Fantasma4500
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PTFE coating easily done
i got an idea, i looked up solvents for PTFE, which is obviously very useful for coating certain parts of whatever might get in contact with very
reactive stuff, say SO3 and NO2 and the stuff alike..
apparently its very few flourine containing oils that have some weak solvent effect at higher temperatures (300*C?)
so this isnt really useful for doing at home, or well not a possibility for me as it would be a tough quest to just acquire the solvent..
so i thought.. i can make PTFE powder by sandpaper..
combining this with epoxy as the grapite-epoxy-PbO2 anode idea (mix epoxy and graphite, coat with epoxy-PbO2)
i believe this has been found to actually work
so if i could make a really nice surface of PTFE sticking very well to the epoxy not letting any gas to have contact on the weak plastic, then this
could sound promising??
this seems too easy, like theres some thing i forgot.. please disapprove this, it cant be that easy to make normal plastic chemically resistant.. (:?
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Organikum
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You have the chemical and physical resistance of epoxy now, logically. And your PTFE powder will slowly get loose and contaminate whatever else is
around.
You can glue PTFE - sheets for example with epoxide based glues after treating the surface with a contoction of sodium or lihium dissolved in some
solvent, such primers are commercially available. Usually one side PTFE sheet gets treated and is glued to whatever and the other untreated side shows
it resistance. Only at the seams epoxy is exposed and this can be minimised by good design.
Without primer the PTFE does not really stick to the epoxy and will come off as epoxide erodes.
If you want to make something more resistant to chemical attack then you might look into sol-gel technology and glasscoatings made this way.
Everything needed is available and not too expensive and given enough time to cure it produces perfect glasslayers even without heat-curing. There are
many variations the latest I saw which I thought to be interesting was with zeolithes in the gel.
Here is the patent
/ORG
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Fantasma4500
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well yes, it will have the resistance of epoxy, basically, if the gas can get in contact with the epoxy and its not entirely blocked by the PTFE layer
PTFE of any time is pretty hard to acquire where i live, i was lucky to find some hose in china on ebay, tho. so i can easily sandpaper it down to a
fine powderish substance..
but.. i undestand it as i need to treat the surface of.. PTFE with some sort of solvent for lithium or sodium, as in metal..? i think this will be
quite hard because i cant really make it cover a decent area unless if i powder it..
so zeolites are basically some sort of metal to other element chemical compounds thats highly resistant, or did i misunderstand something? because if
i think about resistant stuff i think aluminium oxide... that could possibly be made succesfully as a proper coating, i doubt it will be that hard to
get to stick to epoxy glue.. or perhaps even glasspowder?
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zed
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There are commercial products available, for producing Teflon coatings on metal surfaces.
Paint the product on, and bake it in a stove or furnace.
The way I remember it, the stuff ain't cheap.
Still, if you want to use a teflon coating to convert a high pressure gas cylinder into a reaction vessel, it's a hell of a lot cheaper than buying a
Stainless Steel Parr pressure Reactor.
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Fantasma4500
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well yes, i assumed that as PTFE lasts very long..
the problem i have is that i need to coat a bottle cap, which happens to fit nearly too well on my 250 mL erlenmeyer flask 
i have thought about covering it completely with teflon tape, which should have a complete outer layer of PTFE/teflon
i have a hose of real PTFE, so i use that as a source of PTFE if i need some..
but stainless steel wouldnt be useful as SO3 would tear through that like nothing
could be interesting to look into what this ... ''paint'' would be consisting of, tho..
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garage chemist
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You need an aqueous dispersion of PTFE particles, which is an article of commerce.
Dip your metal part in it, let dry, and sinter the powder to solid PTFE at around 300°C. Repeat until you have built up the desired thickness.
PTFE coatings are generally produced by sintering the powder, possibly aided by pressing the powder during sintering. Forget about epoxy or other
binders, they defeat the original purpose of PTFE coating a metal part, the chemical resistance.
There is an OTC product called "PTFE Spray" of "Teflon Spray", which comes in a spray can and is used as a dry lubricant for moving parts. You know
what I mean? This is a dispersion of fine PTFE particles in a liquid carrier, and might just be what you need. If you want to experiment with
sintering PTFE coatings, start with this product.
