Unalloyed Copper Research Articles

Effect of surface corrosion on the zeta potential of copper in acidic solutions

The comprehensive investigation was conducted to analyze the corrosion behavior and surface potential of pure copper surfaces in various acidic solutions. We carried out Zeta potential measurement, electrochemical measurement and in situ Raman spectroscopy to investigate the corrosion process and surface potential of copper in acidic solutions with different pH. It was found that the variation in zeta potential with pH corresponds to the corrosion behavior of copper during this process. In 1mmol / L aqueous chloride media, when the pH is greater than 3.5, unalloyed copper is oxidized to monovalent copper. At this stage, as the pH decreases, the zeta potential gradually increases. When the pH reaches 3.5, the Zeta potential reaches the highest, and the rate of cuprous oxide formation reaches the maximum. When the pH continues decrease, unalloyed copper begins to be oxidized to divalent copper, and the zeta potential will also decrease, the surface charge state shifts to the positive direction. Furthermore, our experimental findings are complemented by Density Functional Theory (DFT) calculations.

The Geochemistry of Unalloyed Copper Metallurgical Group Indicates Copper Ore Sources in the Late Bronze and Early Iron Ages of the Urals

Trace elements in copper artifacts from Late Bronze and Early Iron Age sites in the Urals, formerly attributed to the metallurgical group of “chemically pure” copper, were analyzed using the method of laser ablation inductively coupled plasma mass spectrometry. The metal of which artifacts included in this group are made reveals geochemical markers suggesting that “pure” copper actually falls into several subgroups. The PCA analysis of the results identifies 11 clusters corresponding to various sources of copper ores and their mixtures. At least seven principal associations can be linked to copper deposits of different geological types and origin: Au-Te-Bi, Au-Se-Te-Sb, Fe-Co-Ni-As-Sb, Fe-Co-Ni -Zn, Se-Co-Fe, Ag-Pb-Ni, and Sb-Pb-Zn-As. Also, several mixed associations reflect the fusion of copper items and metal scrap initially obtained from different sources: Sn-Pb, Fe-Co-Ni-Zn + Sn, Fe-Co-Ni + Au-Te-Bi-Ag, Fe-Co-Ni + Au-Te-Bi + Sn. A separate association, for which the ore source remains unknown, consists of artifacts characterized by a low content of trace elements, jointly making up less than 0.01 wt%. The largest sample in the Late Bronze Age “pure copper” group falls within the Sn-Pb cluster representing a mixture of local copper and imported Sn-containing copper scrap. Judging by trace elements, the main sources of ore in the “pure copper” group of the Itkul and Sarmatian cultures were the Gumeshki mine and another unidentified source. Both could have been used already in the Final Bronze Age.

Геохимия металлургической группы «чистой» меди: индикатор источников медной руды на Урале в позднем бронзовом – раннем железном веках

Представлены результаты исследования элементов-примесей в артефактах, относящихся к металлургической группе «чистой» меди, с памятников позднего бронзового и раннего железного веков Урала с использованием метода масс-спектрометрии с индуктивно связанной плазмой и лазерным пробоотбором. Состав металла артефактов имеет геохимические маркеры, позволяющие разделить «чистую» медь на несколько подгрупп. По результатам анализа главных компонент элементов-примесей в «чистой» меди выделены 11 кластеров, характеризующих различные источники медной руды, а также их смеси. Выявлено как минимум семь основных ассоциаций, отражающих геолого-генетические типы медных месторождений — источников руды в древности (Au-Te-Bi, Au-Se-Te-Sb, Fe-Co-Ni-As-Sb, Fe-Co-Ni-Zn, Se-Co-Fe, Ag-Pb-Ni, Sb-Pb-Zn-As), а также несколько смешанных, показывающих сплавление медных изделий и лома, металл которых получен из руд разных месторождений (Sn-Pb, Fe-Co-Ni-Zn + Sn, Fe-Co-Ni + Au-Te-Bi-Ag, Fe-Co-Ni + Au-Te-Bi + Sn). Отдельную группу составляют предметы с очень низким содержанием элементов-примесей (суммарно < 0,01 мас. %). Для них источник руды установить сложно. В позднем бронзовом веке самую большую выборку в группе «чистой» меди составляет кластер Sn-Pb, указывающий на смешение местной меди и импортированного оловосодержащего медного лома. Судя по элементам-примесям, основными источниками руды для «чистой» меди иткульской и сарматской культур были Гумёшевский рудник и еще один неустановленный. Они могли использоваться уже в финале эпохи бронзы.

