Comparative study of Nb, Nb-10W, and Nb-16Ta-12W corrosion behavior in sodium hydroxide solutions

The electrochemical behavior of mobium, Nb-10W, and Nb-16Ta-12W alloys is investigated in sodium hydroxide solutions at different temperatures, using open-circuit potential (OCP) measurements, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). OCP and polarization measurements show that the three materials are spontaneously active in 10, 15, and 30 wt.% NaOH at 25, 50, and 75 degreesC. The anodic polarization curves show in all cases a dissolution-passivation peak followed by a current plateau, corresponding to oxides formation. The spontaneous active corrosion of the three materials mainly leads to the formation of sodium niobates, as detected by X-ray diffraction analysis of the corrosion products. The evolution of the corrosion current densities obtained from Tafel extrapolation of polarization curves and the polarization resistance values determined from EIS measurements indicate that the corrosion rates of Nb, Nb-10W and Nb-16Ta-12W alloys increase with increasing NaOH concentration and temperature. In all cases, the increasing order of corrosion resistance is: Nb < Nb-10W < Nb-16Ta-12W. (C) 2004 Elsevier Ltd. All rights reserved.