Metastable Pitting of Aluminum and Criteria for the Transition to Stable Pit Growth

Abstract

Analysis of current spikes associated with pitting events was performed on high purity A1 loop wire electrodes over a range of C1-concentrations (10 -5 to 1M) and potentiostatieally applied potentials. A distribution of pitting and repassivation potentials was observed at each C1 concentration. Factors controlling the transition from metastable to stable pitting were identified by comparing the electrochemical behaviors of stable pits at elapsed times equal to the mean lifetime of metastable pits. This comparison also provided insight on the origins of statistical distributions of pitting potentials. The key differences were that (i) stable pits had a faster rate of rise in pit current which implies a faster growth rate and, subsequently, larger pit radii at times equal to metastable pit lifetimes, and (if) stable pits satisfied the criterion IpJrpi t > 10 -2 A/em, at all times during growth, indicating that a concentrated A1C13 solution must be maintained for pit survival. However, the pit growth rates were ohmically limited near the pitting potential. Chromate inhibitor decreased the metastable pit nucleation rate and minimized pit growth rates so that the 10-~A/cm criterion was difficult to achieve; hence the chance for pit stabilization was reduced.

Chloride Ion Interactions with Oxide-Covered Aluminum Leading to Pitting Corrosion: A Review

“…The average value of E pit for Al in 0.1 M NaCl is -0.670 V sce ± 20 mV. 31,39,43,61,67,73,80 Maitra and Verink report that the amount of Cl − increased as polarization time increased (0.5 to 24 hours). Also, sputter profiling showed that the Cl − was present in the oxide film and that the Cl − signal diminished as the oxide/metal interface was approached.…”

Lithium salts as leachable corrosion inhibitors and potential replacement for hexavalent chromium in organic coatings for the protection of aluminum alloys

“…16,17 Chromates are well-known for their corrosion inhibiting efficiency over a wide pH range and their ability to reduce the oxygen reduction reaction. 18,19 Unfortunately, Cr(VI)-based compounds are toxic and known carcinogens, and new regulations and legislations are restricting their current and future use. [20][21][22] Over the years, extensive research has been conducted to find environmentally friendly alternative inhibitors that perform equal or better compared to Cr(VI)-containing inhibitors.…”

Electrochemical Characterisation to Study the Pitting Corrosion Behaviour of Beryllium

“…It is well established that metastable pits sometimes form several hundred milli volts below the pitting potential and during the induction time for stable pit formation. There are a number of studies for metastable pits on steel and aluminium (Blanc & Mankowski, 1997;Pride et al, 1994) but few on beryllium (Lillard, 2000).…”