Search Results (129)

Magnesium reduction of Ta₂O₅ (tantalum pentoxide) is a metallurgical process widely used to extract metallic tantalum powder from its oxide form using magnesium as a reducing agent in a molten salt medium. This study explores the mechanisms and patterns of phase transformation during the magnesium reduction of Ta₂O₅ in a molten salt medium, focusing on the influence of temperature and time on the physical and chemical properties of the resulting tantalum powder. The results reveal that under various reaction conditions in a molten salt medium, the magnesium reduction of Ta₂O₅ follows four distinct pathways: Ta₂O₅ → Ta, Ta₂O₅ → MgTa₂O₆ → Ta, Ta₂O₅ → MgTa₂O₆ → Mg₄Ta₂O₉ → Ta, and Ta₂O₅ → Mg₄Ta₂O₉ → Ta. Each pathway significantly affects the physical and chemical properties of the resulting tantalum powder. Using a uniform mixing method, the reaction proceeds directly from Ta₂O₅ to Ta powder in a single step. As the reaction temperature increases from 600 °C to 900 °C, the average particle size of the tantalum powder enlarges from 30 nm to 150 nm, with the product phase transitioning from a mixture of Ta and Ta₂O to a single Ta phase. Additionally, prolonged holding time improves the uniformity of the tantalum powder’s particle distribution. This study accomplishes directional control over the phase transformation and the properties of tantalum powder during the reduction process, thus offering valuable guidance for the preparation of high-performance tantalum powder. Full article

Hydrogen peroxide is a promising alternative to hydrogen gas for fuel cells, as it can act as the oxidizing and reducing agent and be stored in a stable liquid form, it simplifies the structure of the fuel cell. This study aims to investigate the use of antimony, bismuth, indium, tantalum, silver, dysprosium, erbium, gadolinium, holmium, and terbium as electrodes for the first time in a single-compartment hydrogen peroxide fuel cell. In this study, the procedure for custom electrodes for these metals is documented. The performance of the electrodes was evaluated by measuring the open circuit potential, comparing the cyclic voltammograms and observing the physical reactions of the cell combinations. The results of the study show the catalytic reaction is likely due to the formation of molecular oxide layers on the electrode surface. It was evident that an acidic peroxide electrolyte favors the best catalytic reaction. Tantalum and antimony were found to be the best-performing electrodes in this electrolyte, providing the best stability and performance. Full article

Monodisperse films of spherical tantalum oxide (V) nanoclusters and spherical tantalum nanoclusters with a tantalum oxide shell with diameters of 1.4–8 nm were obtained by magnetron sputtering. The size of the deposited nanoclusters was controlled using a quadrupole mass filter. The chemical composition was certified using the XPS method. Using the Reflected Electron Energy Loss Spectroscopy (REELS), the dependence of the band gap width on the nanocluster size was determined. It was found that starting from a certain nanocluster size, the band gap width increases as the nanocluster size decreases. Based on experimental data and a theoretical model, the effective mass of electrons dependence as a function of nanocluster size was obtained. Full article

Niobium (Nb) and tantalum (Ta) are quoted as “strategic” or “critical” elements for contemporaneous society. The main sources of Nb and Ta are minerals of the pyrochlore supergroup (PSGM) and the columbite group (CGM) mined from different magmatic lithologies. Textures and chemical compositions of PSGM and CGM often provide key information about the origin of NbTa mineralization. Therefore, we decided to carry out a detailed study of the relations between the PSGM and CGM and their post-magmatic transformations, and the Madeira peralkaline pluton (Brazil) is an ideal object for such a study. Textures of the PSGM and CGM were studied using BSE imaging and SEM mapping, and their chemical compositions were determined using 325 electron microprobe analyses. Pyrochlore from the Madeira granite can be chemically characterized as Na, Ca-poor, U- and Pb-dominant, and Sn- and Zn-enriched; REE are enriched only during alteration. Two stages of alteration are present: (i) introduction of Fe + Mn, with the majority of them consumed by columbitization; (ii) introduction of Si and Fe, and in lesser amounts also Pb and U: Si, Pb, and U incorporated into pyrochlore, iron forming Fe-oxide halos around pyrochlore. During both stages, F and Na decreased. In the case of a (nearly) complete pyrochlore columbitization, U and Th were exsolved to form inclusions of a thorite/coffinite-like phase. In contrast to altered pyrochlores from other localities, pyrochlore from Madeira shows a relatively high occupancy of the A-site. Although Madeira melt was Na-, F-rich, contemporaneous crystallization of cryolite consumed both elements and pyrochlore was, from the beginning, relatively Na-, F-poor. Full article

