Inhibition Studies of the Synergistic Effect of Rosemary oil and Zinc Oxide on S41003 Ferritic Steel Corrosion in Dilute Sulphuric and Hydrochloric Acid Solutions

Abstract

Corrosion inhibition studies of the synergistic properties of the combined admixture of Rosemary oil and zinc oxide (ROZ) on S41003 ferritic steel in 1M HCl and H 2 SO 4 acid were done with potentiodynamic polarization, weight loss analysis, open circuit potential measurement, optical microscopy and ATR-FTIR spectroscopy. Results showed the admixed compound to be highly effective with maximum inhibition efficiencies of 93.68% and 93.26%, 98.93% and 90.5% in HCl and H 2 SO 4 acid solutions from the electrochemical tests with dominant cathodic type inhibition characteristics. ROZ addition significantly shifts the corrosion potential values of S41003 to cathodic potentials from open circuit potential evaluation in both acid media signifying specific corrosion inhibition behavior without applied potential. Identified functional groups of alcohols, phenols, 1°, 2° amines, amides, carbonyls (general), esters, saturated aliphatic, carboxylic acids, ethers, aliphatic amines, alkenes, aromatics, alkyl halides and alkynes within ROZ compound aggregated completely on S41003 steel surface in HCl and partially in H 2 SO 4 solution. Thermodynamic calculations showed physisorption molecular interaction and adsorption according to Langmuir and Frumkin isotherm models. Optical microscopy images of ROZ inhibited and uninhibited S41003 samples slightly differ from each other due to pre-adsorbed corrosive anions on the steel surface before ROZ inhibition.