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Liquidus slopes of impurities in ITS-90 fixed points from the mercury point to the copper point in the low concentration limit.

Pearce, J V; Gisby, J A; Steur, P P M* (2016) Liquidus slopes of impurities in ITS-90 fixed points from the mercury point to the copper point in the low concentration limit. Metrologia, 53 (4). pp. 1101-1104.

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Abstract

A knowledge of the effect of impurities at the level of parts per million on the freezing temperature of very pure metals is essential for realisation of ITS-90 fixed points. New information has become available for use with the thermodynamic modelling software MTDATA, permitting calculation of liquidus slopes, in the low concentration limit, of a wider range of binary alloy systems than was previously possible. In total, calculated values for 536 binary systems are given. In addition, new experimental determinations of phase diagrams, in the low impurity concentration limit, have recently appeared. All available data have been combined to provide a comprehensive set of liquidus slopes for impurities in ITS-90 metal fixed points. In total, liquidus slopes for 838 systems are tabulated for the fixed points Hg, Ga, In, Sn, Zn, Al, Ag, Au, and Cu. It is shown that the value of the liquidus slope as a function of impurity element atomic number can be approximated using a simple formula, and good qualitative agreement with the existing data is observed for the fixed points Zn, Al, Ag, Au and Cu, but curiously the formula is not applicable to the fixed points Hg, Ga, In, and Sn. Some discussion is made concerning the influence of oxygen on the liquidus slopes, and preliminary calculations using MTDATA are discussed.

Item Type: Article
Keywords: SPRTs, ITS-90, impurities, liquidus slopes, temperature metrology
Subjects: Engineering Measurements
Engineering Measurements > Thermal
Identification number/DOI: 10.1088/0026-1394/53/4/1101
Last Modified: 02 Feb 2018 13:13
URI: http://eprintspublications.npl.co.uk/id/eprint/7147

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