In order to enhance the corrosion resistance of tantalum, the double-glow plasma (DGP) metallurgy technique was used to prepare TaC coatings on the tantalum. The morphology, microstructure, and phase constituents of TaC were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Nano-indentation tests were used to evaluate the mechanical properties of the coatings. The specimens were immersed in NaCl-KCl molten salt at 830 °C to evaluate their corrosion resistance. The results showed that the coating prepared by the DGP technique has a thickness of approximately 5 µm, the diffusion layer has a thickness of 2.5 µm, and the nano-indentation hardness is measured to be 17.27 GPa. The high-temperature stable ceramic phase enhances the high-temperature oxidation resistance of pure tantalum (Ta), while the dense corroded surface and oxidation products improve the anti-corrosion property of TaC coatings. Full article

The reinforcement of cast Cantor’s-type high-entropy alloys by MC carbides and their effect on the hot oxidation behavior were investigated. Three equimolar CoNiFeMnCr alloys without or with carbon and with either hafnium or tantalum were elaborated. Their as-cast microstructures were specified. Oxidation tests were carried out in air at 1100 °C. Flexural creep tests were performed at 1100 °C at 10 MPa. The carbide-free CoNiFeMnCr alloy was single-phased. The version with Hf and C added and the one with Ta and C added contained interdendritic eutectic script HfC and TaC carbides, respectively. After oxidation for 50 h at 1100 °C, all alloys were covered by a (Cr,Mn)₂O₃ scale with various proportions of Cr and Mn. HfO₂ or CrTaO₄ also formed. Oxidation resulted in a deep depletion in Cr and in Mn in the subsurface. Oxidation is much faster for the three alloys by comparison with chromia-forming alloys. Their bad oxidation behavior is obviously due to Mn and protection by coating is to be considered. The creep deformation of the carbide-free CoNiFeMnCr alloy was very fast. The creep resistance of the two versions reinforced by either HfC or TaC deformed much slower. The addition of these MC carbides led to a deformation rate divided by five to ten times. Now, creep behavior comparisons with commercial alloys are to be conducted. They will be performed soon. Full article

Recent progress has seen multiple Ta₂O₅ polymorphs generated by different synthesis techniques. However, discrepancies arise when these polymorphs are produced in widely varying thermodynamic conditions and characterized using different techniques. This work aimed to characterize and compare Ta₂O₅ particles formed at high and low temperatures using nanosecond pulsed laser ablation (PLA) and continuous wave (CW) laser heating of a local area of tantalum in either air or an ¹⁸O₂ atmosphere. Scanning electron microscopy (SEM) and Raman spectroscopy of the micrometer-sized particles generated by PLA were consistent with either a localized amorphous Ta₂O₅ phase or a similar, but not identical, crystalline β-Ta₂O₅ phase. The Raman spectrum of the material formed at the point of CW laser impingement was in good agreement with the previously established ceramic “H-Ta₂O₅” phase. TEM and electron diffraction analysis of these particles indicated the phase structure matched an oxygen-vacated superstructure of monoclinic H-Ta₂O₅. Further from the point of laser impingement, CW heating produced particles with a Raman spectrum that matched β-Ta₂O₅. We confirmed that the high-temperature ceramic phase characterized in previous work by Raman spectroscopy was the same monoclinic phase characterized in different work by TEM and could be produced by direct laser heating of metal in air. Full article

A cubic pyrochlore with the composition Bi_1.865Co_1/2Fe_1/2Ta₂O_9+Δ (space group Fd-3m, a = 10.5013(8) Å) was synthesized from oxide precursors using solid-phase reactions. These ceramics are characterized by a porous microstructure formed by randomly oriented grains of an elongated shape with a longitudinal size of 0.5–1 µm. The electronic state of cobalt and iron ions in oxide ceramics was studied by NEXAFS and XPS spectroscopy. The parameters of the XPS spectra of Bi4f, Bi5d, Ta4f, Co2p, and Fe2p ionization thresholds for a complex pyrochlore were compared with the parameters of the corresponding oxides of the transition elements. The energy position of the XPS-Ta4f and -Ta5p spectra is shifted towards lower energies compared to the binding energy in tantalum(V) oxide by 0.75 eV. According to XPS spectroscopy, bismuth and tantalum cations have the corresponding effective charge of +3 and +(5-δ). The NEXAFS-Fe2p spectrum of ceramics coincides with the spectrum of Fe₂O₃ in its main spectrum characteristics and indicates the content of iron ions in the oxide ceramics in the form of octahedral Fe(III) ions, and according to the character of the Co2p spectrum, cobalt ions are predominantly in the Co(II) state. Full article

