High Bi Content Research Articles

Thermal hysteresis in the structural, magnetic and transport properties of hard magnetic MnBi films

In this work, the magnetic and transport properties associated with structural changes in MnBi hard magnetic films, with different Bi concentrations, were detailed. Two particular temperature regimes were studied. In the first place, at temperatures close to and below 260 °C (melting temperature of Bi in the samples) the resistance of the MnBi films underwent strong changes, showing thermal hysteresis, and depending on the amount of Bi in the samples. Thus, these resistance changes were attributed to the presence of unalloyed Bi in the samples. The maximum value ​​of the relative change of resistance, ΔRI/R(T2) (where ΔRI=R(T1)-R(T2) being T1 and T2 the temperatures just immediately below and above the structural transition) was around 180 % for the sample with the highest Bi concentration. Second, at temperatures above 260 °C, both the magnetic moment and the resistance of the samples also showed significant changes around the transition from the Low Temperature (α-MnBi) to the High Temperature (β-MnBi) phase. These changes, which were attributed to this structural transition, also presented thermal hysteresis and also depended on the Bi concentration of the samples. However, contrary to the previous situation, the samples with the lowest amount of unalloyed Bi, and consequently with the highest value of the MnBi volume fraction presented a maximum value of the ΔRII/R(T4) ratio, (where ΔRII=R(T3)-R(T4) being T3 and T4 the temperatures immediately above and below the structural transition from the β to the α MnBi phase) this magnitude reaching a maximum value of 25 % for the sample with the lowest Bi content.

Optimizing the thermoelectric performance of Bi-Sb-Te thin films through compositional engineering

The objective of the present investigation was to systematically investigate the structural and thermoelectric (TE) properties of BixSb2-xTe3 thin films with varying content of Bi. We investigated the impact of different atomic percentages of Bi (4, 6, 8 at. %) on the properties of carrier transport and TE performance. In general, the Seebeck coefficient remained consistent across the thin films. For the 8 at. % Bi thin film, the Seebeck coefficient and electrical conductivity were measured at 230 μV/K and 730 S/cm, respectively, at room temperature. These values were more than 20 times greater than the electrical conductivity observed in the thin films with compositions of 6 and 4 at. % Bi. As a result, the Bi-Sb-Te compound exhibited a TE power factor (PF) of 38x10−4 W/mK2 at 40 °C, surpassing the PFs observed in previous compositions. The analysis of surface microstructure, combined with atomic force microscopy and Kelvin probe microscopy images, revealed that the transport of carriers in films with high Bi content was impeded by the size of particles and scattering sites. On the other hand, an augmentation in Bi content promoted the transfer of charge through crystalline regions, hence improving the mobility of carriers and the total electrical conductivity. The aforementioned results emphasize the significant influence of Bi content on the electrical properties of semiconductors and demonstrate the effectiveness of compositional engineering based on Bi content in the development of TE materials with superior performance. The present study investigates the influence of Bi content on the electrical properties of Bi-Sb-Te thin films, demonstrating that compositional adjustments based on Bi content can impact the performance of TE materials. These findings contribute to the understanding of material optimization in the field of TE.

A good balance between the efficiency of ionizing radiation shielding and mechanical performance of various tin-based alloys: Comparative analysis

