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