11.3 - Electroplating

Electroplating is a process in which a thin layer of metal is deposited onto the surface of an object using an electric current. This process is widely used to improve the appearance, prevent corrosion, and reduce friction of metal objects.

Electroplating involves the use of an electrolytic cell, where a metal cation in a solution is reduced onto a surface by passing an electric current through it.

The principle behind electroplating is based on the laws of electrolysis. When an electric current is passed through an electrolyte, the metal ions in the solution get reduced at the cathode (the object to be plated), and the metal from the anode dissolves to replenish the metal ions in the solution.

The electroplating setup consists of the following components:

• Electrolyte: A solution containing metal salts of the metal to be plated (e.g., silver nitrate solution for silver plating).
• Two electrodes: The anode (positive electrode) made of the metal to be plated (e.g., silver) and the cathode (negative electrode) made of the object to be electroplated (e.g., a piece of copper or iron).
• Power Source: A direct current (DC) power supply that provides the necessary electric current.

During the electroplating process:

• The object to be electroplated is connected to the cathode (negative terminal) of the power supply.
• The metal from the electrolyte solution is deposited onto the object at the cathode as a thin, even layer.
• The anode, made of the same metal as the one being plated, gradually dissolves to release metal ions into the solution.

The chemical reactions occurring at the anode and cathode during electroplating are:

• At the Cathode (Object being plated): $$ \text{Metal ion (aq)} + e^- \rightarrow \text{Metal (s)} $$
• At the Anode (Electrode made of metal): $$ \text{Metal (s)} \rightarrow \text{Metal ion (aq)} + e^- $$

For example, in the case of silver electroplating, the electrolyte solution contains silver nitrate (AgNO₃). When current passes through the solution, silver ions (Ag⁺) are reduced at the cathode, plating the object with silver:

• At the Cathode (Object to be plated): $$ \text{Ag}^+ (aq) + e^- \rightarrow \text{Ag} (s) $$
• At the Anode (Silver electrode): $$ \text{Ag} (s) \rightarrow \text{Ag}^+ (aq) + e^- $$

Electroplating is used in various applications:

• In the jewelry industry to give objects a shiny, attractive finish.
• In the automotive industry to coat parts with metals like chrome for protection against corrosion and wear.
• To prevent rusting of iron and steel by plating with metals such as zinc (galvanization).
• In the electronics industry to provide a conductive coating on components like connectors and contacts.

The quality and thickness of the electroplated layer depend on several factors:

• Current Density: A higher current density leads to faster deposition but may result in an uneven coating.
• Concentration of Electrolyte: A higher concentration of metal ions in the electrolyte solution leads to better plating efficiency.
• Time: Longer electroplating times result in thicker coatings.
• Temperature: Higher temperatures can speed up the plating process but may also affect the quality of the deposit.