Nickel Buildup In Bright Nickel Solutions

A. We have experienced this problem in the past and remedied it by decreasing the anode area by removing a basket.

A. Hello:

You have got some good replies for your query. I will try to tackle it in a slightly different way. Mostly when nickel solution builds up, it is Nickel sulphate which increases. The simple reason being the difference in anode and cathode efficiencies and the general habit of adding sulfuric acid for pH adjustment.

What happens in these build up problems, we stop adding nickel sulphate but we still add nickel chloride because it goes down as the bath plates.

We can manipulate a little here, instead of adding sulfuric acid we can add hydrochloric acid which further replenishes the required nickel chloride and also adjusts pH. But we do not end up increasing the nickel metal concentration in the bath as we are not adding any nickel salt. So now you have 3 options or I would prefer a combination of all 3:

1. Adjust your anode to cathode ratio (also you want to see if all anodes and cathodes are getting the right amount of current).

2. Use some insoluble anodes.

3. Start using hydrochloric acid for pH adjustments.

If I were you I would prefer a combination of 1st and 3rd approach.

Regards,

A. Hi Chi Cheng

I am not saying that in nickel plating, nickel sulphate increases and nickel chloride decreases.

Because generally we add sulfuric acid to control the pH of the bath so it creates more sulphate ion in the bath which eventually end up in increasing the nickel sulphate concentration. Whereas nickel chloride is consumed as chlorine is evolved at anode and at the drag out(basically nickel chloride's function is to provide solution conductivity whereas nickel sulphate is the primary source of nickel ions, essential in the plating).

As we do not add hydrochloric acid so we end up going down in chloride concentration and we have to add nickel chloride and not nickel sulphate.

Here is a danger. Each addition of nickel chloride is further increasing NICKEL ION as well which reacts with sulphate ion of sulfuric acid and create more nickel sulphate within the bath.

These situation worsens if we have minimum drag out.(Principally we try to reduce drag out but it does not help if we have already high nickel concentration).

To be short, I think sometime we may add hydrochloric acid instead of sulfuric acid. But be careful it reacts faster.

A. Warning! too much chloride is not good for the ductility of the deposit.

In this way: as chloride increases the tensile strength goes up
Hardness goes up
ELONGATION GOES DOWN
INTERNAL STRESS GOES UP

For some applications one has to be careful; for example, on parts where welding is necessary, firearms, parts exposed to heat or parts which receive some kind of bending.

I suggest finding the cause of the build up if that is a problem.

Actually I don't know why the nickel build up is a problem or its consequences.
without measurement is difficult to say how much is too much.

A. Hi, Bernardo.

Approximately 2:1 anode:cathode ratio is typical. Good luck.

Regards,

A. Hello Thomas,
Most nickel baths require an anode to cathode ratio of 1:1 minimum. I have found that a 2:1 ratio works well. What you have to consider however is that the baskets face the parts and cover most of the cathode area. I have also found it is beneficial to have the outside of the rack extend 1.5" beyond the outside edge of the anode basket. The reason for this is that the high current density area is the outside of your rack(s), and this technique will help you with a tighter distribution thickness throughout the rack. If your nickel metal concentration in the bath is not climbing with the current ratio, and Your deposit thickness is where it should be, I really wouldn't be too concerned.

  Here are two things that occurred to me, which might not apply to your situation, but might help us not mislead other readers ...

1. Plating is complicated, and thumb rules sometimes apply only to very specific things. Excessive/insufficient anode area can cause problems in some types of plating, but it can be complex. For example, in hexavalent chrome plating, different anode-cathode ratios can cause reduction/oxidation of chrome between hexavalent/trivalent and can be a major design issue. In copper plating it is my understanding that excessive anode area (and/or use of non-phosphorized anodes) can cause passivation via a build-up of a less-conductive copper-rich film around the anodes, whereas in nickel plating passivation of the anodes is more likely from insufficient rather than excessive anode area. Nickel plating usually uses sulfur-depolarized anodes to aid dissolution, and sometimes controlled amounts of chloride as well. As Mark says, excessive anode area can lead to too much dissolution and thus a rising nickel concentration -- which brings me to thought #2 ...

2. As I've learned from thousands of amateur and hobbyist Q&A's here, non-optimum operational parameters don't always manifest themselves as poorly plated parts, but sometimes simply as difficulty in maintaining the equilibriums we need for production plating. A hobbyist may successfully plate a part and call it done, and claim it was easy ... whereas the production plater is concerned not just with that one part, but the condition he has left the plating tank in when he finished. Thus, you might be able to successfully plate a part in a plating solution with higher concentration than the readers suggest, but if such operations result in leaving the tank with an ever higher concentration of nickel and ever higher pH, or whatever parameters are creeping up or down on you, you may not consider it okay even if you're doing satisfactory plating over the short run :-)

Regards,

A. Hi again Thomas. My knowledge comes only from books, hanging around plating shops, feedback from consulting assignments, and curating this site for 25 years -- not from actually doing any plating myself. So there is a lot of stuff that I'm not qualified to comment on, but this thread 7124 offers lots of interesting perspectives & experience on this issue of nickel anode area earlier on in the discussion.

As for removing nickel anodes when not in use, it is recommended for Wood's Nickel Strike tanks because it is vital to hold the nickel concentration and pH low. But in working with many hundreds of nickel plating shops over my career, I've never seen one that routinely removed their anodes when not in use. However, if a tank is not going to be used for extended periods of weeks or months, I would expect problems like the anode bags clogging from disuse, the need to sand the contact hooks and anode bars, the desire to "magnet" the tank against fallen parts, etc., ... so maybe adding the removal/reinstallation of anodes to the periodic maintenance program makes sense anyway :-)

Regards,