RESTSTRAHLEN BAND STUDIES OF POLYCRYSTALLINE BERYLLIUM-OXIDE

New experimental bulk reflectance and emittance spectra from the 9-15- mum reststrahlen band region of polycrystallline beryllium oxide are r eported. Note that the polycrystalline material exhibits a dip at 10 m um, which is not present in spectra for single crystals. The possible origins of this feature are discussed including absorption by a surfac e oscillation excited at boundaries of 20-mum crystalline grains. Owin g to the reststrahlen band, beryllium oxide is selectively low, emitti ng 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 ai r pollution. Using an established acceleration procedure, we simulated such pollution, and the increase in emittance was measured. It was ob served that the emissivity increased from 0.31 for a clean surface to 0.36 for a surface heavily polluted by an industrial atmosphere.