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1.
《文物保护研究》2013,58(4):326-337
AbstractAlthough 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. 相似文献
2.
ABSTRACTThis 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. 相似文献
3.
《文物保护研究》2013,58(4):227-236
AbstractThis 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. 相似文献
4.
AbstractThe long-term stabilization of marine archaeological iron, whether cast or wrought, continues to challenge conservators responsible for treatment of this material. Results and observations obtained from past treatments highlight the daunting, prolonged, and laborious efforts required to desalinate large and complex ferrous artifacts recovered from the ocean. In general, the higher an artifact's chloride level, the less stable it is. Consequently, any stabilization treatment must involve the removal of as much Cl?1 as possible without affecting the integrity of the corroded artifact. This problem is particularly acute with corroding cast iron objects that have formed thick, fragile, and highly unstable corrosion layers. Over the course of the twentieth century, conservators have used a variety of techniques in an attempt to mitigate the negative effects of chloride ions on iron artifacts and prevent disintegration. In spite of early promise, each of these stabilization techniques has significant disadvantages, particularly with regard to treatment efficiency, duration of treatment, and/or unacceptable risks to the artifact during treatment. For these reasons, conservators and conservation scientists at the Warren Lasch Conservation Center in Charleston, South Carolina, decided to look at the possibility of using subcritical fluids to stabilize archaeological iron. This paper compares the efficiency and effectiveness of traditional stabilization techniques (i.e. alkaline soaking and cathodic polarization) to subcritical fluids on wrought iron rivets and metal shavings from the H.L. Hunley submarine as well as Civil War era cast iron artillery shells recovered from a marine environment. 相似文献
5.
《文物保护研究》2013,58(2):125-134
AbstractA small but significant proportion of the archaeological iron objects in the British Museum collection have been problematic in that some of them have required repeated treatment. The deterioration of iron objects during storage was studied using microscopy, Raman spectroscopy, X-ray diffraction, scanning electron microscopy/energy dispersive X-ray analysis, X-ray fluorescence spectroscopy and ion chromatography. A total of 125 iron objects, including 56 from two British Roman sites and 69 from three Anglo-Saxon sites, were studied. Both surface corrosion and corrosion layers on polished cross-sections were investigated. The study revealed that the present condition of the iron objects varies; some are in a stable condition and others have been deteriorating, with pitting and weeping present on the surface. No treatment method had stopped corrosion for every object, although the alkaline sulphite treatment seemed to be more effective than the other methods. The results also showed that chloride ions can be present at the interface of the metal and inner corrosion layers. It is recommended that iron objects which have been mechanically cleaned without desalination treatments are kept in a dry environment to prevent further deterioration. 相似文献
6.
《文物保护研究》2013,58(1):29-41
AbstractChloride-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. 相似文献
7.
《文物保护研究》2013,58(3):274-282
AbstractA study of the composition and phase distribution of the corrosion layers on three ferrous objects, excavated at K2 (Bambandyanalo), an archaeological site in South Africa, was conducted. The objective of the study was to obtain information that can contribute to conservation procedures to be performed on the iron artefacts from this site. Examination of cross sections by means of energy-dispersive X-ray spectroscopy coupled to a scanning electron microscope (SEM–EDX), X-ray powder diffraction (XRD), and micro-Raman spectroscopy revealed the same corrosion composition and structure for all the objects under study, namely an internal layer adjacent to the metal surface with ghost inclusions and an external layer containing quartz grains. The study also revealed that the presence of magnetite (Fe3O4), maghemite (γFe2O3), and lepidocrocite (γ-FeOOH) within the internal layer is the only difference between the chemical compositions of iron corrosion products within the two layers. The results also made it possible to retrace the corrosion history during burial and long-term storage. 相似文献
8.
《文物保护研究》2013,58(4):232-240
AbstractThe method of removing chlorides from archaeological iron objects using hydrogen plasma at low pressure has been studied and improved. To carry out the initial experiments and to limit the use of ancient material, synthetic samples were made from iron powder and corrosion products consisting mainly of akaganeite. The time and the temperature required for the complete removal of the chlorides were determined. It was also possible to demonstrate that magnetite, and iron above 400°C, are the final reaction products of the reduction of akaganeite. 相似文献
9.
