Method for synthesizing ultrafine flaky alpha-al2o3 powder at low temperature

Abstract

The application discloses a method for synthesizing superfine flaky alpha-Al2O3 powder at low temperature, which uses aluminum as an aluminum source, inorganic acid as a solvent and urea as a precipitant, and does not add any additive, template and crystal seed. First, the aluminum is added into the inorganic acid, ammonia water is used to adjust the PH value to 7, then ammonium sulfate and urea are added and fully mixed, and then molten salt is added and fully stirred to form a mixed solution; then the mixed solution is loaded into a reaction kettle to perform hydrothermal reaction at a certain temperature to obtain a precipitate. The precipitate is dried to obtain an aluminum oxide precursor; after being calcined at 560-800 DEG C, the aluminum oxide precursor is washed and dried to obtain high-purity flaky alpha-Al2O3 powder with a particle size of 100-500 nm. The preparation method has the advantages of low synthesis temperature, simple process, easily-obtained materials, high aluminum oxide purity and wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of inorganic functional materials preparation technology, specifically to a method for low-temperature synthesis of ultrafine flake-like α-Al2O3 powder. Background Technology

[0002] α-Al2O3 possesses a series of excellent physical and chemical properties, including high melting point, high hardness, excellent wear resistance, oxidation resistance, corrosion resistance, good insulation, large surface area, small coefficient of thermal expansion, good thermal shock resistance, fine particle size, and high hardness. It is widely used in important industrial fields such as chemical industry, energy, automobile, defense, microelectronics, and aerospace.

[0003] Currently, methods for preparing α-Al₂O₃ include solid-state methods, hydrothermal methods, sol-gel methods, and molten salt methods. The synthesis temperature of α-Al₂O₃ is generally above 1000℃, and a large amount of mineralizing agent is required, leading to high production costs and high impurity content in the alumina products. CN116253346A describes a low-temperature preparation method for α-alumina powder. This method mainly involves ball milling aluminum hydroxide, α-phase alumina seed crystals, and calcination aids in a specific ratio, followed by drying and calcination. An inert gas is introduced during the calcination process to obtain α-alumina powder. Although this method uses a synthesis temperature of 600–1000℃, which is relatively low, the need for an inert gas during calcination places high demands on the kiln equipment, resulting in high production costs. CN109650423A describes a method for preparing highly dispersed flake-like α-Al₂O₃ powder. This method involves uniformly mixing an aluminum source, molten salt, crystal form control agent, carbonate, and dispersant, drying the mixture, calcining it at 900–1200℃, removing the molten salt, and then freeze-drying to obtain flake-like α-alumina powder. This method uses a high calcination temperature, resulting in flake-like α-alumina powder containing a large amount of impurities, significantly affecting its properties. CN1936114A describes a method using Al(OH)₃ or γ-Al₂O₃, first calcined at 550–650℃ to generate an amorphous state, then adding molten salt and α-Al₂O₃ seed crystals for mixing. The synthesis temperature for micron-sized α-Al₂O₃ powder is 660–1300℃. This method also uses a high pretreatment temperature, resulting in relatively large particle sizes of the synthesized Al₂O₃ powder, failing to reach the nanoscale, thus limiting its application. These problems restrict the development of α-Al₂O₃ powder preparation. Therefore, it is necessary to lower the synthesis temperature of α-Al2O3 and simplify the preparation process. In particular, it is difficult and even more difficult to achieve the goal of balancing low-temperature synthesis of α-Al2O3 with morphology control. Summary of the Invention

[0004] In order to overcome the problems of the prior art, the present invention provides a method for low-temperature synthesis of ultrafine flake-shaped α-Al2O3 powder that is low in cost, simple in process, and suitable for large-scale production.

[0005] The technical solution of this invention is: a method for low-temperature synthesis of ultrafine flake-like α-Al2O3 powder, characterized by comprising the following steps:

[0006] Step 1: Use sandpaper to sand the surface of the aluminum metal to remove the dense aluminum oxide film on its surface, and then cut the aluminum metal into aluminum sheets.

