Process for providing aluminum substrates with light-absorptive surface layer
AssigneeVereinigte Metallwerke Ranshofen-Berndorf Aktiengesellschaft
InventorHerbert Meissner
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Abstract
To provide a substrate of aluminum with a dark surface layer of high absorption/emission ratio for luminous energy, the degreased and pickled substrate is immersed in a hot chromating bath until an oxide coating of not more than 2.5.mu. thickness is formed thereon. This coating is then colored black in a hot, acidic dyeing solution (pH between about 0.5 and 5) of potassium permanganate and a nitrate of cobalt or copper.
Claims6
A process for providing a substrate of aluminum with a dark surface layer of high absorption/emission ratio for luminous energy, comprising the steps of immersing said substrate in an oxidizing bath for a period just sufficient to form an oxide coating of not more than about 2.5.mu. on a surface thereof, rinsing the surface so coated, and thereafter immersing said substrate in an acidic aqueous solution of potassium permanganate and a nitrate of cobalt or copper, said solution having a pH between substantially 0.5 and 5 and a temperature between substantially 90.degree. and 100.degree. C., the proportion of potassium permanganate in said solution ranging between substantially 1 and 200 grams per liter, the proportion of the nitrate in said solution ranging between substantially 1 and 100 grams per liter.
Dependencies are inferred from the claim text.