Thiosemicarbazone derivatives as corrosion inhibitors for mild steel in 15 % HCl

The first time comparative evaluation of the anti-corrosion performance of 2-benzylidenehydrazinecarbothioamide (BHC), 2-(4-(dimethylamino)benzylidene)hydrazinecarbothioamide (DMBHC), 2-(4-(diethylamino)benzylidene)hydrazinecarbothioamide (DEBHC), and its reactants against mild steel (MS) in 15 % HCl using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), temperature (303.15–333.15 K) based gravimetric analysis, SEM, 3D-optical profilometer and density functional theory (DFT) were investigated. Furthermore, electrochemical analyses based on concentration variation and immersion were carried out in this study. The list of reactants considered for investigation comprises benzaldehyde (Bz), 4-dimethylaminobenzaldehyde (DMBz), 4-diethylaminobenzaldehyde (DEBz), and thiosemicarbazide (TSC). The electrochemical analysis demonstrated that with an optimal concentration of 4 mM and a temperature of 303.15 K, the corrosion inhibition efficiencies of BHC, DMBHC, and DEBHC were 98.70 %, 95.01 %, and 93.39 %, respectively. PDP studies confirmed that all the synthesized molecules acted as mixed-type inhibitors, covering both anodic and cathodic active sites on the MS surface, thus preventing corrosion. Meanwhile, gravimetric studies at 303.15 and 333.15 K revealed inhibition efficiencies of 91.2 and 68.89 % for BHC, 90.51 and 78.55 % for DMBHC, 95.6 and 86.93 % for DEBHC with 4 mM concentration. The adsorption of the inhibitor followed the Langmuir adsorption isotherm, and the thermodynamic parameters ( K ads , Δ G ads , Δ H ads , and Δ S ads ) were evaluated. The results indicated that the inhibitor's adsorption occurred through a combination of chemisorption and physisorption. • Comparative study of substituted thiosemicarbazone derivatives was investigated. • Corrosion resistance of mild steel is assessed in 15 % HCl with prepared Schiff base. • Performance is evaluated by gravimetric, electrochemical, and theoretical studies. • Corrosion inhibition efficiency follows the order DEBHC > DMBHC > BHC at 333.15 K.