Abstract
The corrosion inhibition of carbon steel (CS) using the “green” inhibitor, polyvinyl pyrrolidone (PVP) was investigated. This study was conducted at pH 7 and pH 8 in an aerated medium containing 0.1 M NaCl. The effects caused by some additives (KI and untreated clay) were investigated. The study was done over a range of concentrations, temperatures and times. Gravimetric method and electrochemical methods (electrochemical impedance spectroscopy (EIS) and potentiodynamic polarisation) were applied. The adsorption of PVP led to the formation of a protective film on the metal/solution interface and an increase in the thickness of the electronic double layer as revealed by EIS results. Tafel results indicated that PVP is a mixed-type inhibitor, affecting the iron dissolution and the cathodic reaction as well. The addition of KI to PVP and NaCl-containing solutions significantly increased the inhibition efficiency, while the addition of UC reduced the inhibition efficiency. The adsorption mechanism was fitted with a Langmuir isotherm. The kinetic and thermodynamic parameters (E*app, K, ∆G°ads, ∆H° and ∆S°) were evaluated. The thermodynamic parameters support the % IE results of WL, EIS, and Tafel indicating that PVP is a good corrosion inhibitor for CS in solutions containing NaCl at pH7 and pH8. The addition of KI additives improves the % IE of PVP especially at pH8.