Impedance studies of the inhibition of the corrosion of mild steel in 0.1 m sulphuric acid with 10% methanol by thiosemicarbazide derivatives

Abstract

Selected substituted thiosemicarbazides and thiosemicarbazones have been studied as corrosion inhibitors for mild steel in sulphuric acid using electrochemical techniques. The impedance measurements typically gave a single relaxation or semicircle comprising the charge transfer resistance in parallel with the double-layer capacitance. Inhibitor efficiencies and the adsorption isotherms were calculated from the charge transfer resistance values, whilst the capacitance-potential diagrams provided mechanistic information on the adsorption of these types of compounds. Thiosemicarbazide and its derivatives act as mixed adsorption type inhibitors, increased adsorption resulting from an increase in the electron density at the reactive ▪C=S group by suitable substitution of a terminal hydrogen in the hydrazino or thiamido groups of the thiosemicarbazide molecule. The substituted compounds were classified into three distinct groups according to their molecular structure and electrochemical response.