Niobium Compounds Research Articles

Rf surface resistance measurements of binary and ternary niobium compounds

The superconducting properties of binary and ternary niobium compounds for rf applications are investigated. The materials under study are niobium nitride (NbN), niobium-titanium nitride (NbTiN), and niobium tin (Nb3Sn). Preparation techniques of the compounds are discussed. NbN and NbTiN are obtained by thermal reaction of bulk Nb in nitrogen atmosphere. Nb3Sn has been obtained using a technique originally developed for high-field magnet fabrication and modified to be applied to rf cavity production. The experimental apparatus and measurement technique are described. In particular the raw experimental data have been carefully analyzed to obtain important informations on fundamental material parameters. The effect of field penetration in the superconductor and the influence on the experimental results of the normal metallic substrate on which the superconductor is grown is also considered. The measurements show that NbN and Nb3Sn are effectively potentially good materials for rf applications due to their low theoretical BCS surface resistance. So far the results obtained with NbTiN are more difficult to interpret because the quality of the material did not allow sufficiently accurate collection of data.

The oxidation-sulfidation of FeNb alloys at 600–800°C in H 2-H 2S-CO 2 mixtures

The corrosion of the two pure metals and of two Fe-Nb alloys containing 15 and 30 wt% Nb has been studied at 600–800°C in H 2-H 2S-CO 2 gas mixtures providing a sulfur pressure of 10 −8 atm and oxygen pressures of 10 −24 atm at 600°C and 10 −20 atm at 700–800°C. Both iron and the two alloys corroded according to an approximate parabolic rate law, with an instantaneous rate constant increasing with time. The rate constants for corrosion decreased with an increase in the Nb content of the alloys under constant temperature but increased with temperature for the same alloy. In all cases the rate constants were slightly lower than those for the corrosion in H 2-H 2S mixtures under the same temperature and sulfur pressure, but remained still quite high as compared to the rate of corrosion of pure niobium due to the lack of formation of a protective layer of niobium compounds. The scales were duplex, presenting an outer layer of pure FeS and an inner complex layer containing a mixture of FeS, double sulfide, niobium oxides and some double oxide. Islands of the Nb-rich Fe 2Nb phase remained partly unsulfidized in the inner scale region for the most concentrated alloy. The corrosion behaviour observed is a result of the low solubility of niobium in iron and of the two-phase nature of the alloys.

Recycling of strategic metals from industrial slag by a hydro-and pyrometallurgical process

Tin slag may contain up to 25% of (Nb+Ta) 2 O 5. Tantalum and niobium are used in advanced technologies. Classical methods for the extraction of these elements are based on the full dissolution of these slags by HF or (HF+H 2 SO 4). This leads to high reagent consumption, due to presence of Si, Fe, Mn, Ca, Al oxides, and the production of toxic wastes. This paper describes a new approach for the characterization and extraction of these metals based on a combined hydro- and pyrometallurgical process. The planning of successive alkaline and acid leaching of this slag based on the “pseudo-structure” of these amorphous materials permits a selective dissolution of the economic metals, a lower consumption of chemical reagents, especially HF, less toxic residues and a high grade concentrate (up to 60% of pentoxide of tantalum and niobium) with a satisfactory recovery rate (about 85%). These concentrates are subjected to a subsequent selective carbochlorination, at temperatures lower than 500°C, leading to full extraction of niobium compounds at 300°C and that of tantalum at 500°C.

Preparation, Characterization and Catalytic Activity of Niobium Oxynitride and Oxycarbide in Hydrotreatment

ABSTRACTOxynitride and oxycarbide of niobium present metallic and acidic catalytic functions as evidenced by molecular probe reactions: isomerization of cyclohexane and hydrodenitrogenation of 1–4 tetrahydroquinoline. The proximity of the two functions leads to the concept of “dual site” by selective inhibition of the metallic and acid sites. Substitution of nitrogen of the oxynitride by carbon to form the oxycarbide produces a large enhancement of the metallic character of the surface. The oxynitride was shown to present a more acidic and a less hydrogenating activity as compared to the activity of the oxycarbide. Both compounds of niobium have been compared to molybdenum oxynitride.

