A low-temperature preparation method for flaky interlocking hexagonal α-Al2O3 powder

Abstract

The present invention discloses a low-temperature preparation method of a flaky interlocking regular hexagonal α-Al2O3 powder, which is characterized in that it comprises the following steps: Step 1: Aluminum sec-butoxide or aluminum isopropoxide is mixed and stirred with n-butanol, and then a mineralizer is added to stir it and configure it to form A solution; Step 2: Deionized water, acetonitrile and n-butanol are mixed and configured to form B solution; Step 3: Solution B is slowly added dropwise to the A solution obtained in step 1 to obtain a milky white flocculent substance, and then filtered, dried, ground and sieved to obtain a precursor powder; Step 4: The precursor powder is calcined to prepare α-Al2O3 powder with a flaky interlocking regular hexagonal morphology. The present invention solves the problems of difficult preparation, complex process and high energy consumption of flaky alumina. The present invention is simple to operate, is conducive to large-scale production, and the prepared product can be applied to the fields of low-temperature sintering ceramics, pigments, cosmetics, automotive topcoats, toughened ceramics, etc.

Description

Technical Field

[0001] The invention relates to the technical field of inorganic powder synthesis, and in particular to a low-temperature preparation method of flaky interlocking regular hexagonal α-Al2O3 powder. Background Art

[0002] Alumina, due to its physical and chemical properties, has a wide range of applications in electronics, ceramics, catalysts, and other fields. However, the phase transition temperature for transitional alumina to form α-Al2O3 crystals is above 1200°C. At this point, solid-phase mass transfer is the primary mechanism of production. While traditional high-temperature sintering methods can produce alumina, they suffer from high energy consumption and high costs. With increasing demands for environmental protection and energy efficiency, the development of low-temperature, low-cost alumina production technologies has become increasingly important.

[0003] Flake alumina possesses excellent comprehensive properties, including a high melting point, high hardness, high mechanical strength, excellent wear resistance, chemical resistance, oxidation resistance, and heat resistance. Flake alumina is micron-sized and nanometer-thick, with a high aspect ratio, combining the properties of both nanometers and micrometers. Its moderate surface activity allows it to effectively bind to other active groups while resisting aggregation, facilitating efficient dispersion. It is suitable for applications in pigments, cosmetics, automotive topcoats, coatings, refractories, and toughened ceramics. Currently, flake alumina is prepared using methods such as gelation, molten salt, explosion, and hydrothermal methods.

[0004] For example, Chinese patent CN103013443B discloses an α-Al2O3-based abrasive containing a flaky structure and a method for preparing the same. The abrasive particles produced by this invention contain a flaky structure and have the characteristics of good self-sharpening properties and long durability. However, the sol-gel method used for preparation is relatively complex, environmentally unfriendly, and has high production costs. CN114958035A uses an aluminum salt aqueous solution to react with an alkaline solution to produce a colloid, which is then calcined at 550°C to produce γ-alumina, which is then mixed and ground with molten salt and finally calcined to produce flaky alumina. WO2008 / 026829 A1, US10647861 B2, US11479681B2, etc. use aluminum sulfate as the main aluminum source, react by adding a sodium carbonate aqueous solution, and simultaneously add a portion of a morphology modifier to produce a colloid. The solution is then dried and calcined to produce flaky alumina. This process is cumbersome to prepare the precursors, has a long process, and results in high energy consumption and significant losses. Chinese patent CN104724743A discloses a method for preparing flaky nano-α-Al2O3, which comprises mixing aluminum hydroxide and cyclotrimethylene trinitramine uniformly, placing the mixture in a spherical explosion container, detonating the mixture with an electric detonator, and collecting the powdered product after the detonation to obtain flaky nano-α-Al2O3. Although this method is simple and economical, the risk of detonation by the detonator is too high, and the resulting flaky structure is uneven, resulting in a low flaky yield. Chinese patent CN103241753B discloses a method for preparing α-Al2O3, which comprises using ammonium nitrate or ammonium chloride as a mineralizer, mixing the mixture with a hydrated alumina raw material, and then calcining and cooling the mixture to obtain an α-Al2O3 with a uniform particle size distribution and a large specific surface area. The alumina formed by this method easily agglomerates, and a product with fine particles, a light degree of agglomeration, and good dispersibility cannot be obtained. Therefore, it is necessary to develop a method that is simple in process and low in cost while ensuring that the morphology of flaky alumina is controllable, so as to compensate for the high cost and energy consumption that limit the utilization of flaky alumina. Summary of the Invention

