Isotope Effects in Diffusions of H and D in Hydrogen Isotope Exchange in Oxide Ceramics

• Published in: Journal of Nuclear Science and Technology 2002-04, Vol.39 (4), p.359-362
• Main Authors: SODA, Kazuo, IIZUKA, Emi, TSUCHIYA, Bun, MORITA, Kenji, IWAHARA, Hiroyasu
• Format: Article
• Language: English
• Subjects: 0.05; 0.95; 3-δ; Applied sciences; Controled nuclear fusion plants; elastic recoil detection analysis; Energy; Energy. Thermal use of fuels; Exact sciences and technology; exchange of hydrogen isotopes; H, D; hydrogen diffusion; Installations for energy generation and conversion: thermal and electrical energy; isotope effects; mass balance equations; rate equations; SrCe
• ISSN: 0022-3131; 1881-1248
• DOI: 10.1080/18811248.2002.9715203

In order to clarify the contribution of the hydrogen ion diffusion to the hydrogen isotope exchange at room temperature in a proton-conducting ceramics SrCe 0.95 Yb 0.05 O 3-δ , the concentration change of hydrogen isotopes, H and D, in the ceramics has been measured by elastic recoil detection analysis as a function of the irradiation time of a 0.5-keV molecular hydrogen ion beam after the hydrogen isotope implantation. The rate for the decrease of D implanted with 5-keV D ± 2 beam on the 0.5-keV H ± 2 irradiation is 1.1-1.4 times larger than that of H implanted with 5-keV H ± 2 beam on the 0.5-keV D ± 2 irradiation. With use of mass balance equations (rate equations) and the observed rates for the isotope decrease, the ratio of the diffusion constants for H and D is estimated as 2-4, which is larger than the classical ratio of √2 but comparable with a reported ratio, 2.5, of ionic conductivities for H and D at room temperature. The present results suggest that the observed large isotope effect in the hydrogen exchange in the ceramics may arise mainly from difference in the dissociative adsorption rate for water molecules at the surface rather than the rate for the hydrogen ion diffusion.