A study of rosemary oil as a green corrosion inhibitor for steel in 2 M H3PO4

Purpose To evaluate the effect of natural rosemary oil as non toxic inhibitor on the corrosion of steel in H 3 PO 4 media at various temperatures. Design/methodology/approach The oil was hydro‐distilled. The oil was used as inhibitor in various corrosion tests. Gravimetric and electrochemical techniques were used to characterise the corrosion mechanism. Findings Chromatographic analysis by GC showed that the oil was rich in 1,8‐cineole. The oil was a good inhibitor. But, its efficiency decreased with temperature. Research limitations/implications The inhibition efficiency increased with the concentration of the natural oil to attain 73 per cent at 10 g/l. Good agreement between the various methods explored was observed. Polarisation measurements showed that rosemary oil acted essentially as a cathodic inhibitor. Practical implications The efficiency of the oil increased with the concentration but decreased with the rise of temperature in the 298‐348 K range. The natural oil could thus be used in chemical cleaning and pickling processes. Originality/value The originality of this work is the finding of a safe and cheap inhibitor from natural plants.