A nickel-coated aluminum powder and a method for producing the same

Abstract

The application discloses a kind of nickel-coated aluminum powder and preparation method thereof, the nickel-coated aluminum powder is with gas atomized aluminum powder as matrix, by dilute alkali to the surface of aluminum powder is washed rapidly, then by liquid phase reduction, the nickel of a certain thickness is coated, finally is washed, reduction, screening is obtained.The nickel-coated aluminum powder prepared by the method of the application is uniform, compact, bright, compact, with low resistance, good conductivity, strong corrosion resistance, compared with the nickel-coated powder on the market, has more excellent conductivity, the resistivity of the conductive adhesive tape made does not change within 48 hours at 200 DEG C high temperature.In addition, it can be added to paint, ink, plastic, etc., and inorganic materials or organic high-conductivity materials with conductive properties can be prepared, mainly used for military product protective sleeve and spraying, especially in the surface of metal aluminum material as a base hard surface direction can be widely used.

Description

Technical Field

[0001] This invention relates to the field of powder metallurgy technology, specifically to a nickel-coated aluminum powder and its preparation method. Background Technology

[0002] Conductive adhesive is an adhesive that exhibits a certain degree of conductivity after curing or drying. It typically consists of a base resin and conductive fillers (conductive particles) as its main components. The conductive particles are bonded together by the adhesive action of the base resin, forming a conductive path and achieving a conductive connection between the bonded materials. With the rapid development of miniaturization and micro-miniaturization of electronic components and the high density and high integration of printed circuit boards, conductive adhesive pastes can achieve very high line resolution. Furthermore, the process is simple and easy to operate, improving production efficiency. Therefore, conductive adhesives and pastes are an ideal choice to replace lead-tin soldering for achieving conductive connections.

[0003] Conductive adhesives are classified according to their conductive particles into: silver-based, copper-based, nickel-based, and carbon-based conductive adhesives. Silver-based adhesives have a resistivity of less than 0.01 ohms / cm and offer magnetic shielding of over 75dB. Copper-based adhesives have a resistivity of 0.075-0.10 ohms / cm and are only suitable for low-frequency magnetic shielding. Nickel-based adhesives have a resistivity of 1.0 ohms / cm and offer magnetic shielding of 60-75dB (5-1800MHz). Carbon-based adhesives have a resistivity of 30-50 ohms / cm and offer magnetic shielding of 30-50dB (50-450MHz). None of these conductive adhesives can simultaneously provide both effective magnetic shielding and good conductivity. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problem that existing conductive adhesives cannot simultaneously achieve magnetic shielding effect and conductivity. It provides a nickel-coated aluminum powder that can be used to prepare composite conductive adhesives. With gas-atomized aluminum powder as the core, by coating the aluminum powder with a certain thickness of nickel, it can achieve both magnetic shielding effect and improved conductivity and oxidation resistance, and the manufacturing cost is low.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned nickel-coated aluminum powder.

[0006] To achieve its purpose, the present invention adopts the following technical solution:

[0007] A method for preparing nickel-coated aluminum powder includes the following steps:

[0008] Step 1: Soak the atomized aluminum powder in dilute alkali to wash away the oxide layer on the surface of the aluminum powder, then filter and set aside for use.

[0009] Step 2: Inhibit the surface activity of aluminum powder to ensure that the aluminum powder does not easily react with water or reducing solution: Add the aluminum powder after alkaline leaching and filtration in Step 1 to a zinc sulfate solution with an inhibitor concentration of 5-15% by mass and volume, soak for 30 minutes, filter dry and set aside. This ensures that the aluminum powder activity is passivated and that the morphology of the aluminum powder is not damaged, thus preventing it from reacting with water. The inhibitor is any one of tartaric acid, sodium potassium tartrate, or alcohol.

