In open-circuit potential measurements of certain Cu-based alloys in NaOH solutions oscillations were observed in Cu-A1 and Cu-Ag-A1. Studies with various electrolyte concentrations and rotation speeds of the electrode led to a possible explanation of the phenomenon in terms of A1 dissolution altering the main Cu dissolution/passivation process. The accumulation of aluminate ions on the interphase and its transportation to the bulk solution are the main causes of the oscillations.The copper-based alloys have been developed to produce materials with better properties than pure copper for specific purposes. Particularly, Cu-A1-Ag alloys present shape memory effect and are of special interest in electronics and dentistry. The electrochemical behavior of Cu-A1-Ag alloys is the subject of investigations in our laboratories. The study of microstructural features and the mechanism of anodic oxidation of Cu-A1-Ag alloys in 0.5 mol/liter NaOH have been reported previously, t'2 The observation of unexpected potential oscillations during the open-circuit potential measurements stimulated our interest in this phenomenon.Most oscillatory phenomena involving electrochemical systems described in the literature are related to oscillations which arise during the anodic polarization of different metals such as Zn, 3' 4 Fe, 5 and Cu. ~-~ Cathodic oscillations also are known. ~'~3 With regard to copper electrodissolution, oscillations occurred in deoxygenated chlorate 14 and acidic chloride. ~'8-~ Periodic formation and dissolution of CuO film in the former case, and CuC1 film in the latter were recognized as the basis of the phenomenon. Various models to explain this phenomenon have been proposed. 8'~-z~ However, copper oscillations in neutral chloride or in alkaline media have never been reported, while anodic and cathodic oscillations are well known in the literature. Open-circuit potential oscillations are unusual? One which has been well described in the literature is related to the Fe/H2SO4 electrode in the presence of BrO~ ions? There is a natural oscillatory phenomenon observed during opencircuit potential measurements of a Cu-Ag-A1 alloy in NaOH solutions. ExperimentalThe alloy studied here was prepared from 99.99% Cu, A1, and Ag according to the procedure described previously. 17 As determined by spectrographic analysis its composition was the following: Ag, 49.9%; Cu, 45.7%; and A1, 3.9%. The material was annealed at 830~ for 140 h and cooled slowly. After which the alloy presents two phases: a~ (a solid solution of A1 and Ag in Cu) and a2 consisting of a solid solution of A1 and Cu in Ag, as observed via scanning electron microscope (SEM) and energy-dispersive x-ray (EDX) ~ which has been described in the literature. TM Working electrodes were then made by embedding alloy cylinders in Araldite holders to expose a disk with a diameter of 4.0 mm to the solution. Electrode potentials were measured with respect to a reversible hydrogen electrode in the same solution (hess), connected to the cell via a Luggin capilla...
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