Realization of the Gallium Triple Point at NMIJ/AIST |
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Authors: | T Nakano O Tamura H Sakurai |
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Affiliation: | (1) National Metrology Institute of Japan, AIST, 1-1-1 Umezono, Tsukuba Ibaraki, 305-8563, Japan |
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Abstract: | The triple point of gallium has been realized by a calorimetric method using capsule-type standard platinum resistance thermometers
(CSPRTs) and a small glass cell containing about 97 mmol (6.8 g) of gallium with a nominal purity of 99.99999%. The melting
curve shows a very flat and relatively linear dependence on 1/F in the region from 1/F = 1 to 1/F = 20 with a narrow width of the melting curve within 0.1 mK. Also, a large gallium triple-point cell was fabricated for the
calibration of client-owned CSPRTs. The gallium triple-point cell consists of a PTFE crucible and a PTFE cap with a re-entrant
well and a small vent. The PTFE cell contains 780 g of gallium from the same source as used for the small glass cell. The
PTFE cell is completely covered by a stainless-steel jacket with a valve to enable evacuation of the cell. The melting curve
of the large cell shows a flat plateau that remains within 0.03 mK over 10 days and that is reproducible within 0.05 mK over
8 months. The calibrated value of a CSPRT obtained using the large cell agrees with that obtained using the small glass cell
within the uncertainties of the calibrations. |
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Keywords: | Gallium ITS-90 Triple point |
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