Reduction of half-sandwich niobium compounds: tertiary phosphine and carbonyl derivatives of (pentamethylcyclopentadienyl)niobium(III)

Reduction of half-sandwich niobium compounds: tertiary phosphine and carbonyl derivatives of (pentamethylcyclopentadienyl)niobium(III)

Metal-metal-bonded compounds of lower-valent niobium and tantalum. Compounds containing the [Nb2Cl7(PR3)2]- and [Nb3Cl10(PR3)3]- ions and some clues as to how higher-nuclearity clusters are formed

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMetal-metal-bonded compounds of lower-valent niobium and tantalum. Compounds containing the [Nb2Cl7(PR3)2]- and [Nb3Cl10(PR3)3]- ions and some clues as to how higher-nuclearity clusters are formedF. Albert Cotton and Maoyu ShangCite this: Inorg. Chem. 1993, 32, 6, 969–976Publication Date (Print):March 1, 1993Publication History Published online1 May 2002Published inissue 1 March 1993https://doi.org/10.1021/ic00058a037RIGHTS & PERMISSIONSArticle Views95Altmetric-Citations19LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (942 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Niobium compounds and alloys

H.C. Starck GmbH & Co. KG is a leading producer of metal and ceramic powders. One of the main areas of H.C. Starck production is niobium compounds and their alloys. In the following paper the various processes for the production of niobium compounds and alloys are summarized. Some new areas of application are presented and some highlights on how niobium compounds and alloys will impact future demand for niobium in nonferrous applications are given.

Niobium and Niobium Compounds

Niobium and Niobium Compounds

Dalton communications. Niobium and tantalum oxo compounds: synthesis and crystal structure of the tetranuclear tantalum(V) oxo cluster [{TaOCl2(O2CC6H4Me-p)}4

Products from the reaction of MCl5(M = Nb or Ta) with acids RCO2H (R = aryl) include the tetranuclear tantalum oxo cluster [{TaCl2(µ-O)(O2CC6H4Me-p)}4] containing a Ta4O4 core, dinuclear [{NbCl3-(O2CR)}2(µ-O)], and the monosubstituted [TaCl4(O2CR)].

Ceramic materials for producing high-purity compounds of niobium and tantalum

Ceramic materials for producing high-purity compounds of niobium and tantalum

Four coordinate oxo-phenoxide compounds of niobium(V): Synthesis and characterization of [Nb(O)(O-2,6-R 2C 6H 3) 3], R  Me (1), R  tBu (2)

The yellow, crystalline four-coordinate compounds [Nb(O)(O-2,6-R 2C 6H 3) 3], R = Me ( 1), R = tBu ( 2), have been synthesized in good yield via the reaction of [Nb(O)Cl 3(CH 3CN) 2] with LiO-2,6-R 2C 6H 3.

Catalytic properties of niobium sulphides in the conversion of nitrogen containing molecules

The catalytic properties of niobium sulphides, i.e. NbS 3 and Nb 1.12S 2 have been examined in the conversion of nitrogen-containing molecules (n-pentylamine and pyridine), and in the hydrogenation of biphenyl. Compared to MoS 2, NbS 3 and Nb 1.12S 2 show higher activities for all these reactions and a peculiar ability to perform CN and CC bond cleavage. The activities for these last reactions have been related to the acid-base properties of niobium compounds. Moreover, the trisulphide is more active than Nb 1.12S 2. These differences in activities are discussed in relation to the structural features of both sulphides and the existence in NbS 3 of S 2 2− groups and metal-metal pairing.

