Method for preparing needle-shaped aluminum oxide by soft template method

Abstract

The invention discloses a method for preparing needle-shaped aluminum oxide by a soft template method. The method comprises the following steps: providing a soluble aluminum salt solution containing a template agent and an alkaline solution; dropwise adding an alkaline solution into the soluble aluminum salt solution until the pH value of the mixed solution is 7.0-10.0, and stirring to obtain a uniformly distributed mixed solution; carrying out heat preservation reaction on the mixed solution at 70-90 DEG C, then carrying out solid-liquid separation, drying and grinding, and carrying out primary ball milling to obtain a precursor; and pre-calcining the precursor at 400-600 DEG C, carrying out secondary ball milling, and calcining at 1100-1200 DEG C to obtain the needle-like aluminum oxide. According to the preparation method disclosed by the invention, the preparation of large-particle needle-like aluminum oxide can be realized at low temperature and normal pressure.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum oxide preparation, and in particular relates to a method for preparing needle-shaped aluminum oxide using a soft template method. Background Art

[0002] Needle-shaped alumina is a high-performance inorganic fiber material with many remarkable properties, such as high temperature resistance, wear resistance, oxidation resistance, low thermal conductivity, low thermal expansion coefficient, good seismic resistance, high modulus, high plasticity, high toughness, high strength, high insulation and high dielectric constant, etc. These properties make needle-shaped alumina widely used in many fields.

[0003] Large-particle needle-shaped alumina (with a diameter of not less than 2 μm and a length of not less than 8 μm) has more significant advantages in mechanical properties and can be used in insulation materials, fiber protection, reinforcement materials, electronic devices and other fields.

[0004] However, the current preparation processes for needle-shaped alumina are mostly for small-particle fibrous alumina, while there is a lack of reports on the preparation process for large-particle needle-shaped alumina. Summary of the invention

[0005] In view of this, the primary purpose of the present invention is to provide a method for preparing needle-shaped alumina by a soft template method, by which large-particle needle-shaped alumina can be prepared at low temperature and normal pressure.

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

[0007] The present invention first provides a method for preparing needle-shaped aluminum oxide using a soft template method, comprising the following steps:

[0008] Providing a soluble aluminum salt solution and an alkaline solution, wherein the soluble aluminum salt solution contains a template;

[0009] Adding alkaline solution dropwise to the soluble aluminum salt solution until the pH of the mixed solution is 7.0-10.0, and stirring until the mixed solution is evenly distributed;

[0010] The mixed solution is kept at 70-90° C. for reaction, then solid-liquid separation and drying and grinding are performed, and a precursor is obtained by ball milling once;

[0011] The precursor is pre-calcined at 400-600° C., ball-milled for a second time, and then calcined at 1100-1200° C. to obtain needle-shaped aluminum oxide.

[0012] In a further embodiment, the concentration of the soluble aluminum salt solution is 0.2 to 2 mol / L.

[0013] In a further embodiment, the soluble aluminum salt is at least one of aluminum chloride, aluminum nitrate, and ammonium aluminum sulfate.

[0014] In a further embodiment, the amount of the template added is 0.5 wt% to 3 wt% based on the soluble aluminum salt.

[0015] In a further embodiment, the template agent is hexadecyltrimethylammonium bromide, PEG2000 or P123.

[0016] In a further embodiment, the pH of the alkaline solution is between 11 and 12.

[0017] In a further embodiment, the alkaline solution is an aqueous ammonia solution, and the concentration of the aqueous ammonia solution is 1-5 mol / L.

[0018] In a further embodiment, the dropping speed of the alkaline solution does not exceed 5 ml / min.

[0019] In a further embodiment, in the first ball milling and the second ball milling steps, the ball-to-material ratio is (8-12):1, the ball milling speed is 400-600 rpm, and the ball milling time is 6-12 hours.

[0020] In a further embodiment, the particle size of the precursor powder does not exceed 200 mesh.

[0021] In a further embodiment, the needle-shaped aluminum oxide has a diameter of 2 to 5 μm and a length of 8 to 15 μm.

[0022] Beneficial effects of the present invention:

[0023] The method for preparing needle-shaped alumina in the present invention optimizes the raw material matching process, especially adopts a ball milling process to release stress and control size for the precursor, and adopts a pre-calcination process combined with secondary ball milling before calcination to reduce stress and reduce the generation of pores, thereby achieving the preparation of large-particle needle-shaped alumina at low temperature and normal pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the scanning electron microscope (SEM) characterization result of the needle-shaped alumina prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] Embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0027] The invention provides a method for preparing needle-shaped alumina by a soft template method. The method realizes the preparation of large-particle needle-shaped alumina at low temperature and normal pressure. The diameter of the prepared needle-shaped alumina particles is 2-5 μm and the length is between 8-15 μm.