[0007] Step 2: Slowly add the aluminum sheet prepared in Step 1 into the inorganic acid, stir thoroughly to prepare an aluminum salt solution, and then add ammonia to adjust the pH of the aluminum salt to 7.

[0008] Step 3: Add ammonium sulfate, urea, and molten salt to the aluminum salt solution obtained in Step 2 and mix thoroughly to prepare a mixed solution;

[0009] Step 4: The mixed solution obtained in Step 3 is loaded into a reaction vessel and subjected to a hydrothermal reaction at a certain temperature to obtain a precipitate. After drying the precipitate, an alumina precursor is obtained.

[0010] Step 5: The alumina precursor obtained in Step 4 is calcined to obtain an α-Al2O3 powder mixture;

[0011] Step 6: Wash the α-Al2O3 powder mixture obtained in Step 5 with anhydrous ethanol and deionized water at least 3 times each, and dry it to obtain ultrafine flake α-Al2O3 powder.

[0012] In step two, the aluminum salt concentration is 0.01–0.5 mol / L.

[0013] The inorganic acid in step two is one of dilute hydrochloric acid, dilute nitric acid, or dilute sulfuric acid, and its molar ratio with that of elemental aluminum is 3:1.

[0014] In step three, the molar ratio of urea to aluminum ions is 5:1, the molar ratio of aluminum salt to ammonium sulfate is 2.5:1, and the molar ratio of aluminum salt to molten salt is 1:2.

[0015] In step three, the molten salt is any one or a mixture of two of NaCl and KCl; the molten salt is any one or a mixture of two of sodium bromide and potassium bromide; or the molten salt is LiCl.

[0016] When there are two types of molten salt, the molar ratio of KCl to NaCl or the molar ratio of KBr to NaBr is 1 to 3:1.

[0017] The hydrothermal reaction in step four is carried out at a temperature of 80–120°C for 3–10 hours.

[0018] In step five, the calcination temperature is 560–800℃, and the holding time is 2–8 hours.

[0019] The particle size of the ultrafine flake-like α-Al2O3 powder obtained in step six is ​​100–500 nm.

[0020] The present invention has the following beneficial effects:

[0021] The principle of this invention for the low-temperature synthesis of α-Al₂O₃: SO₄²⁻ is synthesized using a hydrothermal method. 2- Preventing multinuclear complexes ([Al) x (H2O) y ] m+ The polymerization process forms aluminum hydroxide agglomerates, promoting the formation of spherical Al4(OH)₂. 10 The conversion of SO4, with the addition of NaCl and KCl molten salts, under low-temperature conditions, maximizes the solubility, diffusivity, and reactivity of the reactants, significantly improving the uniformity and reaction rate of the diffusion-controlled solid-phase reaction, thereby greatly reducing the synthesis temperature of the prepared product. Na⁺ (ionic radius 0.102 nm) and K⁺ (0.138 nm) in the molten salt synergistically adsorb onto the α-Al₂O₃ surface with residual SO₄²⁻: Na⁺ preferentially adsorbs onto the (001) crystal plane, enhancing the inhibitory effect of SO₄²⁻ on longitudinal growth; Li + K⁺ reduces the surface energy of the (100) crystal plane, promoting lateral ion diffusion. Therefore, α-Al₂O₃ can only be synthesized at a low temperature of 560℃ under the coupling effect of hydrothermal and molten salt, achieving controllable morphology and size. At the same time, the calcination process does not produce any harmful gases, making it green and environmentally friendly.

[0022] This invention synthesizes α-Al₂O₃ at 560–800℃ using a hydrothermal + molten salt coupling method without adding any dispersants, templates, seed crystals, or additives. It directly synthesizes 100–500 nm α-Al₂O₃ powder with uniform dispersion and high purity, eliminating the need for airflow pulverization. The preparation method of this invention features low synthesis temperature, simple process, and readily available materials, thus possessing broad market application prospects. Attached Figure Description

[0023] Figure 1 X-ray diffraction pattern of α-Al2O3 powder synthesized in Example 5;

[0024] Figure 2 This is a scanning electron microscope image of the α-Al2O3 powder synthesized in Example 3. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Example 1

[0026] Step 1: Sand the surface of the aluminum metal with sandpaper to remove the dense aluminum oxide film on the surface, then cut 0.27g of aluminum metal into small aluminum flakes.