Critical temperature of superconductivity and X-ray crystallographic studies of Nb0.78Al0.17Ge0.05 of A15 structure

Compounds of niobium and aluminium and of niobium, aluminium and germanium which crystallize in the A15 structure were prepared by sintering and by floating-zone methods. Single crystals of up to 1 × 1 × 1 mm were obtained for the composition Nb0.78Al0.17Ge0.05. Transition temperatures to superconductivity ranged from midpoint values of 18.6 to 19.4 K over intervals of 3 K. Single-crystal X-ray diffraction measurements were made at 293 and at 11–12 K. Powder diffractometer data were obtained at 293 K. The structure was refined with both powder data (Rietveld technique) and single-crystal data. Photographic powder patterns were obtained from room temperature down to 11.7 K. No phase transition was observed. No evidence was found for deviations from the A15 structure.

Synthesis, structure and reactivity of new low-valent mono(η-arene)niobium compounds

The new compounds [Nb(η-C6H5Me)(PMe3)3R](R = H or SiMe3), [Nb(η-C6H5Me)(tmps)], [Nb(η-C6H5Me)(tmps)H][tmps = MeSi(CH2PMe2)3], [Nb(η-C6H5Me)(η-C5H5)(PMe3)], [Nb(η-C6H5Me)(η-C9H7)(PMe3)], [Nb(η5-C9H7)(CO)3(PMe3)], [Nb(η-C6H5Me)(η5-C7H9)(PMe3)], [Nb(η-C7H7)(η4-C7H8)(PMe3)], [Nb(CO)3(PMe3)4][Nb(CO)5(PMe3)], [Nb(η-C7H7)(CO)2(PMe3)], [Nb(η-C6H5Me)2X](X = Br, I, Me, Ph or CH2Ph), [{Nb(η-C6H5Me)(µ-SR)2}2](R = CH2Ph, Me or Bu) and [{Mo(η-C6H5Me)(µ-SePh)2}2][PF6]2 have been prepared (indicates the crystal structure has been determined). Evidence for the anions [Nb(η-C6H5Me)(PMe3)3]– and [Nb(η-C6H5Me)(tmps)]– is presented.

The Reduction of the NbX5/AlX3 System with Aluminum in the Presence of Aromatic Hydrocarbons: An Approach to Niobium(II), Niobium(I), and Niobium(0) Organometallics

The niobium(0) compound [Nb(mes)2] (mes = 1,3,5‐trimethylbenzene) was prepared not only by metal atom–ligand cocondensation, but also according to Equation (a). The chemical behavior of this compound is similar to that of the analogous complex [V(mes)2]. For example, it reacts under carbon monoxide atmosphere to give the green salt [Nb(mes)2(CO)][Nb(CO)6]. This new, simple approach to niobium(0) compounds should facilitate their study (DME = dimethoxyethane). equation image

Transition orthorhombic … rutile in xMFeO 4-(1 − x)ZnF 2 phases ( M = Ta, Nb and x > 0.7)

xMFeO 4-(1 − x)ZnF 2 solid solutions with M = Ta, Nb are synthesized and studied by means of X-ray diffraction measurements. They exist only in the limited domain x ≥ 0.75. Niobium compounds always present an orthorhombic structure of α-PbO 2 type while tantalum phases have a rutile structure above 700°C and the orthorhombic structure at lower temperatures. For the orthorhombic phases x = 0.9, a surstructure of wolframite type appears. Tantalum orthorhombic phase x = 0.9 has a ferrimagnetic behavior under 150 K. The others exhibit antiferromagnetism.

Solid state structure of the tantalum bis-aryl compounds Ta(OAr-2,6R 2) 3(C 6H 5) 2 (R = CH 3, Pr i; OAr-2,6R 2 = 2,6-dialkylphenoxide): Observation of a lack of correlation of MOAr distances and MOAr angles for aryloxide derivatives of niobium(V) and tantalum(V)

