Ta Content Research Articles

Relationship Between Nb-Ta Enrichments and Highly-Fractionated Granitic Magma Evolution in South China: Geochronological, Zircon Hf Isotopic and Geochemical Evidence From Jianfengling Granite

The Jianfengling granite is an important ore-forming rock unit in the Xianghualing orefield in Nanling region (South China), and its magmatic evolution is vital to understand the regional niobium (Nb)-tantalum (Ta) mineralization. The Jianfengling granite comprises three gradual transitional lithofacies: porphyritic biotite monzogranite (mesophase facies), biotite monzogranite (transition facies) and topaz biotite monzogranite (central facies). All the three biotite monzogranite lithofacies are characterized by being rich in SiO2 and Al2O3, poor in TFe2O3, CaO, MgO, TiO2, MnO and P2O5, and are peraluminous high-K calc-alkaline. These rocks are remarkably enriched in Rb, Th, U, Nb and Ta, strongly depleted in Ba and Sr, and slightly depleted in Zr. The LREE/HREE decreases gradually from porphyritic biotite monzogranite, through biotite monzogranite to topaz biotite monzogranite, with increasing convex (“M-type”) lanthanide tetrad effect, which similar to the highly-fractionated granite. The high Th-U (Thavg. = 2051.56°ppm; Uavg. = 1,498.23°ppm, respectively) and low Th-U (Thavg. = 708.14°ppm; Uavg. = 441.57°ppm, respectively) zircon grains from porphyritic biotite monzogranite yielded weighted average 206Pb/238U ages of 161.3 ± 1.6 Ma (MSWD = 1.3, n = 13) and 158.7 ± 2.0 Ma (MSWD = 1.7, n = 13), respectively, consistent with the large-scale magmatic-mineralization event in the Nanling region (ca. 160–150 Ma). The εHf(t) values of the high Th-U (-6.48 to -2.51) and low Th-U (-6.58 to -1.12) zircon grains from the porphyritic biotite monzogranite indicate that the causative magma was formed from partial melting of the Mesoproterozoic Cathaysian basement rocks in a lithospheric extension setting. The Nb and Ta contents increase with fluorine from the porphyritic to topaz biotite monzogranite, indicating that the Nb-Ta enrichment may have caused by the gradual increase of fluxing content (fluorine) during the fractionation of the Jianfengling granitic magma.

Combinatorial design of amorphous TaNiSiC thin films with enhanced hardness, thermal stability, and corrosion resistance

Amorphous TaNiSiC and TaNiC films (with varying Ta/Ni and Si/C ratios) were deposited using combinatorial magnetron sputtering. The TaNiSiC films remained X-ray amorphous after four hour-long annealings up to 700 °C, while TaNiC alloys with high Ni and C contents crystallized. These differences were attributed to a strong driving force for separation of Ni and C in TaNiC, whereas the addition of Si, due to its solubility in the other elements, reduced the elemental segregation in TaNiSiC. The as-deposited TaNiSiC films exhibited hardnesses of 9–12 GPa. Annealing led to an increase in hardness by 2–4 GPa, due to decreases in average atomic distance, as evidenced by X-ray diffraction measurements. Potentiodynamic polarizations from –0.7 to +1.5 V vs. Ag/AgCl (3 M NaCl) in 10 mM sodium borate showed lower current densities by up to 2 orders of magnitude with increasing Ta content (28–52 at.%). Changes in Si/C content (7–13 at.% Si) had no effect. However, optical microscopy showed that TaNiSiC films with high Si/low C contents (13/10 at.%) suffered much less localized etching compared to TaNiC films. Thus, Si had a significant role in increasing the mechanical strength, corrosion resistance, and thermal stability of the TaNiSiC films.

