Method for preparing molecular ceramic high-strength high-modulus continuous alpha-Al2O3 fiber at low temperature

Abstract

The invention belongs to the technical field of preparation of special fibers, and relates to a method for preparing molecular ceramic high-strength high-modulus continuous alpha-Al2O3 fibers at low temperature. The preparation method comprises the following steps: adding aluminum nitrate, aluminum chloride and aluminum particles into deionized water, fully stirring and uniformly mixing, adding nitrilotriacetic acid, citric acid and magnesium carbonate, continuously stirring until the materials are uniformly mixed, and condensing and refluxing until the materials are transparent to obtain the aluminum sol. The preparation method comprises the following steps: adding acetic acid and stirring, then adding TEOS (tetraethyl orthosilicate), then adding PVP (polyvinyl pyrrolidone), fully stirring and uniformly mixing, adding an acid-base regulator, concentrating, carrying out dry spinning to obtain fibers, then heating to 880-1200 DEG C, and calcining, the tensile strength of the fibers reaches 2.82 GPa, the tensile modulus is 318 GPa, and the tensile strength and the tensile modulus of the fibers are obviously higher than those of traditional high-temperature calcined fibers.

Description

Technical Field

[0001] The invention belongs to the technical field of special fiber preparation and relates to a method for preparing molecular ceramics with high strength and high modulus continuous α-Al at low temperature. 2 O 3 Fiber method. Background Art

[0002] α-Al 2 O 3 Fiber is an important high-performance ceramic material, which is widely used in many fields due to its excellent performance. This fiber has good high temperature stability, chemical stability, wear resistance, low thermal expansion coefficient and good electrical insulation. It has an irreplaceable position in aerospace, energy, electronics, materials science and other applications in high temperature and corrosive environments.

[0003] Traditional methods usually require high temperature conditions (usually above 1600°C) to prepare α-Al 2 O 3 Fibers, which leads to high energy consumption and high production costs. High temperature requirements not only increase energy consumption, but also cause equipment wear and material loss, limiting the large-scale production and sustainable manufacturing of fibers. Some traditional preparation methods have very strict requirements on the selection of raw materials, limiting the types and quality of available starting materials. This may lead to rising costs of raw materials and increase the complexity of the production process. High-temperature preparation methods are often accompanied by high-temperature emissions and greenhouse gas emissions, which have a negative impact on the environment. This conflicts with sustainable development and environmental protection requirements, and also increases the challenges of regulatory compliance. Some traditional preparation methods have challenges in production efficiency and scale, and cannot meet the needs of different scales and outputs. This limits the α-Al 2 O 3 Fibers are widely used, especially in large-scale and industrial production. Summary of the invention

[0004] The present invention is aimed at the traditional molecular ceramic continuous α-Al 2 O 3 The defects of high temperature and long time treatment in fiber preparation process are proposed. A new type of low temperature preparation of molecular ceramics with high strength and high modulus continuous α-Al 2 O 3 Fiber method.

[0005] In order to achieve the above object, the present invention is implemented by adopting the following technical solutions: A low-temperature preparation of high-strength and high-modulus continuous α-Al molecular ceramics 2 O 3 The fiber method, the steps are as follows: (1) Add aluminum nitrate, aluminum chloride, and aluminum particles to deionized water and stir thoroughly to mix them evenly. Add nitrilotriacetic acid, citric acid, and magnesium carbonate and continue stirring until the mixture is evenly mixed. Condensate and reflux until transparent to obtain aluminum sol.

[0006] (2) Add acetic acid to the aluminum sol and stir for at least half an hour, then add TEOS, and then add PVP and stir well to mix, to obtain sol A.

[0007] (3) Adding an acid-base regulator to sol A to adjust the pH to 5.5-6.5, and concentrating to obtain a spinning sol. The stable aluminum sol formed during the concentration process contains a variety of polyhedral precursors (such as Al13 polymers), which preferentially form an ordered crystal structure when heated.

