Metals Sn Research Articles

Employing Non-Noble Metals As Catalysts for CO2 Electroreduction

CO2 electroreduction to fuels is one of the most viable solutions for tackling both the issues of global warming and energy crises. It is due to the fact that the products such as formic acid, methanol, etc. which are obtained by electroreduction of CO2 could be employed as hydrogen carriers or directly as fuels. This phenomenon attracts huge research towards the process and its bottlenecks for making it commercial. The major hurdles regarding catalysis of CO2 electroreduction process are low solubility of CO2 in aqueous solutions and low product yields.In our previous works, we have already demonstrated the employment of gas diffusion electrodes for non – noble metal catalysts such as Pb, Bi and Sn. The usage of gas diffusion electrodes enables us to exploit the three phase contact of CO2 gas – solid catalysts – liquid electrolyte and shows higher product (formate ion) yield.[1] Additionally, we have also shown through another work that the ternary eutectics of these three non – metal catalysts employed exhibits higher activity for CO2 electroreduction than singular pure metals or any other binary or ternary alloyed compositions of the metals.[2] In this work, we want to exploit the conclusions from both the works and subject ternary alloy composition of Pb – Bi – Sn metals in gas diffusion electrode configuration for the process of CO2 electroreduction. Based on the previous two results, author believes that this would enable us to obtain higher product yield and hence better energy efficiency which would be a step forward towards sustainable development.Reference:[1] A. S. Kumawat and A. Sarkar (2017), Comparative study of carbon supported Pb, Bi and Sn catalysts for electroreduction of carbon dioxide in alkaline medium, Journal of Electrochemical Society, 164 (14), H1112 – H1120. doi: 10.1149/2.0991714jes[2] A. S. Kumawat and A. Sarkar (2019), Electrochemical reduction of CO2 on Pb – Bi – Sn metal mixtures – Importance of Eutectics, SN Applied Sciences 1: 301. doi: 10.1007/s42452-019-0313-y

Accumulation and translocation of heavy metals in water hyacinth: Maximising the use of green resources to remediate sites impacted by e-waste recycling activities

Abstract Abandoned e-waste recycling sites can still cause heavy metal pollution in the nearby aquatic environment, where the heavy metals in sediment can be remobilized and dispersed by water current. Water plants may be used to prevent the dispersal of heavy metals and remediate contaminated sites without substantially disturbing the environment. Here, we examined the degree of heavy metal contamination in sediment along a river (Lian River, South China) previously influenced by e-waste recycling activities, and evaluated the capacity of water hyacinth for remediating contaminated sites by measuring the accumulation and translocation of heavy metals. We found that the sediment adjacent to the abandoned e-waste recycling site was still heavily contaminated (Igeo > 3) with various heavy metals (Ag, Cd, Cu, Pb, Sb, Sn and Zn), which can disperse to the nearby region via water current. Water hyacinth not only accumulated a variety of heavy metals (i.e. non-selective uptake), but also increased their uptake and translocation in the more contaminated sites, indicating its good capacity to remove heavy metals from water. Nevertheless, the concentrations of heavy metals in the edible part of water hyacinth (i.e. leaves) were still far below the maximum tolerable levels as animal feed (except Cu for sheep) due to the limited translocation. This study provides important insights into the possibility of using water hyacinth as the natural resource for multiple purposes (e.g. animal feed and biofuel) in addition to remediation of contaminated sites.

Applicability of Wiedemann-Franz Law to Thermal Conductivity of Molten Field’s Metal

The thermal conductivity of metals and alloys is an important physical property. The thermal conductivity of metals and alloys in the liquid state is usually hard to be measured, because it is difficult to exclude the effect of convection. As such, as a convenient approach, the Wiedemann-Franz law has been used for the estimation of thermal conductivity of metals and alloys in the liquid state. However, some reports show the deviation from Wiedemann-Franz law of pure Sn and Sn-based metals in the liquid state. Measuring the thermal conductivity of various Sn-based alloys in the liquid state is of significant importance to identify its heat transfer in terms of whether the deviation from Wiedemann-Franz law is observed. In this study, Field’s metal is focused on as one of the Sn-based alloys. Then, its thermal conductivity in the solid and liquid states with various temperature ranges by employing the transient hot wire method. This method is appropriate due to its nature of dealing with the convection-including problems. Finally, the adaptability of Wiedemann-Franz law is analyzed by using the obtained thermal conductivity and electric conductivity data. In this study, the deviation from Wiedemann-Franz law was observed in the liquid state.