Effect of Ta on the microstructure and mechanical properties of W Ta alloys prepared by arc melting

Herein, W–xTa alloys (x = 0, 10, 20, 30, 40, and 50 wt%) were fabricated using the arc-melting method to improve the strain capacity of tungsten. The effects of Ta on the microstructure and mechanical properties of the fabricated alloys were investigated. The WTa alloys with different Ta contents formed a single-phase WTa solid solution after arc melting, and their average grain size changed from 1056 to 243 μm with increasing Ta content, indicating a grain refinement effect. The hardness, compressive strength, and compressive strain of W improved after the addition of Ta, with the compressive strength and compressive strain of W40Ta reaching 1.63 GPa and 9.54%, respectively, thus achieving the best comprehensive mechanical properties. The fracture surface diagram suggested that a mixed fracture mode of intergranular fracture and transgranular dissociation fracture gradually formed with the increasing of Ta content. Transmission electron microscopic analysis showed that the dislocation density of the compressed W40Ta alloy increased considerably compared with that of pure W, edge dislocation slip was also found to be an important slip mechanism in addition to screw dislocation slip. This study provides insights into the performance optimization, reinforcement design, and strengthening mechanisms of W–xTa alloys.

Effect on impact properties of adding tantalum to V-4Cr-4Ti ternary vanadium alloy

Four V-Ta-4Cr-4Ti quaternary alloys containing different quantities of Ta were investigated to determine the effect of Ta content on the Charpy impact properties. Five button-shaped ingots of the V-4Cr-4Ti ternary alloy and V-xTa-4Cr-4Ti quaternary alloys (x = 3, 9, 15, and 22 wt.%) were fabricated on a laboratory scale by using non-consumable arc-melting in an argon atmosphere. Charpy impact tests were conducted at temperatures ranging from 77 K to 293 K using an instrumented impact tester. Both the upper shelf energy and the ductile–brittle transition temperature increased with increasing Ta content. The addition of 3 wt.% Ta resulted in solid solution strengthening without any degradation of the Charpy impact properties. Thus, the addition of 3 wt.% Ta (V-3Ta-4Cr-4Ti) is an appropriate amount to use in blanket structural materials for nuclear fusion reactors. The spectra of TEM-EDS for V-3Ta-4Cr-4Ti quaternary alloy indicate that there is no significant enrichment of Ta in the matrix as compared with that in the precipitate. However, thermal aging may result in the formation of the Laves phase, causing the degradation of Charpy impact properties. The characterization of precipitates, thermal aging, and creep tests of the V-3Ta-4Cr-4Ti quaternary alloy need to be investigated to determine the optimum Ta content.

Tannic acid enhanced the emulsion stability, rheology and interface characteristics of Clanis Bilineata Tingtauica Mell protein stabilised oil‐in‐water emulsion

SummaryClanis Bilineata Tingtauica Mell Protein (CBTMP) was one of the new natural insect protein resources. However, due to its strong surface hydrophobicity and poor emulsion stability, its application has greatly been limited. In this study, Pickering emulsions were prepared by CBTMP–Tannic acid (CBTMP–TA) particles and soybean oil (φ = 50%). The presence of TA significantly increased the zeta‐potential (from −23.5 ± 0.73 to −29.23 ± 0.58 mV) and three‐phase contact angle (from 129.9 ± 4.53° to 87.27 ± 3.20°) of complex, especially the concentration of TA was 0.4 mm. Besides, the stability of emulsions was significantly improved according to the results of the droplet size and static multiple light scattering. Furthermore, rheological properties including viscosity, thixotropy and creep recovery were significantly enhanced, which indicated the formation of a more stable network structure. Interfacial behaviour (Interfacial tension, interfacial film viscoelasticity and diffusion rate) of emulsions was significantly changed, forming a more stable interfacial layer as TA content increased. The CBTMP–TA complex was adsorbed at the interface and the adsorption rate was also mainly affected by the content of TA. The study indicated CBTMP–TA compositions to enhance stability, rheological behaviours and interfacial characteristics, and demonstrated the potential applications of insect protein resources in food emulsion systems.

