Niobium Compounds Research Articles

10th International Symposium on Group IV, V, VI elements

For the first time the international symposium on group V elements included group IV and VI elements: titanium chromimu halfnium and chromium, molybdenum, and tungsten. This symposium series began in 1992 and it was originally dedicated to niobium compounds [1]. Three years later, again in Tokyo, the second symposium remained with niobium materials and catalysts [2]. After another three years, the symposium shifted to Rio de Janeiro and expanded to include vanadium and tantalum group V elements [3]. The symposium has been held every three years thereafter in Spain [4,5], Hancock Massachusetts [6], Poland [7], Italy [8], and New Delhi in 2019 [9]. Due to COVID the 10th symposium, held in Montreal, was delayed by one year and it was expanded to include Group IV and VI elements.

Corrosion Protection of Electrogalvanized Steel by Surface Treatments containing Cerium and Niobium compounds

Corrosion Protection of Electrogalvanized Steel by Surface Treatments containing Cerium and Niobium compounds

КАЛЬЦИЕТЕРМИЧЕСКИЕ ПОРОШКИ НИОБИЯ

The reduction of niobium compounds Nb2O5 and Mg4Nb2O9 by calcium vapor in the temperature range of 750–850 °C has been studied. The features of the porous structure of the obtained niobium powders are established, and the effect of the Mg4Nb2O9 particle size on the completeness of reduction, which increases with a decrease in the average particle size of magnesium niobate, is shown.

Niobium: The Focus on Catalytic Application in the Conversion of Biomass and Biomass Derivatives.

The world scenario regarding consumption and demand for products based on fossil fuels has demonstrated the imperative need to develop new technologies capable of using renewable resources. In this context, the use of biomass to obtain chemical intermediates and fuels has emerged as an important area of research in recent years, since it is a renewable source of carbon in great abundance. It has the benefit of not contributing to the additional emission of greenhouse gases since the CO2 released during the energy conversion process is consumed by it through photosynthesis. In the presented review, the authors provide an update of the literature in the field of biomass transformation with the use of niobium-containing catalysts, emphasizing the versatility of niobium compounds for the conversion of different types of biomass.

Synthesis of a highly active Nb2O5 for 1,2-cyclohexanediol production

A commercial niobium oxide was used to form a gelled material, which was lyophilized producing a novel polyoxoniobate catalyst (L-AmNbO) containing peroxo groups. The activity of this new catalyst was assessed through oxidation reactions of the cyclohexene. In the presence of L-AmNbO catalyst, the oxidation of cyclohexene with H2O2 reached 90% of conversion after 12 h at 75 °C, with selectivity for 1,2-cyclohexanediol (∼ 50%). The catalytic results and the surface properties of this new material indicated that it can be a promising catalyst for niobium compounds applications in the selective oxidation of cyclohexene.

Solvent-Impregnated Sorbents for Tantalum from Niobium Separation Using a Fixed-Bed Column.

Reactor-grade niobium steel is used as a construction material for nuclear reactors. In this case, the presence of tantalum, which is characterized by a 20 times higher active cross section for capturing thermal neutrons than the cross section of niobium (181Ta: 21.3 barn), cannot exceed 100 ppm. Analytical methods for quality and new separation method development control need very pure niobium matrices—niobium compounds with a low tantalum content, which are crucial for preparing matrix reference solutions or certified reference materials (CRMs). Therefore, in this paper, a new, efficient method for separating trace amounts of Ta(V) from Nb(V) using extraction chromatography with the use of sorbents impregnated with methyl isobutyl ketone MIBK solvent is proposed. Various types of MIBK-impregnated sorbents were used (AG® 1-X8 Anion Exchange Resin, AMBERLITE™ IRC120 Na Ion Exchange Resin, SERVACEL® Cellulose Anion Exchangers DEAE 52, active carbons of various grain size, carbonized blackcurrant pomace, carbonized chokeberry pomace, bentonite, and polyurethane foam in lumps). The highest tantalum removal efficiency was determined using active coal-based materials (>97%). The separation effectivity of tantalum from niobium was also determined in dynamic studies using a fixed-bed column with MIBK-impregnated active carbon. Solutions of various Nb:Ta weight ratios (1:1, 100:1, 1000:1) were used. The most impressive result was obtaining 70 mL of high purity niobium solution of tantalum content 0.027 ppm (in relation to Nb) with 88.4% yield of niobium from a solution of Nb:Ta, weight ratio 1000:1 (purge factor equaled 35,000). It proves the presented system to be applicable for preparation of pure niobium compounds with very low contents of tantalum.

