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.     

Analysis of niobium alloys

An ion-exchange method was applied to the analysis of synthetic mixtures representing various niobium-base alloys. The alloying elements which were separated and determined include vanadium, zirconium, hafnium, titanium, molybdenum, tungsten and tantalum. Mixtures containing zirconium or hafnium, tungsten, tantalum and niobium were separated by means of a single short column. Coupled columns were employed for the resolution of mixtures containing vanadium, zirconium or titanium, molybdenum, tungsten and niobium. The separation procedures and the methods employed for the determination of the alloying elements in their separate fractions are described.     

Determination of niobium in rocks, ores and alloys by atomic-absorption spectrophotometry

Niobium, in concentrations as low as 0.02% Nb(2)O(5), is determined in a variety of materials without separation or enrichment. Chemical and ionization interferences are controlled, and sensitivity is increased, by maintaining the iron, aluminium, hydrofluoric acid and potassium content within certain broad concentration limits. There is close agreement with the results of analyses by emission spectrographic, electron microprobe and X-ray fluorescence methods.     

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.     

Determination of trace phosphorus in zirconium-niobium alloy and Zircaloy by UV-vis spectrophotometry

A spectrophotometric method has been developed for the determination of traces of phosphorus in zirconium based alloys (Zr-2.5Nb and Zircaloy). It is achieved by selective fluoride complexation controlled by boric acid. The samples were dissolved in HF and fluoro-complexes of the matrices were formed by maintaining the concentration of HF while the excess HF was controlled by boric acid. After the formation of phosphomolybdate, extracted into n-butyl acetate, ion-associated with crystal violet and the absorbance was measured at 582 nm. The results obtained by this procedure were in close agreement with the certified reference material (CRM) values and further these values were compared with the values determined by Glow Discharge-Quadrupole Mass Spectrometry (GD-QMS). The potential interferences like fluoride, silicon, arsenic(V), niobium, titanium, tantalum, etc., were tolerable to large level. LOD (3 s) was found to be 0.055 mg kg(-1) with a precision (R.S.D.) of 2-3% and molar absorptivity was 2.7x10(5) L mol(-1) cm(-1).     

X-ray fluorescence determination of niobium in iron-niobium alloys

Summary An X-ray fluorescence method is described for the determination of niobium in iron-niobium alloy in the concentration range from 0.1–2% of niobium. The sample is dissolved in a mixture of nitric and hydrofluoric acid and is converted to a stable oxide. This oxide is uniformly ground with boric acid and a weighed quantity of it is pressed into a circular pellet. The pellet is exposed to an X-ray beam from a tungsten target. The resulting fluorescent X-ray beam is dispersed using an LiF crystal and the intensity of the NbK -line is measured by a scintillation counter. A set of synthetic standards covering the above range is prepared using highpurity chemicals and a working curve for the estimation of niobium is established. The accuracy of the method is checked by analysing synthetic samples. The standard deviation of the method ranged from 0.5% at 5% Nb to 3.5% at 0.1% of Nb concentration.

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Röntgenfluorescenzspektroskopische Niobbestimmung in Eisen-Niob-Legierungen

Zusammenfassung Die Methode erlaubt eine Niobbestimmung im Konzentrationsbereich von 0,1–2% Niob. Die Probe wird in Salpetersäure/Flußsäure gelöst und in ein stabiles Oxid überführt, das mit Borsäure vermahlen und zu einer Tabelette gepreßt wird. Zur Röntgenfluorescenzmessung (W-Röhre, LiF-Kristall) wird die NbK -Linie herangezogen (Szintillationszähler). Mit Hilfe hochreiner Reagentien wurden synthetische Standards für den genannten Konzentrationsbereich hergestellt. Die Genauigkeit wurde mit Hilfe synthetischer Proben überprüft (Standardabweichung 0,5 % bei 5% Nb, 3,5% bei 0,1% Nb).

