Awright! That did it! DIE global climate!!

http://home.mindspring.com/~dforcier/cow-fire.jpg

Best two posts in the thread, so far. Thanks guys!

A butyl rubber (or latex for that matter) tube is not an impermeable membrane, i.e. it has lots of little holes that allow gas to pass out of it. For CO2, the gas dissolves in the rubber and, like a wet cardboard...sorry...corrugated fiber board box, the CO2 seeps out. Basically, it just passes through.

However the tube isn't going to hold any gas forever. For the other gasses, the holes and channels that make up the box just take a little longer to get through. Kinda like when you put oil in that box. The oil will eventually seep out but it will take longer because it doesn't dissolve in the box. The loss of pressure in the tube is driven by the Principle of Le Chatelier. In a nutshell, Le Chatelier's principle says that any system not at equilibrium will try to get to equilibrium. As my old chemistry teacher put it, "Every thing goes the way the wind blows." The tube has channels and holes that allow gases to pass in both directions. Gas can go in and go out, albeit slowly. Since the pressure in the tube is higher than the pressure outside the tube, the gas tends to go out rather than in, i.e. that's the way the wind is blowing;)

Put any gas in the tube under pressure and it's going to find a way out. Helium and CO2 will find a way out rather quickly (on the order of hours), air (78% N2 and 19% O2) will find a way out in a matter of days. N2 by itself is going to have pretty much the same rate. O2...well, I don't know but putting pure O2, a oxidizable organic polymer, and heat together is likely not a combination I'm going to test any time soon:eek: I think I'll stay away from methane for the same reason. Boomba! Boomba!

Other exotic gases might take less time or more time than air. It's kind of hard to predict. But the problem with any gas is that you'll have to fill the tire from time to time. Exotics are exotic because they are rare and difficult to isolate. Therefore they cost more. And the benefit is probably pretty low. Air and a pump are still pretty economical.

Now if you want to do something, design a better tube. Mylar is far less permeable than rubber. It'd hold gas for a very long time but it has no puncture resistance and no...zero...nada...zilch elasticity. Urethane was tried for a while and it works...sorta. It's not as elastic as rubber, it holds pressure slightly better, it has better puncture resistance than mylar but less - way less - than rubber, and it is a royal pain to patch...and costs around 5 times as much as rubber. Not a whole lot of plusses;)

Ok, how about sulphur hexafluoride then? :D
Not for the WW crowd, though!

It'll make you voice real low;) But a cylinder of it cost around $800. Tad expensive (about $8/lb). Don't know what it'd do with rubber. And it is heavier than air...for those weight wienies;)

Military Aircraft use dry Nitrogen in their tires.

Nitrogen is a by-product of Oxygen. Oxygen is compressed and extracted at Air Bases for air-crews to breathe at high altitude.

Benefits of Dry Nitrogen include: No corrosion to wheels (oxidation is caused by oxygen), zero moisture means no condesation, and Nitrogen will not add oxygen to a fire, should the tire burn through.

Yes, argon would work. Argon molecular weight is ~40 and air has a MW of ~30. Argon is not diatomic like all other noble gases. The Argon would have no water vapor, much like dry nitrogen.

Based on the molecular weight difference, a bicycle tire filled with Argon would stay inflated ~25% longer than one using air. Mixing air with Argon would pose no problems should that be necessary. A schrader adapter would be needed since no industrial pressure regulators work with presta valves. Otherwise, Argon should work well. Good luck with that.

Edit: This post is retracted! Do not use Argon with Buna-N bicycle tire inner tubes!

Sorry but nitrogen and oxygen are both elemental gases. That means that one can't be made from the other. Nitrogen and oxygen are distilled from air through some rather complex expansion/compression operations. As others have noted both here and in other posts on this topic, nitrogen doesn't add any benefit in bicycling. Just expense.

Noble gases aren't diatomic. Noble gases are labeled as such because the don't usually get involved in all that silly electron sharing goofiness that other elements like doing 'cause they got all the electrons they need. They stand apart and look down their noses at the other elements.

