A kind of nano-strip aluminum oxide and its preparation method and application

Abstract

The present invention discloses a strip-shaped aluminum oxide, and its preparation method and application. The preparation method of a nano-strip-shaped aluminum oxide of the present invention comprises the following steps: mixing an aqueous solution of aluminum sulfate 18hydrate and an aqueous solution of sodium hydroxide to generate aluminum hydroxide; placing the mixed solution into a hydrothermal reactor for high-temperature hydrothermal reaction; and calcining at 1000-1200°C under atmospheric atmosphere to obtain nano-strip-shaped aluminum oxide. The nano-alumina prepared by the present invention is in the form of long strips, with a uniform shape and high purity. The particle size is mainly concentrated in the range of 50.75nm to 91.28nm, and has a larger specific surface area. When used as a thermal conductive filler in the preparation of thermal conductive ink, the long strip-shaped structural feature can play a better connecting role, and the thermal conductive path is shorter, so it is expected that the product will have a better thermal conductive effect.

Description

Technical Field

[0001] The invention relates to nano strip aluminum oxide and a preparation method and application thereof. Background Art

[0002] Thermally conductive electronic inks primarily provide excellent heat dissipation for products, and they have broad application prospects in the microelectronics field. As a key branch of functional inks, thermally conductive electronic inks not only serve as packaging and decorative materials but also significantly enhance product heat dissipation through their unique composition and preparation methods.

[0003] Nanoalumina's role in thermally conductive electronic inks is to improve the ink's insulation and thermal conductivity. As a multifunctional nanomaterial, nanoalumina demonstrates unique properties and potential applications in a wide range of fields. In thermally conductive electronic inks, the addition of nanoalumina significantly improves the ink's insulation and thermal conductivity. Specifically, the addition of nanoalumina forms a thermally conductive network, significantly enhancing the ink's thermal conductivity. Furthermore, due to its excellent electrical insulation and stability, nanoalumina's addition significantly enhances the ink's insulation performance, ensuring the safe and stable operation of electronic devices.

[0004] In the existing alumina preparation technology, the preparation process is complicated, the particle size distribution of the obtained nano-alumina is not concentrated, and the shape of the nano-alumina is irregular or mostly granular. When it is used to prepare thermally conductive electronic ink, its thermal conductivity is insufficient, making the quality of the electronic ink not outstanding enough. Summary of the Invention

[0005] In view of this, the main technical problem solved by the present invention is to prepare a nano-strip aluminum oxide with better thermal conductivity, high purity and concentrated particle size distribution.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for preparing nano-strip aluminum oxide comprises the following steps:

[0008] An aqueous solution of aluminum sulfate 18hydrate and an aqueous solution of sodium hydroxide are mixed to react to generate aluminum hydroxide;

[0009] placing the mixed solution into a hydrothermal reactor for high-temperature hydrothermal reaction;

[0010] The nano-strip aluminum oxide is obtained by calcining at 1000-1200° C. in an atmospheric atmosphere.

[0011] In the present invention, the molar ratio of aluminum sulfate 18hydrate to sodium hydroxide in the aqueous solution of aluminum sulfate 18hydrate and the aqueous solution of sodium hydroxide is 1:3.

[0012] During the mixing process of the two solutions, the pH value of the solution must always be maintained at 4-5. Since the aqueous solution of aluminum sulfate 18hydrate is acidic, the amount of the aqueous solution of aluminum sulfate 18hydrate added during the mixing process is kept greater than the amount of the aqueous solution of sodium hydroxide added, thereby controlling the pH value to be lower during the mixing process.

[0013] In the present invention, an aqueous solution of aluminum sulfate 18hydrate and an aqueous solution of sodium hydroxide are mixed to generate aluminum hydroxide precipitate. During the solution mixing process, the generated aluminum hydroxide is greatly affected by the pH value of the solution. Maintaining the solution to be acidic can ensure the smooth generation of aluminum hydroxide.

