A preparation method of high-strength η-alumina

Abstract

The present invention belongs to the technical field of alumina production, and in particular to a method for preparing high-strength η-alumina, comprising the following steps: S1: stirring and dissolving aluminum isopropoxide and anhydrous ethanol in a constant temperature water bath at 30°C, adding deionized water dropwise during the stirring process, and then reacting for a period of time to obtain a transparent sol; S2: adding concentrated ammonia water dropwise to the transparent sol, adjusting the pH value of the system to 9.5, transferring the sol to a closed container, and aging at room temperature for 24 hours to form a gel; S3: placing the gel in a vacuum drying oven, drying it for 12 hours at 60°C and a vacuum degree of 0.08MPa to obtain a dry gel; S4: placing the dry gel in a muffle furnace, heating it from room temperature to 350°C at a heating rate of 3°C / min, and keeping it at 350°C for 2 hours for pre-calcination. Compared with the η-alumina prepared by the traditional method, the strength of the η-alumina is increased by 50%, which can better meet the application scenarios with strict requirements on the mechanical properties of the material.

Description

Technical Field

[0001] The invention belongs to the technical field of alumina production, and particularly relates to a method for preparing high-strength η-alumina. Background Art

[0002] The surface acidity of η-alumina is stronger than that of ordinary alumina, which gives it a unique role in some catalytic reactions and can better adsorb and activate reactant molecules. η-alumina has a pore volume and specific surface area that are not much different from those of γ-alumina. The larger specific surface area means that it can provide more active sites, which is conducive to the adsorption of substances and the progress of chemical reactions. However, η-alumina under traditional preparation processes has the problem of poor strength and is difficult to meet the strict requirements of high-end fields for the mechanical properties of materials. Existing technologies have deficiencies in regulating the crystal transformation and microstructure construction of alumina, resulting in many internal defects in the product and weak grain boundary bonding, which greatly limits the application expansion of η-alumina in fields such as high-speed cutting tools and aerospace high-performance components. Summary of the Invention

[0003] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for preparing high-strength η-alumina to solve the problems in the above-mentioned background technology.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] A method for preparing high-strength η-alumina, wherein the alumina is crystalline alumina with uniform grain size, an average grain size of about 50 nm, and a grain boundary width of 2-3 nm, comprising the following steps:

[0006] S1: Aluminum isopropoxide and anhydrous ethanol were stirred and dissolved in a constant temperature water bath at 30°C. Deionized water was added dropwise during the stirring process, and then reacted for a period of time to obtain a transparent sol;

[0007] S2: Add concentrated ammonia water to the transparent sol to adjust the pH value of the system to 9.5, transfer the sol to a sealed container, and age it at room temperature for 24 hours to form a gel;

[0008] S3: The gel was placed in a vacuum drying oven and dried at 60°C and a vacuum degree of 0.08 MPa for 12 hours to obtain a dry gel;

[0009] S4: pre-calcining the dry gel in a muffle furnace, heating the temperature from room temperature to 350°C at a rate of 3°C / min, and keeping the temperature at 350°C for 2 hours;

[0010] S5: After the pre-calcination is completed, the temperature is further increased to 1000°C at a heating rate of 5°C / min, and kept at 1000°C for 5 hours to perform the main calcination to obtain high-strength η-alumina.

[0011] Furthermore, in step S1, the mass ratio of the aluminum isopropoxide, anhydrous ethanol and deionized water is 1-1.2:3.945:0.2, the deionized water droplet addition rate is controlled at 2-3 drops / second, and stirring is continued during the droplet addition process until fully dissolved. The stirring speed is 200 r / min, and the reaction time after full dissolution is 3 hours.

[0012] Furthermore, during the stirring process of step S1, magnetic stirring is used in combination with ultrasonic-assisted dispersion technology to promote sufficient hydrolysis and polycondensation of aluminum isopropoxide, so that the distribution of aluminum hydroxide precursor in the sol is more uniform and the particle size is more consistent.

[0013] Furthermore, in step S2, the concentrated ammonia solution is added at a rate of 1-2 drops per second, and stirring is continued for 1 hour after the addition is completed.

