Estimation of the parameters of oxide film growth on nickel-based alloys in high-temperature water electrolytes

The Mixed-Conduction Model (MCM) has been adapted to obtain the main kinetic and transport parameters for passive film growth on nickelbased alloys in high-temperature electrolytes. For the purpose, a procedure for the calculation of these parameters from electrochemical impedance spectroscopic data measured on Ni-15% and Ni-20%Cr alloys in 0.1M Na2B4O7 at 300°C in a wide potential range has been devised. The obtained sets of parameters have been used to successfully predict the steady-state current density versus potential dependence for the two Ni-Cr alloys, as well as the thickness versus time dependence for films grown on Alloy 600 at times ranging between a few minutes and a few thousand hours. The calculations are supported by results of previous XPS measurements of film growth on Alloy 600 showing that the barrier layer growing in the early stage consists of Cr2O