Study of the properties of a multi-component inhibitor used for water treatment in cooling circuits

This work is devoted to the corrosion inhibition of a carbon steel in a 200 mg l^–1 NaCl solution by an original multicomponent inhibitor: fatty amines in association with phosphonocarboxylic acid salts and a biocide at low dosage. Its principal advantage is the absence of toxicity and its biodegradability. Steady-state current–voltage curves were combined with electrochemical impedance measurements to characterize the inhibitive properties of each compound and to optimize the concentration of the compounds in the mixture. Phosphonocarboxylic acid salts were observed to act as an anodic inhibitor whereas mixed action was shown for fatty amines. The inhibitive efficiency was increased when the phosphonocarboxylic acid salt concentration was increased whereas for fatty amines an increase of the concentration did not improve corrosion inhibition. Optimal concentrations of fatty amines and phosphonocarboxylic acid salts were determined. X-ray photoelectron spectroscopy (XPS) was used to analyse the layer formed on the metal surface by the inhibitive mixture. The film was composed of an iron oxide/hydroxide mixture incorporating the organic compounds. The inhibitive molecules interact with the iron oxides.