[0014] Furthermore, during the aging process of step S2, a weak alternating electric field is applied to the sealed container, with the electric field strength controlled at 5-10 V / cm and the frequency at 50-100 Hz, to promote the directional migration and orderly arrangement of particles in the sol, accelerate the formation of the three-dimensional network structure of the gel, and make the network structure denser and more stable.

[0015] Furthermore, during the drying process of step S3, a dynamic vacuum drying method is adopted to regularly change the vacuum degree, which varies periodically between 0.07-0.09 MPa, and each cycle lasts for 2 hours.

[0016] Furthermore, during the pre-calcination process in step S4, a gas circulation device is provided inside the muffle furnace to circulate the gas in the furnace at a flow rate of 0.5 to 1 L / min, ensuring that the temperature uniformity deviation in the furnace is controlled within ±5°C.

[0017] Furthermore, during the main calcination process in step S5, an appropriate amount of inert gas is introduced into the muffle furnace, and the gas flow rate is controlled at 10 to 20 mL / min.

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

[0019] 1. By precisely controlling the reaction temperature, pH value, raw material dosage and reaction time, combined with innovative process methods such as alternating electric field aging and dynamic vacuum drying, the prepared η-alumina has a denser microstructure. Scanning electron microscopy showed that the grain size is uniform, the average grain size is about 50nm, the grain boundary width is only 2-3nm, the grain boundaries are tightly bonded, and there are almost no obvious defects, which is a significant improvement compared to traditional methods. Observation under a high-resolution transmission electron microscope showed that the atoms at the grain boundaries are arranged in an orderly manner, with a small amount of dislocation defects, but they have little effect on the bonding strength of the grain boundaries. Electron backscatter diffraction (EBSD) analysis showed that the orientation distribution of the grains is relatively uniform, with no obvious preferred orientation, which helps to improve the isotropic properties of the material;

[0020] 2. The η-alumina prepared by the present invention has a compressive strength of 500 MPa, which is 50% higher than that of η-alumina prepared by traditional methods, and can better meet the application scenarios with strict requirements on the mechanical properties of materials. In the tensile test, its tensile strength reached 200 MPa and its elongation was 5%, showing good strength and certain plasticity. In the impact test, its impact toughness reached 15 J / cm², which is about 40% higher than that of products prepared by traditional methods, indicating that the material has better resistance to impact loads;

[0021] 3. The entire preparation process is relatively simple to operate, requires minimal equipment, and has low raw material costs, making it promising for industrial production. Cost accounting shows that raw material costs are approximately 20% lower than those of traditional methods, while production efficiency is increased by 30%. In industrial production, large-scale reactors and automated control systems can further improve production efficiency and product quality stability. Furthermore, this preparation method has low energy consumption, meeting the development requirements of energy conservation and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of a process for preparing high-strength η-alumina according to the present invention; DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments.

[0024] Raw Material Preparation: Aluminum isopropoxide with a purity of at least 99.5% should be used as the aluminum source. Ensure it is sealed and stored in a dry, cool place in a nitrogen-filled, sealed container to prevent deterioration due to moisture absorption and oxidation during storage. Before opening the raw material package, place it in a nitrogen-filled glove box to avoid potential damage from brief contact with air. Deionized water (conductivity controlled below 0.1 μS / cm) is used as the hydrolysis reagent and must be purified again by passing it through an ion exchange resin column before use to further reduce the presence of trace impurities. 25% concentrated ammonia water is used as the precipitant modifier and must be calibrated before use to ensure accuracy. Anhydrous ethanol is used as the dispersion solvent. Rectified-grade anhydrous ethanol with a purity of at least 99.9% is used. Strict control of raw material purity and storage conditions ensures pure raw materials for subsequent precise reactions and prevents impurities from interfering with reaction progress and product quality.

