Preparation method of monodisperse spherical alumina powder with uniform granularity

Abstract

The invention relates to a preparation method of monodisperse spherical alumina powder with uniform granularity. The preparation method comprises the following steps: dissolving and stirring an aluminum source, a precipitator and a dispersing agent in ultrapure water to prepare an aluminum oxide precursor solution; transferring the prepared aluminum oxide precursor solution into a hydrothermal reaction kettle, carrying out heating reaction, after the hydrothermal reaction is finished, naturally cooling to room temperature, alternately and respectively washing with ultrapure water and ethanol, and drying to obtain aluminum oxide precursor powder; and sintering the prepared aluminum oxide precursor powder in a muffle furnace in an air atmosphere to obtain the spherical aluminum oxide powder. The hydrothermal method is adopted to react in a high-temperature and high-pressure environment, so that the reaction uniformity is improved, and the spherical aluminum oxide precursor with uniform granularity and consistent morphology is obtained. The bending strength of the obtained ceramic material is remarkably improved, and the highest bending strength reaches 245MPa. The method has wide application prospects in the fields of heat-conducting composite materials, integrated circuit films, substrate materials, 3D printing materials, precision polishing materials and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of ceramic powder preparation. Specifically, it relates to a production process of monodisperse and uniform-sized spherical alumina. In particular, a method for preparing monodisperse and uniform-sized spherical alumina powder is proposed. Background Art

[0002] As an important raw material for structural ceramics, functional ceramics, and electronic ceramics, alumina powder has broad application prospects in the engineering field. With the continuous advancement of new material research and development, the requirements for material properties are increasing day by day. As the basic raw material for various alumina materials, the performance standards of alumina powder have also been improved accordingly. Among them, monodisperse and uniform-sized spherical alumina powder, with its unique performance advantages, further expands the boundaries of high-end applications. In the field of structural ceramics, spherical α-alumina powder, with its high purity, densification characteristics, and controllable microtopography, provides a key material basis for the preparation of high-performance alumina ceramics. By using monodisperse and narrow particle size distribution spherical powder, uniform packing and low-defect forming of ceramic green bodies can be achieved. After high-temperature sintering, a fine microstructure with uniform grain size and clean grain boundaries can be obtained. This structural advantage enables pure alumina ceramics to exhibit excellent mechanical properties. Therefore, the preparation of dispersed and uniform-sized spherical α-alumina powder has become the key to achieving high-performance ceramics. However, the currently prepared alumina powder still faces problems such as uneven particle size distribution and obvious agglomeration phenomena, which directly affect the forming process and final properties of ceramics. Uneven particle size leads to uneven packing density of the powder, which in turn affects the densification process of the ceramic green body. The agglomeration phenomenon causes particles to adhere to each other, forming larger agglomerates, which not only reduces the fluidity of the powder but also limits the densification degree during the ceramic sintering process. In addition, the presence of agglomerated particles will form larger grains during the sintering process, resulting in a decrease in the mechanical properties of alumina ceramics. For example, the literature "Improving the flexural-strength-to-density ratio in alumina ceramics with the addition of silicon nitride" (Ceramics International, 2021; 47(3): 3964-3971) reported that the powder with uneven particle size and agglomeration phenomenon has a flexural strength of only 83.8 MPa for its ceramics. To overcome these problems, it is necessary to optimize the powder preparation process, especially to conduct in-depth research and improvement in particle size control and deagglomeration to improve the overall performance of ceramic materials and meet the requirements of high-end applications.

