Watts Nickel Plating Problem: pH is too low. Why? How to Fix?

A. Yes, Pedro, more deposition at the corners and/or the ends of the piece than in the middle.

In JM's case, boric acid content or micro throwing power might have something to do with the problem, but a common cause of dog boning is simply poor anode sizing or placement. Remember that Faraday's Law tells us that plating thickness is directly proportional to current, and that current tends to take the path of least resistance, so if the anodes are as long or longer than the work, dog boning is a surety :-)
Luck & Regards,


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

A. Hello Pedro, Ted gave some great advice and I just wanted to add what I have experienced with dog boning. In the Printed Circuit Board industry dog boning was common until plated holes got so small and multilayer boards got so thick, acid copper baths and current density had to be adjusted for compensation. High acid, lower metal content, solution carriers, good cathode bar and solution agitation, lower current density applied with anode to cathode ratio of 2:1. With working with 10 mil holes and board thicknesses of .125" we could get surface to hole ratios of 1 to 1.2.

If you make sure your work is lower than the anodes as Ted points out, you will want to look at things like getting a full chemical analysis, rack and solution movement improvements and possibly a current density adjustment. This would go for other plating, not just copper. Good Luck and hope this helps.

A. Nickel carbonate is not very soluble. Do not add it to a nickel plating tank directly. The best way is to make a slurry of water and nickel carbonate and recirculate it into a filter. Transfer the filter hoses into the nickel tank, turn on some agitation and run the filter until the pH reaches the value you want. Remove the filter, clean it and use it for continued filtration of the nickel tank. I prefer to use nickel oxide in the same way as above. It has less impurities than nickel carbonate and dissolves easier, but it's possibly more difficult to locate a source for small amounts. If the pH of your nickel plating solution is going down while plating it is an indication of insoluble anodes, or not enough anode area (anode CD too high causing polarization). A normal operation of nickel plating solution requires the addition of acid to maintain the pH.

A. The amount of nickel carbonate will depend on its purity, the pH level and the tank volume. However, nickel carbonate is a potential carcinogen and personally I do not like using it; I prefer altering the pH with sodium hydroxide. I appreciate the increase in sodium ions is supposed to increase stress, but I have not knowingly experienced it. If you really want to use nickel carbonate, make it into a slurry and slowly add it to a by-pass tank and gently agitate the tank until it has all dissolved. It is very insoluble and prone to "glob up" if you are not careful; it will also effervesce vigorously, so wear a respiratory mask. Monitor the pH as you add the carbonate, but allow the tank about 10 minutes to "relax" before taking the pH again - it is like a piece of good roasting meat! You can take the batch bath pH up quite high before anything significant happens and once it is returned to the bulk tank the extra acid will be consumed by any hydroxide that is formed in the treatment tank. The real trick to keeping the pH under control is to keep the bath under control. It looks like you are using a sulphamate bath, so in theory you should be able to control the pH by having adequate boric acid (at least 30 g/l and preferably 35-40) and, more importantly, to have the correct nickel anodes. You should use sulfur depolarised nickel and these will dissolve in a sulphamate bath without the addition of chloride. However, most platers prefer to add about 10 g/l nickel chloride "just in case" (This is their very own comfort blanket!). If you do not use SDP nickel, you must use nickel chloride -- I would suggest about 30 g/l -- but be aware this will adversely affect your stress. The anodic reaction will thus be primarily the dissolution of nickel and not the discharge of oxygen, which results in the decreased pH.

A. Indeed, double check your Nickel Anode pellet material. Pure Nickel pellets are for Chloride strike baths, and SDP pellets, a common type are known as "S-Rounds" are for sulphate & sulfamate build baths. Pure Nickel pellets in a sulfamate bath won't corrode at all therefore the only reaction available at the anode will be water hydrolysis yielding sulfamic acid & oxygen...causing pH to drop. Even with S-Rounds if this acid formation reaction is still a pest you can shut it down by adding a bit of NiBr anode corrodant. With proper anodes, Boric acid content, and a bit of NiBr anode corroder you should be fine. The Ni Carbonate works excellently, but you will have to experiment a bit with beakers to determine your own dosage chart because you will be adding it to a buffered system. But I think you'll need to wait a lot longer than the aforementioned 10 minutes for equilibrium! I used to wait sometimes up to 2 hours for pH stability.

If your anode area is just too small due to space restrictions and they continue to throw off a lot of acid, you can still help them out a bit by flushing them with plating solution during plating. This requires specialized anode assemblies plumbed directly in line with the filters.

A. I would not think hydrogen peroxide is, Steve. But in the thread which we appended your inquiry to, Don Baudrand says yes to the nickel oxide.

A. Steve, I am guessing that you purchased the old West Plating outfit in Belfast. Been awhile since I lived in Maine (1986) I was that plater in Camden. Did a lot of stove parts for Bea Bryant in Thorndike. Anyway. Since you probably have limited access to chemical and do not wish to spend a ton on Nickel Carbonate or Oxide, I suggest using NaOH DILUTE! (AR grade the best) With lots and lots of agitation. It is a long process as you do not wish to overshoot. Make sure your Boric acid is where it should be and remember it is a buffer so as you add the Caustic you will suddenly get a jump in pH. Calibrate your meter well or make sure your pH papers are fresh. You will need to filter well and I suggest Dummy Plating prior to use. Test a part and look for roughness on the shelf. Bigger question: why is pH so low? How's your anodes and bags? Did you just overshoot on a downward adjustment? Can't say I haven't done that more than a dozen times.

A. Steve,

Sorry for slow response. I would not worry about the Sodium. If pH is coming back on line just hold that course. Your efficiency will be lower so plating times more. Stress could be an issue but since yours is decorative just keep an eye on it. Hard way to make a buck isn't it?

A. If the pH of a Watts type nickel is decreasing instead of the normal rise I would suspect that you have clogged anode bags or empty anode baskets which are causing hydrogen^oxygengas to evolve.

Hi. I believe that our always astute Mr. Packman made a little typo. The plating solution, when unable to dissolve nickel at the anodes for the reasons he mentioned, evolves oxygen gas. Oxygen evolving from the water leaves the solution with excess hydrogen ion, causing the dropping pH.

Regards,

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

A. Dear Friend,

When you pass current, hydrogen evolves from cathode and oxygen evolves from anode. Since nickel is a high efficiency bath the decrease of hydrogen or increase of pH will be lower. So it is recommended to go for a buffer salt of around 45 gpl, normally boric acid. Then check the pH once in a hour or so and add some acid to maintain the pH.

Regards

A. Hi friend,
This is common. Please ensure pH before reducing. Normally pH should adjust with vigorous agitation. Anyway there is no problem. Actually pH 3.8 is good for nickel plating bath. You can continue the production. Simultaneously pH will rise, or else you reduce the anode area for one day production. This will increase pH of the bath in good manner.
Don't try to add caustic soda [affil links] to raise pH. It will create a lot of problems in the future.
GOOD LUCK.

A. Just another note to consider. Be sure you are not dragging in any acid to the bath, or low ph rinse (from stagnant rinses).

A. Hi Debra
Dave Kinghorn offer good advice on this subject.
Obviously your anodes are not dissolving correctly causing you to experience pH dropping.
To find out how much NiCO3 YOU need, do a lab test of taking say 1 liter in a container and adding weighed small amounts of NiCO3 to find out how much is needed for your particular circumstance. Take note of how long it takes for the reaction to complete.
Each situation is different so you need to experiment to find out what you need, not some theoretical amount.