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topic 5481

Adding Sodium Hypophosphite to an Eless Nickel Bath




(2000)

Hi,

Currently our facility is having problems with non-electrical deposition of nickel (Nickel Chloride, buffers, Sodium Hypophosphite, Ammonium Hydroxide for pH). I've been looking at the relationship between pH and the effect pH has on chemical additions. The trend I notice is that adding Sodium Hypophosphite to a bath with low pH (pH = 6.8)causes some kind of instability to the bath chemistry and the autocatalytic reaction becomes "hyperactive" (can't think of a better word right now). This causes concern because the addition of Sodium Hypophosphite seems to be very sensitive to bath pH and our procedures don't follow the recommendation of the manufacturer.

The main discrepancy is that the manufacturer recommends (or even emphasizes) adding Ammonium Hydroxide until the bath pH is 7.00 before adding any Sodium Hypophosphite and we specifically add Sodium Hypophosphite before we ever add Ammonium Hydroxide. I'm wondering if anybody could chemically explain why it's necessary (or not necessary) to add Ammonium Hydroxide before the addition of Sodium Hypophosphite. Thanks for any help. Mac

Maclaine Pahl
Sony - Springfield, OR, USA


(2000)

Your vendors tech service (not the salesman) is the best source of why they think that way. Generally speaking, the higher the pH, the more active the solution. The higher the hypo, the more active the solution. same for temp. My guess is that they are using full strength ammonia for PH adjustment which has to be added very slowly or you will probably get localized destruction of the bath. My further guess is that the hypo is in a relatively more dilute solution. Since you have to add water frequently to an EN tank, Try diluting your additions before making them and bleed them into the tank, or do it before it comes to temp. A simple practice that extends the life of the solution.

James Watts
- Navarre, Florida


(2000)

The ammonium hydroxide that you use for pH correction is also building complexes with the nickel in your bath, so with lower pH (This means lower ammonium hydroxide too) the stability of your bath is lower. Regards Marcus

Marcus Hahn
-



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