Q. We are a decorative plating company with gold over bright nickel being one of our specialties. We continue to have problems with gold peeling from the bright nickel layer. The worst cases are parts that are nickel plated elsewhere and shipped to us for gold plating. K.P.
A. This is a question I am asked quite often. Here’s what I wrote in an earlier column: Your problem is with the nickel plate becoming passive. This is a common problem whenever you are dealing with nickel alloys and nickel-plated surfaces. The nickel surface essentially becomes chemically inactive and will not bond with other materials, in this case, gold. This process takes place whenever the surface is exposed to the air. The oxygen in the air reacts with the nickel to form nickel oxide.
To get consistent results, the nickel surface must always be activated prior to gold plating. The parts should be pre-cleaned in a mild alkaline soak cleaner followed by an activation step. There are a number of different activation procedures available such as cathodic activation in dilute sulfuric acid, proprietary activators or a Woods’ nickel strike.
It’s important that as soon as you complete the activation step you go directly to the gold plating step. Failure to do so can result in surface passivation all over again.