The noble gases are helium, neon, argon, krypton (no, not dangerous to Superman:rolleyes:), xenon and radon. Xenon and radon are kind of dirty nobles however. Xenon like a nice tumble with the scullery maid every once in a while;) Xenon especially likes hanging around with those trollops, oxygen and fluorine. Radon is dirty and nasty enough that it will just fall apart all on it's own, shooting off a gamma ray here and there. It has been know to take a tumble with that **** fluorine too.

I wouldn't predict anything about pressure holding in a bicycle tire based on molecular weight. The mechanism of how the gas gets out of the tube is just too complex for that simple an explanation. Argon might hold longer but it might not. CO2 (44 Da) has a much higher molecular weight then nitrogen (28 Da) oxygen (32 Da) or Argon (39 Da) but it is well know to pass through the rubber faster than N2 or O2.

I understood what he meant. The nitrogen is "made" during the same process that isolates (makes) oxygen from air.

I like the tutorial on the aristocratic (OCP?) gases.

It's actually the other way around. Oxygen is 'made' during the process to isolate N2 from air. N2 is more important, economically, then O2. And, if you make liquid N2, O2 will condense in it. We don't leave open vessels of N2 about for that reason. You can concentrate O2 in it and go Boomba! Boomba!

http://www.putgrandprixondvd.com/graphics/AronSmall.jpg

/ Long, wordy post snipped
// Use air

The dude meant to say "Nitrogen is a by-product of Oxygen production." Cut him some slack.

EDIT: like DMF said...

Well, actually in this context (the context mentioned by hotbike) you are wrong: the dude clearly stated that:

Now you hate me, I know...

I watched a Mythbusters once that experimented with filling footballs with helium to see if you could kick them farther. No dice, in such a small area it doesn't make any real difference, either in weight or in performance. Maybe for a poser though it would give them a "mental edge".

Mythbusters: where science and correct methodology go to die.

BTW: it's "volume" the word you're looking for, not "area".

The raidus is just over 10 percent larger than oxygen and nitrogen, so you'd get a very MILD difusion benefit. It's a slightly heavier-so do you want to carry a couple of extra ounces around?

It's intert, so your tubes might dryrot a little slower.
Then again, nitrogen is almost as inert as a noble gas so you could get most of that same benefit without the expense of argon.

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.

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.

To say it scientifically: diffusion of a certain molecule or ion in gases and liquids has ****-all to do with their diffusibility in solids.

BTW. CO2 will seep through tubes quicker than "normal air".

Helium is produced from natural gas.

well, you learn new sh1t all the time. i always thought it was made by compressing air and pulling off the other gasses as they liquified. OK, so we will run out of easily-obtained He sooner or later then. :o

Wait until fusion reactors become popular. Then you'll have helium as a byproduct of fusing deuterium and tritium.

Ever tried sucking up a helium-filled balloon, and then talking? Is mucho fun. I must admit, I am culpable of releasing into the atmosphere a couple of liters of helium for the purpose of sheer jakassery.

FWIW, this article describes the process of permeation related to vacuum quality. http://www.vacuumlab.com/Articles/VacLab30.pdf

This reference describes the viscous and molecular leakage constants for gases relative to helium:
http://www.lacotech.com/products/997...eaktechref.pdf

In the Lacotech document, Argon constants are slightly less than those for nitrogen or air and thus Argon molecular leaks would be at slightly lower rates than for nitrogen or air. However, Argon would need to be tested with Buna-N material for any meaningful bicycle tire permeation data.

Edit: Based on Buna-N compability with Argon from this elastomer manufacturer:
http://www.ind-ex.biz/catalog_images/IndexCatalog.pdf,
Argon has poor compability with Buna-N, Nitrile, and NRBT rubber. A Buna-N tire inner tube will fail prematurely when used with Argon!

As such, I retract my previous post and warn against using Argon in bicycle tires!

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.