Metal carbide-carbon peritectic systems as high-temperature fixed points in thermometry

WC - C, Cr3C2 - C and Mn7C3 - C peritectic systems were investigated for their potential of serving as high-temperature reference points in thermometry. Mixtures of high-purity graphite powder with W, Cr and Mn powder of 99.99%, 99.9% and 99.95% purity by mass, respectively, were placed in graphite blackbody crucibles and melting/freezing plateaus were observed by means of a radiation thermometer. The observed melting temperatures were 2749 degrees C ( WC - C), 1826 degrees C (Cr3C2 - C) and 1331 degrees C (Mn7C3 - C), with a repeatability - in each case - of 0.02 K. The melting range for WC - C and Cr3C2 - C peritectics was roughly 0.1 K. WC - C showed a flat freezing plateau that agreed with the melting plateau within the repeatability. The three fixed points are possible candidates, like the metal ( carbide) - carbon eutectic fixed points, in the realization of an improved high-temperature scale above the copper point.