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It seems like glass-coated stir bars are a specialty item. Standard stir bars are coated in PTFE. Is PTFE resistant to all typical lab solvents? Or is there a reference to check to ensure it is inert to the chemicals being stirred?

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  • $\begingroup$ PTFE is resistant to all typical lab solvents and even non typical. $\endgroup$ – Mithoron Jun 26 '15 at 17:06
  • $\begingroup$ Perhaps it's easier to give examples of things one might use in a lab that are not compatible with PTFE? $\endgroup$ – feetwet Jun 26 '15 at 17:08
  • $\begingroup$ Probably only strongest redox stuff would be real problem. $\endgroup$ – Mithoron Jun 26 '15 at 18:04
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    $\begingroup$ PTFE is attacked by alkali metals, most notably by the liquid sodium/potassium alloy $\ce{NaK}$. $\endgroup$ – Nicolau Saker Neto Jun 26 '15 at 18:39
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Labware manufacturers will often put out chemical compatibility charts for their products. A search on Google for the phrase ptfe chemical resistance yields a large number of hits, of varying thoroughness.

One fairly comprehensive one is this one from ThermoFisher Scientific.

Scanning it, PTFE has "Excellent" resistance listed for most solvents, except for pure 3-phenyl-2-propenal, which is "merely" "Good" ("Little or no damage after 30 days of constant exposure.") Lists from other sources have a different sets of compounds, some of which caution against conditions like "dry fluorine" or some rarer compounds. This one lists fluorine, gold monocyanide, and diethylamine as not recommended. (Though a number of other sources - including ThermoFisher - say diethylamine is perfectly fine.)

So PTFE is resistant to pretty much all lab solvents which a major manufacturer of lab equipment thinks it's relevant to mention - but if you have something that you think may be atypical or which you have particular concerns about, do a search for that particular compound or contact the manufacturer for their recommendations.

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This may not be the answer that you are looking for, but I remember a project, for which we had to replace PTFE stirring bars with their glass-coated counterparts.

It is true that PTFE is resistant to most of the solvents used, but it is not really hard and resistant to abrasion.

In a study where aqueous suspensions of metal silicides were stirred, we recognized very soon that the PTFE covers didn't last very long. The stirring bars were polished down to the metal core, which spoiled the experiment. Glass-covered stirring bars turned out to be a viable alternative here.

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