Metal finishing Q&As since 1989
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Dissolve Al from Au and Ni
I am trying to dissolve an Al mandrel from a Au/Ni/Au electroform. NaOH takes the Ni through 25 millionth of Au. Any suggestions for an enchant.
Rick Hines- Sitlwell, Kansas
Muriatic acid (HCl) works fine. Both gold and nickel are inert in chloride environments. Aluminum will etch quickly. I'm not sure I understand the problem with caustic however ... it should work as well.
Milt Stevenson, Jr.
Syracuse, New York
Hi,
I disagree with the previous answer. Nickel is not inert in chloride environment (less in presence of gold which forms a galvanic cell of around 1.73 Volts). I would recommend 25% sulfuric acid which is less aggressive to nickel (though not to human tissues). There are, of course other alternatives with organic acids but I ignore the correct concentrations or additives. Gold is indeed totally tolerant to all (except AR).
Guillermo MarrufoMonterrey, NL, Mexico
I don't see how the nickel can come through the gold, however I have seen aluminum redeposit on the gold under certain conditions. If this is the problem you can acid dip in 50% HCl for 1-2 minutes. The aluminum will gas slightly and then reveal the gold underneath and the nickel will appear dull grey.
Russell Richter- Danbury, Connecticut, USA
I would try a caustic solution to dissolve the aluminum or you could try trisodium phosphate [on eBay or Amazon].
Stephen T. Dowden- Olathe, Kansas
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