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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.
《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
3.
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
4.
《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
5.
《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
6.
《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
7.
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
8.
AbstractThe use of sodium nitrite (NaNO2) as a corrosion inhibitor for wet archeological metal objects presents potential advantages of near neutral pH, low concentration, effectiveness on several metals, and compatibility with organic materials. The effectiveness of NaNO2 as a corrosion inhibitor for storage of chloride-containing marine archeological metal objects from the wreck of the USS Monitor was evaluated using marine-corroded carbon steel analogs. The samples were tested in varying concentrations of NaNO2 and evaluated visually and by monitoring solution chemistry using ion chromatography (IC). It was found that a concentration of 1000 ppm NaNO2, replaced four times, was effective at protecting corroded carbon steel in the presence of chlorides. Nitrite solutions were no more rapid than sodium hydroxide (NaOH) at extracting chlorides from marine steel at equal concentrations and were considerably slower than 2% NaOH. IC analyses indicated that NO2 does not easily oxidize to NO3 under normal conditions, but does so readily when a polarizing current is applied, making nitrites unsuitable for electrolytic reduction treatments. Sodium nitrite does show promise as a storage solution prior to desalination of marine metals or after desalination to prevent flash corrosion during rinsing baths. 相似文献
9.
《文物保护研究》2013,58(3):161-171
AbstractFour iron meteorite fragments and 13 archaeological iron objects were exposed to a lowpressure hydrogen plasma for up to two weeks in a pilot apparatus. In the experiment the objects acted as cathodes in a 600–1600V d.c. electrical field. While the chlorine-containing β-FeOOH, akaganeite, was present in all objects before the test, no akaganeite and no chlorides were present afterwards. The objects, including one meteorite which had been exposed for more than 5000 years to seawater, were found to be stable after the glow discharge treatment. The major mineral after treatment was identified as magnetite, and the objects generally assumed an iron-grey surface colour. No sputtering and no reduction to free iron took place under the test conditions, operating at or below 120°C and at pressures of O·4–1mb hydrogen. 相似文献
10.
SummaryThe rate at which chloride ions diffuse from archaeological iron into a treatment solution depends on how the chloride ions are initially distributed in the corrosion layer. This paper compares solutions of the diffusion equation for two limiting cases: (1) where the chloride ions are initially spread uniformly through the corrosion layer; and (2) where the chloride ions are initially concentrated at the interface between the iron and the corrosion layer. Although the first model has been used in the past to describe chloride ions diffusing from marine iron, the second is more appropriate in cases where corrosion has drawn chloride ions toward the iron surface. Because diffusion processes in archaeological iron are complicated, the limitations of both these models are discussed. 相似文献
11.
《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
12.
《文物保护研究》2013,58(3):179-190
AbstractTesting of chemical stabilization treatments and desiccated and anoxic storage microclimates for the protection of archaeological iron stored in unsuitable climatic conditions was carried out by the conservation department of the Japanese Institute of Anatolian Archaeology at the Kaman-Kalehöyük excavation in Turkey. The chemical stabilization treatments involved alkaline sulfite, barium hydroxide and sodium hydroxide. Environmental stabilization was explored using RP-A oxygen scavengers in Escal® bags as part of the Revolutionary Preservation System (RP System®) manufactured by Mitsubishi Gas Chemical Company, Inc. The efficiency of the chemical treatments was examined by comparison with mechanically cleaned iron objects. The efficiency of the storage systems was determined by comparing the chemically and non-chemically treated objects in the RP System® using RP-A scavengers and in polyethylene ziplock bags containing silica gel. The efficiency of these treatments and storage systems was examined and assessed at Kaman after a period ranging from 7 to 9 years. The anoxic and desiccating properties of the RP System® resulted in superior protective qualities over polyethylene bags with silica gel. The RP System® compensated for inadequate chemical stabilization and protected iron that had not been chemically stabilized. 相似文献
13.
《文物保护研究》2012,57(1):28-36
ABSTRACTA pre-restoration diagnosis revealed a high amount of pyrite in the wood of the Lyon Saint-Georges 4 shipwreck (end of the second century). The occurrence of this phase is supposed to result from the microbiologically influenced corrosion of the iron fasteners. So, all the nails and metallic elements were removed from the remains before treatment and the wreck was consolidated by polyethylene glycol impregnation coupled to a specific desalination process. Treated and non-treated samples extracted from the wreck were studied in order to identify the iron/sulfur-containing compounds present in the wood before and after treatment and figure out its effect. Sample analyses relied on an original approach combining magnetic characterization methods and more common elemental and structural analysis methods. The results showed that the treatment was effective in removing soluble salts. However, a large amount of unstable iron sulfides remained inside the wood. 相似文献
14.
《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
15.
Julie Unruh 《文物保护研究》2013,58(2):81-92
SummaryAt the archaeological site of Gordion, Turkey, all registered ceramics are routinely desalinated. The standard desalination treatment was investigated by the author with a view to minimizing damage to the ceramics, as well as the amount of water used and the time taken for desalination. An equation that standardizes conductivity measurements in disparate desalination situations is presented. A series of experiments was performed to clarify the behavior of salts at Gordion. Two variables which directly affect the amount of water needed for desalination were considered: the frequency of water changes and the weight-to-volume ratio. The experimental results were compared to on-site experience, and a revised endpoint for desalination is proposed. 相似文献
16.