Microstructure and Composition Comparison of Ti‐ and Ta‐Doped Nb3Al Superconducting Wires Fabricated by RHQT Process

Herein, the microstructure and composition of the Ti‐ and Ta‐doped Nb3Al superconductor fabricated by rapid heating, quenching, and transformation (RHQT) process are compared. After rapid heating and quenching (RHQ) process, body‐centered cubic (bcc) phase is formed in all the wires, showing dark stripe and bright contrast morphology in the backscattered electron (BSE) images. After transformation heat‐treatment, all wires consist of A15 phase and show the same morphology as that of the quenched samples. Near‐stoichiometric composition is shown in 3 at% Ti‐ and Ta‐doped Nb3Al samples, but when doping amount is 10 at%, Ti‐doped sample has constant Nb content of 67 at% and Ta‐doped sample has Al + Ta content of 25 at%. Superconducting properties of both 3 at% Ti‐ and Ta‐doped Nb3Al samples are comparable and much superior than that of 10 at% doped samples, including critical temperature (Tc), critical current density (Jc), and irreversible field (Birr). Though 10 at% Ta‐doped Nb3Al has higher Tc than 10 at% Ti‐doped sample, it presents wider ΔTc value and lower Jc performance. When increasing the measurement temperature from 8 to 10 K, the decay ratio of Birr value for Ti‐doped Nb3Al superconductor follows the scaling law; however, the Ta‐doped samples are not the case.

Synergistic effects of Re and Ta on the distribution of W in Ni-based superalloys

The distributions of tungsten (W) in Ni-based single crystal superalloys with different Re and Ta contents are characterized and specified by atom probe tomography. The results show that Ta changes the partitioning behavior of W and rejects it from the γ′-precipitate to the γ-matrix, while Re shows the opposite effect, which is consistent with the simulations via Thermo-Calc. Moreover, significant behaviors of W segregation at γ/γ′ interface are found in 2Ta2Re, 5Ta2Re, and 5Ta0Re alloys, contributing to the decrease in the interfacial energy. W interfacial segregations are conducive to decrease the interfacial energy. By comparing alloys with different W contents, W segregation is irrelevant to the W content, but highly W-partitioning-dependent. Additionally, nano-indentation tests also show that the addition of Re can significantly increase the hardness of γ-matrix, while Ta is conducive to strengthen within both γ-matrix as well as γ′-precipitates which is clarified by the solid solution strengthening calculations.

Effect of Tantalum content on microstructure and mechanical properties of CoCrNiTax medium entropy alloys

CoCrNi medium entropy alloy (MEA) has potential applications in cryogenic environment due to its strength and plasticity enhancement at low temperatures. However, the poor strength at the room temperature limits its widespread application. In this work, the alloying element, Tantalum (Ta), was chosen to strengthen CoCrNi MEA and CoCrNiTax MEAs with different Ta content were designed and prepared. The effect of Ta content on the microstructure and mechanical properties of the corresponding alloys were investigated. It was found that Ta-enriched Laves phase was formed due to the addition of Ta element. The alloy's microstructure experienced from hypoeutectic to eutectic, and then to hypereutectic morphology evolution with increasing Ta addition. CoCrNiTa0.4 alloy was a fully eutectic microstructure with fine lamellar colonies. Its yield strength reached about 2150 MPa, which was greatly improved compared with CoCrNi MEA. In order to understand the strengthen mechanism of CoCrNiTax MEAs, strength contribution of the alloy's individual phase to the lamellar colonies was investigated by the high-throughput nanoindentation mapping technique. It is indicated that Laves phase had very high hardness increasing from ≈16.12 GPa to ≈18.14 GPa, almost 3 times than that of FCC phase (≈6.03 GPa). The strengthening of CoCrNiTax MEAs should be attributed to the production of the hard Laves phase and lamellar colonies.