The Sn-Bix (x = 30, 40, 50, 60 and 70%) radiation shielding alloys were prepared using a melting process of the alloying material in a ceramic crucible at 200 °C for 120 min. The structural characterization for synthesized samples was carried out using X-ray Diffraction technique (XRD). The hardness and elastic properties of the prepared alloys was measured using micro-indentation creep technology and tensile test machine respectively. XRD pattern indicated that that the crystal size of Sn phase is lowered by increasing Bi concentration in the Sn matrix. The hardness decreases as the dwell time increases. The hardness values and elastic properties (in terms of young modulus) were significantly improved due to the decrease in the crystallite size by increasing Bi content. The stress exponent (n) value increase by increasing Bi content which mean that the mechanical properties improved due to increment of resistance. Furthermore, the produced alloys' nuclear shielding ability was investigated. The μm values were calculated using MCNP simulation code and XCOM software over a broad energy range of 0.015 MeV–15 MeV with good agreement between them. Several characteristics are estimated in order to properly understand the researched alloy's radiation and properties of neutron shielding. The findings showed that a higher Bi concentration causes the crystal size to decrease, improving the radiation shielding and mechanical qualities. The alloy Sn-70% Bi has a maximum increase of vicker hardness, tensile strength, and young's modulus. The findings of the shielding parameters indicate that the alloys under study are efficient gamma shielding materials in contrast to other typical shielding materials and materials that have been examined recently. The highest mechanical efficiency and rather strong gamma-ray shielding capabilities are found in the Sn–70Bi alloy. Owing to its ability to effectively balance mechanical performance and shielding, the Sn–70Bi are approved for use in radiation protection. In addition, when compared to all other manufactured alloys, typical neutron shielding materials, and recently investigated materials, the results further demonstrate that the Sn–70Bi alloy has the best neutron attenuation capability. Furthermore, in terms of mass stopping power (MSP) and projected range (PR), the Sn–70Bi alloy demonstrates the most effective attenuation for alpha particles (He+2) and protons (H+1). These results imply that the Sn–70Bi alloy provide superior mechanical performance and nuclear shielding for a range of applications including industrial, medicinal, and nuclear waste storage in the future.

Electrodeposition of bismuth, tellurium and bismuth telluride through sub-10 nm mesoporous silica thin films

Templated electrodeposition is an efficient technique for the bottom-up fabrication of nanostructures and can effectively control the size and shape of the electrodeposits. Here, mesoporous silica thin films with highly ordered mesopores and a regular three-dimensional mesostructure were synthesised as templates for electrodeposition. The mesoporous silica films have small mesopores (∼8 nm) and complex mesopore channels (Fmmm mesostructure with the [0 1 0] axis perpendicular to the substrate). Electrodeposition of bismuth, tellurium and bismuth-tellurium was investigated from electrolytes containing [NnBu4][BiCl4], [NnBu4]2[TeCl6] and [NnBu4]Cl dissolved in dry dichloromethane. Top-view SEM images showed Bi, Te and Bi doped-Te nanoparticles in the mesopores and cross-section SEM showed there were a few Te nanowires, in addition to the particle aggregations on the surface. This is a promising observation as it demonstrates the possibility of preparing sub-10 nm nanowires by templated electrodeposition even though the deposits are not uniformly electrodeposited in all the mesopores. EDX shows the deposited Bi-Te nanoparticles were tellurium-rich, XRD shows they were trigonal tellurium (ICSD 65692). A variety of parameters including the choice of pulsed electrodeposition conditions and [NnBu4][BiCl4] concentration (2.25 mM and 3 mM) were investigated in order to control the composition of the deposit. All samples prepared by pulsed electrodeposition showed very low Bi:Te ratio (Bi/Te<0.02), whereas samples deposited for 5 min at −0.6 V achieved high Bi content (Bi/Te=0.49).

Bismuth drug-inspired ultra-small dextran coated bismuth oxide nanoparticles for targeted computed tomography imaging of inflammatory bowel disease