《文物保护研究》2013,58(3):155-171
AbstractThe presence of iron oxides (lepidocrocite, goethite) in archeological wood may result in a degradation of the wood matrix. Extraction of these iron oxides is largely dependent on their solubility. In this study, balsa wood samples were impregnated with iron oxides to test extraction treatments. Additionally, archeological wood samples were also examined to determine treatment efficiency. Electrophoresis and simple immersion treatments were performed using various chemical solutions: a neutral and a conductive substance (potassium nitrate), an acid (acetic acid), three alkaline chelating agents (tri-ammonium and tri-sodium citrate and sodium oxalate), three acidic and slightly acidic chelating agents (ethylenediaminetetraacetic acid (EDTA), citric acid, and oxalic acid), and a reductant (sodium dithionite). Potassium nitrate did not extract sufficient amounts of iron, irrespective of whether the treatment was conducted by electrophoresis or simple immersion; any observable dissolution was attributed to protonation because of the acidic pH around the anode (as low as 3). Dissolution in acetic acid did not extract iron with either treatment. Strong chelating agents improved extraction, and these compounds gave the best results for simple immersion, particularly EDTA. This chemical is well adapted for use on archeological objects because of its chemical properties (stability constant, speciation based on pH). The addition of sodium dithionite to the solution improved dissolution. Even though electrophoresis improved extraction (in particular for tri-ammonium citrate), none of the tested chelating chemicals were suitable for electrophoresis because of a significant increase in temperature as well as high anode corrosion. The presence of iron sulfide in the archeological wood limited the effectiveness of the tested chemicals. A pre-treatment in sodium persulfate was expanded to include oxidized iron sulfide in oxy/hydroxide iron, which improved the extraction rate. 相似文献
17.
Historic parchment is a complex biological material, and due to various methods of production or inks used, unknown environmental histories of objects and heterogeneous nature of animal skin, it represents a particular analytical challenge. Due to the number of variables it is likely that patterns in degradation of these historic objects can only be revealed by surveying the material properties of a significant number of real objects. In this work, a sacrificial collection of ca. 100 historic parchments (fifteenth to twentieth century) was characterized using a range of techniques available to conservation practitioners that can usefully be used to reliably and rapidly characterize parchment. We focused on micro-destructive methods, such as shrinkage temperature (Ts), as the most widely used indicator of parchment degradation. Lipid content, roughness, and ink pH were additionally measured, while a limited number of samples containing iron gall ink were also examined using scanning electron microscopy (SEM) and SEM-EDX, to explore the distribution of ink components. Even in the absence of detailed environmental histories, it is possible to acknowledge the significance of the effect of iron gall ink and its acidity, and of lipids on parchment degradation, as measured using Ts. This research reports valuable reference data, while the collection remains accessible for further research. 相似文献
18.
《文物保护研究》2013,58(3):180-197
AbstractCorrosion rates are presented for metals in the aqueous solutions intended for treating both the wood and the metal components of a waterlogged wood-metal composite object. The metals include lead, mild steel, cast iron and the copper alloys of bronze, cast brass and wrought brass. The corrosion rates were determined using a standard weight-loss method in which clean metal surfaces were immersed in the solutions for two months at room temperature. The treatment solutions included Acrysol® G-11O for lead, Witcamine® RAD 1100 for copper alloys and Pluracol® 824 or the corrosion inhibitor Hostacor® KS 1 in PEG 400 for iron. These treatment solutions were prepared in distilled water as well as in a synthetic seawater. For reference, metal corrosion rates were also determined in distilled water, synthetic seawater and PEG 400. The results demonstrate that, in general, clean metal surfaces corrode more slowly in the treatment solutions than in PEG 400 solutions. However, before recommending these solutions for the treatment of composite objects, further testing is needed to determine how effective they are in reducing the corrosion rates of metals covered with a thick corrosion crust, and to see if Acrysol G-110 is capable of bulking and consolidating waterlogged wood. 相似文献
19.
A technical study was conducted on a group of copper alloy artifacts excavated from the burial tumulus of Lofkënd (fourteenth–ninth century BCE) to identify the alloy compositions and methods of manufacture. The surface corrosion was also examined in order to understand the diagenetic processes affecting the preservation of the finds and their condition. Portable X-ray fluorescence spectroscopy, metallographic examination, and X-ray powder diffraction (XRD) analysis were used to characterize the alloy composition and identify the corrosion products present. XRD analysis showed the presence of brochantite (Cu4SO4(OH)6) on five of the metallic artifacts. Brochantite is not commonly reported on archaeological bronzes from terrestrial sites, but is more readily found on copper alloy objects exposed to sulfur pollutants in the air or soil. The possible conditions that could have led to the formation of this corrosion on the bronzes from Lofkënd are discussed in the context of the particular burial environment found at the tumulus. 相似文献
20.