[0014] After the addition of the aqueous solution of aluminum sulfate 18hydrate is completed, the remaining aqueous solution of sodium hydroxide is continued to be added, and then the pH of the mixed solution is adjusted to 5.5-7.5. Within this pH value range, the aluminum hydroxide precipitate in the solution is in a very sensitive state, so that in further hydrothermal treatment, the sensitive aluminum hydroxide is recrystallized from dispersed fine grains under hydrothermal conditions, and the aluminum hydroxide crystals grow along the axial direction. Finally, during calcination, based on the shape of the aluminum hydroxide crystals, a long strip-shaped nano-alumina product is obtained, and the particle size distribution of the nano-alumina is relatively concentrated.

[0015] As a preferred embodiment of the present invention, the substance added to adjust the pH value of the mixed solution in the present invention is preferably ammonia water. Its advantage is that other impurities will not be introduced after addition. In addition, in the subsequent hydrothermal step, ammonia water will have gas overflow at high temperature, increasing the pressure in the hydrothermal reactor, and the hydrothermal efficiency is higher.

[0016] As a preferred embodiment of the present invention, the mass percentage concentration of the ammonia water is 20-23 wt%.

[0017] As a preferred embodiment of the present invention, the concentration of the aqueous solution of aluminum sulfate 18hydrate is 100g / mL, and the concentration of the aqueous solution of sodium hydroxide is 18g / mL; the volume ratio of the aqueous solution of aluminum sulfate 18hydrate to the aqueous solution of sodium hydroxide is 1:1, and the aqueous solution of aluminum sulfate 18hydrate and the aqueous solution of sodium hydroxide are mixed dropwise under stirring. The dropwise addition method is used to directly generate aluminum hydroxide precipitation. The dropwise addition speed is preferably 20-50ml / min, and the dropwise addition speed of the aqueous solution of aluminum sulfate 18hydrate is greater than the dropwise addition speed of the aqueous solution of sodium hydroxide to ensure that the pH of the mixed solution is 4-5.

[0018] As a preferred embodiment of the present invention, the temperature of the hydrothermal reactor is 120-140° C., and the hydrothermal reaction time is 2-4 hours.

[0019] As a preferred embodiment of the present invention, the calcination time of aluminum hydroxide is 1 to 3 hours.

[0020] As a preferred embodiment of the present invention, the aluminum hydroxide is filtered and washed with water before calcination, and then dried.

[0021] The nano-aluminum oxide produced by the present invention is in the form of long strips, with uniform shape and high purity. The particle size is mainly concentrated in the range of 50.75nm to 91.28nm, and it has a larger specific surface area. It is used as a thermal conductive filler in the preparation of thermal conductive ink. The long strip structural characteristics can play a better connecting role and the thermal conduction path is shorter, so it can be expected that the product has a better thermal conductivity effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is one of the SEM images of the long strip of aluminum oxide according to the preferred embodiment of the present invention;

[0023] Figure 2 This is the second SEM image of the long strip of aluminum oxide according to the preferred embodiment of the present invention;

[0024] Figure 3 This is a Malvern particle size distribution instrument test result diagram of the long strip of aluminum oxide according to the preferred embodiment of the present invention;

[0025] Figure 4 is a SEM image of the aluminum oxide of Comparative Example 1 of the present invention;

[0026] Figure 5 This is an SEM image of the aluminum oxide of Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to understand the present invention more clearly and intuitively, the present invention will be further described below with reference to the accompanying drawings.

[0028] The method for preparing nano-strip aluminum oxide of the present invention comprises the following steps:

[0029] Mixing an aqueous solution of aluminum sulfate 18hydrate and an aqueous solution of sodium hydroxide, wherein the pH of the solution during the mixing process is 4 to 5;

[0030] The mixed solution is placed in a hydrothermal reactor for high-temperature hydrothermal reaction; the hydrothermal reactor temperature is 120-140° C., and the hydrothermal reaction time is 2-4 hours; the aluminum hydroxide is filtered and washed with water, and then dried;

[0031] The nano-strip aluminum oxide is obtained by calcining at 1000-1200° C. for 1-3 hours in an atmospheric atmosphere.

