Effect of Surface Microstructures on the Infrared Emissivity of Graphite

The effect of surface microstructures of graphite on the infrared emissivity was investigated in the wavelength region from 5.5 m to 17 m at temperatures from 1300 K to 1900 K. The results indicated that the surface microstructures and the changes of them with temperature had an important effect on the emissivity of graphite. The normal emissivity decreased with an increase of the smooth area on the sample surface. The directional emissivity had changed little with the detected angle from 0 to 60, which meant that the samples in this experiment could be seen as diffuse. Because of scattering and reflection of electromagnetic waves by the surface, the normal emissivity increases with the surface roughness. Furthermore, a modified model was proposed to calculate the normal emissivity. The calculated results were in good agreement with the values obtained at 1477 K, while differences of about 10 % at 1778 K were considered to be caused by limitations of the model and the complex surface.