The NIST eutectic project: construction of Co–C, Pt–C and Re–C fixed-point cells and their comparison with the NMIJ

Abstract

The National Institute of Standards and Technology (NIST) has initiated a project on novel high-temperature fixed-points by use of metal (carbide)–carbon eutectics to lower uncertainties in thermodynamic temperature measurement. As the first stage of the NIST eutectic project, a comparison of Co–C, Pt–C and Re–C eutectic fixed-point cells was conducted between the NIST and the National Metrology Institute of Japan (NMIJ) at the NIST to verify the quality of the NIST eutectic cells in addition to checking for possible furnace and radiation thermometer effects on the eutectic fixed-point realizations. In the comparison, two high-temperature furnaces, two radiation thermometers and one gold-point blackbody were used. A Nagano M furnace and a Linear Pyrometer 3 radiation thermometer were transferred from NMIJ and were used in conjunction with a Thermo Gauge furnace and an Absolute Pyrometer 1 radiation thermometer of NIST to check the dependence on the measurement equipment. The results showed that Co–C cells agreed to 73 mK. The melting temperature of the NIST Pt–C cell was approximately 270 mK lower than that of the NMIJ cell, with a comparison uncertainty of roughly 110 mK (k = 2), due to the poor purity of Pt powder. Although the Re–C comparison showed instability of the comparison system, they agreed within 100 mK. Though further improvement is necessary for the Pt–C cell, such as the use of higher purity Pt, the filling and measuring technique has been established at the NIST.