[LabKid (OP)]

I'm a bit un-qualified to answer this question myself, and I've spent quite some time looking around on the internet for an answer. After awhile of not finding anything I decided to post it up here and see what some of you think. Steel in question is MIL-A-12560 grade steel plating, and the amount of fluoroantimonic acid is a kilogram.

[chiralSPO]

Fluoroantimonic acid has the chemical formula HSbF₆, and a molar mass of 236.76 g/mol. It is a very strong acid, in that it is capable of protonating almost anything, but that doesn't necessarily mean that it is the best at dissolving (eating through) materials.

I don't think that metals like steel are soluble in HSbF₆, and protonating steel won't change its solubility, so really the question at hand is one about the chemical reactions:

HSbF₆ --> H⁺ + SbF₆^–
and
Fe + 2 H⁺ --> Fe⁺⁺ + H₂

These reactions indicate the dissociation of the acid into free protons (hydronium ions) and hexafluoroantimonate ions, and the reaction of protons with metallic iron (steel), resulting in soluble ferrous ions and hydrogen gas.

Based on this stoichiometry, it would take 2 moles of  acid to react with one mole of iron (molar mass of 56 g/mol). One kg of the acid contains just over 4 moles (1000/236.76 = 4.22 moles), so this would eat away 2.11 moles of iron, or roughly 120 grams.

In contrast, one kg of sulfuric acid, which is H₂SO₄, could consume roughly 560 grams of iron. Sulfuric acid is no where near as "strong" based on dissociation constant, but it has a much higher concentration of reactive protons per unit mass.

i hope this helps!

[LabKid (OP)]

Thanks for the very informative answer! It does, however, leave me with one followup question. Would it be possible using any acid to dissolve a circular (Or cubic, it's not really important) hole 5 centimeters deep with  a diameter of 1 centimeter using any combination of acids or electrical currents in under 10 minutes? It's only 5 cm2, however it is 5 centimeters deep and from what I've found many acids tend to act rather slowly. For simplicity's sake assume there are no limitations on the electrical current or amount of acid we could apply.

[RD]

...Steel in question is MIL-A-12560 grade steel plating, and the amount of fluoroantimonic acid is a kilogram.

So you want to make a hole in the type of steel used to make safe-deposit boxes, (as used to store valuables).  ;¬)

Careful not to spill any of that acid on gold jewelry, as it will dissolve that too.

[chiralSPO]

Aqua regia, a mixture of hydrochloric and nitric acids, is one of the most aggressive acids I can think of. I don't think it could work its way through that much steel in that amount of time without some very fancy engineering (maybe a power-wash filled with hot aqua regia?) In any case, I would not recommend trying this--it would be very dangerous, would certainly splash acid (even if not using the high powered spray), evolve toxic and corrosive gases, and probably destroy whatever is on the other side of the steel.

[William McC]

Thanks for the very informative answer! It does, however, leave me with one followup question. Would it be possible using any acid to dissolve a circular (Or cubic, it's not really important) hole 5 centimeters deep with  a diameter of 1 centimeter using any combination of acids or electrical currents in under 10 minutes? It's only 5 cm2, however it is 5 centimeters deep and from what I've found many acids tend to act rather slowly. For simplicity's sake assume there are no limitations on the electrical current or amount of acid we could apply.

Steel burns, so you can blow that hole in under 120 seconds with a large oxygen and acetylene torch. For stainless steel you would use a mix of gasses with a plasma torch. By adding helium and or hydrogen to nitrogen, you can blow a hole so fast in thick stainless that you just need to be careful of where all that plasma and molten metal goes.

Having done a lot of demo with oxygen and acetylene over the years, I am sure of the speed you can move right through heavy steel, burning it as you go for added heat. The torch in the short video is very good up to about an inch of steel. But it will slowly cut 2" steel. To do 5 centimeter I would get a larger torch however you could use those little tanks.

The torch in the video will not cut stainless steel though, because stainless steel will not burn.

youtu.be/KgPne_kM7yU

Sincerely,

William McCormick

[William McC]

You would be much better off drilling a hole it would be much quicker. Today we have magnetic drill presses that are battery operated, and they can drill that hole hole in minutes. If you drill with a high speed battery operated hand held drill a pilot hole first you can punch the step up hole in under 2 minutes. The pilot hole can be drilled in about a minute and half.

Sincerely,

William McCormick

[LabKid (OP)]

I know there are much easier ways of getting through steel, but I was more looking to see how accurate the spy movies are where they burn through that much steel in a matter of seconds sometimes.

Thanks everyone for the answers!

[chiralSPO]

the spy movies are quite unrealistic in this regard (and many others)