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BromicAcid
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PTFE (Teflon) Sintering, coating, forming, and its decomposition.
PTFE can be bought by the pound in pyro as a halogen donor or for infrared flares. In addition I've seen it by the pound on eBay in blocks. I
do have a pound of the stuff laying around in prill form and found this useful piece of information from teflon.com:
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Sintering:Adequate sintering requires a programmable oven. The temperature is slowly raised from room temperature to 363° to 382°C (685° to
720°F). Hold times at these temperatures vary with part geometry and dimensions. The oven temperature is then slowly lowered to room temperature.
Stock shapes that are not properly sintered exhibit inferior physical properties (specific density, tensile strength, elongation, flex life),
electrical properties, and permeation and chemical resistance.
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It also mentions pre-forming at high pressure but maybe this could be carried out without that just to add chemical resistance. Teflon coating items
in my labratory would be quite useful. It would be much better if it just melted and one could dip into it to coat but that seems from teflon.com
like it would not convey the chemical and mechanical properties one would expect from PTFE.
Does anyone have any experience with teflon at high temperature? One post from Organikum states:
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Teflon (PTFE) is only useful up to the rated temperatures (~250°C). At about 550°C it decomposes. Thats good so, as by thermolysis of PTFE you can
gain TFA (trifluoroacetic acid) in about 18% yield.
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What about other decomposition products, this actually seems to be the hot topic recently on the internet as there was that exposae on TV recently on
teflon coatings decomposing at high temperature. I've seen HF, F2C=CF2, F3CCF3 and many other things listed among the decomposition products and
I understand that it might be quite the mix but does anyone have a more concise study on the products?
E.b.C:title
[Edited on 10-7-2005 by chemoleo]
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Proteios
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From my undergraduate polymer chem.....PTFE unzips to give TFE (radical unzipping... the exact reverse process of radiacal polyermisation, which is
thermodynamically more favourable at lower T).... The reaction is remarkable clean, however kinetically slow.... unzipping only occurs at the ends of
the chains..... so to unzip the stuff you have to hold it at the right temperature and wait for the thermodynamics to do their stuff.
As for giving it excess heat.... dunno what that would do... but given the composition of PTFE is C and F.....fluorinated carbons is about the limit
of what you can get off. The composition of hot air is only N and O... neither of which i can see reacting with TFE. As for getting HF.... maybe if
steam were present.
[Edited on 31-5-2004 by Proteios]
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Cyrus
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Earlier on this site, I found a post in a nitric acid thread about heating up teflon tape with a burner to make a teflon sheet- Is that possible? It
isn't even in prill form, and it sounds like the heat needs to be very regulated.
It would make a nice disposable coating on stoppers though...
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Theoretic
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PTFE decomposes to give a reportedly extremely toxic fluorocarbon among everything else (don't remember its name), has been tried as a war gas...
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BromicAcid
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Carbonyl Flouride would make sense in the presence of oxygen considering Organikum stated trifluoroacetic acid was possible. Maybe I should try
destructive distillation of a block of teflon and try to see if I can condense any products out 
| Quote: | | Earlier on this site, I found a post in a nitric acid thread about heating up teflon tape with a burner to make a teflon sheet- Is that possible?
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I always thought teflon tape was an adulterated form of teflon. Even moderate heating causes it to curl up on itself when I work with it so I
don't think it would fuse together to sheets readily. Possibly if you had it laid out on an object and pressed onto a hotplate though it might
hold its form but I still don't think that thin a sheet would fuse together.
[Edited on 6/2/2004 by BromicAcid]
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Cyrus
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Teflon (ab)use for mad science
Teflon is really easy to get, and really inert, and the only problem is that we can't form it into shapes as needed.
If teflon can be sintered, the problem is solved.
My goal is to produce thin "monolithic" teflon sleeves or glindemann rings to seal ground glassware. The official teflon rings used as
seals are described here.
~http://www.glindemann.net/business.htm~ Has anyone used these? The idea is very intruiging, but the rings are very expensive.
