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topic 11784

Passivated SS and outgassing problems on optics


We use passivated SS 303 and SS304 parts in optical and fiber optic assemblies. Occasionally I detect a 'burnt' odor to the parts after passivating, sometimes more than others, sometimes no detectable odor. In some of our fiberoptic assemblies, we use a fiber which transmits very high intensity light. Outgassing of nearly any material, particularly adhesives, will, over time, undergo some photochemical reaction and polymerize on the end of the fiber depositing a film which grows with time and degrades the light coming out of the fiber. We believe we see this problem of outgassing coming from passivated stainless steel parts also. It could be very low level of outgassing. The occasional odor a smell also makes me suspicious.

What is it I am smelling on passivated SS parts?

We need passivated parts to really clean the parts and prevent rusting. Some assemblies go underwater.

Is there any change to the passivation process which I might request from our vendors (passivating house) which would eliminate or reduce the 'smell' or any potential outgassing? Thanks.

Steve W. Kerrigan
- Shoreview, Minnesota


Hello Steve!

303 stainless steel is a free machining grade, meaning it has controlled amounts of manganese sulfide inclusions to help break the chips when you machine it. My GUESS is that you smell only the 303 parts, and not the 304. Switch from 303 to 304 and I'd bet your problem will vanish. You may also find that your passivation bath will give you fewer problems, since the 303 is commonly done in a type 2 bath (with sodium dichromate added) whereas 304 is most commonly type 6, with its easier control.

Then again, you might also consider citric acid passivation. You can find vendors readily on this site. If you do, let us know if it solves your problem, OK?

Good luck!

lee gearhart
Lee Gearhart


Well, you could ask the folks that passivate your product exactly what acid they use to passivate. Commonly, nitric acid 20-40% ,H20 60-80% and 2% sodium dichromate is used. Many companies have found that mixture to be too strong, and have switched to the same amounts of sodium citrate, water, sodium dichromate. This mix is easier to neutralize and usually prevents the outgassing problem. Ask these folks to repeat the de-ionized hot water rinse which should be a standard part of their process, anyways. Nitric acid is usually too volatile for precise stainless parts, therefore more neutralization is usually required.

Good luck!

Jeff Swayze
body jewelry - B.C.


Does the smell resemble sulfur? 303 has some in it to make more machine friendly. If you wish to have your vendors return parts that are free of this you could spec the "Coke" test. Which uses a lead acetate strip and "Classic Coke" to test for free sulfides. Coke specs this so fittings don't affect the taste of the product. Basically, put some passivated parts in a sealable container, add enought coke to cover them, tape the test strip to the lid and seal for 4 hours. If strip turns dark, no good. I bet Lee jumps in and states that citric passivate works better than the old Type II here. I will concur 100%.

Jon Quirt
- Fridley, Minnesota


THANK YOU! A simple accelerated test! But it is not so accelerated, Sounds like the test does allow some leaching.

pooky tom pullizi signature
Tom Pullizzi
Falls Township, Pennsylvania

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