《文物保护研究》2013,58(2):50-58
AbstractThe interrelationship between the various chloride ion containing compounds associated with the corrosion of iron in a marine environment is reviewed, and their role in corrosion promotion is evaluated as a basis for the selection of conservation techniques with a high probability of success. 相似文献
10.
《文物保护研究》2013,58(4):205-206
AbstractThe deterioration of Bronze Age objects from the archaeological site at Fort-Harrouard (France) has been studied, firstly, in relation to their external appearance and the elemental composition of the sound metal. A relationship between the composition of the corroded surface and the underlying sound metal was deduced. In addition, examination of metallographic sections of one of the bronzes allowed the differentiation of corrosion processes which are related to the shape of the object: the stratification of the corrosion products and the intergranular and transgranular corrosion processes. The existence of a pseudomorphic microstructure suggests that the mechanism of deterioration may be stratigraphic, which may be explained by the growth of the corrosion products in fissures which do not involve periodic precipitation. 相似文献
11.
《文物保护研究》2013,58(4):297-307
AbstractWet organic archaeological materials extracted from seawater may suffer damage as a result of degradation influenced by micro-organisms. One of the most common phenomena is indirectly induced by sulphate-reducing bacteria (SRB). Due to their metabolic activity in anoxic conditions, SRB generate hydrogen sulphide from sulphate ions present in seawater. When steel items are in contact with organic matter in presence of sulphides, corrosion of the metal leads to the precipitation of Fe(II) sulphides. These phases are responsible for dramatic post-excavation damage: their oxidation during storage or exhibition in museums leads to the formation of voluminous crystals, which may cause cracking and crumbling, and lead to the production of sulphuric acid. In order to characterize Fe(II) sulphides and their by-products, 13 waterlogged samples were analysed by environmental scanning electron microscopy, micro-Raman spectroscopy, and X-ray diffraction. Experiments were performed on untreated wood fragments, on a fragment of rope, and on mineral concretions scratched from the surface of wood remains, all extracted from different shipwrecks. Mackinawite was detected inside the fragments and between the fibres of the rope. Greigite was detected in scattered locations. Pyrite and sulphated phases, like gypsum and iron sulphates, were identified at the surface of the wood fragments and in the mineral concretions. 相似文献
12.
《文物保护研究》2013,58(3):136-142
AbstractVarious desalination methods had been used in the past to treat a large collection of archaeological iron objects. In order to establish whether desalination treatments had been effective, the condition of the objects was assessed and the data analyzed using statistical methods. It was found that objects which had been treated using desalination methods were less likely to re-corrode, and the conclusion was that the development of more effective techniques of chloride removal would be useful. 相似文献
13.
CORROSION AND CONSERVATION OF A SILVER VISCERAL VESSEL FROM THE BEGINNING OF THE SEVENTEENTH CENTURY
《文物保护研究》2013,58(3):114-117
AbstractTwo different cleaning methods were found necessary to remove silver chloride corrosion products from different areas of a silver canopic vessel containing about 6% of copper. Two possible mechanisms of silver corrosion which could have led to the differing silver chloride corrosion products are put forward. 相似文献
14.
《文物保护研究》2013,58(4):147-152
AbstractIn order to test some of the methods of archaeological bronze conservation, a procedure was perfected that reproduces the structure and composition of original patinas. Then the most common methods of treatment were applied on test samples thus prepared and on archaeological items. This experiment has allowed us to choose the best treatment in accordance with the following requirements: restraint of corrosion, speed of operation, lack of colour alteration and avoidance of break-up or solution of patina. 相似文献
15.
《文物保护研究》2013,58(4):197-204
AbstractThis work combines our observation that the details of marble statues that have already been lost from the calcite surface are preserved in the gypsum layer, with our research on the mechanism of marble sulfation, to lead to a consolidation of the gypsum, transforming it back to calcium carbonate (calcite) using carbonate ions in solution. Our research shows the mechanism of the conversion of gypsum to calcite, the rate determining steps being the desorption and diffusion of CO2?3 We found that the reproduction of the surface detail and the improvement of the mechanical properties was very satisfactory. 相似文献
16.
