Modified coated aluminum powder, method for preparing the same, and use thereof

Abstract

The application discloses modified coated aluminum powder and a preparation method and application thereof, and belongs to the technical field of metal powder surface modification. In the application, micron-sized spherical aluminum powder is first ultrasonically dispersed in an alcohol-water mixed solvent, and polyacrylic acid is added to realize uniform pre-coating on the surface; then, by taking tetraethyl orthosilicate as a silicon source and controlling the hydrolysis rate through ammonia water, a porous silica outer layer is constructed in situ on the surface of the aluminum powder; finally, through high-temperature carbonization in an inert atmosphere, the polyacrylic acid is converted into a continuous conductive carbon layer, and modified aluminum powder with a three-layer core-shell structure of aluminum core-conductive carbon layer-porous silica is prepared. In the application, the porous coating layer is prepared under high-alkali conditions, the excellent oxidation resistance and corrosion resistance of silica are retained, and the electronic conduction is ensured to be smooth, so that the drawbacks of strong insulation of traditional dense silica coating and poor protection of single carbon coating are solved. The preparation process is simple and controllable, the coating layer is firmly combined, the powder has good dispersibility, the conductive performance of the obtained product is stable, the product can be widely applied in the fields of conductive coating, electromagnetic shielding material, battery conductive filler and the like, and has high practical value.

Description

Technical Field

[0001] This invention belongs to the field of metal powder surface modification technology, specifically relating to a modified coated aluminum powder, its preparation method, and its application. Background Technology

[0002] Aluminum powder, with its low density, low cost, and excellent electrical and thermal conductivity, is widely used in high-end fields such as conductive functional coatings, lithium-ion battery anode materials, electromagnetic shielding composite materials, and metal-based filler materials. However, aluminum powder is extremely chemically reactive, and its surface is easily and rapidly oxidized at room temperature and pressure to form an insulating alumina film. In humid, acidic, and alkaline environments, it is also prone to corrosion and hydrogen evolution reactions, which not only lead to a sharp decline in the conductivity of the powder but also cause agglomeration and clumping problems, severely limiting its application in high-precision and high-stability conductive fields.

[0003] Current aluminum powder surface modification technologies mainly rely on inorganic oxides and polymer coatings. Among these, silica (SiO2) is a commonly used inorganic coating material due to its strong chemical stability, excellent corrosion resistance, and low cost. It can form a physical protective layer on the aluminum powder surface, effectively blocking oxygen and moisture erosion and improving the aluminum powder's oxidation and corrosion resistance. However, conventional SiO2 coatings have a dense insulating structure, which completely blocks the internal conductive pathways of the aluminum powder. This causes the volume resistivity of the coated aluminum powder to soar by tens of times, resulting in a loss of conductivity and failing to meet the requirements of conductive applications. While coating with conductive metals or carbon materials can retain conductivity, the protective layer is loose, has weak adhesion, and is prone to peeling off, significantly reducing its protective effect over long-term use.

[0004] Furthermore, existing composite coating technologies mostly employ a step-by-step process of first inorganic coating and then conductive modification, which suffers from drawbacks such as cumbersome processes, poor interlayer bonding, and difficulty in controlling coating uniformity. Moreover, dense inorganic coating layers cannot simultaneously provide protection and conductivity, and the process for controlling the porous structure is complex, making large-scale production difficult. Therefore, developing an aluminum powder modification technology that combines highly efficient oxidation and corrosion resistance with excellent conductivity, a uniform and dense coating layer, strong bonding, and a simple process has become a pressing technical challenge in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a modified coated aluminum powder, its preparation method, and its applications. A three-layer core-shell structure is constructed: an aluminum core, a conductive carbonized layer, and a SiO2 outer layer. The conductive carbon layer is prepared simultaneously through pre-coating with polyacrylic acid (PAA), controlling the amount of ammonia used, achieving rapid SiO2 deposition and pore creation, and high-temperature carbonization.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: S1. Pre-dispersion of micron-sized aluminum powder and coating with polyacrylic acid: Micron-sized spherical aluminum powder is added to a mixed solvent of anhydrous ethanol and deionized water and ultrasonically dispersed to prepare an aluminum powder suspension with a solid content of 10%-15%; polyacrylic acid (PAA) is added to the suspension, the temperature is raised to 40℃-60℃, and the mixture is stirred at a constant temperature for 60min-90min, so that the polyacrylic acid uniformly coats a polymer adsorption layer on the surface of the aluminum powder through electrostatic adsorption and hydrogen bonding coordination, thus obtaining a polyacrylic acid-coated aluminum powder dispersion; The PAA has an average molecular weight of 5000, the mass ratio of PAA to aluminum powder is 0.15-0.2:1, and the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 2:1-1.2.