Synthesis and Characterization of Ti-Ta-Shape Memory Surface Alloys Formed by the Electron-Beam Additive Technique

The electron-beam cycling additive technique was proposed for the formation of shape memory Ti-Ta coatings on titanium substrate. On a commercially pure Ti plate, Ta film with a thickness of about 4 μm was deposited by direct current (DC) magnetron sputtering. The sample was then subjected to an electron-beam surface alloying by a scanning electron beam. On the already-formed Ti-Ta surface alloy, a Ta coating with the same thickness was further deposited and the specimen was again subjected to electron-beam alloying for the second cycle. The same procedure was repeated for the third cycle. The structure obtained after each cycle Ti-Ta coatings was studied by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDX). The Young’s modulus, hardness, and shape memory effect (SME) were studied by nanoindentation experiments. The results showed that the thickness of the Ti-Ta coatings is about 50 μm in all cases, where the Ta content increases after each technological cycle. It was found that the obtained phase composition is in the form of a double-phase structure of α’ martensitic and β phases, where the highest amount of beta is registered in the case of the Ti-Ta coating obtained after the third cycle. The results obtained for the Young’s modulus and hardness showed that both mechanical characteristics decrease significantly after each cycle. Additionally, the elastic depth recovery ratio increases with an increase in the number of cycles.

Preparation of Vanillin Derivatives Based on Schiff Base Reaction

This study introduced the aldehyde monomer derived from vanillin (4,4-[(1,4-phenylenedimethylene) dioxy] -bis (3-methoxybenzaldehyde), BA), followed by reaction with tris (2-aminoethyl) amine (TA) and diamine (DA) to prepare a series of polyimine films (BADT-X). By adjusting the ratio of TA and DA, BADT-X with different degrees of cross-linking can be obtained, thereby the performance of the film could be tuned. The physical results show that with the increase of TA content, the mechanical performance of BADT-X has been improved from 31.20 to 45.95MPa, furthernore, the degradation temperature (Td5%) increased from 166.66 to 272.80 °C, and the char yield of all BADT-x was more than 45% at 600 °C. Meanwhile, the quick reshape properties of this polyimine film can be accomplished without any external catalyst in 5 mins at elevated temperature.

Chemical evolution of micas and Nb-Ta oxides from the Koktokay pegmatites, Altay, NW China: Insights into rare-metal mineralization and genetic relationships

This study focuses on the differences in the mineralization potentials and genetic relationships between representative rare-metal pegmatites and the muscovite granite in the Koktokay field in Altay, China, as well as the possible roles that magmatic and/or hydrothermal activities played in enriching the related rare metals. To this end, the major- and trace- element compositions of micas, the major- element compositions of Nb-Ta oxides, and the Li isotopic compositions of Li-rich muscovite, lepidolite, and spodumene were systematically analyzed. The major element compositions of the micas in the No. 1 and No. 2 pegmatites are quite similar. However, the MgO (0.89–2.18 wt%) and F (0.66–2.01 wt%) contents of the micas in the contact zone of the No.3 pegmatite are higher than those of the micas in the No. 1 and No. 2 pegmatites. In addition, the MnO (0.37–0.46 wt%) and MgO (0.39–0.59 wt%) contents of the micas in the muscovite granite are distinctly higher than those of the micas in the studied pegmatites. The trace-element compositions reveal that the primary micas from the small No. 1 and No. 2 pegmatites have significantly lower Li, Be, Ta, and Cs contents and a narrower range of fractionation relative to those in the large No. 3 pegmatite, indicating a significant difference in the rare-metal mineralization potentials of these pegmatites. Moreover, there is a large difference in the δ7Li values of the Li-rich minerals in the muscovite granites (−4.37–0.07‰), No. 3 (4.3–6.81‰) and No. 1 (7.44–14.65‰) pegmatites. These results support the hypothesis that the muscovite granite and pegmatite dikes may have formed independent of each other, and that their formations were a consequence of multi-stage magmatic activities. In addition, the Nb-Ta oxides in the outer zones are mainly columbite-(Mn). The large differences in the Nb/Ta ratios of the columbite-(Mn) (1.83–14.91) and primary micas (2.22–10.41) in the outer zones could be the result of silicate-silicate melt immiscibility. Furthermore, the low Nb/Ta ratios (commonly < 5) of the bright overgrowths of the columbite-(Mn) may have crystallized directly from a hydrous alkali-halogen-rich melt rather than from a hydrothermal fluid. The distinctly higher Ta (39–167 ppm), Cs (275–579 ppm), and B (213–245 ppm) contents; considerable Li contents (400–554 ppm), and lower Nb/Ta ratios (0.5–3.2) of the hydrothermal micas suggest that hydrothermal processes played an important role in the additional enrichment of the related rare metals (e.g., Ta, Cs, Li, and B).

