Corrosion behavior of Zr, Ti, Ta and Nb in sodium hydroxide solutions

Abstract

Corrosion behaviors of metal applicable as nuclear energy and bio-material were investigated in sodium hydroxide solutions. Tested materials were zirconium, titanium, tantalum and niobium. They were immersed in 0.1 to 6.1 mol/dm3 sodium hydroxide solutions for 48 h, and then weight loss measurement, XRD and XPS analyses were conducted. Potentiodynamic polarization curves were obtained in some solutions. The corrosion rates were greater in the order of Nb>Ta>Ti>Zr. Polarization curves showed that Ti, Ta and Zr passivated, however, Nb corroded. XRD patterns showed that Nb dissolved as niobate compounds. XPS spectra showed that Zr and Ti formed oxide films such as ZrO 2 and TiO 2 on their surface. SEM photographs indicated that uniform corrosion occurred for tested materials. There existed the differences of the stable species among the thermodynamic, corrosion test and surface analysis data. It is expected for expanding the thermodynamics data of these materials in the alkali region.