High Nb Contents Research Articles

Polymetallic tungsten skarn mineralisation related to the Periadriatic intrusion at Lienzer Schlossberg, East Tyrol, Austria

Abstract A regional tungsten anomaly was discovered and explored in the Lienzer Schlossberg area that is part of the crystalline Austroalpine nappe complex of the Eastern Alps in the 1970/80-ties. Tungsten is present as scheelite, which occurs in steeply SSW dipping WNW-ENE oriented quartz veinlets and joints within the porphyritic dioritic to tonalitic/granodioritic host rocks of the Oligocene Lienz/Edenwald intrusion and in the exoskarn, which developed at the contact of the intrusion with Ca-rich lithologies. The skarn system is characterised by two stages: (1) a primary high-temperature calc-silicate stage characterised by grossular, diopside-hedenbergite, vesuvianite, wollastonite and Ca-plagioclase and (2) a retrograde skarn stage including scheelite-bearing massive sulphide ores (pyrrhotite, chalcopyrite, tremolite-actinolite, diopside-hedenbergite) and scheelite-rich fault rocks with calcite, sericite and chlorite. The two ore stages, the mineral paragenesis and composition is like that of a reduced tungsten skarn; i.e., garnet is grossular-rich, clinopyroxene is diopside-hedenbergite. Vesuvianite contains up to 1.8 mass % fluorine. Scheelite has been studied by cathodoluminescence (CL), electron probe microanalysis and laser ablation-inductively coupled plasma-mass spectrometry. Three types of scheelite (Scheelite 1–3) are distinguished. In short-wave UV light, all types show blue fluorescence but CL revealed internal micro-textures in scheelite grains which are dominated by oscillatory zoning. Prolonged hydrothermal activity is indicated by dissolution-replacement and overgrowth textures affecting the primary zonation and trace element composition of scheelite. The distribution of rare earth elements (REE) in Scheelite 1 in tonalite-hosted quartz veinlets shows a convex (i.e., middle REE-enriched), heavy REE-depleted pattern with negative Eu anomalies (EuA ). The evolution of REE patterns from skarn-hosted Scheelite 2 and 3 illustrates a gradation of convex REE patterns with high ΣREE and distinct negative Eu anomalies to relatively flat REE patterns with small to no EuA . Scheelite at Lienzer Schlossberg has one of the highest ΣREE+Y contents of all scheelite-bearing ore settings in the Eastern Alps but incorporates minor Mo and the least Sr. High Na and Nb contents together with the positive correlation of REE+Y vs. Na+Nb+Ta suggests that the main exchange vectors for REE incorporation in scheelite is via a combined coupled substitution mechanism. Results of this study confirm the genetic similarity with reduced tungsten skarns and highlight the tungsten potential of this area.

Study on the Effect of Niobium on the High Temperature Oxidation Resistance of Ferritic Stainless Steel

More and more cars are installing urea selective catalytic reduction (SCR) systems to solve the problem of exhaust emissions, which often operates at high temperatures in the exhaust system and is prone to failure of the exhaust pipe due to high-temperature oxidation. And niobium containing ferritic stainless steel has been widely used in the manufacturing of automotive exhaust pipes. In order to extend the service life of ferrite stainless steel exhaust pipes, niobium plays a crucial role as an added alloying element. The solid solution and precipitation of niobium in ferritic stainless steel will give ferritic stainless steel more excellent high temperature resistance. The precipitation of Nb can change the organizational structure in steel and refine the grains. However, if the content is not properly controlled, large particles of (Nb, Ti) C will precipitate, which will reduce the high temperature oxidation resistance. In this paper, the high temperature oxidation behavior of two kinds of ferritic stainless steels with different Nb content at 700 °C, 800 °C and 900 °C was studied. The microstructure of the oxide film on the surface of the material, the thickness of the oxide layer on the cross section, the distribution of chemical composition, the existence form and distribution of Nb element were analyzed by SEM, EDS, XRD and TEM. The results show that the higher the niobium content, the better the high temperature oxidation resistance, and the higher the temperature, the more obvious the high temperature oxidation resistance of niobium. This is because the high Nb content steel is easy to precipitate NbN and other Nb-containing precipitates at the grain boundary, which is helpful to the high temperature resistance. In the case of less Nb content, its ability to generate (Nb, Ti) C precipitates and coarsen at high temperatures reduces its high-temperature resistance.

