What happens when a Pb–Sn coating deposited on low carbon steel is exposed in an HCl‐polluted wet environment? Development of a corrosion mechanism
Abstract
This article synthesizes all the results obtained to establish a global corrosion mechanism when a Pb–Sn coating deposited on low carbon steel is corroded in an HCl-polluted wet environment. The successive stages of the process are shown. In HCl-polluted environment, coupled with water, acid chlorides provide an aggressive electrolyte particularly favorable to corrosion. In contact with this electrolyte, lead products are created as PbCO3 and PbCl2, showing the impact of the surrounding atmosphere. In parallel, the electrolyte concentrates in Sn2+ until saturation, and tin precipitates under different forms. Due to the lead consumption, the lead corrosion products layer breaks, and the coating thins, diffusion pathways are created and the steel oxidizes. Iron corrosion products are similar with or without a coating except for the presence of a tin-rich filament. Lead is no longer present. The different stages of the mechanism are compared to corrosion phenomena observed during the use of Pb–Sn alloys to provide effective solutions to minimize or even avoid the phenomenon of corrosion.
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