What is the affect of using different voltages in the electroplating process?

A. Hi Cora. Hopefully you've had a chance to review our short paper on "Faraday's Law of Electrolysis" because it directly answers 95% of your question, while explaining exactly what is happening and why.

The deposition rate is directly proportional to the current after taking 'efficiency' into account. 'Efficiency' is the percentage of the electricity which deposits metal as opposed to electrolizing the water into hydrogen and oxygen or hydroxide, and the paper explains why 'efficiency' tends to decrease at higher voltages/ higher currents.

While there is nothing wrong with testing/tracking voltage vs. mass change as you are doing, instead of testing/tracking current vs. mass change, it is tracking of indirect variables. It's a bit like tracking how many pretzels you can eat and still safely drive, if each pretzel is washed down with a swallow of beer.

It is difficult to say exactly why your efficiency dropped to zero at 5 volts, but it may be related to what is going on at the anode (the dissolving electrode) rather than the cathode. Some things that have been reported widely, even on the pages of this site, include 1). that nickel anodes can 'passivate' (become inactive and no longer dissolve) if the current on them is too high; and 2). that copper anodes can stop conducting current or at least greatly slow down if the amount of dissolved copper surrounding them gets too high. Although I am not familiar with your particular case, it is possible that something similar is happening to you at high voltage.

But this issue you are encountering is a good example of why we should try to track the direct variables rather than the indirect ones. It's possible for someone to change their mind and not follow every single pretzel with a slug of beer or to follow the very salty ones with two or three slugs. Similarly, your question might be easier to answer if we knew the current flowing at 5 volts vs. at lower voltages, not just the voltage.

Luck & Regards,

A. Hello, Richard.
Theoretically, what controls how much plated metal is deposited is how much current (amperage) has flowed for how long (i.e., how many electrons have been transferred). This principle is known as Faraday's Law of Electrolysis if you want to do some background research. But to visualize it simply, you can think of it as: "if your battery moves the negatively charged electrons to the other pole, the positively charged metal ions will move to the other pole to catch up". At its simplest, that's how electroplating works: pull the electrons away from a metal anode, and move them to the cathode, and you are left with positively charged ions at the anode, which dissolve into the solution, migrate to the cathode, and rejoin with the electrons to become metal again.

According to another law, Ohm's Law, the amount of current flow will be proportional to the voltage: Amps=Volts/Ohms.

So, if the real world didn't rear its ugly head, the resistance would be essentially constant, and you would control the current by controlling the voltage, and your experiment would work and would prove what you'd like it to prove. However ...

Even if you were using industrial strength plating solutions, 12 volts would be too much and 9 volts might be too much because the zinc ions simply can't migrate through the solution quickly enough to keep up. What happens then is that the excess negative and positive charges at the electrodes cause the water in the solution to break up into H+ and O--, liberating hydrogen and oxygen gas, to balance those charges. This is called inefficiency.

With the very mild acid (vinegar) that you are using, very little zinc can be held in solution; the zinc concentration is much lower than in industrial plating solutions and even 6 volts is way too much. The zinc ions in solution can't nearly keep up, so you'll get great inefficiency, substantial liberation of hydrogen, and 'burning' even at 6 volts. You may be able to discern differences between plating rates for 1-1/2 volts and 3 volts though.

Q. Dear Ted: Thank you for a very helpful and detailed response. Your answer clearly explains why our higher voltages did not work as well as the lower 1.5 or 3.0 volt tests.

One final question about coating Zinc on Copper:

What do the zinc and copper metals become in the electroplating process when charged and immersed in the Epsom salt, vinegar and sugar solution and Zinc is the anode and Copper the cathode. Does the dissolved Zinc simply become ZN- and Copper Cu+?

Thanks again for your very kind assistance!

A. As long as the copper is the cathode rather than the anode, it doesn't dissolve into solution, it simply stays metallic copper. The Zinc metal at the anode, however, has its electrons stripped from it so it becomes Zn++ (an ion with a deficit of two electrons). Why it becomes Zn++, rather than Zn+ or Zn+++ might be beyond your daughter's age level but you can read my Presentation on Faraday's Law, and see how she receives it. When those ions get to the cathode they meet up with the electrons, and are reduced back to Zn metal.

A. Hi, Vivian. Yes, your question shows your confusion -- and I don't even know what "values" you are talking about. Sorry.

Do you very clearly, and without the least bit of confusion, understand exactly what "voltage" is? Do you very clearly, and without the least bit of confusion, understand exactly what you mean by "rate of electroplating"? A meaningful question can't be asked, and a meaningful answer provided unless the words that are used have clear, unambiguous meaning to you. You can't hope to sort out the confusion until you clearly understand the meaning of the words you are using, so please start there.