[0025] Sol preparation: In a constant temperature water bath at 30°C, 100g of aluminum isopropoxide was slowly added to 500mL of anhydrous ethanol while stirring continuously at a stirring speed of 200r / min to fully dissolve it. The stirring paddle was made of polytetrafluoroethylene to prevent metal materials from contaminating the reaction system. When adding aluminum isopropoxide, a special funnel was used with a fine filter at its outlet to prevent lumpy impurities in the aluminum isopropoxide from entering the reaction system. Subsequently, 20mL of deionized water was added dropwise at a rate of 2-3 drops / second. Stirring was continued during the addition process. The reaction was continued for 3 hours to obtain a uniform and transparent sol. The reaction vessel was a jacketed glass reactor. The jacket was connected to the constant temperature water bath via a circulating water pump to ensure precise control of the reaction temperature. The temperature fluctuation range was controlled within ±0.5°C. The stirring process used magnetic stirring combined with ultrasonic-assisted dispersion technology. The speed of the magnetic stirrer was adjusted by a high-precision speed controller to ensure stable speed. The ultrasonic generator was set to 50W power and 40kHz frequency, and the ultrasonic probe was inserted into the reaction solution to a depth of 5cm. The high-frequency oscillation of ultrasound promoted the dispersion of microscopic particles, resulting in more complete hydrolysis and polycondensation of aluminum isopropoxide, and a more uniform distribution and consistent particle size of the aluminum hydroxide precursor. During the reaction, a small amount of sol was sampled every 30 minutes for particle size analysis. The changes in the precursor's particle size were monitored in real time using a laser particle size analyzer to ensure that the reaction progressed as expected.

[0026] Gel Formation: Concentrated aqueous ammonia was slowly added dropwise to the sol to adjust the pH to 9.5 at a rate of 1-2 drops / second. Stirring was continued for 1 hour after the addition was complete. The sol was then transferred to a sealed container and aged at room temperature for 24 hours to form a gel. During the addition of concentrated aqueous ammonia, the pH of the solution was monitored in real time using a high-precision pH meter with an accuracy of ±0.01. The aging container was a stainless steel container lined with polytetrafluoroethylene (PTFE) to ensure a tight seal and prevent contamination of the gel. During the aging process, a weak alternating electric field was applied to the sealed container with a controlled electric field strength of 5-10 V / cm and a frequency of 50-100 Hz. This alternating electric field was applied via specially designed electrode plates made of inert metal, such as platinum, to prevent redox reactions that could affect gel formation. The alternating electric field promoted directional migration and orderly alignment of particles in the sol, accelerating the formation of the gel's three-dimensional network structure and making it denser and more stable. A small amount of gel was taken out every 6 hours, and its microstructural changes were observed using a scanning electron microscope to record the growth of the gel network.

[0027] Drying treatment: The gel was placed in a vacuum drying oven and dried at 60°C and a vacuum degree of 0.08 MPa for 12 hours to obtain a dry gel. The heating element of the vacuum drying oven uses a ceramic heating rod, which has the characteristics of fast heating and uniform temperature. During the drying process, a dynamic vacuum drying method is adopted, that is, the vacuum degree is changed regularly, and it changes periodically between 0.07-0.09 MPa, and each cycle lasts for 2 hours. The vacuum degree change is monitored in real time by a vacuum degree sensor, and the vacuum degree adjustment is precisely controlled by the regulating valve of the vacuum pump. This method avoids the problem of local water vapor accumulation caused by uneven drying, reduces stress concentration inside the dry gel, and reduces the probability of cracks and defects. During the drying process, the mass of the dry gel is weighed every hour, and the weight loss of the dry gel is monitored by gravimetric analysis to determine the progress and effect of the drying.

[0028] Precalcination: The xerogel was placed in a muffle furnace and heated from room temperature to 350°C at a rate of 3°C / min, then held at 350°C for 2 hours. A gas circulation system, consisting of a high-temperature-resistant blower and flow ducts, circulated the gas within the muffle furnace at a flow rate of 0.5 to 1 L / min, ensuring temperature uniformity within the furnace within ±5°C. During the heating process, the furnace temperature was monitored in real time by thermocouples with an accuracy of ±1°C. The temperature data was transmitted to a temperature controller for precise control of the heating rate. This uniform temperature field ensured uniform heating of the xerogel, resulting in more consistent decomposition of organic components and crystal transformation of aluminum hydroxide, minimizing internal structural variation in the product. A thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC) were used to simultaneously monitor mass changes and thermal effects during the precalcination process. The TGA had a sensitivity of 0.1 μg and the DSC had a resolution of 0.1 mW, enabling precise monitoring of material changes during the precalcination process and enabling precise control of the precalcination process.

