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"Are yellow chromate and yellow passivate the same?"



Current posting:

November 5, 2021

Comment: I do believe that chromates and passivates are different.

Ted - as you mentioned when discussing ASTM B633, Type V is a passivate and uses trivalent chromium while Type III is a chromate and uses hexavalent chromium. Although you are correct that the industry usually uses them interchangeably, I don't think they should be considered the "same" for this reason: they differ chemically... 'chromate' is a reference to salts that contain the chromate anion, CrO42-. This anion contains chromium in its Cr6+ (hexavalent) state.

See other sources here:
www.dekalbmetal.com/wp-content/uploads/2016/08/Chromate-vs-Passivate.pdf

zincplating.company/understanding-the-difference-between-chromates-and-passivates/

R Sedgebeer
engineer - Bremerton, Washington
^


November 2021

A. Thanks, R. You are correct and your references are correct.

A piece of improper slang that others often use and that I have used as well is 'trivalent chromate' -- whereas there can actually be no such thing because it is an oxymoron -- the chemical meaning of 'chromate is' CrO4 in which the chrome must be hexavalent.

But your clarification doesn't negate the real-world communication problem that whether customers specify 'zinc and yellow passivate' or 'zinc and yellow chromate' we still don't know whether they actually want a trivalent passivate or a hexavalent chromate. Ideally they should offer a specification but they often don't because, being human, at the time of the order they "just want it plated" and no hassles, but at the time of delivery they naturally want it to be exactly what their customer actually wants :-)

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^




Closely related Q&A's, oldest first:

January 26, 2012

Q. Hello everybody

As a total amateur I came across some problems, when buying fasteners.
I'd appreciate if you could answer me the following questions:

1.) Is a yellow chromated and yellow passivated fastener the same?
2.) "Black finish" screw same as black passivated, black oxide finish?
3.) When not the same, what is the difference between chromate and passivate?
4.) In a catalog I've read the following: "Plating for Grade 8: Yellow chromate offers a greater degree of protection from white corrosion than clear chromate. Standard minimum thickness for commercial zinc-yellow plating is 0.00020 inches." So is now Yellow chromate the same as yellow plating?

I know these are many questions, but as a layman I am so confused now, I hope you can bring some light into the dark!

Thank you very much for your answer!

Arthur

Arthur Meier
- Upper Saddle River, New Jersey
^


January 27, 2012

A. Hi, Arthur.

I will answer your questions, but need to remind you that copywriters are not there to inform us ... they are there to sell us on whatever they have to offer! Thus, if they are trying to sell their cheaper, thinner and less protective zinc plating against others who are offering thick and corrosion resistant hot dip galvanizing, they invent phrases like "electro galvanized", which they subsequently feel entitled to shorten to "galvanized" (against howls from metal finishers) in order to insert another layer of obfuscation :-)

So, just because we tell you what these words mean to a metal finisher today doesn't mean the copywriters will follow those definitions tomorrow. They'll probably try their best not to :-)

1. Yes, "yellow chromated" and "yellow passivated" are the same -- meaning an electroplated finish (usually zinc plating because it's the least expensive) followed by a chromate conversion coating which shall be yellow in color.

2. "Black finish" doesn't imply anything except the color. Black passivated would mean zinc plating with a black chromate conversion coating. Black oxide is a different finish entirely, but means the same thing as "gun bluing"; it can tend to look matte black on a rough surface but a jewel-like royal blue to navy blue on a highly polished surface. Black oxide offers no corrosion resistance by itself, but depends on the oil or wax on it to retard rust.

3. Passivate is a tricky one because it means different things for different substrates. Passivation of stainless steel is a completely different process than passivation/chromating of zinc plating.

4. Traditional hexavalent chromate is inherently a yellow-ish/honey-ish/amber-ish color. So, in the old days, a dark yellow chromate implied a significantly thicker and more corrosion-resistant coating than a clearer chromate. Today, as a result of RoHS and changing times, trivalent chromate is more common and this is not necessarily yellow. Today a yellow color is often nothing but dye. "Yellow plating" is a somewhat meaningless phrase, but what often happens is "zinc plating with yellow chromate" gets abbreviated as "zinc, yellow" or "yellow zinc" on purchase orders and packing slips.

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^


November 8, 2012

thumbs up signWell said Ted!

James Struck
- Lancaster, Pennsylvania, USA
^



September 17, 2014

Q. I have got an enquiry from my client asking for tubes with yellow zinc plating. From the above post it seems that plating is only related to coating/surface protection of tubes.
Please confirm that plating has nothing to do with the shape of tubes.

