Radiochemical separation of zirconium from niobium with salicylhydroxamic acid

Salicylhydroxamic acid was employed (or the rapid radiochemical separation of zirconium from niobium. Neutron-deficient isotopes of the 2 elements formed in the spallation of niobium with 340-MeV protons were used as tracers.The method was employed in the study of short-lived zirconium and niobium activities using scintillation γ-spectrometry. The procedure is complete in about 7 min, and gives a chemical yield of the order of 50–60% and a decontamination factor of at least 5· 10⁴.     

Gravimetric separation of titanium and zirconium from Niobium with Phenylacetylhydroxamic acid

Phenylacetylhydroxamic acid is used to separate titanium and zirconium from niobium in an oxalate medium at pH 6.5–7.5 in presence of ammonium chloride at room temperature. The method is accurate when the ratio of (TiO₂ + ZrO₂) : Nb₂O₅ is 10 : 1 to 1 : 1 ; when the niobium concentration is higher, reprecipitation is necessary. Tantalum, citrate, tartrate, lactic acid, EDTA, and a large excess of oxalate interfere.     

Sine-wave polarographic determination of zirconium or niobium in aqueous media

The sine-wave polarographic determination of zirconium in aqueous media was investigated using solutions which were 0.55 – 5.5·10^-3M in zirconyl chloride and 1 M in potassium chloride and had been adjusted to pH 2.0 with hydrochloric acid. It was possible to determine zirconium in the concentration range of 0.05 to 0.4 mg per ml. The sine-wave polarographic behavior of zirconium in aqueous solutions in the pH range 2–3 is discussed. The sine-wave polarographic determination of niobium in aqueous media was investigated using concentrated sulfuric acid containing 5 to 0.1 mg of niobium per ml in a supporting electrolyte of citric acid; the determination of niobium was possible down to 0.1 mg of niobium per ml of concentrated sulfuric acid although the D.C. polarographic method was impractical for the determination of less than 0.5 mg of niobium per ml.     

Reversed phase chromatographic separation of zirconium,niobium and hafnium tracers with HDEHP

Effective separation of the congeneric pair of elements, zirconium and hafnium and also niobium which was in admixtures with zirconium as daughter in its isotopic form were achieved through reversed phase column and paper extraction chromatographic procedures using di-(2-ethylhexyl)phosphoric acid (HDEHP) as the liquid exchanger. In reversed phase column chromatographic separation, the tracers,⁹⁵Zr,⁹⁵Nb and^175,181Hf, were extracted by HDEHP impregnated on kieselguhr and were sequentially eluted with 6N H₂SO₄+xN oxalic acid+H₂O₂(where x=0.1, 0.5 and 2). Similarly, in reversed phase paper chromatographic study in which a coating of HDEHP on Whatman No. 1 chromatographic paper was used as stationary phase, the mobile phase, 18N H₂SO₄+0.1N oxalic acid + H₂O₂, helped in separating the elements with favorable separation factors. Under the optimal conditions, the separation and decontamination of the elements in both methods were found to be quantitative, as verified by -spectrometric studies.     

Analytical aspects of some organic acids

Summary o-Phenylenedioxydiacetic acid has been found to be a selective reagent for the estimation of zirconium. As little as 2.1 mg of zirconium can be easily estimated. The composition of the precipitate varies somewhat and therefore, direct weighing is not possible. This difficulty is overcome by igniting as oxide. Be²⁺, Ca²⁺, Ba²⁺, Zn²⁺, Hg²⁺, Al³⁺, Ce³⁺, Ti⁴⁺, Th⁴⁺, UO²⁺, Mn²⁺, Fe³⁺, Co²⁺, and Ni²⁺, ions do not interfere. Although V₂O₂ ⁴⁺ and Cr³⁺ ions are not precipitated in neutral or slightly acidic solutions they contaminate the zirconium precipitate, at about 0.30 N HCl concentration. The amount of contamination is so small that it is removed by double precipitation. This method gives satisfactory results even in the presence of small amounts of SO₄ ^2–ions.     

Solvent extraction and separation of zirconium,niobium and tantalum by 2-carbethoxy-5-hydroxy-1-(4-tolyl)-4-pyridone

Summary Extraction of zirconium, niobium and tantalum from oxalic and hydrofluoric acid solutions, by 2-carbethoxy-5-hydroxy-1-(4-tolyl)-4-pyridone (HA) dissolved in chloroform was studied. Extraction mechanism for the extraction of zirconium from oxalate solutions and of niobium from fluoride solutions is proposed. Separation of zirconium and niobium from oxalate solution as well as from fluoride solution and tantalum and niobium from fluoride solution is described. Back-extraction of these metals is possible by hydrofluoric and oxalic acid. Results obtained show that the efficiency of extraction by HA decreases in the sequence tantalum > niobium > zirconium.