[0008] (4) Dry spinning to obtain fibers, the fibers are placed in a calcining furnace and preheated at 550-650°C for 2.5-3.5 hours, then heated to 880-1200°C and calcined for 25-35 minutes; after calcination, they are slowly cooled to room temperature to obtain continuous α-Al 2 O 3 fiber.

[0009] Preferably, in step (1), the mass ratio of aluminum nitrate: aluminum chloride: aluminum particles is (10-15): (10-15): (0.5-2); the mass fraction of nitrilotriacetic acid in the aluminum sol is 0.3-0.6%, the mass fraction of citric acid is 0.3-0.6%, the mass fraction of magnesium carbonate is 0.05-0.2%, and the condensation reflux temperature is 50-120°C.

[0010] Preferably, in step (2), the mass fraction of acetic acid in the sol A is 0.05-0.2%, and the mass fraction of PVP is 0.05-2%.

[0011] Preferably, the acid-base regulator in step (3) is dilute hydrochloric acid or dilute ammonia water.

[0012] The technical solution provided by the present invention is that in the sol preparation stage, citric acid and nitrilotriacetic acid are used as chelating agents to form stable Al-O-Al, Al-O-Mg and Mg-O-Mg complexes with the aluminum source to prevent impurities from interfering and improve the uniformity of the precursor sol. The magnesium carbonate sintering aid can be decomposed to generate magnesium oxide during the calcination process, which reduces the crystal interface energy, makes the nucleation and growth of the α phase easier, ensures the grain refinement, and the formed network structure is conducive to stabilizing the crystal growth at low temperature and promoting the α-Al 2 O 3 The formation of phase, and magnesium oxide can effectively inhibit the abnormal growth of grains, strengthen the matrix structure by forming magnesium oxide distribution phase, so that the fiber has higher fracture toughness, and the nano-scale α-Al 2 O3 The grains are closely arranged, which improves the modulus of the fiber. After adding TEOS, the density and strength of the fiber precursor are improved through the synergistic effect with the aluminum complex, and then the addition of PVP further increases the viscosity of the solution and the tensile properties of the fiber.

[0013] Compared with the prior art, the advantages and positive effects of the present invention are: 1. The solution proposed by the present invention can achieve α phase transformation at 900°C, which greatly reduces the preparation temperature and energy consumption. The reduction of calcination temperature reduces the use of high-temperature equipment and significantly improves the economy and sustainability of the process.

[0014] 2. The present invention reduces the energy consumption required for high-temperature calcination, while reducing the wear and maintenance costs of high-temperature equipment, and has a better industrialization prospect.

[0015] 3. Under low-temperature calcination conditions, the grain size of the present invention is controlled at about 30 nm, which significantly improves the density and mechanical properties of the fiber. The fiber tensile strength reaches 2.82 GPa and the tensile modulus is 318 GPa, both of which are significantly higher than traditional high-temperature calcined fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 are XRD patterns of different materials, where a is the α-Al prepared in Example 1 2 O 3 Fiber, b is the material prepared in Example 2, c is the material prepared in Comparative Example 1, and d is the material prepared in Comparative Example 2.

[0017] Figure 2 The α-Al prepared in Example 1 2 O 3 SEM image of fiber bundle. DETAILED DESCRIPTION

[0018] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described below in conjunction with specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0019] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments of the following disclosure.

