From: mingos@vax.oxford.ac.uk
Newsgroups: sci.chem
Subject: Re: Teflon: question about heating.
Date: 24 Jul 92 11:20:54 GMT
Organization: Oxford University VAXcluster

In article <1992Jul22.221548.17086@yrloc.ipsa.reuter.COM>, loc@yrloc.ipsa.reuter.COM (Leigh Clayton) writes:
> 
>  I'm not normally a reader of sci.chem, but this question came up in
> rec.food.veg a while ago and I hope someone here can lay it to rest. I will
> read sci.chem for a while so you can respond either by mail or a post; I'll
> summarise to rec.food.veg but not here unless people ask me to.
> 
>  I posted this article to sci.materials, and got one response suggesting
> that the gas Teflon *may* emit when heated too much is Phosgene. The respondant
> was a bit cautious, though, since Phosgene seems to contain Chlorine and it
> isn't obvious where that would come from. Since the interest in rec.food.veg
> seems to still be there, I'm trying again this time to sci.chemistry; maybe
> we'll get better luck. I don't read sci.chemistry though, so if anyone does
> decide to post an answer, please post to rec.food.veg as well.
> 
>        -----------Begin previously posted article--------------
> 
>  In article <1992Jun11.152827.4156@bb1t.monsanto.com> tjfeue@bb1t.monsanto.com
> (I think. He may have been responding to an earlier post) suggests that Teflon
> should not be overheated because it will emit a dangerous gas that will kill
> pet birds (and presumably people).
> 
>  Teflon is (according to my American Heritage) a trade name for
> polytetrafluoroethylene. My organic chemistry is rather tentative, but I decode
> that name to look a bit like this:
> 
>        F F F F F
>        | | | | |
>   ... -C-C-C-C-C ...
>        | | | | |
>        F F F F F
> 
>  This is sort of a chlorine-less, polymerised CFC. Containing Fluorine it
> clearly *could* be convinced to emit Fluorine gas, which is indeed very toxic
> (though why it would kill a pet bird and leave a human around to gripe about it
> is a bit of a mystery to me). But I would expect this compound to be quite
> heat-stable (and indeed, fluorine gas being well known to be so toxic I can't
> imagine regulatory agencies allowing anything likely to emit it in cooking
> utensils for home use). Of course, the indicted gas may not be fluorine, since
> there are lots of dangerous gases in the world (like cyanide, which is made out
> of just carbon and nitrogen, so there's likely some way to make it out of
> Teflon (or wood) and air too, but I'd be surprised to see a lot of it made just
> by heating the stuff too hot).
> 
>  This strikes me as a typical urban myth, but I'm cross-posting to the
> sci.materials group in the hope that someone there will know (or be willing to
> find out) exactly how thermally stable the stuff is.
> 
> 
> -----------------------------------------------------------
> Leigh Clayton                     loc@yrloc.ipsa.reuter.COM
>     -or-                        loc@ipsaint.ipsa.reuter.COM

 When heated above a temperature of (I believe, please correct me if wrong, I
can't be bothered to go down to the library ) about 400c, PTFE will begin to
decompose, and emit fluorine gas.  I guess that if anyone leaves a PTFE coated
pan on a gas or electric ring without looking after it, it will easily get hot
enough to decompose, but then, if they're as terminally stupid as that, they'll
probably die in the ensuing fire rather than the fluorine cloud :-) 

Gavin

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Gavin Whittaker                                      The more knowledge,  
Inorganic Chemistry Dept                             the more sorrow.
Oxford University
Oxford                                                      - Ecclesiastes
England
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Newsgroups: sci.chem