Widespread PREMA in the upper mantle indicated by low-degree basaltic melts

Studies of ocean island basalts have identified a Prevalent Mantle (PREMA) component as a fundamental feature of mantle geochemical arrays; however, its origin and distribution are highly controversial, including its potential link to plumes sourced in low-shear-wave velocity provinces (LLSVPs) above the core-mantle boundary. In this study, we interrogate the compositional systematics of ~ 3500 Cenozoic oceanic and continental sodic basalts to provide insights into the origin and distribution of PREMA. We find that low-degree basaltic melts with high Nb concentrations located away from deep-mantle plumes have PREMA-like Sr-Nd-Hf isotopic signatures, implying that PREMA is highly fusible and not exclusively associated with LLSVPs. Geochemical modelling and mantle convection simulations indicate that PREMA could have been generated soon after Earth accretion, experiencing only minimal melting or enrichment, and then scattered throughout the upper mantle, rather than being the result of mixing between depleted and enriched mantle components.

Contribution discrepancy of two distinct wall rocks to wolframite mineralization from Dongshanwan quartz-vein tungsten deposit, Southern Great Xing’an Range, China

The Southern Great Xing’an Range is a significant polymetallic metallogenic belt in Northeast China. The ages of granite related to tungsten mineralization have been well quantified, however, the timing and mechanism of quartz vein-type wolframite deposition remain unclear. Therefore, our study focused on the Dongshanwan tungsten deposit, representing a typical wolframite-bearing quartz vein-type deposit in the Southern Great Xing’an Range. Quartz vein-type tungsten mineralization was mainly contained in the Early Cretaceous granite porphyry, with few exceptions in the Permian tuff. Representative wolframite samples were collected from intragranitic (Wol-I) and intra-tuff (Wol-II) quartz veins for wolframite U–Pb dating, electron probe microanalysis (EPMA), and trace elemental analysis. Wolframite U–Pb dating recognized an Early Cretaceous mineralization event at 139–141 Ma, consistent with the previous Dongshanwan granite’s ages (∼142 Ma) but much younger than tuff (∼260 Ma). All the wolframite samples belonged to the ferberite series (FeO/MnO = 4.0–6.9), which indicates a link to the highly fractionated granite. Wol-I showed high contents of Nb, Ta, Sc, and HREEs and a strongly negative Eu anomaly (0.02–0.29), while these elements in Wol-II were approximately one order of magnitude lower than in Wol-I and the Eu anomaly was highly variable (0.17–1.02). The redox characteristics reflected by the Eu anomaly of wolframite may correspond to the variations in oxygen fugacity. Based on petrology, geochemistry, and element mass migration, this study suggests that the granite porphyry and tuff in the Dongshanwan deposit contributed differently to the wolframite precipitation even if the ore-forming fluids were of a common magmatic-hydrothermal origin. The exsolved fluid reserved in the closed system interacts with granite to achieve continuous enrichment in Nb, Ta, Sn, and REEs and accepts external Fe supply from granite alteration to precipitate Wol-I. In contrast, the fluids in relatively open and non-granitic systems have lower Nb, Ta, Sn, and REEs than the former, and Fe supply depends on the alteration of tuff. The abundance of fluorite and the non-CHARAC (CHArge-and-RAdius-Controlled) behavior of Y/Ho and Zr/Hf in the wolframite suggested that fluorine plays an important role in the migration and enrichment of tungsten and other elements during tungsten mineralization.

High-Nb alkaline mafic dykes in the central Alps witness to the Triassic evolution of the Adria passive margin

The Edolo diabase dykes intruded the Variscan basement in the central Southalpine domain. Biotite 40Ar / 39Ar dating shows that the emplacement occurred during the final stage of Permian-Triassic lithospheric thinning. In this phase on the Adria passive margin, middle Triassic magmatism with disputed arc affinity is followed by a late Triassic alkaline event associated with continental rifting. The Edolo diabase dykes are Ti-rich and alkaline, with high Nb and Ta contents and ratios in igneous amphibole, biotite, and ilmenite. These features are typical of the late Triassic magmatism. In contrast, the early-crystallized clinopyroxene shows low Nb and Ta contents and ratios and an apparent arc affinity may be thus envisaged in the clinopyroxene parental melt. However, given the coexistence of both features in the same dykes, their composition cannot be interpreted in terms of transition between tectonic environments. Instead, it is likely attributed to the heterogeneity of the Adriatic lithosphere inherited from the Variscan to Permian evolution, which underwent asthenospheric upwelling due to Permian-Triassic extensional tectonics.

