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This Cream Eats Metal
January 27, 2010 6:36 PM   Subscribe

Are there any types of substances that cause rapid metallic corrosion? For some reason, I've always imagined that there was a magic acidic cream or salve that you could rub on, say, a metal barn roof, and it would corrode very, very quickly. Is this completely a fantasy, or is this somehow based in something that exists?
posted by lifeofthunder to Science & Nature (20 answers total) 5 users marked this as a favorite
 
Depends on the metal. For instance regular HCl will eat through zinc just about like you imagine. Steel, not so much.
posted by sanka at 6:37 PM on January 27, 2010


Hydroflouric acid will eat through anything except teflon. It can't be stored in glass because it will eat through that.

It's the strongest acid it is possible for there to be.
posted by Chocolate Pickle at 6:39 PM on January 27, 2010 [1 favorite]


Mercury will do a number on aluminum, but it's not quite the "hot-knife-through-butter" thing you may have in mind.
posted by tellumo at 6:42 PM on January 27, 2010


Try Aqua Regia. It eats all kinds of stuff, including noble metals.
posted by fremen at 6:51 PM on January 27, 2010 [1 favorite]


Hydrofluoric acid the strongest acid it is possible for there to be.

Depending on the measure of strength you use, it's not even close. But in terms of corrosiveness, yes, that's true. HF will dissolve glass and all metals except iridium.

Here's HF going to town on aluminum foil.

Here it is dissolving granite to extract strontium.
posted by jedicus at 7:09 PM on January 27, 2010


It's the strongest acid it is possible for there to be.

Geez, even your link says "it is technically a weak acid", right there in the second sentence of the first paragraph. The thing about HF is that it's not particularly acidic (pKa ~3, compared to H2SO4 @ ~-3, or HCl @ ~-8), but it is widely reactive.

sanka's got it, and fremen's pretty much right in that combinations of nitric & hydrochloric acid are reactive with most metals.
posted by Pinback at 7:12 PM on January 27, 2010


Hydroflouric acid will eat through anything except teflon. It can't be stored in glass because it will eat through that.

It's the strongest acid it is possible for there to be.


It's actually a pretty weak acid, with a pKa of only about 3.15. It's unusual in it's ability to dissolve glass, but that has more to do with oxide chemistry than with the strength of the acid. HF kind of got a niche application in dissolving oxides in general.

If you're interested in just general metal corrosion, you'd probably be better off with plain old HCl, or muriatic acid.
posted by mr_roboto at 7:13 PM on January 27, 2010


If you rub a stream of hot oxygen over steel, it will corrode through in seconds. Cheating a bit, I know, but that's how a cutting torch works. The acetylene's just there as a pre-heat, and the steel to magnetic ironic oxide reaction is hilariously exothermic. In theory, you could probably turn off the acetylene and still cut.
posted by scruss at 7:21 PM on January 27, 2010


In terms of a magic cream (instead of just a boring ol liquid), you'd have to make a binder that itself wouldn't react with the etchant; Silica (silicon dioxide) is incompatible with HF but should be okay for hydrochloric or nitric acids. If you wanted to strive for the creamiest texture, you'd probably have to use some sort of organic polymer as the binding agent, which would rule out the use of nitric or sulphuric acid, as those react with organic species.

Now whose body are you trying to dispose of?
posted by beepbeepboopboop at 7:25 PM on January 27, 2010


How to rust/patina metal.
posted by availablelight at 7:59 PM on January 27, 2010 [1 favorite]


I stand corrected on the strength of HF.
posted by Chocolate Pickle at 7:59 PM on January 27, 2010


Hmm...as do I. Apparently HF also cannot dissolve nickel and its alloys, gold, platinum, and silver.
posted by jedicus at 8:56 PM on January 27, 2010


Kind of what scruss says - In a cutting torch you heat the metal with the oxygen and acetylene flame and then blast it with oxygen using the iron as your fuel source. There is a tool called a thermal lance that you can use where a piece of iron pipe is the fuel source. I get to spend a day cutting steel stalactites off a ladle cover with one of these when I was working summers at a steel mill during college. Big fun.

If you ever need a pile of rust for some purpose or another, mix bleach and white vinegar and drop in a chunk of steel wool. The bleach is an oxidizing agent and the vinegar is an acid - together they, uh, well, they don't fight crime unless crime is made of iron. Then they kick its ass. Stronger acid / oxidizer combos will do more of the same.

At some point in the eighties I read a sort of paranoid fantasy about the terrorists coming to get us (I think by G. Gordon Liddy) but unlike real life where terrorists either weaponize everyday stuff or kill people the same ways people have been killing one another for years, the authors terrorists had magic markers of death that would let you draw lines on an airplane and then the airplane would be all brittle and disintegrate.
posted by Kid Charlemagne at 9:51 PM on January 27, 2010


Aqua Regia. Eats through gold.

Don't fuck around with HF.
posted by Civil_Disobedient at 10:08 PM on January 27, 2010


Also, I believe the strongest acid is Fluoroantimonic acid. But that's not really an indication of its corrosive strength.
posted by Civil_Disobedient at 10:25 PM on January 27, 2010


the authors terrorists had magic markers of death that would let you draw lines on an airplane and then the airplane would be all brittle and disintegrate.

That definitely was good ol' G. Gordon, writing in Omni magazine in January 1989.
posted by codswallop at 10:53 PM on January 27, 2010 [2 favorites]


Mercury is bad juju for lots of (but not all) metals, which is why it isn't even allowed in a lot of industrial areas. The consequences of a spill would be too risky. That's not to say it would disintegrate the jail bars before your eyes, though.
posted by ctmf at 11:10 PM on January 27, 2010


I believe your best bet would be something highly radioactive which gave off an ion of some kind as it decayed.

Ordinary chemical reactions are driven by chemical potentials of a few electron volts, but the decay of a single radioactive atom can easily generate energies in the millions of electron volts. This is the main reason effective containment of high level radioactive waste has proven to be such an elusive goal.

The problem with a highly radioactive 'cream' is that it would tend to boil away from its own internally generated heat. Therefore, you'd want to choose something with the highest possible boiling point. A powder containing a mixture of ordinary tungsten and tungsten187 (with a halflife of ~24 hrs. and decay by the emission of a 1.3 Mev electron) would be a candidate.

Putting such a thing together and carrying it around to apply it is another matter.
posted by jamjam at 12:46 AM on January 28, 2010


Perhaps the Alkahest, which is a universal solvent. It is completely a fantasy, but it probably is somehow based in something that exists.
posted by Phanx at 1:45 AM on January 28, 2010


"While experimenting with methods to make the miniature church roof in the Storybook Land Canal Boat Ride appear realistically old and weathered, a designer discovered that urine has an extremely corrosive effect on metal. So..."
-from Little-Known Facts about Well-Known Places: Disneyland by David Hoffman.
posted by Monday at 4:17 AM on January 28, 2010


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