In this study, we introduced a modified cathodic cage plasma deposition (CCPD) system to synthesize a Ti–Nb–C–N-based composite coating on AISI-4340 steel. This composite coating is widely applied in ...orthopedic joint implants due to its effective bioactivity and wear resistance. In the existing CCPD system, a metallic cathodic cage of a specific material is used to deposit the coating of such material. Thus, it cannot be used to deposit the coating of a composite material. Here, we inserted composite material rings (80% TiO
2
+ 10% Nb
2
O
5
+ 10% graphite) on the lid of the cathodic cage, where the cathodic cage holds these rings and works as a counter electrode for plasma generation. The composite coating is synthesized in nitrogen plasma at various temperatures (300–400 °C) and various hydrogen contents (20, 50, and 80%). It is observed that the hardness of AISI-4340 steel (280 HV
0.25
) can be increased up to 1430 HV
0.25
for coating deposited at 400 °C and 50% hydrogen, which is 5 times higher than the untreated sample. The XRD pattern shows that composite coating consists of TiN, Ti
2
N, NbN, NbC, and TiO
2
. The contents of oxide phase TiO
2
are reduced by adding hydrogen gas to the processing environment; thus, the nitride-based composite coating can be synthesized. The wear volume is significantly reduced by composite coating, specifically while using higher hydrogen contents and higher temperatures. This study shows that this modified CCPD system can improve the hardness and wear resistance by synthesizing this composite coating. In contrast with conventional techniques, separate metallic targets for each element in composite coating (titanium, niobium, and carbon targets) are not required, simple equipment, rough vacuum level are required, and high-processing efficiency are advantages of this system.
Graphical abstract
•Nb2O5 nanoparticle core-amorphous carbon shell materials were prepared by a simple method.•Amorphous carbon shell was formed by one-step process with annealing.•Pyrolysis reaction can significantly ...influence the structural evolution of Nb2O5.•The materials show fast Li storage kinetics for hybrid supercapacitors.•The electrodes exhibit excellent long-term cycling stability.
The hybrid supercapacitor concept involving a battery electrode and a supercapacitor electrode was recently introduced to meet the demand for high energy and power electrochemical energy storage devices. To successfully apply this device, high-capacity and rate electrode materials for Li storage should be developed. Niobium pentoxide (Nb2O5) has recently attracted considerable attention owing to its reasonable capacity, excellent rate capability, and cycling stability. However, the low electronic conductivity of the material is a major limitation. To address this issue, carbon incorporation is usually performed. Herein, we report Nb2O5 nanoparticle core-amorphous carbon shell materials prepared by hydrothermal reaction and one-step carbon formation with annealing. During the one-step process, it was found that pyrolysis of a carbon precursor could significantly influence the structural evolution of Nb2O5 with increasing temperature. In addition, Nb2O5 is reduced to NbO2 in Ar atmosphere with further increase in temperature. The niobium oxide-carbon core-shell structure was thoroughly examined by using transmission electron microscopy. It was demonstrated that the proposed carbon-coated materials exhibited excellent electrochemical properties in terms of rate and cycle performances.
Machine technology frequently puts magnetic or electrostatic repulsive forces to practical use, as in maglev trains, vehicle suspensions or non-contact bearings. In contrast, materials design ...overwhelmingly focuses on attractive interactions, such as in the many advanced polymer-based composites, where inorganic fillers interact with a polymer matrix to improve mechanical properties. However, articular cartilage strikingly illustrates how electrostatic repulsion can be harnessed to achieve unparalleled functional efficiency: it permits virtually frictionless mechanical motion within joints, even under high compression. Here we describe a composite hydrogel with anisotropic mechanical properties dominated by electrostatic repulsion between negatively charged unilamellar titanate nanosheets embedded within it. Crucial to the behaviour of this hydrogel is the serendipitous discovery of cofacial nanosheet alignment in aqueous colloidal dispersions subjected to a strong magnetic field, which maximizes electrostatic repulsion and thereby induces a quasi-crystalline structural ordering over macroscopic length scales and with uniformly large face-to-face nanosheet separation. We fix this transiently induced structural order by transforming the dispersion into a hydrogel using light-triggered in situ vinyl polymerization. The resultant hydrogel, containing charged inorganic structures that align cofacially in a magnetic flux, deforms easily under shear forces applied parallel to the embedded nanosheets yet resists compressive forces applied orthogonally. We anticipate that the concept of embedding anisotropic repulsive electrostatics within a composite material, inspired by articular cartilage, will open up new possibilities for developing soft materials with unusual functions.
