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Isotopic and Other Influences of the Realization of the Triple Point of Hydrogen



B Fellmuth, L Wolber, Y Hermier, F Pavese, PPM Steur, I Peroni, A Szmyrka-Grzebyk, L Lipinski, Weston L. Tew, H Nakano, H Sakurai, O Tamura, D I. Head, K D. Hill, A G. Steele


Within an international collaboration of the eight metrological institutes represented by the authors, the dependence of the triple-point tmeperature of equilibrium, hydrogen on the deuterium content at low concentrations has been precisely determined so that the uncertainty in realizing the triple point as a temperature fixed point might be reduced by nearly one order of magnitude. To investigate the thermodynamic properties of the hydrogen-deuterium mixtures and to elucidate the factors that influence the melting temperature, 28 sealed fixed-point cells have been filled and measured, and some of these have been compared with an open-cell system. Hydrogen has with a deuterium content ranging from 27.2 mu mol D/mol H to 154.9 mo mol D/mol H was studied using cells containing five different types of spin-conversion catalyst, with different catalyst-to-liquid volume ratios (a few per cent to more than 100%) and of different designs. The latter consideration is especially influential in determining the thermal behavior of the cells and, thus, the temperature measurement errors. The cells were measured at the eight participating institutes in accordance with a detailed protocol that facilitates a direct comparison of the results. Through analysis of the measurements, significant inter-institute deviations due to different measurement facilities and methods have beeb ruled out with respect to the determination of both the melting temperatures and the thermal parameters of the cells. The uncertainty estimates for the determination of the deuterium content have been verified by including isotopic analysis results from four different sources. The slope of the dependence of the triple-point temperature of equilibrium hydrogen isotopic mixtures on the deuterium content has been deduced from the melting temperatures of those sample portions not in direct contact with the catalysts. Evaluation of the data using different mathematical methods has yielded an average value of 5.42molK per mol D/mol H. This is close to the literature value of 5.6mol K per mol D/mol H that was obtained at higher deuterium concentrations.


Fellmuth, B. , Wolber, L. , Hermier, Y. , Pavese, F. , Steur, P. , Peroni, I. , Szmyrka-Grzebyk, A. , Lipinski, L. , Tew, W. , Nakano, H. , Sakurai, H. , Tamura, O. , Head, D. , Hill, K. and Steele, A. (2005), Isotopic and Other Influences of the Realization of the Triple Point of Hydrogen, Metrologia (Accessed December 7, 2023)
Created July 31, 2005, Updated October 12, 2021