Effects of strong acids on the electrochemical behavior Ni₈₉P₁₁ glassy alloy

The effects of the H₂SO₄ and H₃PO₄ concentration and immersion times on electrochemical behavior of amorphous Ni₈₉P₁₁ alloy were studied using electrochemical polarization and impedance techniques at 30°C. The formation of elemental phosphorus plus NiS or P₂O₅ on the alloy surface in H₂SO₄ or H₃PO₄ solution respectively, are confirmed by XPS method and the formation of nickel oxides is excluded. In both acids, a passive region is observed, and a gradual increase of the current density continues, indicating that the dissolution of Ni through the passive film is occurring. Nyquist plots exhibited only one capacitive semicircle with an open end in most of the applied frequency ranges. The capacitive loop is mainly due to the charge transfer resistance of the alloy. The existence sometimes of another capacitive loop confirms the diffusion process on the passive layer.