Investigating the treatment of chloride-infested archaeological iron objects

Archaeological iron objects become infested with chloride ions during burial. These enhance electrochemical corrosion, acidify the pore solution and form hygroscopic p-FeOOH. Controlling chloride-induced corrosion requires <15% relative humidity (RH) this is difficult to achieve in practice. Iron objects are at significant risk when dry storage is not maintained. Alkaline deoxygenated solutions remove chloride ions from objects. A large quantitative dataset was needed to evaluate the chloride extraction efficiency, the relationship between chloride concentration and corrosion rate and the risks posed by aqueous treatments. Using 120 archaeological iron nails as sample material, and recording chloride extraction behaviour for each individual object, three treatments were tested nitrogen-deoxygenated 0.1M NaOH (20 C) and alkaline sulphite (0.1M NaOH/0.05M Na2S03) at 20 C and 60 C. Objects were subsequently digested to measure residual chloride. Chloride extraction efficiency was 60-99% in most cases 87% of treatments resulted in residual chloride levels <1000 ppm. Accelerated corrosion tests showed that treated objects were more stable than untreated. Post-treatment scanning electron microscopy identified chloride ions in corrosion products or within slag inclusions, but none at the metal/corrosion interface. The transformation of synthetic P-FeOOH showed that 0.5M NaOH or 0.1M NaOH/0.05M Na2S03 (60 C) produced the maximum transformation (c.50%) to a-FeOOH and/or a-Fe203. It could not be confirmed whether this reaction occurs on objects. Risk to objects was evaluated by assessing physical damage during treatment and modelling chemical residues. Less than 2% of objects experienced total fragmentation 69% experienced no change. The most likely chemical residue from alkaline sulphite is Na2S04 this poses no threat to objects at RH <76%. The research reported here is a substantial addition to the body of data about desalination treatment. It improves understanding of the benefits and risks of treatment in relation to developing improved conservation strategies for highly chloride-contaminated objects

An evaluation tool for Age-Friendly and Dementia Friendly Communities.

PURPOSE: The purpose of this paper is to report how an evaluation tool originally developed for Age-Friendly Cities was pilot-tested in the context of the Dementia Friendly Community (DFC) initiative of the city of Sheffield/UK. It presents finding and outputs on which other communities with dementia friendly agendas can draw. DESIGN/METHODOLOGY/APPROACH: The original evaluation tool was adapted to a focus on dementia friendliness. Data collection involved scoping conversations, documentary analysis, interviews and group discussions. Following evidence appraisal, Sheffield's approach to dementia friendliness was assessed. A local steering group was central to the study. FINDINGS: The evidence indicates areas of strength in Sheffield's approach to dementia friendliness: involvement of older people; service provision; collaboration; monitoring and evaluation. Scope for improvement was identified around resource allocation, and use of existing guidance on dementia friendliness. Recommendations for policy and practice include enhancing pooling of resources, more detailed recording of resources allocated to dementia-related activity, and collection of evidence on how people affected by dementia have shaped the city's DFC initiative. Key research outputs are an adaptable logic model and an emerging evaluation framework for DFCs. RESEARCH LIMITATIONS/IMPLICATIONS: The study was a short pilot with limited resources. Its findings and outputs must be considered preliminary. ORIGINALITY/VALUE: The findings and outputs provide a basis for further research. The study has suggested key components of an evaluation framework for DFCs. It is informing ongoing work to develop such a framework.Funded by the National Institute for Health Research (NIHR) School for Public Health Research (SPHR) in the UK as part of the Ageing Well Programme, 2012-2017

Quantifying effectiveness of chloride desalination treatments for archaeological iron using oxygen measurement

Alkaline deoxygenated aqueous treatments are employed to remove damaging chloride ions (Cl⁻) from excavated archaeological iron objects; however, their effectiveness is either qualitatively assessed or anecdotal. A novel oxygen measurement technique is used to assess pre- and post-treatment corrosion rates of individual archaeological iron objects; these rates are related to their Cl⁻ content before and after treatment. Ten archaeological iron nails were individually sealed in reaction vessels conditioned to 80% relative humidity (RH) at 20 ºC. The oxygen partial pressure inside each vessel was measured remotely over the course of 37 days using an OxyMini fibre-optic meter and a sensor spot inside each vessel. Control vessels containing nitrogen gas revealed negligible leakage. Objects were removed and treated for two weeks in an alkaline sulphite (0.1 M NaOH / 0.05 M Na2SO3) solution at 60 ºC and the extracted Cl⁻ was recorded quantitatively and then the objects were placed back in the oxygen measurement vessels (80% RH and 20 ºC). After recording oxygen consumption, nitric acid digestion was used to determine the residual Cl⁻ content. Half of the ten objects that were treated had their oxygen consumption rate reduced by 91% or more, with the oxygen consumption rate of the remaining reducing by 49-71%. Object Cl⁻ contents reduced from between 336-3487 parts-per-million (ppm) before treatment to a maximum of 364 ppm after treatment. A linear correlation between pre-treatment Cl⁻ content and oxygen consumption rate existed but was not apparent post-treatment, suggesting that the readily accessible soluble Cl⁻, which is removed by a single two-week bath, is the most significant driver for corrosion. Half of the objects were still measurably consuming oxygen after treatment but it is expected that this slower corrosion rate should significantly increase overall lifespan. A single, brief, alkaline deoxygenation treatment is a useful addition to preventive conservation strategies for vulnerable iron objects. Use of oxygen partial pressure measurement to assess corrosion rates provides a new insight into the effectiveness of treatments for quantifying corrosion risk, determining the success of conservation strategies, developing management procedures and cost benefit analysis