[0003] At present, there are various methods for synthesizing spherical alumina powder, including spray pyrolysis, homogeneous precipitation method, hydrothermal method, high-energy ball milling method, etc. For example, the literature "High-surface-area corundum by mechanochemicallyinduced phase transformation of boehmite" (Science, 2019; 366(6464): 485-489) reported that high-purity spherical nano-α-Al2O3 powder was synthesized by high-energy ball milling method using γ-AlOOH as raw material. The surface of the obtained powder was relatively rough and had a large specific surface area, which made it easy for obvious agglomeration to occur between the powders. The literature "Hydrothermal synthesis and adsorption property of porous spherical Al2O3nanoparticles" (Materials Research Express, 2019; 6(7):075023) reported that spherical porous Al2O3 nano-powder was synthesized by hydrothermal method using C6H5(NH4)3O7·2H2O and Al(NO3)3·9H2O as raw materials. This method has the advantages of simple operation and low cost, but the sphericity of its particles is poor and the agglomeration phenomenon is obvious, as Figure 1 shown. During the process of synthesizing spherical alumina powder, the control of particle size is closely related to the dispersibility. Spherical alumina powder has symmetry and a uniform surface, which can effectively reduce the friction and mutual attraction between particles. This shape helps to reduce the agglomeration phenomenon. Nano-powder has a higher specific surface area, which although helps to enhance the interaction force between particles, is extremely prone to causing agglomeration. Therefore, there are still certain challenges in aspects such as the uniformity of particle size and dispersibility in current research. The spherical α-alumina powder prepared by these methods has defects such as difficult size regulation, easy agglomeration, and wide particle size distribution. How to prepare alumina powder with good sphericity, uniform dispersion, and small particle size is still one of the key points of current research. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a preparation method for spherical alumina with uniform particle size and high dispersion by synergistically regulating the concentration of aluminum ions, the ratio of sulfate to nitrate, the ratio of aluminum ions to urea, and hydrothermal conditions. This method fully mixes the aluminum source, precipitating agent, dispersant, and deionized water, and then conducts a high-temperature and high-pressure reaction in a closed container to generate an alumina precursor, which is transformed into alumina powder during the subsequent sintering process. The prepared powder has complete grain development, uniform particle size, and high particle dispersibility.

[0005] The technical solution of the present invention is as follows:

[0006] A method for preparing monodisperse and uniform-sized alumina powder, comprising the following steps:

[0007] Step 1: Dissolve and stir an aluminum source, a precipitating agent, and a dispersing agent in ultrapure water to obtain an alumina precursor solution;

[0008] Step 2: Transfer the alumina precursor solution prepared in Step 1 to a hydrothermal reaction kettle, heat it up for reaction. After the hydrothermal reaction is completed, cool it naturally to room temperature, wash it alternately with ultrapure water and ethanol respectively, and obtain alumina precursor powder after drying;

[0009] Step 3: Sinter the alumina precursor powder prepared in Step 2 in a muffle furnace under an air atmosphere to obtain spherical alumina powder.

[0010] In the said Step 1, the aluminum source is a mixture of aluminum sulfate octadecahydrate and aluminum nitrate nonahydrate or aluminum sulfate octadecahydrate; the precipitating agent is urea; the dispersing agent is polyethylene glycol.

[0011] In the said Step 1, the concentration of aluminum ions in the alumina precursor solution is 0.01 - 0.2 mol / L. -1 .

[0012] In the said Step 1, the molar ratio of aluminum ions to the precipitating agent is 1:(2 - 10).

[0013] In the said Step 1, the molar ratio of sulfate radical to nitrate radical is 1:(0 - 8).

[0014] In the said Step 1, the dosage of the dispersing agent is 1 - 10 g / L, and the solvent is ultrapure water measured per liter. -1 , and the solvent is ultrapure water measured per liter.

[0015] In the said Step 2, the hydrothermal reaction conditions are a reaction temperature of 105°C - 130°C and a reaction time of 1 - 3 h.

[0016] In the said Step 2, the obtained powder is washed alternately with ultrapure water and ethanol respectively for 3 times or more.

[0017] In the said Step 3, the sintering conditions of the alumina precursor powder are 1100 - 1200°C.

[0018] In the present invention, the prepared alumina powder is made into a ceramic green body, and the green body is sintered and then subjected to a flexural strength test. The flexural strength shows a significant performance improvement, with a maximum of 245 MPa and a minimum of 179 MPa.