Separating and recycling metal mixture of pyrolyzed waste printed circuit boards by a combined method

Waste printed circuit boards (WPCBs) contain a variety of valuable and hazardous materials. Recycling WPCBs is an important subject not only for environmental protection but also for sustainable development of resources. In this work, a new method combined low-temperature alkaline smelting with liquid-liquid phase separation is proposed to separate and recycle metal mixture in pyrolysis residue of WPCBs of mobile phones. During the low-temperature alkaline smelting process, amphoteric metals Al, Pb, Si, Sn, and Zn are firstly separated and recycled from the metal mixture with the separation rates of 99.5%, 81.6%, 97.8%, 88.4% and 95.7%, respectively. To separate the remaining metal mixture mainly containing elements Cu, Fe, Cr, Ni, Au and Ag, a liquid-liquid phase separation system is designed. As a result, the noble metals Au and Ag are concentrated in the copper-rich substance to form a high-value group, while the elements Ni and Cr distribute in the iron-rich substance. The iron-rich substance can be reused in the liquid-liquid phase separation process. In the super-gravity field, the recycling rates of the metals Au, Ag, Cr and Ni reach 98.1%, 99.8%, 95.6% and 75.4%, respectively. Furthermore, the iron-rich substance can be reused back to the liquid-liquid separation system. The copper-rich substance enriched by the noble metals can be efficiently recovered with low energy consumption and less pollution. This work provides an environmentally friendly and efficient route for separating and recycling the metal mixture in WPCBs.

Metals, arsenic, pesticides, and microcystins in tilapia (Oreochromis niloticus) from aquaculture parks in Brazil.

The production of Nile tilapia (Oreochromis niloticus) in Brazil exhibits the highest growth rate in the world and represents approximately 45% of the total fish production. The objective of the present study was to assess the risk for human health due the consumption of tilapia farmed in net cages in eight aquaculture parks in Brazil. The concentrations of pesticides (40 compounds), metals (Mn, Ni, Zn, Cd, Pb, and Sn), arsenic, and cyanotoxins (microcystins) were evaluated in 16 fish from each park. Among analyzed pesticides, pyraclostrobin (0.18-0.32mg/kg) and fenthion (0.0026-0.0037mg/kg) exhibited values above the limit of quantification in the tilapia from Aracoiaba, Castanhão, and Ilha Solteira. The highest concentrations of As (0.44μg/g) in fish tissues were found in Juara, Mn (0.21μg/g) in Castanhão, and Zi (11.5μg/g) were found in Três Marias. Furnas and Linhares exhibited the lowest metal concentrations. The estimated daily intake of muscle by the average Brazilian with 70kg body weight is below the reference dose for all studied metals in all parks. Total free microcystins showed an accumulation pattern (muscle < gill < liver). The highest concentration in muscle was found in Castanhão (1043μg/kg) samples. The results showed that fish exhibited metal, As, and pesticide tolerable daily intake (TDI) below the limit and pose low risk for human consumption. Otherwise, TDI for microcystins in fish of all studied parks was above the maximum level recommended by the World Health Organization, indicating that there exists a toxicity risk of fish consumption.

A low-temperature limit for growth of ZnO nanowires by using of laser ablation processes

The contribution deals with growth of ZnO nanowires on metal catalysts by using of pulsed laser deposition and with the influence of growth temperature. The process of nanowires preparation comprised two technological steps—both were based on pulsed laser ablation processes: (1) production of metal nanoparticles by laser ablation in liquids and (2) pulsed laser deposition of ZnO nanowires by ablation of ZnO target on substrate with metal nanoparticles. Nanoparticles from various metals (Au, Ag, Ni, Cu, Al, Mg, Zn, Sn and BiSn alloy) were prepared by pulsed laser ablation at 1064 nm in deionised water. Colloids contained metal nanoparticles were applied on Si (100) substrates, and after drying, nanoparticles served as catalysts of VLS crystallisation. Temperatures in interval 600—200 °C were experimentally compared for the nanowires growth with applied ablation laser working at 248 nm. The lowest achieved temperature value for growth of ZnO nanowires was 425–450 °C. However, among applied metals Cu and Al nanoparticles only successfully catalysed ZnO nanowires at this temperature. Properties of prepared samples were investigated by scanning electron microscopy and photoluminescence. Experimental results revealed that along with the growth temperature, selection of proper metal catalyst is also important factor for nanowires crystallisation.

