Determination of niobium, tantalum, zirconium, and hafnium by atomic emission spectrometry using directed thermochemical reactions

A method is proposed for determining niobium, tantalum, zirconium, and hafnium in mineral stocks. It is based on the preliminary synthesis of analyte complexes in hydrofluoric acid containing cadmium oxide. It was shown by spectrographic measurements that the decomposition products of complexes in a small chamber electrode of an ac carbon arc are volatile individual analyte fluorides.     

Separation of trace concentrations of tantalum from niobium and some other heavy metal ions by extraction with N-oxide of trioctylamine

The distribution of tantalum(V) between 0.1M trioctylamine oxide dissolved in xylene and sulphuric acid solutions has been studied. On the basis of results on the distribution, it is concluded that at sulphuric acid concentration 0.5M, tantalum is probably extracted by a solvate mechanism as the complex Ta(OH) (SO₄)₂·3TOAO. It has also been shown that tantalum can be quantitatively separated from niobium, uranium, thorium and rare earth elements by extraction with N-oxide of trioctylamine from 0.5M sulphuric acid solution.     

Comparison of standards in the Karl Fischer method for water determination.

The use of 4-(5-nonyl)pyridine oxide and trioctylamine oxide for the extraction of niobium(V) from different mineral acid solutions is described. The influence of the concentration of the solvents, acids and salting-out agents is discussed. Separations of niobium(V) from tantalum(V) and zirconium(IV) have been achieved.     

Niobium,tantalum, and titanium fluoride solutions

Parameters for the preparation of concentrated tantalum, niobium, and titanium fluoride solutions by dissolution of their oxides or hydroxides in hydrofluoric acid were studied. Anatase titania, niobium oxide, and tantalum oxide calcined to 900°C were found to have high dissolution rates. Solid phases separated upon the dissolution of niobium, tantalum, and titanium oxides in hydrofluoric acid were identified as NbO₂F, TaO₂F, Ta₃O₇F, and TiOF₂. Niobium hydroxide dissolution in an autoclave at the atmospheric pressure gave various complex salts: NH₄NbOF₄ and (NH₄)₃Nb₂OF₁₁.     

Colorimetric determination of niobium in titanium alloys

There is need for a method for the determination of niobium in titanium alloys, since niobium-titanium alloys are becoming increasingly important. The determination of niobium in this type of alloy is an extremely difficult matter. Many approaches were tried before the problem was solved. In the method proposed in this paper the sample is dissolved in a mixture of hydrofluoric and nitric acids, the solution evaporated to a small volume, and boric acid added. Two tannic acid separations are then made to separate the niobium from the bulk of the titanium. The niobium, is determined colorimetrically by the thiocyanate method using a water-acetone medium. A study was made of the possible interference of elements that might be present in titanium alloys. It was found that the presence of tantalum causes two opposing tendencies. Tantalum can cause high results for niobium because it forms a complex with thiocyanate which is visually colorless but shows some absorption. Tantalum can cause low results for niobium by hindering the development of the niobium color. The resultant effect of the tantalum depends upon the amount of tantalum present, the amount of niobium present and the ratio of tantalum to niobium. The presence of more than one per cent. tungsten can lead to high results for niobium. Other elements that might be present in titanium alloys do not interfere with the method. The procedure is designed for titanium alloys containing 0.05 to 10 per cent. niobium. The method is reasonably rapid. Six determinations can be finished in two days. The method should be applicable to many other materials besides titanium alloys.     

Formation and distribution of neutral vanadium, niobium, and tantalum oxide clusters: single photon ionization at 26.5 eV

Neutral vanadium, niobium, and tantalum oxide clusters are studied by single photon ionization employing a 26.5 eV/photon soft x-ray laser. During the ionization process the metal oxide clusters are almost free of fragmentation. The most stable neutral clusters of vanadium, niobium, and tantalum oxides are of the general form (MO2)0,1(M2O5)y. M2O5 is identified as a basic building unit for these three neutral metal oxide species. Each cluster family (Mm, m=1,...,9) displays at least one oxygen deficient and/or oxygen rich cluster stoichiometry in addition to the above most stable species. For tantalum and niobium families with even m, oxygen deficient clusters have the general formula (MO2)2(M2O5)y. For vanadium oxide clusters, oxygen deficient clusters are detected for all cluster families Vm (m=1,[ellipsis (horizontal)],9), with stable structures (VO2)x(V2O5)y. Oxygen rich metal oxide clusters with high ionization energies (IE>10.5 eV, 118 nm photon) are detected with general formulas expressed as (MO2)2 (M2O5)y O1,2,3. Oxygen rich clusters, in general, have up to three attached hydrogen atoms, such as VO3H1,2, V2O5H1,2, Nb2O5H1,2, etc.     

