A method for preparing spherical α-Al2O3 nanoparticles

Abstract

The present invention provides a method for preparing spherical α-Al2O3 nanoparticles, comprising the following steps: adding malic acid to an alcohol aluminum compound in a polar organic solvent, and drying to obtain an anhydrous aluminum gel; wherein the molar ratio of [AlO6] octahedron to [AlO4] tetrahedron in the anhydrous aluminum gel is 5.8-6:4-4.2; and calcining the anhydrous aluminum gel at 760-900°C to directly transform the γ-Al2O3 nanoparticles produced during the calcination into α-Al2O3 nanoparticles. The present invention aims to address the problem of abnormal grain growth that occurs during high-temperature calcination of α-Al2O3 nanoparticles by providing a method for preparing α-Al2O3 nanoparticles at low temperatures using an anhydrous sol-gel method, and to achieve effective regulation of grain morphology in the method.

Description

Technical Field

[0001] The present invention belongs to the technical field of ceramic material preparation, and particularly relates to a low-temperature preparation method for spherical α-Al2O3 nanoparticles. Background Art

[0002] Alumina has high mechanical strength, melting point and hardness, as well as good chemical stability and corrosion resistance. Under certain conditions, it also has good optical properties and electrical conductivity. Therefore, it is widely used in aerospace, electronic devices, precision instruments, medicine and other fields. The most common crystal forms of Al2O3 are α, β and γ. α-Al2O3 is the most stable crystal form in nature. α-Al2O3 is commonly known as corundum and belongs to the trigonal crystal system. The oxygen atoms are approximately hexagonally packed, and the Al atoms are distributed in the O 2- The octahedral coordination center surrounded by ions occupies 2 / 3 of the octahedral voids. It is the crystal form with the tightest crystal structure, highest stability, low chemical activity and best electrochemical properties. Other isomeric crystal forms can be converted into α-Al2O3, but the transformation of unstable Al2O3 to α-Al2O3 usually requires passing through multiple intermediate phases, resulting in a higher activation energy. It is usually necessary to achieve the transformation of unstable Al2O3 to α-Al2O3 under high temperature and high pressure.

[0003] Spherical precursor nanoparticles are typically first prepared by liquid-phase methods (e.g., homogeneous precipitation, hydrothermal, microemulsion, and spray pyrolysis), followed by high-temperature calcination to obtain spherical α-Al2O3 nanoparticles. However, due to the high activation energy barrier and the sporadic nature of nucleation, the formation of α-Al2O3 typically requires high-temperature calcination of at least 1200°C. High-temperature calcination tends to sinter and melt spherical alumina particles that are in contact with each other, forming a worm-like microstructure, which eliminates the advantages of the spherical morphology. Therefore, for spherical α-Al2O3 nanoparticles, how to reduce the generation of intermediate phases, thereby lowering the calcination temperature and shortening the holding time, is not only energy-efficient but also crucial for maintaining its spherical morphology. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem that α-Al2O3 nanoparticles are prone to abnormal grain growth when calcined at high temperature, and to provide a method for preparing α-Al2O3 nanoparticles at low temperature by a water-free sol-gel, and to achieve effective control of the grain morphology in this method.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for preparing spherical α-Al2O3 nanoparticles comprises the following steps:

[0007] Adding malic acid to an alcohol aluminum compound in a polar organic solvent and drying the mixture to obtain an anhydrous aluminum gel; wherein the molar ratio of [AlO6] octahedron to [AlO4] tetrahedron in the anhydrous aluminum gel is 5.8-6:4-4.2;

[0008] The anhydrous aluminum gel is calcined at 760-900° C., so that the γ-Al 2 O 3 nanoparticles generated during the calcination process are directly transformed into α-Al 2 O 3 nanoparticles.

[0009] The polar organic solvent includes N,N-dimethylformamide and N,N-dimethylacetamide.

[0010] The aluminum alkoxide compound includes aluminum isopropoxide.

[0011] The method for preparing spherical α-Al2O3 nanoparticles further comprises a step of condensation and reflux.

[0012] The preparation method of the spherical α-Al2O3 nanoparticles comprises the steps of adding malic acid and a stabilizer to an alcohol aluminum compound in a polar organic solvent, and drying to obtain an anhydrous aluminum gel.