Adjusting the γ/α2 and Ti2AlC phase on microstructure evolution and improving mechanical properties at room and elevated temperatures with the addition of Ta

Alloys of Ti-46Al-6Nb-2.5C-xTa (at. %) were prepared to adjust the γ/α2 phase, refine microstructures, and improve mechanical properties at room and elevated temperatures simultaneously. Phase contents, lamellar colony size, Ti2AlC morphology, compressive and tensile properties, and related mechanisms were discussed. The results show that the relative content of the γ phase increases and the relative content of the α2 phase decreases when Ta content increases from 0 to 2.0 at. %. The solid solution effect of Ta in reinforcing phases contributes to the absence of brittle B2 phase. The content of small length-diameter ratios of Ti2AlC particles increases. The lamellar colony size decreases from 29.9 to 21.6 μm. The constitutional undercooling and heterogeneous nucleation are increased by Ta during the solidification process. Compressive strength increases from 1974 to 2330 MPa when Ta content increases to 0.8 at. %, and the strain increases from 19.8 to 28.2% when Ta content increases to 1.2 at. %. The tensile strength of the Ti-46Al-6Nb-2.5C-2.0Ta alloy increases from 460 to 503 MPa and its strain increases from 4.1 to 8.3%, when temperature increases from 750 to 950 °C. The refinement of lamellar colonies and Ti2AlC, solid solution of Ta, and the ratio of γ/α2 are the main reasons for improving mechanical properties of Ti-46Al-6Nb-2.5C-2.0Ta alloy.

Enhancement in thermoelectric properties of ZrNiSn-based alloys by Ta doping and Hf substitution

Though half-Heusler alloys are listed among the mid-high temperature thermoelectric materials with excellent thermoelectric and mechanical properties, their thermal conductivities remain high and limit their practical applications. In this work, the thermal conductivities and electrical conductivities of ZrNiSn-based alloys were synergistically optimized by Ta doping and Hf substitution. The samples were fabricated using levitation melting combined with spark plasma sintering. When compared with the pristine ZrNiSn, the electrical conductivity in Zr0.68Hf0.3Ta0.02NiSn increases from 7.3 × 104 to 12.9 × 104 S·m−1, and the lattice thermal conductivity declines from 4.1 to 2.7 W·m−1·K−1 at 923 K. As a result, an enhanced ZT of 0.94 for Zr0.68Hf0.3Ta0.02NiSn is achieved, which is a nearly 56% enhancement over pristine ZrNiSn. Furthermore, the microhardness, Young's modulus, and shear modulus in Zr1-x-yHfxTayNiSn (x = 0, 0.2, 0.3, 0.4; y = 0, 0.02) alloys are substantially improved upon increasing the Ta and/or Hf content, far exceeding those in other conventional thermoelectric materials.

