Anti-corrosion Properties of Rosemary Oil and Vanillin on Low Carbon Steel in Dilute Acid Solutions

The corrosion inhibition effect of rosemary oil and vanillin (ROV) on low carbon steel in 1 M HCl and H₂SO₄ media was studied through potentiodynamic polarization, weight loss analysis, optical microscopy and IR spectroscopy. Results showed optimal inhibition performance of the compound, but more effectively in HCl solution at 92.57 and 94% compared to 64.57 and 64.55% in H₂SO₄ from both electrochemical test. Identified functional groups of the admixture from IR spectroscopy completely adsorbed on the steel in HCl, but partially in H₂SO₄. Thermodynamic calculations showed chemisorption and physiochemical adsorption according to Langmuir, Freundlich and Temkin isotherm model. Micro-analytical images revealed a well-protected ROV inhibited steel surface in comparison to images from the corroded stainless steel. The inhibition behavior of ROV was determined to be mixed type.