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Using caustic to dissolve aluminum

We currently coat thin sheets of Al 6061 with electroplated nickel. Then we cut the ends of the nickel sheet, exposing the aluminum at both ends of the sheet. Then we immerse the nickel-coated aluminum parts into a 50% caustic (by mass) solution at around 250 F. We want to completely remove the aluminum. At times, the rate of removal is very good, but the etch rate decays. By changing the bath, the rate is seen to improve, but we want to not be changing the bath all the time. Something about the changing chemistry of the bath is believed to be the culprit. Any ideas on what might cause the rates of dissolution to decline quickly with time?

Kevin W. Kelly

2006

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First of two simultaneous responses --

Increased aluminum content perhaps?

Bill Grayson
metal finishing - San Jose, California
2006

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Second of two simultaneous responses --

A chemical reaction occurs due to an unbalanced situation. That's the motor. The more unbalance there is, the higher the speed. The closer the balance the slower the speed. When a balance is reached it stops.

Guillermo Marrufo

2006