Differential-pulse polarographic determination of chromium and nickel in zircaloys using microsamples

Abstract

Abstract. Three methods were developed for the analysis of the alloying elements chromium and nickel in Zircaloy-2 and Zircaloy-4, alloys of zirconium used extensively in the nuclear industry as nuclear fuel sheathing. Zircaloy was dissolved in hydrofluoric acid followed by oxidation of Cr(III) to Cr(VI) by perchloric acid. The polarographic peak of CrO~-in alkaline medium was used to determine Cr. Nickel was determined, after HF dissolution, using the polarographic peak of the nickel-ammonia complex, Ni (NH3) ~ +. In an alternative method for Ni, the sample was dissolved in HF and the polarographic peak of the nickel-fluoride complex, Ni F42 -, was used. Careful control of fluoride ion concentration and the pH eliminated the harmful effect of fluoride on the capillary behaviour of the dropping mercury electrode. The detection limits for chromium, nickel-ammonia and nickel-fluoride in Zircaloys were 0.0016, 0.0033, and 0.0041%, respectively.Key words: zircaloy, chromium, nickel, polarography.In the nuclear industry a rigorous quality control programme is in use for monitoring the zirconium alloys Zircaloy-2 and Zircaloy-4 as nuclear fuel sheathing. The determination of the percentage of alloying elements in Zircaloys represents a maj or part of this programme, as the mechanical and corrosion properties of these alloys are influenced by the concentrations of their constituent elements. The concentrations of alloying elements in Zircaloy-2 are Cr (0.05-0.15%), Ni (0.03 0.08%), Fe (0.07-0.2%) and Sn (1.2-1.7%), while in Zircaloy-4 the alloying elements are Cr (0.07-0.13%), Fe (0.18-0.24%) and Sn (1.2-1.7%).Several techniques have been applied for the quantitation of the alloying elements in Zircaloys, such as spectrophotometry, which has been adopted by the American Society for Testing and Materials (ASTM) [1]. Other spectrophotometric methods have also been employed [2,3]. Other techniques have also been applied, such as X-ray fluorescence spectrometry [-4,5], activation analysis [6][7][8], ICP