[0032] After the aqueous solution of aluminum sulfate 18hydrate and the aqueous solution of sodium hydroxide are completely mixed, the pH of the mixed solution is adjusted to 5.5 to 7.5.

[0033] The substance added to adjust the pH value of the mixed solution in the present invention is preferably ammonia water. Its advantage is that it will not introduce other impurities after addition. In addition, in the subsequent hydrothermal step, ammonia water will overflow gas at high temperature, increasing the pressure in the hydrothermal reactor and making the hydrothermal efficiency higher.

[0034] The mass percentage concentration of the ammonia water is 20-23 wt %.

[0035] The volume ratio of the aqueous solution of aluminum sulfate 18hydrate to the aqueous solution of sodium hydroxide is 1:1. The aqueous solution of aluminum sulfate 18hydrate and the aqueous solution of sodium hydroxide are mixed by dropwise addition, and the dropping speed is preferably 20-50 ml / min.

[0036] Preferred Embodiments

[0037] The method for preparing aluminum oxide in this embodiment comprises the following steps:

[0038] Add deionized water to a beaker and dissolve aluminum sulfate 18hydrate into an aqueous solution with a concentration of 100 g / L. Add deionized water to a beaker and dissolve sodium hydroxide into an aqueous solution with a concentration of 18 g / L.

[0039] Add 100 ml of bottom water to a 2000 ml beaker; in the embodiment, a stirring blade is provided in the reactor, and the addition of bottom water can ensure that the aluminum sulfate 18hydrate and sodium hydroxide added dropwise can react quickly during stirring during the initial reaction;

[0040] 500ml of an aqueous solution of aluminum sulfate 18hydrate and 500ml of an aqueous solution of sodium hydroxide were taken separately, stirred, and added dropwise to a beaker. The amount of aluminum sulfate 18hydrate added was greater than the amount of sodium hydroxide added. The excess aluminum sulfate 18hydrate was added to maintain the pH of the solution between 4 and 5. A white precipitate of aluminum hydroxide formed during the dropwise mixing process. The reaction in the beaker was uniform and stable during the dropwise addition. Compared to the reaction resulting from direct addition of the two solutions, which exhibited large fluctuations and poor particle size uniformity, the slow dropwise addition yielded better control of the aluminum hydroxide particle size, resulting in uniform and concentrated particle size. The dropwise addition rate of the aluminum sulfate 18hydrate and sodium hydroxide solutions was 20-50ml / min. By ensuring that the dropwise addition rate of the aluminum sulfate 18hydrate solution was greater than that of the aluminum hydroxide solution, a pH meter was used to control the pH of the mixed solution to 4.0-5.0. After the addition of both solutions, 20-23wt% ammonia was added to adjust the pH to 5.5-7.5. The mixed solution was then placed in a hydrothermal reactor, hydroheated at 120°C for 4 hours, taken out, filtered and washed, and the filter cake obtained was dried at 105°C. The dried sample was placed in a calcining furnace and calcined at 1100°C for 2 hours in an atmospheric atmosphere to obtain strip-shaped alumina.

[0041] In this embodiment, the aluminum sulfate 18hydrate raw material is purified before use to remove trace amounts of heavy metal impurities.

[0042] The test standard for the alumina product in this embodiment is: GB / T 24487-2022;

[0043] The alumina particle size was tested by Malvern particle size distribution instrument;

[0044] The whiteness of alumina is tested by Minolta Whiteness Meter 2600d;

[0045] Alumina metal was tested using a Shimadzu atomic absorption furnace.

[0046] The purity of the prepared aluminum oxide was tested, and the purity of the aluminum oxide reached 99.78%. The test results are shown in Table 1.

[0047] Table 1

[0048]

[0049] In addition, the aluminum oxide was scanned by electron microscope, and the results were as follows: Figure 1-2 As shown, the particle size of the aluminum oxide prepared in this embodiment is close to the result of the particle size distribution instrument test.

