KINETICS OF ALTERNATING CURRENT ELECTROCHEMICAL AND CORROSION PROCESSES.

摘要

This thesis is comprised of an experimental investigation of the effect of alternating current (AC) and alternating voltage (AV) on several electrochemical systems, and a theoretical analysis of the AC effect on a copper/copper ion system. The electrodeposition of zinc with superimposed AC has also been examined. The rotating electrode technique was employed to carry out the investigations.;Superimposed AC (or AV) changed the exchange current densities and the apparent Tafel slopes of the electrode reaction. In the case of the Cu/Cu('2+) system, the anodic current density exhibited a maximum with respect to superimposed AC or AV. The number of electrons transferred remained as two even with AC application, and the determination of the reaction order with AC was not successful due to the variation of the transfer coefficients. Scanning electron micrographs revealed a change in the surface morphology of Cu deposits obtained with AC. The superimposition of AV seemed more pronounced than that of AC but the effect of both AC and AV modulations were similar.;AV modulation on the mild steel electrode increased the exchange current density with an increase in AV. The kinetic parameters of the Fe('2+)/Fe('3+) system could not be evaluated due to the nonlinear nature of the polarization curves, and a procedure to evaluate them has been suggested. The superimposition of AC during zinc electrodeposition resulted in a fairly uniform deposit and a significant reduction in the formation of zinc dendrites.;The proposed theoretical model for AC modulation on a rotating disk electrode for a metal/metal ion system incorporated the double layer capacitance, the variation in the surface concentration with AC and the ohmic potential. The model predictions gave a qualitative agreement with the experimental results. The reasons for quantitative discrepancies have also been discussed.;It was found that AC and AV superimposition shifted the rest potential in the active direction in systems such as Cu/Cu('2+) (metal/metal ion) in acid sulfate solutions, mild steel in HC1 (mixed potential), and Zn/Zn('2+) in chloride solutions. The rest potential shift was in the noble direction in the Fe('2+)/Fe('3+) (redox) system.