Method for preparing alpha-al2o3 material at low temperature with external electric field assistance

Abstract

This invention discloses a method for low-temperature preparation of α-Al₂O₃ materials assisted by an external electric field. The method utilizes an electric field to lower the phase transition barrier, achieving a complete transformation from amorphous or metastable phases to the α phase at temperatures between 500 and 900°C. The method includes two implementation methods: bulk material preparation and thin film / coating preparation. Conductive electrodes are placed at both ends of an Al₂O₃ green blank or an Al₂O₃ precursor thin film / coating deposited on a metal substrate. The material is then subjected to segmented heat treatment in a protective atmosphere. In the second stage of heat treatment, an electric field of 60–600 mV / mm² is applied, and the material is held at this temperature for 1–5 hours before cooling. This invention effectively suppresses abnormal grain growth, yielding dense, high-purity α-Al₂O₃ materials. High-quality coatings can be directly prepared on metal substrates such as aluminum alloys, copper alloys, and stainless steel. It has advantages such as simple process, low energy consumption, and wide applicability, and has broad application prospects in catalyst supports, functional ceramics, and surface protection.

Description

Technical Field

[0001] This invention belongs to the field of inorganic non-metallic material preparation technology, specifically relating to a method for low-temperature preparation of α-Al2O3 materials assisted by an external electric field. Background Technology

[0002] Alumina (Al₂O₃) is the second most abundant oxide material in the Earth's crust after silicon dioxide. Among the dozen or so known allomers of alumina, α-Al₂O₃ (corundum) is the only thermodynamically stable phase. With its extremely high hardness, excellent wear resistance, outstanding chemical inertness, high-temperature thermal stability, high light absorption properties, and high dielectric constant, α-Al₂O₃ has become one of the most widely used structural and functional ceramic materials. It plays an irreplaceable and important role in many high-end fields such as catalyst supports, high-temperature refractories, functional ceramics, aerospace protective coatings, and composite materials.

[0003] However, the preparation of α-Al₂O₃ is significantly constrained by a high phase transformation barrier. Traditional preparation processes typically require heating the precursor to above 1200℃ to overcome the enormous kinetic barrier and achieve the transformation from amorphous or metastable phases (such as γ-Al₂O₃, θ-Al₂O₃, etc.) to the stable phase α-Al₂O₃. This high-temperature sintering process has obvious drawbacks: on the one hand, it consumes a huge amount of energy and has stringent equipment requirements, increasing production costs and process complexity; on the other hand, high temperatures easily induce abnormal grain growth, making it difficult to control the microstructure of the material and thus deteriorating its mechanical properties. To reduce the α-phase transformation temperature, existing technologies have developed various improved processes, but many shortcomings remain: for example, while seed-induced methods can reduce the nucleation barrier by adding corundum particles, they easily lead to agglomeration and the introduction of impurities; while hot isostatic pressing can effectively promote phase transformation densification, the equipment is expensive and difficult to achieve large-scale industrial production.

[0004] Especially in the field of functional ceramic thin film and coating preparation, obtaining high-purity α-Al₂O₃ films on metal substrates is even more difficult. Conventional physical / chemical vapor deposition techniques such as magnetron sputtering and atomic layer deposition typically only yield amorphous or metastable Al₂O₃ under process conditions below 800°C, requiring high-temperature annealing above 1000°C to transform it into the α-phase. This high-temperature post-processing directly limits its application on heat-sensitive metal substrates. Many high-performance metal substrates (such as aluminum alloys, copper alloys, and stainless steel) cannot withstand temperatures above 1000°C; otherwise, they will soften, deform, melt, or undergo phase transformation embrittlement, leading to substrate structural failure. In summary, existing technologies struggle to balance low-temperature preparation with α-phase purity, necessitating the development of a new method for directly preparing α-Al₂O₃ under medium-to-low temperature conditions. Summary of the Invention

[0005] To address the challenges of existing technologies, this invention provides a method for the low-temperature preparation of α-Al2O3 via electro-induced phase change. This invention introduces an external electric field during the heat treatment stage of the alumina precursor and uses current induction to lower the phase change barrier. Under conditions far below the traditional phase change temperature (500~900℃), a complete transformation from an amorphous or metastable phase to the α phase is achieved, thereby obtaining a dense, crack-free α-Al2O3 material.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing αAl2O3 material at low temperature by electro-induced phase change includes the following steps:

[0008] (1) Prepare an Al2O3 precursor, wherein the precursor is an Al2O3 green blank or an Al2O3 precursor film / coating located on a metal substrate;

[0009] (2) Conductive electrodes are arranged at both ends of the Al2O3 green blank or at both ends of the metal substrate on which Al2O3 precursor film / coating is deposited;

[0010] (3) The Al2O3 precursor with the electrodes arranged is placed in a heat treatment furnace and heat-treated in an inert atmosphere, a reducing atmosphere, an oxidizing atmosphere, a vacuum atmosphere, an air atmosphere or a mixture thereof.

