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A hydrazide derivative containing quinoline moiety namely 2-[(2-methylquinolin-8-yl)oxy]acetohydrazide (MQH) has been synthesized and its corrosion inhibition performance and adsorption behaviour on mild steel in 0.5 and 1 M HCl solution have been tested by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The inhibition efficiency of MQH increases with increase in its concentration and decreases with increase in HCl concentration. Further the, inhibition efficiency of MQH increases in 0.5 M HCl and decreases in 1 M HCl with increase in temperature. Polarisation curves indicate that MQH is a mixed inhibitor, affecting both cathodic and anodic corrosion currents. The adsorption of MQH at the mild steel/HCl solution interface obeys Langmuir adsorption isotherm model and inhibition process follows mixed adsorption with predominantly chemisorption in 0.5 M and physisorption in 1 M HCl. The activation and thermodynamic parameters for the corrosion inhibition process have been calculated to explore the mechanism of corrosion inhibition.

Mild steel (a low carbon steel) is an affordable engineering material used for many purposes in various environments including mild acidic environment with some precautions. The corrosion behaviour of mild steel (MS) in 0.5 M H2SO4 and 0.5 M HCl, in the temperature range (303–323 K) without and with the inhibitor N-[(3,4-dimethoxyphenyl) methyleneamino]-4-hydroxy-benzamide (DMHB), was investigated using Potentiodynamic polarization and Electrochemical impedance spectroscopy (EIS) techniques supplementing with surface characterization study using scanning electron microscope (SEM) and atomic force spectroscopy (AFM). Experimental observations were found to be in agreement with Density functional theory (DFT) calculations. The inhibition efficiency increases with increase in DMHB concentration and showed maximum inhibition efficiency of 86% in 0.5 M H2SO4 and 81% in 0.5 M HCl, respectively, at concentration of 3 × 10─3 M at 303 K. The inhibition efficiency of DMHB obtained relatively at its lower concentration (3 × 10─3 M) compared to other reported related compounds confirms its potential towards corrosion inhibition. The variation in the kinetic and thermodynamic parameters indicated physisorption of DMHB on MS and its mixed type inhibitive action followed Langmuir’s isotherm model. DFT calculations go along with the experimental results, signifying the potential corrosion inhibition behaviour of DMHB for MS in both the acid media.

This research investigates the effect of Schiff base, namely, N'-[4-(dimethylamino) benzylidene]-4-hydroxybenzohydrazide (SB) on the corrosion mitigation of mild steel (MS) in hydrochloric acid medium (HCl) using potentiodynamic polarization (PDP) technique. The study highlights the effect of SB concentration, HCl concentration, and temperature on the corrosion current density (icorr) and inhibition efficiency (IE). The adsorption of SB onto the MS surface was justified with the support of kinetic and thermodynamic parameters. The morphological behavior of the MS surface was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). A blend of statistical study and interaction plots has been applied to obtain a thorough understanding of the corrosion parameters. Experimental results obtained by PDP measurements revealed that tested compounds had a good anti-corrosion capacity. The main and interaction effects of the parameters on the response were analyzed using Box-Behnken Design. An empirical model equation from experimental results elucidates the relationship among the variables. The optimized parameters for the maximum output were recognized. The maximum IE of 81.5 was predicted by RSM with temperature (A = 30 °C), HCl concentration (B = 0.5 M), and Inhibitor concentration (C = 0.0001 M). Using RSM, further analyses regarding individual and interaction effects between the variables can be more comprehensive. Few more parameters such as pH and time can be included in the future study. Graphic Abstract