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

Abstract

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.     

Influence of crucial parameters on the dechlorination treatments of ferrous objects from seawater

Abstract

This article compares chemical dechlorination treatments (immersion in sodium hydroxide or alkaline sulphite) and electrochemical treatments of iron bars from the Gallo-Roman period excavated from a marine environment. Some important parameters, such as storage before treatment, temperature, solution composition, and drying after treatment, were varied during the study to assess their influence on the chloride extraction process. The kinetics of these treatments depend mainly on chloride diffusion through the corrosion layers. The kinetics are promoted by high temperatures and, in the case of electrolysis, by the electric field effect. The reduction of corrosion products during electrolysis occurs only for objects previously stored in air. In fact, the manner in which the objects are stored before treatment is critical in the dechlorination processes. The sooner the objects are treated after excavation (with water storage), the better the removal of chloride ions, in both chemical immersion and electrolysis treatments. But if the object is stored in air, material losses occur, and only electrolysis results in complete extraction of the chlorides. These differences are due to modifications in the corrosion products during storage. Drying after treatment also has a significant impact on the composition of the corrosion layers. If the objects are dried too quickly, Fe(OH)₂ oxidizes into FeOOH, which thus forms a layer with low cohesion.     

New insights on the corrosion of ancient bronzes using X-ray powder diffraction: The importance of paratacamite,sampleite, and connellite

Research employing X-ray powder diffraction shows that clinoatacamite as the phase which should be predominant in the chloride-induced corrosion of ancient bronzes is not necessarily the dominant copper trihydroxychloride species at all, since mixtures are common, and other phases such as paratacamite or the dubious mineral phase anarakite have relevance to the corrosion products or patina of bronze antiquities. The potential reasons for this are discussed and related to the compositional parameters of ancient bronzes as well as the burial environment. Paratacamite is still identified, even in the absence of zinc, which is supposed to be the major stabilizing influence on the paratacamite lattice. X-ray power diffraction has been employed in the examination of a range of ancient bronzes from Chinese, Egyptian, Ecuadorian, Lydian, Albanian, Palestinian, and Greek contexts. This study has revealed that, far from being exotic novelties, the occurrence of both sampleite and connellite as important corrosion products of ancient bronzes has been underestimated in the published literature. Many occurrences of sampleite are related to the decomposition of contiguous human remains rather than to arid environmental factors which is the explanation for the occurrence in a geological environment, but in a burial environment other factors come into consideration.     

The impact of Korean television drama viewership on the social perceptions of single life and having fewer children in married life

The purpose of this study was twofold. On the ground of Gerbner's cultivation theory, it examined the effect of South Korean drama consumption on the perceived prevalence of single life and having fewer children in married life. It also tested the causality of cultivation effects through a priming methodology. Results indicated that the perceived prevalence of having fewer children in married life was significantly affected by exposure to dramas which positively feature single life and having fewer children in married life on television. The findings provide public health policy-makers and communication campaigners with valuable theoretical relationships, as well as their practical implications.