CORROSION INHIBITION PERFORMANCE OF COMMIPHORAMYRRHA AND CYMBOPOGON OIL EXTRACT ON A36 CARBON STEEL CORROSION IN SULPHATE AND CHLORIDE ELECTROLYTE

Corrosion resistance of A36 carbon steel was assessed in 0.5 M H2SO4 and HCl media in the presence of specific concentrations of Commiphoramyrrha (CM), Cymbopogon (CP) essential oil extracts and their combined admixture (CMCP). Values from potentiodynamic polarization showed CM extract reacted poorly in both acids at low concentration, but effectively at higher concentrations with optimal performance of 89.76% and 92.83%. CP extract generally performed effectively with inhibition values above 90%. CMCP performed very poorly in H2SO4 compared to its performance in HCl which was generally above 80% inhibition efficiency. The oil extracts exhibited mixed-type inhibition effect coupled with dominant anodic shift in corrosion potential and similar anodic slope configuration at all extract concentrations. ATR-FTIR spectra plots showed that most of the identified functional groups within the extract molecules generally adsorbed unto the A36 steel surface. Curves from open circuit potential analysis showed CM extract in H2SO4, and CP extract in H2SO4 and HCl solution significantly decreased the thermodynamic tendency of A36 steel to degrade. The curves of other extracts displayed significant time and extract concentration dependent active-passive transition behavior. Optical images of the unprotected steel exhibited severe general and localized surface deterioration compared to the inhibited steel with significantly protected morphology. Weight-loss analysis showed the effective protection effect of CP extract in both acids and CMCP in H2SO4 is independent of time and concentration from the onset of exposure compared to their remaining counterparts whose performance significantly varies over time and is concentration dependent. X-ray phase identification diagrams and identified patterns list revealed the presence of FeO(OH) on the steel surface without oil extracts while the phase compounds identified in the presence of the extracts are FeNi and Fe3C.