Niobium Content Research Articles

Hydrodeoxygenation of phenol over Ni/Ce1-xNbxO2 catalysts

This work investigated the effect of different niobium concentration on the performance of Ni/Ce1-xNbxO2 catalyst for hydrodeoxygenation of phenol in gas phase at 300 °C. Also, the structural modification promoted by Nb addition was studied by several techniques. In situ X-ray diffraction and Raman analyses indicated that high niobium concentration lead to Nb2O5 oxide with hexagonal structure, while in situ X-ray photoelectron spectroscopy (XPS) experiments indicated an enrichment of the surface with Nb. In general, the incorporation of niobium changed the lattice parameter of ceria and promoted the formation of oxygen vacancies as observed by XPS and X-ray absorption near edge structure (XANES) analyses, which favored the activity of the sample. Increasing Nb content increased the selectivity to deoxygenated products (benzene). The superior benzene selectivity is likely due to the higher interaction between the oxygen of phenol molecule and the oxophilic sites represented by the Nb5+ cations of the support that promotes the hydrogenation of carbonyl group.

The influence of niobium content and initial microstructure of steel on the occurrence of Lüders band at the start of the plastic flow during cold deformation

In this paper, the results of a research on influence of niobium and initial microstructure on start of plastic flow of a material and formation of Lüders bands during cold plastic deformation in niobium microalloyed steel are presented. Research was carried out on hot rolled strips from low carbon steel and three steels with the same base chemical composition but with different amount of niobium: 0.035% Nb, 0.048% Nb, 0.060% Nb. Niobium microalloyed steel strips are rolled with selected parameters of thermomechanical treatment and additionally heat treated with the goal of achieving inhomogeneous microstructure. Static tensile testing was performed on samples, while simultaneously being recorded with thermographic camera. The results of thermographic measurements were analysed with software package Irbis 3 professional. The initial microstructure is tested for all samples. During the start of plastic flow in all microalloyed steel samples, with fine-grained homogeneous microstructure, inhomogeneous deformations are created. These were not found on samples which do not contain microalloying element niobium. In area of inhomogeneous deformations, Lüders bands are formed and propagate through the deformation zone. Lüders band was not found in microalloyed steels with coarse grain. The tests show that the addition of micro-alloying element niobium affects Lüders bands formation but the content of niobium in steel has no effect on the appearance of the Lüders bands. Additionally, it was found that the initial microstructure has a great influence on Lüders bands occurrence.

Simulation of atomic displacements cascades in α-zirconium near β-Nb-20%Zr precipitate

The evolution of atomic displacements cascades near the spherical binary precipitate Nb-20%Zr with the bcc lattice in the hcp α-Zr matrix was simulated using the method of molecular dynamics. The cascade is initiated by a 10 keV primary-knocked Zr atom at a distance ∼10 Å from the surface of spherical binary precipitate of radius ∼50 Å. The simulation results show that at the stage of the primary radiation damage, a change in the composition of the binary precipitate takes place. After passage of the cascade process, a considerable concentration of niobium in interstitial sites outside the precipitate is observed near the surface. The precipitate mitigates the propagation of atomic displacements cascade. In most cases, we observed cascade flow around the sphere accompanied by weak penetration into the precipitate structure.

Application of glycerol to synthesis of solvo-surfactants by using mesoporous materials containing niobium

Abstract A series of niobium-incorporated MSU-X and SBA-16 mesoporous molecular sieves was synthesized under different templates, initial Si/Nb molar ratios or hydrothermal parameters. The catalytic activities of niobium-containing mesoporous materials in the acetalization of glycerol were investigated at the same time. This paper reports on the acetalization of glycerol in acetone to give solketal (4-hydroxymethyl-2,2-dimethyl-1,3-dioxolane), an oxygenated compound useful as chemical and fuel additive for gasoline, diesel and biodiesel. The explored synthesis parameters strongly influence the niobium content and textural properties in studied materials and, subsequently, the catalytic activities. High conversions were achieved (∼90%), though water was present in the reaction system. The results show that niobium-containing materials are water tolerant, reusable catalysts for glycerol acetalization.

