to obtain aluminum carboxylate stock solution;

[0052] The molar ratio of aluminum hydroxide, formic acid, and malonic acid is 1:1:3.5;

[0053] The molar ratio of aluminum hydroxide to deionized water is 1:20;

[0054] (2) Activation: The aluminum carboxylate stock solution is subjected to segmented temperature control to adjust the composition of the aluminum carboxylate, thereby obtaining aluminum sol; specifically:

[0055] The aluminum carboxylate stock solution was heated to 80°C at a heating rate of 5°C / min and held for 5 hours. This step was for the removal of excess carboxylic acid. The solution was then heated to 100°C at a heating rate of 3°C / min and held for 3 hours to obtain aluminum sol precursor No. 1. One part by weight of aluminum sol precursor No. 1 was dispersed in 1.5 parts by weight of water to obtain aluminum sol No. 1. Aluminum sol No. 1 was then heated to 150°C at a heating rate of 3°C / min and held for 3 hours to obtain aluminum sol precursor No. 2. One part by weight of aluminum sol precursor No. 2 was dispersed in 1.5 parts by weight of water to obtain aluminum sol No. 2.

[0056] The average molecular weight of aluminum carboxylate in the No. 1 aluminum sol precursor is 175 g / mol.

[0057] The aluminum carboxylate precursor No. 2 has an average molecular weight of 155 g / mol.

[0058] The pH of the No. 1 aluminum sol is 3;

[0059] The pH of the No. 2 aluminum sol is 4;

[0060] 2. Preparation of single-phase mullite sol

[0061] A single-phase mullite sol was prepared using aluminum isopropoxide, tetraethyl orthosilicate, and aluminum nitrate as raw materials; specifically:

[0062] (1) Preparation of single-phase mullite sol stock solution: Dissolve aluminum nitrate in water and stir at room temperature until dissolved; then add aluminum isopropoxide and stir at room temperature for 5 min; then add tetraethyl orthosilicate and stir at room temperature for 1 h; then heat to 50℃ and stir for 3 h to obtain single-phase mullite sol stock solution.

[0063] The molar ratio of aluminum isopropoxide to aluminum nitrate is 2.5:1;

[0064] The molar ratio of aluminum to silicon is 2.8:1;

[0065] The molar ratio of aluminum nitrate to water is 1:30;

[0066] (2) Temperature activation: The single-phase mullite sol stock solution is subjected to segmented temperature control to adjust the composition and obtain the mullite sol precursor; specifically:

[0067] The single-phase mullite sol stock solution was heated to 70°C at a heating rate of 5°C / min and held for 5 hours for solvent removal. The solution was then heated to 100°C at a heating rate of 3°C / min and held for 3 hours to obtain the first single-phase mullite sol precursor.

[0068] 3. Preparation of sol

[0069] The No. 1 single-phase mullite sol precursor was added to the No. 2 aluminum sol at a mass ratio of 2:1. The mixture was stirred at room temperature for 30 min. Then, it was vacuum concentrated at 40℃ and 0 MPa for 1 h to obtain alumina spinning sol.

[0070] The viscosity of the alumina spinning sol is 30 Pa·s;

[0071] 4. Spinning and heat treatment

[0072] (1) Spinning: Alumina spinning sol is dry spun to obtain alumina gel fiber. The sol temperature during dry spinning is 30℃, the tunnel temperature is 60℃, and the spinning speed is 100m / min.

[0073] (2) Drying: The alumina gel fiber was dried in a 50℃ forced-air oven for 1 hour to obtain dried alumina gel fiber;

[0074] (3) Heat treatment: The dried alumina gel fiber was heated to 650℃ at a heating rate of 3℃ / min and held for 50min; then heated to 1100℃ at a heating rate of 5℃ / min and held for 60min to obtain a multiphase alumina fiber with mullite and γ-alumina crystal phases.

[0075] The ceramic conversion rate of the multiphase alumina fiber is 45%, and the ceramic fiber density at 1100℃ is 3.1 g / cm³. 3 The tensile strength of the bundled fibers is 1.8 GPa, and after heat treatment at 1100℃ in air for 5 hours, the fiber strength is retained at 81%.

