J. V. Widiatmo

Estimation of impurity effect in aluminium fixed-point cells based on thermal analysis

The impurity effect on fixed-point temperature realization by thermal analysis has been assessed. For such an assessment, the following actions were conducted: (1) the fabrication of aluminium point cells using 6N or higher-grade aluminium samples from different sources (manufacturers), (2) temperature measurements during solidification and thermal analyses based on freezing curves obtained from the measurements, (3) direct cell comparison among cells of different nominal purities and (4) calculation of the departure of the freezing point from the ideally defined freezing point by applying the sum of individual estimates (SIE). Two aluminium point cells were prepared in action (1) using 6N-grade and one cell using 6N5-grade aluminium samples. To realize a fixed point using the cells, a fixed-point furnace was developed and evaluated. Temperature measurements in action (2) were conducted at different rates of solidification and in accordance with the one using the liquid–solid interface technique. Gradients of freezing curves were derived in the thermal analysis, and from their dependence on the rate of solidification, the impurity effect was evaluated. Indirect cell comparison was also derived using the difference in the gradients. It was found that the indirect cell comparison was in satisfactory agreement with the direct cell comparison, which was obtained from action (3). It was also found that the departure of the thermal analysis from the SIE obtained from action (4) was within the uncertainty. This fact may imply a possible application of thermal analysis for estimating the effect of impurities in the realization of the aluminium point, especially for 6N-grade aluminium fixed-point cell as used in the present study.

Deep Ocean Temperature Measurement with an Uncertainty of 0.7 mK

AbstractThe uncertainty of deep ocean temperature (~1°C) measurement was evaluated. The time drifts of six deep ocean standards thermometers were examined based on laboratory calibrations as performed by the manufacturer in triple point of water (TPW) cells and gallium-melting-point (GaMP) cells. The time drifts ranged from −0.11 to 0.14 mK yr−1. Three of the six thermometers were evaluated at the National Metrology Institute of Japan in five TPW cells and a GaMP cell, and the temperature readings agreed with the realized temperature of the national standard cells of Japan within ±0.14 and ±0.41 mK for TPW and GaMP, respectively. The pressure sensitivities of the deep ocean standards thermometers were estimated by comparison with conductivity–temperature–depth (CTD) thermometers in the deep ocean, and no notable difference was detected. Pressure sensitivities of the two CTD thermometers were examined by laboratory tests, and the results suggest that the deep ocean standards thermometers have no pressure s...

Study on the realization of indium point

Indium-point cells were fabricated in NMIJ/AIST using high grade indium samples purchased from some different metal sources. The quality of the indium-point cells were evaluated by conducting temperature measurements during the solid-liquid equilibrium condition, under which the indium fixed-point is defined. Comparisons of fixed-point temperature realized within the cells including the conventional and the newly developed ones were also conducted. The results of these comparisons, termed as direct cell comparisons, as well as the above mentioned temperature measurements under the solid-liquid equilibrium were used to evaluate the effect of impurities to the realization of the indium point. The present paper outlined the cell fabrication, the temperature measurements and the evaluation of impurity effect to the indium point realization.

Study on the realization of tin point

Tin-point cells were fabricated using high grade tin samples purchased from some different metal sources. Temperature measurements during the solid-liquid equilibrium condition, under which the tin point is defined, were conducted for evaluating the quality of the cells. Different methods for the realization of tin point were compared by means of the fabricated cells. Comparisons of tin-point temperatures realized using the conventional and the newly developed cells were also conducted. On the other hand, chemical assay provided by the tin sample manufacturer was used to estimate the tin point departure from that ideally defined by the International Temperature Scale of 1990 (ITS-90). The tin point departure, the cell comparison results and the analysis of the temperature measurements during the solid-liquid phase change were discussed for estimating the uncertainty of tin-point realization due to impurity existence. The present paper outlines the apparatus which includes the tin cell and the furnace, the temperature measurements and the evaluation of impurity effect to the tin point realization.

Anomalous behavior of a tin point cell

At NMIJ, AIST, ensembles of fixed point cells are maintained for each defining fixed point to underpin the confidence for the maintenance of the national standards for thermometry. As a routine work, fixed point cells for the same temperature are realized simultaneously and the temperature differences between them are measured when the liquid fraction (1/F) is between 1 and 2. An anomalous temperature difference of approximately 0.2 mK was observed for one tin point cell. In this paper, we report the details of this anomalous temperature difference, and also the analysis to elucidate its cause. We assume that such anomalous behavior probably occurred due to condensation of impurities by employing a specific realization method repeatedly. Also we present that the anomalous behavior appears to be resolved by adopting another realization method during the experiments conducted under the present work.