Determination of niobium and tantalum in binary alloys and zirconium alloys

Recent developments in the metallurgy of niobium, tantalum and zirconium have necessitated provision of analytical procedures for determining niobium and tantalum in the presence of each other and in the presence of zirconium. For this purpose, absorptioinetric procedures based on the formation of yellow coloured complexes, between pyrogallol and niobium or tantalum, have been critically examined. Direct absorptiometric procedures are described, which are suitable for determining niobium or tantalum in the range 2 to 7%; when either of these metals exceeds 7%, differential absorptiometric procedures are recommended. Corrections must lie made for absorption due to the presence of other metals which form complexes with pyrogallol. In tlie determination of niobium or tantalum up to 5%, the precision of the method is about ±0.05%. About 12 determinations can be made in a day, by one analyst.     

Separation and determination of tantalum and niobium by precipitation from homogeneous solution

An attempt to separate niobium and tantalum by precipitation from homogeneous solution by thermal decomposition of their peroxy complexes, in the presence of tannin and oxalate, has been only moderately successful. A more satisfactory separation of tantalum and niobium for ratios from 50:1 to 1:30 is obtained by extracting the bisulphate melt with ammonium oxalate before adding hydrogen peroxide, hydrochloric acid and tannin. For a tantalum/niobium ratio of 1:1 the niobium coprecipitation is reduced to 5 %. Furthermore, two alternative possibilities are presented: (1) a quantitative recovery of a tantalum precipitate at small oxalate and high tannin concentration, leaving 90% of the tantalum-free niobium in solution; (2) an 85 % recovery of niobium-free tantalum at high oxalate and small tannin concentration. A study of the coprecipitation process of niobium shows that the distribution coefficients follow a logarithmic pattern, true homogeneous mixed crystals being formed.     

Spectrophotometric determination of tantalum with 4,5-dibromo-o-nitrophenylfluorone

Micro amounts of tantalum can be determined directly by spectrophotometry with 4,5-dibromo-o-nitrophenylfluorone, citric acid, hydrogen peroxide and Triton X-100 in 0.5–5 mol l^?1 sulphuric acid. The apparent molar absorptivity of tantalum at 530 nm is 1.84 × 10⁵ l mol^?1 cm^?1. Beer's law is obeyed for 0–10 μg of tantalum in 25 ml of solution at 530 nm and a large amount of niobium and most foreign ions can be tolerated. Results obtained by applying the proposed method to niobium oxide, ferroniobium, nickel-base alloy and a mineral are satisfactory. The synthesis of the complexing agent is described.     

Determination of the States of Oxidation of Metals in Thin Oxide Films by X-Ray Photoelectron Spectroscopy

The states of oxidation of molybdenum, tungsten, niobium, and tantalum in thin oxide films of variable composition were determined by X-ray photoelectron spectroscopy. It was found that the metals occurred in different states of oxidation in thin oxide films prepared by the irradiation of metal surfaces with low-energy oxygen ions under high-vacuum conditions. The concentrations of metals in different states of oxidation essentially depend on the radiation dose and the reactivity of metals.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 5, 2005, pp. 490–494.Original Russian Text Copyright © 2005 by Alov.     

Extraction Recovery of Tantalum(V) and Niobium(V) from Hydrofluoric and Hydrofluoric-Sulfuric Acid Aqueous Solutions with Octanol

Comparative study of extraction of tantalum(V) and niobium(V) with octanol and tributyl phosphate was made. The data on distribution of tantalum(V) and niobium(V) between octanol and hydrofluoric and hydrofluoric-sulfuric acid aqueous solutions were obtained. The flowsheet for preparation of pure tantalum and niobium oxides was developed.     

Destructive and non-destructive determination of titanium in yttrium,niobium and tantalum oxides by photon activation

Destructive and non-destructive procedures have been developed for the determination of titanium by photon activation analysis. The non-destructive analyses with an internal standard method are performed on niobium and tantalum oxides while destructive determinations, including non-isotope addition and radiochemical separation, are applied to yttrium oxide samples.     

Precipitation and determination of tantalum and niobium from homogeneous solution with 3:3' :4' :5:7-pentahydroxyflavanone

3:3,:5:7-Pentahydroxyflavanone in fairly concentrated acidic solution (6-9N) does not precipitate tantalum and niobium ; however, on heating or boiling, in the presence of air, this flavanone is transformed into 3:3':4':5:7-pentahydroxyflavone, which precipitates any tantalum and niobium present in the solution. Under the precipitation conditions, racemisation of the flavanone also takes place. The racemised flavanone which is less soluble than the original d-form may accompany the tantalum and niobium precipitates without affecting the quantitative determination of these elements.

The precipitation of the tantalum and niobium complexes can be controlled by regulating the acidity and the duration of boiling, as well as the concentration of the flavanone. Experimental data and procedures are given for the precipitation and determination from homogeneous solution of tantalum and niobium complexes. Zirconium and molybdenum do not interfere with the determination. Titanium must be absent or present only in minute quantity.

Since the generation of the precipitating reagent, flavone, from the flavanone is comparatively slow, the precipitation of tantalum and niobium is uniform throughout the solution. By this technique, adsorption and co-precipitation of potassium and sulphate ions in the solution are shown to be negligible. This is in contrast to the less effective dropwise addition of the flavone reported by earlier investigators, in which adsorption and co-precipitation were pronounced.