[0076] This embodiment also provides a multiphase alumina fiber obtained by the aforementioned preparation method.

[0077] Example 2

[0078] A method for preparing multiphase alumina fibers, specifically comprising:

[0079] 1. Preparation of aluminum sol

[0080] Aluminum sol was prepared using aluminum hydroxide, monocarboxylic acid, and dicarboxylic acid as raw materials; specifically:

[0081] (1) Preparation of aluminum carboxylate stock solution: Take deionized water and heat it to 75°C, add aluminum hydroxide, stir for 20 min, add formic acid and malonic acid, stir for 20 min, heat to boiling at a heating rate of 20°C / min, keep warm and reflux for 6 h, cool, filter, take the filtrate to obtain aluminum carboxylate stock solution;

[0082] The molar ratio of aluminum hydroxide, formic acid, and malonic acid is 1:0.6:2.7;

[0083] The molar ratio of aluminum hydroxide to deionized water is 1:25;

[0084] (2) Activation: The aluminum carboxylate stock solution is subjected to segmented temperature control to adjust the composition of the aluminum carboxylate, thereby obtaining aluminum sol; specifically:

[0085] The aluminum carboxylate stock solution was heated to 85°C at a heating rate of 6°C / min and held for 5.5 h; this stage was for the removal of excess carboxylic acid. The solution was then heated to 120°C at a heating rate of 4°C / min and held for 3.5 h to obtain aluminum sol precursor No. 1. One part by weight of aluminum sol precursor No. 1 was dispersed in 1.8 parts by weight of water to obtain aluminum sol No. 1. Aluminum sol No. 1 was then heated to 180°C at a heating rate of 4°C / min and held for 3.5 h to obtain aluminum sol precursor No. 2. One part by weight of aluminum sol precursor No. 2 was dispersed in 1.8 parts by weight of water to obtain aluminum sol No. 2.

[0086] The average molecular weight of aluminum carboxylate in the No. 1 aluminum sol precursor is 172 g / mol.

[0087] The aluminum carboxylate precursor No. 2 has an average molecular weight of 150 g / mol.

[0088] The pH of the No. 1 aluminum sol is 3.3;

[0089] The pH of the No. 2 aluminum sol is 4.6;

[0090] 2. Preparation of single-phase mullite sol

[0091] A single-phase mullite sol was prepared using aluminum isopropoxide, tetraethyl orthosilicate, and aluminum nitrate as raw materials; specifically:

[0092] (1) Preparation of single-phase mullite sol stock solution: Dissolve aluminum nitrate in water and stir at room temperature until dissolved; then add aluminum isopropoxide and stir at room temperature for 30 min; then add tetraethyl orthosilicate and stir at room temperature for 3 h; then heat to 80℃ and stir for 5 h to obtain single-phase mullite sol stock solution.

[0093] The molar ratio of aluminum isopropoxide to aluminum nitrate is 3.5:1;

[0094] The molar ratio of aluminum to silicon is 3.2:1;

[0095] The molar ratio of aluminum nitrate to water is 1:50;

[0096] (2) Temperature activation: The single-phase mullite sol stock solution is subjected to segmented temperature control to adjust the composition and obtain the mullite sol precursor; specifically:

[0097] The single-phase mullite sol stock solution was heated to 90°C at a heating rate of 8°C / min and held for 8 hours for solvent removal. The solution was then heated to 120°C at a heating rate of 5°C / min and held for 5 hours to obtain the first single-phase mullite sol precursor.

[0098] 3. Preparation of sol

[0099] The No. 1 single-phase mullite sol precursor was added to the No. 2 aluminum sol at a mass ratio of 3:1. The mixture was stirred at room temperature for 40 min. Then, it was vacuum concentrated at 60℃ and 0.03 MPa for 1.5 h to obtain alumina spinning sol.

