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Need help with plating silver over chrome

Hi.. I have a problem plating silver over chrome. After electrocleaning I acid dipped in 10% H2SO4 and after silver strike and plating with Silver, it peeled. I tried acid dipping in 50% HCl and 25% HCl. There wasn't any peeling but my substrate turned hazy. What should I do? The base of my substrate is plastic but it is coated with Cu and Ni and Cr.

I know there isn't anything wrong with my silver solution cos I am able to plate silver over nickel with no problem.

Sarah Ho
Lab technologist - Singapore
June 7, 2011

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June 9, 2011

Good day Sarah.Stripping chrome can be done in various ways. I prefer to use spent electrocleaner solution (NaOH) anodically.
Once you can see "gassing" on the item you have effectively removed the chrome. Now you have a nickel substrate with an "oxide" on the surface. You need to clean this oxide with an acid dip (preferably with fluorides). Clean and activate with A) 1-5% H2SO4 cathodic
B) Wood's nickel strike
and a flash of nickel to give your Ag strike an "active" substrate. Good luck.

Eric Bogner
- Toronto, Ontario, Canada

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Hi Sarah,

You may try diluted chromic acid. Also, your plating part shall be voltage carrying prior enter into silver strike so plating happen immediately once the part contact with bath solution to avoid chromium substrate got chance to passivate inside silver strike bath.

Regards,
David

David Shiu
- Singapore
June 9, 2011

Is possible to plate silver over chromium? I have plated zinc over hard chromium but the hard chrome is dull.

Daniel Hernandez
- Bucaramanga Santander Colombia
June 9, 2011

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Hi Daniel,

hard chrome plating on zinc substrate is possible with all properties which hard chrome has to offer (brightness, hardness, microcracks etc). However, as you describe it, it seems that your zinc is being etched by the chrome.
I recommend you to apply a pre-voltage onto your zinc plated parts while entering your hard chroming process. Also be careful with your trivalent vs primary catalyst & secondary catalyst & temperature.

Greetings,
dominik

Dominik Michalek
- Melbourne, Australia
First of two simultaneous responses -- June 10, 2011

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THE BEST IF YOU CAN GET THE PLASTIC PLATED ONLY WITH COPPER, YOU CAN DO AN ACTIVATION AND PLATE NICKEL + SILVER WITHOUT PROBLEMS. IF YOU TRY TO PLATE DIRECTLY ON CHROME ITS BETTER TO PLAY LOTTERY AND IF YOU TRY TO GET OUT THE CHROME YOU PROBABLY DAMAGE THE NICKEL OR MAKE IT VERY PASSIVE.
NORMALLY THESE LAYERS ARE LOW THICKNESS SO THE BEST IS THE FIRST OPTION

Ricardo Burstein
Bnei Berak, Israel
Second of two simultaneous responses -- June 11, 2011

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June 14, 2011

1. You cannot plate silver on chromium.
2. Your parts are coated with nickel and chromium. The chromium is good for the cycle as it prevents the yellowing and passivating of the nickel.
3. The first step in your cycle should be - chromium removing. Either with HCl or as some people recommended, by anodic process in alkaline solution.
4. BUT, anodic process makes nickel passive so I prefer HCl.
5. H2SO4 - is not to be used in order to remove the chromium layer.
6. Activation - the Nickel must be electrolytically activated. The best activation is cathodic in an alkaline cyanide solution. As you have cyanide in your premises anyway (for the silver plating), this is the best process.
7. My friend Ricardo recommended not to plate nickel at all, only copper. In this case the copper should be a highly bright acidic process and the silver sould be plated right after the copper with no delay.
8. Plating nickel plus chromium and then removing the chromium, allows for delay (even a few days)between the nickel and the silver.

Sara Michaeli
Tel-Aviv-Yafo, Israel

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Hi,
Why to plate on Chrome! Remove the chrome layer by simple methods - Activate and then plate Silver!!
Regards

T.K. Mohan
plating process supplier - Mumbai, India
June 14, 2011