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topic 28434

Electroplating copper onto nickel using a copper sulfate bath

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A discussion started in 2004 but continuing through 2019

2004

Q. Hello,

I am a freshman student in an honors chemistry class. I have conducted an electroplating experiment that tested the effect of different amounts of copper sulfate [linked by editor to product info at Amazon] in the bath(g) on the change in mass of a nickel from before it was plated to after it was plated with copper. I had 100 trials total. The four amounts of copper sulfate tested were 5g, 10g, 15g,and 20g dissolved in 150mL of water. From the results I gathered my data showed that there is virtually no difference in how much copper was plated on the nickel despite the different amounts that were used. I am now writing my lab report and my teacher wants me to find out why there was no difference between in the change of the mass of the nickels. My experiment obviously showed that the amount of copper sulfate in the plating bath has no effect on how much the nickel is plated but I really need to know why.

I am sorry if this is a stupid question, but I am not very familiar with this site and do not know if it has already been answered elsewhere, and I don't have a lot of time. I appreciate any help you can give me. Thank you and please respond as soon as you can.                                 

Melissa A [last name deleted for privacy by Editor]
student - Columbia, Missouri, United States


2004

A. Not a stupid question at all, Melissa. You are very industrious to plate 100 samples, good for you, and your results are exactly correct! Here is what happens--

The copper ions are sitting in solution, doing essentially nothing until you apply electricity. Then, when you apply electricity and a copper ion is touching your nickel cathode, two electrons flow into it reducing it from a Cu++ ion to a Cu0 metal atom. So the amount of copper deposited is proportional to the number of electrons that flowed, i.e., the coulombs or ampere-seconds, NOT the copper concentration. This is Faraday's Law, and we're very happy you demonstrated it so well.

There is, however, a second reaction that occurs to a much lesser degree. Those two electrons can sometimes instead be wasted in the liberation of hydrogen from water,
2H2O + 2e => H2 + 2OH.

If 100 percent of your electricity goes into depositing copper, the process is said to be operating at 100 percent efficiency. If 10 percent of the electricity goes into liberating hydrogen from water, the process is operating at 90 percent efficiency. At high copper concentrations and reasonable current, like you used, copper plating is close to 100 percent efficient because it is much easier to reduce copper than hydrogen; but if you lower the copper concentration way down, the efficiency will drop off. You can understand this by remembering that I started by saying "a copper ion is touching your nickel cathode". Suppose that the concentration is so low that at a given instant no copper ions are near or touching the cathode? The electricity still needs to flow, and will do so by liberating hydrogen from the water.

You did a great experiment and demonstrated Faraday's Law -- with the great 'control' of showing that copper concentration within reasonable limits has no effect on plating rate! (but had you run another trial with a greatly reduced copper concentration, you might have seen the reduced efficiency that results from too little copper in solution).

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



February 1, 2009

Q. I am helping my 7th grade child with a science project that involves ECD of copper using different concentrations of copper sulfate solution. At higher concentrations it went pretty well and he observed nicely deposited copper formations. At successively lower concentrations there seemed to be increased bubbling (presumably electrolysis of water?) but also the deposits were black. Is this an optical property of the deposited copper, CuO or something else?

Thanks,
Dan

Dan Abraham
hobbyist - Northport, New York, US


February 1, 2009

A. Hi, Dan. The black deposit you are seeing is called "burning" or "smut", and I can tell you basically what it is, but it's hard to put a fine point on it in terms of percentages, because it is the result of a process that is out of control and therefore erratic and unpredictable. One component of it is a very finely deposited copper powder (if powders are fine enough they tend to look black because the tiny balls bounce light away at skew angles instead of reflecting it back.

It is caused, as previously mentioned, by trying to plate at a higher voltage/current than the solution can sustain. The electricity must take two paths to complete the circuit, electrons flow through the copper wire, while positively charged copper ions flow through the solution. If there isn't enough copper in the solution to sustain the current you are passing through the wire, the instant a copper ion reaches the cathode it is instantly reduced to a spec of powder instead of slowly growing a proper grain structure. Additionally, water is hydrolyzed into hydrogen and oxygen to try to carry the current.

It is possible to successfully plate copper with a low concentration of copper in the solution, but you must plate at a lower voltage and consequently slower so the small concentration of copper ions is sufficient to match the electrons you are passing through the wire. Good luck.

Regards,

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



March 16, 2010

Q. My name is Aditi and I'm doing a chemistry project on Electrolysis. I'm in the ninth grade. I'm plating a steel rod with copper from a CuSO4 solution. I want to know what reactions take place and whether the SO4 ions will rush to the other electrode.

