CORROSION OF NICKEL-CHROMIUM DEPOSIT ON AISI-316L STAINLESS-STEEL IN RADIOACTIVE WATER WITH AND WITHOUT FLUORIDE AT PH-4

The electrochemical behavior of samples was studied using potentiodynamic techniques at low scan rates, cyclic voltammetry at high scan rates and electrochemical impedance spectroscopy. The surfaces were examined and analyzed by scanning electron microscopy and X-ray microanalysis, respectively. The results from these different methods are discussed. They show that the deposit is more easily corroded than the AISI 316L stainless steel in presence or absence of fluoride. With fluoride and at the prepassive potentials, the Warburg straight line indicates that there is ionic diffusion in the nickel-chromium deposit oxide. The equivalent circuits for the nickel-chromium are proposed and indicate that the deposit can take part in localized corrosion. The use of high scan rates shows the transient kinetics of the oxide formation in presence of fluoride. With fluoride, the pitting currents are higher for nickel-chromium deposits. The SEM photographs and polarization curves shaw that the Ni-Cr deposit is locally corroded by fluoride, leading to the possibility of crevice formation under this and in 316L stainless steel.