Long-Term Stability of WC-C Peritectic Fixed Point

Abstract

The tungsten carbide–carbon peritectic (WC-C) melting transition is an attractive high-temperature fixed point with a temperature of $2747.5\,^\circ {\hbox {C}}$. Earlier investigations showed high repeatability, small melting range, low sensitivity to impurities, and robustness of WC-C that makes it a prospective candidate for the highest fixed point of the temperature scale. This paper presents further study of the fixed point, namely the investigation of the long-term stability of the WC-C melting temperature. For this purpose, a new WC-C cell of the blackbody type was built using tungsten powder of 99.999 % purity. The stability of the cell was investigated during the cell aging for 50 h at the cell working temperature that tooks 140 melting/freezing cycles. The method of investigation was based on the comparison of the WC-C tested cell with a reference Re-C fixed-point cell that reduces an influence of the probable instability of a radiation thermometer. It was shown that after the aging period, the deviation of the WC-C cell melting temperature was $-0.12\,^\circ {\hbox {C}}$ with an uncertainty of $0.14\,^\circ {\hbox {C}} \ (k~=~2)$.