[0027] Step 2: Slowly add the thin aluminum flakes from Step 1 to 200ml of dilute hydrochloric acid. The molar ratio of dilute hydrochloric acid to aluminum is 3:1. Stir thoroughly to prepare an aluminum salt solution. After cooling to room temperature, add ammonia to adjust the pH of the aluminum salt to 7.

[0028] Step 3: Add 0.004 mol / L ammonium sulfate, 0.05 mol / L urea, and 0.02 mol / L NaCl to the aluminum salt solution obtained in Step 2 and mix thoroughly to prepare a mixed solution;

[0029] Step 4: The mixed solution obtained in Step 3 is loaded into a reaction vessel and subjected to hydrothermal reaction at 80°C for 3 hours to obtain a precipitate. After drying the precipitate, an alumina precursor is obtained.

[0030] Step 5: Calcine the alumina precursor obtained in Step 4 at 800℃, keep it at that temperature for 4 hours, and then cool it to obtain an α-Al2O3 powder mixture;

[0031] Step 6: Wash the α-Al2O3 powder mixture obtained in Step 5 with anhydrous ethanol and deionized water at least 3 times each, and dry it to obtain ultrafine flake α-Al2O3 powder.

[0032] The particle size of the ultrafine flake-like α-Al2O3 powder obtained in step six is ​​400-500 nm. Example 2

[0033] Step 1: Sand the surface of the aluminum metal with sandpaper to remove the dense aluminum oxide film on the surface, then cut 2.7g of aluminum metal into small aluminum flakes.

[0034] Step 2: Slowly add the thin aluminum flakes from Step 1 to 200ml of dilute sulfuric acid. The molar ratio of dilute sulfuric acid to aluminum is 3:1. Stir thoroughly to prepare an aluminum salt solution. After cooling to room temperature, add ammonia to adjust the pH of the aluminum salt to 7.

[0035] Step 3: Add 0.04 mol / L ammonium sulfate, 0.5 mol / L urea, and 0.2 mol / L KCl to the aluminum salt solution obtained in Step 2 and mix thoroughly to prepare a mixed solution;

[0036] Step 4: The mixed solution obtained in Step 3 is loaded into a reaction vessel and subjected to hydrothermal reaction at 100°C for 5 hours to obtain a precipitate. After drying the precipitate, an alumina precursor is obtained.

[0037] Step 5: The alumina precursor obtained in Step 4 is calcined at 700℃, kept at that temperature for 5 hours, and then cooled to obtain an α-Al2O3 powder mixture.

[0038] Step 6: Wash the α-Al2O3 powder mixture obtained in Step 5 with anhydrous ethanol and deionized water at least 3 times each, and dry it to obtain ultrafine flake α-Al2O3 powder.

[0039] The particle size of the ultrafine flake-like α-Al2O3 powder obtained in step six is ​​400-450 nm. Example 3

[0040] Step 1: Sand the surface of the aluminum metal with sandpaper to remove the dense aluminum oxide film on the surface, then cut 13.5g of aluminum metal into small aluminum flakes.

[0041] Step 2: Slowly add the thin aluminum flakes from Step 1 into 200ml of dilute nitric acid. The molar ratio of dilute nitric acid to aluminum is 3:1. Stir thoroughly to prepare an aluminum salt solution. After cooling to room temperature, add ammonia to adjust the pH of the aluminum salt to 7.

[0042] Step 3: Add 0.2 mol / L ammonium sulfate, 2.5 mol / L urea, and 1.0 mol / L LiCl to the aluminum salt solution prepared in Step 2 and mix thoroughly to prepare a mixed solution;

[0043] Step 4: The mixed solution obtained in Step 3 is loaded into a reaction vessel and subjected to hydrothermal reaction at 120°C for 10 hours to obtain a precipitate. After drying the precipitate, an alumina precursor is obtained.

[0044] Step 5: The alumina precursor obtained in Step 4 is calcined at 600℃, kept at that temperature for 8 hours, and then cooled to obtain an α-Al2O3 powder mixture;

[0045] Step 6: Wash the α-Al2O3 powder mixture obtained in Step 5 with anhydrous ethanol and deionized water at least 3 times each, and dry it to obtain ultrafine flake α-Al2O3 powder.