So far I plan to wrap a few turns of teflon tape around a steel rod and rotate the rod above a hot plate for an hour or so. We'll see how it
goes.
I also have a few pounds of solid teflon cylinder.... lots of fluorine in there. Is there any practical way to extract the fluorine? Molten sodium
forming sodium fluoride? I know heating it produces a medley of compounds.
Also, the teflon rod could be ground up and the powder pressed and sintered to form various shapes, but that's ambitious!
Has anyone had success with teflon sintering of any kind?
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neutrino
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I have found that the 'fluoro ski wax' sold on eBay can be successfully melted into a clear/white solid. It's basically a very fine
white powder of what is said to be PTFE. On the other hand, 'pure' PTFE plumbing tape doesn't melt well, decomposing in the process. It
might be worth a try to melt it slowly, though.
I know that low molecular weight teflon can be melted without problem, although I have no idea where you'd find this.
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sparkgap
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As I recall Radio Shack makes a suspension (or was that emulsion, it really isn't clear to me) of Teflon in water that they sell as lubricant. I
remember using it back when I played with slot cars. You might want to Google about.
Particulate Teflon can be sintered. That's how it's used in some applications.
Oh, and molten sodium does react with Teflon. 
sparky (~_~)
[Edited on 10-7-2005 by sparkgap]
"What's UTFSE? I keep hearing about it, but I can't be arsed to search for the answer..."
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Blackout
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I've heard that teflon decompose at 245°C or 280°C, can someone confirm this?
[Edited on 10-7-2005 by Blackout]
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12AX7
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Something like that. Good reason not to leave your burner on too high when searing in teflon pans.
IIRC, it has very little (but measurable) decomposition by 500°F or so, but more fluorides are dangerously released hotter of course.
One thing about teflon that prevents it from use structurally, even for bearings: it creeps and (eventually) squidges out. Given enough time, you may
well be able to "forge weld" powder at room temperature for the same reason, but I don't know if the molecules tend to intertwine as
necessary. Heat wouldn't hurt, at any rate.
Tim
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ordenblitz
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24/40 Teflon Sleeves sell for around 10 bucks each.
http://www.bestlabdeals.com/product_p/chemmp0282.htm
http://unitedglasstech.com/glassware_accessories1.htm
http://www.prismresearchglass.com/product.aspx?productID=636...
Kind of spendy when used as received.
What I do is cut them into 4 or 5 smaller rings that actually seal better with less installation force. The narrower contact area allows for slightly
more flexibility in joints as well. The only place I would worry is in very high vacuum applications where they could stress the contact point to a
narrow area in the joint, or so I envision.
I bought a pack of sleeves a few years ago and have been happily reusing my snippets ever since with no problems.
Enjoy!
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jimwig
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Uncle Fester wrote a book called "Vest Busters" that talks using PTFE to coat bullets.
He gives some relevant data to this thread.
I just saw that DuPont has come out with a much more useable (read appliable) form of teflon. Will try to post URL.
Of course teflon is available in rods, sheets, etc and can be machined into most shapes.
BTW the density of teflon is surprising- first time i picked up a piece it felt as dense as a similar size piece of steel.
jimwig
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ProfMadScientist
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Teflon Sintering
I use Teflon and other fluorpolymer compounds all the time and our company fabricates many systems requiring a Teflon (Dupont's trade name for
PTFE), or PFA (properties similar to Teflon but easier to work with.
Teflon Flows and sinters well with ther right heat and pressure. This is frequently used to "weld" Teflon components together. Temperatures
required for clean surfaces range from 400 to 600 F depending upon pressure applied. The chemical industry frequently makes Teflon envelope gaskets
for industry by sintering 2 sheets of Teflon together with a stainless steel screen in between. This makes a better long term seal as the SS screen
reduces the flow of the Teflon under pressure.
Just remember when sintering Teflon, the three variables are temperature, force, and time. More of one means that less of the other is required. Also,
there must be absolutely NO oil or grease on the surfaces!
