Corrosion inhibition of aluminum in biodiesel by ethanol extracts of Rosemary leaves

• Rosemary extract has good inhibition efficiency for aluminum in biodiesel.
• Phenolic diterpenes, flavonoids and triterpenes were found to be the active ingredient.
• The Rosemary extract decreases the rate of corrosion by the adsorption process.
• Physisorption of the Rosemary extract was proposed from ΔGoads values.
• Results from electrochemical and weight loss measurements are quite comparable.

Rosemary extract was used to control aluminum corrosion in biodiesel. Weight loss and polarization methods were used to test corrosion inhibitor efficiency. Surface morphology was tested by scanning electron microscopy (SEM). The inhibition efficiency increased with increase in extract concentration and decreased with temperature, suggesting the occurrence of physical adsorption. Adsorption of extract on aluminum surface is spontaneous and obeys Langmuir's isotherm. Polarization measurements revealed that Rosemary extract act as a mixed-type inhibitor with predominant anodic effectiveness. The activation energy as well as the heat of adsorption were calculated and discussed.

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