《文物保护研究》2013,58(1):49-58
AbstractBlack weathering layers on stone often contain iron. This is particularly true for the Turonian sandstones which were used extensively in architecture and sculpture in Saxony. In order to obtain more knowledge about the oxidic iron phases, samples were collected in the city of Dresden. Mineralogical and analytical characterization was provided for the black layers and the supporting stone. Material originating from Cotta and Posta stone was submitted to Mössbauer spectroscopy. After ample comparisons of Mössbauer parameters and evaluation of infrared spectra it was concluded that the predominant neogenic iron phase is not iron(III) oxide hydrite (ferrihydrite) Fe2O3·1·8H2O or jarosite KFe3(SO4)2(OH)6 or goethite α-FeO(OH) but a defectively ordered precursor of this last compound, characterized by different environments of the iron(III) ions. By the reducing action of organic matter, magnetite Fe4O4 is formed and this contains up to 45% of the iron present in a black layer. 相似文献
17.
《文物保护研究》2013,58(2):147-153
AbstractThe compound 5-amino-2-mercapto-1,3,4-thiadiazole (AMT) is utilized in the conservation of archaeological and artistic bronze artifacts, for their protection and for the removal of corrosion products. Many authors have discussed the utility and efficacy of this, but few have studied the products resulting from the reaction of AMT with bronze or with the corrosion products of bronze; this leaves the restorer with many doubts concerning the acceptability of this method. This paper discusses the study of products obtained from the reaction of AMT with synthesized corrosion products of bronze (malachite, paratacamite and brochantite) and with the commercial bronze alloy TM 23 (Cu 72%, Pb 15%, Zn 8% and Sn 5%). It was found that the film obtained from the direct reaction of AMT with the bronze alloy can be AMT itself, or the metallic complex Cu(C2H2N3S2)2·H2O if AMT is applied in a solution of an oxidizing acid. These results are expected to be of value to conservation scientists and restorers/ conservators concerned with the use of AMT for the conservation of bronze artifacts. 相似文献
18.
《文物保护研究》2013,58(1):38-41
AbstractA white deposit was observed on the glass lids of boxes used to store archaeological textile fragments for some 40 years. It was identified as sodium formate formed from formaldehyde given off by cardboard in the boxes. Heavy metal ions in some samples of the deposit originated, via the textile fragments, from corroded bronze ornaments in the graves. 相似文献
19.
《文物保护研究》2013,58(3):148-152
AbstractMineralogical changes which occur during the reaction of copper(II) chloride with carbonate in aqueous solution have been investigated, and compared with those involving copper(I) chloride, nantokite, CuCI, and copper artifacts coated with malachite, CU2CO3(OH)2 The reactions observed and the products obtained are seen to have implications with respect to the use of aqueous sodium carbonate solutions to stabilize archaeological copper objects. The frequent observation of the mineralogically rare species chalconatronite, Na2Cu(CO3)2·3H2O, on the surface of treated objects is readily explained by known reaction chemistry. Its formation can be minimized by washing the object after treatment. 相似文献
20.
《文物保护研究》2013,58(4):245-252
AbstractCross sections are frequently used in the stratigraphic study of pictorial structures. Thanks to cross sections, it is possible to study and record original and non-original strata that may provide important information regarding the artist's technique and later restoration processes. This information helps conservators design different strategies in processes such as cleaning. However, it is often in cleaning where the advantages and limitations of cross sections become obvious. When dealing with a complex structure, cross sections may not be enough to record in a comprehensive and accurate manner all the strata removed during cleaning. In some cases, the conservator may obtain during cleaning a great amount of stratigraphic information that is not visible in the cross sections. Therefore, it may be necessary to resort to other recording systems, such as the stratigraphic unit recording sheet and the stratigraphic diagram, which are frequently used in archaeological stratigraphy. This article demonstrates how cross-section analysis was combined with stratigraphic study during the cleaning of two panel paintings to gain an improved understanding of their complicated layer structure. 相似文献