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A solidification approach to correcting for impurity uncertainties in fixed points.

Malik, Z; Hunt, J D*; Davies, H; Lee, P D*; Lowe, D; Quested, P N (2011) A solidification approach to correcting for impurity uncertainties in fixed points. Int. J. Thermophysics, 32 (7-8). pp. 1589-1601.

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Uncertainty estimation for the effect of impurities on fixed points requires an accurate assay of the fixed-point material. To apply a correction also needs a knowledge of the liquidus slope of the solute binary system. Two methods are presented here for giving a realistic uncertainty and potential for correction without detailed knowledge of the impurities present. Both methods are based on the Scheil equation. The first method uses the gradient at about 50% solid; and where some limited knowledge of impurities is available, this method can, in cases where the bulk of impurities segregate preferentially into the liquid phase, be used to apply a correction. To apply an uncertainty simply knowing typical impurities for a particular metal may be considered sufficient. The second method involves a best fit for the four variables in the Scheil equation. It is shown that this second method can work even where multiple impurities are present, but that when applied to real data, problems arise due to deviations from Scheil behavior. This deviation is thought to be due to difficulties in maintaining a uniform solid/liquid interface at the end of a freeze

Item Type: Article
Subjects: Engineering Measurements
Engineering Measurements > Thermal
Identification number/DOI: 10.1007/s10765-011-0925-y
Last Modified: 02 Feb 2018 13:14
URI: http://eprintspublications.npl.co.uk/id/eprint/5234

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