Removing "remelt" after EDM on platinum-iridium
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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.
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.
"PlaterB" Berl Stein
Rochester, New York
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.Rudy Sedlak
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