[0046] The particle size of the ultrafine flake-like α-Al2O3 powder obtained in step six is ​​100–300 nm.

[0047] like Figure 2 As shown, the alumina particles obtained in Example 3 of this invention generally appear as nano-sized, fine, flake-like particles with a particle size of 100–300 nm under a scanning electron microscope. Example 4

[0048] Step 1: Sand the surface of the aluminum metal with sandpaper to remove the dense aluminum oxide film on the surface, then cut 2.7g of aluminum metal into small aluminum flakes.

[0049] Step 2: Slowly add the thin aluminum flakes from Step 1 into 200ml of dilute nitric acid. The molar ratio of dilute nitric acid to aluminum is 3:1. Stir thoroughly to prepare an aluminum salt solution. After cooling to room temperature, add ammonia to adjust the pH of the aluminum salt to 7.

[0050] Step 3: Add 0.04 mol / L ammonium sulfate, 0.5 mol / L urea, 0.1 mol / L NaCl and 0.1 mol / L KCl (KCl and NaCl molar ratio 1:1) to the aluminum salt solution obtained in Step 2 and mix thoroughly to prepare a mixed solution;

[0051] Step 4: The mixed solution obtained in Step 3 is loaded into a reaction vessel and subjected to hydrothermal reaction at 80°C for 6 hours to obtain a precipitate. After drying the precipitate, an alumina precursor is obtained.

[0052] Step 5: The alumina precursor obtained in Step 4 is calcined at 600℃, kept at that temperature for 5 hours, and then cooled to obtain an α-Al2O3 powder mixture.

[0053] Step 6: Wash the α-Al2O3 powder mixture obtained in Step 5 with anhydrous ethanol and deionized water at least 3 times each, and dry it to obtain ultrafine flake α-Al2O3 powder.

[0054] The particle size of the ultrafine flake-like α-Al2O3 powder obtained in step six is ​​300-400 nm. Example 5

[0055] Step 1: Sand the surface of the aluminum metal with sandpaper to remove the dense aluminum oxide film on the surface, then cut 2.7g of aluminum metal into small aluminum flakes.

[0056] Step 2: Slowly add the thin aluminum flakes from Step 1 into 200ml of dilute nitric acid. The molar ratio of dilute nitric acid to aluminum is 3:1. Stir thoroughly to prepare an aluminum salt solution. After cooling to room temperature, add ammonia to adjust the pH of the aluminum salt to 7.

[0057] Step 3: Add 0.04 mol / L ammonium sulfate, 0.5 mol / L urea, 0.133 mol / L KCl and 0.067 mol / L NaCl (KCl to NaCl molar ratio 2:1) to the aluminum salt solution prepared in Step 2 and mix thoroughly to prepare a mixed solution;

[0058] Step 4: The mixed solution obtained in Step 3 is loaded into a reaction vessel and subjected to hydrothermal reaction at 80°C for 6 hours to obtain a precipitate. After drying the precipitate, an alumina precursor is obtained.

[0059] Step 5: The alumina precursor obtained in Step 4 is calcined at 560℃, held at that temperature for 5 hours, and then cooled to obtain an α-Al2O3 powder mixture.

[0060] Step 6: Wash the α-Al2O3 powder mixture obtained in Step 5 with anhydrous ethanol and deionized water at least 3 times each, and dry it to obtain ultrafine flake α-Al2O3 powder.

[0061] The particle size of the ultrafine flake-like α-Al2O3 powder obtained in step six is ​​200–400 nm.

[0062] like Figure 1 As shown, the alumina powder prepared in Example 5 of this invention was tested by XRD: the prepared sample was pure α-Al2O3. This conforms to the standard card in PDF#08-5137. Example 6

[0063] Step 1: Sand the surface of the aluminum metal with sandpaper to remove the dense aluminum oxide film on the surface, then cut 2.7g of aluminum metal into small aluminum flakes.