[0007] S2. Rapid in-situ deposition of SiO2 layer Tetraethyl orthosilicate (TEOS) was added to the above polyacrylic acid-coated aluminum powder dispersion as a silicon source. After rapid stirring and uniform mixing, concentrated ammonia solution with a mass fraction of 25% was added dropwise to adjust the pH of the system to 10.0-11.0. The reaction was carried out at a constant temperature of 30℃-40℃ for 4-6 hours. In this step, excess ammonia significantly increases the SiO2 deposition rate, preventing the SiO2 grains from forming a dense arrangement. This results in a non-dense SiO2 coating layer being formed in situ outside the polyacrylic acid coating layer. After the reaction is complete, the mixture is cooled to room temperature, filtered, and washed with ethanol to obtain a three-layer precursor powder consisting of an aluminum core, a polyacrylic acid layer, and a SiO2 layer.

[0008] S3. High-temperature carbonization to prepare conductive carbon layer The precursor powder was placed in a vacuum drying oven and dried at 70-80℃ for 4-6 hours to remove residual solvent. Then it was transferred to a tube furnace and inert protective gas of nitrogen or argon was introduced. The temperature was increased to 450-600℃ at a heating rate of 6-12℃ / min and carbonized for 2-4 hours. During the high-temperature carbonization process, the polyacrylic acid on the surface of the aluminum powder is fully decomposed and carbonized by heat, transforming into a continuous and dense conductive carbon layer. The carbon layer is tightly bonded to the aluminum powder matrix and the outer SiO2 layer without interface gaps. After cooling to room temperature, modified coated aluminum powder is obtained.

[0009] A modified coated aluminum powder The powder prepared by the above method has a three-layer core-shell structure: the core is micron-sized spherical aluminum powder, the middle layer is a continuous and dense conductive carbon layer formed by carbonization of polyacrylic acid, and the outer layer is a porous silica layer. The powder has both excellent antioxidant and corrosion resistant properties and conductive properties.

[0010] Application of a modified coated aluminum powder Used in conductive coatings, it combines anti-corrosion and conductive functions, and the coating / electrode does not oxidize and maintains stable conductivity over long-term use.

[0011] The beneficial effects of this invention are as follows: (1) Advantages of polyacrylic acid (PAA) pre-coating: Polyacrylic acid forms a uniform adsorption layer on the surface of aluminum powder, which not only prevents the aluminum powder from agglomerating and improves its dispersibility, but also serves as a subsequent carbon source to provide raw materials for the conductive carbon layer. At the same time, it serves as a transition layer for SiO2 deposition, which enhances the bonding force between SiO2 and the aluminum powder matrix.

[0012] (2) Ammonia water regulation of SiO2: Under the normal amount of ammonia water, SiO2 deposition is slow and a dense insulating layer is formed. Excessive ammonia water greatly increases the hydrolysis rate and deposition rate, and SiO2 grains grow and stack rapidly to form through pores. This not only retains the antioxidant and corrosion-resistant protective properties of SiO2, but also avoids the dense layer from blocking the conductive path. At the same time, the pores can improve the dispersibility of powder in slurry.

