Argon in tyres?
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Hi I'm new here... but I have some curiosity in this scientific assertion.
Can you refer me to any publications or online literature for the diffusion characteristics of CO2?
Because right now I tend to believe that the molecular size determines the diffusive characteristics of a gas rather than its solubility in solids - this abstract's last sentence seems to imply that concentration has a relatively small influence on diffusion - the classic pressure gradient, temperature, etc. factors appear to be more important for carbon dioxide diffusion rather than chemical solubility (influenced by concentration). Although CO2 is well known to dissolve in water, however. I'm not sure how it would do in polymers.
I've always thought CO2 was used for those quick-fill canisters b/c it had good diffusion characteristics.
Here we also see that the diffusion coefficient for CO2 is lower than O2, which itself is lower than H2O - almost completely hierarchical on size.
Can you refer me to any publications or online literature for the diffusion characteristics of CO2?
Because right now I tend to believe that the molecular size determines the diffusive characteristics of a gas rather than its solubility in solids - this abstract's last sentence seems to imply that concentration has a relatively small influence on diffusion - the classic pressure gradient, temperature, etc. factors appear to be more important for carbon dioxide diffusion rather than chemical solubility (influenced by concentration). Although CO2 is well known to dissolve in water, however. I'm not sure how it would do in polymers.
I've always thought CO2 was used for those quick-fill canisters b/c it had good diffusion characteristics.
Here we also see that the diffusion coefficient for CO2 is lower than O2, which itself is lower than H2O - almost completely hierarchical on size.
After numerous, and I mean numerous, discussions on this topic many of us have come to the conclusion that the CO2 isn't just diffusing through the rubber but it is dissolving in the rubber and passing out. The N2 and O2 in air follow a diffusion pathway and thus take longer to get through the rubber.
I know of no one who has done a controlled experiment, however it wouldn't be hard to do as a homebrew measurement.
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I'm also dubious that they would use compressed or liquid O2 on aircraft. They probably use O2 concentrators like old people use. Much less likely to go Boomba! Boomba! if you happen to put a hole in the aircraft
As for the "Nitrogen is a by-product of Oxygen" comment. I understand what he meant but other people might not. Lots of people have goofy ideas about chemistry and where stuff comes from. I just wanted to clarify it. I'm going to go clarify the He from natural gas thing next
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the atomic radius of argon (48 pm) is much smaller than the molecular radius of N2 and O2 (bond length 120 pm, atomic radius 74 pm), so it will leak out of a tyre much faster. the molecular or atomic mass has very little to do with its diffusion rate, it is almost all dependent on size. the mass will make it a little heavier in a tyre at the same pressure (argon and air have different densities at same pressure).
it is the diffusibility of a gas through rubber or latex that determines the rate of loss, not the solubility (since the diffusion loss is orders of magnitude higher than the evaporative loss of dissolved gas from the surface of the polymer). diffusion rate is proportional to size, so smaller molecules (or atoms) diffuse much faster. there is very little *********** due to electronic interactions with the tyre material, since both matrix and diffusing molecule are non-ionic, non-polar materials. the size/diffusion relationship is not linear, so smaller molecules diffuse much faster than larger molecules.
edit: i learn later that this helium part is wrong: we extract helium from natural gas, not by compression from the air. my bad.
Helium is not in danger of being depleted by our using it in balloons, etc. we extract it from the air, and it is all vented back to the atmosphere, so its a closed cycle. there is a small continuous loss of He from the earth by it being blown away from the upper atmosphere by solar wind, and simply by diffusion (it's not held very tightly by gravity), but this is nothing to do with our industrial processes using He.
Helium is not in danger of being depleted by our using it in balloons, etc. we extract it from the air, and it is all vented back to the atmosphere, so its a closed cycle. there is a small continuous loss of He from the earth by it being blown away from the upper atmosphere by solar wind, and simply by diffusion (it's not held very tightly by gravity), but this is nothing to do with our industrial processes using He.
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Again to be precise, helium is 'isolated' from natural gas. Natural gas is a mixture of hydrocarbon gases that can not 'produce' an element like helium. Helium is 'produced' from radioactive decay of higher elements...or by squishing two hydrogen atoms together.