[0011] (4) During the heat treatment process, an external electric field is applied to the precursor through the conductive electrode;

[0012] (5) After heat treatment and energization, cool to room temperature to obtain α-Al2O3 bulk material or thin film / coating.

[0013] Furthermore, the Al2O3 green body is formed by pressing Al2O3 powder, wherein the Al2O3 powder is amorphous Al2O3 powder, γ-Al2O3 powder, or a mixture of the two, and the mixing mass ratio of the mixture is 1:100~100:1.

[0014] Furthermore, the pressure during pressing of the Al2O3 green body is 10~200 MPa, and the holding time is 20~600 s.

[0015] Furthermore, the conductive electrode is graphite, platinum electrode, or platinum wire.

[0016] Furthermore, the gas flow rate of the heat treatment atmosphere is 20-300 sccm.

[0017] Furthermore, the heat treatment is divided into two stages. In the first stage, the heating rate is 2~10°C / min, the holding temperature is 200°C, and the holding time is 1~5h. In the second stage, the heating rate is 10~25°C / min, the holding temperature is 500~900°C, and the holding time is 2~10h.

[0018] Furthermore, the external electric field is applied in the second stage of the heat treatment, with an electric field strength of 60~600mV / mm² and an application time of 1~5h.

[0019] Furthermore, the cooling process is divided into two stages: the first stage: cooling to 200°C at a rate of 1~10°C / min; the second stage: cooling to room temperature along with the furnace.

[0020] An α-Al2O3 material prepared by the method described above, wherein the material is in bulk or thin film / coating form, and has a dense structure and high α-phase purity.

[0021] Application of the aforementioned α-Al2O3 material in the fields of catalyst support, high-temperature refractory materials, functional ceramics, aerospace protective coatings, or composite materials.

[0022] The beneficial effects of this invention are as follows:

[0023] (1) By introducing an external electric field during the heat treatment of Al2O3 precursor, the present invention uses the electric field to induce a reduction in the phase transition barrier, and successfully reduces the preparation temperature of α-Al2O3 from more than 1200°C in the traditional process to 500~900°C. Experiments show that the complete transformation of the α phase can be achieved at around 750°C, which significantly reduces energy consumption and equipment requirements.

[0024] (2) The method of the present invention breaks through the limitations of traditional high-temperature processes on substrates. Since the heat treatment temperature is much lower than the phase transformation or melting temperature of metal substrates, high-purity and dense α-Al2O3 films / coatings can be directly prepared on metal substrates that are not resistant to high temperatures, such as steel, aluminum alloys, copper alloys, magnesium alloys, and zinc alloys. This effectively avoids the problems of high-temperature softening, deformation, or embrittlement of the substrate and expands the application range of α-Al2O3 in the field of metal surface protection.

[0025] (3) The present invention effectively suppresses abnormal grain growth and crack defects commonly found in high-temperature sintering by controlling the phase transformation process through electric field. The α-Al2O3 bulk materials and thin films / coatings prepared have high density, high α phase purity and good microstructure controllability.

[0026] (4) The method of the present invention has strong universality. It is not only applicable to bulk green blanks of amorphous and γ-phase Al2O3 powder, but also to Al2O3 precursor thin films / coatings prepared on metal substrates by magnetron sputtering, chemical vapor deposition, sol-gel and other methods. It does not require expensive single crystal substrates or high-voltage equipment. The process is simple and controllable and has good prospects for industrial application. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0028] Figure 1 These are the X-ray diffraction (XRD) patterns of the Al2O3 bulk materials prepared in Examples 1-3 of this invention;

[0029] Figure 2 These are scanning electron microscope (SEM) images of the fracture surface of the Al2O3 bulk materials prepared in Examples 1-3 of this invention;

[0030] Figure 3 These are the X-ray diffraction (XRD) patterns of Al2O3 thin films / coatings prepared on metal substrates in Examples 4-6 of this invention;

[0031] Figure 4 These are scanning electron microscope (SEM) images of the Al2O3 thin films / coatings prepared on metal substrates in Examples 4-6 of this invention, and corresponding macroscopic images of the surface of the thin films / coatings.

