Nb Oxide Research Articles

MICROLITE AND TANTALITE IN THE LCT GRANITIC PEGMATITES OF LA CANALITA, NAVASFRIAS Sn-W DISTRICT, SALAMANCA, SPAIN

The La Canalita pegmatites in the Navasfrias Sn–W district, in Spain, are a group of Li-rich LCT rare-element pegmatites hosted by metamorphic rocks. It consists of several dikes up to 1 m thick, 16 m in length and of unknown depth that were mined during the 40s and 50s for tin. Here, we document the Ta-rich oxide minerals, such as those of the columbite–tantalite group, tapiolite-(Fe) and microlite. It is possible to distinguish a primary assemblage, formed of extremely Mn-rich columbite and tantalite, and microlite, the latter forming the host of columbite-(Mn) exsolution lamellae in the intermediate parts of the dikes. The influence of metasomatic fluids led to the formation of a lepidolite–albite late unit and the crystallization of a secondary assemblage consisting of tantalite-(Fe), tantalite-(Mn) and tapiolite-(Fe). Uranium-rich microlite (up to 6% wt. UO 2 ) is present in this assemblage, replacing tantalite. Subsequently, the entrance of hydrothermal fluids, probably mixed with metamorphic fluids, caused a partial greisen-like alteration of the pegmatite bodies and formed a second generation of microlite replacing tapiolite, with high Ca and Ta and low F contents. The lack of a chemically suitable protolith in the surrounding metamorphic rocks, combined with the mineralogical paragenesis containing U-rich microlite, together with the composition of the Sn, Nb and Ta oxide minerals of the pegmatite dikes, suggest that the Cadalso – Casillas de Flores batholith is the most probable source of the melts forming the La Canalita pegmatite dikes.

Ab Initio of Nb Oxides as Support Materials for Pt Catalyst

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Preparation of Superconducting Niobium Tips for Atomic-Resolution Scanning Tunneling Microscopy/Spectroscopy

We present a new reliable method to prepare superconducting niobium (Nb) tips for scanning tunneling microscopy/spectroscopy (STM/STS). Sharp Nb tips were fabricated by chemical etching using an electrolyte based on a hydrofluoric acid and hydrogen peroxide solution, followed by field evaporation utilizing field ion microscopy to remove Nb oxide layers from the tip apex. STM/STS measurements of Si(111) and Au(111) surfaces confirmed that the tips had atomic resolution capability together with bulk-like superconducting properties, indicating that the prepared Nb tips can be used as a unique probe for investigating local superconducting and magnetic properties on an atomic scale.

Heat Treatment and Oxidation Characteristics of Nb-20Mo-15Si-5B-20(Cr,Ti) Alloys from 700 to 1400°C

Nb-20Mo-15Si-5B-20(Cr,Ti) alloys have been subjected to annealing treatment for 2 hours in a range of temperatures from 700 to 1400oC and quenched in water to perform the microstructural characterization for these two new alloys. As cast structure consists of a solid solution phase, , and silicides (Nb5Si3) in both alloys but Cr alloy also contains NbCr2 and Nb3Si phases. Heating to higher temperature introduces Ti silicides in the microstructure for Ti alloy. The oxidation in air has been conducted on these alloys in the same temperature range for 24 hours. Weight gain per unit area as a function of temperature provides the oxidation curves while characterization techniques using SEM, EDS on SEM, x-ray mapping, and XRD has yielded the analyses of the oxide scale. The scale consists of various oxides of Nb, Mo, Cr, Si, and Ti. Cr alloy appears to offer higher oxidation resistance in the selected range of oxidation temperatures.