Fragment of a central-type large structure located in southern Uganda and its metallogenic value

For the southern regions of Uganda, the metallogenic value of the regional arc belt of dikes of the main and ultrabasic composition was considered. It is shown that it is part of the arc sector of a large central-type structure with a diameter of about 700 km. It had a long development in the Riphean sequence of tectono-magmatic activation. This structure was formed over 1,37 billion years ago and reformed approximately 1 billion years ago and at the end of the Riphean sequence (0,5—0,6 billion years ago).This structure includes all major deposits of Sn, W, Na, Nb, Ni, REE and Au in Burundi, Congo, Rwanda, Tanzania and Uganda. In Uganda, the Sn, W and rare metals fields are controlled by small intrusions of granite with an age of 1 billion years and crossing nodes of radial faults, which are the central-type structures of small order that are included in the central part of the allocated megastructure. Materials in the relationship of ore-grade gold mineralisation with the crossing nodes of large arc, radial and overfault-shift faults are given.

Vapor Transport and Deposition of Cu-Sn-Co-Ag Alloys in Vesicles in Mafic Volcanic Rocks

AbstractMetallic sublimates coated by sulfides and chlorides line the vesicle walls of mafic volcanic lava and bombs from Kīlauea, Vesuvius, Etna, and Stromboli. The metallic sublimates were morphologically and compositionally similar among the volcanoes. The highest concentrations of S and Cl occurred on the surface of the sublimates, while internally they had less than 1 wt % S and Cl in most cases, leading us to classify them as alloys. The major components of the alloys were Cu, Sn, Co, and Ag based on electron microprobe analyses and environmental scanning electron microscope element maps. Alloy element maps showed a covariance of Cu-Sn, while Co and Ag concentrations varied independently. Laser ablation-inductively coupled plasma-mass spectrometry analysis of matrix glass and melt inclusions in bombs from Stromboli showed appreciable amounts of Cu, Co, and Sn. We propose a model for the origin of the metallic grains, which involves syneruptive and posteruptive magma degassing and subsequent cooling of the basalt vesicles. During syneruptive vapor phase exsolution, volatile metals (Cu, Co, and Sn) partition into the vapor along with their ligands, S and Cl. The apparent oxygen fugacity (fO2) in these vapor bubbles is low because of the relative enrichment of the exsolved gas phase in H2 relative to H2O in silicate melts, due to the much higher diffusivity of the former in silicate melts. The high fH2 and low fO2 induces the precipitation of metal alloys from the vapor phase. Subsequently, the reducing environment in the vesicle dissipates as the cooling vapor oxidizes and as H2 diffuses away. Then, metal-rich sulfides (and chlorides) condense onto the outer surfaces of the metal alloy grains either due to a decrease in temperature or an increase in fO2. These alloys provide important insights into the partitioning of metals into a magmatic volatile phase at low pressure and high temperature.

Effect of prothioconazole on the degradation of microplastics derived from mulching plastic film: Apparent change and interaction with heavy metals in soil

Microplastic pollution is a major global environmental problem in both aquatic and terrestrial environments. Pesticides are frequently applied to agricultural soil to reduce the effects of pests on crops, but may also affect the degradation of plastics. In this study, we generated microplastics from polyethylene (PE) film and biodegradable poly(butylene adipate-co-terephthalate) (PBAT) film and determined (1) the effect of prothioconazole on degradation of the microplastics, and (2) the adsorption and release characteristics of heavy metals (Cr, Cu, As, Pb, Ba, and Sn) by the microplastics during degradation process. Changes of surface functional groups and morphologies were measured by FTIR and SEM, while metal concentrations were determined by ICPMS. Prothioconazole was found to promote plastic degradation. PBAT degraded faster and adsorbed more heavy metals from the soil than PE. Whether the microplastics adsorb or release heavy metals depended on the metal and their concentrations. Prothioconazole inhibited the adsorption of Cr, As, Pb and Ba by microplastics, promoted the adsorption of Cu, and had no significant effect for Sn. These results can help to assess the ecological risk of microplastic pollution from plastic mulch when combined with heavy metals.