[0032] Figure 5 This is a macroscopic view of the back side of the Al2O3 thin film / coating prepared in Comparative Example 1 of this invention. Detailed Implementation

[0033] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0034] Examples 1-3 are Al2O3 bulk samples prepared according to the present invention.

[0035] Example 1

[0036] (1) A certain amount of γ-Al2O3 powder was mixed evenly with 2wt% polyvinyl alcohol (PVA) binder and pressed under a pressure of 10 MPa for 20 s to obtain Al2O3 green body;

[0037] (2) After coating both ends of the Al2O3 green blank with a sintering-resistant metal conductive paste, it is connected to a platinum sheet as a wire;

[0038] (3) The Al2O3 green blank is suspended in a tube furnace and argon gas of 20 sccm is introduced as a protective atmosphere. In the first stage of heat treatment, the temperature is raised to 200°C at a heating rate of 2°C / min and held for 1 h. Then the temperature is raised to 500°C at a heating rate of 10°C / min and held for 2 h.

[0039] (4) In the second stage of heat treatment, an electric field is applied to the Al2O3 green blank through a power source, with a voltage density of 60 mV / mm. 2 The voltage was applied for 1 hour.

[0040] (5) After heat treatment and power-on, the sample is cooled to 200°C at a cooling rate of 5°C / min, and then cooled to room temperature with the furnace to obtain Al2O3 bulk material.

[0041] The X-ray diffraction (XRD) pattern and scanning electron microscope (SEM) image of the Al2O3 bulk material prepared in this embodiment are shown below. Figures 1-2 As shown.

[0042] Example 2

[0043] (1) Select γ-Al2O3 powder, add 2wt% PVA binder and mix evenly, press under 100Mpa pressure for 200s to obtain Al2O3 green body;

[0044] (2) Connect platinum electrodes as wires to both ends of the green body;

[0045] (3) Introduce argon gas at a flow rate of 100 sccm. In the first stage of heat treatment, heat the gas to 200°C at a rate of 5°C / min and hold for 1.5 h; then heat the gas to 600°C at a rate of 15°C / min and hold for 4 h.

[0046] (4) In the second stage of heat treatment, an electric field is applied to the Al2O3 green blank through a power source, with a voltage density of 420 mV / mm. 2 The application time is 2 hours;

[0047] (5) Cool down to 200°C at 5°C / min and then cool with the furnace.

[0048] The X-ray diffraction (XRD) pattern and scanning electron microscope (SEM) image of the Al2O3 bulk material prepared in this embodiment are shown below. Figures 1-2 As shown.

[0049] Example 3

[0050] (1) Select amorphous Al2O3 powder, add PVP binder, and press for 600s under a pressure of 200Mpa;

[0051] (2) Platinum wires are connected to both ends of the green body;

[0052] (3) Argon gas is introduced at a flow rate of 250 sccm. In the first stage of heat treatment, the temperature is increased to 200°C at 7°C / min and held for 3.5h; then the temperature is increased to 550°C at 14°C / min and held for 7h.

[0053] (4) In the second stage of heat treatment, an electric field is applied to the Al2O3 green blank through a power source, with a voltage density of 600 mV / mm. 2 The application time is 3.5 hours;

[0054] (5) Cool down to 200°C at 5°C / min and then cool with the furnace.

[0055] The X-ray diffraction (XRD) pattern and scanning electron microscope (SEM) image of the Al2O3 bulk material prepared in this embodiment are shown below. Figures 1-2 As shown.

[0056] Examples 4-6 are Al2O3 thin film / coating samples prepared in this invention.

[0057] Example 4

[0058] (1) The steel substrate was ultrasonically cleaned three times with deionized water, anhydrous ethanol and acetone respectively to remove oil stains; the film / coating was prepared by sol-gel method, aluminum nitrate and amine complexing agent were dissolved in an appropriate amount of alcohol solvent at a molar ratio of 1:1 and stirred until completely dissolved to obtain aluminum sol. The concentration of aluminum source in the sol can be controlled between 0.05 and 5M; the aluminum sol was coated on the surface of the steel substrate by spin coating method. The spin coating parameters can be selected as the classic 3000rpm and 30s. After preheating at 50~150°C for 0.5~1h, an Al2O3 film / coating sample with a thickness of 0.05~5μm was obtained.

