CN111020542A

CN111020542A - Method for preparing aluminum alloy silver coating by utilizing dopamine

Info

Publication number: CN111020542A
Application number: CN201911401266.6A
Authority: CN
Inventors: 邵艳群; 魏新利; 陈鑫; 叶章豪; 贺四江; 张容容; 林雨婷; 陈孔发
Original assignee: Fuzhou University
Current assignee: Fuzhou University
Priority date: 2019-12-31
Filing date: 2019-12-31
Publication date: 2020-04-17

Abstract

The invention discloses a method for preparing an aluminum alloy silver coating by utilizing dopamine, belonging to the technical field of surface treatment. The traditional silver plating mode is mainly electroplating, the process is complex, cyanide contains high toxicity, and the method reduces a uniform silver plating layer on the surface of the aluminum alloy by using polydopamine with reducibility and adhesiveness as an intermediate layer. The material used in the invention is environment-friendly and nontoxic, and can effectively reduce the thickness of the plating layer and greatly simplify the plating process while ensuring that the use requirements of electrical conductivity, thermal conductivity, resistance and the like are met.

Description

Method for preparing aluminum alloy silver coating by utilizing dopamine

Technical Field

The invention belongs to the technical field of surface treatment, and particularly relates to a method for plating silver on an aluminum alloy surface.

Background

Since the new century, the economic development of China is high, and the demand for electric power is increased sharply, so that the total electricity consumption in the whole country in 2018 reaches 6.85 trillion kilowatts, a high-voltage power grid transmission system is developed rapidly along with the increase of the power consumption, and the demand for electric power facilities is increased again and again. The aluminum alloy has excellent physical properties, low material density, high specific strength, good ductility and mechanical properties close to steel materials, has good electric and heat conducting capabilities, and simultaneously, the aluminum element is the element with the highest content in the earth crust, so the aluminum alloy is widely applied to electric power systems, such as a long-distance transmission conductive material steel bar aluminum stranded wire, a transformer substation high-voltage circuit breaker, a disconnecting switch movable contact and a disconnecting switch static contact, and the like. But the defect is that the chemical property is too active, the aluminum is easy to corrode in a complex environment, in addition, the aluminum can spontaneously form an oxide film in an atmospheric environment, the heat conductivity and the electric conductivity of the oxide film are poor, when a large current passes through the oxide film, a large amount of ohmic heat can be generated, various precise components in the transformer substation are in a high-temperature environment for a long time, and the risk of high-temperature failure is increased.

In order to reduce the contact resistance of the aluminum alloy surface, a common scheme is silver plating treatment on the aluminum alloy surface. Silver has high electrical conductivity (63.01 MS/m), high thermal conductivity (429W/mK) and low contact resistance (1.6X 10)^-8Omega.m) is relatively easy to obtain, and the traditional method for preparing the aluminum alloy silver coating is electroplating in a cyanidation system, and usually needs to undergo several steps of surface treatment, alkaline etching, acidification, primary zinc immersion, secondary zinc immersion, copper plating and silver plating, so that the process is complicated, the toxicity of cyanide is high, and the method is a threat to the health of workers. Furthermore, since the plating layer of the electroplating process is thick, at least above 200 μm and even up to 500 μm, this also results in difficult control of tolerances of the precision parts in the high-voltage substation,the development trend is to develop a non-toxic and simple method for preparing the thin silver coating.

Disclosure of Invention

Aiming at the problems of the traditional silver plating mode in the aspects of process, plated part thickness and the like, the invention provides the method for preparing the aluminum alloy silver plating layer by utilizing the dopamine, so that the preparation process is simplified while the thickness of the plating layer is reduced under the condition of meeting the use requirements of electrical conductivity, thermal conductivity and resistance, and the whole process is environment-friendly and nontoxic.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for preparing an aluminum alloy silver coating by utilizing dopamine is characterized in that a uniform polydopamine coating is generated on the surface of an aluminum alloy, and then a uniform silver coating is reduced and adsorbed on the basis of taking polydopamine as an intermediate layer. The method specifically comprises the following steps:

(1) preparing a dopamine-containing Tris (hydroxymethyl) aminomethane (Tris) buffer solution, placing the polished aluminum alloy sample in an oscillating buffer solution to enable dopamine to spontaneously polymerize, washing with deionized water, and then drying in vacuum to obtain a polydopamine-coated aluminum alloy sample;

(2) and (2) adding ammonia water into a silver nitrate solution to prepare a 2wt% silver-ammonia solution, placing the sample obtained in the step (1) into the silver-ammonia solution, reducing silver ions in the solution into a simple substance by utilizing reducibility and adhesiveness of polydopamine, adsorbing the simple substance on the surface, cleaning and drying to obtain an Ag coating layer uniformly covered.