[0013] The stabilizer includes glacial acetic acid.

[0014] The heating rate of the calcination is 2-10° C. / min and the holding time of the calcination is 2-30 hours.

[0015] The molar weight ratio of the aluminum alcohol compound, malic acid and polar organic solvent is 1-5:1-30:15-25.

[0016] The molar ratio of the aluminum alcohol compound, malic acid, stabilizer and polar organic solvent is 1-5:1-30:1-5:15-25.

[0017] The average particle size of the spherical α-Al2O3 nanoparticles is 40-100 nm.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The invention provides a preparation method of spherical α-Al2O3 nanoparticles, which can prepare spherical α-Al2O3 nanoparticles through a single phase change at low temperature, thereby preventing the abnormal growth of aluminum oxide nanoparticles. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1a The SEM image of the spherical α-Al2O3 nanoparticles prepared in Example 1 is shown; Figure 1a The magnification is 10,000 times;

[0021] Figure 1bThe SEM image of the spherical α-Al2O3 nanoparticles prepared in Example 1 is shown; Figure 1b The magnification is 30,000 times;

[0022] Figure 2 shows the XRD patterns of α-Al2O3 nanoparticles prepared in Examples 1-4;

[0023] Figure 3a The SEM image of the spherical α-Al2O3 nanoparticles prepared in Example 5 is shown; Figure 3a The magnification is 10,000 times;

[0024] Figure 3b The SEM image of the spherical α-Al2O3 nanoparticles prepared in Example 5 is shown; Figure 3b The magnification is 30,000 times;

[0025] Figure 4 The Al2O3 gels obtained in Example 1 and Comparative Examples 1-2 are shown. 2p XPS spectra;

[0026] Figure 5 The XRD patterns of spherical α-Al2O3 nanoparticles prepared in Example 1 and Comparative Examples 1-2 are shown;

[0027] Figure 6 shows the XRD patterns of α-Al2O3 nanoparticles prepared in Examples 6-11;

[0028] Figure 7 Shown Figure 6 Enlarged view of part A in the middle. DETAILED DESCRIPTION

[0029] It is well known that various intermediate phases are produced during the preparation of α-Al2O3 nanoparticles. For example, when preparing α-Al2O3 nanoparticles using hexagonal boehmite, κ′-Al2O3 and κ-Al2O3 phases are produced, while when preparing α-Al2O3 nanoparticles using γ-boehmite, δ-Al2O3 and θ-Al2O3 phases are produced. These phase transitions can lead to abnormal particle growth. To reduce phase transitions and prevent abnormal particle growth, the present invention provides a method for preparing spherical α-Al2O3 nanoparticles. Specifically, the method comprises the following steps: adding malic acid to an aluminum alkoxide compound in a polar organic solvent, and drying to obtain an anhydrous aluminum gel; the anhydrous aluminum gel has a molar ratio of [AlO6] octahedron to [AlO4] tetrahedron of 5.8-6:4-4.2; and calcining the anhydrous aluminum gel at 760-900°C, causing the γ-Al2O3 nanoparticles produced during the calcination process to directly transform into α-Al2O3 nanoparticles. In the preparation method of α-Al2O3 nanoparticles provided by the present invention, the anhydrous sol prepared by mixing an alcohol aluminum compound with malic acid is a transparent sol, which achieves a full chelation bond between the acid and the aluminum source. Using malic acid as a chelating agent to chelate aluminum ions will produce more [AlO6] octahedrons. Because in the lattice of γ-Al2O3, Al 3+ Fill in O 2- In the stacked tetrahedral and octahedral voids. In the a-Al2O3 lattice, O 2- For hexagonal close packing, Al 3+ Symmetrically distributed around the octahedral coordination centers formed by oxygen ions, the entire crystal can be viewed as a large "molecule" composed of countless octahedral [AlO6] atoms bonded together in a coplanar manner. Therefore, the phase transition from γ-Al2O3 to α-Al2O3 involves a shift in the oxygen sublattice from cubic close-packed to hexagonal close-packed, achieved by shearing along a specific direction of the oxygen close-packed planes sandwiching the Al ions occupying the tetrahedral interstices. Consequently, a higher proportion of [AlO6] octahedral structures reduces the shearing of these oxygen close-packed planes, thereby lowering the activation energy required for the phase transition and facilitating the low-temperature synthesis of α-Al2O3. Therefore, a higher proportion of [AlO6] octahedral structures indicates a lower activation energy required for the phase transition. The use of malic acid as a chelating agent avoids the reactions of various intermediate phases, achieving complete conversion to α-Al2O3 through a single transformation of γ-Al2O3 at temperatures between 500°C and 900°C. This effectively lowers the calcination temperature, maintaining excellent particle morphology while also saving energy.

