Realization of the Triple Point of Hg and Observation of a Large Supercooling Using Small Glass Cell

Matsumoto²,

2020

Metrologia

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We performed a precise temperature measurement of the triple point of carbon dioxide (CO2), which is one of the secondary reference points of the International Temperature Scale of 1990 (ITS–90), using an adiabatic calorimeter with five capsule-type standard platinum resistance thermometers (SPRTs). Impurity analyses showed that the purity of the CO2 sample was 99.999 37%. A thermal treatment process before the realization of the triple point reduced the width of the melting curve of the triple point of CO2 and increased the linearity of the melting curves with respect to the inverse of the melting fraction F. We determined the triple-point temperature of CO2 at the liquidus point by extrapolating the six melting curves obtained after the thermal treatment process. The triple-point temperature of CO2 measured in this work is 216.590 90 K 0.36 mK (k = 1). This result indicates that the triple point of CO2 can potentially be used as a fixed point based on the ITS–90 to replace the triple point of mercury.

Section: Analytementioning

confidence: 54%

Realization of the triple point of carbon dioxide evaluated by the ITS–90

Matsumoto²,

2020

Metrologia

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“…To estimate effects of type II non-uniqueness, we used T-T 90 and T 90_CSPRT -T 90_ICVGT obtained earlier by NMIJ/AIST [34][35][36]. Figure 4 shows T-T 90 obtained using a 3 He constant volume gas thermometer, as described in an earlier report [34]. The value of T-T 90 was obtained using the ITS-90 based on the ICVGT, T 90_ICVGT [34].…”

Section: Resultsmentioning

confidence: 99%

“…Figure 2 shows a schematic side view of a sensing element of a PT-1000 and a photo of the PT-1000 and a CSPRT. For this study, we use eight CSPRTs, which were conventional type with 25 Ω at TPW and CSPRTs of the same type as those described in earlier reports [2][3][4][5]. All CSPRTs were calibrated at eight defining fixed points of the ITS-90 in the lowtemperature range below the TPW.…”

Section: Methodsmentioning

confidence: 99%

“…the triple points of water (TPW: 273.16 K), Hg (TPHg: 234.3156 K), Ar (TPAr: 83.8058 K), O 2 (TPO 2 :54.3584 K), Ne (TPNe:24.5561 K), and equilibrium H 2 (TPeH 2 : 13.8033 K), and two other fixed points of around 17.0 K and 20.3 K (FP17 K and FP20 K) realized by equilibrium H 2 vapor pressure or an interpolating constant volume gas thermometer [1]. The National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (NMIJ/AIST) developed calibration systems for capsule-type SPRTs (CSPRTs) directly at each fixed point [2,3]. These systems can calibrate CSPRTs with low uncertainty.…”

Section: Introductionmentioning

confidence: 99%

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ITS-90 non-uniqueness and evaluation of characteristics of new 1000 Ω type platinum resistance thermometers for low-temperature measurement

Imamura³

et al. 2020

Meas. Sci. Technol.

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For use in a low-temperature region below the triple point of water (TPW), the National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (NMIJ/AIST) developed a precise comparison system of capsule-type standard platinum resistance thermometers (CSPRTs) for dissemination of the International Temperature Scale of 1990 (ITS-90). This study compared eight CSPRTs with a reference CSPRT using the comparison system to study non-uniqueness at low temperature. We also evaluated characteristics of a new type of low-temperature PRT with about 1000 Ω of resistance at TPW (PT-1000s), which was recently developed by Netsushin Co, Ltd. to obtain better temperature sensitivity of resistance at a low temperature. The PT-1000 sensor is made from a high-grade platinum wire, similarly to standard PRTs of the ITS-90. We calibrated four PT-1000s based on the ITS-90 and evaluated their characteristics by comparison with a reference CSPRT. Results indicate that the character of the temperature scale of PT-1000s is very close to that of CSPRTs down to 14 K.

“…The International Temperature Scale of 1990 (ITS-90) defined fixed points and subranges to be used for the calibration of a standard platinum resistance thermometer (SPRT) between 13.8033 K and 1234.93 K [1,2]. Among these fixed points, the triple point temperature of mercury is required to perform calibrations within the subrange from 13.8033 K to 273.16 K [3][4][5][6][7][8][9][10]. However, due to the toxicity of mercury, its use has been curtailed in recent years, so it would be helpful to assess means by which the ITS-90 process can be maintained if mercury is no longer readily available.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of the triple point temperature of sulfur hexafluoride and the associated uncertainty at NMIJ/AIST

2020

Metrologia

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This study determined the triple point temperature of sulfur hexafluoride (SF6), as well as the associated uncertainty, to evaluate the potential use of this value as an alternative to the triple point of mercury as a fixed point defined in the International Temperature Scale of 1990 (ITS-90). The triple point temperature was obtained using an adiabatic calorimeter incorporating a sealed cell made from oxygen-free copper. The cell was filled with 99.9992% SF6 and included three standard platinum resistance thermometers that had been calibrated at eight fixed points defined by the ITS-90 protocol. Applying a thermal treatment to the solidified sample prior to determining the triple point temperature was found to decrease the width of the melting curve. Based on melting curves acquired following this thermal treatment, the triple point temperature of SF6 was found to be 223.556 47(53) K. The temperature scale constructed using SF6 was found to be consistent with that generated using mercury within a maximum deviation of 70 K from 13.8033 K to 273.16 K.