[0013] (3) Synchronous carbonization molding: One-step high-temperature carbonization realizes the transformation of polyacrylic acid polymer layer into highly conductive carbon layer. The carbon layer has excellent conductivity and forms a synergistic conductive network with aluminum powder core, which makes up for the weak insulation of SiO2 layer and ensures the overall conductivity of powder. Moreover, the carbon layer is chemically bonded to aluminum matrix and SiO2 outer layer, and the coating is firm and not easy to fall off. Attached Figure Description

[0014] Figure 1 This is a scanning electron microscope (SEM) image of the modified coated aluminum powder in Example 1 of the present invention; Figure 2 This is the EDS energy dispersive spectroscopy (EDS) analysis diagram of the modified coated aluminum powder in Example 1 of the present invention; Figure 3 This is a comparison curve of the oxidative weight gain of the samples in Example 1 and Comparative Examples 1-3; Figure 4 The images show the electrochemical impedance spectroscopy (EIS) spectra of the samples in Example 1 and Comparative Examples 2-3. Detailed Implementation

[0015] To make the above-mentioned objectives, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to examples. The following content is merely illustrative and explanatory of the concept of the present invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, as long as they do not deviate from the inventive concept, all of which should fall within the protection scope of the present invention. The preparation method of the present invention will be described below through specific embodiments.

[0016] Example 1 S1. Micron-sized aluminum powder pre-dispersion and polyacrylic acid coating Weigh 100g of spherical aluminum powder, add anhydrous ethanol and deionized water in a volume ratio of 2:1, mix and ultrasonically disperse for 25min to prepare an aluminum powder suspension with a solid content of 15%; add 18g of polyacrylic acid to the suspension, with a polyacrylic acid to aluminum powder mass ratio of 0.18:1, heat to 50℃, and stir at a constant temperature for 75min to obtain an aluminum powder dispersion uniformly coated with polyacrylic acid.

[0017] S2. Rapid in-situ deposition of SiO2 layer Add 75g of tetraethyl orthosilicate to the dispersion, stir and mix well, then slowly add 25% concentrated ammonia water to adjust the pH of the system to 10.5, and react at 35℃ for 5h. After the reaction is completed, cool to room temperature, filter, and wash three times with anhydrous ethanol to obtain aluminum core-polyacrylic acid layer-SiO2 layer precursor powder.

[0018] S3. High-temperature carbonization to prepare conductive carbon layer The precursor powder was vacuum dried at 75℃ for 5 hours, placed in a tube furnace and protected with nitrogen, heated to 520℃ at a rate of 9℃ / min, and carbonized at that temperature for 2.5 hours. After natural cooling, the modified coated aluminum powder was obtained.

[0019] Example 2 S1. Weigh 100g of spherical aluminum powder, add anhydrous ethanol and deionized water in a volume ratio of 2:1.1 to prepare a mixed solvent, and ultrasonically disperse to prepare an aluminum powder suspension with a solid content of 12%; add 15g of polyacrylic acid, heat to 40℃ and stir for 90min.

[0020] S2. Add 60g of tetraethyl orthosilicate, add 25% concentrated ammonia to adjust the pH to 10.0, react at 30℃ for 6h, then filter and wash to obtain the precursor.

[0021] S3. Vacuum dry at 70℃ for 6 hours, then heat to 450℃ at 6℃ / min under argon protection, and carbonize for 4 hours to obtain the finished product.

[0022] Example 3 S1. Weigh 100g of spherical aluminum powder, mix it with anhydrous ethanol and deionized water in a volume ratio of 2:1.2, and ultrasonically disperse it to prepare an aluminum powder suspension with a solid content of 10%; add 20g of polyacrylic acid, and stir at a constant temperature of 60℃ for 60min.

[0023] S2. Add 90g of tetraethyl orthosilicate, add 25% concentrated ammonia to adjust the pH to 11.0, react at 40℃ for 4h, and then filter and wash.

