"Pete Keillor" wrote
in message
...
On Tue, 21 Dec 2010 13:17:11 -0500, "Phil
Kangas"
wrote:


"Pete Keillor" wrote
in message
. ..
On Tue, 21 Dec 2010 06:00:10 -0500,
lid wrote:

On Mon, 20 Dec 2010 21:12:54 -0500, "Phil
Kangas"
wrote:

I'm going to try this url to see if it works.
This video is of mercury attacking aluminum.
Can you explain the reaction?
phil k.



http://tinyurl.com/286pl63




And now you know why it is illegal to bring
mercury filled
thermometers onto commercial aircraft flights.
Dave

Just a guess. If mercury alloys with or
dissolves aluminum, then the
dissolved aluminum would react rapidly with
oxygen to aluminum oxide,
and being dissolved be unable to form the
tough
aluminum oxide coating
that normally stops this reaction. So the
aluminum is depleted in
solution, more dissoves, and so on.

Pete Keillor

So the mercury has a greater affinity for oxygen
than the
aluminum? What is the grey matter produced from
the
reaction? Is it a hazardous substance?
phil k.


No, I don't think the mercury is oxidizing.
It's just providing a
source of aluminum to oxidize, and the aluminum
can't form a stable
oxide coating, which on bare aluminum happens in
seconds. The only
role of the mercury is to form a semiliquid
alloy with the aluminum,
and keep doing that as aluminum in the alloy
reacts with oxygen.

If I'm correct, the grey stuff would just be
aluminum oxide, probably
contaminated with mercury. The mercury would
make it hazardous.
Aluminum oxide by itself is a very good
insulator to very high
temperatures, also very good against corrosion.
Which is why when it
forms directly on aluminum metal it protects the
metal quite well. It
just can't form a tightly bonded layer to
aluminum when forming on the
mercury alloy.

In 1980 I worked on an experimental cell to
electolytically produce
magnesium and chlorine gas from a molten salt
bath at 700 C. Steel
lasted days at best in there. The 99.5% alumina
(aluminum oxide)
brick the cell was constructed from was as good
at shutdown as when
the thing was constructed. There were about
200,000 bricks in that
cell. It wasn't cheap.

Pete Keillor

For some crazy reason I can't stop thinking about
this experiment.
The mercury appears to head for the saw cut end
first and reacts
with it pretty fast. But then it stops producing
that gray stuff on the
cut end and goes to work on the stock oxide layer.
Then it is
bubbling at the entry line which leads me to think
there must be
gas that is being released by the reaction.
Oxygen? The oxide
layer on the cut end would not be as thick as the
stock layer.
And the dark gray color? WTF Was the aluminum
surface
scratched after the mercury was put on giving it a
path to go to
work?
phil k.