Method for Measuring High Temperature Spectral Emissivity of Nonconducting Materials

Abstract

A new method, based upon the integral blackbody technique, for measuring the normal spectral emissivity of nonconducting materials at high temperatures is described. A small cylindrical sample (5.21 mm diam x 9.53 mm length) is mounted within a long, thin-walled, metallic tube that is heated by the passage of direct current. Lateral holes in the tube wall permit an optical system to alternately detect the spectral radiance from the sample and from a cavity when both are at the same temperature. The major sources of error have been analyzed and the overall performance evaluated. Data are presented on a series of new, commercial ceramics, silicon carbide and silicon nitride, for the spectral region 1.5-15 jim and the temperature range 1300-1900 K. Temperature levels to 3000 K have been achieved with a specially configured graphite composite sample. These results indicate that the method provides a useful tool for studying the effects of fabrication processes and environmental influences on the radiative properties of materials at high temperatures.