[0024] S3. Vacuum drying at 80℃ for 4 hours, heating to 600℃ at 12℃ / min under nitrogen atmosphere, carbonizing at this temperature for 2 hours, and then cooling to obtain modified aluminum powder.

[0025] Comparative Example 1 Spherical aluminum powder with the same particle size and purity as in Example 1 was selected and directly tested for performance without any coating or modification treatment, serving as a blank control group.

[0026] Comparative Example 2 This comparative example only adjusts a single variable. All raw material dosages, dispersion conditions, coating process, reaction temperature and time, drying and carbonization parameters are exactly the same as in Example 1, except that the pH value of the ammonia water system is changed to 9.

[0027] Specific steps: The preparation was carried out strictly in accordance with all the operating procedures of Example 1. The pH value of the system was adjusted to 9 only when 25% concentrated ammonia was added. No other operating steps or process parameters were changed. Finally, the coated aluminum powder prepared under pH=9 conditions was obtained, and a dense silica coating layer was formed under these conditions.

[0028] Comparative Example 3 The steps of adding tetraethyl orthosilicate and SiO2 deposition were omitted. Only the aluminum powder was coated with PAA and then carbonized at high temperature. The remaining process parameters were exactly the same as in Example 1.

[0029] Specific steps: Prepare PAA-coated aluminum powder dispersion according to Example 1, filter directly, wash three times with anhydrous ethanol, vacuum dry at 75°C for 5 hours, then transfer to a tube furnace, introduce nitrogen as a protective gas at a flow rate of 130 mL / min, heat to 520°C at a heating rate of 9°C / min, hold for carbonization for 2.5 hours, and after natural cooling, obtain coated aluminum powder with only an aluminum core-conductive carbon layer structure and no SiO2 protective outer layer.

[0030] Application Examples: The modified coated aluminum powder prepared in Example 1, polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) were mixed in a mass ratio of 5:1:20 and stirred to form a uniform negative electrode slurry. The slurry was then coated and vacuum dried at 80°C for 12 hours.

[0031] Similarly, the modified coated aluminum powder in Example 1 was replaced with the aluminum powder in Comparative Examples 1-3.

[0032] Figure 1 SEM scanning electron microscope image of modified coated aluminum powder in Example 1 of this invention.

[0033] As can be clearly observed from the SEM morphology images, the modified spherical aluminum powder particles have complete and undamaged morphology; the outer coating layer of the aluminum powder is continuous and complete, and the surface layer exhibits a loose and porous microstructure without a dense and smooth coating interface. This confirms that the present invention successfully constructs a SiO2 coating layer on the outer layer of the powder through high alkali control. The coating integrity is high, and the layer contains a large number of through pores, which not only achieves all-round coating protection, but also reserves channels for electron conduction.

[0034] Figure 2EDS energy dispersive spectroscopy analysis diagram of modified coated aluminum powder in Example 1 of this invention.

[0035] EDS elemental distribution maps showed that four characteristic elements—Al, C, Si, and O—were simultaneously detected on the sample surface. This indicates that the aluminum core-conductive carbon layer-SiO2 structure was successfully constructed.

[0036] Figure 3 Bar chart comparing the oxidation weight gain rate of Example 1 and Comparative Examples 1-3 samples after incubation at 300℃ for 2 hours.

[0037] The horizontal axis represents Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively, and the vertical axis represents the oxidation weight gain rate (%). The lower the weight gain value, the stronger the oxidation resistance of the powder.

[0038] Comparative Example 1 shows that the pure aluminum powder columnar structure is the tallest, with an oxidation weight gain rate of 8.76%. It is extremely prone to oxidation and failure at high temperatures and has the worst oxidation resistance. Comparative Example 3, with only a conductive carbon layer coated without a silicon dioxide protective layer, showed an oxidation weight gain of 5.24%, indicating a much weaker protective capability than the SiO2-coated system. Comparative Example 2: Dense silica-coated aluminum powder prepared at low pH showed the lowest column height, an oxidation weight gain of only 1.18%, and the best oxygen isolation effect. The oxidation weight gain rate of Example 1 of this invention is 1.23%, and the column height is close to that of Comparative Example 2, indicating excellent antioxidant properties. This shows that porous silica still has a strong oxygen barrier effect and can effectively inhibit the oxidation and corrosion of aluminum matrix.

