The stable formation of ionic vacancy in a liquid solution was theoretically examined by means of a mean-field approximation based on Debye-Hückel’s framework. As the process of the vacancy formation, metal deposition from electrolyte solution was adopted, where anions associated with metallic ions adsorbed at electrical double layer were transcribed to the inner wall of the vacancy during the reaction. Then, it was concluded that since the formation energy of the vacancy is cancelled out by the electric work between the charged inner wall and its ionic atmosphere, the vacancy is stably self-organized. In copper deposition from potassium chloride solution and sulfuric acid solution, by measuring the partial molar volumes of the vacancies with gravity electrode, the radius of the vacancy theoretically predicted was experimentally validated.
A resistance-wire type strain gauge assembly affixed to the reverse side of the copper plating substrate was used to measure the real-time variation of the internal strain developed during zinc-cobalt alloy deposition by periodic reverse current electrolysis. Zinc content of the alloy deposits obtained at E=−1.06 V (vs. Ag/AgCl/saturated KCl) was 86.0 mol%, and these deposits always exhibited a compressive internal strain and a zinc-rich γ-phase structure. The internal strain, however, sharply shifted towards the tensile direction as soon as part of the zinc was selectively leached from the alloy deposits. This shows that the formation of compressive strain depends not only on the crystal structure of the deposits, but also related to the slightly greater zinc content compared with the stoichiometric amount of zinc that would be found in true γ-phase Co5Zn21. On the other hand, during periodic reverse current electrolysis conditions of cathode pulse Tc=5 s and anode pulse (Ta) 0.1 to 5 s, the internal strain cyclically changed from the compressive direction during the cathode deposition of the zinc-rich γ-phase alloy at Ec=−1.06 V, to the tensile direction during the anodic part (Ea=−0.70 V or −0.90 V) of the cycle, in which selective electrolytically dissolution of zinc from the alloy deposits occurred. Especially, under the plating condition of Ec=−1.06 V, Ea=−0.70 V, Tc=5.0 s and Ta=0.23 s, we obtained the stress-free zinc-cobalt alloy deposits.
Electrochemical noises generated during pitting corrosion of pure iron in bicarbonate solution containing chloride ion were analyzed by using the wavelet transformation with the channel flow double electrode (CFDE). The Fe electrode on which the passivation film was formed in bicarbonate solution was used as the working electrode. Fe(II) or Fe(III) ions emitted from the working electrode was detected by the detecting electrode at the downstream of the working electrode. The working and detecting electrode currents were decomposed as a function of the frequency in time domain by using wavelet transformation. The electrochemical noises having characteristics of rapid rise and slow recovery (RR) appeared repeatedly in the working electrode current. The number of the RR-type noises counted by the values of power spectrum density was equal to that of the pits generated on the working electrode after the electrochemical noise measurement. The dissolution of Fe(II) ion was found to be synchronized with the RR-type noises generation by comparison with the wavelet coefficients. In addition, it was qualitatively proved that Fe(III) ion was dissolved prior to RR-type noise generation.