[sdiy] Panel Finish

[Tony Rolando]

Yes, I think it was the poly that was yellowing on my older panels.

I dropped the AL in a vat of diluted acid before printing and painting.

Tony

Scott wrote:
> Well, it was that thin oxide coating I was referring to.  My panels are still relatively bright, even after a year or 2 of being bare.  I thought aluminum oxidized to a dull gray.  That still wouldn't' be all bad, but the shiny brushed look they've got now is better.
> And as others have mentioned, I have read that nothing sticks to the oxidized aluminum, and envision a cracking, peeling finish in 10 years time..  I have no idea, though, how finishes will really hold up.
>
> -----Original Message-----
> From: David G. Dixon [mailto:dixon at interchange.ubc.ca] 
> Sent: Wednesday, April 01, 2009 11:36 AM
> To: Scott; synth-diy at dropmix.xs4all.nl
> Subject: RE: [sdiy] Panel Finish
>
> Hello, Scott.
>
> Here is the good news: Aluminum doesn't oxidize!
>
> As you may know, aluminum is characterized as a "reactive" metal because it
> is so far down on the electrochemical series.  If ground to a fine powder
> and mixed with iron oxide, it will actually catch fire (these are the simple
> ingredients of the famous "thermite" bomb).  However, aluminum has one
> all-important redeeming feature which allows us to forget all that in
> everyday use: It forms a very coherent passive layer in the presence of
> oxygen.
>
> Yes, aluminum does oxidize; very rapidly, in fact, according to the
> following reaction:
>
> 2 Al(metal) + 3/2 O2(g) ==> Al2O3(s)
>
> However, this reaction only proceeds to the extent that a mono-molecular
> layer of aluminum oxide forms on the surface.  This oxide layer is so thin
> that it is totally transparent, and the aluminum surface looks perfectly
> pristine.  The only problem with aluminum is that it has absolutely no
> resistance to acid attack.  In acid, because aluminum is so far down the
> electrochemical series (far lower than hydrogen gas), the following
> reactions will occur.  First, the oxide layer is dissolved away:
>
> Al2O3(s) + 6 HX(aq) ==> 2 AlX3(aq) + 3 H2O(l)
>
> Where X is any common acid anion (chloride, nitrate, sulfate, etc).  This
> leaves the bare aluminum underneath unprotected, and it can then react
> electrochemically with the acid (i.e., corrode) to form hydrogen gas:
>
> 2 Al(metal) + 6 HX(aq) ==> 2 AlX3(aq) + 3 H2(g)
>
> You may have noticed that aluminum foil will develop holes if used to cover
> acidic food like spaghetti sauce.  This tells you how un-resistant to acid
> it is.
>
> Indeed, some researchers (including two professors in my department) are
> looking at aluminum as a virtual "gas tank" for hydrogen-powered cars.  Of
> course, this is a totally stupid idea (sh!) because the manufacture of
> metallic aluminum (by molten salt electrolysis from anhydrous alumina in the
> famous "Hall-Heroult" cell) is one of the most energy-intensive and
> environmentally unfriendly processes around (and is also, unfortunately, the
> only industrially viable way to make aluminum).  Not only is the process
> very inefficient with respect to electricity usage, but it also converts
> vast quantities of carbon to carbon dioxide through the consumption of huge
> graphite electrodes.  Hydrogen generated in this way would cost much more
> energy to produce than that generated by simple electrohydrolysis or fuel
> cells, which can run off of fuel made from agricultural waste.  Also, in
> order to use aluminum in this way, one would have to carry around not only
> huge chunks of aluminum in ones car, but also large quantities of
> concentrated acid solution to dissolve it in (I'd really hate to be the cop
> at the scene of THAT accident!) and all of the associated
> corrosion-resistant (read: expensive) equipment with which to pump it
> around.  Oy!
>
> I am in the process of making Al synth module panels pretty much exactly
> like you are: bare aluminum with DecalPRO dry transfer decals affixed
> (www.pulsarprofx.com) and covered with acrylic clear-coat to protect it.  It
> should last indefinitely!  Just keep acid away from the bare aluminum!
>
> Cheers,
> Dave
>
> David G. Dixon
> Professor
> Department of Materials Engineering
> University of British Columbia
> 309-6350 Stores Road
> Vancouver, B.C. V6T 1Z4
> Canada
>  
> Tel 1-604-822-3679
> Fax 1-604-822-3619
>  
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>  
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>   
>> -----Original Message-----
>> From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
>> bounces at dropmix.xs4all.nl] On Behalf Of Scott
>> Sent: Wednesday, April 01, 2009 7:56 AM
>> To: synth-diy at dropmix.xs4all.nl
>> Subject: [sdiy] Panel Finish
>>
>> Is there any long term problem w/ spraying bare aluminum w/ lacquer or
>> poly?  I've been making panels by transferring an image  to the bare
>> (silver) aluminum, then coating.   Will the aluminum still oxidize under
>> the finish and cause trouble 10 or 20 years down the road?
>>
>> thanks!   - still trying to work out the best diy method for panels!  (I
>> used to (about 10 years ago now) use some translucent paper, glued on,
>> then sprayed w/ poly.  That looked great until a few years later when the
>> paper started absorbing moisture and expanding/wrinkling!  So far this
>> toner transfer is working well)  Unfortunately I like black graphics on
>> the bare metal.  I've found several people have posted great explanations
>> for their methods of making professional looking black panels w/ white
>> text, but not black text on silver.  The toner transfer does look good,
>> but I have concerns about the longevity.
>>
>> thanks again
>>
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