RADIANCE TEMPERATURES (IN THE WAVELENGTH RANGE 522-906NM) OF NIOBIUM AT ITS MELTING-POINT BY A PULSE-HEATING TECHNIQUE

Radiance temperatures (at six wavelengths in the range 522-906 nm) of niobium at its melting point were measured by a pulse-heating technique. The method is based on rapid resistive self-heating of the specimen from room temperature to its melting point in less than 1 s and on simultaneously measuring the specimen radiance temperatures every 0.5 ms with a high-speed multiwavelength pyrometer. Melting was manifested by a plateau in the radiance temperature-versus-time function for each wavelength. The melting-point radiance' temperatures for a given specimen were determined by averaging the measured temperatures along the plateau at each wavelength (standard deviation of an individual temperature from the mean: 0.1-0.4 K). The melting-point radiance temperatures for niobium were determined, by averaging the results at each wavelength for 10 specimens (standard deviation: 0.3 K), as follows: 2497 K at 522 nm, 2445 K at 617 nm, 2422 K at 653 nm, 2393 K at 708 nm, 2337 K at 809 nm, and 2282 K at 906 nm. Based on estimates of the random and systematic errors arising from pyrometry and specimen conditions, the total error in the reported values is about 5 K at 653 nm and 6 K at the other wavelengths.