CO2 solution in rubber

[HarryCoyote]

CO2 leaks faster in automotive tires than air despite atomic/molecular weight. This is said to be due to a CO2  "solution" related "thing". Does CO2 go into a true solution and create ions?

See https://physics.stackexchange.com/questions/187868/what-are-possible-explanations-for-the-permeabili... for "solution" verification.

Thanks,

Harry

[scooke]

There are many more factors than simply atomic size or mass in diffusion!  Whether you want to consider it a form of a "solid-state solution" or not is just modeling nomenclature.  Also, there are many solutions involving non-ionic species.  CO2 in hydrocarbons (like rubber) is one of them.

Best regards,

Steven

[HarryCoyote]

Thanks for the reply, Steven.

Agreed, CO2, polymers and "leakage" is pretty deep. I think that you can agree that CO2 leakage in automotive tire rubber (my specific interest) is illogically higher than expected, particularly, compared to nitrogen and oxygen. My question is focused on another potential effect. Specifically, can the CO2 in solution, in the rubber, create carbonic acid that would be detrimental to the steel belts in the tread?

[scooke]

Dear Harry,

That really shouldn't be a problem.  CO2 requires a fair amount of water to convert to carbonic acid.  That is also a much milder acid than other common inorganic acids.  It is more likely that steel belting in tires will rust from the water, oxygen, and heat in the tires than from carbonic acid.

Anyway, given that CO2 is really a poor tire inflation gas I don't see why you'd want to use it.  If you want "high-performance" inflation gases to enhance tire life you will do much better with nitrogen.  If you want to do a lot of high-speed (hot tires!) driving, argon is the best gas to use.

https://air-source.com/blog/how-argon-is-used-in-luxury-car-tires/ 

https://www.popularmechanics.com/cars/a3894/nitrogen-in-tires/ 

Best regards,

Steven

[HarryCoyote]

Steve,

Thanks for the quick response ... great info.

Why CO2 - The off-road community lowers and raises pressure to accommodate conditions. CO2 stored in the liquid state fills more tires per tank than any other compressed gas. I used to lecture about responsible 4WD use and lead tours at  at 31 SoCal colleges. I could help more of those without onboard compressors with CO2. Also a bicycle racer can fix and fill a flat quicker with CO2 than a pump. Both markets have many products available to fill those needs.

FYI, I publish an offroad newsletter and I'm gathering info to publish an article recommending against CO2 use.

I wonder if NASCAR et al use argon?

Re nitrogen being better, involuntarily, we all end up closer to 100% nitrogen in our tires with every compressed air top off.

I may wear out my welcome with the next question but you seem to have a pretty good handle gas concepts. On my tours, I had a massive data gathering base to study "things". Long story short, tire temperature and pressure do not follow Boyle's Law. I attribute it to the water vapor in the tire but that doesn't follow water vapor pressure concepts. Got any thoughts on this?

[scooke]

Harry,

My entire career has been in one part or another of industrial gases, including a very long stint as an international expert in carbon dioxide applications. It is the most versatile of all of the gases and has a very unfair representation due to climate hysteria (unfounded) these days.

I have also used the huge volume capacity of the liquid phase to extend many expansion functions, most notably during the Paintball sports phase. I played around with tire inflation as well. As you noted, IF you really need to adjust the pressure of a tire system periodically, the loss factor using CO2 is not going to be a problem. The gain in economy and convenience makes CO2 the best choice for large or rapid adjustments, with only a hand pump being more reliable.

I don’t know off-hand, but I’m pretty sure that with the rapid tire changes in professional racing, they probably don’t use argon to prevent interior oxidation. They might use nitrogen. https://www.tirerack.com/upgrade-garage/should-i-use-nitrogen-in-my-tires

BOTH nitrogen and oxygen actually leak out (usually through seals and valves) fairly equally rather than diffusing through the rubber. “Topping off” with compressed air is not really increasing the nitrogen ratio in the tire, and it will certainly never get anywhere near 100%.

Real-world applications of the gas laws usually require all three (Boyle’s, Charles’, and Guy-Lussac’s Laws) as we rarely hold one of the components at a fixed value. With regards to the inflation of tires, the most important fact about Boyle’s Law is that it only holds when the temperature is constant, which is notably never the case when inflating tires! With the further expansion of any inflated tire, the only thing that you are really measuring with any sort of confidence is the pressure.

I would need to see your test/measurement setup and your data to comment on whether you are properly using Boyle’s Law.

Cheers,

Steven

[HarryCoyote]

Once again, I'm humbled and grateful with your response.

First, I agree with you re the CO2 boogieman hoax.

My temp versus pressure data is long gone but it goes something like this. I had a tour in the Parque Nacional Constitucion de 1857, Baja Norte, Mexico. The last day/night before heading back to the USA was spent at ~4K' and ~32F. The predeparture ritual was check and adjust your tire pressure to whatever you ran. My presumption here is that the tires had normalized to ~32 - tree-shaded campsite at a hot spring. We then headed east and down out of the mountains to ~ 50~100' above sea level. We then turned due north  on an absolutely straight, fast (~40 MPH) road for 40 miles to the border crossing. I was in constant radio contact with all participants. About 25~30 miles up the road, I announce a potty break and asked for a left, right side tire pressure check. I'd then work my way back with my point and shoot IR thermometer and ask for pressure readings. The temp from the 32 start was typically left, ~70/80 and the right side was 100/120 and the pressure was, depending on what they ran, a 4 to 15 PSI difference. My memory is questionable and I could not find my old (circa 1985) data logs ... still looking. I measure the tire and rim in several places and was reasonably satisfied that all had mostly normalized.

Re NASCAR - it exclusively uses nitrogen to the best of my knowledge. I'm told that they use it for economy, cheaper than dry compressed air and because it is dry, hence my water vapor, pressure concerns.

For my article, may I quote you either in detail or anonymously?

I was unsuccessful at including links and attaching my newsletter Tires reprint. Got an email add to send it to?

Thanks again,

Harry

[scooke]

Harry,

I've been an avid bicyclist for over 65 years!  It's a very big sport competitively and personally here in the Philippines.  Taking this out of the initial "Ask a Chemist" Q&A you may contact me at drwhocooke@yahoo.com for further discussions and references.

Cheers,

Steven

[Philliprjun]

The behavior of CO2 in the context of automotive tires is influenced by its physical and chemical properties. When CO2 is used to inflate tires, it behaves differently from air (which is primarily composed of nitrogen and oxygen). One key factor is the size of the gas molecules. CO2 molecules are smaller and more mobile than the larger nitrogen and oxygen molecules in air. As a result, CO2 is more prone to electrical estimating diffuse through the rubber materials of the tire, leading to a faster rate of leakage.  

[emyRica]

Carbon dioxide (CO2) does not readily form ions when dissolved in water or other solvents, unlike some other substances like salts or acids. Instead, CO2 primarily exists as dissolved CO2 molecules in a solution. The phenomenon you mentioned regarding CO2 leaking faster from automotive tires than air can be explained by https://focusautodetailing.com/ several factors, including the size of the CO2 molecules, their solubility, and their diffusion rates.