The effect of metallurgical structure on the chloride-induced corrosion of archaeological wrought iron

Nordgren, Eric 2016. The effect of metallurgical structure on the chloride-induced corrosion of archaeological wrought iron. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Summary Archaeological wrought iron artefacts are subject to damaging corrosion while in the burial environment and when subjected to environmental changes after excavation. The role of water, oxygen, and chloride corrosion accelerators are central to iron corrosion processes. Intrinsic factors such as the amount and distribution of slag in wrought iron may also play a role in corrosion processes. This study examined a range of factors that impact on understanding conservation desalination treatments to mitigate corrosion by removing chlorides. While examining the effect of slag on corrosion rate and chloride content formed the core of this project, cracking morphologies within corrosion product layers and their influence on corrosion rates measured by oxygen consumption produced outcomes of interest for designing the practicalities of treatment procedures. The slag content of the wrought iron objects examined in this study did not correlate with either their corrosion rate or their chloride content. In line with other authors, clustering of chloride around slag inclusions was identified. This confirmed slag does act as a focus for developing corrosion centres, which will offer challenges for chloride removal and hence provide opportunity for post-treatment corrosion. The alkaline sulphite washing applied to the iron nails produced results that aligned with those reported in other studies and confirmed its relative efficiency for removing chloride. Of major relevance to conservators designing alkaline washing techniques is assigning treatment time and specifying treatment environment. These decisions are aided by evidence provided in this study, which showed that immersing the chloride ii containing corrosion product β-FeOOH in alkaline sulphite entirely transformed it to other iron oxides in only 30 days. During this process it will release its chloride, which will be available for diffusion into the wash solution making a more complete desalination process possible.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	History, Archaeology and Religion
Subjects:	C Auxiliary Sciences of History > CC Archaeology Q Science > Q Science (General)
Date of First Compliant Deposit:	19 January 2017
Last Modified:	12 Nov 2021 13:25
URI:	https://orca.cardiff.ac.uk/id/eprint/97535

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