WOOD’S NICKEL STRIKE
What happens when “tramp” metals such as copper, lead and chromium build up in a Wood’s nickel strike bath? Can this be a cause of roughness in the subsequent plating step?
Q. What happens when “tramp” metals such as copper, lead and chromium build up in a Wood’s nickel strike bath? Can this be a cause of roughness in the subsequent plating step? O.C.
A. Wood’s nickel strikes are very sensitive to metallic impurities. When the strike bath is contaminated with heavy metals, the usual results are brittleness and a darkening of the deposit.
A strike deposit is usually very thin and examination of the strike layer may not show any signs of pitting and roughness. However, the incipient form of these problems may be present. Usually pitting and roughness show up when the strike layer is plated with a heavier layer of metal. The top layer of metal can act as a “magnifying glass” and that’s when evidence of pits and roughness will be seen.
What to do? All of the standard causes of roughness should be looked for: Anode bags that are missing or torn, particulate matter getting into the bath and/or the nickel content in the strike bath exceeding 10 oz/gal. Most importantly, make sure your Wood’s nickel strike bath is properly filtered.
Something else to be aware of: If you have a heavily contaminated bath, some of the contaminating metals will deposit with the nickel. This can give you a surface that varies in potential and will affect the metal layer plated on the strike layer.
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