[0030] Preferably, the polar organic solvent is N,N-dimethylformamide or N,N-dimethylacetamide, which are more polar than malic acid. Of course, other polar organic solvents that can dissolve malic acid can also be used to implement the present invention.

[0031] Preferably, the aluminum alcoholate compound can be aluminum isopropoxide. Of course, other aluminum alcoholate compounds, such as aluminum pentaerythritol, etc. can also realize the present invention.

[0032] Preferably, the method for preparing the spherical α-Al2O3 nanoparticles further comprises a condensation reflux step. Since the reaction of aluminum alcoholate and malic acid is an exothermic reaction, condensation reflux can save solvent.

[0033] Preferably, the method for preparing the spherical α-Al2O3 nanoparticles comprises the steps of adding malic acid and a stabilizer to an aluminum alcohol compound in a polar organic solvent, followed by drying to obtain an anhydrous aluminum gel. The addition of the stabilizer can improve the stability of [AlO6], thereby preventing its conversion to [AlO4].

[0034] Preferably, the stabilizer comprises glacial acetic acid.

[0035] Preferably, the calcination heating rate is 2-10°C / min. When the calcination temperature remains the same, changing the heating rate results in a shorter calcination time, weaker particle coarsening, and the particles maintain excellent morphology and have a smaller particle size. When the heating rate is increased, the total heat treatment time of the sample is reduced. Furthermore, the sample with a heating rate of 10°C / min exhibits better particle morphology and a smaller particle size, ultimately yielding α-Al2O3 nanoparticles with a particle size of 40-50 nm.

[0036] Preferably, the molar ratio of the aluminum alcohol compound, malic acid, and polar organic solvent is 1-5: 1-30: 15-25. Under this ratio, an anhydrous aluminum gel with a higher proportion of [AlO6] octahedrons can be obtained.

[0037] Preferably, the molar ratio of the aluminum alcohol compound, malic acid, stabilizer, and polar organic solvent is 1-5: 1-30: 1-5: 15-25. Under this ratio, an anhydrous aluminum gel with a higher proportion of [AlO6] octahedrons can be obtained.

[0038] The method provided by the invention can prepare spherical α-Al2O3 nanoparticles with an average particle size of 40-100 nm.

[0039] The present invention is further described below with reference to specific embodiments.

[0040] Example 1

[0041] 4.0848 g of aluminum isopropoxide was dissolved in 30 g of N,N-dimethylformamide, placed in a 60°C oil bath, refluxed, and stirred for 24 hours until the aluminum isopropoxide was fully dissolved. 8.0545 g of malic acid was then added as a chelating acid and stirred for 2 hours. Subsequently, 1.201 g of glacial acetic acid was added as a stabilizer and stirred for another 2 hours to obtain an anhydrous Al sol. This was then dried at 80°C to obtain an anhydrous Al gel. This was then calcined in a muffle furnace at a heating rate of 2°C / min to 900°C and held for 2 hours to obtain α-Al2O3 nanoparticles.

[0042] Figure 1a and Figure 1b The SEM image of the spherical α-Al2O3 prepared in Example 1 is shown. As can be seen from the figure, the particle size of the α-Al2O3 nanoparticles prepared in Example 1 is 40-100 nm.

