It keeps increasing (exponentially slower, thus with a finite total depth) even without any other chemical.
Anyway, out on the world there are many chemicals that can make it deeper, can peel it from the metal so another layer forms, or can mix with it and make it less insulating. I would be surprised if loses are as low as 1% as people point on this thread, but shouldn't be very large either.
You might want to include the end of that sentence: "...in the exothermic chemical process of combustion, releasing heat, light, and various reaction products."
This confirms the, imo, common-sense position that no, oxidation is not just a slow fire. A fire is a specific type of oxidation process that involves the production of significant light and heat. In other words, it is only true that oxidation is a slow fire if one adopts a definition of fire that is significantly different from its ordinary usage.
A fire releases the "heat, light and various reaction products" that it does because of the speed of oxidation. It's obvious even from the snippet I posted that slow oxidation is not actually a fire.
Fire is a phenomena whereby a fuel is combined with an oxidizer to make a new product in a manner that releases heat (ie: an exothermic redox reaction).
Rusting of metals fits that bill since heat is in fact released (just a super tiny amount and rather slowly), so it's _technically fire_ - although fire more commonly implies the rapid release of copious amounts of energy as part of the process.
Anyway, out on the world there are many chemicals that can make it deeper, can peel it from the metal so another layer forms, or can mix with it and make it less insulating. I would be surprised if loses are as low as 1% as people point on this thread, but shouldn't be very large either.