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Residues of alkaline sulphite treatment and their effects on the corrosion of archaeological iron objects

Rimmer, Melanie and Watkinson, David 2011. Residues of alkaline sulphite treatment and their effects on the corrosion of archaeological iron objects. Presented at: METAL 2010, Charleston, SC, USA, 11-15 October 2010. Published in: Mardikian, P., Chemello, C., Watters, C. and Hull, P. eds. METAL 2010: Proceedings of the Interim Meeting of the ICOM-CC Metal Working Group. Clemson, SC: Clemson University, pp. 16-22.

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Abstract

The formation of chemical residues on archaeological iron following its treatment in aqueous alkaline sulphite (NaOH/ Na2SO3) is simulated by evaporating selected ion mixtures to dryness. The residues are identified by X-ray diffraction (XRD) and their influence on iron corrosion is investigated by mixing them with iron powder and dynamically recording the weight change of these powder mixtures at fixed temperature and relative humidity (RH) in a climatic chamber.Ferrous chloride was dissolved in Na2SO4 to simulate Fe2+/Cl⁻ contaminated Na2SO4 solution. This formed FeSO4·4H2O/FeSO4·7H2O/NaCl upon evaporation. Evaporating a FeCl2/NaOH/Na2SO3 solution produced either Na2SO4/NaCl/γ- FeOOH or Na6(CO3)(SO4)2/Na2SO4/NaCl/γFeOOH mixtures according to ion concentration in the initial solution. Iron powder and various residues were mixed and exposed at 75% RH and 20oC; Na2SO4/Fe did not corrode iron; FeSO4·7H2O/Fe produced minimal corrosion of iron; during the hydration phase of FeSO4·4H2O to FeSO4·7H2O iron corroded; a NaCl/FeSO4·7H2O/FeSO4·4H2O mixture corroded iron rapidly. Overall, at 75% RH, soluble chloride residues offer a more immediate and significant corrosion risk to iron than Na2SO4 ,FeSO4·7H2O and FeSO4·4H2O.

Item Type: Conference or Workshop Item (Paper)
Book Type: Edited Book
Date Type: Publication
Status: Published
Schools: History, Archaeology and Religion
Subjects: C Auxiliary Sciences of History > CC Archaeology
Q Science > QD Chemistry
Publisher: Clemson University
Funders: AHRC
Related URLs:
Date of First Compliant Deposit: 30 March 2016
Last Modified: 04 Jun 2017 03:53
URI: http://orca-mwe.cf.ac.uk/id/eprint/28515

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