Re: broken steel screws in aluminum casting - the nitric acid


"Grant Erwin" <grant@xxxxxxxxxxxxxxxxxx> wrote in message
news:11pviunatm4dg99@xxxxxxxxxxxxxxxxxxxxx
> I got a little bit of 70% nitric acid, potent stuff. I cut the end off a
screw
> of the same exact type as I previously dissolved in alum, put it in the
bottom
> of a small glass, and added about 10 drops of nitric acid. Naturally, I
wore
> face shield and gloves, and used an exhaust fan. Nitric is pretty nasty.
Anyway,
> it was cooking along nicely for a few minutes but then it seems to have
slowed
> down quite a bit. It's been going about 8 hours now, and I'm wondering if
there
> is enough oomph in the little bit of acid I put on it, barely enough to
cover
> the bottom of a small water glass.
>
> Thing is, my actual screw, which is in an aluminum casting, won't have
much acid
> around it either.
>
> I suppose I could try drawing the liquor out carefully after it slows, and
> adding a few more drops.
>
> Anyway, tomorrow I'll take the piece out and weigh it and I'll get a rate
of
> dissolution and then I'll compare it to how the alum did.
>
> GWE

I'm no chemist, but I think the it's the hydrogen in nitric that does the
work. Needless to say, just because you still have a liquid doesn't mean
you still have what you started with. Just like consuming gasoline in your
car, you've used up the part that made it nitric acid (HN03), so it is now
something else. It's likely the action will have ceased completely, and
you'll have to add more, or pour out the old and start with new. When I
refined gold, the amount of nitric used was critical, due in part to having
to get rid of it before I could recover the gold from solution. I found
that an ounce of nitric in conjunction with 4 parts of HCL would dissolve a
troy ounce of gold. Less would always leave some gold undisclosed.

Harold


.

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