Eric,
Thanks, you are right, it was PFIB: I remembered the PF bit, but Mr
Alzheimer had seized the IB. Yes, I had heard the horror stories. One
employer I had in the early 1960s machined a lot of Teflon, including
grinding it. While I was there, he introduced a no-smoking policy in the
workshops for this reason, but none of the machine operators turned up
his toes prior to the ban. Would it be a reasonable hypothesis that, of
the 30 operators or so, half would have smoked in the workshop prior to
the ban and that the chances of, say, 1 of them receiving a chip on a
lit fag end over, say, five years would be high, when there was Teflon
swarf and dust all over the place, including on the clothing (the damn
stuff was so charged that it literally flew at the operators)? Yet not
one was even hospitalised, let alone kicked the bucket. As this was in
Switzerland and not Austria, I don't think Goodnight Vienna was
apposite, maybe Hello, Lausanne!
Personally, I find it difficult to imagine how Teflon (or a VP soldering
fluid) can change readily to (CF3)2.C=CF2 from its -(CF2)n-
construction, even though the F:C ratio is correct. It would imply
extremely high energy would be needed to change the bonds to exactly
that formation, unless the polymer was not pure. However, anything is
possible and small quantities are feasible, I suppose!
Brian
OTOH, I had a customer who had an employee who smoked in the presence of
a heavy concentration of 1,1,1-trichloroethane vapours (machine had
leaked and he was swabbing the liquid from the floor) and who got
pulmonary oedema, as a result of phosgene. Fortunately not fatal, but
sufficient for a couple of weeks in hospital and a permanent resultant
weakness of the lungs. Another client had a low-level phosgene problem
with the same solvent, being used for defluxing in a vapour degreaser in
the same room as the soldering machine. The operators claimed headaches.
Carbon badges detected phosgene at the limit of measurement.
Investigation showed that, whereas it would normally require about
380-400°C for TCA to decompose, tin oxide at 250°C catalysed a minute
decomposition of the vapours, just sufficient to be unpleasant, despite
the extraction from the machine.
Eric Dawson wrote:
>
> Brian,
> Thanks for stating the facts so clearly. It's such a long time since vapour
> phase was popular and it was misunderstood then.
> The toxic thermal degradation product, by the way, is PFIB,
> perfluoroisobutylene. I heard horror stories of this chemical being produced
> during the early days of machining PTFE when the perpetrator was smoking as
> well. A sliver lands on the lighted end, he inhales and Goodnight Vienna.
> Was this an urban myth?
> Regards
> Eric Dawson
>
> > -----Original Message-----
> > From: Brian Ellis [SMTP:[log in to unmask]]
> > Sent: Wednesday, October 17, 2001 7:38 AM
> > To: [log in to unmask]
> > Subject: Re: [TN] Vapor Phase Soldering material
> >
> > Back in the days? Vapour-phase soldering is still done! The great
> > advantages of perfluorocarbons over other halocarbons are that a) they
> > are chemically extremely stable because the C-F covalent bond requires
> > much energy to break them; b) they are virtually non-toxic (for the same
> > reason: they do not break down in the body). In fact they can be used to
> > replace blood in the body for short periods as they do allow oxygen to
> > be dissolved and some "sportsmen" have even injected PFCs into the
> > bloodstream to improve their endurance performance by a higher
> > oxygenation; c) they are very inert chemically; d) they withstand high
> > temperatures; e) they are NOT ozone-depleting. Teflon is a solid PFC.
> > The disadvantages are a) that they are very expensive; b) they are
> > EXTREMELY global-warming (typically 1 kg of PFC is equivalent to 10
> > tonnes of carbon dioxide which is roughly equivalent to half the
> > emissions of a medium car during its lifetime); c) their stability
> > (~10,000 years atmospheric residence time) is such that end-of-life
> > disposal is very difficult and costly.