[0028] The main steps of the preparation method of the present invention are as follows:

[0029] Solution preparation

[0030] In the present invention, firstly, a soluble aluminum salt solution and an alkaline solution are prepared separately.

[0031] The soluble aluminum salt solution is formed by dissolving the soluble aluminum salt in deionized water, and a certain amount of template agent is added to the solution.

[0032] Specifically, the "soluble aluminum salt" described herein mainly refers to an inorganic salt of metallic aluminum and has a certain solubility in water. Specific examples include aluminum chloride, aluminum nitrate, ammonium aluminum sulfate, etc., but are not limited thereto.

[0033] The "template" described herein refers to a surfactant, which is used as a soft template to prepare needle-shaped alumina by utilizing the ordered aggregates formed by weak interactions between surfactant molecules. These templates can guide the distribution of alumina through a specific structural interface, thereby obtaining alumina with a needle-shaped structure. Specifically, different surfactants have different groups, and the same group molecules are neatly arranged inside the solution. Surfactants generally have two different groups, one is hydrophilic and the other is non-hydrophilic, which can change the morphology of the precursor by affecting the balance of the aqueous solution. In a suitable solution system, the soft template becomes a micelle and forms a micelle complex by interacting with the precursor (such as hydrogen bonds, hydrophilic-hydrophobic interactions, electrostatic interactions, etc.), and then the final product is prepared by subsequent treatment. In the present invention, specific examples of the surfactants include CTAB, PEG2000 or P123, but are not limited to these.

[0034] In the present invention, the concentration of the soluble aluminum salt solution is preferably 0.2-2 mol / L, for example, it can be any concentration of 0.2 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.7 mol / L, 2 mol / L. The amount of the template added can be adjusted according to the amount of the soluble aluminum salt. When the amount of the soluble aluminum salt is low, the amount of the template added is reduced accordingly, and when the amount of the soluble aluminum salt is high, the amount of the template added is also increased accordingly. In some preferred embodiments of the present invention, the amount of the template added is 0.5 wt%-3 wt% based on the soluble aluminum salt, for example, it can be any value of 0.5 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, 3 wt%.

[0035] In the present invention, the alkaline solution refers to a solution with a pH of 11 to 12 and capable of undergoing a precipitation reaction with a soluble aluminum salt to generate aluminum hydroxide. In some specific embodiments of the present invention, the alkaline solution is an aqueous ammonia solution, and the concentration of the aqueous ammonia solution is adjusted according to the concentration of the soluble aluminum salt. In some specific implementation cases, the concentration of the aqueous ammonia solution is 1 to 5 mol / L, for example, any value of 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L or 5 mol / L.

[0036] Add dropwise

[0037] Specifically, an alkaline solution is added dropwise to the soluble aluminum salt aqueous solution until the pH of the mixed solution is 7.0-10.0, and then the mixed solution is stirred until the mixed solution is evenly distributed.

[0038] In some specific embodiments of the present invention, a precipitation reaction is carried out by dropwise addition of a soluble aluminum salt and ammonia water: Al 3+ +3NH3·H2O=Al(OH)3↓+3NH4 + , generating an aluminum hydroxide precursor.

[0039] In the present invention, the pH of the mixed solution is adjusted to 7.0-10.0, which can ensure obvious precipitation and form a regular needle-shaped aluminum oxide morphology.

[0040] Furthermore, in the present invention, the dropping speed of the alkaline solution should not be too fast, because too fast dropping speed can easily lead to uneven precipitation. Therefore, preferably, the dropping speed of the alkaline solution does not exceed 5 ml / min.

[0041] reaction

[0042] Specifically, the mixed solution is kept at 70-90°C for reaction, and after the reaction is completed, it is cooled to room temperature. The precursor is obtained by precipitation through the kept reaction at this temperature. The specific kept reaction time can be carried out as needed. Preferably, in some specific embodiments of the present invention, the kept reaction time is 3-4 hours.

[0043] Centrifugal drying

[0044] The mixed solution after the reaction is centrifuged at least once with deionized water and ethanol respectively. Preferably, it is centrifuged three times with deionized water and then three times with ethanol to achieve solid-liquid separation, and the precipitate at the bottom after centrifugation is dried and ground to obtain a precursor.

