Removing Nickel Plate from Kovar

Question:

What is the safest way to remove nickel plate from Kovar? We tried using 50/50 nitric acid and ended up damaging the parts. K.S.

Answer:

Kovar is an alloy of iron (~50%) and nickel (~46%) with small amounts of other "goodies" added. As you already have found out, stripping of a plated deposit is never a straightforward autopilot process. Mixtures of sulfuric acid and nitric acid are sometimes used but if you are not averse to using a cyanide-based solution you might try the following:

• Sodium cyanide 10 oz/gal
• Sodium hydroxide 2 oz/gal
• m-nitrobenzene 4 oz/gal
• sulfonic acid
• Temperature 120-150F

Keep in mind that this is a cyanide containing solution and must be handled with great care. The waste from this stripping solution must be disposed of properly. There are a large number of companies that sell proprietary non-cyanide containing stripping solutions. You can find them listed under Stripping Solutions, metal on the Suppliers page at PF Online or in the 2001 Products Finishing Directory & Technology Guide.