[0064] Step 2: Slowly add the thin aluminum flakes from Step 1 into 200ml of dilute nitric acid. The molar ratio of dilute nitric acid to aluminum is 3:1. Stir thoroughly to prepare an aluminum salt solution. After cooling to room temperature, add ammonia to adjust the pH of the aluminum salt to 7.

[0065] Step 3: Add 0.04 mol / L ammonium sulfate, 0.5 mol / L urea, 0.15 mol / L KCl and 0.05 mol / L NaCl (KCl to NaCl molar ratio 3:1) to the aluminum salt solution prepared in Step 2 and mix thoroughly to prepare a mixed solution;

[0066] Step 4: The mixed solution obtained in Step 3 is loaded into a reaction vessel and subjected to hydrothermal reaction at 80°C for 6 hours to obtain a precipitate. After drying the precipitate, an alumina precursor is obtained.

[0067] Step 5: The alumina precursor obtained in Step 4 is calcined at 560℃, held at that temperature for 5 hours, and then cooled to obtain an α-Al2O3 powder mixture.

[0068] Step 6: Wash the α-Al2O3 powder mixture obtained in Step 5 with anhydrous ethanol and deionized water at least 3 times each, and dry it to obtain ultrafine flake α-Al2O3 powder.

[0069] The particle size of the ultrafine flake-like α-Al2O3 powder obtained in step six is ​​200-300 nm. Example 7

[0070] Step 1: Sand the surface of the aluminum metal with sandpaper to remove the dense aluminum oxide film on the surface, then cut 2.7g of aluminum metal into small aluminum flakes.

[0071] Step 2: Slowly add the thin aluminum flakes from Step 1 into 200ml of dilute nitric acid. The molar ratio of dilute nitric acid to aluminum is 3:1. Stir thoroughly to prepare an aluminum salt solution. After cooling to room temperature, add ammonia to adjust the pH of the aluminum salt to 7.

[0072] Step 3: Add 0.04 mol / L ammonium sulfate, 0.5 mol / L urea, and 0.2 mol / L NaBr to the aluminum salt solution obtained in Step 2 and mix thoroughly to prepare a mixed solution;

[0073] Step 4: The mixed solution obtained in Step 3 is loaded into a reaction vessel and subjected to hydrothermal reaction at 80°C for 6 hours to obtain a precipitate. After drying the precipitate, an alumina precursor is obtained.

[0074] Step 5: Calcine the alumina precursor obtained in Step 4 at 700℃, keep it at that temperature for 4 hours, and then cool it to obtain an α-Al2O3 powder mixture.

[0075] Step 6: Wash the α-Al2O3 powder mixture obtained in Step 5 with anhydrous ethanol and deionized water at least 3 times each, and dry it to obtain ultrafine flake α-Al2O3 powder.

[0076] The particle size of the ultrafine flake-like α-Al2O3 powder obtained in step six is ​​400-450 nm. Example 8

[0077] Step 1: Sand the surface of the aluminum metal with sandpaper to remove the dense aluminum oxide film on the surface, then cut 2.7g of aluminum metal into small aluminum flakes.

[0078] Step 2: Slowly add the thin aluminum flakes from Step 1 into 200ml of dilute nitric acid. The molar ratio of dilute nitric acid to aluminum is 3:1. Stir thoroughly to prepare an aluminum salt solution. After cooling to room temperature, add ammonia to adjust the pH of the aluminum salt to 7.

[0079] Step 3: Add 0.04 mol / L ammonium sulfate, 0.5 mol / L urea, and 0.2 mol / L KBr to the aluminum salt solution obtained in Step 2 and mix thoroughly to prepare a mixed solution;

[0080] Step 4: The mixed solution obtained in Step 3 is loaded into a reaction vessel and subjected to hydrothermal reaction at 80°C for 6 hours to obtain a precipitate. After drying the precipitate, an alumina precursor is obtained.

[0081] Step 5: Calcine the alumina precursor obtained in Step 4 at 700℃, keep it at that temperature for 4 hours, and then cool it to obtain an α-Al2O3 powder mixture.

[0082] Step 6: Wash the α-Al2O3 powder mixture obtained in Step 5 with anhydrous ethanol and deionized water at least 3 times each, and dry it to obtain ultrafine flake α-Al2O3 powder.

