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Due to strict environmental regulations, the use of toxic chemicals as corrosion inhibitors for the oil-well acidizing is restricted. Environmentally benign Vanillin-modified chitosan (Van-Cht) is synthesized using a microwave-induced green synthetic protocol and thoroughly characterized by FTIR and NMR spectroscopy. The inhibitor has been evaluated for the first time for carbon steel in 15% HCl. The corrosion inhibition performance was assayed using weight loss and electrochemical methods complemented with the surface analysis of the corroded carbon steel samples without and with the inhibitor immersed in the corrosive medium. Results obtained showed that the Van-Cht acted by adsorption on the surface of carbon steel to inhibit corrosion and exhibited a mixed-type behavior with cathodic predominance. The adsorption of Van-Cht on the carbon steel surface obeyed the Langmuir isotherm. The excellent corrosion inhibition efficiency of > 98% observed at a concentration of 500 mg L−1. Surface analysis using SEM and FTIR-ATR measurements supported the adsorption of Van-Cht inhibitor on the carbon steel surface. The pKa analysis proved that the inhibitor Van-Cht exists mainly in the protonated form at the experimental pH. The density functional theory (DFT) analysis proved that the protonated form of the Van-Cht inhibitor behaves better compared to that of the Van and neutral Van-Cht. [ABSTRACT FROM AUTHOR]

An amine-functionalized glucose namely hexamethylene-1,6-bis(N-d-glucopyranosylamine) (HGA) was synthesized and characterized. The corrosion inhibition behavior of HGA on API X60 steel in 3.5 wt% NaCl saturated with CO2 was evaluated by electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation (EFM), linear polarization resistance (LPR), potentiodynamic polarization (PDP) and scanning electron microscopy (SEM). The adsorption of HGA on the API X60 mild steel surface obeyed the Langmuir isotherm. The results of potentiodynamic polarization indicated that the HGA molecule behaved as a mixed type inhibitor by reducing both the anodic and the cathodic electrochemical reactions. The maximum corrosion inhibition efficiency obtained was 91.82% at a concentration of 2.27 × 10−4 M (100 ppm). HGA reduced the extent of localized pitting corrosion on the steel surface. The inhibitor is protonated in the system and assumes a parallel orientation during adsorption on the steel. The oxygen and nitrogen atoms serve as reactive centers for adsorption, based on quantum chemical calculations and Monte Carlo simulations in the protonated form. [ABSTRACT FROM AUTHOR]

The inhibition effect of four pyrimidine derivatives (PPDs) on the corrosion of mild steel in hydrochloric acid medium has been investigated using gravimetric measurements, electrochemical impedance spectroscopy, potentiodynamic polarization, and energy dispersive x-ray spectroscopy (EDX) techniques. Electrochemical impedance spectroscopy (EIS) data showed that the addition of PPDs increases the charge-transfer resistance (Rct) and decreases the double-layer capacitance (Cdl). Potentiodynamic polarization revealed that PPDs acted as mixed-type inhibitors but are predominantly cathodic. The adsorption of studied compounds obeyed the Langmuir's adsorption isotherm. EDX and quantum chemical calculations support the experimental results. [ABSTRACT FROM PUBLISHER]