Anodizing

[doktor]

I found this web site http://sites.gulf.net/riders/anodize.htm
and was wondering if anyone has done this. It sounds fairly easy although taking it to a shop and having them do it would be easier still. I mean this is sulfiric acid and stuff. So if anyone has tried it let me know if its easy dangerous or otherwise. Thanks

 

[vdi_nenna]

I'd say be very careful. In high school I was doing an experiment in biology and I opened a bottle w/ Sulfuric Acid and just the fumes cause a super strong burning sensation in my sinus and lungs. Bad stuff. Also, when anodizing, a small current is used, I'm not too sure how, but it sounds like a bad combo to mess with.

My brother told me to use 2:1 or 1:1 clear vinager and water. Let it soak for a few hours, then wash with water and dry off completely. May not be as effective, but it sure is safer.

Be careful.

Vince

 

[grataku]

It sounds like fun, if you are not afraid of chemistry AND if you start with a very small scale set up.
The instructions are somehow vague and so you better get a handle on exactly what kind of concentrations you need and how much current. I am thinking you are going to want to do aluminum panels not guns, right? If the figures given in the guide are correct, you may need an actual car battery as a current source maybe with a rehostat to control the anodization rate. You should see an active and uniform H2 evolution, not too active, if you don't see that it means that your part is dirty or you don't have enough current to get the job done. That will result in uneven surface activation and bad coloring.
Avoid using surfactants to clean the part stick to isopropanol to degrease, and then go to acetic acid (fairly concentrated, the real deal not vinager) or nitric (fairly diluted). Do not expose the surfaces that have been in the acid to air. What I mean is wash the acid off with distilled water then, without leaving the H2O drip off, quickly dunk the piece in the sulfuric acid solution and fire up the current.
NO metal other than Al should be in the anodization bath at any time and you should make sure that you have a good electrical contact between the the piece and the electrode.

I thought about anodizing myself, the problem is to get a good looking surface to start with. Fine sand blasting or brushing would be great but since I don't have the setup to do either I leave it to the pros.

 

[GRollins]

grataku,
I'm interested in the site, but haven't been able to link to it yet. This PC (at work) keeps looking at me cross-eyed when I try to go there.
However, whilst I'm waiting to get through, two things that work well for cleaning and/or surfacing Al:
1) Ordinary sandpaper. Aluminum is a fairly soft metal; it's not hard to sand. Anywhere from, say, 50 grit, on up to about 220-320 grit will give you a range of 'brushed' finishes. Surprisingly, the coarser end of the spectrum (80-100 grit) will give you a surface about like you're accustomed to seeing on 'real' gear. I would have thought that it would take finer grits, but this is something that I've played with off and on. Use even pressure and long, straight strokes. Even one curved or hooked stroke will show against the light and take several more strokes to erase.
2) Sodium hydroxide (aka Lye, Drain Cleaner, etc.) leaves a very nice, soft looking, matte finish on aluminum. You either like the result or you don't; you only get the one result. Ten or twenty minutes submersion in a solution of 1 tablespoon sodium hydroxide/1 quart water will do just fine. Sometimes I use 2 tablespoons. Use a plastic or glass container--do not use a metal container. Glass baking dishes work nicely. The reaction will be slow to start. Do not heat. Just be patient. You will get hydrogen gas, so no smoking and no candlelit dinners, even though the amount of H2 given off is so small as to not support prolonged combustion. In fact, you'd have to work at it to get it to light in the first place, but play it safe. When you're done, pour the rest down the drain and get a clear drain as a fringe benefit.
Both of these techniques have the advange of being cheap. Use normal precautions when working with sodium hydroxide, as it's not mother's milk, but it isn't going to climb out of the container and bite you, either. Just use your noodle, okay?
Note that Audio Research uses brushed aluminum fronts with no anodizing as far as I can tell. If you happen to like that look (I prefer black or gold, myself), you can do it cheaply and quickly at home with option number 1. I use #2 for the aluminum ground plates I make to link the big bulk caps in power supplies. There's no reason not to use it for a face plate.
Back to trying to get to the anodizing site...

