The triple point of nitrogen

International temperature scales define several fixed points, which temperature values are determined with a very high precision. Some of them, which are in a low-temperature range, are called gaseous fixed points because the reference substances under a normal condition -in a room-temperature range -appear in a gaseous state. These reference substances are called by physicists cryocrystals or quantum crystals when occurring in a low temperature in a solid state. The substances play an important role in a standard thermometry. The triple point of argon, oxygen, neon and hydrogen are primary fixed points of the International Temperature Scale of 1990 (ITS-90) [1]. The triple points of nitrogen, methane and carbon dioxide are secondary fixed points of the scale [2]. Also, the solid-solid phase transitions in the cryocrystals are secondary fixed points of the scale. The highest accuracy methods of measurements applied in a standard thermometry enable the determination with a very small uncertainty of the phase transition temperatures, its reproducibility and stability. The reproducibility and stability of the transition temperature are the most important factors deciding about usefulness of these points in thermometry. Using the highest accuracy methods, better than 1 mK, which at present are used in metrology only can give a new information about nature and properties of investigated substances important also for physicists. PACS: 64.60.Ej Studies/theory of phase transitions of specific substances; 64.75.-g Phase equilibria; 67.90.+z Other topics in quantum fluids and solids.

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“…In the low-temperature range, the International [4][5][6][7] and results of the measurements are presented in this paper.…”

Section: Temperature Scalementioning

confidence: 99%

“…4. Determination of the triple-point temperature of nitrogen in the pulse heating method [6]. F corresponds to the fraction of melted substance.…”

Section: Triple Pointsmentioning

confidence: 99%

Cryocrystal phase transitions applied as temperature standards

Szmyrka-Grzebyk

Kowal

2009

Low Temperature Physics

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“…The mean value for the difference between the UME cell and the Italian standard is −119.0 µK, with a standard deviation of 49.5 µK. Because these differences were larger than 100 µK (an acceptable value for national standard water cells) from the Key Com [11][12][13][14]. A model of the multicompartment cell manufactured by IMGC (presently INRIM), shown in Fig.…”

Section: Thermometric Cellsmentioning

confidence: 99%

Measuring Systems for Thermometer Calibration in Low-Temperature Range

et al. 2011

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“…Impurity data for the fixed-point cells 3Ar and 2O2 were already given in [8]. The impurity levels of the other two fixed-point cells, 7Ne and 14eH2, are omitted here for lack of space, but they are of comparable quality.…”

Section: Scale Realizationmentioning

confidence: 99%

“…Nitrogen was chosen because previous measurements of its triple point demonstrated its good thermometric properties [4][5][6][7]. The results for the triple point were published in [8], and results for the solid α-β transition are presented here.…”

mentioning

confidence: 99%

The α–β Transition of Nitrogen

Lipiński¹,

Kowal²,

Szmyrka-Grzebyk³

et al. 2007

Int J Thermophys

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It is well-known that, aside from its triple point, nitrogen exhibits a solidto-solid transition at about 35 K that is of some interest as a secondary reference temperature. During the recently published highly accurate measurements of the triple point of nitrogen (Metrologia 43, 435 (2006)), an extensive study was made also of the solid α-β transition of nitrogen, using both the continuous heating method and the pulse-heating method. This transition is of significantly lower quality than the triple point of nitrogen. A very high thermal resistance and a large time constant characterize the transition. Therefore, even the determination of the self-heating of the thermometer requires a very long time. A value of T 90 = 35.620 K with an expanded uncertainty U = 8 mK for the coverage factor k = 2 was found, differing by +6 mK from the published CCT-recommended value. The reproducibility of the value was better than ±5 mK. In addition to the temperature value found for the transition, a comparison is made with previous measurements on this point, and an overview is given of the available information about it.

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The triple point of nitrogen

Cited by 8 publications

References 24 publications

Cryocrystal phase transitions applied as temperature standards

Cryocrystal phase transitions applied as temperature standards

Measuring Systems for Thermometer Calibration in Low-Temperature Range

The α–β Transition of Nitrogen

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