Indirect Determination of the Thermodynamic Temperature of a Gold Fixed-Point Cell

Authors: Battuello, M.¹; Girard, F.²; Florio, M.²

Source: International Journal of Thermophysics, Volume 31, Numbers 8-9, September 2010 , pp. 1491-1497(7)

Publisher: Springer

Abstract:

Since the value T ₉₀(Au) was fixed on the ITS-90, some determinations of the thermodynamic temperature of the gold point have been performed which form, with other renormalized results of previous measurements by radiation thermometry, the basis for the current best estimates of (T − T ₉₀)_Au = 39.9 mK as elaborated by the CCT-WG4. Such a value, even if consistent with the behavior of T − T ₉₀ differences at lower temperatures, is quite influenced by the low values of T _Au as determined with few radiometric measurements. At INRIM, an independent indirect determination of the thermodynamic temperature of gold was performed by means of a radiation thermometry approach. A fixed-point technique was used to realize approximated thermodynamic scales from the Zn point up to the Cu point. A Si-based standard radiation thermometer working at 900 nm and 950 nm was used. The low uncertainty presently associated to the thermodynamic temperature of fixed points and the accuracy of INRIM realizations, allowed scales with an uncertainty lower than 0.03 K in terms of the thermodynamic temperature to be realized. A fixed-point cell filled with gold, 99.999 % in purity, was measured, and its freezing temperature was determined by both interpolation and extrapolation. An average T _Au = 1337.395 K was found with a combined standard uncertainty of 23 mK. Such a value is 25 mK higher than the presently available value as derived by the CCT-WG4 value of (T − T ₉₀)_Au = 39.9 mK.

Keywords: Gold fixed point; Radiation thermometry; Thermodynamic temperatures

Document Type: Research article

DOI: http://dx.doi.org/10.1007/s10765-010-0784-y

Affiliations: 1: Thermodynamics Division, Istituto Nazionale di Ricerca Metrologica (INRIM), Torino, Italy, Email: m.battuello@inrim.it 2: Thermodynamics Division, Istituto Nazionale di Ricerca Metrologica (INRIM), Torino, Italy

Publication date: 2010-09-01

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