849 0195-928X/03/0500-0849/0 © 2003 Plenum Publishing Corporation International Journal of Thermophysics, Vol. 24, No. 3, May 2003 (© 2003) A Multiwavelength Reflectometric Technique for Normal Spectral Emissivity Measurements by a Pulse-Heating Method 1 1 Paper presented at the Sixteenth European Conference on Thermophysical Properties, September 1–4, 2002, London, United Kingdom. Fan Yi, 2,3 Sun Xiaogang, 2 and F. Righini 4 2 Harbin Institute of Technology, P.O. Box 308, 92 West Dazhi St., Harbin 150001, People’s Republic of China. 3 To whom correspondence should be addressed. E-mail: djm@hope.hit.edu.cn 4 CNR Istituto di Metrologia ‘‘G. Colonnetti,’’ Strada delle Cacce 73, 10135 Torino, Italy. A new technique has been developed for the direct measurement of the normal spectral emissivity at several wavelengths in pulse-heating conditions, adding some novel features to previous versions of this type of apparatus. Pulse-heating experiments were performed on niobium strip specimens, taking the specimen from room temperature to the melting point using rapid resistive self-heating. The normal spectral emissivity was measured at three wavelengths by a multi- wavelength reflectometric technique. At the same time, the radiance temperature was measured at the same wavelengths by a high-speed pyrometer from approx- imately 1100 K to the melting point. Details of the method, the measurement apparatus, and the calibration technique are described. Preliminary results for the normal spectral emissivity of niobium at 633, 750, and 900 nm over a wide temperature range are presented. KEY WORDS: high-speed multi-wavelength pyrometer; multi-wavelength reflectometric technique; niobium; normal spectral emissivity; pulse-heating method. 1. INTRODUCTION The pulse-heating technique is considered a very accurate method for the measurement of several thermophysical properties (heat capacity, enthalpy, heat of fusion, electrical resistivity, hemispherical total emissivity, thermal expansion, etc.) at high temperatures, because it overcomes limitations of