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Pyro
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for most all things, including SO3 and NO2 normal glass will do.
for small objects I have found that a good tight wrap in teflon tape followed by heating works very well. however coating the inside of anything, no
way!
all above information is intellectual property of Pyro.  |
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Fantasma4500
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Quote: Originally posted by garage chemist  | You need an aqueous dispersion of PTFE particles, which is an article of commerce.
Dip your metal part in it, let dry, and sinter the powder to solid PTFE at around 300°C. Repeat until you have built up the desired thickness.
PTFE coatings are generally produced by sintering the powder, possibly aided by pressing the powder during sintering. Forget about epoxy or other
binders, they defeat the original purpose of PTFE coating a metal part, the chemical resistance.
There is an OTC product called "PTFE Spray" of "Teflon Spray", which comes in a spray can and is used as a dry lubricant for moving parts. You know
what I mean? This is a dispersion of fine PTFE particles in a liquid carrier, and might just be what you need. If you want to experiment with
sintering PTFE coatings, start with this product. |
well yes.. sounds like something that could be possible, the problem would still be that the plastic surface would become exposed more and more as the
hot SO3 goes to the surface, and if its a oil it should just drip down, also SO3 should be able to react with the oil and.. oil in boiling H2SO4..
i actually saw this oil thing when i was searching for PTFE tape but i didnt see it as actually possibly working, but again heating the PTFE and
pressing plastic parts isnt a really good idea as im using a plastic screw lid with a much lower melting point than 300*C which is around the melting
point of PTFE.. (:
if i were to use metal parts i would need to first get some person to make it for me, then comes the price and also the risk of breaking the neck of
my precious erlenmeyer flasks, plastic is good for this cause as it would probably break before my flask would and it can get really tight as it will
start bending before breaking the flask, again..
if i could get the oil to evaporate somehow that would be perfect, next problem would be to get the PTFE to stick to the plastic..
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Fantasma4500
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| Quote: Originally posted by Pyro | for most all things, including SO3 and NO2 normal glass will do.
for small objects I have found that a good tight wrap in teflon tape followed by heating works very well. however coating the inside of anything, no
way!
|
true.. problem is that i would need it to be able to fit 9/11 mm PTFE hose and a 250 mL erlenmeyer flask, except for that it would cost some money to
get a hold of it, if i would ever be able to find it..
but i have thought of the teflon tape... but would this mean that PTFE tape shrinks down when heated?? because that would be the ultimate for wrapping
stuff up..
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Fantasma4500
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okay- so this same thing im still wondering about, i found mentions of people having used "PTFE" paint
but.
"The chemical resistance of PTFE is outstanding, there are no solvents which could dissolve PTFE at room temperature and the surface of PTFE at room
temperature is affected only by molten alkali and fluorine in some cases"
https://fluorocarbon.co.uk/news-and-events/post/10/what-is-p...
https://www.youtube.com/watch?v=UjIc3n9zy1k
"Teflon is a synthetic fluoropolymer made up of tetrafluoroethylene monomer. The chemical name of Teflon is poly (1,1,2,2 tetrafluoroethylene). It is
a thermoplastic polymer. Teflon chemical formula is (C2F4)n."
what is actually going on here? hes spraying something on there, it appears to be in a plastic bottle- no way thats 300*C+
ive looked it up a bunch of times and they will always try to claim pans have PTFE
i do vaguely remember some other less resistant polymer they use
https://patents.google.com/patent/US5459191A/en
1. A process for dissolving tetrafluoroethylene polymers comprising, contacting a solvent which is a perfluorinated cycloalkane with a polymer
containing tetrafluoroethylene units under autogenous pressure at a high enough temperature and for a sufficient amount of time to dissolve said
polymer, provided that:
said solvent may be substituted with one or more perfluoroalkyl and perfluoroalkylene groups, but the total number of carbon atoms in said
perfluoroalkyl and perfluoroalkylene groups is less than the total number of ring carbon atoms in said solvent;
the critical temperature of said solvent is about 340° C. or more; and
the melting point of said polymer is about 250° C. or more.