The aim of this study is to investigate the antibacterial capabilities of different coating durations of three nanoparticle (NP) coatings: molybdenum (Mo), tantalum (Ta), and zinc oxide (ZnO), and their effects on the surface characteristics of 316L stainless steel (SS). The coated substrates underwent characterization utilizing field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectrometry (EDX), and X-ray diffractometer (XRD) techniques. The antibacterial efficacy of NPs was evaluated using the agar diffusion method. The FE-SEM and EDX images confirmed the presence of nano-sized particles of Mo, Ta, and ZnO on the surface of the substrates with perfectly symmetrical spheres and a uniform distribution of the NPs. All groups demonstrated antibacterial activity, and the ability to inhibit the growth of Streptococcus mutans and Lactobacillus acidophilus bacteria. The ZnO group had the most potent antibacterial effect, followed by the Mo group, while the Ta group had the least effect. A direct-current (DC) plasma sputtering system was used to produce nano-coatings of high purity that were homogeneous, crack-free and showed no sign of delamination. Bacterial strains exposed to Mo, Ta, and ZnO coated surfaces exhibited a significant loss of viability in a time-dependent manner. The optimum sputtering time to ensure the best antibacterial properties and preserve the resources was 1 hour (h) for Mo, 3 h for Ta and 6 h for ZnO. Full article

Ti/IrO₂-Ta₂O₅ electrodes are extensively utilized in the electrochemical industries such as copper foil production, cathodic protection, and wastewater treatment. However, their performance degrades rapidly under high current densities and severe oxygen evolution conditions. To address this issue, we have developed a composite anode of Ti/Ta-Ti/IrO₂-Ta₂O₅ with a Ta-Ti alloy interlayer deposited on a Ti substrate by double-glow plasma surface alloying, and the IrO₂-Ta₂O₅ surface coating prepared by the traditional thermal decomposition method. This investigation indicates that the electrode with Ta-Ti alloy interlayer reduces the agglomerates of precipitated IrO₂ nanoparticles and refines the grain size of IrO₂, thereby increasing the number of active sites and enhancing the electrocatalytic activity. Accelerated lifetime tests demonstrate that the Ti/Ta-Ti/IrO₂-Ta₂O₅ electrode exhibits a much higher stability than the Ti/IrO₂-Ta₂O₅ electrode. The significant improvement in electrochemical stability is attributed to the Ta-Ti interlayer, which offers high corrosion resistance and effective protection for the titanium substrate. Full article

We report on the use of an atmospheric pressure, open-air plasma treatment to remove Li₂CO₃ species from the surface of garnet-type tantalum-doped lithium lanthanum zirconium oxide (Li_6.4La₃Zr_1.4Ta_0.6O₁₂, LLZTO) solid-state electrolyte pellets. The Li₂CO₃ layer, which we show forms on the surface of garnets within 3 min of exposure to ambient moisture and CO₂, increases the interface (surface) resistance of LLZTO. The plasma treatment is carried out entirely in ambient and is enabled by use of a custom-built metal shroud that is placed around the plasma nozzle to prevent moisture and CO₂ from reacting with the sample. After the plasma treatment, N₂ compressed gas is flowed through the shroud to cool the sample and prevent atmospheric species from reacting with the LLZTO. We demonstrate that this approach is effective for removing the Li₂CO₃ from the surface of LLZTO. The surface chemistry is characterized with X-ray photoelectron spectroscopy to evaluate the effect of process parameters (plasma exposure time and shroud gas chemistry) on removal of the surface species. We also show that the open-air plasma treatment can significantly reduce the interface resistance. This platform demonstrates a path towards open-air processed solid-state batteries. Full article

In this paper, Cr (8 μm)/Ta (3 μm) bilayer coatings deposited on a Zr-1Nb alloy substrate were investigated and compared with a Cr-coated alloy under high-temperature steam oxidation at 1200–1400 °C. The bilayer coatings with α- and β-Ta interlayers were obtained by magnetron sputtering. The Cr/Ta-coated samples were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), and optical microscopy (OM). The coating with an α-Ta interlayer can suppress the interdiffusion of chromium and zirconium more effectively up to 1330 °C in comparison with the coating having a β-Ta interlayer. The weight gain of the α-Ta-coated samples after oxidation at 1200 °C for 2000 s was 5–6 times lower than that of the Cr-coated Zr alloy samples. Oxidation at 1400 °C for 120 s showed no significant difference in the weight gain of the Cr- and Cr/Ta-coated Zr-1Nb alloy samples. It was shown that the effect of suppression of Zr-Cr interdiffusion by the barrier coating (α- and β-Ta) is only short-term. Full article

