STUDY OF CARBON STEEL CORROSION INHIBITION BY ZIZIPHUS SPINA-CHRISTI (L) LEAF EXTRACT

Abstract

This study evaluated the inhibition efficiency of the inhibitor in protecting carbon steel from corrosion in a 1M HCl hydrochloric acid solution at different temperatures (280, 300, 320 K) and various concentrations (100–600 ppm). Results from weight loss measurements showed a significant decrease in corrosion rate (CR) with increasing inhibitor concentration, dropping from 1.250 for the blank samples to 0.085 at a concentration of 600 ppm at 280 K. The highest inhibition efficiency (IE%) value reached 93.2% with a surface coverage of 0.932 at the same concentration. Results also indicated that increasing temperature leads to an increase in corrosion rate and a relative decrease in inhibition efficiency. The chemical explanation for the high inhibition efficiency is attributed to the formation of an integrated protective layer on the metal surface via a mixed adsorption mechanism (physical and chemical) adhering to the Langmuir Isotherm. This mechanism relies mainly on direct Donor-Acceptor interaction, where free electron lone pairs from heteroatoms (O, N) and -electron clouds in the aromatic rings of the inhibitor are donated to the vacant d-orbitals of iron (Fe) atoms. This adsorption leads to the displacement of water molecules and aggressive chloride ions (Cl^-) from the surface, causing an increase in activation energy (Ea) for the dissolution/chemical process and forming a hydrophobic barrier that hinders charge transfer at the interfacial boundary.