electroplating refers to a surface processing method in which the cations of the metal to be plated in the plating solution are deposited on the surface of the base metal by electrolysis in a salt solution containing the metal to be plated, so as to form a coating. The performance of the coating is different from that of the base metal and has new characteristics. According to the function of the coating, it can be divided into protective coating, decorative coating and other functional coatings.

Edit the basic principle of electroplating in this paragraph

Electroplating is an electrochemical process as well as a redox process. The basic process of electroplating is that the parts are immersed in a solution of metal salts as the cathode, the metal plate as the anode, and the required coating is deposited on the parts after being connected with a DC power supply. For example, in nickel plating, the cathode is a part to be plated and the anode is a pure nickel plate, and the following reactions occur at the anode and cathode respectively: cathode (plated part): Ni2++2e→Ni (main reaction) 2H++e→H2↑ (side reaction) anode (nickel plate): Ni-2e → Ni2+(main reaction) 4oh-4e → If the side reaction of hydrogen ion reduction to hydrogen on the cathode is dominant, it is difficult for metal ions to precipitate on the cathode. According to experiments, the possibility of electrodeposition of metal ions from aqueous solution can be obtained from the periodic table of elements, as shown in Table 1.1. Anodes are divided into soluble anodes and insoluble anodes, most of which are soluble anodes corresponding to the coating, such as zinc anode for zinc plating, silver anode for silver plating, and tin-lead alloy anode for tin-lead alloy plating. However, due to the difficulty of anode dissolution in a few electroplating, platinum or titanium anodes are mostly used, such as acid gold plating. The main salt ions in the plating solution are supplemented by adding prepared standard gold-containing solution. Pure lead, lead-tin alloy and chromium plating anode are used.

Editing this technological process

generally includes three stages: pretreatment before electroplating, electroplating and post-plating treatment. Complete process:

1. pickling → electroplating hardware and decorative plating process

copper → pattern transfer → acid degreasing → secondary countercurrent rinsing → micro-etching → secondary pickling → tin plating → secondary countercurrent rinsing 2. countercurrent rinsing → pickling → pattern electroplating copper → secondary countercurrent rinsing → nickel plating → secondary washing → citric acid pickling → gold plating →

2. The coating should be fine, flat and even in thickness.

3. The coating should have specified thickness and as few pores as possible.

4. The coating should have specified indexes, such as brightness, hardness and conductivity. 5. The electroplating time and the temperature of the electroplating process determine the thickness of the coating.

Edit the factors that affect the quality of electroplating process in this paragraph

Main salt system

Each plating species will develop a variety of main salt systems and corresponding additive systems, such as cyanide zinc plating, zincate zinc plating, chloride zinc plating (or potassium salt zinc plating), ammonia salt zinc plating, sulfate zinc plating and other systems. Each system has its own advantages and disadvantages, such as good dispersion and depth of cyanide zinc plating solution, fine crystallization of coating, good adhesion to substrate, good corrosion resistance, wide process range, stable and easy operation of plating solution, and less sensitive to impurities, etc. However, it is highly toxic and seriously pollutes the environment. Chloride zinc plating solution is a single salt plating solution without complexing agent, and the wastewater is very easy to treat. The brightness and flatness of the coating are better than other systems; High current efficiency and fast deposition speed; Steel with low hydrogen overpotential, such as high carbon steel, castings and forgings, is easy to be plated. However, due to the weak acidity of chloride ions, it will cause certain corrosion to the equipment, on the other hand, this plating solution is not suitable for deep-hole or tubular parts that need auxiliary anode.

additives

additives include brighteners, stabilizers, softeners, wetting agents, low-zone moving agents, etc. The brighteners are divided into main brighteners, carrier brighteners and auxiliary brighteners, etc. For the same main salt system, there are great differences in the quality of the coatings obtained by using additives made by different manufacturers. Generally speaking, the additives from developed countries such as Europe, America and Japan are the best, followed by Taiwan Province, and those from mainland China are relatively inferior to the first two categories.

the combination of the main salt and additives from a specific manufacturer determines the overall performance of the plating solution. Excellent additives can make up for some shortcomings of the main salt. For example, the deep plating ability of the plating solution obtained by combining excellent chloride zinc plating additives with the main salt is better than that of many cyanide zinc plating solutions.

plating equipment

Hangers: square hangers are used in conjunction with square plating tanks, and circular hangers are used in conjunction with circular plating tanks. Circular plating tanks and hangers are more conducive to ensuring uniform current distribution. For square hangers, it is necessary to add current dispersion devices such as barbed wire around the hangers or shorten the length of anode plates on both sides, and use elliptical anode arrangement as shown in the figure. Stirring device: promote the flow of solution, make the distribution of solution state uniform, and eliminate the stay of bubbles on the surface of workpiece. Power supply: DC, with good stability and small ripple coefficient.

post-treatment

after electroplating, various treatments are carried out on the coating to enhance various properties of the coating, such as corrosion resistance, discoloration resistance and weldability. Dehydration treatment: add dehydrating agent to water, such as after-treatment of bright nickel plating.

passivation treatment: improve the corrosion resistance of the coating, such as zinc plating.

anti-discoloration treatment: add anti-discoloration agents to water, such as silver plating, tin plating and imitation gold plating. Treatment to improve solderability: such as tin plating, the quality of post-treatment technology directly affects the quality of these functions of the coating.

Edit the classification of electroplating in this paragraph

Classification according to coating composition

Chromium plating

Chromium is a silvery white metal with a microstrip sky blue. Although the potential of the electrode is very negative, it has a strong passivation performance, which is quickly passivated in the atmosphere, showing the properties of precious metals, so the chromium plating on iron parts is cathode plating. Chromium layer is very stable in the atmosphere and can keep its luster for a long time. It is very stable in corrosive media such as alkali, nitric acid, sulfide, carbonate and organic acid, but it can be dissolved in halogen acids such as hydrochloric acid and hot concentrated sulfuric acid.

