Electroplating is not only an electrochemical process, but also a redox process. The basic process of electroplating is to immerse the parts in the solution of metal salt as the cathode and the metal plate as the anode. After connecting with the DC power supply, the required coating is deposited on the parts.
For example, during nickel plating, the cathode is the part to be plated and the anode is pure nickel plate. The following reactions occur at the cathode and anode respectively:
Cathode: Ni2 + + 2e → Ni (main reaction)
2H + + e → H2 ↑ (side reaction)
Anode (nickel plate): ni-2e → Ni2 + (main reaction)
4OH - - 4E → 2H2O + O2 + 4E (side reaction)
Not all metal ions can be deposited from aqueous solution. 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 the experiment, the possibility of electrodeposition of metal ions from aqueous solution can be obtained from the periodic table of elements.
The anode is divided into soluble anode and insoluble anode, most of which are soluble anode corresponding to 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 in anodic dissolution, insoluble anodes are used in a few electroplating processes. For example, platinum or titanium anodes are mostly used in acid gold plating. The main salt ions in the plating bath are supplemented by adding standard gold containing solution. Chromium plating anode uses pure lead, lead tin alloy, lead antimony alloy and other insoluble anode.