[Edit] I'm sorry to harp on this but the term 'production' implies reaction to make something. Burning natural gas 'produces' CO2 and water. The oxygen, carbon and hydrogen are still there but their form has changed. To say that you have 'produced' nitrogen from oxygen or helium from natural gas, implies that, somehow, you have done a reaction and made these elements from other stuff. Elements aren't made from anything short of nuclear reactions.
[Edit] I'm sorry to harp on this but the term 'production' implies reaction to make something. Burning natural gas 'produces' CO2 and water. The oxygen, carbon and hydrogen are still there but their form has changed. To say that you have 'produced' nitrogen from oxygen or helium from natural gas, implies that, somehow, you have done a reaction and made these elements from other stuff. Elements aren't made from anything short of nuclear reactions.
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Last edited by cyccommute; 08-23-07 at 09:03 AM.
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I looked at the tables, and to be honest, I don't understand exactly what the manufacturer meant by the "Compatibility Charts". Does "2-MODERATE TO SEVERE" mean that Argon will damage the tube or that it will easily leak (permeate through the wall, actually) out? The former seems implausible, as Argon is inert as a dead stubborn donkey.
By severe effect they probably mean that it will swell the elastomer and may make it weaker. It's not a chemical reaction but a physical change. In an o-ring, swelling is not good...especially if you are trying to seal a moving part. Swollen o-rings on valves, for example, won't let them reseat and seal. That makes them leaky...not usually a good thing
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At one time, the sole commercial source of Helium was a field in the Panhandle of Texas. For some reason that gas is extremely high in He. During the 30s the US imposed an embargo on Germany and it could no longer get He for its zeppelins. So they filled Hindenburg with hydrogen instead -> boom!
Extraction from other sources is a relatively recent occurrence. I remember talk when I was in school about what would happen when the He ran out. In retrospect it was a rehearsal for the same talk about oil. 'Course, without natural gas we can still produce power and probably plastics, but we'll have a heck of a time getting Helium!
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There's more to the story. Natural gas is a fossil fuel, meaning it used to be carbon-based lifeforms. Most Helium left the atmosphere (it's so light that it just drifts away) long before the proto-gas compost got smooshed and buried. But, He is also formed by the radioactive decay of elements such as uranium and we think this is how it gets into the gas.
At one time, the sole commercial source of Helium was a field in the Panhandle of Texas. For some reason that gas is extremely high in He. During the 30s the US imposed an embargo on Germany and it could no longer get He for its zeppelins. So they filled Hindenburg with hydrogen instead -> boom!
At one time, the sole commercial source of Helium was a field in the Panhandle of Texas. For some reason that gas is extremely high in He. During the 30s the US imposed an embargo on Germany and it could no longer get He for its zeppelins. So they filled Hindenburg with hydrogen instead -> boom!
#83
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But you would be wrong to think that the problem with the Hindenburg was the hydrogen: what actually burnt was the light-reflecting paint on the outer cotton coat. This paint contained, among other things, iron-oxide, aluminum powder and some flammable plasticy stuff. Anyhow, unbeknown to the chemists of the time, iron-oxyde + aluminum can work as an explosive and is extremely flammable. It's unknown what was the reason for the initial ignition of the ship, but at any rate, the paint in the coating caused the ship's doom. The hydrogen had nothing to do with it - in fact, the Germans had lots of experience with hydrogen-filled blimps, used for years without a single accident.
https://en.wikipedia.org/wiki/Hindenburg_disaster
(My personal opinion is that a helium Hindenburg would have docked safely that day, without any problems at all.)
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Why not coat the inside of the tube with that stop leak stuff they use in helium balloons to keep them inflated longer?
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Some thougts, from a former paintballer:
Some paintball fellows thought of using compressed helium instead of CO2 or Compressed air, or EVEN compressed nitrogen...
What they found, however, is that the helium escaped between the O-rings designed to keep other compressed gasses in. Gasses compressed at high pressures, as much as 800PSI.
Likely, a tire would not be terribly likely to hold 100 psi for a long time, and even if it did how much would you trust the valve?
Some paintball fellows thought of using compressed helium instead of CO2 or Compressed air, or EVEN compressed nitrogen...
What they found, however, is that the helium escaped between the O-rings designed to keep other compressed gasses in. Gasses compressed at high pressures, as much as 800PSI.