My favorite is PFA because it welds much easier. For PFA, you simply heat the two parts with a radiant heater until transparent and press them
together. Teflon requires much more force and time.
When coating other materials with PTFE or other fluoropolymers, you either need a special primer and/or a very rough surface (both is better).
Professional Mad Scientist
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Cyrus
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Oh, I forgot about BromicAcid's thread, good thing they were merged.
I tried heating teflon tape wrapped around a copper tube to 450F in the oven for approximately 1 hr, nothing happened. This isn't too surprising,
considering the temperatures needed according to earlier posts.
Cyrus
edit- ProfMadScientist, that's very interesting. I think I'll try cleaning the teflon tape first, and then heating it. I hope teflon tape
works because it would be much easier to form into glindemann rings than teflon powder. How chemically inert is TFA?
[Edited on 12-7-2005 by Cyrus]
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Fleaker
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I know for a fact that the teflon on aluminum pans produces some noxious fumes when it decomposes at about *575C. (I was melting some aluminum scrap,
and decided to throw a frying pan in). I removed the pan from the fire, and it had changed from that characteristic shiny black coating to a wierd
blue. I'll never over heat PTFE again  because it made an awful stink.
Telfon labware would be very nice because it's inert to most anything (physically and chemically) from cryogenic temperatures to
what, 200C? I also like that it's easier to pour dangerous chemicals drop by drop (I only have a beaker with a teflon rim and lip to facilitate
accurate pouring). One other PTFE item I purchased was a 150mL reagent bottle that I plan to store bromine in. The stopper is PTFE so it will take the
halogen well.
It really is a shame that Teflon beakers and flasks are so expensive, at least out of Fisher and Labware Direct.
Oh, hello Cyrus, don't see you on ABYMC as often :-\
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neutrino
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You really need to shop around. For example, take a look at this.
edit: I forgot to mention, those 24/40 sleeves are dirt cheap--10/$15. Too bad about the minimum order, though.
[Edited on 23-7-2005 by neutrino]
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saps
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PTFE
this is off topic but...
Is "Virgin White Teflon" pure PTFE, or is it PTFE mixed into plastic??
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Fleaker
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I don't think $35 is cheap for a 400mL beaker. It does beat the prices of the other two however, so I can't complain.
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saps
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this is off topic but...
Is "Virgin White Teflon" pure PTFE, or is it PTFE mixed into plastic??
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12AX7
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Uh, virgin, meaning unaduterated, hymen still in place. 
Like, virgin aluminum is aluminum fresh from the pot line. It's in Webster's.
Tim
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BromicAcid
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Virgin white could also be refering to a pure color, not necessarily the purity of the compound.
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Madandcrazy
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Virgin white ?
The PTFE are feasibility suitable forming
some liquids into plastic and blocking the
heat, for instance to prepare a hexol block.
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bio2
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Virgin in this context means no re-cycled content. It has nothing to do with purity, color or anything else.
The white PTFE tape is only PTFE and will melt together if for example wrapped on a glass rod and rolled on the ceramic hotplate with the temp
carefully controlled.
The colored teflon tapes are alloys and won't sinter due to scorching.
Teflon has a coating that can be applied at home oven temps. It's been out a few years now.
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Fleaker
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Bio, didn't Cyrus already try melting them together? He did it at 450F which might not have been hot enough and others mentioned that pressure
must be used to get it to weld properly.
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bio2
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Not near hot enough as the plastic must be at the glass transition temp (goes clear just before it melts) at least but perhaps pressure allows fusing
at lower temps.
My PTFE tape (she was a Virgin) started to fuse at about 245deg a little below the melting point using some hand pressure by rolling on the ceramic
surface which had an insulated mercury thermometer attached. That's Celcius bubba!
Took a couple tries to get it right and the key here is very SLOW even heating.
I've never tried it, but I sure want a gallon of the "paint" to coat some SS for condensers etc. For some reason they don't
reccomend painting copper. Check it out, it's some pricey stuff though!
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