[0010] Step 3: Coating nickel with aluminum powder: Inject a nickel sulfate solution with a nickel ion concentration of 40-60 g / L into the reaction vessel. Add the aluminum powder (after surface activity inhibition in Step 2) in one go, depending on the type of nickel-coated aluminum to be prepared. Stir and heat. When the solution temperature rises to 50-60℃, add the reducing agent at a rate of 1.2-1.4 L / min and adjust the pH of the solution to 6-8. Stop adding the reducing agent when the solution becomes colorless. Continue the reaction for 30 min. The coating is complete, and nickel-coated aluminum powder is obtained.

[0011] Step 4: Wash, filter, and dry the nickel-coated aluminum powder from Step 3 to obtain dry powder. Then, introduce hydrogen gas to reduce the powder, causing the coating layer to shrink and become dense, thereby improving its conductivity.

[0012] Step 5: Sieve the nickel-coated aluminum powder according to the particle size requirements to obtain finished nickel-coated aluminum powder with different particle size compositions. This nickel-coated aluminum powder can be used to prepare composite conductive adhesives.

[0013] As a further improvement to the technical solution of this invention, in step one, the dilute alkali is a sodium hydroxide solution with a pH of 7-8, and the soaking time is 3-5 minutes. Because aluminum powder has high reactivity, choosing a lower alkali concentration and a shorter soaking time can prevent the aluminum powder from reacting with the dilute alkali.

[0014] Furthermore, in step three, the reducing agent is any one of hydrazine hydrate, sodium sulfite, or sodium hypophosphite.

[0015] Furthermore, in step four, the reduction temperature is 300-400℃.

[0016] Furthermore, in step four, a steel strip reduction furnace is used for reduction, and the speed of the steel strip is adjusted to 10-15Hz.

[0017] The beneficial effects of this invention are as follows:

[0018] 1. The nickel-coated aluminum powder of this invention uses gas-atomized aluminum powder as a matrix. The surface of the aluminum powder is rapidly washed with dilute alkali, and then an organic inhibitor is added to a zinc sulfate solution to suppress the surface activity of the aluminum powder. Finally, a certain thickness of nickel is coated onto the powder through liquid-phase reduction. The nickel-coated aluminum powder produced by this method has superior conductivity compared to commercially available nickel-coated powders. The conductive tape made from this powder exhibits no change in resistivity at 200°C for 48 hours.

[0019] 2. The nickel-coated aluminum powder prepared by the method of the present invention has a uniform, dense, and bright coating with good density. It has the characteristics of low resistance, good conductivity, and strong corrosion resistance. When added to coatings, inks, plastics, etc., it can produce inorganic or organic high-conductivity materials with conductive properties. It is mainly used for protective covers and spraying of military products, especially as a base coat on the surface of aluminum metal. Attached Figure Description

[0020] Figure 1 This is an electron microscope image of the nickel-coated aluminum powder prepared in Example 1 of the present invention. Detailed Implementation

[0021] The preparation process of the nickel-coated aluminum powder of the present invention will be further explained below with reference to specific embodiments.

[0022] Example 1: Ni 60 Al 40 Preparation of nickel-coated aluminum powder

[0023] This embodiment provides a method for preparing nickel-coated aluminum powder, which includes the following steps:

[0024] Step 1: Add 20 kg of atomized aluminum powder to the alkaline washing tank, soak it in a sodium hydroxide solution with pH=7.5 for 4 minutes, then filter it dry. Return the filtrate to the tank for reuse next time.

[0025] Step 2: Add the alkaline-washed and filtered aluminum powder to a passivation tank containing 5g of sodium potassium tartrate in a 10% (mass / volume fraction) zinc sulfate solution. Soak for 30 minutes, then filter dry. Return the filtrate to the passivation tank for future use. Wash the filtered aluminum powder three times with pure water and then filter dry again for later use.

