The dependence of the melting temperatures of the eutectics Fe–C and Co–C, designed for thermocouple thermometry, on the furnace offset temperature during the preceding freeze

We have studied the pre-freezing furnace offset temperature dependence of the melting temperature of the Fe–C eutectic system, designed for thermocouple thermometry, and compared the results to those measured accordingly for the Co–C eutectic system. When the pre-freezing offset temperature was changed from −3 K to −70 K, the shift of the melting temperature of the Fe–C eutectic system increased by 0.1 K. Our results suggest that care must be taken on deciding and controlling the furnace offset temperature during the preceding freeze as well as the furnace offset temperature during the melt when the melting temperature of the Fe–C system is used as a reference temperature for thermocouple calibrations. Under careful control of the offset temperature of the furnace, its effect via pre-freeze or melt on the melting temperature of the Fe–C cell can be confined to as low as 0.04 K for thermocouple calibrations.