Chloride Removal From Archaeological Cast Iron by Pulsating Current

Abstract

The electrochemical stabilization of archaeological cast iron, currently used in restoration and conservation, is designed to extract chlorides by applying an electrical field between the metal (object containing a metal core), which is cathodically polarized, and a stainless steel cage, which is anodically polarized. However, stabilization of artifacts in potentiostatic mode is a relatively long procedure and weakens the artifacts because of the hydrogen evolution when the applied voltage is too negative. In an effort to reduce the secondary effects caused by hydrogen, we decided to study the use of pulsating currents. The aim is to be selective with respect to the reactions produced and to increase the rate of dechlorination treatment. By applying a pulsating signal with a constant current and a limit potential (Elim, Elim <E), the same quantity of chloride (100%) was extracted in the same treatment time as in potentiostatic mode. After optimizing the pulse parameters (i, ton, toff, Elim), the extraction ratio (QCl/Qtotal) increased from 0·17 (potentiostatic mode) to 0·49 (pulsating mode) and side-effects due to hydrogen were avoided.