Design of TiZrNbTa multi-principal element alloys with outstanding mechanical properties and wear resistance

Body-centered cubic (BCC) multi-principal element alloys (MPEAs) have drawn particular attention as orthopedic implant materials recently, due to their high strength and excellent biocompatibility. However, these alloys often exhibit limited tensile ductility and relatively high Young's modulus, which remain challenges for their potential biomedical applications. In this work, a synergistic design of high-performance biomedical MPEAs based on the principles of valence electron concentration theory and average shear modulus mismatch for solid-solution strengthening is reported. Three TiZrNbTa MPEAs (Ti45Zr45Nb5Ta5, Ti42.5Zr42.5Nb5Ta10, Ti40Zr40Nb5Ta15) with different Ta content were designed. All the alloys exhibited single BCC structure and possessed outstanding tensile ductility (≥18.8%), as well as low Young's modulus (59.3±2.1–73.1±1.0 GPa). The yield strengths of these alloys are increasing with the increase of the Ta content, which can be correlated with the average shear modulus mismatch. In particular, Ti40Zr40Nb5Ta15 alloy exhibits the highest yield strength (∼990.0±14.3 MPa) and high wear resistance for biomedical applications. Theoretical calculation suggested that the strength of the TiZrNbTa alloys is mainly attributed to the solid-solution strengthening effect, and increasing the Ta content can effectively enhance this effect.

Evaluation of Low Chilling Strawberry (Fragraria ananassa) Varieties with Respect to Yield and Quality in Eastern Nepal

The experiment entitled “Evaluation of low chilling strawberry (Fragraria ananassa) varieties with respect to yield and quality in eastern Nepal” was conducted in Dharan and Biratnagar of Nepal with five varieties ‘EMCO 33’, ‘EMCO 32’, ‘Florida Fortuna’, ‘Florida Beauty’ and ‘Sweet Sensation’. The experiment was laid out in Factorial RCBD where variety and location were considered as factors. From the experiment, the highest number of fruits per plant (13.22) and maximum fruit set (95.72%) were recorded with the variety ‘EMCO 33’. However, the maximum number of fruits per plot (444.25) with only 14.04 % of unmarketable fruit and the highest yield of 9068.75 grams per plot with 7976.00 grams of marketable yield per plot was obtained with variety ‘EMCO 32’ in Dharan. Comparing the length and diameter of fruit variety ‘EMCO 32’ (49.00 cm×43.42 cm) and variety ‘EMCO 33’ (49.04 cm×38.41 cm) seems more appealing in form. pH, vitamin C, and TA content were found higher in variety ‘EMCO 33’ (3.48, 71.89 mg/g, and 0.90 % respectively) and higher TSS content (6.57 0 Brix) was obtained with variety ‘EMCO 32’ with no interaction effect for quality traits. Thus among treatment combinations variety ‘EMCO 32’ followed by ‘EMCO 33’ in Dharan conditions is preferable to other treatments and also both the varieties perform well compared to other varieties in Biratnagar conditions also. However, still more studies are required to assess the varietal performance and it would be premature to recommend a suitable variety for given locations.

The Magmatic-Hydrothermal Ore-Forming Processes of the Tonggou Cu-Zn Deposit, NW China: Constraints from Magnetite Chemistry and Fluid Inclusions

