Kunio Takada1 and Kichinosuke Hirokawa1
1The Research Institute for Iron, Steel and Other Metals, Tohoku University, Sendai
Recently, various samples containing rare earth elements have actively been studied from standpoints of metallurgy, solid state physics and non-stoichiometric chemistry. As the vehicle for these investigations, effective analytical methods of those elements are required. Determination of rare earth elements in various samples by the X-ray fluorescence method and those of impurity levels in high pure rare earths by the d.c. arc emission spectrographic method have been studied. In the X-ray fluorescence method, rare earth elements were precipitated as fluoride. Compared with the rare earth oxide, the rare earth fluoride precipitate absorbed little moisture and carbon dioxide in atmosphere. Furthermore, its preparation procedure was easier rather than the glass bead technique. Detection limits of rare earth elements were extended by this fluoride procedure because of no dilution with the fusing agent. Detection limits for Y (YK α ) and Yb (YbL α 1) were about 5 μ g, for Ce(CeL β 1) and Gd(GdL α 1) about 20 μ g, and those elements of about 50 μ g were analyzed with the coefficient of variation less than 2%, respectively. Many reports have been published for the chemical analysis of high-purity rare earths by the d.c. arc emission method. Most of those reports were concerned with the determination of impurity rare earths in pure rare earths (e.g. Y, La, Eu, Yb, etc.) which gave simple spectra with rather less lines and low background. The satisfactory results were obtained by d.c. arc emission for 10 ppm Eu in Yb and for 10 ppm Y in La. On the other hand, few have been reported on the determination of high pure rare earths (e.g. Ce, Pr, Nd, Sm, etc.) with multi-component emssion spectral lines of strong intensity and high background. Therefore, the determination of 10∼500 ppm Y2O3 in Sm2O3 was investigated by the d.c. arc emission spectrographic method. Yttrium was separated from samarium as double salt with saturated sodium sulfate solution. The determination of trace yttrium in high-purity Sm2O3 became possible by the separation procedure. The best yttrium spectrum line for determination in the range of 3100∼4700 Å was YII 3633.123 Å and other lines could not be employed because of weak line intensity and high interference by samarium spectra. By the method proposed, trace amounts of Y2O3 in Sm2O3 were determined, and the coefficient of variation of sample containing 108 ppm Y2O3 in Sm2O3 was about 10%.
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