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Letter 030
"Etching" platinum-iridium after EDM
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I am looking for any information that will help develop a process
to remove surface remelt material from a platinum-iridium alloy after
electrical discharge machining. The material is machined using a
copper-zinc alloy wire, and the remelt material contains some copper
and zinc. We would like to be able to remove the copper and zinc
(from the inside of a small cylinder) while holding the dimensional
tolerances and surface finish on the rest of the part. Any
insight is appreciated. Thanks.
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Larry Hanke
materials testing laboratory
Minneapolis, Minnesota
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It is likely that a nitric acid solution of a moderate
strength 20-40% will dissolve Cu-Zn without touching the
noble metals. You'll have to experiment a bit with the
concentration and immersion time, but it should be doable.
 
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If all you want to do is remove Copper and Zinc from
Platinum and Iridium any number of etches for Copper should
be able to do the job. And remove the Zinc almost
incidentally. A Persulfate/Sulfuric Acid Microetch for small
amounts of work, or a Ammoniacal etch for large amount
should do the job with no attack on the substrate. Contact a
vendor of Printed Circuit Board processing chemicals for the
Persulfate, or use generic Sodium Persulfate at 8 oz/gal in
2 percent Sulfuric, at 80-100 F.
Rudolf Sedlak
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