[0020] Example 1 Weigh 500g of deionized water, add 30g of aluminum nitrate, 30g of aluminum chloride, and 2g of aluminum particles, stir at 200rpm for 30min to mix thoroughly, add 2.82g of nitrilotriacetic acid, 2.82g of citric acid, and 0.6g of magnesium carbonate, and continue stirring at 200rpm for 10min. Then condense and reflux at 115℃ to prepare a transparent aluminum sol. Subsequently, add 5.7g of acetic acid, continue stirring at 200rpm for half an hour, and then add 10g of tetraethoxysilane (TEOS) and 100mL of ethanol. After mixing evenly, add 6.5g of thickener PVP to ensure the spinnability of the sol. After testing, the pH of the mixed solution is about 6.8 at this time, and the pH is adjusted to about 6 by adding 10% ammonia water by mass. Then, the fiber was heated to 85°C and stirred slowly to concentrate the sol to form a spinning sol (solid content 75%) for dry spinning at a spinning speed of 500 m / min, a spinning temperature of 40°C, and a humidity of 55%. The collected fiber was placed in a calcining furnace and preheated to 600°C at a rate of 30°C / min for 3 hours, then heated to 900°C at a rate of 6°C / min for 30 minutes, and finally cooled slowly and naturally to room temperature to obtain continuous α-Al with a diameter of 6-7μm and a grain size of 30nm. 2 O 3 Fiber (such as Figure 2 As shown). After testing, the obtained fiber density is 3.8g / cm 3 , the tensile strength is 2.82GPa and the tensile modulus is 318Gpa.

[0021] Traditional α-Al 2 O 3 The fiber preparation temperature is above 1600°C. High temperature calcination will cause excessive grain growth, generate internal cracks, and cause the fiber performance to deteriorate. This embodiment uses a relatively low temperature calcination process to obtain a fiber with a dense internal structure, small grain size, and low porosity. Figure 1 a is the α-Al prepared in this example 2 O 3 XRD pattern of the fiber, the material prepared in this embodiment is in α-Al 2 O 3 When the crystalline phase is formed, it has the characteristics of high density and low porosity, which is the fundamental reason for its high mechanical strength and modulus. In this embodiment, under low temperature calcination, the tensile strength and modulus of the fiber reach the highest value, the grain size is controlled at nanometer level, and the density is close to the theoretical value.

[0022] Example 2 The present embodiment is consistent with the embodiment 1 unless otherwise specified.

[0023] Weigh 500g of deionized water, add 30g of aluminum nitrate, 30g of aluminum chloride, and 2g of aluminum particles (diameter 1-10mm, purity > 99.5%), stir at 200rpm for 30min to mix thoroughly, add 2g of nitrilotriacetic acid, 2g of citric acid, and 0.5g of magnesium carbonate, and continue stirring at 200rpm for 10min. Then condense and reflux at 85℃ to prepare a transparent aluminum sol. Subsequently, add 4.9g of acetic acid, continue stirring at 200rpm for half an hour, and then add 10g of tetraethoxysilane (TEOS) and 100mL of ethanol. After mixing evenly, add 5g of thickener PVP, and adjust the pH to about 6 by adding 10% ammonia water by mass. Then heat and concentrate to form a spinning sol for dry spinning. The collected fibers were placed in a calcining furnace and preheated to 550°C at a rate of 30°C / min for 2.5h, then heated to 1100°C at a rate of 6°C / min for 30min, and finally cooled slowly to room temperature. 2 O 3 Fiber. After testing, the fiber density is 3.75g / cm 3 , tensile strength is 2.65GPa, and tensile modulus is 300Gpa. Figure 1 b is the α-Al prepared in this example 2 O 3 The XRD pattern of the fiber shows that the fiber prepared in this embodiment fully meets the requirements of α-Al 2 O 3 crystalline structure.

[0024] Example 3 The present embodiment is consistent with the embodiment 1 unless otherwise specified.

[0025] Weigh 500g of deionized water, add 30g of aluminum nitrate, 30g of aluminum chloride, and 2g of aluminum particles, stir at 200rpm for 30min to mix thoroughly, add 2g of nitrilotriacetic acid, 2g of citric acid, and 0.5g of magnesium carbonate, and continue stirring at 200rpm for 10min. Then condense and reflux at 85℃ to prepare a transparent aluminum sol. Subsequently, 4.9g of acetic acid was added, and after continuing to stir at 200rpm for half an hour, 10g of tetraethoxysilane (TEOS) and 100mL of ethanol were added. After mixing evenly, 5g of thickener PVP was added, and the pH was adjusted to about 6 by adding 10% ammonia water by mass fraction. Then heat and concentrate to form a spinning sol for dry spinning. The collected fibers were placed in a calcining furnace and preheated to 600℃ at a rate of 30℃ / min for 3h, then heated to 1200℃ at a rate of 6℃ / min for 30min, and finally slowly cooled to room temperature naturally. The continuous α-Al with a diameter of 6-7 μm and a grain size of 80 nm was obtained.2 O 3 Fiber. After testing, the fiber density is 3.70g / cm 3 , tensile strength is 2.5GPa, and tensile modulus is 270Gpa.