[0045] Among them, centrifugation, drying, etc. are operations well known to those skilled in the art. In some specific embodiments of the present invention, the centrifugal speed is 6000-8000 rpm, the time is 3-6 min; the drying temperature is 70-90° C., and the time is 10-14 h.

[0046] One ball mill

[0047] In the present invention, the precursor is subjected to a ball milling to achieve the purpose of releasing stress and controlling size. Specifically, the ball milling used in the present invention is a wet ball milling, and the dried precursor is added to a ball milling jar for ball milling, wherein the ball-to-material ratio is preferably (8-12):1, the ball milling medium is anhydrous ethanol, the rotation speed is 400-600rpm, and the time is 6-12h;

[0048] Finally, the ball-milled precursor is sieved through a 200-mesh sieve to facilitate uniform heating during the subsequent calcination process and improve the quality of the product.

[0049] Calcination

[0050] Specifically, the ball-milled precursor is first pre-calcined at 400-600°C for 2-4 hours and then ball-milled for the second time, and the second ball-milling process is the same as the first ball-milling process; and then calcined at 1100-1200°C for 2-4 hours to obtain alumina crystals. Pre-calcination combined with secondary ball-milling can further reduce stress and pores to control the acquisition of large-particle needle-shaped alumina.

[0051] The present invention is described below by means of specific examples. It should be noted that the following specific examples are only for illustrative purposes and do not limit the scope of the present invention in any way. In addition, unless otherwise specified, methods without specific conditions or steps are conventional methods, and the reagents and materials used can be obtained from commercial channels.

[0052] Example 1

[0053] This embodiment provides a method for preparing needle-shaped aluminum oxide using a soft template method, and the specific steps are as follows:

[0054] (1) Solution preparation: Weigh 21.73 g of aluminum chloride hexahydrate and add it to 300 ml of deionized water. Stir magnetically at 330 r / min for 1 h. After it is completely dissolved, add 0.6 g of hexadecyltrimethylammonium bromide (CTAB) and stir evenly to make it completely dissolved. At the same time, prepare 400 ml of 1 mol / L ammonia solution.

[0055] (2) Under stirring conditions, add aqueous ammonia solution to the aluminum chloride solution at a rate not exceeding 5 ml / min; use a pH meter to monitor the pH change of the mixed solution in real time until the mixed solution maintains pH = 7.0 to 10.0 for a long time, then stop stirring until the mixed solution is evenly distributed.

[0056] (3) The mixed solution was transferred to a three-necked flask and kept at 70°C for 4 h. After the reaction was completed, the mixture was cooled to room temperature.

[0057] (4) The reaction mixture was placed in a centrifuge tube, centrifuged at 8000 rpm for 5 min, centrifuged three times with deionized water, ultrasonicated for 30 min, and centrifuged three times with ethanol. The precipitate at the bottom after centrifugation was dried, the oven temperature was adjusted to 80 ° C, and dried for 12 h, and then ground to obtain the precursor.

[0058] (5) The precursor was placed in a ball mill and ball milled once. The mass ratio of the precursor to the ball milling ball was 1 / 10. Anhydrous ethanol was added and ball milled at 500 rpm for 6 h. The precursor powder was then sieved through a 200-mesh sieve.

[0059] (6) The precursor after the first ball milling is placed in an alumina crucible, pre-calcined at 500° C. for 2 h in a muffle furnace, and then ball milled for the second time according to step (5). The ground powder is calcined at 1100° C. for 2 h to obtain needle-shaped alumina crystals.

[0060] Figure 1 The SEM characterization results of the aluminum oxide in this example are shown. It can be seen that the prepared aluminum oxide is needle-shaped, with a length of about 10 μm and a diameter of about 3 μm, and is a large-particle needle-shaped aluminum oxide.

[0061] Example 2

[0062] This embodiment provides a method for preparing needle-shaped aluminum oxide using a soft template method, and the specific steps are as follows:

[0063] (1) Solution preparation: Weigh 33.75 g aluminum nitrate nonahydrate into 300 ml deionized water and stir magnetically at 330 r / min for 1 h. After the solution is completely dissolved, add 0.6 g of soft template P123 and stir evenly to dissolve it completely. At the same time, prepare 200 ml of 2 mol / L ammonia solution.