Thanks in advance.

amina khatoon
- pune,maharashtra,india
^


September 2014

A. Hi Amina. I will be happy to confirm that !

... but only if I am also allowed to remark that miscommunication/misunderstanding is the single number one problem in business, and asking a third party what the first party probably meant can sometimes aggravate those miscommunications :-)

Luck & Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^



Bichromate vs passivation

June 14, 2017

Q. Please help, I have been selling stud bolts, zinc plated with yellow or clear passivate, now I've got a request for zinc plated / bichromate ... please is it the same thing as passivation?

Adeniyi Egbemode
- Nigeria
^


June 2017

A. Hi Adeniyi. Yes, "passivation" of zinc electroplating, and "chromate conversion coating" / "bichromating" / "dichromating" of zinc electroplating are all the same thing. And, yes, it is most often done in clear or yellow color, but can be done in olive green or black as well. Zinc electroplating is virtually never done without it.

However, these days there are RoHS, WEEE, automotive, and other environmental pressures to not use toxic hexavalent chromate, and to employ trivalent chromates instead (the phrase 'trivalent chromate' is actually an oxymoron because the "-ate" implies hexavalent according to chemical naming rules, but the phrase is widely used nonetheless).

So what will be important for you to determine is whether your customer wants a trivalent passivation/conversion coating to comply with environmental standards, or the old fashioned hexavalent chromate. It would actually be best to use specifications like ASTM B633 [affil. link to spec at Techstreet] rather than loose terms like 'zinc plated with yellow or clear passivate'.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^



August 29, 2017

Q. Hi,

I was thinking of using a yellow passivated zinc finish to some internal steelwork balustrades.

I see it contains Chlorine and Cyanide. Does anybody know if the finish is toxic and to be avoided?

May thanks in advance

Thomas Teggin
Green and teggin Architects - Greater London, uk
^


August 2017

A. Hi Thomas. You probably read the earlier entries on this page, so I won't repeat them; I'll just summarize that "yellow passivated zinc finish" means zinc electroplating followed by a yellowish chromate conversion coating.

Re. chlorine: no, there is no chlorine involved. The plating solution might be chloride-based, but the chloride itself is no more dangerous than the chloride in table salt.

Re. cyanide content: In the old days of 50 years ago the zinc plating solution was usually cyanide based; today it rarely is. But in any case, the zinc is metal; any cyanide, acid, or anything else used in the process has been neutralized and rinsed off. It was also common until about 20 years ago to lace the chromate conversion coating with a small amount of cyanide, because it accelerated the process. But if you specify "RoHS-compliant trivalent chromate conversion coating" you should have no worries about cyanide, hexavalent chromium, or any other toxin.

What may be a concern is suitability and appearance.. .

Suitability: This is a corrosion resistant finish that you will see on fasteners; brackets, mounting plates, and chassis for electronic devices, underhood and internal parts in automobiles, internal parts in inexpensive door locks and closing mechanisms, hinges (it looks sort of like brass), etc. But if this balustrade is actually a handrail, it will probably not hold up well to abrasion and finger oils and perspiration.

Appearance: This is generally not considered a decorative finish. The reason to note this is that although you might find the "industrial" look of it pleasing, any given look to it might be considered random & coincidental, so for an application like this you will need samples and a sample board of acceptable parts because if, for example, half is done by one company and half by another, the parts may all look generally yellow but terribly different. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^



October 23, 2017

thumbs up sign This is not a question, but a compliment. Ted, your answers to various questions and how you answer the questions should be printed out and stuck up on the walls of everyone who answers questions on the Web.

Informative, succinct and so clear that even a bloke like me can understand them.

Many thanks.
Rod

Rod Baker
AfricanBrandLink - Fish Hoek, South Africa
^


October 2017

Hi cousin Rod. Thank you very much for such kind words.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^



August 6, 2019

Q. Hello, can anyone tell me the difference in functionality and appearance between the finishing types III (colorless chromate conversion coatings) and V (colorless passivate) which are mentioned in table 2 of ASTM B633 [affil. link to spec at Techstreet] .

Daniel Padilla
- Gomez Palacio, Durango, Mexico
^


August 2019

A. Hi Daniel. Type V is intended to offer the functionality and appearance of Type III, but without using the older traditional hexavalent chromate (the chemical whose toxicity and carcinogenicity made Erin Brockovich a household name). It tends to be higher technology and highly proprietary, and it's not necessarily a drop-in replacement, but the general answer is that the world is rapidly moving towards Type V and phasing out Type III. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^


August 7, 2019

Hi Ted, I've been searching this forum for a while and I can tell you this is a great site. THANKS.

Daniel Padilla [returning]
- Gomez Palacio, Durango, Mexico
^

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