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

Abstract

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 °C (WC–C), 1826 °C (Cr3C2–C) and 1331 °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.

Investigation of Impurity Elimination Effect in Metal–Carbon Alloys

“…High-quality melting plateaux observed for W-C and Cr-C peritectic systems [2] prepared from low-purity metals (just 4N and 3N purity for W and Cr, respectively) seem to support our conjecture that multi-component eutectic/peritectic-based fixed points have lower aforementioned "purity thresholds" than the ITS-90 fixed points based on single-component metals.…”

“…The potential M(C)-C peritectic fixed points proposed recently [2] have no less intricate structure and phase-transition mechanism (kinetics) than eutectics, and thus are expected to be similar to the eutectic fixed points in this respect ("sensitivity" to "impurity factor"). High-quality melting plateaux observed for W-C and Cr-C peritectic systems [2] prepared from low-purity metals (just 4N and 3N purity for W and Cr, respectively) seem to support our conjecture that multi-component eutectic/peritectic-based fixed points have lower aforementioned "purity thresholds" than the ITS-90 fixed points based on single-component metals.…”

Experimental Investigation of the Cr3C2–C Peritectic Fixed Point

“…In this paper, we describe the experimentally evaluated fixed-point performance of the Cr 3 C 2 -C peritectic point (1,826 • C), as a follow-up to an earlier investigation reporting the first observations of melting and freezing of metal carbide-carbon (MC-C) peritectic points [1]. In another paper in these proceedings by the authors, the Cr 3 C 2 -C peritectic point is studied for the purpose of understanding the peritectic reaction involved [2].…”

Numerical Prediction of Eutectic Temperature Using a Multi-phase-Field Model

“…Invariant reactions such as the eutectic reactions [2,3] and the peritectic reactions [4] in metal-carbon or carbidecarbon binary systems are proposed as additional fixed points at elevated temperatures. Considerable experimental research has been conducted to confirm the reliability of the new fixed points [5,6].…”