Mechanistic Analysis of Anodic Dissolution of Zr in Acidic Fluoride Media

Abstract

Anodic dissolution of Zr in 10 mM HF was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy. The surface state of the electrode was analyzed using X-ray photon spectroscopy, and the surface morphology was characterized using atomic force microscopy. EIS data acquired at multiple dc potentials were subjected to mechanistic analysis. Reaction mechanism analysis approach reveals that at least four intermediates are required to describe the observed results. The intermediates are likely to be Zr sub-oxides, oxyfluorides and ZrO2. The proposed mechanism successfully predicts the major features observed in polarization and impedance spectra. At low overpotentials, the fractional surface coverage of Zr3+ species is higher than that of Zr4+ species, and the electrochemical dissolution rate is higher than the chemical dissolution rate. As the overpotential increases, the surface is covered with Zr4+ species and chemical dissolution rate becomes comparable to electrochemical dissolution rate. Although the surface is covered with Zr4+ species at higher overpotentials, significant chemical and electrochemical dissolution processes continue to occur and hence Zr is not protected in acidic fluoride media under anodic conditions.