Bismuth (Bi)-based computed tomography (CT) imaging contrast agents (CAs) hold significant promise for diagnosing gastrointestinal diseases due to their cost-effectiveness, heightened sensitivity, and commendable biocompatibility. Nevertheless, substantial challenges persist in achieving an easy synthesis process, remarkable water solubility, and effective targeting ability for the potential clinical transformation of Bi-based CAs. Herein, we show Bi drug-inspired ultra-small dextran coated bismuth oxide nanoparticles (Bi2O3-Dex NPs) for targeted CT imaging of inflammatory bowel disease (IBD). Bi2O3-Dex NPs are synthesized through a simple alkaline precipitation reaction using bismuth salts and dextran as the template. The Bi2O3-Dex NPs exhibit ultra-small size (3.4 nm), exceptional water solubility (over 200 mg mL−1), high Bi content (19.75 %), excellent biocompatibility and demonstrate higher X-ray attenuation capacity compared to clinical iohexol. Bi2O3-Dex NPs not only enable clear visualization of the GI tract outline and intestinal loop structures in CT imaging but also specifically target and accumulate at the inflammatory site in colitis mice after oral administration, facilitating a precise diagnosis and enabling targeted CT imaging of IBD. Our study introduces a novel and clinically promising strategy for synthesizing high-performance Bi2O3-Dex NPs for diagnosing gastrointestinal diseases.

Characterization of deep ore-forming fluid in the Zhaoxian gold deposit within the Jiaodong gold province: insights from quartz vein fluid inclusion, in-situ trace element analysis, and S isotopic composition in pyrite

The Jiaodong gold province, situated in the southeastern margin of the North China Craton, is globally renowned for its substantial gold reserves exceeding 5,000 tonnes. The Zhaoxian gold deposit is part of the significant Jiaojia gold belt within the Jiaodong gold province. Fieldwork has identified four distinct stages of ore formation in this study: an early barren quartz vein stage (Stage 1) containing fine-grained pyrite; a gold-bearing stage (Stage 2) consisting of quartz, pyrite, and native gold; a polymetallic sulfide-rich stage (Stage 3) comprising quartz, polymetallic sulfides, and native gold; and a late-stage (Stage 4) primarily composed of quartz and calcite with minimal pyrite content. We conducted fluid inclusion analysis using microthermometry and Raman spectroscopy techniques to examine the fluid characteristics. In-situ analysis of trace elements in pyrite was performed to investigate the fluid composition and evolution. Additionally, we determined the sulfur isotope composition in pyrite to analyze the source of sulfur. Our findings indicate that the ore-forming fluid in the Zhaoxian gold deposit belongs to a medium-to-low-salinity H₂O-NaCl-CO₂-CH₄ system. Fluctuations in Au and As concentrations observed along with oscillating zones and sulfide inclusions during Stage 2 suggest potential fluid boiling processes occurring during mineralization. High concentrations of Ag, Cu, Zn, Cd, In, Pb, and Bi without oscillating zones during Stage 3 imply precipitation of polymetallic sulfides under stable fluid conditions. The δ34S values observed in the Zhaoxian gold deposit are slightly higher than those found in granitoids from other areas within Jiaodong but similar to those seen in other deposits within the Jiaojia gold belt region. In conclusion, magmatic-hydrothermal ore-forming fluids were involved along with significant fluid-rock interaction during metallogenic processes of the Zhaoxian gold deposit.

Photoinduced transformations in (As1–xBix)2S3 glass observed by Raman spectroscopy

AbstractRaman spectra of (As1–xBix)2S3 glass samples with x ≤ 0.2 measured at the excitation with above‐bandgap (532 nm) laser light at a relatively low power density (Pexc = 4 kW/cm2) clearly confirm the amorphous character, thereby markedly extending the known compositional interval of existence of the (As1–xBix)2S3 glass previously known (x ≤ 0.06). Spectra measured at an increased Pexc (40 kW/cm2) reveal a photostructural transformation in the illuminated area of the glass leading to an additional contribution of Bi–S bonds as well as to an increasing number of cage‐type As4S4 units with homopolar As–As bonds. A number of new features in a broad range up to about 1,000 cm−1, which emerge in the Raman spectra of the (As1–xBix)2S3 glasses with high (x ≥ 0.14) Bi content and increase in intensity with the exposure time, are related to a photochemical transformation, namely, oxidation of arsenic and sulphur on the (As1–xBix)2S3 glass surface with formation of units containing arsenate AsO43− and sulphate SO42− ions. These processes are irreversible and occur only in the presence of a sufficient amount of bismuth.