[0064] (2) Under stirring conditions, add aqueous ammonia solution to the aluminum nitrate solution at a rate not exceeding 5 ml / min; simultaneously, use a pH meter to monitor the pH change of the mixed solution in real time until the mixed solution maintains a pH of 7.0 to 10.0 for a long time, then stop stirring to obtain a uniformly distributed mixed solution.

[0065] (3) The mixed solution was transferred to a three-necked flask and kept at 70°C for 4 h. After the reaction was completed, the mixture was cooled to room temperature.

[0066] (4) The reaction solution was placed in a centrifuge tube, centrifuged at 8000 rpm for 5 min, centrifuged three times with deionized water, ultrasonicated for 30 min, and centrifuged three times with ethanol. The precipitate at the bottom after centrifugation was dried, the oven temperature was adjusted to 80 ° C, and dried for 12 h, and the precursor was ground.

[0067] (5) The precursor was placed in a ball mill for ball milling, with the mass ratio of the precursor to the ball milling ball being 1 / 10. Anhydrous ethanol was added and the ball milling was performed at 400 rpm for 8 h. The precursor powder was dried and passed through a 200-mesh sieve.

[0068] (6) The ball-milled precursor is placed in an alumina crucible, pre-calcined at 400° C. for 4 h in a muffle furnace, and then ball-milled for the second time according to step (5). The ground powder is calcined at 1150° C. for 4 h to obtain needle-shaped alumina crystals.

[0069] In this embodiment, the diameter of the needle-shaped aluminum oxide is about 4 μm, and the length is about 12 μm.

[0070] Example 3

[0071] This embodiment provides a method for preparing needle-shaped aluminum oxide using a soft template method, and the specific steps are as follows:

[0072] (1) Solution preparation: Weigh 14.49 g aluminum chloride hexahydrate and add it to 300 ml deionized water. Stir magnetically at 330 r / min for 1 h. After it is completely dissolved, add 0.07 g PEG2000 and stir evenly to dissolve it completely. At the same time, prepare 400 ml of 1 mol / L ammonia solution.

[0073] (2) Under stirring conditions, add aqueous ammonia solution to the aluminum chloride solution at a rate not exceeding 5 ml / min; use a pH meter to monitor the pH change of the mixed solution in real time until the mixed solution maintains pH = 7.0 to 10.0 for a long time, then stop stirring and stir evenly until the solution becomes clear.

[0074] (3) The mixed solution was transferred to a three-necked flask and kept at 80°C for 3.5 hours. After the reaction was completed, the mixture was cooled to room temperature.

[0075] (4) The reaction solution was placed in a centrifuge tube, centrifuged at 6000 rpm for 4 min, centrifuged three times with deionized water, ultrasonicated for 30 min, and centrifuged three times with ethanol. The precipitate at the bottom after centrifugation was dried, the oven temperature was adjusted to 80 ° C, and dried for 12 h, and the precursor was ground.

[0076] (5) The precursor was placed in a ball mill for ball milling, with the mass ratio of the precursor to the ball milling ball being 1 / 10, and anhydrous ethanol was added. After ball milling at 600 rpm for 10 h, the precursor powder was sieved through a 200-mesh sieve.

[0077] (6) The ball-milled precursor is placed in an alumina crucible, pre-calcined at 600° C. for 3 h in a muffle furnace, and then subjected to secondary ball milling according to step (5). The ground powder is calcined at 1200° C. for 3 h to obtain needle-shaped alumina crystals.

[0078] In this embodiment, the diameter of the needle-shaped aluminum oxide is about 2 μm, and the length is about 8 μm.

[0079] Example 4

[0080] This embodiment provides a method for preparing needle-shaped aluminum oxide using a soft template method, and the specific steps are as follows:

[0081] (1) Solution preparation: 142.29 g of ammonium aluminum sulfate was weighed and added to 300 ml of deionized water. The solution was stirred at 330 r / min for 1 h. After the solution was completely dissolved, 4.27 g of hexadecyltrimethylammonium bromide was added and stirred evenly to completely dissolve the solution. Meanwhile, 400 ml of 5 mol / L ammonia solution was prepared.

[0082] (2) Under stirring conditions, add aqueous ammonia solution to the aluminum chloride solution at a rate not exceeding 5 ml / min; use a pH meter to monitor the pH change of the mixed solution in real time until the mixed solution maintains pH = 7.0 to 10.0 for a long time, then stop stirring and stir evenly until the solution becomes clear.

[0083] (3) The mixed solution was transferred to a three-necked flask and kept at 80°C for 3.5 hours. After the reaction was completed, the mixture was cooled to room temperature.

