Effect of the addition of potassium iodide and thiourea on the corrosion inhibition effect of aqueous extract of Ayapana triplinervis towards mild steel in HCl at elevated temperatures-theoretical, electrochemical and surface studies

Abstract

The enhanced protection of mild steel in an acidic medium is assured with the synergistic interaction of aqueous extract of Ayapana triplinervis (AYW) and thiourea or KI. The addition of 5 mM KI to the reaction mixture improves the inhibition efficiency to 91 % at 323 K. But at room temperature, higher efficiency is achieved by the addition of 5 mM thiourea to the reaction mixture. Herein the synergistic pair AYW-KI system resists the corrosion process by getting adsorbed on the metallic surface via chemisorption while AYW-TU pair by physisorption. The better surface coverage ensured by the synergistic AYW-KI pair through the horizontal arrangement of THQ and the vertical orientation of KI is conformed through the Biovia material studio analysis. XPS elemental analysis supports the plausible formation of co-ordinate type bonding between the metal and the synergistic pairs.