Impact of varying Nb content on conventional superconductivities in Nb-Si systems

Due to the superior properties of niobium silicon-based alloy materials, we systematically studied the structural stability, electronic properties and the relationship between Nb concentration and superconductivity of binary Nb-Si system under pressures below 40 GPa. We have identified three stable structures Nb5Si3, NbSi2 and Nb3Si, that have been experimentally confirmed under ambient pressure, as well as a new ground state stable structure Nb3Si2 above 37 GPa. Electronic structure calculations reveal that all the compounds are metallic. Furthermore we calculated the superconductivity transition temperatures of Nb3Si, γ-Nb5Si3, NbSi2, and Nb3Si2 at ambient pressure, finding that the critical temperature is closely related to the Nb-d states at the Fermi level and the vibration of Nb atoms. The calculated result of Nb3Si (TC=17.8 K) is in accordance with experimental observations, and the critical temperatures of γ-Nb5Si3 and Nb3Si2 are 7.7 K and 3.8 K respectively. In addition, we observed that the phase with a higher superconducting temperature tends to appear in compounds with higher Nb content. This may provide valuable insights into the influence of different structures and chemical compositions on superconducting performance, offering guidance for the design and synthesis of novel superconducting materials.

Room temperature nanoindentation creep behavior of CoNiCrMo-based high entropy amorphous alloy coatings prepared by HVAF

The present study aimed to explore the creep behavior of CoNiCrMo-based high entropy amorphous alloy coatings at room temperature using nanoindentation creep experiments. The coatings were subjected to different loading rates to assess their performance. The findings indicate that the high entropy effect of the (Co0.33Ni0.33Cr0.23Mo0.1)80-xNbx(B0.7Si0.3)20 (x = 0, 2 and 4 at. %) high entropy amorphous alloy coatings has a notable impact on the creep resistance and facilitates a uniform plastic deformation during creep. The shear transition zone (STZ) size and the free volume content during creep deformation exhibit an increase in response to the concentration of Nb. This phenomenon can be attributed to the elevated atomic packing density and the hindered movement of atoms resulting from the incorporation of Nb. Nb content has a favorable impact on the creep stress index, increasing creep stress. Also, the high concentration of Nb is found to mitigate the propensity of the stress exponent to drop with increasing loading rates. The high entropy effect of the as-sprayed coatings promotes high creep resistance and homogenous creep deformation.

Geochronology, Mineralogy, and Geochemistry of the Tonsteins from the Permo–Carboniferous Benxi Formation, Ordos Basin, North China Craton

AbstractTonstein layers are found worldwide in the Permo–Carboniferous coal‐bearing strata. This study investigates the geochronology, mineralogy, and geochemistry of four tonstein samples from the Permo–Carboniferous Benxi Formation, Ordos Basin, North China Craton (NCC). The typical features of the studied tonsteins include thin beds, lateral continuity, angular quartz grains, and euhedral zircons with similar U‐Pb ages, indicating a significant pyroclastic origin. In addition, the tonstein samples have low TiO2/Al2O3 ratios (<0.02) and rare earth elements and yttrium (REY) concentrations with obvious negative Eu anomalies, indicating that the tonsteins have a felsic magma origin. Moreover, compared with the mean composition of clay shale, the studied tonsteins are characterized by high concentrations of the elements Nb and Ta, which may affect the concentration of the corresponding elements in surrounding coal seams. The zircon U‐Pb ages of the tonsteins (293.9–298.8 Ma) provide a precise chronological framework on the Benxi Formation in the Ordos Basin, constraining the Gzhelian–Aselian stages. The tonsteins were probably sourced from arc volcanism along the western margin of the NCC during the early Permian, implying that the Alxa Terrane had not amalgamated with the NCC at that time.

Pegmatite zonation and the use of muscovite as a geochemical indicator for tin-tantalum-tungsten mineralization: Case studies from the Kalehe and Idjwi areas, Democratic Republic of Congo