[0026] Step 3: Prepare 600L of nickel sulfate solution with a nickel ion concentration of 58g / L and inject it into the reactor. Add 22g of aluminum powder (after passivation treatment by washing and filtering in Step 2), stir, and heat. When the solution temperature rises to 55℃, add sodium hypophosphite as a reducing agent at a rate of 1L / min, and adjust the pH to 7.5 with sodium hydroxide solution. After the solution turns colorless, stop adding sodium hypophosphite and continue the reaction for 30 minutes. The coating is then complete, and nickel-coated aluminum powder is obtained.

[0027] Step 4: Wash the nickel-coated aluminum powder five times. The washing is considered qualified if the sulfate content in the last wash water is less than 0.3 g / L. Filter and dry to obtain dry powder. Then, reduce it with hydrogen in a steel strip reduction furnace at a reduction temperature of 320℃ and a steel strip speed of 13 Hz to shrink and densify the coating layer and improve its conductivity.

[0028] Step 5: Pass the powder through a 300-mesh sieve to obtain the required nickel-coated aluminum powder product. Its technical specifications are shown in Table 1.

[0029]

[0030] Table 1 provides the main chemical composition, particle size distribution, and bulk density of the prepared nickel-coated aluminum powder. The powder was passed through a 300-mesh sieve to ensure uniform particle size, which is essential for conductive adhesive fabrication. Resistance values ​​were measured after the conductive shielding adhesive was formed.

[0031] The conductive shielding adhesive was prepared as follows: 60g of silicone, 3g of vulcanizing agent, and 3g of curing agent were uniformly added to a rubber mixing mill and repeatedly extruded for 10 minutes. Then, 100g of the prepared -300 mesh nickel-coated aluminum powder was weighed and added to the mixing mill, and the mixture was extruded for 20 minutes. After uniform mixing and extrusion, the prepared silicone was placed in a mold and cured at 172℃ and 10MPa for 10 minutes to obtain the conductive shielding adhesive. The resistance values ​​are shown in Table 2 below.

[0032]

[0033] Currently, conductive shielding adhesives made with nickel-coated graphite powder have a resistivity of 26.5 mΩ. Compared with the conductive adhesives made with nickel-coated aluminum powder of this invention, the conductive adhesives of this invention have superior conductivity.

[0034] Example 2

[0035] This embodiment provides a method for preparing nickel-coated aluminum powder, which includes the following steps:

[0036] Step 1: Add 20 kg of atomized aluminum powder to the alkaline washing tank, soak it in a sodium hydroxide solution with pH=7.8 for 4 minutes, then filter it dry. Return the filtrate to the tank for reuse next time.

[0037] Step 2: Add the alkaline-washed and filtered aluminum powder to a passivation tank containing 5g of sodium potassium tartrate in a 12% (mass / volume fraction) zinc sulfate solution. Soak for 30 minutes, then filter dry. Return the filtrate to the passivation tank for future use. Wash the filtered aluminum powder three times with pure water and then filter dry for later use.

[0038] Step 3: Prepare 600L of nickel sulfate solution with a nickel ion concentration of 45g / L and inject it into the reactor. Add 18g of aluminum powder (after passivation treatment in Step 2, followed by washing and filtration), stir, and heat. When the solution temperature rises to 50℃, add hydrazine hydrate as a reducing agent at a rate of 1.4L / min, and adjust the pH to 6.5 with sodium hydroxide solution. After the solution turns colorless, stop adding sodium hypophosphite and continue the reaction for 30 minutes. The coating is then complete, yielding nickel-coated aluminum composite powder.

[0039] Step 4: Wash the nickel-coated aluminum composite powder five times. The washing is considered qualified if the sulfate content in the last wash water is less than 0.3 g / L. Filter and dry to obtain dry powder. Then reduce it with hydrogen in a steel belt reduction furnace to shrink and densify the coating layer and improve its conductivity.

[0040] Step 5: Pass the powder through a 300-mesh sieve to obtain the required nickel-coated aluminum powder composite conductive powder product. Its technical specifications are shown in Table 3.