[0043] Example 2

[0044] 4.0848g of aluminum isopropoxide was dissolved in 30g of N,N-dimethylformamide, placed in a 60°C oil bath, refluxed, and stirred for 24 hours until the aluminum isopropoxide was fully dissolved. 8.0545g of malic acid was then added as a chelating acid and stirred for 2 hours. 1.201g of glacial acetic acid was then added as a stabilizer and stirred again for 2 hours to obtain an anhydrous Al sol. An anhydrous Al gel was obtained by drying at 80°C. The sol was then calcined in a muffle furnace, heated to 875°C at a heating rate of 2°C / min, and held for 2 hours to obtain α-Al2O3 nanoparticles. The α-Al2O3 nanoparticles prepared in Example 2 had a particle size of 40-100nm.

[0045] Example 3

[0046] 4.0848g of aluminum isopropoxide was dissolved in 30g of N,N-dimethylformamide, placed in a 60°C oil bath, refluxed, and stirred for 24 hours until the aluminum isopropoxide was fully dissolved. 8.0545g of malic acid was then added as a chelating acid and stirred for 2 hours. 1.201g of glacial acetic acid was then added as a stabilizer and stirred again for 2 hours to obtain an anhydrous Al sol. An anhydrous Al gel was obtained by drying at 80°C. The sol was then calcined in a muffle furnace, heated to 850°C at a heating rate of 2°C / min, and held for 2 hours to obtain α-Al2O3 nanoparticles. The α-Al2O3 nanoparticles prepared in Example 3 had a particle size of 40-100nm.

[0047] Example 4

[0048] 4.0848g of aluminum isopropoxide was dissolved in 30g of N,N-dimethylformamide, placed in a 60°C oil bath, refluxed, and stirred for 24 hours until the aluminum isopropoxide was fully dissolved. 8.0545g of malic acid was then added as a chelating acid and stirred for 2 hours. 1.201g of glacial acetic acid was then added as a stabilizer and stirred again for 2 hours to obtain an anhydrous Al sol. An anhydrous Al gel was obtained by drying at 80°C. The sol was then calcined in a muffle furnace, heated to 825°C at a heating rate of 2°C / min, and held for 2 hours to obtain α-Al2O3 nanoparticles. The α-Al2O3 nanoparticles prepared in Example 4 had a particle size of 40-100nm.

[0049] Figure 2 The XRD patterns of the α-Al2O3 nanoparticles prepared in Examples 1-4 are shown. As can be seen from the figures, α-Al2O3 nanoparticles can be produced at temperatures above 825°C. Furthermore, when the heating rate and holding time remain the same, varying the calcination temperature reveals that as the temperature increases, the characteristic peak of γ-Al2O3 appears first. As the temperature rises, γ-Al2O3 gradually and directly transforms into α-Al2O3, until it is completely converted into α-Al2O3. No other phase transitions occur in between.

[0050] Comparative Example 1

[0051] 4.0848 g of aluminum isopropoxide was dissolved in 30 g of N,N-dimethylformamide, placed in a 60°C oil bath, refluxed, and stirred for 24 hours until the aluminum isopropoxide was fully dissolved. 11.5272 g of citric acid was then added as a chelating acid and stirred for 2 hours. Subsequently, 1.201 g of glacial acetic acid was added as a stabilizer and stirred for another 2 hours to obtain an anhydrous Al sol. This was then dried at 80°C to obtain an anhydrous Al gel. This was then calcined in a muffle furnace, heating to 900°C at a rate of 2°C / min and holding for 2 hours to obtain α-Al2O3 nanoparticles.

[0052] Comparative Example 2

[0053] 4.0848 g of aluminum isopropoxide was dissolved in 30 g of N,N-dimethylformamide, placed in a 60°C oil bath, refluxed, and stirred for 24 hours until the aluminum isopropoxide was fully dissolved. 5.4048 g of lactic acid was then added as a chelating acid and stirred for 2 hours. Subsequently, 1.201 g of glacial acetic acid was added as a stabilizer and stirred for another 2 hours to obtain an anhydrous Al sol. This was then dried at 80°C to obtain an anhydrous Al gel. This was then calcined in a muffle furnace, heating to 900°C at a rate of 2°C / min and holding for 2 hours to obtain α-Al2O3 nanoparticles.

[0054] Figure 4The XPS graphs of the anhydrous Al sols prepared in Comparative Examples 1-2 and Example 1 are shown. From the graph, it can be seen that the anhydrous Al sol prepared in Example 1 has the highest proportion of [AlO6] octahedron, which can reach 58%-60%.

