THE INHIBITION EFFECT OF TWO COMMERCIAL COMPOUNDS ON INTERFACE STEEL / NATURAL SOFTENED WATER

The protection against the corrosion of the carbon steel in aqueous environment by commercial inhibitors, based of nitrite and alkanolamine, has been studied by electrochemical impedance spectroscopy (EIS) and several analytic methods. An inhibitor’s efficiency has been determined with the two compounds on polished surface in presence of softened water. The results show that the two inhibitors act by the formation of protective layer on interface steel/electrolyte but the efficiency is more important in the case of the nitrite compound thanks to the formation of film with thickness estimated by Atomic force microscopy (AFM) at 0.8 μm after 102 days of immersion. In the case of the nitrites, the inhibitor film is a porous layer, weak conductor and presents a considerable increase of the charge transfer resistance with time. This is a result of an interest protection of the surface against corrosion. The low frequencies limit (L LF) reaches about 150 kOhm cm2 after 59 days of immersion. In the case of the alkanolamine, XPS (X-Rray Spectroscopy) show that the film formed is richer of Fe ions but is offered a considerable protection of the interface, its thickness is about 0.26 μm and L LF reaches about 35.5 kOhm cm2 after 61 days of immersion. The influence of surface state is discussed in this paper, in fact on raw surface steel, no inhibitor efficiency is observed. A few protections are given with a crude surface in contact with water softened in presence of the nitrite compound.