Thermal emissivity and solar absorptivity of aluminum coated with double layers of aluminum oxide and silicon oxide.
A technique using evaporated Al coated with double layers of Al(2)O(3) and silicon oxide to produce surface films having low solar absorptivity (alpha) and high total normal and hemispherical emissivities (epsilonN and epsilon) is described. High vacuum evaporation with an electron gun was used for preparing undecomposed films of Al(2)O(3) and SiO(2). alpha and epsilonN were determined from reflectance measurements made in the wavelength region from 0.2micro to 50micro. epsilon was measured calorimetrically by a transient thermal method. alpha of all Al + Al(2)O(3) + silicon oxide film combinations was determined to be about 0.12. The greatest increase in epsilonN and epsilon was obtained when Al was first coated with Al(2)O(3) about lambda/4 thick at 10micro and then overcoated with 2000 A to 4000 A of silicon oxide. With such film combinations alpha/epsilon 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.
Hass
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Ramsey
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Heaney
J B
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Triolo
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