No abstract

In this work, the inhibition behaviour of rare earth (RE) salts (Y(NO 3 ) 3 .6H 2 O, CeCl 3 .7H 2 O) in conjunction with metasilicates (Na 2 SiO 3 .5H 2 O) for carbon steel A37 and in aerated 3%NaCl solutions has been investigated. Corrosion inhibition power evaluation and surface layer characterisation have been carried out by electrochemical measurements (potentiodynamic polarisation and impedance) followed by X-ray photoelectron spectroscopy. It was demonstrated that the binary RE/SiO 22 3 improved the protective role of oxide/hydroxide films formed on the steel. Electrochemical tests showed that the cathodic and anodic reactions were both inhibited to some extent, leading to a decreased rate of the global corrosion process. The maximum protective inhibition against corrosion attack was evident when an RE/SiO 22 3 ion mixture was added. Surface analysis revealed the diverse nature of inhibitor coverage on the steel.

Electrochemical measurements (steady-state current-voltage curves and AC impedance) were coupled with mass-loss measurements, SEM examinations, and EDSX analyses to investigate the inhibition of corrosion of a carbon steel by a mixture of phosphonic acid HEDP (acid 1, hydroxyethylene, 1-1 diphosphonic) and sodium metasilicate pentahydrate Na 2 SiO 3 . 5H 2 O in an industrial hard water containing 3.10 À3 M Ca 2þ ions. At pH 7, HEDP and Ca 2þ act in a synergistic manner, by formation of a HEDP and calcium containing layer. Addition of silicate at this pH value, allows to reach an efficiency of 94% due to an additive inhibition effect. At pH 11, metasilicate, HEDP, and Ca 2þ ions reinforce the passive layer in a synergistic way. The mixture (1.7 · 10 À5 M HEDP þ 2.6 · 10 -3 M SiO 2À3 ) in the Ca 2þ containing electrolyte is shown to be able to inhibit efficaciously the corrosion of iron at room temperature, considering uniform corrosion at pH 7 or pitting corrosion at pH 11.