Predicting the adsorption properties of carbon dioxide corrosion inhibitors using a structure-activity relationship

This paper presents a fundamental study of the influence of various chemical inhibitors on the corrosion rate of mild steel in brine electrolyte under carbon dioxide conditions. The corrosion inhibitors were fitted to a Temkin adsorption isotherm, and various fundamental constants of adsorption (i.e., adsorption equilibrium constants and molecular interaction constants) have been obtained. The inhibitor adsorption mechanism has been discussed in terms of thermodynamics (i.e., DeltaH, DeltaG, and DeltaS), and this revealed that some compounds chemisorb onto the steel electrode. In addition, molecular modeling was undertaken using PCS-SPARTAN Plus and HyperChem Professional, and the various molecular parameters have been correlated with the thermodynamic adsorption properties of the inhibitors. Three-parameter and four-parameter fits for both negative and positive models are discussed. Multiple linear regression was performed on various combinations of molecular descriptors to describe the enthalpies and entropies of adsorption. Similarly, principal component analysis (PCA) was employed to corroborate the scientifically based selection of molecular descriptors used in the multivariate regression models. (C) 2004 The Electrochemical Society.