Atmospheric Corrosion

SKPFM measured Volta potential correlated with strain localisation in microstructure to understand corrosion susceptibility of cold-rolled grade 2205 duplex stainless steel

“…In dry air, the passivating layer of stainless steels consists of a thin film oxide/oxyhydroxide layer, usually 1-3 nm [25,46,47]. In humid air above 60% RH, at least ten monolayers of water will be adsorbed resulting in thicker passivating layers which decreases the Volta potential difference [25,48].…”

“…Air was bubbled through a 5 litre flask containing 5 M NaCl solution, heated by a water bath to 60°C, creating a humid gas atmosphere which was directed to the chamber (a Perspex enclosure) housing the entire AFM setup. According to Leygraf et al [25], at least six to ten monolayers of water with chloride species should form at 86% RH supporting a correlation of Volta potential measurements with local electrochemical activity. Temperature and relative humidity (RH) were recorded during the measurement with an EL-USB-2-LCD temperature and humidity data logger.…”

“…These humidity values were chosen to obtain information about the effect of water multi-layer coverage on Volta-potential differences, invoking "solution-like" behaviour [25]. The humidity was controlled in a sealed AFM chamber.…”

“…However, SKPFM Volta potential differences in air may not always correlate with corrosion potentials measured in aqueous solution, and interpretation of SKPFM data regarding corrosion phenomena need to be treated with caution [15]. This shortfall can be minimised by conducting SKPFM measurements in humid air (>60% relative humidity), where several mono-layers of water are present on the metal surface, mimicking "solution-like" behaviour [25].…”

The influence of the constituent elements on the corrosion mechanisms of silver alloys in sulphide environments: the case of sterling silver

“…The corroded layer structure is the result of overlapped layers with distinct compositions, continuously growing at different rates. The corrosion of Ag and Cu in high sulphide environments has been widely investigated, 11,13,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] however, the inuence of the constituent elements on the corrosion mechanism of sterling silver was, from our knowledge, not studied yet.…”