[0005] In order to overcome the problems of the prior art, the present invention provides a low-cost, simple process, and low-temperature preparation method for flaky interlocking regular hexagonal α-Al2O3 powder suitable for large-scale production.

[0006] The technical solution of the present invention is: a low-temperature preparation method of flaky interlocking regular hexagonal α-Al2O3 powder, characterized by comprising the following steps:

[0007] Step 1: Mix aluminum sec-butoxide or aluminum isopropoxide and n-butanol and stir them evenly, then add a mineralizer and stir them evenly to prepare solution A;

[0008] Step 2: Mix deionized water, acetonitrile and n-butanol to prepare solution B;

[0009] Step 3: Slowly add the solution B prepared in step 2 to the solution A prepared in step 1 to obtain a milky white flocculent, which is then filtered, dried, ground, and sieved to obtain a precursor powder;

[0010] Step 4: calcining the precursor powder prepared in step 3 to prepare α-Al2O3 powder with a flaky interlocking regular hexagonal morphology;

[0011] The mineralizer in step 1 is one of aluminum fluoride, potassium fluoride and sodium fluoride;

[0012] In the step 1, the molar ratio of aluminum sec-butoxide or aluminum isopropoxide, the mineralizer, and n-butanol is 1:0.1-0.6:0.25-0.75;

[0013] The molar ratio of deionized water, acetonitrile, and n-butanol in step 2 to aluminum sec-butoxide or aluminum isopropoxide in step 1 is 2-4:3-5:0.25-1.25:1;

[0014] The calcination temperature in the step 4 is 950-1200° C., the holding time is 0.5-1.5 h, and the heating rate is 3-5° C. / min.

[0015] The drying process in step 3 is to keep the temperature in an oven at 80-100° C. for 6-12 hours.

[0016] The grinding process in step 3 is to grind the dried product in a mortar.

[0017] The screening process in step 3 is to pass through a 200-325 sieve.

[0018] The α-Al2O3 powder with interlocking regular hexagonal morphology in step 4 has a thickness of 100 to 300 nm and a diameter of 1 to 3 μm, and has an interlocking micro-nano structure formed by assembling regular hexagonal structures.

[0019] To ensure the uniformity and controllability of the morphology, the present invention uses acetonitrile and n-butanol to control the hydrolysis and condensation rates of aluminum sec-butoxide, uses water, highly polar n-butanol and acetonitrile organic solvents to form a soft template as a protective layer, selects fluoride as a mineralizer, and utilizes F element oxidation adsorption on the (0001) basal plane to reduce the surface energy of the (0001) crystal plane. The driving force required to generate a new (0001) plane of the same area is smaller than that of the (1010) plane. Therefore, the growth of α-Al2O3 crystals becomes anisotropic, resulting in a significantly faster expansion rate of the (0001) crystal plane. As a result, the alumina particles tend to form a regular lamellar structure, and an α-Al2O3 powder with interlocking lamellar hexagonal morphology is prepared.

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

[0021] The present invention is simple to operate and is conducive to large-scale production. It not only reduces the conversion of the transition phase Al2O3 to α-Al2O3, but also produces an impurity-free, regular-shaped α-Al2O3 powder with a hexagonal structure free of impurities and an interlocking hexagonal structure. The structure achieves nanometer-scale thickness and micrometer-scale radially, achieving both nanometer and micrometer performance. This solves the problems of difficult, complex, and energy-intensive preparation of flaky alumina. The product produced by the present invention can be applied to low-temperature sintered alumina ceramics, pigments, cosmetics, automotive topcoats, toughened ceramics, and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a SEM morphology image of the particles prepared in Example 1 of the present invention;

[0023] Figure 2 This is a TEM morphology image of the particles prepared in Example 1 of the present invention;

[0024] Figure 3 This is a particle size distribution diagram of particles prepared in Example 1 of the present invention;

[0025] Figure 4 This is the XRD pattern of the sample prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] Example 1

[0028] Step 1: dissolving aluminum sec-butoxide in n-butanol and stirring to mix evenly, then adding aluminum fluoride as a mineralizer and stirring to mix evenly to obtain solution A, wherein the molar ratio of aluminum sec-butoxide: aluminum fluoride: n-butanol is 1:0.1:0.75.