Spatial Characteristics, Risk Assessment, and Source Analysis of Elements in Surface Sediments from the Baiyangdian Lake

In this paper, nutrient elements (N and P), heavy metals (Pb, Cu, Zn, Cd, Cr, Co, Ni, and Sn), and grain size in surface sediments of Baiyangdian Lake, northern China, are studied. We also analyze the spatial variation in elemental characteristics and undertaken a pollution risk assessment. By combining data with information on the river sediment characteristics, we use multivariate statistical methods to reveal the sources and variation of elements in sediments. The results showed that the average contents of heavy metals in surface sediments from the lake and associated rivers were higher than background values. Within the area of the lake, nutrient elements are relatively high in the northwest region but low in the southeast region, and heavy metals are relatively high in the middle of the lake but low in the southern and northern areas. The sequence of comprehensive pollution index (I) in sediments was Cd > Pb > Cr > Cu=Zn > Ni > Sn > Co, with Cd being assessed as severe pollution and other elements as moderate pollution, although severe pollution of Cr was found in the Zaolinzhuang area. The order of potential ecological risk coefficients (Eri) was determined as Cd > Pb > Cu > Cr > Ni > Zn, whereby Cd was associated with a strong potential ecological risk (except in the Caiputai area) and other elements were associated with a slight potential ecological risk. Differences in the lake sediment texture were found to be slight. Non-point source pollution after rivers flow into the lake was determined as the main reason for the spatial variation of elements in the surface sediments of Baiyangdian Lake, although point source pollution in the villages surrounding the lake should not be ignored, especially with respect to N, P, Pb, and Cr.

Characterization of dusts from secondary copper production

Various types of waste, including dusts, are produced in the pyrometallurgical production of copper from secondary raw materials. According to the European Waste Catalogue and Hazardous Waste List, dusts from secondary copper production are classified as hazardous waste. In secondary copper production 3.87 million tons of copper were produced worldwide in 2017. The dusts are produced in the following thermal operations: reduction of the melt in the shaft furnace (shaft furnace dust), converting (converter dust), and pyrometallurgical refining (refining dust). These dusts contain significant amounts of heavy metals (Zn, Pb, and Sn) in oxidic forms. The dusts are regarded as secondary raw materials, and it is necessary to look for ways of extracting these heavy metals. The aim of this work was to characterize the individual types of dust and determine their quantitative and qualitative composition. The content of heavy metals in copper shaft furnace dust is (52.16% Zn, 19.33% Pb), in copper converter dust (32.40% Zn, 14.46% Pb), and in refining dust (32.99% Zn).

ОСОБЕННОСТИ ЭЛЕМЕНТНОГО СОСТАВА ВОЛОС СТУДЕНТОВ, ПРИБЫВШИХ НА УЧЕБУ В МОСКОВСКИЙ МЕГАПОЛИС ИЗ РАЗЛИЧНЫХ РЕГИОНОВ МИРА

The purpose of this study was to study the elemental status of first-year students of the Russian University of Friendship of Peoples who arrived to study from various climatogeographic regions of the world. Studies have shown that first-year students who came to study from different climatogeographic regions of the world are characterized by significant differences in the elemental composition of hair. Students from Latin America are characterized by a relatively high level of toxic metals Al, As, Hg, Sn, and students from Africa stand out by the highest levels of Al, B, Cd, Fe, I, Mn, Ni, Pb, Si, Sn, V. students from Iran and Azerbaijan revealed the minimum value of Co, Cu, Fe, I, Mg, Mn, Sn, V among all the studied groups. It was established that there are significant differences in the content of Ca, K, Mg, Na, P in the hair of male students from different regions of the world. Male students from Africa were characterized by the lowest Ca and P content in their hair, and the highest Mg content. The lowest content of K and Na was found in students from the countries of the Near and Middle East.

