Marine archaeological iron corrosion and the mechanisms and kinetics of dechlorination treatments
File(s)
Author(s)
Ramsay, Alex
Type
Thesis
Abstract
The shipwreck of King Henry VIII’s prized flagship, the Mary Rose, is one of the best preserved marine archaeological Tudor finds in modern history. However, since its excavation in 1982, conservators and scientists have been in a relentless battle to mitigate the degradation of this important piece of cultural heritage. The major universal problem faced by metal conservators is the reignition of corrosion upon excavation and exposure of iron materials to atmospheric conditions. In marine archaeological iron this is further complicated by the ingress of Cl- from time in burial. The use of alkaline washing as a conservation treatment for the removal of Cl- is a common strategy which has been employed for many of the Mary Rose cast iron cannonballs. A suite of ex-situ microscopy and spectroscopy techniques have been used in this work to determine the efficacy of the various dechlorination treatments undertaken on this collection. It has been shown that to varying degrees, the treatments drive Cl- removal from marine iron’s most destructive corrosion product’s, β-FeO(OH, Cl) and β-Fe2(OH)3Cl, transforming them to more stable products such as α-FeO(OH) and Fe3O4. The corrosion layer profile for both conserved and unconserved iron artefacts have been determined, providing information about both their corrosion during burial and subsequent corrosion product transformations from dechlorination treatments. Novel in-situ spectroscopic experiments have been conducted to determine the mechanisms and kinetics of β-Fe2(OH)3Cl dechlorination in real time and its transformation to α-FeO(OH) and Fe3O4. Intermediates to this transformation such as GR1(Cl-) and Fe(OH)2 were identified at certain spatial areas of the corrosion layer, indicating the influence of local pore environment on their formation. By fully understanding these dechlorination mechanisms, new alkaline based washing treatments can be developed, preserving the integrity of these objects, and allowing for their display and enjoyment by the public.
Version
Open Access
Date Issued
2024-06-15
Date Awarded
01/01/2025
Advisor
Ryan, Mary
Schofield, Eleanor
Cibin, Giannantonio
Sponsor
The Scorpion Charitable Trust
Engineering and Physical Sciences Research Council
Publisher Department
Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)