The Passivity and Breakdown of Beryllium in Aqueous Solutions

Abstract

The passivity of 98.5 % pure beryllium (Be) has been studied as a function of pH. Below pH 2, Be exhibited active dissolution at all applied anodic potentials In solution pH 2-12.5 it is shown that Be exhibited passive anodic behavior at potentials between the open circuit potential and 0.6 V vs. saturated calomel electrode (SCE).. Anodic polarization above 0.6 V SCE in the pH range of 2- 12.5 lead to an abrupt increase in the passive current density followed by oxygen evolution. This abrupt increase was attributed to a change in the specific resistivity of the passive film above 0.6 V SCE as determined by electrochemical impedance spectroscopy (EIS). EIS experiments were also used to show that the oxide growth rate on Be was 6.4 Å/V over the potential range of 0-4V. At higher anodization potentials the growth rate appeared to be somewhat lower. Br akdown of passivity was studied in chloride and fluoride solutions. In chloride, attack was found to be localized while in fluoride, attack was localized only at concentrations below 10-3 M. Above fluoride concentrations of 10-3M, uniform attack was observed. In solutions containing both fluoride and chloride ions, the presence of the fluoride increased the passive current density of beryllium, but had no effect on the pitting potential. Key Words beryllium, pitting, chloride, passivity, electrochemical impedance spectroscopy, anodization, oxide