[0029] Main Calcination: After the pre-calcination, the temperature is raised to 1000°C at a rate of 5°C / min and held at 1000°C for 5 hours to produce high-strength η-alumina. During the main calcination, an appropriate amount of inert gas (such as argon) is introduced into the muffle furnace at a controlled flow rate of 10-20 mL / min. The argon flow rate is precisely controlled by a mass flowmeter with an accuracy of ±0.1 mL / min. The argon gas isolates the material from external impurities, promotes alumina crystal growth, and inhibits abnormal grain growth, resulting in high-strength η-alumina with uniform grain size, clear grain boundaries, and tight bonds. X-ray diffractometer (XRD) is used to monitor the alumina crystal phase transitions during the main calcination process in real time. The XRD scan rate is 0.05° / s with a step size of 0.02°, ensuring the final product is high-purity η-alumina and enabling precise control of crystal phase transitions. After calcination, the product was sliced and its microstructure was observed by transmission electron microscopy (TEM) to further analyze the grain growth and microscopic characteristics of the grain boundaries.

[0030] Example 1

[0031] The preparation was carried out according to the raw material preparation and parameters of each step in the above technical solution. The final η-alumina was tested:

[0032] Density test: Use Archimedes drainage method to weigh the sample in the air, then suspend it with a thin wire and immerse it in deionized water to weigh it. (where m1 is the mass of the sample in air and m2 is the mass of the sample in water), the calculated density is 3.5 g / cm³.

[0033] Compressive strength test: Use an electronic universal testing machine to process the sample into a cube with a size of 10mm×10mm×10mm. Apply pressure at a loading rate of 0.5mm / min until the sample is broken. Record the maximum load at the time of failure. According to the formula (F is the failure load, S is the compressive area of the sample) The calculated compressive strength is 500 MPa.

[0034] Microstructure observation: Scanning electron microscopy (SEM) observation at a magnification of 10,000 times revealed uniform grain size, an average grain size of approximately 50 nm, and a grain boundary width of approximately 2-3 nm. The atoms at the grain boundaries were closely arranged with high bonding strength. Energy spectrum analysis showed uniform element distribution at the grain boundaries with almost no impurity segregation.

[0035] Hardness test: Using a Vickers hardness tester, the loading load is 1kgf, the loading time is 15s, and the average value is taken after 5 measurements at different positions of the sample. The Vickers hardness reaches 1500HV.

[0036] Wear resistance test: A reciprocating friction and wear tester was used, with a Si3N4 ceramic ball with a diameter of 6mm as the grinding material, a test load of 5N, a reciprocating frequency of 2Hz, a stroke of 5mm, and a test time of 1h. The wear rate was calculated by measuring the mass difference before and after wear of the sample. Under the same friction conditions, its wear rate was only 60% of that of the product prepared by the traditional method.

[0037] Example 2

[0038] In the sol preparation step, the amount of anhydrous ethanol was adjusted to 120 g, and the other step parameters remained unchanged. The prepared η-alumina was tested:

[0039] Density: The density measured by Archimedes displacement method is 3.55g / cm³.

[0040] Compressive strength: Using an electronic universal testing machine, the test was carried out at the same loading rate and sample size, and the compressive strength was increased to 520MPa.

[0041] Microstructure: SEM analysis at a magnification of 10,000 times showed that the grain size increased slightly, with an average grain size of about 60 nm, but the grain boundary width remained at 3-4 nm, and the grain boundary bonding was in good condition.

[0042] Toughness test: The fracture toughness was measured using the single edge notched beam method (SENB). The sample was processed into a rectangular beam with a prefabricated crack and loaded at a loading rate of 0.05 mm / min on an electronic universal testing machine. According to the formula (P is the fracture load, a is the crack length, B is the sample thickness, W is the sample width, and Y is the geometric factor) and its fracture toughness reaches 5.5 MPa・m¹ / ².

