Recommended List of Common Impurities for Metallic Fixed-point Materials of the ITS-90
Dean C. Ripple, Anatoly Pokhodun, Peter Steur, Gregory F. Strouse
Working Group 1 of the Consultative Committee for Thermometry (CCT) has recommended methods for estimating the uncertainties of fixed-point temperatures attributable to chemical impurities . These methods require chemical analysis of all commonly found impurities in the fixed-point material. The document CCT/05-08 states: "Chemical assays should include, as a minimum, all of the common elements that are normally found in a particular fixed-point material. It is the intention of WG1 to prepare Appendices/Addenda for a list of such elements for the respective ITS-90 fixed points." The present document provides a list of these common impurities, for each of the metals with fixed-point temperatures defined on the International Temperature Scale of 1990 (ITS-90): mercury, gallium, indium, tin, zinc, aluminum, silver, gold, and copper. For each of these elements, we have collected either chemical assays of various material lots or documentary standards that specify the common impurities found in a particular material.
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