P-Type Semiconduction in Oxides with Cation Lone Pairs

Semiconducting oxides are valuable as thin-film displays or solar cell electrodes and are recently of interest as back-end-of-line devices. There are numerous high-mobility n-type semiconducting oxides, but there is a lack of p-type oxides with similar mobility. This led to a search for additional p-type oxides using high-throughput calculations. We find that many of these proposed oxides possess cation s-like lone-pair states. The defect energies of some of these oxides are calculated here in detail. SnTa2O6 is found to be promising p-type oxide based on its low effective hole mass owing to its cation lone-pair character, wide stability range, and absence of compensating native defects. This leads to a desirable p-type doping limit range, which includes the valence band edge, but other oxides with structures more closely based on perovskite configuration are more n-type rather than p-type. The experimentally observed p-type conductivity in related niobium compounds is also discussed. The valence band edge of the disordered SnTa2O6 phase has a mixed O(p)–Sn(s)–O(p) character; thus, it is relatively insensitive to disorders, indicating that it could also make an effective p-type amorphous semiconductor.

NIOBIUM’S BEHAVIOR IN AQUEOUS HYDRO­FLUORIC ACID SOLUTION

Thanks to the unique combination of physicochemical properties, niobium and its compounds are widely used in various fields of science and technology. The main areas of niobium’s applications are the production of superconductors, nuclear energy, chemical engineering, metallurgy, manufacture of optically active materials, thin-film lithium batte­ries, fuel cells. The aim of this work is to study the processes that take place on the niobium electrode in aqueous solutions of hydrofluoric acid, as well as to establish the composition of niobium compounds that are formed. The paper presents the results of studies the behavior of the niobium electrode in aqueous solutions 0.25 N. hydrofluoric acid. The kinetic para­meters of the processes occurring at the phase boundary are determined. It was found that the anodic polarization of the niobium electrode is accompanied by the formation of a passive layer, the destruction of which is facilitated by increasing the polarization potential and fluorine anions, in the presence of which complex fluoroiobate anions [NbF7]2- and [NbOF5]2-are formed. Cathodic polarization of niobium is accompanied by the formation of hydrides on its surface, which causes an increase in the overvoltage of hydrogen evolution. The anodic polarization of the niobium electrode in a solution of hydrofluoric acid causes the formation on its surface of a passive layer, which is destroyed with increasing potential. In the Nbo–NbO2–0.25 –0.25 n HF system, [NbF7]2-anions are formed, as evidenced by bands in the region of 500 nm on the electron absorption spectra. The rate constants of [NbF7]2- and [NbOF5]2- formation are estimated at 3.78 • 10-3 s-1 and 5.18 • 10-3 s-1, respectively. The reduction of hydrogen at the niobium cathode from a solution of hydrofluoric acid is accompanied by the formation of hydrides, which causes an increase in the overvoltage of hydrogen evolution and high values of the angular coefficients of the Tafel dependence.

Biodiesel Production over Niobium-Containing Catalysts: A Review

Nowadays, the synthesis of biofuels from renewable raw materials is very popular. Among the various challenges involved in improving these processes, environmentally benign catalysts compatible with an inexpensive feedstock have become more important. Herein, we report the recent advances achieved in the development of Niobium-containing heterogeneous catalysts as well as their use in routes to produce biodiesel. The efficiency of different Niobium catalysts in esterification and transesterification reactions of lipids and oleaginous raw materials was evaluated, considering the effect of main reaction parameters such as temperature, time, catalyst load, and oil:alcohol molar ratio on the biodiesel yield. The catalytic performance of Niobium compounds was discussed considering the characterization data obtained by different techniques, including NH3-TPD, BET, and Pyr-FT-IR analysis. The high catalytic activity is attributed to its inherent properties, such as the active sites distribution over a high specific surface area, strength of acidity, nature, amount of acidic sites, and inherent mesoporosity. On top of this, recycling experiments have proven that most Niobium catalysts are stable and can be repeatedly used with consistent catalytic activity.