Effect of niobium on microstructure and precipitation in As-annealed Sanicro 25 steel

ABSTRACT The chemical compositions of Sanicro 25 stainless steel added with different concentrations of niobium (Nb) (0, 0.29, 0.58, and 0.86 wt-%) were investigated. X-ray diffraction analysis showed that the matrix of all the prepared materials was austenite. The average grain size decreased from 426 to 90 µm with the increase in Nb content. Electron backscatter diffraction and energy dispersive X-ray spectroscopy analyses showed that Cr23C6 was the main precipitate in the Nb-free steel, whereas Nb(C, N) were the main precipitates in Nb-containing steel. The increase in Nb content also increased the volume fraction and average particle size of the precipitates.

Enrichment on Bangka tin slag’s tantalum and niobium oxide contents through non-fluoride process

This research explored how non-fluoride solutions including 8M NaOH, 0.8, 1.6 and 2.4 M H 2 SO 4 , and 0.1, 0.4 and 0.8 M HClO 4 increased the contents of tantalum and niobium oxide through leaching. Before leaching, Bangka tin slag (BTS) was characterized through XRF. The slag was then 900⁰C-roasted, quenched, and dewatered. Next, BTS underwent a sieving process with size classifications of +100, -100+150, -150+200, -200+250, and -250 mesh. After that, the -200+250 mesh slag was leached with 8M NaOH. Then, the leached product was divided into two, one of which was 0.1, 0.4, and 0.8 M HClO 4 -leached and the rest of which was leached with 0.8 M HClO 4 followed by 0, 0.8, 1.6, and 2.4 M H 2 SO 4 at 25⁰C within 2 hours. All the residues characterization used an XRF while that of filtrates used an AAS as well as an ICP-OES. The motives that drive this investigation are the deficit of tantalum supply and its status as one of the technology-critical elements. In addition to that, most of prior investigations enhanced the contents of tantalum and niobium oxide using fluoride acid while this study ventured non-fluoride solutions. The result shows that perchlorate acid followed by sulfuric acid leaching slightly enriches the tantalum and niobium contents. However, this method is the most effective among NaOH, HCIO 4 , and HCIO 4 followed by H 2 SO 4 leaching. This finding is a form of scientific effort to maintain the tantalum supply through utilizing worthless waste of tin smelting

The influence of niobium on the structure of Nb2O5–ZnO–P2O5 glasses

Bulk glasses of the compositional series (A) xNb2O5–(50-x)ZnO–50P2O5 and (B) xNb2O5–50ZnO-(50-x)P2O5 were prepared to investigate possible substitution of cation (Zn2+), series A, and anion (PO3−), series B, with niobium and the effect of this substitution on the structure, density, molar volume, glass transition temperature and coefficient of thermal expansion. The structure was studied by Raman and 31P MAS NMR spectroscopies. The chemical model, based on the idea of chemical compounds as components with the lowest Gibbs energy and therefore the most stable, and on the results of 31P MAS NMR spectroscopy, was proposed for series B. It was found that niobium acts in glasses of series B only as a cation NbO3+, unlike the original idea of forming an anion of NbO−, that is, similarly to series A, where it replaces the cation. This leads to a change in the metaphosphate network of series B to the network that is similar to series A glass. The validity of this idea was verified by experimentally obtained compositional dependencies of molar volume, glass transition temperature and thermal expansion coefficient. Changes observed in thermal measurements indicate the evolution of a more rigid structure and more intensive cross-linking of the phosphate chains with increasing content of niobium.

Thermal and spectroscopic properties studies of Er3+-doped and Er3+/Yb3+-codoped niobium germanate glasses for optical applications

Er3+-doped and Er3+/Yb3+-codoped GeO2-Nb2O5-K2O glasses were prepared by conventional melt-quenching method. Thermal and spectroscopic analysis were performed. The niobium insertion into the glass structure has decreased the OH groups resulting in a slight increase in the luminescence efficiency as the niobium content. Glass network structure is modified depending on rare earth doping concentration and niobium content. The number of bridge oxygen bonds and nonbridge oxygen bonds is altered and consequently the crystallization composition. The spectroscopic features were discussed in terms of niobium concentration and its influence on the applications as optical devices. The addition of niobium broadens the emission band in the region of 1.5 µm covering C, S and L-telecommunication bands. The gain coefficient has calculated establishing high potentiality to use the niobium germanate glasses for optical amplification. The codoping by Er3+/Yb3+ intensifies the emission in the NIR and visible (upconversion) region in relation to the doped samples and may be interesting for application as visible and near-infrared emitters. In addition, the codoped samples with variable niobium contents have potential as visible tunable phosphors emitting either green or red light. Accordingly, the niobium germanate glasses are interesting matrices for rare earth ions doping and for the development of optical devices, such as visible and NIR laser and optical amplifiers.

