Electrochemical behavior of aluminum bronze in sulfate-chloride media

Abstract

The electrochemical behavior, especially the corrosion and passivation, of a Cu-Al bronze was investigated. Conventional electrochemical techniques including open-circuit potential, anodic polarization, cyclic voltammetry and electrochemical impedance spectroscopy were used. It was found that the addition of chloride ion up to 0.15 M in 0.5 M Na 2 SO 4 solution decreases the corrosion rate due to the formation of CuCl, whereas at higher concentration of the chloride ion, the corrosion rate increases due to the formation of the soluble CuCl 2 -. The activation energy was found to be 10 kJ mol -1 . This value indicates that the corrosion process is under diffusion control. The impedance measurements showed that the passive film can be represented by a duplex layer, a relatively thick porous outer film on top of a thin compact layer. An equivalent circuit was used to explain and analyze the impedance data. The model includes another R-C combination and Warburg impedance in addition to the simple Randles cell to account for the spontaneously formed passive film and the diffusion phenomena.

Corrosion of Bronzes by Extended Wetting with Single versus Mixed Acidic Pollutants

“…The film resistance ( R f ) describes the patina passivity as well as the film capacitance ( C f ). The resistance ( R ct ) and capacitance ( C ct ) of charge transfer relate to the reaction kinetics [ 31 , 37 ]. The resistance of the electrolyte is represented by R e .…”

“…The resistance of the electrolyte is represented by R e . The Warburg ( W ) represents diffusion phenomena as well as the patina porosity [ 5 , 31 , 37 ]; the constant phase element (CPE) related to the capacitance ( Q ) shows the inhomogeneous character of the system, frequently considered as electrode roughness. The n index is present only with Q and the values are between 1 and 0.…”

“…This index decrease in its values with the increase of the surface roughness. It can also represent the inhomogeneity porosity related to the Warburg element ( n close to 0.5), indicating a possible presence of a diffusion mechanism inside the layer [ 37 ]. The single circuit element cannot be distinguished, allowing the sums of the resistances ( R t = R e + R f + R ct ) and of the capacitances ( C t = C f + C ct + Q ) to be found.…”

“…The relative thickness T of the patina (single or multilayer) can be evaluated using the following equation [ 37 ]: …”

Electrochemical Stability of Cu–10Al–10Zn, Cu–10Al–10Ni, and Cu–10Ni–10Zn Ternary Alloys in Simulated Physiological Solutions

“…It is clear that the Cu-10Ni-10Zn has the highest total impedance and the higher and more flat phase maximum indicating its passive behavior [44]. The impedance data were analyzed using software provided with the impedance system where the dispersion formula was used [5,45,46]. For a simple equivalent circuit model consisting of a parallel combination of a capacitor, C dl , and a resistor, R ct , in series with a resistor, R s , representing the solution resistance, the electrode impedance, Z, is represented by the mathematical formulation:…”