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topic 3113

Formula for Blue Chromate (Passivation) for Zinc Plating


(1999)

Q. I need to know a make up formula for blue/clear zinc passivate solution ...

I have one: 5 grams Sodium Dichromate and 25 mls Nitric acid per litre, 25 seconds immersion time. But this is from a pretty old source and I wanted to check on the current formulae. Thanks.

Will Hamlyn
London, UK


(1999)

A. That formula may be as good as any for a non-proprietary, Will; over here in the U.S. nobody (well, virtually nobody) mixes their own chromates anymore. Sorry but I, and most of us here, don't know the formulations for the newer generation of chromates as they are trade secrets not public domain knowledge. Good luck.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(1999)

Q. That's as may be, but I wish to ... so can anybody be a little more helpful as to the chemistry involved? Thanks.

Will Hamlyn
London UK


(1999)

A. Dear Will, a chromate composed only of sodium dichromate and nitric acid may be no better than a nitric acid bright dip which brightens zinc & cadmium electrodeposits, i.e., there may be no residual zinc salts left on the "converted" surface of the zinc deposit. The dichromate may be useful in passivating any unplated steel which may exist in internal areas or as porosity on the plated surface.

See Chemical Conversion Coatings by Robert F. Ayres, 46th Annual Technical Proceedings of the American Electroplaters' Society, 1959 for a good discussion. Mr. Ayres also has references listed at the end of the paper including some patents. Contact the Society (www.nasf.org) for reprints, and search patents for other additives.

tom pullizzi monitor
Tom Pullizzi
Falls Township,
   Pennsylvania 



A. Hi again Will. You asked for the "current formulae". Again, all current formulas are trade secrets because tens or hundreds of millions of dollars was invested to develop RoHS-compatibility along with good corrosion resistance. But if your interest is actually in the chemistry involved in chromating, Biestek and Weber's "Electrolytic and Chemical Conversion Coatings" [Porcullis Press Ltd., ISBN 0 901994782] has a 123-page chapter which covers the chemistry exhaustively. It was translated from the Polish in 1976, so doesn't give "current" formulas though. Best of luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



(2003)

Q. Dear Everybody, I'm new in here! Can anybody can tell me, if I applied the blue zinc as a passivating material in our screw for the connector, what standard do I need to follow? Please help!

Joe [last name deleted for privacy by Editor]
- Hong Kong


(2003)

A. Hello Joe. What you are looking for is a zinc plating specification. You can find U.S. military specs for this, ASTM and SAE/AMS specs, and others -- a good starting point may be ASTM B633 [link by ed. to spec at TechStreet] or AMS2402 [link by ed. to spec at TechStreet] . Good luck.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



November 11, 2013 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. My field is zinc electroplating. I made blue chromating by myself; it's mixed by four chemical elements, i.e., sodium dichromate, sodium sulphate, sodium fluoride and nitric acid. The result of the finishing is very blue, but it fails in Salt Spray Test. It can only achieve 24 hour with white rust, <5%. It should be achieve 48 hours to meet the standard. Do you have any suggestion which part I should decrease or increase? Thanks.

Sianturi Asmer
- Bekasi, Indonesia


November 13, 2013

A. Hi Sianturi. 24 hours is the expected number for traditional blue chromates. As previously mentioned, I don't know the formulas for superior formulations because in general they are retained as trade secrets rather than public domain knowledge. But you should be aware that chromates based on hexavalent chromium (sodium dichromate) are now forbidden worldwide in whole industries (automotive for example) and on all materials in many countries (RoHS, WEEE, and other standards). Please purchase trivalent chromating solutions from the suppliers as it is the only way forward unless you can make truly substantial investments in development efforts. If you will be staying with hexavalent chromate, the previously mentioned book by Biestek and Weber will surely help you. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



November 14, 2013

Q. I WOULD LIKE TO KNOW THE DIFFERENCE BETWEEN ASTM B 633 AND AMS 2402 STANDARD REQUIREMENTS

KURINGI ANAND
- CHENNAI, TAMILNADU, INDIA


November 21, 2013

A. Hi Kuringi. ASTM specs are published by the American Society for Testing Materials and AMS specs are published by the Society of Automotive Engineers. Unfortunately there really isn't a good answer to your question. These specs are multiple-page detailed documents and you can't certify accordance with the general thrust of them, you have to have the spec in your possession and certify compliance to the last word. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


May 25, 2014 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I want to know about blue chromate conversion coating formula. I mean chromate passivating solution which is used after Zinc plating.

Ghasem Ebrahimi
- Karaj, Iran


May 2014

A. Hi Gaseem. As you see, we appended your inquiry to a thread which may answer it for you. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



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