Growth mechanisms of cerium layers on galvanised steel

In recent times, a good deal of research efforts have been devoted to develop new environmentally friendly corrosion inhibitors as an alternative to the classic systems based on chromates. In this way, rare earth salts have demonstrated a high efficiency in different metal/corrosive systems. Lanthanide salts are classified as cathodic inhibitors, although, it is not clarified the species which contribute to the formation, in the cathodic areas, of the oxide/hydroxide of the lanthanide ion. In this work, the inhibitor behaviour of CeCl3 for galvanised steel in aerated NaCl solutions has been investigated. SEM and EDS studies showed that Ce is initially stochastically dispersed onto the metallic surface, forming a continuous film on its surface after prolonged immersion time. Electrochemical calculations seem to indicate that, under experimental conditions only Ce3+ is expected on the metallic surface and this is consistent with experimental findings