A cobalt-carbon eutectic fixed point for the calibration of contact thermometers at temperatures above 1100°C

A vertical cobalt-carbon (Co-C) eutectic fixed point cell was constructed at PTB to demonstrate its use for improvement of the calibration of noble-metal thermocouples at temperatures above 1100 degrees C. The melting and freezing temperatures of the Co-C eutectic were measured in different high-temperature furnaces at PTB and INMETRO (Brazil) to show its stability by using a Pt/Pd thermocouple. The reproducibility of all measured electromotive forces at the inflection points of the melting curves amounts to a value of about 0.06 degrees C. No drift in the melting temperature was observed. Therefore, the Co-C eutectic fixed point cell can be used as an adequate transfer standard for dissemination of the International Temperature Scale of 1990 (ITS-90) in the temperature range above the freezing point of copper.