[0059] (2) After coating both ends of the Al2O3 thin film / coating sample with a sintering-resistant metal conductive paste, it is connected to a platinum sheet as a wire;

[0060] (3) The Al2O3 thin film / coating sample was suspended in a tube furnace, and argon gas of 20 sccm was introduced as a protective atmosphere. The temperature was increased to 200°C at a heating rate of 2°C / min and held for 1 h. Then, in the first stage of heat treatment, the temperature was increased to 500°C at a heating rate of 10°C / min and held for 2 h.

[0061] (4) In the second stage of heat treatment, an electric field was applied to the Al2O3 thin film / coating sample by means of a power source, with a voltage density of 60 mV / mm. 2 The voltage was applied for 2 hours.

[0062] (5) After heat treatment and power-on, the sample is cooled to 200°C at a cooling rate of 5°C / min, and then cooled to room temperature with the furnace to obtain Al2O3 thin film / coating sample.

[0063] The X-ray diffraction (XRD) pattern and scanning electron microscope (SEM) image of the Al2O3 thin film / coating sample prepared in this embodiment are shown below. Figures 3-4 As shown.

[0064] Example 5

[0065] (1) The magnesium alloy substrate was ultrasonically cleaned three times with deionized water, anhydrous ethanol and acetone respectively to remove oil stains; the film / coating was prepared by sol-gel method. Aluminum nitrate and amine complexing agent were dissolved in an appropriate amount of alcohol solvent at a molar ratio of 1:1 and stirred until completely dissolved to obtain aluminum sol. The concentration of aluminum source in the sol was controlled between 0.05 and 5 M; the aluminum sol was coated on the surface of copper alloy substrate by spin coating method. The spin coating parameters were selected as 2000 rpm and 45 s. After preheating at 100°C for 1 h, Al2O3 film / coating samples with a thickness of 0.05~5 μm were obtained.

[0066] (2) After coating both ends of the Al2O3 thin film / coating sample with a sintering-resistant metal conductive paste, it is connected to a platinum sheet as a wire;

[0067] (3) The Al2O3 thin film / coating sample was suspended in a tube furnace, and nitrogen gas of 100 sccm was introduced as a protective atmosphere. The temperature was increased to 200°C at a heating rate of 5°C / min and held for 1.5 h. Then, in the first stage of heat treatment, the temperature was increased to 600°C at a heating rate of 15°C / min and held for 4 h.

[0068] (4) In the second stage of heat treatment, an electric field was applied to the Al2O3 thin film / coating sample by means of a power source, with a voltage density of 420mV / mm² (optimal parameter) and a voltage application time of 2h;

[0069] (5) After heat treatment and power-on, the sample is cooled to 200°C at a cooling rate of 5°C / min, and then cooled to room temperature with the furnace to obtain Al2O3 thin film / coating sample.

[0070] The X-ray diffraction (XRD) pattern and scanning electron microscope (SEM) image of the Al2O3 thin film / coating sample prepared in this embodiment are shown below. Figures 3-4 As shown.

[0071] Example 6

[0072] (1) The zinc alloy substrate was ultrasonically cleaned three times with deionized water, anhydrous ethanol and acetone respectively to remove oil stains; the film / coating was prepared by sol-gel method. Aluminum nitrate and amine complexing agent were dissolved in an appropriate amount of alcohol solvent at a molar ratio of 1:1 and stirred until completely dissolved to obtain aluminum sol. The concentration of aluminum source in the sol was controlled between 0.05 and 5 M; the aluminum sol was coated on the surface of copper alloy substrate by spin coating method. The spin coating parameters were selected as 2000 rpm and 45 s. After preheating at 100°C for 1 h, Al2O3 film / coating samples with a thickness of 0.05~5 μm were obtained.

[0073] (2) After coating both ends of the Al2O3 thin film / coating sample with a sintering resistant metal conductive paste, it is connected to a platinum wire as a conductor;

[0074] (3) The Al2O3 thin film / coating sample was suspended in a tube furnace and evacuated to a vacuum level of 1×10⁻⁶. -5 Pa was heated to 200°C at a heating rate of 10°C / min and held for 2 hours. Then, in the first stage of heat treatment, the temperature was increased to 700°C at a heating rate of 20°C / min and held for 3 hours.

