Dissolution du nickel en transpassivite 2eme partie: etude du degagement d'oxygene simultane et influence du pH

The oxygen discharge was studied in the transpassive range of nickel on 0·5M H₂SO₄. The potential range is separated into two parts, the experimental data indicating that, above 1650 mV/sce the oxygen discharge occurs alone and between 1360 and 1650 mV/sce two reactions namely nickel dissolution and oxygen discharge occur simultaneously. A model is proposed where two OH^? ions are simultaneous adsorbed on the first formed layer of Ni(OH), a fraction of the surface is covered by Ni(OH)₃. The oxygen discharge is also a multistep reaction. Between 1360 and 1650 mV/sce, the dissolution of metal and the oxygen discharge are in competition at all times, the surface is covered simultaneously by Ni(OH)₂ and Ni(OH)₃.The calculated curves are in good accord with the potentiostatic curves, the influence of pH is correlated with the experimental data.