The central part of the Karagwe-Ankole Belt (KAB) in the Great Lakes area of Central Africa is rich in various rare and strategic elements. The area north of Kalehe and Idjwi island within the Sud-Kivu Province of eastern Democratic Republic of the Congo (DRC) contains Nb, Ta, Sn and W mineralization hosted in pegmatites and quartz veins that are related to leucogranite intrusions. In this work, two granite-pegmatite fields were studied: the Bugarula field in the northern part of Idjwi island and the Kalehe field, along the west coast of Lake Kivu, with a view to determine the co-genetic link between different pegmatites and leucogranites in these regions. Based on mineralogical assemblages, five pegmatite zones were identified, occurring with some spatial overlap, but with an overall increasing distance from the inferred parental granite: 1) albite pegmatites, 2) two-mica pegmatites, 3) muscovite pegmatites, 4) beryl-bearing Nb–Ta–Sn mineralized pegmatites and 5) tourmaline-bearing Nb–Ta–Sn mineralized pegmatites. Muscovite compositions were analyzed from each zone and used to calculate pegmatite fractionation trends by using Rayleigh fractionation modelling. The model uses published partition coefficients (Kd) and measured contents of K, Rb and Cs in muscovite. Muscovites from the consecutive pegmatite zones in both the Bugarula and Kalehe pegmatite fields record a continuous fractionation trend, indicating a co-genetic magmatic evolution. A parental leucogranitic composition of 3.6 wt% K2O, 8 ppm Cs and 300 ppm Rb was iteratively determined to yield a best fit fractionation trend with the data. This composition is within the range of exposed leucogranites sampled in this study, which average at 4.2 wt% K2O, 7 ppm Cs and 400 ppm Rb (n = 12). It should be noted that individually, none of the sampled leucogranites gave satisfactory fractionation trajectories that would suggest a direct co-genetic link between them and the pegmatites. In the Idjwi granite-pegmatite field, the degree of fractionation with respect to the inferred parental leucogranite ranges from 20% to 99% for the least fractionated and most evolved Nb–Ta–Sn mineralized pegmatites, respectively. In the Kalehe area, fractionation values also range from 22% up to 99% for the least fractionated and most evolved (mineralized) pegmatites, respectively. Muscovites from mineralized pegmatites of zones 4 and 5 show high concentrations of Nb, Ta and Sn. As such, we show that muscovite compositions in these pegmatites provide a powerful tool to track Nb–Ta, Sn (and W) enrichment and potential mineralization. These high degrees of fractionation associated with the enrichment in economically interesting elements are similar to reported values for pegmatite fields elsewhere in the Karagwe-Ankole Belt.

Early to Middle Jurassic (ca. 182–164 Ma) fractionated granitoids in the Korean Peninsula: Implication for the tectonomagmatic history of East Asia

The Jurassic granitoids (200–164 Ma) are distributed in the Korean Peninsula due to the Paleo-Pacific plate subduction. Early Jurassic (200–182 Ma) granitoids are mainly distributed in the southern Korean Peninsula. By contrast, Early to Middle Jurassic (182–164 Ma) granitoids are distributed in the central Korean Peninsula. In this study, we report detailed petrology, zircon U–Pb ages, and whole-rock geochemistry from the Seoul–Uijeongbu and Pocheon–Gimhwa pluton units in the central Korean Peninsula. The Seoul–Uijeongbu unit is dominated by biotite granite, with minor porphyritic biotite and garnet-biotite granite while the Pocheon–Gimhwa unit consists of biotite granite and porphyritic biotite granite, garnet-biotite granite, and two-mica granite. Zircon U–Pb age from those granites gives 180–167 Ma. The granitoids in the Pocheon-Gimhwa unit formed through fractional crystallization from biotite granite and porphyritic biotite granite to garnet-biotite granite, and two-mica granite based on gradually decreasing their Nb/Ta, Zr/Hf, and Eu/Eu* ratios. The strongly fractionated granitoids are garnet-biotite granite and two-mica granite. The LILE enrichment, Ta–Nb, Sr–P, and Eu–Ti troughs, and Ba depletion in most granitoids are similar to those of granitoids due to the subduction in the arc environment. Thus, these Jurassic granitoids (180–167 Ma) are mainly peraluminous granites with moderate crystal fractionation corresponding to I-type granite. Alkali feldspar granite associated with ore mineralization occurs in the Gwanaksan pluton from the southwestern Seoul–Uijeongbu unit. The alkali feldspar granite displays distinct negative Eu anomaly with high contents of Rb, Hf, Cs, and Nb compared with other granites. These characteristics imply that alkali feldspar granite experienced strong hydrothermal activity leading to feldspar ore mineralization compared to the other granites. The formation of a wide range of moderately evolved peraluminous granitoids is presumed to be related to rapid flat-subduction during 182–164 Ma, and the mineralization-related alkali feldspar granite indicates the termination of Jurassic granitoid magmatism in the central Korean Peninsula.

