Measurement of the radiance temperature (at 655 nm) of melting graphite near its triple point by a pulse-heating technique

Measurements of the radiance temperature of graphite at 655 nm have been performed in the vicinity of its triple point by means of a rapid pulse-heating technique. The method is based on resistively heating the specimen in a pressurized gas environment from room temperature to its melting point in less than 20 ms by passing an electrical current pulse through it and simultaneously measuring the radiance temperature of the specimen surface every 120 μs by means of a high-speed pyrometer. Results of experiments performed on two different grades of POCO graphite (AXM-5Q1 and DFP-1) at gas pressures of 14 and 20 MPa are in good agreement and yield a value of 4330±50 K for the radiance (or brightness) temperature (at 655 nm) of melting graphite near its triple point (triple-point pressure, ∼ 10 MPa). An estimate of the true (blackbody) temperature at the triple point is made on the basis of this result and literature data on the normal spectral emittance of graphite.