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12AX7
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[*] posted on 16-5-2005 at 23:11
Copper electroplating


Need bright finish plating copper on graphite. Have tried three useless electrolytes, need help. Google has proven useless...

Tim
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[*] posted on 17-5-2005 at 02:55
Copper Sulphate


Try that one. It worked for my nephew when I demonstrated on carbon rods for his
science project.




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[*] posted on 17-5-2005 at 03:31


Any idea for concentration, current density, alignment of moon with...?

Tim
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[*] posted on 17-5-2005 at 04:31
Concentration


If the solution is a deep blue color than your concentration is more than high enough.
How much voltage/amperage are you running ?




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[*] posted on 17-5-2005 at 04:45


Found this (table 4) :)
http://www.pfonline.com/articles/pfd0014.html

I was running maybe 20-100mA/in^2, about 20 ohms in series with my 5V power supply (over about 4 square inches).

Tim
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[*] posted on 17-5-2005 at 12:54


12AX7,

Bright copper deposit is not easy to get. There is lots of info on the net, but I did some experiments with copper sulfate here.

Professionals use cyanide salts. Very poisonous. The best plating I ever did was nickel plating using ascorbic acid (vitamin C) look here.

I would try some vitamin C additive, although it may precipitate the copper.

Good luck.
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[*] posted on 17-5-2005 at 23:34


Copper Sulfate is what I use for my plating projects.
IRC the concentration only matters against the calculations you consider. How much copper do I want to plate? How many years do I want to do it in?

Consider:
2bplated: Cu(2+) + 2e- --> Cu(s) at the Cathode.. Ered = 0.3419

Sacr. Cu: Cu(s) --> Cu(2+) + 2e- at the anode.

So the e- coef is 2. take your average amperage and the e- coef and drop it into your calculations. (plug and chug). and you will see how long it will take you to do the plating if optimal conditions.

Then you can decide what concentration of the CuSO4 you want to use. If you have a Cu anode, more Cu will go into solution at the same rate as it comes out of solution. I have used 0.1 M solutions to do objects that are in close proximity (around 6 inches apart), I have also used the... 'eh... the solution is transparent/blue, that will do' method for larger objects. Be mindful that nature tends to take the shortest path, so you might have to rotate your object every set time period if you want even coating.

If you already know all of this, my point is that using 20-100 mA it will take awhile to get any substantial coating. (but I guess this also depends on how we differ time)

Useful equations:
#Coulombs = (amps)(sec)
Mol(e-) = #coulombs (c) / 96,500(c/mol)
mol(subst) = mol(e-)/n((e-)coef)
grams = mol * g/mol
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[*] posted on 18-5-2005 at 01:47


Thanks for the details but deposition rate isn't really a worry (nor throwing power, I was just going to use two anodes on either side anyway :) ), getting a tight, bright coating is. So far I've only had loose, foamy, red stuff, no matter what the current. Oh, and I tried a previous solution with a sugar addition, to no avail.

Gonna go shopping for some real CuSO4 tomorrow I guess...

Tim

[Edited on 18-5-2005 by 12AX7]
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[*] posted on 18-5-2005 at 08:25


when choosing materials to go into an electrolysis bath, you must allways give their standard reduction potentials a quick look over to make sure Cu is what will be reduced. (and hopefully Cu is also oxidized). you want the reduction potentials for the reduced to be as most pos/least neg. and the oxidation (still using the same reduction potential) to be most neg/least pos.

CuSO4 is a clear blue liquid, or as a aqua blue colored powder. It is considered a poison if that helps.
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[*] posted on 18-5-2005 at 16:22


I had a recipe from an electroplating book that I had a while ago. It contained CuSO4, H2SO4, a tiny bit of HCl, and a very tiny bit of thiourea. If you search the technochemistry section of this board for an electroplating thread (by Tacho IIRC), I'm pretty sure I gave the ratios there, but I can't remember them currently.



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[*] posted on 21-5-2005 at 16:20


Cyrus is right, it generally takes more than just CuSO4 to plate. (Many years ago I worked in a plating shop.) The acid Cu salt plating baths all require a small addition of the associated acid (sulfuric for copper sulfate, fluoboric for copper fluoborate, etc), plus a nearly microscopic amount of HCl for a few Cl ions, like a few ml per 100 gallons. Various carriers and brighteners (usually organic) also help with leveling, smoothness, etc. Agitation is usually required, too, either mechanical, clean air, or both.

Almost all workpiece materials need an initial strike plate of a few hundredths of a mil, or a non-conductive coating may form over the material the instant you drop it an acid-salt bath. The strike is usually done with a cyanide bath, but can also be done with a very expensive electroless solution. It usually helps to rinse the piece in a very dilute solution of the associated acid (3-5% v/v) before placing it in the bath. Some materials, like iron or zinc and their alloys, won’t plate in an acid bath at all, so you need an alkaline bath like copper pyrophosphate. In any bath, your anodes must be high purity, low oxide copper.

Also, when setting the current, it’s not total amps that are important, but amps-per-square-foot (“ASF”). Anywhere from 20 to 60 ASF is best in acid Cu, IIRC. Voltage should not exceed 12VDC.

finishing.com has a decent forum for particular questions. Also google’ing acid copper plating ASF will give you a ton of useful/interesting hits, including recipes.

