Abstract
The electrochemical behaviour of Nb–20Ta alloy has been investigated in sodium hydroxide solutions at different temperatures, using open circuit potential measurements, potentiodynamic polarisation, and electrochemical impedance spectroscopy (EIS). The open circuit potential and polarisation measurements have shown that the alloy is spontaneously active in 10, 15 and 30 wt-%NaOH at 25, 50, and 75°C. The anodic polarisation curves show in all cases a dissolution/passivation peak followed by a current plateau, corresponding to oxides formation. The active corrosion of the Nb–Ta alloy leads to the formation of sodium niobate–tantalate compounds, as detected by X-ray diffraction analysis of the corrosion products. Corrosion current densities obtained by Tafel extrapolation of polarisation curves indicate that the corrosion rate of Nb–20Ta alloy increases with increasing sodium hydroxide concentration and temperature. The corrosion resistance of the Nb–20Ta alloy is intermediary between those of pure niobium and pure tantalum.
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