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Can't get jet black passivation on Zinc-nickel plated parts

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My customer spec. is to have jet black passivation, whereus our process that produces brownish tint with black colour after passivation. What is possible remedy to get jet black colour..

Parthasarathy
Manager - Chennai, Tamil Nadu, India

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Does it absolutely have to be zinc-nickel? I think you'll find that a reliable black is a lot easier if the plating is zinc-iron.

Ted Mooney, P.E. finishing.com Brick, New Jersey

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Hai!
In your letter there is no clear picture about plating. The sustrate should be Zinc(acid) plated, followed by nickel plating. Then the thickness sholud be more than 20 micron. If the substrate plated like that u can achieve the desire colour.
GOOD LUCK

P.KARTHIKEYAN
- Bangalore, Karnataka, India.

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Please verify with your chemical supplier latest development in trivalent chromates will help you to achieve with 80 to 90% Jet black finish (aceptable level)

P. Gurumoorthi     electroplating process chemicals Chennai, Tamilnadu, India

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Parthasarathy,
Please give more detailes about your customer spec. and also full detailes of what is your plating process.There are lots of developments happening in Zinc plating.
Alkaline cyanide free Zinc iron plating, followed by trivalent passivation is the answer.If u come out with more detailes, u will get good suggestions.
p.S. It is nice to see Gurumoorthi back!
Regards

T.K. Mohan     plating process supplier  Mumbai, India

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Dear Mr Parthasarathy,

Try doing an XRF analysis of the Nickel - Zinc percentages on the parts that don't look so good with black. You may find that they have a higher percentage of Nickel in them
and you may have to increase 2-3% of Zinc in the plated alloy to get a pleasing black.

Khozema Vahanwala Saify Ind   Bangalore, Karnataka, India