Bellows and furnace covers in the unalloyed copper metallurgy of the Chalcolithic Southern Levant: reassessing the evidence from Abu Matar

AbstractUnalloyed copper objects were produced in the Chalcolithic Southern Levant in a two‐step process. Copper ore was smelted in pit furnaces, and the mechanically extracted copper prills melt in crucibles and cast into objects. However, the air supply remained unknown, and practical considerations shed doubt on the validity of some of the reconstructed practices. To refine the reconstruction, the metallurgical material from Abu Matar was reassessed. Most importantly, several previously unreported fragments suggest the use of bellows and covering the furnace with large pottery fragments. Our results provide probably the earliest evidence for the use of bellows.

First evidence for alloying practices in the Chalcolithic Southern Levant (4500–3800 BCE) as revealed by metallography

Excavations at the Chalcolithic site Fazael in the central Jordan Valley uncovered a large number of metal items, many of them polymetallic copper alloys cast in the lost wax technique. Metallography and SEM–EDS analysis on a subset of the assemblage confirm previous notions of the lost wax metallurgy in the Chalcolithic Southern Levant but extend them significantly in three aspects: The Fazael metal assemblage is slightly depleted in its arsenic content compared to metal assemblages from other sites, silt-sized quartz inclusions in unalloyed and polymetallic copper items, and the presence of unalloyed copper inclusions. These latter provide the earliest direct evidence for mixing of different metal types in West Asia, potentially alloying or recycling.

Identification of Fazael 2 (4000–3900 BCE) as first lost wax casting workshop in the Chalcolithic Southern Levant

Apart from many lost wax cast metal fragments, crucible fragments and several heated sediment nodules were found at the Chalcolithic site Fazael 2 (central Jordan Valley). Petrographic investigations on the heated sediment nodules revealed many features characteristic of the Chalcolithic Southern Levantine lost wax casting moulds. Heating temperatures were assessed using infrared spectroscopy, showing that casting did not vitrify the clay fraction in the moulds. Consequently, Fazael is the first identified Chalcolithic Southern Levant production site for lost wax cast metal items. These findings confirm the existence of a metallurgical tradition with lost wax casting in the Jordan Valley parallel to the unalloyed copper metallurgy in the Northern Negev. Moreover, crucibles and heated sediment nodules are made of local ferruginous loess, a material not mentioned in previous studies on lost wax casting mould fragments. Therefore, the existence of more than one such production site must be assumed.

Cu-10 wt.% Al Alloys Produced by Spark Plasma Sintering of Powder Blends and a Mechanically Alloyed Mixture: A Comparative Investigation

Cu–Al bronzes are interesting metallic materials, demonstrating higher hardness, higher wear resistance, higher corrosion resistance and a lower friction coefficient as compared with unalloyed copper. The powder metallurgy approach to the fabrication of these alloys presents opportunities to tailor their phase composition and grain size. In the present work, the structural characteristics, phase composition and properties of Cu-10 wt.% Al alloys obtained by spark plasma sintering (SPS) of powder blends and a powder obtained by mechanical alloying (based on Cu(Al) solid solution) are reported. Alloys with different interaction degrees between the metals were obtained by SPS. The blends demonstrated better sinterability than the mechanically alloyed powder: a nearly fully dense alloy was obtained by SPS of the blend at 480 °C, whereas a temperature of 800 °C was necessary to consolidate the mechanically alloyed powder. The hardness and electrical conductivity of the sintered alloys were comparatively analyzed. It was shown that the Cu-10 wt.% Al alloys obtained without the mechanical alloying stage possess hardness and electrical conductivity comparable to those of the alloys obtained from the mechanically milled powder.

The Technology and the Provenance Study on Gilt-Copper Crown Excavated from Tomb No.63 of the Ancient Tumuli in Gyo-dong/ Songhyeon-dong, Changnyeong

An excavation project conducted by the Gaya National Research Institute of Cultural Heritage discovered a gilt-copper crown in Tomb No. 63 of the ancient tumuli in Gyodong and Songhyeon-dong, Changyeong. This study analyzed the aforementioned crown and identified the certified group and the source of raw materials according to the manufacturing technique. Scientific analysis confirmed that the crown was made of unalloyed copper and the surface was plated with gold and silver using the mercury amalgam technique. The gilded surface color is divided into red and yellow, and this is presumed to be due to differences in manufacturing processes such as thickness and heat treatment according to the number of times it was gilded. The copper raw material used to manufacture the crown is identified as Zone 3 including Jeolla-do, Chungcheong-do, and northern Gyeongsang-do, and the origin of the raw material and excavation site are not the same. Therefore, it is judged that raw materials from a different region than the excavated area of Changnyeong were used, and the possibility that these were supplied from other regions and manufactured in Changnyeong cannot be excluded.