[0043] High-temperature stability test: The material was placed in a high-temperature box-type resistance furnace, kept at 800°C for 10 hours, and then naturally cooled to room temperature. The material was then tested according to the above-mentioned compressive strength test method. The compressive strength only decreased by 5%.

[0044] Example 3

[0045] In the sol preparation step, the amount of aluminum isopropoxide added was adjusted to 110 g, and the other step parameters remained unchanged. The prepared η-alumina was tested:

[0046] Density: Using the Archimedes displacement method, after accurately measuring the sample's mass in air and water, the calculated density is 3.52 g / cm³. Due to variations in the amount of aluminum isopropoxide, the mass of the final product changes, resulting in corresponding fluctuations in density under the same volume measurement conditions.

[0047] Compressive Strength: Using an electronic universal testing machine, samples were processed into 10mm×10mm×10mm cubes. Pressure was gradually applied at a loading rate of 0.5mm / min until the sample failed. The maximum load at failure was recorded, and the calculated compressive strength was 510MPa. Compared to the base dosage of 100g, the increased amount of aluminum source results in a thicker alumina matrix, further enhancing its resistance to deformation and failure under pressure.

[0048] Microstructure: Detailed SEM observation and analysis at 10,000x magnification revealed relatively uniform grain size, with an average grain size of approximately 53nm and grain boundary widths ranging from 2.5 to 3nm. The moderate addition of aluminum sources provides a more robust material foundation for grain growth, resulting in a slight increase in grain size and changes in grain boundary width.

[0049] Hardness test: Using a Vickers hardness tester, we applied a 1 kgf load for 15 seconds. Five measurements were taken at different locations on the sample, and the average was taken. The Vickers hardness reached 1520 HV. Changes in the microstructure directly affect the material's compressive strength, resulting in an increase in hardness.

[0050] Thermal conductivity testing: Samples were tested at room temperature using a laser flash thermal conductivity tester. The results showed a thermal conductivity of 15 W / (m·K). Changes in the material's microstructure and adjustments to the composition ratio affect its thermal conductivity.

[0051] Wear resistance testing: Using an 8mm diameter alumina ceramic pin as the counter-wear material, the pin was subjected to a load of 8N at a speed of 200 rpm for 1.5 hours on a pin-on-disc wear tester. After the test, the wear loss was calculated by measuring the difference in mass before and after wear. The results showed a mere 0.05mg of wear. The optimized microstructure and increased hardness contribute to the material's excellent wear resistance.

[0052] Comparative Example 1

[0053] η-alumina was prepared using a traditional precipitation method, with aluminum sulfate as the aluminum source and ammonia as the precipitant. The precipitation reaction was followed by calcination. The resulting η-alumina was tested:

[0054] Density: The density measured by Archimedes displacement method is 3.2g / cm³.

[0055] Compressive strength: tested using an electronic universal testing machine, the compressive strength is only 330MPa.

[0056] Microstructure: SEM observation shows that there are many pores and defects in the microstructure. The average grain size is 100nm, the grain boundary width is 5-8nm, the atomic arrangement at the grain boundary is disordered, and there are obvious gaps and dislocations.

[0057] Hardness: measured with a Vickers hardness tester, with the same loading load and time as in the embodiment, the Vickers hardness is only 1000 HV.

[0058] Toughness: Single-edge notched beam method test shows fracture toughness of only 4.0 MPa・m¹ / ².

[0059] Corrosion resistance test: The material was processed into thin slices with a size of 20mm×20mm×2mm, soaked in 5% hydrochloric acid solution for 24 hours, taken out, rinsed with deionized water, and dried. The mass loss rate was calculated by measuring the mass difference before and after soaking. Obvious corrosion pits appeared on the surface, and the mass loss rate reached 10%.

[0060] Comparative Example 2

[0061] In the sol preparation step, the amount of aluminum isopropoxide added was adjusted to 80 g, and the other step parameters remained unchanged. The prepared η-alumina was tested:

[0062] Density: The density measured using the Archimedes displacement method is 3.45 g / cm³. This is because the mass of the final product changes as the amount of aluminum isopropoxide is reduced. Under the same volume measurement conditions, the calculated density changes accordingly.

