Molten Bi Research Articles

Au-Bi-Te(-Cu) Mineralization in the Wawa Gold Corridor (Ontario, Canada): Implications for the Role of Bi-Rich Polymetallic Melts in Orogenic Au Systems

The Wawa Gold Corridor, a series of Archean orogenic Au deposits in the Michipicoten greenstone belt, Canada, comprises two styles of Au mineralization: (1) syn-deformation gold associated with pyrite and arsenopyrite; and (2) late- to post-deformation gold associated with chalcopyrite and Bi-Te(-S) phases. Through petrographic and mineral–chemical analysis, it was determined that gold in the latter assemblages precipitated from Bi-rich polymetallic melts during hydrothermal overprinting of the earlier Au-As-S mineralization; this event was likely driven by the emplacement of Archean lamprophyres. The formation and evolution of these melts was governed by fluid–pyrite reaction interfaces, where the bulk composition of the melts was broadly controlled by the trace-element chemistry of the sulphide minerals in the local host rocks. This suggests that the melt-formation event involved mobilization of existing metal endowments related to early Au events, rather than addition of new Au, Bi, and Te. Thus, the deposition of high-grade Au by Bi-rich melts was dependent on pre-existing sulphide mineralization, both as a source of metals and as micro-environments that stabilized the melts. The paragenesis documented in the Wawa Gold Corridor (i.e., early hydrothermal Au-As-S mineralization and late melt-related Au-Bi-Te mineralization) has been previously recognized in numerous other orogenic and non-orogenic Au deposits. Herein, it is suggested that this apparent consistency in the timing of melt events across multiple systems probably reflects the physicochemical conditions (i.e., fO2-aH2S) of orogenic fluids being incompatible with molten Bi. Bi-rich polymetallic melts are hence unlikely to form primary Au mineralization in orogenic systems but can, however, have a significant impact on the ultimate deposit-scale distribution of Au via secondary mobilization and enrichment.

Liquid Bi–Pb and Bi–Li alloys: Mining thermodynamic properties from ab-initio molecular dynamics calculations using thermodynamic models

Ab-initio molecular dynamics (AIMD) simulations, coupled with thermodynamic models, can be used to extract thermodynamic properties such as mixing enthalpies, activities and free energies in the liquid state, even when the published AIMD data provide no direct access to such information. In order to demonstrate this fact, in the present work we used AIMD structural data from the literature on molten Bi–Pb and Bi–Li alloys as raw material for describing thermodynamic properties. The analytical description is divided in two parts. In the first part, we employ the Bethe-Peierls (quasi-chemical) approximation in the disordered state to describe the thermodynamics of Bi–Pb molten alloys, since it is verified experimentally that this binary liquid is practically a regular solution. The agreement with experimental activity and mixing enthalpy measurements from the literature is excellent. Conversely, the same approach cannot be applied to liquid Bi–Li alloys, in which the presence of transient clusters with composition around 75 at% Li prevents the use of the Bethe-Peierls model. Therefore, in the second part of the work, we used the original and a modified version of the Quasi-Lattice model to successfully describe the AIMD data and accordingly write the thermodynamic properties of liquid Bi–Li alloys. Also in this case, it is seen that a good agreement was reached between the results derived from AIMD calculations and experimental thermodynamic measurements from the literature. We conclude that AIMD calculations for liquid melts, although computationally expensive, can be very accurate, and therefore could be applied in thermodynamic descriptions, with an appropriate thermodynamic model, even when the original AIMD calculations were not explicitly concerned with thermochemical data.

Solution-Liquid-Solid Growth of CuInTe2 and CuInSe xTe2- x Semiconductor Nanowires.

