:The corrosion inhibition of iron (Fe) metal in acidic medium (0.5N HCl) in the presence of synthesized4-ethylcyclohexanonethiosemicarbazone (ECHTSC) has been investigated by the weight loss method. The protective layer of thiosemicarbazone on Fe surface was confirmed by scanning electron microscopy (SEM). Inhibition efficiency, corrosion rate and surface coverage were evaluated at different concentrations of thiosemicarbazone in 0.5N HCl. The adsorption equilibrium constant (K ads ) and standard free energy of adsorption (ΔG ads ) were calculated. The values of free energy of adsorption (ΔG ads ) revealed that the inhibitor was adsorbed on the Fe surface via both physical and chemical adsorption nmechanisms.

The electrochemical behaviour of 4-tertbutylcyclohexanone semicarbazone (TBCHSC) and its Co(II) complex was investigated by a glassy carbon electrode, cyclic voltammetry technique. Semicarbazone synthesized from the condensation of 4tertbutylcyclohexanone and semicarbazide hydrochloride (1:1 molar ratio) was further treated with cobalt(II) acetate (2:1 molar ratio), to form the Co(II)-semicarbazone complex. The semicarbazone was studied in buffer solutions (Britton-Robinson universal buffer and phosphate buffer), with a pH in the range of 3 to 11. The reduction process was found to be irreversible and diffusion controlled, for both semicarbazone and its Co(II) complex. The effects of change on the sweep rate, concentration, pH and solvent were evaluated. The semicarbazone reduction mechanism was suggested on the basis of the obtained results. Kinetic parameters, such as charge transfer coefficient (αn), diffusion coefficient (D0 1/2), and rate constant (k°f,h), were calculated from cyclic voltammetric measurements. Semicarbazone and its Co(II) complex were tested against bacterial and fungal species. The metal complex had higher activity than the free ligand.