Experimental and theoretical evaluation of two pyridinecarboxaldehyde thiosemicarbazone compounds as corrosion inhibitors for mild steel in hydrochloric acid solution

•The studied inhibitors contain both pyridine ring and Schiff’s base structure.•The inhibitors show good inhibitive properties for mild steel in HCl.•The inhibitors adsorb on mild steel surface both physically and chemically.•The PZC measurements show the mild steel surface was positively charged.

The inhibition effect of two Schiff’s base derivatives on the corrosion of mild steel in 1.0 M HCl solution was studied by electrochemical techniques, SEM and theoretical calculation methods. The experimental results show that the inhibition efficiency of 2-pyridinecarboxaldehyde thiosemicarbazone (2-PCT) is higher than that of 4-pyridinecarboxaldehyde thiosemicarbazone (4-PCT), and both the two compounds are good inhibitors for mild steel in 1.0 M HCl. Potentiodynamic polarization curves show that the two inhibitors act as mixed type inhibitors. The adsorption of inhibitors obeys the Langmuir adsorption isotherm, and the thermodynamic parameters (Ea, Kads  , ΔGads0) were calculated and discussed. The mechanism of inhibition was determined by PZC measurements and theoretical calculation methods.