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

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 CrO₄^2– 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)₆²⁺. In an alternative method for Ni, the sample was dissolved in HF and the polarographic peak of the nickel-fluoride complex, NiF₄^2–, 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.