Production of reference “ancient” Cu-based alloys and their accelerated degradation methods

A large number of bronze artefacts found during archaeological excavations carried out in Italy in different contexts have been studied. Their chemical composition and metallurgical features have been determined by the combined use of different analytical surface and bulk techniques, such as optical microscopy (OM), scanning electron microscopy with energy dispersive X-ray micro-analysis (SEM-EDS), X-raydiffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The study of the corrosion products grown on the archaeological Cu-based artefacts and of their metallurgical features has revealed the quite ubiquitous and nearly constant presence of chlorine as the main corroding agent, and the different structures of the alloys. This information has been used to produce reference Cu-based alloys, whose chemical composition and micro-chemical structure is similar to that of the ancient alloys, and to propose the guidelines for carrying out the accelerated degradation tests to produce corroded samples for testing corrosion inhibiting products. The proposed tests were based on soil, chemical and (chemical+soil)-induced degradation, and the micro-chemical structure of the artificially produced corrosion layers has been compared to those grown on archaeological artefacts during burial. The comparison shows that the (chemical+soil)-induced degradation produces “patinas” that are similar to those grown on archaeological artefacts from a chemical, structural and micro-morphological point of view. PACS 68.55.Jk; 68.35.Dv; 68.37.Hk; 68.55.Nq; 81.05.Ba     

Large scale investigation of chemical composition, structure and corrosion mechanism of bronze archeological artefacts from Mediterranean basin

A large number of Cu-based archaeological artefacts from the Mediterranean basin have been selected for investigation of their chemical composition, metallurgical features and corrosion products (i.e. the patina).The guidelines for the selection of the Cu-based artefacts have taken into account the representativeness of the Mediterranean archaeological context, the manufacturing technique, the degradation state and the expected chemical composition and structure of the objects.The results show wide variation of the chemical composition of the alloys that include all kinds of ancient Cu-based alloys such as low and high tin, and also leaded bronzes, copper and copper-iron alloys.The examination of the alloy matrix shows largely different metallurgical features thus indicating the use of different manufacturing techniques for producing the artefacts. The results of the micro-chemical investigation of the patina show the structures and the chemical composition of the stratified corrosion layers where copper or tin depletion phenomenon are commonly observed with a remarkably surface enrichment of some soil elements such as P, S, Ca, Si, Fe, Al and Cl. This information indicates the strict interaction between soil components and corrosion reactions and products. In particular, the ubiquitous and near constant presence of chlorine in the corrosion layers is observed in the patina of the archaeological Cu-based artefacts found in different contexts in Italy, Turkey, Jordan, Egypt, Spain and Tunisia. This latter occurrence is considered dangerous because it could induce a cyclic corrosion reaction of copper that could disfigure the artefact.The micro-chemical and micro-structural results also show that another source of degradation of the bronze archaeological artefacts, are their intrinsic metallurgical features whose formation is induced during the manufacturing of the objects, carried out in ancient times by repeated cycles of cold or hot mechanical work and thermal treatments. These combined treatments induce crystallisation and segregation phenomena of the impurities along the grain boundaries and could cause mechanical weakness and increase the extent of the inter-granular corrosion phenomena. PACS 68.55.Jk; 68.35.Dv; 68.37.Hk; 68.55.Nq; 81.05.Bx     

Unusual surface degradation products grown on archaeological bronze artefacts

Within the framework of the EFESTUS project funded by the European Commission a large number of Cu-based archaeological artefacts from the Mediterranean basin have been studied to investigate their chemical composition, metallurgical features and corrosion products nature (i.e. the patina). By means of the combined use of X-ray photoelectron spectroscopy (XPS), optical microscopy (OM), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS) and X-ray diffraction (XRD) the bronze artefacts have been studied for the detailed identification of the corrosion products and their micro-chemical structure in order to achieve information about degradation agents and mechanisms. In the present work, some examples of unusual corrosion products formed on the objects during the long-term burial are presented and related to the peculiar local context revealing the strong interaction between the bronze artefact and the chemical components found in the archaeological site.     