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Zusammenfassung Die Extraktion von Zirkonium, Niob und Tantal aus oxalsauren und fluorwasserstoffsauren Lösungen mit Hilfe einer chloroformischen Lösung von 2-Carbäthoxy-5-hydroxy-(4-tolyl)-4-pyridon wurde untersucht. Ein Extraktionsmechanismus für Zirkonium aus Oxalatlösungen und für Niob aus Fluoridlösungen wurde vorgeschlagen. Die Trennung von Zirkonium und Niob aus einer Oxalatlösung oder aus einer Fluoridlösung sowie von Tantal und Niob aus einer Fluoridlösung wurde beschrieben. Die Rückextraktion dieser Metalle mit Flußsäure und Oxalsäure ist möglich. Die Ergebnisse zeigen, daß die Effizienz der Extraktion in der Reihenfolge Tantal > Niob > Zirkonium abfällt.

     

A Novel Niobium Cluster Aqua Ion with Capping μ4‐Se Ligand

The aqueous solution chemistry of niobium is underexplored, and well characterized aqua complexes are scarce. In this contribution, a new niobium aqua complex was obtained by treatment of Zn‐reduced ethanolic solution of NbCl₅ with HCl in the presence of a selenide source (ZnSe). This is the first example of selenium containing aqua complex of niobium. The yellow‐green aqua complex was isolated by cation‐exchange chromatography and transformed into corresponding isothiocyanate complex by ligand exchange, which was crystallized as (PyH)_4.5[H_1.5Nb₄SeO₅(NCS)₁₀] · 0.5H₂O. X‐ray structural analysis revealed a metal‐metal bonded tetranuclear {Nb₄(μ₄‐Se)(μ₂‐O)₅}⁴⁺ core with a capping μ₄‐Se ligand.     

The determination of carbon in the refractory metals zirconium,niobium, tantalum and tungsten by instrumental deuteron activation analysis

Instrumental activation analysis is used for the determination of carbon in the refractory metals zirconium, niobium, tantalum and tungsten, based on the ¹²C(d, n)¹³N reaction induced by 5–7-MeV deuterons. ¹³N(t_{$\text{1}\text{2}$} = 10.0 min) is detected via its annihilation radiation. The contribution of ¹³N to the annihilation activity is separated from that of other β⁺-emitters by decay-curve analysis. The method is free of nuclear interferences. The possible spectrometric interferences are discussed. Concentrations of 65.1, 24.8, 1.04 and <0.015 μg C g^-1, with relative standard deviations of 4.0, 5.9 and 14.0%, were obtained for zirconium, niobium, tantalum and tungsten, respectively.     

Zr2N2Se: The First Zirconium(IV) Nitride Selenide by the Oxidation of Zirconium(III) Nitride with Selenium

The oxidation of zirconium(III) nitride (ZrN) with suitable amounts of selenium (Se) in the presence of sodium chloride (NaCl) as flux yields small yellow brownish platelets of the first zirconium(IV) nitride selenide with the composition Zr₂N₂Se. The new compound crystallizes in the hexagonal space group P6₃/mmc (no. 194) with a = 363.98(2) pm, c = 1316.41(9) pm (c/a = 3.617) and two formula units per unit cell. The crystallographically unique Zr⁴⁺ cations are surrounded by three selenide and four nitride anions in the shape of a capped trigonal antiprism. The Se^2– anions are coordinated by six Zr⁴⁺ cations as trigonal prism and the N^3– anions reside in tetrahedral surrounding of Zr⁴⁺ cations. These [NZr₄]¹³⁺ tetrahedra become interconnected via three edges each to form $\rm^{2}_{\infty}$ {[(NZr_4/4)₂]²⁺} double layers parallel to the (001) plane, which are held together by monolayers of Se^2– anions.     

Thermodynamic investigations of uranium-rich binary and ternary alloys

Uranium–zirconium, uranium niobium, and uranium–zirconium–niobium alloys were synthesized by the arc melting technique and their phase transition temperatures were determined using a high temperature calorimeter. Heat capacities of U–7 wt%Zr, U–7 wt%Nb, U–5 wt%Zr–2 wt%Nb, U–3.5 wt%Nb–3.5 wt%Zr, and U–2 wt%Zr–5 wt%Nb were measured using a differential scanning calorimeter in the temperature range 303–921 K. A set of self-consistent thermodynamic functions such as entropy, enthalpy, and Gibbs energy function data for these binary and ternary alloys were reported for the first time using heat capacity data obtained in this study and required literature data.     

