I have some really old but strong casters which were once cleanly
galvanized but which have corroded through the zinc in many places.
They appear basically sound, though. I am contemplating heating a strong
solution of lye, then shutting off the heat (no open flame!) and putting
in the casters (sans wheel, of course) with the goal being to remove all
dirt, oil, grease, and, of course, zinc. Then I'd rinse in boiling water
after which they should self-dry quickly. Then I could brush off any rust
and prime the tops and then weld them to a plate, after which I'd paint
the plate and the casters all together, then reinstall the wheels.

I believe that the lye will dissolve the zinc, releasing hydrogen. I'd
do this outside, in free air, with no open flames nearby.

Anyone have any comments? Experience?

GWE

"Grant Erwin" (clip)I believe that the lye will dissolve the zinc (clip)
^^^^^^^^^^^^^^
Wouldn't muriatic acid work better? (And probably be a little less
hazardous.)

On Tue, 23 Nov 2004 22:24:50 GMT, "Leo Lichtman"
wrote:


"Grant Erwin" (clip)I believe that the lye will dissolve the zinc (clip)
^^^^^^^^^^^^^^
Wouldn't muriatic acid work better? (And probably be a little less
hazardous.)

I'm not sure which is more hazardous. But the muriatic acid will
remove all the rust. Then the part will rust really fast when exposed
to air. With lye the part won't rust so fast. If lye will remove zinc
the way it removes aluminum that seems like the way to go.
ERS

Grant Erwin wrote:
....
I believe that the lye will dissolve the zinc, releasing hydrogen. ...

I don't think so. Lye is NaOH, a reaction with zinc would give what?
Sodium zinc?? No such thing, AFAIK. Muriatic acid (HCl) and zinc gives
zinc chloride and hydrogen.

Bob

Bob Engelhardt wrote:

Grant Erwin wrote:
...

I believe that the lye will dissolve the zinc, releasing hydrogen. ...


I don't think so. Lye is NaOH, a reaction with zinc would give what?
Sodium zinc?? No such thing, AFAIK. Muriatic acid (HCl) and zinc gives
zinc chloride and hydrogen.

Bob

I have certainly seen nameplates dissolve in lye when I was soaking paint
off of castings. Sure bummed me out at the time. Let's see ..

Zn + (Na+) + 2(H+) + 3(OH-) - (Zn++) + (Na+) + H2 + 3(OH-) ?

Remember, in any aqueous solution there is always *some* H+ around, even
in a strong basic solution.

From the Agency for Toxic Substances and Disease Registry:

"Sodium hydroxide dissolves easily in water generating a great deal of heat. It
reacts with acids (also generating a lot of heat); halogenated organic
compounds; metals such as aluminum, tin, and zinc; and nitromethane. Sodium
hydroxide is corrosive to most metals."

Also see http://www.btc-bci.com/~billben/rust.htm -- apparently some guys
actually ADD zinc to lye and then put in rusty parts, counting on the zinc
to strip the oxygen ions off of the Fe(X)O(Y) [rust] molecules.

Grant

Grant Erwin wrote:
....
Zn + (Na+) + 2(H+) + 3(OH-) - (Zn++) + (Na+) + H2 + 3(OH-) ?
....

"Sodium hydroxide ... reacts with ... zinc; ...

Well, you clearly know WAY more about this than I do. Please ignore my
previous ignorant post. And thanks for the enlightenment - I'll know to
be careful when using lye to strip paint from galvanized stuff.

Now, about the reaction: it shows (I think) a result of zinc and sodium
ions in solution. What happens if that water is evaporated? Do you get
elemental zinc and sodium? And the sodium burns off?

Bob

Tim Williams wrote:


Zn + (Na+) + 2(H+) + 3(OH-) - (Zn++) + (Na+) + H2 + 3(OH-) ?

This was a wild-ass guess, Tim.

"Sodium hydroxide ... reacts with ... zinc; ...

This wasn't. This you can see on hundreds of Web sites by googling on
"lye zinc".

You say the H+ ion does it; then why doesn't the zinc dissolve in pH 7
water, ionized or not?

??

I'm not aware of any solution outside of electrochemistry or displacement
(where a more reactive metal begets the less reactive one) that allows
metals to be in solution *as metal*.

My equation above doesn't explicitly state this, but this is intended to
show what *might* happen when you put zinc into a lye solution. It goes in
as metallic zinc but you are dead right, then it goes into solution. I only
put it in there because I was trying to balance the equation. I am *not*
claiming to be an expert here, far from it -- I'm looking for guidance.
You appear to be skeptical that zinc will dissolve in lye. I'm real OK with
that! I'll let you know what happens.

Grant

Yup, there it is:

Zinc is amphoteric and forms salts with alkalis. For example, Zinc dissolves in
hot concentrated caustic soda solution with the liberation of hydrogen gas and
the formation of sodium zincate.

Zn + 2 NaOH == Na2ZnO2 + H2

That's similar to my equation, but written differently. Same concept though ..
put zinc metal into lye, out bubbles hydrogen, zinc dissolves. - GWE

Grant Erwin wrote:
I have some really old but strong casters which were once cleanly
galvanized but which have corroded through the zinc in many places.
They appear basically sound, though. I am contemplating heating a strong
solution of lye, then shutting off the heat (no open flame!) and putting
in the casters (sans wheel, of course) with the goal being to remove all
dirt, oil, grease, and, of course, zinc. Then I'd rinse in boiling water
after which they should self-dry quickly. Then I could brush off any rust
and prime the tops and then weld them to a plate, after which I'd paint
the plate and the casters all together, then reinstall the wheels.

OK, I took a 1-pound can of Red Devil lye, and a 10-quart stainless pot (I
have an old one I use for this kind of thing). I removed the wheels from
the casters and arranged them in the pot, then filled it with hot water from
the tap and poured in the whole can of lye. A day later, I reached into the
pan with long pliers and removed the casters and ran them under hot tap
water while scrubbing them lightly with a 3M pad. Then I dried them with a
paper towel and hit them with a water displacing spray to dry.

The heavy rust is completely gone. The areas that were rusted have a
different look, you might say they were stained black, but there isn't
any rust left. At first I thought the zinc remained, because most of the
metal was still so shiny. But after looking at it dry, in bright sunlight,
I now think the zinc plating is entirely gone as well. I'm going to weld
them onto a steel plate and I'll know for sure then if there's any zinc
left -- after spending a year doing nothing but cutting, fitting and
welding galvanized angle in the shipyards, I'll never forget that smell.

I had thought what would happen was that the lye would simply dissolve
the zinc. What I found out was that with the zinc ions in solution, they
reduced the rust back to iron, similar to electrolytic derusting, only
with no electricity. Very cool.

Grant