Isotopic Effects on the Temperature of the Triple Point of Water

Abstract

An investigation into the effects of isotopic composition on the triple point temperature of water has been carried out at the National Institute of Metrology (NIM), China, since redefinition of the kelvin with respect to Vienna Standard Mean Ocean Water (V-SMOW) was officially proposed by the Consultative Committee for Thermometry (CCT) in 2005. In this paper, a comparison of four cells with isotopic analyses and relevant results corrected for isotopic composition, employing the isotope correction algorithm recommended by the CCT, is described. The results indicate that, after application of the corrections, the maximum temperature difference between the cells drops from 0.10 mK to 0.02 mK and that these cells are in good agreement within 0.02 mK. Also, temperature deviations arising from isotopic variations fall in the range from −55.9 µK to +40.7 µK. We consider that the distillation temperature and degassing time of the production procedure lead to isotopic variations.

Report on NIM-NMC bilateral comparison: SPRT calibration comparison from −190°C to 420°C

“…Here, the average uncertainty of isotopic composition is 0.03mK. At the present definition for the water triple point, the maximum temperature difference among the four NIM cells drops from 0.10mK to 0.02mK after application of the isotope correction[3].…”

The Long-Term Drift of Triple-Point-of-Water Cells

“…Unfortunately, we have no knowledge regarding the isotopic compositions and chemical impurities of the water in the old and new cells. However, effects of isotopic composition on the triple-point temperature of water have been investigated using similar new cells with known isotopic compositions, and the results have been published [7].…”