[0029] Step 2: Mix deionized water, n-butanol, and acetonitrile and stir them uniformly to obtain solution B. The molar ratio of deionized water, acetonitrile, n-butanol, and aluminum sec-butoxide in step 1 is 2:3:0.25:1.

[0030] Step 3: After completing the configurations in steps 1 and 2 above, obtain solutions A and B respectively. Slowly add solution B dropwise to solution A and stir evenly to obtain a milky white flocculent.

[0031] Step 4: The milky white flocs obtained in step 3 are filtered, dried, ground, and sieved to obtain a precursor powder. The drying conditions are: keeping the temperature in an 80°C oven for 6 hours, and grinding the powder until it passes a 200-mesh sieve.

[0032] Step 5: calcining the precursor powder obtained in step 4 at 1150° C. with a holding time of 0.5 h and a heating rate of 5° C. / min to prepare α-Al 2 O 3 powder.

[0033] Example 2

[0034] Step 1: dissolving aluminum sec-butoxide in n-butanol and stirring to mix evenly, then adding sodium fluoride as a mineralizer and stirring to mix evenly to obtain solution A. The molar ratio of aluminum sec-butoxide: sodium fluoride: n-butanol is 1:0.2:0.5.

[0035] Step 2: Mix deionized water, n-butanol, and acetonitrile and stir them uniformly to obtain solution B. The molar ratio of deionized water, acetonitrile, n-butanol, and aluminum sec-butoxide in step 1 is 4:4:0.5:1.

[0036] Step 3: After completing the configurations in steps 1 and 2 above, obtain solutions A and B respectively. Slowly add solution B dropwise to solution A and stir evenly to obtain a milky white flocculent.

[0037] Step 4: The milky white flocs obtained in step 3 are filtered, dried, ground, and sieved to obtain a precursor powder. The drying conditions are: keeping the temperature in a 90°C oven for 10 hours, and grinding the powder until it passes a 250-mesh sieve.

[0038] Step 5: calcining the precursor powder obtained in step 4 at 950° C. for 1.5 h at a heating rate of 3° C. / min to prepare α-Al 2 O 3 powder.

[0039] Example 3

[0040] Step 1: dissolving aluminum sec-butoxide in n-butanol and stirring to mix evenly, then adding potassium fluoride as a mineralizer and stirring to mix evenly to obtain solution A. The molar ratio of aluminum sec-butoxide: potassium fluoride: n-butanol is 1:0.5:0.3.

[0041] Step 2: Mix deionized water, n-butanol and acetonitrile and stir them uniformly to obtain solution B. The molar ratio of deionized water, acetonitrile, n-butanol and aluminum sec-butoxide in step 1 is 4:5:1:1.

[0042] Step 3: After completing the configurations in steps 1 and 2 above, obtain solutions A and B respectively. Slowly add solution B dropwise to solution A and stir evenly to obtain a milky white flocculent.

[0043] Step 4: The milky white flocs obtained in step 3 are filtered, dried, ground, and sieved to obtain a precursor powder. The drying conditions are: keeping the temperature in an oven at 100°C for 6 hours, and grinding the powder until it passes a 325-mesh sieve.

[0044] Step 5: calcining the precursor powder obtained in step 4 at 1200° C. with a holding time of 0.5 h and a heating rate of 5° C. / min to prepare α-Al 2 O 3 powder.

[0045] Example 4

[0046] Step 1: dissolving aluminum isopropoxide in n-butanol and stirring to mix evenly, then adding aluminum fluoride and stirring evenly to obtain solution A. The molar ratio of aluminum isopropoxide:aluminum fluoride:n-butanol is 1:0.6:0.25.