Grey

 

[GRollins]

Okay, got in first try, that time.
Fascinating. Rit dye after the sulfuric acid? Hmmm. One wonders if the same result would result from dying the metal after immersion in a sodium hydroxide solution.
Sounds like an excuse for an Evil Experiment...I will report soon.

Grey

(Grey exits stage left, grubbing hands together in proper Mad Scientist fashion, to the sound of demented, cackling laughter...)

 

[Koy]

I have heared about using FeCl3 for aluminum several years ago. How do you get black colour after sodium hydroxide? It results in gray surface. You have to add some dye.

 

[GRollins]

Using Lye as a precursor to dyeing the metal does not work. The dye does not 'take.' I fizzed a small scrap of .040" aluminum in a sodium hydroxide solution for about 10 minutes, then rinsed it and put it in a bath of Rit Yellow #1 for 2 hours while I was busy doing other things. Even after that length of time, there was no detectable color to the metal.
Note that there are about a thousand variables I could play with here: Time, temperature, concentrations of solutions, in addition to adding current (which I did not do). I did not pursue the variations, as it would mean that I'd have to break out all my old chemistry texts and study up on things that would not have a direct bearing on getting sound out of my system. If someone wants to play with this more, please do, and report any results.
A brain twister: Since I was using a base instead of an acid, perhaps I should use current, but reverse polarity. Assuming that such a thing were to work, would it be proper to refer to the result as "Cathodizing?"
My reasoning (presumed faulty at this point) for those who thought that I'd lost my mind, was thus: Placing aluminum in sulfuric acid will yield aluminum sulfate. Aluminum sulfate is very soluble and will not remain on the surface of the metal, especially after rinsing. The net effect would be to give the metal a thorough cleaning prior to immersion in dye. Perhaps dye adheres to (pure) aluminum, but not to aluminum oxide. Since the aluminum hydroxide created in the lye bath also (presumably--it's not especially soluble in water, but is soluble in alkaline solutions such as the lye bath) leaves the surface of the metal, I was hoping for a clean aluminum surface to which (with luck) the dye might adhere. The role of the current? Dunno. My guess/hope was that it was there to assist in destruction of the aluminum oxide (think rubies and sapphires, here) coating on the metal. Didn't work out. As I said above, there are a lot of variables here. It's possible that judicious juggling of parameters would do the trick. It might also waste a lot of time.
Koy:
When I use a sodium hydroxide bath, the metal comes out silver, not gray, albeit with a matte finish. Yes, it looks a bit gray while in the solution, but not after rinsing. I'm not sure how you're getting a gray surface. A reliable gray finish might be attractive if we can figure out how you're getting it.

Grey

 

[Jon T]

The current in the anodizing process causes aluminum oxide to form on the surface of the metal. The sulfuric acid is just an electrolyte -- you could use others, but you must be sure that it doesn't react when a current is passed through it and it doesn't dissolve the aluminum. (i.e. a salt solution will form sodium hydroxide a chlorine gas when you run a current through it and nitric acid will eat your Al)

Anodizing is basically the electrolysis of water. The H2O molecules split into hydrogen and oxygen ions. The negatively charged oxygen ions are attracted to the positively charged anode and react with the surface of the aluminum to form an oxide layer. The hydrogen ions go to the cathode and are released as H2 gas.

The dye penetrates pores in the oxide structure and are then sealed in place by the final boiling step that converts the oxide to a hydrated form. The dye will not stick to pure aluminum.

I'm not entirely sure what is happening when you use Sodium Hydroxide. I know that it can be used instead of nitric acid to prepare a surface for anodizing and that if you leave it in long enough, it will eat away the aluminum. It may be as simple as just being an etching process that leaves a rough, opaque surface, similar to etching glass with acid.

-Jon