Locust Bean Gum as Corrosion Inhibitors in NaCl Solution

Abstract

In this research, the inhibitive performance of locust bean gum (LBG) on the corrosion behavior of AISI 304 stainless steel (AISI 304SS), E150 Al alloy and copper in 0.15 M NaCl containing various amounts (10^–3, 10^–2, 10^–1, 1, 1.5 and 2 g L^–1) of LBG were researched using potentiodynamic polarisation, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy dispersive X‑ray analysis (EDS) and inductively coupled plasma optical emmision spectrometry (ICP-OES) methods. Polarisation curves indicated that LBG was acting as mixed type inhibitor. All electrochemical measurements showed that inhibition efficiencies increased with increasing LBG concentration. It was determined that the increase of inhibitor efficiency by concentration resulted from the adsorption of LBG to metal surface, and the adsorption fitted to the Langmuir adsorption isotherm equation. The variation in inhibitive efficiency mainly depends on sugar units present in the LBG molecule. The best inhibition shows in 0.15 M NaCl + 2 g L^–1 LBG solution. LBG reduced corrosion by slowing the rate of reactions formation without changing anodic and cathodic reactions. In addition, LBG adsorptioned on active sites caused the reduction of corrosion due to geometric block effect. SEM results show that metal surfaces are highly damaged in an inhibitor-free environment. The SEM images with inhibitor environment show that the surface is more homogeneous and smooth. The results of EDS show that the presence of oxygen in the inhibitor medium results in the formation of surface metal oxides, and therefore the reduction of corrosion.