Effect of molecular structure of two fluorescein molecules on the corrosion inhibition of mild steel in 1 M HCl solution

Novel chitosan-oligosaccharide derivatives as fluorescent green corrosion inhibitors for P110 steel

In the exploitation of seawater resources, the transported pipelines are frequently corroded, resulting in economic losses and environmental pollution. The development of corrosion inhibitors is an effective measure to mitigate the corrosion of metals in seawater. In this work, novel chitosan oligosaccharide derivatives (CF) were synthesized as fluorescent eco-friendly corrosion inhibitor by modifying fluorescent monomers. The characterization of CF revealed excellent fluorescence intensity, promising the potential for on-line detection. The inhibition performance of CF on P110 in 3.5 wt% NaCl solution was investigated through experimental evaluation and theoretical analysis. The electrochemical measurements indicated that the corrosion inhibition efficiency was increased from 61.00 % to 91.19 % with the introduction of fluorane. Adsorption isotherm and XPS analysis demonstrated that CF is designed to protect metal by forming the composite film on P110 through physical and chemical adsorption. In addition, theoretical calculations revealed differences in the interaction energies, radial distribution functions and diffusion coefficients of inhibitors on the Fe (110) surface. These theoretical results aligned with the experiments and confirmed the excellent ability of CF in metal corrosion protection from the molecular perspective. This new chitosan derivative provides new possibilities for the development of the green composite inhibitor that allows on-line detection.

Adsorption and Surface Analysis of Sodium Phosphate Corrosion Inhibitor on Carbon Steel in Simulated Concrete Pore Solution

Corrosion of steel-reinforced concrete exposed to marine environments could lead to structural catastrophic failure in service. Hence, the construction industry is seeking novel corrosion preventive methods that are effective, cheap, and non-toxic. In this regard, the inhibitive properties of sodium phosphate (Na3PO4) corrosion inhibitor have been investigated for carbon steel reinforcements in 0.6 M Cl- contaminated simulated concrete pore solution (SCPS). Different electrochemical testing has been utilized including potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott-Schottky plots to test Na3PO4 at different concentrations: 0.05, 0.1, 0.3, and 0.6 M. It was found that Na3PO4 adsorbs on the surface through a combined physicochemical adsorption process, thus creating insoluble protective ferric phosphate film (FePO4) and achieving an inhibition efficiency (IE) up to 91.7%. The formation of FePO4 was elucidated by means of Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Quantum chemical parameters using density functional theory (DFT) were obtained to further understand the chemical interactions at the interface. It was found that PO43- ions have a low energy gap (ΔEgap), hence facilitating their adsorption. Additionally, Mulliken population analysis showed that the oxygen atoms present in PO43- are strong nucleophiles, thus acting as adsorption sites.