Anodic Dissolution of Iron in Acid Sulfate Under Mass Transport Control

Abstract

is clear that there is a strong (111) preferred orientation for Cu plated from the cyanide bath, which is reduced by 70% via interspersion of the Ag layers (at the 6.5% level).A very significant finding from Table II1 is that Ag displacement deposition apparently occurs epitaxially and exclusively on Cu(lll) planes. Only the (111) orientation is detected for Ag in the as-deposited multilayer, and the diffracted x-ray intensity is 6.6% of that for Cu(lll) in the same specimen. Assuming that (111) diffraction is equivalent for Cu and Ag, which should be a reasonable approximation for metals having the same crystal structure, this percentage should reflect the concentration of Ag in the displacement layers, which is 5.5%. In view of the limitations on such an assumption, the agreement is good, suggesting that nearly 100% of the Ag grows epitaxially on Cu(111) planes.

On the onset of current oscillations at the limiting current region emerged during iron electrodissolution in sulfuric acid solutions

“…This behaviour indicates that the formation of the ferrous salt layer is controlled by mass-transport conditions (convection and migration in the solution) but not on mass-transport through the film pores. This is in agreement with previous studies, which suggest the existence of a liquid salt layer with a viscosity higher near the electrode than in the bulk of the solution, based on additional information obtained from electrohydrodynamic impedance measurements [45]. During our experiments with a downward-facing Fe electrode, a descending dense fluid was observed from the Fe surface in agreement with those data.…”

“…In situmicroscopic observations by Epelboin et al [65] as well as by Beck and Alkire [41,42] agree with a crystalline structure. Other studies by Teschke et al [23] and Barcia et al [24,28,45] are in agreement with the formation of FeSO 4 ·7H 2 O, but they suggest a colloidal viscous, nonsolid layer.…”

“…This suggestion is based on injecting experiments conducted at potentials close to the passive-active transition region. In contrast, studies, which suggest the formation of a ferrous salt, are mainly based on experimental data associated with potentials either at the beginning of the LCR or within the LCR, but at potentials far enough from the passive-active transition region [23,24,28,29,[41][42][43][44][45]65].…”

“…Therefore, the overall anodic dissolution reaction in the active state, and the overall passivation reaction at higher potentials may be represented as It is the formation of this salt film that leads to the partial passivation of the Fe electrode resulting in the emergence of the LCR between the active and passive states. Both the salt film formation and the LCR have been studied extensively because of the significance of the salt film on the iron passivation, pit repassivation during pitting corrosion and electropolishing [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52]. Supersaturation of metal salt solutions close to the Fe surface was found to occur prior to the salt precipitation [41][42][43].…”

Hydrodynamic and Mass Transport Coupled through the Viscosity: Analysis of Steady-State and EHD Impedance

“…Moreover, the expected high-frequency limit for phase angle of 180 • was experimentally obtained at p values lower than expected. These results induced the authors 7 to assume an empirical viscosity gradient profile from the electrode to the bulk solution. A viscosity gradient profile may be attributed to a concentration gradient from the surface to the bulk solution.…”