     

Determination of niobium in steels

The determination of niobium at levels of 0.01% and below is required in certain specifications for stainless-steel welding electrodes, containing 2-3% molybdenum and 0.01% titanium. A method has been developed, based on initial extraction of niobium thiocyanate into butyl acetate followed by stripping with fluoride and re-extraction of niobium thiocyanate after masking of the fluoride by addition of boric acid. The absorbance of the extract is measured at 385 nm. Mo, Ti, V and W can be tolerated at 50 times the concentration of Nb. For higher amounts of Mo, corrections can also be applied. Ta should, however, be restricted to ten times the Nb level. Precision and accuracy of the method are satisfactory. The time taken for an individual determination is about an hour. The method is applicable to mild, low-alloy, stainless and niobium-stabilized steels.     

Determination of niobium and tantalum in some ores and special alloys by inductively coupled plasma atomic emission spectrometry

A fast analytical method for the determination of niobium and tantalum in ores and special alloys by inductively coupled plasma atomic emission spectrometry has been developed. Optimum conditions for the determination of both metals in the plasma were worked out and possible interferences were studied before attempting the determination in the real samples. Ores are dissolved in a mixture of HCl, HF and H₃PO₄ acids while for the special alloy a HCl+H₂O₂ mixture is used. The resulting solutions are diluted to the mark with tartaric acid before their final direct nebulization into the plasma. Other elements present did not interfere in the determination of Nb or Ta at concentration levels similar to those found in the analyzed samples. The results obtained determining niobium and tantalum in pyrochlore and special alloys by the proposed procedure are in good agreement with the certified values.     

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.     

Analysis of alloys of titanium,niobium and tantalum by ion exchange

A procedure for the analysis of alloys of titanium, niobium and tantalum is described. After dissolution the metals are separated by ion exchange in hydrochloric-hydrofluoric acid media. Finally the metals are determined spectrophotometrically,     

Determination of niobium and tantalum with quinaldinohydroxamic acid

Summary A new method has been described for the gravimetric estimation, from a tartrate solution, of niobium and tantalum by quinaldinohydroxamic acid. In theph range of 5.0 to ammoniacal, both the elements are quantitatively precipitated from an ice-cold solution in presence of ammonium chloride and can be separated from quite a large number of ions using EDTA as a masking agent.Niobium complex can be dried at 110 C and weighed for the direct determination of niobium or the complex can be ignited to pentoxide. Tantalum complex, however, needs ignition to pentoxide.

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Zusammenfassung Es wird eine Methode zur gravimetrischen Bestimmung von Niob und Tantal beschrieben. Hierbei werden beide Elemente im Gebiet zwischenph 5 und ammoniakalischem Medium aus eisgekühlter, ammoniumchloridhaltiger Lösung mit Hilfe von Chinaldinhydroxamsäure ausgefällt. Eine größere Zahl von Fremdionen stört nicht, wenn man der Lösung Tartrat und äDTA zusetzt. Der Niobkomplex kann entweder bei 110 C getrocknet und anschließend ausgewogen oder auch zum Pentoxid verglüht werden. Tantal kann nur durch Verglühen bestimmt werden.

     

Determination of niobium in pyrochlore ore by differential pulse polarography

A differential pulse polarographic method has been developed for the quantitative determination of niobium in pyrochlore ore. One-step polarographic curves were obtained in 0.01 mol L(-1) EDTA as supporting electrolyte. Analytical curves indicated that response was linearly dependent on Nb(V) concentration between 1.6 and 8.6 mg L(-1) in the pH range 2-5. The system is quasi-reversible and controlled by diffusion in 0.01 mol L(-1) EDTA as supporting electrolyte; the electrode process involves one-electron reduction of Nb(V) to Nb(IV). The results obtained so far for niobium in pyrochlore ore were comparable with those obtained by X-ray fluorescence determination. Ions such as Fe(III), Cr(III), As(III), Cu(II), Ni(II), Co(II), Mn(II), Sn(IV), Zn(II), V(V), Ta(V), W(VI), Ce(IV), and Ti(IV) did not interfere. Possible interference from Pb(II) can be avoided by complexation with the supporting electrolyte in the pH range 3.5 to 4.6; Mo(VI) ions can be tolerated when their concentration is one-tenth that of Nb(V).     