In the present study, tantalum and niobium oxides were fused with potassium bisulphate. There is no necessity using hydrofluoric acid to dissolve these oxides and therefore no polyethylene apparatus is required.     

Spectrophotometric Determination of Simultaneously Present Niobium and Tantalum

The formation of niobium(V) and tantalum(V) complexes of 2,3,4-trioxyphenylazo-5-sulfonaphthalene in the presence of cetyltrimethylammonium bromide was studied by spectrophotometry. The effect of surfactants on the chemical and analytical properties of niobium(V) and tantalum(V) complexes of this reagent was studied. Procedures were developed for the spectrophotometric determination of niobium and tantalum present simultaneously as mixed-ligand complexes. The procedures were tested on model solutions.     

Solvent extraction separation of tantalum from niobium on macro scale using di(2-ethylhexyl) phosphoric acid as extractant

A solvent extraction procedure for the separation of niobium and tantalum has been developed. The method consists of extracting tantalum from its aqueous mixture with niobium, with the help of di(2-ethylhexyl)phosphoric acid (HDEHP) in n-heptane. The aqueous feed consists of niobium and tantalum in an aqueous medium containing hydrochloric and oxalic acids. The concentrations of niobium and tantalum were raised to 1 mg/ml in the aqueous solution. The extraction efficiency of tantalum under these conditions was found to be 85%. Effects of chloride and oxalate ions as well as those of the concentration of HDEHP on the extraction efficiency were studied and discussed in detail.     

Separation of niobium and tantalum by extraction chromatography with bis(2-ethylhexyl)phosphoric acid

A novel method is developed for the reversed-phase extractive chromatographic separation of niobium and tantalum with bis(2-ethylhexyl)phosphoric acid. Niobium is extracted from 1-10M hydrochloric acid and can be stripped with 3M sulphuric acid containing 2% hydrogen peroxide. Tantalum is extracted from 0.1-2M hydrochloric acid and can be stripped with 0.1M hydrochloric acid containing 2M tartaric acid. It is possible to separate niobium and tantalum, in different ratios, from multicomponent mixtures.     

Analytical applications of infra-red spectroscopy : The behaviour of the oxinates of niobium,tantalum and associated elements

The behaviour of the oxinates of niobium, tantalum and associated metals in the infra-red region was studied and a method developed for the determination of niobium and tantalum. Vanadium caused no interference, but other heavy metals, such as molybdenum, manganese and cobalt, which interfered were removed by preliminary treatment when the method was applied to the determination of niobium and tantalum in steels.     

Separation of niobium and tantalum with phenylarsonic acid

Phenylarsonic acid permits satisfactory separation of niobium and tantalum and estimation of tantalum from an oxalate solution containing sulphuric acid up to pH 5.8. For complete precipitation of niobium the pH should exceed 4.8. In mixtures, tantalum is precipitated below pH 3.0 and niobium is then precipitated above pH 5.0. When the oxalate concentration is high, recovery of niobium with cupferron is recommended. When the ratio of Nb₂O₅, to Ta₂O₅ exceeds 2:1, reprecipitation of tantalum is necessary. The effect of interfering ions is studied.     

Isolation of niobium,tantalum, and titanium complex fluoride salts with alkali metal cations

Fluoride and oxofluoride salts of niobium, tantalum, and titanium were isolated. They precipitated from aqueous solutions and upon washing of organic extracts with aqueous solutions of ammonium, potassium, and sodium salts. The compositions of the isolated compounds were studied. Different compositions were established for the niobium salts that precipitated upon the dissolution of unwashed niobium hydroxide in hydrofluoric acid under the atmospheric pressure, in an autoclave, and upon addition of sodium, potassium, and ammonium salts to purely fluoride solutions of niobium, as well as for the tantalum ammonium and sodium salts isolated from aqueous and organic solutions. The data obtained can be used for the synthesis of niobium, tantalum, and titanium complex fluoride salts with various compositions.     

Cathodoluminescence (CL) and CL spectra of microwave plasma-enhanced CVD diamond

Recent research work is reported on cold cathode luminescence (CL) microscopy and CL microspectrophotometry of diamond produced by means of plasma-activated mixtures of hydrogen and methane gases. Diamond layers of octahedral, cubooctahedral or cubic habit on SiAlON substrates as well as ballas-type layers were investigated. Diamond was also deposited on sheet substrates of titanium, niobium, tantalum, chromium, molybdenum, tungsten, iron (spheroidal and lamellar cast iron), cobalt and nickel. Studying CL colors together with CL spectra has proved to be a reliable diagnostic method for differentiating between the morphological properties of CVD diamond on SiAlON substrates. It is however not possible with this method to clearly differentiate all diamond layers on any one of the sample substrates investigated. These findings could justify a future application of both CL microscopy and CL microspectrophotometry in production control.