The Tonggou deposit is a porphyry Cu and vein-type Cu-Zn mineralization system located in the Bogda Orogenic Belt, north of Eastern Tianshan. Systematic fluid inclusion analyses were performed on granular quartz from the magnetite–quartz stage and pyrite–chalcopyrite–quartz stage from the porphyry Cu mineralization. During the early stage of porphyry Cu mineralization, the ore-forming fluids were at high temperatures (450–501 °C) and high salinity (51.2–55.2 wt.% NaCl equiv.) H2O-NaCl hydrothermal fluids with fluid boiling. These fluids evolved to high temperature (412–450 °C) and intermediate to low salinity (8.3–14.2 wt.% NaCl equiv.) H2O-NaCl hydrothermal fluids during the pyrite–chalcopyrite–quartz stage. In addition, magnetite from the Tonggou deposit was studied as a marker for the ore-forming process evolution of porphyry and vein-type mineralization. Sampled magnetite can be divided into MagI (allotriomorphic magnetite from altered granodiorite), MagII (magnetite from altered granodiorite found in veinlets or as granular aggregates), MagIII (from the magnetite–quartz stage of porphyry mineralization), and MagIV (from the polymetallic sulfide–epidote–quartz stage of vein-type mineralization). Magnetite LA-ICP-MS data indicate a hydrothermal origin. The contents of Ti, Si, Al, and Ta are controlled by temperature, and these elements gradually decrease from MagI to MagIV. Moreover, fO2 has considerable influence on the substitution of Sn, V, and Mn in magnetite, and the contents of these elements generally decrease from MagI to MagIII—increasing only in MagIV. Indeed, high fO2 in the polymetallic sulfide–epidote–quartz stage (MagIV) of vein-type mineralization is shown by the presence of a replacement texture in ilmenite grains within hydrothermal magnetite. On the other hand, magnetite samples from the Tonggou deposit have relatively low Ti + V contents compared to other porphyry Cu deposits—plotting in the skarn field of the (Ti + V) vs. (Ca + Al + Mn) diagram—and shows negative correlations in the (Ti + V) vs. Sn diagram. These data indicate that the porphyry Cu mineralization at Tonggou formed at relatively lower fO2 conditions than the Tonggou vein-type mineralization and other typical porphyry Cu deposits. Finally, porphyry and vein-type mineralization at Tonggou are both sourced from the porphyry system, as a result of ore-forming fluid transfer to a different location.

Nb and Ta intracrustal differentiation during granulite-facies metamorphism: Evidence from geochemical data of natural rocks and thermodynamic modeling

Abstract Both continental crust and depleted mantle are characterized by subchondritic Nb/Ta, leading to a mass imbalance when compared to the bulk Earth. Even though several potential high-Nb/Ta reservoirs in Earth’s core and undepleted mantle have been proposed, little attention has been given to those in the crust. Here we present bulk-rock and rutile geochemical data for samples from a lower crustal pelitic granulite, North China Craton, which exhibit systematic variation in their Nb and Ta contents. High-temperature (HT) and ultrahigh-temperature (UHT) granulite residues exhibit Nb/Ta ratios that are close to chondritic and subchondritic, respectively, whereas leucosomes from UHT granulite mostly have suprachondritic Nb/Ta. These variations are best explained via competition for Nb and Ta between biotite and rutile during metamorphism, although initial bulk-rock Nb/Ta values also have an effect. As biotite preferentially incorporates Nb over Ta, the early stages of biotite dehydration melting produce a high-Nb/Ta residue and a low-Nb/Ta melt; however, geochemical modeling suggests that once biotite is depleted, the Nb/Ta ratio of the system is instead controlled by rutile growth, which promotes the formation of a lower Nb/Ta residue and a higher Nb/Ta melt, even though the volume of melt produced at this stage may be small. We propose that in situ and in-source leucosomes and leucocractic veins in UHT terranes may retain a high-Nb/Ta geochemical signature. However, residual crustal-derived A2-type granites that experience significant fractionation of Nb- or Ta-bearing minerals during crystallization or contamination from other low-Nb/Ta sources cannot retain this high-Nb/Ta ratio, even though these ratios are generally higher than that of S-type granites. Anhydrous partial melting of metapelite can generate Nb-rich melts, such that high-temperature leucosomes, in addition to related A2-type granites, may represent significant Nb deposits.

Low-cost (ZrCu)50-xTax high temperature shape memory alloys showing excellent shape memory effect

ZrCu-based alloys, as one of the most potential high-temperature shape memory alloys, show quite high martensitic transformation temperature, relatively low price for the raw materials, and good casting fluidity. In this work, the martensitic transformation (MT) and shape memory effect of (ZrCu)50-xTax high-temperature shape memory alloys were systematically investigated. Both X ray diffraction and SEM backscattered electron image demonstrated the coexistence of the main phase monoclinic martensite phase and the second phase Ta2Cu. SEM results also revealed that increasing Ta content resulted in a larger volume fraction of Ta2Cu phase. Differential scanning calorimetry results showed that the MT temperatures remarkably increased with Ta addition. The ductility of the (ZrCu)50-xTax alloys was reduced to some degree with increasing Ta content. The shape memory effect was improved significantly, in which (ZrCu)98Ta2 alloy showed the 6.19% maximum recovery strain during 8% pre-strain under compression at 25 ​°C.

