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topic 52627

Electroformed copper turns black when dissolving aluminum mandrel

A discussion started in 2009 but continuing through 2018

July 15, 2009

Q. Hi

I am producing very low quantity copper electroforms with high precision mandrels made with 6061 T6 aluminium and, although I am very happy with the growth I achieve, the problem is that when I erode the mandrel using a 40 grams/litre solution of caustic it turns the copper black. Is there a way of either cleaning the copper with zero etching of the copper or, better still, preventing the black layer being formed in the first place?

Many Thanks


Lee Osborne
Shop manager - Cornwall, England

July 22, 2009

A. Try to dissolve the copper oxide in a diluted sulfuric acid. If if does not work good enough, add 1-2 ml/l hydrogen peroxide

In any case, a slight etching of the copper will occur

sara michaeli
sara michaeli signature 
Sara Michaeli
chemical process supplier
Tel-Aviv, Israel

Aluminium from dissolving mandrel plates out on electroform

January 9, 2018

Q. I have been electroforming copper onto aluminium formers. In removing the aluminium afterwards I have tried using HCl + Water. I found this to be a little slow and in some, strange cases, it eats the copper that I want left intact.

So I changed this to using Sodium Hydroxide to be used to remove the Aluminium. While this works really fast, when the temperature is set at 70 °C, I found a really unexpected result, the Aluminium seems to plate onto the copper. While this is not pure Aluminium it probably is Al(OH)4 or something like this, according to the chemical reactions. How do I avoid this? Presumably this is not usual.

Craig Donaldson
University of Strathclyde - Glasgow, Scotland

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