[0019] The sintering conditions of the alumina green body are 1700°C, and after sintering, a three-point flexural test is carried out according to the standard of GB / T 6569 - 1986.

[0020] Monodisperse and uniformly sized spherical alumina powders were obtained by co-regulating the aluminum ion concentration, the ratio of sulfate to nitrate, the ratio of aluminum ion to urea, and the hydrothermal conditions. Scanning showed that the powders had uniform particle size, narrow particle size distribution range, high dispersibility, and no agglomeration phenomenon. After using the prepared alumina powders for ceramic preparation, the obtained ceramic materials showed significant performance improvement in flexural strength. It has broad application prospects in fields such as thermal conductive composites, integrated circuit thin films, substrate materials, 3D printing materials, and precision polishing materials. Figure 2 As shown, the powders have uniform particle size, narrow particle size distribution range, high dispersibility, and no agglomeration phenomenon. After using the prepared alumina powders for ceramic preparation, the obtained ceramic materials showed significant performance improvement in flexural strength. It has broad application prospects in fields such as thermal conductive composites, integrated circuit thin films, substrate materials, 3D printing materials, and precision polishing materials.

[0021] The present invention has the following beneficial effects compared with the prior art:

[0022] (1) The present invention uses the hydrothermal method to react under high temperature and high pressure conditions, improving the uniformity of the reaction, thereby obtaining spherical alumina precursors with uniform particle size and consistent morphology, as shown. Figure 2 In addition, the alumina precursors prepared by the hydrothermal precipitation of aluminum salts have high structural stability and good topological inheritance, and α-Al2O3 is formed after high-temperature sintering.

[0023] (2) By regulating the raw material ratio and hydrothermal conditions, the prepared alumina powders have the characteristics of good sphericity, high dispersion degree, and narrow particle size distribution range, as shown. Figure 3 As shown.

[0024] (3) After using the prepared alumina powders for ceramic preparation, the obtained ceramic materials showed significant performance improvement in flexural strength, with a maximum of 245 MPa and a minimum of 179 MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art.

[0026] Figure 1 is the SEM image of alumina prepared in the literature;

[0027] Figure 2 is the SEM image of the alumina precursor prepared in Example 1 of the present invention;

[0028] Figure 3 is the SEM image of the alumina powder prepared in Example 1 of the present invention;

[0029] Figure 4 is the XRD pattern of the alumina powder prepared in Example 1 of the present invention;

[0030] Figure 5 is the particle size analysis chart of the alumina powder prepared in Example 1 of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0031] The technical solution of the present invention will be described in detail below in conjunction with specific embodiments. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Unless otherwise defined, all technical and scientific terms used herein shall have the meanings commonly understood by those skilled in the technical field of the present invention.

[0032] The present invention provides a spherical alumina powder material with high dispersibility and uniform particle size, and its preparation method includes the following steps:

[0033] A preparation method of spherical alumina includes the following steps:

[0034] Step 1: Dissolve and stir an aluminum source, a precipitating agent, and a dispersant in ultrapure water to obtain a precursor solution.

[0035] Step 2: Transfer the alumina precursor solution prepared in Step 1 to a hydrothermal reaction kettle, heat it up for reaction, after the hydrothermal reaction is completed, naturally cool it to room temperature, wash it 3 times alternately with ultrapure water and ethanol respectively, and dry it to obtain an alumina precursor powder.

[0036] Step 3: Sinter the alumina precursor powder prepared in Step 2 in a muffle furnace under an air atmosphere to obtain an alumina powder.

[0037] Step 4: Prepare a ceramic from the alumina powder in Step 3 and perform a three-point bending test according to the standard of GB / T 6569-1986.

[0038] Based on the above embodiments, the present invention gives specific embodiments of the following spherical alumina materials and their preparation methods.