"dissolving tetrafluoroethylene polymers" - this implies they use actual solvents and not sintering
however- it appears that it <might> be possible to just coat steel with NaSiO4, letting this solution evaporate makes it stick very well to
steel, but upwards 180*C this decomposes and bubbles up- maybe i wasnt gentle enough with the heating
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Herr Haber
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Would Viton powder do ? It is supposed to be soluble in acetone.
I think I got another soluble fluoropolymer from Leonid in Ukraine but never tried it.
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
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macckone
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Viton will dissolve in hot MEK given enough time. But coating with the mix is not likely to be useful.
Commercial PTFE dispersions use finely divided (10um) PTFE dispersed in an amine based dispersant and water.
The sintering step is done in an inert atmosphere (usually argon but nitrogen or CO2 should work).
It usually takes several coats to get an impermeable barrier.
Alternatively you could use teflon tape and do the same sintering process.
Third alternative is powder coating where the item to be coated is heated to 327C and the powder is sprayed on.
That method works will for items that can be induction heated to a precise temperature.
The final method is powder molding where the powder is placed in a mold around the object and then sintered.
Sintering temperature is a limiting factor and it off-gasses fluorine compounds during sintering.
It is very sticky above 300C as it reaches the melting point.
nichrome 80 is required for resistance wire exposed to the gases.
kanthal isn't resistant to fluorine.
You want to stop sintering as soon as the temperature reaches the melting point to prevent degradation.
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Mateo_swe
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I think you would need to do the same as they do when manufacturing fryingpans and similar with a teflon non-stick layer.
Its some kind of teflon paint that needs to be put in an oven at high temp to cure it.
You can probably order the teflon paint but i guess they want more than you are willing to pay for it.
These days they dont want to sell to individuals, just to comany´s.
Maybe you can get some for free if you have a potential product you are developing.
Some social engineering goes a long way if you are good with words.
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Fyndium
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I've dreamed of enameled reactor vessels. They are apparently used in chemical industry and are basically glass coated steel with properties of both.
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Fantasma4500
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uhuh- so fluoropolymer paint is practically not a thing anymore. i suppose if you have a chunk of teflon you could maybe just heat up a pot and grind
it onto there?
now i just got to think of oil industry where they have gigantic tanks composed of carbon steel and stainless steel, these 2 alloys are combined by
explosive force, something like 30mm thick layer of high end explosives to join about same thickness of metal plates
maybe its possible to join teflon tape to a steel container, if you fill it up with water and put in a small charge? i think having the PTFE sticking
to the container is gonna be half the struggle. barely feasible.
coming to think of it, you can already get pots that are entirely covered in fluoro-polymers, typically aluminium pots.
hmm- let me explain my current findings. i have not yet gotten to test chemical resistance
A1: i coated NaSiO4 solution onto 2mm carbon steel coldpressed steel plate and put in oven at 60*C, completely clear coating
A2 180*C- a bit optimistic, it boiled up
A3 100*C - some boiling up
A4 first 60 then 80*C- no problem
A5 directly into 80*C (measured it to be 85*C hot actually)
A6 80 then 100*C, no problem with hitting 100 if its going in at 80 first
i thereafter put the A6 into 180*C and it boiled up badly, ruining the coating. so obviously what i have here isnt actual glass since it boils up at
180*C, i have my hopes up for chemical resistance though.
https://gyazo.com/1f103f87a2d31bdc23ad5712a513f1f4
close up of the 2 where coating got damaged
https://gyazo.com/cd5b452882ba6ff482165d3294c8cbfc
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Mateo_swe
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Waterglass NaSiO4 is commonly used in DIY ovens and furnaces where its often sprayed onto ceramic heat insulating blankets.
It is very tolerant to heat but i dont know how its chemical resistance is, have you looked into it?
I know one can make small round microwave oven containers with ceramic blankets sprayed with waterglass.
Then a coating of coarse silicon carbide is applied on the inside with a light spraying with waterglass to make it stick.
The silicon carbide layers are done several times for a thicker layer but not too thick as it then will crack from heat expansion.
When heated in the micro the silicon carbide will glow with heat and the surrounding waterglass ceramic blanket will insulate and keep the heat
inside.
It gets very, very hot inside.
Intresting, there are videos on it on youtube, but not really relevant here.
But silicon carbide, thats pretty resistant to chemicals i think, and heat.
Maybe it can be used to make a coating somehow.
