Plating Aluminum with copper, electrolysis or other?

[Flashman]

Howdy good folks,

 

I've gotten myself into a bit of a conundrum. I need some copper plating on an aluminum alloy surface. My chemistry is about 20 years rusty, but I understand this is meant to be "difficult" to "unpossible" with a simple CuSO4 electroplating setup.

 

However, I remember achieving a reasonable plating on aluminum before, many years back, when I was a kid with a model train transformer and a bag of CuSO4...

 

So, been looking around here and on the rest of the net for tips... it occurs to me that I could use some method not regarded as commercially viable, either due to time factors, or current consumed or whatever. I don't really care about the quality of the plating, in as much as it can be porous or rough or streaky or lumpy or have green and purple spots in it, as long as it stays more or less stuck to the aluminum, and is more or less a copper surface.

 

Now, for some odd reason instead of trying to figure out exactly how I did it, I thought I'd start out with some stuff I pulled up of the web...

http://chestofbooks.com/reference/Henley-s-20th-Century-Formulas-Recipes-Processes-Vol3/Plating-of-Aluminum.html

 

""Make a bath of cupric sulphate, 30 parts; cream of tartar, 30 parts; soda, 25 parts; water, 1,000 parts. After well scouring the objects to be coppered, immerse in the bath.""

 

So last night I tried that, with baking soda, I was figuring with cream of tartar and either baking soda or washing soda, I'd end up with Rochelle salt, the baking soda would just make more carbon dioxide. Scrubbed a sample piece of aluminum with steel wool and dilute sodium hydroxide, rinsed it and put it straight in there, for an hour, nothing, then put it in a warm water bath, nothing... not even a hint of a tint on the darn thing... bah. I was hoping at least to get something of a strike coat (is that the right word) so I could electroplate more on top.

 

Now I figured I may as well try some current through that solution since Rochelle salt is recommended in other electroplating recipes, so gave it about 6 volts and it fizzed merrily and gave me a peel off sheet of copper foil.

 

So, I scrubbed it off with steel wool and NaOH again and tried again with minimum voltage, half a volt give or take, and 10 minutes gave it a tint I couldn't rub off with a paper towel, looks promising..

 

Giving it an hour or two at that sometime today to see what happens.

 

Anyway, complete and abject failure of the bath in the first place had me wondering if the "soda" should have been lye. Also wondering if it should be aiming at an excess of tartaric acid or not to be a little acidic, didn't know whether proportions were by weight or volume, mixed it by volume.

 

Still also trying to figure what "went right" when I did it so many years back, I was plating all sorts of scraps just of the hell of it, might have had a carbon anode, might have had a nail, so don't know what the hell my solution ended up containing by the time I got the aluminum in it. Could have been acidic by then with sulphuric acid due to depletion. Also used tap water, which had at the time flouride ions in it, which I've heard mentioned for plating aluminum...

 

Anyway, what I need is some way to get some sort of copper plating on aluminum alloy with "household" chemicals, don't want to be messing around with cyanides or anything that takes 2 weeks to get hold of.

 

Thanks for any hints about what is supposed to happen, and how to tweak things,

 

Flashman.

[Mr Skeptic]

You may also consider anodizing aluminum. Some of the aspects to anodizing aluminum would be relevant to electroplating aluminum, as for both processes you need to deal with the aluminum oxide layer. Also, the porous nature of anodized aluminum should hold onto any coating much better to prevent it from peeling off.

[Flashman]

Thanks, I wanted to anodize something else, but been hitting a brick wall locally for getting sulphuric acid, well as battery acid anyway.

 

I wouldn't like to think of trying to plate on top of anodizing, even if it wasn't sealed, I'd be thinking the tubes would plug early, and you wouldn't get anything like a plating on it. If I just wanted it copper colored it would probably be a better way to go. I need the copper for it's chemical properties rather than it's appearance.

[Mr Skeptic]

In the article about anodizing, it mentioned that copper in aluminum alloys made it more prone to corrosion. I dunno if that has any bearing on electroplating as well though.

 

As for sulfuric acid, it should be pretty easy to get. Others here should know where.

[Flashman]

Thanks for pointing that out, I'm not particularly worried about corrosion at the moment. This will be something of a proof of concept thing. Not quite sure but I think the alloy involved might have a small fraction in it already.

 

I'm reading about zincate baths to prep the aluminum, but I would rather steer clear of zinc because it has effects on the process I'm trying to achieve with the copper. The copper is required as a catalyst. The part will see heat up to around 150C but normally about 100C. I'm thinking the zinc will migrate to the surface, which would be bad, and any porosity of the surface would let the zinc get involved. This would tend to form acids, and I would have a corrosion problem.

 

Hmmm pondering stannate baths (tin) gotta figure how the heck I would get tin or tin oxide, and whether it would mess anything up like I suspect zinc would.... wondering if food cans have any amount of tin on them still and whether I could get tin oxide by boiling them in 3% H2O2...

 

What I seem to be seeing happening is that at .5V I can get a "tint" coating of copper attached to the aluminum, which won't rub off with a paper towel or scratch with a fingernail. However, I'm not sure but I don't seem to get much of an increase in that plating with time at .5V, it seems like it stops at some point. Therefore having got what seemed like a firm foundation, I upped voltage to 1.5 and got peeling copper foil again, leaving the aluminum clean and scratching off. This is on a test piece that has been scoured with steel wool in a sodium hydroxide solution. So is there some voltage at which it's "blowing off" the plate? Or some critical voltage where I can get it to continue plating reallllly slowly?

 

Bugger! Just found out tin might be as bad as zinc. They both catalytically promote an oxidation reaction, which I do not want. Don't know if I can figure out which is the "least worst". I think I had it figured that zinc would only be a problem in the upper temperature range. Tin is usually in combination with something like nickel or platinum, so trying to find out what it does on it's own or in combo with copper is difficult.

[watchitburn]

Most Plumbing Solder is about 95% Tin with some copper and selenium in it, should work out, I've used it for other experiments that required tin.