[0083] The particle size of the ultrafine flake-like α-Al2O3 powder obtained in step six is ​​400-500 nm. Example 9

[0084] Step 1: Sand the surface of the aluminum metal with sandpaper to remove the dense aluminum oxide film on the surface, then cut 2.7g of aluminum metal into small aluminum flakes.

[0085] Step 2: Slowly add the thin aluminum flakes from Step 1 into 200ml of dilute nitric acid. The molar ratio of dilute nitric acid to aluminum is 3:1. Stir thoroughly to prepare an aluminum salt solution. After cooling to room temperature, add ammonia to adjust the pH of the aluminum salt to 7.

[0086] Step 3: Add 0.04 mol / L ammonium sulfate, 0.5 mol / L urea, 0.1 mol / L KBr and 0.1 mol / L NaBr (KBr and NaBr molar ratio 1:1) to the aluminum salt solution obtained in Step 2 and mix thoroughly to prepare a mixed solution;

[0087] Step 4: The mixed solution obtained in Step 3 is loaded into a reaction vessel and subjected to hydrothermal reaction at 80°C for 6 hours to obtain a precipitate. After drying the precipitate, an alumina precursor is obtained.

[0088] Step 5: Calcine the alumina precursor obtained in Step 4 at 600℃, keep it at that temperature for 4 hours, and then cool it to obtain an α-Al2O3 powder mixture.

[0089] Step 6: Wash the α-Al2O3 powder mixture obtained in Step 5 with anhydrous ethanol and deionized water at least 3 times each, and dry it to obtain ultrafine flake α-Al2O3 powder.

[0090] The particle size of the ultrafine flake-like α-Al2O3 powder obtained in step six is ​​300-400 nm. Example 10

[0091] Step 1: Sand the surface of the aluminum metal with sandpaper to remove the dense aluminum oxide film on the surface, then cut 2.7g of aluminum metal into small aluminum flakes.

[0092] Step 2: Slowly add the thin aluminum flakes from Step 1 into 200ml of dilute nitric acid. The molar ratio of dilute nitric acid to aluminum is 3:1. Stir thoroughly to prepare an aluminum salt solution. After cooling to room temperature, add ammonia to adjust the pH of the aluminum salt to 7.

[0093] Step 3: Add 0.04 mol / L ammonium sulfate, 0.5 mol / L urea, 0.133 mol / L KBr and 0.067 mol / L NaBr (KBr and NaBr molar ratio 2:1) to the aluminum salt solution obtained in Step 2 and mix thoroughly to prepare a mixed solution;

[0094] Step 4: The mixed solution obtained in Step 3 is loaded into a reaction vessel and subjected to hydrothermal reaction at 80°C for 6 hours to obtain a precipitate. After drying the precipitate, an alumina precursor is obtained.

[0095] Step 5: Calcine the alumina precursor obtained in Step 4 at 600℃, keep it at that temperature for 4 hours, and then cool it to obtain an α-Al2O3 powder mixture.

[0096] Step 6: Wash the α-Al2O3 powder mixture obtained in Step 5 with anhydrous ethanol and deionized water at least 3 times each, and dry it to obtain ultrafine flake α-Al2O3 powder.

[0097] The particle size of the ultrafine flake-like α-Al2O3 powder obtained in step six is ​​200–400 nm. Example 11

[0098] Step 1: Sand the surface of the aluminum metal with sandpaper to remove the dense aluminum oxide film on the surface, then cut 2.7g of aluminum metal into small aluminum flakes.

[0099] Step 2: Slowly add the thin aluminum flakes from Step 1 into 200ml of dilute nitric acid. The molar ratio of dilute nitric acid to aluminum is 3:1. Stir thoroughly to prepare an aluminum salt solution. After cooling to room temperature, add ammonia to adjust the pH of the aluminum salt to 7.

