Selective leaching
In metallurgy, selective leaching, also called dealloying, demetalification, parting and selective corrosion, is a corrosion type in some solid solution alloys, when in suitable conditions a component of the alloys is preferentially leached from the initially homogenous material. The less noble metal is removed from the alloy by a microscopic-scale galvanic corrosion mechanism. The most susceptible alloys are the ones containing metals with high distance between each other in the galvanic series, e.g. copper and zinc in brass. The elements most typically undergoing selective removal are zinc, aluminium, iron, cobalt, chromium, and others. Leaching of zinc The most common example is selective leaching of zinc from brass alloys containing more than 15% zinc (dezincification) in the presence of oxygen and moisture, e.g. from brass taps in chlorine-containing water. Dezincification has been studied since the Civil War era, and the mechanism by which it occurs was under extensive examination by the 1960s. It is believed that both copper and zinc gradually dissolve out simultaneously, and copper precipitates back from the solution. The material remaining is a copper-rich sponge with poor mechanical properties, and a color changed from yellow to red. Dezincification can be caused by water containing sulfur, carbon dioxide, and