Structure and Magnetic Properties of Fe-Cu-Nb-Si-B with Various Niobium Concentration

The microrelief of the contact, free sides and cuts of three metal alloys with various niobium contents were studied. It is shown that samples with high niobium content are X-ray amorphous, the alloys FeCu1Si16B6, FeCu1Nb3Si16B6are characterized by an amorphous-crystalline structure. The change in the magnetic characteristics and electrical resistance of alloys in the course of thermomagnetic annealing is studied. It is shown that an increase in the Nb content in an alloy increases its temperature stability and the temperature of the onset of crystallization processes.

Investigation on Microsegregation of IN718 Alloy During Additive Manufacturing via Integrated Phase-Field and Finite-Element Modeling

In this work, we apply a multi-scale model combining finite-element method (FEM) and phase-field model (PFM) to simulate the evolution of solidification microstructures at different locations within a molten pool of an additively manufactured IN718 alloy. Specifically, the FEM is used to calculate the shape of molten pool and the relative thermal gradient G at the macroscale. Then, the calculated thermal information is input into PFM for microstructure simulation. Finally, the morphology of solidification structures and formation of Laves phase at different sites are studied and compared. We found that the solidification site with a large angle between the temperature gradient and the preferred crystalline orientation could build up a high niobium (Nb) concentration in the liquid during solidification but has less possibility of forming continuous long chain morphology of Laves phase particles. This finding provides an understanding of the microstructure evolution inside the molten pool of IN718 alloy during solidification. Further, the finding indicates that the site with a large misorientation angle will have a good hot cracking resistance after solidification.

Argon and argon-hydrogen shielding gas effects on the laves phase formation and corrosion behavior of Inconel 718 gas tungsten arc welds

Argon-Hydrogen shielding gas mixture induced a steep temperature gradient and enhanced the instantaneous cooling rate of the weld. The welds obtained by Argon-Hydrogen have finer grain structure than the Argon-Shielded welds. The reduction of laves phase segregated at the interdendritic region has lower Niobium concentration which improves the corrosion resistance of the welds.

MWW layered zeolites modified with niobium species - Surface and catalytic properties

New heterogeneous catalysts were obtained by modification of MWW zeolites (MCM-22 and MCM-56) by swelling and pillaring with niobiosilicate, achieved by two different methods. The main differences between these methods were time and temperature at which the modification was carried out, the concentration of a base used during the modification, and the water content in the catalysts used for further modification. The XRD analysis proved that both methods used gave MCM-36 structure, in all cases pillaring led to an increase in surface area, but some differences in final materials were noted, depending on the pillaring procedure. Both NbMCM-36 zeolites exhibited different content of micropores (lower in the zeolites synthesized from MCM-22), different loading with niobium species (higher in the material prepared from MCM-56) and similar acidity strength. Both niobium containing zeolites were active catalysts in liquid phase cyclohexene oxidation with H2O2 and were successfully used in the second run. Niobium played a role of H2O2 activator. Texture parameters and content of niobium was crucial for the effective discoloration of methylene blue with the use of hydrogen peroxide.

The role of the anode material and water matrix in the electrochemical oxidation of norfloxacin

The roles of the anode material, boron-doped diamond (BDD), with different boron (B) and substrate Silicon (Si) or Niobium (Nb) content, and one dimensionally stable anode (DSA®), were evaluated in the oxidation of norfloxacin (NOR) by electrochemical advanced oxidation process (EAOP). The effect of other components in real wastewater on the performance of EAOP was also studied. The anode materials were characterized by cyclic voltammetry, regarding diamond quality, electro-generation of oxidants and NOR oxidation mechanism (direct and/or indirect). The results showed that the anode material influences on the NOR oxidation pathway, due to distinct characteristics of the substrate and the coating. Apparently, low difference in diamond-sp³/sp2-carbon ratio (Si/BDD100 × Si/BDD2500) does not leads to significant differences in the EAOP. On the other hand, the variation in the sp³/sp2 ratio seems to be higher when Si/BDD2500 and Nb/BDD2500 are compared, which would explain the best current efficiency result for Si substrate. However, the Nb substrate presented a similar current efficiency and a 60% lower energy consumption. Dissolved organic matter (DOM) present in the real wastewater affect the EAOP-Nb/BDD due to HO and persulfate ions scavenged. However, when supporting electrolyte was added to a real wastewater spiked with NOR, the NOR decay reaches similar values found to the synthetic one. Due to the energy saving and mechanical properties, Nb substrate presents some technological advantages in relation to Si, which can facilitate the application to industrial levels.