Purpose: We investigated the characteristics of radiation-induced current in nano-porous pellet and thin-film anodized tantalum exposed to kVp X-ray beams. We aim at developing a large area (≫cm²) thin-film radiation sensor for medical, national security and space applications. Methods: Large area (few cm²) micro-thin Ta foils were anodized and coated with a counter electrode made of conductive polymer. In addition, several types of commercial electrolytic porous tantalum capacitors were assembled and prepared for irradiation with kVp X-rays. We measured dark current (leakage) as well as transient radiation-induced currents as a function of external voltage bias. Results: Large transient currents (up to 50 nA) under X-ray irradiation (dose rate of about 3 cGy/s) were measured in Ta₂O₅ capacitors. Small nano-porous Ta and large-area flat Ta foil capacitors show similar current–voltage characteristic curve after accounting for different X-ray attenuation in capacitor geometry. The signal is larger for thicker capacitor oxide. A non-negligible signal for null external voltage bias is observed, which is explained by fast electron production in Ta foils. Conclusions: Anodized tantalum is a promising material for use in large-area, self-powered radiation sensors for X-ray detection and for energy harvesting. Full article

Glass properties play crucial roles in ensuring the safety and reliability of electronic packaging. However, challenges, such as thermal expansion and resistance to acid corrosion, pose long-term service difficulties. This study investigated the impact of the microstructure on acid resistance by adjusting the glass composition. A glass material with excellent acid resistance was obtained by achieving a similar coefficient of thermal expansion to tantalum; it exhibited a weight loss rate of less than 0.03% when submerged in 38% sulfuric acid at 85 °C for 200 h. Theoretically, this glass can be used to seal wet Ta electrolytic capacitors. Differential scanning calorimetry (DSC) was used to analyze the glass transition temperature and thermal stability of borosilicate glasses. X-ray diffractometry (XRD), scanning electron microscopy (SEM), and Raman spectroscopy were used to study the microstructure of the amorphous phase of the borosilicate glass, which revealed a close relationship between the degree of network phase separation in the borosilicate glass and the degree of polymerization (isomorphic polyhedron value, IP) of the glass matrix. The IP value decreased from 3.82 to 1.98 with an increasing degree of phase separation. Boron transitions from [BO₄] to [BO₃] within the glass network structure with increasing boron oxide content, which diminishes the availability of free oxygen provided by alkaline oxide, resulting in a lower acid resistance. Notably, the glass exhibited optimal acid resistance at boron trioxide and mixed alkaline oxide contents of 15% and 6%, respectively. Raman experiments revealed how the distributions of various bridging oxygen atoms (Q_n) affect the structural phase separation of the glass network. Additionally, Raman spectroscopy revealed the depolymerization of Q₄ into Q₃, thereby promoting high-temperature phase separation and highlighting the unique advantages of Raman spectroscopy for phase recognition. Full article

Co doped bismuth magnesium tantalate with a pyrochlore structure (sp. gr. Fd-3m) was synthesized for the first time using the standard ceramic method. Single phase Bi₂Mg_1−xCo_xTa₂O₉ samples were found to be formed when x < 0.7 in the X-ray phase analysis. However, with a higher cobalt content in the samples, the impurity phase β-BiTaO₄ (sp. gr. P-1) is detected, and its amount is proportional to the degree of cobalt doping. The formation of solid solutions is evidenced by a uniform increase in the unit cell parameter of the Co,Mg co doped bismuth tantalate phase with an increase in the content of cobalt ions in the samples from 10.5412(8) (x = 0.3) to 10.5499(8) Å (x = 0.7). The samples exhibit a porous microstructure consisting of chaotically oriented and partially fused elongated grains measuring 1–2 μm. The dependence of the ceramic grain size on the n(Mg)/n(Co) ratio was not determined. X-ray spectroscopy (ear dge X-ray bsorption ine tructure (NEXAFS) and X-ray photoelectron spectroscopy (XPS)) was used to study the charge state of ions in Bi₂Mg_1−xCo_xTa₂O₉. The NEXAFS and XPS data showed that doping with cobalt and magnesium did not change the bismuth and tantalum oxidation states in pyrochlore; in particular, the ions maintained their oxidation states of Bi(+3), Mg(+2) and Ta(+5). The energy position of the peaks of the Ta4f-, Ta5p-, Ta4d spectra had a characteristic shift towards lower energies compared to the binding energy in pentavalent tantalum oxide Ta₂O₅. A shift towards lower energies is characteristic of a decrease in the effective positive charge; in particular, for the Ta4f and Ta4d spectra we presented, this energy shift was ΔE = 0.65 eV, and in the region of the Ta4d edge—0.55 eV. This in turn allowed for us to assume that tantalum atoms have the same effective charge +(5-δ). The oxidation state of cobalt ions was predominantly 2+ and partially 3+, according to NEXAFS spectroscopy data. Full article