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Recently, looking for information for worldbuilding purposes of my story, I found a post about how in a more oxygen rich atmosphere, the oxidation processes would take place more quickly.

Subsequently, I asked a question where they denied this information and let me know that the proportion of oxygen in an atmosphere, at least at levels that are breathable for the human being, would not affect the oxidation processes.

So, here's my question, what kind of gases present in an atmosphere would make the oxidation processes faster than those produced on Earth?

In case you are interested in the context, I would like to know this information, since in the story I am thinking the rapid wear of ferrous metals has forced humanity to look for new alternatives in other materials, less malleable or durable, to forge weapons.

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    $\begingroup$ Fluorine works wonders. Or the amazing chlorine trifluoride. Or the majestic dioxygen difluoride. Or is it that you want to have humans in this world too? And anyway, iron does not rust in dry air; it needs water to rust. And it rusts very very quickly in marine environments -- oxygen and salt water droplets in the air will make short work of iron objects. $\endgroup$ – AlexP Mar 25 '18 at 21:44
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    $\begingroup$ On the other hand, iron is so much cheaper than bronze (the only other reasonable metal for making tools in a pre-industrial society) that it's more practical to make cheap iron tools which rust quickly than to make expensive bronze tools which last longer. $\endgroup$ – AlexP Mar 25 '18 at 21:51
  • $\begingroup$ What kind of oxidation processes? Just iron? Or all of them? Because there are a ton of them, and increasing the rate of aluminum oxidation wouldn't do much, since aluminum oxide is not porous and protects to metal from further reactions. $\endgroup$ – Xavon_Wrentaile Mar 25 '18 at 23:39
  • $\begingroup$ @Xavon_Wrentaile Mainly, oxidation focused on ferrous metals. $\endgroup$ – JAMS Mar 25 '18 at 23:54
  • $\begingroup$ Oxidizers and catalysts? $\endgroup$ – pojo-guy Mar 26 '18 at 2:23
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To oxidize iron you need oxygen, and water.

Things which improve electrical conductivity of water improve its ability to cause rust: usually that means ions dissolved in the water. Salt (sodium chloride) is the one we encounter most. Salt added to roads to help melt ice can facilitate rust. Salt spray / salt fog in ocean areas can facilitate rust. Other dissolved ions in salt fog might also play a role.

http://scienceline.ucsb.edu/getkey.php?key=552

People who live near the ocean know this. The reason is that the process of rusting involves electrons moving around, and electrons move more easily in salt-water than they do in clean water. A simple test of this is to see how easily current flows in clean water (it does not), and then add salt to the water (then current does flow easily)... Water is the enabler of fast oxidation of iron so freshwater will also cause rust. However, salt water is a very good conductor (lots of dissociated ions) and so there are a number of electrolysis reactions that tremendously accelerate corrosion in salt water. For example if you have iron in contact with salt water and also in contact with another metal such as aluminum (also in contact with the water) you effectively get a battery which drives very fast corrosion processes.

Here is a great free full text scholarly overview of marine atmospheric effects that increase corrosion. I did not know about the SO₂ one!

Marine Atmospheric Corrosion of Carbon Steel: A Review

In 1973 Barton noted that the mechanism governing the effects of chloride ions (Cl⁻) in AC had not been completely explained, and that the higher corrosion rate of steel in marine atmospheres could also be due to other causes, such as: (a) the hygroscopic nature of Cl⁻ species (sodium chloride (NaCl), calcium chloride (CaCl₂), magnesium chloride (MgCl₂)), which promotes the electrochemical corrosion process by favouring the formation of electrolytes at relatively low relative humidity (RH); and (b) the solubility of the corrosion products.

SO₂ is neat because I think it is not acting as electrolyte to increase conductivity, but as an oxygen donor.

SO₂ gives rise to the formation and propagation of sulfate “nests”, according to reactions, which start to appear at isolated points on the surface but whose number increases until all the surface is coated with a rust film... SO₂ is much more aggressive to steel when its concentration exceeds 0.1 mg·m⁻³, a level that is easily reached in many towns, especially in winter. Fortunately, the SO₂ concentration in urban air has decreased greatly in recent years due to efforts to reduce pollution


But here is an end run around objections about the harshness of such atmospheres on your humans, or the fact that people do use iron in environments like this:

Worldbuild up some super fierce iron-oxidizing microbes. https://en.wikipedia.org/wiki/Iron-oxidizing_bacteria

These things exist in the world. In your world they can fix their own nitrogen and carbon dioxide, and for energy they oxidize metallic iron. It is a baby step away from creatures that really exist as you will read in the link. These micro-organisms will not be interested in humans, only iron. You would need to keep your iron under oil to keep it from being colonized and rusting away.

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  • $\begingroup$ Excellent idea! Thank you very much! $\endgroup$ – JAMS Mar 26 '18 at 0:17
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Your wording implies a difficult situation: your phrasings such as "levels that are breathable for human beings" and "...forces humanity..." imply that the goal is not just to have high oxidization rates, but to have humans live in it.

This is troublesome because humans are generally constructed of reducing agents: humans oxidize. If you increase the oxygen enough to cause oxidization of metals, you increase the oxygen enough to cause the oxidization of the tissue of our lungs. Changing the material to an oxidizer other than oxygen doesn't help all that much. You still have the issue of a corrosive gas that you are breathing into your lungs.

The tricky thing about oxidization is that redox equations (the equations which use an oxidizer to oxidize a fuel) are tremendously broad. If you try to increase one, you increase all of them.

If you're willing to tweak the genetics of these humans, there might be more options. We could always evolve to withstand a higher oxidizer load. Or maybe there's some other options. Does the reaction have to be a simple oxidization reaction? What if your humans developed a resistance to mercury. Mercury amalgamates with quite a large number of metals, including gold. The results are typically structurally weak. If your environment had a lot of mercury in it, this could be a problem. Gallium is also known to amalgamate and attack metals. Putting them together can be even more impressive.

This is definitely not precisely what you were after, dealing with liquid metals, but it may be the kind of head start you need to formulate your world!

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Nitrite oxidation in the freezing process (in your case of atmospheric gases) is the fastest process there is. Lipid perodoxation however is can cause damage when a living thing is exposed, it is cancerous & mutagenic.

https://www.researchgate.net/figure/The-UVA-induced-decomposition-of-nitrite-NO2-can-have-different-effects-on-lipid_fig3_235366724

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