[0050] In this embodiment, the aluminum hydroxide generated by the mixed solution undergoes hydrothermal treatment. During this process, the aluminum hydroxide generated by the mixed solution grows again under the high-temperature hydrothermal reaction conditions to remove the ions adsorbed on the surface. At the same time, the aluminum hydroxide grows axially during the re-growth process, and the crystals grow again into strip-shaped aluminum oxide with uniform particle size and shape. The morphology and particle size of the aluminum oxide obtained by calcining the aluminum hydroxide are also directly affected, and the quality is improved. The aluminum oxide product obtained by calcining is tested by a Malvern particle size distribution instrument, and it is found that the particle size of the aluminum oxide is mainly concentrated in the range of 50.75nm to 91.28nm (the results are shown in FIG. Figure 3 shown).

[0051] Comparative Example 1

[0052] The difference between this embodiment and the preferred embodiment is that no hydrothermal treatment is performed. The specific preparation process is as follows:

[0053] Add deionized water to aluminum sulfate 18hydrate in a beaker to dissolve it into an aqueous solution with a concentration of 100 g / L. Add deionized water to sodium hydroxide in a small cup to dissolve it into an aqueous solution with a concentration of 18 g / L.

[0054] Add 100 ml of bottom water to a 2000 ml beaker; the reactor is equipped with a stirring blade. The addition of bottom water can ensure that the aluminum sulfate 18hydrate and sodium hydroxide added dropwise can fully react during the initial reaction.

[0055] Take 500ml of an aqueous solution of aluminum sulfate 18hydrate and 500ml of an aqueous solution of sodium hydroxide, respectively, start stirring, and add the aqueous solution of aluminum sulfate 18hydrate and the aqueous solution of sodium hydroxide dropwise to a beaker. During this process, ensure that the amount of the aqueous solution of aluminum sulfate 18hydrate added is greater than the amount of the aqueous solution of sodium hydroxide added. The excess amount of aluminum sulfate 18hydrate is added to control the pH value of the solution to 4-5. During the dropwise mixing process, a white precipitate of aluminum hydroxide is formed. The aqueous solution of aluminum sulfate 18hydrate and the aqueous solution of sodium hydroxide are added at a rate of 20-50ml / min. By controlling the dropwise addition rate of the aqueous solution of aluminum sulfate 18hydrate to be greater than the dropwise addition rate of the aqueous solution of aluminum hydroxide, the pH of the mixed solution can be controlled to 4.0-5.0 with a pH meter. After the addition of the two solutions, 20-23wt% ammonia water is added to adjust the pH to 5.5-7.5. The filter cake obtained after suction filtration and water washing is dried at 105°C. The dried sample is directly placed in a calciner and calcined at 1100°C in an atmosphere for 2 hours.

[0056] Aluminum sulfate 18hydrate reacts with sodium hydroxide to form aluminum hydroxide. The aluminum hydroxide has not been hydrothermally treated, so the aluminum hydroxide is gradually generated during the dropwise addition process. Without hydrothermal reaction and recrystallization, the aluminum hydroxide aggregates into agglomerates, and the structural quality of the aluminum oxide obtained by calcination is affected. The aluminum oxide obtained in Comparative Example 1 was scanned by electron microscope, and the results are as follows: Figure 4 As shown, it can be seen that the alumina prepared without hydrothermal reaction aggregates into agglomerates.

[0057] Comparative Example 2

[0058] The difference between this embodiment and the preferred embodiment is that the pH of the solution is not controlled. The specific preparation process is as follows:

[0059] Add deionized water to a beaker and dissolve aluminum sulfate 18hydrate into an aqueous solution with a concentration of 100 g / L. Add deionized water to a beaker and dissolve sodium hydroxide into an aqueous solution with a concentration of 18 g / L.