Ternary CuInTe2 and quaternary CuInSe xTe2- x nanowires were successfully synthesized for the first time by a solution-liquid-solid (SLS) mechanism. Crystalline, straight, and nearly stoichiometric CuInTe2 and CuInSe xTe2- x nanowires were readily achieved by using the molecular precursors and in the presence of molten Bi nanoparticles and coordinating capping ligands. The temperature and reactant order-of-addition of this reaction strongly affected the composition of the reaction product and the morphology obtained. These CuInTe2 and CuInSe xTe2- x nanowires are outstanding light absorbers from the near-IR through the visible and ultraviolet spectral regions and, thereby, comprise new soluble and machinable "building blocks" for applications in solar-light utilization.

Enhancement of melt-spun process Bi–Ag lead-free solder for high temperature applications

The enhancement of lead free solders has emerged as one of the most important issues in the electronics assembling industries. Bi–Ag hypo and eutectic alloys have been considerd as one of the lead free solders that can replace the Pb–Sn solder for high temperature applications. This study investigates the effect of various compositions of silver on the mechanical, thermal and electrical properties of the melt-spun process Bi–Ag hypo and eutectic alloys was directionally solidified using copper wheel technology.The microhardness (Hv), creep resistance were measured from solidified ribbons.The results showed that presence of α-Bi phase, Ag99.5Bi0.5 (with a cubic structure Fm-3m) and Ag0.97Bi0.03 (with a cubic structure Fm-3m) embedded in Bi matrix. Furthermore, the eutectic composition Bi—2.5 wt% Ag shows the more regular microstructure than hypo eutectic composition. It is also concluded that the solderability of solder is significantly imported due to the surface tension of molten Bi–Ag lead-free solder decreases with the Ag content. The obtained results show a surprising desirable decrease in melting temperature with increasing Ag from 269 to 261 °C. Also, it was found that the eutectic composition Bi—2.5 Ag exhibit good mechanical properties superior to hypo-eutectic composition.

Growth kinetics of bismuth nickel intermetallics

Bismuth (Bi)-based systems are of great interest as it is considered to potentially replace high lead (Pb)-content solders used in high temperature electronics. In particular, molten Bi strongly reacts with Ni to form higher melting point intermetallic compounds (IMCs) via transient liquid phase (TLP), which can offer a joining method alternative to the traditional solder approach. A fundamental understanding of nucleation and growth of intermetallic phases is crucial to create a reliable joint. Two intermetallic phases form between Bi and Ni (Bi3Ni, BiNi). In this study, growth kinetics for Bi3Ni and BiNi was investigated, both of which show a parabolic growth behavior. Bi3Ni exhibits rapid growth and apparent activation energy of 65.5 kJ/mol at lower temperatures (from 160 to 240 °C) and of 132.9 kJ/mol at higher temperatures (> 240 °C), where the transition is likely due to a viscous-flow nature near melting temperature of Bi. On the other hand, BiNi grows at a later stage with a slower rate with the apparent activation energy of 125.6 kJ/mol (from 260 to 340 °C). In addition, based on the formation sequence and growth direction of these IMCs, interdiffusion coefficients for each of these IMCs were determined. Micro-hardness tests show that Bi3Ni is softer and more brittle than BiNi.

Synthesis, Crystal and Electronic Structure of the Titanium Bismuthides Sr5Ti12Bi19+x, Ba5Ti12Bi19+x, and Sr5–δEuδTi12Bi19+x (x ≈ 0.5–1.0; δ ≈ 2.4, 4.0)

Crystals of the new ternary bismuthides AE5Ti12Bi19+x (AE = Sr, Ba) and Sr5–δEuδTi12Bi19+x (δ ≈ 2.4, 4.0; x ≤ 1.0) were grown using an excess of molten Bi as a flux. The title compounds crystallize in the cubic non‐centrosymmetric space group P43m and are structurally related to the antimonides Ba5M12Sb19+x (M = Ti, V, Nb). The crystal structure features Ti atoms stuffed in the γ‐brass‐like sub‐lattice made of AE (AE = Sr, Ba, Eu) and Bi atoms. The arrangement of the AE atoms, on its own, represents a framework consisting of interconnected regular tetrahedra and octahedra. Another notable attribute of the AE5Ti12Bi19+x structure is the disordered Bi moiety located at the center of the unit cell and showing homoatomic Bi–Bi bonding. Electronic structure calculations and electrical resistivity measurements indicate metallic behavior of the new bismuthides. Magnetization measurements on samples of Sr5–δEuδTi12Bi19+x show paramagnetic behavior consistent with the 2+ ground state for Eu. The measurements also confirm no magnetic ordering down to 3 K, stemming from the geometrically frustrated exchange interactions of the Eu2+ cations.

