broken steel screws in aluminum casting - the nitric acid
 

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

broken steel screws in aluminum casting - the nitric acid
 

"Grant Erwin" wrote in message
...
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

broken steel screws in aluminum casting - the nitric acid
 

Grant Erwin wrote:

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

You do consume the acid as it dissolves the metal. You'll bubble off
hydrogen while the iron is being oxidized, ultimately you'll have a
solution of ferrous (ferric? ick) nitrate (or whatever) and no acid.

I suspect that if you just drip more acid around the screw you'll get it
down to where it needs to do its work -- but you'll also have some
dripping out of the hole, which may not be what you want.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

broken steel screws in aluminum casting - the nitric acid
 

"Harold and Susan Vordos" wrote in message
...

"Grant Erwin" wrote in message
...
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.

I'm not a chemist either, but I wonder if H+ is the worker here. If it was
, it seems to me that sulfuric acid would work as well as nitric and that's
apparently not the case. Nitrate (NO3-) is known as a good oxidizer, so I'm
thinking that it is the active component in nitric acid, perhaps oxidising
the iron in steel to Fe(NO3)2 or some other form. Googling the subject has
not been productive for me, but a post to sci.chem would probably turn up
the correct reaction. Once that is known it should be a simple matter to
calculate how much nitric acid would be needed to dissolve the screw or tap,
as the case may be.

BTW, somewhere in the results of a Google search it was suggested that
concentrated nitric acid be diluted before application.

Assuming reaction to Fe(NO3)2, you'd have:

2 HNO3 + Fe = Fe(NO3)2 + H2

so you'd need 2 moles of ntric (126 grams) for every mole of iron (55.8
grams) in the tap, or roughly 2-1/4 gram of pure nitric per gram of iron.
For a 70% nitric acid solution that would be a litlle over 3 grams nitric
per gram of iron and a 1:1 dilution of nitric acid would require around 6
grams nitric acid per gram of iron. The approach is correct, I think, but
the reaction could be all wrong. Note that hydrogen is released in the
above reaction. If the solution bubbles, some sort of gas is being released
and hydrogen is probably more likely than oxygen.

Mike

broken steel screws in aluminum casting - the nitric acid
 

Grant

You've used up the acid. Add more (no need to decant, it's liquid after
all so it will diffuse) and it should eat the metal again. It will
probably take 5 - 10 ml of 70% HNO3 to eat a small screw. When you get
to taking out the screw from the aluminum, build a dam around the hole
with modeling clay and then rise the acid off with a baking soda rinse
when you're done. Just rinse it down the drain, the beasties at the
treatment plant like nitrates.

By the way, general rule in chem labs is rinse and dump 3 times.

Jim

broken steel screws in aluminum casting - the nitric acid
 

I'm not a chemist either but IIRC from chemistry its the greater
abundance of H+ ions over OH- that makes something acidic, a greater
abundance of OH- over H+ makes it basic. This applies to all chemicals
IIRC not just Nitric acid. A measure of the abundance is the pH scale
with neutral pH being 7 and reducing as it becomes more acidic,
increasing as it becomes more basic. Now I can remember that the pH
number represents the exponent on the H+ ion concentration but can't
remember what the units are.

Harold and Susan Vordos wrote:

"Grant Erwin" wrote in message
...

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

broken steel screws in aluminum casting - the nitric acid
 

Jim McGill wrote:
Grant

You've used up the acid. Add more (no need to decant, it's liquid after
all so it will diffuse) and it should eat the metal again. It will
probably take 5 - 10 ml of 70% HNO3 to eat a small screw. When you get
to taking out the screw from the aluminum, build a dam around the hole
with modeling clay and then rise the acid off with a baking soda rinse
when you're done. Just rinse it down the drain, the beasties at the
treatment plant like nitrates.

By the way, general rule in chem labs is rinse and dump 3 times.

Jim

I've got a degree in chemistry, and Jim is right on target. No need to
remove the old acid - the new will mix thoroughly.

Nitric acid and concentrated sulfuric acid are, in addition to being
strong acids, strong oxidizing agents. Which means they will, under
certain circumstances, passivate metals such as aluminum and stainless
steel. The passivation will actually prevent the metal from corroding.

Keep in mind that the acid will take quite a bit longer to work in the
hole, since it can't get at all surfaces of the broken screw as it did
with the test piece. It works quicker with a tap, where it will work
down along the flutes. Or with a drilled piece.

John Martin

broken steel screws in aluminum casting - the nitric acid
 

"Mike Henry" wrote in message
...
snip-----

I'm not a chemist either, but I wonder if H+ is the worker here. If it
was
, it seems to me that sulfuric acid would work as well as nitric and
that's
apparently not the case. Nitrate (NO3-) is known as a good oxidizer, so
I'm
thinking that it is the active component in nitric acid, perhaps oxidising
the iron in steel to Fe(NO3)2 or some other form. Googling the subject
has
not been productive for me, but a post to sci.chem would probably turn up
the correct reaction. Once that is known it should be a simple matter to
calculate how much nitric acid would be needed to dissolve the screw or
tap,
as the case may be.

BTW, somewhere in the results of a Google search it was suggested that
concentrated nitric acid be diluted before application.

Assuming reaction to Fe(NO3)2, you'd have:

2 HNO3 + Fe = Fe(NO3)2 + H2

so you'd need 2 moles of ntric (126 grams) for every mole of iron (55.8
grams) in the tap, or roughly 2-1/4 gram of pure nitric per gram of iron.
For a 70% nitric acid solution that would be a litlle over 3 grams nitric
per gram of iron and a 1:1 dilution of nitric acid would require around 6
grams nitric acid per gram of iron. The approach is correct, I think, but
the reaction could be all wrong. Note that hydrogen is released in the
above reaction. If the solution bubbles, some sort of gas is being
released
and hydrogen is probably more likely than oxygen.

Mike

While I can't confirm what you said, Mike, I recall that on rare occasions
I'd have a minor hydrogen fire------which indicates to me that you are on
the right track. If the hydrogen was being consumed, there'd be nothing to
burn. It's obvious it is liberated, with the metal in question taking its
place.

Harold

broken steel screws in aluminum casting - the nitric acid
 

I recall seeing a chart for corrosion capacities for various chemicals
vs. steel. Nitric acid was much less corrosive when the steel was
immersed than when the steel was suspended in the acid vapor.
Unfortunately I can't find that chart right now. This could have
something to do with the passivation John Martin mentioned.

Cheers,

Kelley

On 14 Dec 2005 09:54:14 -0800, "John Martin"
wrote:


Jim McGill wrote:
Grant

You've used up the acid. Add more (no need to decant, it's liquid after
all so it will diffuse) and it should eat the metal again. It will
probably take 5 - 10 ml of 70% HNO3 to eat a small screw. When you get
to taking out the screw from the aluminum, build a dam around the hole
with modeling clay and then rise the acid off with a baking soda rinse
when you're done. Just rinse it down the drain, the beasties at the
treatment plant like nitrates.

By the way, general rule in chem labs is rinse and dump 3 times.

Jim

I've got a degree in chemistry, and Jim is right on target. No need to
remove the old acid - the new will mix thoroughly.

Nitric acid and concentrated sulfuric acid are, in addition to being
strong acids, strong oxidizing agents. Which means they will, under
certain circumstances, passivate metals such as aluminum and stainless
steel. The passivation will actually prevent the metal from corroding.

Keep in mind that the acid will take quite a bit longer to work in the
hole, since it can't get at all surfaces of the broken screw as it did
with the test piece. It works quicker with a tap, where it will work
down along the flutes. Or with a drilled piece.

John Martin