[0100] The viscosity of the alumina spinning sol is 34 Pa·s;

[0101] 4. Spinning and heat treatment

[0102] (1) Spinning: Alumina spinning sol is dry spun to obtain alumina gel fiber. The sol temperature during dry spinning is 40℃, the tunnel temperature is 70℃, and the spinning speed is 200m / min.

[0103] (2) Drying: The alumina gel fiber was dried in a 65℃ forced-air oven for 2 hours to obtain dried alumina gel fiber;

[0104] (3) Heat treatment: The dried alumina gel fiber was heated to 700℃ at a heating rate of 4℃ / min and held for 60min; then heated to 1100℃ at a heating rate of 6℃ / min and held for 80min to obtain a multiphase alumina fiber with mullite and γ-alumina crystal phases.

[0105] The ceramic conversion rate of the multiphase alumina fiber is 47%, and the ceramic fiber density at 1100℃ is 3.1 g / cm³. 3The tensile strength of the bundled fibers is 1.9 GPa, and after heat treatment at 1100℃ in air for 5 hours, the fiber strength is retained at 83%.

[0106] This embodiment also provides a multiphase alumina fiber obtained by the aforementioned preparation method.

[0107] Example 3

[0108] A method for preparing multiphase alumina fibers, specifically comprising:

[0109] 1. Preparation of aluminum sol

[0110] Aluminum sol was prepared using aluminum hydroxide, monocarboxylic acid, and dicarboxylic acid as raw materials; specifically:

[0111] (1) Preparation of aluminum carboxylate stock solution: Take deionized water and heat it to 85°C, add aluminum hydroxide, stir for 25 min, add acetic acid and oxalic acid, stir for 25 min, heat to boiling at a heating rate of 22°C / min, keep warm under reflux for 9 h, cool, filter, take the filtrate to obtain aluminum carboxylate stock solution;

[0112] The molar ratio of aluminum hydroxide, acetic acid, and oxalic acid is 1:0.9:3.3;

[0113] The molar ratio of aluminum hydroxide to deionized water is 1:35;

[0114] (2) Activation: The aluminum carboxylate stock solution is subjected to segmented temperature control to adjust the composition of the aluminum carboxylate, thereby obtaining aluminum sol; specifically:

[0115] The aluminum carboxylate stock solution was heated to 95°C at a heating rate of 7°C / min and held for 7.5 h. This stage was for the removal of excess carboxylic acid. The solution was then heated to 140°C at a heating rate of 5°C / min and held for 4 h to obtain aluminum sol precursor No. 1. One part by weight of aluminum sol precursor No. 1 was dispersed in 2.5 parts by weight of water to obtain aluminum sol No. 1.

[0116] The average molecular weight of aluminum carboxylate in the No. 1 aluminum sol precursor is 168 g / mol.

[0117] The pH of the No. 1 aluminum sol is 3.7;

[0118] 2. Preparation of activated silica sol: Take silica sol with a silica content of 30% by mass, add small molecule carboxylic acid to adjust the pH to 3, stir at 30℃ for 30 min to obtain activated silica sol No. 1;

[0119] The small molecule carboxylic acid is formic acid;

[0120] 3. Preparation of sol: Mix No. 1 activated silica sol and No. 1 aluminum sol at a mass ratio of 1:2.3. React at 40℃ for 3 hours. Add 1% by mass of spinning aid and stir at room temperature for 30 minutes. Then concentrate under vacuum at 40℃ and 0 MPa for 1 hour to obtain alumina spinning sol.

[0121] The spinning aid is polyethylene glycol;

[0122] The viscosity of the alumina spinning sol is 30 Pa·s;

[0123] 4. Spinning and heat treatment

[0124] (1) Spinning: Alumina spinning sol is dry spun to obtain alumina gel fiber. The sol temperature of dry spinning is controlled at 45℃, the channel temperature is 90℃, and the spinning speed is 400m / min.

[0125] (2) Drying: The alumina gel fiber was dried in a 70℃ forced-air oven for 2.5h to obtain the dried alumina gel fiber;

[0126] (3) Heat treatment: The dried alumina gel fiber was heated to 720℃ at a heating rate of 4.5℃ / min and held for 60min. Then it was heated to 1300℃ at a heating rate of 7.5℃ / min and held for 110min to obtain a multiphase alumina fiber with mullite and α-alumina crystal phases.

