摘要：A preliminary investigation on the extracts of an agricultural produce, Onion (Allium Cepa), was studied for its corrosion inhibiting effects in a pipeline-steel/hydrochloric acid corrosion system using gravimetric and thermometric techniques in addition to optical microscopy examinations performed on specimens during natural exposure tests. The corrosion rate of steel increased with increase in time of immersion in HCl whereas it decreased as the concentration of the extract was increased in the corrosion system. In freely corroding state, the corrosion rates ranged from 2.15 mmpy to 1.08 mmpy in 10 M and 5 M hydrochloric acid respectively. Such difference in corrosion rates are attributable to large difference in concentrations of the corrodants. At an inhibitor concentration of 20 %, the corrosion rates decreased to 1.3x10-2 mmpy and 2.5x10-4 mmpy respectively corresponding to inhibition efficiencies of between 83 % and 92 %. The adsorption of active components in the extracts on the corroding surfaces obeyed the Langmuir adsorption isotherm. From examinations performed on painted steel specimens during natural exposure tests, the onion extracts, dispersed in a white colored alkyd paint system, prevented paint delamination over a period of 168 h. Whereas the specimens painted with uninhibited alkyd paint suffered major paint delamination over the same exposure period.