Aditi L.
Student - Pune, Maharashtra, India


October 2013

A. Hi Aditi. Sorry, but your experiment will not be successful because electroplating copper onto a steel rod is a problem. Copper is more noble than steel, so copper will deposit onto the rod without any electricity applied. As for the reaction involved, the copper sulphate ionizes into Cu++ and SO4- -, and the Cu++ ions migrate over to the steel surface. When they reach it, they "steal" electrons from the steel because they are more noble than the steel is. Thus the copper ions become neutralized and deposit as copper metal onto the rod, while simultaneously the iron (steel) atoms lose their electrons and ionize into solution. When the steel surface is completely covered with copper metal, the reaction will stop.

However, if you apply electricity at that point, you can make it continue. You'll pump electrons to the cathode, where they will continue to reduce Cu++ ions to copper metal, and the electrons you pulled from the anode will cause the copper atoms of the anode to dissolve into solution as Cu++ ions.

Regards,

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



Need very heavy copper plating on top of nickel plating

January 10, 2019

Q. Dear sir. I run a small electronics company (mostly power electronics) and we need to have a thick copper plate applied to a nickel plated spring clip and a nickel (or gold) plated magnet. The cladding must be a minimum of .32mm but we prefer .4mm [ed note: 0.016"] thick. I have contacted every plater in the country (Guatemala) -- they do not "experiment" so we are on our own.

Our need is estimated to be 2000 clips and 1500 magnets per year. Also we are somewhat space limited -- a process that requires ten different baths even if it is less costly would not be as suitable as one that requires less space but is more costly. Any suggestions or advice would be greatly appreciated.
Sincerely ,

Robert Lackey
Field Effect Transistor Co. - Teculutan , Zacapa , Guatemala
  ^- Privately contact this inquirer -^


January 2019

A. Hi Robert. 3500 parts per year is only 15-20 per working day, so your production needs are not far beyond an experimental laboratory. But the only practical way to get the copper on them is probably electroplating, and these thicknesses are in the range of usual electroforming thicknesses and will likely require a plating time of almost a full day.

Before plating, the parts will require electrocleaning, rinsing, acid dip neutralization, rinsing, Wood's Nickel Striking, and rinsing before the copper plating. A possible alternative for less space is sandblasting followed by rinsing and Woods's Nickel Striking.

The plating is thick enough that maybe, depending on the shape of the parts, you can rely on a shrink-wrap cohesion effect more than adhesion to keep the copper attached to the parts. So maybe you can just sandblast the parts, rinse off the dust, and quickly start copper plating without the strike. (Must the nickel plating be retained?)

Years ago I was involved with the re-plating of the ironwork of Philadelphia city hall's William Penn clock tower; the original plating (acid copper plating directly onto iron & steel) was in the same general thickness range as you are contemplating and worked for many decades ... but once it became perforated there was rapid horrible undercutting corrosion because there was zero adhesion.

Regards,

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


January 12, 2019

Q. Thank you mister Mooney for your advice ... it sounds like it is doable. You asked if the nickel is necessary -- no, I just mentioned it because it was there, but I believe good adhesion is necessary because of flexing and the high amps that will be passing through the part.

I do have a few follow up questions if you don't mind --
1. in this application sand blasting is unacceptable due to the stress risers it would leave (it is a spring) but we have bead blasting, hot caustic soda bath, hot ferric chloride bath (with or without 5% nitric acid ) would any of these do what the sand blasting was intended to do?
2. after the Wood's Nickel Strike you say to copper plate , but a quick search of the internet turns up at least a dozen different copper plating methods, does it matter which one I choose? (many chemicals are not available here , for example we make our own Ferric chloride , so having several choices is a good thing from a chemical availability aspect).
Thank you in Advance.
Sincerely,

Robert Lackey [returning]
Field Effect Transistor Co. - Teculutan Zacapa Guatemala


January 2019

A. Hi again Robert. If at all possible you should be buying your plating solutions from a reputable plating process provider. If that is impossible, then you need to at least build a good plating library so you can research the matter.

Old nickel plating is difficult to activate for good adhesion even with a Wood's Nickel Strike. And chemically removing it without proprietaries or creating an environmental mess with nitric acid is difficult; blasting is better. Personally I would guess the best procedure for good adhesion on springs with old nickel plating would be to blast the old nickel off, then either nickel strike or cyanide copper strike, then acid copper plate.

But you don't build a plating plant based on theory. You need to try these things before you build a plant to do them.

Regards,

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

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