Grain alignment due to magnetic-field annealing in MnBi:Bi nanocomposites

High-anisotropy arc-melted and field-annealed Mn100−xBix (x = 50–65) alloys have been investigated. Samples predominantly consist of low-temperature phase (LTP) MnBi and elemental Bi, where the LTP volume fraction and sample magnetization decrease with increasing x. All samples are hard ferromagnetic at room temperature and demonstrate a structural and magnetic phase transition at 630 K. For Mn35Bi65, the highest values for coercivity (4.6 kOe), magnetization remanence ratio (0.97), and energy product (4.9 MGOe) are measured at 540 K, near the melting point of bismuth. We explain the trend in magnetic properties as a consequence of c-axis alignment of MnBi grains facilitated by the molten Bi during magnetic field annealing.

Controlling Magnetic Ordering in Ca1–xEuxCo2As2 by Chemical Compression

To investigate the interplay between electronic structure and itinerant magnetism, Ca1–xEuxCo2As2 solid solutions (x = 0, 0.1, 0.3, 0.4, 0.5, 0.6, 0.65, 0.7, 0.9, 1.0) were prepared by reactions between constituent elements in molten Bi. All of the samples crystallize in the ThCr2Si2 structure type. The crystal structure refinement revealed the formation of Co vacancies, the concentration of which decreases as the Eu content increases. The Eu site exhibits mixed valence in all samples. X-ray absorption near-edge structure spectroscopy revealed that the average Eu oxidation state decreases from +2.17 at 0 < x ≤ 0.6 to +2.14 at x ≥ 0.65. The same borderline behavior is observed in magnetic properties. The substitution of Eu for Ca causes the transition from the antiferromagnetic (AFM) ordering of Co moments in CaCo2As2 to ferromagnetic (FM) ordering of Co moments in Ca1–xEuxCo2As2 with 0.1 ≤ x ≤ 0.6. At higher Eu content, AFM ordering of Eu moments is observed, whereas the Co sublattice exhibits only parama...

Energy storage materials with oxide-encapsulated inclusions of low melting metal

A composite energy storage material (ESM) with inclusions of a low-melting point metal encapsulated in protective metal oxide shells is prepared and characterized. ESM precursor is a metal matrix composite with metal oxide inclusions. Controlled redox reaction between the matrix and inclusions yields a composite with inclusions of an oxide encapsulated, easy to melt metal. Al/Bi2O3 nanocomposite thermites served as precursors for ESM with Al matrix and Bi inclusions encapsulated with Al2O3. Thermal and mechanical properties of the ESM were compared to those of reference binary Al/Bi and ternary Al/Bi/Al2O3 materials. The material containing encapsulated Bi inclusions stored energy by melting and solidifying Bi inclusions repeatedly. The inclusions did not drift upon heating; composite structure remained largely intact upon thermal cycling. Conversely, the structure of reference materials with similar compositions but without encapsulated Bi inclusions was not preserved upon thermal cycling. Molten Bi tended to separate from Al and form coarse network of inclusions. Upon cycling, Bi accumulated on surface of the material. Difference in mobility between encapsulated and non-encapsulated Bi inclusions caused differences in the mechanical properties of the composites. Materials with encapsulated Bi inclusions were much stronger and capable of retaining their structure and strength despite thermal cycling.

