Importance

Loading Importance Indicators...

Abstract

A dark-colored, wave-length selective oxide film on aluminum is prepared thereby that the metal subsequent to a cleaning treatment is submerged into a bath consisting of an aqueous solution having pH 8.9-10.9 and at a temperature of from 20.degree. to 100.degree. C. under conditions which result in an electrode potential of between -1.1 and -0.6 volt relative to a saturated calomel electrode. The said potential can advantageously be maintained by either addition of H.sub.2 O.sub.2 to the bath or by electric polarization. In a more specific embodiment of the process there is used an aqueous solution of 1-100 g NH.sub.4 Cl or (NH.sub.4).sub.2 SO.sub.4 per liter solution with or without addition of aluminate ions AlO.sub.2 -- or Ca.sup.++, the pH of the solution, if necessary, being adjusted to pH 9 by addition of NH.sub.3, NaOH, KOH, Ca(OH).sub.2 and that the content of silicon, chromium and phosphorus each is maintained under 10 ppm.

Loading the Abstract Image...

First Claim