Nanostructural characterization of sputter deposited Ti-Nb coatings byautomated crystallographic orientation mapping

AISI 316 L stainless steel (SS) and CrCo alloys are commonly used for manufacturing biomedical implants due to their reasonably adequate bulk properties. Commercially pure (CP) Ti and its alloys are more biocompatible, but also significantly more expensive, than SS and CoCr alloys; they have an additional advantage compared to SS and CoCr alloys: their elastic modulus values are more compatible with those of the human bones (10–40 GPa). An interesting option would be to coat an implant with a TiNb thin film having adequate composition and thickness so that the coating would enhance the material biocompatibility. In this work, TiNb coatings were deposited on AISI 316L stainless steel and silicon substrates by magnetron sputtering and then were characterized by scanning and transmission electron microscopy (STEM) coupled with energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM) coupled with automatic crystal orientation mapping (ACOM). The results show that films form a homogenous solid solution and that the growth modes are not modified by the Nb content and substrate material. Also, the texture changes together with the grain growth morphology with the increase in the niobium content. For a columnar structure characteristic of zone II of the zone structure diagram (SZD) there are strongly marked textures in {113} for the x-axis, {110} for the y-axis, and {111} for the z axis. These are suppressed when the growth type changes for the T zone with the variation in the alloying element content, and that could be due to the high mobility generated during the deposition process.

In vitro evaluation of niobia added soda lime borosilicate bioactive glasses

In the present study, systematic and detailed investigations have been reported, in terms of bioactivity, cytocompatibility and mechanical hardness of a synthetic material that is proposed as a bone implant material in in-vitro conditions. The objective of the present study is to explore the effect of niobium addition on bioactivity and cytocompatibility of soda lime borosilicate bioglasses. Synthesis of bioglasses is carried out by conventional melt-quenching method. Simulated body fluid is prepared by Tas method. The bioactivity study was done for twenty-one days of immersion in simulated body fluid. XRD, FTIR, and SEM-EDS are showed formation of hydroxyapatite layer on the niobium added soda lime borosilicate glass even at a higher concentration (10 mol %) of niobium content. Degradation test was performed as per ISO 10993. The results obtained from degradation studies have demonstrated that weight loss of niobia mixed soda lime borosilicate glasses decreased with the increase of niobia. Cytocompatibility study has been studied by MTT Assay with osteoblast cells (MG-63). Cell viability is not affected by the addition of niobium content. Niobium added soda lime borosilicate glasses are both bioactive and cytocompatible. Hence it can be concluded that niobia mixed borosilicate glasses may be used as potential material in bone tissue engineering.

Influence on the weld strength of high-strength fine-grained structural steels by thin-film-coated GMA welding electrodes

The increasing demand for high-strength fine-grain steels for the purpose of reducing the weight of steel structures and increasing payloads, is driving forward the development of fine-grain steels. However, with the currently available welding consumables, it is not possible to achieve the strengths of modern fine-grain steels with a grade of S1300QL in the weld metal. As a result, there is a need for novel welding consumables, which guarantee high-strength joints. The application of thin, functional layers on GMA welding electrodes by a PVD coating process makes it possible to influence the mechanical-technological properties to an extent which cannot be achieved by state-of-the-art technology. The sputtering of different elements on the substrate material of GMA electrodes and the layer thickness has an influence on the welding process and the welding metal. Especially, the influence on the microstructure by a niobium coating of different layer thickness is presented. Furthermore, the changes in the mechanical properties of the weld metal depending on the layer thickness or rather the niobium content are shown. In particular, the fine-grain and carbide-forming effect of niobium and the influence on the mechanical properties are presented. Here niobium contents between 0.5 wt.-% and 1.5 wt.-% are in the focus of investigations.

