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topic 10210

Function of Boric acid in Nickel Plating


A discussion started in 2001 but continuing through 2019

2001

Q. Could anyone please advise me of the function that Boric Acid plays in Nickel Plating? Does it act as a buffer for pH control?

Andrew Elliott
- Sheffield, UK


2001

A. Yup. A portion of the water in the solution hydrolizes as H2 gas and 2OH-. The H2 evolves as a gas, leaving the 2OH- behind to try to lower ^ raise the pH from where you wanted to hold it.

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


2001

A. Ted and I rarely disagree, but he had an "OOPS" here. The remaining OH, as stated, is a hydroxyl group and would actually raise the pH.

Boric acid, H3BO3, has the capability of ionizing with an H+ and a H2BO3- which provides one hydrogen ion to react with an available OH-. Actually, you can titrate a saturated boric acid solution with 0.1N NaOH and done carefully, find three separate pH's that it will try to hold.

The purpose of all this is: hydrogen forms nascent hydrogen, H2, at the surface of the plated part, leaving a two free OH- groups which raises the pH at the surface of the part and a couple of millionths of the solution (which is the diffusion or barrier layer). This higher pH typically forms a black deposit or at least, a nasty one. The H+ from the boric acid reacts with the OH- to hold the pH stable.

The beauty of a buffer is it is bi directional, resisting movement in either direction, thus it takes an available hydrogen and goes back to the original ion. This is why agitation is so important in most baths and you have to add acid to a nickel tank.

Drag out is by far the biggest loss of boric from a tank. Actual use or destruction is very minimal.

This is also why it is so hard to change a pH on a tank. You add and add and very little happens and then it abruptly changes a huge amount.

It is much more complicated, but that is the short version of it.

James Watts
- Navarre, Florida


2001

thumbs up sign Indeed it was an "oops". The OH- is left behind as I said, but this does indeed raise the pH, not lower it. Thanks for your far more detailed explanation as well, Jim.

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



To minimize your searching efforts and to offer multiple viewpoints, we've combined some threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.



2002

Q. Why do we add boric acid in watt's solution? It it to control rate of deposition? If that's the case will boric acid control rate of deposition in say copper sulphate solution?

Ravi SHankar
Purdue University - West Lafayette, Indiana, USA


2002

A. Boric acid is added to lots of nickel plating solutions, and indeed many others, to act as a pH buffer. When metal is electrodeposited onto a cathode, the pH in the immediate vicinity of the cathode increases to very high levels. It can reach up to pH 11 or 12 very near to the surface of the electrode. The higher the cathodic current density, the higher the pH will rise. However, at pHs above about 6, nickel is precipitated as nickel hydroxide and if this happens at the cathode surface, the deposit will look very dark and is known as "burnt". To overcome this, boric acid is added to the bath as this controls and reduces the changes in pH, thus preventing the precipitation of hydroxides. However, boric acid is only useful at pHs above about 4, so where it is of little use in very acidic solutions such as acid copper. You can, in theory, run a nickel bath at very low pH's, but at these low pH's the efficiency will fall off dramatically as you will co-deposit hydrogen;! this will also lead to hydrogen entrapment and subsequent embrittlement of the deposit. In many applications, such as aerospace, this would be a total no-no.

Most nickel baths use between 30 and 40 g/l of boric acid; personally I like to run at levels closer to 40 than 30 as I have found it keeps the bath in better control. As a side issue, I have come across one well known company who operates a nickel electroforming bath at 120g/l boric acid, but they operated a sulphamate nickel bath at 90C. What I did find surprising about their bath was it didn't suffer from any stress or apparent breakdown of sulphamate to ammonia and sulphate. Their "trick" was to regularly replace some of the electrolyte and always keep it hot - if they didn't, the pipes got clogged with boric acid crystals and once this happens it is a real pig trying to redissolve it!

For many years there has been some conjecture as to whether boric acid is co-deposited with the nickel; some sophisticated analytical techniques have shown traces of boron in nickel deposits, but the levels are so low as to be of no importance.

In summary, boric acid is added to help keep the nickel in solution and to improve the quality of the deposit as well as increase the operating range of the electrolyte.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK



My nickel bath has crystals, what can I do to liquify/dissolve them?

