electroplating

Electroplating is a method of depositing a thin metal coating onto a conductive substrate by passing an electric current through an electrolyte containing dissolved metal ions. The coated metal is reduced from ions at the cathode, while the anode may dissolve to replenish ions. The resulting layer adheres to the surface and can impart corrosion resistance, hardness, or decorative appeal.

The process relies on electrochemistry, governed by Faraday's laws, and requires an electrolytic bath, typically containing a metal salt, a supporting electrolyte, and sometimes complexing agents. The substrate acts as the cathode while an inert or soluble metal anode supplies ions. Upon current application, metal ions are reduced and deposited on the surface.

Common coating metals include copper, nickel, chromium, silver, gold, tin, and zinc. Baths may be cyanide-based or cyanide-free; cyanide baths pose safety and environmental concerns. Bath composition, pH, temperature, and current density influence deposit quality, with typical temperatures from room to a few tens of degrees Celsius.

Process steps usually include cleaning, degreasing, activation, masking of areas not to be plated, plating, rinsing, drying, and inspection. Thicknesses range from a few micrometers to tens of micrometers, controlled by current, time, and agitation. Problems such as porosity, blistering, roughness, hydrogen embrittlement, or poor adhesion may occur.

Electroplating is used for corrosion protection, wear resistance, solderability, electrical contact improvement, and decorative finishes. It contrasts with electroless plating, which deposits metal through chemical reduction without external current, and with electroforming, which builds up thick metallic parts. Environmental and safety considerations include waste treatment and regulation of hazardous substances in plating baths.