[0047] Step 2: Mix deionized water, n-butanol, and acetonitrile and stir them uniformly to obtain solution B. The molar ratio of deionized water, acetonitrile, n-butanol, and aluminum isopropoxide in step 1 is 3:5:1.25:1.

[0048] Step 3: After completing the configurations in steps 1 and 2 above, obtain solutions A and B respectively. Slowly add solution B dropwise to solution A and stir evenly to obtain a milky white flocculent.

[0049] Step 4: The milky white flocs obtained in step 3 are filtered, dried, ground, and sieved to obtain a precursor powder. The drying conditions are: keeping the temperature in an 80°C oven for 12 hours, and grinding the powder until it passes a 250-mesh sieve.

[0050] Step 5: calcining the precursor powder obtained in step 4 at 950° C. with a holding time of 1 h and a heating rate of 4° C. / min to prepare α-Al 2 O 3 powder.

[0051] like Figure 1 As shown, the aluminum oxide particles produced in this embodiment of the present invention exhibit a DNA-like structure under a scanning electron microscope, consisting of interlocking hexagons with a thickness of approximately 100 to 300 nm and a radial size of approximately 1 to 3 μm. The individual hexagons can reach nanometer-scale thickness and micrometer-scale radial dimensions, achieving dual nano- and micrometer-scale properties.

[0052] like Figure 2 As shown, the aluminum oxide particles prepared in the embodiment of the present invention exhibit a hexagonal morphology of about 1 to 3 μm in radial direction under a projection electron microscope.

[0053] like Figure 3 As shown, the alumina powder prepared in the embodiment of the present invention has a wide particle size distribution range and a relatively uniform particle size distribution when tested by a laser particle size analyzer, with 3 μm accounting for the highest proportion.

[0054] like Figure 4 As shown, the alumina powder prepared in the embodiment of the present invention is tested in XRD: the prepared sample is pure α-Al2O3 in crystal form at 950°C, which is consistent with the standard card (PDF#89-7716), indicating that pure α-Al2O3 can be obtained in a wider temperature range.

[0055] The above embodiments are merely illustrative of the principles and effects of the present invention, as well as some embodiments of its application, and are not intended to limit the present invention. It should be noted that a person skilled in the art can make several modifications and improvements without departing from the inventive concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A low-temperature preparation method for interlocking hexagonal α-Al2O3 powder, characterized in that The following steps are involved: Step 1: Mix aluminum sec-butoxide or aluminum isopropoxide and n-butanol and stir them evenly, then add a mineralizer and stir them evenly to prepare solution A; Step 2: Mix deionized water, acetonitrile and n-butanol to prepare solution B; Step 3: Slowly add the solution B prepared in step 2 to the solution A prepared in step 1 to obtain a milky white flocculent, which is then filtered, dried, ground, and sieved to obtain a precursor powder; Step 4: calcining the precursor powder prepared in step 3 to prepare α-Al2O3 powder with a flaky interlocking regular hexagonal morphology; The mineralizer in step 1 is one of aluminum fluoride, potassium fluoride and sodium fluoride; In the step 1, the molar ratio of aluminum sec-butoxide or aluminum isopropoxide, the mineralizer, and n-butanol is 1:0.1-0.6:0.25-0.75; The molar ratio of deionized water, acetonitrile, and n-butanol in step 2 to aluminum sec-butoxide or aluminum isopropoxide in step 1 is 2-4:3-5:0.25-1.25:1; The calcination temperature in step 4 is 950-1200°C, the holding time is 0.5-1.5h, and the heating rate is 3-5°C / min; The α-Al2O3 powder of the fourth step has a thickness of 100 to 300 nm and a diameter of 1 to 3 μm, and has a flaky interlocking micro-nanostructure formed by assembling regular hexagonal structures; The drying process in step 3 is to keep the temperature in an oven at 80-100°C for 6-12 hours; The grinding process in step 3 is to grind the dried product in a mortar; The screening process in step 3 is to pass through a 200-325 mesh sieve.

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