Petrological, geochemical and geodynamic evolution of the Wadi Al-Baroud granitoids, north Arabian-Nubian shield, Egypt

The Wadi Al-Baroud area, in Egypt's Eastern Desert, exposes Neoproterozoic rocks of the Arabian-Nubian Shield (ANS), including both syntectonic granitoids (granodiorite and tonalite) and post-collisional granites. We present field work, petrographic study, mineral compositions, and whole-rock geochemistry results from these granitoids and discuss their petrogenesis, magmatic sources, evolution, and tectonic significance. The syntectonic granitoids show subduction affinity and an anomalous steep trend of K-enrichment that suggests assimilation of a granitic component during their evolution. The post-collisional granites form two plutons, on opposite sides of Wadi Al-Baroud, named here the Ras Baroud pluton (RBP) and the Abu Hawis pluton (AHP). They intruded the syntectonic granitoids with sharp intrusive contacts. The post-collisional plutons are devoid of mafic enclaves and are cut by very few dikes. They dominantly consist of biotite monzogranite that grades into muscovite monzogranite. The latter lithology hosts Nb-Ta oxide minerals (columbite, tantalite, and wodginite) displaying a variety of textural and compositional features. The cores are primary columbite-(Mn), whereas rims are overgrown or partly replaced by tantalite-(Fe) and wodginite due to late interactions with highly fractionated residual melt. The highly-evolved AHP and RBP granites are typical of the post-collisional granitoids of the ANS, including high concentrations of rare earth elements (REE), Ta, Hf, Nb, Zr, Y, and Rb; elevated ratios of Ga/Al; and low contents of Sr, CaO, and MgO. Their geochemistry suggests that the parental magma of both plutons formed from an I-type tonalitic source rock that underwent partial melting during the thermal disturbance that followed a lithospheric delamination event during the post-collisional stage of the East African Orogeny. The variations in major oxide and trace element contents among individual samples of the AHP and the RBP cannot be explained as a liquid line of descent due to fractional crystallization; rather we interpret them as sampling variable proportions of an evolved liquid and the solid crystals in equilibrium with that liquid.

Effect of Metal-Substitution within Ruthenium Oxide on Structure and Oxygen Evolution Activity and Stability

The development and utilization of proton exchange membrane water electrolyzers (PEMWEs) is hindered by the cost, activity, and stability of the oxygen evolution reaction (OER) electrocatalyst. Iridium oxide (IrOx) is currently the go-to OER electrocatalyst, as it has been shown to have relative high activity and stability when compared to other OER active catalysts. However, iridium is one of the rarest elements in the Earth’s crust, and therefore cost is a major limitation of iridium-based electrocatalysts. Ruthenium oxide (RuO2) is much lower cost and more active than iridium oxide; however, RuO2 it is unstable in acidic media and undergoes degradation over time. We investigated substituting niobium, tantalum, and zirconium, which are OER-stable metals, into RuO2 to improve the OER stability. Our study explored the effects of different metals and varied concentrations within RuO2 (Ru1-xMxO2, M = Nb, Ta, and Zr) on the structure, morphology, OER activity, and stability. The structure and morphology were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy, and scanning electron microscopy. Preliminary results from XRD showed observable phase separation at higher concentrations of Nb, Ta, and Zr and less phase separation at lower concentrations for Nb and Ta. There was no observable phase separation for Zr at lower concentrations. XRD peak shifts were observed and indicate the incorporation of the metal ions into the crystal structure of rutile RuO2. The OER activities and stabilities of Ru1-xMxO2 were measured using a rotating disk electrode configuration and compared with synthesized RuO2. Our preliminary results show that the OER activity and stability are strongly affected by the addition of the different metals and could be attributed to morphology and structural changes. Our findings help to further the development of lower cost, high activity, and increased stability OER electrocatalysts, which are crucial to the large-scale adoption of PEMWE’s.

High-Temperature Electromechanical Properties Single Crystalline Lithium Niobate-Lithium Tantalate Solid Solutions at Different Oxygen Partial Pressures

