The addition of molybdenum to amorphous Fe-18C alloy results in passivation by anodic polarization even in 1N HCl. However, its addition in a large amount increases the anodic current density in both the active and passive regions and lowers the corrosion potential. X-ray photo-electron spectroscopy was used to determine the correlation between the composition of surface film and the corrosion resistance of alloys. The alloying with a proper amount of molybdenum facilitates the formation of molybdenum-enriched surface film as a result of active dissolution and hence assists the passivation by the formation of passive hydrated iron oxy-hydroxide film. However, the excess addition of molybdenum leads to an excess increase in the anodic activity of alloys and accordingly is not greatly effective for increasing the corrosion resistance
