Method for synthesizing superfine flaky alpha-Al2O3 powder at low temperature

Abstract

The invention discloses a method for synthesizing superfine flaky alpha-Al2O3 powder at low temperature, which comprises the following steps: by taking a metal aluminum simple substance as an aluminum source, an inorganic acid as a solvent and urea as a precipitator, adding no additive, template or seed crystal, firstly adding the metal aluminum simple substance into the inorganic acid, regulating the pH value to 7 by using ammonia water, then adding ammonium sulfate and urea, fully mixing, and then adding a catalyst to prepare the superfine flaky alpha-Al2O3 powder. Adding molten salt, and fully stirring to prepare a mixed solution; filling the mixed solution into a reaction kettle, and carrying out hydrothermal reaction at a certain temperature to obtain a precipitate; drying the precipitate to obtain an aluminum oxide precursor; and calcining at the temperature of 560-800 DEG C, washing and drying to obtain the high-purity flaky alpha-Al2O3 powder with the particle size of 100-500nm. The preparation method provided by the invention is low in synthesis temperature, simple in process, easily available in required materials, high in aluminum oxide purity and wide in application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inorganic functional material preparation, and particularly relates to a method for synthesizing ultrafine flaky alpha-Al2O3 powder at low temperature. BACKGROUND

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

[0003] At present, the methods for preparing alpha-Al2O3 include solid phase method, hydrothermal method, sol-gel method and molten salt method, and the synthesis temperature of alpha-Al2O3 is basically above 1000 DEG C, and a large amount of mineralizer needs to be added, so that the production cost of the alumina product is high, and the product has the defects such as high impurity content. CN116253346A introduces a low-temperature preparation method of alpha-alumina powder, which mainly mixes aluminum hydroxide, alpha-alumina seed crystal and calcination aid in proportion by ball milling, and then performs calcination after drying, and inert gas needs to be introduced during the calcination process, so that alpha-alumina powder is obtained. Although the synthesis temperature of this method is 600-1000 DEG C, the relative synthesis temperature is relatively low, but inert gas needs to be introduced during the calcination process, which has high requirements for the kiln equipment and high production cost. CN109650423A introduces a preparation method of high-dispersion flaky alpha-Al2O3 powder, which uniformly mixes an aluminum source, a molten salt, a crystal form control agent, a carbonate and a dispersant, dries, calcines at 900-1200 DEG C, removes the molten salt and then freeze-dries, so that flaky alpha-alumina powder is obtained. The calcination temperature of this method is relatively high, and the synthesized flaky alpha-alumina powder contains a large amount of impurities, which has a great influence on the performance of the alpha-alumina powder. CN1936114A introduces that Al(OH)3 or gamma-Al2O3 is first calcined at 550-650 DEG C to generate amorphous state, then molten salt and alpha-Al2O3 seed crystal are added and mixed, and the synthesis temperature of micron-grade alpha-Al2O3 powder is 660-1300 DEG C. The pre-treatment temperature of this method is relatively high, and the relative particle size of the synthesized Al2O3 powder is relatively large, which cannot reach the nanometer level and is limited in use. The above problems restrict the development of the preparation of alpha-Al2O3 powder. Therefore, it is necessary to reduce the synthesis temperature of alpha-Al2O3, simplify the preparation process, and especially to control the morphology of the low-temperature synthesized alpha-Al2O3, which is difficult and not easy to realize. SUMMARY

[0004] The present application is provided to overcome the problems in the prior art, and provides a method for synthesizing ultrafine flaky alpha-Al2O3 powder at low temperature, which is low in cost, simple in process and suitable for large-scale production.

[0005] The technical scheme of the present application is: a method for synthesizing ultrafine flaky alpha-Al2O3 powder at low temperature, characterized by comprising the following steps: Step one: polish the surface of the elemental metal aluminum with sandpaper to remove the dense aluminum oxide film on the surface, and then cut the elemental metal aluminum into aluminum flakes; Step two: slowly add the aluminum flakes treated in step one into an inorganic acid, fully stir to prepare an aluminum salt solution, and then add ammonia water to adjust the pH of the aluminum salt to 7; Step three: add ammonium sulfate, urea and fused salt into the aluminum salt solution prepared in step two, fully mix to configure a mixed solution; Step four: put the mixed solution prepared in step three into a reaction kettle, and perform hydrothermal reaction at a certain temperature to obtain a precipitate, which is dried to obtain an aluminum oxide precursor; Step five: calcine the aluminum oxide precursor prepared in step four to obtain an alpha-Al2O3 powder mixture; Step six: clean the alpha-Al2O3 powder mixture prepared in step five with anhydrous ethanol and deionized water for at least 3 times, and dry to obtain ultrafine flaky alpha-Al2O3 powder.

