Oscillatory passive active transition during the corrosion in nickel chromium layer systems

The electrochemical corrosion of the porous layer system nickel/chromium was investigated combining classical open circuit measurements, cyclic voltammetry, and zero-resistance Ammeter experiments. Under moderate conditions as there are low chloride concentration, pH 6, and high oxygen content the nickel layer acts as sacrificial anode, whereas at the chromium top layer oxygen reduction takes place. Under conditions of limited access of oxygen into pores potential oscillations occur which indicates a change of corrosion mechanism. Thereby the anode reaction changes between nickel and chromium dissolution. The respective cathode reaction is oxygen reduction or hydrogen evolution. The modeling of the potential oscillation reveals the character of the potential-dependent Flade potential as function of the proton concentration.