Electroplating is the application of electrolytic cells in which a thin layer of metal is deposited onto an electrically conductive surface. Electroplating is a plating process that uses electrical current to reduce cat ions of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal. Electroplating is primarily used for depositing a layer of material to bestow a desired property (e.g., abrasion and wear resistance, corrosion protection, lubricity, aesthetic qualities, etc.) to a surface that otherwise lacks that property. Another application uses electroplating to build up thickness on undersized parts. The process used in electroplating is called electro-deposition. It is analogous to a galvanic cell acting in reverse. The part to be plated is the cathode of the circuit. In one technique, the anode is made of the metal to be plated on the part. Both components are immersed in a solution called an electrolyte containing one or more dissolved metal salts as well as other ions that permit the flow of electricity. A power supply supplies a direct current to the anode, oxidizing the metal atoms that comprise it and allowing them to dissolve in the solution. At the cathode, the dissolved metal ions in the electrolyte solution are reduced at the interface between the solution and the cathode, such that they "plate out" onto the cathode. The rate at which the anode is dissolved is equal to the rate at which the cathode is plated, vis-a-vis the current flowing through the circuit. In this manner, the ions in the electrolyte bath are continuously replenished by the anode. Other electroplating processes may use a non consumable anode such as lead. In these techniques, ions of the metal to be plated must be periodically replenished in the bath as they are drawn out of the solution.
WHY ELECTROPLATING DONE?
There are several reasons why you might want to coat a conductive surface with a metal. Silver plating and gold plating of jewelry or silverware typically is done to improve the appearance and value of the items. Chromium plating improves the appearance of objects and also improves its wear. Zinc or tin coatings may be applied to confer corrosion resistance. Sometimes electroplating is done simply to increase the thickness of an item.
HOW ELECTROPLATING WORKS ?
Electroplating works like a galvanic cell in reverse. An electrical current reduces cations from a solution so that they can coat a conductive material with a thin layer.
A Closer Look at Electroplating:
In one form of a electroplating, the metal to be plated is located at the anode of the circuit, with the item to be plated located at the cathode. Both the anode and the cathode are immersed in a solution which contains a dissolved metal salt (e.g., an ion of the metal being plated) and other ions which act to permit the flow of electricity through the circuit. Direct current is supplied to the anode, oxidizing its metal atoms and dissolving them in the electrolyte solution. The dissolved metal ions are reduced at the cathode, plating the metal onto the item. The current through the circuit is such that the rate at which the anode is dissolved is equal to the rate at which the cathode is plated.
A simple example of the electroplating process is the electroplating of copper in which the metal to be plated (copper) is used as the anode and the electrolyte solution contains the ion of the metal to be plated (Cu2+ in this example). Copper goes into solution at the anode as it is plated at the cathode. A constant concentration of Cu2+ is maintained in the electrolyte solution surrounding the electrodes: Anode: Cu(s) → Cu2+(aq) + 2 e-
Cathode: Cu2+(aq) + 2 e- → Cu(s)
Common Electroplating Processes:
CuCu20% CuSO4, 3% H2SO4electrotype
AgAg4% AgCN, 4% KCN, 4% K2CO3jewelry, tableware