Synthesis, crystal structure, and magnetism of A2Co12As7 (A=Ca, Y, Ce–Yb)

Ternary intermetallics, A2Co12As7 (A=Ca, Y, Ce–Yb), have been synthesized by annealing mixtures of elements in molten Bi at 1223K. The materials obtained crystallize in the P63/m variant of the Zr2Fe12P7 structure type. The unit cell volume shows a monotonic decrease with the increasing atomic number of the rare-earth metal, with the exception of Ce-, Eu-, and Yb-containing compounds. An examination of these outliers with X-ray absorption near edge structures (XANES) spectroscopy revealed mixed valence of Ce, Eu, and Yb, with the average oxidation states of +3.20(1), +2.47(5), and +2.91(1), respectively, at room temperature. Magnetic behavior of A2Co12As7 is generally characterized by ferromagnetic ordering of Co 3d moments at 100–140K, followed by low-temperature ordering of rare-earth 4f moments. The 3d-4f magnetic coupling changes from antiferromagnetic for A=Pr–Sm to ferromagnetic for A=Ce and Eu–Yb. Polarized neutron scattering experiments were performed to support the postulated ferro- and ferrimagnetic ground states for Ce2Co12As7 and Nd2Co12As7, respectively.

Gold Refining by Bismuth Melts in the Iron Oxide-Dominated NICO Au-Co-Bi ( Cu W) Deposit, NWT, Canada

The NICO Au-Co-Bi(±Cu±W) deposit is located in the Great Bear magmatic zone, NWT, Canada, where numerous polymetallic, iron oxide-dominated mineralized systems have been recognized. Petrographic, electron microprobe analysis (EMPA), and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) studies of host-rock alteration and ore mineralogy, together with sulfarsenide geothermometry, have been carried out to constrain the nature of alteration and/or mineralization assemblages in this deposit. Metasedimentary rocks of the Treasure Lake Group host NICO and are pervasively altered to an assemblage of ferrohornblende I + actinolite I + biotite I + magnetite I ± orthoclase, which is cut by barren veins composed of quartz ± ferrohornblende-orthoclase-calcite (Set 1). These alteration events are overprinted by metasomatic prograde and retrograde mineralized assemblages and both brittle and ductile deformation accompanied the metasomatism. The prograde assemblage (>400°C) consists of cobaltite, Co-rich loellingite, and Co-rich arsenopyrite (stage I), magnetite II, ferrohornblende II, actinolite II, biotite II, pyrite, and minor scheelite and orthoclase. The earliest retrograde mineralization consists of arsenopyrite (stages II and III), which contains variable amounts of Co, together with native Bi (±bismuthinite) and Au, with lesser magnetite, marcasite, pyrite, hastingsite, and minor quartz. The preservation of solidified native Bi droplets suggests a temperature range of 270° to <400°C for precipitation of this assemblage. The final stage of retrograde mineralization consists of a chalcopyrite-bismuthinite-hematite-chlorite assemblage, together with hastingsite ± emplectite, which formed at temperatures of less than 270°C. Textural and trace element evidence indicates that the Au and Bi present within arsenides and sulfarsenides in the NICO system resulted from the initial partitioning of structurally bound Au and/or “invisible” (nanometer-sized particles) of Au and Bi into the prograde sulfarsenide and arsenide phases, which contain up to 81 ppm Au. The Au and Bi were remobilized following retrograde alteration of those minerals to arsenopyrite II. Molten Bi droplets are interpreted to have scavenged Au insitu, resulting in the formation of the Bi-Au inclusions observed in arsenopyrite II. The second mechanism of gold refining is explained by the occurrence of contemporaneous Bi (±Te) melt and hydrothermal fluids that also could have fractionated gold during transport in solution and deposited it in fractures, interstitially to earlier mineral grains, and as disseminations within Ca-Fe-amphibole-magnetite-biotite-altered rocks. Overall, the gold upgrading at NICO is consistent with the liquid bismuth collector model, suggesting that this process was an important control on gold concentration in this and potentially other Au-Bi-Te-Fe-As-S-rich iron oxide-copper-gold (IOCG) deposits.

