Sciencemadness Discussion Board

PTFE (Teflon) Sintering, coating, forming, and its decomposition.

BromicAcid - 30-5-2004 at 19:00

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:
Quote:

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.

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:
Quote:

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.

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]

Proteios - 30-5-2004 at 22:56

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]

Cyrus - 31-5-2004 at 13:10

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...

Theoretic - 2-6-2004 at 10:24

PTFE decomposes to give a reportedly extremely toxic fluorocarbon among everything else (don't remember its name), has been tried as a war gas...

BromicAcid - 2-6-2004 at 13:36

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?

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]

Teflon (ab)use for mad science

Cyrus - 9-7-2005 at 23:09

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?

neutrino - 10-7-2005 at 06:14

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.

sparkgap - 10-7-2005 at 07:44

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. :D

sparky (~_~)

[Edited on 10-7-2005 by sparkgap]

Blackout - 10-7-2005 at 08:45

I've heard that teflon decompose at 245°C or 280°C, can someone confirm this?

[Edited on 10-7-2005 by Blackout]

12AX7 - 10-7-2005 at 10:04

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

ordenblitz - 10-7-2005 at 11:14

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!

jimwig - 10-7-2005 at 15:34

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

Teflon Sintering

ProfMadScientist - 11-7-2005 at 07:16

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).

Cyrus - 11-7-2005 at 16:54

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]

Fleaker - 22-7-2005 at 11:31

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 :-\

neutrino - 22-7-2005 at 17:40

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]

PTFE

saps - 22-7-2005 at 18:28

this is off topic but...

Is "Virgin White Teflon" pure PTFE, or is it PTFE mixed into plastic??

Fleaker - 22-7-2005 at 18:42

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.:)

saps - 22-7-2005 at 18:58

this is off topic but...

Is "Virgin White Teflon" pure PTFE, or is it PTFE mixed into plastic??

12AX7 - 22-7-2005 at 19:36

Uh, virgin, meaning unaduterated, hymen still in place. :P

Like, virgin aluminum is aluminum fresh from the pot line. It's in Webster's.

Tim

BromicAcid - 22-7-2005 at 19:38

Virgin white could also be refering to a pure color, not necessarily the purity of the compound.

Madandcrazy - 24-7-2005 at 07:45

Virgin white ?

The PTFE are feasibility suitable forming
some liquids into plastic and blocking the
heat, for instance to prepare a hexol block.

bio2 - 31-7-2005 at 03:44

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.

Fleaker - 2-8-2005 at 13:23

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.

bio2 - 13-8-2005 at 23:58

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!

Fleaker - 14-8-2005 at 08:56

Do you have any links for the teflon paint, I'm wondering how useful it would be for coating a fumehood?

Teflon®-S One Coat

bio2 - 14-8-2005 at 23:44

The Teflon S #5 is the one you want

http://www.dupont.com/teflon/coatings/basic_types.html

The 6 Basic Types of DuPont Teflon Coatings
DuPont Teflon® industrial coatings can be used on carbon steel, aluminum, stainless steel, steel alloys, brass, and magnesium, as well as non-metallics such as glass, fiberglass, some rubber, and plastics. Optimum adhesion is obtained by roughening the surface before applying the coating. Except where specifically mentioned, most Teflon® industrial coatings require a primer coat.

1. Teflon® PTFE
PTFE (polytetrafluoroethylene) nonstick coatings are two-coat (primer/topcoat) systems. These products have the highest operating temperature of any fluoropolymer (260°C/500°F), an extremely low coefficient of friction, good abrasion resistance, and good chemical resistance. PTFE is available only in water-based liquid form.

2. Teflon® FEP
FEP (fluorinated ethylene propylene copolymer) nonstick coatings melt and flow during baking to provide nonporous films. These coatings provide excellent chemical resistance. In addition to low friction, FEP coatings have excellent nonstick properties. Maximum use temperature is 204°C/400°F. FEP is available in water-based liquid and powder forms.

3. Teflon® PFA
Like FEP, PFA (perfluoroalkoxy) nonstick coatings melt and flow during baking to provide nonporous films. PFA offers the additional benefits of higher continuous use temperature (260°C/500°F), film thicknesses up to 1,000 micrometers (40 mils), and greater toughness than PTFE or FEP. This combination of properties makes PFA an excellent choice for a wide variety of uses, especially those involving chemical resistance. PFA is available in both water-based liquid and powder forms.

