Electrochemical and surface topographic studies of oxide film passivation of aluminum

Passivation of corroding surfaces in aluminum etch pits and tunnels was investigated by step reductions and cathodic pulses in applied etching current. Morphology study shows that, in the early stage of passivation, the corroding surface consisted of recessed patches, which are actively dissolving surface, and flat passive area. These active patches are found within the potential range between the potential of zero charge (E[subscript]PZC) and the repassivation potential, and the actively corroding area increases with potential, from zero near E[subscript]PZC to the entire surface at the repassivation potential. A mathematical model describing the progress of passivation was developed and compared to experimental measurements. The calculation indicated that patchwise passivation takes place in times less than 100 [mu]s and the fractional active area is a function of potential below the repassivation potential. It thus suggests that the patches are islands of specifically adsorbed chloride ions, so that the passivation is controlled by desorption of these ions. For cathodic current pulses, the effect of pulse time and current pulse ratio on passivation and pit nucleation was investigated through the morphological study of actively dissolving tunnel tip surface and accompanying potential transients

Electrochemical and surface topographic studies of oxide film passivation of aluminum

Passivation of corroding surfaces in aluminum etch pits and tunnels was investigated by step reductions and cathodic pulses in applied etching current. Morphology study shows that, in the early stage of passivation, the corroding surface consisted of recessed patches, which are actively dissolving surface, and flat passive area. These active patches are found within the potential range between the potential of zero charge (E[subscript]PZC) and the repassivation potential, and the actively corroding area increases with potential, from zero near E[subscript]PZC to the entire surface at the repassivation potential. A mathematical model describing the progress of passivation was developed and compared to experimental measurements. The calculation indicated that patchwise passivation takes place in times less than 100 [mu]s and the fractional active area is a function of potential below the repassivation potential. It thus suggests that the patches are islands of specifically adsorbed chloride ions, so that the passivation is controlled by desorption of these ions. For cathodic current pulses, the effect of pulse time and current pulse ratio on passivation and pit nucleation was investigated through the morphological study of actively dissolving tunnel tip surface and accompanying potential transients.</p

Electrocatalytic activity of Cu electrode in electroreduction of CO2

The electrocatalytic activity of Cu electrode in the electrochemical reduction of carbon dioxide (CO2) was investigated. Electroreduction mechanism of CO2 was studied by the adsorption/desorption behaviors of reacting species by using an in-situ electrochemical quartz crystal microbalance. (EQCM) and the surface changes measured by ex-situ SEM, AES, and XRD analysis. During cathodic reduction of CO2 on Cu, the adsorption of amorphous carbon was observed. After electrolysis time of 1 h at constant cathodic potential, the poisoning of amorphous carbon resulted in the decrease of the faradaic efficiency for the formation of hydrocarbons such as CH4 and C2H4. On the other hand, the potential modulation method caused the change of the surface structure of copper, i.e. the formation of cuprous oxide (Cu2O). This structural change prevented the adsorption of amorphous graphite and the constant production rate of methane was obtained in long-term electrolysis

Evolution of Microscopic Surface Topography during Passivation of Aluminum

The time evolution of microscopic topography on corroding aluminum surfaces during oxide film passivation was characterized. Passivation was studied after galvanostatic etching in 1N at 65°C, in both aluminum etch tunnels (by scanning electron microscopy) and micron‐size cubic etch pits (by atomic force microscopy). Step reductions of applied current initiated passivation. At times of 1 to 300 ms after current steps, the corroding surface was microscopically heterogeneous, consisting of a number of small corroding patches 0.1 to 1 μm in width, which were surrounded by passive surface. As some patches grew by dissolution, others were passivated, until eventually only one patch remained on the pit or tunnel surface. The topography of the corroding surface was controlled by the potential: the surface dissolved uniformly at the repassivation potential , while partial passivation to produce patches occurred at potentials more cathodic than . Patches were unstable at potentials below and would ultimately passivate. Topographic evolution during passivation was very similar for pits as for tunnels, except that the time scale of the process is much longer for tunnels than for pits (200–300 ms vs. 11–20 ms). The difference of time scales was due to the different corroding surface areas of pits and tunnels. Patches are probably defined by a surface layer which inhibits passivation.This article is from Journal of the Electrochemical Society 141 (1994): 1446–1452, doi:10.1149/1.2054944. Posted with permission.</p