Synthesis, Structures, and Magnetic Properties of Rare-Earth Cobalt Arsenides, RCo2As2 (R = La, Ce, Pr, Nd)

Four rare-earth cobalt arsenides, RCo2As2 (R = La, Ce, Pr, Nd), were obtained by reactions of constituent elements in molten Bi. The use of Bi flux also allowed the growth of representative single crystals. All compounds are isostructural and belong to the ThCr2Si2 type (space group I4/mmm). The formation of Co vacancies is observed in all structures, while the structures of La- and Ce-containing compounds also show incorporation of minor Bi defects next to the R crystallographic site. Correspondingly, the general formula of these materials can be written as R1–xBixCo2−δAs2, with x/δ = 0.03/0.1, 0.05/0.15, 0/0.2, and 0/0.3 for R = La, Ce, Pr, and Nd, respectively. All compounds exhibit high-temperature ferromagnetic ordering of Co magnetic moments in the range 60–200 K. Electronic band structure calculations revealed a high peak in the density of states at the Fermi level, thus supporting the itinerant nature of magnetism in the Co sublattice. The magnetic ordering in the lanthanide sublattice takes place...

Recrystallized Arrays of Bismuth Nanowires with Trigonal Orientation

We demonstrate methods to improve the crystalline-quality of free-standing Bi nanowires arrays on a Si substrate and enhance the preferred trigonal orientation for thermoelectric performance by annealing the arrays above the 271.4 °C Bi melting point. The nanowires maintain their geometry during melting due to the formation of a thin Bi-oxide protective shell that contains the molten Bi. Recrystallizing nanowires from the melt improves crystallinity; those cooled rapidly demonstrate a strong trigonal orientation preference.

Low-Temperature Photoluminescence Study of CdTe:In Crystals Annealed in Molten Bismuth

We used a low-temperature photoluminescence (PL) technique to investigate CdTe:In crystals after annealing in molten bismuth (Bi). The two annealed samples showed different resistivities after the treatment. For both samples, we observed very strong emissions in the excitonic spectral region and revealed fine structures of exciton emissions in the PL spectrum. In the sample with high resistivity, we found one ionized donor-bound exciton peak, (D+,X), that we ascribed to incorporated Bi atoms occupying Cd sites in the CdTe. The temperature dependence of the (D+,X) peak emission had an associated activation energy of 3.59 meV for the exciton bound to this ionized donor. Meanwhile, a donor–acceptor pair peak at 1.5315 eV, which was absent from the PL of the low-resistivity sample, suggested the likelihood of some Bi atoms occupying Te sites in the high-resistivity sample. Our findings highlight the need for detailed investigation of annealing conditions to ensure precise control of the electrical properties of the material during annealing in molten Bi.

Damping behavior in Al 18B 4O 33w/Al composite containing an interfacial layer with low melting point metal particles

A SnO 2·Bi 2O 3 coating was deposited on the surface of Al 18B 4O 33 whiskers. A pure aluminum matrix composite reinforced by an Al 18B 4O 33 whisker with SnO 2·Bi 2O 3 coatings was fabricated by squeeze casting method. Sn and Bi particles were introduced to whisker/Al interface during the squeeze casting, resulting in the formation of the Bi–Sn two-component eutectic. The effects of the coating contents on the damping properties of the coated composites at various temperatures, frequencies, and strain amplitudes were examined. The results of the damping characterization indicated that the damping capacity of the coated composites strongly depends on the coating contents, strain amplitudes and vibration frequencies. A damping peak at about 150 °C appeared in the coated composites, and the damping mechanism is related to the interfacial slip caused by the molten Bi–Sn eutectic. A critical temperature in the damping-temperature curves of the coated composites has been found for the first time when the vibration frequencies changed. The dominant damping mechanisms changed from the dislocation damping to the interfacial damping below and above the critical temperature, respectively. The critical temperature decreases with the increasing of coating contents.

