Jawaharlal Nehru Technological University Hyderabad B.Tech IV ELECTROMETALLURGY AND CORROSION ENGINEERING Previous Question Paper (July - 2021 - R16)

Faraday's laws of electrolysis govern the quantitative aspects of electrochemical reactions. The first law states that the mass of a substance deposited or liberated at an electrode is directly proportional to the quantity of electricity passed through the electrolyte. The second law states that when the same quantity of electricity is passed through different electrolytes, the masses of substances deposited at the electrodes are proportional to their chemical equivalent weights.

Cathodic reactions involve the reduction process where electrons are consumed. Common cathodic reactions include the discharge of metal ions (Mⁿ⁺ + ne^- → M) or the reduction of dissolved oxygen (O₂ + 2H₂O + 4e^- → 4OH^-) or hydrogen evolution (2H⁺ + 2e^- → H₂). Anodic reactions involve the oxidation process where electrons are released. Common anodic reactions include metal dissolution (M → Mⁿ⁺ + ne^-) or the evolution of oxygen (2H₂O → O₂ + 4H⁺ + 4e^-).

Polarization is the phenomenon where the potential of an electrode deviates from its equilibrium (reversible) potential due to the passage of an electric current. This deviation results in an overpotential, which acts as a resistance to the electrochemical reaction.

There are three primary types of polarization:

1. Activation Polarization: Occurs when the rate of the electrochemical reaction is controlled by the kinetics of the electron transfer step at the electrode-electrolyte interface. It is significant at low current densities.
2. Concentration Polarization: Occurs when the rate of the reaction is limited by the diffusion of reactants to or products away from the electrode surface. This happens when the concentration of ions near the electrode differs from the bulk solution concentration.
3. Resistance (Ohmic) Polarization: Results from the voltage drop due to the electrical resistance of the electrolyte solution or the presence of a surface film on the electrode.

Polarization is a critical factor in corrosion engineering and electroplating, as it determines the actual rate at which electrochemical processes occur in practical systems.