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Towards quantitatively assessing the success of dodecanoic acid as an inhibitor for the treatment of archaeological iron nails

Watkinson, David, Emmerson, Nicola and Channell, Ian 2017. Towards quantitatively assessing the success of dodecanoic acid as an inhibitor for the treatment of archaeological iron nails. Presented at: European Corrosion Congress 2017, Prague, Czech Republic, 3-7 September 2017.

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Abstract

Controlling the post-excavation corrosion of archaeological iron nails infused with chloride ions from their burial environment is a longstanding problem. While desiccation is proven to prevent corrosion, it requires significant outlay and ongoing management for its continued success1. Desalination enhances stability but treatment effectiveness is unpredictable2. Inhibitors potentially offer a labour saving cheap solution for long-term storage of archaeological iron objects, with the ideal treatment being immersion in the inhibitor to deliver an object that is stable in aggressive relative humidity (RH). Unfortunately, inhibitors may change object aesthetics, pose health risks and there is limited quantitative evidence-based assessment of their effectiveness on archaeological iron. Recently, attention has turned to low toxicity natural inhibitors. Linear sodium carboxylates have shown effectiveness on modern steel analogues and archaeological surfaces when tested by electrochemical immersion techniques3. This study determined quantitatively the impact of a standardised dodecanoic acid treatment on the corrosion rate of 20 archaeological nails from the Roman site at Caerleon (South Wales). Prior to treatment, individual corrosion rates were determined by sealing each nail in its own reaction vessel with the interior controlled to 80% RH, then remotely recording oxygen depletion inside the vessel via light striking an oxygen sensor within it. Treatment of each nail involved an aqueous 0.1M dodecanoic acid solution, with pH adjustment to manipulate solubility and prevent gelling. Each nail was immersed in its own 100ml dodecanoic acid solution for 24 hours followed by controlled 12 hour desiccation prior to re- measuring oxygen consumption rates at 80% RH. No object ceased to consume oxygen. Seventeen nails (85%) returned lower oxygen consumption rates but with no discernible pattern, as both major and minor rate reductions occurred. Three nails (15%) had increased corrosion rate. The nature, form and location of chloride in archaeological iron and corrosion layer composition and morphology introduce a wide range of sample variables that are considered when discussing outcomes. Although reproducibility limitations exist, this methodology offers an evidence based route for predicting the success of an inhibitive system in its working context.

Item Type: Conference or Workshop Item (Paper)
Status: Unpublished
Schools: History, Archaeology and Religion
Subjects: A General Works > AM Museums (General). Collectors and collecting (General)
C Auxiliary Sciences of History > CC Archaeology
Q Science > Q Science (General)
Date of First Compliant Deposit: 10 March 2021
Last Modified: 17 Mar 2021 16:00
URI: https://orca.cardiff.ac.uk/id/eprint/139436

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