Abstract
In order to develop alloy resistance in aggressive sulphat ion, the corrosion behavior of metallic glasses Ni92.3Si4.5B32, Ni82,3Cr7Fe3Si4.5B3.2 and Ni75.5Cr13Fe4.2Si4.5B2.8 (at %) at different concentrations of H2SO4 solutions was examined by electrochemical methods and Scanning Electron Microscope (SEM) and X-ray Photoelectron Microscopy (XPS) analyses. The corrosion kinetics and passivation behavior was studied. A direct proportion was observed between the corrosion rate and acid concentration in the case of Ni92.3Si4.5B32 and Ni75.5Cr13Fe4.2Si4.5B2.8 alloys. Critical concentration was observed in the case of Ni82,3Cr7Fe3Si4.5B3.2 alloy. The influence of the alloying element is reflected in the increasing resistance of the protective film. XPS analysis confirms that the protection film on the Ni92.3Si4.5B32 alloy was NiS which is less protective than that formed on Cr containing alloys. The corrosion rate of Ni82,3Cr7Fe3Si4.5B3.2 and Ni75.5Cr13Fe4.2Si4.5B2.8. alloys containing 7% and 13% Cr are 7.90-26.1x10(-3) mm/y which is lower about 43-54 times of the alloy Ni92.3Si4.5B32 (free of Cr). The high resistance of Ni75.5Cr13Fe4.2Si4.5B2.8 alloy at the very aggressive media may due to thicker passive film of Cr2O3 which hydrated to hydrated chromium oxyhydroxide.