Petrography and Geochemistry of the Jajarm Bauxite ore Deposit, Northeast Iran: Implications for Source Rock Material and Ore Genesis

The Jajarm bauxite deposit, northeast Iran, is the largest such deposit in Iran. The deposit is sandwiched between the Triassic Elika formation and the Jurassic Shemshak formation, housed within karstic features developed within the former unit. The deposit generally shows an internal layering defined by the following four distinct horizons (from bottom to top): (a) a lower argillaceous horizon, approximately 50-80 cm thick, is mainly composed of clay minerals that directly overlies the carbonate footwall (Elika formation); (b) a bauxitic clay layer approximately 2-3 m thick that consists mainly of hematite, kaolinite, anatase, and diaspore; (c) a red bauxite layer (the main high-grade ore), about 5 m thick and composed of diaspore, kaolinite, anatase, and hematite; and (d) an upper kaolinitic layer that is 20-50 cm thick, composed mainly of kaolinite, and overlain by the Shemshak formation. Detailed petrographic studies reveal diagenetic alteration of the bauxitic protolith. The main observed bauxite textures are microgranular, oolitic, pisolitic, fluidal-collomorphic, and microclastic. Microgranular and microclastic textures associated with the residual fractured and corroded quartz grains, as well as feldspar grains are almost completely replaced by platy diaspore. Geochemical analyses of the red bauxite reveal enrichment of less mobile elements (Nb, Th, Zr, Mo, Ga, and Cr) and depletion of mobile elements (Rb, K, Na, Sr, La, Mg, and Pb); the opposite result is obtained for the bauxitic clay. Chondrite-normalized REE (Rare Earth Element) patterns for the upper kaolinite layer are similar to those for the underlying red bauxite, and the patterns obtained for the lower argillaceous layer are similar to those for the overlying argillaceous bauxite horizon. Ce shows a positive anomaly in the red bauxite and a negative anomaly in the bauxitic clay. The correlation coefficients calculated between REE and other elements demonstrate that the likely REE-bearing minerals are oxides of Ti and Nb, clay minerals, and zircon. In contrast to the present diasporic mineralogical composition of the Jajarm bauxite, the geochemical and mineralogical data indicate an original gibbsitic composition. Finally, the observed mineralogical and textural evidence, combined with the evidence provided by variation diagrams and REE patterns, indicates a mixed origin for the Jajarm bauxite from both basic igneous and sedimentary rocks. In fact, bauxitization was initiated on basic source rocks and continued during reworking and replacement within the karstic features.

Protein Adsorption on Amorphous Metal Oxide Thin Films: An FTIR/ATR and Ellipsometry study

The adsorption of bovine serum albumin (BSA) and fibrinogen proteins dissolved on Phosphate buffer solution onto Ta, Nb and Ti oxide thin films was studied. The metal oxide thin films were deposited by magnetron sputtering on Si(100) wafers and characterized by contact angle measurements and profilometry. Spectroscopic ellipsometry was employed to characterize the kinetics of the protein adsorption process in-situ at the solid-liquid interface and the optical properties of the adsorbed protein layer formed after 45 minutes of immersion of the thin film in the protein solution. Infrared spectroscopy was used to study the proteins within the adsorbed layer. A trend indicating that the surface mass density of the adsorbed protein layer increases as the Rt (peak-to-valley height) surface roughness parameter increases was observed for fibrinogen and BSA. An increment in the surface mass density of the adsorbed protein layer was also observed onto surfaces with higher polar components of the surface energy. BSA and fibrinogen seemed to more readily adsorbed onto tantalum oxide than onto titanium oxide.

M 5O 14-like V–Mo–Nb oxide catalysts: Structure and catalytic performance

Within Mo 5O 14-like structural type for mixed V–Mo–Nb oxides, the effect of vanadium and niobium content and treatment temperature on the phase composition, structure and catalytic properties of the samples in oxidative dehydrogenation of ethane has been studied. The limits of V and Nb content in the ternary Mo 5O 14-like oxide are determined. V–Mo–Nb oxides are shown to be the substitution solid solutions of composition (Mo 0.6V z Nb 0.4− z ) 5O 14 (0 < z < 0.2) based on binary oxide (Mo 0.6Nb 0.4) 5O 14. The structure of crystalline V–Mo–Nb oxides is refined. Crystallization of Mo 5O 14-like structure occurs at temperatures ≥550 °C. Below 550 °C, V–Mo–Nb oxides are nanocrystalline materials having a disordered layered structure with the interlayer distance of ca. 4 Å. The structural model of nanocrystalline oxides is discussed. The role of Nb in the formation of ternary V–Mo–Nb oxide compounds is revealed, and the surface state of these oxides at different temperatures is analyzed. The low-temperature V–Mo–Nb oxides are the most active catalysts in the reaction of ethane oxidative dehydrogenation. They are characterized by the ratio V/Nb ≈ 1 in the Mo 5O 14-like structure.