Wettability of amorphous and nanocrystalline Fe78B13Si9 substrates by molten Sn and Bi

The wettability of amorphous and annealing-induced nanocrystalline Fe78B13Si9 ribbons by molten Sn and Bi at 600 K was measured using an improved sessile drop method. The results demonstrate that the structural relaxation and crystallization in the amorphous substrates do not substantially change the wettability with molten Bi because of their invariable physical interaction, but remarkably deteriorate the wettability and interfacial bonding with molten Sn as a result of changing a chemical interaction to a physical one for the atoms at the interface.

Can elemental bismuth be a liquid crystal?

A number of anomalies have been reported in molten Bi, including a first-order liquid–liquid transition at 1010 K and ambient pressure, which is irreversible at cooling rates of several degrees per minute. An interpretation of these effects as due to long-range bond-orientational order is suggested. Significant evidence for directionality in liquid Bi, albeit only at temperatures close to melting, is available in experiments made circa 1930. Further experimentation is called for.

Effect of direct electric current on wetting behavior of molten Bi on Cu substrate

The effect of direct electric current on the wetting behavior of molten Bi on Cu substrate at 370°C was investigated by the sessile drop method. The wettability of molten Bi on Cu without an applied current is poor and the spreading time required to form the steady-state contact angle (about 102°) is approximately 30 min. With the increase of the applied electric current, the spreading of molten Bi on Cu is accelerated significantly and the steady-state contact angle decreases considerably. The cross-section SEM micrographs of the solidified Bi droplet on Cu substrate show that the electric current has a marked effect on the convection of melt. Correspondingly, the application of an electric current obviously enhances the dissolution of Cu into Bi melt, which may change the wetting triple line configuration. The improvement of wettability induced by electric current is also related to the additional driving force for wetting provided by the electromagnetic pressure gradient force.

Improvement in electrical stability of ZnO varistors by infiltration of molten Bi 2O 3

The infiltration of molten Bi 2O 3 into ZnO varistors was carried out. The sintered varistor disks doped with Bi 2O 3 were painted by Bi 2O 3 paste on the surfaces and then were reheat-treated. The DC degradation test was carried out to demonstrate the electrical stability of varistors. The influence of the Bi 2O 3 infiltration on the electrical nonlinear characteristics and stability of varistors was analyzed by capacitance–voltage ( C– V) measurements and impedance spectroscopy. The results showed that the Bi 2O 3 infiltration process at temperatures from 800 to 900 °C reduced the donor density in ZnO grains and inhibited the decrease of grain boundary resistance of varistors caused by degradation. The samples infiltrated with Bi 2O 3 at 850 and 900 °C exhibited an excellent electrical stability and maintained relatively high nonlinear characteristics. The enhancement in the electrical stability may be attributed to the diffusion of oxygen into the body of ceramics facilitated by the infiltration of molten Bi 2O 3.

A Comparison of Molten Sn and Bi for Solid Oxide Fuel Cell Anodes

Molten Sn and Bi were examined at 973 and for use as anodes in solid oxide fuel cells with yttria-stabilized zirconia (YSZ) electrolytes. Cells were operated under “battery” conditions, with dry He flow in the anode compartment, to characterize the electrochemical oxidation of the metals at the YSZ interface. For both metals, the open-circuit voltages (OCVs) were close to that expected based on their oxidation thermodynamics, for Sn and for Bi. With Sn, the cell performance degraded rapidly after the transfer of approximately of charge due to the formation of a layer at the YSZ interface. At , the anode impedance at OCV for freshly reduced Sn was approximately but this increased to well over after the transfer of of charge. Following the transfer of at , the formation of a thick layer was confirmed by scanning electron microscopy. With Bi, the OCV anode impedance at was less than and remained constant until essentially all of the Bi had been oxidized to . Some implications of these results for direct carbon fuel cells are discussed.