The Passivity and Breakdown of Beryllium in Aqueous Solutions

Abstract

The passivity of 98.0% pure beryllium has been studied in ambient temperature aqueous solutions as a function of pH. Below solution pH 2, potentiodynamic polarization curves exhibited active dissolution at all applied anodic potentials. In solution pH 2 to 12.5 it is shown that beryllium exhibits passive anodic behavior at potentials below 0.6 V vs. (saturated calomel electrode) SCE. Anodic polarization above 0.6 V SCE in the pH range of 2 to 12.5 led to a "stepped increase" in the passive current density followed by oxygen evolution. This stepped increase was associated with a change in the specific resistivity of the passive film above 0.6 V SCE as determined by electrochemical impedance spectroscopy (EIS). EIS results were analyzed in the context of an equivalent circuit model which incorporated two time constants, one associated with the oxide film and the other associated with the electrode/solution interface. From these EIS experiments, the oxide growth rate was determined to be 6.0 A/V over the potential range of 0 to 4 V. At higher anodization potentials the growth rate appeared to be somewhat lower. Breakdown of passivity was studied in chloride and fluoride solutions. In chloride, the attack was found to be localized while in fluoride, the attack was localized only at concentrations below 10' M. Above io-M, uniform attack was observed. In the pH range of 2 to 12.5, the pitting potential of beryllium in chloride environments was found to be independent of pH. 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. IntroductionBeryllium has a hexagonal close-packed structure (hcp), high specific heat and thermal conductivity, and high specific strength and stiffness. It is an attractive engineering material for nuclear applications due to its low neutron

Electrochemical Characterisation to Study the Pitting Corrosion Behaviour of Beryllium

“…This relationship is very close to that observed by Hill et al (1998) for beryllium grade S200D (see Equation 4). …”

“…The morphology of corrosion pits in polycrystalline commercial beryllium on electrochemical polarisation in 0.01M KCl solution was described by Hill et al (1998). It was observed that the corrosion pits in beryllium have the same size and shape as the beryllium grain morphology.…”

Effect of pitting corrosion in NaCl solutions on the statistics of fracture of beryllium

“…This surface film is either BeO or its hydrate (BeO⅐(H 2 O) x ) and is on the order of 20 Å in thickness. [1] The oxide formed is in a state of compression, since the volume occupied by the oxide is 1.68 times that of the metal used to form the oxide. [2] Thus, the oxide layer formed on the surface of beryllium is resistant to cracking or spalling.…”

“…[1,2,3] This breakdown of passivity in beryllium occurs at localized sites in a sporadic and stochastic manner. [4,5] Pitting is an insidious form of corrosion, since it can go unnoticed and can lead to catastrophic metal failure.…”

Effect of electrodeposition current density on the microstructure and the degradation of electroformed iron for degradable stents

“…It is believed that in the case of bcc Fe single crystals, the close-packed planes be the most susceptible to pitting corrosion [34]. Schreiber et al [35] studied the effect of grain orientation and grain boundaries on anodic dissolution rate of iron and found that grains with (1 1 1) planes parallel to the surface had the highest dissolution rate.…”