[0055] Figure 5 The XRD patterns of the spherical α-Al2O3 prepared in Comparative Examples 1-2 and Example 1 are shown. From the figure, it can be seen that the Al2O3 prepared in Comparative Examples 1-2 still contains the γ-Al2O3 phase, while the Al2O3 prepared in Example 1 has been completely converted into α-Al2O3.

[0056] Example 5

[0057] 4.0848 g of aluminum isopropoxide was dissolved in 30 g of N,N-dimethylformamide, placed in a 60°C oil bath, refluxed, and stirred for 24 hours until the aluminum isopropoxide was fully dissolved. 8.0545 g of malic acid was then added as a chelating acid and stirred for 2 hours. Subsequently, 1.201 g of glacial acetic acid was added as a stabilizer and stirred for another 2 hours to obtain an anhydrous aluminum sol. This was then dried at 80°C to obtain an anhydrous aluminum gel. This was then calcined in a muffle furnace at a heating rate of 10°C / min to 900°C and held for 2 hours to obtain α-Al2O3 nanoparticles. Figure 3a and Figure 3b The SEM image of the spherical α-Al2O3 prepared in Example 5 is shown; it can be seen from the figure that the particle size of the α-Al2O3 nanoparticles prepared in Example 5 is 40-60nm.

[0058] From Example 1 and Example 5, it can be seen that when the calcination temperature is the same, when the heating rate is changed, the shorter the calcination time, the weaker the particle coarsening phenomenon, the particles maintain excellent particle morphology, and the particle size is smaller. Figure 3a and Figure 3b The results show that when the heating rate is accelerated, the total heat treatment time of the sample is reduced. Therefore, the particle morphology of the sample with a heating rate of 10℃ / min is better, and its particle size is smaller and more uniform.

[0059] Example 6

[0060] 4.0848g of aluminum isopropoxide was dissolved in 30g of N,N-dimethylformamide, placed in a 60°C oil bath, refluxed, and stirred for 24 hours until the aluminum isopropoxide was fully dissolved. 8.0545g of malic acid was then added as a chelating acid and stirred for 2 hours. 1.201g of glacial acetic acid was then added as a stabilizer and stirred again for 2 hours to obtain an anhydrous Al sol. An anhydrous Al gel was obtained by drying at 80°C. The sol was then calcined in a muffle furnace, heated to 760°C at a heating rate of 10°C / min, and held at that temperature for 30 hours to obtain α-Al2O3 nanoparticles. The α-Al2O3 nanoparticles prepared in Example 3 had a particle size of 40-100nm.

[0061] Example 7

[0062] 4.0848g of aluminum isopropoxide was dissolved in 30g of N,N-dimethylformamide, placed in a 60°C oil bath, refluxed, and stirred for 24 hours until the aluminum isopropoxide was fully dissolved. 8.0545g of malic acid was then added as a chelating acid and stirred for 2 hours. 1.201g of glacial acetic acid was then added as a stabilizer and stirred again for 2 hours to obtain an anhydrous Al sol. An anhydrous Al gel was obtained by drying at 80°C. The sol was then calcined in a muffle furnace, heated to 780°C at a heating rate of 10°C / min, and held at that temperature for 30 hours to obtain α-Al2O3 nanoparticles. The α-Al2O3 nanoparticles prepared in Example 3 had a particle size of 40-100nm.

[0063] Example 8

[0064] 4.0848g of aluminum isopropoxide was dissolved in 30g of N,N-dimethylformamide, placed in a 60°C oil bath, refluxed, and stirred for 24 hours until the aluminum isopropoxide was fully dissolved. 8.0545g of malic acid was then added as a chelating acid and stirred for 2 hours. 1.201g of glacial acetic acid was then added as a stabilizer and stirred again for 2 hours to obtain an anhydrous Al sol. An anhydrous Al gel was obtained by drying at 80°C. The sol was then calcined in a muffle furnace, heated to 800°C at a heating rate of 10°C / min, and held at that temperature for 30 hours to obtain α-Al2O3 nanoparticles. The α-Al2O3 nanoparticles prepared in Example 3 had a particle size of 40-100nm.