An integrated analytical characterization of corrosion products on ornamental objects from the necropolis of Colle Badetta-Tortoreto (Teramo, Italy)

Selected groups of copper-based artifacts found during archaeological excavations of the necropolis of Colle Badetta-Tortoreto (Teramo, Italy) were investigated in order to determine the chemical composition and metallurgical features of the alloys and the micro-chemical and micro-structural nature of the corrosion products grown during the long-term burial. The investigated Cu-based artifacts were ornamental objects, such as rivets, buckles and small rings that were applied to large belts to form complex patterns with the addition of small and large shaped pieces of amber. The analytical characterization was performed by using different surface and bulk techniques, such as Optical Microscopy (OM), Scanning Electron Microscopy coupled with energy dispersive X-ray micro-analysis (SEM-EDS), X-ray Diffraction (XRD).     

Uncommon corrosion phenomena of archaeological bronze alloys

In the framework of the EFESTUS project (funded by the European Commission, contract No. ICA3-CT-2002-10030) the corrosion products of a large number of archaeological bronze artefacts are investigated by means of the combined use of scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and optical microscopy (OM) and tentative correlation of their nature with the chemical composition of the artefacts and the burial context is proposed.The results provide good insight into the corrosion layers and evidence in some bronze Roman coins and artefacts; the occurrence of uncommon corrosion phenomena that give rise to the formation of a yellowish-green complex chlorine-phosphate of lead (pyromorphite, (PbCl)Pb₄(PO₄)₃) and of a gold-like thick layer of an iron and copper sulphide (chalcopyrite, CuFeS₂). The micro-chemical and micro-structural results show that the coins were buried in a soil enriched in phosphorus for the accidental presence of a large amount of decomposing fragments of bones or in an anaerobic and humus rich soil where the chalcopyrite layer has been produced via the interaction between the iron of the soil, the copper of the coin and the sulphur produced by the decomposition of organic matter in an almost oxygen free environment. Finally, some unusual periodic corrosion phenomena occurring in high tin bronze mirrors found at Zama (Tunisia) are described. PACS 68.55Jk; 68.35 Dv; 68.37Hk; 68.55 Nq; 81.05 Bx     

Production of reference alloys for the conservation of archaeological silver-based artifacts

In the framework of the EC PROMET project, the chemical composition and metallurgical features of a large number of archaeological artifacts were investigated by different analytical surface and bulk techniques, such as Optical Microscopy (OM), Scanning Electron Microscopy coupled with energy dispersive X-ray micro-analysis (SEM-EDS), X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). The study of the corrosion products grown on the archaeological Ag-based artifacts revealed a quite ubiquitous and nearly constant presence of chlorine from the soil as the main corroding agent, mainly producing chlorargyrite (AgCl). Results of this extensive chemical, physical and metallurgical characterization were used to produce modern reference Ag-based alloys with a chemical composition and micro-chemical structure similar to that of ancient alloys. Furthermore, these reference Ag-based alloys were submitted to an accelerated degradation method in order to produce corroded samples to be used as sacrificial materials for testing corrosion inhibiting products. The production of artificial “patinas” and corrosion layers was made by a chemical and soil-induced degradation procedure. The comparison of the micro-chemical structures of natural and artificial corrosion layers shows that the selected degradation method produces “patinas” resembling those grown on archaeological artifacts from a chemical, structural and micro-morphological point of view.     

