Abstract
This study investigates the morphology, composition and corrosion resistance of hot dip galvanized (HDG) steel bolts in fresh water, 1% NaCl saltwater in the presence of protective compounds L-Tryptophan and three conventional corrosion inhibitors: Inhibitor 1-VCI (amine-carboxylates-based), Inhibitor 2 (based on carboxylate acid), and Inhibitor 3 (water-based, carboxylate acid). Quantitative tests performed include gravimetric analysis and electrochemical techniques, such as linear polarization, Tafel extrapolation, and Electrochemical Impedance Spectroscopy (EIS). Electrochemical measurements determined the polarization resistance Rp, corrosion rate vcorr, and corrosion potential Ecorr. Furthermore, Scanning Electron Microscopy (SEM) and ATR-FTIR spectrometry were used to evaluate and characterize the formed layers on the surface of hot-dip galvanized steel samples. The results reveal that upon corrosion new compounds are formed onto the exposed areas of the treated bolts such as zinc-carbonates, zinc-hydroxides, etc. The presence of these compounds on the surface of the HDG steel bolts hinders the corrosion process by reducing the rate of the anodic and cathodic reactions. The gravimetric test showed that L-tryptophan in distilled water has mass increase, resulting from the formation of white deposits on the sample surface. In fresh water and distilled water, the best corrosion resistance was achieved with Inhibitor 1-VCI, while L-tryptophan showed best results in 1% NaCl solution.
Highlights
Zinc is one of the most widely used metallic materials in many applications, like coating for steel or as an alloying element in brass and other alloys
In fresh water and distilled water, the best corrosion resistance was achieved with Inhibitor 1-VCI, while L-tryptophan showed best results in 1% NaCl solution
From the visual assessment results obtained after 24 h immersion of the samples in aqueous solutions with and without inhibitors, it is apparent that Inhibitor 1 in water and distilled water showed the best results, that is, no visible corrosion occurrence, whereas in 1% NaCl solution the surface changes were more pronounced, in the form of black spots
Summary
Zinc is one of the most widely used metallic materials in many applications, like coating for steel or as an alloying element in brass and other alloys. The use of zinc as a corrosion-resistant coating is usually limited to atmospheric corrosion, while in more aggressive environments it is necessary to protect steel with alternative corrosion protection methods. The influence of organic, environmentally friendly corrosion inhibitors for zinc protection is increasingly being investigated [3,4]. One of these environmentally friendly corrosion inhibitors is L-tryptophan, an amino acid from the indole group, which has shown good properties in zinc protection in sodium chloride solution at a concentration of 1
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