[0039] The bar chart illustrates that the SiO2 outer layer prepared by this invention does not weaken the inorganic protective performance and can achieve an antioxidant effect close to that of a dense coating layer.

[0040] Figure 4 EIS Nyquist curves of AC impedance for Example 1 and Comparative Examples 2-3.

[0041] In the Nyquist spectrum, the diameter of the arc represents the electrochemical interface impedance value. The smaller the arc diameter, the better the conductivity of the powder and the smaller the charge conduction resistance.

[0042] Comparative Example 2: The dense SiO2-coated sample has the largest arc diameter and extremely high interface impedance. The dense insulating layer completely blocks the electron transport path, and the conductivity is basically lost. Comparative Example 3 has only a conductive carbon layer without an outer protective layer, the smallest arc diameter, and the best conductivity, but it lacks an anti-corrosion structure. In Embodiment 1 of the present invention, the diameter of the arc is smaller than that of the densely coated sample but slightly larger than that of the single carbon layer coated sample, resulting in low interfacial impedance and unobstructed conductive pathways.

[0043] Combining oxidation curves and impedance curves confirms that the outer SiO2 layer of this invention balances protection and permeability, unlike dense coating layers which block conductive channels. The middle conductive carbon layer can construct a stable conductive network, achieving a two-way balance between protective and conductive properties.

Claims

1. A method for preparing modified coated aluminum powder, characterized in that, Includes the following steps: S1. Pre-dispersion of micron-sized aluminum powder and coating with polyacrylic acid: Micron-sized spherical aluminum powder is ultrasonically dispersed in a mixed solvent of anhydrous ethanol and deionized water to prepare an aluminum powder suspension with a solid content of 10%-15%; polyacrylic acid is added to the suspension to obtain a polyacrylic acid-coated aluminum powder dispersion; wherein the mass ratio of polyacrylic acid to aluminum powder is 0.15-0.2:1, and the volume ratio of anhydrous ethanol to deionized water is 2:1-2:1.2; S2. In-situ rapid deposition of SiO2 layer: Tetraethyl orthosilicate was added to the dispersion, and concentrated ammonia solution with a mass fraction of 25% was added dropwise to adjust the pH of the system to 10.0-11.

0. The reaction was carried out at a constant temperature of 30℃-40℃ for 4-6 hours. After cooling, filtration and washing, aluminum core-polyacrylic acid layer-SiO2 layer precursor powder was obtained. S3. High-temperature carbonization to prepare conductive carbon layer: After vacuum drying of precursor powder, nitrogen or argon inert gas is introduced and the temperature is raised to 450-600℃ at a heating rate of 6-12℃ / min and held for carbonization for 2-4 hours. After cooling, modified coated aluminum powder is obtained.

2. The method for preparing modified coated aluminum powder according to claim 1, characterized in that: The average molecular weight of the polyacrylic acid described in step S1 is 5000.

3. The method for preparing modified coated aluminum powder according to claim 1, characterized in that: After adding polyacrylic acid in step S1, heat the mixture to 40℃-60℃ and stir it at a constant temperature for 60min-90min.

4. The method for preparing modified coated aluminum powder according to claim 1, characterized in that: In step S3, the precursor powder is vacuum dried at a temperature of 70-80℃ for 4-6 hours.

5. A modified coated aluminum powder, characterized in that, It is prepared by the preparation method described in any one of claims 1-4.

6. An application of the modified coated aluminum powder as described in claim 5, characterized in that, It is used in conductive coatings, conductive fillers for lithium-ion batteries, and electromagnetic shielding composite materials.

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