[0006] The concentration of the aluminum salt in step two is 0.01-0.5 mol / L.

[0007] The inorganic acid in step two is one of dilute hydrochloric acid, dilute nitric acid and dilute sulfuric acid, and the molar ratio of the amount to the elemental aluminum is 3:1.

[0008] The molar ratio of urea to aluminum ions in step three is 5:1, the molar ratio of the aluminum salt to ammonium sulfate is 2.5:1, and the molar ratio of the aluminum salt to the fused salt is 1:2.

[0009] The fused salt in step three is any one of NaCl and KCl or a mixture of the two; the fused salt is any one of sodium bromide and potassium bromide or a mixture of the two; the fused salt is LiCl.

[0010] 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.

[0011] The temperature of the hydrothermal reaction in step four is 80-120℃, and the time is 3-10h.

[0012] The calcination temperature in step five is 560-800℃, and the holding time is 2-8h.

[0013] The particle size of the ultrafine flaky alpha-Al2O3 powder obtained in step six is 100-500nm.

[0014] The present application has the following beneficial effects: The principle of low-temperature synthesis of alpha-Al2O3 of the present application is: through hydrothermal method, SO4 2- Prevent the polynuclear complex ([Al x (H2O) y ] m+ ) polymerization to form aluminum hydroxide agglomeration, promote the conversion of aluminum hydroxide to spherical Al4(OH) 10 SO4, while adding NaCl and KCl molten salt, under low temperature conditions, the molten salt is in a molten state, which maximizes the solubility, diffusivity and reactivity of the reactants, greatly improves the uniformity and reaction speed of the diffusion-controlled solid phase reaction, thereby greatly reduces the synthesis temperature of the product. Na⁺(ionic radius 0.102 nm) and K⁺(0.138 nm) in the molten salt are cooperatively adsorbed on the surface of alpha-Al2O3 with residual SO4²⁻: Na⁺ is preferentially adsorbed on 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, under the coupling effect of hydrothermal and molten salt, alpha-Al2O3 can be synthesized at a low temperature of 560℃, achieving controllable morphology and size. At the same time, the calcination process does not produce any harmful gas, which is green and environmentally friendly.

[0015] The present application synthesizes alpha-Al2O3 at 560-800℃ by using the hydrothermal + molten salt coupling method without adding any dispersant, template, seed crystal and additive, without airflow pulverization, directly synthesizing 100-500nm alpha-Al2O3 powder with uniform dispersion and high purity. The preparation method of the present application has low synthesis temperature, simple process, and the required materials are easy to obtain, so it has broad market application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 X-ray diffraction pattern of alpha-Al2O3 powder synthesized in Example 5; Figure 2 Scanning electron microscope image of alpha-Al2O3 powder synthesized in Example 3. DETAILED DESCRIPTION

[0017] The present application will be further described in detail below in combination with the drawings and specific embodiments. Example 1

[0018] Step one: polish the surface of metallic aluminum with sandpaper, remove the dense aluminum oxide film on the surface, then cut 0.27g of metallic aluminum into small aluminum flakes; Step two: slowly add the small aluminum flakes of step one into 200ml dilute hydrochloric acid, the molar ratio of dilute hydrochloric acid to aluminum single is 3:1, fully stir to prepare an aluminum salt solution, then cool to room temperature and add ammonia water to adjust the PH of the aluminum salt to 7; 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; 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. 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; 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.

[0019] The particle size of the ultrafine flake-like α-Al2O3 powder obtained in step six is ​​400-500 nm. Example 2

[0020] 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. 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. 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; 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. 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. 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.

[0021] The particle size of the ultrafine flake-like α-Al2O3 powder obtained in step six is ​​400-450 nm. Example 3

[0022] 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. 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. 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 obtained in Step 2 and mix thoroughly to prepare a mixed solution; 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. 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; 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.

[0023] The particle size of the ultrafine flake-like α-Al2O3 powder obtained in step six is ​​100–300 nm.

