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.