Computational Design of a Novel Medium-Carbon, Low-Alloy Steel Microalloyed with Niobium

The design of a new steel with specific properties is always challenging owing to the complex interactions of many variables. In this work, this challenge is dealt with by combining metallurgical principles with computational thermodynamics and kinetics to design a novel steel composition suitable for thermomechanical processing and induction heat treatment to achieve a hardness level in excess of 600 HV with the potential for good fracture toughness. CALPHAD-based packages for the thermodynamics and kinetics of phase transformations and diffusion, namely Thermo-Calc® and JMatPro®, have been combined with an interdendritic segregation tool (IDS) to optimize the contents of chromium, molybdenum and niobium in a proposed medium-carbon low-manganese steel composition. Important factors taken into account in the modeling and optimization were hardenability and as-quenched hardness, grain refinement and alloying cost. For further investigations and verification, the designed composition, i.e., in wt.% 0.40C, 0.20Si, 0.25Mn, 0.90Cr, 0.50Mo, was cast with two nominal levels of Nb: 0 and 0.012 wt.%. The results showed that an addition of Nb decreases the austenite grain size during casting and after slab reheating prior to hot rolling. Validation experiments showed that the predicted properties, i.e., hardness, hardenability and level of segregation, for the designed composition were realistic. It is also demonstrated that the applied procedure could be useful in reducing the number of experiments required for developing compositions for other new steels.

Effect of Nb doping on microstructures and thermoelectric properties of SrTiO3 ceramics**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0403803), the National Natural Science Foundation of China (Grant Nos. 51774065, 51525401, 51690163, and 51601028), and the Dalian Support Plan for Innovation of High-level Talents (Top and Leading Talents) (Grant No. 2015R013).

Nb-doped SrTiO3 thermoelectric ceramics with different niobium concentrations, sintering temperatures and Sr-site vacancies are successfully prepared by high energy ball milling combined with carbon burial sintering. For fully understanding the effect of niobium doping on SrTiO3, thermoelectric transport properties are systematically investigated in a temperature range from 300 K to 1100 K. The carrier mobility can be significantly enhanced, and the electrical conductivity is quadrupled, when the sintering temperature rises from 1673 K to 1773 K (beyond the eutectic temperature (1713 K) of SrTiO3–TiO2). The lattice vibration can be suppressed by the lattice distortion introduced by the doped niobium atoms. However, Sr-site vacancies compensate for the lattice distortion and increase the lattice thermal conductivity more or less. Finally, we achieve a maximum value of figure-of-merit zT of 0.21 at 1100 K for SrTi0.9Nb0.1O3 ceramic sintered at 1773 K.

Fabrication, structural and electrical properties of Sr(V,Nb)O3-δ perovskite materials

The SrV1-xNbxO3-δ materials with different niobium content in perovskite B-sublattice were prepared by a solid-state reaction process. The microstructure and phase compositions of obtained samples were analyzed by the X-ray diffraction technique (XRD) and scanning electron microscopy (SEM). The electrical conductivity of samples was measured by a DC 4-wire method in range of 100–600 °C in different gas conditions. The oxidation state of the niobium and vanadium cations in the structure was determined by the X-ray photoelectron spectroscopy (XPS). The obtained results were discussed and analyzed in comparison to the previous literature reports and defect chemistry models.

Effect of Nb addition on microstructure and corrosion resistance of novel stainless steels fabricated by direct laser metal deposition

The study demonstrated the successful fabrication of novel stainless steels by direct laser metal deposition with the aim of investigating the impact of niobium content (Nb = 0, 0.25, 0.75, 1.25 wt%) on their microstructure and electrochemical properties. The microstructure and phase evolution of the as-built stainless steels were studied using scanning electron microscope (SEM) and electron back-scatter diffraction (EBSD). Corrosion behavior of the samples was evaluated using electrochemical workstation in 3.5 wt% NaCl. Experimental results have shown that the crystal structure of as-built stainless steels was BCC with a small trace of dispersive carbides and FCC phase. Grain refinement was observed with increasing niobium content. Large-angle boundaries were obtained in different Nb-containing samples with distribution from 50° to 60°. An increase in niobium content extremely improved the corrosion resistance of as-built stainless steels and the as-built samples with 1.25 wt% exhibited the best corrosion resistance among the tested samples as indicated by its lowest corrosion rate, which was an order of magnitude lower than that of Nb-free samples.