[0024] 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

[0025] 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. 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. 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; 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. 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. Step six: the α-Al2O3 powder mixture prepared in step five is washed with anhydrous ethanol and deionized water for at least three times, and then dried to obtain the ultrafine flaky α-Al2O3 powder.

[0026] The particle size of the ultrafine flaky α-Al2O3 powder obtained in step six is 300-400 nm. Example 5

[0027] Step one: the surface of the elemental metal aluminum is polished with sandpaper to remove the dense aluminum oxide film on the surface, and then 2.7 g of elemental metal aluminum is cut into fine aluminum flakes; Step two: the fine aluminum flakes in step one are slowly added into 200 ml of dilute nitric acid, the molar ratio of dilute nitric acid to elemental aluminum is 3:1, and the aluminum salt solution is prepared by fully stirring, and then ammonia water is added to adjust the PH of the aluminum salt to 7 after cooling to room temperature; Step three: 0.04 mol / L of ammonium sulfate, 0.5 mol / L of urea, 0.133 mol / L of KCl and 0.067 mol / L of NaCl (the molar ratio of KCl to NaCl is 2:1) are added to the aluminum salt solution prepared in step two and fully mixed to configure a mixed solution; Step four: the mixed solution prepared in step three is loaded into a reaction kettle, and a hydrothermal reaction is carried out at 80°C for 6h to obtain a precipitate, and then the precipitate is dried to obtain an aluminum oxide precursor; Step five: the aluminum oxide precursor prepared in step four is calcined at 560°C for 5h, and then cooled to obtain an α-Al2O3 powder mixture; Step six: the α-Al2O3 powder mixture prepared in step five is washed with anhydrous ethanol and deionized water for at least three times, and then dried to obtain the ultrafine flaky α-Al2O3 powder.

[0028] The particle size of the ultrafine flaky α-Al2O3 powder obtained in step six is 200-400 nm.

[0029] As Figure 1 shown in the XRD test of the aluminum oxide powder prepared in Example 5: the prepared sample is pure α-Al2O3, which is consistent with the standard card of PDF#08-5137. Example 6

[0030] Step one: the surface of the elemental metal aluminum is polished with sandpaper to remove the dense aluminum oxide film on the surface, and then 2.7 g of elemental metal aluminum is cut into fine aluminum flakes; Step two: the fine aluminum flakes in step one are slowly added into 200 ml of dilute nitric acid, the molar ratio of dilute nitric acid to elemental aluminum is 3:1, and the aluminum salt solution is prepared by fully stirring, and then ammonia water is added to adjust the PH of the aluminum salt to 7 after cooling to room temperature; Step three: 0.04 mol / L ammonium sulfate, 0.5 mol / L urea, 0.15 mol / L KCl and 0.05 mol / L NaCl (molar ratio of KCl and NaCl 3:1) were added into the aluminum salt solution prepared in step two and mixed thoroughly to form a mixed solution; Step four: the mixed solution prepared in step three was loaded into a reaction kettle and hydrothermal reaction was carried out at 80℃ for 6h to obtain a precipitate, and the precipitate was dried to obtain an alumina precursor; Step five: the alumina precursor prepared in step four was calcined at 560℃ for 5h, and after cooling, an α-Al2O3 powder mixture was obtained; Step six: the α-Al2O3 powder mixture prepared in step five was washed with anhydrous ethanol and deionized water for at least 3 times, and after drying, an ultra-fine flaky α-Al2O3 powder was obtained.

[0031] The particle size of the ultra-fine flaky α-Al2O3 powder obtained in step six is 200-300nm. Example 7

[0032] Step one: the surface of the elemental metal aluminum was polished with sandpaper to remove the dense aluminum oxide film on the surface, and 2.7g of elemental metal aluminum was cut into fine aluminum flakes; Step two: the fine aluminum flakes in step one were slowly added into 200ml of dilute nitric acid, the molar ratio of dilute nitric acid to aluminum single element was 3:1, and the aluminum salt solution was prepared by fully stirring, and after cooling to room temperature, ammonia water was added to adjust the PH of the aluminum salt to 7; Step three: 0.04 mol / L ammonium sulfate, 0.5 mol / L urea, 0.2 mol / L NaBr were added into the aluminum salt solution prepared in step two and mixed thoroughly to form a mixed solution; Step four: the mixed solution prepared in step three was loaded into a reaction kettle and hydrothermal reaction was carried out at 80℃ for 6h to obtain a precipitate, and the precipitate was dried to obtain an alumina precursor; Step five: the alumina precursor prepared in step four was calcined at 700℃ for 4h, and after cooling, an α-Al2O3 powder mixture was obtained; Step six: the α-Al2O3 powder mixture prepared in step five was washed with anhydrous ethanol and deionized water for at least 3 times, and after drying, an ultra-fine flaky α-Al2O3 powder was obtained.

