The inhibitive effect of the natural juice of onion bulb on the corrosion of zinc in HCl solution
was determined using hydrogen evolution and weight loss measurements as well as potentiostatic
technique. Potentiodynamic anodic polarization was used to determine the effect of the juice on pitting
corrosion of zinc in NaCl solution. It was found that the presence of onion juice reduces markedly the
corrosion rate of zinc in the acid solution. The inhibition efficiency increases as the juice concentration
is increased. Moreover, the presence of the juice in NaCl solution shifts the pitting potential toward
more positive direction. The inhibitive effect of onion juice was discussed on the basis of adsorption of
its components on the metal surface. Such adsorption is found to follows Langmuir adsorption
isotherm. Negative values were calculated for the energy of adsorption indicating the spontaneity of the
adsorption process. The formation of insoluble complexes as a result of interaction between the juice
components and zinc cations was also discussed.