LiNbO3 (LN) is one of the most investigated electro-acoustic and electro-optical materials. Its high piezoelectric coefficients are a favorable condition for its use beyond optical applications, which includes, for example, high-temperature actuators. Compared for example to crystals of the langasite family, LN shows significantly higher piezoelectric coefficients but limited thermal stability. The latter is caused by evaporation of Li2O and related changes of e.g. electrical conductivity. As a consequence, long-term applications of LN are limited to temperatures of a few hundred degrees Celsius. A related material that offers improved thermal stability is LiNbO3 (LT). However, the Curie temperature is only about 600 °C. Furthermore, the piezoelectric coefficients are lower than for LN. The miscibility of LN and LT over the entire compositional range should allow, however, to tailor the crystal properties and, for example, to take advantage of the high piezoelectric coefficients of LT and the better thermal stability of LT. Therefore, the subject of this study are lithium niobate-lithium tantalate (LiNb1-xTaxO3, LNT) solid solutions with respect to their electroacoustic properties at temperatures between 400 and 900 °C. The objectives include the determination, understanding and correlation of defect structures, electronic and atomic transport and acoustic losses in LNT over a wide temperature range.The electromechanical properties of LNT crystals are determined as function of temperature and oxygen partial pressure (pO2) and compared with those of the congruent edge compounds LN and LT. Characterization methods include impedance spectroscopy, application of 6Li as tracer in combination with secondary ion mass spectrometry, resonant piezoelectric spectroscopy, noncontacting resonant ringdown spectroscopy and laser vibrometry. The latter reflects displacements of the sample surface even in the order of nanometers which enables the identification of the resonant modes.LNT crystals with different Nb-Ta compositions prepared by Czochralski growth and a µ-pulling down process are used to determine the overall electrical conductivity by electrical impedance spectroscopy. Further, Z- and Y-cut plates are applied as bulk acoustic wave resonators to measure the acoustic loss. When determined in air, the temperature-dependent electrical conductivity of LNT below about 600 °C is virtually independent of composition. In particular, for each sample a single activation energy is found from 400 to 600 °C which is the same for all samples within the error margins. Furthermore, the diffusive ion transport studied directly using 6Li tracers results in good agreement with the electrical conductivity when the diffusion coefficients are converted correspondingly using the Nernst-Einstein relation. Consequently lithium-ion migration can explain the overall electrical conductivity. Above about 600 °C the behavior depends on composition. At high Nb contents, a continuous increase of the slope of the electrical conductivity in an Arrhenius representation with temperature is observed, which is attributed to thermal instability.The pO2 dependent electrical conductivity shows constant values at high pO2. At sufficiently low pO2, a slope of -1/4 in a double logarithmic representation is found (see attached figure). This slope indicates electronic conduction which is caused by compensation of NbLi antisite defects. The behavior is already reported for LN by Smyth et al. (Ferroelectrics 50 (1983) 93). As the slope is independent of the composition x, it can be concluded that the same defect formation occurs in LNT. Important with respect to thermal stability is that, at a given temperature, the increase in conductivity for Ta-rich compositions starts at lower pO2 than for Nb-rich compositions.The acoustic loss is determined in a wide temperature range by the methods mentioned above. It shows some impact of the metal electrodes at low temperatures. In air and at temperatures above about 400 °C the acoustic loss is governed by the piezoelectric/carrier relaxation. It is caused by the motion of charge carriers in an oscillating piezoelectric field and, therefore, related to electrical conductivity. The finding is confirmed by modelling with independent materials data including electrical conductivity. Low pO2 result in additional loss contributions.In summary, the study leads to an understanding of the acoustic losses of LNT at high temperatures, which provides opportunities to reduce them. Furthermore, it becomes clear that Ta-rich compositions exhibit improved thermal stability. Figure 1

Electrolysis Process-Facilitated Engineering of Primary Particles of Cobalt-Free LiNiO2 for Improved Electrochemical Performance.

The particle morphology of LiNiO2 (LNO), the final product of Co-free high-Ni layered oxide cathode materials, must be engineered to prevent the degradation of electrochemical performance caused by the H2-H3 phase transition. Introducing a small amount of dopant oxides (Nb2O5 as an example) during the electrolysis synthesis of the Ni(OH)2 precursor facilitates the engineering of the primary particles of LNO, which is quick, simple, and inexpensive. In addition to the low concentration of Nb that entered the lattice structure, a combination of advanced characterizations indicates that the obtained LNO cathode material contains a high concentration of Nb in the primary particle boundaries in the form of lithium niobium oxide. This electrolysis method facilitated LNO (EMF-LNO) engineering successfully, reducing primary particle size and increasing particle packing density. Therefore, the EMF-LNO cathode material with engineered morphology exhibited increased mechanical strength and electrical contact, blocked electrolyte penetration during cycling, and reduced the H2-H3 phase transition effects.

Phase Discovery and Selected Synthesis of Subvalent Niobium Tellurides Using a Polytelluride Flux Strategy.

