The effect of concentration and structure of LA/CE based inhibitors on the corrosion rate of mild steel in aqueous chloride solution

This paper discusses the effectiveness and mechanism of inhibition of a number of green corrosion inhibitors for mild steel, based on Cerium (III) and Lanthanum (III). These compounds include cerium hydroxy naphthoate (Ce(HNpt) 3 ), lanthanum hydroxy naphthoate (La(HNpt) 3 ), cerium hydroxy cinnamate (Ce(HCin) 3 ) and lanthanum hydroxy cinnamate (La(HCin) 3 ). Linear Polarization Resistance (LPR) measurements showed that lanthanum compounds, even at very low concentrations (100ppm), had a strong corrosion inhibiting effect with a large reduction in corrosion rate. However, in the case of the cerium compounds the effect on corrosion rate was much less. The mechanism of corrosion inhibition was investigated by using potentiodynamic polarization techniques. The results suggested that the lanthanum based compounds act as anodic inhibitors and improve the resistance of mild steel against pitting corrosion and localized attack. Scanning Electron Microscopy (SEM) combined with Energy Dispersive X-ray Spectroscopy (EDXS) indicated the presence of a more adherent film in the case of lanthanum based compounds than for the cerium compounds. The presence of the film is thought to be responsible for the observed corrosion inhibition.