Storage of iron objects

It is not uncommon to find that the crusts covering marine iron artefacts have been removed by their excavators. Since the metal is permeated by chlorides, it is essential to keep the object immersed in an alkaline solution to favour the passivation of the metal (Ecorr increases continuously). The monitoring of the metal and its storage solution are essential and are considered preliminary steps for the stabilization of chlorinated material by electrolytic polarization.

The Ecorr versus time plots (below) show an unexpected electrochemical behaviour of the swivel gun; at least during the first two immersions (black and white plots)‚. Ecorr decreases and its value remains stable for a long period. This behaviour is due to the slow penetration of the KOH solution to the metal surface via the corrosion product layer. If this decrease in Ecorr is repeated during successive baths, the rise of Ecorr for the third and fourth baths is faster„. The plots on the right show that the majority of chlorides contained in the material are extracted during the first two baths, once the solution has reached the metal / corrosion product layer interface (Degrigny 2010).