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

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 degreesC, 2290 degreesC and 2474 degreesC, 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 degreesC, nickel-carbon (1329 degreesC, palladium-carbon (1492 degreesC, rhodium-carbon (1657 degreesC, platinum-carbon (1738 degreesC, and ruthenium-carbon (1953 degreesC. These nine fixed-point temperatures cover the range from the copper point to 2500 degreesC. The evaluated melting-point repeatabilities (standard deviations) were generally better than 0.1 degreesC. 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.