Achieving high selectivity and conversion efficiency simultaneously is a challenge for visible‐light‐driven photocatalytic CO2 reduction into CH4. Here, a facile nanofiber synthesis method and a new ...defect control strategy at room‐temperature are reported for the fabrication of flexible mesoporous black Nb2O5 nanofiber catalysts that contain abundant oxygen‐vacancies and unsaturated Nb dual‐sites, which are efficient towards photocatalytic production of CH4. The oxygen‐vacancy decreases the bandgap width of Nb2O5 from 3.01–2.25 eV, which broadens the light‐absorption range from ultraviolet to visible‐light, and the dual sites in the mesopores can easily adsorb CO2, so that the intermediate product of CO* can be spontaneously changed into *CHO. The formation of a highly stable NbCHO* intermediate at the dual sites is proposed to be the key feature determining selectivity. The preliminary results show that without using sacrificial agents and photosensitizers, the nanofiber catalyst achieves 64.8% selectivity for CH4 production with a high evolution rate of 19.5 µmol g−1 h−1 under visible‐light. Furthermore, the flexible catalyst film can be directly used in devices, showing appealing and broadly commercial applications.
Flexible mesoporous black Nb2O5−x nanofibers that contain abundant oxygen‐vacancies are fabricated with an electrospinning technique followed by a room‐temperature defect control strategy. The Nb2O5−x catalyst has a low bandgap width of 2.25 eV that broadens the light‐absorption range from the ultraviolet to visible‐light, and shows a unique reaction router for photocatalytic CO2 reduction to CH4 with a selectivity of 64.8%.
For the purpose of obtaining a niobium-microalloyed steel with a preferable ultrafine-grained ferrite microstructure, a thermomechanical controlled processing (TMCP) strategy that included a hot ...shear deformation conducted near the local phase transformation temperature and a subsequent cooling process is proposed. As a large plastic strain was enforced by the simple hot shear deformation, severe plastic deformation (SPD) of the niobium-microalloyed steel was realized. The proposed TMCP strategy was simulated physically on a Thermecmastor-Z compression machine combined with a multi-type cooling system. Various cooling rates of different cooling methods resulted in reconstructive and displacive phase transformations from γ-Fe to α-Fe and led to different microstructural morphologies. In addition to phase transformations, the precipitation of carbides, grain growth, plastic deformation, discontinuous dynamic recrystallization (dDRX) of retained austenite grains, and continuous dynamic recrystallization (cDRX) of ferrite grains occurred during hot shear and subsequent cooling. The effects of the strain rate and forming temperature on the microstructural and textural evolution of niobium-microalloyed steel during hot shear and subsequent cooling were investigated and discussed. A niobium-microalloyed steel with a homogenous ultrafine-grained ferrite microstructure and intense γ-fiber texture was fabricated when the forming temperature, strain rate of hot shear deformation, and cooling rate of subsequent mist cooling were 1073 K, 20 s−1, and 10 K·s-1, respectively.
