<b>Metal Coordination Effects on Dithiocarbamate Adsorption and Corrosion Protection of Mild Steel in Hydrochloric Acid</b>

Sodium <i>N</i>-methyl-<i>N</i>-phenyldithiocarbamate and its Mn(II), Fe(III), Co(II), Ni(II), and Zn(II) complexes were assessed for mild-steel corrosion protection in 1.0 M HCl using potentiodynamic polarization, electrochemical impedance spectroscopy, adsorption isotherms, SEM, and XRF.

All compounds exhibited concentration-dependent inhibition through spontaneous adsorption and behaved as mixed-type inhibitors with a pronounced anodic tendency. Metal coordination strengthened adsorption and favoured formation of compact interfacial films, as reflected by reduced corrosion current densities, increased charge-transfer resistance, and enhanced inhibition compared with the free ligand. Langmuir and Temkin models supported spontaneous adsorption involving both physisorption and chemisorption, while SEM and XRF provided morphological and compositional evidence of inhibitor-derived surface films.