Chapter 9 - Spectral Emissivity Measurements

Abstract

Abstract This chapter describes the wide variety of experimental instrumentation and methods used for spectral emissivity measurements at both ambient and elevated temperatures, along with specific examples of materials studied. There are a number of measurement principles and methods to determine the spectral emissivity, because the emissivity can be defined by not only Planck's law but also Kirchhoff's law; the spectral emissivity depends on the direction of the emission, and the materials of interest are sometimes semitransparent or contaminated. The normal spectral emissivity of materials is of considerable interest for both practical and scientific reasons. The measurement methods for spectral emissivity are mainly categorized into two groups: (a) comparison between spectral radiation intensities measured from the sample and a blackbody, and (b) spectral reflectance measurements. Experimental difficulties that can be encountered in the spectral emissivity measurements at ambient temperatures are quite different from those at high temperatures. At high temperatures, it is particularly important to maintain or identify the physical and chemical conditions of the sample surfaces. Several experimental studies, using a variety of techniques, of solid and liquid metals and ceramics at ambient and high temperatures above 2000 °C are presented.