Thermoelectric Properties of Ta-doped Zr0.6-xTi0.4TaxNiSn n-type Half-Heusler Materials

Half-Heusler (HH) thermoelectric materials are promising for mid- to high-temperature applications, and MNiSn (M = Ti, Zr, Hf) is a representative n-type HH alloy. In general, the M sites are mixed with isoelectronic elements Ti, Zr, and Hf, to lower the lattice thermal conductivity, and the Sn sites are doped with Sb to adjust the electron concentration. However, Hf is a rare element in earth’s crust, and the volatility of Sb makes it difficult to maintain the initial Sb amount during material synthesis. In this study, as an alternative, Ta was added in the M sites along with the host elements Ti and Zr to produce Hf-free Zr0.6-xTi0.4TaxNiSn alloys (0 ≤ x ≤ 0.04), and the effects of Ta doping on the thermoelectric properties were analyzed. The electrical conductivity of Zr0.6-xTi0.4TaxNiSn increased with Ta content, and the electron concentration increased almost linearly, reaching 5.6 × 1020 cm -3 at x = 0.04. By adding Ta, the maximum power factor also increased by approximately 17% to 3.94 × 10-3 W m-1K-2 at x = 0.02. The lowest lattice thermal conductivity (κlat) was observed at x = 0.02, reaching approximately 1.9 W m-1K-1 at 723 K, but overall, a dramatic decrease in κlat was not observed with Ta doping in Zr0.6-xTi0.4TaxNiSn. This is probably due to the existing effect of Zr/Ti mixing at the M sites, which enhances phonon scattering. A maximum figure of merit (zT) of 0.91 was obtained in Zr0.58Ti0.4Ta0.02NiSn at 873 K, which is a high value for ZrNiSn-based Hf-free HH materials. In conclusion, Ta doping is a viable method to replace Sb doping in ZrNiSn-based HH alloys.

Phase, mechanical property and corrosion resistance evaluation of W-Nb-Ta-Ti and W-Nb-Ta-Ti-N medium entropy alloy thin films

Multicomponent alloy thin films including high entropy alloy (HEA) and medium entropy alloy (MEA) thin films have drawn lots of attention from researchers and industries because of their outstanding properties, such as high hardness, good wear and corrosion resistance. Among several kinds of multicomponent alloy systems, the refractory HEA and MEA are characterized by their high temperature strength and stable thermal properties. In this work, the W-Nb-Ta-Ti and W-Nb-Ta-Ti-N refractory MEA thin films were fabricated by a magnetron co-sputtering system. The structure of W-Nb-Ta-Ti-N coatings changed from BCC to B1 FCC nitride phase when the nitrogen concentration reached 42.6 at.%. The microstructure of BCC structured W-Nb-Ta-Ti-N thin films changed from a coarse columnar to a dense feature as the nitrogen content increased from 0 to 16.2 at.%. A maximum hardness of 24.4 GPa was obtained for the BCC structured W34.3Nb21.7Ta26.4Ti1.4N16.2 thin film. The best adhesion property and the lowest coefficient of friction were found for the FCC W31.1Nb9.6Ta13.1Ti3.6N42.6 nitride thin film. The corrosion resistance of 304SS substrate in 5 wt% NaCl aqueous solution was greatly enhanced by the deposition of the W-Nb-Ta-Ti and W-Nb-Ta-Ti-N refractory MEA thin films. The best corrosion resistance can be seen for the nitrogen-free W37.9Nb25.8Ta28.8Ti7.5 thin film due to its dense microstructure, highest Ta and Nb contents, high configurational entropy and sluggish diffusion effects.