Abstract
The influence of NO 2 − on the corrosion of Ni in acid phosphate solutions were analysed by means of potentiodynamic scans and impedance spectroscopy under electrode rotation. The complex nitrite reduction reaction involves adsorbed intermediates which interfere with the surface process occurring during the active dissolution and passivation of Ni. Near the corrosion potential, the reduction of NO 2 − follows a Tafel’s behaviour independent from nitrite concentration and electrode rotation speed, denoting a surface-controlling step. Without NO 2 −, the adsorption of H predominates in the cathodic polarisations. The adsorption of NO 2 − near the corrosion potential has several consequences: (i) it brings about a lower surface coverage of NiOH decreasing the rate of Ni active dissolution and (ii) its preferential adsorption against that of passivating species, such as NiOH and Ni(OH) 2, hinders the formation of the pre-passive layer at low pH-values increasing the passivation current.
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