The Source, Mobility and Fate of Bismuth (Bi) in Legacy Mine Waste, Yxsjöberg, Sweden

The usage of bismuth (Bi), a critical and strategic raw material, has increased in the last 10 years. At present, the knowledge of Bi geochemistry is too limited to develop accurate mine waste and water management strategies to prevent environmental impact. Therefore, its geochemistry was studied in historical tailings in Yxsjöberg, Sweden. Intact tailings cores and shore samples were geochemically and mineralogically analyzed. Groundwater was sampled between 2016 and 2021 and analyzed for 71 elements and (SO4, F, Cl). The results were correlated with metals and dissolved organic matter (DOC), which have been previously published. The total concentrations, sequential extraction and scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM–EDS) mapping indicated that Bi had been mobilized from the primary mineral bismuthinite (Bi2S3). In the oxidized tailings from both the cores and shore, Bi was hypothesized to have adsorbed to iron (Fe) (hydr)oxides, which prohibited high concentrations of Bi leaching into the groundwater and surface water. Dissolved Bi in groundwater was significantly correlated with DOC. In surface water, dissolved Bi was transported more than 5 km from the tailings. This study indicates that Bi can become mobile from legacy mine waste due to the oxidation of bismuthinite and either be scavenged by adsorption of Fe (hydr)oxides or kept mobile in groundwater and surface water due to complexation with DOC.

Tunable light emission of Bi and V-doped borosilicate glasses for application in white light-emitting diodes

Melt-quenched borosilicate glasses, co-doped with Bi and V ions, exhibited broad visible spectrum emissions. Bi ions primarily existed as Bi3+, acting as network modifiers, lowering the glass transition temperature linearly with increasing Bi content. V5+ ions adopted tetrahedral coordination as [VO4]3- units. Photoluminescence of Bi ions is shifted from blue to longer wavelengths with higher Bi content, associated with the stabilization of Bi2+ and the presence of Bi3+ in different local environments. Combined with V ions, the glasses emitted light covering the entire visible spectrum, offering the potential for white LED applications with correlated color temperatures ranging from 6135 to 4010 K. The highest QY was 11.9 and 8.0 % upon excitation at 325 and 340 nm.

Plasmonic active “hot carriers” facilitating photocatalytic CO2 reduction and 2,4-dichlorophenol oxidation over Bi-deposited BiOBr with abundant oxygen vacancies

Plasmon-induced semiconductors have attracted considerable interest in photocatalysis. Herein, this work describes the tremendous potential of plasmonic photocatalysts in photocatalytic CO2 reduction and 2,4-DCP oxidation. BiOBr with high concentrations of plasmonic Bi and oxygen vacancies were synthesized by reductive propylene glycol and lignin. Bi0.908O0.862Br exhibited excellent photocatalytic efficiency of CO2 reduction (CO: 62.94 μmol g-1h−1) and 2,4-DCP oxidation (94.65 %), which was attributed to the surface plasmon resonance (SPR) effect based on the experiments and DFT theoretical simulation. As demonstrated, the SPR effect induced by plasmonic Bi and oxygen vacancies can not only rationally enlarge the light-responsive region, but also induce abundant “hot carriers” and photothermal effect, eventually lowering the energy barriers of photocatalytic reactions. Meanwhile, a bulk-to-surface charge transfer channel was created to realize the high separation efficiency of photogenerated carriers. Moreover, plasmonic Bi and oxygen vacancies could act as adsorption sites to promote the activation of CO2 and O2 substrates. This work provides a new perspective for designing plasmonic photocatalysts to realize environmental remediation and energy conversion.

