[NewCandle] Silver aluminum screening experiment

[Keith Nagel]

Hey Nick,

You write:
>I tend to think that some of the growth
>betrays subtle alloying from other constituents of the
>aluminum.

At first I thought perhaps the aluminum was codepositing
with the silver, but I have come to find over the years
that it is next to impossible to get aluminum to plate
out of an aqueous solution, even as an alloy with
other metals ( especially so, as that was what I was
trying to do ). Of course, one could certainly experiment
with this by using copper rather than aluminum as the
displacing metal, or doping with copper nitrate.

>Another thing I noticed was that even with etching of
>the Al surface before putting it in the flask, the
>silver dendrites began at only a comparative few
>distinct nucleation sites.  Maybe 8 or 10 on the
>piece.  By chance?  Or maybe micro-gouges where the
>native oxide was cracked a bit.

Yes. Once the process starts, the silver becomes
the cathode and reduction occurs there at the
expense of aluminum dissolution elsewhere. You
can see from my concentration study that it is
possible to prevent that from happening by making
the solution so dense that all the aluminum surface
gets covered by silver. Then, no growth.

Etching with aluminum will create more possible
growth sites. If you can electropolish a piece
of aluminum to get a truly flat and uniform
surface, that would be more instructive.

Perhaps you should image a piece of alumninum
( etched or polished ) after 1 hour of exposure to 
the silver solution and
look for those nascent growth sites. This might
give us more insight into that important initial process.

I'm pleased you are finding this system as beautiful to
work with as I have. I like carbon, and I wouldn't
be here without it, but I assert it is not the only
game in town. I consider this silver displacement system to be a form
of artificial life. Imagine my delight when I discovered
that growth on one of my solid plates was stimulated
by sunlight and grew towards the light! Not really
surprising as silver is photosensitive, but at what
point do you stop talking about these things as dumb
hunks of metal and start talking about them as plants?

K.