Transition metal subchalcogenides involve electron-rich metals and can facilitate an in-depth understanding of the relationships among quantum properties such as superconductivity, charge density wave, and topological band structures. However, effective experimental routes toward synthesizing transition metal subchalcogenides are still lacking, hindering the development of new quantum materials. Herein, we propose a eutectic polytelluride flux strategy as an excellent solution to address phase discovery and crystal growth in transition metal subtelluride systems. We report new phases easily and selectively synthesized using a eutectic "K3Te4" polytelluride flux upon adjusting the ratio of Nb metal to flux in the starting materials (K/Nb/Te = 3:x:4). Using a high Nb content in the solvent (x = 2 and 1), crystals of KNb3Te3O0.38 and K0.9Nb3Te4 are obtained. Both subtellurides exhibit diverse Nb clusters, including face-sharing and edge-sharing Nb6 octahedral columns and zig-zag Nb chains. Reducing the Nb content to x = 0.33 leads to the formation of a layered compound, K1.06NbTe2. This compound comprises a NbTe6 trigonal prism with K intercalated between the layers. Single crystals of known binary Nb tellurides can also be grown using another eutectic flux "KTe3.2", and the obtained NbTe2 exhibits a new polymorphism with extra trimerization along the b-axis in the Nb-Nb bonded double zig-zag cluster. Precise control over the structural dimensionality and oxidation state, combined with the facile crystal growth process, makes our synthetic strategy an efficient route to explore quantum materials in transition metal subchalcogenides.

Modifying Microstructure and Mechanical Properties of Mo-Nb Single Crystals via Thermal Annealing

Molybdenum-Niobium (Mo-Nb) single crystals possess excellent mechanical properties, such as high strength and low creep rate at high temperatures, which leads to Mo-Nb single crystals’ potential application in the irradiated and aerospace environment. Mechanical properties at high temperatures are closely related to structural defects, including the density of dislocation and low-angle grain boundaries in a single-crystal Mo alloy. It is well known that the density of defects is mainly contributed to by processing and annealing. To clarify the microstructural evolution of Mo-Nb single-crystal alloys, thermal annealing tests with temperatures varying from 1100 °C to 1700 °C were conducted. Two Nb contents (3 at.% and 6 at.%) were chosen to investigate the effect of Nb content on the thermal stability (≤1700 °C) of single-crystal Mo-Nb alloys. Samples with high Nb content (6 at.%) soften after annealing, while ductility at room temperature obviously enhances In the low Nb content (3 at.%) sample, however, hardening and softening occur after low (1100 °C) and high temperature annealing, respectively. The evolution of mechanical properties could be mainly attributed to the change of density in the low-angle grain boundary. Furthermore, the changing Nb element and dislocation density during annealing are still important to the strength and ductility of Mo-Nb single crystals.

Flow-through Gas Phase Photocatalysis Using TiO2 Nanotubes on Wirelessly Anodized 3D-Printed TiNb Meshes.

In this work, for the first time 3D Ti-Nb meshes of different composition, i.e., Ti, Ti-1Nb, Ti-5Nb, and Ti-10 Nb, were produced by direct ink writing. This additive manufacturing method allows tuning of the mesh composition by simple blending of pure Ti and Nb powders. The 3D meshes are extremely robust with a high compressive strength, giving potential use in photocatalytic flow-through systems. After successful wireless anodization of the 3D meshes toward Nb-doped TiO2 nanotube (TNT) layers using bipolar electrochemistry, they were employed for the first time for photocatalytic degradation of acetaldehyde in a flow-through reactor built based on ISO standards. Nb-doped TNT layers with low concentrations of Nb show superior photocatalytic performance compared with nondoped TNT layers due to the lower amount of recombination surface centers. High concentrations of Nb lead to an increased number of recombination centers within the TNT layers and reduce the photocatalytic degradation rates.

Tearing on the southward subducting Kelameili oceanic lithosphere in the early Devonian: Evidence from the magmatism in the Harlik arc, southern Altaids

