Optically black coating and process for forming it

Details Optically black coating and process for forming it Optically black coating and process for forming it

1977-01-13

1978-09-05

Andrews, R. L.

Chemistry: electrical and wave energy

Processes and products

204 29, 204 35N, 204 58, C25D 1108, C25D 1118, C25D 1124

Patent

active

041117620

ABSTRACT:
A product capable of extremely high absorption of electromagnetic radiation, including visible light, useful in optical applications and as a decorative panel comprises a body made of anodizable metal, preferably aluminum having a roughened surface over which an oxide layer is deposited by anodization. The anodized surface is characterized by a roughened surface of pronounced peaks and valleys and a columnar, fault-ridden structure of the anodized oxide layer itself.
The product is made by honing the anodizable metal surface by impacting it with aluminum oxide particles, preferably of 100 to 200 mesh size, to form peaks and valleys thereon. After honing, the surface is anodized under controlled conditions to develop the oxide layer thereover. After anodizing, the surface may be dyed and sealed. A vacuum drying and hydrogen fluoride treatment step to dry and "water-proof" the surface may be utilized to eliminate reflectance peak values at certain wavelengths.
When dyed black, more than 98% of the impinging radiation of the vast majority of wavelengths of up to 120 microns is absorbed and dissipated by the surface. More than 98% of infrared radiation (above about 7.8 microns wavelength) is absorbed and dissipated by the undyed surface.

REFERENCES:
patent: 3488103 (1970-01-01), Webb
patent: 3891516 (1975-06-01), Chu
Handbook of Chem. & Physics, 32nd Ed., p. 1729.
Surface Treatment of Al by Wernick et al., 3rd Ed., 1964, pp. 52-53, 347.
Objectives in Corrosion Protection of Bright Decorative Trim & Their Implementation", 48th Annual Tech. Proceedings A.E.S., 1961, p. 126.
Electroplating Engineering H. Book, 2nd Ed., A. K. Graham et al., 1962, pp. 437-438.

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