TY - JOUR A1 - Rudtsch, S. A1 - Fahr, M. A1 - Fischer, J. A1 - Gusarova, Tamara A1 - Kipphardt, Heinrich A1 - Matschat, Ralf T1 - High-Purity Fixed Points of the ITS-90 with Traceable Analysis of Impurity Contents N2 - The International Temperature Scale of 1990 (ITS-90) is based on thermodynamic equilibrium states of ideally pure substances. The largest contribution to the uncertainty budgets of most metallic fixed points is the influence of impurities on the fixed-point temperature. Therefore, a traceable chemical analysis of the remaining impurities with small uncertainty is the basis of further progress. Further requirements are better knowledge of the phase diagrams at very low impurity contents, impurity segregation, and the quantification and correction of thermal effects during a fixed-point realization. In this article, current and future activities at PTB and BAM in order to develop improved metallic fixed-point cells of the ITS-90 are reviewed. KW - Chemical analysis KW - Fixed points KW - Impurities KW - ITS-90 KW - Phase diagrams KW - Thermal effects PY - 2008 U6 - https://doi.org/10.1007/s10765-007-0358-9 SN - 0195-928X SN - 1572-9567 VL - 29 IS - 1 SP - 139 EP - 150 PB - Springer CY - Dordrecht AN - OPUS4-17455 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Rudtsch, S. A1 - Gusarova, Tamara A1 - Aulich, A. A1 - Fahr, M. A1 - Fischer, J. A1 - Kipphardt, Heinrich A1 - Matschat, Ralf A1 - Panne, Ulrich T1 - Procedure for the impurity-related correction at the indium fixed-point N2 - Determining the influence of impurities on the fixed-point emperatures of the ITS-90 requires the completion of several tasks. In this paper, the Progress made at Physikalisch-Technische Bundesanstalt (PTB) and BAMFederal Institute for Materials Research and Testing is presented and remaining questions are discussed. The projected characterization procedure at PTB, which is based on the established SIE method (sum of the individual estimates), using a new indium fixed-point cell is described as an example. This procedure includes an SI-traceable chemical Analysis of the material in the fixed-point cell with sufficiently low uncertainties, the individual experimental determination of the influence of the quantified impurities on the fixed-point temperature, and the establishment of direct links to the phase-transition temperatures of the national standard and of an assumed material of ideal purity. A characteristic difference to the common practice is the chemical analysis of the fixed-point metal being done after determining the cell’s freezing temperature. This allows for the detection and consideration of contamination and purification effects due to the filling process, or due to the contact with the carbon crucible and other parts of the fixed-point cell. A chemical analysis of an indium fixed-point was carried out by BAM with relative measurement uncertainties below 30 % which have not been previously achieved. The results provide evidence for the precipitation of some impurities, which is apparently inconsistent with the corresponding binary phase diagrams, but was explained in a recent publication. Implications for the use of the SIE method shall be described briefly at the end. KW - Chemical analysis KW - Fixed-points KW - Impurities KW - ITS-90 PY - 2011 U6 - https://doi.org/10.1007/s10765-011-0915-0 SN - 0195-928X SN - 1572-9567 VL - 32 IS - 1-2 SP - 293 EP - 302 PB - Springer CY - Dordrecht AN - OPUS4-23373 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -