Stripping electrolytic zinc from aluminium cathodes - using aluminium cathodes provided with a steam-treated oxide coating of high density

摘要

Electrolytically deposited Zn is stripped from Al cathodes more easily by coating the Al cathodes with an oxide layer which is made denser by treating in a hot aq. phase or steam to give an oxide layer of 0.5-7 mu thickness and ensuring adhesion of Zn corresponding to 100-275 N/cm2. The Al cathodes are anodically oxidised and the layer is treated with salt-free water or an alk. chromate soln. at 90-100 degrees C. The Al cathodes are anodically oxidised in a sulphuric acid soln. to give an oxide layer of max. 10 mu thickness, and the layer is made denser by treating with an alk. chromate soln. contg. 50-100 g/l K2Cr2O7 and 10-20 g/l NaOH at 90-100 degrees C, or steam at 100 degrees C for max. 3 min. The treated Al surface is then washed in water at 40-60 degrees C.