ОНГОНИТОВЫЕ ДАЙКИ ВОСТОЧНОГО КАЗАХСТАНА И СПЕЦИФИКА ИХ РУДОНОСНОСТИ

Goal of the research is to study regularities, age, material composition and ore content of ongonite-like dike belts of East Kazakhstan. Methods are field works carried out within Kalba-Narym shear zone where dike belts are developed. Geological and structural position of dikes and their age ratio to granitoids of Kalba-Narym pluton and ore formations have been determined. The samples were selected from varieties of ongonite dikes. Microprobe analyses have been carried out on a scanning election microscope JSM 6390 with an energy-dispersive add-on device, besides, mass-spectrometer researches have been conducted on ICP-MS. The purpose of these is to identify mineralogical and geochemical specialization of dike rocks. Findings. The following has been found due to the conducted researches and comparison analysis with other regions: Two groups of heterochronous dike belts were formed during Hercynian Period in geological structures of East Kazakhstan comprised in general system of Central Asian belt. The dike belts belong to gabbro- diorite – granodiorite – plagiogranite series, and the groups are of pre-batholite (C2-3–C3) and post-batholite (P2) types. Late postbatholite dikes of quartz porphyrites and quartz albitophyres of Mirolyubovsky complex (P2) refer to ongonites. Probably, they are derivatives of deep residual magma chambers. In the course of the work, ongonites geochemical differentiation into rare metals(Ti, Nb, Li, Sn, W and other) and rare alkalies has been established. The researches have shown that ongonite-like dikes are of post-mineral nature that is proved by their position in relation to ore bodies and by other factors. Besides, no rare metal ore of practical significance has been found within these dikes. Scientific novelty and practical application. It can be assumed that greater development of gabbro- diorite – granodiorite – plagiogranite dikes within the known and supposed ore fields, as well as specialization of rocks that dikes are composed of, enable to consider them as prospecting indicators of concealed rare metal objects. To study dike formations of this kind is very important for reconstruction of geodynamic environments, for development of correlation patterns of granitoid magmatism and for studying ore formation processes. By all means, all this can be used in geologic mapping practice, especially on the closed territories.

Enhancement of the Yield of Ammonia by Hydrogen‐Sink Effect during Plasma Catalysis

AbstractPlasma‐catalytic ammonia synthesis has been known since the early 1900s, but only until now efforts to optimize catalysts for this purpose are emerging. Here, we investigate various transition metals, low‐melting‐point metals, and gallium‐rich alloy catalysts for their activity towards ammonia production under a plasma environment. The best three pure metal catalysts were Ni, Sn and Au, which are not traditional catalysts for the current industrial ammonia synthesis. The ammonia yields for these catalysts were 34 %, 29 %, and 19 %, respectively. Synergistic effects were detected when employing alloys, as some alloys presented ∼25–50 % higher yields than their constituent metals. The employed metals were classified into two categories. Category I metals (Cu, Ag, Au and Fe), which are nitrophobic (excluding Fe, the Haber‐Bosch catalyst) and poor hydrogen sinks. For these metals, the measured concentration of Hα in the gas phase tended to correlate inversely with ammonia yield and directly with the H binding strength on the catalyst surface. Category II metals (Ga, In, Sn and Ni), which are good hydrogen sinks, tend to have a lower concentration of Hα in the gas phase than that of category I metals, which is consistent with their expected sink behavior. For these metals, the concentration of Hα correlates with ammonia yield. Plasma characterization experiments and DFT calculations suggest that the higher performance of Ni and Sn is related to the benefit of dissolving hydrogen to slow down H recombination, which is a feature that could be potentially optimized in future studies by rationally altering the catalyst composition.