Separation of niobium and tantalum with cupferron

An attempt to separate niobium and tantalum by cupfcrron was only moderately successful at pH 4.5 to 5.5 in the presence of a magnesia mixture as a coagulating agent. A more satisfactory separation of niobium and tantalum from each other, tried out up to ratios of 30:1 and 1.30, is effected with Sn⁺² or Sn⁺⁴ as a co-precipitating agent under the conditions described niobium can be separated, in the presence of complexone III, from almost all the ions except U, Be, Ti and PO₄^-3. Iron and other tervalent elements, when present in 100 fold excess with respect to niobium, require double precipitation The method gives highly satisfactory results when applied to the analysis of niobium in niobium-molybdenum stainless steel.The use of titanium as a co-precipitant is less successful than that of tin     

Preparation and Characteristics of Nb<Superscript>5+</Superscript>, Ta<Superscript>5+</Superscript>/TiO<Subscript>2</Subscript> Nanoscale Powders by Sol–Gel Process Using TiCl<Subscript>3</Subscript>

Nanoscale TiO₂ powders doping with niobium and tantalum were prepared using TiCl₃ as a source matter. Characterization of the materials was performed by Thermoanalys, particle size, XRD, BET, FTIR, Magnetic Susceptibility. The influence of niobium and tantalum ions on the phase transition was studied, the changes in the crystal size and microstain distributions obtained at 400C were analyzed. The results show that the substitutes of Nb^{5 +}, Ta^{5 +} for Ti⁴⁺ in the anatase structure cause distortions and improve to form rutile. When the dopant content is over certain molar percent, biphase reappears. The IR spectra and magnetic susceptibility indicate the Nb–Nb (or Ta–Ta) bonds along c-axis in rutile by two Nb^{5 +} (Ta^{5 +}) ions located in sites adjacent along the c-axis appear with the dopant content. The magnetic characteristics at rutile showed a weak paramagnetism.     

Separation of protactinium from uranium and other reaction products in the reaction of 60 MeV/nucleon 18O with natural uranium

Protactinium was produced by the reaction of 60 MeV/nucleon ¹⁸O with natural uranium. A simple, relatively fast radiochemical procedure was developed, which can be used for the extraction separation of protactinium from uranium and from the complex reaction products using 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone and tri-iso-octylamine as extractants. Measurements of the gamma-ray spectra for the separated protactinium fractions were performed with a HPGe detector. The measured g-ray spectrum of protactinium shows that the decontamination from the main impurity elements, especially zirconium and niobium, is quite satisfactory.     

Intercalation of an oxalatooxoniobate complex into layered double hydroxide and layered zinc hydroxide nitrate

A Zn/Al layered double hydroxide with molar ratio of 3 was prepared by coprecipitation in alkaline pH and used as a matrix to intercalate the ionic complex diaquadioxalatooxoniobate(V) (DDON), derived from NH₄[NbO(C₂O₄)₂(H₂O)₂]2H₂O. In a similar way, the layered zinc hydroxide nitrate, Zn₅(OH)₈(NO₃)₂2H₂O, was synthesized, preexpanded with azelate ions (⁻OOC(CH₂)₇COO⁻), and then intercalated with the niobium complex. For both layered matrices, the results from X-ray powder diffractometry, Fourier transform infrared spectroscopy, and thermal analysis (TG/s-DTA) indicate the presence of the oxalate ion. In addition, results from X-ray photoelectron and Raman spectroscopy indicate the presence of the niobium center bonded to oxygen atoms. Finally, diffuse reflectance UV–vis spectroscopy suggests that the niobium centers are coordinated to oxalate ions. This is the first report of the intercalation of niobium into a layered matrix.     

Separation of95Zr and95Nb by means of sorption on silica gel from hydrochloric acid solutions

The adsorption behaviour of zirconium and niobium on silica gel from hydrochloric acid solutions was studied by batch equilibrations and passage through columns. On the basis of this, new methods are suggested for the separation and purification of⁹⁵Zr and⁹⁵Nb in hydrochloric acid and hydrochloric acid—methanol solutions. The methods are comparatively simple and rapid, and both zirconium and niobium can be obtained in a radiochemically pure state.     

The determination of zirconium in its binary alloys with niobium and tantalum

A procedure is presented for the determination of zirconium in the presence of niobium or tantalum. The bulk of the niobium or tantalum is first removed by extracting with hexone from a 10M hyclrofluoric acid, 6M sulphuric acid solution of the sample. The zirconium is then. separated from any unextractcd earth, acid element by precipitation with ammonium hydroxide followed by the addition of hydrogen peroxide. Under these conditions, both the niobium and tantalum form soluble peroxy complexes whereas the zirconium is completely precipitated from solution. After the separation of the precipitate by filtration, it is re-dissolved in hydrochloric acid and the zirconium concentration is finally determined by titration with ethylenediaminetetraacetic acid.     

