Le 17/08/2012 16:25, Invisible nous fit lire :
> So, we put an old Maxtor harddrive in a glass measuring beaker, and
> stood it in one of our fume cupboards.
> 
> We poured nitric acid on it. Nothing.
> 
> The guy opened a bottle of sulphuric acid, which was smoking slightly.
> Pour some of that in... a tiny amount of fizzing. That's about it.
> 

Red alert. Mixing Nitric acid with Sulphuric acid is a cocktail to make
nitroglycerin from glycerine. The smallest part of grease might turn
dangerous once dried.


> So we stand at look at it for a moment. And then my college decides to
> add a little hydrochloric acid.

Great, now the cocktail is a mix of Sulphuric acid and Aqua regia, the
solvent for gold & platinum.
(for gold, the proportion are 2/3 Nitric, 1/3 Chloridric; it goes to 7/9
and 2/9 for platinum, IIRC)

All the water generated by Aqua regia attacking the metal will get
captured by the Sulphuric acid.

Notice that Aqua regia is unstable: it will generate chlorine gaz and
nitric oxyd (Cl2 and NO) with water.
Adding water to Sulphuric acid is exothermic. (it generates heat)

> 
> Woah... I'm not sure what the chemistry of this is, but now it's foaming
> like hell, and there's huge clouds of dark brown smoke coming off it.
> Uh, yeah, I think we close the fume hood now...
> 
> After a few minutes it eventually stopped fizzing. There's still some
> kind of brown vapour issuing from it though. And the black paint is
> slowly falling off, revealing the dully silver metal beneath.
> 
> It will be interesting to see if there's anything left by Monday. My
> college thinks it will have been reduced to sludge by then. I suspect
> it'll still be in once piece, just slightly corroded around the outside.

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