Extraction of copper and the co-leaching behaviour of other metals from waste printed circuit boards using alkaline glycine solutions

Waste printed circuit boards (WPCBs) are a complicated and valuable fraction of electric and electronic waste. The recycling of them is critical to avoid environmental pollutions and to reuse resources. In particular, the e-waste import bans have been implemented in many traditional waste-importing countries in recent years, which is making the sustainable recycling essential and crucial for the advanced economies. In this study, a sustainable approach using alkaline glycine solution for the extraction of copper (Cu) from WPCBs, and the leaching behaviour of other metals (Ni, Al, Fe, Pb, Sn, Co, Zn, Au, Ag and Pd) is presented. Various leaching parameters, including initial pH, glycine concentration, solid content, oxidant, particle size, temperature and time were investigated. A maximum Cu extraction of 96.5 % was achieved, with high co-extraction of base metals (BMs). The extraction of BMs was dependent on the pH of leaching solution, which was highly correlated with other variables. BMs extraction was largely influenced by glycine concentration and solid content, while the sensitivity to H2O2, temperature, and particle size was insignificant. SEM-EDS analysis of leaching residue indicated that the unleached Cu may be locked in inert layers, e.g. Sn/solder materials. The kinetic analysis showed that the extraction of Cu from WPCBs (100 % <2 mm) at room temperature with ambient O2 in air as an oxidant was mainly controlled by internal diffusion.

Environmental chronic exposure to metals and effects on attention and executive function in the general population

Heavy metals are neurotoxic, associated with brain dysfunction, and have been linked with cognitive decline in adults. This study was aimed to characterize chronic exposure to metals (Cd, Be, Co, Hg, Sn, V, Al, Ba, Cr, Cu, Fe, Li, Mn, Ni, Pb, and Zn) and metalloids (As, B, Sb) and assess its impact on cognitive performance of Tehran's residents, capital of Iran. Scalp hair samples gathered from 200 volunteered participants (110 men and 90 women), aged 14–70 years and quantified by inductively coupled plasma atomic emission spectroscopy (ICP-OES). Attention and executive function, two measures of cognitive performance, were characterized using the trail making test (TMT) part A and B, respectively. Mental flexibility was characterized as the Delta TMT B-A scores and cognitive efficiency or dissimulation as the ration between TMT B and A scores. A comprehensive questionnaire was used to gather information on demographic and socioeconomic as well as lifestyle and health status. The highest and lowest mean concentrations were observed for B (325 μg/g) and As (0.29 μg/g), respectively. Results indicated that chronic metal exposure measured in hair changed significantly based on gender and age (p < 0.05). The levels of Cr, Fe, Ni, Si, Hg, Pb and B were significantly higher in males' hair, whereas those of Ag and Ba were greater in females' hair (p < 0.05). The results of the cognitive TMT test were significantly different between gender and age groups (p < 0.05). Moreover, results revealed that As, Hg, Mn, and Pb levels in hair were significantly associated with poorer participants' performance scores in the TMT test (p < 0.05). Age, gender, cigarette smoking, water-pipe smoking, traffic density in the area of residence, and dental amalgam filling were significant factors affecting the TMT test scores. The results suggest that chronic exposure to metals has detrimental effects on attention, executive function, mental flexibility and cognitive efficiency.

Analysis of Indium and Tin in Different Scrap Liquid Crystal Display Glass by Heavy Metal Digestion Method

Disposing of liquid crystal display (LCD) waste has significant effects on the environment, human and animal health, and metal resources by extension if inappropriately treated. In this study, we have developed a process for the separation of indium–tin oxide (ITO) glass from the LCD panel and evaluated the best digestion process for the analysis of In and Sn from ITO glass. The digestion process of scrap LCD in this work involves the separation of the polarizing film from ITO glass by environmentally friendly cold thermal shock method with liquid nitrogen, the removal of liquid crystals between the ITO glass substrates by ultrasonic cleaning, and the analysis of In and Sn from ITO glass by acid digestion method with a suitable reagent. Various brands of scrap LCDs were treated with six different digestion methods to determine In and Sn concentrations. The result of this study indicates that aqua-regia digestion procedure was the best method for the analysis of In and Sn. The concentrations of In and Sn in various brands of LCDs were in the range of 233–332 mg/kg and 43–421.5 mg/kg, respectively. Further, the analysis of In and Sn metals at different locations of the same scrap LCD was also carried out and it was observed that the concentrations of these metals (In—0.0278–0.0369% and Sn—0.0033–0.0078%) were significantly similar, with slight variations in their percentages.