Simultaneous determination of trace niobium, tantalum and tungsten in ferrous and non-ferrous alloys

A method is presented for the determination of niobium, tantalum and tungsten in steel and non-ferrous alloys, based on hydrolysis with sulphurous acid followed by X-ray fluorescence measurements. The limit of determination is about 0.002% and the standard deviation is 0.002 at the 0.05% level. Results below 0.01% by this method are only semiquantitative.     

Determination of cerium in ferrous alloys

A method for the determination of cerium in ferrous alloys is described. Cerium (with lead and bismuth) is separated from other elements by anion exchange in a medium consisting of 95% methanol and 5% 5 N nitric acid; cerium alone is tlien eluted with 90% methanol-10% 6 N hydrochloric acid and determined in the eluate by titration with EDTA to xylenol orange indicator. Application of the method to several steel samples was successful.     

Determination of tin in titanium alloys

Tin-titanium alloys are becoming increasingly important; consequently a good method is needed for the determination of tin in this type of material. In this paper an accurate iodometric procedure is proposed for the determination. The sample is dissolved in sulfuric acid and the titanium oxidized with potassium permanganate. Tartaric acid is added and the tin precipitated with hydrogen, sulfide. The sulfide precipitate is dissolved in a mixture of sulfuric, perchloric and nitric acids and the solution evaporated to fumes of sulfuric acid. Water and hydrochloric acid are added, and the tin is reduced with lead and antimony trichloride and titrated with iodine. A study was made of the interfering elements that might be found in titanium alloys. The effect of antimony trichloride in reducing interference from copper was investigated. The method is recommended for titanium alloys containing 0.05 to 5.0 per cent. tin.     

Determination of nickel in gold-nickel alloys

An ion exchange separation based on the difference in adsorption from a chloride solution combined with an EDTA titration is suggested as a rapid and accurate method for the determination of nickel in nickel-gold alloys.     

Determination of phosphorus in hypereutectic aluminium-silicon alloys

A reproducible method is described for determination of small amounts of phosphorus (from 0.0005% to 0.02%) in hypereutectic aluminium-silicon complex alloys. The method permits the separate determination of phosphorus in acid-soluble and acid-insoluble fractions. Phosphomolybdate is extracted with n-butanol-chloroform solvent mixture and back-extracted with a btannous chloride reducing solution. The phosphorus content of a sample cut into small pieces decreases during storage; loss of phosphorus is negligible on acid dissolution under oxidizing conditions.     

Determination of copper in white-metal bearing alloys

A method is proposed for the determination of copper in white-metal bearing alloys by direct controlled-potential electrolysis with a tantalum cathode at -0.32 V vs. SCE in a sulphate/bisulphate buffered electrolyte (pH 2) with fluoroboric acid and sodium tartrate as masking agents. Only Bi(III) interferes. Any co-deposited Bi can be corrected for by its spectrophotometric determination with Semi-Xylenol Orange after preconcentration with La(III) as carrier, from an ammoniacal solution containing the redissolved deposit. Any residual Cu(II) in the electrolyte is determined by spectrophotometry with 2,9-dimethyl-1, 10-phenanthroline. The standard deviation of this method has been found to be 0.03 mg (n = 12) and its relative standard deviation from 0.03 to 0.17%. It has been successfully used for referee analysis and certification of standard reference materials.     

近场激光热透镜光谱分析法测定铌

采用氦-氖激光器(632．8nm)观测了铌(V)与2-(5-溴-2-吡啶偶氮)-5-二乙氨基苯酚(5-Br-PADAP)和酒石酸所形成的紫蓝色三元配合物的激光热透镜效应，建立了近场激光热透镜光谱分析法测定铌的新方法。铌(V)质量浓度在0-500ng/mL范围内与热透镜信号强度呈良好的线性关系，检出限为5ng/mL。该方法已应用于钢样及铌矿样中铌的测定。