[0033] The particle size of the ultra-fine flaky α-Al2O3 powder obtained in step six is 400-450nm. Example 8

[0034] Step one: the surface of the elemental metal aluminum was polished with sandpaper to remove the dense aluminum oxide film on the surface, and 2.7g of elemental metal aluminum was cut into fine aluminum flakes; Step two: slowly add the fine aluminum flake of step one into 200ml dilute nitric acid, the molar ratio of dilute nitric acid and aluminum is 3:1, fully stir to prepare aluminum salt solution, after cooling to room temperature, add ammonia water to adjust the PH of aluminum salt to 7; Step three: add 0.04mol / L ammonium sulfate, 0.5mol / L urea and 0.2mol / L KBr into the aluminum salt solution prepared in step two, fully mix to configure into mixed solution; Step four: put the mixed solution prepared in step three into reaction kettle, carry out hydrothermal reaction at 80℃ for 6h to obtain precipitate, dry the precipitate to obtain aluminum oxide precursor; Step five: calcine the aluminum oxide precursor prepared in step four at 700℃, keep warm for 4h, after cooling, obtain α-Al2O3 powder mixture; Step six: clean the α-Al2O3 powder mixture prepared in step five with anhydrous ethanol and deionized water for at least 3 times, after drying, obtain ultra-fine flaky α-Al2O3 powder.

[0035] The particle size of the ultra-fine flaky α-Al2O3 powder obtained in step six is 400-500nm. Example 9

[0036] Step one: polish the surface of aluminum metal with sandpaper, after removing the dense aluminum oxide film on the surface, cut 2.7g aluminum metal into fine aluminum flake; Step two: slowly add the fine aluminum flake of step one into 200ml dilute nitric acid, the molar ratio of dilute nitric acid and aluminum is 3:1, fully stir to prepare aluminum salt solution, after cooling to room temperature, add ammonia water to adjust the PH of aluminum salt to 7; Step three: add 0.04mol / L ammonium sulfate, 0.5mol / L urea, 0.1mol / L KBr and 0.1mol / L NaBr (the molar ratio of KBr and NaBr is 1:1) into the aluminum salt solution prepared in step two, fully mix to configure into mixed solution; Step four: put the mixed solution prepared in step three into reaction kettle, carry out hydrothermal reaction at 80℃ for 6h to obtain precipitate, dry the precipitate to obtain aluminum oxide precursor; Step five: calcine the aluminum oxide precursor prepared in step four at 600℃, keep warm for 4h, after cooling, obtain α-Al2O3 powder mixture; Step six: clean the α-Al2O3 powder mixture prepared in step five with anhydrous ethanol and deionized water for at least 3 times, after drying, obtain ultra-fine flaky α-Al2O3 powder.

[0037] The particle size of the ultra-fine flaky α-Al2O3 powder obtained in step six is 300-400nm. Example 10

[0038] Step one: the surface of the elemental aluminum is polished with sandpaper to remove the thin film of dense aluminum oxide on the surface, and then 2.7 g of elemental aluminum is cut into fine aluminum flakes; Step two: the fine aluminum flakes of step one are slowly added to 200 ml of dilute nitric acid, the molar ratio of dilute nitric acid to elemental aluminum is 3:1, and the aluminum salt solution is prepared after fully stirring. After cooling to room temperature, ammonia water is added to adjust the PH of the aluminum salt to 7; Step three: 0.04 mol / L ammonium sulfate, 0.5 mol / L urea, 0.133 mol / L KBr and 0.067 mol / L NaBr (molar ratio of KBr and NaBr 2:1) are added to the aluminum salt solution prepared in step two and fully mixed to configure a mixed solution; Step four: the mixed solution prepared in step three is loaded into a reaction kettle, and a hydrothermal reaction is carried out at 80℃ for 6h to obtain a precipitate, and the precipitate is dried to obtain an alumina precursor; Step five: the alumina precursor prepared in step four is calcined at 600℃, and after cooling for 4h, an α-Al2O3 powder mixture is obtained; Step six: the α-Al2O3 powder mixture prepared in step five is washed with anhydrous ethanol and deionized water at least three times, and after drying, an ultra-fine flaky α-Al2O3 powder is obtained.

