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topic 3827

Need to do yellow chromate on Electroless Nickel

hill cross banner (1999)

Customer is requesting yellow chromate on the surface of mid phos electroless nickel. The nickel is plated over cast aluminum. While this might not be unusual- the request if the surface of the nickel to be yellow is a bit unusual. ? can't make it work. any ideas? Anyone out there have any experience with this. possible or not and thanks for any quick responses.

todd huehn
- Blaine, Minnesota


First of two simultaneous responses--

(1999)

Hi Todd.

When you use chromate on the EN parts you passivate the area. But you should use 50 gram per litre chromic acid. No heat treatment after plating. I think you get a better result in a high phosphor 10-14%.

Regards,

anders sundman
Anders Sundman
3rd Generation in Plating
Consultant - Arvika, Sweden



Second of two simultaneous responses--

(1999)

We've used a mild chromate rinse to passivate the nickel surface but you won't get "Yellow Chromate" film. Nickel is not like Zinc or Aluminum where the chromate film thickness builds.

jim conner
Jim Conner
Anoplex - Dallas, Texas USA


(1999)

Dear Mr Anders Sundman and Mr Jim Conners,

I wonder if the idea of passivating nickel by using 5% Chromic Acid comes from the notion that since Chrome is normally plated over Nickel, it will also passivate Nickel if Nickel plated deposits are immersed in a chromate dip. I have no knowledge that this actually works to passivate the Nickel, although it may work to give it a yellower colour. With so many Suppliers of Proprietary Chemicals there would have been someone with a product ready to milk the market if this actually could work. If anyone in the world has such a product then I would like to be contacted by them since I have a problem of my nickel plating rusting after some time despite the standard 5% chrome dip and hot NaOH dip after that. regards,

Khozem Vahaanwala
Khozem Vahaanwala
Saify Ind supporting advertiser
Bangalore, Karnataka, India

saify logo


(1999)

Mr Khozema. British Aero Space has made a test. When using a high phosphorus 10-14 % with 40 micron nickel deposit. You should not rinse the part in NaOH dip after passivate in chromic acid. I hope Jim can explain it better for you.

Best Regard

anders sundman
Anders Sundman
3rd Generation in Plating
Consultant - Arvika, Sweden



(1999)

A NaOH dip may accelerate the corrosion of the Nickel depending on the Phosphorus content.

A Chromic acid dip will reduce the activity of the freshly deposited Nickel.

It's not uncommon for poorly rinsed parts to tarnish and stain due to the high activity of the new coating. The Chromic acid will help slow down the oxidation of the Nickel by leaving a very thin film on the surface. There are other products that may help without the use of Chrome. Most Nickel suppliers will have these.

jim conner
Jim Conner
Dallas, Texas USA

(1999)

Khozema, Anders and Jim are right. You cannot dip the chromated parts in alkaline solutions this is not because of the substrate materials but chromium itself. Trivalent chromium hydroxide or oxide is amphoteric, that is, it dissolves in both acid solution and alkaline solution.

Ling

Ling Hao
- Grand Rapids, Michigan


(1999)

It is not common, but not rare, to dip nickel plated parts in a dilute solution of chromic acid. It does very little for the nickel since it is dilute. It does minorly help form an oxide layer, but it is close to irrelevant. The more common use is a "cheat" when a customer has specked out a plate that is too thin. The chromic solution forms a very thin chromate coating on the steel, thru the pores, which lasts just long enough to keep tiny rust spots from forming until it has been on his shelf for a couple of weeks. JIT users have it gone before that happens. It is a lousy cure, but the customer is always right, even when he is wrong.

James Watts
- Navarre, Florida


(1999)

Thanks everyone especially Mr Todd for posing his problem which answered a lot of my possible questions !

Is there yet any other process unexamined to minimize corrosion in DC plated Nickel ? Is pulse plating the only other answer or can we look for any other post treatment /sealing ?

thanks in advance ,

Khozem Vahaanwala Khozem Vahaanwala
Saify Ind 
Bangalore, Karnataka, India



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