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topic 28032

Electroplating with Brass (Electrodeposition of Brass)


A discussion started in 2004 but continuing through 2019

2004

Q. Brass is an alloy of zinc and copper. How then is it possible to electroplate with brass? Why doesn't the brass dissociate in the bath into copper and zinc?

Gordon James Stopps
hobbyist - Toronto, Ontario, Canada


2004

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.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey
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Need to Speed Up Deposition in Brass Plating

2003

Q. What are the conditions of work of a brass bath to get a good speed of deposition in brass bath top layer?

Diogo Cavalcanti
Home Hardware - Caxias do Sul, RS, Brasil


2003

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
from Abe Books
or
info on Amazon
or
see our Review

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.

Ted Mooney, finishing.com
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Ted Mooney, P.E.
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April 15, 2014

Q. Good evening,
I need the answer for the following questions in detail:

Q1: when we use low voltage in the electroplating of brass, we noticed that the zinc ions are deposited rather than the copper and the color was white? We use brass plate as anode and spoon as cathode and brass solution contains:
   - 40 grams of brass salts (copper sodium cyanide and zinc sodium cyanide),
   - sodium sulphite, and sodium cyanide,
   - and we add ammonium chloride to the solution
We fix the temperature, distance between cathode and anode, pH (9.8-10.8) copper content 60% and zinc 30% in solution and just change the voltage.

Q2: Write the oxidation-reduction reaction which occurs in the brass solution?

Q3: Why do we use ammonium chloride and sodium sulphite and sodium cyanide in this solution?

Q4: What are the advantage of using the cyanide bath in brass electroplating?

Brass solution : Zonax brass 75 g/l and 3 g ammonium chloride. Brass contains 70% copper And 30% zinc

ammar othman
electroplating student - jordan-amman


A. Hi Ammar. Sorry that no one helped you yet. Perhaps if you started with one particular question where you needed help, the results might have been better since no stranger is going to spend hours trying to complete your entire lab project for you. Further, questions 2 through 4 look like you just copied them right off your assignment and want someone else to do the assignment for you :-)

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 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
Lowenheim
from Abe Books

or

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,

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Ted Mooney, P.E. RET
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April 4, 2016

Q. Sir,

Please explain to me about Brass electrolyte.

Rate of deposition of zinc and copper?

What is the ratio of metal deposits from electrolytic solution and anode?

santosh tiwari
- Delhi, India


April 2016

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,

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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
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April 19, 2016

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.

dave wichern
Dave Wichern
Consultant - The Bronx, New York



February 28, 2019

Q. Want to do natural brass finish plating (reddish brass finish) on nickel plated or copper plated surface; we are using cyanide based bath.

vasanth kumar
Gold & brass plating - chennai,Tamil nadu, india


February 2019

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" [link is to info about book at Amazon] 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,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
We need "Aloha" now more than ever



April 25, 2019

Q. My company has met some problems of electroplating with brass (imitation gold color). We are using cyanide-based bath and Our problem is that when we finish the brass plating after water cleaning, blowing dry and baking, there would appear not obvious red strips on the sample surface. At first, we think that was caused by the water stain but after we strengthen the blowing dry the red parts were still at. Can anyone give some suggestions to improve our problems.

Jimmy, Chung
ziyong enterprise co., ltd - Tainan, Taiwan



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