Electroplating with Brass (Electrodeposition of Brass)

A. Hi Ankit,
There is actually very little difference between electroplating and electroforming except that electroforming is usually thicker. So, if you need only a very thin electroform layer, yes, it can be done in brass.

However, brass is an alloy, which means it needs strong complexors, whether cyanide or proprietary, and the more you ask of it, the more it can go wrong. Even "heavy brass plating" is only about half a mil in thickness (0.0005"), and I would probably expect trouble at greater thicknesses. Any reason you can't electroform whatever it is out of copper and then apply a decorative brass electroplate?

Luck & Regards,


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

A. Either approach should be okay, but if you are looking for bright brass an easier way to go may be to start with with nickel plating under the brass.

A. Hi Gordon. It does dissociate into copper and zinc ions. And then the copper and zinc ions deposit on the item to be plated and are reduced to copper and zinc metal, creating the brass alloy.

That is not to say it's easy to brass plate--there are difficulties: for example, copper is a much more noble metal than zinc, so we would expect the deposit to be virtually pure copper if it were plated from a simple salt (students make 1.1 volt lemon batteries and potato batteries by putting a galvanized nail and a copper penny into a lemon; that's how powerfully the copper wants to come out of solution compared to the zinc).

But when copper cyanide and zinc cyanide are mixed in a reasonable ratio, the cyanide fights hard to hold onto the copper, so the concentration of free copper ions is very low, so you are able to plate the brass alloy. Cyanide is a dangerous chemical and there are other complexers these days that allow brass plating -- but you can't do it out of a simple chloride or sulphate salt.

A. Hi Diogo.

The only thing that can be done and must be done to increase the plating speed is to increase the current density -- because moving electrons from the anode to the cathode via electric current is, according to Faraday's Law, what makes a proportional number of metal ions move from the anode to the cathode.

"Electrodeposition of Alloys: Principles & Practice"
by Abner Brenner

on AbeBooks

or eBay or

Amazon

(affil links)

How to achieve this, while avoiding consequent problems like burning, is, of course, difficult to resolve in the abstract. But impelling jets of solution onto the cathode at high speed is perhaps the most promising way, since it minimizes the thickness of the boundary layer through which the ions must diffuse and, by rapid replacement of solution, it also keeps plenty of metal ions available, rather than having the area starved for metal.

Are you using a cyanide or non-cyanide brass plating bath, Diogo?

It may be possible to increase the temperature of the bath, which leads to greater ion mobility and thus theoretically allows faster plating speed, or to increase the metal concentration -- but these things may also affect the "balance" of the bath (Copper is far more noble than zinc, so it's quite a trick that we are able to plate brass at all :-)

You might be interested in Brenner's "Electrodeposition of Alloys", because as you change voltages, currents, temperature, and concentration you have a propensity to change the alloy composition. Best of luck, and get back to us.

A. Hi Ammar. Sorry that no one helped you yet. Perhaps if you started with one particular question where you need help, the results might get better since no stranger is going to complete your entire lab project for you (and questions 2 through 4 look like they might be copied right off your assignment :-)

But as for Q1: As mentioned earlier, copper is far more noble than zinc, and will preferentially deposit from a simple salt. To counteract that and make brass plating possible, it is necessary to complex the copper with cyanide, to greatly reduce the number of free copper ions available for electrodeposition. Even when this is done, however, it requires careful balancing of all parameters to get a balanced deposit of copper and zinc. Your experiment demonstrates that if the voltage is very low, things go out of balance, with the copper too complexed for any of it to deposit; but if you increase the voltage, you overcome the complexing sufficiently to deposit a proportion of zinc.

"Modern Electroplating"
by F.A. Lowenheim

on AbeBooks

or eBay

or Amazon

(affil links)

It is noted in Lowenheim's "Modern Electroplating" →
that with some brass plating baths the proportion of zinc rises with higher current density, and for others it decreases. He includes a graph by Compton, Ehrhardt, & Bittrich for one bath which exhibits highest zinc concentration at about 0.3 A/dm2, and declining whether the current is increased or decreased. Lowenheim has an excellent theoretical and practical treatment of brass and other alloy plating baths. Please try to find a copy in your school library; if it's not there, and you can't find another good book on the subject, please suggest it to your advisor. Good luck.

Regards,

A. Hi Santosh. Most brass plating electrolyte are cyanide-based, and the cyanide complex allows practical ratios of copper and zinc to be deposited for brass deposits (today there are also some proprietary brass plating baths available that do not require the use of cyanide).

"Modern Electroplating" describes the composition of 10 different cyanide-based plating baths and includes 233 references. It is the best starting point that I know of for a theoretical investigation; but what people visiting this page may not necessarily realize is that, in general, users do not attempt to formulate electroplating baths; rather they purchase them from suppliers who have spent years perfecting them, and offer them as proprietary processes. Good luck.

Regards,

A. The Cu/Zn ratio in the deposit is not, as you might think, determined by the Cu/Zn ratio in the bath. It depends more on the cyanide/zinc ratio.

pH control is also crucial. There are two different levels at which brass is plated - one in the mid tens, one in the upper 11's, if memory serves.

Do some library research. This information is out there.

