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

A. Hi, Pooja Lad,

I believe Trevor wrote that because there are many organic additives in a Nickel Bath, such as brightener, leveler and wetter.

A concentrated acid is very reactive and might break some of these organic compounds, leaving its traces in the bath. Not only will they stop working as they should, but these traces may also cause some burning in your deposit.

Before knowing this I used to add concentrated acid and never had a problem - preventive maintenance with active carbon filtering should avoid this -- but since we know what could happen, might as well avoid more problems and add diluted acid .

Regards,

A. I would keep pH probe in bath and a dosing pump which will add as soon as pH increases. Continuous dosing will control bath better. By the way how much pH are you maintaining? 5 is too high for Watts bath.

A. Calculate additions?

The normal way is to add small amounts 1/4 ml/L mix well (four hours or so) then see what has happened.

There is the problem that the boric acid acts as a buffer so you will add acid and see little change.

Do not get tempted to go overboard with the amounts added.

Keep a notebook of what is being added and the effect so if it happens again you can make the equivalent of several additions at once. (If you do this once more do not go over board with the additions).

A. Dear Beningna,

You can try this :

1) Take a liter of your sample solution (pH 5)

2) Add H2SO4 in small measured amount to, say, pH 4.5

3) Now interpolate this amount of H2SO4 added to your 1 liter samples solution to your actual bath volume. You would have the actual quantity of H2SO4 to be added to your bath to bring down pH to 4.5

4)Add in, say, 3 installments and constantly check your pH.

It works for me, good luck!

Regards,

A. All of the previous answers are good guidance. I just wanted to point out that sometimes I suggest using dilute hydrochloric acid (reagent grade) instead of dilute sulfuric acid. The reason is that it is one way of maintaining the nickel chloride in the solution while lessening additions of nickel salts. Further, if sulphate is rising, it allows an alternative.

A. pH should be maintained at 3.9-4.5.
Use sulfuric acid to maintain the pH, not hydrochloric.
Too high chlorides have a detrimental effect on ductility and while adding hydrochloric acid you cause corrosion of the equipment

A. Are you using bar anodes? What is the specification of your nickel anodes? Are you adding the acid directly over the anodes? Is the final pH within limits after you add the acid? Do you use anode bags? Do you have a lot of nickel precipitate on your anode bags above solution level until you add acid? What is the concentration of each of the sulfuric and hydrochloric acids before you mix them 1:1.5?
Best wishes,

A. Hello Sastri,
The reason your Ni metal is too high is because of the addition of HCl. As Sarah mentioned, you should not be adding HCl. The bath make up contains a certain level of NiCl2. Nickel chloride is in the bath to facilitate proper anode corrosion. If the chloride level is too high, your anode dissolution rate increases, in turn the Ni metal concentration in the bath rises. I was never a big fan of adding concentrated acids to lower ph values, you tend to over shoot your target. I have had success in adding a 10-20% dilution. Good Luck!

A. Sastry, You should not use hydrochloric acid to reduce the pH of a Watts bath - always use sulfuric acid. Hydrochloric acid will induce stress in your deposits and is very corrosive to most metals; it also smells! Also, never use concentrated acids - I would suggest 10% strength. Whenever you add acid to the bath, do is slowly and make sure the bath is well agitated. I am not sure why you see increases in both nickel sulphate and chloride when you add hydrochloric acid, but the way I analysed a nickel bath was to find the total nickel content and then the total chloride - this gives you they nickel chloride content and the rest of the nickel is sulphate. If you regularly need to alter the pH, this could be because there is insufficient boric acid, I would use about 30-35 g/l, although higher levels aren't particularly detrimental

A. The solubility of the boric acid is a function of temperature, about 6 oz/gal for 120 °F, if you have too much it falls out and causes pitting. Raise the pH with Nickel Carbonate and then filter. Lower the pH with sulfuric acid. Three possibilities with your pitting. (1) mentioned above if the boric acid is too high and falling out. (2) organic contamination which your should carbon treat with sulfur free activated carbon. (3) Metallic contamination which you should electrolytically (dummy) plate out at low current density.

A. 1) pH 5.0 NICKEL BATH TOO HIGH, KEEP 3.8 TO 4.5
2) MAKE SURE UNPLATED PARTS ARE CLEAN
3) CHECK SURFACE TENSION, A

Thank you Mr. Patel. It seems peculiar that a plating company I obtained the bath from would say the ph is supposed to be 6 to 7 which is unheard of in my study. I am plating in small 3 gallon buckets, yet I have the nickel dialed in good now ranging at 4. Thanks again.