[0100] Step 3: Add 0.04 mol / L ammonium sulfate, 0.5 mol / L urea, 0.15 mol / L KBr and 0.05 mol / L NaBr (KBr and NaBr molar ratio 3:1) to the aluminum salt solution obtained in Step 2 and mix thoroughly to prepare a mixed solution;

[0101] Step 4: The mixed solution obtained in Step 3 is loaded into a reaction vessel and subjected to hydrothermal reaction at 80°C for 6 hours to obtain a precipitate. After drying the precipitate, an alumina precursor is obtained.

[0102] Step 5: Calcine the alumina precursor obtained in Step 4 at 600℃, keep it at that temperature for 4 hours, and then cool it to obtain an α-Al2O3 powder mixture.

[0103] Step 6: Wash the α-Al2O3 powder mixture obtained in Step 5 with anhydrous ethanol and deionized water at least 3 times each, and dry it to obtain ultrafine flake α-Al2O3 powder.

[0104] The particle size of the ultrafine flake-like α-Al2O3 powder obtained in step six is ​​200-300 nm.

[0105] Comparative Example 1

[0106] Referring to Example 5 of the present invention, the only difference from Example 5 is that NaCl and KCl molten salts are not added in step three.

[0107] Comparative Example 2

[0108] Referring to Example 5 of the present invention, the only difference from Example 5 is that in step four, a reaction vessel is not used, but the reaction is directly heated.

[0109] The relevant data for the synthesis of α-Al2O3 in Example 5 and Comparative Examples 1-2 are shown in Table 1.

[0110] Table 1

[0111] As shown in Table 1, in Example 5 of the present invention, without adding NaCl and KCl molten salts and keeping other conditions unchanged, only spherical γ-Al2O3 can be synthesized at 560℃, or without using a reaction vessel and keeping other conditions unchanged, only 1-2μm sheet-like γ-Al2O3 can be synthesized at 560℃. Therefore, the hydrothermal + molten salt coupling effect fails, thereby increasing the synthesis temperature of α-Al2O3.

[0112] The above embodiments are merely illustrative of the principles and effects of the present invention, as well as some examples of its application, and are not intended to limit the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention.

Claims

1. A method for low-temperature synthesis of ultrafine flaky α-Al2O3 powder, characterized in that The method comprises the following steps: Step 1: polishing the surface of the metal aluminum element with sandpaper to remove the dense aluminum oxide film on the surface, and then cutting the metal aluminum element into aluminum flakes; Step 2: slowly adding the metal aluminum flakes treated in step 1 into an inorganic acid, fully stirring, preparing an aluminum salt solution, and then adding ammonia water to adjust the pH of the aluminum salt to 7; Step 3: adding ammonium sulfate, urea and fused salt into the aluminum salt solution prepared in step 2, fully mixing, and configuring into a mixed solution; Step 4: loading the mixed solution prepared in step 3 into a reaction kettle, performing hydrothermal reaction at 80-120℃ to obtain a precipitate, the time being 3-10h, drying the precipitate to obtain an aluminum oxide precursor; Step 5: calcining the aluminum oxide precursor prepared in step 4 at 560-800℃, and keeping the temperature for 2-8h to obtain an α-Al2O3 powder mixture; Step 6: cleaning the α-Al2O3 powder mixture prepared in step 5 with anhydrous ethanol and deionized water for at least 3 times, drying to obtain an α-Al2O3 powder with a particle size of 100-500nm.

2. The method of claim 1, wherein: The concentration of the aluminum salt in step 2 is 0.01-0.5mol / L.

3. The method of claim 1, wherein: The inorganic acid in step 2 is one of dilute hydrochloric acid, dilute nitric acid and dilute sulfuric acid, and the molar ratio of the inorganic acid to the metal aluminum element is 3:

1.

4. The method of claim 1, wherein: The molar ratio of urea to aluminum ions in step 3 is 5:1, the molar ratio of aluminum salt to ammonium sulfate is 2.5:1, and the molar ratio of aluminum salt to fused salt is 1:

2.

5. The method of claim 1, wherein: The fused salt in step 3 is any one of NaCl, KCl or a mixture of the two; the fused salt is any one of NaBr, KBr or a mixture of the two; the fused salt is LiCl.

6. The method of claim 5, wherein: When the fused salt is two kinds, the molar ratio of KCl to NaCl or the molar ratio of KBr to NaBr is 1-3:1.

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