3. Consider that the cathodic reaction for deposition of metal Mj in an alloy, i.e., M(aq)...

 

Transcribed Image Text:

3. Consider that the cathodic reaction for deposition of metal Mj in an alloy, i.e., M(aq) + nje Mj(alloy) is operating in the Tafel region under complete kinetic control. Under such conditions, one form of the Butler-Volmer equation is as follows: ij= njFkj bj (1 - aj) nje FE Cjs exp RT where = kj rate constant for the above reaction a; transfer coefficient for the above reaction Cjs surface concentration of M;j+ nj = number of electrons transferred in overall reaction nje number of electrons transferred in elementary rate-determining step b; stoichiometric coefficient of Mi in elementary rate-determining step Use the following information to determine the pH, Fe2+ concentration and the cathode potential that are required to carry out Ni-Fe alloy deposition at 25C under the following conditions: - overall current density through the cathode is 200 A/m - H evolution consumes 9% of the total current density - - - composition of alloy being plated is 80% Ni and 20% Fe by mass concentration of Ni+ in the electrolyte is 0.6 mol/litre kinetic parameters for Ni deposition in the alloy are kn = 3.5 x 10-11 m/sec and aNi = 0.65 kinetic parameters for Fe deposition in the alloy are kre = 1.3 x 10-12 m/sec and are = 0.46. kinetics of H2 evolution can be described by an expression similar to that of metal deposition: KH2 = 1.3 x 10-8 m/sec and OH2 = 0.70. - nje 1 and b; 1 for each reaction. Assume that the anodic reaction does not involve Fe2+ or H+ ions and that the reaction rates are entirely controlled by kinetics. 3. Consider that the cathodic reaction for deposition of metal Mj in an alloy, i.e., M(aq) + nje Mj(alloy) is operating in the Tafel region under complete kinetic control. Under such conditions, one form of the Butler-Volmer equation is as follows: ij= njFkj bj (1 - aj) nje FE Cjs exp RT where = kj rate constant for the above reaction a; transfer coefficient for the above reaction Cjs surface concentration of M;j+ nj = number of electrons transferred in overall reaction nje number of electrons transferred in elementary rate-determining step b; stoichiometric coefficient of Mi in elementary rate-determining step Use the following information to determine the pH, Fe2+ concentration and the cathode potential that are required to carry out Ni-Fe alloy deposition at 25C under the following conditions: - overall current density through the cathode is 200 A/m - H evolution consumes 9% of the total current density - - - composition of alloy being plated is 80% Ni and 20% Fe by mass concentration of Ni+ in the electrolyte is 0.6 mol/litre kinetic parameters for Ni deposition in the alloy are kn = 3.5 x 10-11 m/sec and aNi = 0.65 kinetic parameters for Fe deposition in the alloy are kre = 1.3 x 10-12 m/sec and are = 0.46. kinetics of H2 evolution can be described by an expression similar to that of metal deposition: KH2 = 1.3 x 10-8 m/sec and OH2 = 0.70. - nje 1 and b; 1 for each reaction. Assume that the anodic reaction does not involve Fe2+ or H+ ions and that the reaction rates are entirely controlled by kinetics.