Glass–metal objects from archaeological excavation: corrosion study

This paper contributes to the investigations on history, technology, and degradation of middle age objects (metallic rings with mounted glass beads) recently excavated under the Main Square in Krakow (Poland). Moreover, they were discovered in soil layers differing by chemical composition and microclimate parameters. Historical material is indeed very limited in terms of quantity and sample size, and the following nondestructive analyses were applied: scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDXS), X-ray diffraction (XRD), and X-ray fluorescence spectroscopy (XRF). The glass and the metal were separately tested. Metallography on cross-sections (by both optical and scanning electron microscopy) was applied only on microfragments sampled from metallic rings. The achieved results pointed out how the local microclimate affected the degradation of the analyzed rings developing locally different corrosion processes. Each tested glass of “ring eye” shows a specific chemical composition. All glass pieces were covered by silica gel, and locally more advanced corrosion has been found.     

Combined use of SEM-EDS, OM and XRD for the characterization of corrosion products grown on silver roman coins

In the framework of the PROMET project (European Commission contract No. 509126) aimed to develop new analytical techniques and materials for monitoring and protecting metal artefacts and monuments from the Mediterranean region, the corrosion products grown on silver Roman coins during archaeological burial is studied by means of scanning electron microscopy combined with energy dispersive spectrometry (SEM-EDS), X-ray diffraction (XRD) and optical microscopy (OM) techniques. PACS 68.55.Jk; 68.35.Dv; 68.37.Hk; 68.55.Nq; 81.05.Bx     

Corrosion behaviors in physiological solution of cerium conversion coatings on AZ31 magnesium alloy

In this paper, a non-toxic Ce-based conversion coating was obtained on the surface of bio-medical AZ31 magnesium alloys. The micro-morphology of the coating prepared with optimal technical parameters and immersed in physiological solution (Hank's solution) in different time was observed by scanning electron microscopy (SEM), composition of the cerium conversion coating and corrosion products in Hank's solution were characterized by X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS), respectively. In addition, the corrosion property in Hank's solution was studied by electrochemical experiment and immersion test. The results show that the dense Ce-based conversion coating is obtained on the surface of AZ31 magnesium alloys in optimal technical parameters and the conversion coating consists of a mass of trivalent and tetravalent cerium oxides. The cerium conversion coating can provide obvious protection of magnesium alloys and can effectively reduce the degradation speed in Hank's solution. Also the degradation products have little influence on human body.     

Microchemical investigation of Greek and Roman silver and gold plated coins: coating techniques and corrosion mechanisms

Within the framework of a project financially supported by the European Commission (contract Nr. 509126, acronym PROMET) the metallurgical techniques used by Romans and Greeks for coating the copper core of coins with a thin or thick layer of gold or silver are studied by means of the combined use of scanning electron microscopy combined with energy dispersive spectrometry (SEM-EDS) and optical microscopy (OM) techniques.This approach is utilised to gain further insight into the micro-chemical structure of the external regions of the coins as well as into the bulk metallurgical features. The results indicate that several methods were used by the Greek and Roman craftsmen including the mechanical application of a thin malleable gold or silver foils to be welded via thermal treatment. The analytical approach is also used for investigating the corrosion products grown on the coins during the long-term burial and for identifying degradation mechanisms.PACS 68.55Jk; 68.35 Dv; 68.37Hk; 68.55 Nq; 81.05 Bx     

Effect of laser treatment on the surface of copper alloys

The paper presents the results of laser cleaning of the archaeological metal objects using two time widths of pulsed laser radiation, which are around 150 μs and around 120 ns. Two archaeological objects made of copper alloys were studied: a bow and a ring. Both objects came from a cemetery which is located in the garden complex of Wilanow Palace in Warsaw and are dated from XII to XIII century. The bow and bronze ring had ornamental longitudinal grooving and were part of burial jewellery. The materials of which these artefacts were made of, as well as corrosion products on these objects, were studied by using a variety of analytical techniques. The phase composition of the corrosion layers was determined by using Raman spectroscopy. The surface topography as well as the chemical composition of the deposits and cleaned surfaces were investigated. The samples were examined using scanning electron microscopes equipped with EDS. The investigations included observations in SE and BSE modes and point analyses of the chemical composition by EDS.     