Heat plus corrosive chemicals are not the easiest challenge, thats for sure.
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Mateo_swe
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You can melt PTFE powder and coat the inside of a vessel but it requires rather high temps (PTFE mp 327°C).
And make it stick to the surface might be a problem.
PTFE powder is avaliable here, its about 30Euros for a kilo.
I have no idea if thats cheap or expensive.
PTFE, trade name TEFLON, powder 20-70 μm
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Fyndium
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They sell ceramic fiber blanket readily that withstands temps up to 1300-1500C. I have a high temp kiln based on raku design that works great. It is
stupid to make firebrick kilns, when you got tens, possibly hundreds of kilos of thermal mass to heat up, when you can do that with less than 1kg of
fabric woven in shape. Heats up instantly and insulates as well or even better.
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Fantasma4500
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as for chemical compatability- i might get to test this today, i know this is typically used for steel elements that goes into concrete to keep them
from corroding and it does a very good job at this
NaSiO4 with HCl forms SiO2 ppt and- supposedly NaCl
one fellow chemist used this to make some very fine SiO2- this could likely be a great pathway for catalysts
ive played around with making NaSiO4/sand mixtures, its quite fragile but resists heat very well, as my pictures explain it tends to bubble up with
excess heating, this is likely the part where it cements and binds the sand..? typically these mixtures are advised to be blasted at high temperature
to get it to properly heal, the surface feels kinda like plastic. and with acids it would form SiO2.. so if you coat it plenty with saturated
solutions it should maybe just... passivate with SiO2? silicone polymers is an option too, but i know that NOx/HNO3 eats through silicone tubing
eventually
i think to have PTFE adhere you must clean the whole thing up very throughly, im mostly worried about the toxicity of the fluorine compounds coming
off from that, heat it up to 300+*C and just pumping in some PTFE should work- or just get solid PTFE and hold onto the surfaces while its quite well
warmed up- kinda like rubbing a stick of butter onto warm bread
@Mateo_swe
Seram Coatings – THERMAL SPRAYING OF SILICON ...https://www.seramcoatings.com
22 Mar 2022 — Seram Coatings´ product ThermaSiC enables SiC (Silicon Carbide) to be applied as a coating by thermal spraying for the first time.
thermal spraying- my guesstimate alerts me that this is some very high end equipment- probably around same spectrum as titanium nitride coating of
drillbits using plasma titanium nitride... im not sure if this is feasible for me- google validates my paranoia, 2730*C melting point for silicon
carbide- hm! maybe PbO2 coated lead containers would work? rather easy. or just platinizing the whole bunch, platinum is very annoying to dissolve in
acids.
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Mateo_swe
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I once saw PTFE 3D printing filament but i cant find it now.
Not really relevant for coating stuff but it would be very nice to be able to make my own PTFE things to use in chemistry.
The hotend probably needs to be upgraded to a higher temp variant but otherwise it might work to 3D print with PTFE.
That Silicon Carbide spray seem very interesting, i wonder if its available for sale somewhere online and what the cost is.
It says its to be applied using thermal spraying, i wonder what temperatures to use.
It might be hard to do this in the garage for an ordinary individual that doesnt have a high-temp oven big enough to allow spraying of an object.
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Herr Haber
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Mateo, that's not what those filaments are for. You dont 3D print PTFE parts. (But just saying this makes me dream).
But Antiswat, PTFE paints *are* a thing. I just dont know if the product would be of use to you. There are brands selling anti graffiti hydrophobic
paint that contains silica and some kind of fluoropolymer. The silica takes a shape that makes it even harder for liquids to stick to PTFE. I dont
know how this would react to high temperatures though.
As for the simpler process I suggested earlier I suppose it's easier said than done. I remember returning a pair of PTFE coated pincers to a supplier.
The thin coating was pealing off after being dipped in 80% H2SO4 for seconds.
Some PTFE ware are not meant to withstand chemicals, just not to contaminate what they are put in contact with I guess.
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
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macckone
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Ptfe emulsion coating.
Will need to be sintered.
US $10.00 | 50-200gram PTFE Emulsion Coating Polytetrafluoroethylene Concentration Dispersion DF-301 Waterborne
https://a.aliexpress.com/_mtioIzA
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Texium
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