Treatment of the tantalum dichloride compounds Ta(OAr-2,6Me 2) 3Cl 2 or Ta(OAr-2,6Pr 2 i) 3Cl 2 (OAr-2,6Me 2 = 2,6-dimethylphenoxide; OAr-2,6Pr 2 i = 2,6-diisopropylphenoxide) with phenyl lithium (2 equiv) leads to the formation of the bis-phenyl compounds Ta(OAr-2,6Me 2) 3(C 6H 5) 2 ( 1) and Ta(OAr-2,6Pr 2 i) 3(C 6H 5) 2 ( 2), respectively, in moderate yields. Single crystal X-ray diffraction analyses of both 1 and 2 show them to be isostructural. In both compounds a trigonal bipyramidal environment about the metal centre is evident with trans, axial aryloxide oxygen atoms. Short TaO distances in the range of 1.848(5)-1.881(3) Å and almost linear TaOAr angles are present. The central coordination environments in 1 and 2 are strikingly similar to those found for the biscyclometallated compound Ta(OC 6H 3Ph-C 6H 4) 2(OAr-2,6Ph 2). Combining the structural data for 1 and 2 with those of other alkyl, aryloxide compounds of niobium(V) and tantalum(V) shows that the MOAr distances span a narrow range of 1.85-1.95 Å, while the corresponding MOOAr angles vary from 135 to 180° with no correlation between the two parameters. Crystal data for TaO 3C 36H 37 ( 1) at 19°C: a = 19.313(3), b = 11.652(1), c = 15.288(1) Å, β = 113.13(1)°, Z = 4, d calc = 1.446 g cm −3 in space C2/ c; for TaO 3C 48H 61 ( 2) at 21°C: a = 11.955(2), b = 19.585(2), c = 19.337(2) Å, β = 103.742(9)°, Z = 4, d calc = 1.309 g cm −3 in space group P2 1/ n.

ARXPS analysis and oxidation of niobium compounds

In oxidation the interface stoichiometry and the micro-structure of the interface are of crucial importance. Both aspects are enlightened by ARXPS (angle resolved photo electron spectroscope). ARXPS results on Nb compound surfaces are used to present a detailed model for the oxide growth on, and oxide pick-up into, these metals. The effect of strain and of metallic interface compounds on the oxidation is discussed.

Drop calorimetry of the compounds NbCl5, TaCl5, RbNbCl6, CsNbCl6, RbTaCl6, and CsTaCl6

Enthalpy contents for NbCl5, TaCl5, RbNbCl6, CsNbCl6, RbTaCl6, and CsTaCl6 were measured as functions of temperature using a high temperature aluminum block drop calorimeter. It was found that the solid compounds RbNbCl6, CsNbCl6, RbTaCl6, and CsTaCl6 undergo allotropie solid–solid transformations and the enthalpies and entropies associated with these phase changes, as well as from fusion, have been evaluated.Molar heat capacities for the systems investigated are reported as linear functions of temperature.The molar heat capacities for solid and molten NbCl5 or TaCl5 were used together with available vapour pressure data to express enthalpies and free energies of vaporization for these compounds as functions of temperature through the third law calculation method. Keywords: calorimetry, heat capacities, transition enthalpies, niobium compounds, tantalum compounds.

Non-centrosymmetrical phases in alkali metal oxyfluoroniobates

Abstract Among the known ferroelectrics most common are niobium compounds such as double oxides crystallized in the type of perovskite, pyrochlorine, tangsten bronzes, LiNbO3, etc.1 Double oxides containing niobium (Y) are characterized by the structures with all NbO7 6- octahedrons forming a solid framework. Substitution of an oxide ion by its steric analogue-fluoride ion opens up greater possibilities for us to synthesize the compounds. Alongside the compounds isostructural of the corresponding double oxides with the framework-type structures, one may obtain new ones, which structure differs in the manner of octahedral junction. The increase in F/O ratio leads to the decrease in the number of common octahedral components for Nb(0, F)6 to produce the structures of a layered-, chain- and isIand-type.2.3 On the other hand, a change in the F/O ratio affects the length and degree of covalency in the bond Nb-(0, F) inside the niobium-bearing element of the structure, thus determining the dielectric properties...