JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Tech IV Year ELECTROMETALLURGY AND CORROSION ENGINEERING Previous Question Paper (February/March - 2022 - R16)

Electroplating of copper is a process used to deposit a layer of copper onto a substrate to improve conductivity, appearance, or as a base for further plating. The process typically utilizes an acidic copper sulfate bath or a cyanide-based bath.

In an acidic sulfate bath, the electrolyte consists of copper sulfate (CuSO₄) and sulfuric acid (H₂SO₄). The copper anode (Cu) undergoes oxidation, releasing copper ions into the solution, while the cathode (the object to be plated) undergoes reduction, where copper ions gain electrons to form a metallic copper coating.

The sulfuric acid increases the conductivity of the bath, and additives such as brighteners or leveling agents are often added to ensure a smooth, uniform, and bright deposit. Proper surface preparation, including degreasing and pickling, is essential to ensure good adhesion of the copper layer to the substrate.

Testing methods for electrodeposits are categorized into physical, chemical, and electrochemical tests. Common methods include thickness measurement (e.g., microscopic, coulometric, or X-ray fluorescence), adhesion testing (e.g., bend test, burnishing test), and corrosion resistance testing (e.g., salt spray test).

1. Salt Spray Test: This is an accelerated corrosion test used to evaluate the protective quality of the electroplated coating. The samples are placed in a closed chamber and exposed to a fine mist of sodium chloride (NaCl) solution. The duration of the test and the appearance of corrosion products (rust or white spots) on the surface indicate the porosity and protective ability of the coating.

2. Adhesion Test (Bend Test): This is a simple destructive method to check the mechanical bond between the coating and the base metal. The plated specimen is bent repeatedly through a specific angle or around a mandrel until failure occurs. If the coating peels, flakes, or blisters during or after bending, it indicates poor adhesion, likely due to improper surface preparation or incompatible plating conditions.