44086

Gold nickel adhesion problems  

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We have a Citrate based bath. The PH is on the high side never low. To maintain the bath citric acid is added daily keeping the PH from 3.8 to 4.2. The bath may be saturated or possibly there is an organic contamination. Any response or suggestion would be appreciated.

Colleen L Khalifa
- LA, CA, USA

The adhesion problem is probably related more to the condition of the nickel surface more than the capability of the gold plating bath. Are these parts freshly nickel plated without only a delay of under a minute before gold plating? If it's "old" nickel plating it must be activated, probably with a Wood's nickel strike.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

Colleen,
In acid gold (citrate) formulations, there are buffer salts that have to be added occasionally to the bath to buffer the ph. You do lose some of this chemical to dragout so it has to be replenished. The baume has to be below the max limit when you add the buffer salts, however. If you don't have a lab analysis procedure, your gold supplier should be able to provide one for you.
Like Ted said, the ph of the gold bath has little to do with adhesion problems. At a higher ph you would plate a little faster, and if it is a hardened gold you will also plate out a slightly higher gold purity - with the higher ph. Good Luck!

Mark Baker
Process Engineer - Syracuse, New York