Likely, a tire would not be terribly likely to hold 100 psi for a long time, and even if it did how much would you trust the valve?
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The anecdote by cyccommute is correct. It turns out that my previous assertions were wrong.
I have done some further research on the subject. It appears that atomic diffusion is in fact a function of the solubility. Here's what I found from tables in a book (I'll reference on demand):
-carbon dioxide diffuses the fastest.
-oxygen diffuses slower than carbon dioxide.
-nitrogen diffuses slower than oxygen.
-argon diffuses slower than nitrogen.
-(inferential) neon diffuses slower than argon.
-(inferential) helium (possibly) diffuses slower than neon.
These values apply only for natural/isoprene rubbers.
I have done some further research on the subject. It appears that atomic diffusion is in fact a function of the solubility. Here's what I found from tables in a book (I'll reference on demand):
-carbon dioxide diffuses the fastest.
-oxygen diffuses slower than carbon dioxide.
-nitrogen diffuses slower than oxygen.
-argon diffuses slower than nitrogen.
-(inferential) neon diffuses slower than argon.
-(inferential) helium (possibly) diffuses slower than neon.
These values apply only for natural/isoprene rubbers.
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Race cars use pure nitrogen in those tires because ambient air can have too much moisture. When that moisture boils, you can have all kinds of problems. We cyclists never deal with anything close to those kinds of speeds and cornering forces. The same can be said of our street cars.
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finally an answer to the question. smaller => leaks out faster. More expensive initially,and leaks out faster. Heavier => slower.
By the way. I think moisture from the air would slowly collect in the tube, after repeated refilling. I wonder how much would collect in a month if you pump up your tires every day?
By the way. I think moisture from the air would slowly collect in the tube, after repeated refilling. I wonder how much would collect in a month if you pump up your tires every day?
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The Olympic people experimented with various exotic gases for many years. They found out through scientific experiment there's little difference as far as efficiency in a bicycle tire. Hydrogen, they recommend to stay away from due to its flammable content. Does anybody remember their history from the zeppelin the Hindenburg? I would agree with most of the posts - air, it's free and readily available.
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I should note that not all heavy molecules work. It has to be a large molecule with low solubility in latex.
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finally an answer to the question. smaller => leaks out faster. More expensive initially,and leaks out faster. Heavier => slower.
By the way. I think moisture from the air would slowly collect in the tube, after repeated refilling. I wonder how much would collect in a month if you pump up your tires every day?
By the way. I think moisture from the air would slowly collect in the tube, after repeated refilling. I wonder how much would collect in a month if you pump up your tires every day?
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Race cars use pure nitrogen in those tires because ambient air can have too much moisture. When that moisture boils, you can have all kinds of problems. We cyclists never deal with anything close to those kinds of speeds and cornering forces. The same can be said of our street cars.
The moisture in air can condense during compression, especiallly after the air (which is heated by the compressor) is cooled down. So compressor tanks have a water valve in the bottom. Big industrial compressors have heat exchangers to cool the compressed air which condenses the water more completely. The water valve in the sump is sometimes put on an automatic timer, or there is a level sensor in a small sump which tells a valve to open to discharge the condensate. The point is, once air is compressed properly (with heat exchangers and a tank to remove water), there is LESS humidity in that air. And when the air pressure is relieved from the tank (at say 110 psi) to a wheel (from about 26 to 42 psi, depending up car weight, tires, and conditions) the moisture is already "boiled". That is, its a gas and there's no liquid water to boil. And there's very little of it. So the "dew point" (temperature at which water condenses) is very low.
For bikes that use tubes and are pumped up using a hand pump without any heat exchanger or tank with sump, you can be creating liquid moisture within the tube. A small amount. So if you are running tubes and don't use a compressor with a tank and drain valve, N2 might make a slight difference. For a bike using sealant, the added moisture is ridiculously small compared with the amount of sealant, and probably adds to sealant life by replacing sealant water that has evaporated. Also for bikes, the permeability of O2 vs N2 doesn't make much difference unless you are speaking of weeks of riding. During which you will probably be topping off the pressure anyway. So IMHO, unless you use tubes and don't use an air compressor to inflate, substituting dry N2 is a needless expense. I'm also of the opinion that it's a pretty ridiculous and fairly needless expense and conceit to use dry N2 even if you do have tubes and normally use a hand pump - the effect is just too small. And there's like a gazillion bikes out there that use hand-pumped air without issues.