[0039] Example 1:

[0040] Step 1: Weigh 0.7997 g of aluminum sulfate octadecahydrate, 1.35 g of aluminum nitrate nonahydrate, 3.6036 g of urea, and 0.6 g of polyethylene glycol 2000, add them to 600 ml of ultrapure water, stir well until dissolved, so that the aluminum ion concentration is 0.01 mol / L -1 , the molar ratio of aluminum ion to urea = 1:10, the molar ratio of sulfate radical to nitrate radical is 1:3, and the concentration of polyethylene glycol is 1 g / L -1 , and prepare a precursor solution.

[0041] Step 2: Transfer the alumina precursor solution prepared in Step 1 into a hydrothermal reactor. The hydrothermal temperature is 118 °C and the time is 1 h. After the hydrothermal reaction is completed, naturally cool it to room temperature. Wash the obtained powder alternately with ultrapure water and ethanol three times each. After suction filtration, place it in an oven at a temperature of 80 °C for 12 h. After drying, an alumina precursor powder with an average particle size of about 450 nm is obtained. The particle size is uniform, the dispersibility is high, and there is no agglomeration phenomenon. Its scanning diagram is as shown in Figure 2 shown.

[0042] Step 3: Put the dried precursor powder in Step 2 into a muffle furnace for sintering. The sintering temperature is 1100 °C to obtain a spherical α-alumina powder material with high dispersibility, uniform particle size and an average particle size of about 460 nm. Its scanning diagram, X-ray diffraction spectrum and particle size analysis are respectively as shown in Figure 3 , Figure 4 and Figure 5 shown. Its particle size distribution diagram is unimodal and the average particle size is 460.5 nm. By coordinately regulating the aluminum ion concentration, the ratio of sulfate to nitrate, the ratio of aluminum ion to urea, and the hydrothermal conditions, the effects of small particle size and no agglomeration of the powder are successfully achieved, enabling the particles to be uniformly distributed in a smaller size, and effectively suppressing the mutual attraction between particles, thus avoiding the agglomeration phenomenon.

[0043] Step 4: Prepare ceramics from the alumina powder in Step 3 and conduct a three-point bending test according to the standard of GB / T 6569-1986. The bending strength of the sintered ceramics is 229 MPa.

[0044] Example 2:

[0045] Step 1: Weigh 0.3332 g of aluminum sulfate octadecahydrate, 1.5 g of aluminum nitrate nonahydrate, 1.5 g of urea and 0.5 g of polyethylene glycol 2000, add them to 200 ml of ultrapure water, and stir well until dissolved to make the aluminum ion concentration 0.025 mol / L -1 , the molar ratio of aluminum ion to urea = 1:5, the molar ratio of sulfate to nitrate is 1:8, and the concentration of polyethylene glycol is 2.5 g / L -1 to prepare a precursor solution.

[0046] Step 2: Transfer the alumina precursor solution prepared in Step 1 into a hydrothermal reactor. The hydrothermal temperature is 118 °C and the time is 1.5 h. After the hydrothermal reaction is completed, naturally cool it to room temperature. Wash the obtained powder alternately with ultrapure water and ethanol three times each. After suction filtration, place it in an oven at a temperature of 80 °C for 12 h. After drying, an alumina precursor powder with an average particle size of about 100 nm is obtained. The obtained powder has uniform particle size, high dispersibility and no agglomeration phenomenon.

[0047] Step 3: Put the dried precursor powder in Step 2 into a muffle furnace for sintering at a sintering temperature of 1150 °C to obtain a spherical α-aluminum oxide powder material with high dispersibility, uniform particle size and an average particle size of about 100 nm.

[0048] Step 4: Prepare ceramics from the aluminum oxide powder in Step 3 and conduct a three-point bending test according to the standard of GB / T 6569-1986. The bending strength of the sintered ceramics is 245 MPa.

