Acid Corrosion Inhibition of Steel by Lamotrigine

Corrosion inhibition effect of lamotrigine on steel in 1.0？M？HCl and 0.5？M？H2SO4 was studied by techniques like weight loss, polarisation, and electrochemical impedance spectroscopy. Results indicated that lamotrigine is more competent in HCl than in H2SO4 and is justified by scanning electron micrographs. Protection efficiency increased with the concentration of inhibitor and decreased with temperature. Adsorption study revealed the comprehensive adsorption of lamotrigine molecules on steel surface. 1. Introduction HCl and H2SO4 acids are widely used in processes like acid pickling, acid cleaning, acid descaling, and oil-well acidizing [1, 2], where the intention is to remove surface scales and deposits keeping the base metal intact. But acids, after the removal of scales and deposits, invariably attack the precious metal leading to deleterious consequences of acid corrosion. Use of inhibitors is the most practical method to combat this. Inhibitors are organic molecules which possess π-electrons, hetero atoms like nitrogen, sulphur, and oxygen [3, 4]. These inhibitors generally act by adsorbing on the metal surface forming a thin protective film. In acid media, electron-rich center gets protonated to become cation, electrostatically binds to cathodic sites of metal thereby hinders cathodic reaction. Electron-rich spots of unprotonated molecule finds anodic reactive sites thus reduce anodic reaction. Thus, a heterocyclic organic molecule comprehensively acts. Recently, considerable amount of effort has been devoted to develop novel and efficient corrosion inhibitors. It is found that molecules containing both N and S can claim excellent inhibition compared with those containing only N or S [5, 6]. bis thiadiazole derivatives [7], thiosemicarbazide derivatives [8], Benzimidazole derivatives [9], and purines [10] have been verified to be efficient inhibitors for steel. Generally acid pickling is carried out at high temperature [11, 12]. In that case efficiency of the inhibitor generally goes down. Hence, it is important to find inhibitor which is fair at elevated temperatures. The study by Tang et al. [13], Singh and Quraishi [7] showed that thiadiazoles retain inhibition efficiency up to 45°C, bis-thiadiazoles up to 65°C, respectively, and was attributed to chemisorption of inhibitor molecule on steel surface. Oguzie et al. argue that inhibitors containing sulphur heteroatom favor chemisorption whereas nitrogen favour physisorption, on the surface of steel, in acidic media [14]. This made us choose lamotrigine which has potential characters to perform