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

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.