Last time I checked, sodium hypochlorite was a strong oxidizing agent.
Rust is caused by the oxidation of iron.
Based on these two facts, my guess would be the detergent contains sodium hypochlorite.Why do detergent cause iron nails to rust?
You do know that sodium hypochlorite is common household bleach, right? Like Chlorox and the like.
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It isn't so much the detergent, but more the water in it. Iron rusts when exposed to both oxygen and moisture. Because it is soaked in the detergent, it will have absorbed moisture. The subsequent reaction with the air will initiate rusting.
If the detergent is acidic or basic, it may speed up the reaction with air.
It's probably not the detergent. It's the act of getting the nail exposed to water. Letting it air dry helps the iron decompose to iron oxide (rust). Iron oxide is more stable than plain iron. If you don't want this to happen, dry off the nail right after it gets wet.
In short: rusting is accelerated by abundance of both water and oxygen close to iron surface, and by presence of salts and acids in the water. Peroxide does not have much effect on rusting if the nail is submerged in peroxide solution, but will accelerate rusting if it is sprayed on the nail or the nail is suspended above it. Higher temperature will speed up rusting.
Now, in detail. The reaction of rusting requires presence of both water and oxygen molecules near iron surface. Therefore just submerging the nail in still water is a very slow way to make it rust, because there's not that much dissolved oxygen in water. Rusting will be greatly accelerated if instead water is sprayed on the nail or misted, or if the nail is just dipped regularly, or it can also be wrapped in a wet rug. Anything that keeps the nail surface exposed to both moisture and air. Even better if you can supply concentrated oxygen instead of air.
It would seem then that adding peroxide to water could provide extra oxygen, but what happens when you put iron in 3% peroxide is that iron accelerates decomposition of peroxide into water and oxygen and very soon after you drop the nail in the solution there will be no peroxide left. You can still use peroxide as the source of oxygen for a longer time if you spray the solution onto the nail (so that fresh peroxide is supplied), or don't let the nail touch the peroxide solution altogether, e.g. by hanging it above a bowl with the solution.
Rusting is also an electrochemical reaction, which means that in addition to the chemical changes there's current of electrons involved. Pure water is a poor conductor (particularly distilled water) so adding salts to act as electrolytes and increase electrical conductivity will speed up rusting. Regular table salt or sea salt will work great. There is a well known problem with car bottoms rusting because of salt on the roads in winter. For the same reason sea water makes things rust faster than fresh water.
Rusting is helped along by acidity. I am not talking about using strong acids: they will corrode the nail and form salts of iron instead of rust. What you want is just some acidity of the solution, e.g. add vinegar or use lemon or orange juice. Obviously, you can combine an acid and salt together for even greater effect. How about wrapping the nail in a rug moistened with salted lemon juice?
I know that household bleach (sodium hypochlorite) is often claimed to speed up rusting as well. I am not sure about that. Obviously, it is a salt and adding bleach will help with conductivity, but I am not sure why it would work better than sodium chloride. I don't see bleach mentioned by professionals who rust iron things to make them look old (see the link below). Now, a one-to-one solution of household bleach and vinegar will work great for rusting, however! mixing chlorine bleach with vinegar produces poisonous chlorine gas, and I wouldn't recomment trying this at home. If you still feel that you absolutely must, do it outside and keep your face away from the mixture.
When doing experiments rusting a piece of iron make sure the metal surface is not covered with any protective films, like machine oil for example. You can just wash the nail with dish washing soap to remove any oils.
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