Abstract
The gravimetric method was used to study the inhibitory properties of four direct dyes (Direct Black 22, Direct Red 23, Direct Yellow 12, and Direct Black 101), two acid dyes (Methyl Orange and Methyl Red) and one reactive dye (Reactive Black 5) during the corrosion of aluminum in 0.1 M sodium hydroxide solutions at room temperature. The effects of halide salts addition (0.1 M NaCl or KI) to dye solutions were also investigated. The inhibition efficiency of these dyes increased with the concentration and addition of halide salts. The activation energy values calculated for the corrosion process suggested that the inhibitor molecules were physically adsorbed on the Al surface. Corrosion inhibition efficiency increased with dye concentration, with a maximum value of 77% obtained for 2.5 mM Direct Yellow 12 (DY12) in the presence of 0.1 M KI. Corrosion inhibition is attributed to the adsorption of dye onto the Al surface via a physical adsorption mechanism. Quantum chemical calculations using the density functional theory (DFT, B3LYP/6-31G) and semi-empirical AM1 and PM3 methods were performed on the 7 studied dyes to determine the relationship between their molecular structure and corrosion inhibition efficiencies. Also, the calculation was made for Bismarck Brown to use it as a model quality test. (C) 2014 Elsevier B.V. All rights reserved.