The influence of Bi2O3 on structural and enhancing physical properties of Li2O–Fe2O3–In2O3–P2O5 glasses

Glasses based on the Li2O–Fe2O3–In2O3–Bi2O3–P2O5 system were prepared as potential low-melting sealing glasses. The modifications of the glass structure were characterized by means of XRD and FTIR spectroscopy as a function of Bi2O3/P2O5 substitutions. The bulk density, together with other parameters, was also calculated. The amorphous nature was observed for all glass samples except the highest Bi-content. FTIR and Raman spectrum reveal that the prompt polymerization of the phosphate chains by increasing the Bi2O3 content and forming P–O–Bi bonds and the existence of different structural groups FeO6, FeO4, BiO6, PO4, PO3 and PO. The dilatometry measurements showed an increase in both transition (Tg) and softening (Ts) temperatures with Bi-content. Conversely, coefficients of thermal expansion decreased from 120 × 10−7/°C to 80 × 10−7/°C. The dissolution rate of the prepared glasses was tested, and the results showed significantly improved glass stability. Finally, the obtained glasses have a suitable working temperature, suitable thermal expansion values, and good thermal and chemical stability, making them a prospective candidate for low-temperature sealing materials.

Architecting Bismuth Molybdate Nanoparticles with Abundant Oxygen Vacancies and High Bismuth Concentration for Efficient N2 Electroreduction to NH3

AbstractN2 electroreduction reaction (NRR) enables an eco‐friendly NH3 synthesis under mild conditions, which is regarded as a carbon‐neutral alternative technology to the traditional Haber–Bosch process. However, its practical applications are seriously impeded by the difficulty in N2 adsorption and activation over catalysts, as well as the competing hydrogen evolution reaction (HER). In this work, a novel bismuth molybdate nanocatalyst with sufficient oxygen vacancies and high Biconcentration (41.9 at%), BiMoO‐OVs, is synthesized and demonstrated as an excellent NRR electrocatalyst. Benefiting from synergistic effect of the adequate Bi active centers with inert HER activity provided by the high concentration of Bi, and the reinforced N2 adsorption and activation ability of oxygen vacancies, the as‐synthesized BiMoO‐OVs presents a high Faradaic efficiency of 16.38% with a NH3 yield rate of 3.65 µg h−1 cm−2 at −0.4 V (vs RHE) in neutral electrolyte, which outperforms those of most Bi‐based NRR nanocatalysts. Noticeably, it also presents excellent electrochemical durability for at least 24 h. The present work provides a simple and effective strategy for designing low‐cost and high‐performance Bi‐based catalysts.

Structural evolution and thermoelectric properties of Mg3SbxBi2−x thin films deposited by magnetron sputtering

Mg3Bi2-based compounds are of great interest for thermoelectric applications near room temperature. Here, undoped p-type Mg3SbxBi2−x thin films were synthesized using magnetron sputtering (three elemental targets in Ar atmosphere) with a growth temperature of 200 °C on three different substrates, namely, Si as well as c- and r-sapphire. The elemental composition was measured with energy-dispersive x-ray spectroscopy and the structure by x-ray diffraction. The electrical resistivity and the Seebeck coefficient were determined under He atmosphere from room temperature to the growth temperature. All samples are crystalline exhibiting the La2O3-type crystal structure (space group P-3m1). The observed thermoelectric response is consistent with a semiconductive behavior. With increasing x, the samples become more electrically resistive due to the increasing bandgap. High Bi content (x &amp;lt; 1) is thus beneficial due to lower resistivity and a higher power factor near room temperature. Thermoelectric thin films synthesized at low temperatures may provide novel pathways to enable flexible devices on polymeric and other heat-sensitive substrates.

Study of Bond Formation in Ceramic and Composite Materials Ultrasonically Soldered with Bi-Ag-Mg-Type Solder.

