Impurity Correction Techniques Applied to Existing Doping Measurements of Impurities in Zinc
- 146 Downloads
Impurities represent the most significant source of uncertainty in most metal fixed points used for the realization of the International Temperature Scale of 1990 (ITS-90). There are a number of different methods for quantifying the effect of impurities on the freezing temperature of ITS-90 fixed points, many of which rely on an accurate knowledge of the liquidus slope in the limit of low concentration. A key method of determining the liquidus slope is to measure the freezing temperature of a fixed-point material as it is progressively doped with a known amount of impurity. Recently, a series of measurements of the freezing and melting temperature of ‘slim’ Zn fixed-point cells doped with Ag, Fe, Ni, and Pb were presented. Here, additional measurements of the Zn–X system are presented using Ga as a dopant, and the data (Zn–Ag, Zn–Fe, Zn–Ni, Zn–Pb, and Zn–Ga) have been re-analyzed to demonstrate the use of a fitting method based on Scheil solidification which is applied to both melting and freezing curves. In addition, the utility of the Sum of Individual Estimates method is explored with these systems in the context of a recently enhanced database of liquidus slopes of impurities in Zn in the limit of low concentration.
KeywordsFixed points Impurities ITS-90 Scheil SPRT
This work was funded by the UK National Measurement System for Engineering and Flow Metrology and the National Natural Science Foundation of China (No. 51206152).
- 1.B.W. Mangum, P. Bloembergen, B. Fellmuth, P. Marcarino, A.I. Pokhodun, On the Influence of Impurities on Fixed-point Temperatures. Document CCT/99-11, submitted to the 20th Meeting of the CCT (1999)Google Scholar
- 2.B. Fellmuth, K.D. Hill, P. Bloembergen, M. de Groot, Y. Hermier, M. Matveyev, A. Pokhodun, D. Ripple, P.P.M. Steur, Methodologies for the Estimation of Uncertainties and the Correction of Fixed-Point Temperatures Attributable to the influence of Chemical Impurities. Working Document of the Consultative Committee on Thermometry CCT/05-08 (2005)Google Scholar
- 6.P. Bloembergen, H. Zhang, W. Dong, T. Wang, Two-front melting analyzed in a one-dimensional representation for the eutectic Pt-C, in AIP Conference of Proceedings, vol. 1552, 340–345 (2013)Google Scholar
- 7.J.V. Pearce, R.I. Veltcheva, M.J. Large, Impurity and thermal modeling of SPRT fixed-points, in 9th International Temperature Symposium. AIP conference on proceedings vol. 1552, p. 283 (2013)Google Scholar