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Letter 15014
Phosphate Buffered Saline Solution
Corrosion Problems
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I have been testing an electroless nickel phosphurus (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 dH2O. 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
possibiliies.
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
++
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.
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