Mechanism of the corrosion inhibition of Zn Anode in NaOH by gelatine and some inorganic anions

The quantity of electricity required for passivation of Zn anode in NaOH solutions has been determined in absence and presence of different concentrations of gelatine, phthalic acid, sodium sulphide, sodium silicate or potassium chromate. The results obtained for gelatine in dilute alkali conform with a simple Langmuir model, whereas deviations are observed for the rest of the additives. The concentrations needed to establish a certain inhibiting efficiency increase wth increase in alkali concentration. The results are interpreted in the light of dissolution-precipitation mechanism.