[0041]

[0042] Example 3

[0043] This embodiment provides a method for preparing nickel-coated aluminum powder, which includes the following steps:

[0044] Step 1: Add 25 kg of atomized aluminum powder to the alkaline washing tank, soak it in a sodium hydroxide solution with pH=7.8 for 4 minutes, then filter it dry. Return the filtrate to the tank for reuse next time.

[0045] Step 2: Add the alkaline-washed and filtered aluminum powder to a passivation tank containing 8g of tartaric acid in a 12% (mass-volume fraction) zinc sulfate solution. Soak for 30 minutes, then filter dry. Return the filtrate to the passivation tank for future use. Wash the filtered aluminum powder three times with pure water and then filter dry for later use.

[0046] Step 3: Prepare 600L of nickel sulfate solution with a nickel ion concentration of 60g / L and inject it into the reactor. Add 52g of aluminum powder (passivated and washed dry in Step 2), stir, and heat. When the solution temperature rises to 60℃, add sodium hypophosphite as a reducing agent at a rate of 1.2L / min. Adjust the pH to 7.5 with sodium hydroxide solution. After the solution turns colorless, stop adding sodium hypophosphite and continue the reaction for 30 minutes. The coating is then complete, and nickel-coated aluminum composite powder is obtained.

[0047] Step 4: Wash the nickel-coated aluminum composite powder five times. The washing is considered qualified if the sulfate content in the last wash water is less than 0.3 g / L. Filter and dry to obtain dry powder. Then reduce it with hydrogen in a steel belt reduction furnace to shrink and densify the coating layer and improve its conductivity.

[0048] Step 5: Pass the powder through a 300-mesh sieve to obtain the required nickel-coated aluminum powder composite conductive powder product. Its technical specifications are shown in Table 4.

[0049]

Claims

1. A method for preparing nickel-coated aluminum powder, characterized in that, Includes the following steps: Step 1: Soak the atomized aluminum powder in dilute alkali, filter it dry and set aside for later use; Step 2: Inhibit the surface activity of aluminum powder: Add the aluminum powder filtered and dried after alkaline leaching in Step 1 to a zinc sulfate solution with an inhibitor concentration of 5-15% by mass and volume, soak for 30 minutes, and then filter and set aside; the inhibitor is any one of tartaric acid, sodium potassium tartrate, or alcohol. Step 3: Coating nickel with aluminum powder: Inject a nickel sulfate solution with a nickel ion concentration of 40-60 g / L into the reaction vessel. Add the aluminum powder (after surface activity inhibition in Step 2) in one go, depending on the type of nickel-coated aluminum to be prepared. Stir and heat. When the solution temperature rises to 50-60℃, add the reducing agent at a rate of 1.2-1.4 L / min and adjust the pH of the solution to 6-8. Stop adding the reducing agent when the solution becomes colorless. Continue the reaction for 30 min. The coating is complete, and nickel-coated aluminum powder is obtained. Step 4: Wash, filter, and dry the nickel-coated aluminum powder from Step 3 to obtain dry powder, and then reduce it by passing hydrogen gas to shrink and densify the coating layer. Step 5: Sieve the powder according to the particle size requirements to obtain nickel-coated aluminum powder products with different particle size compositions.

2. The method for preparing nickel-coated aluminum powder according to claim 1, characterized in that, In step one, the dilute alkali is a sodium hydroxide solution with a pH of 7-8, and the soaking time is 3-5 minutes.

3. The method for preparing nickel-coated aluminum powder according to claim 2, characterized in that, In step three, the reducing agent is any one of hydrazine hydrate, sodium sulfite, or sodium hypophosphite.

4. The method for preparing nickel-coated aluminum powder according to claim 1, characterized in that, In step four, the reduction temperature is 300-400℃.

5. The method for preparing nickel-coated aluminum powder according to claim 4, characterized in that, In step four, a steel strip reduction furnace is used for reduction, and the steel strip speed is adjusted to 10-15Hz.

6. Nickel-coated aluminum powder prepared by the method for preparing nickel-coated aluminum powder according to any one of claims 1-5.

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