"James Lerch" wrote in message
...
Greetings All,

Before I tell the story, here's a link to the results:
http://lerch.no-ip.com/atm/Projects/Anodize/

Neato!

I was wandering thru the local hardware store when I found a bottle of
concentrated sulphuric acid, which happened to be labeled as "Drain
Cleaner"...... I chuckled a little as I thought to myself "That's not
drain cleaner, that's anodizing electrolyte"

Ah, must be in a red bottle? Or possibly a store brand.

Next I added the electrolyte (maybe a pint) to the gallon bucket half
full of water. The decision on how much electrolyte to add was based
solely on the feeling of unrest that came as the bucket of solution
started getting REALLY warm (maybe 120F).

Yep, sulfuric acid makes a nice amount of heat when dissolved. Taking
precautions, I've tried to make it splatter to see if it happens, but so far
it's just gotten warm, no boiling yet. Given the amount of heat it makes, I
don't doubt it can and will splatter, I just haven't seen it yet.
*shrug*

At this point, I know I'm doing something, but the question is how
long should I let this run?

I would say until the current stops.

Other sites said to let it run until the current flow pretty
much stops, as the aluminum oxide which makes the anodizing coating is
non conductive, so a fully formed coating shouldn't conduct..

Indeed, the same process is used in millions of electrolytic capacitors.
You're using some right now, inside your computer and monitor, indeed they
are almost ubiquitous with electronics. These consist of a coil of aluminum
foil and paper, the paper being soaked with a proprietary electrolyte which
has low resistivity. (Apparently, exact composition is a tightly guarded
industry secret.)

Anyways, these capacitors degrade with time if unused - the oxide layer
decomposes and the voltage rating drops. Instead of throwing them out, you
can "reform" them by applying a small current which anodizes it (slowly so
as not to overheat it). After a long time, maybe a few hours if you are
impatient (depends how hard you push it), it'll be back up to rated voltage.
Electrolytics go up to 500V, you can imagine how thick that anodized layer
must be :-)

Not knowing how long to let the process run, I went with the "More is
better" theory and let it run till the current dropped off and the
bubble formation was nearly non existent.

Fair enough. You can also start at a low voltage, say 1-5V range, and use a
variac or adjustable power supply or steps of voltages to climb up to say 20
to 50V. To make a more consistent deposit you'd want a current-limited
supply: set it to top out at say 30V, supplying a constant 1 or 20 or 50
amperes (for however big your workpiece is) all the while until it gets
there. Consider two things: electrons (and thus current) flow as long as
there is enough voltage to overcome whatever (namely, the oxide layer), and
each number of electrons (namely, something like 26.7Ah per mole, aluminum
needs three) oxidizes a certain amount of aluminum such that it forms the
anodized layer. You can see that 1. it will take a certain number of
electrons to get to a given voltage, and 2. it takes a certain voltage for a
certain total transfer, or whatever.

I would guess hard anodizing is as high as 100V, unless there's a different
chemistry at work in that process. As I said, you can theoretically go up
to 500V, and personally I don't see any reason why you can't go beyond,
except for practical reasons of course.

It took about 40 minutes for the part to "cook" completely, IE very
little current flow, and very little bubble formation.

That long probably isn't necessary, although I doubt it hurts anything. I
once was messing with a similar weak sulfuric acid solution myself,
something I tried was anodizing aluminum, I hooked it up and immediately the
power supply grunted with effort as probably 20-30A flowed through the small
fragment, then within a few seconds, it diminished until I couldn't tell a
difference in the current level, dipping and removing the piece to check.
That was something like 6V.

I then removed
the part, and gave it a cold water rinse. At this point the part had
a gray / green tint, and lost ALL the luster it had prior to being
"Cooked"

Sounds about right.

snip

I can't comment on the dyeing...

Tim

--
"California is the breakfast state: fruits, nuts and flakes."
Website: http://webpages.charter.net/dawill/tmoranwms