In the Tris buffer solution containing dopamine, the concentration of the dopamine is 2mg/ml, the concentration of the Tris buffer solution is 10mM, and the pH value is 8.5.

In the step (1), the continuous oscillation time is 24 hours, the drying temperature is 60 ℃, and the drying time is 4 hours.

The concentration of the silver-ammonia solution in the step (2) is 2wt%, and the reaction time is 3-5 h.

The thickness of the poly dopamine coating is about 30 mu m, and the thickness of the silver coating is 30-50 mu m.

The invention has the advantages that:

(1) the preparation process is simple, and comprises two steps of plating the polydopamine layer on the surface of the aluminum alloy and plating silver on the surface of the polydopamine layer, so that the traditional silver plating process is greatly simplified.

(2) Dopamine, Tris buffer solution, silver ammonia solution and the like are used as raw materials, so that the cost is low, and compared with cyanide silver plating, the method is safe, environment-friendly and nontoxic.

(3) Due to the adoption of the two-step silver plating method, compared with the traditional method, the thickness of the plating layer is controlled in a smaller range, and the tolerance of a precision part can be effectively reduced.

Drawings

FIG. 1 is a scanning electron micrograph of the surface topography of the polydopamine-coated aluminum alloy prepared in example 4;

FIG. 2 is a surface energy spectrum of polydopamine coated aluminum alloy prepared in example 4;

FIG. 3 is a scanning electron micrograph of the surface topography of the aluminum alloy covered with the silver plating layer prepared in example 4;

fig. 4 is an X-ray diffraction pattern of the silver-plated layer-covered aluminum alloy prepared in example 4.

Detailed Description

In order to make the content of the present invention more comprehensible, the technical solutions of the present invention are further described below with reference to specific embodiments.

Example 1

(1) Preparing 10mM Tris buffer solution, wherein the pH value is 10.2, dissolving 2mg/ml dopamine in the buffer solution, placing the polished aluminum alloy sample in the buffer solution, oscillating for 24 hours, cleaning with deionized water, and drying in vacuum for 4 hours at 60 ℃;

(2) adding ammonia water into a silver nitrate solution to prepare a 2wt% silver-ammonia solution, placing the sample obtained in the step (1) into the silver-ammonia solution for 3 hours, reducing silver ions in the solution into a simple substance by utilizing the reducibility and the adhesiveness of dopamine, adsorbing the simple substance on the surface, cleaning and drying the sample to obtain a final sample; due to the fact that Tris buffer is too strong in alkalinity, the polymerization amount of polydopamine is reduced, the nonuniformity of a sample is increased, and reduced silver ions are greatly reduced.

Example 2

(1) Preparing a Tris buffer solution (pH =8.5 and 10 mM) containing 2mg/ml of dopamine, placing the polished aluminum alloy sample in the buffer solution, oscillating for 12 hours, cleaning with deionized water, and drying in vacuum for 4 hours at the temperature of 60 ℃;

(2) adding ammonia water into a silver nitrate solution to prepare a 2wt% silver-ammonia solution, placing the sample obtained in the step (1) into the silver-ammonia solution for 3h, reducing silver ions in the solution into a simple substance by utilizing the reducibility and the adhesiveness of dopamine, adsorbing the simple substance on the surface, cleaning and drying the sample, and obtaining the final sample.