This research aimed to study a Bi-Ag-Mg soldering alloy and the direct soldering of Al2O3 ceramics and Ni-SiC composites. Bi11Ag1Mg solder has a broad melting interval, which mainly depends on the silver and magnesium content. The solder starts to melt at a temperature of 264 °C. Full fusion terminates at a temperature of 380 °C. The microstructure of the solder is formed by a bismuth matrix. The matrix contains segregated silver crystals and an Ag (Mg, Bi) phase. The average tensile strength of solder is 26.7 MPa. The boundary of the Al2O3/Bi11Ag1Mg joint is formed by the reaction of magnesium, which segregates in the vicinity of a boundary with a ceramic substrate. The thickness of the high-Mg reaction layer at the interface with the ceramic material was approximately 2 μm. The bond at the boundary of the Bi11Ag1Mg/Ni-SiC joint was formed due to the high silver content. At the boundary, there were also high contents of Bi and Ni, which suggests that there is a NiBi3 phase. The average shear strength of the combined Al2O3/Ni-SiC joint with Bi11Ag1Mg solder is 27 MPa.

Shear Fatigue Analysis of SAC-Bi Solder Joint Exposed to Varying Stress Cycling Conditions

Sn–Ag–Cu (SAC) solder alloys are frequently used in electronic assemblies, and their fatigue resistance under various stress cycles is a significant factor that influences the reliability of electronics. Three distinct SAC-based solder joints (SAC305, SAC-Q, and SAC-R) were examined under various stress amplitude cycling and ambient temperature conditions. The stress on individual solder joints alternates between mild stress (MS) and harsh stress (HS) until complete failure. The hysteresis loop was investigated and compared under various stress amplitude cycles. In addition, the morphology and microstructure of the solder joints were analyzed. The results revealed that SAC-Q, with high Bi and Ag content, demonstrated superior fatigue resistance compared with SAC305 and SAC-R under varying stress amplitude conditions. The inelastic work increased with each change between the MS and HS cycles. SAC-Q exhibited solid solution and precipitate hardening mechanisms through the presence of bismuth (Bi) and silver (Ag) in the tin (Sn) lattice. At the same time, SAC305 showed Ag3Sn precipitates hardening, whereas SAC-R, with no Ag, demonstrated solid solution hardening exclusively. Different failure mechanisms were observed depending on the alloy composition and strain rate. SAC305 and SAC-R exhibited ductile failure. However, SAC-Q experienced an interfacial fracture. Excessive Bi may lead to the embrittlement of solder joints and a change in the failure mechanisms during mechanical testing.

Trace Element Composition of Molybdenite: Deposit Type Discrimination and Limitations

Molybdenite is a common sulfide hosting many trace elements. Trace elements in molybdenite from individual deposits have been widely used to constrain the source and conditions of ore-forming fluids. However, the relationship between the trace element composition of molybdenite and deposit types has not been well investigated from a large dataset. Here, simple statistics and partial least squares–discriminant analysis (PLS-DA) were used to determine whether different types of deposits can be distinguished by trace elements in molybdenite and what factors control the variations in trace element composition based on published laser ablation ICP–MS data. Molybdenite from porphyry deposits is separated from that from quartz veins, greisen Sn–W, granite vein Mo, and granodiorite Mo deposits. The former is characterized by relatively high Re, Cu, Ag, Se, Pb, Bi, and Te contents, whereas the latter has higher Ni, Co, Sn, Sb and W contents. Molybdenite from the quartz vein Au ± W deposits (Au-dominated), and porphyry Cu–Au–Mo (moderate Au) are separated from other deposits without gold due to positive correlations with Au, Sb, Te, Pb, and Bi for the former. Assemblages of Au–Sb–Te–Pb–Bi in molybdenite are thus useful to discriminate as to whether deposits contain gold and the degree of gold mineralization. Higher oxygen fugacity is responsible for the relative enrichment of W in molybdenite from greisen Sn–W deposits, whereas lower oxygen fugacity results in the relative enrichment of Re in molybdenite from porphyry Cu ± Mo ± Au and Mo ± Cu ± Au deposits. There are some limitations to using molybdenite as an indicator mineral because of the complex occurrences of elements in molybdenite, large compositional variations within a specific deposit type, and an imbalanced dataset. To develop molybdenite as an indicator mineral tool, further work should be carried out to overcome these limitations. This study provides an attempt to classify deposit types using molybdenite trace elements and has important implications for ore genesis research and mineral exploration.