[0065] Example 9

[0066] 4.0848g of aluminum isopropoxide was dissolved in 30g of N,N-dimethylformamide, placed in a 60°C oil bath, refluxed, and stirred for 24 hours until the aluminum isopropoxide was fully dissolved. 8.0545g of malic acid was then added as a chelating acid and stirred for 2 hours. 1.201g of glacial acetic acid was then added as a stabilizer and stirred again for 2 hours to obtain an anhydrous Al sol. An anhydrous Al gel was obtained by drying at 80°C. The sol was then calcined in a muffle furnace, heated to 810°C at a heating rate of 10°C / min, and held at that temperature for 30 hours to obtain α-Al2O3 nanoparticles. The α-Al2O3 nanoparticles prepared in Example 3 had a particle size of 40-100nm.

[0067] Example 10

[0068] 4.0848g of aluminum isopropoxide was dissolved in 30g of N,N-dimethylformamide, placed in a 60°C oil bath, refluxed, and stirred for 24 hours until the aluminum isopropoxide was fully dissolved. 8.0545g of malic acid was then added as a chelating acid and stirred for 2 hours. 1.201g of glacial acetic acid was then added as a stabilizer and stirred again for 2 hours to obtain an anhydrous Al sol. An anhydrous Al gel was obtained by drying at 80°C. The sol was then calcined in a muffle furnace, heated to 820°C at a heating rate of 10°C / min, and held at that temperature for 30 hours to obtain α-Al2O3 nanoparticles. The α-Al2O3 nanoparticles prepared in Example 3 had a particle size of 40-100nm.

[0069] Example 11

[0070] 4.0848g of aluminum isopropoxide was dissolved in 30g of N,N-dimethylformamide, placed in a 60°C oil bath, refluxed, and stirred for 24 hours until the aluminum isopropoxide was fully dissolved. 8.0545g of malic acid was then added as a chelating acid and stirred for 2 hours. 1.201g of glacial acetic acid was then added as a stabilizer and stirred again for 2 hours to obtain an anhydrous Al sol. An anhydrous Al gel was obtained by drying at 80°C. The sol was then calcined in a muffle furnace, heated to 825°C at a heating rate of 10°C / min, and held at that temperature for 30 hours to obtain α-Al2O3 nanoparticles. The α-Al2O3 nanoparticles prepared in Example 3 had a particle size of 40-100nm.

[0071] Figure 6 The XRD patterns of the α-Al2O3 nanoparticles prepared in Examples 6-11 are shown. Figure 7 Shown Figure 6 A magnified view of the middle part A. Figure 6 and Figure 7 It can be seen that at 760 °C, γ-Al2O3 nanoparticles can directly transform into α-Al2O3 nanoparticles without undergoing other phase transitions.

[0072] Example 12

[0073] 4.0848 g of aluminum isopropoxide was dissolved in 30 g of N,N-dimethylformamide, placed in a 60°C oil bath, refluxed, and stirred for 24 hours until the aluminum isopropoxide was fully dissolved. 8.0545 g of malic acid was then added as a chelating acid and stirred for 2 hours to obtain an anhydrous aluminum sol. This was then dried at 80°C to obtain an anhydrous aluminum gel. The sol was then calcined in a muffle furnace, heated to 900°C at a rate of 2°C / min, and held for 2 hours to obtain α-Al2O3 nanoparticles. The α-Al2O3 nanoparticles prepared in Example 12 had a particle size of 40-100 nm.

[0074] Example 13

[0075] 20.42g of aluminum isopropoxide was dissolved in 109.64g of N,N-dimethylformamide, placed in a 60°C oil bath, refluxed, and stirred for 24 hours until the aluminum isopropoxide was fully dissolved. 13.41g of malic acid was then added as a chelating acid and stirred for 2 hours to obtain an anhydrous Al sol. This was then dried at 80°C to obtain an anhydrous Al gel. The sol was then calcined in a muffle furnace, heated to 900°C at a rate of 2°C / min, and held for 2 hours to obtain α-Al2O3 nanoparticles. The α-Al2O3 nanoparticles prepared in Example 12 had a particle size of 40-100nm.

