JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV ELECTROMETALLURGY AND CORROSION ENGINEERING Previous Question Paper (September - 2021 - R16)

Electroplating is an electrolytic process used to deposit a thin, uniform layer of a metal onto the surface of another metal or conductive object to improve its appearance, corrosion resistance, or mechanical properties. The object to be plated acts as the cathode, while the coating metal acts as the anode in an electrolytic bath containing metal ions.

(i) Throwing power refers to the ability of an electroplating bath to produce a deposit of uniform thickness on a cathode of irregular shape. A bath with high throwing power ensures that recessed areas receive a sufficient amount of metal deposition compared to protruding areas.

(ii) Current efficiency is the ratio of the actual mass of metal deposited at the cathode to the theoretical mass calculated by Faraday's laws of electrolysis. It is expressed as a percentage, reflecting how much of the total current passed through the cell is effectively used for the desired metal deposition reaction rather than side reactions like hydrogen evolution.

(i) Copper plating is typically performed using an acid copper sulfate bath or a cyanide bath. In an acid bath, the electrolyte consists of copper sulfate and sulfuric acid. The copper anode dissolves into the solution as Cu²⁺ ions, which are then reduced at the cathode to form a dense, bright copper layer. It is widely used as an undercoat for other metals to improve adhesion and conductivity.

(ii) Zinc plating (galvanizing) is primarily used for sacrificial protection of steel against corrosion. It is commonly carried out in alkaline cyanide baths or acid chloride baths. The zinc anode provides a continuous supply of Zn²⁺ ions. Because zinc is more anodic than iron, it corrodes preferentially, protecting the underlying steel even if the coating is scratched. The process is essential for automotive parts and structural steel components.