Example 3

(1) Preparing a Tris buffer solution (pH =8.5 and 10 mM) containing 2mg/ml of dopamine, placing the polished aluminum alloy sample in the buffer solution, oscillating for 24 hours, cleaning with deionized water, and drying in vacuum for 4 hours at the temperature of 60 ℃;

(2) and (3) placing the sample in a 2wt% silver nitrate solution for 3h, reducing silver ions in the solution into a simple substance by utilizing the reducibility and the adhesiveness of dopamine, adsorbing the simple substance on the surface, cleaning and drying the sample, and obtaining the final sample.

Example 4

(2) adding ammonia water into a silver nitrate solution to prepare a 2wt% silver-ammonia solution, placing the sample obtained in the step (1) into the silver-ammonia solution for 3h, reducing silver ions in the solution into a simple substance by utilizing the reducibility and the adhesiveness of dopamine, adsorbing the simple substance on the surface, cleaning and drying the sample, and finally obtaining a uniformly-covered silver plating layer, wherein the thickness of the polydopamine plating layer is 30 microns, and the thickness of the silver plating layer is 30 microns.

Fig. 1 and fig. 2 are a scanning electron micrograph and an energy spectrum picture of the surface morphology of the poly-dopamine coated aluminum alloy, and the electron micrograph shows that the surface of the aluminum alloy is relatively flat and has no polishing traces, which indicates that a layer of poly-dopamine layer is successfully coated on the surface of the aluminum alloy, and an energy spectrum of a component C, O of poly-dopamine also indicates that the poly-dopamine is rich in content and is uniformly distributed.

Fig. 3 is a scanning electron microscope photograph of the surface morphology of the aluminum alloy covered with the silver coating, and it can be seen that a large amount of silver simple substances are adsorbed on the surface of the polydopamine layer, and the reason for forming the morphology is that catechol groups on the polydopamine layer firstly have a chelation reaction with metal ions adsorbed around the catechol groups, and then the metal ions are reduced in situ by using the strong reducibility of the catechol groups to generate metal nanoparticles, so that the silver coating is formed on the surface of the polydopamine layer in this way.

Fig. 4 is an X-ray diffraction pattern of the aluminum alloy covered with the silver plating layer, and it can be seen that diffraction peaks corresponding to (111), (200), (220), (311), (022) crystal planes of aluminum and silver are respectively observed at about 38 °, 44 °, 64 °, 77 °, and 82 °, indicating that the silver plating layer has a higher occupancy ratio on the surface of the aluminum alloy.

The above description is only a preferred embodiment of the present invention, and should not be taken as limiting the invention in any way, and all technical solutions that fall under the spirit of the present invention are included in the scope of the present invention.

Claims

1. A method for preparing an aluminum alloy silver coating by utilizing dopamine is characterized by comprising the following steps: and generating a uniform polydopamine coating on the surface of the aluminum alloy, and reducing and adsorbing a uniform silver coating on the basis of taking polydopamine as an intermediate layer.

2. The method for preparing an aluminum alloy silver coating using dopamine as claimed in claim 1, wherein: the method specifically comprises the following steps:

(1) preparing a Tris buffer solution containing dopamine, placing the polished aluminum alloy sample in an oscillating buffer solution to enable the dopamine to spontaneously polymerize, washing with deionized water, and then drying in vacuum to obtain a polydopamine-coated aluminum alloy sample;

(2) and (2) adding ammonia water into a silver nitrate solution to prepare a silver-ammonia solution, placing the sample obtained in the step (1) into the silver-ammonia solution, reducing silver ions in the solution into a simple substance by utilizing reducibility and adhesiveness of polydopamine, adsorbing the simple substance on the surface, cleaning and drying to obtain a uniformly covered silver coating.

3. The method for preparing the aluminum alloy silver coating by using dopamine according to claim 2, characterized in that: in the Tris buffer solution containing dopamine, the concentration of the dopamine is 2mg/ml, the concentration of the Tris buffer solution is 10mM, and the pH value is 8.5.

4. The method for preparing the aluminum alloy silver coating by using dopamine according to claim 2, characterized in that: in the step (1), the continuous oscillation time is 24 hours, the drying temperature is 60 ℃, and the drying time is 4 hours.

5. The method for preparing the aluminum alloy silver coating by using dopamine according to claim 2, characterized in that: the concentration of the silver-ammonia solution in the step (2) is 2wt%, and the reaction time is 3-5 h.