Reststrahlen band studies of polycrystalline beryllium oxide.

New experimental bulk reflectance and emittance spectra from the 9-15-µm reststrahlen band region of polycrystallline beryllium oxide are reported. Note that the polycrystalline material exhibits a dip at 10 pm, which is not present in spectra for single crystals. The possible origins of this feature are discussed including absorption by a surfaceboscillation excited at boundaries of 20-µm crystalline grains. Owing to the reststrahlen band, beryllium oxide is selectively low, emitting in the primary atmospheric window, which makes this material useful for frost prevention when electrical conductors cannot be used. This protection is susceptible to reduction by surface contaminants from air pollution. Using an established acceleration procedure, we simulated such pollution, and the increase in emittance was measured. It was observed that the emissivity increased from 0.31 for a clean surface to 0.36 for a surface heavily polluted by an industrial atmosphere.