[0075] (4) In the second stage of heat treatment, an electric field was applied to the Al2O3 thin film / coating sample by means of a power source, with a voltage density of 600mV / mm² and a voltage application time of 3h;

[0076] (5) After heat treatment and power-on, the sample is cooled to 200°C at a cooling rate of 10°C / min, and then cooled to room temperature with the furnace to obtain Al2O3 thin film / coating sample.

[0077] The X-ray diffraction (XRD) pattern and scanning electron microscope (SEM) image of the Al2O3 thin film / coating sample prepared in this embodiment are shown below. Figures 3-4 As shown.

[0078] Comparative Example 1

[0079] This comparative example aims to highlight the necessity of the low-temperature preparation process of the present invention for protecting the metal substrate.

[0080] (1) An Al2O3 precursor film was prepared on the surface of a steel substrate using the same process as in Example 4;

[0081] (2) No electrode leads are provided;

[0082] (3) Place the sample in a tube furnace and heat it to a high temperature of 1200°C using conventional processes and keep it at that temperature for 2 hours;

[0083] (4) Cool to room temperature with the furnace.

[0084] The macroscopic back view of the thin film / coating sample prepared in this embodiment is shown below. Figure 5 As shown.

[0085] refer to Figure 1 Analysis of the X-ray diffraction (XRD) patterns of the Al2O3 bulk materials prepared in Examples 1-3 of this invention reveals that when the electric field strength is low, the Al2O3 bulk materials mainly exhibit typical amorphous or metastable γ-Al2O3 characteristics, with no obvious α-Al2O3 diffraction peaks observed. As the applied electric field strength gradually increases, characteristic α-Al2O3 diffraction peaks begin to appear in the patterns, indicating that the phase transition process has begun. This is especially true when the applied electric field strength exceeds 420 mV / mm. 2 The spectrum exhibits sharp and high-intensity diffraction peaks, whose positions closely match the characteristic peak positions of the standard card (PDF#10-0173) for α-Al₂O₃, and no obvious impurity phase diffraction peaks were detected in the entire spectrum. This indicates that the applied electric field can effectively overcome the potential barrier in the phase transition process of the Al₂O₃ precursor, inducing the precursor to transform from an amorphous or γ phase to a thermodynamically stable α phase.

[0086] refer to Figure 2 Based on the scanning electron microscope (SEM) images of the Al2O3 bulk materials prepared in Examples 1-3 of this invention, it can be seen that when the electric field strength is in the lower range, only fine nanosheet structures can be observed in the Al2O3 bulk materials, and no obvious crystalline phase is observed. When the electric field strength reaches 420 mV / mm... 2 At this point, distinct Al2O3 grains can be observed. As the electric field strength continues to increase, the grains grow, reaching a maximum strength of 600 mV / mm. 2 At that time, obvious cracks and abnormally grown grains appeared. The SEM morphology was compared with... Figure 1 Comparison of the XRD results reveals that the applied electric field not only promotes the transformation of the amorphous phase to the α phase but also significantly improves the crystallinity of the material. These microscopic observations confirm that by controlling the electric field strength within a reasonable process window, the process of this invention can obtain α-Al₂O₃ bulk materials with high crystallinity, high density, and no cracks.

[0087] refer to Figure 3 Analysis of the X-ray diffraction (XRD) patterns of Al2O3 thin films / coatings prepared on different metal substrates in Examples 4-6 of this invention revealed that, when an application of 420 mV / mm² was performed... 2 After applying an electric field, the Al2O3 thin film / coating samples exhibited sharp and clear α-Al2O3 phase characteristic diffraction peaks.

[0088] refer to Figure 4Based on the scanning electron microscope (SEM) images of the Al2O3 thin films / coatings prepared in Examples 4-6 of this invention, the α-Al2O3 thin films / coatings prepared using the method of this invention have dense and continuous surfaces, and are free from obvious cracks and other defects. Figure 3 The results show that the electric field-assisted processing technology of the present invention has broad applicability, and it is not only applicable to the sintering of bulk materials, but can also be successfully applied to the field of thin films / coatings, which greatly expands the application scope of the technology.

[0089] refer to Figure 5 For the thin film / coating sample (Comparative Example 1) processed using a traditional high-temperature (1200℃) process, macroscopic photographs of the back side of the substrate show that the metal substrate could not withstand the high-temperature heat treatment, resulting in severe oxidation and thermal deformation, which led to the surface coating peeling off and failing. This result directly demonstrates that the traditional high-temperature sintering process is completely infeasible on metal substrates with limited thermal stability, thus highlighting the engineering application significance of the low-temperature preparation process of this invention in the field of metal surface protection.