Z
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[*] posted on 7-10-2006 at 08:15


Well, if no one minds me resurrecting an old topic, I had some success this morning after work with getting a nice SHINY coating of copper on a quarter.

For those who might be interested, here's how:

I spent some time last night surfing, looking up what additives go into a copper plating bath besides CuSO4. The thing that struck me was a series of pages that mentioned Thiourea. Knowing thta a variant of this is contained in Tanr-X, I decided to add that to some copper salts and see what happened. The results weren't encouraging at first. It looked like a black sooty deposit building up on the cathode (not like copper at all!) but I was used to this happening, and decided to see what happened if i just let the reaction keep going. Well, after a minute or two of plating, I removed the cathode, wiped off the black deposit, and voila! a layer of copper that was shinier than the metal it had been plated over!

So, the whole process from start to finish, to see if anyone else who wants to can duplicate my results:

1. Make a saturated solution of MgSO4 (plain old epsom salt)
2. Use a copper anode and an aluminum, copper, or carbon cathode (tried them all, they all work for this part)
3. I used 6v DC at 2.1A
4. A precipitate of Cu(OH)2 will form, allow the reaction to continue until you have "a bunch of it" (about an hour)
5. Filter the solution (which will now be very blue) to get the Copper Hydroxide (which will be a blue gooey mess)
6. Dissolve the Copper Hydrovide in dilute acetic acid, I used about 200ml. This makes Copper Acetate with some excess acetic acid hanging around.
7. Add about 10ml of Tarn-X to the copper acetate.
8. Use a copper anode and the object to be plated as a cathode, I used 9V DC (simple 9v battery) as a power supply.
9. Gently agitate the cathode for about 2 minutes, or longer to get a thicker copper layer.
10. Remove the cathode and wipe clean, optionally, clean further with Tarn-X or acetone.

Tell me if this works as well for you as it did for me.




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[*] posted on 7-10-2006 at 09:19


Hmm, thiourea seems to be the key here.

"Tarn-X MSDS" shows thiourea, sulfamic acid and a surfactant as ingredients. Will have to pick up a bottle some time.

Tim




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[*] posted on 7-10-2006 at 20:57


Is' tarn-x' one of those jewellery polishing solutions where you just drop your goodies in and it goes shiny? Maybe I can find a local equivalent.



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[*] posted on 15-6-2007 at 21:27


Hmm, that reminds me, I'm finally doing real copper electroplate, and it's coming out well too.

The lynch pin was Tarn-X.

My bath is roughly 20g/100ml CuSO4.5H2O (recrystallized for idle enjoyment, excessively pure compared to what all else is in here), maybe 20ml H2SO4 (~92%) and maybe 500ml total (the balance being tap water...eww, calcium). About five drops of Tarn-X, giving a white precipitate (detergents), supply the thiourea necessary to get a useful plate. Obviously, I have been exceedingly lax in the blend.

Right now I have this in a polypropylene container with flattened copper tubing winding around inside. The copper strap is connected to the positive supply via a 3.9 ohm 5W resistor, and the cathode substrate is my graphite chlorate cell anode (having had its acidy-chloriney-salty content leached out much better this time, as I'm replating its top connection for good this time *knock on wood*), hanging from the ceiling with some wires.

The supply is about 4V, and the resistor seems to be getting pretty warm (a couple of watts corresponds to a cell voltage of 1-2V, typical for copper), so I should have a deposit of roughly...hmm what will I have...

I want to run for about 36 hours. Let's assume current is 1A. That's 129.6 kiloseconds, or about as many kilocoulombs. A faraday is C/mol, so dividing I get 1.34 mol e-, or 0.67 mol Cu, or 52.7 grams.

I have a square prismatic surface of about 1.5 x 1.5" plus 1.5 x 3" * 4 sides, or 20.25 in^2, or 130 cm^2. This gives current as 7.6 mA/cm^2, rather low. (Fair enough, I don't have any circulation -- the slow rate will help out with the diffusion!) The deposit therefore will be around 0.4g/cm^2, or 13 ounce.

I might go and increase the current flow...

Tim




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[*] posted on 9-2-2008 at 23:02


So do you think plain old urea would work also? I suppose I'll just have to try it.
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[*] posted on 9-2-2008 at 23:55


I've tried it, to no success.

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[*] posted on 10-2-2008 at 01:57


have you tried PCR? (periodic current reversal)
you could make that with a simple astable a relay and a resistor.

you simply forwards charge 90% of the time and reverse charge 10% of the time, I think you can do it with the same mark/space ratio 50:50 using 10% of the current as reverse bias also.

basicaly it`s stops the plating from going spongy, it can also be used to recharge ordinary zinc/carbon cells too.

it`s worth a shot and wouldn`t take above 20 mins to knock up.

I`v found that having your copper sulphate soln too strong will also make the plating spongy, try something like a 10% CuSO4 soln first.


[Edited on 10-2-2008 by YT2095]




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[*] posted on 10-2-2008 at 08:54


Excessive current density also produces spongy deposit, even in the presence of thiourea.

Tim




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