A measurement technique for hemispherical total emissivity using feedback-controlled pulse current heating

Abstract

A new measurement technique for hemispherical total emissivity of electrical conductors at high temperatures (above 1500 K) which uses feedback-controlled pulse heating has been developed. In this technique, a specimen is heatedrapidly in vacuum by resistive self-heating up to a preset high temperature in a short time (about 200 ms), and then is maintained at that temperature under brief steady-state conditions (about 500 ms). In order to achieve fast feedback temperature control, a computer-controlled system with a solid-state switch, which regulates the current through the specimen, is employed. The radiance temperature of the specimen is measured with a high-speed radiation thermometer. In order to determine the true temperature, the normal spectral emissivity of the specimen is measured with a laser ellipsometer. Hemispherical total emissivity is determined at the plateau of temperature by the use of a steady-state heat balance equation based on the Stefan-Boltzmann law. Preliminary experiments were conducted on strip-shaped specimens of tantalum and molybdenum in the temperature range approximately 1900 to 2800 K.