The coexistence of adakites, high-Mg andesites (HMAs) and Nb-enriched basalts (NEBs) records special subduction geodynamics, for instance, subduction initiation, subduction of oceanic ridges or slab tearing, which are widespread in the circum-Pacific subduction zone. The Altaids in Central Asia shared similar tectonic evolution to the western Pacific. However, slab tearing has not been widely reported, which hinders a better comparison between the Altaids and the western Pacific. In this study, we report the contemporaneous early Devonian granodiorites and mafic microgranular enclaves (MMEs) in the Sidingheishan area of the Harlik arc, southern Altaids. The granodiorites have high Sr (534–683 ppm) but low Y (7.79–10.2 ppm) and Yb (0.71–1.68 ppm) contents, with corresponding high Sr/Y values (29.78–76.93). In combination with their juvenile isotopes (initial 87Sr/86Sr = 0.70333–0.70356, εNd(t) = +7.4 − +8.01) and high Mg# numbers (50.9–53), they indicate that their primitive magmas were derived from slab melting. The MMEs show similarly high Sr contents (507–696 ppm), and identically juvenile isotopic signatures (initial 87Sr/86Sr = 0.70346–0.70356, εNd(t) = +7.14 − +7.5) to their host granodiorites. However, their relatively low silica contents (55–60 wt%), evolved Mg# numbers (44.8–55.2) and high Nb contents (12.7–24.7 ppm) demonstrate that they are the fractionation products of NEBs, which were produced by the partial melting of the mantle that was previously metasomatized by these adakitic magmas. Considering all the available evidence, we propose a slab tearing model in which the southward subducting Kelameili oceanic lithosphere underneath the Harlik arc underwent rollback in the early Devonian and its differential rollback rates caused slab tearing. Subsequent asthenosphere upwelling stimulated the Kelameili oceanic lithosphere to melt, producing the adakitic magmas, some of which intruded the crust after limited interaction with the mantle peridotites and underwent crystallization of dominant amphibole in the crust. The rest reacted completely with the mantle peridotites, which underwent further melting to produce the Nb-enriched basaltic magmas. They intruded into the adakitic magma chamber after fractional crystallization of olivine, clinopyroxene and garnet in the deep, forming the MMEs and promoting the remobilization of those hornblendites. This study reveals the development of slab tearing that are closely associated with slab rollback in the Altaids, providing further evidence that argues for the similarity between the Altaids and the western Pacific.

Scheelite composition fingerprints pulsed flow of magmatic fluid in the Fujiashan W skarn deposit, eastern China

Abstract Scheelite (CaWO4) is an economically important W mineral in skarns that form when magmatic fluids exsolved from a granitic intrusion react with carbonate wall rocks. In the Fujiashan W skarn deposit, scheelite formed during four stages of the hydrothermal skarn development. We present cathodoluminescence (CL) images and in situ trace element and Sr-O isotope data of scheelite from these four stages, i.e., scheelite in prograde and retrograde skarn, quartz-sulfide veins, and late calcite replacements. Scheelite from prograde skarn and quartz sulfide veins are homogeneous and show oscillatory zoning textures in CL images, whereas scheelite from retrograde skarn and late carbonate stages display dissolution-reprecipitation and patchy textures. The brightness of CL textures decreases with a higher substitution of Mo. Molybdenum-rich scheelite (up to 2.1 wt%) is characterized by relatively high contents of Nb and Ta (up to 156 and 0.9 ppm, respectively), positive Eu anomalies, high-δ18O values (5.2 to 5.9‰), and relatively low-87Sr/86Sr values (0.70661 to 0.70727), and has grown in a system with a continuous supply of magmatic fluid. Molybdenum-poor scheelite (0.2 wt%) has low contents of Nb and Ta, negative Eu anomalies, low-δ18O values (4.2 to 4.3‰), and relatively high-87Sr/86Sr ratios (0.70748 to 0.70804). This type of scheelite formed in a system with a restricted flow of magmatic fluid during scheelite precipitation became increasingly depleted in elements that substitute into scheelite. The continued reaction of the magmatic fluid with the wall rocks and the precipitation of minerals from the fluid resulted in a systematic change of the δ18O and 87Sr/86Sr ratios. Chemical and isotopic variations in scheelite may reflect the pulsed flow of a magmatic fluid and do not require the involvement of different fluids or contrasting redox conditions.

Understanding the nanoscale chemistry of as-received and fast neutron irradiated Nb3Sn RRP® wires using atom probe tomography

Atom probe tomography (APT) has been used to study the effect of fast neutron irradiation on the local chemistry of Nb3Sn samples. Two RRP® wires doped with 2 at% Ti were analysed, one in the as-received condition and the other irradiated to a neutron fluence (E > 0.1 MeV) of 2.82 × 1022m−2 in the TRIGA-II reactor. The irradiated sample had a reduced T c, an increase in F p, a shift in the peak of the F p curve suggesting the introduction of secondary point pinning, and an increase in the estimated scaling field B*. APT analysis has shown that polycrystalline Nb3Sn has three distinct regions of composition, near stoichiometry Nb3Sn (low Nb), regions with a higher Nb content than expected in equilibrium Nb3Sn (high Nb) and grain boundaries. The summed composition of these three regions lies within the Nb3Sn phase for both the as-received and irradiated samples. The distinct regions of high Nb Nb3Sn demonstrate incomplete diffusion in the as-received sample, and the reduction in volume of these high Nb regions after irradiation implies significant radiation induced diffusion has occurred. The presence of other features in the atomic-scale chemistry, such as the extent of Cu segregation at grain boundaries, three types of dislocation array, and unreacted Nb nanoparticles, are compared between samples.