Zinc, an important nonferrous metal, is the fourth most used metal in the world. It has innumerable uses in industrial as well as in other segments. The primary utility of zinc is in galvanization and as an anode in the battery. Steel coated with zinc, which is known as galvanized steel, is widely used in industries. Even though zinc protects many metals from undergoing corrosion, by itself, it undergoes corrosion in several acidic, alkaline, and neutral environments. The corrosion behavior of zinc is significant in all industries where it is utilized either directly or indirectly in the form of a sacrificial coating. In-depth analysis of the reported literature indicated that corrosion attenuation of zinc in acidic and alkaline medium was studied by many researchers, and various classes of inhibitors were tried under varying experimental conditions. Most inhibitors can be amalgamated as excellent inhibitors with an inhibition efficiency of 80–90%. Even though this is a subject of intense research, systematic documentation on the same is not available in the literature. This review consolidates research work on corrosion and inhibition studies of zinc and galvanized steel over a period of three decades.
The objective of the work is to introduce and establish anticorrosion capabilities of a novel biopolymer glycogen (GLY) against sulfamic acid (NH2SO3H) induced corrosion of zinc. The corrosion and inhibition studies were done by electrochemical techniques such as potentiodynamic polarization (PDP) measurements and electrochemical impedance spectroscopy technique (EIS). Conditions were optimized to get maximum inhibition efficiency by varying the concentration of the inhibitor in the temperature range of 303–323 K. Activation and thermodynamic parameters were evaluated and discussed in detail. Suitable adsorption isotherm was proposed to fit the experimental results. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and atomic force microscopy (AFM) studies were performed before and after the addition of inhibitor. Adsorption of inhibitor was further confirmed by UV–Visible spectroscopy. Quantum chemical calculations were done to establish the correlation between the structure of the inhibitor and its inhibition efficiency. Energy of HOMO, LUMO, energy gap ∆E, dipole moment (µ) Mullikan charges were calculated. Different theoretical factor descriptors like the hardness (η), and softness (σ) electronegativity (χ), global electrophilicity (ω), nucleophilicity (ε) and fraction of electron transferred (ΔN) were calculated. Inhibition efficiency of glycogen increased with increase in its concentration and with temperature. Maximum efficiency of 72% could be achieved for the addition of 0.05 g L−1 of GLY at 323 K. Results were fitted into Langmuir adsorption iostherm. The surface of the metal turned visibly smoother in the presence of GLY. In addition the EDX studies showed increase in carbon content which re-affirmed the adsorption of GLY on the metal surface. The density functional theory (DFT) based theoretical studies supported the experimental observations.
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