A Method for the Spectrographic Determination of Trace Impurities in Niobium

Niobium is a member of a group of metals under investigation to evaluate their suitability for use in the nuclear reactor field Because of the complex chemistry involved in the determination of trace impurities in niobium by classical methods, spectrographic methods have been devised. This paper describes a method for the spectrographic determination of 14 elements present in niobium. The elements determined and their concentration ranges include boron, 0 0001 to 0 0015%, aluminum, cadmium, chromium, cobalt, iron, manganese, molybdenum, nickel, silicon, tin and titanium, 0.001 to 0.1%; tantalum, 0.025 to 1.5 percent; and zirconium, 0.001 to 1.5%.

The analysis involves the conversion of niobium to the oxide by heating the metal in platinum at 800°C until oxidation is complete. A 10 mg sample plus 10 mg of lithium carbonate, as a spectrographic buffer, and 25 μg of lanthanum, as an internal standard, is excited in a 20-ampere d.c. arc. The spectrogram obtained is used for the determination of all the elements listed with the exception of aluminum, boron, silicon, zirconium and tantalum'. The latter are determined from a spectrogram obtained by the excitation of a separate 20 mg sample of niobium oxide. The coefficient of variation is of the order of 10 percent for the various impurities.