[0127] The ceramic conversion rate of the multiphase alumina fiber is 47%, and the ceramic fiber density at 1300℃ is 3.2 g / cm³. 3 The tensile strength of the bundled fibers is 2.2 GPa, and after heat treatment at 1200℃ in air for 5 hours, the fiber strength is retained at 81%.

[0128] This embodiment also provides a multiphase alumina fiber obtained by the aforementioned preparation method.

[0129] Example 4

[0130] A method for preparing multiphase alumina fibers, specifically comprising:

[0131] 1. Preparation of aluminum sol

[0132] Aluminum sol was prepared using aluminum hydroxide, monocarboxylic acid, and dicarboxylic acid as raw materials; specifically:

[0133] (1) Preparation of aluminum carboxylate stock solution: Take deionized water and heat it to 90°C, add aluminum hydroxide, stir for 30 min, add formic acid and malonic acid, stir for 30 min, heat to boiling at a heating rate of 25°C / min, keep warm and reflux for 10 h, cool, filter, take the filtrate to obtain aluminum carboxylate stock solution;

[0134] The molar ratio of aluminum hydroxide, formic acid, and malonic acid is 1:0.5:2.5;

[0135] The molar ratio of aluminum hydroxide to deionized water is 1:40;

[0136] (2) Activation: The aluminum carboxylate stock solution is subjected to segmented temperature control to adjust the composition of the aluminum carboxylate, thereby obtaining aluminum sol; specifically:

[0137] The aluminum carboxylate stock solution was heated to 100℃ at a heating rate of 8℃ / min and held for 8 hours. This step was for the removal of excess carboxylic acid. The solution was then heated to 150℃ at a heating rate of 5℃ / min and held for 5 hours to obtain aluminum sol precursor No. 1. One part by weight of aluminum sol precursor No. 1 was dispersed in 2.5 parts by weight of water to obtain aluminum sol No. 1.

[0138] The average molecular weight of aluminum carboxylate in the No. 1 aluminum sol precursor is 175 g / mol.

[0139] The pH of the No. 1 aluminum sol is 4;

[0140] 2. Preparation of activated silica sol: Take silica sol with a silica content of 40% by mass, add small molecule carboxylic acid to adjust the pH to 4, stir at 50℃ for 60 min to obtain activated silica sol No. 1;

[0141] The small molecule carboxylic acid is acetic acid;

[0142] 3. Preparation of sol: Activated silica sol No. 1 and aluminum sol No. 1 are mixed at a mass ratio of 1:3.5. The mixture is reacted at 60℃ for 5 hours. Then, a spinning aid with a mass fraction of 3% is added and stirred at room temperature for 60 minutes. Finally, the mixture is concentrated under vacuum at 60℃ and 0.03MPa for 3 hours to obtain alumina spinning sol.

[0143] The spinning aid is polyvinyl alcohol;

[0144] The viscosity of the alumina spinning sol is 50 Pa·s;

[0145] 4. Spinning and heat treatment

[0146] (1) Spinning: Alumina spinning sol is dry spun to obtain alumina gel fiber. The sol temperature during dry spinning is 50℃, the tunnel temperature is 100℃, and the spinning speed is 500m / min.

[0147] (2) Drying: The alumina gel fiber was dried in an 80℃ forced-air oven for 3 hours to obtain dried alumina gel fiber;

[0148] (3) Heat treatment: The dried alumina gel fiber was heated to 750℃ at a heating rate of 5℃ / min and held for 70min; then heated to 1300℃ at a heating rate of 8℃ / min and held for 120min to obtain a multiphase alumina fiber with mullite and α-alumina crystal phases.

[0149] The obtained multiphase alumina fibers were subjected to XRD analysis, and the XRD patterns are shown below. Figure 1 As shown;

[0150] The ceramic conversion rate of the multiphase alumina fiber is 48%, and the ceramic fiber density at 1300℃ is 3.3 g / cm³. 3 The tensile strength of the bundled fibers is 2.3 GPa, and after heat treatment at 1200℃ in air for 5 hours, the fiber strength is retained at 80%.

