Performance of WC–C peritectic and Ru–C eutectic fixed points

Abstract

Two types of high-temperature fixed points (HTFPs) were evaluated by VNIIOFI, NIM, KRISS and NMIJ. WC–C peritectic point cells manufactured independently in different National Metrology Institutes (NMIs) were compared for the first time, and agreement of the melting temperatures for three high-quality cells at the level of 0.05 °C was demonstrated. This confirms, in conjunction with previous results that verified their long-term stability, high repeatability and reproducibility, the high potential of the WC–C cell as the highest-temperature reference point for radiation thermometry.The performance of the Ru–C eutectic fixed point was verified by evaluating Ru–C cells manufactured from 99.999% purity Ru materials from different manufacturers. These cells used considerably purer materials than those used in previous studies. New Ru–C cells were constructed from the best performing materials, and the t90 values of these cells were measured at the four NMIs on their locally-realized ITS-90 scale. The values agreed within 0.25 °C among the four NMIs, and the t90 value of Ru–C was determined to be 1953.64 °C with an expanded uncertainty of 0.20 °C. Both results confirmed that performance of WC–C and of Ru–C is comparable to or exceeds that of the HTFPs evaluated in the Consultative Committee for Thermometry’s HTFP project, and both fixed points have capability as a reference fixed points to be included in the future MeP-K in terms of thermodynamic temperature T.