ELECTROCHEMICAL ASSESSMENT AND MONITORING OF STABILIZATION OF HEAVILYCORRODED ARCHAEOLOGICAL IRON ARTIFACTS

Stabilisation treatments for heavily corroded archaeological iron arte facts are often carried out in solutions considered to be non-corrosiv e on the basis of their behaviour towards clean metal. This paper desc ribes the application of d.c. and a.c. electrochemical techniques to s uch artefacts in some standard treatment solutions, including sodium h ydroxide and carbonate-bicarbonate buffers, and compares the results w ith those obtained with artificially precorroded steel electrodes. The results for electrochemical impedance spectroscopy and linear polaris ation are shown to be consistent but complementary. It is shown that t here are extremely rapid electrochemical processes occurring during im mersion in sodium hydroxide solutions, but these are not solely relate d to corrosion, whereas the samples in carbonate-bicarbonate buffers s how a more normal corroding metal response. Both solutions are able to passivate the precorroded electrodes but evidence of complete passiva tion is not seen with the archaeological artefacts, even after several months, although the corrosion potential rises to values typical of p assive iron.