Method of measuring emissivities of metals m the infrared

Abstract

A method of measuring normal spectral emissivities in the infrared region from 1 to 13μs is described. It consists of comparing the rate of emission of radiant energy from a blackbody with that from the specimen. The two observed radiances are made equal by adjusting the temperatures. An equation is derived for use in calculating the emissivity for the observed temperatures. The main sources of error arise in the measurement of the temperature of the specimen and the temperature of the blackbody. As an example of the method, the normal spectral emissivity of gold has been measured in the range from 4 to 13μ at temperatures from 550 to 1,000 °K. The emissivity was found to range from 0.014 at 4μ and 550 °K to 0.0256 at 9μ and 1,000 °K. A table is included which lists the values of emissivity from 4 to 13μ and from 550 to 1,000 °K at intervals of 50 °K.