How to Detect presence of Clear Chromate

A. The best thing to do for the future is to specify an iridescent yellow chrome with a color standard, so that light finishes can be rejected.

A. Hi, folks. Tom's advice to Jay was excellent at the time, and it could still be considered good with some provisos ... but things have changed. The world has moved away from hexavalent chromating, and the only chromates that are both hex-free and which meet MIL-DTL-5541 [on DLA] are the NAVAIR-developed so called TCP (tri-chrome passivation) finishes.

TCP is thin and almost clear, and it is generally believed that dyeing them greatly reduces their corrosion resistance. So what you need these days is a test for the TCP finish. Please read on for claims that such tests exist and, further, that a well trained eye can see the TCP finish. Good luck!

Regards,

A. Hi, Ken. Adding yellow dye can be done with some of the thicker types of hex-free conversion coatings -- but the MIL-C-5541 approved TCP processes cannot be dyed (the film is too thin); attempts to dye it have all reduced the corrosion resistance.

The characteristic golden color of hexavalent chromium is not a dye; it is the natural color of the toxin, and it's what allows us to instantly recognize that handling the object will expose us to carcinogenic hexavalent chromium.

So this blowhard (me) gets to say it again: Why make parts look like they are toxic, carcinogenic, and forbidden by the EU, even though you have invested the time, effort and extra cost to make sure they are actually safe and "green"?

It seems at least possible to me that the EU may decide that testing for hex chrome is so burdensome and expensive for inexpensive fasteners that they may address this via the timesaver of applying the simple preliminary filter that "if it's golden color it must be rejected".

A. I've come across a few that have an inherent color (other than gold) - I don't remember which though. And I know that most can be dyed. But, what Ted says makes sense - if you are going to dye it, why dye it to match an older process that is on the way to being phased out? Why not blue, or green, or anything other than gold?

Q. The answer to the question of why you would want a RoHS gold Alodine replacement with the same coloration is simple, because your customers like it!

Also, if it turns out to be so simple for the EU to identify and "reject" parts for the presence of chromium by, "it looks gold", then so be it. I'll be glad to accept all the gold plated parts they can filter out for me!

A. Gold chromate will never be mistaken for gold, Ken :-)

'Product stewardship' was a crucial part of 'mission statement' last decade, But management themes come and go, and I guess responsibility isn't particularly "in" so far this decade. Leadership is always in, and if ever there was a right time for we in the industry to work to get our customers to understand and to think fresh instead of dyeing non-toxic finishes the inherent, characteristic color of the toxin, now would be the time.

The new "TCP / I can't see" replacement technology is colorless and very thin and my understanding is that attempts to dye it yellow or black so far have significantly reduced the corrosion resistance. Pastels are pastel because they lack saturation, so they may be more doable with these very thin coatings. If pastel pink or pale violet or light spring green were a quick and reliable indicator of the presence of a toxin-free TCP coating, we'd have the win-win situation we need :-)

In line with what Ted said - While the customer is always right, that doesn't mean that they are always educated or unwilling to be persuaded. Dyeing the parts yellow is just silly - silly from an environmental perspective in that it makes them much harder to tell apart from hex-chrome containing parts when it comes to recycling and such and silly from a business perspective with it making it impossible to brag about how "my parts are better for the environment -- just look at the color! (rather than that old toxic yellow)"

Yeah, the customer may want gold colored parts right now; that is no reason why we shouldn't be encouraging them to change.

A. We have been using TCP for a year now. I can tell you that it is not entirely colorless, but you won't a good gold out of it. When properly applied, TCP should have a very, very, very light tinge of brown. You have to know what your looking for. As to the dye, I've had numerous discussions with the folks at NAVAIR. The problem with dye is that it contaminates the bath to the point that salt spray failure occurs. NAVAIR has been working on this aspect for a few years but to no avail.

A. Trivalent Tester LLC has recently developed a drop test kit to enable verification of the presence of TYPE II Trivalent Chromium Conversion Coating on an aluminum substrate.

A. Hi Vinoo. We appended your inquiry to a thread which answers most of your questions. Although chromate conversion coatings are not conductive per se, if the process is performed to the MIL spec, the sheet should be sufficiently conductive as the spec calls for conductivity. But this is not an absolute, and my understanding is that pressure must be maintained to insure it.

Regards,

A. Hi John. Justin seems to imply that what you need for the new colorless trivalent chromates is an inspector with experience and a really good eye. That's certainly a point worth investigating as we are all jointly taking a serious risk in using 'invisible' surface treatments. As for visible 'tracers', the thing is, if the product is listed in the QPL, it's listed; and if it's not, it's not, and can't be used for MIL-DTL-5541 parts.

Regards,