[0039] The particle size of the ultra-fine flaky α-Al2O3 powder obtained in step six is 200-400 nm. Example 11

[0040] Step one: the surface of the elemental aluminum is polished with sandpaper to remove the thin film of dense aluminum oxide on the surface, and then 2.7 g of elemental aluminum is cut into fine aluminum flakes; Step two: the fine aluminum flakes of step one are slowly added to 200 ml of dilute nitric acid, the molar ratio of dilute nitric acid to elemental aluminum is 3:1, and the aluminum salt solution is prepared after fully stirring. After cooling to room temperature, ammonia water is added to adjust the PH of the aluminum salt to 7; Step three: 0.04 mol / L ammonium sulfate, 0.5 mol / L urea, 0.133 mol / L KBr and 0.067 mol / L NaBr (molar ratio of KBr and NaBr 2:1) are added to the aluminum salt solution prepared in step two and fully mixed to configure a mixed solution; Step four: the mixed solution prepared in step three is loaded into a reaction kettle, and a hydrothermal reaction is carried out at 80℃ for 6h to obtain a precipitate, and the precipitate is dried to obtain an alumina precursor; Step five: the alumina precursor prepared in step four is calcined at 600℃, and after cooling for 4h, an α-Al2O3 powder mixture is obtained; Step six: the α-Al2O3 powder mixture prepared in step five is washed with anhydrous ethanol and deionized water for at least three times, and then dried to obtain the ultrafine flaky α-Al2O3 powder.

[0041] The particle size of the ultrafine flaky α-Al2O3 powder obtained in step six is 200-300 nm.

[0042] Comparative Example 1 With reference to Example 5 of the present application, the only difference between Example 5 and Comparative Example 1 is that no NaCl and KCl molten salt is added in step three.

[0043] Comparative Example 2 With reference to Example 5 of the present application, the only difference between Example 5 and Comparative Example 2 is that no reaction kettle is used in step four, but the reaction is directly heated.

[0044] The data related to the synthesis of α-Al2O3 in Example 5 and Comparative Examples 1-2 are shown in Table 1.

[0045] Table 1

[0046] As shown in Table 1, in Example 5 of the present application, no NaCl and KCl molten salt is added, and other conditions are unchanged, and only spherical γ-Al2O3 can be synthesized at 560℃, or no reaction kettle is used, and other conditions are unchanged, and only 1-2 μm flaky γ-Al2O3 can be synthesized at 560℃, so the coupling effect of hydrothermal and molten salt is invalid, thereby increasing the synthesis temperature of α-Al2O3.

[0047] The above examples only exemplarily illustrate the principles and effects of the present application, and part of the applied examples, and are not used to limit the present application; it should be noted that, for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application.

Claims

1. A method for low-temperature synthesis of ultrafine flake-like α-Al₂O₃ powder, characterized in that... Includes the following steps: Step 1: Sand the surface of the aluminum metal with sandpaper to remove the dense aluminum oxide film on the surface, and then cut the aluminum metal into aluminum sheets. 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. 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; 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. Step 5: The alumina precursor obtained in Step 4 is calcined to obtain an α-Al2O3 powder mixture; 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.

2. The method according to claim 1, characterized in that: In step two, the aluminum salt concentration is 0.01–0.5 mol / L.

3. The method according to claim 1, characterized in that: 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.

4. The method according to claim 1, characterized in that: 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.

5. The method according to claim 1, characterized in that: 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.

6. The method according to claim 5, characterized in that: 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.

7. The method according to claim 1, characterized in that: The hydrothermal reaction in step four is carried out at a temperature of 80–120°C for 3–10 hours.

8. The method according to claim 1, characterized in that: In step five, the calcination temperature is 560–800℃, and the holding time is 2–8 hours.

9. The method according to claim 1, characterized in that: The particle size of the ultrafine flake-like α-Al2O3 powder obtained in step six is ​​100–500 nm.

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