Experimental and theoretical study of uracil and adenine inhibitors in Sn-Ag alloy/nitric acid corroding system

Two environmentally safe materials, uracil and adenine, were tested experimentally as inhibitors for the corrosion of 70Sn-Ag alloy in aggressive nitric acid solution by electrochemical techniques, as well as theoretically, by comparing some of their quantum chemical properties. Potentiodynamic measurements were used to calculate the corrosion rate in the absence and presence of the inhibitor. Results showed that uracil and adenine molecules can suppress both the cathodic and anodic processes of Sn-Ag alloy corrosion via their adsorption on the alloy surface according to the Langmuir adsorption isotherm. The apparent activation energy was found to increase with increasing inhibitor concentration, and it is always higher for adenine compared to uracil, suggesting that adenine is a more efficient inhibitor than uracil at comparable conditions. This is also corroborated by the values of the resistances for the charge transfer and the adsorbed layer, as well as some thermodynamic functions for adsorption, being all higher for adenine than uracil. The electronic properties of the two inhibitors, obtained using the incomplete neglect of differential overlap quantum chemical approach, were correlated with their experimental findings and support the conclusion that adenine is superior than uracil in inhibiting the acidic corrosion of Sn-Ag alloy. (C) 2008 The Electrochemical Society.