N2 (mw 28) is a smaller molecule than O2 (mw 32) but IIRC the permeability of O2 through rubber is actually higher. So with air, you'd theoretically lose pressure faster as the O2 leaks out. A ridiculously small difference for passenger tires but it might make a difference for race cars. For passenger cars, its also ridiculous because most cars tires are inflated with compressed dry(er) air. So moisture is an issue. There's also a separation going on. Suppose O2 does leak out faster than N2. As an extreme example, assume that O2 leaks out, and N2 doesn't leak at all. Now suppose you put 100 psi in your road tires. 80% is N2, 20% is O2. Assume you lose 5 psi. Now you are at 80%/0.95 N2 and 15%/0.95 O2. 84.21% N2 and 15.79% O2. You top off with air. Do the math: you now have 84% N2 and 16% O2. Assume you've lost another 5 psi. Because you have less O2, this takes a lot longer. But it happens, and you top off. So now you're at 88% N2 and 12% O2. After a while, you get to about 99.2% N2! Every time the tire leaks down its leaking mostly O2 and the gas inside the tire keeps getting enriched in N2.
The point is, by topping off your car tires with compressed air, there is minimal moisture remaining. And because the O2 leaks out preferentially (which is the whole point of using N2), you automatically get a gas mixture that is enriched in N2 in your tire. For free!
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I agree with cyccocommute on the Argon issue and the technical issues of diffusivity of a gas through rubber. It's not just a matter of molecular size. Compatibility (essentially solubility) must be considered. It's complex.
BTW, notwithstanding my blather above, If I were going to insist upon something other than air, I'd use (cheaper) dry N2 before I went with Argon. And if you're a gram counter, N2 is about 5 grams per wheel lighter than argon!
BTW, notwithstanding my blather above, If I were going to insist upon something other than air, I'd use (cheaper) dry N2 before I went with Argon. And if you're a gram counter, N2 is about 5 grams per wheel lighter than argon!
Last edited by WizardOfBoz; 12-01-19 at 11:46 AM.
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I have my doubts that the military does their own oxygen concentration. Like most other stuff the military does, it probably buys it from some one like Airliquide. Those guys process millions of tons of the stuff per year.
I'm also dubious that they would use compressed or liquid O2 on aircraft. They probably use O2 concentrators like old people use. Much less likely to go Boomba! Boomba! if you happen to put a hole in the aircraft
I'm also dubious that they would use compressed or liquid O2 on aircraft. They probably use O2 concentrators like old people use. Much less likely to go Boomba! Boomba! if you happen to put a hole in the aircraft
FWIW: the Blackbirds stored oxygen in liquid form. From my favorite book on the subject:
https://books.google.com/books?id=De...olume&q=oxygen
If you like airplane engineering, this is a fascinating look at the development of a unique airplane:
https://www.amazon.com/Archangel-Sen.../dp/1563479338
You'd probably enjoy the information regarding the lubricants developed just for the Blackbirds.
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Not exactly. There's a difference between "extracted from" and "produced from". He is an element and it takes pretty extreme conditions (like the core of the sun) to "produce" He from hydrogen. There is a small amount (on the order of 1%) of He in natural gas due to decay of elements like thorium and uranium.
The He is extracted from natural gas (mostly ethane and methane) by liquifying the hydrocarbons producing LNG, and then removing nitrogen from the remaining off gases.
It is key to understand that He can only be extracted, and not produced. There's a finite amount in natural gas reserves.
https://gasliquids.com/pdfs/2016_HeliumInNaturalGas.pdf
The He is extracted from natural gas (mostly ethane and methane) by liquifying the hydrocarbons producing LNG, and then removing nitrogen from the remaining off gases.
It is key to understand that He can only be extracted, and not produced. There's a finite amount in natural gas reserves.
https://gasliquids.com/pdfs/2016_HeliumInNaturalGas.pdf
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Race cars use pure nitrogen in those tires because ambient air can have too much moisture. When that moisture boils, you can have all kinds of problems. We cyclists never deal with anything close to those kinds of speeds and cornering forces. The same can be said of our street cars.