[0151] This embodiment also provides a multiphase alumina fiber obtained by the aforementioned preparation method.

[0152] Comparative Example 1

[0153] Based on Example 1, the second step of heating and activation in the second step of preparing single-phase mullite sol is omitted. Correspondingly, the single-phase mullite sol stock solution obtained in the first step of preparing single-phase mullite sol stock solution is directly used to replace the No. 1 single-phase mullite sol precursor in the third step of preparing sol.

[0154] The problem with this comparative example is that the solid content of the alumina spinning sol obtained in step 3 is low, which leads to a decrease in spinnability in step 4 spinning and heat treatment. It also affects the ceramic conversion rate of the obtained multiphase alumina fibers, reducing the ceramic conversion rate to 37%.

[0155] Comparative Example 2

[0156] Based on Example 4, the activation step (2) in the first step of preparing aluminum sol is omitted. Correspondingly, the aluminum carboxylate stock solution obtained in the first step of preparing aluminum carboxylate stock solution is directly used to replace aluminum sol No. 1 in the third step of preparing sol.

[0157] The second step of activating the silica sol is omitted. Accordingly, silica sol with a silica content of 40% by mass is directly used in the third step of preparing the sol to replace the No. 1 activated silica sol in an equal amount.

[0158] The problem with this comparative example is that, due to the lack of activation of the aluminum sol and silica sol, their activity is low, and a clear, spinnable alumina spinning sol was not obtained in the third step of sol preparation.

[0159] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0160] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing multiphase alumina fibers, characterized in that, It consists of the following steps: spinning, drying, and heat treatment; The spinning process involves dry spinning of alumina spinning sol to obtain alumina gel fibers. The crystal phase of the multiphase alumina fiber is one of a composite crystal phase of mullite and γ-alumina or a composite crystal phase of mullite and α-alumina. When the crystal phase of the multiphase alumina fiber is a composite crystal phase of mullite and γ-alumina, the preparation method of the alumina spinning sol in the spinning process is as follows: add the No. 1 single-phase mullite sol precursor to the No. 2 alumina sol and stir at room temperature for 30-40 min; then concentrate under vacuum for 1-1.5 h to obtain the alumina spinning sol. The preparation method of the No. 1 single-phase mullite sol precursor consists of the following steps: preparing single-phase mullite sol stock solution and activating it by heating. The heating activation process in the preparation of the No. 1 single-phase mullite sol precursor involves heating the single-phase mullite sol stock solution to 70-90℃ at a heating rate of 5-8℃ / min and holding it for 5-8 hours for solvent removal; then heating it to 100-120℃ at a heating rate of 3-5℃ / min and holding it for 3-5 hours to obtain the No. 1 single-phase mullite sol precursor. The preparation method of the No. 2 aluminum sol consists of the following steps: preparing aluminum carboxylate stock solution and activating it; The activation process in the preparation of aluminum sol No. 2 involves heating the aluminum carboxylate stock solution to 80-100℃ at a heating rate of 5-8℃ / min and holding it for 5-8 hours; then heating it to 100-150℃ at a heating rate of 3-5℃ / min and holding it for 3-5 hours to obtain aluminum sol precursor No. 1; dispersing 1 part by weight of aluminum sol precursor No. 1 in 1.5-2.5 parts by weight of water to obtain aluminum sol No. 1; then heating aluminum sol No. 1 to 150-250℃ at a heating rate of 3-5℃ / min and holding it for 3-5 hours to obtain aluminum sol precursor No. 2; and then dispersing 1 part by weight of aluminum sol precursor No. 2 in 1.5-2.5 parts by weight of water to obtain aluminum sol No.

