High-temperature fixed points in the range 1150  C to 2500  C using metal-carbon eutectics

Abstract

The melting and freezing plateaus of three metal-carbon eutectic alloys, cobalt-carbon, iridium-carbon and rhenium-carbon, were observed by radiation thermometry for the first time, and their repeatability evaluated. The observed melting temperatures were 1324 °C, 2290 °C and 2474 °C, respectively. A small dependence of the freezing temperature on the cooling rate was observed for the cobalt-carbon eutectic. Six metal-carbon eutectic points have previously been reported by the present authors: these, with their melting temperatures, are iron-carbon (1153 °C), nickel-carbon (1329 °C), palladium-carbon (1492 °C), rhodium-carbon (1657 °C), platinum-carbon (1738 °C), and ruthenium-carbon (1953 °C). These nine fixed-point temperatures cover the range from the copper point to 2500 °C. The evaluated melting-point repeatabilities (standard deviations) were generally better than 0.1 °C. The metal-carbon eutectic points seem to be a promising way of realizing fixed points for practical calibration of radiation thermometers. The two fixed points above 2500 K in particular are potentially useful for thermodynamic temperature determination based on thermal radiation, as well as for radiometry and photometry.