> >
> > The fluids, be they pure PFCs or PFEs, used for soldering are
> > sufficiently stable at 210 - 260°C that there is little significant
> > decomposition. Water hardly enters into the equation because it is
> > boiled off instantaneously, even if there be some condensation on the
> > cooling coils. Theoretically, there may be some hydrogen fluoride
> > generated (no hydrofluoric acid), but I believe that the quantities
> > would be really negligible, in practice. With the presence of other
> > organics from the flux residues, I would personally be more concerned
> > with trifluoroacetic acid, another nasty, but I have not heard of any
> > cases. Carbonyl fluoride is also not to be excluded, also very toxic.
> > There is another fluoro-compound, whose name escapes me for the moment,
> > which did cause some concern in the early days, which is toxic in the
> > ppb range. However, in practice, I have never heard of any of these
> > toxic substances being present in sufficient quantity to be of practical
> > concern.
> >
> > The real crunch comes when there is a secondary blanket, used in the
> > early days to reduce losses of the primary fluid. This was initially
> > always a pure CFC-113 (e.g., Freon TF, Arklone P etc.). Later, because
> > of the ozone depletion potential of CFC-113 being as high as 0.8, a
> > lower BP PFC was also proposed. CFC-113 does decompose at the vapour
> > temperature of the primary fluid, so that the interface zone between the
> > two vapours was always a hotbed of chemical reactions. This certainly
> > produced, especially in the presence of water, whose BP was higher than
> > that of the secondary fluid, a whole panoply of acids and other toxic
> > substances. For this reason, these machines had both a molecular sieve
> > to de-water the condensed vapours, but also a filter to remove the
> > acids, otherwise the stainless steel tank corroded into holes in a
> > matter of months. It is possibly this that you are thinking of. The most
> > important decomposition product was hydrogen chloride, which becomes
> > hydrochloric acid in the presence of water, but there was also phosgene,
> > hydrogen fluoride, trichloroacetic acid and goodness knows what else. I
> > feel reasonably certain (abstraction of any environmental effects), if
> > vapour phase soldering with a CFC-113 secondary blanket were invented
> > for the first time today, it would never be allowed into a workshop
> > because of the H&S aspects.
> >
> > Hope this makes it clear.
> >
> > Brian
> >
> > "Marsico, James" wrote:
> > >
> > > Back in the days of vapor phase soldering, I seem to recall that
> > > hydrofluoric acid was a bi-product of the fluorinert mixed with water,
> > or
> > > was it the Freon mixed with the fluorinert? Could anyone elaborate?
> > >
> > > Jim Marsico
> > > Senior Engineer
> > > Production Engineering
> > > EDO Electronics Systems Group
> > > [log in to unmask] <mailto:[log in to unmask]>
> > > 631-595-5879
> > >
> > >
> > --------------------------------------------------------------------------
> > -------
> > > Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
> > > To unsubscribe, send a message to [log in to unmask] with following text
> > in
> > > the BODY (NOT the subject field): SIGNOFF Technet
> > > To temporarily halt delivery of Technet send the following message: SET
> > Technet NOMAIL
> > > Search previous postings at: www.ipc.org > On-Line Resources & Databases
> > > E-mail Archives
> > > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
> > additional
> > > information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
> > ext.5315
> > >
> > --------------------------------------------------------------------------
> > -------
> >
> > --------------------------------------------------------------------------
> > -------
> > Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
> > To unsubscribe, send a message to [log in to unmask] with following text in
> > the BODY (NOT the subject field): SIGNOFF Technet
> > To temporarily halt delivery of Technet send the following message: SET
> > Technet NOMAIL
> > Search previous postings at: www.ipc.org > On-Line Resources & Databases >
> > E-mail Archives
> > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
> > additional
> > information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
> > ext.5315
> > --------------------------------------------------------------------------
> > -------
>
> ---------------------------------------------------------------------------------
> Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
> Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
> Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
> information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
> ---------------------------------------------------------------------------------
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------
|