2005

Q. I work in a small PCB house and we have a nickel bath to plate edge connectors. Sometimes it gets a lot of use and other times it just sits idle. We have a problem with crystal formation which occupies quite a bit of our bath. We would like to "de-crystallize" the nickel and continue to use it, is this possible? What techniques can we use to liquefy these nickel crystals and incorporate the nickel back into our plating process?

Cliff Heckenberg
- Ohio,USA


2005

A. Recrystallization comes from loss of water and consequent cooling. Add the required amount of water to restore original level, a little heat and patience. No big deal. Then analyze chemistry.

Guillermo Marrufo
Monterrey, NL, Mexico


simultaneous 2005

A. The crystals are probably boric acid, if I had to guess. When you aren't using the tank are you letting it cool down? My nickel tanks run boric acid at close to the solubility limit so the boric can crystalize out at lower temps. You will probably cause roughness if you add them directly to the tank. Put the crystals in an anode bag and drape the bag over the side of the tank when it is at temperature.

Trent Kaufman
Trent Kaufman
   electroplater
Galva, Illinois



2005

A. By "liquify" I presume you mean dissolve. I also assume the bath only shows these crystals when it has been idle and allowed to go cold. The best thing to do is to make the bath up to its correct volume (specification) and then turn on the heaters. If there are a lot of crystals around the heater, you may want to turn the pumps on first and allow them to start to dissolve, otherwise you may burn them out. Analyse the bath to make sure its in spec before you use it.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK


2005

A. Probably what you've got is boric acid precipitating out; many nickel baths run with the boric acid concentration close to saturation. As a rule, heating the bath with agitation will redissolve the crystals. I used to run into this with a tab plater; the crystals would plug the sparger holes in the plating cell.

James Totter
James Totter, CEF
- Tallahassee, Florida


2005

A. What kind of nickel plating solution is it? Is it Sulfamate?
If sulfamate and it has been heated or run at too high anode current density then you have broken down the SN radical into ammonia and sulfate. Go get an ammonia analysis because you may have to dump the bath. Let us know the ammonia content.

If it is simply Boric Acid in a sulfamate bath, you must know that the solubility is limited by the operating temperature. If it does not dissolve at your operating temperature, then you have too much, get it out, filter it out.

The old timers used to say to hang a bag of boric acid in the corner of the tank. That is OK for a sulfate solution. That is not OK for a sulfamate solution. Over the weekend it cools and falls out. On Monday morning the lab tech titrates and adds more boric acid but it will not go in.

Come back with some more information.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como
and co-author of The Sulfamate Nickel How-To Guide



August 5, 2018

Q. Hi! We are running Ni baths using Ni sulfate solution; and white precipitate forms above the anodes and anode basket readily than those baths using Ni sulfamate. Is this really normal? How do we minimize or eliminate the formation of precipitate? Our preventive countermeasure is to check the baths every day and remove the precipitate manually

Kim Bernat
- Laguna, Philippines


August 2018

A. Hi Kim. Yes, this is almost surely boric acid. Please double check what concentration you are trying to hold, and the temperature of the bath. You asked the same question two weeks ago as topic 11706 and Robert Probert answered it the same way. Good luck!

Regards,

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



May 12, 2019

Q. I have faced very fine roughness of whitish color only on the stay. This does not seem like roughness due to sand or dust, and only on stay. Filtration is good, no organic impurities as I perform carbon treatment

I plate on sanitary fittings. For two or three days we face a problem you can see in the pictures, only on stay...

10210-1b   10210-1a   10210-1c  

Boric is 56 g/l
Nickel is 78 g/l

If this is due to high boric then please tell me how to reduce it.

Bilal Asghar
- Gujranwala, Punjab , Pakistan


May 2019

A. Hi Bilal. I don't know what you mean by "only on stay"; sorry, but the word 'stay' doesn't mean anything to me in this context.

It is difficult to be sure based on little data (plus your concentrations don't sound right), but it does look like excessive boric acid. Lower the temperature by 15-20 °C and filter the bath. When you reheat it, increasing the solubility, the problem should be gone. Good luck.

Regards,

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



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