Accumulation of transition metals and metalloids in sulfidized stromatolites of the 3.48 billion–year–old Dresser Formation, Pilbara Craton

Stromatolites of the ~3.48 billion–year–old Dresser Formation (Pilbara Craton, Western Australia) provide some of the oldest convincing evidence of life on Earth. Here, we augment previous evidence with a detailed investigation of the concentrations and distributions of various transition metals (Cr, Mn, Co, Ni, Cu, Zn, Mo, Se, Ag, Sn, Au, Hg, and Pb) and metalloids (As, Sb, and Te) in unweathered samples of strongly sulfidized stromatolites from drill cores. High–resolution elemental mapping and in situ compositional analysis of sulfides (pyrite and sphalerite) show that these sedimentary and hydrothermally sourced elements are strongly concentrated in texturally distinctive, nano-porous pyrite enriched in autochthonous organic matter, which forms the major, petrogenetically earliest component of wrinkly laminated and digitate growth fabrics within the stromatolites. Repeated cyclic alternations of various transition metals and metalloids (most importantly Ni and Zn), plus the presence of disconformities and overgrowth relationships between wrinkly stromatolite laminae, suggest that these element accumulations were primarily established by depositional processes during continuous stromatolite formation. Because transition metals and metalloids generally have strong affinities for organic matter, and can play active roles in biochemical processes, we interpret these element accumulations in the Dresser Formation stromatolites to be the result of binding to organic matter of living microbial communities and/or dead biomass, and perhaps also microbial utilization. Collectively, our results show that the precise characterization of transition metal–metalloid concentrations and distributions can unveil element enrichment patterns suggestive of biological activity, even in some of Earth’s oldest stromatolites.

Electro-work hardening of metals induced by the athermal electromigration effect

Direct current stressing treatment has been proposed as an effective potential method to modify the microstructures and optimize the mechanical properties of metals. Two contributions that could give rise to variations in the microstructure and mechanical properties of metals are involved in the direct current stressing treatment: thermal effects from Joule heat generation and athermal effects from electron-lattice interaction. The present study, for the first time, provides direct evidence of the work hardening behavior of pure Sn metals induced by the athermal electromigration effect, which is referred to the “electro-work hardening.” The micro-hardness of the Sn strip increased for all of the current densities (4–7 × 103 A/cm2) and current stressing times (1 h and 6 h) that were investigated. The maximum micro-hardness increment achieved could be as high as 27.3% at 5 × 103 A/cm2 for 1 h as compared with the as-annealed Sn strip benchmark. The thermal benchmark experiment further evidences that the thermal Joule heating effect did not contribute to any variations in the micro-hardness, suggesting the predominant athermal effect of electromigration. The high-resolution transmission electron microscope lattice images further revealed a high volume of dislocations produced in the Sn matrix, which was responsible for the electro-work hardening behavior. The electro-work hardening mechanism incorporated in a direct current stressing treatment can be applied in metals without the need for macroscopic mechanical deformation pre-treatment, which is regarded as a non-deformation material treatment. This innovative method for inducing work hardening is considered to have great potential for applications in which products have already been shaped.

Study on heavy metals’ influence on buried cultural relics in soil of an archaeological site

ABSTRACT The protection of cultural relics in a chariot pit in the ancient ruins has become an important issue. In order to study the spatial distribution, speciation of heavy metals in soil at a cemetery where an ancient chariot was buried and the influence heavy metals have had on the cultural relics. Heavy metals in soil samples surrounding the cultural relic were analyzed via atomic absorption spectrometry (AAS) using a wet digestion method combined with a three-step sequential extraction procedure. Results for seven heavy metals (Cu, Pb, Zn, Cr, Fe, Mn and Sn) and the speciation of six heavy metals (Cu, Pb, Zn, Cr, Fe and Mn) indicated that their contents exceeded local soil background values, indicating that the soil around the site had been contaminated to a certain degree. Analysis of their speciation showed that Mn mainly existed in the form of a reducible fraction in the soil, while the other elements were mainly in the form of a residual fraction. Correlation analysis showed that, except for the HOAc soluble fraction, a significant positive correlation existed between the content of the different forms and their total amounts. Heavy metals present in the soil surrounding the ancient relic predominantly influence the relic due to their related chemical reactions. In particular, copper and iron have a significant influence on corrosion of the cultural relics in this chariot pit.