[0063] Compressive strength: Using an electronic universal testing machine, pressure was applied to a 10mm x 10mm x 10mm cube sample at a loading rate of 0.5mm / min until the sample failed. The maximum load at failure was recorded, and the compressive strength was calculated to be 460MPa. Due to the reduced aluminum source, the alumina matrix formed was relatively small, and its ability to resist deformation and failure under pressure decreased.

[0064] Microstructure: SEM analysis at 10,000x magnification reveals relatively small grain size, with an average grain size of approximately 45nm and a grain boundary width of approximately 2-2.5nm. The change in the aluminum source affects the crystal growth environment, restricting grain growth, resulting in smaller grains and narrower grain boundaries.

[0065] Hardness test: Using a Vickers hardness tester, with a load of 1 kgf for 15 seconds, and taking the average of five measurements at different locations on the sample, the Vickers hardness reached 1400 HV. This is due to changes in the microstructure, which alters the material's ability to resist indentation.

[0066] Friction coefficient test: Using a friction coefficient tester, under dry friction conditions, with 45-gauge steel as the abrasive material, a load of 10N, and a sliding speed of 0.1m / s, the test results showed a friction coefficient of 0.35. Changes in the material's microstructure and hardness affect its surface friction characteristics.

[0067] Comparative Example 3

[0068] The same raw material preparation and preparation steps as in Example 1 were used, with the only difference being that no alternating electric field was applied to the sealed container during the gel formation step, and the gel was formed by natural aging at room temperature for 24 hours. The prepared η-alumina was tested:

[0069] Density: Using the Archimedean displacement method, the sample was weighed in air, then suspended by a thin wire and immersed in deionized water. The calculated density was 3.4 g / cm³. This was lower than the 3.5 g / cm³ obtained in Example 1, where an alternating electric field was applied. This may be due to the lack of an alternating electric field, resulting in a less dense gel network structure and more micropores within the final product.

[0070] Compressive strength: Using an electronic universal testing machine, the sample was processed into a cube measuring 10 mm × 10 mm × 10 mm. Pressure was applied at a loading rate of 0.5 mm / min until the sample failed. The maximum load at failure was recorded, and the compressive strength was calculated to be 420 MPa. This is significantly lower than the 500 MPa in Example 1, indicating that the alternating electric field significantly enhances the material's strength. Without the alternating electric field, the particles cannot be arranged in an orderly manner, resulting in insufficient grain boundary bonding strength and a decrease in compressive strength.

[0071] Microstructure: Scanning electron microscopy (SEM) observation at 10,000x magnification revealed uneven grain size, with an average grain size of approximately 65 nm and a grain boundary width of approximately 4-5 nm. Atomic arrangement at the grain boundaries was relatively loose, resulting in low bonding strength. Energy spectrum analysis revealed a certain degree of elemental segregation at the grain boundaries. Compared to Example 1, without the guidance of the alternating electric field, the grains grew in disorder, and the grain boundary quality deteriorated.

[0072] Hardness test: Using a Vickers hardness tester, with a load of 1 kgf for 15 seconds, five measurements were taken at different locations on the sample, taking the average value. The Vickers hardness was 1300 HV, lower than the 1500 HV in Example 1, indicating that differences in the microstructure have weakened the material's ability to resist indentation.

[0073] Wear resistance testing: A reciprocating tribometer was used, with a 6mm diameter Si3N4 ceramic ball as the abrasive material. The test load was 5N, the reciprocating frequency was 2Hz, the stroke was 5mm, and the test duration was 1h. The wear rate was calculated by measuring the mass difference between the sample before and after wear. Under the same friction conditions, the wear rate was 1.5 times that of the product prepared in Example 1, indicating that the material prepared without the application of an alternating electric field has poor wear resistance, which is related to the loose grain boundary bonding and uneven grain structure in the microstructure.

[0074] By comparing Comparative Example 3 with Example 1, it is clearly shown that applying an alternating electric field during the gel formation process has a positive effect on the density, compressive strength, microstructure, hardness and wear resistance of the high-strength η-alumina.