Fast pyrolysis as a tool for obtaining levoglucosan after pretreatment of biomass with niobium catalysts

Levoglucosan (LGA) is a promising chemical platform derived from the pyrolysis of biomass that offers access to a variety of value-added products. We report an efficient route to produce LGA via the pretreatment of biomass with niobium compounds (oxalate, chloride and oxide) followed by fast pyrolysis coupled with gas chromatography-mass spectrometry (Py-GC–MS) at temperatures of 350–600 °C. Catalytic pretreatment reduces the quantity of lignin in the biomass, concentrates the cellulose and enhance LGA formation during fast pyrolysis. The pretreatment also removes alkaline metals, preventing competitive side reactions. The effect of several parameters such as catalyst weight, time, temperature, and solvent, with the optimal pretreatment conditions determined to be 3 (wt.%) niobium oxalate for 1 h at 23 °C in water. Pretreatment increased the LGA yields by 6.40-fold for sugarcane bagasse, 4.15-fold for elephant grass, 4.13-fold for rice husk, 2.86-fold for coffee husk, and 1.86-fold for coconut husk as compared to the raw biomasses. These results indicate that biomass pretreatment using niobium derivates prior fast pyrolysis can be a promising technique for biomass thermochemical conversion in LGA and others important pyrolytic products.

CBN-based cutting tools with niobium compounds as a binder phase.

cBN-based materials are well known for their high chemical inertness and high performance. The variation of binder phase type and amount enable improvement of performance even more. Comprehensive investigation of the influence of type of niobium compound (NbC and NbN) as a binder phase for cBN-based materials were done. Samples were prepared by high pressure high temperature (HPHT) sintering under pressure of 7.7 GPa. Sintered samples were investigated in terms of phase composition (XRD), microstructure (SEM, EDX) and mechanical properties. Performance of investigated tools were tested in conditions of high speed machining of Inconel 718 alloy and Caldie tool steel.

Hexanuclear Niobium Cluster Compounds with Protonated N‐Base Cations

Octahedral clusters of the [M6X12] type offer numerous possibilities to form structural arrangements through different choices of bonding situations. In this paper a series of new cluster compounds of the transition metal niobium is described, which consist of the [Nb6Cl18]2–, and in one case [Nb6Cl18]3–, anion and protonated N‐base cations ([MIm‐H]+, [nPr3N‐H]+, [TMGu‐H]+, and [Tzn‐H]+). They all are prepared using water scavenger compounds [SOCl2 or (Ac)2O] under oxidising conditions, resulting in two‐electron (or one‐electron, respectively) oxidized cluster units with respect to the starting material [Nb6Cl14(H2O)4]·4H2O. Of five members of this group single‐crystal X‐ray structures were determined. The cluster anions exist in all structures as discrete units. The acidic H atoms of all N‐bases are hydrogen bonded to H acceptors, in 4 cases to outer, exo bonded Cl atoms of the cluster unit and in one case to the O atom of a co‐crystallized THF molecule. In [TMGu‐H]2[Nb6Cl18] chains of cluster anions exist hydrogen‐bonded through bridging [TMGu‐H]+ cations. ESI mass spectra of [MIm‐H]2[Nb6Cl18]·2SOCl2 and [TMGu‐H]2[Nb6Cl18] show the expected isotopic distribution patterns for the anions together with other peaks associated to chloride mass losses and/or reduction processes.