Spontaneous passivity of amorphous bulk Ni–Cr–Ta–Mo–Nb–P alloys in concentrated hydrochloric acids

Rod-shaped amorphous bulk Ni–Cr–Mo-22 at.%Ta-14 at.%Nb–P alloys resistant to concentrated hydrochloric acids were prepared by copper-mold casting. Alloys of amorphous single phase and mixture of nanocrystalline phases in the amorphous matrix were all spontaneously passive in 6 and 12 M HCl and were immune to corrosion in 6 M HCl, although the corrosion weight loss was detected for heterogeneous alloys in 12 M HCl. Spontaneous passivation is due to presence of stable air-formed films in which chromium was particularly concentrated in addition to enrichment of tantalum and niobium. The angle resolved X-ray photoelectron spectroscopy revealed that chromium and molybdenum are rich in the inner part of the film. The major molybdenum species is in the tetravalent state, although penta- and hexavalent state molybdenum is also included. The high corrosion resistance was interpreted in terms of the high stability of the outer triple oxyhydroxide, Cr_1−x−yTa_xNb_yO_z(OH)_3+2x+2y−2z, and the effective diffusion barrier of the inner Mo⁴⁺ and Cr³⁺ oxide layer. Contribution to the Fall Meeting of the European Materials Research Society, Symposium D: 9th International Symposium on Electrochemical/Chemical Reactivity of Metastable Materials, Warsaw, 17th-21st September, 2007.     

Preparation and Mo¨ssbauer studies of (FeyNb1−y)1+xS2 compounds

The phase relations for iron niobium sulfides (Fe_yNb_1?y)_1+xS₂ have been examined by varying the partial pressure of sulfur at 950°C. While niobium is difficult to dissolve in iron sulfide, iron dissolves in niobium sulfide up to about 35% of the total metal sites. Iron niobium sulfide has the layered hexagonal type structure (2s-Nb_1+xS₂) with change in the lattice parameters depending on both the value of x and the amount of the iron dissolved. The Mo¨ssbauer spectra of sulfides with three different Fe/Nb ratios, 1/9(y =1/10), 1/4(y =1/5), and 1/2(y =1/3) were taken at 77 and 295 K. Each spectrum is composed of a quadrupole doublet which can be attributed to the Fe²⁺ ions in high spin state. The quadrupole splitting at 295 K decreases markedly with decrease in x which is related to change of the lattice parameters. Fe atoms cannot enter at random into all metal sites, and prefer to intercalate in the sites of partially filled layers. Possible models for the cation distribution in each metal layer are discussed.     

SNMS and GDOES studies of the oxidation behavior of TiAl modified by niobium addition

TiAl-based intermetallic alloys are promising candidates as structural materials for high temperature applications. However, industrial application is hindered by insufficient oxidation resistance at temperatures above 700?°C in air. The oxidation resistance can be improved by the addition of ternary and quaternary alloying elements, such as niobium. In several studies it has been demonstrated that this element can reduce the oxidation rate dramatically although the underlying mechanism is not yet fully understood. In the present study the influence of niobium on the high temperature oxidation behavior at 800?°C of Ti-48Al-2Cr was investigated. Niobium was added by alloying as well as by ion implantation. Some specimens were pre-oxidized prior to ion implantation. Thus, it could be demonstrated that niobium is not only active when present in the bulk alloy, but also when located in the initially formed corrosion scale. Moreover, the implantation experiments revealed that the often suggested “doping mechanism” of the titania lattice by Nb⁵⁺ ions cannot play an important role explaining the beneficial effect of Nb. The morphology and composition of the scales formed during oxidation were studied by glow discharge optical emission spectroscopy (GDOES) and secondary neutral mass spectrometry (SNMS). The latter technique was also used in combination with two-stage oxidation experiments using the isotope tracers ¹⁸O and ¹⁵N.     

Extraction-photometric determination of thorium with chlorophosphonazo-III

A simple and rapid spectrophotometric determination of thorium is described. The thorium-chlorophosphonazo-III complex is extracted into 3-methyl-1-butanol from 2.0–3.0 M hydrochloric acid solution. Maximum absorbance occurs at 620 and 670 nm and Beer's law is obeyed at the latter wavelength over the range of 0–15 μg per 10 ml of the organic phase. The molar absorptivity is 12.2·10⁴ l mole^-1 cm^-1 at 670 nm. Thorium can be determined in the presence of fluoride, oxalate, sulfate and EDTA. Many common cations do not interfere, but uranium, zirconium and niobium interfere seriously.