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Phosphate Buffered Saline Solution Corrosion Problems

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I have been testing an electroless nickel phosphorus (360 Brass Substrate) plating for use in our chemically harsh environment. I tested a 6-8% Nickel and a 10% Nickel combination and after two days in an agitated bath my test parts turned a bronze color. Our solution is a phosphate buffered saline which includes a NaCl, KH2PO4, Na2HPO4,and KCL in a 1000 ml of deionized H2O. Can anyone suggest a plating that will not oxidize in this environment. We have previously been using a 316 SST that has worked, but we are looking for plating possibilities.

David Willford
- Richland, Washington

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Dave,

Only precious metals and some exotic intermetallic or PVD compounds will not oxidize. Other protective metals such as EN, chrome, plain Ni, Tin-Ni, even SS will passivate which is a form of oxidation (some change in color, some do not). About ceramics, they also will not oxidize because they are already oxides (well, many of them).

Guillermo Marrufo
Monterrey, NL, Mexico

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A high phosphorus (10% or more) will not turn color if the plating solution is free from divalent sulfur, cadmium, or other reactive trace materials commonly used as stabilizers. Select a proprietary product that will pass the "nitric acid test" that is will not blacken in 30 seconds exposure to 50% by vol nitric acid. Ask your supplier. If he cannot help, contact me.

Don Baudrand Don Baudrand, Consultant   Poulsbo, Washington