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In our lab, we commonly use a mixture of sulfuric acid and nitric acid to clean borosilicate glassware. I'd like to clean some PTFE pieces in there, too, but not sure if they will dissolve or not.

Does anyone have any first-hand experience with this, and know whether or not a sulfuric acid/nitric acid mixture dissolve PTFE?

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  • $\begingroup$ Just out of curiosity, what is on the PTFE and why do you think you need such harsh cleaning conditions? $\endgroup$ – Nope Sep 11 '13 at 13:21
  • $\begingroup$ PTFE = Polytetrafluoroethylene, a polymer commonly known as Teflon. en.wikipedia.org/wiki/Polytetrafluoroethylene $\endgroup$ – user809695 Sep 11 '13 at 16:12
  • $\begingroup$ Be aware that some PTFE items (more often mechanical mechanical components) are made from a sintered product (has a faintly dimpled texture like expanded polystyrene scaled down) that may have voids that trap the acid, I would keep these out or take care of how they will be used. PTFE intended for chemical handling should be the virgin material and void free, I would risk some items to test. $\endgroup$ – KalleMP Mar 7 '16 at 19:47
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For having used "sulfonitric acid" (sulfuric and nitric acids mixture) for at least 2 decades, PTFE is definitely stable to such a mixture.


Safety on the use of "sulfonitric acid"

I know it is off-topic but I think that safety should be learned as light touches, not as a-difficult-to-swallow course. (Please tell me if it is not in accordance with the site's rules).

You can safely use "sulfonitric acid" (i.e. usually a mixture of one volume of conc. sulfuric acid poured slowly into one volume of conc. nitric acid) to clean glassware and PTFE-ware if you follow some common sense rules. Explosions (or at least too vivid reactions) reported were the direct consequences of a poor understanding of what "sulfonitric acid" does.

  1. Handle it under a fume hood (I told you it was common sense!!)
  2. NEVER pour sulfonitric acid on organic material as the latter will be oxidized in an explosive way! Every piece of glassware should first:

    • Be cleaned as much as possible with any solvent or manually removing solid substance which is stuck where it should not be,
    • Be thoroughly rinced with a solvent miscible with water (acetone, methanol, ethanol...),
    • Be thoroughly rinced with tap water, in order to eliminate most of any organic solvent,
    • Only then can you pour the sulfonitric acid onto your glassware and let it do its magick.
  3. Do not think that a plastic which can seemingly resist any solvent will actually resist exposure to sulfonitric acid! PTFE will resist but not common plastic materials.

If you follow these rules, there is no reason why you should experience any dangerous reaction in your lifetime. Be especially careful with sintered funnels.

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I can't claim to have any personal experience with that sulfuric acid/nitric acid cleaning mixture specifically, but, as far as I'm aware, PTFE is generally inert towards acids. As a testament to that, it is apparently the material used for storing fluoroantimonic acid. I found a chemical resistance chart confirming its stability against strong acids. It is evidently resistant to concentrated sulfuric and nitric acids, as well as aqua regia (a concentrated mixture of nitric acid and hydrochloric acid). I have used the last of those for cleaning PTFE lab equipment before with no problems.

Having said all that, it would be wise to consult the handling and safety data for your particular labware to be certain.

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