Crystal structures of crown and aza-crown ether complexes with zirconium, hafnium, niobium, and tantalum fluorometallates

A systematic X-ray diffraction study of the interaction products of Zr(IV), Hf(IV), Nb(V), and Ta(V) oxides (fluorides) with crown-ethers (CEs) in aqueous solutions of hydrofluoric acid is performed. It is shown that oxygen-containing CEs form oxonium complexes with [NbF6]s- and [TaF6]s- hexafluorometallate anions. In two systems, [cis-syn-cis-DCH18C6-H3O][TaF6] and [B18C6·H3O][TaF6], the phenomenon of supramolecular isomerism is found, which is caused by a change in the conformation of the macrocycle or by a partial redistribution of intermolecular hydrogen bonds. The use of aza-crown ethers as extractants made it possible to extract unique hydrolytically unstable anions, the products of incomplete fluorine substitution for oxygen atoms in the starting oxides in the form of crystalline complexes with a composition of [(HA15C5)2][Ta2F10O] and [(HA18C6·H2O)(A18C6·H2O)] [(H2O)Nb2F9O]. In [(18C6)(H7O3)2×(Hf2F10·2H2O)], [(HA18C6)(M2F10·2H2O)·(H3O)·H2O], and [(H2DA18C6) (M2F10·2H2O)·2H2O] (M=Zr, Hf) complexes, the metals are extracted in the form of identical (M2F10·2H2O)2s- anions with a similar topology. The performed study demonstrates that macrocyclic complexones are undoubtedly promising to extract Zr(IV), Hf(IV), Nb(V), and Ta(V) from fluorine-containing aqueous solutions.

Model representation of the physicochemical and diffusion properties during thermal extraction of gas from alloyed uranium dioxide

The release of the process gases H 2 , H 2 O, CO, CO 2 , and Ar from alloyed samples of uranium dioxide by oxides of Nb, Ce, Al, Si, and Fe has been studied by means of thermal extraction in vacuum at 1873 K. The niobium concentration in U 1-y Nb y O 2 was 0.06-0.2 mass % (y = 0.001-0.004), the cerium content was 0-25 mass% (y = 0-0.3434), and the content of mullite or Indian red did not exceed 0.25 mass%, the oxygen potential ΔG O2 of the surface of the samples ranged from -400 to -300 kJ/mole at 1873 K. It was determined that the specific gas release from alloyed samples of uranium dioxide depends on the content of niobium, cerium, and impurity carbon as well as the porosity and the radial gradient of the departure from stoichiometry. A model is proposed for the physicochemical and diffusion processes accompanying the thermal extraction of gas from alloyed uranium dioxide.

Oxidation Behavior of Nb-20Mo-15Si-5B-20Cr and Nb-20Mo-15Si-5B-20Ti Alloys Up To 1300{degree sign}C

Nb-20Mo-15Si-5B-20Cr (Cr alloy) and Nb-20Mo-15Si-5B-20Ti (Ti alloy) alloys have been subjected to oxidation in air for 24 hours in a range of temperatures from 700 to 1300{degree sign}C. As cast structures contain Nbss, Nb5Si3, and Nb3Si in both alloys but Cr alloy also contains NbCr2. Cr alloy exhibits better oxidation resistance than Ti alloy. Oxidation characterization has been carried out for samples heated in 700-1300{degree sign}C temperature range. Large number of oxides of Nb, Mo, Si, Cr, and Ti has been observed as characterized by XRD, x-ray mapping, and EDS on SEM. The scale in immediate contact with the alloy substrate has been found to usually contain Mo oxides. Swollen oxide/metal mixture appears at 900, 1200 and 1300{degree sign}C for Ti alloys and between 1100 and 1300{degree sign}C for Cr alloy.