Assessing the effects of alkaline desalination treatments for archaeological iron using scanning electron microscopy

Archaeological iron objects are often vulnerable to severe post-excavation corrosion induced by chloride ions, a corrosion accelerator. To reduce this problem, alkaline deoxygenated desalination treatments may be used to remove chloride ions. There is very little information on the mechanisms and efficacy of such treatments and they are not in general use by British conservators. As part of a larger study, some iron objects were desalinated and a scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectrometry (EDX) was used to analyse eight polished cross-sections of treated and untreated archaeological iron nails to investigate whether differences between treated and untreated nails could be detected with this method. The analysis showed clear differences between the treated and untreated halves of the iron nails. Untreated nails showed regions of high chlorine content that appeared to be mobile and caused corrosion on the polished surfaces of the samples, despite storage at low humidity. Chlorine-containing corrosion products were identified as akaganéite using Raman spectroscopy. The majority of the treated samples showed no fresh corrosion or areas of very high chlorine content except near slag inclusions surrounded by metal. These caused fresh corrosion, presumably due to the inability of the treatment solution to reach these deep-seated areas. The use of SEM-EDX showed that desalination of the objects had a positive impact on the stability of archaeological iron. It also showed some of the limitations of desalination, such as its inability to remove deepseated chloride ions. Although not an extensive study, this information is useful in understanding the effects of treatment on a detailed level and will complement existing data on the effectiveness of treatments

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

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

The efficiency of chloride extraction from archaeological iron objects using deoxygenated alkaline solutions

Chloride-contaminated archaeological iron is unstable and problematic to store and display within museum collections. Reducing its chloride ion content using aqueous desalination followed by storage in controlled relative humidity offers one treatment option. This study reports a quantitative assessment of chloride extraction by aqueous deoxygenated alkaline desalination solutions from 120 individual archaeological iron nails. The three treatment methods comprised alkaline sulphite solution (0.1 M NaOH/0.05 M Na2SO3) at room temperature and at 60°C and sodium hydroxide solution (0.1 M) deoxygenated using a nitrogen gas positive pressure system at room temperature. Chloride extraction was monitored using a specific ion meter. The nails were digested after treatment to measure their residual chloride content. A wide range of extraction patterns emerged, with the majority of individual treatments extracting 60–99% of the chloride present. Residual chloride levels for 87% of the objects fell below 1000 ppm and 42% were below 200 ppm. Although no treatment extracted 100% of the chloride in the object, alkaline desalination produced very significant reductions in chloride content. The impact of this on future corrosion of the objects is discussed. This quantitative and statistically viable assessment of deoxygenated desalination treatments provides evidence to support their use in conservation practice, which will impact on procedures for the preservation and management of archaeological heritage

The impact of chloride desalination on the corrosion rate of archaeological iron

Although desalination of archaeological iron reduces its chloride concentration and enhances object stability, the reduction in corrosion rate that this produces has never been quantified. This study measures post-treatment corrosion rates in accelerated corrosion environments to identify the impact of removing chloride ions on corrosion rate. Thirty-five archaeological iron nails, treated individually in either alkaline sulphite or nitrogen-deoxygenated sodium hydroxide, were exposed to 75°C and 75% relative humidity together with 31 untreated objects from the same archaeological sites. Object weight change and visual examination of physical change before and after the test period were used to monitor corrosion. 77% of treated objects showed no weight gain and no visible signs of corrosion, while 90% of untreated objects did corrode. The impact of chloride on corrosion of untreated objects was clearly established by a significant linear correlation between chloride content and weight gain. Treated objects with <400 ppm chloride content showed no corrosion behaviour. Corrosion of treated objects was attributed to incomplete treatment: 93% of objects treated to <5 mg/l Cl− in the final solution bath displayed no corrosion behaviour. Based on these results, desalination of iron objects to enhance their stability offers a valuable option for reducing corrosion rates of archaeological iron, which should increase object lifespan. The results also raise the question of whether low levels of post-treatment residual chloride produce corrosion of any significance. Answering this will be an important step forward for managing the preservation of archaeological iron

The Influence of relative humidity and intrinsic chloride on post-excavation corrosion rates of archaeological wrought iron

This study examined the impact of relative humidity (RH) on the corrosion rate of 129 archaeological iron nails from two sites. Oxygen consumption of individual nails in controlled RH was used as a corrosion rate proxy to deliver quantitative data on corrosion rate as a function of RH. This was negligible at 20% RH, slow up to 40% RH for both sites, and increased rapidly at 60% RH for Roman nails from Caerleon (Wales) and at 70% RH for medieval nails from Billingsgate (London). The nails were digested and their chloride content was determined and related to their oxygen consumption at specific RH values. While a generic pattern of corrosion as a function of chloride was identified, for any single concentration of chloride corrosion rate was not predictable. Desiccation is in common use to control post-excavation corrosion of archaeological iron; quantifying how differing levels of desiccation changed corrosion rate provided a scaled tool for identifying corrosion risk, estimating object longevity, and calculating cost benefit for storage options

Guidelines for the storage and display of archaeological metalwork

This is a guide for Heritage Professionals on how to control the corrosion of archaeological metal objects during storage and display. It is a practical guide with clear statement of the underpinning theory behind the strategies and procedures recommend, with the inclusion of the evidence base that supports them