[0075] Comparisons between the Examples and Comparative Examples fully demonstrate the significant advantages of the preparation method of the present invention in improving η-alumina strength, optimizing its microstructure, and enhancing its overall mechanical properties. Furthermore, it exhibits significant advantages in wear resistance, high-temperature stability, and corrosion resistance, further broadening its application areas. For example, in the aerospace field, it can be used to manufacture key components such as engine blades, improving their service life and reliability. In the field of electronic packaging, it can be used as a high-performance heat dissipation material, where its excellent mechanical properties and thermal stability meet the requirements of complex operating environments.

[0076] The above are only embodiments of the present invention, and the circuits, electronic components and modules involved are all prior art, which can be fully implemented by those skilled in the art. It is needless to say that the content protected by this application does not involve improvements to software and methods. Common knowledge such as the specific structures and characteristics known in the scheme are not described in detail here. Ordinary technicians in the field are aware of all common technical knowledge in the technical field of the invention before the application date or priority date, can obtain all prior art in the field, and have the ability to apply conventional experimental means before that date. Ordinary technicians in the field can improve and implement this scheme in combination with their own abilities under the inspiration given by this application. Some typical known structures or known methods should not become obstacles for ordinary technicians in the field to implement this application. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention. These will not affect the effect of the implementation of the present invention and the practicality of the patent.

Claims

1. A method for preparing high-strength η-alumina, wherein the alumina is crystalline alumina with uniform grain size, an average grain size of 50 nm, and a grain boundary width of 2-3 nm, characterized in that: The following steps are included: S1: Aluminum isopropoxide and anhydrous ethanol were stirred and dissolved in a constant temperature water bath at 30°C. Deionized water was added dropwise during the stirring process, and then reacted for a period of time to obtain a transparent sol; S2: Add concentrated ammonia water to the transparent sol to adjust the pH value of the system to 9.5, transfer the sol to a sealed container, and age it at room temperature for 24 hours to form a gel. During the aging process, apply a weak alternating electric field to the sealed container with an electric field strength of 5-10 V / cm and a frequency of 50-100 Hz; S3: The gel was placed in a vacuum drying oven and dried at 60°C and a vacuum degree of 0.08 MPa for 12 hours to obtain a dry gel; S4: pre-calcining the dry gel in a muffle furnace, heating the temperature from room temperature to 350°C at a rate of 3°C / min, and keeping the temperature at 350°C for 2 hours; S5: After the pre-calcination is completed, the temperature is further increased to 1000°C at a heating rate of 5°C / min, and kept at 1000°C for 5 hours to perform the main calcination to obtain high-strength η-alumina.

2. The method for preparing high-strength η-alumina according to claim 1, wherein: In step S1, the mass ratio of the aluminum isopropoxide, anhydrous ethanol and deionized water is 1-1.2:3.945:0.2, the deionized water droplet addition rate is controlled at 2-3 drops / second, and stirring is continued during the droplet addition process until fully dissolved. The stirring speed is 200 r / min, and the reaction time after full dissolution is 3 hours.

3. The method for preparing high-strength η-alumina according to claim 2, wherein: During the stirring process of step S1 , a magnetic stirrer is used in combination with ultrasonic-assisted dispersion technology for stirring.

4. The method for preparing high-strength η-alumina according to claim 1, wherein: In step S2, the concentrated ammonia solution is added at a rate of 1-2 drops / second, and stirring is continued for 1 hour after the addition is completed.

5. The method for preparing high-strength η-alumina according to claim 1, wherein: During the drying process of step S3, a dynamic vacuum drying method is adopted, and the vacuum degree is regularly changed, periodically varying between 0.07-0.09 MPa, with each cycle lasting 2 hours.

6. The method for preparing high-strength η-alumina according to claim 1, wherein: During the pre-calcination process of step S4, a gas circulation device is provided inside the muffle furnace to circulate the gas in the furnace at a flow rate of 0.5 to 1 L / min.

7. The method for preparing high-strength η-alumina according to claim 1, wherein: During the main calcination process in step S5, an appropriate amount of inert gas is introduced into the muffle furnace, and the gas flow rate is controlled at 10 to 20 mL / min.

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