ГЕОЛОГИЧЕСКАЯ ПОЗИЦИЯ И ЗОЛОТО-ВИСМУТОВАЯ МИНЕРАЛИЗАЦИЯ МЕСТОРОЖДЕНИЯ НАМОВСКОЕ (ЮЖНЫЙ СИХОТЭ-АЛИНЬ, ДВ РОССИИ)

Based on the results of a comprehensive geological and mineralogical-geochemical study of the ores of the Namovskoye deposit, new data have been obtained that reflect the specifics of mineralization. The ores of the deposit were formed in close connection with the manifestation of Early Cretaceous monzonitoid magmatism against the background of active left-hand movements along the Central Sikhote-Alin fault. U-Pb dating of the ore-bearing dike yielded an age of 103 Ma. The ores of the deposit, in addition to native gold, contain high concentrations of Ag, Bi, and Cu. A variety of bismuth minerals were found in the ores: sulfide (bismuthinite), telluride (hedleyite), sulfotellurides (tetradymite, joseite-А and joseite-В), Ag sulfobismuthite (matildite), Pb-Bi sulfosalts (aschamalmite, cannizzarite, cosalite, lillianite, nuffieldite, galenobismuthite), an intermetallic compound of gold (maldonite), and native bismuth. Silver minerals were also found: chloride (cerargyrite), sulfide (acanthite), and telluride (hessite). The typomorphic features of ore minerals and the geological structure of the Namovskoye deposit assign it to the gold deposits formed in a transform continental margin setting. A mantle source of ore mineralization is suggested.

Influence of Ca addition on microstructural characteristics and mechanical properties of Mg–5Bi–3Al alloy extruded at extremely high speed

In this study, the effects of Ca addition on the microstructural characteristics and mechanical properties of a Mg–Bi–Al alloy extruded at high speed were investigated by analyzing extruded Mg–5Bi–3Al (BA53) and Mg–5Bi–3Al–0.5Ca (BAX530) alloys fabricated at a speed of 70 m/min. The homogenized BA53 billet contained fine and coarse Mg3Bi2 particles, whereas the homogenized BAX530 billet contained only coarse Mg2CaBi2 particles. Both alloys exhibited fully recrystallized microstructures and similar grain sizes upon extrusion at the high speed. Ca-induced texture weakening did not occur in the extruded BA53 alloy because the added Ca was completely consumed during the formation of Mg2CaBi2 particles. Abundant fine Mg3Bi2 particles were uniformly distributed throughout the extruded BA53 alloy, whereas the extruded BAX530 alloy contained coarse Mg2CaBi2 particles. The addition of Ca to the BA53 alloy decreased the tensile strength by ∼10%, primarily due to weakened particle hardening. Under tension, an increased number of {10–11} contraction and {10–11}-{10–12} double twins were formed and a larger number of twin variants were activated in the extruded BAX530 alloy than in its Ca-free counterpart; consequently, Ca addition enhanced the tensile elongation of the extruded alloy by ∼21% via suppressing the local strain concentration. Thus, the addition of a small amount of Ca can enhance the tensile ductility of high-speed-extruded Mg–Bi-based alloys with high Bi contents without altering the alloy texture.

