Peeling problem with nickel electroforming
June 7, 2012Q. I am not a chemist nor am I a professional at electroforming. Circumstance has made me the person in charge of electroforming at my laboratory. I did not have a mentor nor a background in electroplating before I started.
I am operating the German-made electroforming unit.
The processing parameters are as following;
Temp : 52 ~54°
pH : 3.8 ~ 5
Total volume of electrolyte : 240 liters
Flow rate of electrolyte : 64 liters/minute
Concentration of Ni(NH2SO)2 4H2O : 345 ~ 355 grams/liter
Concentration of NiCl2 6H2O : 5 grams/liter
Concentration of H2BO3 : 35 grams/liter
One day I conducted few electroforming experiments and found that there were something wrong with my result.
The electroformed surface is not as good as before.
I do maintenance task regularly and do not know what to check for sorting out the problem.
For better explanation, I attached the pictures of the result.
Could anyone please check the result and give some feedback if anything has to be checked ( for example, electrolyte, cell, pH, Temp or else)
I have been electroforming for about one year and I have never had this kind of problem.
Any comments will be appreciated.
- Seoul, South Korea
A. Kim, this electroform, to be honest, is pretty rubbish. You seem to have a good control system in your bath, but I would recommend a couple of things. Firstly, the pH should be run between 3.8 and 4.3, certainly not as high as 5.0 for nickel sulphamate. Secondly, the filtration rate is rather high - I reckon you are doing about 16 tank turnovers per hour. I am a strong advocate of good filtration in electroforming, but I would suggest reducing it to about half this (8 turnover per hour).
I presume the temperature is in Centigrade and not Fahrenheit - if is it is OK, if it is fahrenheit, it is too low.
You do not mention the operating current density - I would suggest that your nickel bath would be best operated at about 20-30 ASF (2-3 A/dm2).
Next, I would check the bath composition - the deposit is clearly highly stressed and I wonder if you have accidentally added nickel chloride instead of nickel sulphamate. The bath is very basic and doesn't even have any wetting agent in it. I would suggest you check what the solution should be and make sure that all components are in there.
Next you should check the behaviour of the bath by a Hull Cell - this will tell you if there is any contamination in the bath.
If you find anything wrong with the bath, in terms of wrong composition or contamination, I suggest you dump this bath and start again - it is producing such poor electroforms it is not worth trying to recover it. Your production manager will probably go apoplectic at the suggestion, but I think that is that is the best route in the long run.
Coming back to your filtration rate, is the return pipe from the pump anywhere near the plating area? It is possible that the high velocity of electrolyte coming from the pipe is impacting on the plating surface and causing surface disruption. The easiest option here is to move the pipe, if that is possible - if not, you will have to move the workpiece.
Hopefully, once you have worked through this list of suggestions, your problem has been resolved. Good luck
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Trevor Crichton R&D practical scientist The Pheasantries - Chesham, U.K. |
June 20, 2012
Q. I am very thanks for your comments.
However, I have a question on your comment.
Could you please tell me the meaning of turnover?
Do you mean that I should decrease the flow rate of electrolyte by half?
Cheers mate! TA!
- Seoul, South Korea
A. Hi Kim.
In case it's a few days before Trevor gets back to carry on the conversation, a "turnover" is a filtration rate that is expressed in units of tank volume. If your tank volume is 240 liters, and your filtration rate is 64 liters/minute, it will take you 240/64 = 3.75 minutes to "turn over" the tank, i.e., to send all of the contents of the tank through the filter. Since there are 60 minutes in an hour, this is 60/3.75 = 16 "turnovers". It is recognized that this is an "average" rate and that you are not necessarily sending each and every individual molecule of solution through the filter every 3.75 minutes.
Regards,
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 Ted Mooney, P.E. RET finishing.com Brick, New Jersey |
A. Hi
I think that temperature increases and maybe you are adding additive in your bath or adding waste to bath. But important for this problem is temperature, and you can give best electrodeposition in 1-1.5 A/dm^2. Other than this you have large stress. Good luck.
- Iran
