MODELING OF THE PASSIVATION MECHANISM OF FE-CR BINARY-ALLOYS FROM AC-IMPEDANCE AND FREQUENCY-RESOLVED RRDE .2. BEHAVIOR OF FE-CR ALLOYS IN 0.5 M H2SO4 WITH AN ADDITION OF CHLORIDE

In a previous investigation, three Fe-Cr alloys with various Cr conten ts were examined in 0.5 M H2SO4 with and without an addition of chlori de. These studies were performed with simultaneous analysis of ac impe dance and frequency resolved rrde (rotating ring disc electrode), dete rmined simultaneously at different potentials in the active-to-passive transition range. A reaction model was developed based on the experim ental results. The proposed model describes the main features of the c haracteristic behaviour of the electrode process in a simplified manne r rather than giving a detailed description of the full reaction. The model was initially developed to describe the behaviour of Fe-Cr alloy s in 0.5 M H2SO4 without an addition of chloride and has now been exte nded to 0.5 M H2SO4 With chloride. The simulated model is fitted to th e experimental polarization curve and thereafter the impedance is calc ulated. Then the emission efficiency of iron species and the different ial capacitance, that is the relaxation of the electrical charge store d at the electrode surface as adsorbed species under ac potential pert urbation, are also simulated. (C) 1997 Elsevier Science Ltd.