Complementary use of X‐ray methods to study ancient production remains and metals from Northern Portugal

Archaeological artefacts recovered at Castanheiro do Vento (Northern Portugal) were characterised by integrating macro and micro‐energy dispersive X‐ray fluorescence spectrometry (EDXRF) and scanning electron microscopy with X‐ray microanalysis. The collection includes metallurgical remains (ceramic crucibles, a metallic nodule and a vitrified fragment) and metals (tools and ornaments) whose chronology spans from the Chalcolithic to the Roman Age. The study of production remains was able to identify distinct copper‐based metallurgical operations including the smelting of copper ores, the melting of copper and tin and/or the melting of bronze scrap. Micro‐EDXRF identified copper and arsenical copper tools as well as bronze and leaded bronze ornaments. The composition of tools (Cu with varying As contents: 0.46–3.6%) reveals an incipient technology, typical of the Chalcolithic till the Middle Bronze Age. On the contrary, ornaments are composed by different alloys – low tin bronze (4.8% Sn), high tin bronze (14.9% Sn) and high tin‐leaded bronze (16.5% Sn and 2.4% Pb) ? evidencing technological and economic choices that clearly indicate a late period such as the Roman Age. In conclusion, this multiproxy approach was able to study those ancient artefacts with a minimum impact on their archaeological and museological significance while providing important answers to the interpretation of the archaeological settlement and to better understand the metallurgical evolution in the Portuguese territory. Copyright © 2014 John Wiley & Sons, Ltd.     

Bronze roman mirrors: the secret of brightness

The surface microchemical structure of high tin leaded bronze Roman mirrors has been studied by means of scanning electron microscopy combined with energy dispersive spectrometry (SEM-EDS), X-ray diffraction (XRD) and optical microscopy (OM) techniques. The results allowed understanding of the origin of their high chemical stability and silvery-lustrous appearance. Indeed, some areas of the selected Roman mirrors are still characterised by a highly reflective and silver coloured surface even though they have been buried in the soil for about 2000 years. The micro-chemical results obtained from these areas have revealed that the mirror surface was tin enriched via inverse-segregation phenomenon by tailoring the cooling parameters. Furthermore, the presence of tin could be likely enhanced via cycles of oxidation and selective copper corrosion processes, thus resulting in a tin surface enrichment as a semi-transparent amorphous-like tin oxide (SnO₂) film, as well as a copper depletion at the outer surfaces.     

Microstructure and corrosion properties of thick WC composite coating formed by plasma cladding

The thick Ni-coated WC coatings, in a matrix of Nickel-based alloys, were prepared on AISI 1045 steel using plasma cladding equipment. A pre-placed layer of uniform mixture, with different weight fractions of Ni-coated WC powder and Nickel-based alloy powder, on the steel substrate was melted at the high temperature of the plasma jet. The coating composition, microstructure and microhardness were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS) and microhardness testing. The experimental results show that the metallurgical bond was formed between the coating and substrate. The XRD results show that the coatings contain γ-Ni, carbides (such as M₂₃C₆ and M₇C₃) and boride (such as Fe₂B, Fe₃B phases). SEM shows that all the coatings are crack-free with lower porosity (<1%). It is found that the microhardness and the electrochemical behavior of the coatings are depended on the content of Ni-coated WC powder. The corrosion mechanism for the coatings may be due to the microgalvance corrosion between the phases in the cladding coatings.     

In vitro degradation of AZ31 magnesium alloy coated with nano TiO2 film by sol-gel method

A nano TiO₂ film was coated on AZ31 alloy substrate by sol-gel method. The TiO₂ film was characterized by X-ray diffractometry (XRD), differential scanning calorimetry-thermogravimetric analysis (DSC-TG), field emission scanning electron microscopy (FE-SEM) and energy dispersion spectroscopy (EDS). The degradation of the nano-TiO₂ coated alloy was evaluated by immersion test and electrochemical measurement. An attempt was made to relate corrosion of coated alloys with the annealing treatment and resultant structural evolution.     

