Method for the darkening of a surface layer of a piece of...

Details Method for the darkening of a surface layer of a piece of... Method for the darkening of a surface layer of a piece of...

2007-12-25

2007-12-25

Tsang-Foster, Susy (Department: 1753)

Metal treatment

Process of modifying or maintaining internal physical...

Processes of coating utilizing a reactive composition which...

C205S333000

Reexamination Certificate

active

10852870

ABSTRACT:
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.

REFERENCES:
patent: 1953997 (1934-04-01), Cushman et al.
patent: 3723102 (1973-03-01), Lowe
patent: 4574041 (1986-03-01), Zahavi et al.

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