[0090] This invention, through verification of Al2O3 bulk materials and Al2O3 thin films / coatings in the embodiments, confirms that the high phase transformation barrier of Al2O3 materials from metastable phases (such as amorphous phases, γ phases) to thermally stable α phases can be overcome by utilizing an external electric field-assisted processing process. Experimental results show that this method is not limited to specific precursor states but has significant universality. High-purity α-Al2O3 materials can be successfully obtained by adjusting appropriate electric field parameters for both pressed Al2O3 bulk materials and Al2O3 thin films / coatings deposited on metal substrates. The resulting Al2O3 materials are not only dense in structure but also possess high α-phase purity, thus enabling a wider range of applications.

[0091] Experimental results from different embodiments of this invention consistently demonstrate the universality of the method. For different types of Al2O3 powder materials and Al2O3 films / coatings deposited on different substrates in the embodiments, the application of an external electric field can induce the transformation of the Al2O3 precursor from an amorphous phase and transition phase to the α phase. Experimental results show that the process described in this invention can effectively control the phase transformation kinetics using an external electric field for different types of substrates and precursors, thereby obtaining dense, high-purity α-Al2O3 materials. This universality greatly expands the application range of this technology, especially overcoming the structural failures such as melting and embrittlement that occur in many high-performance metal substrates (such as steel, aluminum alloys, copper alloys, and magnesium alloys) under traditional high-temperature processes (>1200°C). This invention can be used in catalyst supports, high-temperature refractory materials, functional ceramics, aerospace protective coatings, composite materials, or other fields requiring high-performance α-Al2O3 materials.

[0092] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed herein should be included within the scope of protection of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing α-Al₂O₃ materials at low temperature through electroinduced phase change, characterized in that, Includes the following steps: (1) Prepare an Al2O3 precursor, wherein the precursor is an Al2O3 green blank or an Al2O3 precursor film / coating located on a metal substrate; (2) Conductive electrodes are arranged at both ends of the Al2O3 green blank or at both ends of the metal substrate on which Al2O3 precursor film / coating is deposited; (3) The Al2O3 precursor with the electrodes arranged is placed in a heat treatment furnace and heat-treated in an inert atmosphere, a reducing atmosphere, an oxidizing atmosphere, a vacuum atmosphere, an air atmosphere or a mixture thereof. (4) During the heat treatment process, an external electric field is applied to the precursor through the conductive electrode; (5) After heat treatment and energization, cool to room temperature to obtain α-Al2O3 bulk material or thin film / coating.

2. The preparation method according to claim 1, characterized in that, The Al2O3 green body is formed by pressing Al2O3 powder, wherein the Al2O3 powder is amorphous Al2O3 powder, γ-Al2O3 powder, or a mixture of both, and the mixing mass ratio of the mixture is 1:100 to 100:

1.

3. The preparation method according to claim 1, characterized in that, The pressure during pressing of the Al2O3 green body is 10~200 MPa, and the holding time is 20~600 s.

4. The preparation method according to claim 1, characterized in that, The conductive electrode is a graphite electrode, a platinum electrode, or a platinum wire.

5. The preparation method according to claim 1, characterized in that, The gas flow rate of the heat treatment atmosphere is 20-300 sccm.

6. The preparation method according to claim 1, characterized in that, The heat treatment is divided into two stages. In the first stage, the heating rate is 2~10°C / min, the holding temperature is 200°C, and the holding time is 1~5h. In the second stage, the heating rate is 10~25°C / min, the holding temperature is 500~900°C, and the holding time is 2~10h.

7. The preparation method according to claim 6, characterized in that, The applied electric field is applied in the second stage of the heat treatment, with an electric field strength of 60–600 mV / mm² and an application time of 1–5 h.

8. The preparation method according to claim 1, characterized in that, The cooling process is divided into two stages: the first stage: cooling to 200°C at a rate of 1-10°C / min; the second stage: cooling to room temperature along with the furnace.

9. An α-Al₂O₃ material prepared by the method according to any one of claims 1-9, characterized in that, The material is in bulk or thin film / coating form, and has a dense structure and high α-phase purity.

10. The application of the α-Al2O3 material as described in claim 9 in the fields of catalyst support, high-temperature refractory materials, functional ceramics, aerospace protective coatings, or composite materials.

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