Investigation of the catalytic activities of sulfated mesoporous Ti, Nb, and Ta oxides in 1-hexene isomerization

In the present work, a series of porous transition metal (Ti, Nb, and Ta) oxides with different pore sizes (12–30 Å) were synthesized using a ligand-assisted amine templating approach. The as-synthesized samples were further treated with 1M sulfuric acid and were characterized by nitrogen adsorption/desorption, powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and elemental analysis (EA). The experimental results in the isomerization of 1-hexene were compared with the commercially available zeolites (HY-zeolite and H-ZSM5) and the ion exchange resin Amberlyst 15. The best results were achieved when using C 12H 2SO 4 mesoporous Ta oxide, which possesses a Ho of −8.2 and 19.8 mmol g −1 acid sites. The conversion of 1-hexene to trans/cis 2-isomers reaches 95.89% in 4 h and the ratio of trans/cis isomers reaches up to 3.7 after 6 h, which is very close to their theoretical ratio in thermodynamic equilibrium (3.37) under the same conditions. This conspicuously high selectivity and short reaction time were not detected with the Ta materials synthesized with C 18 or C 6 templates, nor with Ti and Nb materials of any pore size under the same reaction conditions. Temperature-programed desorption (TPD) of ammonia was used to investigate the much higher activity of the Ta materials. The results showed that the Ta materials had a much greater concentration of Brønsted sites in the active Ho range for this reaction than the Nb materials. The unique performance of the C 12H 2SO 4 Ta material was thus attributed to its high BET surface area, increased concentration of effective Brønsted acid sites and optimal pore size for this particular reaction.

Agglomeration suppression behavior and mechanisms of Ag–Cu and Ag–Nb thin films

Agglomeration behavior of Ag–Cu and Ag–Nb thin films prepared by sputtering was investigated. The films were annealed at 400–600 °C in vacuum and their surface morphologies and resistivities were characterized. It was found that agglomeration was suppressed in both Ag–Cu and Ag–Nb films. The resistivity of Ag–Cu films remained low even when the Cu concentration was increased. However, the resistivity of the Ag–Nb films increased with Nb concentration. We found that 0.4 at% Nb and 2.1 at% Cu were optimum alloying concentrations from the standpoint of both morphology and resistivity. The mechanisms of agglomeration suppression for the Ag–Cu and Ag–Nb films appeared to be different. XRD measurements of the Ag–Cu films showed a marked preferential orientation for (111) in the case of as-deposited films. This suggested that the annealing-induced orientation change in the crystal grains of the Ag–Cu films was minimal. On the basis of XPS measurements, it is believed that the Nb oxides surrounding the Ag grains led to agglomeration suppression in the Ag–Nb film.

Photodegradation of BiNbO4 Powder during Photocatalytic Reactions

BiNbO4 powders prepared by solid state reaction were tested for photocatalytic activity in methanol solutions under UV irradiation. When the material is tested without the presence of a Pt cocatalyst, photocatalytic activity for H2 evolution is superior to that of TiO2. It was also found that BiNbO4 photodegrades into metallic Bi and reduced Nb oxides after use; materials were characterized by SEM, XRD, and XPS. Adding Pt to the surface of the photocatalyst increases photocatalytic activity and importantly, helps to prevent photodegradation of the oxide material. With 1 wt % Pt loading, photodegradation is essentially absent.

Ｎｂナノ粒子を用いた反応性複合無電解Ｎｉ‐Ｐめっき膜の合金化

Composite plating improves functionalities of wear resistance, corrosion resistance, lubricity, etc. through co-deposition with suitable particles. For this study, reactive metallic particles were introduced intentionally as a dispersant. Heat treatment was used to form an alloy with a plated matrix. Composite plating films were formed using electroless Ni-P plating with Nb powder of two types as dispersants: nanopowder (ca. 300 nm diameter) and micropowder (ca. 50 μm diameter). The composite plating film was alloyed using heat treatment at 800°C for 1 hour under vacuum conditions. X-ray diffraction (XRD) analysis confirmed that the proportion of alloy to reactive composite film with nanopowder was much larger than that with micropowder. Results of X-ray photoelectron spectroscopy (XPS) analyses suggest that a selective Nb oxide was formed on the composite film surface when using Nb nanopowder. On the other hand, almost no Nb micropowder was changed to alloy or oxide in the composite films. Using nanopowder, much of the composite plating film formed reactive composite plating film alloy during heat treatment.

