Q. Our company specializes in plating gold over nickel. Many times, we find that the gold does not adhere to the nickel plate and peeling results. This is especially bothersome with parts that are nickel-plated elsewhere and shipped to us for gold plating. What can we do to prevent this peeling?—S.Y.
A. Your problem is with the nickel plate going passive. This is a common problem when 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 when the surface is exposed to the air, although passivation can also take place if the nickel-plated parts are not directly exposed to air but instead are held in a rinse tank prior to gold plating.
To get consistent results, the nickel surface must always be activated prior to gold plating. The parts should be precleaned in a mild alkaline soak cleaner, then an activation step should follow. Cathodic activation in dilute sulfuric acid, proprietary activators or a Woods nickel strike are all possibilities.
As soon as the activation step is complete, it is most important that you go directly to the gold-plating step. Failure to do so can result in passivation of the surface all over again.