| Abstract: | SUMMARIES. 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 017 (potentiostatic mode) to 0˙49 (pulsating mode) and side-effects due to hydrogen were avoided.
CONCLUSION. In this study, artificially chlorinated cast iron specimens were used to compare a pulsating current treatment technique with treatment by cathodic polarization. Among the different pulsating modes tested, the one using constant current and a limit potential (Elim<E) seems to be of great interest. We demonstrated that treatment using optimized pulsating currents (i = i1 during t = ton , i = 0 during t = toff) and limit potential (Elim<E) was as efficient as the potentiostatic treatment. The same quantity of chlorides (100%) was extracted during the same treatment time. But, in addition, this method was less damaging to the artifacts since the extraction ratio QCl /Qtotal increased from 0˙17 in potentiostatic mode to 0˙49 in pulsating mode with an optimized constant current (i = -300A during ton = 60s, i = 0 during toff = 30s) and limit potential (Elim = -1400mV/SSE<E). A complete experimental programme has to be performed to show that this technique can be further optimized. This will involve pursuing the present study in greater detail with respect to the pulse parameters i1 ton, toff and Eim and also observing the influence of temperature and the nature of the electrolyte (sodium carbonate, ammonia). |
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