Influence of WC replacement by TiC and (Ta,Nb)C on the oxidation resistance of Co-based cemented carbides

The effect of partial replacement of WC by cubic refractory carbides (TiC and (Ta,Nb)C) on the oxidation resistance of WC–Co cemented carbides at 600 and 800 °C is investigated by using TGA, DTA, in-situ synchrotron XRD and SEM/EDX. At 600 °C, the oxidation kinetics obeys a linear function and the increasing content of (Ta,Nb)C causes a reduction of the oxidation rate, which is significantly further decreased by alloying with TiC. In contrast, at 800 °C, the oxidation kinetics follows a parabolic law. In addition, results reveal that an improvement of oxidation resistance at 800 °C is only attained by TiC addition. The oxide scale consists mainly of Co3O4, WO3 and CoWO4. Inclusions of TiO2 within the scale were observed for TiC contents above 14 mol%. Thus, the main factor affecting the oxidation resistance is the content of WC after the replacement by the mixed carbides and the passivation effect of the Ti, Ta and Nb oxides.

17O and 15N Solid State NMR Studies on Ligand-Assisted Templating and Oxygen Coordination in the Walls of Mesoporous Nb, Ta and Ti Oxides

A multinuclear solid state NMR approach is applied to four templated mesoporous oxides (silica, titania, niobia and tantala) to include (15)N and (17)O magic angle spinning (MAS) NMR and double resonance (15)N-(93)Nb, (17)O Rotational-Echo Adiabatic Passage Double Resonance (REAPDOR). The templated samples were ramped in steps of 20 degrees C for 2 days up to typically 110 degrees C where the samples were left for 2-4 days. (15)N MAS NMR shows that amines are the only species present in the TiO2, Nb2O5, and Ta2O5. In SiO2, amines are only present as a minor coordination (10 +/- 2%), but there are several strong ammonium (15)N resonances. The REAPDOR experiments show that the nitrogen interacts with niobium, confirming a ligand interaction between the Nb and N, as previously believed. In the case of silica, the amine is quaternized and there is apparently no interaction with the Si, suggesting a RNH3(+) (-)O-Si- hydrogen-bonding interaction with the walls. (17)O MAS NMR provides the clearest indication of the local wall structure. In the aged, templated samples in all cases only OM2 coordinations are present which is very different from the pure bulk oxides (apart from SiO2) and must be due to the effects of amine coordination at the metal centers. On removal of the template, these oxides behave differently, with Ta2O5 showing a mixture of OTa2 (85 +/- 5%) and OTa3 (15 +/- 5%) which is similar to the types of coordination found in the bulk oxide. The previously reported (17)O MAS NMR data from heat-treated mesoporous niobia shows only ONb2, which is very highly ordered. In contrast for titania, the OTi2 coordination is immediately lost on removal of the template to be replaced by a mixture of OTi3 (60 +/- 5%) and OTi4 (40 +/- 5%), with the OTi4 becoming dominant above 250 degrees C, very different behavior from the corresponding bulk oxide. In summary, this NMR study shows that the local oxygen coordination in amine-templated mesoporous transition metal oxides is present as OM2 which is relatively rare in bulk oxides. The data indicates that the template interaction is largely controlled by the N-M dative bond to the wall, suppressing higher oxygen coordination numbers. Qualitatively it appears that the strength of this interaction varies greatly in the different mesoporous oxides.

Mesostructured mixed Mo–V–Nb oxides for propane ammoxidation

Abstract Mesostructured Mo–V–Nb mixed oxide phases were prepared by reacting inorganic precursors in the presence of cationic, anionic and alkylamine surfactants. The occurrence of these mesostructured phases was explained in part by charge-matching considerations at the inorganic–organic interface. Other interactions, such as covalent bonding between the surfactant headgroup and metal atoms, could direct the self-assembly process. Despite of the limited thermal stability of the mesophases, the air-calcined phases were catalytically active and selective for propane ammoxidation to acrylonitrile and acetonitrile. The selectivities to acrylonitrile and acetonitrile were as high as 26 and 49 mol%, respectively, at 66% propane conversion.

