Recently as suggestion came across my desk that there might be a benefit to inflating tires with pure nitrogen gas, as opposed to the compressed air that is normally used (at least for passenger cars and most commercial trucks.) After some research, I found out that some race-car drivers and all (or most) commercial airliners use nitrogen to inflate their tires.
A number of reasons were advanced to explain this:
1) In applications where the tires heat up, using N2 instead of air reduces the amount of oxygen available to fuel a fire in the event of a crash and tire blowout.2) Compressed air contains small amounts of water vapor, which may condense at inflation pressure, and as tires heat and cool, this may result in unpredictable effetcs. (think of an airliner tires that are exposed to temperatiures at 10,000 meter altitude and then, upon landing, hit the ground at start spinning as theplane is going a couple hundred km/hr, and then braking very suddenly.)
3) Using Nitrogen in the tire prevents oxidation of the rubber in the tire carcass (that's a technical industry term, by the way), at least on the inside of the tire, anyway. This increases tire life, compared to the use of compressed air (which is essentially a 80% N2 - 20% O2 mix).4) Using N2 in the tire prevents oxidation of the steel wheel rim (assuming you're using steel rims), thus preventing rust flakes that might insinuate their way into the valve seat and cause slow leaks.
5) N2 diffuses more slowly than air through the tire, thus allowing tires inflated with nitrogen to hold their inflation pressure longer than tires inflated with compressed air.Because air is 80% N2 and the molecular mass of N2 and O2 are so similar (28 for N2 vs. 32 for O2 and 29 for air), I'm somehwat skeptical of these claims. I've tried googling on the subject, but didn't find the enlightenment for which ZI'm seeking. There was some stuff on membrane gas permeation, which reintroduced me to something called "Graham's Law of effusion," which then sent me to my 22-year old P-chem textbook to look it up. This didn't help, Graham's Law states that effusion (or diffusion) rates are inversely proportional to the molecular mass, which kind of messes up (5), because N2, having a lower molecular mass, would diffuse through the tire slightly faster than either oxygen or air. Now maybe if you inflated tires with CO2, which has a molecular mass of 44, you might see some reduced diffusion.
As far as (2) goes, from my college day recollection of hooking up compressed air to analytical instruments, it's possible to provide water-free compressed air, so why bother with nitrogen?
I couldn't come up with any theoretical reason or find anything in the engineering literature to evaluate any of the other supposed benefits of inflating tires with nitrogen instead of air. If anyone here can point me to some citable technical sources, I'd sure appreciate it.
Thanks in advance,
Joe