Selective alkaline etching soln. for copper and copper alloys - useful in brasses and bronzes, even when lead is present, completely removes copper to exclusion of nickel

摘要

An effective etching soln. is claimed for the selective removal of Cu or Cu alloys from a Ni substrate. This soln. is alkaline (pH adjusted to 9-11 by NH3) and contains, (g/l) a metal or NH4 chlorite 3-90; and a metal or NH4 carbamate 50-200. USE/ADVANTAGE - Fully removes Cu to the exclusion of Ni. Useful in situations when other etching agents cannot be used, e.g. for certain bronzes and brasses, and esp. when Pb is present. In an example, precisely weighed plates of the purest Cu and different Cu-Zn alloys (including those contg. Pb) and Cu-Sn alloys were mechanically treated by ultramilling to a Ra value of less than 15 micron, then galvanically coated with Ni on one side. The Cu was then removed by placing in a soln. made from deionised water and contg. (g/l) NaClO230 and (NH4)(OCONH2) 122, and the pH adjusted to 10 by NH3 at room temp. for more than 1 hr. until the Cu concn. in the soln. was constant. The plates were then removed, rinsed clean, and reweighed. No Ni ions were detected in the spent etching soln., and screening electron microscopy of the etched plates' surface showed that no corrosive action of the soln. on the Ni had taken place.