Superconductivity and low-temperature specific heat in IrY eutectics

Low-temperature specific heat data on Ir-20 at% Y eutectic composition alloys characterised by scanning electron microscopy for micro-structural analysis are presented. The data agree with the results of Fradin et al.: the superconductivity in Ir-20 at% Y composition alloys stems due to the presence of YIr₃ compound with PuNi₃ structure.     

电炉渣超微粉改性生物质废弃物制备生态活性炭的光谱学分析

利用木材、竹子、等其他生物资源制备具有发达多孔结构与丰富比表面积的活性炭,存在生产成本较高、不利于生态环境的可持续发展、使用寿命短和失效后容易造成室内环境二次污染的问题。冶金固体废弃物与生物质废弃物是工业生产与农业生产主要的副产品,因利用难度大、附加值低且成本高,导致大量堆放和填埋,不仅造成生态环境的污染,而且极大的浪费潜在资源。面对上述问题,利用冶金固体废弃物与生物质废弃物开发一种价格低廉且性能优越的生态活性炭,既是冶金固体废弃物与生物质废弃物的高附加值利用与资源可持续发展的重要途径之一,也是大幅降低改性活性炭生产成本与提高经济效益的重要途径之一。以核桃壳与电炉渣为研究对象,利用电炉渣中含有的金属氧化物对生物质废弃物进行改性处理制备用于甲醛降解的生态活性炭,依据《室内装饰装修材料人造板及其制品中甲醛释放限量》(GB18580-2017)对生态活性炭性能进行测试。利用X-射线光电子能谱(XPS)对元素含量进行测试与分析,X-射线荧光光谱仪(XRF)对化学成分进行测试与分析,傅里叶变换红外光谱仪(FTIR)对结构组成进行测试与分析,X-射线衍射仪(XRD)对矿物组成进行测试与分析,扫描电子显微镜(SEM)对微观结构进行测试与分析,激光粒度仪(LPSA)对粒度分布进行测试与分析和比表面积及孔径测定仪(BET)对孔结构进行测试与分析,以揭示核桃壳与电炉渣制备生态活性炭的机理,以及生态活性炭对甲醛的降解机理。结果表明:核桃壳超微粉与电炉渣超微粉进行复合制备具有良好降解甲醛性能的生态活性炭,不仅实现了冶金固体废弃物与生物质废弃物的高附加值的利用,而且提出了"以废治危"的新室内空气甲醛治理理念。电炉渣超微粉较好的被包裹于生态活性炭层状结构中,提高生态活性炭的粉化率,形成粒径较小的颗粒,有利于提高生态活性炭与甲醛的降解作用面积。电炉渣超微粉中含有Fe元素、Mn元素与Ti元素,Fe元素具有磁性促使大量甲醛在生物质活性炭孔结构表面形成富集,Mn元素与Ti元素对已经富集的甲醛进行催化降解,实现吸附降解与催化降解的协同作用。     

Corrosion protection of Mg/Al alloys by thermal sprayed aluminium coatings

The protective features of thermal sprayed Al-coatings applied on AZ31, AZ80 and AZ91D magnesium/aluminium alloys were evaluated in 3.5 wt.% NaCl solution by electrochemical and gravimetric measurements. The changes in the morphology and corrosion behaviour of the Al-coatings induced by a cold-pressing post-treatment were also examined. The specimens were characterized by scanning electron microscopy, energy dispersive X-ray analysis and low-angle X-ray diffraction. The as-sprayed Al-coatings revealed a high degree of porosity and poor corrosion protection, which resulted in galvanic acceleration of the corrosion of the magnesium substrates. The application of a cold-pressing post-treatment produced more compact Al-coatings with better bonding at the substrate/coating interface and higher corrosion resistance regardless of the nature of the magnesium alloy.