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How to do passivation

I have a porous media in Stainless Steel 316L. I need to form a passive layer around the particles to achieve radiative properties of a non-metallic (for Heat Tranfer studies). How can I do the passivation and control the thickness of the passive layer?

Hi Sheila:

I know that stainless 316L, as well as other free machining stainless steels is passivated by immersion in 20% nitric acid (at 70% conc.)+ 4-6% sodium dichromate + water by 30 min. If substrate is porous, special steps might be required to permit capillary action (perhaps temperature changes to soak it in). This treatment will attack lead. What I don't know is if it will change radiation properties and give you what you want.

Good luck,

Sheila:

Refer to ASTM A967-99. This specification will allow you to use a much better solution than the dangerous nitric acid. citric acid formulations are available on the marketplace that do a better job, and safer.

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