The Triple-point Temperature of Pure Equilibrium Deuterium

Abstract

A study specifically intended to measure the triple-point temperature of both n-D2 and e-D2 containing a volume fraction of HD not higher than 0.0001 has been completed. It was performed by measuring samples of gas in metal sealed cells. The cells, after being checked for a non-increasing HD contamination within the stated limits, were filled by directly connecting them to the outlet of a thermal-diffusion column for isotopic separation, known to produce D2 with a HD volume fraction not larger than 0.00003. In the case of e-D2, additional studies were performed on the effect of deuterating the catalyst or on high-temperature activation of the catalyst. Results proved that it is possible to obtain good results for e-D2 with partially deuterated catalyst, but this does not allow a reliable control of the contamination. An alternative procedure to full deuteration has been found, which uses commercial hydrous ferric oxide heated to about 400 °C, and commercially available deuterium, produced by isotopic separation and showing a purity better than 99.99%. Temperature values (18.7327 ± 0.0003) K for n-D2 and (18.6983 ± 0.0003) K for e-D2 on NPL-IPTS-68 were obtained at the liquidus point; the best thermodynamic values for these triple points are (18.7232 ± 0.001) K and (18.6888 ± 0.001) K respectively; e-D2 can be used as a first-quality temperature reference point.

Recommended values of temperature on the International Temperature Scale of 1990 for a selected set of secondary reference points

“…These problems have now been satisfactorily resolved and the point has been promoted to Table 1. There have been four, more recent, independent determinations of the triple-point temperature [6][7][8][9]202], with the result shown in Table 1. The combined standard uncertainty of the four measurements is 0,3 mK, although the between-set component of the standard deviation is 0,4 mK, indicating that there are probably still some small unresolved systematic uncertainties in at least one of the experiments.…”

Triple Point of Pure and Impure Deuterium

“…This was clearly a vast improvement over the commonly available commercial-grade D, of 99.5% purity. As a result, TP temperatures yielded by these samples (T(equi1ibrium)= 18.701 K, [4], and T(norma1) = 18.732 K, [5D were higher than any observed before *. These values were later changed to 18.6983 K and 18.732, K respectively [6].…”

“…The only way toward high-purity D, appeared to be a very special preparation of cells followed by direct filling at the D, production plant where HD contamination can be kept very low. For these reasons a cooperative program between IMGC and Mound' laboratory was set up to build cells with particular care in order to avoid HD formation within the cells [4] and then to fill them directly at the purification column which produces ultra-pure D, . Among these cells, two contained some catalyst prepared with great care to reduce contamination.…”

On the degree of objectivity of uncertainty evaluation in metrology and testing

“…If no more than one realization exist, the concept itself may vanish for lack of evidence: if only one copy of a standard is considered -or exists -and is circulated for measurement among all possible laboratories, practical differences between the concepts of 'realized quantity' and 'quantity' may become ambiguous; only those arising from the imprecision of the investigations concerning the 'realized quantity' remain. If only one realization of a physical state -e.g., of the triple point of a substance -is available, no experimental evidence can be brought for the temperature value of the pure substance, unless the substance is so close to the zero-impurity condition that the effect of correction for this systematic effect can demonstrated to be irrelevant for the stated level of uncertainty [20]. Also the size of the unit of a quantity (item (ii) above), is no more an issue for measurements performed with the same standard.…”