The working principle of electroplating

- Mar 14, 2018 -

Electroplating requires a low-voltage, high-current power supply to the electroplating bath and an electrolyzer composed of a plating solution, parts to be plated (cathode) and an anode. The composition of the electroplating bath varies depending on the plating layer, but contains a main salt that provides metal ions, a complexing agent that can complex metal ions in the main salt, a buffer for stabilizing the pH of the solution, and an anode activator. Special additives (such as brighteners, grain refiners, levelers, wetting agents, stress relieving agents, and fog suppressants). The electroplating process is a process in which a metal ion in a plating solution is reduced to a metal atom by an electrode reaction under the action of an external electric field, and metal deposition is performed on the cathode. Therefore, this is a metal electrodeposition process including liquid phase mass transfer, electrochemical reaction and electrocrystallization.

In the plating bath containing plating solution, the cleaned and specially pre-treated pieces to be plated are used as cathodes, and the anodes are made of plated metal, and the two poles are respectively connected to the positive and negative electrodes of the DC power source. The plating solution consists of an aqueous solution containing a metal-plating compound, a conductive salt, a buffer, a pH adjuster, and an additive. After the power is applied, the metal ions in the plating solution move to the cathode under the action of a potential difference to form a plating layer. The metal of the anode forms metal ions into the plating solution to maintain the concentration of the metal ions being plated. In some cases, such as chrome plating, insoluble anodes made of lead and lead-antimony alloys are used, which only serve to transmit electrons and conduct current. The chromium ion concentration in the electrolyte needs to be maintained by periodically adding a chromium compound to the bath. When electroplating, the quality of the anode material, the composition of the plating solution, the temperature, the current density, the electrification time, the stirring intensity, the precipitated impurities, the power waveform, etc. all affect the quality of the plating and need to be controlled in a timely manner.

First, the electroplating solution has six elements: main salt, additional salt, complexing agent, buffer, anodic activator, and additives.

Electroplating principle includes four aspects: electroplating solution, electroplating reaction, electrode and reaction principle, metal electrodeposition process.

Electrochemical reaction in electroplating reaction: The figure below is a schematic diagram of an electroplating device. The part to be plated is a cathode, which is connected to the negative pole of a DC power source. The metal anode is connected to the positive pole of a DC power source, and the anode and cathode are immersed in the plating solution. When a certain potential is applied between the yin and yang electrodes, the following reaction occurs at the cathode: metal ions Mn+ diffused from the inside of the plating solution to the electrode and the plating solution obtain n electrons from the cathode, and are reduced to metal M. On the other hand, at the anode, a completely opposite reaction occurs with the cathode, that is, dissolution of the metal M occurs at the anode interface, and n electrons are generated as metal ions Mn+.

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