[0026] Comparative Example 1 The difference between this comparative example and Example 1 is that the amount of magnesium carbonate added is 0.06 g, and the rest of the preparation process is the same as that of Example 1. Figure 1 As shown in c, this comparative example forms γ-Al 2 O 3 +α-Al 2 O 3 The composite crystal form has a tensile strength of 2.1 GPa, a tensile modulus of 230 GPa, a grain size of 90 nm, and a density of 3.4.

[0027] Comparative Example 2 The difference between this comparative example and Example 1 is that magnesium carbonate is not added, and the other preparation processes are consistent with Example 1. Figure 1 As shown in d, this comparative example forms γ-Al 2 O 3 +α-Al 2 O 3 Composite crystal form, low crystallinity, the tensile strength is 1.0GPa, the tensile modulus is 130Gpa, the grain size is 180nm, and the density is 2.8. The grain size is too large and the degree of densification is not enough.

[0028] Comparative Example 3 The difference between this comparative example and Example 1 is that the amount of magnesium carbonate added is 5.8g, and the rest of the preparation process is consistent with Example 1. The tensile strength is 1.5GPa, the tensile modulus is 150Gpa, the grain size is 7nm, and the density is 2.0. Excessive magnesium carbonate content affects the crystal transformation, the grain growth is too restricted, and the hollowing is serious and cannot be better densified. After testing, only γ-Al 2 O 3 Crystal form, no α-Al 2 O 3 Crystal form.

[0029] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing molecular ceramic high-strength and high-modulus continuous α-Al2O3 fibers at low temperature, characterized in that: Here are the steps: (1) Add aluminum nitrate, aluminum chloride, and aluminum particles to deionized water and stir to mix well, add nitrilotriacetic acid, citric acid, and magnesium carbonate and continue stirring until the mixture is well mixed, condense and reflux until transparent, and obtain aluminum sol; (2) Add acetic acid to the aluminum sol and stir for at least half an hour, then add TEOS, and then add PVP and stir and mix thoroughly to obtain sol A; (3) adding an acid-base regulator to sol A to adjust the pH to 5.5-6.5, and concentrating to obtain a spinning sol; (4) Dry spinning to obtain fibers, the fibers are placed in a calcining furnace and preheated at 550-650°C for 2.5-3.5 hours, then heated to 880-1200°C and calcined for 25-35 minutes; after calcination, they are slowly cooled to room temperature to obtain continuous α-Al2O3 fibers.

2. The method for preparing molecular ceramic high-strength and high-modulus continuous α-Al2O3 fibers at low temperature according to claim 1, characterized in that: In step (1), the mass ratio of aluminum nitrate: aluminum chloride: aluminum particles is (10-15): (10-15): (0.5-2); the mass fraction of nitrilotriacetic acid in the aluminum sol is 0.3-0.6%, the mass fraction of citric acid is 0.3-0.6%, the mass fraction of magnesium carbonate is 0.05-0.2%, and the condensation reflux temperature is 50-120°C.

3. The method for preparing molecular ceramic high-strength and high-modulus continuous α-Al2O3 fibers at low temperature according to claim 1, characterized in that: In step (2), the mass fraction of acetic acid in sol A is 0.05-0.2%, and the mass fraction of PVP is 0.05-0.2%.

4. The method for preparing molecular ceramic high-strength and high-modulus continuous α-Al2O3 fibers at low temperature according to claim 1, characterized in that: The acid-base regulator in step (3) is dilute hydrochloric acid or dilute ammonia water.

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