Harry c
Gold Member
Since this Nitrogen fill and Calcium Chloride topic continues to come up and at the risk of insulting someone (not intended) or of being perceived as displaying "my hat size" 
(also not intended), I've done a few calculations as to how much rust can be expected inside a wheel/ tire loaded with Calcium Chloride, windshield washer fluid, or any other water based material that does not include a specific corrosion inhibitor. I am not advocating use of any of the mentioned liquids or gasses. Use what you feel is best. "Just the facts Ma'am" )
For anyone interested, the physical principles used are Boyles Law and the Ideal Gas Laws. Also used is Avogodro's number. Please feel free to check my numbers as I rounded some values and did very quick calculations.
To the chase: Air is a combination of several gasses: Nitrogen, about 75% by weight (80% by volume), Oxygen, about 25%. Other gasses such as Argon are present but in such small amounts they will be ignored for this discussion. The chemical formula for rust is Fe2 O3. You can't have rust without Oxygen.
Sparing all the calculations: It appears my BX rear tire at 75% liquid fill holds about 6 gallons of air. I normally maintain around 15 PSI in the tire. Rough numbers, 13 grams of Oxygen are contained by this much air at this pressure. Iron rust formula is Fe2 O3. This much Oxygen can rust 30 grams or about 1 ounce of iron. This is about 1/4 of a cubic inch of steel. This assumes 100% reaction of all available Oxygen (doesn't happen) with only the steel ( probably more reacts with the rubber tire).
Next item: Nitrogen expands at the same rate as any other gas when the temperature rises. (Google: Ideal Gas Law) This includes air. The advantage of Nitrogen in a NASCAR tire is the lack of liquid water that can be present in compressed air. BTW, have you drained your compressor tank lately? When the temperature of the tire gets above the boiling point of water, the liquid can change to steam raising the pressure more than would be expected with dry air. I do not see this as a problem in tractor tires. Mine never get into the 220 degree range.
All this being said, I did have a wheel rust out with Calcium Chloride. The valve was leaking slightly allowing the liquid to keep the outside lip of the wheel damp with the solution. I knew the rust would occur but never "got around" to replacing the valve core or even just screwing on a valve cap. I seldom used the tractor and it was stored in a humid basement storage area. The lip finally rusted through after 4 or 5 years of leaking. When I pulled the tire, the inside of the rim had no rust. The other rim is 30+ years old with no problem.
Something else just occured to me. Any tubeless tire filled with the somewhat wet air as you get from a standard compressor would have far more Oxygen available than a fluid filled tire. Shouldn't it rust out sooner??? Gotta stir the pot a little!
(also not intended), I've done a few calculations as to how much rust can be expected inside a wheel/ tire loaded with Calcium Chloride, windshield washer fluid, or any other water based material that does not include a specific corrosion inhibitor. I am not advocating use of any of the mentioned liquids or gasses. Use what you feel is best. "Just the facts Ma'am" ) For anyone interested, the physical principles used are Boyles Law and the Ideal Gas Laws. Also used is Avogodro's number. Please feel free to check my numbers as I rounded some values and did very quick calculations.
To the chase: Air is a combination of several gasses: Nitrogen, about 75% by weight (80% by volume), Oxygen, about 25%. Other gasses such as Argon are present but in such small amounts they will be ignored for this discussion. The chemical formula for rust is Fe2 O3. You can't have rust without Oxygen.
Sparing all the calculations: It appears my BX rear tire at 75% liquid fill holds about 6 gallons of air. I normally maintain around 15 PSI in the tire. Rough numbers, 13 grams of Oxygen are contained by this much air at this pressure. Iron rust formula is Fe2 O3. This much Oxygen can rust 30 grams or about 1 ounce of iron. This is about 1/4 of a cubic inch of steel. This assumes 100% reaction of all available Oxygen (doesn't happen) with only the steel ( probably more reacts with the rubber tire).
Next item: Nitrogen expands at the same rate as any other gas when the temperature rises. (Google: Ideal Gas Law) This includes air. The advantage of Nitrogen in a NASCAR tire is the lack of liquid water that can be present in compressed air. BTW, have you drained your compressor tank lately? When the temperature of the tire gets above the boiling point of water, the liquid can change to steam raising the pressure more than would be expected with dry air. I do not see this as a problem in tractor tires. Mine never get into the 220 degree range.
All this being said, I did have a wheel rust out with Calcium Chloride. The valve was leaking slightly allowing the liquid to keep the outside lip of the wheel damp with the solution. I knew the rust would occur but never "got around" to replacing the valve core or even just screwing on a valve cap. I seldom used the tractor and it was stored in a humid basement storage area. The lip finally rusted through after 4 or 5 years of leaking. When I pulled the tire, the inside of the rim had no rust. The other rim is 30+ years old with no problem.
Something else just occured to me.
Any tubeless tire filled with the somewhat wet air as you get from a standard compressor would have far more Oxygen available than a fluid filled tire. Shouldn't it rust out sooner??? Gotta stir the pot a little!
