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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