The chromium layer has high hardness, good wear resistance, strong reflective ability and good heat resistance. There is no obvious change in luster and hardness below 5°C; When the temperature is greater than 5°C, it begins to oxidize and discolor; It begins to soften when it is greater than 7 C. Because of its excellent performance, chromium plating layer is widely used as the outer surface layer and functional coating to protect a decorative coating system.

copper plating

The copper plating layer is pink, soft, with good ductility, electrical conductivity and thermal conductivity, and easy to polish. After proper chemical treatment, decorative colors such as bronze, bronze green, black and natural color can be obtained. Copper plating is easy to lose its luster in the air, and it reacts with carbon dioxide or chloride to form a layer of basic copper carbonate or copper chloride film on the surface, and it will generate brown or black copper sulfide under the action of sulfide. Therefore, as a decorative copper plating layer, it is necessary to coat an organic covering layer on the surface.

Cadmium plating

Cadmium is a silvery soft metal with luster. Its hardness is harder than tin and softer than zinc, its plasticity is good, and it is easy to forge and roll. The chemical properties of cadmium are similar to that of zinc, but it is insoluble in alkaline solution, soluble in nitric acid and ammonium nitrate, and slowly soluble in dilute sulfuric acid and dilute hydrochloric acid. Cadmium vapor and soluble cadmium salt are toxic, and cadmium pollution must be strictly prevented. Because cadmium pollution is very harmful and expensive, zinc plating or alloy plating is usually used to replace cadmium plating. At present, the types of cadmium plating solutions widely used in domestic production are: amino-carboxyl complex cadmium plating, acid sulfate cadmium plating and cyanide cadmium plating. In addition, there are cadmium plating on pyrophosphate, alkaline triethanolamine and HEDP.

tin plating

tin has a silvery white appearance, with an atomic weight of 118.7, a density of 7.3g/cm^3, a melting point of 232℃, and valence of divalent and tetravalent, so the electrochemical equivalent tin plating

amounts are 2.12g/A.h and 1.17g/A.h, respectively. Tin has the advantages of corrosion resistance, non-toxicity, easy iron welding, softness and good ductility. Tin coating has the following characteristics and uses: 1. High chemical stability; 2. In electrochemical series, the standard potential of tin is positive, which is a cathodic coating for steel. Only when the coating has no pores can it effectively protect the matrix; 3, tin has good conductivity and is easy to weld; 4. The crystallization of tin began to change from -13℃ to -3℃, and it will be completely transformed into a crystal isom, commonly known as "tin plague", at which time it has completely lost its properties; 5. Like zinc and cadmium coatings, tin can grow into whiskers under high temperature, humidity and closed conditions, which is called long hair; 6. After tin plating, it can be redissolved in hot oil above 232℃ to obtain a shiny patterned tin layer, which can be used as a decorative coating for daily necessities.

zinc plating

zinc is easily soluble in acid and alkali, so it is called amphoteric metal. Zinc hardly changes in dry air. In humid air, a basic zinc carbonate film will be formed on the surface of zinc. In the atmosphere containing sulfur dioxide, hydrogen sulfide and maritime, the corrosion resistance of zinc is poor, especially in the atmosphere containing organic acids at high temperature and humidity, the zinc coating is easily corroded.

The standard electrode potential of zinc is-.76 V. For steel substrate, zinc coating belongs to anodic coating, which is mainly used to prevent the corrosion of steel, and its protective performance is closely related to the coating thickness.

after passivation treatment, dyeing or coating with light protector, the protective and decorative properties of zinc coating can be significantly improved. In recent years, with the development of zinc plating process and the adoption of high-performance brightener for zinc plating, zinc plating has entered protective-decorative application from pure protective purpose.

there are two kinds of zinc plating solutions: cyanide plating solution and cyanide-free plating solution. Cyanide plating solution can be divided into micro-cyanide, low-cyanide, medium-cyanide and high-cyanide. Cyanide-free plating solutions include alkaline zincate plating solution, ammonium salt plating solution, sulfate plating solution and ammonia-free chloride plating solution. Cyanide zinc plating solution has good plating ability, and the obtained coating is smooth and detailed, which has been used for a long time in production. However, because cyanide is highly toxic and seriously pollutes the environment, low-cyanide, micro-cyanide and cyanide-free zinc plating solutions have been adopted in recent years.

according to the way of obtaining the coating, it is divided into

Rack Plating, conventional Barrel Plating, brush plating, pulse electroplating, electroforming, decorative electroplating, such as gold plating, silver plating, copper/nickel/decorative chromium electroplating, such as zinc plating, wear-resistant electroplating, such as hard chromium plating, functional electroplating to improve solderability, such as tin plating to enhance conductivity, such as silver plating, gold plating

. Electroplating alloys include copper-based alloy, zinc-based alloy, cadmium-based alloy, indium-based alloy, lead-based alloy, tin-based alloy, nickel-based alloy, cobalt-based alloy and palladium-nickel alloy. Composite electroplating includes: nickel-based composite electroplating, zinc-based composite electroplating, silver-based composite electroplating and diamond inlay composite electroplating.

Edit anode mud

anode mud

Mud-like fine particles that fall on the bottom of electrolytic cell during electrolytic refining. It is mainly composed of impurities insoluble in electrolyte and metals to be refined in anode crude metal. It often contains precious and valuable metals, which can be recycled as raw materials for refining precious metals such as gold and silver.