Thermoelectric Performance of Sn and Bi Double-Doped Permingeatite

In this study, mechanical alloying was performed to synthesize permingeatite Cu3Sb1-x-ySnxBiySe4 (0.02 ≤ x ≤ 0.06 and 0.02 ≤ y ≤ 0.04) doped with Sn and Bi. Hot pressing was subsequently conducted to achieve dense sintered bodies. When the Bi content was constant, the carrier concentration increased with the Sn content, but the mobility decreased owing to the increased carrier concentration. In contrast, when the Sn content was constant, the carrier concentration and mobility were not significantly affected by the Bi content. Higher electrical conductivity was observed in specimens with a higher Sn content or lower Bi content; consequently, Cu3Sb0.92Sn0.06Bi0.02Se4 exhibited the highest electrical conductivity. The Seebeck coefficient increased with temperature, and it is inferred that the permingeatite doped with Sn/Bi does not undergo an intrinsic transition until 623 K. In contrast to the electrical conductivity, a higher Seebeck coefficient was obtained in the specimens with a lower Sn content or higher Bi content; consequently, Cu3Sb0.94Sn0.02Bi0.04Se4 exhibited the highest Seebeck coefficient. Cu3Sb0.92Sn0.06Bi0.02Se4 exhibited the maximum power factor, depending on the electrical conductivity and Seebeck coefficient. The electronic thermal conductivity was not significantly affected by temperature, but the lattice thermal conductivity decreased as the temperature increased. However, the thermal conductivity decreased with increasing temperature. Sn doping effectively reduced the lattice thermal conductivity, whereas Bi doping effectively reduced the electronic thermal conductivity; consequently, Cu3Sb0.94Sn0.02Bi0.04Se4 exhibited the lowest thermal conductivity. Finally, the highest dimensionless figure-of-merit of 0.75 was achieved at 623 K by Cu3Sb0.92Sn0.06Bi0.02Se4.

Trace elements and in situ sulfur isotopes of pyrite from the Baiyunpu Au deposit in central Hunan, South China: Implications for gold mineralization

The Central Hunan metallogenic province, located in the southeastern part of the Yangtze Block, South China, is one of the most important Sb–Au metallogenic belts in China. The Baiyunpu gold deposit is one of the important Carlin‐type gold deposits occurring in Devonian sedimentary strata in Central Hunan. Optical microscopy and in situ laser ablation (multi‐collector) inductively coupled plasma mass spectrometry (LA‐[MC]‐ICP‐MS) are used to determine the texture, trace element compositions and sulfur isotope for pyrites from the pre‐ore and syn‐ore stages to constrain the sources of reduced sulfur and metals and the mechanism of gold precipitation. Four generations of pyrite were identified by petrography and pyrite compositions. Pre‐ore Py1 is characterized by relatively low concentrations of As, Au, Sb and Cu and high concentrations of Co, Ni, Bi and Pb. Py1 has positive δ34S values of 6.5–10.1‰, which we ascribe to a bacterial reduction of marine sulfate in closed marine systems, or from weak Rayleigh fractionation by bacterial sulfate reduction (BSR) or thermochemical sulfate reduction (TSR) during sedimentary‐diagenetic processes. Pre‐ore Py2 presents as rims of Py1 and contains relatively high As (69,530 ppm), Sb (123.2 ppm) and low Au (4.89 ppm). Compared with Py2, Py3 has relatively high Au (194.4 ppm) and Cu (24.6 ppm) and low As (40,801 ppm). We interpret that Py2 and Py3 could have precipitated from an Au‐free but As‐rich early hydrothermal fluids or from low‐Au and As‐rich fluids at the beginning of the ore stage. The δ34S values of Py2 and Py3 in the Baiyunpu deposit are concentrated in a narrow range of −1.2 to 1.2‰, suggesting the involvement of magmatic sulfur. Syn‐ore pyrites (Opy) are enriched in Au (517.8 ppm), As (39,719 ppm), Cu (261.9 ppm) and Sb (171.4 ppm). Irregular boundaries between Py1 and Opy suggest that the replacement may have been important for the formation of pyrites at the syn‐ore stage. The variation of As concentration in Opy1, Opy2 and Opy3 appear to have recorded fluctuations in the chemical composition of ore fluids. The δ34S values of Opy (0.1–5.9‰) are slightly higher than Py2 and Py3 due to mixing with sedimentary components with elevated δ34S values in late‐stage hydrothermal fluids. Profile analyses for Baiyunpu auriferous pyrite grains suggest that Au was positively correlated with Cu, but not with As. The correlation between Au, Cu and As in Opy may be dominated by their concentrations of ambient evolving fluids.