[0049] Example 3:

[0050] Step 1: Weigh 0.7997 g of aluminum sulfate octadecahydrate, 1.35 g of aluminum nitrate nonahydrate, 3.6036 g of urea and 0.6 g of polyethylene glycol 2000, add them to 600 ml of ultrapure water, and stir well until dissolved to make the aluminum ion concentration 0.01 mol / L -1 , make the molar ratio of aluminum ion to urea = 1:10, the molar ratio of sulfate radical to nitrate radical is 1:3, and the concentration of polyethylene glycol is 1 g / L -1 , and prepare a precursor solution.

[0051] Step 2: Transfer the aluminum oxide precursor solution prepared in Step 1 to a hydrothermal reaction kettle, with a hydrothermal temperature of 130 °C and a time of 1 h. After the hydrothermal reaction is completed, naturally cool it to room temperature. Wash the obtained powder alternately with ultrapure water and ethanol 3 times each, and after suction filtration, put it into an oven at an oven temperature of 80 °C for 12 h. After drying, an aluminum oxide precursor powder with an average particle size of about 500 nm is obtained.

[0052] Step 3: Put the dried precursor powder in Step 2 into a muffle furnace for sintering at a sintering temperature of 1100 °C to obtain a spherical α-aluminum oxide powder material with high dispersibility, uniform particle size and an average particle size of about 500 nm.

[0053] Step 4: Prepare ceramics from the aluminum oxide powder in Step 3 and conduct a three-point bending test according to the standard of GB / T 6569-1986. The bending strength of the sintered ceramics is 223 MPa.

[0054] Example 4:

[0055] Step 1: Weigh 7.997 g of aluminum sulfate octadecahydrate, 13.5 g of aluminum nitrate nonahydrate, 36.036 g of urea and 6 g of polyethylene glycol 2000, add them to 600 ml of ultrapure water, and stir well until dissolved to make the aluminum ion concentration 0.1 mol / L -1 , make the molar ratio of aluminum ion to urea = 1:10, the molar ratio of sulfate radical to nitrate radical is 1:3, and the concentration of polyethylene glycol is 10 g / L -1 , and prepare a precursor solution.

[0056] Step 2: Transfer the alumina precursor solution prepared in Step 1 into a hydrothermal reactor. The hydrothermal temperature is 105 °C and the time is 3 h. After the hydrothermal reaction is completed, naturally cool it to room temperature. Wash the obtained powder alternately with ultrapure water and ethanol three times respectively. After suction filtration, put it into an oven. The oven temperature is 80 °C and the time is 12 h. After drying, an alumina precursor powder with an average particle size of about 1.2 μm is obtained.

[0057] Step 3: Put the dried precursor powder in Step 2 into a muffle furnace for sintering. The sintering temperature is 1100 °C to obtain a spherical α-alumina powder material with high dispersibility, uniform particle size and an average particle size of about 1.2 μm.

[0058] Step 4: Prepare ceramics from the alumina powder in Step 3 and conduct a three-point bending test according to the standard of GB / T 6569-1986. The bending strength of the sintered ceramics is 190 MPa.

[0059] Example 5:

[0060] Step 1: Weigh 13.35 g of aluminum sulfate octadecahydrate, 4.8 g of urea and 0.2 g of polyethylene glycol 2000, add them to 200 ml of ultrapure water, and stir well until dissolved to make the aluminum ion concentration 0.2 mol / L -1 , make the molar ratio of aluminum ion to urea = 1:2, the molar ratio of sulfate radical to nitrate radical is 1:0, and the concentration of polyethylene glycol is 1 g / L -1 , and prepare a precursor solution.

[0061] Step 2: Transfer the alumina precursor solution prepared in Step 1 into a hydrothermal reactor. The hydrothermal temperature is 120 °C and the time is 2 h. After the hydrothermal reaction is completed, naturally cool it to room temperature. Wash the obtained powder alternately with ultrapure water and ethanol four times respectively. After suction filtration, put it into an oven. The oven temperature is 80 °C and the time is 12 h. After drying, an alumina precursor powder with an average particle size of about 10 μm is obtained.

