The Determination of Niobium in Iron and Steel by thd Extraction Spectrophotometric Method

An extraction spectrophotometric method with sulfochlorophenol S for the determination of niobium was investigated, and applied to the determination of niobium in iron and steel.The niobium sulfochlorophenol S complex is formed quantitatively in 1.2∼2.4 N, hydrochloric acid media, and this complex is quantitatvely and easily extracted with n-butyl alcohol in the presence of diphenylguanidine. The absorption maximum of the extracted complex is at a wavelength of 650 milli microns.Iron, molybdenum and zirconium interfere with the determination of niobium, but these interferences can be eliminated to some extent by the use of thioglycollic acid and EDTA. The presence of sulfates of chromium and nickel lowers the absorbance for the determination of niobium; the coexistence of more than 2 mg each of chromium and nickel and of more than 0.5 mg of chromium and 1 mg of nickel interfere with the determination of 10γ and 20γ of niobium, respectively.The addition of more than 0.5 mL of sulfuric acid (1+10) in the presence of 0.5 mL of phosphoric acid (1+10), lowers the absorbance for the determination of 20γ of niobium.The sample was fumed with a mixture of sulfuric and phosphoric acids for dissolving completely the carbides and tungstic acid after the sample was dissolved in aqua regia.As a result of the present experiment, the author succeeded in establishing a method in which 0.01 to 2% niobium contained in iron and steel can precisely be measured without difficulty.