[0076] Example 14

[0077] 20.42g of aluminum isopropoxide was dissolved in 36.54g of N,N-dimethylformamide, placed in a 60°C oil bath, refluxed, and stirred for 24 hours until the aluminum isopropoxide was fully dissolved. 80.545g of malic acid was then added as a chelating acid and stirred for 2 hours to obtain an anhydrous Al sol. This was then dried at 80°C to obtain an anhydrous Al gel. The sol was then calcined in a muffle furnace, heated to 900°C at a rate of 2°C / min, and held for 2 hours to obtain α-Al2O3 nanoparticles. The α-Al2O3 nanoparticles prepared in Example 12 had a particle size of 40-100nm.

[0078] Example 15

[0079] 20.42g of aluminum isopropoxide was dissolved in 109.64g of N,N-dimethylformamide, placed in a 60°C oil bath, refluxed, and stirred for 24 hours until the aluminum isopropoxide was fully dissolved. 13.41g of malic acid was then added as a chelating acid and stirred for 2 hours. 6.05g of glacial acetic acid was then added as a stabilizer and stirred again for 2 hours to obtain an anhydrous Al sol. An anhydrous Al gel was obtained by drying at 80°C. The sol was then calcined in a muffle furnace, heated to 900°C at a heating rate of 2°C / min, and held for 2 hours to obtain α-Al2O3 nanoparticles. The α-Al2O3 nanoparticles prepared in Example 12 had a particle size of 40-100nm.

[0080] Example 16

[0081] 20.42g of aluminum isopropoxide was dissolved in 36.54g of N,N-dimethylformamide, placed in a 60°C oil bath, refluxed, and stirred for 24 hours until the aluminum isopropoxide was fully dissolved. 80.545g of malic acid was then added as a chelating acid and stirred for 2 hours. 6.05g of glacial acetic acid was then added as a stabilizer and stirred again for 2 hours to obtain an anhydrous Al sol. An anhydrous Al gel was obtained by drying at 80°C. The sol was then calcined in a muffle furnace, heated to 900°C at a heating rate of 2°C / min, and held for 2 hours to obtain α-Al2O3 nanoparticles. The α-Al2O3 nanoparticles prepared in Example 12 had a particle size of 40-100nm.

Claims

1. A method for preparing spherical α-Al2O3 nanoparticles, characterized in that: The steps include: An aluminum alkoxide compound is added with malic acid in a polar organic solvent, and dried to obtain an anhydrous aluminum gel; in the anhydrous aluminum gel, the molar ratio of [AlO6] octahedron to [AlO4] tetrahedron is 5.8-6:4-4.2; calcining the anhydrous aluminum gel at 760-900° C., so that the γ-Al2O3 nanoparticles generated during the calcination process directly transform into α-Al2O3 nanoparticles; The molar ratio of the aluminum alcohol compound, malic acid and polar organic solvent is 1-5:1-30:15-25; The polar organic solvent includes N,N-dimethylformamide and N,N-dimethylacetamide.

2. The method for preparing spherical α-Al2O3 nanoparticles according to claim 1, wherein: The aluminum alkoxide compound includes aluminum isopropoxide.

3. The method for preparing spherical α-Al2O3 nanoparticles according to claim 1, wherein: The method for preparing spherical α-Al2O3 nanoparticles further comprises a step of condensation and reflux.

4. The method for preparing spherical α-Al2O3 nanoparticles according to claim 1, wherein: The method comprises the steps of adding malic acid and a stabilizer to an alcohol aluminum compound in a polar organic solvent, and drying to obtain anhydrous aluminum gel.

5. The method for preparing spherical α-Al2O3 nanoparticles according to claim 4, characterized in that: The stabilizer includes glacial acetic acid.

6. The method for preparing spherical α-Al2O3 nanoparticles according to claim 1, wherein: The heating rate of the calcination is 2-10°C / min; The calcination holding time is 2-30 hours.

7. The method for preparing spherical α-Al2O3 nanoparticles according to claim 4, wherein: The molar ratio of the aluminum alcohol compound, malic acid, stabilizer and polar organic solvent is 1-5:1-30:1-5:15-25.

8. The method for preparing spherical α-Al2O3 nanoparticles according to claim 1, wherein: The average particle size of the spherical α-Al2O3 nanoparticles is 40-100 nm.

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