Bronze plating solution composition, analysis, and parameters

A. Remberto,
Macdermid has a bronze solution that we use for antique gold and nickel-free plating for jewellery. I do not know the hardness but you could try Macdermid.

Regards

A. Mr. Brito
We also use some Macdermid chemicals to make up a Bronze plating bath. We use oxygen free copper anodes, potassium stannate, potassium hydroxide, potassium cyanide, and Rocheltex.

Concentrations are as follows:

Copper 5 oz/gal
Stannate 1.5 oz/gal
Hydroxide 0.7 oz/gal
Cyanide 5 oz/gal

Sincerely,

"The Properties of Electrodeposited Metals and Alloys"
by William Safranek

on eBay or

AbeBooks

or Amazon

(affil links)

A. Hi Remberto,
Most plating textbooks will give you bronze formulations. "Modern Electroplating" [on AbeBooks, eBay, or Amazon affil links] , for example, offers:

Potassium stannate 60 g/l
Potassium hydroxide 7.5 g/l
Copper cyanide 40 g/l
Potassium cyanide 90 g/l
Free potassium cyanide 34 g/l
(plus wetting agent, addition agent, brightener)

It looks like nearly any bronze deposit will be at least 40 Rc (although this is based on a conversion chart because the data is usually offered in kg/mm2 microhardness), but Safranek ⇨
offers lots of data on hardness vs. other parameters and says hardness is maximum at 15% tin and when operating the bath at lower than usual temperatures.

Readers: Please don't assign other readers the project of supplying you with dry abstract data! Please try your best to make the forum interesting to all by introducing yourself, what you want to plate, and why such data will help. Thanks!

Luck & Regards,

A. Hi Terry. The vendors of the solutions, unless you are using home-brews, have procedures that are proven.

The Metal Finishing Guidebook has a nice section on analysis.

Commercial books such as The Chemical Analysis of Electroplating Solutions [affil link on Amazon or eBay or AbeBooks affil links] are good.

The Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon affil links] edited by Durney has an analysis section.

Do not forget to analyze your prep cleaners and acids also.

A. Don't blindly accept any published analysis procedure, even Metal Finishing's. Always prepare a bench top (laboratory) test solution and perform the analysis procedure on it. Then muck up the test solutions; i.e. add carbonates to your alkaline cleaners and cyanide solutions, add copper to your acid activators. Analyze these test solutions with the same procedure you initially tried. If you get the same results and the results agree with what you actually put in, then you got a reliable procedure. We found that the normal analysis procedure for alkaline solutions was useful for only newly make baths. As the baths aged they got stronger when using a phenolphthalein titration endpoint. We now use methyl orange ⇦ this on eBay or Amazon [affil links] and phenolphthalein ⇦ this on eBay & Amazon [affil links] endpoints (to calculate carbonate increase and hydroxide decrease). This method has given us some measure of reliability for determining concentration of active ingredients in alkaline cleaners.

A. DEAR FRIEND,
THERE ARE LOTS OF VARIETY OF WETTING AGENTS UTILIZED IN SEVERAL ALLOY PLATING PROCESSES. THEY ARE IN FACT CONFIDENTIAL AND CAN BE SYNTHESIZED VERY EASILY.

A. Hi Abbas,
Proprietary brass plating baths are a much better idea for small processors like imitation jewelry makers, and their wetting agents are trade secret, but if you just want to do some experiments, sodium lauryl sulphate and sodium laureth sulphate are the most readily available wetting agents and are used in a variety of applications including some electroplating.
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Cathodic current density between 20 and 50 ASF; anodic current density less than 20 ASF.
(Assuming it is a cyanide bath!)

A. I would define plating as a process to deposit a metal or alloy onto a surface by means of a liquid that contains metallic ions. Now, how do you know the part was plated if you didn't do it? Could it be processed by a different method? I can think of at least five different processes that can produce a rather thick layer like that.

1- conventional thermospray (porous fair bond)
2- plasma spray (less porous better bond)
3- HVOF (almost zero pores good bond)
4- spark deposition (zero pores weld bond)
5- high energy cladding (same).

All have advantages and disadvantages over plating of course, but are not proprietary.

P.S. Frequent readers are welcome to remind me or correct me.

A. If the Cu-Sn plating contains phosphorus, it was most likely deposited using an alkaline pyrophosphate solution (in order to avoid the use of cyanide in the plating bath). No ASM specification currently exists to govern alkaline Cu-Sn electroplating. However, AMS2429 governs plating production of 90Cu-10Sn nitriding stop-off in a cyanide acid bath. The cyanide acid bath is a much more efficient and time-friendly process, and will typically provide a much more uniform plating layer than the alkaline bath; however, due to environmental and health considerations with the cyanide bath, more shops are considering use of the pyrophosphate alkaline baths.

A. Hi, Chuck. Considering the wastewater treatment uncertainties and the safety dangers, no one would use cyanide if it weren't better and cheaper :-)

But pyrophosphate can work, and is available from the site's supporting advertiser EPI / Electrochemical Products Inc. [a finishing.com supporting advertiser] and probably other vendors; such vendors will offer technical data sheets for the setup.

One further possibility (which has found use on brass lamps) is to do bright nickel plating and follow it with a bronze-toned electrophoretic lacquer instead of brass or bronze plating. Good luck.
Regards,

A. Hi Dawn. I'm not fully understanding your description but am guessing that your plating racks (the fixtures that your parts are mounted on) are equipped with "auxiliary anodes" -- electrodes which are not designed to dissolve into the solution like consumable anodes, but to selectively deliver electricity to specific areas of your parts (like deep recesses)?

The "right" or "best" material for auxiliary anodes is usually platinum clad titanium, as it will have a very long life, but it is very expensive. For a bronze plating bath you want your consumable anodes of copper to dissolve into the solution, but you'd like your auxiliary anodes to last forever.

Regards,

A. If mild steel is causing problems, I would personally try something else.
Hard copper comes to mind as being a bit less contaminating than iron. If it dissolves too fast it will throw off your copper - tin ratio.

I am not aware of any 400 series tool steel. There is 400 series stainless steel which is used for knives, etc.
"tool Steel" would normally be a 4xxx series.

400 series nickel rod might be a decent alternative. No chrome and no steel. I think that it would dissolve slower, but I am NOT positive about that. I have used it for an aux anode in selective nickel planting.

A. If the bronze plating solution is alkaline, then the titanium will anodize and stop passing current (just like titanium anode baskets in a cyanide solution).

A. The anodes for alkaline bronze plating is MMO = mixed metal oxide.

A. Do you add copper cyanide directly? Is there now a different person doing the additions?

The only thing I can think of is that the CuCN being added is not properly dissolving. I have never run one of these baths, but the way I would do this is to suspend the CuCN in warm DI water, then add sufficient NaCN such that a transparent, light yellow solution is obtained.

Needless to say, this should all be done with a proper fume removal system by a trained individual wearing the prescribed PPE.

A. Hi Christina. Although it is obviously a poor idea to leave parts hanging in a solution, sodium hydroxide and cyanide probably won't substantially hurt the parts if they are bare steel. If they are zinc diecastings though, or preplated/coated with anything, they're probably ruined. Get back to us with what you find, please.

Regards,