The corrosion of excavated archaeological iron with details on weeping and akaganéite

Selwyn, Lyndsie S.; Sirois, P.I.; Argyropoulos, V.

doi:10.1179/sic.1999.44.4.217

Cited by 98 publications

(39 citation statements)

References 43 publications

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“…[12][13] The tunnels in the akaganeite structure, with a diameter of 0.21 nm to 0.24 nm, can be stabilized by H 2 O molecules 13 and/or by Clions, and Cllevels ranging from 2 mol% to 7 mol% have been reported. 7 The crystalline structure has a tetragonal or monoclinic unit cell, although this has also given rise to much controversy.…”

Section: Introductionmentioning

confidence: 97%

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Environmental Conditions for Akaganeite Formation in Marine Atmosphere Mild Steel Corrosion Products and Its Characterization

Morcillo¹,

González‐Calbet²,

Jiménez³

et al. 2015

Corrosion

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The corrosion of mild steel in chloride-rich atmospheres is a highly topical issue. The formation of the oxyhydroxide akaganeite (β-FeOOH) in this type of atmosphere leads to a notable acceleration of the steel corrosion process. The scientific literature contains many references to outdoor marine atmospheric tests, but so far has failed to clarify two basic matters in relation to akaganeite: the environmental conditions necessary for its formation, and its morphological characterization. Research has been performed at three atmospheric corrosion stations located at Cabo Vilano wind farm (Camariñas, Spain) at different distances from the shoreline (332, 590, and 2,400 m), with chloride deposition rates of 390, 74, and 29 mg/m2/day, respectively, with the exposure of mild steel specimens for 1 year. This paper reports the environmental conditions that generally led to the formation of akaganeite: an annual average relative humidity of around 80% or higher, and simultaneously, an annual average chloride deposition rate of approximately 60 mg/m2/day or higher. Rigorous characterization of akaganeite was performed by x-ray diffraction, scanning electron microscopy/energy dispersive spectroscopy, and transmission electron microscopy/selected area electron diffraction.

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Section: Introductionmentioning

confidence: 97%

“…16 According to many authors 9,13,[17][18] akaganeite forms mainly in the inner part of the corrosion layer near the metal-oxide interface of corroded steel. But akaganeite has also been identified in the outer part of thick rust layers formed on carbon steels exposed to air in a coastal region.…”

Section: Introductionmentioning

confidence: 99%

Environmental Conditions for Akaganeite Formation in Marine Atmosphere Mild Steel Corrosion Products and Its Characterization

Morcillo¹,

González‐Calbet²,

Jiménez³

et al. 2015

Corrosion

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“…Archaeological iron is damaged by chloride ions, which diffuse into the object during burial (Turgoose 1982(Turgoose , 1985. After excavation, oxidation forms ferrous chloride and akaganéite (β-FeOOH), which create significant pressure within the corrosion layers and cause cracking, fragmentation and break-up of objects (Turgoose 1982;Selwyn et al 1999;Loeper-Attia 2007). Although the basic principles of this process are well understood, information regarding the three-dimensional distribution of chloride ions within the object and its relationship to patterns of cracking and the development of corrosion behaviour is not currently available.…”

Section: Introductionmentioning

confidence: 99%

The Use of Neutron Analysis Techniques for Detecting The Concentration And Distribution of Chloride Ions in Archaeological Iron

et al. 2013

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Chloride (Cl) ions diffuse into iron objects during burial and drive corrosion after excavation. Located under corrosion layers, Cl is inaccessible to many analytical techniques. Neutron analysis offers non-destructive avenues for determining Cl content and distribution in objects. A pilot study used prompt gamma activation analysis (PGAA) and prompt gamma activation imaging (PGAI) to analyse the bulk concentration and longitudinal distribution of Cl in archaeological iron objects. This correlated with the object corrosion rate measured by oxygen consumption, and compared well with Cl measurement using a specific ion meter. High-Cl areas were linked with visible damage to the corrosion layers and attack of the iron core. Neutron techniques have significant advantages in the analysis of archaeological metals, including penetration depth and low detection limits.

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“…In low humidity storage high chloride concentration and low surface pH may favour formation of solid ferrous chloride, which can corrode iron in its FeCl 2 .4H 2 O form [4]. At higher humidities, cited as being around 55% relative humidity @25 o C, FeCl 2 .4H 2 O can either dissolve or hydrolyse to βFeOOH [4,6,7] and acidic, hygroscopic moisture droplets containing Fe 2+ and Clions with βFeOOH skins may form [8,9]. The loss of metallic iron and formation of voluminous βFeOOH at metal anodes causes separation between the hard, dense corrosion layer and the iron core [8,9].…”

Section: Introductionmentioning

confidence: 99%

“…At higher humidities, cited as being around 55% relative humidity @25 o C, FeCl 2 .4H 2 O can either dissolve or hydrolyse to βFeOOH [4,6,7] and acidic, hygroscopic moisture droplets containing Fe 2+ and Clions with βFeOOH skins may form [8,9]. The loss of metallic iron and formation of voluminous βFeOOH at metal anodes causes separation between the hard, dense corrosion layer and the iron core [8,9]. The resulting cracked, spalling, acid-ridden chloride-rich object is of no use for interpretative purposes and is highly unstable.…”

Section: Introductionmentioning

confidence: 99%

The Role of βFeOOH in the Corrosion of Archaeological Iron

Watkinson

Lewis

2004

MRS Proc.

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The chloride bearing corrosion product akaganéite (βFeOOH) can form during postexcavation corrosion of chloride infested archaeological iron and is able to corrode iron in contact with it. Its action on iron is examined using βFeOOH synthesized from ferrous chloride and iron powder. Using weight measurements the hygroscopicity of βFeOOH is established. The influence of relative humidity on the corrosion of iron powder mixed with βFeOOH is examined by dynamic mass change within a climatic chamber. At 20 o C and 12% relative humidity, iron in contact with βFeOOH did not corrode. At 15% relative humidity slight iron corrosion was detected after 160 hours, but at 35% relative humidity corrosion occurred after a few hours. Surface adsorbed chloride was removed from βFeOOH by aqueous washing and this reduced its hygroscopicity. The reported metastability of βFeOOH was examined via XRD of a 23 year old sample, which was found to be still entirely composed of βFeOOH. These results provide better understanding of βFeOOH corrosion of iron, corrosion control of chloride infested iron using dry storage and the effect of aqueous washing on archaeological iron.

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The corrosion of excavated archaeological iron with details on weeping and akaganéite

Cited by 98 publications

References 43 publications

Environmental Conditions for Akaganeite Formation in Marine Atmosphere Mild Steel Corrosion Products and Its Characterization

Environmental Conditions for Akaganeite Formation in Marine Atmosphere Mild Steel Corrosion Products and Its Characterization

The Use of Neutron Analysis Techniques for Detecting The Concentration And Distribution of Chloride Ions in Archaeological Iron

The Role of βFeOOH in the Corrosion of Archaeological Iron

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