4. Teflon® ETFE
ETFE is a copolymer of ethylene and tetrafluoroethylene and is also sold under the Tefzel® trademark. Although not fully fluorinated, ETFE has excellent chemical resistance and can operate continuously at 149°C/300°F. This resin is the toughest of the fluoropolymers and can be applied at film builds up to 1,000 micrometers (40 mils) to provide a highly durable finish. ETFE is available in powder form.

5. Teflon®-S One Coat
These solvent-based liquid coatings are formulated with special blends of fluoropolymers and other high-performance resins to improve toughness and abrasion resistance. Because the film components stratify during baking, most of the fluoropolymer properties (such as low friction and nonstick character) are retained. The resins provide adhesion and abrasion resistance. These products can sometimes be applied to smooth, clean metal. Bake requirements vary, depending on the specific coating, from 163°C/325°F to 316°C/600°F.

6. Teflon®-S Dry Lubricant
Dry lubricant coatings are special versions of Teflon®-S technology designed to provide lubrication under high-pressure/velocity (PV) conditions. These products are solvent-based, one-coat systems that are usually cured between 260°C/500°F and 371°C/700°F.

Teflon Navigation

Fleaker - 20-8-2005 at 14:52

Thanks for posting that info. I think I'll go with PFA. But how to apply that to the laminate I'm using for the fume hood?

Hm, might have to rethink the construction materials. Perhaps I could use aluminum plate and roughen it up with emery and then bake on the PFA.

DrP - 26-5-2006 at 07:08

Sorry to drag this up again but I have some work to do with PTFE which will be destryed by fire. What are the current views of people as to the safety of the PTFE decomposition products. I have heard and read mixed opinions. I want to be aure as I really don't like the sound of polymer flu - even though it is only a tempory and non fatal illness.

Quote:
"DrP
Hazard to Others

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posted on 6-1-2006 at 10:33

I needed a high temp resistant polymer for a test I was doing - I thought about using PTFE - this would be great, however I believe that HF is generated when the stuff burns and that it has a habbit of dissolving furnace linings apparently (being SiO2) .

This can't be very concentrated as I've heard the effects of being near to burning PTFE lead to something they call polymer flu (rather than death) - like the flu but much much worse. I got some samples of a PTFE emulsion but decided not to go ahead with the experiments just in case.

Also - parrots and budgies kept in kitchins have died due to PTFE linings degrading from saucepans and frying pans giving small amounts of HF.


12AX7
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posted on 6-1-2006 at 11:32

Although I'm sure HF is present in small amounts, Teflon decomposition is mostly a hodge-podge of perfluoroalkanes and -enes, with varying amounts of oxygen and hydrogen depending on conditions I'm sure. Nothing healthy at any rate.

Tim "



Here are some links to sites which list decomposition products and mention posible hazards:

http://www.bt-co.com/safety.htm
http://www.fluoridealert.org/pesticides/teflon.decomposition...


So what do you think??? Does anyone know for sure what the hazards are or are we still just guessing? Thanks.


PS - (Tim - sorry, I don't disbelieve you, it's just that I want to be REALLY sure I'm not going to get a lungfull of HF as the ventilation arround the furnace is very poor and I will DEFINATELY get to sample some of the fumes given off I'm sure - usually alot of smoke - we have had a fume hood installed over the furnace, but it is a bit crap and some smoke still gets into the room)

Fleaker - 26-5-2006 at 13:01

Just don't do it. I've accidentally melted down teflon coated aluminum products before and they reeked. I got slightly ill and a sore throat and I did it outside. I suggest you burn off the coating in a large campfire before talking it to your furnace.

neutrino - 26-5-2006 at 14:54

This is an old post from RS. I think it is relevant here.
Quote:
Posted by Purple Fire at RS

A friend of my fathers had a pretty close call with some fluorine gas. He owns a company that does something with ceramics (cant remember what). A company that did teflon coatings (I think) went bust, and he bought a small furnace from them that they use for melting the teflon with. They set up this furnace and fired it up, then realised that the temperatures they were using it at were significantly higher than those it had been used for with the teflon. The layer of teflon that had biult up around the sides and floor of the furnace broke down and started giving off fluorine gas. The workshop started filling with the gas and the guy noticed that the windows of his office had started to be attacked and were going cloudy. He got everyone out and no one was hurt, but still...


My guess is that fluorine wasn't actually reacting with the glass, but that some highly-reactive fluorine compound (possibly HF) was. If you do this, definitely do it outside.