CONICET | Buscador de Institutos y Recursos Humanos

The corrosion resistance of Cu alloys, particularly Cu-Ni alloys, strongly depends on the quality of their protective passive film. This study focuses on the influence of Ni as alloying element in the improvement of the corrosion resistance of copper-base alloys, using boric-borate buffer (pH = 7.8) as electrolyte. The rest potential of esach material stabilized after 17 hours. A 30% increase in the Ni content shifts the open circuit potential some 20 mV towards more noble values. The film growth was also evaluated spectrophotometrically, using reflectance spectroscopy. The absorption of the passive films continues increasing even after the corrosion potential has already attained a steady value. This would indicate that the film thickness increases continuously. In the case of Cu90Ni10 the spectral features are almost identical to those of copper. Instead, in the case of Cu70Ni30 a strong absorbance can be observed within 310 and 250 nm, while at the same time the distinctive features of the Cu2O spectrum are very weak. The shifts observed in the peaks when the Ni content in the alloy increases, confirm the extensive incorporation of Ni(II) compounds in the surface film. The composition of the passive layer grown at open circuit potential in aerated boric-borate buffer was also investigated applying a potentiodynamic potential sweep (v = 0.01 V s-1). It can be observed that the oxides reduction is inhibited (or at least hindered) as the nickel content in the alloys increases. It can be concluded that when the nickel content increases up to at least 30%, the composition of the film changes noticeably by the incorporation of Ni(II) compounds. In parallel, the film thickness, estimated from the cathodic charge of the reduction peaks in the voltammograms and the potentiodynamic curves, as well as from the absorbance of the films seems to decrease as the nickel content increases.

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