A DYNAMIC TECHNIQUE FOR MEASURING NORMAL SPECTRAL EMISSIVITY OF ELECTRICALLY CONDUCTING SOLIDS AT HIGH-TEMPERATURES WITH A HIGH-SPEED SPATIAL SCANNING PYROMETER

A dynamic (subsecond) technique is described for measuring normal spec tral emissivity of electrically conducting solids at high temperatures , primarily in the range 1800 K up to near their melting point. The ba sic method involves resistively heating a tubular specimen from ambien t temperature through the temperature range of interest in less than 1 s by passing an electrical current pulse through it, while using a hi gh-speed spatial scanning pyrometer to measure spectral radiance tempe ratures along a 25-mm length on the specimen. This portion of the spec imen includes a small rectangular hole that approximates a blackbody c avity. Measurements of spectral radiance temperature of the specimen s urface as well as specimen true temperature enable the determination o f the normal spectral emissivity of the surface via Planck's law. The applicability of the technique is demonstrated by measurements perform ed on molybdenum in the range 1900-2850 K.