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Removing Plasma Sprayed Silicon

I'm trying to find a less labor-intensive way of removing plasma sprayed silicon (approx. 6 mm thick) from a 304 S.S. substrate. Currently, we are thermal-shocking the coating (heating, then quenching in water) and pounding the coating off, which, of course is time consuming. From my anodizing experience, I believe that a HF, or NHF bath should attack the silicon (and hopefully not the substrate?). For obvious safety reasons, I would prefer not to have large baths of such a nasty chemical in the shop...plus the hassle of neutralizing once the bath becomes spent. Does anyone have any experience in this removal process.. or perhaps have a different idea/chemical bath that I could use?

Marc Green
anodizer - Boise, Idaho
2003

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2003

Hi Marc,

I have been around a lot of flame sprayed stuff, but silicon is not one of them. I would look at seeing if room temp to dry ice in alcohol would be enough of a shock. This will go to somewhere around 50 below. You could try from boiling water to the mixture for even more shock. Liquid nitrogen is much colder and is not terribly expensive when you buy it by the large dewar. This is a best guess based on your present process.

James Watts
- Navarre, Florida

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James...My reasoning for asking this question was to stray away from the "shock" method...as this is a pretty labor intensive process. Was hoping to find a chemical that would dissolve the Si, without attacking the 304 S.S substrate (at the same time, trying to stay away from the hydrofluoric acids) Am I asking for too much?

Marc Green
anodizer - Boise, Idaho
2003

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I am not aware of much that attacks silicon. My thought on going the cold route is that the silicon is a ceramic and should become more brittle than the metal, allowing it to literally be broken off with shock. Also, you do not affect the heat treat status of the metal.I suspect that the coefficient of thermal expansion is greater for the metal, causing it to shrink more than the silicon, which will give you the effect of a minor void between the materials. Heating tends to make them more pliable also. If you do not find a chemical, it would be well worth a try.

Good luck on the chemical route.

James Watts
- Navarre, Florida
2003