Structure and Mechanical Properties of the Layered Composites Made of Multicomponent Niobium Alloys and Hardening Silicon–Carbon Compounds Formed by Solid-Phase Sintering

Abstract—The microstructure and the mechanical properties of the layered composite materials fabricated by diffusion welding of stacks of niobium foils with a one-sided silicon-containing multicomponent metallic coating are studied. The multilayer structure of the composites consists of a viscoplastic niobium alloy and niobium compounds with silicon and carbon. The bending tensile strength of the composites is 200–320 and 260–420 MPa at 1100 and 1300°C, respectively, and is 320–550 MPa at room temperature.

Studies on Intergranular Corrosion Characteristics of Cast Duplex Stainless Steel Stabilized with Niobium

Abstract To study intergranular corrosion (IGC) characteristics, two cast grades of duplex stainless steels, 5A and 5A stabilized with niobium, were produced in a vacuum induction melting furnace. The samples were tested under three different heat-treatment conditions that were selected using a property diagram generated through the TCFE8 database of the Thermo-Calc® software (Thermo-Calc Software, Solna, Sweden). A Feritscope FMP30® (Fischer Technology, Inc., Windsor, CT) was used to measure the ferrite phase content in the samples and compared with that specified in the property diagram. Metallurgical characteristics were analyzed through optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometry. Each heat-treated sample possessed a distinct texture due to the formation of various intermetallic phases in the alloy. The corrosion behavior of the samples was studied using an oxalic acid etch test. Double-loop electrochemical potentiokinetic reactivation and sulfuric acid tests were conducted on the niobium-stabilized samples, and the results demonstrated that the samples possess superior resistance to corrosion compared to those not stabilized with niobium. The addition of niobium produced a mixture of niobium compounds that suppressed the chromium depletion and reduced the degree of sensitization. This study demonstrated the potential of using niobium as a stabilizer in the duplex stainless steel alloy to considerably reduce IGC.

Electrochemical properties of niobium and niobium compounds modified AISI430 stainless steel as bipolar plates for DFAFC

ABSTRACTThe highly conductive and corrosion resistant diffusion layers of niobium, niobium nitrides and niobium carbides have been successfully fabricated on AISI430 stainless steel (430 SS) via a plasma surface diffusion alloying (PSDA) method as bipolar plates for direct formic acid fuel cells (DFAFCs). The surface of niobium carbides modified 430 SS (NbC 430 SS) is relative densification and uniformity without other surface flaw and micropore. Potentiodynamic and potentiostatic polarisation measurements indicate that NbC 430 SS enhances the corrosion resistance more effectively than other modified samples and its corrosion current density is maintained approximately 2.5 μA cm–2 in the simulated anodic environment of DFAFC. Moreover, NbC 430 SS presents a superior hydrophobicity with a contact angle of 105.5° and a lower interfacial contact resistance (ICR) before and after potentiostatic polarisation tests than other specimens. Therefore, NbC 430 SS developed in this work has a great potential to be bipolar plates for DFAFCs.

Effects of raw materials on NaNbO3 nanocube synthesis via the solvothermal method

ABSTRACTA nanocube is a single nanoscale crystal with a cubic shape. Raw materials are an important factor in determining the synthesis of nanocubes. In this study, we investigated various niobium compounds that serve as raw materials, each inducing different effects during nanocube synthesis. Perovskite sodium niobate (NaNbO3) nanocubes were synthesized using a two-step process. The first step in this process, synthesis of the raw materials, was followed by solvothermal synthesis of NaNbO3 nanocubes. The raw material for the first step was obtained by applying heat treatment to a precursor following Nb hydrolysis. The heat treatment was performed at temperatures of 300–1000°C. Nb2O5 was obtained after heat treatment of its precursor, during which its crystalline system morphed into hexagonal, orthorhombic, and monoclinic systems with respective increases in temperature. For the second step, we obtained various NaNbO3 morphologies via the solvothermal method using water, methanol, or ethanol as a reaction medium. NaNbO3 nanocubes were formed by applying the solvothermal method to the synthesized precursor during heat treatment at 800°C. Solvothermal synthesis was performed with methanol as the reaction medium at 200°C, which resulted in the formation of NaNbO3 nanocubes.

