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

Abstract

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 °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 °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.