[0084] (4) The reaction solution was placed in a centrifuge tube, centrifuged at 7000 rpm for 4 min, centrifuged three times with deionized water, ultrasonicated for 30 min, and centrifuged three times with ethanol. The precipitate at the bottom after centrifugation was dried, the oven temperature was adjusted to 80 ° C, and dried for 12 h, and then ground to obtain a precursor.

[0085] (5) The precursor was placed in a ball mill for ball milling, with the mass ratio of the precursor to the ball milling ball being 1 / 10, and anhydrous ethanol was added. After ball milling at 500 rpm for 12 h, the precursor powder was sieved through a 200-mesh sieve.

[0086] (6) The ball-milled precursor is placed in an alumina crucible, pre-calcined at 500° C. for 2 h in a muffle furnace, and then ball-milled for the second time according to step (5). The ground powder is calcined at 1100° C. for 3 h to obtain needle-shaped alumina crystals.

[0087] In this embodiment, the diameter of the needle-shaped aluminum oxide is 5 μm and the length is 15 μm.

[0088] Comparative Example 1

[0089] This comparative example adopts the same implementation as Example 1, except that the precursor is not ball-milled once. Other steps and process conditions are the same as those in Example 1.

[0090] The aluminum oxide obtained in this comparative example is needle-shaped, but its diameter and length are both in the nanometer level, not in the micrometer level.

[0091] Comparative Example 2

[0092] This comparative example adopts the same implementation as Example 1, except that no pre-calcination and secondary ball milling are performed, that is, the precursor powder after the primary ball milling is directly calcined at 1100° C. for 2 h. Other steps and process conditions are the same as those in Example 1.

[0093] The aluminum oxide obtained in this comparative example is needle-shaped, but its diameter and length are both in the nanometer level, not in the micrometer level, and there are a small amount of pores in the crystal.

[0094] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0095] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing needle-shaped aluminum oxide by a soft template method, characterized in that: The following steps are involved: Providing a soluble aluminum salt solution and an alkaline solution, wherein the soluble aluminum salt solution contains a template; Adding alkaline solution dropwise to the soluble aluminum salt solution until the pH of the mixed solution is 7.0-10.0, and stirring until the mixed solution is evenly distributed; The mixed solution is kept at 70-90° C. for reaction, then solid-liquid separation and drying and grinding are performed, and a precursor is obtained by ball milling once; The precursor is pre-calcined at 400-600° C., ball-milled for a second time, and then calcined at 1100-1200° C. to obtain needle-shaped aluminum oxide.

2. The method for preparing needle-shaped aluminum oxide by a soft template method according to claim 1, characterized in that: The concentration of the soluble aluminum salt solution is 0.2-2 mol / L.

3. The method for preparing needle-shaped aluminum oxide by a soft template method according to claim 1, characterized in that: The soluble aluminum salt is at least one of aluminum chloride, aluminum nitrate, and ammonium aluminum sulfate.

4. The method for preparing needle-shaped aluminum oxide by a soft template method according to claim 1, characterized in that: Based on the soluble aluminum salt, the added amount of the template is 0.5wt% to 3wt%.

5. The method for preparing needle-shaped aluminum oxide by a soft template method according to claim 1, characterized in that: The template agent is hexadecyltrimethylammonium bromide, PEG2000 or P123.

6. The method for preparing needle-shaped aluminum oxide by a soft template method according to claim 1, characterized in that: The pH of the alkaline solution is between 11 and 12; Preferably, the alkaline solution is an aqueous ammonia solution, and the concentration of the aqueous ammonia solution is 1-5 mol / L.

7. The method for preparing needle-shaped aluminum oxide by a soft template method according to claim 1, characterized in that: The dropping speed of the alkaline solution does not exceed 5 ml / min.

8. The method for preparing needle-shaped aluminum oxide by a soft template method according to claim 1, characterized in that: In the first ball milling and the second ball milling steps, the ball-to-material ratio is (8-12):1, the ball milling speed is 400-600 rpm, and the ball milling time is 6-12 hours.

9. The method for preparing needle-shaped aluminum oxide by a soft template method according to claim 1, characterized in that: The particle size of the precursor powder does not exceed 200 meshes.

10. The method for preparing needle-shaped aluminum oxide by a soft template method according to claim 1, characterized in that: The diameter of the needle-shaped aluminum oxide is 2 to 5 μm, and the length is 8 to 15 μm.

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