Study on Surface Properties of Unalloyed Copper Implanted with Different Transition Metal ions

Copper is widely used in Integrated Circuits and electronic components. Its corrosion performance and service performance have been paid much attention. We implanted Ti, Cr, Fe, Ni, Zn and other fourth period transition metal ions into unalloyed copper. After that, zeta potential test, electrochemical test and density functional theory calculation were used to study the surface properties of the implanted samples. We found that for copper samples, the zeta potential of implanted samples is related to the type of implanted transition metal ions, that is, the charge state at the solid-liquid interface is related to the type of implanted ions. We use density functional theory calculations to explain this change in surface properties of metal samples before and after ion implantation. We find that the d-band center of the transition metal has a similar trend to zeta potential.

Islamic copper-based metal artefacts from the Garb al-Andalus. A multidisciplinary approach on the Alcáçova of Mārtulah (Mértola, South of Portugal)

A multidisciplinary approach has been applied to investigate the production technology of a collection of copper-based artefacts found during archaeological excavation campaigns carried out in the Almohad neighbourhood of Mārtulah, the Islamic name of modern Mértola (South of Portugal). In stark contrast to other Islamic materials found in the same site such as common and finely decorated pottery, glass, and bone artefacts, metal objects have received less attention despite the high number of artefacts recovered.This study focuses on the chemical characterisation of 171 copper-based artefacts dating back to the 12th and the first half of the thirteenth centuries. The artefacts are daily use objects and consist of personal ornaments (earrings, rings, and casket ornaments), tools (spindles, spatulas, and oil lamp sticks) and artefacts with unknown functions. The analytical results by X-ray fluorescence Spectroscopy (XRF) provided information not only about technological issues but infer as well on the socio-economic implications of metal consumption in Islamic Mértola. Results revealed that metals were produced using a variety of Cu-based alloys, namely unalloyed copper, brasses (Cu + Zn), bronzes (Cu + Sn), and red brasses (Cu + Sn + Zn), with a variable concentration of Pb, without any apparent consistency, as a likely result of recurrent recycling and mixing scrap metals practices or use of mineral raw materials available locally.

Macroscopic Chop Mark Identification on Archaeological Bone: An Experimental Study of Chipped Stone, Ground Stone, Copper, and Bronze Axe Heads on Bone

This paper presents a new macroscopic method for identifying chop marks on archaeological faunal assemblages and highlights the major differences in the morphology of chop marks created by stone and metal axes. The method provides macroscopic criteria that aid in the identification of both complete and incomplete chop mark types as well as the raw material of the axe. Experiments with modern stone (chipped and ground) and metal (copper and bronze) axes found that the degree of fragmentation within a chop mark is related to both the width and sharpness of the axe and can be classed on a scale from 1–5 using a variety of criteria. The experiments demonstrate that sharp chipped stone axes are fragile (often break upon impact) and do not create clean and well-defined chop marks. Ground stone axes are more durable but tend to create very fragmented chop marks without a clean cut (sheared) surface. Unalloyed copper metal axes can create sheared chopped surfaces; however, the relatively soft metal creates more crushing at the point of entry than bronze axes. In contrast, bronze axes are durable and create chop marks with exceptionally low rates of fragmentation resulting in a clean-cut sheared surface that extends into the bone for more than 3 mm. The method is applied to the faunal assemblage from the Early Bronze Age site of Göltepe, Turkey to determine whether the chop marks on bones were made by stone or metal axes at this early metal processing settlement. The results suggest that many of the chop marks were made by metal implements (e.g., axes). Hence, this method provides another means to monitor the adoption rates of new raw materials at a time when both metal and stone axes coexisted.

New results on horse trappings from the Hunnic-period Carpathian Basin based on non-destructive archaeometric analyses

Objects manufactured from pressed gold, gilded silver or copper alloy plates are characteristic assemblages from the Late Hunnic period (5th century AD, 420/430). In this study, horse trappings that belong to the ‘pressed gold plate horizon’ from three archaeological sites in the Carpathian Basin (Léva, Nyíregyháza-Oros and Pécsüszög) were analysed non-destructively by using a handheld X-ray fluorescence spectrometer. The main aims were to determine the chemical composition and the gilding technique used, and to attempt to prove whether the groups in an assemblage are from the same set. The results of the chemical analyses give us the opportunity to confirm whether damaged or presumably lost objects of an assemblage were replaced or repaired. According to the results obtained, the objects were manufactured from gold (Pécsüszög), gilded silver (Nyíregyháza-Oros) or gilded unalloyed copper plates (Léva). Later, replacements can be distinguished based on their chemical composition and manufacturing quality. Two types of gilding were observed: fire gilding with the presence of mercury (Léva), and leaf gilding (Nyíregyháza- Oros).