[0062] Step 3: Put the dried precursor powder in Step 2 into a muffle furnace for sintering. The sintering temperature is 1200 °C to obtain a spherical α-alumina powder material with high dispersibility, uniform particle size and an average particle size of about 10 μm.

[0063] Step 4: Prepare ceramics from the alumina powder in Step 3 and conduct a three-point bending test according to the standard of GB / T 6569-1986. The bending strength of the sintered ceramics is 179 Mpa.

[0064] By coordinately regulating the aluminum ion concentration, the sulfate / nitrate ratio, the aluminum ion / urea ratio, and the hydrothermal conditions, the particle size of the powder was successfully and precisely controlled. The obtained powder has small particle size, no agglomeration, uniform particle size, and narrow distribution range, thus meeting the requirements of specific applications.

[0065] For the technical solutions disclosed and proposed in the present invention, those skilled in the art can achieve them by referring to the content herein and appropriately changing conditions, routes and other aspects. Although the methods and preparation techniques of the present invention have been described through preferred examples, it is obvious that relevant technicians can make changes or re-combinations to the methods and technical routes described herein without departing from the content, spirit and scope of the present invention to achieve the final preparation technique. It should be particularly noted that all similar substitutions and changes are obvious to those skilled in the art, and they are all considered to be included in the spirit, scope and content of the present invention.

Claims

1. A method for preparing a monodisperse and uniform particle size alumina powder, characterized in that, It includes the following steps: Step 1: Dissolve and stir an aluminum source, a precipitant, and a dispersant in ultrapure water to obtain an alumina precursor solution; Step 2: Transfer the alumina precursor solution prepared in Step 1 to a hydrothermal reaction kettle, heat it up for reaction. After the hydrothermal reaction is completed, naturally cool it to room temperature, and repeatedly filter or centrifuge and wash it with ultrapure water and absolute ethanol, and then dry it to obtain an alumina precursor powder; Step 3: Sinter the alumina precursor powder prepared in Step 2 in a muffle furnace under an air atmosphere to obtain spherical alumina powder.

2. The method for preparing monodisperse and uniform particle size alumina powder as claimed in claim 1, characterized in that, In Step 1, the aluminum source is a mixture of aluminum sulfate octadecahydrate and aluminum nitrate nonahydrate or aluminum sulfate octadecahydrate; the precipitant is urea; the dispersant is polyethylene glycol.

3. The method for preparing monodisperse and uniform particle size alumina powder according to claim 2, characterized in that, In step one, the concentration of aluminum ions in the alumina precursor solution is 0.01 to 0.2 mol / L -1 .

4. The method for preparing monodisperse and uniform particle size alumina powder according to claim 2, characterized in that, In Step 1, the molar ratio of aluminum ions to the precipitant is 1:(2-10).

5. The method for preparing monodisperse and uniform particle size alumina powder according to claim 1, characterized in that, In Step 1, the molar ratio of sulfate ion to nitrate ion is 1:(0-8).

6. The method for preparing monodisperse and uniform particle size alumina powder according to claim 1, characterized in that, In Step 1, the dosage of the dispersant is 1 to 10 g / L -1 , and the solvent is ultrapure water, measured per liter.

7. The method for preparing monodisperse and uniform particle size alumina powder according to claim 1, characterized in that, In Step 2, the hydrothermal reaction conditions are a reaction temperature of 105°C - 130°C and a reaction time of 1 - 3 h.

8. The method for preparing monodisperse and uniform particle size alumina powder according to claim 1, characterized in that, In Step 2, the obtained powder is washed alternately with ultrapure water and ethanol for 3 times or more respectively.

9. The method for preparing monodisperse and uniform particle size alumina powder as claimed in claim 1, wherein In Step 3, the sintering conditions of the alumina precursor powder are 1100 - 1200°C.

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