Solid acid NbO
x
/ZrO
2
catalysts containing 0, 0.5, 1.1 and 2.8 wt.% of Nb were prepared for one–pot hydrolysis-dehydration of mechanically activated cellulose in pure hot water to produce glucose ...and 5-hydroxymethylfurfural. The catalysts were characterized (XRD, N
2
adsorption, ICP-OES, UV–Vis DRS) and tested in cellulose processing at 453 K. The catalytic activity increased as follows: 0.5%Nb/ZrO
2
< ZrO
2
< < 1.1%Nb/ZrO
2
~ 2.8%Nb/ZrO
2
. This series was accounted for by the acid-basic properties of ZrO
2
, by the inhibition of its active sites by monomer niobium species and by the appearance of Brønsted acidity upon the formation of NbO
x
-containing polymer structures. The highest glucose and 5-HMF yields (22 and 16 mol%, respectively) were achieved over 2.8%Nb/ZrO
2
.
Graphical Abstract
A water‐soluble tetramethylammonium (TMA) salt of a novel Keggin‐type polyoxoniobate has been isolated as TMA9PV2Nb12O42⋅19H2O (1). This species contains a central phosphorus site and two capping ...vanadyl sites. Previously only a single example of a phosphorus‐containing polyoxoniobate, (PO2)3PNb9O3415−, was known, which is a lacunary Keggin ion decorated with three PO2 units. However, that cluster was isolated as an insoluble structure consisting of chains linked by sodium counterions. In contrast, the PV2Nb12O429− cluster in 1 is stable over a wide pH range, as evident by 31P and 51V NMR, UV/Vis spectroscopy, and ESI‐MS spectrometry. The ease of substitution of phosphate into the central tetrahedral position suggests that other oxoanions can be similarly substituted, promising a richer set of structures in this class.
A phosphorus‐centered and vanadyl‐bicapped Keggin polyoxoniobate, PV2Nb12O429−, has been synthesized and structurally characterized (see picture) as a soluble tetramethylammonium salt, TMA9PV2Nb12O42⋅19H2O. The cluster is stable in the pH range 4–10 and under hydrothermal conditions. Its stability was established by 31P and 51V NMR and UV/Vis spectroscopy, and ESI‐MS.
The Neoproterozoic St Honoré carbonatite complex is one of three currently mined niobium deposits. In these and most other carbonatite-hosted niobium deposits, pyrochlore is the principal ore ...mineral. Four major pyrochlore-bearing rock types are observed in the St Honoré complex, namely, biotitite, magnetite-biotite rock, apatitite and carbonatite. The textural relationships among the different rock types and within each rock type are extremely complex, as are the textures and crystal chemistry of the pyrochlore. Compositionally, there are two major types of pyrochlore. Type-1 is enriched in Ta, U, Zr, Sr, Th, Fe, REE and Cl and Type-2 is a Ca-Na-F-rich pyrochlore, with proportions of other elements close to or below their detection limits. Type-1 pyrochlore is yellow- to red-brown and, in many cases, displays oscillatory zoning. This variety occurs most commonly in the cores of crystals in apatitite, where it has its highest concentrations of the elements listed above. It also is observed in biotitite, but the proportions of the above elements are much lower. Type-2 pyrochlore is light to dark brown and, generally, does not exhibit oscillatory zoning. It forms overgrowths on Type-1 pyrochlore in apatitite and biotitite, and occurs as large crystals in the magnetite-biotite rock (Type-1 pyrochlore is not present in this rock). We propose that Type-1 pyrochlore crystallised from a highly evolved, fluid-undersaturated carbonatitic magma, whereas Type-2 pyrochlore crystallised from a carbonatitic magma that had undergone fluid exsolution, which depleted the magma in elements that tend to partition preferentially into aqueous fluids, i.e., U, Sr, Fe, REE, Ba and Cl.