Characterization of copper & stainless steel interface produced by electron beam powder bed fusion

Unalloyed copper (Cu) powder was deposited and melted onto a pre-existing stainless steel substrate using electron beam powder bed fusion (EB-PBF) additive manufacturing (AM) to form dense, bimetallic structures. The AM fabricated Cu was fully dense, and with strength properties consistent with recent reports on EB-PBF of Cu. The overall bimetallic structures exhibited total elongation of 25–35%, and was dominated by plastic deformation in the Cu region. Tensile failures were typically observed in the Cu portion of the bimetallic bodies demonstrating that the interface was not the source of mechanical failure. The interface region of the bimetallics contained areas of liquid phase separated Cu and Iron (Fe) + Chromium (Cr) rich regions resulting from a metastable miscibility gap in the Cu and Fe phase diagram. Metallurgical and mechanical examinations of the bimetallic structures showed the interface region transitions from an Fe rich mixture to a Cu rich mixture within a few AM layers.

Work on the cutting edge: metallographic investigation of Late Bronze Age tools in southeastern Lower Austria

This paper analyses 20 Late Bronze Age (ca 1080–800 BC) copper alloy objects to discern their manufacture and the skills of local craftsmen. Several tools and jewellery were studied that originated from a bronze workshop located immediately next to the Prigglitz-Gasteil copper ore mining site and several contemporaneous sites in the surrounding area. The samples were studied with optical microscopy (microstructurally), and SEM-EDXS and XRF (chemical analyses). Our analyses are part of a larger study and suggest that the Prigglitz region’s bronze production was not standardized. Particular alloys do not seem to have been chosen for object types or due to their intended use-function. Notably, approximately 20% of the objects contain unalloyed copper inclusions, which are most likely a result of the incomplete mixing of scrap metals and alloys during their production.

Quasi-Static Tensile Properties of Unalloyed Copper Produced by Electron Beam Powder Bed Fusion Additive Manufacturing.

Mechanical properties of powder bed fusion processed unalloyed copper are reported majorly in the as-fabricated condition, and the effect of post-processes, common to additive manufacturing, is not well documented. In this study, mechanical properties of unalloyed copper processed by electron beam powder bed fusion are characterized via room temperature quasi-static uniaxial tensile test and Vickers microhardness. Tensile samples were extracted both perpendicular and parallel to the build direction and assigned to three different conditions: as-fabricated, hot isostatic pressing (HIP), and vacuum annealing. In the as-fabricated condition, the highest UTS and lowest elongation were obtained in the samples oriented perpendicular to the build direction. These were observed to have clear trends between sample orientation caused primarily by the interdependencies between the epitaxial columnar grain morphology and dislocation movement during the tensile test. Texture was insignificant in the as-fabricated condition, and its effect on the mechanical properties was outweighed by the orientation anisotropy. The fractographs revealed a ductile mode of failure with varying dimple sizes where more shallow and finely spaced dimples were observed in the samples oriented perpendicular to the build direction. EDS maps reveal that grain boundary oxides coalesce and grow in HIP and vacuum-annealed specimens which are seen inside the ductile dimples and contribute to their increased ductility. Overall, for the post-process parameters chosen in this study, HIP was observed to slightly increase the sample’s density while vacuum annealing reduced the oxygen content in the specimens.

Enkomi (Cyprus): Using pXRF spectroscopy to identify LBA copper alloys

A collection of 206 copper-base artefacts coming from the Late Bronze Age settlement of Enkomi, located on the east coast of Cyprus, and dated to the 16th-11th centuries BC, was studied and non-destructively chemically analysed using a handheld pXRF instrument. The assemblage consists of various categories of objects, such as weapons, tools, ornaments and scrap metal. The basic aims of the present work are the determination of the alloy type of the artefacts and the comparative study of the copper alloys used in the different chronological phases of Enkomi. The results show that most of the analysed artefacts, in all chronological phases, are made of a copper-tin binary alloy (bronze) with a tin concentration lower than 10 wt%, while some artefacts were made of unalloyed copper. Among the bronze artefacts, there is a group of objects which was found to have a significantly higher tin concentration (>13 wt% Sn). Regarding the other elements, there is a limited number of copper-arsenic and copper-zinc alloys and an extensive presence of lead, although in most artefacts the latter is detected in concentrations lower than 1 wt%. Because lead concentration in local Cypriot ores is unusually low, its presence can be interpreted either as a deliberate or an accidental addition, even at these low concentrations. In addition, the presence of a noteworthy number of scrap metal fragments and the detection of low concentrations of arsenic and lead in most of the studied copper-tin alloy artefacts may suggest the possible use of recycled metal deriving from artefacts dating to earlier periods, namely the Early and Middle Bronze Age, which would originally have contained much higher concentrations of arsenic.