Highly active and selective Nb modified MCM-41 catalysts for Beckmann rearrangement of cyclohexanone oxime to ɛ-caprolactam

The niobium incorporated MCM-41 molecular sieves (Si/Nb-16, 32, 64 and 128) have been synthesized by hydrothermal method using tetradecyltrimethyl ammonium bromide as templates in the absence of auxiliary organics. A combination of various physical techniques was used for characterizing the catalysts, such as X-ray diffraction, N2 physisorption, diffuse reflectance UV–Vis (DR–UV–Vis), Fourier transmission infra red (FT-IR), atomic emission spectroscopy (ICP-AES), and 29Si MAS NMR (magic-angle spinning nuclear magnetic resonance) spectroscopy. Catalyst acidity was measured by (ammonia temperature programmed desorption) NH3-TPD and pyridine FT-IR techniques. The characterization results of DR–UV–Vis, FT-IR, and Si MAS NMR techniques confirm that Nb atoms are isolated and tetrahedrally coordinated in the framework of MCM-41. All the materials exhibit hexagonal arrangement of uniform mesopores. Structural characterization results revealed that two types of Nb oxide species are present, one is framework, and second one is surface type Nb species in all Nb-MCM-41 catalysts. Catalyst samples with higher loading of Nb have shown very good activity. The optimum temperature for this Beckmann rearrangement is 300 °C. The cyclohexanone oxime conversion was about 100% and a caprolactam selectivity of about 95% and more could be achieved. The effect of Si/Nb ratio, temperature, space velocity, etc., on catalyst activity, product selectivity and catalyst stability were discussed. The cyclohexanone oxime conversion was dependent on the temperature and space velocity. The activity at 300 °C for the various catalysts followed the order Nb-MCM-41(Si/Nb-16)>Nb-MCM-41(Si/Nb-32)>Nb-MCM-41(Si/Nb-64)>Nb-MCM-41(Si/Nb-128).

Surface modification of Ti–Nb–Zr–Sn alloy by thermal and hydrothermal treatments

Surface modifications by thermal and hydrothermal treatments in solution with calcium ions were investigated with the aim of improving bioactivity and wear resistance of a Ti–Nb–Zr–Sn alloy. The results showed that the first step of thermal treatment at 600 °C significantly increases the surface hardness and energy by forming oxides of Ti and Nb. The second step of hydrothermal treatment in a boiled supersaturated Ca(OH) 2 solution induces a bioactive layer containing CaTiO 3, CaCO 3, Ca(OH) 2 and TiO 2. Using this treatment, a complete Ca–P layer can be formed within 3 days of soaking in simulated body fluid (SBF). The origin of such fast apatite formation was analyzed by comparison with single step thermal or hydrothermal treatment and with thermal plus hydrothermal treatment without calcium ions. The results suggest that the increase of surface energy by thermal treatment and the incorporation of calcium ions by the hydrothermal treatment in calcium ion solution play important roles in the formation of bioactive apatite.

Electrochemical and XPS studies of corrosion behavior of Ti–23Nb–0.7Ta–2Zr–O alloy in Ringer's solution

Corrosion behavior of a newly developed multifunctional β-type Ti–23Nb–0.7Ta–2Zr–O (mol%, TNTZO) alloy in Ringer's physiological solution was evaluated by open circuit potential, potentiodynamic polarization and X-ray photoelectron spectroscopy (XPS) techniques. Corrosion property of Ti–6Al–4V was also measured for comparison. The results showed that the TNTZO alloy possesses much better corrosion property than the Ti–6Al–4V alloy, corroborated by a high corrosion potential and broad passive region, which is attributed to the stable and inert passive TiO 2 film modified by the oxides of Nb, Ta and Zr on the surface of the TNTZO alloy.