Ask:
I am currently doing an investigation on Nickel electroplating in school. I am having problems as every time I try to electroplate onto a Copper sheet I always get a layer of Nickel(II) Oxide and no Nickel metal. I have tried using different current densities and concentration of substrate solution ( Nickel Chloride). However, I have found out that when I use Ammonium Nickel Sulfate I get a nice shiny coating. Can someone please explain why this is the case?
Expert say:
Interesting, the only thing I can think of is that nickel is usually electroplated at a pH of about 3.5 to 5 (in round terms). I do not know the pH you used with nickel chloride, but I suspect it will be at least 5 and perhaps higher. This will result in the nickel oxide being put down. When you used ammonium nickel sulfate you had the solution buffered at a suitable pH (ie between 3.5 and 5). However, I am surprised you got a bright deposit, unless it was very thin and on to a bright brass plate.
Ask:
Thank you very much for your help. Could you please suggest what I could investigate as a result? My teacher says I should try varying the concentrations of Ammonia and Sulfate but after reading your very generous suggestions, I feel this may be a waste of time and i do not have a lot of time to waste. I was thinking i could maybe try finding an optimum pH at which the nickel electroplating occurs. I was using copper sheets which polished before i used them and i had a very thin layer of nickel plated onto it.
Expert Say:
I would suggest a bath comprising 300g/l nickel sulfate, 30g/l nickel chloride, 40g/l boric acid. Operate at pH = 3.8-4.2 at about 50C. Cathodic current density about 40ASF, anodic cd about 50ASF. This is known as a Watts nickel bath. Add about 0.5g/l sodium saccharin to harden and brighten it. If you want to be really clever, add about 10g/l cobalt sulfate and this will also brighten and harden it.
Others Comment:
The best method to electroplate nickel is definitely the way has suggested. It is a conventional watts bath. A few more things... the pH of the bath has to be in the range of 4.8 to 5.4 and the current density 10 to 15 Amperes/Square feet. Also the surface cleaning and activation prior to the plating is most essential.
Others Comment:
I am doing a semi-similar investigation for my advanced higher investigation, and have found that I also get the best results using a Watts Nickel Bath. My recipe for this is 52.5g nickel (II) sulfate, 7.5g Ammonium chloride and 7.5g boric acid in 500cm3 water. This works best around 35oC and you need a nickel anode obviously.
What I am investigating is the difference produced when varying pH, temp, and current density current per unit area of cathode immersed this worked well for me. Good luck