Provincial Inca metallurgy in northern Chile: New data for the Viña del Cerro smelting site

Metal artifacts were one of the most relevant wealth finance items for the political economy of the Inca empire. Inca provincial expansion in the Collasuyu has largely been explained by the need to intensify mining to satisfy their metallurgical demand. Despite the evidence for many mines and metallurgical activities during the Late Horizon in the southern Andes, it is still not clear how their production was organized and articulated.By studying one of the most important metallurgical centers in northern Chile, Viña del Cerro, we determined the following: first, the metal obtained was unalloyed copper; and second, there is no relevant evidence for the manufacturing of final artifacts in the site, or at any of the major Inca settlements in the Copiapó valley. We argue that tin bronze artifacts in Copiapó were likely imported from abroad and that the local copper production was likely taken elsewhere for processing and final manufacture.New radiocarbon dates indicate that Inca metallurgical activities in Copiapó valley co-opted a previous local site and technology. However, the Incas did not establish an intense occupation there. This case evidences the logistics and challenges of developing a political economy based on wealth finance in the far corners of the Inca Empire, where decentralizing the chaîne opératoire seemed to be the chosen strategy for economic control.

Preliminary Discussion on the Highly Radiogenic Lead in Unalloyed Copper Artifacts of the Eastern Zhou Dynasty: Starting from the Huili Copper Spearheads

The debate about the highly radiogenic lead in Chinese archaeology has never ceased. However, previous studies have mainly focused on high leaded bronzes and lead materials, and with little specific discussion on the unalloyed copper artifacts and the sources of copper materials in China. In this work, a trace of highly radiogenic lead was found in ten copper spearheads unearthed from Huili County, Sichuan Province, southwest China, which inspired our research on this issue. The pXRF results showed that their lead content is extremely low, so the lead isotope ratios can indicate the source of copper, and the data correspond to the local copper deposits. Combined with other relevant highly radiogenic lead isotope data of unalloyed copper artifacts, the results indicate that there were multiple sources of copper ores used in the Shang Dynasty, and copper mines were continuously used in Southwest China until the Eastern Zhou Dynasty.

Characteristic features of metal artifacts excavated in western Yunnan in the Bronze Age

Yunnan province is located in Southwest China. A technical study of the metal artifacts unearthed in western Yunnan can not only improve our understanding of the bronze culture but also fill many gaps in the archaeological studies that have been carried out on prehistoric bronzes from Yunnan. In this paper, we summarize the results of our analyses of bronzes dating from the seventeenth century BCE to the second century BCE. Ninety-nine metal artifacts, including weapons, tools, and decorative objects have been analyzed by optical microscopy and scanning electron microscope (SEM) with energy-dispersive spectroscopy (EDS) to examine the microstructure and composition. The results show that a variety of alloys were employed, including unalloyed copper, copper-tin, copper-tin-lead, copper-arsenic, copper-arsenic-lead, copper-lead-antimony, copper-antimony, lead-antimony-arsenic-copper, carburized bloom steel, and hypoeutectoid steel. The copper alloys were fabricated by casting, cold working after casting, and annealing. This study has expanded our knowledge of bronze culture in these areas and reveals some of the technological relationships among the regions of western and central Yunnan, the northern steppe, and Southeast Asia.

The provenance of Yin-Shang bronzes with highly radiogenic lead isotopes

Even if the lead isotope results are same, the significance of the lead isotopic signature is quite different for the provenance study of the Chinese bronzes. The published data show that the radiogenic lead signatures in the unalloyed copper and the Yin-Shang bronzes with the low lead content are contributed by the copper deposits, while those of the South Africa and Zimbabwe bronzes with highly radiogenic lead were contributed by tin deposits. Combined with the results of lead isotope analysis by LA-MC-ICP-MS and the recent archeological discoveries, it was possible that for the Yin-Shang bronzes with highly radiogenic lead contents, the copper material was derived from Zhongtiao Mountain copper deposits, while the lead material from Huojiagou and Zhenggou in the northern margin of North China Craton, but we prefer that the lead materials were from the southern margin of the North China Craton.