The processes that governed the evolution of the carbonatitic magma (which was mantle-derived and introduced in numerous small batches) and crystallisation of pyrochlore at St Honoré were biotitisation (by the magma), crystallisation of calcite and aqueous fluid exsolution. Biotitisation of the host syenite consumed MgO, H2O and CO2 from each magma batch (the CO2 was released as a gas), leading to the crystallisation of Type-1 pyrochlore in biotitite. This process also locally increased the CaO content of the magma to a level sufficient to saturate it with calcite, leaving a residual phoscoritic magma that crystallised the most Ta-U-enriched variety of Type-1 pyrochlore. Exsolution of the aqueous fluid occurred as a result of prolonged crystallisation and/or pressure release and led to the crystallisation of Type-2 pyrochlore. The evolution of each of the magma batches was different and depended on the extent of biotitisation, on whether calcite crystallised, and on the timing of fluid exsolution. As the two types of pyrochlore and their temporal relationship have been described for many carbonatite complexes, the hypotheses presented in this paper are likely also applicable to the genesis of pyrochlore in these other complexes.
Nanostructured and architectured copper niobium composite wires are excellent candidates for the generation of intense pulsed magnetic fields (∼100T) as they combine both high strength and high ...electrical conductivity. Multi-scaled Cu-Nb wires are fabricated by accumulative drawing and bundling (a severe plastic deformation technique), leading to a multiscale, architectured, and nanostructured microstructure exhibiting a strong fiber crystallographic texture and elongated grain shape along the wire axis. This paper presents a comprehensive study of the effective elasto-plastic behavior of this composite material by using two different approaches to model the microstructural features: full-field finite elements and mean-field modeling. As the material exhibits several characteristic scales, an original hierarchical strategy is proposed based on iterative scale transition steps from the nanometric grain scale to the millimetric macro-scale. The best modeling strategy is selected to estimate reliably the effective elasto-plastic behavior of Cu-Nb wires with minimum computational time. Finally, for the first time, the models are confronted to tensile tests and in-situ neutron diffraction experimental data with a good agreement.
•A hierarchical homogenization strategy is proposed to describe the elastoplastic behavior of architectured and nanostructured Cu-Nb.•The mean field effective model is identified by means of full field finite element simulations.•The model accounts for the double - fiber texture in Copper and the fiber texture in Niobium.•Elastic strains were measured in the individual copper and niobium texture components by neutron diffraction during in situ tensile testing.•Experiments and theory show consistently that plastic activity occurs in oriented grains at a higher applied macroscopic stress than in grains in tensile loading along the wire direction.
Catalytic capacity of ceria mainly stems from a facile switch in the Ce oxidation states from +4 to +4 −
. While various experimental and computational studies pinpoint the reduction chemistry of Ce ...atom through the creation of oxygen vacancies, the analogous process when ceria surface is decorated with cations remains poorly understood. Where such results are available, a synergy between experimental and first principle calculation is scarce. Niobium materials are evolving and their use in catalysis is being widely investigated due to their high surface acidity and thermal and chemical stability. This study aims to report structural and electronic properties of various configurations of mixed Ce–Nb oxides and elaborates on factors that underpin potential catalytic improvements. Evaluations of the samples through X-ray diffraction (XRD), Fourier transform infrared (FTIR), N
-adsorption–desorption, scanning electron microscope (SEM), energy dispersive spectroscope (EDS), and thermogravimetric (TGA) analyses are examined and discussed. First principles density functional theory (DFT) calculations provide structural features of the Ce–Nb solutions at low concentration of Nb
computing atomic charge distribution. Contraction in the lattice parameter after Nb doping was confirmed with both XRD and DFT results. SEM analysis reveals particle growth at the loading of 50 wt%. FTIR results established the Ce–Nb–O bond at 1,100 cm
and the TGA analysis confirms the thermal stability of Nb-doped ceria. Tetrahedral O atoms demonstrate an increase in electronegativity and this in turn facilitates catalytic propensity of the material because the O atoms will exhibit higher affinity for adsorbed reactants. Cerium oxide (CeO
) after Nb doping displays a noticeable band gap narrowing, confirming the possible improvement in the catalytic behavior. The 4d states of the Niobium pentoxide (Nb
) is found to fill up the 4f states of CeO
around the Fermi energy level promoting electrons excitation in the CeO
. Reported electronic, structural, and thermal characteristics herein indicate promising catalytic applications of niobium-promoted ceria.
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