[0060] Add 100 ml of bottom water to a 2000 ml beaker; in the embodiment, a stirring blade is provided in the reactor, and the addition of bottom water can ensure that the aluminum sulfate 18hydrate and sodium hydroxide added dropwise can react quickly during stirring during the initial reaction;

[0061] Separately, take 500ml of an aqueous solution of aluminum sulfate 18hydrate and 500ml of an aqueous solution of sodium hydroxide, start stirring, and add the aqueous solution of aluminum sulfate 18hydrate and the aqueous solution of sodium hydroxide dropwise into a beaker. During this process, the aqueous solution of aluminum sulfate 18hydrate and the aqueous solution of sodium hydroxide are added in equal amounts. A white precipitate of aluminum hydroxide is generated during the gradual addition and mixing. The dripping rate of the aqueous solution of aluminum sulfate 18hydrate and the aqueous solution of sodium hydroxide is 40ml / min. After the two solutions are added, the mixed solution is placed in a hydrothermal reactor, hydrothermally heated at 120°C for 4h, then removed, filtered, washed with water, and the filter cake obtained is dried at 105°C. The dried sample is placed in a calcining furnace and calcined at 1100°C in an atmospheric atmosphere for 2h to obtain strip-shaped alumina.

[0062] In this comparative example 2, aluminum sulfate 18hydrate and sodium hydroxide react to form aluminum hydroxide. The pH value of the mixed solution is not controlled during and after the addition. Therefore, aluminum hydroxide is gradually generated during the addition process. Aluminum hydroxide can be recrystallized into granular form during the hydrothermal process, and the aluminum oxide obtained by calcination is also granular. The aluminum oxide obtained in comparative example 2 was scanned by electron microscope, and the results are as follows: Figure 5 As shown, it can be seen that although recrystallization can be formed without agglomeration during hydrothermal treatment without adjusting the pH, and the particle size of aluminum oxide is relatively concentrated, aluminum hydroxide does not have the ability to grow axially during the hydrothermal reaction, and the shape of aluminum oxide does not have a specific strip structure.

[0063] The above description of the embodiments is intended to facilitate understanding and application of the present invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the embodiments described herein, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing nano-strip aluminum oxide, characterized in that: The steps include: An aqueous solution of aluminum sulfate 18hydrate and an aqueous solution of sodium hydroxide are mixed to react to generate aluminum hydroxide; placing the mixed solution into a hydrothermal reactor for high-temperature hydrothermal reaction; After calcination at 1000-1200℃ in atmospheric atmosphere, nano-strip alumina is obtained; During the mixing process of the aqueous solution of aluminum sulfate 18hydrate and the aqueous solution of sodium hydroxide, the amount of the aqueous solution of aluminum sulfate 18hydrate added is kept greater than the amount of the aqueous solution of sodium hydroxide added so that the pH value of the solution is 4-5; After the addition of the aqueous solution of aluminum sulfate 18hydrate is completed, the remaining aqueous solution of sodium hydroxide is added and the pH of the mixed solution is adjusted to 5.5-7.5; The substance added to adjust the pH value of the mixed solution is ammonia water; The concentration of the aqueous solution of aluminum sulfate 18hydrate is 100 g / L, and the concentration of the aqueous solution of sodium hydroxide is 18 g / L; The volume ratio of the aqueous solution of aluminum sulfate 18hydrate to the aqueous solution of sodium hydroxide is 1:1; The aqueous solution of aluminum sulfate 18hydrate and the aqueous solution of sodium hydroxide are mixed by dropwise addition at a rate of 20-50 ml / min; The hydrothermal reaction vessel was heated to 120° C. and the reaction time was 4 hours.

2. The method for preparing nano-strip aluminum oxide according to claim 1, wherein: The mass percentage concentration of the ammonia water is 20-23 wt %.

3. The method for preparing nano-strip aluminum oxide according to claim 1, wherein: The calcination time of aluminum hydroxide is 1 to 3 hours.

4. The method for preparing nano-strip aluminum oxide according to claim 1, wherein: Aluminum hydroxide is filtered and washed with water before calcination, and then dried.

5. Strip-shaped aluminum oxide obtained according to the preparation method according to any one of claims 1 to 4.

6. Use of the strip-shaped aluminum oxide prepared according to the preparation method according to any one of claims 1 to 4 as a thermally conductive filler in the preparation of thermally conductive ink.

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