Simple Niobium Catalysts Applied in Reflux and Ultrasound-Assisted Systems for Biofuel Synthesis

Using niobium compounds as heterogeneous catalysts in biodiesel production is a promising methodology from economic and environmental viewpoints. However, the application of niobium catalysts still is a challenge due to the high temperatures and pressures for moderate biofuel yields. Therefore, easily handled and applied materials have been developed to optimize biofuel production, which is the goal of this study. Nb2O5 and ammonium niobium oxalate (AmNO) were activated in reflux and ultrasound-assisted system. Nb2O5 showed better activity under reflux, using methanol. The characterizations conclude that the Lewis-acid sites are determinant for higher conversion rather than surface area. AmNO has better activity also in the reflux system at 70 oC, against 170 oC for Nb2O5, reaching above 70% conversion. In addition, reactions in ultrasound-assisted systems are also appealing due to the lower time and temperature, with conversion rates above 40%. Both catalysts showed interesting results under milder conditions than those in the literature.

Molecular Niobium Precursors in Various Oxidation States: An XAS Case Study.

Although X-ray absorption spectroscopy (XAS) has become an indispensable tool in characterization of solid-state materials, it is less of a staple in molecular chemistry of niobium. Scattering X-ray techniques remain relatively unexplored for the systematic study of molecular niobium compounds. Here, we use XAS to probe the niobium environment in commonly used Nb precursors in +V, +IV, and +III oxidation states. Apart from laying out the guidelines for identification of niobium oxidation states, we correlate our data with density functional theory models to provide further structural insight. Of particular note, we are able to shed light on the nature of the commonly used and catalytically competent NbCl3(DME), which had not been previously characterized structurally despite its prevalence in Nb chemistry.

Fluorination of niobium compounds with fluorine for fluoride volatility method

Niobium is one of the fission products contained in spent nuclear fuel. Since niobium pentafluoride (NbF5) has high volatility, it is considered that niobium volatilizes with uranium hexafluoride when applying the fluoride volatility method, which is a promising pyro-reprocessing method. In this study, fluorination behavior characteristics of niobium compounds, such as reaction temperature, volatility, and reaction path, were investigated by thermogravimetric and differential thermal analyses and X-ray diffraction analysis. The target compounds were niobium metal, the niobium oxides NbO, Nb2O3, NbO2 and Nb2O5, and niobium oxyfluoride (NbO2F). All the niobium compounds reacted exothermically and were volatilized completely by the reaction with F2. It was considered that niobium volatilized as NbF5. The fluorination reactions started respectively at 180, 200, 300, and 300 °C for niobium metal, NbO, NbO2 and Nb2O5. In the fluorination of niobium oxides, the intermediate product NbO2F was also fluorinated above 300 °C and volatilized completely. Nb2O3, which seemed to be a mixture of NbO and NbO2, reacted with F2 as described by the summation of the fluorination reactions of NbO and NbO2. The reaction mechanism for the fluorination of niobium compounds obtained in this study is applicable to evaluation of the niobium transfer phenomena in the reprocessing process of the fluoride volatility method.

Niobium Compounds in Transesterification Reactions of Soybean Oil: A Promising Use of NbCl5

In heterogeneous catalysis, many transition metals and its derivatives, such as titanium and iron, have been vastly studied as nanoscale catalysts, but little is known about the use of niobium compounds. Being biodegradable and renewable, biodiesel contribute to the independence from oil and environment protection. In this work we have used different niobium compounds NbCl 5 , C 4 H 4 NNbO 9 .xH 2 O, NbPO 4 and Nb 2 O 5 synthetized by sol-gel technique with high surface area and with different crystalline structures (amorphous and nano crystalline), as a heterogeneous catalyst in biodiesel synthesis from commercial soybean oil. The commercial and the synthesized niobium oxide were used checking the effect of morphology and acidity presented in the yield of biodiesel synthesis. The results obtained were compared these results with the use of amorphous niobium oxide and another oxide catalyst. The biodiesel obtained was characterized by gas chromatography system equipped with a FID detector. NbCl 5 has presented the best yields of conversion among the other niobium derivatives and potential application in Biodiesel synthesis. DOI: http://dx.doi.org/10.17807/orbital.v10i5.1156