Method for the darkening of a surface layer of a piece of material containing zinc

The invention relates to a method for darkening a superficial layer of a workpiece which contains zinc by anodic oxidation. The workpiece is oxidized in a soaking bath containing an aqueous solution comprised of a hydroxide and of a nitrate. The anodic oxidation may be carried out in an aqueous solu...

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Bibliographische Detailangaben
Hauptverfasser:	KRUSE THOMAS, MEISTERJAHN PETER
Format:	Patent
Sprache:	eng
Schlagworte:	APPARATUS THEREFOR CHEMICAL SURFACE TREATMENT CHEMISTRY COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATIONOR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY IONIMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL COATING MATERIAL WITH METALLIC MATERIAL COATING METALLIC MATERIAL DIFFUSION TREATMENT OF METALLIC MATERIAL ELECTROFORMING ELECTROLYTIC OR ELECTROPHORETIC PROCESSES INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION INGENERAL METALLURGY PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTIONOF COATINGS SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THESURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION
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Beschreibung
Zusammenfassung:	The invention relates to a method for darkening a superficial layer of a workpiece which contains zinc by anodic oxidation. The workpiece is oxidized in a soaking bath containing an aqueous solution comprised of a hydroxide and of a nitrate. The anodic oxidation may be carried out in an aqueous solution containing NH.sub.4 NO.sub.3 or NaNO.sub.3, and having a pH value ranging from 8 to 14, at a dipping bath temperature (T) ranging from 15 to 45.degree. C., and with a current density (i) ranging from 3.times.10.sup.-4 to 0.5 A/cm.sup.2. The workpiece is placed in the soaking bath at the beginning of the anodic oxidation after the voltage has already been applied.