Abstract

A technique using evaporated Al coated with double layers of Al2O3 and silicon oxide to produce surface films having low solar absorptivity (α) and high total normal and hemispherical emissivities (N and ) is described. High vacuum evaporation with an electron gun was used for preparing undecomposed films of Al2O3 and SiO2. α and N were determined from reflectance measurements made in the wavelength region from 0.2 μ, to 50 μ. ∊ was measured calorimetrically by a transient thermal method. α of all Al + Al2O3 + silicon oxide film combinations was determined to be about 0.12. The greatest increase in N and was obtained when Al was first coated with Al2O3 about λ/4 thick at 10 μ and then overcoated with 2000 Å to 4000 Å of silicon oxide. With such film combinations α/ values of less than 0.2 could be readily achieved. Surface films of this type were found to be extremely stable during simulated solar uv irradiation.

© 1971 Optical Society of America

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