The adsorption mechanism of Rosmarinus officinalis L. as corrosion inhibitor for Al AA8801 alloy in 1.0M HCl was studied using gravimetric method and thermodynamics studies at 303, 313, 323 and 333K. Inhibitor concentrations ranged between 0 and 1000mg/L. Results show that the adsorption mechanism of Rosmarinus officinalis L. is via physisorption, generally endothermic and accompanied by a resulting decrease in disorder. Inhibitor efficiency largely decreased with increase in temperature, and decrease in concentration of the extract. The presence of an external magnetic field enhanced the dissolution of passivating Al2O3 films, thereby increasing corrosion rate.
The corrosion inhibition of Aluminium alloy AA8011 in 0.25 M hydrochloric acid solution by Rosmarinus officinalis L. (rosemary) leaves extract was studied using the gravimetric technique at 303, 313, 323 and 333K, and in the presence of an external magnetic field. The study reveals that the methanolic extract of rosemary leaves inhibits corrosion of Al in 0.25 M HCl. The inhibition efficiency was found to increase with increase in concentration of the extract, but decreased with increase in temperature. Thermodynamic activation parameters like the activation energy (E a ), ranged from 15.29 to 35.06 kJ/mol, thereby suggesting the mix mechanism of physichemisorption; calculated values of the standard adsorption enthalpies () o ads H were positive indicating an endothermic process, while negative values of entropies () o ads S implied an associative interaction between the inhibitor molecules and the Al surface. The corrosion data was found to be a good fit for the Langmuir (R 2 > 0.98) and Villamil (R 2 > 0.99) isotherm models. Values of the adsorption free energy () o ads G obtained were negative, thereby describing a spontaneous adsorption process. The effect of an external magnetic field was found to have a mixed behaviour in the presence of the R. offinalis L. extract at room temperature. Nonetheless, the corrosion rate was generally found to decrease with increase in strength of the magnetic field.
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