Then make sure what you mean by "the values" and clarify it for us because I don't know what values you are referring to. Good luck.

Regards,

A. Hi Danny.

Although solution concentration and voltage can be important variables for achieving robust, attractive industrial plating, the solution concentration has nothing to do with the theoretical amount of metal that is deposited, and the voltage has only a little to do with it :-)

Please see our presentation on "Faraday's Law of Electrolysis", study it, and try your best to deeply understand it. Once you really understand it, everything will be exceptionally clear.

But, in brief, in electroplating you use a battery or power source to pump electrons from the anode to the cathode though the external copper wiring and, as you do so, you are stealing electrons from the metal of the anode which thereby converts the metal into positively charged metal ions. These ions dissolve into solution, are attracted to and migrate to the cathode, where they rejoin the electrons to form metal once again. So, the amount of metal which moves from the anode to the cathode is thus directly proportional to how many electrons you pump from the anode to the cathode, which is expressed in ampere hours (current x time). Within reasonable limits, solution concentration has nothing to do with it, and voltage is only related due to Ohm's Law that voltage equals current x resistance. But if you try to plate at too high a rate (and 6V is too high!), there will not always be positively zinc ions available at the cathode to join up with the extra electrons your power pack has pumped there ... so the electrons will steel H+ from the water, converting it to H2 gas bubbles. Good luck.

Regards,

A. Hi Ramya. It's a little deep for 7th grade, but an atom of any given metal has a particular number of positively charged protons, which number we call its "atomic number", and an equal number of negatively charged electrons balancing out the charge. If we put a piece of that metal into a watery acid solution and connect the metal to the positive pole of a battery in an electric circuit, we can steal electrons from it, turning the neutral atoms into positively charged ions of the metal, which can dissolve into the plating solution.

The battery pumps those electrons from that anode metal to another piece of metal we put into the solution (called the cathode) through copper wiring. And the dissolved positively charged ions of metal are drawn to the negatively charged cathode. When they get there, they rejoin the electrons and become metal again.

Within practical limits, the higher the voltage, the more current will flow, so the faster the plating. From a theoretical standpoint, the concentration of salt doesn't enter into the plating speed. But in the real world of practical electroplating, some concentrations might be higher than optimal and some might be lower than optimal. There are both theoretical and practical aspects of one metal vs. another that affect the plating speed, but I think that's way beyond 7th grade. For 7th grade the amount of metal moved from anode to cathode is proportional to the current x the time. Good luck.

Regards,

A. Hi. The concentration of the salt does not effect the theoretical plating speed, because that is calculated from Faraday's Law. But as James says, in the real world you will be able to properly plate faster at higher concentrations.

Copper or zinc would be the most practical metals to try to plate. Please see our page on "How Plating Works".

The question of what metal theoretically plates fastest would depend on whether you judge by thickness or weight, and is beyond your grade level; but according to Faraday's Law again, the metal which plates fastest would be the one with the highest gram equivalent weight -- probably gold.

Regards,

A. Hi Joy. The easiest voltages to get your hands on are from 1-1/2 volt dry cell batteries. So 3 voltages worth trying are 1-1/2 volts (one battery), 3 volts (2 batteries in series), and 4-1/2 volts (3 batteries in series).

Regards,

  Thank you so much!

A. Hi Khushin. Please read the article this page references about Faraday's Law of Electrolysis. Then tell us what your hypothesis will be about how voltage could effect the amount of copper electrodeposited, and we can certainly help flesh out what you would need to do to set up an experiment to support or refute it. Good luck.

Regards,

A. Hi Russ. There will be some amount of gassing at any voltage & current (depending on the type of electroplating solution) -- the need is to keep it within boundaries so it does not cause "burning" or other poor plating.

When this site started in 1989, if someone suggested that you forget the 12V battery and purchase a proper power supply, you could have reasonably complained that you didn't have $1000-$1200 for one :-)
But these days small, regulated, adjustable, power supplies can be purchased for less than the cost of a car battery :-)
Please don't try to make do with something that is too high voltage, too high current, where you will have no control, and will have to sacrifice all the other optimum plating conditions to try to work around its limitations. Please get a proper power supply if you want to try to learn electroplating :-)

(The word "galvanizing" is reserved by professionals for the process of dipping into molten zinc, so confusion will probably be minimized if you avoid using the term to refer to electroplating).

Luck & Regards,