A. Hi Vasanth. Red and other color patinas can be applied to brass, but I think I am understanding you to be saying you just want your deposited brass plating to be more on the reddish side, i.e., higher in copper. The previously mentioned "Modern Electroplating" [on AbeBooks, eBay, or Amazon affil links] has all kinds of graphs on the subject, and notes & exceptions & provisos, but the general trends are higher current density, higher temperature, and lower pH generally move towards higher copper content. Good luck.

Regards,

A. Hi Mohd. There are many possible formulations for brass plating. Yours may be a perfect one, but unless a reader has worked with that particular formula they may not be able to suggest what needs adjustment. So please tell us where you found it because with a reference people can have more confidence that it's workable.

Here's what Lowenheim suggests in "Electroplating" ⇦[this on eBay , Amazon, AbeBooks affil links] :

A. Hi again, Mohd. I think you misunderstood me :-(
I am not a chemist and have not spent years developing formulations like you have. My point was that we can offer you published formulations for brass plating solutions, but I certainly can't, and I doubt that anyone can, look at your formulation and tell you what needs tweaking :-)

Here are a number of formulations from Lowenheim's "Modern Electroplating" [on AbeBooks, eBay, or Amazon affil links] :

Note to readers: We generally don't copy charts or tables from books, potentially depriving authors of the reward for their efforts. But we made an exception with these two Lowenheim books because: he passed away 40 years ago; he was a luminary whose work is not recognized widely enough; his daughter Trudy Hayden found us, gave us for free and encouraged us to distribute, a bunch of copies of his books -- so we know his family is not losing any money via this copying, and is happy to see his work widely appreciated.

Luck & Regards,

A. Hi Awder. We appended your question to a thread which includes the brass plating formulas from Lowenheim's books. But you should probably check the libraries for a copy of one of his books because there's more to surgery than choosing the scalpel :-)

Luck & Regards,

A. Hi Ahmed. What is the source of that formula? We don't like to post formulas except with their published sources because we are concerned about violation of copyrights and crowd-sourcing of trade secrets.

I hope someone can help you, but Lowenheim says in Modern Electroplating (1974):

Luck & Regards,

A. According to old Russian book, F.K.Androshenko, V.V.Orehova, K.K. Pavlovskaya: "Pirofosfatnye Elektroliti", Kiev 1965. you can try next 2 solutions:
1.
CuSO4 ....1-2 gms
ZnSO4.....1 gm
Na4P2O7...60 gms
H3C2O4----10 gms
Na2CO3....30 gms
Water......1 lit ,1A/dm2,18-20 °C temp.,brass anodes(min 80 % Cu)

2.
CuSO4 ....1-2 gms
ZnSO4.....0,8-1,5 gm
Na4P2O7...50-60 gms
Na2CO3....10-15 gms
H3BO3.....4-8 gms
Water.......1 lit,0,2-0,3 A/dm2,18-20 °C temp.,brass anodes(min 80% Cu)
Water......1 lit

Hope it helps and good luck!

Expired US patent US 2011/0052937 A1, pyrophosphate brass plating.

Hope it helps and good luck!

A. Hi Mohd. 14 formulations have already been offered on his page, and you can search the site for other threads like topic 4076, "Brass Plating Is Too Yellow" if your brass is not yellow enough.

But maybe the problem is no more complicated than not realizing that you need bright nickel plating under the brass? Please get back to us about the bright nickel plating under your brass plating or the lack of it. The usual procedure when you want dull brass is to plate directly onto the steel, but when you want bright brass to plate onto bright nickel plating.

Luck & Regards,

A. Hi Lokoja. We appended your question to a thread offering over a dozen formulations. Please take two or three paragraphs to fully describe your situation. Thanks.

Luck & Regards,

A. Hi Mohd.

Apologies. As previously noted, I haven't done hands-on brass plating formulation, and can only offer you book knowledge. But we've given you over a dozen formulation tweaks from the industry's luminaries, and referred you to topic 4076 where everyone's brass is "too yellow!". If your brass is still not yellow enough then there seem to be only two possibilities: your supplies are contaminated so your formulations are not working as they're supposed to, or your idea of "yellow" is a bit different than everyone else's and perhaps not obtainable. But good luck.

Regards,

A. Hi Nurul. I understand that you want to deposit a ternary alloy but an important question is why, i.e., what is your actual project or assignment? Because 99% of what we can tell will probably be worthless information to you. For example, and for starters, by far the best way to deposit a ternary alloy is to buy a proprietary plating solution already developed for that purpose...

The reason is that the three metals will have greatly differing deposition potentials; so, if you just mix ions of the three different metals together, copper will deposit to the virtual complete exclusion of the other two metals even if you put 100X as much of them into the solution. The only way you will get an alloy that isn't almost totally copper is by tightly complexing the copper with cyanide or another efficient complexer. Are you trained and equipped to deal with cyanide?

But maybe buying a proprietary plating solution totally defeats the purpose of your project? So please take two or three paragraphs to explain who you are and exactly what your project is that requires you to deposit a ternary alloy. Any particular alloy? When we fully understand exactly what you are trying to do and why, I'm very confident that we can expeditiously help you.

Luck & Regards,