Aylin Aytaç

Effect of heat treatment on electrochemical behaviour of binary aluminium model alloys

Abstract In order to understand the role of various trace, impurity and alloying elements on the electrochemical activation of aluminium in chloride solution, binary alloys of type Al–Pb, Al–Bi, Al–In, Al–Sn, Al–Mg and Al–Zn were investigated by use of electrochemical and surface-analytical techniques. Al–Pb and Al–Bi alloys were electrochemically activated as a result of high temperature heat treatment. However, alkaline etching or mechanical polishing significantly reduced the activation. Alloys Al–In and Al–Sn were electrochemically activated regardless of surface condition. The activation of Al–Pb alloys is attributed to enrichment of lead, presumably in metallic form, at the metal–oxide interface by segregation and diffusion along the grain boundaries. In the presence of chloride, lead destabilises the surface oxide, giving rise to unexpected oxidation of the underlying aluminium at potentials well below the pitting potential. It is suggested that the resulting detachment of the Pb from the aluminium surface causes repassivation. Aluminium is not activated by Mg or Zn as a result of high temperature heat treatment.

Effect of trace elements on electrochemical properties and corrosion of aluminium alloy AA3102

Abstract The purpose of this work is to study the effect of heat treatment and chemical processing on the electrochemical behaviour of aluminium alloy AA3102. Aluminium alloy 3102 was electrochemically activated in chloride solution as a result of heat treatment for periods exceeding 10 min at temperatures higher than 400 °C. The electrochemical activation was determined by the presence of deep negative potential transients when exposed to an acidified chloride solution. Furthermore, the anodic current densities became large at a given potential relative to the as-extruded surface as a result of high temperature heat treatment. This activation phenomenon was attributed to enrichment of the surface by lead, which was present in the material as a trace element. Enrichment of lead at the metal–oxide interface was ascertained by GD-OES depth profiling. Chemical and structural changes occurring in the oxide as a result of heat treatment did not have a direct role in the activation process. It was also shown that enrichment of the surface by lead had a sacrificial effect in protecting the surface against pitting corrosion.

Electrochemistry of the Nickel Electrode as a Cathode Catalyst in the Media of Acidic Peroxide for Application of the Peroxide Fuel Cell

Hydrogen peroxide reduces on the nickel electrode surface in the acidic medium. On the nickel electrode the passive film layers such as NiS and NiOOH form in the peroxide free solution. However the nickel surface was activated with the addition of the peroxide. The cyclic voltammetry (CV) and impedance (EIS) studies verified the passivation and activation states in peroxide free acidic solution and the acidic peroxide solution. The electrochemical reactions of the sulphuric acid and peroxide at nickel electrode were electrochemically analyzed by cyclic voltammetry (CV) and impedance spectroscopy (EIS)