Electrochemical Analysis of Chloride Impacts on Passivation of Archaeological Iron in Desalination Solutions.

Based on the passivation of iron in alkaline solutions, aqueous alkaline treatment has been taken as an effective desalination technique to increase the stability of archaeological iron. However, chlorides may destroy the passivation of iron artifacts, causing damage to the treated artifacts during desalination. In this study, electrochemical and microstructure analyses were carried out in alkaline solutions with known chloride content, using archaeological iron and pre-corroded iron coupons with varying chloride levels within the rust layer. The study revealed that alkalinity ensures passivation even in the presence of chloride within the rust layer. However, the passivation weakens as the concentration of ‘free’ chloride ions in the alkaline solution increases due to their migration from the rust layer, leading to active corrosion. A chloride threshold value (CTV) of 355 ppm in 0.1 mol/L NaOH solution was established as a chloride level for the replacement of the alkaline solution. The determination of CTV based on electrochemical measurements is intended to guide the timely replacement of the desalination solutions, thereby preventing chloride-induced iron corrosion during desalination treatments. [ABSTRACT FROM AUTHOR]