Acid Copper Plating over Zinc

A. Good day Mark.

Wow, cool idea about plating on the pods. I think 500 ml solutions are extremely small given the surface areas and time you will be plating. Concentrations will change quickly and dramatically.
3 L per hour filtration = 6 bath turnovers, that's quite impressive.(Hope your parts won't go swimming)
Yes, wetters are proprietary, as are brighteners for both copper and nickel. (Saccharin and formaldehydes do comprise brightener components for nickel- BUT you didn't read it here!) Mechanical burnishing may help here.
Plating acid copper directly on zinc will prove to be problematic, given the acidic nature of the copper solution attack on zinc based substrate.
Normally, a barrier plating of cyanide copper is required to "seal" the zinc prior to acid copper.(You DON'T want to go the cyanide route based on your lab scale!)
Why not try nickel only as an initial strike to seal the items,acid copper to build thickness. Burnish to brightness/smoothness, and finish with nickel again.Good cleaning, rinsing between solutions.
I understand you have a proper lab set-up, indicating you are familiar with electroplating and are conscientious regarding disposal.
KUDOS TO YOU!
Hope I didn't blow the wind out of your sails, and best of luck on your project!
Regards,

Eric, what you say there makes a great deal of sense. I'll try doing a nickel strike before the copper plating, makes a good bit of sense.
All the same though I'm having a heck of a good time fiddling with this.

A. Good day Marc.

Unfortunately, you cannot buffer an acid copper solution.(The sulfuric gives it the throw)

But, you can "buffer" a nickel solution, i.e., run a watt's nickel at elevated pH -- say 4.6-4.8. This pH will render the efficiency somewhat slower, however all you are attempting to do is lay down some metal to "seal" the zinc prior to acid copper where you are building thickness etc.
Also , there are formulations of other nickel solutions which may suit your purpose, i.e., sulphamate runs at higher pH values.
Don't forget the zinc deposit you have sprayed is EXTREMELY thin in nature, and within it are non-conductive elements.(Years ago I have used nitrocellulose lacquer and "dusted" the parts with graphite powder while the lacquer was still "wet" to gain some measure of conductivity/metallizing prior to plating)
I think 4 A/dm 2 (40 ASF) is too high, it will "burn" off/through the Zn to the substrate.
Maybe 0.5-1-0 A/dm 2 to start to get deposition started and later increase for thickness.
Hope this helps (there are MANY ways to skin a cat/fillet a fish/etc.......)
Regards,

A. Good day Marc.

We need to remember that HCl will strip zinc/zinc plated items. Wood's @ 10% HCl will strip Zn. Normally, plating on Zn requires an acid for activation, H2SO4 @ 0.5-1.0%. Avoid acidic/low ph solutions for plating zinc/zinc alloys. Again, I will reiterate using a higher pH plating solution, such as a Watt's Ni at 300 g/l NiSO4, 40 g/l NiCl (keep it low=Cl will cause base metal attack), 38 g/l H3BO3 at elevated pH values, or even a sulfamate/ semi bright Ni. Hope this helps and good luck.
Regards,

A. Hi Marc. A Wood's bath is needlessly aggressive and inefficient. It's purpose is to activate stainless steel or old nickel plating by attacking and dissolving it while simultaneously depositing a very thin fresh coat of nickel. Not to be confused with Watts bath, which is "standard" nickel plating.

Regards,

A. There are readily available conductive paints consisting of copper powder in an acrylic base, made for what you are trying to do. ("Safer Solutions" is one) You can plate directly out of an acid copper bath and avoid adding an additional step. Probably cheaper and safer to just buy the right conductive paint, than adding a nickel strike. Sealing of organic items to be plated is recommended by some, I can't say as I mostly plate non-porous items.

A. ----- Render surface conductive:

Lacquer plus graphite or copper dust
Buy a conductive paint that serves for that purpose I know that they exist but no idea where you can get those.
Could be used metallization with silver?
Palladium chloride activator? one step or two steps to create nucleation sites.

----- Apply a layer of electroless bath to make a conductive film if you have not created it yet:

Electroless copper
Electroless nickel

If you applied a layer of zinc you can choose an alkaline nickel or cyanide copper or electroless baths but they must not affect the layer of zinc.

Using the Watts bath over zinc will contaminate it due to zinc attack because of the acidity of Watts bath.

A. Woods strike will not work. You could try a sulfamate strike at the highest allowable pH and go in hot.
Sulfamate at the higher pH plates much faster and thicker, so you might get away with it.

A. Hi Ron. You posted your question on a thread about choosing the right voltage for plating, but we moved it here because the heart of it is that you can't acid copper plate onto zinc at any voltage because the copper will immersion-deposit (very little adhesion) even with no electricity applied.

In industry, the usual approach is to cyanide copper plate, but cyanide plating is so dangerous as to be out of the question for hobbyists. Another approach is a proprietary alkaline copper plating solution from EPI / Electrochemical Products Inc. [a finishing.com supporting advertiser] and possibly others. There was a patent (US3082156A) for nickel plating on zinc die castings, and decades ago I saw similar proprietary nickel plating on zinc diecastings but I don't know if anyone offers it today or not.

Regards,

A. 19th-century cyanide-free copper plating solution: Tartrate based copper plating bath.

copper sulphate ⇦this on eBay or Amazon [affil links] 35-40 gms,
Potassium sodium tartrate ⇦this on eBay or Amazon [affil links] 180-190 gms,
sodium hydroxide 50-60gms,
20 °C temp.
0,3-1,5 A/dm2

Hope it helps and good luck!

Thanks Goran! I was aware of the use of potassium sodium tartrate (Rochelle Salt) in cyanide copper plating, where it assists the cyanide in complexing the copper, but had never heard of using it without cyanide as you've introduced here. I wouldn't be terribly optimistic about its ultimate ability to produce satisfactory copper plating on zinc diecastings, but Rochelle salt is so harmless that it's certainly worth adding to the experiments :-)

Regards,

A. That is only recipe from old book (A Complete Treatise on the Electro-deposition of Metals by G.Langbein, New York 1891, page 186), so called Weils copper solution. As far as I Know before 70 -60 years Russians published small monograph on tartrate based plating solutions. Useful link:
https://www.researchgate.net/publication/268362604_Electrodeposition_of_Copper_from_Non-Cyanide_Alkaline_Solution_Containing_Tartrate

Thanks again Goran.

Regards,