2. When the crystal phase of the multiphase alumina fiber is a composite crystal phase of mullite and α-alumina, the preparation method of the alumina spinning sol in the spinning process is as follows: mix No. 1 activated silica sol and No. 1 aluminum sol, react at 40-60℃ for 3-5 hours, add spinning aids, stir at room temperature for 30-60 minutes, and then concentrate under vacuum for 1 hour to obtain alumina spinning sol. The preparation method of the No. 1 activated silica sol is as follows: add a small molecule carboxylic acid to the silica sol to adjust the pH to 3-4, stir at 30-50℃ for 30-60 min to obtain the No. 1 activated silica sol; The preparation method of the No. 1 aluminum sol consists of the following steps: preparing aluminum carboxylate stock solution and activating it; The mass fraction of the spinning aid is 1-3%; In the preparation of aluminum sol No. 2 and aluminum sol No. 1, aluminum carboxylate stock solution is prepared by heating deionized water to 70-90℃, adding aluminum hydroxide, stirring for 15-30 min, adding monocarboxylic acid and dicarboxylic acid, stirring for 15-30 min, heating to boiling at a heating rate of 15-25℃ / min, maintaining the temperature under reflux for 5-10 h, cooling, filtering, and taking the filtrate to obtain aluminum carboxylate stock solution; In the preparation of the aluminum carboxylate stock solution, the monocarboxylic acid is one of formic acid, acetic acid, and propionic acid; The dicarboxylic acid is one of oxalic acid, malonic acid, and succinic acid.

2. The method for preparing multiphase alumina fibers according to claim 1, characterized in that, To prepare the single-phase mullite sol stock solution, aluminum nitrate is dissolved in water and stirred at room temperature until dissolved; then aluminum isopropoxide is added and stirred at room temperature for 5-30 min; then tetraethyl orthosilicate is added and stirred at room temperature for 1-3 h; then the temperature is raised to 50-80℃ and stirred for 3-5 h to obtain the single-phase mullite sol stock solution. In the preparation of the single-phase mullite sol stock solution, the molar ratio of aluminum isopropoxide to aluminum nitrate is 2.5-3.5:1; The molar ratio of aluminum to silicon is 2.8-3.2:1; The molar ratio of aluminum nitrate to water is 1:30-50.

3. The method for preparing multiphase alumina fibers according to claim 1, characterized in that, In the preparation of the No. 1 activated silica sol, the silica sol contains 30-40% silica by mass. In the preparation of the No. 1 activated silica sol, the small molecule carboxylic acid is one of formic acid, acetic acid, and propionic acid.

4. The method for preparing multiphase alumina fibers according to claim 1, characterized in that, The heat treatment involves heating the dried alumina gel fibers to 650-750℃ at a heating rate of 3-5℃ / min and holding for 50-70min; then heating them to 1100-1300℃ at a heating rate of 5-8℃ / min and holding for 60-120min to obtain multiphase alumina fibers.

5. The method for preparing multiphase alumina fibers according to claim 1, characterized in that, When the crystal phase of the multiphase alumina fiber is a composite crystal phase of mullite and γ-alumina, in the preparation of the alumina spinning sol in the spinning process, the mass ratio of No. 1 single-phase mullite sol precursor to No. 2 alumina sol is 2-3:

1. The vacuum concentration temperature is 40-60℃ and the vacuum degree is 0.03MPa.

6. The method for preparing multiphase alumina fibers according to claim 1, characterized in that, When the crystal phase of the multiphase alumina fiber is a composite crystal phase of mullite and α-alumina, in the preparation of the alumina spinning sol in the spinning process, the mass ratio of No. 1 activated silica sol to No. 1 aluminum sol is 1:2.3-3.

5. The spinning aid is one of polyethylene glycol, polyvinyl alcohol, and polyethylene oxide; The vacuum concentration temperature is 40-60℃ and the vacuum degree is 0.03MPa.

7. The method for preparing multiphase alumina fibers according to claim 1, characterized in that, In the preparation of the aluminum carboxylate stock solution, the molar ratio of aluminum hydroxide, monocarboxylic acid, and dicarboxylic acid is 1:0.5-1:2.5-3.

5. The molar ratio of aluminum hydroxide to deionized water is 1:20-40.

8. A multiphase alumina fiber obtained by the preparation method according to any one of claims 1-7.

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