| Zugriffsnummer | 24979 |
| Dokumenttyp | Konferenzartikel in Zeitschrift |
| Peer Review | unbekannt |
| Sprache | Englisch |
| Titel | Further findings of impurity precipitation in metal fixed points |
| Autor(in); Institution |
Fahr, Martin; National Research Council of Canada (NRC), Ottawa, CANADA
Rudtsch, Steffen; 7.4, Temperatur, PTB-Berlin
Aulich, Antje; 7.4, Temperatur, PTB-Berlin
|
| Quelle/Jahr | International Journal of Thermophysics: 32 (2011), 11/12, 2239 - 2251 |
| ISSN | 0195-928X (PRINT) ; 1572-9567 (ONLINE) |
| DOI | |
| Verlag | Dordrecht: Springer |
| Konferenzangaben | TEMPMEKO & ISHM 2010, Portoroz, 31 May - 04 June, 2010, Slovenia |
| Zusammenfassung | Impurities are the source of the largest contribution to the uncertainty budgets in realizing the metal-fixed-point reference temperatures of the ITS-90. Currently, the smallest uncertainties are achievable by accounting for the influences of the impurities independently, as given by the product of the amount of dissolved impurity and the specific influence of that impurity on the phase-transition temperature. The former has to be determined through chemical analysis, which can deliver very detailed information about the concentrations of each element in the metal and even its spatial distribution. However, at these low concentrations, chemical analysis is unable to determine whether or not the impurities are dissolved, because the known methods cannot distinguish between a (solid) solution and a (solid) suspension. The latter, the sensitivity coefficient for each impurity, has to be determined by doping experiments until sufficient public data is available, an activity that several NMIs are currently engaged in. A few of these experiments have indicated that some impurities do not dissolve in the fixed-point metals. Based on this observation, we recently published a paper presenting thermodynamic calculations that predict the formation and precipitation of impurity oxides in metal fixed points. Here we provide further, more distinct proof, based on doping experiments with other material combinations, illustrate the precipitation process on a microscopic level, and present new calculations considering other chemical reactions that may lead to precipitation of even more elements. |
