Surface Structure and Emissivity of Aluminum Nitride Films

In this study, aluminum nitride films were formed on aluminum substrates by gas nitriding in order to improve their low emissivities. To accomplish this, aluminum alloys were subjected to nitriding conditions at 773 and 823 K for 0–5 h, using alumina and magnesium powders. The resulting aluminum nitride films were several micrometers thick and the films were dark brown or black. The surface structures of the aluminum nitride films were investigated using a scanning electron microscope, which showed fine acicular aluminum nitride nodules with diameters on the order of several micrometers. Emissivities were evaluated at 298 K using Fourier transform infrared spectroscopy, in a wavelength range of 2–14 μm. Total emissivities at temperatures between 323 and 383 K were estimated from emissivity results obtained at 298 K. It was subsequently found that emissivity decreases with increasing wavelength and an emissivity of 0.80 was observed at a wavelength of 2 μm. Total emissivity was 0.49 % at 298 K and was in excess of 0.50 between 323 and 383 K.